X-RAY DIAGNOSTICS , СТ, RADIOISOTOPE DIAGNOSTICS, ULTRASOUND, MAGNETIC RESONANCE IMAGING (MRI),

THERMODIAGNOSTIC (THERMOGRAPHY).

Physical and technological bases radial diagnostics with use

Ionizing radiations

5 modalities (or 5 groups of methods) of modern Diagnostic imaging in Radiology:

- X-ray examination;- Nuclear medicine imaging;

- Diagnostic ultrasound;- Magnetic resonance imaging (MRI).

- Thermodiagnostic (Thermography).

• For some 60 years (until the middle of last century) medicine 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.

Radiology consist fromRadiology consist fromradial diagnostics and radial therapy

Radial diagnostic - Universal discipline which studies signs of all illnesses of the human body without exception.

Integration medical specialties: •Radiodiagnosis (roentgenology), •Diagnostics Ultrasound (Dr. ultrasound)•Nuclear medicine imaging

(Radioisotope diagnostics )

•Radial therapy

Diagnostic radiologist

Radiotherapeutics

Thus, modern radial diagnostics uses five methods:

Simple X-rays , CT

Radioisotope scanning

Thermodiagnostic (Thermography)

Magnetic resonance imaging (MRI).

Ultrasound

IONIZINGIONIZING NON-IONIZINGNON-IONIZING

Five methods Radial DiagnosticFive methods Radial Diagnostic

X-rays , CT Radioisotope scanning

Thermography MRI Ultrasound

IONIZINGIONIZING

NON-IONIZINGNON-IONIZING

RADIAL THERAPY

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.Despite of it, an ionizing radiation use for treatment of some chronic illnesses in various branches of medicine, especially in an oncology.

Imaging departments need to be well run and efficiently utilized in order to minimize radiation hazard and be cost-effective.

Modern imaging departments 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 with use ionizing 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 (non ionizing methods)– a. Ultrasound.

– b. Magnetic resonance imaging (MRI).

– c. Thermodiagnostic (Thermography).

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

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

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

• The radiation dose is a measure of the energy deposited. One gray (Gy) is the new Systeme International d'Unites (SI) unit of dose and is defined as 1 joule per kilogram (J/kg). The former unit of dose is the rad. One Rad represents a deposition of 100 ergs per gram. One gray equals 100 rad.

• Some other types of radiation found near nuclear power reactors or in physics laboratories produce different amounts of biologic effect. Differences in biologic effectiveness are included in the dose equivalent units: the Sievert (Sv), which is the SI unit of dose equivalent, and them.

• Table 1 illustrates the relation between units of exposure, dose, and dose equivalent.

Table 1. Radiation UnitsQUANTITY

CONVENTIONAL SI CONVERSION FACTOR

Amount or exposure

Roentgen (R) Coulomb per kilogram (C/kg))

1 R = 2.6 x 104C/kg

Dose

Rad Gray (Gy) 1 Gy=100rad

Dose equivalent Rem Sievert (Sv) 1 Sv = 100 rem

Activity

Curie (Ci) Becquerel (Bq) 1 Ci = 3.7x1010Bq

PHYSICAL PROPERTIES of IONIZING RADIATIONS ::

1.1. Ionizing activityIonizing activity

2. Penetrating activity2. Penetrating activity

3. Fluorescent activity3. Fluorescent activity

4. Photochemical activity4. Photochemical activity

5. Biological activity5. Biological activity

X-rays, which are a form of electromagnetic radiation, travel with the speed of light: 3 X 108 meters per second (6.7 X 108 miles per hour). Figure 1 illustrates the location of x-rays in the electromagnetic spectrum. Only x-rays and gamma rays have enough energy to produce an ion pair by separating an orbital electron from its parent atom. The amount of radiation present is measured by detecting such ionization. Exposure is measured either in units of Coulombs per kilogram (C/kg) or in roentgens (1 R = 258 μC/kg). Although the roentgen is no longer an official scientific unit, it is still widely used in radiology.

High-energy Gamma rays X-rays

Ultraviolet Visible light

Infrared Microwaves Radar

Low-energy RadioFig. 1

X-ray examination methods:

- radiography,

- fluoroscopy,

- fluorography,

- linear tomography,

- - electroroentgenography (Xeroradiography)

- computed tomography.

All X-ray examinations are based on the detection of radiation passed through the patient (transmitted

radiation).

X-rays are generated by X-ray tube ( generator of radiation).

NB! Different tissues provide different degrees of X-ray attenuation.

Attenuation is a loss of X-ray energy. Different tissues allow the

transmission of different amounts of X-ray. X-ray imaging is

the imaging of shadows. X-rays penetrate tissues and are detected

on the other side of the patient by different detectors.

Main groups of X-ray techniques: direct analogue (direct radiography, direct fluoroscopy ,

xeroradiography, conventional tomography). Use X-ray film, fluorescent screen, selenium plate.

indirect analogue techniques (indirect fluoroscopy, fluorography). Use image intensifier and TV-techniques.

digital techniques (digital radiography, digital fluoroscopy/ fluorography, computed tomography )

X-rays are produced by passing a very high voltage across two X-rays are produced by passing a very high voltage across two tungsten terminals within an evacuated tube. One terminal, the tungsten terminals within an evacuated tube. One terminal, the cathode, is heated to incandescence so that it liberates free cathode, is heated to incandescence so that it liberates free electrons. When a high voltage, usually in the range of 50-150 kV, electrons. When a high voltage, usually in the range of 50-150 kV, is applied across the two terminals, the electrons are attracted is applied across the two terminals, the electrons are attracted towards thetowards the anode at high speed. When the electrons hit the anode target, x-rays are produced.

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).

When the high-energy electron beam strikes the rotating anode, x-rays are produced by both brems-strahlung and characteristic x-ray production. About 95% of the electron energy is deposited as heat in the anode, and only about 5% is expended in the production of x-rays.

Projections in conventional radiography

• Projections are usually described by the path of the x-ray beam. Thus

the term PA (posteroanterior) view designates that the beam passes

from the back to the front, the standard projection for a routine chest

film. An AP (anteroposterior) view is one taken from the front. The

term- ' frontal' refers to either PA or AP projection.

• The image on an x-ray film is two-dimensional. All the structures along

the path of the beam are projected on to the same portion of the film.

Therefore it is often necessary to take at least two views to gain

information about the third dimension. These two views are usually at

right-angles to one another, e.g. the PA and lateral chest film.

Sometimes two views at right-angles are not appropriate and oblique

views are substituted.

Science which studies application of x-rays with the purpose Science which studies application of x-rays with the purpose of diagnostics of diseases is named of diagnostics of diseases is named X-ray X-ray DIAGNOSTICDIAGNOSTIC..

27.03.1845 y. – 10.02.1923 y.

X-rays were discovered in 1895 by X-rays were discovered in 1895 by Conrad Roentgen (German Conrad Roentgen (German

physicist.)physicist.)

A house in which was born William Conrad Rentgen. Small town Remshteyd-Lennep near Dusseldorf.

Building of the Vurtsbourgs university where was done invention.

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 . 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. 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.

Conventional (simple) radiographyConventional (simple) radiography

Linear tomography

X-ray film with the direct increase of object investigation

• 3. Fluoroscopy. 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 . 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.

• 4. Videoradiography. As already described, the brightened image produced by an image intensifier can be utilised for videorecording 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.

The perceiving device

Kind information

The fluorescing screen

The plane positive image of object on the fluorescing screen

The perceiving device

Kind information

X-ray an electron - optical converter – the amplifier of the image

The plane positive image of object on the the television screen

Additional methods of a X-ray inspection Additional methods of a X-ray inspection

Fluorography

Photo from the fluorescing screen on a rolled film (the negative image)

• 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.

Aiming X-ray film

• 6. Xeroradiograph. An aluminium plate is coated with a thinlayer of selenium and charged electrically. An X-ray beam is passedthrough the patient on to the plate and this causes an alteration ofthe electrostatic charge corresponding with the image. The imagecan be shown by blowing a thin powder, which adheres in pro portion to the local charge, on to the plate. This is transferred tospecial 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 screeningas described above to obtain images of blood vessels. Preliminaryscreening of the area to be examined is followed immediately byscreening as a bolus of contrast material injected intravenously orintraarterially passes through the blood vessels. The preliminaryimages can be electronically subtracted from the images withcontrast medium. This leaves a clear bone-free image of the bloodvessels which is recorded on cut film. The technique is also referredto as digital subtraction angiography (DSA).

Electroroentgenograph

The electroroentgenogram The electroroentgenogram

The electroroentgenogramThe electroroentgenogram

Digital X-ray scopy or graphy

Digital X-ray diagnostics

• 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 divide on

two groups: roentgen positive (high percent of absorption) and a roentgen

negative (the minimal percent of absorption) and generally used are:

• 1. Positive contrast media: • a. 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.

• b.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 be 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.

• 2. Negative contrast media 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.

The roentgenogram with contrasting object of research with use positive contrast agent (gastrogram, irrigogram, angiogram, urogram)

та

Angiography Angiography

X-RAY MACHINE

1 - X-ray tube on a stand. 2 - High-voltage transformer, rectifiers to change the AC current to DC, and a filament supply to control the temperature of the filament (100-150 Kv applied across the tube). 3 - Table for patient. 4 - control stand (in other room). 5 - perceiving device :

- X-ray film. - Quasi-conductor selenium plates- Fluorescent screen.-Electronically-optical representation amplifier. - Dosimeter detector.

1

5

3

2, 4

AC- alternate currentDC- direct current

Technology of forming of x-ray images

Includes three components: 1 - radiant ( X-ray tube)2 - object research3 - perceiving device (detector) on which we get the visual shadow image of the area that inspects

1

2

3

Technology of formation of the X-ray imagesTechnology of formation of the X-ray images

The Roentgen rays, passing through the body of the patient get

on the one of the detector:

X-ray film,

semiconductor selenium plates,

fluorescent screen,

electronoptical transformer, intensver, TV

dosymmetric detectors.

Absorption of x-rays

• Radiographic and CT images depend on the fact that x-rays are absorbed to a variable extent as they pass through the body. The visibility of normal structures and of disease depends on this differential absorption. X-rays that pass through air are least absorbed and therefore cause the most blackening of the radiograph, where as calcium absorbs the most and so the bones and other calcified structures appear virtually white. The soft tissues, with the exception of fat, e.g. the solid viscera, muscle, blood, fluids, bowel wall, etc., all have similar absorptive capacity and appear the same shade of grey on the conventional radiograph. Fat absorbs slightly fewer x-rays and therefore appears a little blacker than the other soft tissues.

Radiodensity as a function of thickness of the object. Here the object to be filmed is of homogeneous composition and has a stepwise range of thickness. Gray shading indicates degree of

absorption of the x-rays.

Thickness kept constant while composition varies

0,00131,911,34 1,01 - 1,09 0-,94

g/sm2

In Figure A imagine the structures through which the x-ray beam has passed from back to front: skin of the back; subcutaneous fat; lots of muscle encasing the flat blades of the scapulae, vertebral column, and posterior shell of the rib cage; then the lungs with the heart and other mediastinal structures between them; the sternum and anterior shell of the ribs; pectoral muscles and subcutaneous fat; breast tissue and, finally, skin .

Note the additional crescents of density that are added in Figure B, where the x-rays have had to traverse the female breast in addition to all the other tissue layers. Below the shadow of the breast and above that of the diaphragm the film is blacker where more rays have

reached it.

A B

NOTE Always place film so that you seem to be facing the patient.

It is a hat? And what under it?

Various absorption x-ray tissues of a different density create possibility to get diagnostic x-ray images.

research room ( manipulation

room)

Protective wall

Corridor

Photographic Laboratory

room of operator (assistent of doctor)

Doctor’s room

Typical plan of roentgenologic department

Typical plan of cabinet of CT

MAMMOGRAPHYMAMMOGRAPHY

There is a special X-ray method for research of a breast.

X-ray film of a breast

The name of the perceiving device

The name of a technique

The name of the apparatus

Kind of the information

X-ray film

Special methods of a X-ray inspection

Universal X-ray machine

Fistulography

Fistulogram – the roentgenogram after introduction a roentgen contrast substances in ducts of a fistula .

Angiography

Angiograph – the special machine for high-speed filming

Angiogram – a series high-speed filming after a catheterization of vessels and introduction in them a roentgen -contrast agents.

Computed tomography

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.

Computed tomography

• Computed tomography, like conventional radiography, relies on x-rays transmitted through the body. Computed tomography differs from conventional radiography in that it uses a more sensitive x-ray detection system than photographic film, namely gas or crystal detectors (dosimetric detectorss), and manipulates the data using a computer. The x-ray tube and detectors rotate around the patient. The outstanding feature of CT is that very small differences in x-rayabsorption values can be visualized. Compared to conventional radiography, the range of densities recorded is increased approximately 10-fold. Not only can fat be distinguished from other soft tissues, but gradations of density within soft tissues can also be recognized, e.g. brain substance from cerebrospinal fluid, or tumour from surrounding normal tissues. The section level and thickness to be imaged are selected by the operator: the usual thickness is between 1.0 and 10 mm. By moving the patient through the gantry, multiple adjacent sections can be imaged allowing a picture of the body to be built up. Thinner sections provide more accurate information, but more sections are then required for a given volume of tissue.

The The device CT

1- stand which a x-ray tube, dosimetric detectors (gentri), system of collection,

transmissions of impulses on PC.

2 - table for scanning with a cause-conveyer for moving of patient.

3 - computer, in which except for collection signals and reconstruction of image there is saving and transfer information on a control stand.

4 - additional computer and control stand : for the data analysis, selection of areas of the personal interest, reconstructions of image.

1

2

3

4

The x-ray tube and detectors move around the patient enabling a picture of x-ray absorption in different parts of the body to be built up. The time taken for the exposure is in the order of a second or so.

Principle of CT.

X-ray tube

Electronic

detectors

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.

00-1000-1000 10001000 30003000

air water High densestructuresbones

fat

Liver-approx +80 Muscle-approx +55 Kidneys-approx +40

calcification

80- 100

There are two methods of CT scanning: slice-by-slice (usually known as 'conventional' CT) and volume acquisition (usually known as 'spiral' or 'helical' CT). In the conventional slice-by-slice method, the table top supporting the patient comes to a stop for each section. In spiral (helical) CT, the patient is transported continuously through the scanner, so in effect the x-ray beam traces a spiral path, while the data are collected continuously, to create a 'volume of data' within the computer memory. The advantages of spiral CT are:

- a significant reduction in scan times, so much so thatwhole organs can be scanned during a single breath-

hold;- the imaged sections are truly contiguous without gaps or

overlaps due to inconsistent breathing;- better reconstruction to other planes and the possibility

for three-dimensional reconstruction.

Slice-by-slice conventional CT scanning, slices at

specific positions.

Spiral CT scanning

Two methods of CT data collection are in common use: (a) conventional slice-by-slice scanning and (b) spiral (helical) CT, where by the tube rotates continuously and the patient moves gradually through the scanner, so that the effective path of the x-ray beam is a spiral.

Main principles of formation images at CТ

CT tomogram

Three-dimensional reconstructions from spiral CT data. The pelvic

bones, lower spine and femora are shown in three-dimensional

reconstruction. The data can be viewed from any desired direction

by appropriately instructing the computer.

NEW STEP IN CT (multispiral CT)

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:

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.

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

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.

Interventional radiology• Needle biopsy under imaging control is widely practised

both for lung tumours and abdominal masses of all kinds. Transhepatic catheterisation of the portal vein and embolisation of varices.

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

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

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

• Percutaneous removal of residual biliary duct stones through the T' tube tract.

• Percutaneous catheterisation and drainage of intraabdominal abscesses.

dense

Radiation hazards• X-rays used in conventional radiography and CT, as well as gamma rays and

other radionuclide emissions, are harmful. Natural radiation from the sun, radioactivity in the environment, together with atmospheric radioactivity from nuclear bombs and other man-made ionizing radia tions contribute a genetic risk over which an individual doctor has no control. However, ionizing radiation for medical purposes is of several times greater magnitude than all other sources of man-made radiation and is under the control of doctors. It is their responsibility to limit the use of x-rays and other ionizing radiations to those situations where the benefit clearly outbalances the risks. Unnecessary radiation is to be deplored. The principle to be used is the so-called ALARA principle: 'as low as reasonably achievable,. This is achieved by the use of appropriate equipment and good technique - limiting the size of the x-ray beam to the required areas, limiting the number of films to those that are necessary, keeping repeat examinations to a minimum and ensuring that the examination has not already been performed. Just as important as these factors, all of which are really the province of those who work in the x-ray department, is the avoidance of unnecessary requests for x-ray examinations, particularly those that involve high radiation exposure such as barium enema, lumbar spine x-rays and CT examinations. If possible, alternative techniques such as ultrasound or MRI should be considered.