Tissue temperature monitoring for thermal interventional therapy: Comparison of T1‐weighted MR sequences

Abstract

For thermal interventional therapy, near real-time monitoring of temperature changes in the treated area is desirable. In this study, various fast T1-weighted magnetic resonance (MR) imaging protocols were compared to determine the sensitivity and resolution of signal intensity for temperatures within the range of 36 degrees C-66 degrees C in gel phantoms and in vitro porcine liver specimens. The results showed that a T1-weighted fast spin-echo sequence with a TR of 100 msec had better temperature sensitivity and resolution than other sequences with comparable temporal resolutions. The longer imaging times required for fast spin-echo sequences with a TR of 300 msec did not improve temperature sensitivity. The methods introduced to evaluate temperature sensitivity and resolution should prove useful in selecting appropriate MR protocols for monitoring thermal treatment modalities such as interstitial laser therapy, focused ultrasound therapy, or radio-frequency heating.

Monitoring and visualization techniques for MR‐guided laser ablations in an open MR system

“…The days following ILT, in all imaging studies we found a low signal intensity zone on dynamic T1-weighted sequences, hyperintense on T2-weighted images, that (as previous experiments and studies have shown in 13,17,21,30,36) corresponded to tissue necrosis within the tumor ( Figure 6). …”

“…Diffusion sequences [4][5][6]13] have a relatively high sensitivity ad therefore may be used for temperature mapping. But the enhanced temperature sensitivity in diffusion imaging comes at the expense of a low signal-to-noise ratio in the images an requires fast or ultrafast imaging methods to avoid the effect of macroscopic motion.…”

“…Studies in our group [9][10][11][13][14][15][16][17][18][19][20][21] and clinical trials [44][45][46] have shown that relatively fast T1-weighted protocols and SPGR sequences are useful for monitoring thermal changes in tissue. The combination of higher signal levels and faster scans compensates for the lesser temperature contrast, which can be enhanced with the image processing techniques described in this publication.…”

“…Matsumoto et al [9,13] has shown that within the range of 37 -50°C, the relaxation time T1 varies approximately linearly with temperature at a rate of 1%/°C. Thus, MRI can distinguish the normal margins surrounding thermal lesions.…”

MR thermometry

“…The signal decreases with increasing temperature both because the relaxation time increases and the magnetization decreases. The small nonlinear temperature dependence on the equilibrium magnetization is often neglected (26) or, alternatively, Eq. [7] is modified to (27):…”