A preclinical study of diffusion‐weighted MRI contrast as an early indicator of thermal ablation

Abstract

Intraoperative T 2-weighted (T2-w) imaging unreliably captures image contrast specific to thermal ablation after transcranial MR-guided focused ultrasound surgery, impeding dynamic imaging feedback. Using a porcine thalamotomy model, we test the unproven hypothesis that intraoperative DWI can improve dynamic feedback by detecting lesioning within 30 minutes of transcranial MR-guided focused ultrasound surgery. Methods: Twenty-five thermal lesions were formed in six porcine models using a clinical transcranial MR-guided focused ultrasound surgery system. A novel diffusion-weighted pulse sequence monitored the formation of T2-w and diffusionweighted lesion contrast after ablation. Using postoperative T2-w contrast to indicate lesioning, apparent intraoperative image contrasts and diffusion coefficients at each lesion site were computed as a function of time after ablation, observed peak temperature, and observed thermal dose. Lesion sizes segmented from imaging and thermometry were compared. Image reviewers estimated the time to emergence of lesion contrast. Intraoperative image contrasts were analyzed using receiver operator curves. Results: On average, the apparent diffusion coefficient at lesioned sites decreased within 5 minutes after ablation relative to control sites. In-plane lesion areas on intraoperative DWI varied from postoperative T2-w MRI and MR thermometry by 9.6 ± 9.7 mm 2 and −4.0 ± 7.1 mm 2 , respectively. The 0.25, 0.5, and 0.75 quantiles of the earliest times of observed T2-w and diffusion-weighted lesion contrast were 10.7, 21.0, and 27.8 minutes and 3.7, 8.6, and 11.8 minutes, respectively. The T2-w and diffusion-weighted contrasts and apparent diffusion coefficient values produced areas under the receiver operator curve of 0.66, 0.80, and 0.74, respectively. 2146 | ALLEN Et AL. 2 | METHODS 2.1 | Animal model All animal experiments were conducted with the approval of the Institutional Animal Care and Use Committee of the University of Virginia. Experiments were conducted using six 15-28-kg porcine craniotomy models as described by Elias et al. 33 The void created by the missing skull was carefully Conclusion: Intraoperative DWI can detect MR-guided focused ultrasound surgery lesion formation in the brain within several minutes after treatment.

A Review of Imaging Methods to Assess Ultrasound-Mediated Ablation

“…reported a decrease in tissue ADC following ablation in the prostate[48][49][50], uterine fibroids[8,9,47,51], and brain[52][53][54]. The treated lesion size, as measured on diffusion MRI, has been found to correlate well with contrastenhanced T1w images (Figure1(e)) and histopathology.…”

“…These competing effects can make diffusion-based contrast difficult to interpret [ 47 ]. However, several studies have reported a decrease in tissue ADC following ablation in the prostate [ 48 – 50 ], uterine fibroids [ 8 , 9 , 47 , 51 ], and brain [ 52 – 54 ]. The treated lesion size, as measured on diffusion MRI, has been found to correlate well with contrast-enhanced T1w images ( Figure 1(e) ) and histopathology.…”

Intracranial Sonodynamic Therapy With 5-Aminolevulinic Acid and Sodium Fluorescein: Safety Study in a Porcine Model

“…Immediately after the insonation, each subject was removed from the Insightec system and placed prone in an 8-channel imaging coil. MRI images (T1 and T2-weighted SPACE, 3D-MPRAGE, Diffusion-weighted MRI) were then acquired; diffusion-weighted sequences were considered particularly significant as an early indicator of post-treatment lesion ( 21 ). Contrast-enhanced T1 scans were not considered due to the lack of a pathological lesion to produce extravasation of Gadolinium, nor the necessity to asses contrast extravasation as for blood brain barrier opening.…”

Methods for MRI-guided treatment of painful bone metastases with Focused Ultrasound

“…Consequently, beside investigations of EDBS, as proposed in Chapter 5, image-based indicators should also be investigated. Potential image-based predictors have been proposed in the last few years, but their clinical relevance is yet to be validated [82,83,198,199]. Diffusion-weighted MRI (DWI) contrast has shown promising preliminary results in preclinical and clinical studies [82,198,199].…”

“…Potential image-based predictors have been proposed in the last few years, but their clinical relevance is yet to be validated [82,83,198,199]. Diffusion-weighted MRI (DWI) contrast has shown promising preliminary results in preclinical and clinical studies [82,198,199]. The preclinical studies suggested that DWI can detect lesion formation [198] and changes in the muscle overlying the periosteum [199]caused by ablation, while the clinical study showed correlation between the apparent diffusion coefficient with pain relief [82].…”