MR Fingerprinting with b‐Tensor Encoding for Simultaneous Quantification of Relaxation and Diffusion in a Single Scan

Abstract

Although both relaxation and diffusion imaging are sensitive to tissue microstructure, studies have reported limited sensitivity and robustness of using relaxation or conventional diffusion alone to characterize tissue microstructure. Recently, it has been shown that tensor-valued diffusion encoding and joint relaxation-diffusion quantification enable more reliable quantification of compartment-specific microstructural properties. However, scan times to acquire such data can be prohibitive. Here, we aim to simultaneously quantify relaxation and diffusion using MR fingerprinting (MRF) and b-tensor encoding in a clinically feasible time. Methods:We developed multidimensional MRF scans (mdMRF) with linear and spherical b-tensor encoding (LTE and STE) to simultaneously quantify T1, T2, and ADC maps from a single scan. The image quality, accuracy, and scan efficiency were compared between the mdMRF using LTE and STE. Moreover, we investigated the robustness of different sequence designs to signal errors and their impact on the maps.Results: T1 and T2 maps derived from the mdMRF scans have consistently high image quality, while ADC maps are sensitive to different sequence designs. Notably, the fast imaging steady state precession (FISP)-based mdMRF scan with peripheral pulse gating provides the best ADC maps that are free of image distortion and shading artifacts. Conclusion:We demonstrated the feasibility of quantifying T1, T2, and ADC maps simultaneously from a single mdMRF scan in around 24 s/slice.The map quality and quantitative values are consistent with the reference scans.

DTI‐MR fingerprinting for rapid high‐resolution whole‐brain T1, T2, proton density, ADC, and fractional anisotropy mapping

“…Diffusion preparation is a critical step in obtaining accurate and reliable diffusion imaging, however, this step can also introduce shot‐to‐shot phase variation caused by microscopic motions, 57,58 such as cardiac‐cycle motion, which results in unwanted intensity variation in the images. To mitigate this issue, an amplitude stabilizer gradient 19 (dephaser) can be applied before the tip‐up 90° RF pulse to dephase the spins while a rephasing gradient must be applied before each readout in the subsequent readout‐train to rephase the diffusion‐encoded spins as per previous work in diffusion‐MRF 16 . However, this approach comes at a cost of halving the signal 20,59 and the rephasing gradient will also dephase any signal from the recovering Mz during its long readout train, making this approach quite inefficient in encoding diffusion information into the MRF acquisition where lengthy continuous readouts are acquired.…”

“…However, obtaining these contrast images using traditional methods can take a considerable amount of acquisition time, often around half an hour or longer for high isotropic resolution cases, making it impractical for many patients because of the high scan cost and discomfort. Our proposed method, on the other hand, can achieve these high‐resolution contrast images within a much shorter acquisition time (a comparison across similar methods that aim for quantifying T 1 , T 2 , and diffusivity could be found in Table S3), 16,65,66 improving patient comfort and accessibility. Moreover, the simultaneous acquisition of multiple quantitative maps provides a more comprehensive assessment of tissues, advancing from traditional non‐quantitative contrast images to quantitative maps, which has the potential to improve clinical diagnosis and scientific research.…”

“…One of the challenges in diffusion imaging is the sensitivity of accuracy to shot‐to‐shot phase variation induced by physiological motion 25–28 and system imperfections, 29–31 such as eddy currents and imperfect gradient systems. A recent attempt to tackle this issue has provided the ability to acquire T 1 , T 2 , together with the gross anisotropic diffusion measure, at a cost of lengthy scan time 16 . To overcome this challenge, the proposed method incorporates a number of new data acquisition technologies and designs to minimize phase variation, ensuring high accuracy and reliability for the diffusion imaging in this work.…”

Multiparametric MRI

“…Although implementation dependent, it is now possible to obtain 3D whole-brain relaxation maps using indirect or direct methods in less than 6 minutes. In addition to T1 and T2 relaxation times and proton density, some methods also enable simultaneous measurements of diffusion, 23,24 susceptibility, 25 perfusion, 26 magnetization transfer, 27,28 and myelin. 29,30 Advanced reconstruction methods can be applied to multiparametric methods to improve the image quality or reduce the scan time.…”

Magnetic Resonance Fingerprinting

“…28,29 Brain MRF has also been modified for measurement of quantitative properties beyond T1 and T2. Examples include MRF techniques for measurement of combined T1, T2, and T2* mapping [30][31][32][33] ; MRF with b-tensor encoding for combined T1, T2, and apparent diffusion coefficient (ADC) mapping 34 ; and CEST-MRF for brain tumors, 35 vascular MR fingerprinting, 36 and MRF-arterial spin labeling (ASL) for cerebral perfusion. 37 The test-retest repeatability as well as interscanner repeatability across multiple sites have been established for both 2D MRF and 3D MRF sequences.…”