Modified Look-Locker Inversion Research Articles

T1 mapping of the prostate using Single-Shot T1FLASH and MOLLI MRI Techniques: Comparison of artifact burden and image quality

PurposeTo assess artifact burden and image quality of different MRI T1 mapping techniques of the prostate. MethodsParticipants with suspected prostate cancer (PCa) were prospectively enrolled from June-October 2022 and examined with multiparametric prostate MRI (mpMRI; 3 T scanner; T1wi, T2wi, DWI und DCE). T1 mapping was performed before and after administration of gadolinium-based contrast-agent (GBCA) using (i) a modified Look-Locker inversion (MOLLI) technique and (ii) a novel single-shot T1FLASH inversion recovery technique. T2wi, DWI, T1FLASH and MOLLI sequences were systematically examined regarding prevalence of artifacts and image quality using a 5-point Likert-Scale. ResultsA total of n = 100 patients were included (median age: 68 years). T1FLASH maps (pre-and post-GBCA) showed metal artifacts in 7% of cases and susceptibility artifacts in 1%. For MOLLI maps, pre-GBCA metal and susceptibility artifacts were documented in 6.5% of cases each. MOLLI maps post-GBCA showed artifacts in 59% of cases resulting primarily from urinary GBCA excretion and GBCA accumulation at the bladder base (p < 0.01 versus T1FLASH post-GBCA). Image quality for T1FLASH pre-GBCA was rated at a mean 4.9+/-0.4 and for MOLLI at 4.8+/-0.6 (p = 0.14). Post-GBCA image quality was rated at a mean 4.9+/-0.4 for T1FLASH and at 3.7+/-1.1 for MOLLI (p < 0.001). ConclusionsT1FLASH maps provide a fast and robust method for quantification of T1 relaxation times of the prostate. T1FLASH is suitable for T1 mapping of the prostate following administration of contrast agents, while MOLLI T1 mapping is impaired through GBCA accumulation at the bladder base leading to severe image artifacts and reduced image quality.

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.

Bioimpedance Spectroscopy Reveals Important Association of Fluid Status and T1 -Mapping by Cardiovascular Magnetic Resonance.

Extracellular matrix expansion is a key pathophysiologic feature in heart failure and can be quantified noninvasively by cardiac magnetic resonance T1 -mapping. Free water within the interstitial space of the myocardium, however, may also alter T1 -mapping results. To investigate the association between systemic fluid status and T1 -mapping by cardiac magnetic resonance. Prospective, observational single-center study. Two-hundred eighty-five consecutive patients (44.4% female, 70.0 ± 14.9 years old) scheduled for cardiac MR due to various cardiac diseases. 1.5-T scanner (Avanto Fit, Siemens Healthineers, Erlangen, Germany). For T1 -mapping, electrocardiographically triggered modified-Look-Locker inversion (MOLLI) recovery sequence using a 5(3)3 prototype on a short-axis mid-cavity slice and with a four-chamber view was performed. MR parameters including native myocardial T1 -times using MOLLI and extracellular volume (MR-ECV) were assessed, and additionally, we performed bioimpedance analysis (BIA). Furthermore, demographic data and comorbidities were assessed. Wilcoxon's rank-sum test, chi-square tests, and for correlation analysis, Pearson's correlation coefficients were used. Regression analyses were performed to investigate the association between patients' fluid status and T1 -mapping results. A P-value <0.05 was considered statistically significant. The mixed cohort presented with a mean overhydration (OH) of +0.2 ± 2.4liters, as determined by BIA. By MR, native T1 -times were 1038 ± 51 msec and MR-ECV was 31 ± 9%. In the multivariable regression analysis, only OH was significantly associated with MR-ECV (adj. beta: 0.711; 95% CI: 0.28 to 1.14) along with male sex (adj. beta: 2.529; 95% CI: 0.51 to 4.55). In linear as well as multivariable analysis, only OH was significantly associated with native T1 times (adj. beta: 3.750; 95% CI: 1.27 to 6.23). T1 -times and MR-ECV were significantly associated with the degree of OH on BIA measurement. These effects were independent from age, sex, body mass index, and hematocrit. Patients' volume status may thus be an important factor when T1 -time and MR-ECV values are interpreted. 2 TECHNICAL EFFICACY STAGE: 3.

Abstract 11438: Texture Analysis Identifies Differences in Cardiac Magnetic Resonance T1 Maps of Pediatric Heart Transplant Patients with Rejection

Introduction: Graft rejection is a significant contributor to morbidity and mortality in pediatric heart transplant recipients, despite surveillance by endomyocardial biopsy (EMB). Cardiac Magnetic Resonance (CMR) T1 mapping has shown potential for noninvasive diagnosis of rejection. However, variability in normative T1 values across field strengths, vendors, and individual scanners limits the utility of absolute T1 values to diagnose rejection across institutions. Texture analysis is an emerging method for quantifying spatial distribution of relative voxel intensities rather than using the absolute voxel intensities themselves and may serve as an additional method for evaluating T1 maps. Hypothesis: We hypothesized that T1 maps from patients with rejection would exhibit differences in texture features from patients without rejection. Methods: This study included 19 cases from 17 pediatric transplant patients (mean age 11.8 ± 5 year, graft age 5.9 ± 4.7 years, 41% female) who underwent CMR imaging and EMB. 8 short axis slices of breath-held T1 mapping using Modified Look-Locker Inversion (MOLLI) recovery on 1.5T Siemens scanner were obtained. Left ventricular myocardium was semiautomatically segmented from T1 maps, excluding the blood pool and epicardial myocardium. Image texture analysis was performed on a single mid-ventricular slice from each case. Rejection was defined as acute cellular rejection (biopsy grade 1R or higher) or negative biopsy with decreased function requiring treatment. T-test analysis was performed to compare differences in texture analysis between patients with and without rejection. Results: Analysis of T1 maps showed differences (p-value ≤ 0.10) between patients with and without rejection in texture features of energy (0.062 ± 0.012 vs 0.091 ± 0.051), entropy (4.59 ± 0.23 vs 4.23 ± 0.60), and variance (0.031 ± 0.005 vs 0.025 ± 0.009). Discussion: In this small pilot study, texture analysis identified differences in tissue character between patients with and without graft rejection. Evaluation of tissue character via texture analysis may provide an additional method for diagnosis of rejection, given the variability in normative T1 values across institutions.

Technical Note: Fully automatic segmental relaxometry (FASTR) for cardiac magnetic resonance T1 mapping.

Cardiac relaxometry techniques, particularly T1 mapping, have recently gained clinical importance in various cardiac pathologies. Myocardial T1 and extracellular volume are usually calculated from manual identification of left ventricular epicardial and endocardial regions. This is a laborious process, particularly for large volume studies. Here we present a fully automated relaxometry framework (FASTR) for segmental analysis of T1 maps (both native and postcontrast) and partition coefficient (λ). Patients (N=11) were imaged postacute myocardial infarction on a 1.5T clinical scanner. The scan protocol involved CINE-SSFP imaging, native, and post-contrast T1 mapping using the Modified Look-Locker Inversion (MOLLI) recovery sequence. FASTR consisted of automatic myocardial segmentation of spatio-temporally coregistered CINE images as an initial guess, followed by refinement of the contours on the T1 maps to derive segmental T1 and λ. T1 and λ were then compared to those obtained from two trained expert observers. Robust endocardial and epicardial contours were achieved on T1 maps despite the presence of infarcted tissue. Relative to experts, FASTR resulted in myocardial Dice coefficients (native T1: 0.752±0.041; postcontrast T1: 0.751±0.057) that were comparable to interobserver Dice (native T1: 0.803±0.045; postcontrast T1: 0.799±0.054). There were strong correlations observed for T1 and λ derived from experts and FASTR (native T1: r=0.83; postcontrast T1: r=0.87; λ: r=0.78; P<0.0001), which were comparable to inter-expert correlation coefficients (native T1: r=0.90; postcontrast T1: r=0.93; λ: r=0.80; P<0.0001). Our fully automated framework, FASTR, can generate accurate myocardial segmentations for native and postcontrast MOLLI T1 analysis without the need for manual intervention. Such a design is appealing for high volume clinical protocols.

Differentiation between Fabry disease and hypertrophic cardiomyopathy with cardiac T1 mapping

PurposeTo evaluate the potential of non-contrast myocardial T1 mapping on cardiovascular magnetic resonance examination (CMR) in differentiating patients with Fabry disease (FD) from those with hypertrophic cardiomyopathy (HCM) and healthy control subjects. Materials and methodsSeventeen patients with FD (8 men, 9 women; mean age, 48 ±18 [SD] years; [range: 19–73 years]; 53% with left ventricular hypertrophy [LVH]) were matched with 36 patients with hypertrophic cardiomyopathy (HCM) (22 men, 14 women; mean age, 57±16 [SD] years; [range: 22–85 years]) and 70 healthy control subjects (34 men, 36 women; mean age, 38 ±15 [SD] years; [range: 18–65 years]). Cardiac T1 mapping was performed using the modified Look-Locker inversion (MOLLI®) sequence on a 1.5-T magnet. T1 values were calculated, on midventricular section, for septal left ventricular segments (S8–S9) and all mid-ventricular ones (global T1 values; S7–S12). Statistical analysis included unpaired Mann-Whitney test, receiver operating characteristic curve and likelihood ratios. ResultsSeptal native T1 values were significantly decreased in patients with FD (889±61 [SD] ms; range: 784–980ms) compared to those with HCM (995±48 [SD] ms; range: 935–1125ms) (P<0.001) and versus healthy controls (965±29 [SD] ms; range: 910–1028ms) (P<0.001). Global native T1 values were also significantly decreased in patients with FD (891±49 [SD] ms; range 794–970ms) compared to those with HCM (995±34 [SD] ms; range: 952–1086ms) (P<0.001) and versus healthy controls (966±27 [SD] ms; range: 920–1042ms) (P<0.001). A septal left ventricular native T1 cutoff value of 940ms could distinguish FD from HCM with 88% sensitivity (95% CI: 73–100%) and 92% specificity (95% CI: 83–100%). Positive likelihood ratio was 11, negative likelihood ratio was 0.12. Compared to controls, the same threshold could distinguish FD with 88% sensitivity (95% CI: 73–100%) and 86% specificity (95% CI: 78–94%). Positive likelihood ratio was 6.3, negative likelihood ratio was 0.14. T1 value was abnormal in 4 of 8 (50%) of FD patients who did not have LVH. ConclusionNative T1 values are significantly lower in patients with FD by comparison with those with HCM and healthy volunteers.

Myocardial T1-mapping at 3T using saturation-recovery: reference values, precision and comparison with MOLLI

BackgroundMyocardial T1-mapping recently emerged as a promising quantitative method for non-invasive tissue characterization in numerous cardiomyopathies. Commonly performed with an inversion-recovery (IR) magnetization preparation at 1.5T, the application at 3T has gained due to increased quantification precision. Alternatively, saturation-recovery (SR) T1-mapping has recently been introduced at 1.5T for improved accuracy.Thus, the purpose of this study is to investigate the robustness and precision of SR T1-mapping at 3T and to establish accurate reference values for native T1-times and extracellular volume fraction (ECV) of healthy myocardium.MethodsBalanced Steady-State Free-Precession (bSSFP) Saturation-Pulse Prepared Heart-rate independent Inversion-REcovery (SAPPHIRE) and Saturation-recovery Single-SHot Acquisition (SASHA) T1-mapping were compared with the Modified Look-Locker inversion recovery (MOLLI) sequence at 3T. Accuracy and precision were studied in phantom. Native and post-contrast T1-times and regional ECV were determined in 20 healthy subjects (10 men, 27 ± 5 years). Subjective image quality, susceptibility artifact rating, in-vivo precision and reproducibility were analyzed.ResultsSR T1-mapping showed <4 % deviation from the spin-echo reference in phantom in the range of T1 = 100–2300 ms. The average quality and artifact scores of the T1-mapping methods were: MOLLI:3.4/3.6, SAPPHIRE:3.1/3.4, SASHA:2.9/3.2; (1: poor - 4: excellent/1: strong - 4: none). SAPPHIRE and SASHA yielded significantly higher T1-times (SAPPHIRE: 1578 ± 42 ms, SASHA: 1523 ± 46 ms), in-vivo T1-time variation (SAPPHIRE: 60.1 ± 8.7 ms, SASHA: 70.0 ± 9.3 ms) and lower ECV-values (SAPPHIRE: 0.20 ± 0.02, SASHA: 0.21 ± 0.03) compared with MOLLI (T1: 1181 ± 47 ms, ECV: 0.26 ± 0.03, Precision: 53.7 ± 8.1 ms). No significant difference was found in the inter-subject variability of T1-times or ECV-values (T1: p = 0.90, ECV: p = 0.78), the observer agreement (inter: p > 0.19; intra: p > 0.09) or consistency (inter: p > 0.07; intra: p > 0.17) between the three methods.ConclusionsSaturation-recovery T1-mapping at 3T yields higher accuracy, comparable inter-subject, inter- and intra-observer variability and less than 30 % precision-loss compared to MOLLI.

Native Myocardial T1 Mapping, Are We There Yet?

T1 or longitudinal relaxation time is one of the very fundamental magnetic resonance imaging (MRI) time constants and a tissue characterizing parameter. Only during the last decade did it become possible to quantify T1 values of the myocardium through T1 mapping. Evolving from only region of interest analysis and long acquisition times to the pixel-based parametric mapping and short breath-hold sequences, T1 mapping is reaching maturity among cardiac magnetic resonance (CMR) techniques. Both inversion recovery methods such as MOdified Look-Locker Inversion (MOL-LI) and Shortened MOLLI (ShMOLLI) and saturation recovery methods such as Saturation recovery Single-Shot Acquisition (SASHA) are available for T1 quantification with variable degrees of accuracy, precision, and reproducibility. Native (non-contrast) T1 values increase with edema, amyloid deposition, and fibrosis, while they decrease in fat or iron deposition in the myocardium. These features enabled significant expansion of the clinical applications of native T1 mapping where it provides high sensitivity and specificity and even acts as a disease biomarker or a predictor of prognosis. It is of particular usefulness in diffuse myocardial diseases where conventional CMR techniques might be deceiving. A brighter future for the technique is expected if certain challenges are to be faced, examples of which are the need for standardization of normal values, acquisition techniques, and improving analysis tools.

Abstract 10114: Cardiovascular Magnetic Resonance Measurement of Myocardial Extracellular Volume by T1 Mapping Differentiates Athlete's Heart From Hypertrophic Cardiomyopathy

Introduction: Athletes who train regularly can develop left ventricular (LV) hypertrophy, which can be difficult to differentiate from hypertrophic cardiomyopathy (HCM), the leading cause of sudden cardiac death in young athletes. Cardiovascular magnetic resonance (CMR) T1 and extracellular volume (ECV) mapping provide quantitative assessment of myocardial composition. Hypothesis: ECV can differentiate athletic from pathological remodelling. Methods: 35 athletes, 25 HCM patients and 35 volunteers underwent 3.0T CMR protocol including 5b(3s)3b Modified Look-Locker Inversion (MOLLI) T1 maps before and 15 minutes after administration of 0.15mmol/kg intravenous gadobutrol. Native T1 and ECV were measured for each subject and each segment of the American Heart Association model. Results: Native T1 and ECV were both significantly lower in athletes than HCM (1182.8±38.1ms vs 1264.6±50.3ms, P&lt;0.001 and 23.2±2.9% vs 32.3±5.9%, P&lt;0.001 respectively). On receiver operator curve analysis the area under the curve (AUC) to differentiate HCM from athlete for native T1 was 0.91 and ECV 0.95. The AUC to differentiate indeterminate 8-15mm thick segments (Figure) were native T1 0.83, ECV 0.92 and segment thickness 0.80 (P&lt;0.001 for all). The diagnostic accuracy of ECV was superior to native T1 and segment thickness (P=0.001 for both). The optimal cut-off to diagnose HCM in an indeterminate segment was ECV&gt;24.7% (sensitivity 91.7% &amp; specificity 83.2%) and native T1&gt;1226ms (sensitivity 60.0% &amp; specificity 96.7%). Conclusions: ECV measurement by CMR is able to distinguish HCM and athletic remodelling with high diagnostic accuracy and has a potential role in the exclusion of HCM in athletes presenting with left ventricular hypertrophy. Figure: ROC curves for segmental wall thickness (mm), native T1 (ms) and ECV (%) for the detection of HCM against athletes in intermediate wall thickness segments (8-15mm thick). AUCs were 0.80, 0.83, and 0.92 respectively (P&lt;0.001 for all).

Effect of changes to Modified Look-Locker Inversion (MOLLI) sequence on T1 Mapping at 3.0 Tesla in healthy volunteers

Background Diffuse myocardial fibrosis may be quantified with cardiovascular magnetic resonance (CMR) by calculating extra-cellular volume (ECV) from native and post-contrast T1 values. T1 values are affected by field strength and acquisition sequence. The Modified Look Locker Inversion Recovery (MOLLI) method of T1 mapping is a widely used approach, but many different acquisition schemes have been proposed. Flip angle and the effects of the prior inversions have both been suggested as potential targets for change in MOLLI scheme. In a 3,3,5 MOLLI scheme the third acquisition may be influenced by the two previous magnetisation inversions and incomplete recovery. 3,5 may be used as an alternative

Markedly increased volume of distribution of gadolinium in cardiac amyloidosis demonstrated by T1 mapping

To perform myocardial T1 mapping pre- and post-gadolinium (Gd) administration and determine the volume of distribution of Gd (VdGd ) in patients with cardiac amyloidosis to assess extracellular space expansion from amyloid protein deposition. T1 mapping was performed before contrast and 20 minutes following bolus administration of 0.15 mmol/kg of gadopentetate dimeglumine (Magnevist) in five subjects with cardiac amyloidosis and in eight healthy volunteers using previously validated 3-5 Modified Look-Locker Inversion (MOLLI) pulse sequence. The partition coefficient (λ) and VdGd were determined and compared between groups. Before contrast the T1 of the blood and myocardium are longer in amyloidosis as compared to controls (1665 vs. 1509 msec; P = 0.03 and 1144 vs. 963 msec; P < 0.001, respectively). Postcontrast blood T1 was also significantly longer in amyloidosis (486 vs. 408 msec; P = 0.003) with a trend towards shorter T1 in the myocardium (503 vs. 544 msec; P = 0.15). The VdGd was 83% higher in amyloidosis than in controls (0.51 vs. 0.28; P = 0.005). Myocardial VdGd is markedly increased in cardiac amyloidosis, reflecting the increased extracellular space occupied by amyloid proteins. The precontrast T1 of blood and myocardium are increased in amyloidosis extending diagnostic utility in patients who cannot receive Gd.