Hsin-Jung Yang

Free-breathing, motion-corrected, highly efficient whole heart T2 mapping at 3T with hybrid radial-cartesian trajectory.

To develop and test a time‐efficient, free‐breathing, whole heart T2 mapping technique at 3.0T.

Iron-Sensitive Cardiac Magnetic Resonance Imaging for Prediction of Ventricular Arrhythmia Risk in Patients With Chronic Myocardial Infarction Early Evidence

Background—Recent canines studies have shown that iron deposition within chronic myocardial infarction (CMI) influences the electric behavior of the heart. To date, the link between the iron deposition and malignant ventricular arrhythmias in humans with CMI is unknown. Methods and Results—Patients with CMI (n=94) who underwent late-gadolinium-enhanced cardiac magnetic resonance imaging before implantable cardioverter-defibrillator implantation for primary and secondary preventions were retrospectively analyzed. The predictive values of hypointense cores (HIC) in balanced steady-state free precession images and conventional cardiac magnetic resonance imaging and ECG malignant ventricular arrhythmia parameters for the prediction of primary combined outcome (appropriate implantable cardioverter-defibrillator therapy, survived cardiac arrest, or sudden cardiac death) were studied. The use of HIC within CMI on balanced steady-state free precession as a marker of iron deposition was validated in a canine MI model (n=18). Nineteen patients met the study criteria with events occurring at a median of 249 (interquartile range of 540) days after implantable cardioverter-defibrillator placement. Of the 19 patients meeting the primary end point, 18 were classified as HIC+, whereas only 1 was HIC−. Among the cohort in whom the primary end point was not met, there were 28 HIC+ and 47 HIC− patients. Receiver operating characteristic curve analysis demonstrated an additive predictive value of HIC for malignant ventricular arrhythmias with an increased area under the curve of 0.87 when added to left ventricular ejection fraction (left ventricular ejection fraction alone, 0.68). Both cardiac magnetic resonance imaging and histological validation studies performed in canines demonstrated that HIC regions in balanced steady-state free precession images within CMI likely result from iron depositions. Conclusions—Hypointense cores within CMI on balanced steady-state free precession cardiac magnetic resonance imaging can be used as a marker of iron deposition and yields incremental information toward improved prediction of malignant ventricular arrhythmias.

First-pass perfusion CMR with reduced dark-rim artifact and instantaneous image reconstruction using optimized cartesian sampling and apodization

Background Subendocardial dark-rim artifact (DRA) continues to be a major issue that limits the diagnostic performance of first pass perfusion (FPP) CMR. Non-Cartesian approaches such as radial or spiral acquisition have been proposed to minimize DRAs. Among these approaches, those that can operate without the need for breath-holding typically require a time-consuming offline image reconstruction procedure, which limits their clinical accessibility. We propose a free-breathing DRA-reduced FPP scheme with instant image reconstruction on the scanner.

First‐pass myocardial perfusion MRI with reduced subendocardial dark‐rim artifact using optimized Cartesian sampling

The presence of subendocardial dark‐rim artifact (DRA) remains an ongoing challenge in first‐pass perfusion (FPP) cardiac magnetic resonance imaging (MRI). We propose a free‐breathing FPP imaging scheme with Cartesian sampling that is optimized to minimize the DRA and readily enables near‐instantaneous image reconstruction.

Contrast-free T1 mapping at 3T can characterize chronic myocardial infarctions with high diagnostic accuracy

Background Characterizing myocardial infarctions (MIs) on the basis of LGE CMR requires gadolinium infusion, which poses limitations in certain patient populations and imaging workflow. We hypothesized that T1 differences between MI and remote territories at 3T would enable reliable characterization of chronic MI. Methods Canines (n = 29) underwent CMR at 7 days (acute) and 4 months (chronic) following reperfused MIs at 3T (n = 19) and 1.5T (n = 10). Contrast-free T1 maps (MOLLI; 8 TIs with 2 inversion blocks of 3+5 images; minimum TI = 110 ms; ΔTI = 80 ms; TR/TE = 2.2/1.1 ms) and LGE images (IR-prepared FLASH; TI optimized to null remote myocardium; TR/TE = 3.5/1.75 ms) were acquired. MI location, size and transmurality were determined using Mean+5SD criterion relative to remote myocardium. T2 maps (T2-prepared SSFP; T2 preparation times = 0, 24 and 55 ms; TR/TE = 2.8/1.4 ms) were acquired to compare acute and chronic MIs. Commonly used imaging parameters were slice thickness = 6 mm and spatial resolution = 1.3 × 1.3 mm 2. Histological validation was sought to confirm the presence of replacement fibrosis within the chronic infarct zones. Results Contrast-free T1 maps and LGE images of a representative mid-ventricular slice, along with AHA 17-segment bulls-eye plots depicting the MI size and transmurality acquired from a canine scanned imaged 4 months post-MI at 3T are shown in Figure 1. Bland-Altman plots, linear regression plots and receiver-operating characteristic curve comparing T1 maps and LGE images for measuring infarct volume (IV, %LV) and transmurality (IT) in the chronic phase at 3T are also shown. At 3T, T1 maps and LGE images were not different for measuring IV (5.6 ± 3.7% vs. 5.5 ± 3.7%; p = 0.61) and IT (44 ± 15% vs. 46 ± 15%; p = 0.81) in the chronic phase, but were significantly different in the acute phase (IS: 13.3 ± 8.4% vs. 11.6 ± 6.8%, p = 0.007 and IT: 64 ± 19% vs. 56 ± 17%, p = 0.007). At 1.5T, IV and IT were significantly underestimated by T1 maps relative to LGE images during acute (IS: 9.4 ± 5.6% vs. 15.5 ± 9.4%, p < 0.001 and IT: 59 ± 5% vs. 76 ± 6%, p < 0.001) and chronic phases (IS: 2.1 ± 1.2% vs. 4.8 ± 1.8%, p < 0.001 and IT: 47 ± 7% vs. 66 ± 9%, p < 0.001). At 3T and 1.5T, T1 values of the MI remained elevated in both acute (3T: p < 0.001; 1.5T: p < 0.001) and chronic phases (3T: p < 0.001; 1.5T: p = 0.037) compared to remote myocardium (Table 1). At both 3T and 1.5T, relative to the remote myocardium, T2 values of the MI were elevated in the acute phase (p < 0.001 for both cases), but were not different in the chronic phase (3T: p = 0.19, 1.5T: p = 0.55). Ex-vivo TTC and Elastinmodified Masson’s Trichrome (EMT) stainings (Figure 1) confirmed extensive replacement fibrosis within the MI territories at 4 months post MI. Sensitivity and specificity of contrast-free T1 maps at 3T for detecting chronic MIs were 95% and 97%, respectively. Conclusions Contrast-free T1 maps at 3T can determine the location, size and transmurality of chronic MIs with high diagnostic accuracy.

Accuracy and precision of chronic myocardial infarct characterization with native T1 mapping at 3T

Background Native T1-maping at 3T has been shown to reliably characterize chronic myocardial infarctions (MIs). In this study, we evaluated the accuracy and precision of different thresholding techniques and visual delineation for characterizing chronic MIs on native T1 maps at 3T. Results Relative to LGE images, mean infarct size and transmur- ality measured from native T1 maps were significantly over-estimated by Mean+2SD, Mean+3SD, and Mean+ 4SD techniques (p<0.001, for all cases). Mean+6SD cri- terion and visual delineation significantly underesti- mated infarct size (p<0.001 for both cases) and transmurality (p=0.01 for Mean+6SD; p<0.001 for visual) on native T1 maps. Otsus technique showed no differ- ence for measuring infarct size on native T1 maps com- pared to LGE images (p=0.27), but it over-estimated the infarct transmurality (p<0.001). Mean+5SD criterion showed no difference for measuring either infarct size (p=0.61) or transmurality (p=0.81) on T1 maps relative to LGE images. Mean CNR of LGE images was nearly 4-fold higher than that of native T1 maps (p<0.001). Mean+5SD criterion for detecting chronic MIs on native T1 maps at 3T showed the strongest diagnostic perfor- mance (area-under-curve=0.99, p<0.001), while visual delineation showed the weakest diagnostic performance (area-under-curve=0.84, p<0.001). Conclusions Threshold-based analysis using Mean+5SD criterion can accurately and precisely estimate the size, location and transmurality of chronic MIs on native T1 maps as reli- ably as LGE at 3T.

Fast, whole-heart, free-breathing 3D T2 mapping at 3T with application to myocardial edema imaging.

Background Cardiac MRI (CMR) T2 mapping is a proven method for myocardial edema detection. However, the current approach requires multiple breath-holds and can take nearly 10-15 minutes to complete. Faster acquisitions could potentially improve patient comfort and costeffectiveness of CMR exams. the objecttive of this study is to develop and test a free-breathing, three-dimensional, cardiac MR approach which can yield fast, accurate, T2 maps of the whole left ventricle at 3T.

Cardiovascular Magnetic Resonance Assessment of Myocardial Oxygenation

Abstract In this chapter, we provide an overview of the basic biophysical concepts that allow for the assessment of changes in myocardial blood oxygenation. We summarize the preclinical and clinical literature to date in the assessment of myocardial oxygenation as well as the growing literature on image-processing methods that have the capacity to enable accurate visualization and quantification of blood-oxygen-level-dependent (BOLD) signal changes in the myocardium. Finally we review the emerging methods which show promising evidence into how BOLD cardiovascular magnetic resonance (CMR) can become a reliable tool for examining ischemic heart disease in the clinical arena and conclude with a brief outlook on the future of myocardial BOLD CMR.

Influence of Myocardial Hemorrhage on Staging of Reperfused Myocardial Infarctions With T2 Cardiac Magnetic Resonance Imaging: Insights Into the Dependence on Infarction Type With Ex Vivo Validation

OBJECTIVES This study sought to determine whether T2 cardiac magnetic resonance (CMR) can stage both hemorrhagic and nonhemorrhagic myocardial infarctions (MIs). BACKGROUND CMR-based staging of MI with or without contrast agents relies on the resolution of T2 elevations in the chronic phase, but whether this approach can be used to stage both hemorrhagic and nonhemorrhagic MIs is unclear. METHODS Hemorrhagic (n = 15) and nonhemorrhagic (n = 9) MIs were created in dogs. Multiparametric noncontrast mapping (T1, T2, and T2*) and late gadolinium enhancement (LGE) were performed at 1.5- and 3.0-T at 5 days (acute) and 8 weeks (chronic) post-MI. CMR relaxation values and LGE intensities of hemorrhagic, peri-hemorrhagic, nonhemorrhagic, and remote territories were measured. Histopathology was performed to elucidate CMR findings. RESULTS T2 of nonhemorrhagic MIs was significantly elevated in the acute phase relative to remote territories (1.5-T: 39.8 ± 12.8%; 3.0-T: 27.9 ± 16.5%; p < 0.0001 for both) but resolved to remote values by week 8 (1.5-T: −0.0 ± 3.2%; p = 0.678; 3.0-T: −0.5 ± 5.9%; p = 0.601). In hemorrhagic MI, T2 of hemorrhage core was significantly elevated in the acute phase (1.5-T: 17.7 ± 10.0%; 3.0-T: 8.6 ± 8.2%; p < 0.0001 for both) but decreased below remote values by week 8 (1.5-T: −8.2 ± 3.9%; 3.0-T: −5.6 ± 6.0%; p < 0.0001 for both). In contrast, T2 of the periphery of hemorrhage within the MI zone was significantly elevated in the acute phase relative to remote territories (1.5-T: 35.0 ± 16.1%; 3.0-T: 24.2 ± 10.4%; p < 0.0001 for both) and remained elevated at 8 weeks post-MI (1.5-T: 8.6 ± 5.1%; 3.0-T: 6.0 ± 3.3%; p < 0.0001 for both). The observed elevation of T2 in the peri-hemorrhagic zone of MIs and the absence of T2 elevation in nonhemorrhagic MIs were consistent with ongoing or absence of histological evidence of inflammation, respectively. CONCLUSIONS Hemorrhagic MIs are associated with persisting myocardial inflammation and edema, which can confound staging of hemorrhagic MIs when T2 elevations alone are used to discriminate between acute and chronic MI. Moreover, given the poor prognosis in patients with hemorrhagic MI, CMR evidence for myocardial hemorrhage with persistent edema may evolve as a risk marker in patients after acute MI.

Arterial CO2 as a Potent Coronary Vasodilator: A Preclinical PET/MR Validation Study with Implications for Cardiac Stress Testing

Myocardial blood flow (MBF) is the critical determinant of cardiac function. However, its response to increases in partial pressure of arterial CO2 (PaCO2), particularly with respect to adenosine, is not well characterized because of challenges in blood gas control and limited availability of validated approaches to ascertain MBF in vivo. Methods: By prospectively and independently controlling PaCO2 and combining it with 13N-ammonia PET measurements, we investigated whether a physiologically tolerable hypercapnic stimulus (∼25 mm Hg increase in PaCO2) can increase MBF to that observed with adenosine in 3 groups of canines: without coronary stenosis, subjected to non–flow-limiting coronary stenosis, and after preadministration of caffeine. The extent of effect on MBF due to hypercapnia was compared with adenosine. Results: In the absence of stenosis, mean MBF under hypercapnia was 2.1 ± 0.9 mL/min/g and adenosine was 2.2 ± 1.1 mL/min/g; these were significantly higher than at rest (0.9 ± 0.5 mL/min/g, P < 0.05) and were not different from each other (P = 0.30). Under left-anterior descending coronary stenosis, MBF increased in response to hypercapnia and adenosine (P < 0.05, all territories), but the effect was significantly lower than in the left-anterior descending coronary territory (with hypercapnia and adenosine; both P < 0.05). Mean perfusion defect volumes measured with adenosine and hypercapnia were significantly correlated (R = 0.85) and were not different (P = 0.12). After preadministration of caffeine, a known inhibitor of adenosine, resting MBF decreased; and hypercapnia increased MBF but not adenosine (P < 0.05). Conclusion: Arterial blood CO2 tension when increased by 25 mm Hg can induce MBF to the same level as a standard dose of adenosine. Prospectively targeted arterial CO2 has the capability to evolve as an alternative to current pharmacologic vasodilators used for cardiac stress testing.