Adiabatically prepared spin‐lock approach for T1ρ‐based dynamic glucose enhanced MRI at ultrahigh fields

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Purpose Dynamic glucose‐enhanced (DGE)‐MRI based on chemical exchange‐sensitive MRI, that is, glucoCEST and gluco‐chemical exchange‐sensitive spin‐lock (glucoCESL), is intrinsically prone to motion‐induced artifacts because the final DGE contrast relies on the difference of images, which were acquired with a time gap of several mins. In this study, identification of different types of motion‐induced artifacts led to the development of a 3D acquisition protocol for DGE examinations in the human brain at 7 T with improved robustness in the presence of subject motion. Methods DGE‐MRI was realized by the chemical exchange‐sensitive spin‐lock approach based either on relaxation rate in the rotating frame (R1ρ)‐weighted or quantitative R1ρ imaging. A 3D image readout was implemented at 7 T, enabling retrospective volumetric coregistration of the image series and quantification of subject motion. An examination of a healthy volunteer without administration of glucose allowed for the identification of isolated motion‐induced artifacts. Results Even after coregistration, significant motion‐induced artifacts remained in the DGE contrast based on R1ρ‐weighted images. This is due to the spatially varying sensitivity of the coil and was found to be compensated by a quantitative R1ρ approach. The coregistered quantitative approach allowed the observation of a clear increase of the DGE contrast in a patient with glioblastoma, which did not correlate with subject motion. Conclusion The presented 3D acquisition protocol enables DGE‐MRI examinations in the human brain with improved robustness against motion‐induced artifacts. Correction of motion‐induced artifacts is of high importance for DGE‐MRI in clinical studies where an unambiguous assignment of contrast changes due to an actual change in local glucose concentration is a prerequisite.

“…In this study, two CESL‐based DGE contrast metrics were investigated. First, the R 1ρ ‐weighted dynamic glucose‐enhanced (DGE ρ ) contrast calculated according to Schuenke et al:

{DGE}_{normalρ} false(normalt false) = \frac{{normalS}_{50ms} false(ref false) {- S}_{50ms} (t)}{{normalS}_{50ms} false(ref false) \cdot 50ms},

Section: Methodsmentioning

confidence: 99%

“…First, the R 1ρ ‐weighted dynamic glucose‐enhanced (DGE ρ ) contrast calculated according to Schuenke et al:

{DGE}_{normalρ} false(normalt false) = \frac{{normalS}_{50ms} false(ref false) {- S}_{50ms} (t)}{{normalS}_{50ms} false(ref false) \cdot 50ms},

Δ {normalR}_{1 ρ} false(normalt false) {= R}_{1 ρ} false(normalt false) - {normalR}_{1 ρ} false(ref false),

with

R_{1 ρ} false(t false) = \frac{ln [S_{0 .2 ms} false(t false) / S_{50 ms} false(t false)]}{50 ms - 0 .2 ms},

where S 0.2ms (t) are the acquired images for TSL = 0.2 ms (i.e., TSL 2 ), which in the following are referred to as images without R 1ρ weighting.…”

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Dynamic glucose‐enhanced (DGE) MRI in the human brain at 7 T with reduced motion‐induced artifacts based on quantitative R_1ρ mapping

Boyd

Breitling

Zimmermann

et al. 2019

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“…Chemical exchange saturation transfer (CEST) allows for indirect detection of diluted molecules by their saturation transfer to the abundant water pool . Many different diluted solutes were reported to be detectable with CEST such as peptides and proteins, with dependency on protein conformation, creatine, glutamate, or even injected solutes such as iopamidol, glucose, and glucose derivatives …”

Section: Introductionmentioning

confidence: 99%

3D gradient echo snapshot CEST MRI with low power saturation for human studies at 3T

Deshmane

Zaiß

Lindig

et al. 2018

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129

Purpose For clinical implementation, a chemical exchange saturation transfer (CEST) imaging sequence must be fast, with high signal‐to‐noise ratio (SNR), 3D coverage, and produce robust contrast. However, spectrally selective CEST contrast requires dense sampling of the Z‐spectrum, which increases scan duration. This article proposes a compromise: using a 3D snapshot gradient echo (GRE) readout with optimized CEST presaturation, sampling, and postprocessing, highly resolved Z‐spectroscopy at 3T is made possible with 3D coverage at almost no extra time cost. Methods A 3D snapshot CEST sequence was optimized for low‐power CEST MRI at 3T. Pulsed saturation was optimized for saturation power and saturation duration. Spectral sampling and postprocessing (B 0 correction, denoising) was optimized for spectrally selective Lorentzian CEST effect extraction. Reproducibility was demonstrated in 3 healthy volunteers and feasibility was shown in 1 tumor patient. Results Low‐power saturation was achieved by a train of 80 pulses of duration t p = 20 ms (total saturation time t sat = 3.2 seconds at 50% duty cycle) with B 1 = 0.6 μT at 54 irradiation frequency offsets. With the 3D snapshot CEST sequence, a 180 × 220 × 54 mm field of view was acquired in 7 seconds per offset. Spectrally selective CEST effects at +3.5 and –3.5 ppm were quantified using multi‐Lorentzian fitting. Reproducibility was high with an intersubject coefficient of variation below 10% in CEST contrasts. Amide and nuclear overhauser effect CEST effects showed similar correlations in tumor and necrosis as show in previous ultra‐high field work. Conclusion A sophisticated CEST tool ready for clinical application was developed and tested for feasibility.

“…

{normalB}_{1}^{+}

inhomogeneity needs to be taken care of for quantitative imaging at UHF, including CEST. Solutions to the problem of CEST contrast variation caused by

{normalB}_{1}^{+}

inhomogeneity include the use of adiabatic pulses and a simultaneous analysis of

{normalB}_{1}^{+}

from acquired CEST data . Corrections can be applied in postprocessing and/or analysis when extra CEST measurements can be acquired at several levels of saturation

{normalB}_{1}^{+}

amplitude .…”

Section: Discussionmentioning

confidence: 99%

inhomogeneity mitigation in CEST using parallel transmission

Tse

Silva

Poser

et al. 2017