Dynamic T₂ mapping by multi‐spin‐echo spatiotemporal encoding

Abstract

Purpose:To develop a pulse sequence for acquiring robust, quantitative T 2 relaxation maps in real time. Methods: The pulse scheme relies on fully refocused spatiotemporally encoded multi-spin-echo trains, which provide images that are significantly less distorted than spin-echo echo planar imaging-based counterparts. This enables single-shot T 2 mapping in inhomogeneity-prone regions. Another advantage of these schemes stems from their ability to interleave multiple scans in a reference-free manner, providing an option to increase sensitivity and spatial resolution with minimal motional artifacts. Results: The method was implemented in preclinical and clinical scanners, where single-shot acquisitions delivered reliable T 2 maps in ≤200 ms with ≈250 µm and ≈3 mm resolutions, respectively. Ca. 4 times higher spatial resolutions were achieved for the motion-compensated interleaved versions of these acquisitions, delivering T 2 maps in ca. 10 s per slice. These maps were nearly indistinguishable from multiscan relaxometric maps requiring orders-of-magnitude longer acquisitions; this was confirmed by mice head and real-time mice abdomen 7T scans performed following contrast-agent injections, as well as by 3T human brain and breast scans. Conclusion: This study introduced and demonstrated a new approach for acquiring rapid and quantitative T 2 data, which is particularly reliable when operating at high fields and/or targeting heterogeneous organs or regions. K E Y W O R D Sabdominal imaging, breast MRI, multi-spin-echo sequences, quantitative T2 mapping, spatiotemporal encoding

Identification of variable stages in murine pancreatic tumors by a multiparametric approach employing hyperpolarized 13C MRSI, 1H diffusivity and 1H T1 MRI

“…They used 300 ms‐long presaturation pulses with 5.8 μT, stepped over 15 points in 5 kHz increments; they are shown here as S(−5 kHz)/S(0), as this is representative of the MT curve (whose response was ~20 kHz wide). T 2 maps were collected using a multi‐echo SPEN sequence 43 for the sake of speeding up the acquisition, while preventing motion‐derived and other artifacts. This involved the acquisition of five echoes separated by TE = 26 ms times.…”

“…MT was probed using an in‐house–modified RARE sequence. VNMRJ‐based EPI and homebuilt SPatiotemporal ENcoding (SPEN) sequences were written and assayed for DWI 41,42 ; a multi‐spin‐echo SPEN sequence was also written for fast T 2 mapping, 43 as this allowed us to compensate for inhomogeneities and motion artifacts in the abdominal region. These SPEN‐based sequences are available upon request or from https://www.weizmann.ac.il/chemphys/Frydman_group/software, as are the corresponding image processing macros.…”

Ultrafast water–fat separation using deep learning–based single‐shot MRI

“…Nowadays, SPEN MRI has been successfully applied to many fields, such as functional MRI, 23 real-time imaging, 24 diffusion imaging, 25 CEST MRI, 26 and quantitative imaging. 27 Due to special quadratic phase modulation, the SPEN signal holds additional chemical shift information, which can be exploited for ultrafast water-fat separation, as validated in previous studies. 28,29 To the best of our knowledge, single-shot SPEN MRI can accomplish the fastest waterfat separation because only 1 shot is required.…”

“…As an alternative ultrafast method, spatiotemporally encoded (SPEN) single‐shot MRI 21,22 possesses better immunity to the B 0 field inhomogeneity while retaining spatial and temporal resolutions comparable to EPI. Nowadays, SPEN MRI has been successfully applied to many fields, such as functional MRI, 23 real‐time imaging, 24 diffusion imaging, 25 CEST MRI, 26 and quantitative imaging 27 . Due to special quadratic phase modulation, the SPEN signal holds additional chemical shift information, which can be exploited for ultrafast water–fat separation, as validated in previous studies 28,29 .…”

Diffusion and perfusion MRI of normal, preeclamptic and growth-restricted mice models reveal clear fetoplacental differences

“…The experiment’s principles are as described in Refs. 22 , 29 ; they include a selective slice excitation, variable-orientation diffusion-weighting bipolar gradients placed within a full-refocusing period, an interleaved SPEN encoding module including an adiabatic 180° linearly swept pulse applied in the presence of an encoding gradient G e , an acquisition including an oscillating readout gradient scanning k RO interspersed with blipped G a gradients rasterizing the SPEN dimension, and a final hard 180° pulse to enable multi-slice acquisitions. Also included is a variable K shot pulsed gradient along the SPEN direction, allowing for data interleaving and thereby for enhancing the spatial resolution.…”