Sunday, December 27, 2009

Diagnostic radiology / Medical Applications

a) Diagnostic radiology

In a conventional X ray examination, radiation from a machine passes through the patient. X rays penetrate flesh and bone to different degrees and produce images of the internal structures of the body on photographic film. In some cases, the images are captured and processed electronically. The value of these images explains why doctors conduct as many as one diagnostic X ray per person per year in developed countries.

The parts of the body most frequently examined are the chest, limbs, and teeth, each accounting for about 25 per cent of the total number of examinations. Doses are fairly low - about 0.1 mSv from a chest examination, for example. Effective doses from other types of examination, such as the lower spine, are higher because organs and tissues that are more sensitive to radiation are exposed to a greater degree. Examinations of the lower bowel using a barium enema result in a substantial effective dose around 6 mSv; only 1 per cent of all examinations are of this type.



Computed tomography
dose (mSv)

Conventional X ray
dose (mSv)



















Lower spine



Lower bowel



Limbs and joints

Table (11):Typical doses to patients from conventional X ray and computed tomography examinations
( UNSCEAR 2000 Report, Annex D. Vol. 1 Tables 15 and 19 )

The use of computed tomography (CT) has increased considerably in recent years to the point where approximately 5 per cent of all procedures in diagnostic radiology in developed countries are CT scans. With this technique, a fan-shaped beam of X rays is rotated around the patient and registered on the opposite side by a row of detectors. An image of a slice or section through the ­patient is then reconstructed by a computer and conveys superior diagnostic information. However, doses in CT can be an order of magnitude or more higher than those from conventional X ray examinations.

CT examinations are significant contributors to collective dose from medical diagnosis, and in some countries their contribu­tion is above 40 per cent of the total. Examinations of the lower bowel contribute about 10 per cent of the total collective dose and chest examinations about one per cent. It is clear from these figures that some relatively infrequent procedures can give a far greater dose to the population than the more common examinations. This is why a CT scan is not used where an ordinary X ray examination would suffice for a sound diagnosis.

The diagnostic procedure that gives the highest doses, however, is interventional radiology. This is where a physician performing a procedure inside the patient's body uses a series of X rays to 'see' into the patient in real time. This allows a procedure on an internal organ to be carried out without the major surgery that might otherwise have been needed to gain access to the organ. However, these procedures can give patient doses in the range 10-100 mSv and, if not carefully controlled can lead to similarly high doses to surgeons. In some cases, the doses from such procedures have been high enough to cause deterministic effects in patients and surgeons.

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