Prediction of subtle thermal histopathological change using a novel analysis of Gd-DTPA kinetics.

J Magn Reson Imaging 2003 Nov;18(5):585-98

Department of Medical Biophysics, University of Toronto, Toronto, Canada.

Purpose: To investigate Gd-DTPA kinetics as predictors of histopathological changes following focused ultrasound (FUS) thermal ablation for improved planning and assessment.

Materials And Methods: Twenty-nine FUS lesions were created in the thigh muscle of eight rabbits under MR-guidance at 1.5 Tesla. Three rabbits were killed at four hours; and 11 lesions were analyzed with histopathology. Temperature-sensitive MRI using proton-resonant frequency-shift was used for time-dependent temperature measurements. Analysis of the uptake kinetics of Gd-DTPA was performed after Gd-DTPA injection, within 20 minutes after heating and again at two hours after heating. The resulting kinetic maps, permeability (K(trans)) and leakage space (v(e)), were correlated to peak temperatures, T(2)-weighted MR, and histopathology.

Results: Images of K(trans) and v(e) reveal regions of histopathological change not visible on conventional post-therapy MR. At early times after heating, v(e) predicts the area of injury more accurately than T(2) (7 +/- 2% vs. 25 +/- 6% underestimation). A circular region of extensive structural/vascular disruption is indicated only on K(trans) maps. The sharp decrease in K(trans) at the boundary of this region occurs at 47.5 +/- 0.5 degrees C, and may be a better estimate of cell death than the conventional method of temperature threshold (55 degrees C for coagulation) used in therapy planning.

Conclusion: Our results suggest Gd-DTPA kinetics can predict different histopathological changes following FUS ablation and may be valuable for early prediction.

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http://dx.doi.org/10.1002/jmri.10388DOI Listing
November 2003
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