Contrast Timing Is Haemodynamic

01The evidence

• Contrast medium administration protocols specify fixed delays and injection rates, which assumes a predictable circulation time across patients.Contrast medium administration

02The tension

Protocols are fixed because they are simple and because most patients have normal circulation. The patients who most need imaging, those with heart failure or sepsis, are exactly the ones whose circulation is abnormal, and their scans are the ones most likely to be mistimed.

03The theory

A contrast bolus travels with the blood. Its arrival time at a target vessel is the circulation time from injection to that vessel, which is inversely related to cardiac output and directly related to the volume it must traverse.

If timing is haemodynamic, then the optimal delay is a patient-specific quantity computable from a cardiac output estimate. A fixed delay will be early in low-output states and late in high-output states, which is the observed pattern of non-diagnostic scans.

The prediction is that image quality should improve when delay is computed rather than fixed, especially in patients with abnormal haemodynamics, and that a simple bedside estimate should be enough to capture most of the benefit.

The practical consequence is that protocols should include a haemodynamic input, which is available from the patient record, and that scanner software could compute the delay automatically.

04What this is not

05Predictions

• P1Haemodynamic-adjusted delay should improve diagnostic quality in abnormal circulation.
• P2Fixed delays should mistime in the predicted direction at high and low cardiac output.
• P3A bedside estimate should capture most of the improvement.

06What would refute it

Image quality independent of delay adjustment would leave fixed protocols adequate.

07What it would change

It would personalise contrast protocols and reduce repeat scans.