Computerised tomography Health Dictionary

A technique using X-RAYS or ULTRASOUND to build up a focused image of a ‘slice’ through the body at a given level. By producing a series of such slices at di?erent depths, a three-dimensional image of the body structures can be built up.... tomography

Tomography is an X-ray examination technique in which only structures in a particular plane produce clearly focused images. Whole-body computed tomography was introduced in 1977 and has already made a major impact in the investigation and management of medical and surgical disease. The technique is particularly valuable where a mass distorts the contour of an organ (e.g. a pancreatic tumour – see PANCREAS, DISORDERS OF) or where a lesion has a density di?erent from that of surrounding tissue (e.g. a metastasis in the LIVER).

Computed tomography can distinguish soft tissues from cysts or fat, but in general soft-tissue masses have similar appearances, so that distinguishing an in?ammatory mass from a malignant process may be impossible. The technique is particularly useful in patients with suspected malignancy; it can also de?ne the extent of the cancer by detecting enlarged lymph nodes, indicating lymphatic spread. The main indications for computed tomography of the body are: mediastinal masses, suspected pulmonary metastases, adrenal disease, pancreatic masses, retroperitoneal lymph nodes, intra-abdominal abscesses, orbital tumours and the staging of cancer as a guide to e?ective treatment.... computed tomography

See

PET scanning.... positron emission tomography

Also known as ‘expert systems’, these are computer software systems intended to help doctors make clinical decisions. Primary care medicine is especially noted for its uncertainty by virtue of being most patients’ ?rst point of contact with health care, confronting the clinician with many ‘undi?erentiated’ health problems. So far, these systems have not been as e?ective as expected because of a failure to ana-lyse the needs of primary care. Simple procedures to prompt the delivery of treatment to patients with chronic conditions have improved care quality, but work needs to be done on their cost-e?ectiveness. The aim of more complex computerised support systems will be to forecast likely future events and the possible e?ectiveness of proposed interventions, based on available information about the patient and an understanding of the risks and e?cacy of interventions by doctors and other experts.

One example, called ISABEL, can be accessed by paediatricians to check on their diagnosis and management of many childhood disorders.... computerised decision-support systems

See PET SCANNING.... positron-emission tomography (pet)

(CT) a form of X-ray examination in which the X-ray source and detector (CT scanner) rotate around the object to be scanned and the information obtained can be used to produce cross-sectional images (see cross-sectional imaging) by computer (a CT scan). A higher radiation dose is received by the patient than with some conventional X-ray techniques, but the diagnostic information obtained is far greater and should outweigh the increased risk. CT scanning can be used for all parts of the body. The data obtained can be used to construct three-dimensional images of structures of interest. See also multidetector computerized tomography; spiral CT scanning.... computerized tomography

(MDCT) a development of *spiral CT scanning that uses more than one array of detectors opposite the X-ray tube, so that more tissue can be included, with thinner cuts, in a single rotation of the machine. This is particularly important for three-dimensional reconstruction of tissues. It also allows volumetric scanning or *isotropic imaging, which are best achieved when the thickness of the slice is similar to the size resolution of the detectors in the other two planes. Modern CT scanners are now usually equipped with between 16 and 640 detector arrays. The technique is particularly valuable for imaging fast-moving structures, such as the heart.... multidetector computerized tomography

(OCT) a class of optical tomographic techniques that allows extremely high-quality micrometre-resolution three-dimensional images to be obtained from within optical scattering media (e.g. biological tissue). OCT is proving valuable in ophthalmology, for noninvasive imaging of the ocular structures, and in cardiology for visualizing the interior of coronary arteries using a specialized *catheter. See also spectral domain optical coherence tomography.... optical coherence tomography

see SPECT scanning.... single photon emission computed tomography

(Fourier domain OCT) a noncontact noninvasive imaging technique that can reveal layers of the retina by looking at the interference patterns of reflected laser light. Automated software is able to outline the retinal nerve-fibre layer with great precision, which is relevant in glaucoma.... spectral domain optical coherence tomography