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Purpose: The characterization of tissue microstructure using diffusion MRI (dMRI) signals is rapidly evolving, with increasing sophistication of signal representations and microstructure models. However, this progress often requires signals to be acquired with very high b‐values (e.g., b > 30 ms/μm2), along many directions, and using multiple b‐values, leading to long scan times and extremely low SNR in dMRI images. The purpose of this work is to boost the SNR efficiency of dMRI by combining three particularly efficient spatial encoding techniques and utilizing a high‐performance gradient system (Gmax ≤ 300 mT/m) for efficient diffusion encoding. Methods: Spiral readouts, multiband imaging, and sampling on tilted hexagonal grids (T‐Hex) are combined and implemented on a 3T MRI system with ultra‐strong gradients. Image reconstruction is performed through an iterative cg‐SENSE algorithm incorporating static off‐resonance distributions and field dynamics as measured with an NMR field camera. Additionally, T‐Hex multiband is combined with a more conventional EPI‐readout and compared with state‐of‐the‐art blipped‐CAIPIRINHA sampling. The advantage of the proposed approach is furthermore investigated for clinically available gradient performance and diffusion kurtosis imaging. Results: High fidelity in vivo images with b‐values up to 40 ms/μm2 are obtained. The approach provides superior SNR efficiency over other state‐of‐the‐art multiband diffusion readout schemes. Conclusion: The demonstrated gains hold promise for the widespread dissemination of advanced microstructural scans, especially in clinical populations. [ABSTRACT FROM AUTHOR]

Purpose: Enabling fast and accessible myocardial T1 mapping is crucial for extending its clinical application. We introduce Open‐MOLLI‐SMS combining simultaneous multi‐slice (SMS) with auto‐calibration and variable‐rate selective excitation (VERSE)‐multiband pulses to obtain all slices in a fast single‐shot T1 mapping sequence. Methods: Open‐MOLLI‐SMS was developed by integrating SMS with the open‐source method Open‐MOLLI previously implemented in Pulseq. Three methods were integrated for Open‐MOLLI‐SMS: (1) auto‐calibration blip patterns to ensure consistency between the data and coil information; (2) a blipped‐balanced SSFP (bSSFP) readout to induce controlled aliasing in parallel imaging shifts without disturbing the bSSFP frequency response; and (3) a VERSE‐multiband pulse for minimizing the achievable TR and the specific absortion rate (SAR) impact of SMS. Two (SMS2) or three (SMS3) slices were excited simultaneously and encoded with an in‐plane acceleration factor of 2. Experiments were performed in the International Society for Magnetic Resonance in Medicine/National Institute of Standards and Technology phantom and five healthy volunteers. Results: Phantom results show accurate T1 estimates for reference values between 400 to 2200 ms. Artifacts were visible for Open‐MOLLI‐SMS3 but not replicated in vivo. In vivo Open‐MOLLI‐SMS (T1SMS2 = 993 ± 10 ms; T1SMS3 = 1031 ± 17 ms) provided similar values to mean T1 single‐band Open‐MOLLI estimates (T1Open‐MOLLI = 1005 ± 47 ms). Open‐MOLLI‐SMS2 provided the closest estimates to the reference. Conclusion: This proof‐of‐principle implementation study demonstrates the feasibility of speeding up T1‐mapping acquisitions and increasing coverage by combining auto‐calibration strategies with a blipped‐bSFFP readout and VERSE multiband RF excitation pulses. The proposed methodology was built on the Open‐MOLLI mapping sequence, which provides a fast means for prototyping and enables open‐source sharing of the method. [ABSTRACT FROM AUTHOR]

Purpose: To determine if contemporary 0.55 T MRI supports the use of contrast‐optimal flip angles (FA) for simultaneous multi‐slice (SMS) balanced SSFP (bSSFP) cardiac function assessment, which is impractical at conventional field strengths because of excessive SAR and/or banding artifacts. Methods: Blipped‐CAIPI bSSFP was combined with spiral sampling for ventricular function assessment at 0.55 T. Cine movies with single band and SMS factors of 2 and 3 (SMS 2 and 3), and FA ranging from 60° to 160°, were acquired in seven healthy volunteers. Left ventricular blood and myocardial signal intensity (SI) normalized by background noise and blood–myocardium contrast were measured and compared across acquisition settings. Results: Myocardial SI was slightly higher in single band than in SMS and decreased with an increasing FA. Blood SI increased as the FA increased for single band, and increment was small for FA ≥120°. Blood SI for SMS 2 and 3 increased with an increasing FA up to ∼100°. Blood–myocardium contrast increased with an increasing FA for single band, peaked at FA = 160° (systole: 28.43, diastole: 29.15), attributed mainly to reduced myocardial SI when FA ≥120°. For SMS 2, contrast peaked at 120° (systole: 21.43, diastole: 19.85). For SMS 3, contrast peaked at 120° in systole (16.62) and 100° in diastole (19.04). Conclusions: Contemporary 0.55 T MR scanners equipped with high‐performance gradient systems allow the use of contrast‐optimal FA for SMS accelerated bSSFP cine examinations without compromising image quality. The contrast‐optimal FA was found to be 140° to 160° for single band and 100° to 120° for SMS 2 and 3. [ABSTRACT FROM AUTHOR]

Purpose: To determine the feasibility of simultaneous multi-slice (SMS) real-time MRI (RT-MRI) at 0.55T for the evaluation of cardiac function., Methods: Cardiac CINE MRI is routinely used to evaluate left-ventricular (LV) function. The standard is sequential multi-slice balanced SSFP (bSSFP) over a stack of short-axis slices using electrocardiogram (ECG) gating and breath-holds. SMS has been used in CINE imaging to reduce the number of breath-holds by a factor of 2-4 at 1.5T, 3T, and recently at 0.55T. This work aims to determine if SMS is similarly effective in the RT-MRI evaluation of cardiac function. We used an SMS bSSFP pulse sequence with golden-angle spirals at 0.55T with an SMS factor of three. We cover the LV with three acquisitions for SMS, and nine for single-band (SB). Imaging was performed on 9 healthy volunteers and 1 patient with myocardial fibrosis and sternal wires. A spatio-temporal constrained reconstruction is used, with regularization parameters selected by a board-certified cardiologist. Images were quantitatively analyzed with a normalized contrast and an Edge Sharpness (ES) score., Results: There was a statistically significant 2-fold difference in contrast between SMS and SB and no significant difference in ES score. The contrast for SMS and SB were 13.38/29.05 at mid-diastole and 10.79/22.26 at end-systole; the ES scores for SMS and SB were 1.77/1.83 at mid-diastole and 1.50/1.72 at end-systole., Conclusions: SMS cardiac RT-MRI at 0.55T is feasible and provides sufficient blood-myocardium contrast to evaluate LV function in three slices simultaneously without any gating or periodic motion assumptions., (© 2024 The Author(s). Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.)

Purpose: To implement and evaluate a simultaneous multi‐slice balanced SSFP (SMS‐bSSFP) perfusion sequence and compressed sensing reconstruction for cardiac MR perfusion imaging with full left ventricular (LV) coverage (nine slices/heartbeat) and high spatial resolution (1.4 × 1.4 mm2) at 1.5T. Methods: A preliminary study was performed to evaluate the performance of blipped controlled aliasing in parallel imaging (CAIPI) and RF‐CAIPI with gradient‐controlled local Larmor adjustment (GC‐LOLA) in the presence of fat. A nine‐slice SMS‐bSSFP sequence using RF‐CAIPI with GC‐LOLA with high spatial resolution (1.4 × 1.4 mm2) and a conventional three‐slice sequence with conventional spatial resolution (1.9 × 1.9 mm2) were then acquired in 10 patients under rest conditions. Qualitative assessment was performed to assess image quality and perceived signal‐to‐noise ratio (SNR) on a 4‐point scale (0: poor image quality/low SNR; 3: excellent image quality/high SNR), and the number of myocardial segments with diagnostic image quality was recorded. Quantitative measurements of myocardial sharpness and upslope index were performed. Results: Fat signal leakage was significantly higher for blipped CAIPI than for RF‐CAIPI with GC‐LOLA (7.9% vs. 1.2%, p = 0.010). All 10 SMS‐bSSFP perfusion datasets resulted in 16/16 diagnostic myocardial segments. There were no significant differences between the SMS and conventional acquisitions in terms of image quality (2.6 ± 0.6 vs. 2.7 ± 0.2, p = 0.8) or perceived SNR (2.8 ± 0.3 vs. 2.7 ± 0.3, p = 0.3). Inter‐reader variability was good for both image quality (ICC = 0.84) and perceived SNR (ICC = 0.70). Myocardial sharpness was improved using the SMS sequence compared to the conventional sequence (0.37 ± 0.08 vs 0.32 ± 0.05, p < 0.001). There was no significant difference between measurements of upslope index for the SMS and conventional sequences (0.11 ± 0.04 vs. 0.11 ± 0.03, p = 0.84). Conclusion: SMS‐bSSFP with multiband factor 3 and compressed sensing reconstruction enables cardiac MR perfusion imaging with three‐fold increased spatial coverage and improved myocardial sharpness compared to a conventional sequence, without compromising perceived SNR, image quality, upslope index or number of diagnostic segments. [ABSTRACT FROM AUTHOR]

Purpose: To accelerate the acquisition of relaxation‐diffusion imaging by integrating time‐division multiplexing (TDM) with simultaneous multi‐slice (SMS) for EPI and evaluate imaging quality and diffusion measures. Methods: The time‐division multiplexing (TDM) technique and SMS method were integrated to achieve a high slice‐acceleration (e.g., 6×) factor for acquiring relaxation‐diffusion MRI. Two variants of the sequence, referred to as TDM3e‐SMS and TDM2s‐SMS, were developed to simultaneously acquire slice groups with three distinct TEs and two slice groups with the same TE, respectively. Both sequences were evaluated on a 3T scanner with in vivo human brains and compared with standard single‐band (SB) ‐EPI and SMS‐EPI using diffusion measures and tractography results. Results: Experimental results showed that the TDM3e‐SMS sequence with total slice acceleration of 6 (multiplexing factor (MP) = 3 × multi‐band factor (MB) = 2) provided similar image intensity and microstructure measures compared to standard SMS‐EPI with MB = 2, and yielded less bias in intensity compared to standard SMS‐EPI with MB = 4. The three sequences showed a similar positive correlation between TE and mean kurtosis (MK) and a negative correlation between TE and mean diffusivity (MD) in white matter. Multi‐fiber tractography also shows consistency of results in TE‐dependent measures between different sequences. The TDM2s‐SMS sequence (MP = 2, MB = 2) also provided imaging measures similar to standard SMS‐EPI sequences (MB = 2) for single‐TE diffusion imaging. Conclusions: The TDM‐SMS sequence can provide additional 2× to 3× acceleration to SMS without degrading imaging quality. With the significant reduction in scan time, TDM‐SMS makes joint relaxation‐diffusion MRI a feasible technique in neuroimaging research to investigate new markers of brain disorders. [ABSTRACT FROM AUTHOR]

Purpose: Quantitative MRI (qMRI) is of great importance to clinical medicine and scientific research. However, most qMRI techniques are time‐consuming and sensitive to motion, especially when a large 3D volume is imaged. To accelerate the acquisition, a framework is proposed to realize reliable simultaneous multi‐slice T2 mapping. Methods: The simultaneous multi‐slice T2 mapping framework is based on overlapping‐echo detachment (OLED) planar imaging (dubbed SMS‐OLED). Multi‐slice overlapping‐echo signals were generated by multiple excitation pulses together with echo‐shifting gradients. The signals were excited and acquired with a single‐channel coil. U‐Net was used to reconstruct T2 maps from the acquired overlapping‐echo image. Results: Single‐shot double‐slice and two‐shot triple‐slice SMS‐OLED scan schemes were designed according to the framework for evaluation. Simulations, water phantom, and in vivo rat brain experiments were carried out. Overlapping‐echo signals were acquired, and T2 maps were reconstructed and compared with references. The results demonstrate the superior performance of our method. Conclusion: Two slices of T2 maps can be obtained in a single shot within hundreds of milliseconds. Higher quality multi‐slice T2 maps can be obtained via multiple shots. SMS‐OLED provides a lower specific absorption rate scheme compared with conventional SMS methods with a coil with only a single receiver channel. The new method is of potential in dynamic qMRI and functional qMRI where temporal resolution is vital. [ABSTRACT FROM AUTHOR]

PurposeTo present a time-efficient technique for banding reduction in balanced steady-state free precession (bSSFP) imaging using phase-cycled simultaneous multislice (SMS) acquisition with CAIPIRINHA (controlled aliasing in parallel imaging results in higher acceleration).TheoryThe proposed technique exploits the inherent phase modulation of SMS imaging with CAIPIRINHA to acquire multiple phase-cycled images, which can be combined for efficient banding reduction within the same scan time of a single-band bSSFP scan.MethodsBloch equation simulation, phantom and in vivo brain, abdominal and cardiac imaging experiments were performed on healthy volunteers at 3T using multi-channel head and body array coils with SMS acceleration factors of two to four. The performance of banding reduction was quantitatively evaluated based on the percent ripple of signal distribution and signal-to-noise ratio (SNR) efficiency in both phantom and human studies.ResultsThe banding artifact was successfully removed or suppressed using phase-cycled SMS bSSFP imaging across SMS factors of two to four. The performance of banding reduction improved with higher SMS factors along with increased SNR efficiency.ConclusionPhase-cycled SMS bSSFP with CAIPIRINHA is a promising technique for efficient band reduction in bSSFP without prolonged scan time. Further evaluation of this technique in clinical applications is warranted. Magn Reson Med 76:1764-1774, 2016. © 2015 International Society for Magnetic Resonance in Medicine.

Purpose: To enable all‐systolic first‐pass rest myocardial perfusion with long saturation times. To investigate the change in perfusion contrast and dark rim artefacts through simulations and surrogate measurements. Methods: Simulations were employed to investigate optimal saturation time for myocardium‐perfusion defect contrast and blood‐to‐myocardium signal ratios. Two saturation recovery blocks with long/short saturation times (LTS/STS) were employed to image 3 slices at end‐systole and diastole. Simultaneous multi‐slice balanced steady state free precession imaging and compressed sensing acceleration were combined. The sequence was compared to a 3 slice‐by‐slice clinical protocol in 10 patients. Quantitative assessment of myocardium‐peak pre contrast and blood‐to‐myocardium signal ratios, as well as qualitative assessment of perceived SNR, image quality, blurring, and dark rim artefacts, were performed. Results: Simulations showed that with a bolus of 0.075 mmol/kg, a LTS of 240‐470 ms led to a relative increase in myocardium‐perfusion defect contrast of 34% ± 9%‐28% ± 27% than a STS = 120 ms, while reducing blood‐to‐myocardium signal ratio by 18% ± 10%‐32% ± 14% at peak myocardium. With a bolus of 0.05 mmol/kg, LTS was 320‐570 ms with an increase in myocardium‐perfusion defect contrast of 63% ± 13%‐62% ± 29%. Across patients, LTS led to an average increase in myocardium‐peak pre contrast of 59% (P <.001) at peak myocardium and a lower blood‐to‐myocardium signal ratio of 47% (P <.001) and 15% (P <.001) at peak blood/myocardium. LTS had improved motion robustness (P =.002), image quality (P <.001), and decreased dark rim artefacts (P =.008) than the clinical protocol. Conclusion: All‐systolic rest perfusion can be achieved by combining simultaneous multi‐slice and compressed sensing acceleration, enabling 3‐slice cardiac coverage with reduced motion and dark rim artefacts. Numerical simulations indicate that myocardium‐perfusion defect contrast increases at LTS. [ABSTRACT FROM AUTHOR]

Purpose: To develop and evaluate a high spatial resolution (1.25 × 1.25 mm2) spiral first‐pass myocardial perfusion imaging technique with whole‐heart coverage at 3T, to better assess transmural differences in perfusion between the endocardium and epicardium, to quantify the myocardial ischemic burden, and to improve the detection of obstructive coronary artery disease. Methods: Whole‐heart high‐resolution spiral perfusion pulse sequences and corresponding motion‐compensated reconstruction techniques for both interleaved single‐slice (SS) and simultaneous multi‐slice (SMS) acquisition with or without outer‐volume suppression (OVS) were developed. The proposed techniques were evaluated in 34 healthy volunteers and 8 patients (55 data sets). SS and SMS images were reconstructed using motion‐compensated L1‐SPIRiT and SMS‐Slice‐L1‐SPIRiT, respectively. Images were blindly graded by 2 experienced cardiologists on a 5‐point scale (5, excellent; 1, poor). Results: High‐quality perfusion imaging was achieved for both SS and SMS acquisitions with or without OVS. The SS technique without OVS had the highest scores (4.5 [4, 5]), which were greater than scores for SS with OVS (3.5 [3.25, 3.75], P <.05), MB = 2 without OVS (3.75 [3.25, 4], P <.05), and MB = 2 with OVS (3.75 [2.75, 4], P <.05), but significantly higher than those for MB = 3 without OVS (4 [4, 4], P =.95). SMS image quality was improved using SMS‐Slice‐L1‐SPIRiT as compared to SMS‐L1‐SPIRiT (P <.05 for both reviewers). Conclusion: We demonstrated the successful implementation of whole‐heart spiral perfusion imaging with high resolution at 3T. Good image quality was achieved, and the SS without OVS showed the best image quality. Evaluation in patients with expected ischemic heart disease is warranted. [ABSTRACT FROM AUTHOR]

Purpose: Simultaneous multi‐slice acquisitions are essential for modern neuroimaging research, enabling high temporal resolution functional and high‐resolution q‐space sampling diffusion acquisitions. Recently, deep learning reconstruction techniques have been introduced for unaliasing these accelerated acquisitions, and robust artificial‐neural‐networks for k‐space interpolation (RAKI) have shown promising capabilities. This study systematically examines the impacts of hyperparameter selections for RAKI networks, and introduces a novel technique for training data generation which is analogous to the split‐slice formalism used in slice‐GRAPPA. Methods: RAKI networks were developed with variable hyperparameters and with and without split‐slice training data generation. Each network was trained and applied to five different datasets including acquisitions harmonized with Human Connectome Project lifespan protocol. Unaliasing performance was assessed through L1 errors computed between unaliased and calibration frequency‐space data. Results: Split‐slice training significantly improved network performance in nearly all hyperparameter configurations. Best unaliasing results were achieved with three layer RAKI networks using at least 64 convolutional filters with receptive fields of 7 voxels, 128 single‐voxel filters in the penultimate RAKI layer, batch normalization, and no training dropout with the split‐slice augmented training dataset. Networks trained without the split‐slice technique showed symptoms of network over‐fitting. Conclusions: Split‐slice training for simultaneous multi‐slice RAKI networks positively impacts network performance. Hyperparameter tuning of such reconstruction networks can lead to further improvements in unaliasing performance. [ABSTRACT FROM AUTHOR]

Purpose: To 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. Methods: SMS 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. Results: Phantom 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. Conclusions: The 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. [ABSTRACT FROM AUTHOR]

Purpose: To develop a whole‐heart, free‐breathing, non‐electrocardiograph (ECG)‐gated, cardiac‐phase‐resolved myocardial perfusion MRI framework (CRIMP; Continuous Radial Interleaved simultaneous Multi‐slice acquisitions at sPoiled steady‐state) and test its quantification feasibility. Methods: CRIMP used interleaved radial simultaneous multi‐slice (SMS) slice groups to cover the whole heart in 9 or 12 short‐axis slices. The sequence continuously acquired data without magnetization preparation, ECG gating or breath‐holding, and captured multiple cardiac phases. Images were reconstructed by a motion‐compensated patch‐based locally low‐rank reconstruction. Bloch simulations were performed to study the signal‐to‐noise ratio/contrast‐to‐noise ratio (SNR/CNR) for CRIMP and to study the steady‐state signal under motion. Seven patients were scanned with CRIMP at stress and rest to develop the sequence. One human and two dogs were scanned at rest with a dual‐bolus method to test the quantification feasibility of CRIMP. The dual‐bolus scans were performed using both CRIMP and an ungated radial SMS saturation recovery (SMS‐SR) sequence with injection dose = 0.075 mmol/kg to compare the sequences in terms of SNR, cardiac phase resolution and quantitative myocardial blood flow (MBF). Results: Perfusion images with multiple cardiac phases in all image slices with a temporal resolution of 72 ms/frame were obtained. Simulations and in‐vivo acquisitions showed CRIMP kept the inner slices in steady‐state regardless of motion. CRIMP outperformed SMS‐SR in slice coverage (9 over 6), SNR (mean 20% improvement), and provided cardiac phase resolution. CRIMP and SMS‐SR sequences provided comparable MBF values (rest systolic CRIMP = 0.58 ± 0.07, SMS‐SR = 0.61 ± 0.16). Conclusion: CRIMP allows for whole‐heart, cardiac‐phase‐resolved myocardial perfusion images without ECG‐gating or breath‐holding. The sequence can provide MBF if an accurate arterial input function is obtained separately. [ABSTRACT FROM AUTHOR]

Purpose : To develop a novel, simultaneous multi‐slice (SMS) reconstruction that extends an inter‐slice leakage constraint to intra‐slice aliasing with a virtual slice concept for artifact reduction. Methods : Inter‐slice leakage constraint has been used for SMS reconstruction that mitigates leakage artifacts from the adjacent slices. In this work, the leakage constraint is extended to more general framework that includes SMS and parallel MRI as special cases by viewing intra‐slice aliasing artifacts from undersampling as virtual slices while imposing data fidelity to ensure the measurement consistency. In this way, the reconstruction makes it feasible to directly estimate the individual slices from the undersampled SMS acquisition as a one‐step method. The performance of the extended method is evaluated with data acquired using 2D GRE and EPI sequences. Results : Compared to a two‐step method that performs slice unaliasing followed by inplane unaliasing, the proposed one‐step method reduces aliasing artifacts by employing the extended leakage constraint while lowering the noise amplification by improving the conditioning for the inverse problem. Conclusions : The proposed one‐step method takes advantage of virtual slices as additional encoding power for improved image quality. We successfully demonstrated that the proposed one‐step method minimizes a trade‐off between aliasing artifacts and amplified noises over the two‐step method. [ABSTRACT FROM AUTHOR]

Purpose: To achieve motion‐robust diffusion compartment imaging (DCI) in near continuously moving subjects based on simultaneous multi‐slice, diffusion‐weighted brain MRI. Methods: Simultaneous multi‐slice (SMS) acquisition enables fast and dense sampling of k‐ and q‐space. We propose to achieve motion‐robust DCI via slice‐level motion correction by exploiting the rigid coupling between simultaneously acquired slices. This coupling provides 3D coverage of the anatomy that substantially constraints the slice‐to‐volume alignment problem. This is incorporated into an explicit model of motion dynamics that handles continuous and large subject motion in robust DCI reconstruction. Results: We applied the proposed technique, called Motion Tracking based on Simultanous Multislice Registration (MT‐SMR) to multi b‐value SMS diffusion‐weighted brain MRI of healthy volunteers and motion‐corrupted scans of 20 pediatric subjects. Quantitative and qualitative evaluation based on fractional anisotropy in unidirectional fiber regions, and DCI in crossing‐fiber regions show robust reconstruction in the presence of motion. Conclusion: The proposed approach has the potential to extend routine use of SMS DCI in very challenging populations, such as young children, newborns, and non‐cooperative patients. [ABSTRACT FROM AUTHOR]

Purpose: Investigating the utility of RF parallel transmission (pTx) for Human Connectome Project (HCP)‐style whole‐brain diffusion MRI (dMRI) data at 7 Tesla (7T). Methods: Healthy subjects were scanned in pTx and single‐transmit (1Tx) modes. Multiband (MB), single‐spoke pTx pulses were designed to image sagittal slices. HCP‐style dMRI data (i.e., 1.05‐mm resolutions, MB2, b‐values = 1000/2000 s/mm2, 286 images and 40‐min scan) and data with higher accelerations (MB3 and MB4) were acquired with pTx. Results: pTx significantly improved flip‐angle detected signal uniformity across the brain, yielding ∼19% increase in temporal SNR (tSNR) averaged over the brain relative to 1Tx. This allowed significantly enhanced estimation of multiple fiber orientations (with ∼21% decrease in dispersion) in HCP‐style 7T dMRI datasets. Additionally, pTx pulses achieved substantially lower power deposition, permitting higher accelerations, enabling collection of the same data in 2/3 and 1/2 the scan time or of more data in the same scan time. Conclusion: pTx provides a solution to two major limitations for slice‐accelerated high‐resolution whole‐brain dMRI at 7T; it improves flip‐angle uniformity, and enables higher slice acceleration relative to current state‐of‐the‐art. As such, pTx provides significant advantages for rapid acquisition of high‐quality, high‐resolution truly whole‐brain dMRI data. [ABSTRACT FROM AUTHOR]

Purpose: To develop parallel imaging techniques that simultaneously exploit coil sensitivity encoding, image phase prior information, similarities across multiple images, and complementary k‐space sampling for highly accelerated data acquisition. Methods: We introduce joint virtual coil (JVC)‐generalized autocalibrating partially parallel acquisitions (GRAPPA) to jointly reconstruct data acquired with different contrast preparations, and show its application in 2D, 3D, and simultaneous multi‐slice (SMS) acquisitions. We extend the joint parallel imaging concept to exploit limited support and smooth phase constraints through Joint (J‐) LORAKS formulation. J‐LORAKS allows joint parallel imaging from limited autocalibration signal region, as well as permitting partial Fourier sampling and calibrationless reconstruction. Results: We demonstrate highly accelerated 2D balanced steady‐state free precession with phase cycling, SMS multi‐echo spin echo, 3D multi‐echo magnetization‐prepared rapid gradient echo, and multi‐echo gradient recalled echo acquisitions in vivo. Compared to conventional GRAPPA, proposed joint acquisition/reconstruction techniques provide more than 2‐fold reduction in reconstruction error. Conclusion: JVC‐GRAPPA takes advantage of additional spatial encoding from phase information and image similarity, and employs different sampling patterns across acquisitions. J‐LORAKS achieves a more parsimonious low‐rank representation of local k‐space by considering multiple images as additional coils. Both approaches provide dramatic improvement in artifact and noise mitigation over conventional single‐contrast parallel imaging reconstruction. Magn Reson Med 80:619–632, 2018. © 2018 International Society for Magnetic Resonance in Medicine. [ABSTRACT FROM AUTHOR]

Purpose: Simultaneous multi‐slice (SMS) imaging is an advantageous method for accelerating MRI scans, allowing reduced scan time, increased slice coverage, or high temporal resolution with limited image quality penalties. In this work we combine the advantages of SMS acceleration with the motion correction and artifact reduction capabilities of the PROPELLER technique. Methods: A PROPELLER sequence was developed with support for CAIPIRINHA and phase optimized multiband radio frequency pulses. To minimize the time spent on acquiring calibration data, both in‐plane‐generalized autocalibrating partial parallel acquisition (GRAPPA) and slice‐GRAPPA weights for all PROPELLER blade angles were calibrated on a single fully sampled PROPELLER blade volume. Therefore, the proposed acquisition included a single fully sampled blade volume, with the remaining blades accelerated in both the phase and slice encoding directions without additional auto calibrating signal lines. Comparison to 3D RARE was performed as well as demonstration of 3D motion correction performance on the SMS PROPELLER data. Results: We show that PROPELLER acquisitions can be efficiently accelerated with SMS using a short embedded calibration. The potential in combining these two techniques was demonstrated with a high quality 1.0 × 1.0 × 1.0 mm3 resolution T2‐weighted volume, free from banding artifacts, and capable of 3D retrospective motion correction, with higher effective resolution compared to 3D RARE. Conclusion: With the combination of SMS acceleration and PROPELLER imaging, thin‐sliced reformattable T2‐weighted image volumes with 3D retrospective motion correction capabilities can be rapidly acquired with low sensitivity to flow and head motion. Magn Reson Med 80:496–506, 2018. © 2017 International Society for Magnetic Resonance in Medicine. [ABSTRACT FROM AUTHOR]

Purpose: The development of a calibrationless parallel imaging method for accelerated simultaneous multi-slice (SMS) MRI based on Regularized Nonlinear Inversion (NLINV), evaluated using Cartesian and radial fast low-angle shot (FLASH). Theory and Methods: NLINV is a parallel imaging method that jointly estimates image content and coil sensitivities using a Newton-type method with regularization. Here, NLINV is extended to SMS-NLINV for reconstruction and separation of all simultaneously acquired slices. The performance of the extended method is evaluated for different sampling schemes using phantom and in vivo experiments based on Cartesian and radial SMS-FLASH sequences. Results: The basic algorithm was validated in Cartesian experiments by comparison with ESPIRiT. For Cartesian and radial sampling, improved results are demonstrated compared to single-slice experiments, and it is further shown that sampling schemes using complementary samples outperform schemes with the same samples in each partition. Conclusion: The extension of the NLINV algorithm for SMS data was implemented and successfully demonstrated in combination with a Cartesian and radial SMS-FLASH sequence. [ABSTRACT FROM AUTHOR]

Purpose To overcome limitations of previous ultra-high-field arterial spin labeling (ASL) techniques concerning temporal resolution and brain coverage by utilizing the simultaneous multi-slice (SMS) approach. Methods An optimized, flow-alternating inversion recovery quantitative imaging of perfusion using a single subtraction II scheme was developed that tackles the challenges of 7 tesla (T) ASL. The implementation of tailored labeling radiofrequency pulses reduced the effect of transmit field ( [ABSTRACT FROM AUTHOR]

Purpose: Enabling fast and accessible myocardial T 1 mapping is crucial for extending its clinical application. We introduce Open-MOLLI-SMS combining simultaneous multi-slice (SMS) with auto-calibration and variable-rate selective excitation (VERSE)-multiband pulses to obtain all slices in a fast single-shot T 1 mapping sequence., Methods: Open-MOLLI-SMS was developed by integrating SMS with the open-source method Open-MOLLI previously implemented in Pulseq. Three methods were integrated for Open-MOLLI-SMS: (1) auto-calibration blip patterns to ensure consistency between the data and coil information; (2) a blipped-balanced SSFP (bSSFP) readout to induce controlled aliasing in parallel imaging shifts without disturbing the bSSFP frequency response; and (3) a VERSE-multiband pulse for minimizing the achievable TR and the specific absortion rate (SAR) impact of SMS. Two (SMS2) or three (SMS3) slices were excited simultaneously and encoded with an in-plane acceleration factor of 2. Experiments were performed in the International Society for Magnetic Resonance in Medicine/National Institute of Standards and Technology phantom and five healthy volunteers., Results: Phantom results show accurate T 1 estimates for reference values between 400 to 2200 ms. Artifacts were visible for Open-MOLLI-SMS3 but not replicated in vivo. In vivo Open-MOLLI-SMS (T 1 SMS2  = 993 ± 10 ms; T 1 SMS3  = 1031 ± 17 ms) provided similar values to mean T 1 single-band Open-MOLLI estimates (T 1 Open-MOLLI  = 1005 ± 47 ms). Open-MOLLI-SMS2 provided the closest estimates to the reference., Conclusion: This proof-of-principle implementation study demonstrates the feasibility of speeding up T 1 -mapping acquisitions and increasing coverage by combining auto-calibration strategies with a blipped-bSFFP readout and VERSE multiband RF excitation pulses. The proposed methodology was built on the Open-MOLLI mapping sequence, which provides a fast means for prototyping and enables open-source sharing of the method., (© 2023 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.)

Purpose Simultaneous multislice (SMS) imaging is a powerful technique that can reduce image acquisition time for anatomical, functional, and diffusion weighted magnetic resonance imaging. At higher magnetic fields, such as 7 Tesla, increased radiofrequency (RF) field inhomogeneity, power deposition, and changes in relaxation parameters make SMS spin echo imaging challenging. We designed an adiabatic 180° Power Independent of Number of Slices (PINS) pulse and a matched-phase 90° PINS pulse to generate a SEmi-Adiabatic Matched-phase Spin echo (SEAMS) PINS sequence to address these issues. Methods We used the adiabatic Shinnar Le-Roux (SLR) algorithm to generate a 180° pulse. The SLR polynomials for the 180° pulse were then used to create a matched-phase 90° pulse. The pulses were sub-sampled to produce a SEAMS PINS pulse-pair and the performance of this pulse-pair was validated in phantoms and in vivo. Results Simulations as well as phantom and in vivo results, demonstrate multislice capability and improved B1-insensitivity of the SEAMS PINS pulse-pair when operating at RF amplitudes of up to 40% above adiabatic threshold. Conclusion The SEAMS PINS approach presented here achieves multislice spin echo profiles with improved B1-insensitivity when compared with a conventional spin echo. Magn Reson Med 75:709-717, 2016. © 2015 Wiley Periodicals, Inc. [ABSTRACT FROM AUTHOR]

Purpose: Quantitative MRI (qMRI) is of great importance to clinical medicine and scientific research. However, most qMRI techniques are time-consuming and sensitive to motion, especially when a large 3D volume is imaged. To accelerate the acquisition, a framework is proposed to realize reliable simultaneous multi-slice T 2 mapping., Methods: The simultaneous multi-slice T 2 mapping framework is based on overlapping-echo detachment (OLED) planar imaging (dubbed SMS-OLED). Multi-slice overlapping-echo signals were generated by multiple excitation pulses together with echo-shifting gradients. The signals were excited and acquired with a single-channel coil. U-Net was used to reconstruct T 2 maps from the acquired overlapping-echo image., Results: Single-shot double-slice and two-shot triple-slice SMS-OLED scan schemes were designed according to the framework for evaluation. Simulations, water phantom, and in vivo rat brain experiments were carried out. Overlapping-echo signals were acquired, and T 2 maps were reconstructed and compared with references. The results demonstrate the superior performance of our method., Conclusion: Two slices of T 2 maps can be obtained in a single shot within hundreds of milliseconds. Higher quality multi-slice T 2 maps can be obtained via multiple shots. SMS-OLED provides a lower specific absorption rate scheme compared with conventional SMS methods with a coil with only a single receiver channel. The new method is of potential in dynamic qMRI and functional qMRI where temporal resolution is vital., (© 2022 International Society for Magnetic Resonance in Medicine.)

Purpose: To develop a single-shot multi-slice T 1 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., Methods: SMS 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 T 1 precision. Validations of the proposed method are performed for a phantom and for the human brain and liver in 6 healthy adult subjects., Results: Phantom results confirm good T 1 accuracy and precision of the simultaneously acquired multi-slice T 1 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 T 1 maps for 5 slices of a human brain ( 0.75 × 0.75 × 5 mm 3 ) or 3 slices of the abdomen ( 1.25 × 1.25 × 6 mm 3 ) within 4 seconds., Conclusions: The IR SMS radial FLASH acquisition together with a nonlinear model-based reconstruction enable rapid high-resolution multi-slice T 1 mapping with good accuracy, precision, and repeatability., (© 2020 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.)

Purpose: Simultaneous multislice (SMS) imaging is a powerful technique that can reduce image acquisition time for anatomical, functional, and diffusion weighted magnetic resonance imaging. At higher magnetic fields, such as 7 Tesla, increased radiofrequency (RF) field inhomogeneity, power deposition, and changes in relaxation parameters make SMS spin echo imaging challenging. We designed an adiabatic 180° Power Independent of Number of Slices (PINS) pulse and a matched-phase 90° PINS pulse to generate a SEmi-Adiabatic Matched-phase Spin echo (SEAMS) PINS sequence to address these issues., Methods: We used the adiabatic Shinnar Le-Roux (SLR) algorithm to generate a 180° pulse. The SLR polynomials for the 180° pulse were then used to create a matched-phase 90° pulse. The pulses were sub-sampled to produce a SEAMS PINS pulse-pair and the performance of this pulse-pair was validated in phantoms and in vivo., Results: Simulations as well as phantom and in vivo results, demonstrate multislice capability and improved B1 -insensitivity of the SEAMS PINS pulse-pair when operating at RF amplitudes of up to 40% above adiabatic threshold., Conclusion: The SEAMS PINS approach presented here achieves multislice spin echo profiles with improved B1 -insensitivity when compared with a conventional spin echo., (© 2015 Wiley Periodicals, Inc.)