Motion Correction in Proton Resonance Frequency–based Thermometry in the Liver

Abstract

The unique ability of magnetic resonance imaging to measure temperature noninvasively, in vivo, makes it an attractive tool for monitoring interventional procedures, such as radiofrequency or microwave ablation in real-time. The most frequently used approach for magnetic resonance-based temperature measurement is proton resonance frequency (PRF) thermometry. Although it has many advantages, including tissue-independence and real-time capability, the main drawback is its motion sensitivity. This is likely the reason PRF thermometry in moving organs, such as the liver, is not commonly used in the clinical arena. In recent years, however, several developments suggest that motion-corrected thermometry in the liver is achievable. The present article summarizes the diverse attempts to correct thermometry in the liver. Therefore, the physical principle of PRF is introduced, with additional references for necrosis zone estimation and how to deal with fat phase modulation, and main magnetic field drifts. The primary categories of motion correction are presented, including general methods for motion compensation and library-based approaches, and referenceless thermometry and hybrid methods. Practical validation of the described methods in larger patient groups will be necessary to establish accurate motion-corrected thermometry in the clinical arena, with the goal of complete liver tumor ablation.

Validating a Simulation Model for Laser-Induced Thermotherapy Using MR Thermometry

“…The following measures were taken to reduce artifacts: The liver was framed by two agarose gel phantoms (with similar susceptibility as the liver tissue) in the experiments to significantly increase the object volume and thus help stabilize the magnetic field [13,25] and it was also tried to correct for changes in the magnetic field (cf. [14,20,22]).…”

Absolute thermometry using hyperpolarized 129Xe free‐induction decay and spin‐echo chemical‐shift imaging in rats

“…Changes in PRF due to temperature alterations may thus be superimposed with changes due to $$$ {B}_0 $$$ field drift, 8 motion 9,10 or temperature‐associated changes of magnetic susceptibility, the later being particularly relevant in fatty tissues 11 . Depending on location and tissue type, PRF thermometry thus suffers from limited accuracy and reliability 12 .…”

“…Proton resonance frequency (PRF) based MR thermometry is typically used, exploiting the linear relationship of chemical shift of 1 H in water with temperature. PRF-based thermometry has its limitations, however, mainly due to the only minimal change of chemical shift with temperature of 0.01 ppm/ • C. 7 Changes in PRF due to temperature alterations may thus be superimposed with changes due to B 0 field drift, 8 motion 9,10 or temperature-associated changes of magnetic susceptibility, the later being particularly relevant in fatty tissues. 11 Depending on location and tissue type, PRF thermometry thus suffers from limited accuracy and reliability.…”

Investigation of Microwave Ablation Process in Sweet Potatoes as Substitute Liver

“…Additionally, deploying and locating these sensors is also a challenge. Magnetic resonance imaging (MRI)-based thermometry is a non-invasive technique for temperature monitoring during MWA but then the complete intervention has to be performed inside an MRI scanner [ 16 , 17 ]. Hence, microwave imaging using body matched antennas (BMAs) is experimented as an independent non-invasive technique for real-time imaging and monitoring the thermal ablation process [ 18 , 19 ]; however, in [ 18 ], an array of ultra-wideband (UWB) antennas is used in a bistatic radar principle to carry out the reconstruction.…”