MRI‐guided thermal therapy of transplanted tumors in the canine prostate using a directional transurethral ultrasound applicator

Abstract

Purpose: To evaluate MRI-based techniques for visual guidance, thermal monitoring, and assessment during transurethral ultrasound thermal therapy of implanted tumors in an in vivo canine prostate model. Materials and Methods:Transmissible venereal tumors (TVT) were grown in the right lobe of the prostate in four dogs. High-temperature thermal therapy was selectively applied to the tumor-bearing lobe using a transurethral ultrasound applicator with a 180°directional heating pattern. Temperature-sensitive MRI (MRTI) using a fast interleaved gradient-echo echo-planar (iGE-EPI) imaging sequence was used for cumulative thermal dose calculations in multiple image planes during the treatment. The results from MRTI-based dose maps and post-treatment MRI were compared to those from histologic analysis.Results: MRTI monitoring in multiple planes across the prostate guided the use and control of a directive ultrasound applicator for the selective ablation of the sections of the prostate that contained implanted tumors. Findings in gadolinium enhanced MRI obtained immediately after thermal therapy slightly underestimated the size of tissue necrosis after treatment, as verified by histopathologic analysis. Conclusion:The use of multiplanar MRTI with a transurethral ultrasound applicator shows significant potential for selective thermal ablation of prostate tumor and tissue.

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

“…To correct for tissue shrinkage due to processing, the distances between lesion centers before and after fixation were measured. An average shrinkage of 10% was observed and is similar to those reported in rabbit brain (22) and dog prostate (16).…”

“…Planning is usually based on MR-derived thermal indices, in which a coagulation threshold is adopted-in most studies either a dose of 240 minutes at 43°C or a minimum peak temperature of 55°C (8,12). While reports exist that the planned treatment volume agrees with histologically-confirmed necrotic tissue (16), there is greater evidence that this threshold is a conservative estimate (17). Studies by Chung et al (8) showed that the ablation volume was 25% larger than that planned in rabbit skeletal muscle, while a two-fold increase was shown in application to uterine fibroid treatment (B.J.…”

“…For example, despite general agreement that edematous effects often confound the bright ring on T 2 -weighted MRI, studies in rabbit thigh muscle (8) and rabbit brain (10,22,23) demonstrated that this ring correlated with the cell death zone. However, the dark center on T 2 -weighted MRI, which is generally thought to represent coagulated tissue (10), correlated better in rabbit back muscle (12) and liver (24), and inconsistent results were obtained in canine prostate (16). Varied results have been also reported in assessments based on contrastenhanced T 1 -differences.…”

“…Varied results have been also reported in assessments based on contrastenhanced T 1 -differences. In canine prostate (16) and rabbit skeletal muscle (8) the confirmed necrotic region on MRI was shown to be bigger than the dark, nonperfusing center and smaller than the bright, enhancing rim. In normal liver, the necrotic region was shown to correspond to the dark center on contrast-enhanced T 1 (24,25).…”

Key factors that affect sonoporation efficiency in in vitro settings: The importance of standing wave in sonoporation

“…(Current address: Department of Neurosurgery, Osaka University Medical School, 2-2 Yamadaoka, Suita, Oaska, 565-0871, Japan. Phone: +81-6-6879-3652: FAX: +81-6-6879-3659; e-mail : m-kinoshita@nsurg.med.osaka-u.ac.jp) hyperthermia, such as coagulation of tissues [1][2][3][4][5][6][7][8][9][10][11][12], mechnical tissue destruction [13,14], disruption of tight junctions of the vasculature for enhanced local drug delivery [15][16][17][18][19][20], and sonoporation, a transient enhanced permeability of the cell membrane caused by the combination of ultrasound and microbubbles [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. As all of these bio-effects can be created non-invasively in vivo, ultrasound is gathering a great attention as a next generation surgical or drug delivery system.…”