Open Access Objective

OBJECTIVES This study sought to determine whether arterial spin labeled (ASL) cardiac magnetic resonance (CMR) is capable of detecting clinically relevant increases in regional myocardial blood flow (MBF) with vasodilator stress testing in human myocardium. BACKGROUND Measurements of regional myocardial perfusion at rest and during vasodilatation are used to determine perfusion reserve, which indicates the presence and distribution of myocardial ischemia. ASL CMR is a perfusion imaging technique that does not require any contrast agents, and is therefore safe for use in patients with end-stage renal disease, and capable of repeated or continuous measurement. METHODS Myocardial ASL scans at rest and during adenosine infusion were incorporated into a routine CMR adenosine induced vasodilator stress protocol and was performed in 29 patients. Patients who were suspected of having ischemic heart disease based on first-pass imaging also underwent x-ray angiography. Myocardial ASL was performed using double-gated flow-sensitive alternating inversion recovery tagging and balanced steady-state free precession imaging at 3-T. RESULTS Sixteen patients were found to be normal and 13 patients were found to have visible perfusion defect based on first-pass CMR using intravenous gadolinium chelate. In the normal subjects, there was a statistically significant difference between MBF measured by ASL during adenosine infusion (3.67 1.36 ml/g/min), compared to at rest (0.97 0.64 ml/g/min), with p 0.0001. There was also a statistically significant difference in perfusion reserve (MBFstress/MBFrest) between normal myocardial segments (3.18 1.54) and the most ischemic segments in the patients with coronary artery disease identified by x-ray angiography (1.44 0.97), with p 0.0011. CONCLUSIONS This study indicates that myocardial ASL is capable of detecting clinically relevant increases in MBF with vasodilatation and has the potential to identify myocardial ischemia. (J Am Coll Cardiol Img 2011;4:1253– 61) © 2011 by the American College of Cardiology Foundation


Objective
To evaluate the reproducibility of three coronary artery wall imaging techniques.

Background
Coronary wall thickness measurements must be highly reproducible to be useful in longitudinal studies. While 2D turbo-spin-echo (TSE) and spiral techniques are commonly used, 3D techniques reduce partial-volume effects and allow greater vessel coverage. Recently, 3D coronary wall imaging was demonstrated with 100% respiratory efficiency (RE) using beat-to-beat respiratory motion correction (B2B-RMC) [1] which uses motion information determined from low resolution 3D images of the fat around the vessel as a surrogate for vessel motion. Here we assess the reproducibility of this technique together with that of navigator-gated 2D TSE and spiral acquisitions.

Methods
Cross-sectional right coronary artery wall images were obtained in 10 healthy subjects on a Siemens 1.5T Avanto scanner using dark-blood prepared B2B-RMC 3D spiral imaging, navigator-gated 2D TSE imaging and navigator-gated 2D spiral imaging. Acquisition order was randomized and subjects were imaged on two separate occasions to assess inter-study reproducibility using the intra-class correlation-coefficient (ICC) and Bland Altman analysis. All acquisitions used 0.7x0.7mm inplane resolution. B2B-RMC 3D spiral acquisitions acquired 8x3.0mm slices (16x1.5mm reconstructed) and 2D techniques acquired 1x6mm slice. Navigator-gated techniques used a 5mm window while B2B-RMC excluded data acquired at only very extreme respiratory positions, retrospectively correcting the rest. Durations, assuming 100% RE, were 600 cardiac cycles (CC) for B2B-RMC, 75CC for 2D spiral and 202-576CC for 2D 1 Imperial College London, London, UK Full list of author information is available at the end of the article Figure 1 Example images obtained from one volunteer using all techniques. The4x1.5mm slices shown of the 3D acquisition correspond to the single 6mm slices of the 2D acquisitions. There is a high degree of visual similarity between the initial (upper) and repeat images (below) acquired 29 days apart. Respiratory efficiency in the initial studies was 100% B2B-RMC, 40% 2D spiral and 38* TSE. In the repeat studies respiratory efficiency was 100% B2B-RMC, 55% 2D spiral and 40% 2D TSE.
A single slice was selected from each 3D acquisition for comparison with the 2D acquisitions. For all acquisitions, average wall thickness was obtained from circles drawn around the outer and inner edges of the vessel wall. The intra-and inter-observer reproducibility of this measurement technique was analysed in 20 images.

Results
Example images from one subject are shown in figure 1. 92% of acquisitions were successful. RE, wall thickness and acquisition durations are presented in Table 1. B2B-RMC RE was less variable and significantly higher than navigator gating (99.6±1.2%vs.39.0±7.5%,p<0.0001) and there was no significant difference in vessel wall thickness between techniques(p=ns).

Conclusions
ICCs were good for the 2D techniques and excellent for the 3D technique. The high RE of B2B-RMC enables reproducible 3D coronary wall assessment within a reasonable duration which will permit improved assessment of atherosclerotic disease.