Yasutaka Ichikawa

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.

Evaluation of Left Ventricular Volumes and Ejection Fraction Using Fast Steady-State Cine MR Imaging: Comparison with Left Ventricular Angiography

Previous studies demonstrated that magnetic resonance (MR) imaging consistently underestimated angiographic measurements of left ventricular (LV) volumes. The purpose of this study was to determine whether MR imaging with steady-state free precession acquisition (SSFP) can provide improved accuracy and reproducibility in measuring cardiac function in comparison with fast spoiled gradient echo cine MR imaging (SPGR). Twenty patients with cardiovascular diseases who underwent breath-hold cine MR imaging within one week of LV angiography were studied. Two sets of breath-hold cine MR images were obtained, one with SSFP and another with SPGR. The LV volumes determined by two breath-hold cine MR sequences were compared with the results by LV angiography. SPGR cine MR imaging consistently underestimated angiographic LV volumes. The mean difference of LV end-diastolic volume was -22.5 +/- 14.8 ml (p < 0.001) for short-axis planes and -27.7 +/- 21.5 ml (p < 0.001) for long-axis planes. In contrast, LV volumes measured by the SSFP imaging showed a good agreement with the results by angiography. The mean difference of LV end-diastolic volume was -2.5 +/- 14.3 ml (p = N.S.) for short-axis planes and -10.9 +/- 15.1 ml (p < 0.01) for long-axis planes. Standard error of the estimation in measuring LV end-diastolic volume with the SSFP imaging was 3.9% for short-axis images and 4.9% for long-axis images. These values were 7.2% and 8.7% with the SPGR imaging. In conclusion, the SSFP acquisition can provide accurate and noninvasive assessments of LV volumes and ejection fraction within a reduced imaging time.

Quantitative analysis of first-pass contrast-enhanced myocardial perfusion MRI using a Patlak plot method and blood saturation correction.

The objectives of this study were to develop a method for quantifying myocardial K1 and blood flow (MBF) with minimal operator interaction by using a Patlak plot method and to compare the MBF obtained by perfusion MRI with that from coronary sinus blood flow in the resting state. A method that can correct for the nonlinearity of the blood time–signal intensity curve on perfusion MR images was developed. Myocardial perfusion MR images were acquired with a saturation‐recovery balanced turbo field‐echo sequence in 10 patients. Coronary sinus blood flow was determined by phase‐contrast cine MRI, and the average MBF was calculated as coronary sinus blood flow divided by left ventricular (LV) mass obtained by cine MRI. Patlak plot analysis was performed using the saturation‐corrected blood time–signal intensity curve as an input function and the regional myocardial time–signal intensity curve as an output function. The mean MBF obtained by perfusion MRI was 86 ± 25 ml/min/100 g, showing good agreement with MBF calculated from coronary sinus blood flow (89 ± 30 ml/min/100 g, r = 0.74). The mean coefficient of variation for measuring regional MBF in 16 LV myocardial segments was 0.11. The current method using Patlak plot permits quantification of MBF with operator interaction limited to tracing the LV wall contours, registration, and time delays. Magn Reson Med, 2009.

Adipose Tissue Detected by Multislice Computed Tomography in Patients After Myocardial Infarction

OBJECTIVES Our aim was to investigate the frequency of left ventricular (LV) and right ventricular adipose tissue on multislice computed tomography (CT) in patients with a history of myocardial infarction (MI) and to determine correlations with infarct age. BACKGROUND Fat deposition in the ventricular wall has frequently been observed in post-infarct myocardial tissue. However, the in vivo relevance of adipose tissue in MI on CT and correlations with infarct age have not been determined. METHODS Fifty-three patients with a history of MI (mean age 66 +/- 10 years; 38 men, 15 women) and 63 subjects with no history of MI or coronary revascularization (mean age 65 +/- 12 years; 37 men, 26 women) were retrospectively studied for intramyocardial fat on 64-slice cardiac CT. Presence or absence, distribution, and correlations with infarct age of LV adipose tissue were evaluated. RESULTS Compared with noninfarct control subjects, the MI group showed a significantly higher prevalence of fat deposition within LV myocardium on CT (MI group, 62% [33 of 53] vs. control group, 3% [2 of 63]; p < 0.0001). In 32 of 33 patients (97%) with MI and LV fat deposition on CT, adipose tissue was observed in the region perfused by the infarct-related artery and was located in the subendocardium in 30 patients (94%), the middle layer in 1 patient (3%), and the subepicardium in 1 patient (3%). Mean infarct age was significantly higher in patients with LV adipose tissue (8.2 +/- 4.4 years) than in those without adipose tissue (2.2 +/- 2.6 years, p < 0.001). Thirty of 35 patients (89%) with infarct age >or=3 years showed adipose tissue in MI. Conversely, none of 9 patients with infarct age <10 months showed fatty replacement. CONCLUSIONS Myocardial adipose tissue is common in patients with infarct age >or=3 years. CT evaluation of myocardial adipose tissue may be important for accurate interpretation of CT perfusion and infarct imaging of the heart.

Prediction of regional functional recovery after acute myocardial infarction with low dose dobutamine stress cine MR imaging and contrast enhanced MR imaging

PURPOSE Previous studies demonstrated that low-dose dobutamine stress cine magnetic resonance imaging (MRI) and delayed contrast-enhanced MRI can provide assessments of myocardial viability. The purpose of this study was to evaluate the comparative diagnostic values of dobutamine cine MRI and delayed contrast-enhanced MRI for predicting functional recovery of myocardial contraction in patients with acute reperfused myocardial infarction. METHODS Twenty-three patients with myocardial infarction after percutaneous coronary interventions were studied. All patients underwent steady-state cine MRI covering the entire left ventricle at rest and during low-dose dobutamine stress (10 micrograms/kg/min). Delayed contrast-enhanced MR images were acquired to determine transmural extent of hyperenhancement. Second cine MR images in the resting state were obtained 3 to 11 months after revascularization. RESULTS On the first cine MR images in the resting state, 278 (20%) of 1380 segments demonstrated abnormal, regional contraction (systolic wall thickening < 40%). Of the 175 segments showing functional recovery on the following cine MRI, 156 (89%) segments were recognized as reversible by dobutamine cine MRI and 146 (83%) segments by delayed contrast-enhanced MRI. The sensitivity, specificity, and accuracy of dobutamine stress cine MRI was 89%, 80%, and 86%, respectively. These values of contrast-enhanced MRI were 83%, 72%, and 79%, respectively. The area under the receiver operating curve (ROC) was 0.87 by dobutamine cine MRI and 0.78 by delayed contrast-enhanced MRI (p < 0.05). CONCLUSIONS The current results using quantitative segmental analysis indicated that low-dose dobutamine stress cine MRI can predict recovery of myocardial contractility with significantly higher diagnostic performance in comparison with contrast-enhanced MRI in patients with myocardial infarction who underwent revascularization.

Thallium-201 SPECT and Low-Dose Dobutamine Stress Cine MRI for Predicting Functional Recovery of Regional Myocardial Contraction in Patients with Myocardial Infarction

OBJECTIVES The purpose of this study was to compare the diagnostic performances of Tl-201 single photon emission computed tomography (SPECT) and dobutamine stress cine magnetic resonance imaging (MRI) for predicting functional recovery of regional myocardial contraction in patients after myocardial infarction. METHODS Twenty patients underwent Tl-201 SPECT and MRI 3-4 weeks after onset of myocardial infarction. Cine MR images were acquired in the resting state and during dobutamine stress. Tl-201 uptake and systolic wall thickening (SWT) on cine MRI were analyzed on short-axis images by using a 14-segment model. Follow-up cine MR images were obtained 187.1+/-33.5 days after onset. RESULTS The averaged Tl-201 uptake in 54 segments with impaired SWT was 47%+/-20%, being significantly lower than that in 226 segments with preserved SWT (75%+/-18%; p<0.0001). The sensitivity, specificity, and accuracy of dobutamine MRI and Tl-201 SPECT for predicting preserved SWT after 6 months were 89% vs. 80%, not significant (NS); 89% vs. 72%, p<0.01; and 89% vs. 79%, NS, respectively. In the anterior wall and apex, the sensitivity and specificity of SPECT were not significantly different from those of MRI. In the inferior wall and posterolateral wall, however, the specificity of SPECT was substantially lower than that of MRI (53% vs. 88%, p<0.001), resulting in significantly lower accuracy (75% vs. 90%, p<0.01). CONCLUSIONS Both SPECT and dobutamine MRI showed excellent sensitivity for predicting myocardial viability in all left ventricular segments. Decreased specificity of SPECT in the inferior and posterolateral segments resulted in lower overall specificity in comparison with dobutamine MRI.

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.

Diagnostic value of late gadolinium-enhanced MRI and first-pass dynamic MRI for predicting functional recovery in patients after acute myocardial infarction

PurposeThe aim of this study was to determine the comparative diagnostic values of late gadolinium-enhanced magnetic resonance imaging (MRI) and first-pass dynamic MRI for predicting functional recovery of regional myocardial contraction in patients early after acute myocardial infarction.Materials and methodsFirst-pass and late-enhanced MRI were performed in 18 patients 5.5 ± 2.5 days after the onset of myocardial infarction. Images analysis was performed using a 12-segment model. Regional systolic wall thickening (SWT) was measured on cine-MRI obtained 273 ± 130 days later.ResultsLate-enhanced MRI revealed hyperenhancement in all patients, whereas hypoenhancement on first-pass MRI was observed in 67% (12/18) of the patients. The area under the receiver operating characteristics curve was 0.86 for late-enhanced MRI and 0.74 for first-pass MRI (P = 0.27). First-pass MRI was useful for predicting functional recovery of the segments that showed hyperenhancement of >50% of tissue on late-enhanced MRI. In these segments, preserved SWT was observed in 15 of 33 segments (45%) with first-pass hypoenhancement of ≤50% of tissue, but in only 2 of 22 segments (9%) with first-pass hypoenhancement of >50% of tissue.ConclusionWhereas the diagnostic capability of first-pass MRI alone is limited, complementary use of first-pass MRI can enhance the diagnostic performance of late-enhanced MRI because hypoenhancement during first-pass imaging is more specific to nonviable myocardium.

The Effect of Misregistration Between CT-Attenuation and PET-Emission Images in 13N-Ammonia Myocardial PET/CT

In 2-dimensional cardiac PET/CT, misregistration between the PET and CT images due to respiratory and cardiac motion causes tracer uptake to appear substantially reduced. The resolution and quality of the images have been considerably improved by the use of 3-dimensional (3D) PET acquisitions. In the current study, we investigated the impact that misregistration between PET and CT images has on myocardial 13N-ammonia uptake in images reconstructed with 3D ordered-subset expectation maximization combined with time-of-flight and point-spread-function modeling. Methods: Eight healthy volunteers (7 men and 1 woman; mean age ± SD, 53 ± 19 y) underwent 13N-ammonia cardiac PET/CT at rest. First, any misregistration between the PET and CT images was manually corrected to generate reference images. Then, the images were intentionally misregistered by shifting the PET images from the reference images by a degree of 1, 2, 3, 4, 5, 10, and 15 mm along both the x-axis (left) and the z-axis (cranial). For each degree of misregistration, the PET images were reconstructed using the CT-attenuation images. The left ventricular short-axis PET/CT images were divided into 4 segments: anterior wall, inferior wall, lateral wall, and septum. The erroneous decrease in myocardial uptake in basal, mid, and apical slices was visually graded using a 4-point scale (0 = none, 1 = mild, 2 = moderate, and 3 = severe). Wall-to-septum uptake ratios were evaluated for the anterior, inferior, and lateral walls in the basal, mid, and apical slices. Results: A statistically significant reduction in myocardial 13N-ammonia uptake in the anterior (P < 0.01) and lateral (P < 0.05) walls was observed when misregistration was 10 mm or more. The uptake ratios for the anterior, lateral, and inferior walls in the reference images were 1.00 ± 0.04, 0.96 ± 0.08, and 0.91 ± 0.03, respectively. The ratios for the anterior and lateral walls significantly decreased when misregistration exceeded 10 mm (anterior wall, 0.80 ± 0.06, P < 0.0001; lateral wall, 0.82 ± 0.07, P < 0.01), whereas the ratio for the inferior wall was relatively small at all 7 degrees of misregistration (0.86 ± 0.05 at 15-mm misregistration, P = 0.06). Conclusion: In PET/CT images reconstructed with 3D ordered-subset expectation maximization combined with time-of-flight and point-spread-function modeling, we found a statistically significant artifactual reduction in tracer uptake in heart regions overlapping lung when misregistration between PET and CT exceeded 10 mm.

Usefulness of tissue characterization by cardiac magnetic resonance imaging as a complementary method for evaluation of cardiac malignant lymphoma

A 77-year-old woman with a history of malignant lymphoma (diffuse large B cell lymphoma) presented with general fatigue accompanied by cold sweat. A 12-lead electrocardiogram (ECG) revealed monomorphic ventricular tachycardia (VT) with a heart rate of 250 bpm. The VT was treated with direct-current cardioversion. Post-cardioversion ECG showed negative T wave in the precordial lead, and transthoracic echocardiography (TTE) showed apical and lateral left ventricular (LV) wall hypertrophy (Fig. 1A–C). These findings suggested that the VT was induced by hypertrophic cardiomyopathy (HCM). Cardiac magnetic resonance imaging (MRI) was performed for further evaluation. Cine MRI showed myocardial wall thickening with masses on the anterolateral and posterolateral LV walls with regional wall motion abnormality; these findings were not evident on TTE because of the skinnychestwall andhyperinflationof the lungs (Fig. 2A). The LV wall masses showed high signal intensity on T2-weighted imaging, indicating the presence of myocardial edema (Fig. 2B). On rest perfusion MRI, delayed and decreased regional perfusion was easily detected, suggesting that the masses were not normal myocardium but