CT Coronary Calcium Score — Unenhanced ECG-Gated
Carina to below the cardiac apex.
Timings, volumes and delays here are representative values drawn from published guidance. Scanner generation, injector, cardiac output and local preference all move them. Confirm against your department's own protocol before you rely on a number.
When to use it
- Cardiovascular risk stratification in an asymptomatic adult where the result would change a decision about preventive therapy.
- Refining risk when a calculated risk score sits near a treatment threshold.
- As a preliminary acquisition before coronary CT angiography, where local practice includes it.
Technique
- The Agatston method is tied to its acquisition parameters: it was derived at 3 mm sections and has been carried across to multidetector CT at around 120 kV with 2.5-3 mm sections, with tube current adjusted for habitus.
- Deviating from the standard section thickness or tube potential changes the score, so published thresholds and percentile tables no longer apply.
- Typical effective dose is around 1 mSv.
- A calcium score derived from a contrast-enhanced acquisition is not equivalent to a true unenhanced Agatston score.
Where it goes wrong
- Using this study to evaluate acute or stable chest pain answers the wrong question — a zero score does not exclude non-calcified obstructive disease.
- Non-standard reconstruction parameters silently invalidate the numeric result and the percentile.
- Motion at high or irregular heart rates duplicates calcified plaque and inflates the score.
- Scoring off a routine non-gated chest CT gives a categorical estimate at best, not an Agatston number.
Clinical questions that reach this study
Contrast
Acquisition
- Breathing
- Single inspiratory breath-hold.
- Reconstruction
- Contiguous ECG-gated axial sections in a standard kernel, conventionally at 2.5-3 mm, scored by the Agatston method and reported with a percentile for age and sex.
- Preparation
- No contrast, no cannula, no fasting. Heart-rate control is usually unnecessary but helps if the rate is fast and irregular.
Phases
Each phase is authored once and shared across every protocol that uses it, so the physiology below is the same wherever you meet it.
- Non-contrast (unenhanced)No injection. Acquired before any contrast is given.
Shows intrinsic tissue attenuation, and nothing else. The transferable principle is that contrast is anti-signal for anything that is already dense: calcification, acute haemorrhage, urinary and biliary calculi, iodine-containing or haemorrhagic fluid, and intrinsic fat all lose conspicuity, or become uninterpretable, once surrounding tissue enhances. It is also the only baseline against which enhancement can be measured, so any protocol that quantifies enhancement or washout (a lesion "enhances by X HU", adrenal absolute washout, renal mass characterisation) is arithmetically impossible without it. Conversely, an unenhanced series adds dose and no information whenever the question is purely about vascularity or perfusion.
Safety checks this protocol carries
Derived from the contrast agent and phases above, not authored here — which is why they cannot drift apart from what the protocol actually does.
- Child-sized technique and contrast dose· radiographer at scan