Clinically feasible B₁ field correction for multi‐organ sodium imaging at 3 T

Abstract

Sodium MRI allows the non-invasive quantification of intra-organ sodium concentration. RF inhomogeneity introduces uncertainty in this estimated concentration. B 1 field corrections can be used to overcome some of these limitations. However, the low signal-to-noise ratio in sodium MRI makes accurate B 1 mapping in reasonable scan times challenging. The study aims to evaluate Bloch-Siegert off-resonance (BLOSI) B 1 field correction for sodium MRI using a 3D Fermat looped, orthogonally encoded trajectories (FLORET) read-out trajectory.We propose a clinically feasible B 1 field map correction method for sodium imaging at 3 T, evaluating five healthy subjects' brain, heart blood, kidneys, and thigh muscle.We scanned the subjects twice for repeatability measures and used sodium phantoms to determine organ total sodium concentration. Conventional proton scans were compared with sodium images for organ structural integrity. The BLOSI approach based on the 3D FLORET read-out trajectory was used in B 1 field correction and 3D density-adapted radial acquisition for sodium imaging.Results indicate improvements in sodium imaging based on B 1 field correction in a clinically feasible protocol. Improvements are determined in all organs by enhanced anatomical representation, organ homogeneity, and an increase in the total sodium concentration after applying a B 1 field correction.The proposed BLOSI-based B 1 field correction using a 3D FLORET read-out trajectory is clinically feasible for sodium imaging, which is shown in the brain, heart, kidney, and thigh muscle. This supports using fast B 1 field mapping in the clinical setting.

A user independent denoising method for x‐nuclei MRI and MRS

“…One healthy subject recruited through public announcements for another study 33 was used. The local ethics committee approved the study (no.…”

“…A two‐compartment salt‐water phantom was included in the scan of the patient. Further acquisition details can be found in Vaeggemose et al 33 The data analyzed consisted of a 60 × 60 × 60 dimensional dataset ( N X × N Y × N Z ) and was B 1 ‐corrected before denoising.…”

Daytime Variation in Kidney Perfusion, Oxygenation, and Sodium Concentration Assessed by Multiparametric MRI in Healthy Volunteers

“…Sodium images were acquired with a 3D density‐adapted radial acquisition technique with the subject free‐breathing, as described by Nagel et al, 15 and the following imaging parameters: TR = 5.8 msec, TE = 0.31 msec, FA = 20°, FOV = 35 cm 3 , mtx = 35 × 35, averages = 32, bandwidth (BW) = 33.3 kHz and zero‐filled by a factor of 2 in all three dimensions in a total scan time of 12 minutes. The sodium B 1 transmit field was estimated using a FLORET (Fermat looped, orthogonally encoded trajectories) trajectory combined with a Bloch‐Siegert off‐resonance pulse, with TR = 160 msec, TE = 4.75 msec, FA = 45°, FOV = 35 cm 3 , mtx = 30 × 30, averages = 2, and BW = 125 kHz 16 …”

“…Images were processed and analyzed in MATLAB R2020a (MathWorks). B 1 correction was performed as described previously 16 . Reference phantoms consisted of 32 and 80 mM sodium concentrations dissolved in 4% agar.…”

“…B 1 correction was performed as described previously. 16 Reference phantoms consisted of 32 and 80 mM sodium concentrations dissolved in 4% agar. These were placed at the center of the anterior coil element.…”