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

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.