Diagnostic and interventional radiology
Accurate diagnosis is the key to good surgical practice. Over the last two decades the introduction and increased availability of new imaging modalities have made the diagnostic process easier. Imaging helps to resolve the uncertainties of diagnosis based on physical signs and clinical judgement. To achieve the optimum diagnostic potential it is necessary to understand the complexities of modern imaging and to recognise the most appropriate test to fit the clinical context. Communication between the clinician and radiologist is vital for each to understand the clinical problem, and the strengths and weaknesses of the imaging test selected. An ability to interpret images gives a new depth of understanding of the disease process and of the nature and timing of surgical intervention.
There is no standard approach to imaging although some basic principles apply. It is generally good practice to perform the simplest and least expensive test first if this will provide the answer. For example, the plain abdominal film remains the diagnostic cornerstone in assessing the acute abdomen; in a patient with a clear history of biliary colic, a simple ultrasound examination may be sufficient to determine management. However, in a patient with a more complex clinical presentation, it may be more cost-effective to perform a more expensive test [e.g. computerised tomography (CT) scan] early in the diagnostic work-up as this may lead to a more confident diagnosis and management, and potentially shorten the hospital stay. Cost-effectiveness requires that more complex tests are not merely layered on top of existing more standard procedures. Through consultation, the best test must be determined. The selection of the best investigation for a particular clinical context has been made more complex by the rapid changes in existing technology. The development of spiral (helical) CT, for example, has created new diagnostic possibilities based on the patterns of arterial and venous blood flow providing information not previously available on older equipment. Decision making therefore must be tailored to both the available technology and local expertise. It is also essential to view the imaging results in conjunction with the clinical condition of the patient and to treat the patient rather than the X-rays. In a patient with inflammatory bowel disease, for example, the extent and severity of the abnormality demonstrated on a small bowel barium examination may have little correlation with the patient’s clinical presentation (Fig. 2.1). In contrast, a patient with fulminant colitis may be clinically toxic but with only minimal signs on the plain film before the reflex dilatation signaling toxic megacolon develops.
There is a general increase in public awareness of the adverse effect of radiation in the induction of cancer and genetic defects. Most of the received ionising radiation comes from the sun and earth’s core. However, medical radiation accounts for approximately 12 per cent of the total received by humans.
As more nonradiation dependent imaging techniques become more widely available [e.g. ultrasound, magnetic resonance imaging (MRI)], radiation hazard is an increasingly important factor influencing the selection of investigation, particularly in children and young people. The effective dose imparted by a CT scan, for example, is equivalent to 400 chest X-rays (CXRs). However, this theoretical risk must be balanced against the likely diagnostic yield of the examination in terms of benefit to the patient. The aim must be to reduce unnecessary investigations, which not only add needlessly to patient irradiation but also waste limited resources and increase waiting times. The Royal College of Radiologists has published a very useful booklet, Making the Best Use of a Department of Clinical Radiology (see Further reading section). This gives guidelines for investigations most likely to contribute to the clinical diagnosis and management in particular clinical situations. It highlights the chief causes of wasteful use of radiology (Tab. 2.1). Other factors must also be taken into consideration when deciding on the appropriate investigation, including the age and condition of the patient and their ability to undergo the chosen investigation (Tab. 2.2).
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