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Researchers says heavy patients might expect poorer image quality on CT scans of the heart.

The same goes for patients with a high heart rate, as well as black patients, Melvin E. Clouse, MD, of Beth Israel Deaconess Medical Center in Boston, and colleagues reported in the January issue of the American Journal of Roentgenology.

All three factors, along with the presence of a breathing artifact, were significantly associated with poorer image quality in a multicenter, randomized controlled trial (P<0.001).

"Certain patient characteristics, such as size, must be considered when adjusting scanner settings such as kV and mA to scan individuals undergoing coronary CT angiography," the researchers wrote. However, none of these factors was associated with a drop in diagnostic accuracy -- only increasing prevalence of coronary artery calcification and age were significantly associated (P<0.001).

The researchers wrote that physiologic factors including high heart rate, arrhythmia, and high coronary calcium burden continue to limit the diagnostic accuracy of CT compared with coronary angiography, but they haven't been well studied.

So, to investigate patient characteristics associated with image quality and their impact on the diagnostic accuracy of CT scans for the detection of coronary artery stenosis, the researchers assessed 291 patients with suspected disease enrolled in the CORE-64 study (Coronary Evaluation Using Multidetector Spiral Computed Tomography Angiography Using 64 Detectors).

They assessed image quality, as well as the accuracy with which stenoses were detected. They also measured the effect of coronary artery calcification, obesity, heart rate, and heart rate variability on image quality and diagnostic accuracy. Overall, optimal image quality was achieved in 44% of patients, adequate quality in 46%, and poor quality in 10%.

The researchers found that three factors were associated with poorer image quality:

• Increasing body mass index (BMI) (OR 0.89, P<0.001)

• Increasing heart rate (OR 0.90, P<0.001)

• Presence of breathing artifact (OR 4.97, P≤0.001)

"Training patients with breath-hold testing before scanning is important to avoid breathing artifacts that limit image quality," the researchers wrote.

Blacks also had significantly poorer image quality than whites, although the findings were not as strongly significant as expected because the population was small (OR 0.58, P=0.04). Gender, coronary artery calcification, and heart rate variability were not associated with poorer image quality. With regard to diagnostic accuracy, the researchers found a significant association between reduced accuracy and increased coronary artery calcification in a vessel-level analysis.

Older age, too, was associated with worse accuracy, but none of the other factors measured -- including BMI and heart rate -- was associated with accuracy. "Higher heart rate was a predictor of reduced image quality," the researchers wrote. "However, in both patient and vessel analyses, heart rate was not associated with significantly reduced diagnostic accuracy."

The researchers noted that their study was limited by some of its cutoff points, which may preclude it from generalizable applicability.

Source: American Journal of Roentgenology

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