Look-Locker Inversion Recovery Research Articles

Assessment of hepatic fibrosis and inflammation with look-locker T1 mapping and magnetic resonance elastography with histopathology as reference standard

PurposeTo compare the diagnostic performance of T1 mapping and MR elastography (MRE) for staging of hepatic fibrosis and grading inflammation with histopathology as standard of reference.Methods68 patients with various liver diseases undergoing liver biopsy for suspected fibrosis or with an established diagnosis of cirrhosis prospectively underwent look-locker inversion recovery T1 mapping and MRE. T1 relaxation time and liver stiffness (LS) were measured by two readers. Hepatic fibrosis and inflammation were histopathologically staged according to a standardized fibrosis (F0–F4) and inflammation (A0–A2) score. For statistical analysis, independent t test, and Mann–Whitney U test and ROC analysis were performed, the latter to determine the performance of T1 mapping and MRE for fibrosis staging and inflammation grading, as compared to histopathology.ResultsHistopathological analysis diagnosed 9 patients with F0 (13.2%), 21 with F1 (30.9%), 11 with F2 (16.2%), 10 with F3 (14.7%), and 17 with F4 (25.0%). Both T1 mapping and MRE showed significantly higher values for patients with significant fibrosis (F0-1 vs. F2-4; T1 mapping p < 0.0001, MRE p < 0.0001) as well as for patients with severe fibrosis or cirrhosis (F0-2 vs. F3-4; T1 mapping p < 0.0001, MRE p < 0.0001). T1 values and MRE LS were significantly higher in patients with inflammation (A0 vs. A1-2, both p = 0.01). T1 mapping showed a tendency toward lower diagnostic performance without statistical significance for significant fibrosis (F2-4) (AUC 0.79 vs. 0.91, p = 0.06) and with a significant difference compared to MRE for severe fibrosis (F3-4) (AUC 0.79 vs. 0.94, p = 0.03). For both T1 mapping and MRE, diagnostic performance for diagnosing hepatic inflammation (A1-2) was low (AUC 0.72 vs. 0.71, respectively).ConclusionT1 mapping is able to diagnose hepatic fibrosis, however, with a tendency toward lower diagnostic performance compared to MRE and thus may be used as an alternative to MRE for diagnosing hepatic fibrosis, whenever MRE is not available or likely to fail due to intrinsic factors of the patient. Both T1 mapping and MRE are probably not sufficient as standalone methods to diagnose hepatic inflammation with relatively low diagnostic accuracy.

Effect of Myocardial Tissue Characterization Using Native T1 to Predict the Occurrence of Adverse Events in Patients With Chronic Kidney Disease and Severe Aortic Stenosis

Among patients with chronic kidney disease (CKD), aortic stenosis (AS) is associated with a significantly higher rate of mortality. We aimed to evaluate whether diffuse myocardial fibrosis, determined using native T1 mapping, has prognostic utility in predicting major adverse cardiovascular events (MACEs), including all-cause mortality or heart failure hospitalization, in patients with CKD and severe AS who are evaluated for transcatheter aortic valve implantation. Cardiac magnetic resonance with T1 mapping using the modified Look-Locker inversion recovery technique was performed in 117 consecutive patients with severe AS and CKD (stage ≥3). Patients were followed up to determine the occurrence of MACE. The mean age of the 117 patients in the cohort was 82 ±8 years. Native T1 was 1,055 ms (25th- to 75th percentiles 1,031 to 1,078 ms), which is higher than previously reported in healthy controls. Patients with higher T1 times were more likely to have higher N-terminal pro-B-type natriuretic peptide levels (4,122 [IQR 1,578 to 7,980] pg/ml vs 1,678 [IQR 493 to 2,851] pg/ml, p=0.005) and a history of heart failure (33% vs 9%, p=0.034). After median follow-up of 3.4 years, MACE occurred in 71 patients (61%). The Society of Thoracic Surgeons predicted risk of mortality score (hazard ratio [HR] 1.07, 95% confidence interval [CI] 1.02 to 1.12, p=0.006), native T1 >1,024 ms (HR 2.10, 95% CI 1.09 to 4.06, p=0.028), and New York Heart Association class (HR 1.56, 95% 1.09 to 2.34, p=0.016) were independent predictors of MACE. Longer native T1 was associated with MACE occurrence in patients with CKD and severe AS.

Rapid fat-water separated T1 mapping using a single-shot radial inversion-recovery spoiled gradient recalled pulse sequence.

T1 mapping is increasingly used in clinical practice and research studies. With limited scan time, existing techniques often have limited spatial resolution, contrast resolution and slice coverage. High fat concentrations yield complex errors in Look-Locker T1 methods. In this study, a dual-echo 2D radial inversion-recovery T1 (DEradIR-T1) technique was developed for fast fat-water separated T1 mapping. The DEradIR-T1 technique was tested in phantoms, 5 volunteers and 28 patients using a 3 T clinical MRI scanner. In our study, simulations were performed to analyze the composite (fat + water) and water-only T1 under different echo times (TE). In standardized phantoms, an inversion-recovery spin echo (IR-SE) sequence with and without fat saturation pulses served as a T1 reference. Parameter mapping with DEradIR-T1 was also assessed in vivo, and values were compared with modified Look-Locker inversion recovery (MOLLI). Bland-Altman analysis and two-tailed paired t-tests were used to compare the parameter maps from DEradIR-T1 with the references. Simulations of the composite and water-only T1 under different TE values and levels of fat matched the in vivo studies. T1 maps from DEradIR-T1 on a NIST phantom (Pcomp = 0.97) and a Calimetrix fat-water phantom (Pwater = 0.56) matched with the references. In vivo T1 was compared with that of MOLLI: ; . In this work, intravoxel fat is found to have a variable, echo-time-dependent effect on measured T1 values, and this effect may be mitigated using the proposed DRradIR-T1.

The Role of MR Assessments of Cardiac Morphology, Function, and Tissue Characteristics on Exercise Capacity in Well-Functioning Older Adults.

The relationship between resting cardiac indices and exercise capacity in older adults was still not well understood. New developments in cardiac magnetic resonance imaging (MRI) enable a much fuller assessment of cardiac characteristics. To assess the association between exercise capacity and specific aspects of resting cardiac structure, function, and tissue. Cross-sectional study. A total of 112 well-functioning older adults (mean age 69 years, 52 men). All participants underwent 3.0 T MRI, using scan protocols including balanced steady-state free precession cine sequence, modified look-locker inversion recovery, and T2-prepared single-shot balanced steady-state free precession. Demographic and geriatric characteristics were collected. Blood samples were assayed for lipid and glucose related biomarkers. All participants performed a symptom-limited cardiopulmonary exercise test to achieve peakVO2 . Cardiac MRI parameters were measured with semi-automatic software by S.Y., an 18-year experienced radiologist. Demographic, geriatric characteristics and MR measurements were compared among quartiles of peakVO2, with different methods according to the data type. Spearman's partial correlation and least absolute shrinkage selection operator regression were performed to select significant MR features associated with peakVO2 . Mediation effect analysis was conducted to test any indirect connection between age and peakVO2 . A two-sided P value of <0.05 was defined statistical significance. Epicardial fat volume, left atrial volume indexed to height, right ventricular end-systolic volume indexed to body surface area and global circumferential strain (GCS) were correlated with peakVO2 (regression coefficients were -0.040, -0.093, 0.127, and 0.408, respectively). Mediation analysis showed that the total effect of peakVO2 change was 43.6% from the change of age. The proportion of indirect effect from epicardial fat volume and GCS were 11.8% and 15.1% in total effect, respectively. PeakVO2 was associated with epicardial fat volume, left atrial volume, right ventricular volume and GCS of left ventricle. 4 TECHNICAL EFFICACY: Stage 5.

Improving accuracy of myocardial T1 estimation in MyoMapNet.

To improve the accuracy and robustness of T1 estimation by MyoMapNet, a deep learning-based approach using 4 inversion-recovery T1 -weighted images for cardiac T1 mapping. MyoMapNet is a fully connected neural network for T1 estimation of an accelerated cardiac T1 mapping sequence, which collects 4 T1 -weighted images by a single Look-Locker inversion-recovery experiment (LL4). MyoMapNet was originally trained using in vivo data from the modified Look-Locker inversion recovery sequence, which resulted in significant bias and sensitivity to various confounders. This study sought to train MyoMapNet using signals generated from numerical simulations and phantom MR data under multiple simulated confounders. The trained model was then evaluated by phantom data scanned using new phantom vials that differed from those used for training. The performance of the new model was compared with modified Look-Locker inversion recovery sequence and saturation-recovery single-shot acquisition for measuring native and postcontrast T1 in 25 subjects. In the phantom study, T1 values measured by LL4 with MyoMapNet were highly correlated with reference values from the spin-echo sequence. Furthermore, the estimated T1 had excellent robustness to changes in flip angle and off-resonance. Native and postcontrast myocardium T1 at 3Tesla measured by saturation-recovery single-shot acquisition, modified Look-Locker inversion recovery sequence, and MyoMapNet were 1483 ± 46.6ms and 791 ± 45.8ms, 1169 ± 49.0ms and 612 ± 36.0ms, and 1443 ± 57.5ms and 700 ± 57.5ms, respectively. The corresponding extracellular volumes were 22.90% ± 3.20%, 28.88% ± 3.48%, and 30.65% ± 3.60%, respectively. Training MyoMapNet with numerical simulations and phantom data will improve the estimation of myocardial T1 values and increase its robustness to confounders while also reducing the overall T1 mapping estimation time to only 4 heartbeats.

Impact of deep learning architectures on accelerated cardiac T1 mapping using MyoMapNet.

The objective of the current study was to investigate the performance of various deep learning (DL) architectures for MyoMapNet, a DL model for T1 estimation using accelerated cardiac T1 mapping from four T1 -weighted images collected after a single inversion pulse (Look-Locker 4 [LL4]). We implemented and tested three DL architectures for MyoMapNet: (a) a fully connected neural network (FC), (b) convolutional neural networks (VGG19, ResNet50), and (c) encoder-decoder networks with skip connections (ResUNet, U-Net). Modified Look-Locker inversion recovery (MOLLI) images from 749 patients at 3T were used for training, validation, and testing. The first four T1 -weighted images from MOLLI5(3)3 and/or MOLLI4(1)3(1)2 protocols were extracted to create accelerated cardiac T1 mapping data. We also prospectively collected data from 28 subjects using MOLLI and LL4 to further evaluate model performance. Despite rigorous training, conventional VGG19 and ResNet50 models failed to produce anatomically correct T1 maps, and T1 values had significant errors. While ResUNet yielded good quality maps, it significantly underestimated T1 . Both FC and U-Net, however, yielded excellent image quality with good T1 accuracy for both native (FC/U-Net/MOLLI =1217 ± 64/1208 ± 61/1199 ± 61 ms, all p< 0.05) and postcontrast myocardial T1 (FC/U-Net/MOLLI = 578 ± 57/567 ± 54/574 ± 55 ms, all p< 0.05). In terms of precision, the U-Net model yielded better T1 precision compared with the FC architecture (standard deviation of 61 vs. 67 ms for the myocardium for native [p< 0.05], and 31 vs. 38 ms [p< 0.05], for postcontrast). Similar findings were observed in prospectively collected LL4 data. It was concluded that U-Net and FC DL models in MyoMapNet enable fast myocardial T1 mapping using only four T1 -weighted images collected from a single LL sequence with comparable accuracy. U-Net also provides a slight improvement in precision.

Accelerated cardiac T1 mapping with recurrent networks and cyclic, model-based loss.

Using the spin-lattice relaxation time (T1) as a biomarker, the myocardium can be quantitatively characterized using cardiac T1 mapping. The modified Look-Locker inversion (MOLLI) recovery sequences have become the standard clinical method for cardiac T1 mapping. However, the MOLLI sequences require an 11-heartbeat breath-hold that can be difficult for subjects, particularly during exercise or pharmacologically induced stress. Although shorter cardiac T1 mapping sequences have been proposed, these methods suffer from reduced precision. As such, there is an unmet need for accelerated cardiac T1 mapping. To accelerate cardiac T1 mapping MOLLI sequences by using neural networks to estimate T1 maps using a reduced number of T1-weighted images and their corresponding inversion times. In this retrospective study, 911 pre-contrast T1 mapping datasets from 202 subjects (128 males, 56 ± 15 years; 74 females, 54 ± 17 years) and 574 T1 mapping post-contrast datasets from 193 subjects (122 males, 57 ± 15 years; 71 females, 54 ± 17 years) were acquired using the MOLLI-5(3)3 sequence and the MOLLI-4(1)3(1)2 sequence, respectively. All acquisition protocols used similar scan parameters: , , and , gadoteridol (ProHance, Bracco Diagnostics) dose . A bidirectional multilayered long short-term memory (LSTM) network with fully connected output and cyclic model-based loss was used to estimate T1 maps from the first three T1-weighted images and their corresponding inversion times for pre- and post-contrast T1 mapping. The performance of the proposed architecture was compared to the three-parameter T1 recovery model using the same reduction of the number of T1-weighted images and inversion times. Reference T1 maps were generated from the scanner using the full MOLLI sequences and the three-parameter T1 recovery model. Correlation and Bland-Altman plots were used to evaluate network performance in which each point represents averaged regions of interest in the myocardium corresponding to the standard American Heart Association 16-segment model. The precision of the network was examined using consecutively repeated scans. Stress and rest pre-contrast MOLLI studies as well as various disease test cases, including amyloidosis, hypertrophic cardiomyopathy, and sarcoidosis were also examined. Paired t-tests were used to determine statistical significance with . Our proposed network demonstrated similar T1 estimations to the standard MOLLI sequences (pre-contrast: vs. with ; post-contrast: vs. with ). The precision of standard MOLLI sequences was well preserved with the proposed network architecture ( vs. ). Network-generated T1 reactivities are similar to stress and rest pre-contrast MOLLI studies ( vs. with ). Amyloidosis T1 maps generated using the proposed network are also similar to the reference T1 maps (pre-contrast: vs. with ; post-contrast: vs. with ). A bidirectional multilayered LSTM network with fully connected output and cyclic model-based loss was used to generate high-quality pre- and post-contrast T1 maps using the first three T1-weighted images and their corresponding inversion times. This work demonstrates that combining deep learning with cardiac T1 mapping can potentially accelerate standard MOLLI sequences from 11 to 3 heartbeats.

Motion correction for native myocardial T1 mapping using self-supervised deep learning registration with contrast separation.

In myocardial T1 mapping, undesirable motion poses significant challenges because uncorrected motion can affect T1 estimation accuracy and cause incorrect diagnosis. In this study, we propose and evaluate a motion correction method for myocardial T1 mapping using self-supervised deep learning based registration with contrast separation (SDRAP). A sparse coding based method was first proposed to separate the contrast component from T1 -weighted (T1w) images. Then, a self-supervised deep neural network with cross-correlation (SDRAP-CC) or mutual information as the registration similarity measurement was developed to register contrast separated images, after which signal fitting was performed on the motion corrected T1w images to generate motion corrected T1 maps. The registration network was trained and tested in 80 healthy volunteers with images acquired using the modified Look-Locker inversion recovery (MOLLI) sequence. The proposed SDRAP was compared with the free form deformation (FFD) registration method regarding (1) Dice similarity coefficient (DSC) and mean boundary error (MBE) of myocardium contours, (2) T1 value and standard deviation (SD) of T1 fitting, (3) subjective evaluation score for overall image quality and motion artifact level, and (4) computation time. Results showed that SDRAP-CC achieved the highest DSC of 85.0 ± 3.9% and the lowest MBE of 0.92 ± 0.25 mm among the methods compared. Additionally, SDRAP-CC performed the best by resulting in lower SD value (28.1 ± 17.6 ms) and higher subjective image quality scores (3.30 ± 0.79 for overall quality and 3.53 ± 0.68 for motion artifact) evaluated by a cardiologist. The proposed SDRAP took only 0.52 s to register one slice of MOLLI images, achieving about sevenfold acceleration over FFD (3.7 s/slice).

Bowel wall MRI T1 relaxation estimates for assessment of intestinal inflammation in pediatric Crohn's disease.

To compare bowel wall T1 relaxation estimates in young patients with newly diagnosed ileal CD to healthy control participants, characterize their change over time in response to biologic medical therapy, and evaluate their associations with clinical markers of intestinal inflammation. Patients with newly diagnosed ileal CD and healthy control participants were prospectively recruited between December 2018 and October 2021. Patients underwent research MRI examinations of the bowel at baseline and at 6-weeks and 6-months into biologic medical treatment; control participants underwent single MRI examinations. MRI examinations included native T1 relaxometry of the terminal ileum using a modified Look-Locker inversion recovery (MOLLI) sequence. T1 estimates were measured on scanner-generated parametric maps. Clinical markers of intestinal inflammation were recorded at each visit. Group differences were assessed using the Mann-Whitney U test; the Friedman test was used to assess longitudinal changes in T1 estimates. Spearman correlation was used to evaluate associations between T1 estimates and inflammatory markers. Nineteen participants with CD (12 males; median age 14years) and 15 control participants (7 males; median age 17years) were included in the study. Bowel wall T1 estimates in CD patients (median 1302ms) were significantly longer compared to control participants (median 1159ms) (p < 0.001). In CD patients, T1 estimates changed over time after treatment (p = 0.001), with largest reductions between baseline and 6-weeks (p < 0.001). T1 estimates correlated with inflammatory markers, including erythrocyte sedimentation rate (ρ = 0.35; p = 0.01), c-reactive protein level (ρ = 0.34; p = 0.02), and weighted Pediatric Crohn's Disease Activity Index (ρ = 0.39; p = 0.005). T1 estimates did not correlate with serum albumin (ρ = - 0.28; p = 0.051) and fecal calprotectin (ρ = 0.07; p = 0.63). Bowel wall T1 estimates are abnormally increased in newly diagnosed ileal CD patients and decrease in response to medical therapy.

SAturation-recovery and Variable-flip-Angle-based three-dimensional free-breathing cardiovascular magnetic resonance T1 mapping at 3T.

The purpose of the current study was to develop and validate a three-dimensional (3D) free-breathing cardiac T1 -mapping sequence using SAturation-recovery and Variable-flip-Angle (SAVA). SAVA sequentially acquires multiple electrocardiogram-triggered volumes using a multishot spoiled gradient-echo sequence. The first volume samples the equilibrium signal of the longitudinal magnetization, where a flip angle of 2° is used to reduce the time for the magnetization to return to equilibrium. The succeeding three volumes are saturation prepared with variable delays, and are acquired using a 15° flip angle to maintain the signal-to-noise ratio. A diaphragmatic navigator is used to compensate the respiratory motion. T1 is calculated using a saturation-recovery model that accounts for the flip angle. We validated SAVA by simulations, phantom, and human subject experiments at 3T. SAVA was compared with modified Look-Locker inversion recovery (MOLLI) and saturation-recovery single-shot acquisition (SASHA) in vivo. In phantoms, T1 by SAVA had good agreement with the reference (R2 = 0.99). In vivo 3D T1 mapping by SAVA could achieve an imaging resolution of 1.25 × 1.25 × 8mm3 . Both global and septal T1 values by SAVA (1347 ± 37 and 1332 ± 42 ms) were in between those by SASHA (1612 ± 63 and 1618 ± 51 ms) and MOLLI (1143 ± 59 and 1188 ± 65 ms). According to the standard deviation (SD) and coefficient of variation (CV), T1 precision measured by SAVA (SD: 99 ± 14 and 60 ± 8ms; CV: 7.4% ± 0.9% and 4.5% ± 0.6%) was comparable with MOLLI (SD: 99 ± 25 and 46 ± 12 ms; CV: 8.8% ± 2.5% and 3.9% ± 1.1%) and superior to SASHA (SD: 222 ± 89 and 132 ± 33 ms; CV: 13.8% ± 5.5% and 8.1% ± 2.0%). It was concluded that the proposed free-breathing SAVA sequence enables more efficient 3D whole-heart T1 estimation with good accuracy and precision.

High-resolution systolic T1 mapping with compressed sensing for the evaluation of the right ventricle: a phantom and volunteer study.

To investigate the usefulness of high-resolution systolic T1 mapping using compressed sensing for right ventricular (RV) evaluation. Phantoms and normal volunteers were scanned at 3T by using a high-resolution (HR) modified look-locker inversion recovery (MOLLI) pulse sequence and a conventional MOLLI pulse sequence. The T1 values of the left ventricular (LV) and RV myocardium and blood pool were measured for each sequence. T1 values of HR-MOLLI and MOLLI sequences were compared in the LV myocardium, blood pool, and RV myocardium. The T1 values of HR-MOLLI and MOLLI showed good agreement in both phantoms and the LV myocardium and blood pool of volunteers. However, there was a significant difference between HR-MOLLI and MOLLI in the RV myocardium (1258 ± 52ms vs. 1327 ± 73ms; P = 0.0005). No significant difference was observed between the T1 value of RV and that of LV (1217 ± 32ms) in HR-MOLLI, whereas the T1 value of RV was significantly higher than that of LV in MOLLI (P < 0.0001). The interclass correlation coefficients of intraobserver variabilities from HR-MOLLI and MOLLI were 0.919 and 0.804, respectively, and the interobserver variabilities from HR-MOLLI and MOLLI were 0.838 and 0.848, respectively. Assessment of RV myocardium by using HR systolic T1 mapping was superior to the conventional MOLLI sequence in terms of accuracy and reproducibility.

Quantification of Early Diffuse Myocardial Fibrosis Through 7.0 T Cardiac Magnetic Resonance T1 Mapping in a Type 1 Diabetic Mellitus Mouse Model.

Diffuse myocardial interstitial fibrosis (DMIF) is a key factor for heart failure (HF) in diabetic cardiomyopathy. MRI T1-mapping technique can quantitatively evaluate DMIF. To evaluate of early DMIF in a type 1 diabetes mellitus (T1DM) mouse model through 7.0 T MRI T1 mapping. Prospective. A total of 50 8-week-old C57Bl/6J male mice were divided into control (n=20) and T1DM (n=30) groups. A 7.0 T small animal MRI; gradient echo Look-Locker inversion recovery T1-mapping sequence; cine MRI. Scans were acquired in control and T1DM mice every 4 weeks until 24 weeks. End-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF), left ventricle (LV) mass, fractional shortening (FS), and E/A ratio. They were evaluated through echocardiography and cine MRI. The extracellular volume fraction (ECV) was calculated. Sirius Red staining was performed and calculated collagen volume fraction (CVF). Differences in ECV and CVF between two groups were analyzed using one-way analysis of variance. The correlation between ECV and CVF was assessed using Pearson's correlations. Compared with the control group, a progressive decrease in FS, EF, and E/A ratio was observed in the T1DM group. Both ECV and CVF values gradually increased during diabetes progression. A significant increase in ECV and CVF values was observed at 12 weeks (ECV: 32.5% ± 1.6% vs. 28.1% ± 1.8%; CVF: 6.9% ± 1.8% vs. 3.3% ± 1.1%). ECV showed a strong correlation with CVF (r=0.856). ECV is an accurate and feasible imaging marker that can be used to quantitatively assess DMIF changes over time in T1DM mice. ECV has potential to accurately detect DMIF in the early stage and may be a useful imaging tool to assess the need for early intervention in T1DM mice. 1 TECHNICAL EFFICACY: Stage 3.

Preliminary Study on Quantitative Assessment of the Fetal Brain Using MOLLI T1 Mapping Sequence.

Prenatal quantitative evaluation of myelin is important. However, few techniques are suitable for the quantitative evaluation of fetal myelination. To optimize a modified Look-Locker inversion recovery (MOLLI) T1 mapping sequence for fetal brain development study. Prospective observational preliminary cohort study. A total of 71 women with normal fetuses divided into mid-pregnancy (gestational age 24-28 weeks, N=25) and late pregnancy (gestational age > 28 weeks, N=46) groups. A 3 T/MOLLI sequence. T1 values were measured in pedunculus cerebri, basal ganglia, thalamus, posterior limb of the internal capsule, temporal white matter, occipital white matter, frontal white matter, and parietal white matter by two radiologists (11 and 16 years of experience, respectively). The Kruskal-Wallis test was used for reginal comparison. For each region of interest (ROI), differences in T1 values between the mid and late pregnancy groups were assessed by the Mann Whitney U test. Pearson correlation coefficients (r) were used to evaluate the correlations between T1 values and gestational age for each ROI. Intraobserver and interobserver agreement was determined by the intraclass correlation coefficient (ICC). A P value <0.05 was considered statistically significant. Interobserver and intraobserver agreements of T1 were good for all ROIs (all ICCs > 0.700). There were significant differences in T1 values between lobal white matter and deep regions, respectively. Significant T1 values differences were found between middle and late pregnancy groups in pedunculus cerebri, basal ganglion, thalamus, posterior limb of the internal capsule, temporal, and occipital white matter. The T1 values showed significantly negative correlations with gestational weeks in pedunculus cerebri (r=-0.80), basal ganglion (r=-0.60), thalamus (r=-0.68), and posterior limb of the internal capsule (r=-0.77). The T1 values of fetal brain may be assessed using the MOLLI sequence and may reflect the myelination. 3 TECHNICAL EFFICACY: Stage 2.

The utility of splenic imaging parameters in cardiac magnetic resonance for the diagnosis of immunoglobulin light-chain amyloidosis

ObjectivesCardiac magnetic resonance (CMR) imaging is a key test in the diagnosis of cardiac amyloidosis (CA). Extracardiac involvement is common in light chain (AL) amyloidosis and MRI findings may assist in its diagnosis. We sought to investigate the utility of splenic CMR parameters for the diagnosis of CA.MethodsThirty-four patients with AL amyloidosis and 32 patients with severe left ventricular hypertrophy in the setting of aortic stenosis (LVH-AS) who completed 3T cardiac MRI at the time of their diagnosis of AL or LVH-AS were assessed with T1, T2 (modified Look-Locker inversion recovery), extracellular volume (ECV) mapping, and late gadolinium enhancement (LGE) imaging of the heart and spleen.ResultsAge, left ventricular mass index, wall thickness, ejection fraction, and splenic dimensions did not differ significantly between groups. All AL patients had cardiac involvement. T1 and T2 spleen mapping did not differ significantly between groups but AL patients had higher median ECV in the spleen than in LVH-AS (AL 46.9%, LVH-AS: 31%, p < 0.001), and significantly lower short tau inversion recovery ratio (AL: 1.7, LVH-AS: 2.7, p < 0.001) both with very good diagnostic performance to diagnose AL. We identified 16 AL patients with spleen involvement and 16 without. Spleen ECV and “normalized” spleen ratio, defined as the ratio of spleen LGE to muscle values exhibited strong correlation and had excellent diagnostic performance to discriminate those with spleen involvement.ConclusionOur findings show that spleen CMR parameters can identify spleen involvement in AL patients and differentiate them from those without AL amyloidosis.

Liver T1 relaxation time of the 'normal liver' in healthy Asians: measurement with MOLLI and B1-corrected VFA methods at 3T.

Liver T1 is a potential magnetic resonance imaging biomarker for liver diseases. This study aimed to determine the T1 relaxation time of the normal liver (PDFF<5%) in healthy Asian volunteers using modified look-locker inversion recovery (MOLLI) and B1 inhomogeneity-corrected variable flip angle (B1-corrected VFA). 60 healthy Asian volunteers without focal or diffuse liver disease underwent a liver scan at 3T magnetic resonance. Proton density fat fraction (PDFF) and liver stiffness measurements were applied for the quantification of liver fat and fibrosis. T1 mapping was performed with MOLLI and B1-corrected VFA sequences. Bland-Altman, linear regression, Student t-test, and one-way analysis of variance were used for statistical analysis. The mean T1 relaxation times of the whole liver were 901 ± 34 ms by MOLLI, and 948 ± 29 ms by B1-corrected VFA in healthy volunteers. There was a strong correlation (r = 0.86, p < 0.0001) for liver T1 between two T1 mapping methods. There were significant differences between the right and left lobes in liver T1 relaxation times using both methods (p < 0.05). Gender and Asian ethnic disparities had no impact on liver T1 relaxation times. T1 relaxation times of the normal liver (PDFF<5%) in healthy volunteers were established by MOLLI and B1-corrected VFA T1 mapping methods at 3T. It may provide suitable and robust baseline values for the assessment of liver diseases. Gender and Asian ethnic disparities do not impact liver T1 relaxation time measurements.

Native T1 heterogeneity for predicting reverse remodeling in patients with non-ischemic dilated cardiomyopathy.

A recent study has shown that the heterogeneity of native T1 mapping may be a new prognostic factor for patients with non-ischemic dilated cardiomyopathy (NIDCM). This study aimed to investigate the predictive value of native T1 heterogeneity of the left ventricular (LV) myocardium, as assessed by pixel-wise histogram analysis, for predicting left ventricular reverse remodeling (LVRR) by medical therapy in patients with NIDCM. A total of one hundred and thirteen NIDCM patients (mean age: 63 ± 12years; 91 males and 22 females; mean LV ejection fraction (EF): 37 ± 10%) were retrospectively analyzed. T1 mapping images were acquired using a modified look-locker inversion recovery (MOLLI) sequence. We performed histogram analysis of native T1 mapping of LV myocardium, mean (T1-mean) and standard deviation (T1-STD) of native T1 time from each pixel were calculated. Extracellular volume fraction (ECV) was also evaluated. LVRR was defined as LVEF increased ≥ 10% points and decrease in LV end-diastolic volume ≥ 10% at 12months from initiation of medical therapy. Cutoff value of T1-mean and T1-STD was set as median value of each parameter. Sixty (53%) NIDCM patients reached LVRR. Area under the receiver-operating characteristics curve for predicting LVRR was 0.763 (95% confidence interval (CI) 0.679-0.847) for %LGE, 0.757 (95% CI 0.663-0.850) for T1-mean, 0.724 (95% CI 0.625-0.823) for T1-STD, 0.800 (95% CI 0.717-0.882) for ECV, respectively. Proportion of LVRR was significantly lower in NIDCM patients with high T1-mean and high T1-STD (12%) compared to NIDCM with high T1-mean and low T1-STD (65%) (p < 0.001). Adding T1-STD to T1-mean improved AUC from 0.757 to 0.806, comparable to AUC of ECV. Combination of T1-mean and T1-STD, a parameter of heterogeneity of native T1 of the LV myocardium, may be a useful for prediction of LVRR by medical therapy without use of gadolinium contrast for patients with NIDCM.

Simultaneous Multi-Slice Cardiac MR Multitasking for Motion-Resolved, Non-ECG, Free-Breathing T1-T2 Mapping.

The aim of this study is to simultaneously quantify T1/T2 across three slices of the left-ventricular myocardium without breath-holds or ECG monitoring, all within a 3 min scan. Radial simultaneous multi-slice (SMS) encoding, self-gating, and image reconstruction was incorporated into the cardiovascular magnetic resonance (CMR) Multitasking framework to simultaneously image three short-axis slices. A T2prep-IR FLASH sequence with two flip angles was designed and implemented to allow B1+-robust T1 and T2 mapping. The proposed Multitasking-SMS method was validated in a standardized phantom and 10 healthy volunteers, comparing T1 and T2 measurements and scan-rescan repeatability against corresponding reference methods in one layer of phantom vials and in 16 American Heart Association (AHA) myocardial segments. In phantom, Multitasking-SMS T1/T2 measurements showed substantial correlation (R2 > 0.996) and excellent agreement [intraclass correlation coefficients (ICC) ≥ 0.999)] with reference measurements. In healthy volunteers, Multitasking-SMS T1/T2 maps reported similar myocardial T1/T2 values (1,215 ± 91.0/41.5 ± 6.3 ms) to the reference myocardial T1/T2 values (1,239 ± 67.5/42.7 ± 4.1 ms), with P = 0.347 and P = 0.296, respectively. Bland–Altman analyses also demonstrated good in vivo repeatability in both the multitasking and references, with segment-wise coefficients of variation of 4.7% (multitasking T1), 8.9% (multitasking T2), 2.4% [modified look-locker inversion recovery (MOLLI)], and 4.6% (T2-prep FLASH), respectively. In summary, multitasking-SMS is feasible for free-breathing, non-ECG, myocardial T1/T2 quantification in 16 AHA segments over 3 short-axis slices in 3 min. The method shows the great potential for reducing exam time for quantitative CMR without ECG or breath-holds.

Improved cardiac T1 mapping accuracy and precision with a new hybrid MOLLI and SASHA technique: MOSHA

PurposeTo develop and validate a new myocardial T1 mapping sequence (MOSHA) which is based on a combination of the modified Look-Locker inversion recovery (MOLLI) and the saturation recovery single-shot acquisition (SASHA) sequences. MethodsPrior studies have shown that myocardial T1 mapping by SASHA is more accurate but less precise than MOLLI. A new myocardial T1 mapping technique (MOSHA) based on single-shot acquisitions is developed by combining the MOLLI and SASHA sequences. Phantom and patient studies on 15 patients (9 males, median age 21 years) were performed to validate and compare MOSHA with the MOLLI and SASHA sequences in terms of accuracy and precision. ResultsIn the phantom study, MOSHA was as accurate as SASHA (P-value = 0.88) and as precise as MOLLI (P-value = 0.59). Similar trends were observed in the patient study. Compared to SASHA, MOSHA accuracy was comparable for blood pre-contrast (P-value≥0.10) and post-contrast (P-value≥0.70), and for myocardium pre-contrast (P-value = 0.70) and post-contrast (P-value = 0.09). Compared to MOLLI, MOSHA precision was lower for blood pre-contrast (P-value<0.01) and higher for blood post-contrast (P-value≤0.01), and comparable for myocardium pre-contrast (P-value = 0.24) and post-contrast (P-value = 0.07). Synthetic Extracellular volume fraction (ECV) calculated by MOSHA was more precise than those of SASHA and MOLLI (P-value≤0.01). ConclusionIn phantom studies and patients, MOSHA has comparable accuracy as SASHA and nearly similar precision as MOLLI for T1 mapping. Precision of MOSHA was better than MOLLI and SASHA in synthetic ECV measurements. Therefore, it may be a superior choice in clinical practice for a precise and accurate calculation of T1 and ECV.

Accelerated cardiac T1 mapping in four heartbeats with inline MyoMapNet: a deep learning-based T1 estimation approach

PurposeTo develop and evaluate MyoMapNet, a rapid myocardial T1 mapping approach that uses fully connected neural networks (FCNN) to estimate T1 values from four T1-weighted images collected after a single inversion pulse in four heartbeats (Look-Locker, LL4).MethodWe implemented an FCNN for MyoMapNet to estimate T1 values from a reduced number of T1-weighted images and corresponding inversion-recovery times. We studied MyoMapNet performance when trained using native, post-contrast T1, or a combination of both. We also explored the effects of number of T1-weighted images (four and five) for native T1. After rigorous training using in-vivo modified Look-Locker inversion recovery (MOLLI) T1 mapping data of 607 patients, MyoMapNet performance was evaluated using MOLLI T1 data from 61 patients by discarding the additional T1-weighted images. Subsequently, we implemented a prototype MyoMapNet and LL4 on a 3 T scanner. LL4 was used to collect T1 mapping data in 27 subjects with inline T1 map reconstruction by MyoMapNet. The resulting T1 values were compared to MOLLI.ResultsMyoMapNet trained using a combination of native and post-contrast T1-weighted images had excellent native and post-contrast T1 accuracy compared to MOLLI. The FCNN model using four T1-weighted images yields similar performance compared to five T1-weighted images, suggesting that four T1 weighted images may be sufficient. The inline implementation of LL4 and MyoMapNet enables successful acquisition and reconstruction of T1 maps on the scanner. Native and post-contrast myocardium T1 by MOLLI and MyoMapNet was 1170 ± 55 ms vs. 1183 ± 57 ms (P = 0.03), and 645 ± 26 ms vs. 630 ± 30 ms (P = 0.60), and native and post-contrast blood T1 was 1820 ± 29 ms vs. 1854 ± 34 ms (P = 0.14), and 508 ± 9 ms vs. 514 ± 15 ms (P = 0.02), respectively.ConclusionA FCNN, trained using MOLLI data, can estimate T1 values from only four T1-weighted images. MyoMapNet enables myocardial T1 mapping in four heartbeats with similar accuracy as MOLLI with inline map reconstruction.

Native T1 mapping detects both acute clinical rejection and graft dysfunction in pediatric heart transplant patients

BackgroundCardiovascular magnetic resonance (CMR) is emerging as an important tool for cardiac allograft assessment. Native T1 mapping may add value in identifying rejection and in assessing graft dysfunction and myocardial fibrosis burden. We hypothesized that CMR native T1 values and features of textural analysis of T1 maps would identify acute rejection, and in a secondary analysis, correlate with markers of graft dysfunction, and with fibrosis percentage from endomyocardial biopsy (EMB).MethodsFifty cases with simultaneous EMB, right heart catheterization, and 1.5 T CMR with breath-held T1 mapping via modified Look-Locker inversion recovery (MOLLI) in 8 short-axis slices and subsequent quantification of mean and peak native T1 values, were performed on 24 pediatric subjects. A single mid-ventricular slice was used for image texture analysis using nine gray-level co-occurrence matrix features. Digital quantification of Masson trichrome stained EMB samples established degree of fibrosis. Markers of graft dysfunction, including serum brain natriuretic peptide levels and hemodynamic measurements from echocardiography, catheterization, and CMR were collated. Subjects were divided into three groups based on degree of rejection: acute rejection requiring new therapy, mild rejection requiring increased ongoing therapy, and no rejection with no change in treatment. Statistical analysis included student’s t-test and linear regression.ResultsPeak and mean T1 values were significantly associated with acute rejection, with a monotonic trend observed with increased grade of rejection. Texture analysis demonstrated greater spatial heterogeneity in T1 values, as demonstrated by energy, entropy, and variance, in cases requiring treatment. Interestingly, 2 subjects who required increased therapy despite low grade EMB results had abnormal peak T1 values. Peak T1 values also correlated with increased BNP, right-sided filling pressures, and capillary wedge pressures. There was no difference in histopathological fibrosis percentage among the 3 groups; histopathological fibrosis did not correlate with T1 values or markers of graft dysfunction.ConclusionIn pediatric heart transplant patients, native T1 values identify acute rejection requiring treatment and may identify graft dysfunction. CMR shows promise as an important tool for evaluation of cardiac grafts in children, with T1 imaging outperforming biopsy findings in the assessment of rejection.