Fast and Quantitative T1ρ-weighted Dynamic Glucose Enhanced MRI

Purpose Dynamic glucose enhanced (DGE) MRI has shown potential for imaging glucose delivery and blood–brain barrier permeability at fields of 7T and higher. Here, we evaluated issues involved with translating d‐glucose weighted chemical exchange saturation transfer (glucoCEST) experiments to the clinical field strength of 3T. Methods Exchange rates of the different hydroxyl proton pools and the field‐dependent T2 relaxivity of water in d‐glucose solution were used to simulate the water saturation spectra (Z‐spectra) and DGE signal differences as a function of static field strength B0, radiofrequency field strength B1, and saturation time tsat. Multislice DGE experiments were performed at 3T on 5 healthy volunteers and 3 glioma patients. Results Simulations showed that DGE signal decreases with B0, because of decreased contributions of glucoCEST and transverse relaxivity, as well as coalescence of the hydroxyl and water proton signals in the Z‐spectrum. At 3T, because of this coalescence and increased interference of direct water saturation and magnetization transfer contrast, the DGE effect can be assessed over a broad range of saturation frequencies. Multislice DGE experiments were performed in vivo using a B1 of 1.6 µT and a tsat of 1 second, leading to a small glucoCEST DGE effect at an offset frequency of 2 ppm from the water resonance. Motion correction was essential to detect DGE effects reliably. Conclusion Multislice glucoCEST‐based DGE experiments can be performed at 3T with sufficient temporal resolution. However, the effects are small and prone to motion influence. Therefore, motion correction should be used when performing DGE experiments at clinical field strengths.

Section: Discussionmentioning

confidence: 70%

d‐glucose weighted chemical exchange saturation transfer (glucoCEST)‐based dynamic glucose enhanced (DGE) MRI at 3T: early experience in healthy volunteers and brain tumor patients

Sehgal

Yadav

et al. 2019

“…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},

with S 50ms (t) being the acquired R 1ρ ‐weighted images for the spin‐lock time (TSL) = 50 ms (i.e., TSL 1 ), and S 50ms (ref) being the average of the first 20 S 50ms (t) images. Note, in comparison to the original definition, DGE ρ in Equation is divided by the respective TSL = 50 ms to enable a direct comparison of contrast values (in units of Hz) to the second DGE contrast metric investigated in this study (Equation ).…”

Section: Methodsmentioning

confidence: 99%

“…Whether glucose in blood vessels, extracellular glucose, or intracellular phosphorylated glucose derivatives are the driving source for the observed DGE contrast remains to be investigated in depth . Furthermore, the applicability for examinations in humans has already been verified in independent pilot studies based on glucoCEST and glucoCESL . However, DGE contrast maps are prone to motion‐induced artifacts because DGE image series consist of data acquired before, during, and after glucose injection.…”

Section: Introductionmentioning

confidence: 99%

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

Self Cite

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.

“…Current CEST B 0 correction methods rely on data post‐processing and require either a separate field map acquisition or multiple acquisitions with a fine frequency interval to correct the shift in the CEST spectrum caused by zero‐order shim changes . Motion correction is performed retrospectively via rigid or nonrigid registration of CEST offset‐images. However, the CEST signal attenuation caused by geometric distortion because of gradient field variation cannot be corrected in this way.…”

Section: Discussionmentioning

confidence: 99%

“…The effect of motion in CEST MRI is almost unexplored. The few studies that examine motion correction in CEST MRI are based either on rigid image registration or retrospective time domain analysis…”

Section: Introductionmentioning

confidence: 99%

Real‐time simultaneous shim and motion measurement and correction in glycoCEST MRI using double volumetric navigators (DvNavs)

Simegn

Kouwe

Robertson

et al. 2018

Purpose CEST MRI allows for indirect detection of molecules with exchangeable protons, measured as a reduction in water signal because of continuous transfer of saturated protons. CEST requires saturation pulses on the order of a second, as well as repeated acquisitions at different offset frequencies. The resulting extended scan time makes CEST susceptible to subject motion, which introduces field inhomogeneity, shifting offset frequencies and causing distortions in CEST spectra that resemble true CEST effects. This is a particular problem for molecules that resonate close to water, such as hydroxyl group in glycogen. To address this, a technique for real‐time measurement and correction of motion and field inhomogeneity is proposed. Methods A CEST sequence was modified to include double volumetric navigators (DvNavs) for real‐time simultaneous motion and shim correction. Phantom tests were conducted to investigate the effects of motion and shim changes on CEST quantification and to validate the accuracy of DvNav motion and shim estimates. To evaluate DvNav shim and motion correction in vivo, acquisitions including 5 experimental conditions were performed in the calf muscle of 2 volunteers. Results Phantom data show that DvNav‐CEST accurately estimates frequency and linear gradient changes because of motion and corrects resulting image distortions. In addition, DvNav‐CEST improves CEST quantification in vivo in the presence of motion. Conclusion The proposed technique allows for real‐time simultaneous motion and shim correction with no additional scanning time, enabling accurate CEST quantification even in the presence of motion and field inhomogeneity.