MR susceptibility-weighted imaging during transurethral prostate sono-ablation procedures for guidance of device placement to counter effect of intra-prostatic calcifications

Tuesday, March 7, 2023

4:12 PM – 4:21 PM

Location: Phoenix Convention Center, 221AB

Presenting Author(s)

Jessica Lee, MD

Assistant Professor of Clinical Radiology and Biomedical Imaging
Yale School of Medicine

Disclosure(s): No financial relationships to disclose

Author/Co-author(s)

Pejman Ghanouni, MD, PhD

Associate Professor of Radiology
Stanford University Medical Center
DC

Daniel Costa, MD

Associate Professor of Radiology
University of Texas Southwestern Medical Center
CS

Clifford Shin, MD, PhD

Resident
Yale School of Medicine
PK

Pooyan Khalighinejad, MD

Resident Physician
University of Texas Southwestern Medical Center
PS

Preston Sprenkle, MD

Associate Professor of Urology
Yale School of Medicine
Raj Ayyagari, MD, FSIR

Associate Professor
Yale School of Medicine
RS

Robert Staruch, PhD

Director of Clinical Science
Profound Medical
AB

Amanda Beserra, MSc

Lead Clinical Scientist
Profound Medical
SA

Sandeep Arora, MD

Associate Professor of Radiology and Biomedical Imaging
Yale School of Medicine

Disclosure(s):

Jessica Lee, MD: No financial relationships to disclose

Pejman Ghanouni, MD, PhD: Insightec: Advisory Committee or Review Panel Member (Ongoing); Profound Medical: Advisory Committee or Review Panel Member (Ongoing)

Purpose: Men seeking MRI-guided transurethral ultrasound ablation (TULSA) for treatment of prostate cancer (PCa) are screened for calcifications. Large calcifications can block ultrasound (US) and cause inadequate heating. Smaller calcifications (≤3 mm) can be accommodated by aligning the ultrasound applicator (UA) with calcifications between transducer elements. We compare calcification detection and size measurement using susceptibility-weighted MRI (SWI) vs. computed tomography (CT). We also assess the impact of calcifications on ablation coverage benchmarked against a previously-published pivotal trial.

Materials and Methods:

Pre-TULSA screening for calcifications (calcs) was performed with CT for 17 men. The mean (range) of CT slice thickness was 1.6 (0.6-5.0) mm. When relevant calcs were detected, intraprocedural SWI (1.0mm slices) was used to guide positioning of UA elements with respect to calcs. Calcification in-plane & through-plane diameters were measured on CT & SWI, & their impact on ablation coverage was assessed using MR thermometry. Maximum temperature & thermal dose maps from MR thermometry were segmented in 90-degree quadrants across the active UA elements, with presence of calcification assessed based on SWI magnitude & phase images.

Results: 25 prostatic calcs were identified across 17 men. All calcs identified on CT were visible on SWI. In 4 men, SWI phase images were used to differentiate calcs from iron. Mean (range) diameter was 3.8 (1.4-10.4) mm on CT & 4.0 (2.2-10.8) mm using SWI. SWI diameters were larger by median 22% in at least one dimension for all men & in 42/50 measurements overall. With SWI-guided UA placement in 9 men, median (IQR) proportion of target volume reaching boiling temperature was 4.0 (2-8.0) % & 3.0 (0-7.0) % in sectors with & without calcs based on MR thermometry. Adequate thermal dose was achieved in men with & without calcs: 98 (93-100) % vs 98 (95-100) %. In the pivotal trial of 115 patients, which did not have SWI-guided UA placement, 93% (90-98%) of quadrants with calcs reached adequate thermal coverage compared to 98 (93-100)% overall & 6 (1-9)% with calcs had target volume approaching boiling vs 0 (0-5) % overall.

Conclusion: Intraprocedural SWI detected all CT-identified calcifications, tending to overestimate the diameter but guiding effective device positioning. CT remains the gold standard for pre-TULSA calcification screening, and further studies are warranted to optimize SWI protocols, correlate the size of calcifications on CT and SWI, and predict their impact on ablation coverage.