Organization of job and equipment of department of roentgen diagnostics. Technology basis of roentgen diagnostics.
Organization of job and equipment of department of computerized roentgen tomography. Technology basis of computerized roentgen tomography. Organization of job and equipment of diagnostically radio-nuclear laboratory. Technology basis of radio-nuclear investigation
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).
Methods off 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
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
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.
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.
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 (99Tcm).
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
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
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.
