Ultralow-dose CT shows potential to substitute for standard coronary calcium imaging

Compared side-by-side with standard cardiac CT for calcium scoring, ultralow-dose CT shows good sensitivity, specificity and overall accuracy despite its markedly lower radiation dose. In fact, it’s unlikely to miss coronary calcification in patients with at least moderate calcium load and could offer a sensible alternative for some patients sent for coronary CT angiography.

That’s according to researchers at Santa Casa de Misericordia Hospital in Porto Alegre, Brazil, who reviewed 74 cases in which patients with suspected or known coronary artery disease were scanned with both standard coronary calcium score (CCS) and ultralow-dose CT (ULDCT) protocols.

The team’s work was published online April 14 in Clinical Radiology.

Dr. Vinícius Valério Silveira de Souza and colleagues graded coronary artery calcification (CAC) on ULDCT using a scale of zero to three for the complete exam and for each individual coronary segment.

The sum of all individual coronary segment scores generated a ULDCT total CAC score, and the authors compared these results with standard Agatston scores on CCS.

Their key findings:

• Standard CCS detected coronary calcification in 47 patients (63.5 percent), while ULDCT did so in 42 patients (56.8 percent).
• The sensitivity and specificity of the ULDCT total CAC score ≥1 was 80.9 percent and 85.2 percent, respectively, with an accuracy of 82.4 percent.
• The area under the receiver operating characteristic curve for the presence of CAC was 0.87.

Meanwhile, the mean radiation dose length product was 77.7 mGy-cm with CCS versus just 9.3 mGy-cm with ULDCT.

“With a radiation dose similar to frontal and lateral chest radiography, ULDCT was able to match coronary CT angiography (CCTA) scan range acquisition when planned using standard CCS acquisition, despite a significant increase in image noise,” Silveira de Souza et al. write in their discussion. “As the utility of CCS before CCTA has been questioned, ULDCT could be a reasonable alternative for planning the CCTA scan range while still detecting coronary calcification.”

The authors acknowledge several limitations to their study design, including its small sample size.

In their conclusion, the authors reiterate the good sensitivity, specificity and overall accuracy of ULDCT in their study, underscoring the vast reduction in radiation dose. To this they add that ULDCT “enables CCTA coverage to be planned with almost identical performance in comparison to CCS.”

ULDCT “may become a simple and viable alternative to standard CCS acquisition in patients referred to CCTA for which radiation dose would be a major concern,” they write.