Maryam Nezafat

Comparison of spoiled gradient echo and steady-state free-precession imaging for native myocardial T1 mapping using the slice-interleaved T1 mapping (STONE) sequence.

Cardiac T1 mapping allows non‐invasive imaging of interstitial diffuse fibrosis. Myocardial T1 is commonly calculated by voxel‐wise fitting of the images acquired using balanced steady‐state free precession (SSFP) after an inversion pulse. However, SSFP imaging is sensitive to B1 and B0 imperfection, which may result in additional artifacts. A gradient echo (GRE) imaging sequence has been used for myocardial T1 mapping; however, its use has been limited to higher magnetic field to compensate for the lower signal‐to‐noise ratio (SNR) of GRE versus SSFP imaging. A slice‐interleaved T1 mapping (STONE) sequence with SSFP readout (STONE–SSFP) has been recently proposed for native myocardial T1 mapping, which allows longer recovery of magnetization (>8 R–R) after each inversion pulse. In this study, we hypothesize that a longer recovery allows higher SNR and enables native myocardial T1 mapping using STONE with GRE imaging readout (STONE–GRE) at 1.5T. Numerical simulations and phantom and in vivo imaging were performed to compare the performance of STONE–GRE and STONE–SSFP for native myocardial T1 mapping at 1.5T. In numerical simulations, STONE–SSFP shows sensitivity to both T2 and off resonance. Despite the insensitivity of GRE imaging to T2, STONE–GRE remains sensitive to T2 due to the dependence of the inversion pulse performance on T2. In the phantom study, STONE–GRE had inferior accuracy and precision and similar repeatability as compared with STONE–SSFP. In in vivo studies, STONE–GRE and STONE–SSFP had similar myocardial native T1 times, precisions, repeatabilities and subjective T1 map qualities. Despite the lower SNR of the GRE imaging readout compared with SSFP, STONE–GRE provides similar native myocardial T1 measurements, precision, repeatability, and subjective image quality when compared with STONE–SSFP at 1.5T.

Imaging sequence for joint myocardial T1 mapping and fat/water separation

To develop and evaluate an imaging sequence to simultaneously quantify the epicardial fat volume and myocardial T1 relaxation time.

Black blood myocardial T2 mapping

To develop a black blood heart‐rate adaptive T2‐prepared balanced steady‐state free‐precession (BEATS) sequence for myocardial T2 mapping.

Nonrigid active shape model-based registration framework for motion correction of cardiac T1 mapping: ASM-Based Registration for Cardiac T1 Mapping

Accurate reconstruction of myocardial T1 maps from a series of T1‐weighted images consists of cardiac motions induced from breathing and diaphragmatic drifts. We propose and evaluate a new framework based on active shape models to correct for motion in myocardial T1 maps.

Left Atrial Epicardial Fat Volume Is Associated With Atrial Fibrillation: A Prospective Cardiovascular Magnetic Resonance 3D Dixon Study

Background Recent studies demonstrated a strong association between atrial fibrillation (AF) and epicardial fat around the left atrium (LA). We sought to assess whether epicardial fat volume around the LA is associated with AF, and to determine the additive value of LA‐epicardial fat measurements to LA structural remodeling for identifying patients with AF using 3‐dimensional multi‐echo Dixon fat–water separated cardiovascular magnetic resonance. Methods and Results A total of 105 subjects were studied: 53 patients with a history of AF and 52 age‐matched patients with other cardiovascular diseases but no history of AF. The 3‐dimensional multi‐echo Dixon fat‐water separated sequence was performed for LA‐epicardial fat measurements. AF patients had significantly greater LA‐epicardial fat (28.9±12.3 and 14.2±7.3 mL for AF and non‐AF, respectively; P<0.001) and LA volume (110.8±38.2 and 89.7±30.3 mL for AF and non‐AF, respectively; P=0.002). LA‐epicardial fat adjusted for LA volume was still higher in patients with AF compared with those without AF (P<0.001). LA‐epicardial fat and hypertension were independently associated with the risk of AF (odds ratio, 1.17; 95% confidence interval, 1.10%–1.25%, P<0.001, and odds ratio, 3.29; 95% confidence interval, 1.17%–9.27%, P=0.03, respectively). In multivariable logistic regression analysis adjusted for body surface area, LA‐epicardial fat remained significant and an increase per mL was associated with a 42% increase in the odds of AF presence (odds ratio, 1.42; 95% confidence interval, 1.23%–1.62%, P<0.001). Combined assessment of LA‐epicardial fat and LA volume provided greater discriminatory performance for detecting AF than LA volume alone (c‐statistic=0.88 and 0.74, respectively, DeLong test; P<0.001). Conclusions Cardiovascular magnetic resonance 3‐dimensional Dixon‐based LA‐epicardial fat volume is significantly increased in AF patients. LA‐epicardial fat measured by 3‐dimensional Dixon provides greater performance for detecting AF beyond LA structural remodeling.

Improved segmented modified Look-Locker inversion recovery T1 mapping sequence in mice

Object To develop and evaluate a 2D modified Look-Locker (MOLLI) for high-resolution T1 mapping in mice using a 3T MRI scanner. Materials and methods To allow high-resolution T1 mapping in mice at high heart rates a multi-shot ECG-triggered 2D MOLLI sequence was developed. In the proposed T1 mapping sequence the optimal number of sampling points and pause cardiac cycles following an initial adiabatic inversion pulse was investigated in a phantom. Seven native control and eight mice, 3 days post myocardial infarction (MI) after administration of gadolinium were scanned. Two experienced readers graded the visual T1 map quality. Results In T1 phantoms, there were no significant differences (<0.4% error) between 12, 15 and 20 pause cardiac cycles (p = 0.1, 0.2 and 0.6 respectively) for 8 acquisition cardiac cycles for 600bpm in comparison to the conventional inversion recovery spin echo T1 mapping sequence for short T1’s (<600 ms). Subsequently, all in-vivo scans were performed with 8 data acquisitions and 12 pause cardiac cycles to minimize scan time. The mean native T1 value of myocardium in control animal was 820.5±52 ms. The post-contrast T1 measured 3 days after MI in scar was 264±59 ms and in healthy myocardium was 512±62 ms. The Bland-Altman analysis revealed mean difference of only -1.06% of infarct size percentage between T1 maps and LGE. Conclusions A multi-shot 2D MOLLI sequence has been presented that allows reliable measurement of high spatial resolution T1 maps in mice for heart rates up to 600bpm.

Diagnostic accuracy of Dixon water fat suppression coronary artery magnetic resonance angiography at 3.0 Tesla

Background X-Ray coronary angiography (XRA) remains the gold standard for assessment of coronary artery disease (CAD) although has associated clinical risk and financial cost. Coronary artery magnetic resonance angiography (CMRA) requires effective fat suppression as the epicardial vessels are embedded within fat. The aim of this study was to assess the diagnostic performance of non-contrast enhanced whole-heart two-point Dixon multi-echo fatwater separation coronary angiography at 3T in patients with suspected CAD. Methods Prospective, consecutive patients (n = 45) with angina underwent both XRA and free breathing Dixon 3D wholeheart CMRA within 60 days (3T Philips Achieva TX). Imaging parameters included field-of-view = 300 × 300 × 100 mm, resolution = 1.2 × 1.2 × 1.2 mm, TR/TE1/TE2 = 4.0/1.36/2.4 ms, a = 20°, and SENSE = 2 with a nominal scan time of 7:03 mins assuming a heart rate of 60 bpm. Navigator gating window was 5 mm with mid-diastolic image acquisition. A double-blind analysis of the two diagnostic procedures was performed at two independent cen-

Myocardial T1 mapping with spectrally-selective inversion pulse to reduce the influence of fat

Background Changes in the longitudinal relaxation time (T1) of the myocardium are considered an important imaging-based biomarker to detect and quantify diffuse fibrosis. Several sequences have been suggested to measure myocardial T1 values [1]. However, T1 measurements are often influenced by the presence of intramyocardial or epicardial fat [2,3,4]. The aim of this study was to minimize the effect of fat in T1 mapping by the use of a water selective inversion pulse and to investigate the impact of this spectrally-selective inversion pulse on T1 measurements in the presence of field inhomogeneities.

A segmented modified look-locker inversion recovery (MOLLI) sequence for high heart rate T1 mapping of mice

Background Quantitative T1 mapping provides myocardial tissue characterization for assessment of various cardiomyopathies. The Modified Look-locker (MOLLI) sequence is widely used for mapping the T1quantification, where multiple single-shot images are acquired along the T1 recovery curve after an inversion pulse. However, single-shot imaging becomes infeasible for mouse imaging at high heart rates due to motion artifacts and requirements of resolution/coverage. Additionally, typical MOLLI sampling schemes [1] (3-3-5) and the pauses between blocks have to be adapted to the high heart rates in mice. In this work, we propose a segmented acquisition scheme for T1 mapping of mouse at high heart rates. After an initial inversion pulse we acquire segments for 20 images in subsequent heartbeats followed by 20 pause heartbeats to allow for full magnetization recovery. The complete k-space is acquired in this fashion over 5 segments per image. Experiments were performed with a T1 phantom by simulating high heart rates to evaluate the accuracy of the proposed sequence. Proof of concept T1 maps were also acquired in one healthy mouse. Methods