Temperature quantification using the proton frequency shift technique: In vitro and in vivo validation in an open 0.5 tesla interventional MR scannerduring RF ablation
Rm. Botnar et al., Temperature quantification using the proton frequency shift technique: In vitro and in vivo validation in an open 0.5 tesla interventional MR scannerduring RF ablation, J MAGN R I, 13(3), 2001, pp. 437-444
Open magnetic resonance (MR) scanners allow MR-guided targeting of tumors,
as well as temperature monitoring of radio frequency (RF) ablation. The pro
ton frequency shift (PFS) technique, an accurate and fast imaging method fo
r temperature quantification, was used to synthesize thermal maps after RF
ablation in an open 0.5 T MR system under ex vivo and in vivo conditions. C
alibration experiments with 1.5% agarose gel yielded a chen-Acal shift fact
or of 0.011 -k 0.001 ppm/degreesC (r(2) = 0.96). Three gradient echo (GRE)
pulse sequences were tested for thermal mapping by comparison with fiberopt
ic thermometer (Luxtron Model 760) readings. Temperature uncertainty decrea
sed from high to low bandwidths (BW): +/-5.9 degreesC at BW = 15.6 kHz, +/-
1.4 degreesC at BW = 3.9 kHz, and +/-0.8 degreesC at BW = 2.5 kHz. In vitro
experiments (N = 9) in the paraspinal muscle yielded a chemical shift fact
or of 0.008 +/- 0.001 ppm/degreesC. Temperature uncertainty was determined
as +/-2.7 degreesC (BW = 3.9 kHz, TE = 19.3 msec). The same experiments car
ried out in the paraspinal muscle (N = 9) of a fully anesthetized pig resul
ted In a temperature uncertainty of +/-4.3 degreesC (BW = 3.9 kHz, TE = 19.
3 msec), which is higher than it is in vitro conditions (P < 0.15). Quantit
ative temperature monitoring of RF ablation Is feasible in a 0.5 T open-con
figured MR scanner under ex vivo and in vivo conditions using the PFS techn
ique. (C) 2001 Wiley-Liss, Inc.