3T contrast-enhanced whole heart coronary MRA using 32-channel cardiac coils for the detection of coronary artery disease

Abstract

Introduction: The development of contrast enhanced whole heart coronary MR angiography (CMRA) at 3T has shown promising results in clinical studies for the detection of significant coronary artery stenoses. However, the imaging time (~ 9 minutes) and spatial resolution (1.3 × 1.3 × 1.3 mm) remain major limitations. Newly available 32-channel cardiac coils allow greater acceleration factors, and thus reduced imaging time, reduced contrast agent dose and higher spatial resolution. Purpose: To evaluate the diagnostic accuracy of 3T contrast enhanced whole-heart CMRA with an optimized protocol for improved spatial resolution and reduced scan time using a 32-channel cardiac coils. Imaging time, image quality score, and diagnostic accuracy are evaluated in 32 consecutive patients with suspected coronary artery disease using conventional x-ray coronary angiography (CAG) as reference standard. Methods and Materials: 32 patients with suspected coronary artery disease who were scheduled for coronary angiography (CAG) (mean age 62 ± 12 y) underwent MRCA at 3T (MAGNETOM Tim Trio, Siemens) after informed consent was obtained. A 32-channel receiver coil was used for data acquisition (Invivo, Gainesville, FL). For image acquisition an ECG-triggered, navigator-gated, inversion-recovery prepared, segmented gradient-echo sequence was used with an acceleration factor of three in the phase-encoding direction using GRAPPA reconstruction. Imaging parameters included: voxel size 0.55x0.55x0.65 mm (interpolated from 1.1x1.1x1.3 mm), TR/TE = 3.3/1.5 msec, flip angle = 20°, bandwidth = 700 Hz/pixel, TI=200 msec. Contrast agent (0.15 mmol/kg body weight, MultiHance, Bracco, Italy) was intravenously administered at a rate of 0.3 ml/sec. For image analysis, standard 15-segment AHA classification system was used and only segments with a reference diameter of ≥ 1.5 mm were included, excluding those segments distal to complete occlusions. The diagnostic accuracy in detecting significant stenoses (≥50% of vessel lumen) was evaluated on the assessable segments only, as well as on all segments. Both non-assessable segments and the segments of the patients where the scan failed were considered to have a stenosis. Results: Whole-heart CMRA was successfully completed in 30 of 32 (94%) patients who were scheduled for CAG. The averaged imaging time was 5.9 ± 1.2 min. 40 of 392 segments (10%) with a reference luminal diameter > 1.5 mm on QCA were determined as non-assessable. On assessable segments only, the sensitivity, specificity, and accuracy of coronary MRA for detecting significant stenoses were 93% (78-99%), 99% (97-99%), 98%