Hybrid T 2 ‐ and T 1 ‐weighted radial acquisition for free‐breathing abdominal examination

Self Cite

This study aimed to (i) develop Magnetization-Prepared Golden-angle RAdial Sparse Parallel (MP-GRASP) MRI using a stack-of-stars trajectory for rapid free-breathing T1 mapping and (ii) extend MP-GRASP to multi-echo acquisition (MP-Dixon-GRASP) for fat/water-separated (water-specific) T1 mapping. Methods: An adiabatic non-selective 180° inversion-recovery pulse was added to a gradient-echo-based golden-angle stack-of-stars sequence for magnetizationprepared 3D single-echo or 3D multi-echo acquisition. In combination with subspace-based GRASP-Pro reconstruction, the sequence allows for standard T1 mapping (MP-GRASP) or fat/water-separated T1 mapping (MP-Dixon-GRASP), respectively. The accuracy of T1 mapping using MP-GRASP was evaluated in a phantom and volunteers (brain and liver) against clinically accepted reference methods. The repeatability of T1 estimation was also assessed in the phantom and volunteers. The performance of MP-Dixon-GRASP for water-specific T1 mapping was evaluated in a fat/water phantom and volunteers (brain and liver). Results: ROI-based mean T1 values are correlated between the references and MP-GRASP in the phantom (R 2 = 1.0), brain (R 2 = 0.96), and liver (R 2 = 0.73). MP-GRASP achieved good repeatability of T1 estimation in the phantom (R 2 = 1.0), brain (R 2 = 0.99), and liver (R 2 = 0.82). Water-specific T1 is different from in-phase and out-of-phase composite T1 (composite T1 when fat and water signal are mixed in phase or out of phase) both in the phantom and volunteers. Conclusion: This work demonstrated the initial performance of MP-GRASP and MP-Dixon-GRASP MRI for rapid 3D T1 mapping and 3D fat/water-separated T1 mapping in the brain (without motion) and in the liver (during free breathing). With fat/water-separated T1 estimation, MP-Dixon-GRASP could be potentially useful for imaging patients with fatty-liver diseases.

Section: Introductionmentioning

confidence: 99%

Magnetization‐prepared GRASP MRI for rapid 3D T1 mapping and fat/water‐separated T1 mapping

Feng

Liu

Soultanidis

et al. 2021

Self Cite

“…The proposed stack‐of‐stars trajectory acquires different radial views in the same kz partition along the echo train. An alternative approach would be to sample different kz partitions along the echo train such that the center of k‐space is sampled at a specific echo to allow reconstruction of images at a specific T2w contrast . To reconstruct images at multiple T2w contrasts, we are interested in acquiring the same number of radial views for each TE for each partition, therefore the latter sampling scheme does not offer any advantage in scan time reduction.…”

Section: Discussionmentioning

confidence: 99%

“…This approach uses a random phase encode reordering in the ky‐kz plane along with subspace constraints to reconstruct the different T2 contrasts without image blurring. As an alternative to full Cartesian acquisition, a stack‐of‐stars TSE pulse sequence was proposed for motion robust T2w imaging and demonstrated for brain and abdomen imaging …”

Section: Introductionmentioning

confidence: 99%

An efficient 3D stack‐of‐stars turbo spin echo pulse sequence for simultaneous T2‐weighted imaging and T2 mapping

Keerthivasan

Saranathan

Johnson

et al. 2019

Purpose:To design a pulse sequence for efficient 3D T2-weighted imaging and T2 mapping. Methods: A stack-of-stars turbo spin echo pulse sequence with variable refocusing flip angles and a flexible pseudorandom view ordering is proposed for simultaneous T2-weighted imaging and T2 mapping. An analytical framework is introduced for the selection of refocusing flip angles to maximize relative tissue contrast while minimizing T2 estimation errors and maintaining low specific absorption rate. Images at different echo times are generated using a subspace constrained iterative reconstruction algorithm. T2 maps are obtained by modeling the signal evolution using the extended phase graph model. The technique is evaluated using phantoms and demonstrated in vivo for brain, knee, and carotid imaging. Results: Numerical simulations demonstrate an improved point spread function with the proposed pseudorandom view ordering compared to golden angle view ordering. Phantom experiments show that T2 values estimated from the stack-of-stars turbo spin echo pulse sequence with variable refocusing flip angles have good concordance with spin echo reference values. In vivo results show the proposed pulse sequence can generate qualitatively comparable T2-weighted images as conventional Cartesian 3D SPACE in addition to simultaneously generating 3D T2 maps. Conclusion: The proposed stack-of-stars turbo spin echo pulse sequence with pseudorandom view ordering and variable refocusing flip angles allows high resolution isotropic T2 mapping in clinically acceptable scan times. The optimization framework for the selection of refocusing flip angles improves T2 estimation accuracy while generating T2-weighted contrast comparable to conventional Cartesian imaging. K E Y W O R D S 3D T2 mapping, stack-of-stars, turbo spin echo, variable refocusing flip angles | 327 KEERTHIVASAN ET Al.

“…Given the mixture of physiological motion (eg, respiratory, cardiac, and bulk motion), the uncorrelated components obtained by diagonalizing the data matrix by PCA can be insufficient for identifying independent motion signals. To overcome this, the SOBI procedure was applied after the PCA, as recently proposed elsewhere 17,32 . SOBI 30 is an independent component analysis that uses correlations across time for performing signal separation.…”

Section: Methodsmentioning

confidence: 99%

Free‐breathing radial imaging using a pilot‐tone radiofrequency transmitter for detection of respiratory motion

Solomon

Rigie

Vahle

et al. 2020

Self Cite

To describe an approach for detection of respiratory signals using a transmitted radiofrequency (RF) reference signal called Pilot-Tone (PT) and to use the PT signal for creation of motion-resolved images based on 3D stack-of-stars imaging under free-breathing conditions. Methods: This work explores the use of a reference RF signal generated by a small RF transmitter, placed outside the MR bore. The reference signal is received in parallel to the MR signal during each readout. Because the received PT amplitude is modulated by the subject's breathing pattern, a respiratory signal can be obtained by detecting the strength of the received PT signal over time. The breathing-induced PT signal modulation can then be used for reconstructing motion-resolved images from free-breathing scans. The PT approach was tested in volunteers using a radial stackof-stars 3D gradient echo (GRE) sequence with golden-angle acquisition. Results: Respiratory signals derived from the proposed PT method were compared to signals from a respiratory cushion sensor and k-space-center-based self-navigation under different breathing conditions. Moreover, the accuracy was assessed using a modified acquisition scheme replacing the golden-angle scheme by a zero-angle acquisition. Incorporating the PT signal into eXtra-Dimensional (XD) motion-resolved reconstruction led to improved image quality and clearer anatomical depiction of the lung and liver compared to k-space-center signal and motion-averaged reconstruction, when binned into 6, 8, and 10 motion states. Conclusion: PT is a novel concept for tracking respiratory motion. Its small dimension (8 cm), high sampling rate, and minimal interaction with the imaging scan offers great potential for resolving respiratory motion.