Cost-effectiveness of Imaging

For Medical Students

What It Shows

A scan's cost is its price, the delay it adds, the incidental findings it produces and the further tests those generate. 5.1.6 covers imaging pitfalls.

Its benefit is only the change in management it produces, which is often nothing and is occasionally decisive. 5.1.3 covers choosing the investigation.

The test of whether a scan was worth doing is whether anything was done differently because of it.

Where It Misleads

A scan that confirms a decision already made has a low benefit and a real cost, and it is the commonest scan requested. 5.1.2 covers that comparison.

A scan that changes the operation has a high benefit and is worth almost any reasonable cost.

A scan requested for reassurance usually fails on its own terms, because an incidental finding is the opposite of reassuring. 5.1.6 covers imaging pitfalls.

No figures appear for any accuracy comparison on this page, under decision 028, and no cost figure appears either: prices and incidence rates are both the kind of number this environment cannot check.

MRCS Level

How Good It Is

In a viva this is the resource question and the expected answer reaches the change in management quickly.

The expected points are the full cost, the benefit as a change in management, the incidental finding problem, and what a normal result would do.

Say that the benefit is the management change and not the diagnostic yield. 5.1.3 covers choosing the investigation.

Say that an incidental finding has its own cost and name it. 5.1.6 covers imaging pitfalls.

Say that a scan whose normal result changes nothing was not indicated.

Where It Misleads

The reasoning expected is that a test's value depends on the prior probability and on whether either result changes what happens next.

In a knee where the examination has localised the problem the prior is high, the scan confirms, and the value is in the detail rather than the diagnosis. 5.1.2 covers that comparison.

In an unlocalised knee the prior is low, so a positive finding is more likely to be prevalent than causal and the scan has created a problem. 5.6.2 covers meniscal signal grading.

Delay has a cost that is easy to ignore because nobody is billed for it, and in an acute knee it is the dominant cost. 5.1.4 covers imaging pathways.

FRCS Level

Where It Misleads

At decision level cost effectiveness is a service argument that gets made badly in both directions.

Restricting access on cost produces delay, repeat consultations and operations planned on worse information, and those costs land somewhere else in the system. 5.1.4 covers imaging pathways.

Opening access produces incidental findings at scale and a workload of reassurance, which also lands somewhere else. 5.1.6 covers imaging pitfalls.

The useful version of the argument is per presentation rather than per modality, because the same scan is excellent for one question and wasteful for another. 5.1.3 covers choosing the investigation.

A cost effectiveness claim needs figures, and this page states none for the reason the whole section states none.

Fellowship Level

Where It Misleads

At fellowship level the economics are mostly outside the clinician's control and the decisions are still theirs to make.

The marginal scan in a tertiary clinic is usually a repeat, and its value depends entirely on what the first one could not answer. 5.5.1 covers the standard protocol.

Advanced techniques have a cost structure of their own and a benefit that is established in research populations rather than in clinics. 5.18.1 covers quantitative imaging.

An incidental finding transfers cost to the patient as anxiety and to the system as follow up, and neither appears in the price. 5.1.6 covers imaging pitfalls.

Published cost effectiveness work is bound to a health system and a price list, so transferring its conclusions across systems is an extrapolation. 5.1.7 covers evidence based imaging.

The decision that saves the most is usually not to request, and it is the hardest to defend afterwards if anything is later found. 4.23.7 covers the medico legal setting.