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Quantitative T1 mapping using multi-slice multi-shot inversion recovery EPI.

ABSTRACT: An efficient multi-slice inversion-recovery EPI (MS-IR-EPI) sequence for fast, high spatial resolution, quantitative T₁ mapping is presented, using a segmented simultaneous multi-slice acquisition, combined with slice order shifting across multiple acquisitions. The segmented acquisition minimises the effective TE and readout duration compared to a single-shot EPI scheme, reducing geometric distortions to provide high quality T₁ maps with a narrow point-spread function. The precision and repeatability of MS-IR-EPI T₁ measurements are assessed using both T₁-calibrated and T₂-calibrated ISMRM/NIST phantom spheres at 3 and 7 T and compared with single slice IR and MP2RAGE methods. Magnetization transfer (MT) effects of the spectrally-selective fat-suppression (FS) pulses required for in vivo imaging are shown to shorten the measured in-vivo T₁ values. We model the effect of these fat suppression pulses on T₁ measurements and show that the model can remove their MT contribution from the measured T₁, thus providing accurate T₁ quantification. High spatial resolution T₁ maps of the human brain generated with MS-IR-EPI at 7 T are compared with those generated with the widely implemented MP2RAGE sequence. Our MS-IR-EPI sequence provides high SNR per unit time and sharper T₁ maps than MP2RAGE, demonstrating the potential for ultra-high resolution T₁ mapping and the improved discrimination of functionally relevant cortical areas in the human brain.

SUBMITTER: Sanchez Panchuelo RM

PROVIDER: S-EPMC8204273 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Model-based reconstruction for simultaneous multi-slice T1 mapping using single-shot inversion-recovery radial FLASH.

Project description:PurposeTo develop a single-shot multi-slice T1 mapping method by combing simultaneous multi-slice (SMS) excitations, single-shot inversion-recovery (IR) radial fast low-angle shot (FLASH), and a nonlinear model-based reconstruction method.MethodsSMS excitations are combined with a single-shot IR radial FLASH sequence for data acquisition. A previously developed single-slice calibrationless model-based reconstruction is extended to SMS, formulating the estimation of parameter maps and coil sensitivities from all slices as a single nonlinear inverse problem. Joint-sparsity constraints are further applied to the parameter maps to improve T1 precision. Validations of the proposed method are performed for a phantom and for the human brain and liver in 6 healthy adult subjects.ResultsPhantom results confirm good T1 accuracy and precision of the simultaneously acquired multi-slice T1 maps in comparison to single-slice references. In vivo human brain studies demonstrate the better performance of SMS acquisitions compared to the conventional spoke-interleaved multi-slice acquisition using model-based reconstruction. Aside from good accuracy and precision, the results of 6 healthy subjects in both brain and abdominal studies confirm good repeatability between scan and re-scans. The proposed method can simultaneously acquire T1 maps for 5 slices of a human brain ( 0.75×0.75×5mm3 ) or 3 slices of the abdomen ( 1.25×1.25×6mm3 ) within 4 seconds.ConclusionsThe IR SMS radial FLASH acquisition together with a nonlinear model-based reconstruction enable rapid high-resolution multi-slice T1 mapping with good accuracy, precision, and repeatability.

| S-EPMC10409492 | biostudies-literature

Optimized inversion-time schedules for quantitative T1 measurements based on high-resolution multi-inversion EPI.

Project description:PURPOSE:Demonstrate an optimized multi-inversion echo-planar imaging technique to accelerate quantitative T1 mapping by judicious selection of inversion times for each slice. METHODS:Slice ordering is optimized to maximize discrimination between tissues with different T1 values. The optimized slice orderings are tested in the International Society for Magnetic Resonance in Medicine/National Institute of Standards and Technology phantom and compared with an unoptimized 21-measurement acquisition. The utility of the method is demonstrated in a healthy subject in vivo at 3?T and validated with a gold-standard inversion-recovery sequence. The in vivo precision of our technique was tested by repeated scans of the same subject within a scan session and across scan sessions, occurring 28 days apart. RESULTS:Phantom measurements yielded good agreement (R2 ?=?0.99) between the T1 estimates from the proposed optimized protocol, reference values from the National Institute of Standards and Technology phantom and gold-standard inversion-recovery values, as well as a negligible estimation bias that was slightly lower than that from the unoptimized 21-measurement protocol (0.74 versus 19 ms). The range of values for the scan-rescan coefficient of variation was 0.86 to 0.93 (within session) and 0.83 to 0.92 (across sessions) across all scan durations tested. CONCLUSIONS:Optimized slice orderings allow faster quantitative T1 mapping. The optimized sequence yielded accurate and precise T1 maps. Magn Reson Med 79:2101-2112, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

| S-EPMC5811323 | biostudies-literature

Model-based myocardial T1 mapping with sparsity constraints using single-shot inversion-recovery radial FLASH cardiovascular magnetic resonance.

Project description:BackgroundThis study develops a model-based myocardial T1 mapping technique with sparsity constraints which employs a single-shot inversion-recovery (IR) radial fast low angle shot (FLASH) cardiovascular magnetic resonance (CMR) acquisition. The method should offer high resolution, accuracy, precision and reproducibility.MethodsThe proposed reconstruction estimates myocardial parameter maps directly from undersampled k-space which is continuously measured by IR radial FLASH with a 4?s breathhold and retrospectively sorted based on a cardiac trigger signal. Joint sparsity constraints are imposed on the parameter maps to further improve T1 precision. Validations involved studies of an experimental phantom and 8 healthy adult subjects.ResultsIn comparison to an IR spin-echo reference method, phantom experiments with T1 values ranging from 300 to 1500?ms revealed good accuracy and precision at simulated heart rates between 40 and 100?bpm. In vivo T1 maps achieved better precision and qualitatively better preservation of image features for the proposed method than a real-time CMR approach followed by pixelwise fitting. Apart from good inter-observer reproducibility (0.6% of the mean), in vivo results confirmed good intra-subject reproducibility (1.05% of the mean for intra-scan and 1.17, 1.51% of the means for the two inter-scans, respectively) of the proposed method.ConclusionModel-based reconstructions with sparsity constraints allow for single-shot myocardial T1 maps with high spatial resolution, accuracy, precision and reproducibility within a 4?s breathhold. Clinical trials are warranted.

| S-EPMC6751613 | biostudies-literature

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

Project description:ObjectTo develop and evaluate a 2D modified Look-Locker (MOLLI) for high-resolution T1 mapping in mice using a 3T MRI scanner.Materials and methodsTo 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.ResultsIn 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.ConclusionsA 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.

| S-EPMC5679534 | biostudies-literature

3D myocardial T1 mapping using saturation recovery.

Project description:To propose a 3D quantitative high-resolution T1 mapping technique, called 3D SASHA (saturation-recovery single-shot acquisition), which combines a saturation recovery pulse with 1D-navigator-based-respiratory motion compensation to acquire the whole volume of the heart in free breathing. The sequence was tested and validated both in a T1 phantom and in healthy subjects.The 3D SASHA method was implemented on a 1.5T scanner. A diaphragmatic navigator was used to allow free-breathing acquisition and the images were acquired with a resolution of 1.4 × 1.4 × 8?mm3 . For assessment of accuracy and precision the sequence was compared with the reference gold-standard inversion-recovery spin echo (IRSE) pulse sequence in a T1 phantom, while for the in vivo studies (10 healthy volunteers) 3D SASHA was compared with the clinically used 2D MOLLI (3-3-5) and 2D SASHA protocols.There was good agreement between the T1 values measured in a T1 phantom with 3D SASHA and the reference IRSE pulse sequences (1111.6?±?31 msec vs. 1123.6?±?8 msec, P?=?0.9947). Mean and standard deviation of the myocardial T1 values in healthy subjects measured with 2D MOLLI, 2D SASHA, and 3D SASHA sequences were 881?±?40 msec, 1181.3?±?32 msec, and 1153.6?±?28 msec respectively.The proposed 3D SASHA sequence allows for high-resolution free-breathing whole-heart T1 -mapping with T1 values in good agreement with the 2D SASHA and improved precision.2 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:218-227.

| S-EPMC5518207 | biostudies-other

Accurate, precise, simultaneous myocardial T1 and T2 mapping using a radial sequence with inversion recovery and T2 preparation.

Project description:We propose a simultaneous myocardial T1 and T2 mapping technique using a radial sequence with inversion recovery and T2 preparation, which achieves high accuracy and precision, with T1 and T2 reproducibility similar to the Modified Look-Locker Inversion recovery (MOLLI) sequence and the conventional bright blood T2 mapping technique, respectively. The sequence was developed by incorporating gold angle radial fast low angle shot (FLASH) readout combined with an inversion pulse and T2prep pulses. The extended Bloch equation simulation with slice profile correction (BLESSPC) algorithm was proposed to reconstruct T1 and T2 maps at the same time in a few seconds, while maintaining good T1 and T2 estimation accuracy. Accuracy and precision were compared among the proposed technique, MOLLI and conventional T2 mapping techniques using phantom studies, 10 healthy volunteers and three patients. In phantom studies, the proposed technique was more accurate than MOLLI (P < 0.05) while achieving similar precision (P = 0.3) in T1 estimation, and was more accurate (P < 0.05) and precise (P < 0.001) than conventional T2 mapping (two-parameter fitting) in T2 estimation. In vivo, the proposed technique achieved significantly higher T1 values (P < 0.001) and similar reproducibility (P = 0.3) compared with MOLLI, with significantly lower T2 values (P < 0.001) and similar reproducibility (P = 0.6) compared with the conventional T2 mapping technique. Thus, the proposed radial T1-T2 mapping technique allows for accurate, precise, simultaneous myocardial T1 and T2 mapping in an 11-heartbeat single breath-hold acquisition.

| S-EPMC6817390 | biostudies-literature

Dual-polarity slice-GRAPPA for concurrent ghost correction and slice separation in simultaneous multi-slice EPI.

Project description:PURPOSE:A ghost correction strategy for Simultaneous Multi-Slice (SMS) EPI methods that provides improved ghosting artifact reduction compared to conventional methods is presented. Conventional Nyquist ghost correction methods for SMS-EPI rely on navigator data that contain phase errors from all slices in the simultaneously acquired slice-group. These navigator data may contain spatially nonlinear phase differences near regions of B0 inhomogeneity, which violates the linear model employed by most EPI ghost correction algorithms, resulting in poor reconstructions. METHODS:Dual-Polarity GRAPPA (DPG) was previously shown to accurately model and correct both spatially nonlinear and 2D phase errors in conventional single-slice EPI data. Here, an extension we call Dual-Polarity slice-GRAPPA (DPsG) is adapted to the slice-GRAPPA method and applied to SMS-EPI data for slice separation and ghost correction concurrently-eliminating the need for a separate ghost correction step while also providing improved slice-specific EPI phase error correction. RESULTS:Images from in vivo SMS-EPI data reconstructed using DPsG in place of conventional Nyquist ghost correction and slice-GRAPPA are presented. DPsG is shown to reduce ghosting artifacts and provide improved temporal SNR compared to the conventional reconstruction. CONCLUSION:The proposed use of DPsG for SMS-EPI reconstruction can provide images with lower artifact levels, higher image fidelity, and improved time-series stability compared to conventional reconstruction methods.

| S-EPMC6085171 | biostudies-literature

Accuracy, precision, and reproducibility of myocardial T1 mapping: A comparison of four T1 estimation algorithms for modified look-locker inversion recovery (MOLLI).

Project description:PurposeTo compare the accuracy and precision of four different T1 estimation algorithms for modified Look-Locker inversion recovery (MOLLI).MethodsFour T1 estimation algorithms, including the original fit, inversion group (IG) fit, instantaneous signal loss simulation (InSiL), and Bloch equation simulation with slice profile correction (BLESSPC) were studied. T1 estimation accuracy, precision, reproducibility, and sensitivity to heart rate (HR), flip angle (FA), and acquisition scheme (AcS) variations were compared in simulation, phantom, and volunteer studies.ResultsT1 estimation accuracy of IG (-2.4% ± 3.9%) and original fit (-3.2% ± 1.4%) were worse than BLESSPC (0.2% ± 1.5%) and InSiL (-0.7% ± 2.1%). The original fit had the best precision for T1 from 409-1884 ms for the same FA (0.67% ± 0.16% versus 0.90% ± 0.23% using IG, 0.78% ± 0.11% using InSiL, 0.77% ± 0.12% using BLESSPC). BLESSPC generated the most consistent in vivo T1 values over different FAs and AcS, and the T1 estimation reproducibility was similar (P > 0.3) among the four methods when FA = 35°. When using FA = 50°, the reproducibility was significantly improved only when using BLESSPC (1.6% ± 0.9 versus 2.6% ± 1.9%, P < 0.05).ConclusionBLESSPC has superior accuracy and is the least sensitive to FA, HR, and AcS variations. T1 estimation using BLESSPC and FA = 50° is superior to conventional MOLLI with FA = 35° in accuracy and precision. Further clinical studies in varying pathological conditions are warranted to confirm our findings. Magn Reson Med 78:1746-1756, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

| S-EPMC5457913 | biostudies-literature

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

Project description: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.

| S-EPMC5599252 | biostudies-literature

Simultaneous T1 and T2 mapping of the carotid plaque (SIMPLE) with T2 and inversion recovery prepared 3D radial imaging.

Project description:PURPOSE:To propose a technique that can produce different T1 and T2 contrasts in a single scan for simultaneous T1 and T2 mapping of the carotid plaque (SIMPLE). METHODS:An interleaved 3D golden angle radial trajectory was used in conjunction with T2 preparation with variable duration (TEprep ) and inversion recovery pulses. Sliding window reconstruction was adopted to reconstruct images at different inversion delay time and TEprep for joint T1 and T2 fitting. In the fitting procedure, a rapid B1 correction method was presented. The accuracy of SIMPLE was investigated in phantom experiments. In vivo scans were performed on 5 healthy volunteers with 2 scans each, and on 5 patients with carotid atherosclerosis. RESULTS:The phantom T1 and T2 estimations of SIMPLE agreed well with the standard methods with the percentage difference smaller than 7.1%. In vivo T1 and T2 for normal carotid vessel wall were 1213?±?48.3 ms and 51.1?±?1.7 ms, with good interscan repeatability. Alternations of T1 and T2 in plaque regions were in agreement with the conventional multicontrast imaging findings. CONCLUSION:The proposed SIMPLE allows simultaneous T1 and T2 mapping of the carotid artery in less than 10 minutes, serving as a quantitative tool with good accuracy and reproducibility for plaque characterization.

| S-EPMC6252279 | biostudies-literature

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