Physical and technological bases of radial methods of diagnostics with the use of ionizing radiation

Physical and technological bases of radial methods of diagnostics with the use of ionizing radiation.

physical Principles of radiodiagnostics and radiotherapy

Irradiations, which are applied in radiodiagnostics and the radiotherapy can be divided into two groups: ionizing and non-ionizing. Ionizing termed the irradiations, which cause activation and ionization of atoms, transiting through the medium. The non-ionizing radiations do not cause such effect.

According to the physical properties the ionizing irradiations are divided on photon or quantum and corpuscular.

The photon or quantum ionizing irradiations represent a stream of electromagnetic waves. X-ray and gamma radiation belong to them.

The corpuscular ionizing irradiations represent a stream of positive or negative charged or neutral elementary particles. The alpha-particles, beta-particles (electrons and positrons), protons, neutrons, mesons and some other elementary particles belong to them.

Properties of ionizing irradiations:

1.      Ionizing activity

2.      Penetrating activity

3.      Fluorescent activity

4.      Photochemical activity

5.      Biological activity

The non-ionizing irradiations, which are of a wave nature too (slide 1), are applied only in radiodiagnostics (radiotherapy studies only ionizing radiations). Radiowaves which underlie  magnetoresonant diagnostics and infrared waves, which underlie thermo diagnostics belong to them. They also represent a stream of electromagnetic oscillations (waves).

Conditionally the ultrasonic waves are included in the group of non-ionizing radiations, which represent a stream of mechanical, sound oscillations.

Thus, modern radiodiagnostics studies five methods:

1)       magnetoresonant;

2)       thermographic;

3)       ultrasonic;

4)       roentgenological;

5)       radioisotopic

The roentgenological and radioisotopic methods belong to ionizing, others – to non-ionizing methods of radiodiagnostics.

Modern imaging department use a variety of different techniques to provide images of human internal organs and to demonstrate pathological lesions within them. These techniques can be classified as:    1.     Methods using ionising radiation

a. Simple X-rays

b. Computed   X-ray  tomography  –  generally  referred   to  as computed tomography or CT

c. Radioisotope scanning – also referred to as nuclear medicine, radionuclide scanning or scintiscanning.

2. Other methods

a. Ultrasound

b. Magnetic resonance imaging (MRI).

Ionising radiation in large doses has well-known dangers, including carcinogenesis and local tissue damage, but the amounts used in modern imaging practice are usually minimal and innocuous

X-rays were discovered in 1895 by Conrad Roentgen who was then an obscure German physicist. For some 60 years (until the middle of this century) they provided the only practical method of medical imaging. Isotope scanning was introduced into medical practice in the 1950s and ultrasound in the 1960s. CT was developed in the 1970s and MRI in the 1980s. All these methods advanced rapidly and are now important specialties in their own right.

X-rays

X-rays are part of the so-called electromagnetic spectrum (Fig. 1.1). These range from wireless waves at the long end of the spectrum to cosmic rays at the short end. Because of their short wavelength X-rays can penetrate materials which do not transmit visible light. Roentgen’s discovery was the starting point for modern medical radiology and radiotherapy and for many other non-medical sciences which have developed over the years from the use of X-rays. Modern X-ray apparatus is highly sophisticated but the method of producing X-rays remains basically the same as that used by Roentgen himself. High voltage electric current is passed across a vacuum tube. This induces a stream of electrons from an electrically heated metal element (cathode) to strike a metal target (anode) after passing across the vacuum. When the beam of electrons strikes the anode X-rays are produced (Fig. 1.2).

 

Fig. 1.1 The electromagnetic spectrum.

Fig.1.2. Diagram of a modern rotating anode X-ray tube. Electrons at high kV travel across the vacuum from the cathode (A) to the rotating anode (B) to generate the X-rays (shown as arrows emerging from tube).

 

pHYSICAL And TECHNOLOGICAL BASES of roentgenodiagnostic.

Source of irradiation. structure of roentgenodiagnostic instrumentation

The source of radiation of Roentgen rays is the X-ray tube. It represents the glass cylinder with created vacuum and two electrodes – cathode and anode are disposed.

The mechanism of formation of Roentgen rays

On the cathode through the reducing transformer the alternating current by a voltage 12 V moves which heat ups a filament (like, as in an electrical bulb). Due to warming, around of the filament so-called “electronic cloud” is formed. Further, through the system of rectifiers (kenotron) from the high-voltage generator on the tube a direct current by voltage 10-150 V is passed. Thus the directional movement (emission) of electrons from the cathode to the anode begins. At interaction of electrons with the anode atoms is gained deceleration and characteristic X-ray radiations. The process of the formation of Roentgen rays is controllable. The penetrating ability of Roentgen rays directly proportional to the enclosed voltage.

The roentgenodiagnostic unit, which is the electrophysical generator, consists of the X-ray tube placed in a protective metal housing and anchored in the holder, high-voltage generator with the system of rectifiers, table for positioning of the patient, operating board and receiving device.

Object of examination. Artificial contrast study of the object.

Object of a X-ray examination is the man (patient).

At equal thickness of tissues stratums, the radiation is most of all absorbed by an osteal tissue. Twice less it is hold by parenchymatous organs, muscles, fluid mediums of the organism. The most less it is absorbed by a fatty tissue, and gases – air in lungs and stomach, gas in intestine. The more radial absorption by explored body, the more intensive shadow on the receiving device. Nevertheless, a series of organs has poor natural contrast range and with the purpose to improve it, an artificial contrast study is applied. Substances, which are used for the contrast study of organs and systems are termed X-ray contrast substances. The X-ray contrast substance are divided into two groups: roentgenpositive and roentgennegative. Roentgenpositive substances have a high relative density, well absorb Roentgen rays and give on the receiving device the intensive shadow image. They, as a rule, created on the basis of heavy elements: Barium or Iodum. For example: aqueous suspension of the Barii sulfas – for the examination of gastrointestinal tracts; iodic solutions of organic compounds – for examination of the vessels, liver, kidneys and cavities of heart; iodinated oils – for examination of bronchi, lymphatic vessels, cavity of the uterus, fistulas.

Roentgennegative substances very little absorb Roentgen rays and on the receiving device give an enlightenment. It is gases, for example: a carbon dioxide – for administration in the blood; nitrous oxide – in the cavities of the body and fat; Oxygenium – in pleural and abdominal cavities; air – in the digestive channel.

There are two methods of the contrast study of organs: the first is direct, mechanical introduction of the contrast substance (esophagus, stomach, intestine, biliary and urinary tracts, cavity of the uterus, bronchi, lymphatic and blood vessels). Second is based on the ability of some organs to absorb from the blood flow contrast substances, injected into the organism, to concentrate and to discharge them.

Technology of formation of the X-ray image.

The technology of formation of the X-ray image includes three components: a source of irradiation, object of examination and receiving device, on which the visual shadow image of explored site appears. The Roentgen rays, passing through the body of the patient get on the one of receiving devices: X-ray film, semiconductor selenium plates, fluorescent screen, electronnooptical transformer and dissymmetric detectors.

Methods of X-ray examination

According to receiving of the image, the methods of X-ray examination are divided into three groups:

а) for general assignment (universal, basic) – table 1;

b) additional – table 2;

c) special – table 3.

Such division is conditional, however, it is standard in the medical literature.

It is necessary to note, that with the appearance of computer technologies, other division has formed, in which the technological level of receiving of the diagnostic information exists. According to this division, also three groups of methods are distinguished:

а) the traditional or conventional (standard) technologies, last term is more common abroad and at international scientific forums meets rather frequently;

b) computer technologies;

c) intervention technologies.

Table 1

Methods of  X-ray examination of general assignment (universal, basic)

	Name of the receiving device	Name of procedure	Name of the unit	Kind of the information
1	X-ray film	1.Roentgenography (X-ray film)	Universal roentgenodiagnostic unit (device for roentgenography)	Roentgenogram  – plane image of object on the X-ray film (negative) after its exposure, photo processing and exsiccation
		2.Roentgenography with the contrast study of the object of examination by contrast substance (gastrography, irrigography etc.)	– ” –	X-ray roentgenogram with the contrast study of the object of examination by contrast substance (gastrogram, irrigogram)
2	The semiconductor selenium plates	electroroentgenography (xenoroentgenography)	The universal roentgenodiagnostic unit (device for roentgenography) and special unit for it (electrororentgenograph)	An electro X-ray roentgenogram – X-ray image of the object (negative) on a usual paper, which is gained after photoexposure of a charged selenium plate, spraying on the plate of a graphite powder, transference of the image from the plate on a paper and fixing it in fumes of an acetone
3	Fluorescent screen	Roentgenoscopy (X-ray strike-through)	Universal roentgenodiagnostic unit (device for roentgenoscopy)	The plane image of object (positive) on the fluorescent screen
4	X-ray electronooptical transformer or (EOT)– amplifier of the X-ray image (ARI)	Roentgenoscopy with using of ARI or X-ray television strikethrough	Universal roentgenodiagnostic unit with the amplifier of the X-ray image	The plane image of object (positive) on the television screen
5	Dosimetric detectors	1 Digital roentgenography (roentgenoscopy)	Digital roentgenodiagnostic units	The X-ray image ciphered in a numeral code, which can be transmitted to distance with the help of the com­puter, to decode, “to strip” of alien details
		2. Computer tomography (CТ) а) Usual; b) Spiral; c) Electronic	X-ray computer tomograph	Computer tomogram – X-ray image as cross (axial) edges of a body, which can be reconstructed in the plane image

 

Table 2

ІІ. Additional methods of X-ray examination

	Name of the receiving device	Name of procedure	Name of the unit	Kind of the information
1	X-ray film	1 Target roentgenography	Universal roentgenodiagnostic unit	The target roentgenogram – target X-ray of a site, where the pathological changes are revealed
		2 Roentgenography with the direct magnification of the object of examination	– ” –	X-ray film with direct magnification of the object of examination
		3 Tomography (plane, usual)	Universal roentgenodiagnostic unit and special device for it	The tomogram – level-by-level image of plane edges of the object of examination on given depth (negative image)
		4 Photoroentgenography	Fluorograph)	The photofluorogram – photosnapshot from the fluorescent screen of fluorograph on a rolled film (negative image)
		5 mammography	Mammograph – special roentgenodiagnostic unit for examination of breast gland	The mammogram – X-ray film of breast gland

 

Table 3

ІІІ. Special methods of X-ray examination

	Name of the receiving device	Name of procedure	Name of the unit	Kind of the information
1	X-ray film	1 Pneumoencephalography	Universal roentgenodiagnostic unit	The pneumoencephalogram – X-ray film after introduction of gas in ventricles of the brain
		2 Fistulography	– ” –	The fistulogram – X-ray film after introduction of contrast substance in fistulous tracts
		3 Angiography	1 Universal roentgenodiagnostic unit and special angiographic device for it	The angiograms – series of rapid X-ray films after catheterization of vessels and introduction of radiopaque substances
			2 Angiographs – special roentgenodiagnostic high-speed camera

 

Methods of X-ray examination

1. Simple radiography is the method in which an X-ray beam is passed through the patient on to a photographic plate (Fig. 1.3). It has been practised continuously since Roentgen’s original discovery. Modern sophisticated apparatus can produce films with exposures taken within 0.1 of a second or less.

2.    Tomography has been in use for over eighty years but again the method has been steadily improved by technical advances so that today it is possible to demonstrate detail of the inner ear by this technique, including the ossicles. Tomography is a variation of the simple X-ray film method which permits tissue section radiographs to be obtained. During the X-ray exposure the X-ray tube and the X-ray film are moved in opposite directions so as to produce the equivalent of a body section X-ray. The technique is now mainly used in chest work, but is also used in bone work and in other areas.

 

Fig. 1.3 Simple X-ray: A = tube; B = patient; C = X-ray film.

 

 

Fig. 1.4 Diagram to illustrate tomography: A = pivot point of bar connecting tube and films.

Figure 1.4 illustrates the basic technique of tomography. As the tube moves in one direction the film moves in the opposite direction. The two are connected by a rod which can be made to pivot at variable point A. Since A remains stationary during the whole procedure the part of the body in line with A is the only part which will be clearly shown. Several films can be taken at the same time by the use of the so-called multi-section box. Thus multiple body sections can be obtained with a single exposure. Modern apparatus includes specialised tomographic equipment of rotatory and epicyclic movement.

3. Screening and the image intensifier. Screening is the term used for passing an X-ray beam through the patient to impinge on a fluorescent screen. In the past (before 1950) the fluorescent image thus produced was observed from the opposite side of the screen by a radiologist. A darkened room and dark adaptation by the radiologist were necessary, because the brightness of the image was inadequate for daylight viewing. The development of the image intensifier in the 1950s rendered this simple method obsolete. With the image intensifier the fluorescent screen image is viewed through an electronic intensifier and then passed through a television camera to a monitor in a closed circuit television (Fig. 1.5). The monitor is observed by the radiologist. Screening with the image intensifier can be recorded on video and recordings played back at the convenience of the operator. The images can also be recorded on cut film or roll film.

Fig. 1.5 Screening with image intensifier and television link: A = tube;

B = patient; C = fluorescent screen; D = image intensifier; E = television camera; F = closed circuit to television monitor; G = television monitor.

Fig. Basic principles of plain films and fluoroscopy

4.    Videoradiography. As already described, the brightened image produced by an image intensifier can be utilised for video-recording and played back at the convenience of the radiographer.  The method is particularly useful for studying disorders of swallowing (barium   swallow)   and   for   angiography   and   left   ventricular  angiocardiography.

5. Miniature radiography. This method was once widely used in the form of ‘mass miniature radiography’. Since X-rays, unlike light rays, cannot be focused or bent by lenses, miniatures can only be obtained by taking optical photographs of a fluorescent image obtained as described in (3) above. Such miniature films are very much cheaper than conventional X-ray films. Large populations have been rapidly screened by using a 70 mm or 100 mm roll film camera to photograph the chest images of patients standing consecutively before a screening stand. The method however, involves five or six times the radiation dosage of a conventional X-ray film. In this country, therefore, where the pick-up rate for tuberculosis has become negligible, the method has fallen into disuse as a screening procedure.

The method is also used via the image intensifier as a cheaper method of recording such screening examinations as barium meals. There is a considerable cost saving in recording a barium examination on 100 mm film rather than on conventional large films.

6. Xeroradiograph]/. An aluminium plate is coated with a thin layer of selenium and charged electrically. An X-ray beam is passed through the patient on to the plate and this causes an alteration of the electrostatic charge corresponding with the image. The image can be shown by blowing a thin powder, which adheres in proportion to the local charge, on to the plate. This is transferred to special paper and a permanent record obtained.

The advantage of xeroradiography is that it provides soft tissue contrast of sensitivity not obtainable with conventional film. The method was once widely used in mammography for the demonstration of breast tumours.

7.   Digital vascular imaging (DVI) uses image intensifier screening as described above to obtain images of blood vessels. Preliminary screening of the area to be examined is followed immediately by screening as a bolus of contrast material injected intravenously or intra-arterially passes through the blood vessels. The preliminary images  can  be  electronically  subtracted   from  the  images  with contrast medium. This leaves a clear bone-free image of the blood vessels which is recorded on cut film. The technique is also referred to as digital subtraction angiography (DSA).

8.    Special techniques and procedures using X-rays. A wide variety of specialised techniques using X-rays is available to the radiologist. These range from relatively simple and innocuous examinations such as barium meals to complicated and potentially dangerous procedures such as cerebral and coronary angiography which may require general anaesthesia. These techniques are discussed in the appropriate systemic chapters.

Contrast media

Radiology makes great use of media which have a different permeability to X-rays than that of the body. These can be inserted into various cavities and organs, or even into veins or arteries. As a result it is possible to obtain X-ray pictures of the interior of organs or blood vessels. The contrast media generally used are:

1. Salts of heavy metals. Barium is the heavy metal most widely used in radiology. As barium sulphate it has long been used for gastro-intestinal work, both for barium meals and  for barium enemas. Proprietary preparations have come into general usage (e.g. Micropaque) which have special properties allowing the barium to produce better coating of the mucosa.

Sodium iodide has been used as a contrast medium in the past, mainly for cystography.

2. Organic iodide preparations. These were originally introduced for the demonstration of the urinary tract in forms which were excreted by the kidneys after intravenous injection. They were also used for the demonstration of the gall-bladder in a form which could be taken orally, absorbed from the intestines, and then excreted in the liver. Recent decades have witnessed a steady increase and improvement in the types of organic iodides available. These will b described  and  discussed  later.  The  organic  iodides  which  are injected intravenously for pyelograms also became widely used for angiocardiography, arteriography and phlebography. Advances in this field have been rapid and several newer and safer contrast media have been introduced in the past decade. Water soluble organic iodide media were also used for myelography, e.g. iopamidol.

Contrast reactions. It is clear from the above that organic iodide preparations are widely used in imaging departments and that they are administered by intravenous or intra-arterial injection. In a small proportion of people there may be an adverse allergic reaction to the drug. This is usually of a trivial or minor nature, such as sneezing, transient nausea or transient skin wheals and itching, lasting a few seconds or minutes. Very rarely a more serious reaction may occur with collapse of the patient which can prove fatal. To put this risk in perspective it should be pointed out that an imaging department performing 2000 injections a year is only likely to see one such fatal case in 20 years. The people most likely to suffer a severe reaction are asthmatics or those with a history of severe allergy. If there is such a history, an alternative method of investigation is likely to be chosen.

3. Gas. Air and other gases are completely permeable to X-rays and appear on film as negative or black compared to the positive or white appearance of radiopaque substances such as bone, or the varying shades of grey produced by soft tissues. Air is normally present in the lungs and respiratory passages, in the pharynx and paranasal sinuses, and in more or less degree in the alimentary tract, fn all these areas its negative shadow is readily recognised and made use of.

Air can be used together with barium for so-called double contrast’ studies of both the colon and the stomach. The barium coats the mucosa which can be shown and studied in detail following air distension of the viscus. It has also been used in the bladder for double contrast cystography and in joints for arthrography.

In the past it was widely used in the CNS for encephalography and ventriculography but these procedures were rendered obsolete with the advent of CT and MRI.

Recent trends of radiodiagnostic development

Digital (numeral) radiodiagnostics – recent trend of development of the radiology. For comprehension of the essence of this procedure and its advantages, we shall address to technology of the X-ray image formation. It, as is known, includes three components: a source of radiation (X-ray tube), object of examination (man), receiver of irradiation (fluorescent screen, X-ray film, selenium plates, electronooptical transformer, dosimetric detectors). However, this system which properly functioning already during many decades, has an essential deficiency. At each stage of passage of irradiation – through the man, receiver of irradiation – there are numerous noises, or as the experts say, interior noises. The causes of interior noises are numerous: inhomogeneity of X-ray beam and instability of electrical current, which supplies system, inhomogeneity of object of examination and defects on films and screens.

The creators of a new digital method of radiodiagnostics have offered to prolong the technological chain of receiving of the image. The image, which appears on the fluorescent screen, is transmitted to the special device – analog-digital transformer (АDT), in which it is coded in a series of numerals, which are transmitted in the computer. The computer according to the special program handles the image: takes out noises, makes it more legible and contrast, takes away fine, interfering details. If necessary the image can be enlarged or diminished. Further the image gets into the decoder or digital-to-analog transformer (ADT), where the X-ray image is again formed from the series of numerals, but is already much more qualitative.

The described principle of digital technology is applied at a roentgenoscopy and roentgenography. But especially its advantages expressed at a contrast X-ray examination of vessels – angiography. This procedure even has received the name – digital subtraction angiography.

The term “subtraction” means ” allocation “. The first publications about digital subtraction angiography refer to 1985-1986 years and belong to professor A. Savchenko (Russia).

The method is original and simple. Before introducing into the vessel a contrast agent, the numeral note of an explored site of the body is recorded in the storage of computer. The following stage – writing down the image of the same site of the body after introduction of the contrast agent. On last investigation phase will the computer reconstruction of the image is carried out: from the second image allocate the first.

On this image only vessels are visible without bones and soft tissues. The image differs by a high quality and all vascular net, which supplies organ or explored site, is superb visible on it, including fine furcations of vascular sprigs.

 

COMPUTER TOMOGRAPHY

The computer tomography (CT) is one of the variants of the digital (numeral) roentgenography.

The computer X-ray tomography (CTG or CT) is the realization of ideas of the great surgeon N.I.Pirogov: receiving in clinical conditions topography and structure of organs in cross edges. This is the greatest achievement in medicine since the moment of invention of X-rays. South-African physics A.Cormack and English engineer G.Gansfield were awarded by the Nobel Prize in 1979 for invention and clinical trials of computer X-ray tomograph.

The history of computer tomography very original and interesting. Its beginning was founded by the work of two American scientists: the neurologist W.Oldendorf and radiologist D.Cool, who in 1960 having utillized as a source of radiation a radionuclide  Iodum – 131, have made the reconstruction of the image of cross edge of the skull. However, the image was not so qualitative and in that time this work wasn’t appreciated.

After three years, in 1963, the by little-known South-African physics A.Cormack has appeared, in which he has offered a mathematical method of reconstruction of the image of brain by means of highly direct X-ray bundle.

Opposite previous, this article has paid attention of the experts in the brunch … of production of electro musical instruments. One small English firm on production of electro musical instruments, had small, but not bad equipped laboratory under the guidance of unknown engineer G.Gansfield. Having putting aside guitars, scientists for the short period of time have created the new unit, which they have termed ЕМІ-scanner.

April 19, 1972 on the annual congress of the British institute of radiology by G.Gansfield and doctor G.Ambrous was made the report: “Radiology penetrates into the brain”. The success was so evident, that the leading firms on electronics have joined the work at once. In 1974 in USA was designed the tomograph of an essentially new type – for examination of the whole body. For the short period all modern clinics of the world were equipped by computer tomographs. Thus in Japan in 1985 per one million of inhabitants there was 25 computer tomographs, in USA – 7.

The models of units of V and VI generations with not one but about 200 emitters are now produced. The power processor with velocity of information processing up to 10 million operations per one second is applied. Therefore, the time of scanning was reduced to 40-50 msec. The opportunity to see on the screen of the telemonitor contractions of separate cross layers of heart by thickness 1-2 mm in real time has appeared. New methods of CT – spiral and electronic computer tomography more recently have appeared, where the mechanics is exchanged by electronics, the image is three-dimensional, volumetric, that enables in real time to level-by-level “preparate” the heart.

 

Structure of computer tomograph.

The modern construction of X-ray computer tomograph consists of such basic components:

1)       the holder with  built-in X-ray tube, discharge or scintillation dosimetric detectors, system of receiving, transmission of impulses on the computer. Inside the holder there is a hole, in which the table with the patient moves. The snapshots are made perpendicularly to the long axes of a body, or under the slope 15⁰.

2)       the table for scanning equipped with the drive unit for movement of the patient, which is carried out in a horizontal plane automatically on the signal of computer.

3)       the operating board with connected monitor for observation, system of information recording and processing.

4)       the computer, which except the collecting, processing of signals and reconstruction of the image maintains and transmits the information on the operating board and the holder. The information from the computer is given out on the telemonitor, camera or magnetic recorder.

5)      the additional minicomputer for the analysis of data, emphasize of interesting zones, reconstruction of the image, that is receiving of the image in sagittal or frontal plane, definition of the precise sizes of the pathological focus, measurings of density of the focus.

 

The mechanism of formation of the CT image

The patient is in circular system of dosimetric detectors (data units).

The pencil X-ray beam scans the human body on a circle or spiral. Transiting through the tissues, the irradiation is reduced according to the density of these tissues. After passage of beams through the body of the patient they get on sensing dosimetric detectors. Electrical impulses are created in detectors, which after amplification transmitted on the computer. According to special algorithm the impulses are transformed into the numeral code, and further in the image of organs and tissues, which is maintained in the storage of computer. The image is transmitted to the telemonitor. Contradistinction to traditional X-ray films, the image of organs and tissues on CT remains as axial, i.e. cross. The modern units can give edges by thickness of 1-2 mm.

The visual sensing of the image, which arises on the screen of the telemonitor, is possible to process qualitative and quantitative:

–         to increase the image;

–         to increase its separate parts;

–         to measure the precise sizes of the organ or pathological process;

–         to determine density of the tissue in the relevant sites in standard units;

–         by mathematical methods of processing it is possible to reconstruct the image of object in three-dimensional, i.e. volumetric.

The diagnostics by means of CT is based on the direct roentgenological parameters (localization, shape, sizes) considered the exponent of density or absorption.

Exponent of absorption is based on a degree of uptake or reducing of the beam of irradiation at passage through the body of the man. Each tissue depending on density, atomic weight variously absorbs irradiation. That is why for each organ and tissue iorm a designed absorption coefficient (CА) according to the Gansfield’s scale. According to the scale, CА of water accepted for zero, bones, which density is greatest –plus 1000 units (U Н), air – minus 1000 U Н. Thereafter, for each organ the medial exponent of absorption coefficient is detected.

The separate ability CT depends on a series of the factors: localizations, shape, size and density of pathological process. On CT the tumours and other pathological changes in organs with natural contrast range are well found out. Bones, foreign bodies, stones are the best for diagnostics.

The minimal size of formation is 0,5–1 cm if the CA of the affected tissue differs from CA of healthy tissue on 10-15 of U Н.

The method of “amplification” of the image is applied to increasing of separate ability of CT. Intravenously radiopaque drugs are injected, therefore there comes increasing of densitometric difference between the healthy and affected tissues caused by their different blood supply.

The method of “amplification” is used for revealing of metastases of malignant tumours in the liver, where the efficiency of this procedure is 25-30 %, for diagnostics of pathological processes in the brain, mediastinum, organs of a small pelvis.

 

Advantages of computer tomography before the usual X-ray examination

1.      High sensitivity of CT, which permits to differentiate separate organs and tissues on density near 0,5 %. On X-ray films this exponent comprises 10-20 %.

2.      Unlike usual tomography, CT enables to receive the image in the plane of explored edge of 1-2 mm by thickness without stratification of tissues, which disposed above and below.

3.      CT enables to receive the precise quantitative information on the sizes and density both separate organs, and pathological processes.

4.      CT enables to estimate not only process, but also its mutual relation with surrounded tissues, for example, invasion of a tumour in the surrounding organs.

5.      CT enables to receive topograms, that is longitudinal images of explored region like to X-ray films by moving of the patient along a fixed tube. The topograms are used for an establishment of extension of pathological process and determining of the quantity of edges.

 

Examining an X-ray film

The student should develop as a routine a systematic approach to the examination of any X-ray film. But the same principles of a routine systematic approach should be applied to the examination of any film, whether of chest, abdomen, skull, spine or limb.

Computed tomography

A new method of forming images from X-rays was developed and introduced into clinical use by a British physicist Godfrey Hounsfield in 1972. This is now usually referred to as computed tomography (CT) or computerised axial tomography (CAT). This was the greatest step forward in radiology since the discovery of X-rays by Roentgen in 1895. Hounsfield was awarded the Nobel Prize for medicine jointly with Professor A. N. Cormack in 1979. The principle of CT scanning is that conventional X-ray films provide only a small proportion of the data theoretically available when X-rays are passed through human tissues. By using multi-directional scanning of the patient, multiple data are collected concerning all tissues in the path of the X-ray beams. The X-rays fall not on the X-ray film but on to detectors which convert X-ray photons into scintillations. The detector response is directly related to the number of photons impinging on it and so to tissue density since more X-ray photons are absorbed by denser tissues. The scintillations produced can be quantified and recorded digitally. The information is fed into a computer which produces different readings as the X-ray beam traverses round the patient. The computer is required to deal with a vast number of digital readings. These can be presented as a numerical read-out representing the X-ray absorption in each tiny segment of tissue traversed. The information can also be presented in analogue form as a two-dimensional display of the matrix on a screen where each numerical value is represented by a single picture element (pixel).

The first machine had only two detectors and housed a sharply collimated beam of X-rays. The more modern machines use a fan beam and multiple detectors (Fig. 1.6). The early machines were used for head scanning only but these were superseded by ‘body scanners’ which can examine all parts of the body including the head. The original machines took 4V₂ minutes to perform a single tomographic slice but the present generation of machines can obtain scans in times varying from 1 to 10 seconds according to type.

Fig. 1.6 Diagram showing relationship of X-ray tube and ring of detectors in a CT body scanner. The tube rotates around the patient. The detectors remain stationary.

 

Fig. Basic principles of CT.

Data presentation

The analogue images are presented on a cathode ray tube immediately after each section. The picture is usually in grey scale in which the more radiopaque tissue, e.g. bone, appears white and the more radiolucent tissue appears in shades of grey. The range can be varied by changing the gate or window width (W) at will so that the tissues can be evaluated within a wide or narrow range of density. The central point or level (L) of the window can also be varied. The Hounsfield scale is used by most machines in which the fixed points are water at 0, air at -1000, and dense bones at + 1000. Figure 1.7 illustrates the scale and also the expanded central segment which contains most normal tissues.

 

Fig. 1.7 Hounsfield’s scale. The full scale on the left extends over 2000 units. The expanded scale on the right extends over 200 units and includes all body tissues. Head scans are usually done routinely at a window level (L) of 34-40 and a window (W) covering 0-75.

In the last few years there have been major advances in CT technology resulting in the introduction of spiral or helical scanners. Previous scanner X-ray tubes were limited to a single circular traverse of 360° because of twisting of the thick high tension cables connecting them to the generator. These had then to be unwound by reversing the motion. Thus most CT scans required multiple adjacent axial sections to cover the organ or area being scanned, rather like fitting slices of bread together to reconstitute the loaf. The use of so called ‘slip ring’ technology permits current to flow between a stationary ring connected to the generator and a mobile ring moving round it and connected to the tube. This allows continuous circular motion of the tube while current flows. At the same time the patient couch is slowly moved through the gantry allowing the whole organ or area to be scanned. Thus instead of 20 exposures with an interval of a few seconds between each, there is a single exposure only and the examination is concluded in seconds as against the previous 10 minutes or more.

Since the patient moves longitudinally whilst the tube moves in a continuous circular motion the net result is a spiral or helical path for the X-ray beam through the organ being studied. The large block of information  acquired  can  now be  manipulated  by  modern sophisticated computer software to produce 3-D or other types of image which can be viewed from any angle. Computer manipulation can also remove unwanted tissues such as bone which are obscuring detail, and can improve presentation by colour coding.

Uses:

·        Any region of the body can be scanned.

·        Staging tumours for secondary spread.

·        Radiotherapy planning.

·        Exact anatomical detail when ultrasound is not successful.

Advantages

·        Good contrast resolution.

·        Precise anatomical detail.

·        Rapid examination technique.

·        In contrast to ultrasound, diagnostic images are obtained in obese patients as fat separates the abdominal organs.

Disadvantages:

·        High cost of equipment and scan.

·        Bone artefacts in brain scanning.

·        Scanning mostly restricted to the transverse plane.

·        High dose of ionizing radiation for each examination.

Spiral  (helical) scanning: In conventional CT, sections are taken individually with a delay between each one, whereas spiral scanning involves a continuous gradual move­ment of the patient through the scanner tunnel. The principal advantages are much faster scanning times and improved vascular visualization.

Radioisotope scanning

Isotopes of an element are nuclides with the same atomic number and therefore the same chemical and biological behaviour but with a different mass number and often a different energy state, e.g. the isotopes of iodine are ¹²³1,¹²⁵I, and ¹³¹I.

Radionuclides and radioisotopes are radioactive varieties but the terms in practice are interchangeable with nuclides and isotopes. Most of them are made artificially and disintegrate spontaneously, emitting radiation which includes gamma radiation. This is an electromagnetic wave radiation of high penetrating power. The energy is measured in electron-volts (eV).

The half-life of a radioisotope is the time taken for its activity to fall by one-half, e.g 6 hours for technetium (⁹⁹Tc^m).

Almost every organ of the body can be investigated by means of radioisotope scanning. It is important, however, that the radiation dose to the patient should be kept to the minimum by using low doses of substances with short half-lives.

Radionuclide imaging is a valuable diagnostic tool; the principal modality that examines abnormal physiology of the body in preference to anatomical detail.Technetium-99m is the commonest isotope used, and by tagging with certain substances a particular region of interest can be targeted.

Table 1.1 Typical applications of isotopes.

 

Anatomical area	Agent	Application
Respiratory tract	99mTc microspheres Krypton, xenon	Perfusion and ventilation scanning for diagnosis of pulmonary embolus
Cardiovascular	Thallium-201	For infarct imaging as it accumulates iormal myocardium showing a defect corresponding to infarcts
Gastrointestinal	Na pertechnetate and 99mTc-labelledWBCs	Studies to detect Meckel’s diverticulum and inflammatory bowel conditions
Liver and spleen	99m Tc-labelled sulphur colloid	Reticuloendothelial uptake to image focal abnormalities
Biliary system	99mTc HIDA	Useful in cholecystitis and obstruction, as isotope uptake in liver is excreted in bile
Urinary tract	DMSA DTPA MAG3	Studies of renal functional and anatomical abnormalities
Skeletal	99m Tc-labelled phosphonates	Uptake at sites of increased bone turnover, e.g. tumours and arthritis
Thyroid	Iodine-131or99mTc	Assessing focal nodules
Parathyroid	Thallium-201	May visualize adenomas

 

Technique of scanning

The technique of scanning depends on the fact that particular isotopes can be so designed as to be selectively taken up by particular organs.

In the individual organ, lesions such as tumours may take up selectively more of the isotope resulting in so-called ‘hot’ areas on the scan, as in the brain. Alternatively, they may fail to take up the isotope resulting in ‘cold’ areas, as in the liver. The uptake can be recorded as an ‘image’ by scanning machines.

Basically, a scanning machine consists of a detector. This is usually a large crystal of sodium iodide containing thallium iodide as activator. Gamma rays emitted by the isotope and striking the detector are converted directly into light quanta or photons. These are led off into a photomultiplier. This converts the light quanta into a small voltage pulse and the number of pulses is directly related to the original radioactivity.

The gamma camera. The gamma camera is more flexible than the earlier linear, scanner. It has a large stationary crystal which records activity over the whole of its field at the same time. The size of the field is limited by the size of the crystal but the whole field can be shown as an image on a cathode-ray tube and the image can then be photographed with a camera.

Since the activity recorded by the scanners is converted into electrical pulses, these can be recorded in digital form. This digital information can be fed into a computer and manipulated to provide physiological information about what is happening in the particular organ (data processing).

Fig. Basic principles of isotope scanning.

SPECT (single-photon emission computed tomography). A planar tomographic’slice‘ is reconstructed from photons emitted by the radioisotope. This can be compared with CT’slices‘ showing anatomy and shows distribution of radionuclide more clearly.

PET (positron emission tomography). Uses positron-emitting isotopes, many short-lived and cyclotron produced. These agents include radioactive oxygen, carbon and nitrogen. Main clinical applications are in the brain (infarcts and dementia), heart (infarction and angina) and tumours. Accurate studies of blood flow and metabolism are possible using these tracers

 

physical BASES of radioisotopic diagnostics and history of opening of the phenomenon of radioactivity

 

From the course of physics you know, that the atom consists of elementary particles (protons, neutrons, electrons, positrons, neutrino, quantums, mesons, etc.).

According to the planetary theory of Rutherford – Bor, at the centre of the atom there is plusly charged nuclear, which consists of protons and neutrons. Negatively charged electrons rotate on stationary orbits around it.

The quantity of protons in the nuclear of atom corresponds to nuclear charge, and consequently, both quantity of electrons and the serial number of the element in the Mendeleyev’s classification. Total number of protons and neutrons make a mass number of the nuclear or its atomic weight.

Atoms, which have identical number of protons, so the identical chemical properties, are termed as elements. Atoms of one element, which have different number of neutrons in the nuclear are termed as isotopes of this element or nuclides. Now more than 1600 of them are known. The atoms with identical number of protons and neutrons in the nuclear, but different contents of internal energy are termed as isomers. Thus the nuclears with excessive energies are termed metastable and are pointed by the index m.

For example, isomers of technetium: ⁹⁹Тс and ^99mТс;

Isomers of indium: ¹¹³Іn and ^113mIn

The property of transmission of the nuclears of atom of some chemical elements into nuclear of other elements with formation of ionizing radiations is termed as radioactivity. Elements, which have such property, are termed as radioactive isotopes or radionuclides. The process of transformation of one element in others with formation of ionizing radiations has the name of radioactive decay. There are natural and artificial radionuclides.

At the radioactive decay of natural radionuclides three types of ionizing radiations can be gained – alpha, beta and gamma radiation. At decay of artificial radionuclides, beside alpha, beta and gamma radiations, the positron and neutron radiations also can be gained.

Types of the radioactive decay:

1.     Alpha decay

2.     Beta decay (electronic and positron)

3.     Electron trapping (K- trapping)

4.     Internal conversion

5.     Isomeric transitions

6.     Division of heavy nuclears

7.     Synthesis of light nuclears

Each concrete radioactive atom can give only one type of corpuscular radiation. An alpha and (alpha + gamma), beta and (beta + gamma) – radiated nuclides and pure gamma radiated nuclides exist.

The artificial radioactive isotope californium – 252 breaks up with the radiation of neutrons.

Each radionuclide has a proper physical half-life period, (Т 1/2 p), that is the time of breaking up half of atoms of the nuclide. Т 1/2 p is absolutely constant and unchangeable at any conditions (pressure, temperature etc.). We cannot speed up or slow down a physical half-life period, thereafter the process of radioactive decay is unguided, as a counter to the process of formation of Roentgen rays.

Except the physical half-life period there is still biological period of half-excretion of radionuclide (Т 1/2 b) – half diminution of the activity of nuclide by natural biological excretion from an organism (kidneys, gastrointestinal tract, lungs).

The time for which the activity of the radionuclide decreases twice caused by both processes consists the effective period of half-excretion (Т ef.).

Тef =	Tp´Tb
	Tp+Tb

The radioactivity in the Si-system is measured in becquerels (Bc), derivative units: kilobecquerels (kBc), megabecquerel (MBc).

1 Bc is one decay for one second.

This unit is termed in honour of French scientist Anry Becquerel, who in 1896 has revealed the phenomenon of radioactivity for what was awarded with the Nobel Prize.

Miscellaneous unit of radioactivity – Curie unit (1 Cu), (in honour of the Curie family – Marry Sklodowska-Curie, Pyer and Irin Curie, which has revealed artificial radioactivity, for what were awarded with the Nobel Prizes too (slide 3). Derivative units: millicurie (мCu) and microcurie (mcCu).

Dependence between unities:

1 Cu = 3,7 х 1010 Bc

Except the half-life period, each radionuclide has proper radiation energy, which is measured in electron-volts (eV). Derivative units: kiloelectronvolt (keV) and mega-electron-volt (MeV). The energy of gamma-quantums of radionuclide is like its card, according to which the radionuclide can be identified. There are special devices, which are called spectrophotometers, which help to identify the radionuclide, by the energy of gamma-quantum’s. And in instrumentation for radioisotopic diagnostics there is a special device of adjustment of the apparatus on photopeak of energy of the radionuclide for receiving of defined image.

The schema of the structure of radiodiagnostic devices.

The technology of receiving of the diagnostic information at radioisotopic examination essentially differs from the technology of X-ray inspection. As you already know, a source of radiation of Roentgen rays is the X-ray tube, which represents the electrophysical generator. A source of radiation at radioisotopic examination is the radionuclide, at which decay the ionizing radiations are formed. Contradistinction to process of formation of Roentgen rays, the process of radioactive decay is autocratic and unguided, what already was told about.

The receiving device (data unit, detector) of ionizing radiations in the units for the radioisotopic diagnostics is the ionization chamber or scintillation crystal, which catch’s the energy of radiations and through the photoelectric multiplier transmit the signal to the electronic block. It transmutes energy of radiations into the electrical signals, which are recorded by the special device.

 

`        The schema of the radiodiagnostic device:

The detector – electronic block – recording device.

So, the schema of radioisotopic examination can be presented as:the source → detector→ electronic block →receiving device.The source of ionizing radiations at radioisotopic examinations is the radionuclide, which can be used as for laboratory examinations (in vitro), and for clinical (in vivo).

For laboratory (in vitro) diagnostic examinations as a radioactive label two radionuclides are used: gamma-radiated nuclide – 125-Iodum (¹²⁵І) and beta – radiated nuclide – tritium (³Н). The examinations are carried out in test tubes without introduction of radionuclides in the organism of the patient. By means of that content of hormones, enzymes, proteins and other substances in an organism is determined. This method wears the name of the radiocompetitive analysis, and the most widespread method of it is the radioimmunological analysis (RIA).

The principle of radioimmunological examination is based on the competition of two antigens (not labeled and similar to it labeled) for the specific linking system (antibody).

The technology of the radio competitive analysis consists of several stages, last of which is the radiometry of trials, build-up of the calibration curves and determining of the concentration of explored substance.

 

Radio-pharmaceutical substances

For radioisotopic examinations in vivo the radiopharmaceutical substances (RPS) are applied.

RPS is allowed by Pharmcommittee of Ukraine substances for diagnostic or therapeutic application, which contain radionuclides.

RPS for diagnostic application differs from the usual pharmacological substances by introducing into the organism in display doses, and as a result do not cause pharmacological effect.

 

The requirements to RPS:

1. Maximal suit to explored organ or system.

2. The low radiotoxicity, that means except the chemical harmlessness, also a small radial loading on the organism of the patient.

3. Optimum radiation energy for recording by instrumentation for radioisotopic examinations. For the gamma-radiation the optimum energy is 100-300 keV.

 

Producing stages of RPS:

1. Receiving of radionuclides

2. Isolation of radionuclides from target and their cleaning

3. Natural preparation of RPS

After receiving in reactor or cyclotron the radionuclide is isolated from the target and transmuted in the relevant chemical form. For isolation and cleaning chemical methods are used.

For receiving of RPS three basic methods are used: chemical synthesis, biosynthesis and exchange reactions. The first method is the commonest.

 

Preparation RPS on the basis of generating systems

RPS on the basis of short-lived radionuclides is the special group of the labeled diagnostic compound. They are gained from the generator, and special reagents set, which contaiecessary “cold” chemical compounds in radioisotopic laboratories and are used directly before the application.

Received after the system lavage solution is termed 99mTc – pertechnetatum with a physical half-life period of 6 hours, and the energy of gamma radiation of 140 keV. It can be used as in the shape 99mTc – pertechnetatum (for examination of the thyroid gland, malignant tumors of soft tissues), and for preparation of the radio-pharmaceutical substances for the examination of other organs. Today the reagents sets to the generator of technetium for examination almost of all organs are produced. They are prepared directly before the use.

The procedure of the preparation of the RPS rather simple and consists of addition of lavaged solution (technetium – pertechnetatum) to the bottle with the mixture of reagents with keeping the rules of asepsis. In some cases the warming is necessary. The reagent sets for the generator ^99mTc in most cases include two basic components: а) the basic chemical compound, which determines the pharmakokinetics of the future RPS; б) Tin chloride for restitution of ^99mTc, which in such state is capable to complex with the basic substance.

In the generator ^113mIn instead of tin chloride the buffer system (Natrii phosphas) is used which raises рН of prepared drug and makes it suitable for intravenous introduction. Quantity of reagents to the generator ^113mIn is small in comparison with such of the generator ^99mTc.

 

 

 

Methods of radioisotopic diagnostics

 

 

Name of method	Type of the device	Type of the information
I. Radiometry 1. Laboratory in vitro radiometry а) radiocompetitive analysis   – the radioimmunological analysis (RIA); – the immunoradiometric  analysis (IRMA); – the radioreceptor analysis (RRA); – competitive protein interlinking (CPI) b) radiometry of assays of the biological model c) radiometry of the activity of radio-pharmaceutical substances	I. Radiometers 1. Laboratory in vitro radiometers а) gamma – radiometers calibrated on gamma – radiated isotope of iodine125; b) beta radiometers calibrated on beta – radiated isotope of tritium (3Н).           c) gamma – radiometers of trunk type d) calibrator (gamma – radiometer)	I. Numeral (in imp/sec) а) Timer (counter); b) Printer (digital printer)
2. Clinical in vivo radiometry а) distant     б) contact (slide 11)	Clinical in vivo radiometers а) gamma – radiometers – of the hole body; – separate organs b) beta-radiometers – for superficial measurings; – for intracavitary measurings; – for interstitial measurings
ІІ. Radiography or radio­chronography	ІІ.Radiographs or radiochronographs а) gamma – chronographs for examination of time parameters of transport of the RPS b) gamma – chronographs for examination of time and spatial parameters of transport of the RPS.	ІІ. A radiogram or (radiochronogram) – diagram (curve) of transport of the RPS, output: on the paper strip or screen of the display
ІІІ. Radioisotopic visualization or gamma – topography 1. Scanning а) usual, plane   b) profile	ІІІ. gamma – topogram     1. Scanners а) one-detecting; b) two-detecting c) profile scanner (actually, it is the derivate of the scanner and radiograph)	ІІІ. The image of organs and systems of the man, numeral and pictorial information Scanogramm (image of organs or system on the usual paper printed as black-and-white or colour accents (numerals) Profilogram (curve) as the diagram of allocation of the RPS in organism
2. Scintigraphy а) static b) dynamic c) subtraction	1. gamma camera – radiodiagnostic installation	1. Scintigram – the image of organ or system on the screen of the display or on the polarized photographic paper 2. Pictorial information 3. Numeral information 1. Record on a magnetic strip of the computer of the image with one radionuclide 2. Record of the image with another radionuclide 3. Allocation of the second image from the first
3. Radioisotopic computer tomography а) one-photon SPECT b) positron (two-photon) РЕТ	Radioisotopic computer tomograph   а) one-photon emissive b) positron emissive (two-photon)	1. One-photon emissive computer tomogram 2. Positron emissive tomogram

 

RECENT TRENDS of the DEVELOPMENT of RADIOISOTOPIC DIAGNOSTICS

One-photon emissive computer tomography (SPECT)

RPS for SPECT:

^99mTc –НМРАО

^99mTc –glucoheptonate

⁵⁷Со – Bleomycine

²⁰¹Тl – chloride

¹¹¹Іn – monoclonal antibodies → ВW 431/31

¹³¹І – МАА ІМАСІS- І

In comparison with the plane scintigraphy the sensitivity of SPECT is higher.

Axial, sagittal and frontal images are obtained. The most common of RPS is the ^99mTc-НМРАО, which is used for estimation of the bloodflow in organs and tissues.

The special rotation gamma cameras are applied for SPECT and called emissive computer tomographs.

Positron emissive tomography РЕТ

The positron emissive tomography (РЕТ) – has a fantastic sensitivity, but in connection with low separate ability only supplements CТ.

РЕТ gives the information about biological features of organs and systems (functional visualization of organs).

RPS for РЕТ:

1.     [¹⁵О] Н₂О water (marked)

2.     [¹⁸F] FDG (fluorodeoxyglucose) glucose

3.     ¹¹С – thymidine

4.     ¹⁵N – glutamine (of protein)

5.     ¹¹С – alpha-aminoisobutyric acid

6.     ¹¹С – L-methionine

РЕТ are applied for the differential diagnostics of benign and malignant tumours, diseases of the brain.

The carrying out of РЕТ requires special equipment, cyclotron, radiochemical laboratory and computer for data processing. A total cost of all examination is 3 mln 550 thousands of US dollars (1987). The laboratory for carrying out of РЕТ in its staff should have at least 9 men: 1 radiochemist, 2 chemists – mechanic, 3 examinators, 1 doctor, 1 physics, 1 secretary.

РЕТ with the using of the methionine marked ¹¹С permits in condition of alive organism to explore function of tissues and to find out quantitative and qualitative difference betweeormal structures and tumor, to estimate metabolic activity of the tumoral tissue.

Opportunities of РЕТ:

1.     Estimation of organ perfusion.

2.     Study of glucose and protein metabolism.

3.     Examination of a pharmakokinetics of injected medicines.

4.     Patient selection for chemotherapy. At examination of the patients with metastases of colorectal cancer by the method of РЕТ with using of ¹⁸F-uracil in 11 from 52 cases was revealed a high concentration of RPS, in others – low.

5.     At РЕТ with ¹⁸F-fluorodeoxyglucose such fine structures, as upper tubercle and exterior sheath of brain are visualized. Thus the great hopes are assigned on РЕТ at early diagnostics of diseases of the brain, including mental.

 

Regulation of beam examinations, principles and methods of radiation protection

The biological activity of ionizing radiations results in legible regulation of their application and requires using of  safety methods against their harmful influence on the patients and  medical personnel.

Principles of the radiation protection

1.     by screening

2.     by time

3.     by distance

4.     by quantity

 

The indications and contraindications to examinations with application of ionizing radiations:

The radial examinations are carried out according to the strictly particular indications. With the preventive purpose the roentgenological and radioisotopic examinations are not carried out. Contraindications to the examinations with the use of ionizing radiations:

–         to pregnant woman,

–         to children before 14.

X-ray examinations to the women of genesial age, which connected with a rather major irradiation of gonads (examination of intestine, kidneys, vertebrum, pelvis) are recommended to carry out during the first week after the beginning of menses.

Rules of roentgenological and radioisotopic examination of the patients:

–         are carried out only by persons, who have special preparation and  leave for work;

–         all workers of department and patients, who must be examined, should be defend from activity of ionizing radiation

To the work in roentgenological department and the laboratories of radioisotopic diagnostics are prohibited:

persons before 18;

pregnant women;

persons with diseases, which require to avoid the work in the sphere of ionization.

Radiation hazards

Naturally occurring background radiation is present everywhere, the amount increasing with altitude and in areas with large amounts of granite. It is probable that this is responsible for some malignant diseases and some genetic mutations. Both X-rays and gamma rays are ionising radiations and can cause damage to human tissues if administered in very large doses. This can take the form of local damage to the irradiated tissues, resulting in local tissue necrosis, or damage to the sensitive reproductive cells resulting in fetal deformities or sterility. Overdosage can also result in cancerous growths or leukaemia.

The doses administered in modern diagnostic departments using modern apparatus are very low and generally quite innocuous. Thus it has been estimated that a simple chest X-ray is the equivalent of a high altitude flight or of 3 days naturally occurring background radiation at sea-level. CT or interventional radiology may involve significantly more radiation – equalling 1 or 2 years or more of natural radiation – and are therefore only undertaken where the potential benefit to the patient outweighs the slightly increased radiation hazard.

In investigations involving the abdomen the testicles of male patients may be shielded from radiation by a small sheet of lead rubber. The ovaries of females may be similarly protected unless it is necessary to include the pelvis on the film.

Irradiation of the pregnant uterus is avoided wherever possible, and women of childbearing age may be questioned as to the possibility of pregnancy. If they are pregnant the examination can be postponed or a non-radiation technique such as ultrasound should be substituted.

Isotope investigations are generally similar to X-ray investigations in the amount of radiation received by the patient. Thus a kidney isotope study is equivalent to about 6 months of natural radiation, a similar figure to the dose involved in an X-ray of the dorsal spine.

Diagnostic departments carry a radiation hazard warning on the doors of all rooms where ionising radiation is used.

Interventional radiology

In recent decades radiodiagnostic techniques have been increasingly used for therapy as well as for diagnosis. So-called interventional radiology now involves a wide variety of procedures. These include:

1. Percutaneous catheterisation and embolisation in the treatment of tumours; this is mainly to reduce their size and vascularity prior to  operation  in  difficult  cases,  or  as  a  palliative  measure  in inoperable tumours. Percutaneous catheterisation and embolisation is also used for treatment of internal haemorrhage and for the treatment of angiomas and arteriovenous fistulae.

2.    Percutaneous catheterisation with balloon catheters can be used to occlude arteries temporarily, either to stop haemorrhage or to obtain a bloodless field at operation.

3.    Percutaneous catheterisation is also used for the delivery of chemotherapeutic drugs to tumours, or for the delivery of vasospastic drugs in patients with internal haemorrhage. It is also used for thrombolysis by delivering thrombolytic drugs directly to the clot.

4.    Percutaneous transluminal dilatation of arterial stenoses is now being practised for the treatment of localised stenoses in the
femoral and iliac arteries. The method has been extended to many other arteries including the renal artery and the coronary arteries.

5.    Needle biopsy under imaging control is widely practised both for lung tumours and abdominal masses of all kinds.

6.    Transhepatic catheterisation of the portal vein and embolisation of varices.

7.    Transhepatic catheterisation of the bile ducts both for drainage in obstructive jaundice and for dilatation of stenosing strictures or insertion of prostheses.

8.    Needle puncture and drainage of cysts in the kidney or other
organs using control by simple X-ray or ultrasound.

9.    Percutaneous catheterisation of the renal pelvis for antegrade
pyelography or hydronephrosis drainage.

10.  Percutaneous removal of residual biliary duct stones through
the T’ tube tract.

11. Percutaneous  catheterisation  and drainage of intraabdominal abscesses.

 

INTERVENTIONAL RADIOLOGY

RESPIRATORY  TRACT:

Lung biopsy. A needle is inserted directly into the lung or pleural mass and tissue taken for microbiological or histological analysis. The procedure may be performed under fluoroscopy or CT guidance. Abscess drainage. A catheter is introduced percutaneously into a lung abscess to achieve drainage.

Pleural fluid aspiration. Ultrasound is effective in diagnosing pleural fluid. Even small quantities can be visualized and aspirated for analysis.

Empyema drainage. Purulent fluid in the pleural cavity, usually due to infection from adjacent structures, can be drained directly by catheter insertion.

Fig. Respiratory tract interventional procedures

CARDIOVASCULAR  SYSTEM

Angioplasty. Stenoses in the aorta, iliacs, femorals, peripheral vessels, carotids, coronary vessels, renals and virtually any other artery can be dilated by means of balloon inflation. Narrowed arterial segments and occlusions can also be treated by insertion of metallic stents.

Thrombolysis. Recent arterial thrombus can be lysed by positioning a catheter in the thrombus and infusing streptokinase or TPA (tissue plasminogen activator). Contraindications to this procedure include bleeding diatheses and recent cerebral infarction.

Embolization. The deliberate occlusion of arteries or veins for therapeutic purposes. Steel coils, detachable balloons or various other occluding agents are injected directly into the feeding vessels. Indications include arterial bleeding, arteriovenous fistulae and angiomatous malformations.

Vena cava filter insertion. A filter is introduced percutaneously either through the femoral or internal jugular vein and positioned in the inferior vena cava, just below the renal veins, thus preventing further embolization from thrombus originating in pelvic or lower-limb veins.

 

Fig. Cardiovascular svstem interventional procedures.

GASTROINTESTINAL   TRACT

Oesophageal dilatation. A large-diameter balloon is used for dilatation of benign strictures, postoperative anastomotic strictures (e.g. gastro­enterostomy), achalasia and palliation of malignant strictures.

Oesophageal stent. A metallic self-expanding stent is inserted for palliation of malignant oesophageal strictures.

Colonic stricture dilatation. Benign colon strictures, usually anastomotic ones, can be effectively treated by balloon dilatation.

Percutaneous gastrostomy. After gastric distension with air a catheter is inserted directly through the anterior abdominal wall into the stomach.

Embolization. Angiography may localize the bleeding point in severe gas­trointestinal haemorrhage. Control of haemorrhage may be possible by infusion of vasopressin or embolization.

Abscess drainage. Percutaneous drainage of subphrenic and pancreatic collections.

 

Fig.  Gastrointestinal tract interventional procedures.

BILIARY   TRACT

External biliary drainage. In biliary obstruction, a catheter is inserted per-cutaneously through the liver into the bile ducts.

Internal biliary drainage with endoprosthesis. A plastic or metal stent is positioned within the biliary stricture and free internal drainage achieved without the need for any external catheters. The procedure is preferably carried out by endoscopic retrograde cholangiopancreatography (ERCP), but if this fails, the stent can be inserted using a percutaneous approach.

Biliary stone removal. Postoperatively, when aT-tube is in position and a cal­culus remains in the common bile duct, a steerable catheter with a basket can be introduced directly through the T-tube track and the calculus extracted. Removal by an ERCP is also an effective technique.

Biliary duct dilatation: balloon dilatation of benign biliary stricture; liver/sub-phrenic abscess drainage; liver biopsy.

 

Fig.  Biliary tract interventional procedures

 

Fig. Interventional procedures of the urinary tract.

 

URINARY  TRACT

Renal angioplasty. Balloon dilatation of renal artery stenosis or insertion of metallic stents to alleviate the stenosis (treatment of hypertension or to preserve renal function).

Percutaneous nephrostomy. Insertion of a catheter into the pelvicalyceal system to establish free drainage of urine, when the kidney is obstructed.

Ureteric stent. A special catheter positioned so one end lies in the renal pelvis and the other in the bladder, for the relief of obstruction. Introduction is either from the lower ureter after cystoscopy by a urologist or from above percutaneously under radiological control.

Percutaneous stone removal. Removal of a renal calculus, through a percutaneous track from the posterior abdominal wall directly into the kidney.

Embolization of A-V fistulae. A valuable technique of treating fistulae by intro­duction of steel coils or other occluding agents into the feeding vessels.