Meeting Report: Radiological Society of North America (RSNA) 2023


Key Points

  • RSNA 2023 included abstracts that addressed focused ultrasound for prostate cancer, histotripsy, neuromodulation, and improved image quality. 
  • Pejman Ghanouni, MD, PhD, presented a keynote on focused ultrasound outcomes for prostate cancer. 
Radiological Society of North America (RSNA) 2023

RSNA’s 109th Scientific Assembly and Annual Meeting was held in Chicago November 26–30, 2023. There were eight focused ultrasound–related abstracts or sessions this year, down from 26 in 2022. The topics presented included neuromodulation, histotripsy, improving image quality during focused ultrasound procedures, and imaging and treatment for prostate cancer. 

Pejman Ghanouni, MD, PhD, associate professor of radiology (general radiology) and, by courtesy, of neurosurgery, of obstetrics and gynecology, and of urology at Stanford University, presented a keynote on treatment factors associated with oncological efficacy after focal therapy for prostate cancer using MRI-guided focused ultrasound. 

Nathan Loudon, MD, an integrated interventional radiology resident at the University of Michigan, presented an abstract on post embolization syndrome as a possible indication of immune activation from histotripsy. 

“At the poster presentation session, there was a ton of enthusiasm for histotripsy and our research,” said Dr. Loudon. “There are more than 30,000 people who attend RSNA, so it was a great opportunity to connect and exchange ideas with other clinicians and researchers.” 

The full text of the abstracts that may be of interest to the focused ultrasound community are listed below by indication. 

RSNA’s session catalog can be used to search and read the full text for any presentation. Note that searching for key words returns session results, so users must then scroll through the session to find their content of interest; an alternate to scrolling is using “control+F” to search for the key word in each session returned. Virtual access to all RSNA sessions is available until April 30, 2024, at noon CT. 

Focused Ultrasound Abstracts 


Science Session with Keynote: Interventional Radiology (Translational Research) | T3-SSIR02 (1 keynote) 

What Treatment Factors are Associated with Oncological Efficacy after MRI-guided Focused Ultrasound (MRgFUS) Focal Therapy of Prostate Cancer | T3-SSIR02-4 
by Pejman Ghanouni, MD, PhD, Associate Professor of Radiology at Stanford University 

Purpose: A phase 2b multicenter trial assessed efficacy and safety of MRI-guided Focused Ultrasound (MRgFUS) as an alternative to radical therapy for MRI-visible, intermediate-risk Gleason Grade Group (GGG) 2 or 3 prostate cancer. Of 89 men with 24-month biopsy, 78 had no evidence of GGG ≥2 prostate cancer in the treated area [1]. Erectile function and urinary continence outcomes compared favorably to radical therapy [1]. This study presents a retrospective analysis to determine if patient selection or treatment factors are associated with oncologic efficacy of MRgFUS ablation. 

Methods and Materials: Oncologic efficacy was defined by the absence of clinically significant (GGG ≥2) cancer in the treatment zone on 24-month biopsy. Baseline patient, screening characteristics and treatment parameters, such as the ratio of ablated, or non-perfused volume (NPV), to MRI-visible lesion volume, and the ratio of NPV to total prostate volume (Figure 1), were analyzed to determine an association with oncologic efficacy. Impact of ablation on urinary and erectile functional outcomes was also assessed. 

Results: Comparing men with and without GGG ≥2 at 24-month biopsy revealed no difference in baseline characteristics such as patient age, PSA, prostate volume, or total and positive biopsies (Table 1). Overall, the mean lesion volume was 0.82 mL, and the mean non-perfused volume around the MRI-visible lesion was 27 mL. The volume of ablated prostate tissue encompassing the MRI-visible lesion volume (NPV/lesion volume) was twice as large in men without significant cancer on 24-month biopsy of the treated area compared to men with significant cancer. (p=0.018, Table 1). Figure 2 shows that oncologic efficacy increases as the ratio of NPV/lesion volume increases; however, NPV as a fraction of total prostate volume was not associated with oncologic efficacy (Table 1). Among men with new erectile dysfunction or severe urinary symptoms, there was no difference in NPV/lesion volume ratio (p=0.3, p=0.8, respectively). 

Conclusions: Insufficient ablation margin around the MRI-visible lesion was associated with the presence of clinically significant cancer at 24-month biopsy after focal MR guided focused ultrasound ablation. Adequate ablation volume is determined by extent of coverage around the MRI-visible lesion volume, not by the fraction of the prostate volume ablated. Importantly, ablating a larger volume of tissue around the MRI-visible lesion did not increase the risk of erectile or urinary dysfunction at 24 months. 

Clinical Relevance/Application: Focal therapy of prostate cancer must overcome MRI underestimation of tumor extent. A larger volume of ablated tissue relative to targeted tumor volume is associated with better oncologic outcome at 2 years post-ablation. 

Nuclear Medicine & Molecular Imaging Sunday Poster Discussions II | S3B-SPNMMI 

PSMA PET/CT for Localization of Prostate Cancer after Focal Therapy | S3B-SPNMMI-1 
by Mahbod Jafarvand, MD, Nuclear Medicine Resident at UCLA 

Purpose: PSMA-ligand PET has become the first-line imaging tool for staging and re-staging patients with prostate cancer. However, its role in patients with prostate cancer who underwent focal therapy (HIFU, irreversible electroporation, photodynamic therapy, cryoablation, and laser therapy) is still unknown. In this study, we aimed to investigate the diagnostic performances of PSMA PET/CT to detect and localize biochemical recurrence after focal therapy. 

Methods and Materials: This was a retrospective single center study. Patients with the following inclusion criteria were included: focal treatment for prostate cancer, 68Ga-PSMA-11 PET with contrast enhanced CT performed for biochemical recurrence, and no therapy between focal therapy and PET. Three independent blinded readers performed the PET image analysis and a per-region (T, N, M1a, M1b, M1c) centralized majority rule was applied (positivity rate). Inter-reader agreement of the positivity rates was calculated with Fleiss’ kappa. In a sub-cohort of patients with a MRI and biopsy performed within 3 months of PSMA PET, diagnostic accuracy was evaluated on a per-patient and per-segment analysis on standard WB +60 min and the delayed +90 min pelvic images. A single radiologist blinded to PSMA and pathology performed MRI interpretation. Twelve prostatic segments were defined, and for every segment, suspicion for recurrence was assessed. 

Results: Of the 3329 patients with either a PSMA PET scan or focal therapy performed at UCLA, 100 patients met the inclusion criteria. PSMA-PET positivity rate per majority rule was 85/100 (85%) for prostate, 17/100 (17%) for pelvic lymph nodes and 20/100 (20%) for distant metastases. The inter-reader agreement for positivity rate by region was moderate (kappa=0.5). 29 patients had MRI and post-therapy biopsy data available. In these, Per-patient analysis showed a sensitivity of 92% for PSMA and 88% for MRI. Per-segment analysis performed on 297 validated segments resulted in a sensitivity, specificity, positive predictive value and negative predictive value of 53%, 90%, 74% and 78% for PSMA at +60 min, 55%, 92%, 79% and 79% for PSMA at +90 min and 29%, 92%, 72% and 65% for MRI (p<0.01), respectively. All Patients with PSMA SUVmax ≥ 10 had GG ≥3 disease. 

Conclusions: In this retrospective study of 100 patients treated with focal treatment for prostate cancer the PSMA-PET positivity rate was 85% for prostate. The sensitivity per-segment was 55% on delayed +90 min pelvic PSMA PET vs 29% for MRI with a similar specificity of 92%. results suggest that PSMA PET/CT has potential for localization of recurrent prostate cancer after focal therapy. 

Clinical Relevance/Application: PSMA PET appears promising for localization of biochemical recurrence after focal therapy. 

View Digital Presentation:  

Genitourinary Imaging Education Exhibits | GUEE 

MRI after Focal Therapy for Prostate Cancer: What Radiologists Must Know | GUEE-81 
by Rozita Jalilianhasanpour, MD, Radiology Resident at the University of Washington 

Teaching Points: 

  • Overview of the currently available focal treatments for prostate cancer: indications, contraindications, and techniques. 
  • Review of potential complications of each procedure: frequency, diagnosis, and management. 
  • Discussion of expected postoperative MRI findings of each procedure: early and late. 
  • Review of imaging findings of recurrent prostate cancer post focal treatment: diagnosis, mimics, and management. 
  • Discussion of potential pitfalls. 

Table of Contents/Outline: 


  • Rationale for focal therapy. 
  • Potential benefits. 
  • Criticisms to focal therapy. 
  • Importance for radiologists and urologists. 

Treatment Options 

  • Electroporation (NanoKnife): Technique, Post-op appearance (Early and Late), Complications, Recurrence. 
  • HIFU (FocalOne and TULSA): Technique, Post-op appearance (Early and Late), Complications, Recurrence. 
  • Cryoablation: Technique, Post-op appearance (Early and Late), Complications, Recurrence. 
  • Laser Ablation: Technique, Post-op appearance (Early and Late), Complications, Recurrence. 

 View Digital Presentation:  

Prostate Imaging for Recurrent Reporting (PI-RR): A User Guide | GUEE-60 
by Anup Shashindra Shetty, MD, Radiologist at Washington University in St. Louis 

Teaching Points: The Prostate imaging for Recurrence Reporting (PI-RR) system was introduced in 2021 to create standards for reporting pelvic MRI after radical prostatectomy or radiation for treatment of prostate cancer. Using a similar nomenclature as PI-RADS v2.1, PI-RR uses established knowledge of MRI features of recurrent prostate cancer and codifies it systematically to be accessible to prostate MR readers of all experience levels. 

This exhibit is on the RadioGraphics Needs List under Genitourinary Imaging: Pictorial on Guidelines and Reporting Systems. 

This exhibit will: 

1) Discuss the rationale for PI-RR. 

2) Describe technical standards and reporting guidelines. 

3) Illustrate the use of PI-RR to assess for recurrent prostate cancer after radical prostatectomy and radiation therapy though a series of instructive cases. 

4) Describe pitfalls of the current version, including non-applicability for focal therapies. 

5) Detail areas for future development of PI-RR. 

Table of Contents/Outline: 

  • Background: Why PI-RR, including the benefits of standardizing post-treatment prostate MRI 
  • Technical Standards: Requirements, extras (subtraction imaging, 3D volumetric T2 for MPR) 
  • Reporting: Component scores in the PI-RR system shown in a pictorial format 
  • Case Examples: Prostatectomy, external beam radiation, brachytherapy 
  • Pitfalls: Definitions of PI-RR 4/5 for post-prostatectomy based on laterality; susceptibility artifact from brachytherapy seeds and surgical clips; residual prostate tissue after prostatectomy 
  • Future Development: Focal therapy (cryoablation, HIFU, etc.); Integrating PSMA-PET/CT 

View Digital Presentation:  

Genitourinary Imaging (AI for Detection and Characterization of Genitourinary Cancers) | S1-SSGU01 

Multiple Centre External Validation of an AI Solution for Prostate Cancer Diagnostic Imaging | S1-SSGU01-3 
by Francesco Giganti, MD, PhD, Associate Professor and Honorary Consultant in Radiology at University College London 

Purpose: Clinical translation of AI solutions for detection of clinically significant prostate cancer (csPCa) has been limited by the lack of validation on multi-centre datasets including multiple MRI scanners, vendors, field strengths and imaging protocols. Here, we evaluate the ability of an AI solution to generalise to real-world external validation data including blinded validation on an unseen site. 

Methods and Materials: AI-based software was developed using PROSTATEx and retrospective data from five sites (794 patients, 34% csPCa). The software was evaluated on a blinded external validation set (252 patients – 42 per site, 31% csPCa, 9% with prior negative biopsy) of multiparametric (mpMRI) data obtained from six sites; one site was unseen during development, and data from other sites was from later time periods than the development set. This external data included six scanner models from two vendors, with different field strengths (1.5T/3.0T) and acquisition protocols. The software automatically outputs scores intended to identify Gleason score (GS)≥3+4 csPCa per-patient. csPCa was confirmed by biopsy (GS≥3+4 / PI-RADS ≥3), with PI-RADS 1/2 patients that did not receive a biopsy assumed negative. Exclusion criteria included quality issues such as severe motion and metal prostheses, active surveillance, prior prostate or bladder surgery or treatment including brachytherapy, TURP, prostatectomy, ablation, HIFU/focal therapy, or water vapour therapy. Performance was evaluated using ROC analysis, with 95% confidence intervals estimated by bootstrapping. 

Results: For selecting patients for biopsy, the AI identified patients with csPCa with sensitivity 94% (95% CI 88-99%), specificity 57% (49-64%), NPV 95% (90-99%), and AUC 0.85 (0.80-0.90) using mpMRI data from the blinded external validation set. Comparing between sites, the AUC ranged from 0.70-0.98, with a pooled AUC of 0.86±0.11. On the unseen site, the AUC was 0.95 (0.87-1.00). Reporting radiologists had per-patient sensitivity 99% (95% CI 96-100%) due to the assumed ground truth, specificity 73% (67-80%), NPV 99% (98-100%), and AUC 0.95 (0.92-0.97). In a 2019 Cochrane meta-analysis of 12 major studies (37% csPCa), radiologists identified patients with GS≥3+4 csPCa with sensitivity 86% and specificity 42%. 

Conclusions: The proposed AI solution shows comparable performance to radiologists in major expert studies, on a large real-world, multi-centre, external validation dataset with different scanners, vendors, field strengths and imaging protocols. 

Clinical Relevance/Application: AI could support prostate cancer detection in clinical practice, generalises to multiple sites, scanners and imaging protocols, and is robust to novel data. 


Interventional Radiology Wednesday Poster Discussions I | W5A-SPIR (1 abstract) 

Post Embolization Syndrome Following Histotripsy: An Indicator of Immune Activation | W5A-SPIR-3 
by Nathan Loudon, MD, Integrated Interventional Radiology Resident at the University of Michigan 

Purpose: Post-embolization syndrome (PES) is a reported phenomenon that can occur following transarterial chemoembolization (TACE) or radioembolization (TARE). It is thought to occur as a result of immune and inflammatory response to cell death during tumor necrosis. The most commonly described symptoms are pain, fever, and leukocytosis. The purpose of this study was to determine whether these symptoms would be seen following histotripsy at higher or lower frequency compared to TACE or TARE. 

Methods and Materials: This was a single center, IRB-approved retrospective cohort study that compared post-embolization syndrome symptoms of fever, right upper quadrant abdominal pain, and leukocytosis among patients who underwent ablation of liver tumors using histotripsy (n=10), TARE (n=32), or TACE (n=34). Our analysis considered size of largest lesion, tumor type, LR category, and BCLC staging. 

Results: When adjusted for the size of the lesion and tumor type (HCC vs non-HCC), the odds of experiencing fever were 7.17 times higher in patients who underwent histotripsy compared to TACE (95% CI = 1.16 – 52.33, p=.039), and 50 times higher compared to TARE (95% CI = 5.74 – 1589.36, p=.003). The odds of experiencing abdominal pain were 14.70 times higher in the histotripsy group compared to TACE (95% CI = 2.09 – 302.12, p=.02) and 50 times higher compared to TARE (95% CI = 7.02 – 1307.34, p=.001). The histotripsy group had a smaller change in WBC from pre to post treatment compared to TACE (2.49, 95% CI = 0.34 – 4.64, p=0.024), and no statistically significant difference in WBC change compared to TARE. 

Conclusions: As histotripsy becomes a more widely available treatment offered to patients, it is important to understand the range of expected clinical symptoms that can occur following ablation. This study suggests that patients who undergo histotripsy are more likely to experience fever and abdominal pain following ablation compared to TACE and TARE. 

Clinical Relevance/Application: Histotripsy is a novel ablation modality and, as such, its expected post-treatment symptoms are still being elucidated. Preclinical data have shown that histotripsy is highly immunogenic on both a local and systemic level. PES is thought to be a result of inflammatory and immune response to tumor ablation. Studying the incidence of PES in this population could provide valuable insights into the clinical manifestations of immune activity following ablation. 

View Digital Presentation: 


Neuroradiology Education Exhibits | NREE (2 abstracts) 

How to Improve in Intraoperative Image Quality in Transcranial MR-guided Focused Ultrasound Surgery | NREE-107 
by Hiroki Hori, PhD, RT, Department of Medical Education at Mie University Graduate School in Mie, Japan 

Teaching Points: The objective of this exhibit is to provide a method for enhancing of intraoperative image quality in transcranial MR-guided focused ultrasound surgery (TcMRgFUS). TcMRgFUS possesses the distinct advantage of allowing expeditious assessment of therapeutic efficacy post each sonication and intraoperative magnetic resonance (MR) imaging for visualization of the lesion. In circumstances which denotes a lack of desired therapeutic effects and the lesion misses the planned target, subsequent ablation targets can be delicately re-aligned based on the intraoperative image. Thus, the acquisition of high-quality intraoperative images, which can accurately confirm the lesion, is imperative. The accuracy of this re-alignment is contingent upon the quality of the intraoperative image. Unfortunately, the current intraoperative image quality obtained from a 3.0T MRI system, is deficient in precisely identifying the lesion. In view of this limitation, we have been developed and substantiated a method for ameliorating the quality of intraoperative images. 

Table of Contents/Outline: 

1. TcMRgFUS procedure 

a. Overview of TcMRgFUS 

b. Intraoperative T2-weighted image using 3.0T MRI 

2. Method for improving intraoperative image quality 

a. Calculating manual transmitter gain 

b. Acquiring high-quality intraoperative T2-weighted image 

3. Effectiveness of enhancing intraoperative image quality 

a. Clinical images results 

b. Contrast between the lesion and thalamus 

View Digital Presentation:  

Insights into Neural Connections: Neuroimaging and Neuromodulation in Parkinson’s Disease and Essential Tremor | NREE-116 
by Sonoko Oshima, MD, PhD, Visiting Scholar at UCLA Neuroradiology 

Teaching Points: Knowledge on neural connections in movement disorders is crucial to understand mechanisms of clinical manifestations, diagnose the diseases, and maximize benefits and minimize side effects of therapies. The aim of this presentation is to improve radiologists’ role in diagnosing and treating Parkinson’s disease (PD) and essential tremor (ET) by 1) overviewing neural connections between cortex and deep gray matter and 2) discussing neuromodulation therapies for movement disorders, including deep brain stimulation (DBS) and MR-guided focused ultrasound (MRgFUS), from the perspective of neural connections and neuroimaging. 

Table of Contents/Outline: 

1) Neural connections related to Parkinson’s disease and essential tremor 

a. Histological findings 

b. Imaging findings 

2) Neuromodulation therapies: deep brain stimulation (DBS) and MR-guided focused ultrasound (MRgFUS) 

a. Neurophysiological mechanisms 

b. Treatment targets: subthalamic nucleus (STN), globus pallidus interna (GPi), ventral intermediate nucleus (Vim) of the thalamus 

c. Localization of targets by imaging technique: indirect and direct targeting 

d. Postoperative imaging 

View Digital Presentation: