Haiyan Ding

Three-dimensional whole-heart T2 mapping at 3T

Detecting variations in myocardial water content with T2 mapping is superior to conventional T2‐weighted MRI since quantification enables direct observation of complicated pathology. Most commonly used T2 mapping techniques are limited in achievable spatial and/or temporal resolution, both of which reduce accuracy due to partial‐volume averaging and misregistration between images. The goal of this study was to validate a novel free breathing T2 mapping sequence that overcomes these limitations.

Characterization of Compacted Myocardial Abnormalities by Cardiac Magnetic Resonance With Native T1 Mapping in Left Ventricular Non-Compaction Patients – A Comparison With Late Gadolinium Enhancement –

BACKGROUNDnNative T1 mapping is an emerging cardiac magnetic resonance technique for quantitative evaluation of cardiomyopathies. This study aimed to investigate the usefulness of native T1 mapping in characterizing myocardial abnormalities in left ventricular non-compaction (LVNC) by comparing it with late gadolinium enhancement (LGE).nnnMETHODSANDRESULTSnThe study group of 31 LVNC patients and 8 normal controls underwent cardiovascular magnetic resonance to acquire the native T1 maps and LGE images. Of the 31 LVNC patients, 14 had LGE. The mean native T1 value of the normal controls, LGE(-) and LGE(+) patients was 1,098.8±40.8 ms, 1140.6±32.8 ms, and 1181.4±53.7 ms, respectively. Significant differences were found in native T1 between any 2 groups (F=9.74, P<0.001). In discriminating the presence of LGE in LVNC patients, the odds ratio and corresponding 95% confidence interval (CI) of native T1 were, respectively, 2.966 (95% CI: 1.123-7.835, P=0.028) and 4.348 (95% CI: 1.155-16.363, P=0.030) before and after adjusting for confounding factors with an increment of 1 standard deviation.nnnCONCLUSIONSnThe finding that LGE(-) patients had elevated native T1 compared with normal controls suggested native T1 mapping can be used earlier than LGE imaging to detect myocardial fibrosis in LVNC patients. Furthermore, higher native T1 values in LGE(+) patients than in the LGE(-) group suggested native T1 mapping is more sensitive than LGE imaging for identifying myocardial fibrosis in LVNC patients. (Circ J 2016; 80: 1210-1216).

Improvement in B1+ Homogeneity and Average Flip Angle Using Dual-Source Parallel RF Excitation for Cardiac MRI in Swine Hearts

Cardiac MRI may benefit from increased polarization at high magnetic field strength of 3 Tesla but is challenged by increased field inhomogeneity. Initial human studies have shown that the radiofrequency (RF) excitation field (B1 +) used for signal excitation in the heart is both inhomogeneous and significantly lower than desired, potentially leading to image artifacts and biased quantitative measures. Recently, multi-channel transmit systems have been introduced allowing localized patient specific RF shimming based on acquired calibration B1 + maps. Some prior human studies have shown lower than desired mean flip angles in the hearts of large patients even after RF shimming. Here, 100 cardiac B1 + map pairs before and after RF shimming were acquired in 55 swine. The mean flip angle and the coefficient of variation (CV) of the flip angle in the heart were determined before and after RF shimming. Mean flip angle, CV, and RF shim values (power ratio and phase difference between the two transmit channels) were tested for correlation with cross sectional body area and the Right-Left/Anterior-Posterior ratio. RF shimming significantly increased the mean flip angle in swine heart from 74.4±6.7% (mean ± standard deviation) to 94.7±4.8% of the desired flip angle and significantly reduced CV from 0.11±0.03 to 0.07±0.02 (p<<1e-10 for both). These results compare well with several previous human studies, except that the mean flip angle in the human heart only improved to 89% with RF shimming, possibly because the RF shimming routine does not consider safety constraints in very large patients. Additionally, mean flip angle decreased and CV increased with larger cross sectional body area, however, the RF shimming parameters did not correlate with cross sectional body area. RF shim power ratio correlated weakly with Right-Left/Anterior-Posterior ratio but phase difference did not, further substantiating the need for subject specific cardiac RF shimming.

High-resolution quantitative 3D T2 mapping allows quantification of changes in edema after myocardial infarction

Background T2 values are related to the tissue water content, providing useful diagnostic information in cardiac diseases, especially in acute states such as myocardial infarction (MI). Visualization of edema, its regional distribution, and extent in acute and chronic heart disease may be useful as a diagnostic tool and help in guiding treatment in the patients with heart disease. Recently, edema detection (T2 elevation) using quantitative T2 maps has been shown more robust than qualitative clinical T2W imaging.

Improvement in B1+-homogeneity of 3T cardiac MRI in swine with dual-source parallel RF excitation

Background Conventional MRI scanners up to a magnetic field strength of 3T use an integrated birdcage quadrature coil to generate a radio frequency (RF) excitation field (B1+). At 3T, Sung et al. observed a flip angle variation ranging from 31 to 66% over the entire left ventricle (LV) in humans as well as a flip-angle distribution from 34° to 63, for a nominal flip angle of 60°. This not only demonstrates that the B1+ field over the LV is inhomogeneous but also that the average flip angle (RF power setting) can be 20% lower than desired. Such erroneous flip angles may lead to local signal reduction, artifacts, failure of magnetization preparation pulses, and eventually to biased quantitative measures. Recently, it has been shown that multi-channel transmit systems can be used to reduce these inhomogeneities in humans by the use of RF-shimming. Here, we quantify improvements in B1 +-homogeneity at 3T when using dual-source parallel RF excitation, and correlate results with animal size.

Three-dimensional free breathing whole heart cardiovascular magnetic resonance T 1 mapping at 3 T

BackgroundThis study demonstrates a three-dimensional (3D) free-breathing native myocardialxa0T1 mapping sequence at 3xa0T.MethodsThe proposed sequence acquires three differently T1-weighted volumes. The first two volumes receive a saturation pre-pulse with different recovery time. The third volume is acquired without magnetization preparation and after a significant recovery time. Respiratory navigator gating and volume-interleaved acquisition are adopted to mitigate misregistration. The proposed sequence was validated through simulation, phantom experiments and in vivo experiments in 12 healthy adult subjects.ResultsIn phantoms, good agreement on T1 measurement was achieved between the proposed sequence and the reference inversion recovery spin echo sequence (R2u2009=u20090.99). Homogeneous 3D T1 maps were obtained from healthy adult subjects, with a T1 value of 1476u2009±u200953xa0ms and a coefficient of variation (CV) of 6.1u2009±u20091.4% over the whole left-ventricular myocardium. The averaged septal T1 was 1512u2009±u200960xa0ms with a CV of 2.1u2009±u20090.5%.ConclusionFree-breathing 3D native T1 mapping at 3xa0T is feasible and may be applicable in myocardial assessment. The proposed 3D T1 mapping sequence is suitable for applications in which larger coverage is desired beyond that available with single-shot parametric mapping, or breath-holding is unfeasible.

Prolonged QTc indicates the clinical severity and poor prognosis in patients with isolated left ventricular non-compaction

Isolated left ventricular non-compaction (LVNC) is a rare cardiomyopathy that leads to severe clinical complications. This study is to investigate whether or not prolonged QTc is a good indicator for evaluating the severity of fibrosis and predicting the prognosis of LVNC, and if native T1 can be used to quantify the fibrosis. 32 LVNC patients and 14 healthy controls with matched age and sex were examined by CMR and ECG to acquire native T1, QTc interval, and ECG abnormalities. 18 LVNC patients had normal QTc and 14 LVNC patients had prolonged QTc. The mean native T1 value of the normal controls, normal QTc and prolonged QTc patients was 1096.0u2009±u200941.5, 1141.98u2009±u200945.46, and 1182.67u2009±u200942.02xa0ms, respectively. One-way ANVOA showed significant differences in native T1 among three groups (Fu2009=u200914.9, pu2009<u20090.001). In LVNC patients, the QTc interval significantly correlated with LVEF (pu2009=u20090.003, ru2009=u20090.51) and native T1 values (pu2009=u20090.015, Ru2009=u2009−0.47). This suggests that prolonged QTc is associated with more severe compacted myocardial fibrosis, more cardiac dysfunction, and a poorer prognosis in LVNC patients. Follow-up data showed significant differences in adverse events between patients with normal QTc and patients with prolonged QTc (pu2009=u20090.036). Prolonged QTc interval leads to more severe compacted myocardial fibrosis, poorer cardiac dysfunction, and poorer prognosis in LVNC patients.

Is T1-Mapping Truly Superior to Late Gadolinium Enhancement-Imaging in Demonstrating Myocardial Fibrosis in Myopathy- and Non-Myopathy Associated Noncompaction? – Reply –

1. Zhou H, Lin X, Fang L, Zhao X, Ding H, Chen W, et al. Characterization of compacted myocardial abnormalities by cardiac magnetic resonance with native T1 mapping in left ventricular non-compaction patients: A comparison with late gadolinium enhancement. Circ J 2016; 80: 1210 – 1216. 2. Fan KY, Chan CW, Cheng LC, Ko RL, Lam YL, Jim MH, et al. Isolated left ventricular non-compaction: An unusual indication for heart transplantation. Hong Kong Med J 2009; 15: 378 – 380. 3. Maestrini V, Treibel TA, White SK, Fontana M, Moon JC. T1 mapping for characterization of intracellular and extracellular myocardial diseases in heart failure. Curr Cardiovasc Imaging Rep 2014; 7: 9287. 4. Ferreira VM, Piechnik SK, Robson MD, Neubauer S, Karamitsos TD. Myocardial tissue characterization by magnetic resonance imaging: Novel applications of T1 and T2 mapping. J Thorac Imaging 2014; 29: 147 – 154. 5. Maron BA, Towbin JA, Thiene G, Antzelevitch C, Corrado D, Arnett D, et al. Contemporary definitions and classification of the cardiomyopathies: An American Heart Association Scientific Statement From the Council on Clinical Cardiology, Heart Failure and Transplantation Committee; Quality of Care and Outcomes Research and Functional Genomics and Translational Biology Interdisciplinary Working Groups; and Council on Epidemiology and Prevention. Circulation 2006; 113: 1807 – 1816. 6. Chin TK, Perloff JK, Williams RG, Jue K, Mohrmann R. Isolated noncompaction of left ventricular myocardium: A study of eight cases. Circulation 1990; 82: 507 – 513. 7. Oechslin EN, Attenhofer Jost CH, Rojas JR, Kaufmann PA, Jenni R. Long-term follow-up of 34 adults with isolated left ventricular noncompaction: A distinct cardiomyopathy with poor prognosis. J Am Coll Cardiol 2000; 36: 493 – 500.

Non-contrast T1 and T2 relaxometry characterizes reperfusion injury of acute MI in swine

Background Reperfusion injury in acute myocardial infarction (MI) results in edema, necrosis, microvascular obstruction (MVO), and intramyocardial hemorrhage (IMH), the latter presents an interesting clinical target. [1] Cardiovascular MRI has been shown capable of characterizing all of these tissue components. Other than MVO, which is currently detected by flow-deficient regions in contrast enhanced imaging, all other tissue components can be identified by T1 and T2 (T2*). Theoretically, the byproducts of blood breakdown observed with IMH lead to decreased T1 and T2 (T2*). [2] Conversely, free water accumulation (edema) and necrosis lead to increased T1 and T2. [2] Hence, direct and quantitative measurement of relaxation rates is promising in myocardial tissue characterization, avoiding ambiguity typical of weighted images (i.e. T2-weighted spin-echo), undesired signal loss from T2* (weighted) images or the uncertainty introduced by contrast agent kinetics. Hypothesis: Combined T1 and T2 mapping can characterize reperfused MI without contrast agents.

High-resolution whole-heart 3D T2 mapping can assess tissue heterogeneity of chronic MI in swine

Background Remodeling of myocardium after infarction (MI) is linked to ventricular arrhythmias. [1] It has been demonstrated that the presence of scar containing isthmuses of viable myocardium resulting in a heterogeneous zone (HZ) with altered conduction properties which may be part of the critical substrate for post-MI ventricular tachycardia. [2,3] Late gadolinium-enhanced (LGE) imaging is used for MI visualization, clearly depicting infarct size and transmurality due to the excellent contrast achieved between scar and viable tissue. However, with LGE uncertainty can be introduced by contrast agent kinetics. [4] Furthermore, LGE can lack information on tissue heterogeneity beyond “gray” areas that result from partial volume averaging and are assumed to be representative of the HZ. Conversely, scar tissue also exhibits increased T2, as fibrosis, primarily composed of collagen, increases interstitial water per unit volume. [5] Hence, direct and quantitative measurement of T2 relaxation time may be a feasible alternative for delineating viable myocardium and fibrosis with the additional benefit of depicting tissue heterogeneity.