MOLLI T1 Mapping Research Articles

Z-score mapping for standardized analysis and reporting of cardiovascular magnetic resonance modified Look-Locker inversion recovery (MOLLI) T1 data: Normal behavior and validation in patients with amyloidosis

BackgroundT1 mapping using modified Look-Locker inversion recovery (MOLLI) provides quantitative information on myocardial tissue composition. T1 results differ between sites due to variations in hardware and software equipment, limiting the comparability of results. The aim was to test if Z-scores can be used to compare the results of MOLLI T1 mapping from different cardiovascular magnetic resonance (CMR) platforms.MethodsFirst, healthy subjects (n = 15) underwent 11 combinations of native short-axis T1 mapping (four CMR systems from two manufacturers at 1.5 T and 3 T, three MOLLI schemes). Mean and standard deviation (SD) of septal myocardial T1 were derived for each combination. T1 maps were transformed into Z-score maps based on mean and SD values using a prototype post-processing module. Second, Z-score mapping was applied to a validation sample of patients with cardiac amyloidosis at 1.5 T (n = 25) or 3 T (n = 13).ResultsIn conventional T1 analysis, results were confounded by variations in field strength, MOLLI scheme, and manufacturer-specific system characteristics. Z-score-based analysis yielded consistent results without significant differences between any two of the combinations in part 1 of the study. In the validation sample, Z-score mapping differentiated between patients with cardiac amyloidosis and healthy subjects with the same diagnostic accuracy as standard T1 analysis regardless of field strength.ConclusionsT1 analysis based on Z-score mapping provides consistent results without significant differences due to field strengths, CMR systems, or MOLLI variants, and detects cardiac amyloidosis with the same diagnostic accuracy as conventional T1 analysis. Z-score mapping provides a means to compare native T1 results acquired with MOLLI across different CMR platforms.

3D SASHA myocardial T1 mapping with high accuracy and improved precision

PurposeTo improve the precision of a free-breathing 3D saturation-recovery-based myocardial T1 mapping sequence using a post-processing 3D denoising technique.MethodsA T1 phantom and 15 healthy subjects were scanned on a 1.5 T MRI scanner using 3D saturation-recovery single-shot acquisition (SASHA) for myocardial T1 mapping. A 3D denoising technique was applied to the native T1-weighted images before pixel-wise T1 fitting. The denoising technique imposes edge-preserving regularity and exploits the co-occurrence of 3D spatial gradients in the native T1-weighted images by incorporating a multi-contrast Beltrami regularization. Additionally, 2D modified Look-Locker inversion recovery (MOLLI) acquisitions were performed for comparison purposes. Accuracy and precision were measured in the myocardial septum of 2D MOLLI and 3D SASHA T1 maps and then compared. Furthermore, the accuracy and precision of the proposed approach were evaluated in a standardized phantom in comparison to an inversion-recovery spin-echo sequence (IRSE).ResultsFor the phantom study, Bland–Altman plots showed good agreement in terms of accuracy between IRSE and 3D SASHA, both on non-denoised and denoised T1 maps (mean difference −1.4 ± 18.9 ms and −4.4 ± 21.2 ms, respectively), while 2D MOLLI generally underestimated the T1 values (69.4 ± 48.4 ms). For the in vivo study, there was a statistical difference between the precision measured on 2D MOLLI and on non-denoised 3D SASHA T1 maps (P = 0.005), while there was no statistical difference after denoising (P = 0.95).ConclusionThe precision of 3D SASHA myocardial T1 mapping was substantially improved using a 3D Beltrami regularization based denoising technique and was similar to that of 2D MOLLI T1 mapping, while preserving the higher accuracy and whole-heart coverage of 3D SASHA.

Identification of myocardial diffuse fibrosis by 11 heartbeat MOLLI T1 mapping: averaging to improve precision and correlation with collagen volume fraction

ObjectivesOur objectives involved identifying whether repeated averaging in basal and mid left ventricular myocardial levels improves precision and correlation with collagen volume fraction for 11 heartbeat MOLLI T1 mapping versus assessment at a single ventricular level.Materials and methodsFor assessment of T1 mapping precision, a cohort of 15 healthy volunteers underwent two CMR scans on separate days using an 11 heartbeat MOLLI with a 5(3)3 beat scheme to measure native T1 and a 4(1)3(1)2 beat post-contrast scheme to measure post-contrast T1, allowing calculation of partition coefficient and ECV. To assess correlation of T1 mapping with collagen volume fraction, a separate cohort of ten aortic stenosis patients scheduled to undergo surgery underwent one CMR scan with this 11 heartbeat MOLLI scheme, followed by intraoperative tru-cut myocardial biopsy. Six models of myocardial diffuse fibrosis assessment were established with incremental inclusion of imaging by averaging of the basal and mid-myocardial left ventricular levels, and each model was assessed for precision and correlation with collagen volume fraction.ResultsA model using 11 heart beat MOLLI imaging of two basal and two mid ventricular level averaged T1 maps provided improved precision (Intraclass correlation 0.93 vs 0.84) and correlation with histology (R2 = 0.83 vs 0.36) for diffuse fibrosis compared to a single mid-ventricular level alone. ECV was more precise and correlated better than native T1 mapping.ConclusionT1 mapping sequences with repeated averaging could be considered for applications of 11 heartbeat MOLLI, especially when small changes in native T1/ECV might affect clinical management.

Systolic MOLLI T1 mapping with heart rate depends pulse sequence sampling scheme is feasible in patients with atrial fibrillation

Systolic MOLLI T1 mapping with heart rate depends pulse sequence sampling scheme is feasible in patients with atrial fibrillation

ShMOLLI and 5(4R) 3 MOLLI T1 mapping in HCM detect similar ECV despite a difference in absolute T1 measurements

Background T1 mapping and extracellular volume (ECV) measurements enable assessment of diffuse fibrosis in HCM and have been validated against histology. There still remains wide variation in pulse sequences used to measure T1 each with their associated limitations and biases in T1 determination. We sought to compare T1 values and ECV measurements between a 5(4R)3 variant of MOLLI and ShMOLLI in patients undergoing CMR for evaluation of hypertrophic cardiomyopathy (HCM).

Optimized saturation pulse rrains for SASHA T1 mapping at 3T

Background SASHA and MOLLI T1 mapping sequences can have errors in calculated T1 values when their magnetization preparation pulses do not fully saturate/invert magnetization [1,2]. The commonly used 90°-90°-90° saturation pulse train [3] has poor performance at 3T due to large B1 field inhomogeneities. We propose that a new hard RF pulse train with numerically optimized flip angles [4] will offer superior performance and reduce errors in SASHA T1 values due to incomplete saturation.

How accurate is MOLLI T1 mapping in vivo? Validation by spin echo methods.

T1 mapping is a promising quantitative tool for assessing diffuse cardiomyopathies. The purpose of this study is to quantify in vivo accuracy of the Modified Look-Locker Inversion Recovery (MOLLI) cardiac T1 mapping sequence against the spin echo gold standard, which has not been done previously. T1 accuracy of MOLLI was determined by comparing with the gold standard inversion recovery spin echo sequence in the calf muscle, and with a rapid inversion recovery fast spin echo sequence in the heart. T1 values were obtained with both conventional MOLLI fitting and MOLLI fitting with inversion efficiency correction. In the calf (n = 6), conventional MOLLI fitting produced inconsistent T1 values with error ranging from 8.0% at 90° to 17.3% at 30°. Modified MOLLI fitting with inversion efficiency correction improved error to under 7.4% at all flip angles. In the heart (n = 5), modified MOLLI fitting with inversion correction reduced T1 error to 5.5% from 14.0% by conventional MOLLI fitting. This study shows that conventional MOLLI fitting can lead to significant in vivo T1 errors when not accounting for the lower adiabatic inversion efficiency often experienced in vivo.

0294: Extravascular volume by cardiac MR T1 mapping accurately predicts histologically measured fibrosis in valve disease

Valvular heart disease is associated with left ventricular hypertrophy, remodeling and development of diffuse interstitial fibrosis. So far, histopathology remains the gold standard for evaluating diffuse myocardial fibrosis. Gadolinium enhanced Cardiac Magnetic Resonance (CMR) T1 mapping is new method which allows to quantify the myocardial extracellular volume (ECV). Hence, it was suggested that this ECV measurements allows to non-invasive estimate diffuse fibrosis. However validations studies are scars. Therefore the aim of this study was to validate measurements of ECV by T1-Modified Lock-locker (MOLLI) CMR against histological measurement. Between June 2012 and September 2013, 15 patients (age=57±15 years, 73% men) with either severe aortic valve disease (stenosis or regurgitation) or severe mitral regurgitation, but without coronary artery disease preoperatively underwent ECV measurement by CMR MOLLI T1 mapping. LV biopsies were performed at the time of surgery 7±8 days later and stained with Sirius red. The amount of fibrosis quantified by biopsy was 6.6±4.8% [2.1;15.9]. ECV by T1 mapping was 28.3±4.7% [23.3;38.6] (values are presented as mean±SD [min;max]). There was a good correlation between histologically measured fibrosis and T1 mapping ECV (r=0.77, p<0.001, cfr figure). ECV determined by CMR T1 mapping closely correlates with histologically determined diffuse interstitial fibrosis and could thus be used to non-invasively quantify interstitial fibrosis in patients with heart diseases.

Free‐breathing post‐contrast three‐dimensional T1 mapping: Volumetric assessment of myocardial T1 values

To develop a three-dimensional (3D) free-breathing myocardial T1 mapping sequence for assessment of left ventricle diffuse fibrosis after contrast administration. In the proposed sequence, multiple 3D inversion recovery images are acquired in an interleaved manner. A mixed prospective/retrospective navigator scheme is used to obtain the 3D Cartesian k-space data with fully sampled center and randomly undersampled outer k-space. The resulting undersampled 3D k-space data are then reconstructed using compressed sensing. Subsequently, T1 maps are generated by voxel-wise curve fitting of the individual interleaved images. In a phantom study, the accuracy of the 3D sequence was evaluated against two-dimensional (2D) modified Look-Locker inversion recovery (MOLLI) and spin-echo sequences. In vivo T1 times of the proposed method were compared with 2D multislice MOLLI T1 mapping. Subsequently, the feasibility of high-resolution 3D T1 mapping with spatial resolution of 1.7 × 1.7 × 4 mm(3) was demonstrated. The proposed method shows good agreement with 2D MOLLI and the spin-echo reference in phantom. No significant difference was found in the in vivo T1 times estimated using the proposed sequence and the 2D MOLLI technique (myocardium, 330 ± 66 ms versus 319 ± 93 ms; blood pools, 211 ± 68 ms versus 210 ± 98 ms). However, improved homogeneity, as measured using standard deviation of the T1 signal, was observed in the 3D T1 maps. The proposed sequence enables high-resolution 3D T1 mapping after contrast injection during free-breathing with volumetric left ventricle coverage.

MOLLI T1 mapping versus T2 W-SPAIR at 3T: myocardial area at risk measurements and the influence of microvascular obstruction

Background Robust CMR imaging is required for the delineation of myocardial area at risk (AAR), so that the success of reperfusion therapies can be evaluated. In this work, we investigate the performance of T1 mapping in assessing AAR one week post-STEMI, and explore the effect of microvascular obstruction (MVO) on T1 relaxation times. Methods CMR imaging was conducted on a Philips 3T Achieva MRI scanner. T2W-weighted spectral attenuated inversion recovery (T2WW-SPAIR), modified look-locker inversion recovery (MOLLI) T1 mapping and late gadolinium enhancement (LGE) sequences were applied as short axis stacks in 10 healthy volunteers and 62 STEMI patients. Receiver operator characteristic (ROC) analysis was applied to calculate a cut-off T1 to to discriminate AAR from normal myocardium. The presence of LGE was used as the positive ROC test state, while healthy myocardium, as measured in volunteers, was used as the negative ROC test state. For comparison with T1 mapping, the AAR was also measured on T2WW images using a threshold signal intensity > 2SD greater than remote. The derived myocardial edema volumes and salvage indices were compared between MVO+ and MVO- groups. Results For T1 mapping, ROC analysis gave a significantly larger area-under-the-curve (AUC) as compared to T2WWSPAIR for delineating myocardial edema (AUC = 0.89

Effects of heart rate in modified look-locker inversion recovery (MOLLI) T1 mapping

MOLLI is a method of producing a T1 map at end diastole by using the electrocardiogram (ECG) under respiratory arrest to obtain consecutive inversion recovery images with an arbitrary number of MOLLI cycles. Since a variety of heart rates are presumed clinically, it is important to understand their effects on the T1 value and the error of measurement. We investigated the error of measurement in MOLLI T1 mapping caused by changes in the heart rate. Methods MAGNETOM Avanto 1.5T, simulation ECG, and a phantom with an aqueous dilution of Gd-DTPA were used. The phantom contents and T1 values were as follows: olive oil = 213 ms, physiological saline = 3122.9 ms and aqueous dilutions of Gd-DTPA 103.6 ms-1739.9 ms were used. The imaging conditions were as follows: Sequence is single-shot TrueFISP, TR = 700 ms, TE = 1.13 ms, FA = 35 deg, FOV = 360 mm, Resolution=256 x 65%, shot duration time = 123 ms, Bandwidth = 1028 Hz/Px, Reordering=linear, MOLLI TI start = 82 ms, MOLLI TI increment =18 ms resting heart cycle 0-8, iPAT (+). In the experiment, #1 the T1 value was measured by using RR = 800 ms and two sets of MOLLI cycles (LL1=4 images, LL2=4 images) and changing the number of resting heart cycles (RT) between LL1 and LL2 from 0 to 8, and #2 The T1 value was measured by varying RR in the range 400-1000 ms and both for the case of using two sets of MOLLI cycles (LL1=8 images, LL2=2 images) with RT fixed to be 1. and for the case of changing RT from 0 to 10 so that the IR interval between LL1 and LL2 becomes approximately 7200 ms. Results The results #1, The error of measurement was approximately 45% for a T1 value of 103.6ms and approximately 5% for T1 values of 347.8-1044.2 ms, with no dependence on RT. However, for T1 values in the range 1739.9-3122.9 ms, there were large changes with RT, in the range of 10-175%. The results #2, in which RT was fixed, With RT=1, as the heart rate increased the change in the error of measurement became greater, approximately 25-50% for T1 values of 1739.9-3122.9 ms. The results of varying RT are shown in Figure 1 and Figure 2. When RT was adjusted to make the IR interval constant the change in the error of measurement improved to approximately 20-27% for T1 values of 1739.9-3122.9 ms.

Comparison of methods for determining the partition coefficient of gadolinium in the myocardium using T1mapping

To develop and validate modified Look-Locker (MOLLI) protocols to generate myocardial T1 maps within clinically acceptable breath-hold durations and to compare partition coefficients (λ) of gadolinium (Gd)-DTPA determined from either bolus injection (BI) or continuous infusion (CI) techniques. T1 mapping was performed in phantoms and in 10 volunteers on a 1.5T scanner using the standard (3-3-5) MOLLI technique and two MOLLI schemes with shorter breath-hold durations. Imaging was performed precontrast and every 5 minutes following a bolus of 0.1 mmol/kg Gd-DTPA and a 15-minute delayed continuous infusion of 0.001 mmol/kg Gd-DTPA until equilibrium T1 in the myocardium was achieved to enable direct comparison of T1 relaxation times between techniques and λ's between the BI and CI methods. There was good agreement of T1 values between the 3-3-5 standard MOLLI protocol and the modified 3-5 MOLLI protocol in both phantom studies over a range of heart rates and in human subjects. Both MOLLI protocols produced similar measurements of λ using both the BI and CI methods. A reduced breath-hold MOLLI T1 mapping protocol combined with the BI method can accurately characterize T1 and λ in clinically applicable breath-hold durations without requiring a long equilibrium phase infusion.