Introduction
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
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).