Radiology — Radiology, NMC MBBS licence examination syllabus (Nepal Medical Council).
A scan that will not change what you do is not an investigation. It is a delay with a radiation dose attached.
Very few doctors will report images. Almost all of them will request images, several times a day, and will make decisions from the reports that come back.
That is what this chapter covers: which test answers which question, what a request costs the patient, how to look at a film without missing the second abnormality, and why a report is not a diagnosis.
Plain X-ray is cheap, fast and available almost everywhere. It shows bone, air and fluid well, and soft tissue poorly. It uses ionising radiation, though far less than CT.
Ultrasound uses no ionising radiation at all, is portable and can be repeated freely. That makes it the first choice in pregnancy and in children whenever it can answer the question. Its limitations are that it is operator-dependent and that sound will not travel through gas or bone — so it is poor for the lungs and for anything behind bowel gas.
CT is fast and detailed and has become the workhorse of trauma and the acute abdomen. Its cost is a substantially higher radiation dose than plain films, which is why each request should be justified — particularly in young patients.
MRI uses no ionising radiation and gives the best soft tissue detail, especially for the brain, spinal cord and joints. It is slow, expensive and less available — and it carries a safety consideration the others do not: metal. Implants, pacemakers and retained metallic fragments must be established before a patient enters the scanner.
Every request that uses ionising radiation carries a small increase in lifetime cancer risk. That risk is usually worth accepting — but only if the scan will actually help.
The test to apply is simple and demanding: will the result change management? If a normal result and an abnormal result would lead to the same next step, the scan is not justified — however reassuring it might feel to order one, and however much the patient expects it.Two groups need particular thought:
But the reverse error is real too. Withholding a scan that would identify a life-threatening problem in a pregnant woman harms both her and the fetus. A necessary CT in a shocked trauma patient is done. The rule is to ask the question, not to refuse imaging in pregnancy.
No dose figures are given in this chapter, deliberately. Dose depends on the machine, the protocol and the patient, and published comparisons differ widely between sources — so a memorised number would be confidently wrong.
The commonest error in film interpretation is not failing to recognise an abnormality. It is finding one and stopping — the eye settles on the obvious lesion and never examines the rest.
A fixed system prevents that, and it matters more than which system you use. One workable order:
Two errors follow from treating a report as an answer rather than as evidence.
A normal image does not exclude the disease. Early infection may not yet be visible. A small perforation may show no free air. An early ischaemic stroke commonly looks normal on initial CT — which is precisely why that scan is done to exclude bleeding rather than to confirm infarction. If the clinical picture is convincing, act on it and repeat or escalate the imaging.
An abnormal image is not always the explanation. Incidental findings are common, particularly on CT, and most are harmless. Pursuing them generates further tests, anxiety, cost and occasionally procedural harm — for a finding that was never causing symptoms.
The discipline this requires: decide what you think before you look at the report, and notice when the report and the patient disagree. A convincing clinical picture outweighs a reassuring film. Treating the report instead of the patient is how a deteriorating patient gets watched rather than treated.The quality of a report depends heavily on the quality of the request, and this is entirely within your control.
An unhelpful request states a body part and a question mark. "Abdominal pain ? cause" tells the radiologist nothing about where the pain is, how long it has been there, or what you are worried about.
A useful request gives the relevant findings, the duration, and — most importantly — the specific question you want answered. "Right iliac fossa pain 12 hours, tender, raised inflammatory markers, query appendicitis" tells the radiologist exactly where to concentrate.
And say what you fear. A radiologist told that you are worried about a perforation looks specifically for free air. Told nothing, they report what they see in general terms, and a subtle finding you needed may not be commented on.
The broader point: the radiologist is a consultant colleague, not a service counter. Given the clinical problem, they will frequently suggest a better test than the one requested — including sometimes that no imaging is needed at all.
No radiation dose figures, contrast volumes or imaging protocols appear here: dose depends on machine, protocol and patient, and published comparisons differ widely. Use your department's protocols.
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