Updated CT, iterative reconstruction boosts coronary stent eval

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A high-definition CT system equipped with iterative reconstruction software provides more reliable detection of coronary in-stent restenosis (ISR) compared with an earlier system using filtered back projection, according to a study published online Sept. 11 in Radiology.

Despite the advantages of coronary CT angiography, evaluation of ISR remains an ongoing challenge, primarily because quantification of lumen narrowing in this application is limited due to beam-hardening artifacts caused by metallic stents and limitations in spatial resolution.

Daniele Andreini, MD, of the department of cardiovascular imaging at Centro Cardiologico in Milan and colleagues, described the diagnostic performance of conventional CT for ISR evaluation as “reasonable,” with an ISR detection rate of 84 percent. However, stents are unassessable in up to 13 percent of cases.

“In general, severely calcified arteries, high body mass index, and high heart rates decrease diagnostic accuracy of multidetector CT because of beam-hardening artifacts, excessive image noise, and limited temporal resolution,” wrote Andreini et al.

Thus, Andreini and colleagues devised a study and enrolled 180 consecutive patients scheduled to undergo invasive coronary angiography (ICA) for suspected ISR between February 2010 and January 2011.

Ninety patients, comprising group A, were imaged on GE Healthcare's Discovery CT 750 HD system, which employs adaptive statistical iterative reconstruction (ASIR) software. The 90 patients in group B were scanned on a GE LightSpeed VCT XT scanner.

Two readers independently evaluated reconstructed images and graded image quality as: 0 for nondiagnostic quality, 1 for adequate image quality, 2 for good image quality and 3 for excellent image quality. ICA served as the reference standard, and intravascular ultrasound (IVUS) images were obtained for 23 patients in group A and 21 patients in group B.

The researchers reported significant differences between the two groups in terms of image quality and analysis of evaluable versus nonevaluable stents in favor of group 1. In group 1, two beam-hardening artifacts were observed. In contrast, in group 2, 14 stent segments were nonevaluable.

All diagnostic accuracy parameters were higher in group 1 than in group 2, with a positive predictive value of 90 percent in group 1 versus 75 percent in group 2. Other measures, including quantitative analysis of ISR and correlation with IVUS measurements of reference vessel area and stenosis diameter, also favored group 1 compared with group 2.

“The reduction of severe artifacts due to stent blooming may explain the higher assessability of stent-treated segments evaluated with multidetector coronary CT angiography performed with the new scanner in comparison with multidetector CT with standard spatial resolution,” wrote Andreini and colleagues.