Stenosis quantification in coronary CT angiography: impact of an integrated circuit detector with iterative reconstruction.

OBJECTIVES: The objective of this study was to assess the value of an integrated circuit (IC) detector, potentially improving spatial resolution by means of reduced cross talk between detector channels, in coronary computed tomographic (CT) angiography regarding image quality and stenosis quantification compared with conventional detector technology.
MATERIALS AND METHODS: In the ex vivo part of the study, a coronary phantom including 63 defined stenoses and 7 plaque densities (degree of stenosis, 10%-90%; plaque densities, -100 to 1000 Hounsfield unit [HU]) was loaded with contrast agent diluted to 300 HU and placed in an anthropomorphic chest phantom. The phantom was scanned in 0-, 45-, and 90-degree orientations to the z-axis of the CT scanner table. Images were acquired using 128-section dual-source CT equipped with IC and with conventional detector technology. Data were reconstructed with filtered back projection (FBP) and with sinogram-affirmed iterative reconstruction (IR) at a slice thickness of 0.6 mm (increment, 0.4 mm). Data acquired with the IC detector were additionally reconstructed with a slice thickness of 0.5 mm (increment, 0.3 mm) combined with IR. Two readers rated image quality; image noise and degree of stenosis were assessed. In the in vivo part of the study, phantom observations were validated in 30 consecutive patients (11 women; mean [SD] age, 62 [13] years; mean [SD] heart rate, 81 [17] beats per minute) undergoing coronary CT angiography with IC for clinical indications. Images of the patients were reconstructed with FBP (slice thickness, 0.6 mm) and with IR (slice thickness, 0.5 mm) and were assessed for image quality and degree of stenosis. Interreader agreement for image quality was evaluated using intraclass correlation coefficients. The image quality was compared with the Wilcoxon signed rank test. The image noise and the degree of stenosis were compared with the Student t test for paired samples.
RESULTS: The interreader agreement for the assessment of image quality was substantial (intraclass correlation coefficients, 0.79). The image quality was significantly (P < 0.001) higher for the images acquired with the IC detector as compared with the conventional detector. The image noise with IR was significantly (P = 0.020) reduced for the IC detector as compared with the conventional detector. The IC detector yielded significantly more accurate results regarding stenosis grading when compared with the images acquired with the conventional detector regarding both FBP (mean [SD] error FBP, 12.1% [7.6%] vs 13.7% [7.6%]; P = 0.043) and IR (mean [SD] error IR, 10.5% [6.6%] vs 13.0% [6.9%]; P < 0.001). The images with a slice thickness of 0.5 mm reconstructed with IR (mean [SD] error, 8.8% [5.9%]) obtained by the IC detector significantly (P < 0.001) improved measurement accuracy in the phantom as compared with FBP with a slice thickness of 0.6 mm (mean [SD] error, 12.1% [7.6%]). In the patients, we found a significantly (P < 0.001) higher image quality, and stenoses were quantified significantly (P = 0.009) smaller with FBP as compared with IR (mean stenosis, 47.6% vs 42.1%; mean difference, 5.5%).
CONCLUSIONS: Our ex vivo and patient study indicates significantly reduced image noise and more accurate stenosis quantification in coronary CT angiography when acquiring data using an IC detector and combining IR with high-resolution images as compared with conventional detector technology and FBP reconstructions.