Comparison between Three-Dimensional Navigator-Gated Whole-Heart MRI and Two-Dimensional Cine MRI in Quantifying Ventricular Volumes

OBJECTIVE: To test whether the method utilizing three-dimensional (3D) whole-heart MRI has an additional benefit over that utilizing conventional two-dimensional (2D) cine MRI in quantifying ventricular volumes. MATERIALS AND METHODS: In 110 patients with congenital heart disease, a navigator-gated, 3D whole-heart MRI during end-systole (ES) and end-diastole (ED), 2D short-axis cine MRI, and phase contrast MRI of the great arteries were acquired. Ventricular volumes were measured by using a 3D threshold-based segmentation for 3D whole-heart MRI and by using a simplified contouring for 2D cine MRI. The cardiac trigger delays of 3D whole-heart MRI were compared with those of a 2D cine MRI. The stroke volumes calculated from the ventricular volumes were compared with the arterial flow volumes, measured by phase contrast MRI. RESULTS: The ES and ED trigger delays of whole-heart MRI were significantly less than cine MRI for both the left ventricle (−16.8 ± 35.9 ms for ES, −59.0 ± 90.4 ms for ED; p < 0.001) and the right ventricle (−58.8 ± 30.6 ms for ES, −104.9 ± 92.7 ms for ED; p < 0.001). Compared with the arterial flow volumes, 2D cine MRI significantly overestimated the left ventricular stroke volumes (8.7 ± 8.9 mL, p < 0.001) and the 3D whole-heart MRI significantly underestimated the right ventricular stroke volumes (−22.7 ± 22.9 mL, p < 0.001). CONCLUSION: Three-dimensional whole-heart MRI is often subject to early timing of the ED phase, potentially leading to the underestimation of the right ventricular stroke volumes.

Coronary Microembolization with Normal Epicardial Coronary Arteries and No Visible Infarcts on Nitrobluetetrazolium Chloride-Stained Specimens: Evaluation with Cardiac Magnetic Resonance Imaging in a Swine Model

OBJECTIVE: To assess magnetic resonance imaging (MRI) features of coronary microembolization in a swine model induced by small-sized microemboli, which may cause microinfarcts invisible to the naked eye. MATERIALS AND METHODS: Eleven pigs underwent intracoronary injection of small-sized microspheres (42 microm) and catheter coronary angiography was obtained before and after microembolization. Cardiac MRI and measurement of cardiac troponin T (cTnT) were performed at baseline, 6 hours, and 1 week after microembolization. Postmortem evaluation was performed after completion of the imaging studies. RESULTS: Coronary angiography pre- and post-microembolization revealed normal epicardial coronary arteries. Systolic wall thickening of the microembolized regions decreased significantly from 42.6 +/- 2.0% at baseline to 20.3 +/- 2.3% at 6 hours and 31.5 +/- 2.1% at 1 week after coronary microembolization (p < 0.001 for both). First-pass perfusion defect was visualized at 6 hours but the extent was largely decreased at 1 week. Delayed contrast enhancement MRI (DE-MRI) demonstrated hyperenhancement within the target area at 6 hours but not at 1 week. The microinfarcts on gross specimen stained with nitrobluetetrazolium chloride were invisible to the naked eye and only detectable microscopically. Increased cTnT was observed at 6 hours and 1 week after microembolization. CONCLUSION: Coronary microembolization induced by a certain load of small-sized microemboli may result in microinfarcts invisible to the naked eye with normal epicardial coronary arteries. MRI features of myocardial impairment secondary to such microembolization include the decline in left ventricular function and myocardial perfusion at cine and first-pass perfusion imaging, and transient hyperenhancement at DE-MRI.

Delayed Enhancement Magnetic Resonance Imaging Findings in Cardiac Amyloidosis

PURPOSE: To evaluate late gadolinium enhancement (LGE) pattern of left ventricular (LV) myocardium and presence or absence of LGE in other regions of the heart on cardiac magnetic resonance (CMR) imaging in patients diagnosed with cardiac amyloidosis. MATERIALS AND METHODS: From 2009 to 2011, 9 patients who were suspected cardiac amyloidosis underwent CMR. We retrospectively analyzed the presence or absence of LGE and enhancement pattern in LV myocardium, and the presence or absence of LGE in other chambers as well. Also we measured interatrial septal thickness (IST), relative signal intensities of atrial septum and epicardial fat over the left atrial (LA) cavity on delayed enhanced images. MRI parameters in these patients were compared to those of control group of patients with ischemic heart disease by Wilcoxon rank sum test. RESULTS: Of nine patients, LGE were found in 8; subendocardial circumferential pattern in 4 and diffuse pattern in 4. LGE in right ventricle was observed in 7. IST was significantly increased in patients with cardiac amyloidosis (P = 0.02). Ratio of atrial septum to LA cavity and ratio of epicardial fat to LA cavity showed a significant difference (P = 0.0002 and P = 0.0006, respectively). CONCLUSION: In LGE CMR, subendocardial or diffuse enhancement pattern is a typical finding for patients with cardiac amyloidosis. Atrial septum and epicardial fat show relatively increased signal intensities over LA blood cavity.

Clinical Experience with 3.0 T MR for Cardiac Imaging in Patients: Comparison to 1.5 T using Individually Optimized Imaging Protocols

PURPOSE: To report our clinical experience with cardiac 3.0 T MRI in patients compared with 1.5 T using individually optimized imaging protocols. MATERIALS AND METHODS: We retrospectively reviewed 30 consecutive patients and 20 consecutive patients who underwent 1.5 T and 3 T cardiac MRI within 10 months. A comparison study was performed by measuring the signal-to-noise ratio (SNR), the contrast-to-noise ratio (CNR) and the image quality (by grading each sequence on a 5-point scale, regarding the presence of artifacts). RESULTS: In morphologic and viability studies, the use of 3.0 T provided increase of the baseline SNRs and CNRs, respectively (T1: SNR 29%, p < 0.001, CNR 37%, p < 0.001; T2-SPAIR: SNR 13%, p = 0.068, CNR 18%, p = 0.059; viability imaging: SNR 45%, p = 0.017, CNR 37%, p = 0.135) without significant impairment of the image quality (T1: 3.8 +/- 0.9 vs. 3.9 +/- 0.7, p = 0.438; T2-SPAIR: 3.8 +/- 0.9 vs. 3.9 +/- 0.5, p = 0.744; viability imaging: 4.5 +/- 0.8 vs. 4.7 +/- 0.6, p = 0.254). Although the image qualities of 3.0 T functional cine images were slightly lower than those of 1.5 T images (3.6 +/- 0.7 vs. 4.2 +/- 0.6, p < 0.001), the mean SNR and CNR at 3.0 T were significantly improved (SNR 143% increase, CNR 108% increase, p < 0.001). With our imaging protocol for 3.0 T perfusion imaging, there was an insignificant decrease in the SNR (11% decrease, p = 0.172) and CNR (7% decrease, p = 0.638). However, the overall image quality was significantly improved (4.6 +/- 0.5 vs. 4.0 +/- 0.8, p = 0.006). CONCLUSION: With our experience, 3.0 T MRI was shown to be feasible for the routine assessment of cardiac imaging.

Role of multimodality cardiac imaging in preoperative cardiovascular evaluation before noncardiac surgery.

The preoperative cardiac assessment of patients undergoing noncardiac surgery is common in the daily practice of medical consultants, anesthesiologists, and surgeons. The number of patients undergoing noncardiac surgery worldwide is increasing. Currently, there are several noninvasive diagnostic tests available for preoperative evaluation. Both nuclear cardiology with myocardial perfusion single photon emission computed tomography (SPECT) and stress echocardiography are well-established techniques for preoperative cardiac evaluation. Recently, some studies demonstrated that both coronary angiography by gated multidetector computed tomography and stress cardiac magnetic resonance might potentially play a role in preoperative evaluation as well, but more studies are needed to assess the role of these new modalities in preoperative risk stratification. A common question that arises in preoperative evaluation is if further preoperative testing is needed, which preoperative test should be used. The preferred stress test is the exercise electrocardiogram (ECG). Stress imaging with exercise or pharmacologic stress agents is to be considered in patients with abnormal rest ECG or patients who are unable to exercise. After reviewing this article, the reader should develop an understanding of the following: (1) the magnitude of the cardiac preoperative morbidity and mortality, (2) how to select a patient for further preoperative testing, (3) currently available noninvasive cardiac testing for the detection of coronary artery disease and assessment of left ventricular function, and (4) an approach to select the most appropriate noninvasive cardiac test, if needed.