Motonori Nagata

Assessment of Coronary Artery Disease Using Magnetic Resonance Coronary Angiography: A National Multicenter Trial

OBJECTIVES This national multicenter study determined the diagnostic performance of 1.5-T whole-heart coronary magnetic resonance angiography (MRA) in patients with suspected coronary artery disease (CAD). BACKGROUND Whole-heart coronary MRA using steady-state free precession allows noninvasive detection of CAD without the administration of contrast medium. However, the accuracy of this approach has not been determined in a multicenter trial. METHODS Using a 1.5-T magnetic resonance imaging unit, free-breathing steady-state free precession whole-heart coronary MRA images were acquired for 138 patients with suspected CAD at 7 hospitals. The accuracy of MRA for detecting a ≥ 50% reduction in diameter was determined using X-ray coronary angiography as the reference method. RESULTS Acquisition of whole-heart coronary MRA images was performed in 127 (92%) of 138 patients with an average imaging time of 9.5 ± 3.5 min. The areas under the receiver-operator characteristic curve from MRA images according to vessel- and patient-based analyses were 0.91 (95% confidence interval [CI]: 0.87 to 0.95) and 0.87 (95% CI: 0.81 to 0.93), respectively. The sensitivity, specificity, positive and negative predictive values, and accuracy of MRA according to a patient-based analysis were 88% (49 of 56, 95% CI: 75% to 94%), 72% (51 of 71, 95% CI: 60% to 82%), 71% (49 of 69, 95% CI: 59% to 81%), 88% (51 of 58, 95% CI: 76% to 95%), and 79% (100 of 127, 95% CI: 72% to 86%), respectively. CONCLUSIONS Non-contrast-enhanced whole-heart coronary MRA at 1.5-T can noninvasively detect significant CAD with high sensitivity and moderate specificity. A negative predictive value of 88% indicates that whole-heart coronary MRA can rule out CAD.

Diagnostic Accuracy of 1.5-T Unenhanced Whole-Heart Coronary MR Angiography Performed with 32-Channel Cardiac Coils: Initial Single-Center Experience

PURPOSE To compare the imaging time and image quality obtained with whole-heart coronary magnetic resonance (MR) angiography performed with five- and 32-channel coils in healthy subjects and determine the accuracy of MR angiography performed with 32-channel coils in the detection of obstructive coronary artery disease (CAD). MATERIALS AND METHODS The institutional review board approved the study protocol, and all participants provided written informed consent. The authors studied 10 healthy subjects and 67 patients suspected of having CAD who were scheduled for coronary angiography. Unenhanced 1.5-T coronary MR angiography was performed with five- and 32-channel coils in healthy subjects and with 32-channel coils in patients. Clinically significant CAD was defined as a diameter reduction of at least 50% at coronary angiography. The sensitivity and specificity of coronary MR angiography were calculated. RESULTS The mean imaging time was substantially reduced from 12.3 minutes ± 4.2 (standard deviation) with five-channel coils to 6.3 minutes ± 2.2 with 32-channel coils, with equivalent image quality scores. Acquisition of MR angiograms was completed in all 67 patients, with a mean imaging time of 6.2 minutes ± 2.8. The prevalence of CAD in the study population was 58% (39 of the 67 patients). The areas under the receiver operating characteristic curves as determined at vessel- and patient-based analyses were 0.91 and 0.90, respectively; the sensitivity and specificity at vessel-based analysis were 86% and 93%, respectively. CONCLUSION Whole-heart coronary MR angiography performed at 1.5 T with 32-channel coils permits noninvasive detection of CAD with substantially reduced imaging time. This noninvasive approach can be an alternative to multidetector computed tomographic coronary angiography for ruling out obstructive CAD in patients who have a contraindication to contrast material and in young subjects who are at higher risk from ionizing radiation. SUPPLEMENTAL MATERIAL http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.11101323/-/DC1.

Diagnostic accuracy of stress myocardial perfusion MRI and late gadolinium-enhanced MRI for detecting flow-limiting coronary artery disease: a multicenter study

The aim of this study was to determine the diagnostic performance of stress and rest perfusion magnetic resonance imaging (MRI) and late gadolinium-enhanced (LGE) MRI for identifying patients with obstructive coronary artery disease (CAD). A total of 50 patients with suspected CAD underwent stress-rest perfusion MRI, followed by LGE MRI with a 1.5-T system. Stress-rest perfusion MRI resulted in an area under the receiver-operating characteristic curve (AUC) of 0.92 for observer 1 and 0.84 for observer 2 with sensitivity and specificity of 89% (32/36) and 79% (11/14) by observer 1, 83% (30/36) and 71% (10/14) by observer 2, respectively, showing a moderate interobserver agreement (Cohen’s κ = 0.49). While combination of stress-rest perfusion and LGE MRI did not result in improved accuracy for the prediction of flow-limiting obstructive CAD (AUC 0.81 for observer 1 and 0.80 for observer 2), the sensitivity was increased to 92% in both observers with a substantial interobserver agreement (κ = 0.70). Stress-rest myocardial perfusion MRI is an accurate diagnostic test for identifying patients with obstructive CAD.

Quantification of myocardial blood flow using model based analysis of first-pass perfusion MRI: extraction fraction of Gd-DTPA varies with myocardial blood flow in human myocardium.

For the absolute quantification of myocardial blood flow (MBF), Patlak plot‐derived K1 need to be converted to MBF by using the relation between the extraction fraction of gadolinium contrast agent and MBF. This study was conducted to determine the relation between extraction fraction of Gd‐DTPA and MBF in human heart at rest and during stress. Thirty‐four patients (19 men, mean age of 66.5 ± 11.0 years) with normal coronary arteries and no myocardial infarction were retrospectively evaluated. First‐pass myocardial perfusion MRI during adenosine triphosphate stress and at rest was performed using a dual bolus approach to correct for saturation of the blood signal. Myocardial K1 was quantified by Patlak plot method. Mean MBF was determined from coronary sinus flow measured by phase contrast cine MRI and left ventricle mass measured by cine MRI. The extraction fraction of Gd‐DTPA was calculated as the K1 divided by the mean MBF. The extraction fraction of Gd‐DTPA was 0.46 ± 0.22 at rest and 0.32 ± 0.13 during stress (P < 0.001). The relationship between extraction fraction (E) and MBF in human myocardium can be approximated as E = 1 − exp(−(0.14 × MBF + 0.56)/MBF). The current results indicate that MBF can be accurately quantified by Patlak plot method of first‐pass myocardial perfusion MRI by performing a correction of extraction fraction. Magn Reson Med, 2011.

Model-based Iterative Reconstruction for Multi–Detector Row CT Assessment of the Adamkiewicz Artery

PURPOSE To determine if model-based iterative reconstruction (MBIR) can improve visualization of the Adamkiewicz artery on multi-detector row computed tomographic (CT) images compared with adaptive statistical iterative reconstruction (ASIR) and filtered back projection (FBP). MATERIALS AND METHODS This retrospective study was approved by the institutional review board, and written informed consent for the CT examination was obtained. Thirty-three patients underwent contrast material-enhanced 64-section multi-detector row CT for assessment of aortic aneurysm or dissection. Helical data were reconstructed by using FBP, ASIR, and MBIR. The signal-to-noise ratio of the aorta and contrast-to-noise ratio of the anterior spinal artery relative to the spinal cord were measured on multiplanar reformatted images. Visualization of the Adamkiewicz artery and its continuity with the intercostal or lumbar artery were evaluated by using a four-point scale. All image analyses were performed by two blinded, independent observers. The one-way analysis of variance and the Wilcoxon signed-rank test were used for statistical analysis. RESULTS MBIR showed significantly better signal-to-noise and contrast-to-noise ratios than did ASIR and FBP (P < .05 for all comparisons) with good interobserver agreement (intraclass correlation coefficient of 0.93 for signal-to-noise ratio and 0.75 for contrast-to-noise ratio). The visualization score of the Adamkiewicz artery was also significantly better when MBIR was used (3.4 ± 0.8 and 3.6 ± 0.7 for observers A and B, respectively) than when ASIR (2.7 ± 1.1 and 3.0 ± 1.0, respectively) or FBP (2.5 ± 1.2 and 3.1 ± 0.9, respectively) was used. CONCLUSION Use of the MBIR algorithm led to improved multi-detector row CT visualization of the Adamkiewicz artery when compared with the use of ASIR and FBP.

Relation Between Signal Intensity on T2-Weighted MR Images and Presence of Microvascular Obstruction in Patients With Acute Myocardial Infarction

OBJECTIVE In experimental animal models and human autopsy studies, hemorrhagic infarction caused by microvascular injury has been detected after coronary reperfusion. The purpose of this study was to determine whether detection of myocardial edema with T2-weighted MRI is influenced by the presence of microvascular obstruction. SUBJECTS AND METHODS Thirty-seven patients underwent black-blood fat-suppressed T2-weighted, rest perfusion, and late gadolinium-enhanced MRI 5.4 +/- 3.1 days after the onset of acute myocardial infarction. On T2-weighted MR images, the signal intensity in relation to that of remote myocardium was determined in the late gadolinium-enhanced and periinfarction areas. Segment-based analysis was performed to determine whether the presence of microvascular obstruction influences the detection of myocardial edema. RESULTS The averaged signal intensity in the late gadolinium-enhanced area without microvascular obstruction was significantly higher than the signal intensity in remote normal myocardium (relative signal intensity, 1.83 +/- 0.50; p < 0.001). In contrast, the signal intensity in the microvascular obstruction area on T2-weighted images was not significantly different from the signal intensity in remote myocardium (relative signal intensity, 1.14 +/- 0.26). The percentages of late gadolinium-enhanced segments with high signal intensity on T2-weighted MR images were 95% (73/77) without microvascular obstruction and 30% (22/73) with microvascular obstruction. CONCLUSION With T2-weighted MRI, infarction-associated edema can be reliably detected in infarct lesions without microvascular obstruction. Microvascular obstruction, however, does not necessarily exhibit high signal intensity on T2-weighted MRI. Careful attention is required in interpretation of cardiac MR images of patients who have experienced acute myocardial infarction and undergone percutaneous coronary intervention. The findings on T2-weighted MR images can be substantial underestimates of the extent of acute myocardial infarction.

Quantitative Analysis of 1.5-T Whole-Heart Coronary MR Angiograms Obtained with 32-Channel Cardiac Coils: A Comparison with Conventional Quantitative Coronary Angiography

PURPOSE To develop a method to determine significant stenosis at whole-heart coronary magnetic resonance (MR) angiography and to evaluate the accuracy and reproducibility of this approach. MATERIALS AND METHODS The institutional review board approved the study, and all participants provided written informed consent. Sixty-two patients who were suspected of having coronary artery disease (CAD) and were scheduled for conventional coronary angiography were included. Coronary MR angiography was performed by using a 1.5-T imager with 32-channel coils. Luminal narrowing was evaluated with quantitative analysis (QA) of coronary MR angiograms on the basis of the signal intensity profile along the vessel. Percentage stenosis with QA of coronary MR angiograms was calculated as [1 - (SI(min)/SI(ref))] × 100, where SI(min) is minimal signal intensity and SI(ref) is corresponding reference signal intensity. Diagnostic performance of QA of coronary MR angiograms for predicting at least a 50% reduction in diameter was evaluated by using quantitative coronary angiography (QCA), with conventional angiography findings serving as the reference standard. Receiver operating characteristic (ROC) analysis, Spearman rank correlation, Bland-Altman analysis, and Cohen κ analysis were used. RESULTS The areas under the ROC curve in a segment-based analysis for detecting significant CAD were 0.96 (95% confidence interval [CI]: 0.94, 0.98) with QA of coronary MR angiograms and 0.93 (95% CI: 0.88, 0.98) with visual assessment. The correlation coefficients between percentage stenosis with QA of coronary MR angiograms and percentage stenosis with QCA were 0.84 (P < .001), 0.80 (P < .001), and 0.66 (P < .001) in the patient-, vessel-, and segment-based analyses, respectively. CONCLUSION QA of coronary MR angiograms with use of a signal intensity profile along the vessel permits detection of CAD. This method had a diagnostic performance approximately equal to that of visual analysis of coronary MR angiograms with high inter- and intraobserver reliability, allowing for more objective interpretation of coronary MR angiography findings.

Hypertension impairs myocardial blood perfusion reserve in subjects without regional myocardial ischemia.

Quantitative analysis of myocardial perfusion MRI can provide noninvasive assessments of myocardial perfusion reserve (MPR), which is associated with endothelial function. Endothelial function is influenced by various factors, including hypertension, diabetes, dyslipidemia, renal dysfunction and anemia. The purpose of this study was to evaluate which risk factor is the strongest effector of MPR in subjects without regional myocardial ischemia. We studied 110 patients (66 years ±10, male 68%, hypertension 76%, diabetes mellitus (DM) 40% and dyslipidemia 65%) without regional myocardial ischemia. Adenosine triphosphate (ATP) stress and rest first-pass perfusion magnetic resonance (MR) images were acquired with a 1.5-T MR system, and MPR was calculated as the ratio of stress to rest myocardial blood flow (MBF). Average rest MBF in 110 patients was 1.07±0.62 ml min−1 g−1, whereas stress MBF was 3.15±1.93 ml min−1 g−1 and the MPR was 3.33±1.82. Rest MBF correlated significantly with hematocrit, whereas stress MBF showed a strong correlation with estimated glomerular filtration rate (e-GFR). MPR was associated with hypertension, age, e-GFR, hematocrit and left ventricular mass index (LVMI). In multiple regression analysis, hypertension (P=0.003, β=−0.274) showed the strongest correlation with MPR among other risk factors, such as diabetes (P=ns), dyslipidemia (P=ns), e-GFR (P=ns), LVMI (P=0.007, β=−0.248) and hematocrit (P=ns) after adjusting age and gender. Hypertension is the most important effector of MPR in subjects without myocardial ischemia.

Myocardial delayed enhancement with dual-source CT: Advantages of targeted spatial frequency filtration and image averaging over half-scan reconstruction

BACKGROUND Clinical utility of myocardial delayed-enhancement CT is currently limited because of relatively poor contrast-to-noise ratio (CNR) and artifacts. Targeted spatial-frequency filtration (TSFF) is a hybrid algorithm of half- and full-scan reconstruction that can achieve both high temporal resolution and improved stability of myocardial signal. OBJECTIVE The purpose of this study was to evaluate image quality of delayed-enhancement CT using TSFF with image averaging and its reproducibility in infarct assessment in comparison with conventional half-scan reconstruction (HALF). METHODS Forty patients with suspected coronary artery disease underwent delayed-enhancement CT with HALF and TSFF using dual-source CT. Two blinded readers independently determined the presence and size of delayed enhancement. Image quality, signal-to-noise ratio and CNR were assessed. The presence of delayed enhancement on CT was compared with magnetic resonance imaging in 12 patients. RESULTS TSFF with averaging of 4 image stacks acquired during 1 breathhold demonstrated significantly better image quality compared with HALF. Good left ventricular lumen-myocardium contrast was consistently achieved with TSFF in patients who received iodine dose of >600 mg I/kg. The signal-to-noise ratio and CNR were 11.3 ± 4.2 and 4.5 ± 1.6 by TSFF, being significantly higher than those by HALF (7.9 ± 2.9 and 3.3 ± 1.8; P < .01 for both). Interobserver reproducibility of infarct sizing was markedly improved by using TSFF instead of HALF (intraclass correlation coefficient: 0.86 vs 0.50). Agreement with magnetic resonance imaging by kappa statistics was 0.85 with TSFF and 0.74 with HALF. CONCLUSIONS TSFF with image averaging can significantly improve image quality of delayed-enhancement CT and considerably enhances interobserver reproducibility of infarct sizing.

Native T1 mapping in patients with idiopathic dilated cardiomyopathy for the assessment of diffuse myocardial fibrosis: validation against histologic endomyocardial biopsy

Background Late gadolinium enhancement (LGE) MRI provides a significant impact on prognosis in dilated cardiomyopathy (DCM) patients. However, LGE MRI is less suitable for quantifying the degree of fibrosis in diffusely diseased myocardium. T1 mapping technique allows for the quantitative assessment of extracellular volume fraction (ECV), which has been histologically validated against the collagen volume fraction (CVF). Native myocardial T1 also has a potential for the noninvasive detection of myocardial fibrosis. Recent study demonstrated that native myocardial T1 permits the discrimination between normal and diffusely diseased myocardium accurately in DCM patients. However, in-vivo histological validation of native myocardial T1 in DCM patients is still lacking. The aim of this study was to histologically validate native myocardial T1 for the assessment of diffuse myocardial fibrosis in DCM patients.