Technical advances in motion-robust MR thermometry

Abstract

Proton resonance frequency shift (PRFS) MR thermometry is the most common method used in clinical thermal treatments because of its fast acquisition and high sensitivity to temperature. However, motion is the biggest obstacle in PRFS MR thermometry for monitoring thermal treatment in moving organs. This challenge arises because of the introduction of phase errors into the PRFS calculation through multiple methods, such as image misregistration, susceptibility changes in the magnetic field, and intraframe motion during MRI acquisition. Various approaches for motion correction have been developed for real-time, motion-robust, and volumetric MR thermometry. However, current technologies have inherent trade-offs among volume coverage, processing time, and temperature accuracy. These tradeoffs should be considered and chosen according to the thermal treatment application. In hyperthermia treatment, precise temperature measurements are of increased importance rather than the requirement for exceedingly high temporal resolution. In contrast, ablation procedures require robust temporal resolution to accurately capture a rapid temperature rise. This paper presents a comprehensive review of current cutting-edge MRI techniques for motion-robust MR thermometry, and recommends which techniques are better suited for each thermal treatment. We expect that this study will help discern the selection of motion-robust MR thermometry strategies and inspire the development of motion-robust volumetric MR thermometry for practical use in clinics.

Keywords: magnetic resonance thermometry; motion correction; motion robust; proton resonance frequency shift; real‐time MRI.

FIGURE 1

Respiratory-induced motion. (A) Illustration of inhalation and exhalation. (B) T₁-weighted MR images to measure the displacement of the kidney and challenges of proton resonance frequency shift (PRFS) MR thermometry in the kidney. Significant temperature errors were obtained in the abdominal organs of healthy volunteers without heating. Figures reproduced from Kim et al. with permission.

FIGURE 2

Temperature maps from the referenceless (RFL) method in the in vivo brain. The solid red circle shows the region of interest (ROI) where the temperature map was calculated. The red dashed circle shows the reference ROI where the reference image is fitted. Figure reproduced from Zou et al. with permission.

FIGURE 3

Temperature maps reconstructed using principal component analysis (PCA), hybrid referenceless (RFL)–multibaseline (MB), and PCA–projection onto dipole field (PDF) methods. The initial temperature was set at 37°C. Figure reproduced from Tan et al. with permission.

FIGURE 4

Overview of the motion-robust MR thermometry methods and processes: respiratory gating (A), multibaseline (B), referenceless (C), principal component analysis (D), background removal (E), and k-space-based (F) methods.