Background-The extent of the peri-infarct zone by magnetic resonance imaging (MRI) has been related to all-cause mortality in patients with coronary artery disease. This relationship may result from arrhythmogenesis in the infarct border. However, the relationship between tissue heterogeneity in the infarct periphery and arrhythmic substrate has not been investigated. In the present study, we quantify myocardial infarct heterogeneity by contrast-enhanced MRI and relate it to an electrophysiological marker of arrhythmic substrate in patients with left ventricular (LV) systolic dysfunction undergoing prophylactic implantable cardioverter defibrillator placement. Methods and Results-Before implantable cardioverter defibrillator implantation for primary prevention of sudden cardiac death, 47 patients underwent cine and contrast-enhanced MRI to measure LV function, volumes, mass, and infarct size. A method for quantifying the heterogeneous infarct periphery and the denser infarct core is described. MRI indices were related to inducibility of sustained monomorphic ventricular tachycardia during electrophysiological or device testing. For the noninducible versus inducible patients, LV ejection fraction (30Ϯ10% versus 29Ϯ7%, Pϭ0.79), LV end-diastolic volume (220Ϯ70 versus 228Ϯ57 mL, Pϭ0.68), and infarct size by standard contrast-enhanced MRI definitions (PϭNS) were similar. Quantification of tissue heterogeneity at the infarct periphery was strongly associated with inducibility for monomorphic ventricular tachycardia (noninducible versus inducible: 13Ϯ9 versus 19Ϯ8 g, Pϭ0.015) and was the single significant factor in a stepwise logistic regression. Conclusions-Tissue heterogeneity is present and quantifiable within human infarcts. More extensive tissue heterogeneity correlates with increased ventricular irritability by programmed electrical stimulation. These findings support the hypothesis that anatomic tissue heterogeneity increases susceptibility to ventricular arrhythmias in patients with prior myocardial infarction and LV dysfunction.

Purpose To characterize peripheral nerve stimulation (PNS) of an asymmetric head-only gradient coil that is compatible with a commercial high-channel-count receive-only array. Methods Two prototypes of an asymmetric head-only gradient coil set, with 42-cm inner diameter, were constructed for brain imaging at 3T with maximum performance specifications of up to 85 mT/m and 708 T/m/s. 24 volunteer tests were performed to measure PNS thresholds with the transverse (X, left/right; Y, anterior/posterior) gradient coils of both prototypes. 14 volunteers were also tested for the Z-gradient PNS in the second prototype, and were additionally scanned with high-slew-rate EPI immediately after the PNS tests. Results For both prototypes, the Y-gradient PNS threshold was markedly higher than the X-gradient. The Z-gradient threshold was intermediate between those for the X- and Y-coils. Out of the 24 volunteer subjects, only two experienced Y-gradient PNS at 80 mT/m, 500 T/m/s. All volunteers underwent the EPI scan without PNS when the readout direction was set to A/P. Conclusion Measured PNS characteristics of asymmetric head-only gradient coil prototypes indicate that such coils, especially in the A/P direction, can be used for fast EPI readout in high-performance neuroimaging scans with substantially reduced PNS concerns compared to conventional whole-body gradient coils.

Background-MRI can identify patients with obstructive coronary artery disease by imaging the left ventricular myocardium during a first-pass contrast bolus in the presence and absence of pharmacologically induced myocardial hyperemia. The purpose of this multicenter dose-ranging study was to determine the minimally efficacious dose of gadopentetate dimeglumine injection (Magnevist Injection; Berlex Laboratories) for detecting obstructive coronary artery disease. Method and Results-A total of 99 patients scheduled for coronary artery catheterization as part of their clinical evaluation were enrolled in this study. Patients were randomized to 1 of 3 doses of gadopentate dimeglumine: 0.05, 0.10, or 0.15 mmol/kg. First-pass perfusion imaging was performed during hyperemia (induced by a 4-minute infusion of adenosine at a rate of 140 g · kg Ϫ1 · min Ϫ1 ) and then again in the absence of adenosine with otherwise identical imaging parameters and the same contrast dose. Perfusion defects were evaluated subjectively by 4 blinded reviewers. Receiver-operating curve analysis showed that the areas under the receiver-operating curve were 0.90, 0.72, and 0.83 for the low-, medium-, and high-contrast doses, respectively, compared with quantitative coronary angiography (diameter stenosis Ն70%). For the low-dose group, mean sensitivity was 93Ϯ0%, mean specificity was 75Ϯ7%, and mean accuracy was 85Ϯ3%. Conclusions-First-pass