Magnetic Resonance Guidance Research Articles

Stereotactic Magnetic Resonance-Guided Daily Adaptive SABR (SMART) for Localised Non-Metastatic Pancreatic Cancer: First Reported Clinical Outcomes From the UK

AimsPrognosis of locally advanced pancreatic cancer (LAPC) remains poor with limited therapeutic options. Radiation therapy in pancreatic cancer has been restricted by the disease's proximity to radiosensitive organs at risk (OAR). However, stereotactic magnetic resonance-guided adaptive radiation therapy (SMART) has demonstrated promise in delivering ablative doses safely. We sought to report clinical outcomes from a UK-based Compassionate Access Programme that provided access to SMART to patients with LAPC. Materials and methodsThis was a registry retrospective study conducted at a single centre with access to SMART. Patients with LAPC were treated with prescription dose of 40 Gy in 5 fractions. The planning objective was that 98% of PTV received ≥95% of the prescribed dose, prioritising duodenal, stomach and bowel UK SABR consortium constraints. Daily online adaptation was performed using magnetic resonance guidance and on-table re-optimisation. 0–3 months and > 3-month post-treatment-related toxicities, local progression-free survival, metastatic-free survival and overall survival were evaluated. Results55 patients were treated with SMART at our institution from 2020 to 2022. Median follow-up from date of diagnosis was 17 months (range 5–37 months). Median age was 69.87% of patients underwent induction chemotherapy. 71% of patients reported 0–1 grade acute toxicity only. No grade >3 acute toxicity was reported. 5 patients (9%) reported a grade 3 toxicity (fatigue, nausea, abdominal pain, duodenal stricture). No grade >3 toxicity after 3 months was reported. 6 (10%) of patients had grade 3 toxicity (fatigue, nausea, abdominal pain, duodenal haemorrhage). Median local PFS post diagnosis was 17 months (95% CI 15.3–18.7). Median OS post diagnosis was 19 months (95% CI 15.9–22.1). One-year local control post SMART was 65%. ConclusionThis is the first UK-reported experience of MR-guided daily adaptive pancreatic SABR. SMART shows promise in delivering ablative doses with acceptable toxicity rates and good clinical outcomes.

Clinical Workflow of Cone Beam Computer Tomography-Based Daily Online Adaptive Radiotherapy with Offline Magnetic Resonance Guidance: The Modular Adaptive Radiotherapy System (MARS).

The Ethos (Varian Medical Systems) radiotherapy device combines semi-automated anatomy detection and plan generation for cone beam computer tomography (CBCT)-based daily online adaptive radiotherapy (oART). However, CBCT offers less soft tissue contrast than magnetic resonance imaging (MRI). This work aims to present the clinical workflow of CBCT-based oART with shuttle-based offline MR guidance. From February to November 2023, 31 patients underwent radiotherapy on the Ethos (Varian, Palo Alto, CA, USA) system with machine learning (ML)-supported daily oART. Moreover, patients received weekly MRI in treatment position, which was utilized for daily plan adaptation, via a shuttle-based system. Initial and adapted treatment plans were generated using the Ethos treatment planning system. Patient clinical data, fractional session times (MRI + shuttle transport + positioning, adaptation, QA, RT delivery) and plan selection were assessed for all fractions in all patients. In total, 737 oART fractions were applied and 118 MRIs for offline MR guidance were acquired. Primary sites of tumors were prostate (n = 16), lung (n = 7), cervix (n = 5), bladder (n = 1) and endometrium (n = 2). The treatment was completed in all patients. The median MRI acquisition time including shuttle transport and positioning to initiation of the Ethos adaptive session was 53.6 min (IQR 46.5-63.4). The median total treatment time without MRI was 30.7 min (IQR 24.7-39.2). Separately, median adaptation, plan QA and RT times were 24.3 min (IQR 18.6-32.2), 0.4 min (IQR 0.3-1,0) and 5.3 min (IQR 4.5-6.7), respectively. The adapted plan was chosen over the scheduled plan in 97.7% of cases. This study describes the first workflow to date of a CBCT-based oART combined with a shuttle-based offline approach for MR guidance. The oART duration times reported resemble the range shown by previous publications for first clinical experiences with the Ethos system.

Acute toxicity outcomes from salvage high-dose-rate brachytherapy for locally recurrent prostate cancer after prior radiotherapy.

Isolated intra-prostatic recurrence of prostate adenocarcinoma after definitive radiotherapy presents a challenging clinical scenario. Salvage options require specialized expertise and pose risks of harm. This study aimed to present the acute toxicity results from using salvage high-dose-rate brachytherapy (sHDR-BT) as treatment in locally recurrent prostate cancer cases. Seventeen consecutive patients treated with sHDR-BT between 2019 and 2022 were evaluated retrospectively. Eligible patients had to have received curative intent prostate radiotherapy previously, and showed evidence of new biochemical failure. Evaluation with American Urological Association (AUA) and Common Terminology Criteria for Adverse Events (CTCAE) symptom assessments were performed for each case. The median (inter-quartile range) age prior to salvage treatment was 68 (66-74) years. The median post-sHDR-BT follow-up time was 20 (13-24) months. At baseline prior to sHDR-BT, 8 (47%) patients had significant lower urinary tract symptoms. The median AUA score prior to sHDR-BT was 7 (3-18). Three (18%) patients reported irregular bowel function and 2 (12%) reported hematochezia prior to sHDR-BT. One-month post-treatment, the median AUA score was 13 (8-21, p = 0.21). Using CTCAE scoring, there were no cases of grade 2+ bowel or rectal toxicity, and no cases of grade 3+ urinary toxicity. Reported grade 2 urinary toxicities included 10 (59%) cases of bladder spasms, 2 (12%) cases of incontinence, 1 (6%) urinary obstruction, and 4 (24%) reports of urinary urgency. All these adverse events were temporary. This study adds to the existing literature by demonstrating that the acute toxicity profile of sHDR-BT is acceptable even without intra-operative magnetic resonance (MR) guidance or image registration. Further study is ongoing to determine long-term efficacy and toxicity of treatment.

CT versus MR guidance for radiofrequency ablation in patients with colorectal liver metastases: a 10-year follow-up favors MR guidance.

To compare the results of CT- vs MR-guided radiofrequency ablation (RFA) of liver metastases (LM) from colorectal cancer after 10years of follow-up in an observational, retrospective, and multicentric study. A total of 238 patients with 496 LM were treated with RFA either with CT (CT group) or magnetic resonance (MR group) guidance. Every ablated LM was assessed and followed up with diagnostic MRI. Technical success, technique efficacy, predictive factors, recurrence rates, and overall survival were assessed. The CT group comprised 143 patients and the MR group 77 patients. Eighteen patients underwent ablation with both modalities. Technical success per patient and per lesion was 88% and 93% for CT and 87% and 89.6% for MR, and technique efficacy was 97.1% and 98.6% for CT and 98.7% and 99.3% for MR respectively. Local recurrence following the first ablation (primary patency) occurred in 20.1% (CT) vs 4.6% (MR) (p < 0.001). Residual liver tumor, size of LM, and advanced N and M stage at initial diagnosis were independent predictors for overall survival in both groups. The median overall survival measured from first RFA treatment was 2.6years. The 1-year, 5-year, and 10-year survival were 85.9%, 25.5%, and 19.1% respectively. The MR group had significantly better local control compared to the CT group. There was no significant difference in patient survival between the two groups. MR-guided radiofrequency ablation of colorectal liver metastases is safe and effective, and offers better local control than CT-guided ablation. • Imaging modality for radiofrequency ablation guidance is an independent predictor of local recurrence in colorectal liver metastases. • MR-guided radiofrequency ablation achieved better local control of liver metastases from colorectal cancer than CT-guided. • The number and size of liver metastases are, among others, independent predictors of survival. Radiofrequency ablation with MR guidance improved clinical outcome but does not affect survival.

Correction of a transcranial acoustic field using a transient ultrasound field visualization technique.

Ultrasound, due to its noninvasive nature, has the potential to enhance or suppress neural activity, making it highly promising for regulating intractable brain disorders. Precise ultrasound stimulation is crucial for improving the efficiency of neural modulation and studying its mechanisms. However, the presence of the skull can cause distortion in the ultrasound field, thereby affecting the accuracy of stimulation. Existing correction methods primarily rely on magnetic resonance guidance and numerical simulation. Due to the large size and high cost, the MR-guided transcranial ultrasound is difficult to be widely applied in small animals. The numerical simulation usually requires further validation and optimization before application, and the most effective method is to visualize the excited ultrasound field. However, the ultrasound field correction methods based on acoustic field visualization are still lacking. Therefore, a shadowgraph-based transient ultrasonic field visualization system is developed, and an ex vivo transcranial ultrasound field correction is performed. By visualizing the ultrasound field with or without a rat skull and then calculating the time difference of each element's ultrasound wavefront, the parameters for ultrasound field correction can be achieved. The experimental results show that this method can improve both the shape and the size of the focal spot, as well as enhance the acoustic pressure at the focus. Overall, the results demonstrate that the ultrasonic field visualization technology can effectively improve the transcranial ultrasound focusing effect and provide a new tool for achieving precise ultrasonic neural modulation.

Comparative study of CT and MR guided microwave ablation in the treatment of para-vascular VX2 liver tumor model in rabbits.

Objective： To analyze the efficacy of microwave ablation (MWA) guided by computed tomography (CT) and 1.5T magnetic resonance (MR) in the treatment of VX2 para-vascular liver tumor model in rabbits. Materials and Methods Sixty para-vascular VX2 liver tumor models in rabbits were randomly divided into CT-guided microwave ablation group (CT group, n=35) and MR-guided microwave ablation group (MR group, n=35). The complete ablation rate, mean operation time, postoperative complication rate and mean survival time were compared between the two groups. Results In the CT group, the rate of complete ablation was 68.6% (24/35), and the mean operation time was 42.1 ± 9.7 minutes. Three cases had ascites and one case had abdominal wall injury. In the MR group, the rate of complete ablation was 94.2% (33/35), and the mean operation time was 53.4 ± 10.9 minutes. One case was complicated with ascites. No serious complications such as pneumothorax, liver abscess, pleural effusion and diaphragm perforation were found in both groups. Between the two groups, the difference in complete ablation rate was statistically significant (P=0.006 ＜ 0.05). A statistically significant difference can also be found in mean operation time (P ＜ 0.01). The follow-up time was 21 days after the operation. As for the postoperative complication rate (11.4% in the CT group and 2.9% in the MR group, P=0.353) and mean survival time (16.9 ± 1.8 days in CT group, 18.3 ± 2.3 days in the MR group, P=0.925), the differences were not statistically significant. Conclusion Compared with CT guidance, although the microwave ablation time under MR guidance was longer, the complete ablation rate under MR guidance was high, which proved that MR guidance was a more effective way of microwave ablation guidance and was worth promoting in the clinic. In this experiment, the postoperative complication rate was lower in the MR group, although the difference was not statistically significant, which may be related to the small sample size, and the subsequent study on the postoperative complication rate can increase the sample content.

Outcomes of Tolerability, Acute Toxicity and Quality of Life from MR-Guided Radiation Therapy (1.5T MR-Linac) for Liver Metastases in the MOMENTUM Study

Stereotactic body radiation therapy (SBRT) offers an important treatment option for metastatic liver tumors. The introduction of magnetic resonance (MR) guided SBRT has paved the way for optimal tumor visualization and daily plan adaptation. The purpose of this study is to review tolerability of MR-guided SBRT of liver metastases and to present early toxicity and quality of life outcomes. All patients with liver metastases who were treated on a 1.5T MR-Linac and enrolled in the MOMENTUM study (NTC04075305) were included. Patients were treated between April 2019 and December 2022 in 5 different institutes across 3 countries. Descriptive statistics were used to present the tolerability of treatment, toxicity (CTCAE v5.0) and quality of life outcomes (QLQ C30 and EQ 5D-5L) at baseline and 3 months after treatment. A total of 127 patients with liver metastases were included in the analysis. There were 64 females and 63 men, with a median age of 66 years (range 31 to 93). The median ECOG-score was 0 (range 0-2). The most common primary origin was colorectal cancer (66%), followed by bronchus and lung cancer (12%), with ocular melanoma, pancreatic and breast cancer being joint third (all 6-7%). Fractionation schedules ranged from 12 - 67.5 Gy in 2 - 12 fractions. The most commonly prescribed fractionation dose was 60 Gy in 3-5 fractions (53% and 13% respectively) and 50 Gy in 5 fractions (11%). Completion data was available for 116 patients. 112 patients (97%) received all fractions. 4 Patients (3%) did not complete treatment due to technical issues and 2 of the 4 receiving no treatment on the MR-Linac. Physician reported toxicity at 3 months was recorded for 82 patients (66%). No grade 4 or 5 toxicities were reported. There were 12 grade 3 toxicities reported in 6 (7%) patients with 5 deemed radiation therapy related (Table 1) and 34 grade 2 toxicities in 21 (26%) patients. We have presented the largest cohort (to our knowledge) of 127 patients treated using 1.5 Tesla MR Guidance for metastatic liver tumors. 97% of treatments were completed successfully with all treatments being well tolerated. Acute grade 3 toxicity was reported in 7% of patients with no grade 4 or 5 toxicities present. These outcomes suggest radiotherapy on the MR-Linac is a safe and promising treatment for patients with liver metastases. Additional prospective follow up is ongoing for late toxicity events and long-term control data. Table 1: Grade ≥3 toxicity at 3 months related to radiation therapy (total No. of patients was 82) There was QLQ-C30 data on 89 patients at baseline and on 62 patients at 3 months. At 3 months the median score was worse for physical functioning, VAS score and pain.

Magnetic Resonance-guided Procedures: Consensus on Rationale, Techniques, and Outcomes

Magnetic resonance (MR) image guidance has demonstrated significant potential in the field of interventional radiology in several applications. This article covers the main points of MR-guided hepatic tumor ablation as a representative of MR-guided procedures. Patient selection and appropriate equipment utilization are essential for successful MR-guided tumor ablation. Intra-procedural planning imaging enables the visualization of the tumor and surrounding anatomical structures in most cases without application of contrast agent, ensuring optimal planning of the applicator tract. MRI enables real-time, multiplanar imaging, thus simultaneous observation of the applicator and target tumor is possible during targeting with adaptable slice angulations in case of challenging tumor positions. Typical ablation zone appearance during therapy monitoring with MRI enables save assessment of the therapy result, resulting in a high primary efficacy rate. Recent advancements in ablation probes have shortened treatment times, while technical strategies address applicator visibility issues. MR-imaging immediately after the procedure is used to rule out complications and to assess technical success. Especially in smaller neoplasms, MRI-guided liver ablation demonstrates positive outcomes in terms of technical success rates, as well as promising survival and recurrence rates. Additionally, percutaneous biopsy under MR guidance offers an alternative to classic guidance modalities, providing high soft tissue contrast and thereby increasing the reliability of lesion detection, particularly in cases involving smaller lesions. Despite these advantages, use of MR-guidance in clinical routine is still limited to few indications and centers, due to by high costs, extended duration, and the need for specialized expertise. In conclusion, MRI-guided interventions could benefit from ongoing advancements in hardware, software and devices. Such progress has the potential to expand diagnostic and treatment options in the field of interventional radiology.

Dosimetric evaluation of iodine-125 brachytherapy for brain tumors using MR guidance combined with a three-dimensional non co-planar template

PURPOSETo investigate the consistency between preoperative and postoperative dosimetry when 125I brachytherapy for brain tumors is performed with magnetic resonance (MR) guidance and a three-dimensional non co-planar template (3DNPT). METHODS AND MATERIALSThirty patients with brain tumors (metastatic or gliomas) underwent radioactive 125I seed implantation. A preoperative treatment plan was determined with MR imaging, and the operation was done under 3DNPT assistance and MR guidance. The dosimetry was verified postoperatively based on postoperative CT–MR fusion images. Postoperative dosimetric parameters and implant quality indices were defined and compared with those in the preoperative treatment plan. Furthermore, a comparison of preoperative and postoperative doses to normal brain tissues and organs at risk was also performed. RESULTSAll mean postoperative dosimetries were calculated. Target coverage parameters D90, D100, %CTV100, %CTV150, and %CTV200 were 143.6 cGy, 76.6 cGy, 88.2%, 63.1%, and 41.4%, respectively. The values of implant quality indices CI, EI, and HI were 0.75, 0.14, and 0.28, respectively. No significant differences between most preoperative and postoperative dosimetric parameters were found (p > 0.05). The differences were also insignificant for organs at risk. Postoperative %CTV150 and %CTV200 were higher than the preoperative, whereas postoperative HI was significantly lower than in the treatment plan. CONCLUSIONSMagnetic resonance guidance combined with 3DNPT allows accurate positioning and direction in 125I brachytherapy for brain tumors. However, seed distribution and dose homogeneity require further improvement.

Advances in Radiation Oncology for Pancreatic Cancer: An Updated Review

This review aims to summarize the recent advances in radiation oncology for pancreatic cancer. A systematic search of the MEDLINE/PubMed database and Clinicaltrials.gov was performed, focusing on studies published within the last 10 years. Our search queried "locally advanced pancreatic cancer [AND] stereotactic body radiation therapy (SBRT) [OR] hypofractionation [OR] magnetic resonance guidance radiation therapy (MRgRT) [OR] proton" and "borderline resectable pancreatic cancer [AND] neoadjuvant radiation" and was limited only to prospective and retrospective studies and metanalyses. For locally advanced pancreatic cancers (LAPC), retrospective evidence supports the notion of radiation dose escalation to improve overall survival (OS). Novel methods for increasing the dose to high risk areas while avoiding dose to organs at risk (OARs) include SBRT or ablative hypofractionation using a simultaneous integrated boost (SIB) technique, MRgRT, or charged particle therapy. The use of molecularly targeted agents with radiation to improve radiosensitization has also shown promise in several prospective studies. For resectable and borderline resectable pancreatic cancers (RPC and BRPC), several randomized trials are currently underway to study whether current neoadjuvant regimens using radiation may be improved with the use of the multi-drug regimen FOLFIRINOX or immune checkpoint inhibitors.

Adaptive magnetic resonance image guided radiation for intact localized prostate cancer how to optimally test a rapidly emerging technology.

IntroductionProstate cancer is a common malignancy for which radiation therapy (RT) provides an excellent management option with high rates of control and low toxicity. Historically RT has been given with CT based image guidance. Recently, magnetic resonance (MR) imaging capabilities have been successfully integrated with RT delivery platforms, presenting an appealing, yet complex, expensive, and time-consuming method of adapting and guiding RT. The precise benefits of MR guidance for localized prostate cancer are unclear. We sought to summarize optimal strategies to test the benefits of MR guidance specifically in localized prostate cancer.MethodsA group of radiation oncologists, physicists, and statisticians were identified to collectively address this topic. Participants had a history of treating prostate cancer patients with the two commercially available MRI-guided RT devices. Participants also had a clinical focus on randomized trials in localized prostate cancer. The goal was to review both ongoing trials and present a conceptual focus on MRI-guided RT specifically in the definitive treatment of prostate cancer, along with developing and proposing novel trials for future consideration. Trial hypotheses, endpoints, and areas for improvement in localized prostate cancer that specifically leverage MR guided technology are presented.ResultsMultiple prospective trials were found that explored the potential of adaptive MRI-guided radiotherapy in the definitive treatment of prostate cancer. Different primary areas of improvement that MR guidance may offer in prostate cancer were summarized. Eight clinical trial design strategies are presented that summarize options for clinical trials testing the potential benefits of MRI-guided RT.ConclusionsThe number and scope of trials evaluating MRI-guided RT for localized prostate cancer is limited. Yet multiple promising opportunities to test this technology and potentially improve outcomes for men with prostate cancer undergoing definitive RT exist. Attention, in the form of multi-institutional randomized trials, is needed.

2450-MHz microwave ablation of liver metastases under 3.0 T wide-bore magnetic resonance guidance: a pilot study

To investigate the feasibility and effectiveness of 3.0 T wide-bore magnetic resonance (MR)-guided microwave ablation (MA) of liver metastases (LM). From October 2018 to May 2020, 39 patients with 63 LM were treated with 3.0 T wide-bore MR-guided 2450-MHz MA therapy. The procedure parameters, technical success, complications, biochemical index changes, local tumor response, local tumor progression (LTP), 12-month disease-free survival (DFS) and 12-month overall survival (OS) were recorded and analyzed. The mean tumor maximum diameter and total procedure time were 3.0 cm and 55.2 min, respectively. Technical success was 100%, but 5 cases (12.8%) had grade-1 complications. Alanine transaminase, aspartate transaminase and total bilirubin showed a slight transient increase on day 3 (P < 0.05) and returned to normal by day 30 (P > 0.05). The complete ablation rates for ≤ 2.5 and > 2.5 cm lesions were 100% and 92.5%, respectively. During the median follow-up of 12.0 months, the LTP rate was 4.8% (3/63), and the 12-month DFS and OS rates were 61.3% and 92.2%, respectively. 3.0 T wide-bore MR-guided MA for LM is a safe and effective approach, especially for small LM.

A Prospective Study of Stereotactic Body Radiotherapy (SBRT) with Concomitant Whole-Pelvic Radiotherapy (WPRT) for High-Risk Localized Prostate Cancer Patients Using 1.5 Tesla Magnetic Resonance Guidance: The Preliminary Clinical Outcome.

Simple SummaryMagnetic resonance (MR)-guided stereotactic body radiotherapy (MRgSBRT) with concomitant whole-pelvic nodal radiotherapy (WPRT) represents a novel radiotherapy paradigm for high-risk prostate cancer (HR-PC), potentially improving online image guidance and clinical outcomes. This is the first prospective study aims to report the preliminary clinical experiences and treatment outcome of 1.5 Tesla adaptive MRgSBRT with concomitant WPRT in HR-PC patients (72.5 ± 6.8 years). Forty-two consecutive localized HR-PC patients were treated by online adaptive MRgSBRT (8 Gy(prostate)/5 Gy(WPRT) × 5 fractions) combined with androgen deprivation therapy (ADT) and followed up (median: 251 days, range: 20–609 days). The maximum cumulative acute gastrointestinal (GI)/ genitourinary (GU) grade 1 and 2 toxicity rates were 19.0%/81.0% and 2.4%/7.1%, respectively. The subacute (>30 days) GI/GU grade 1 and 2 toxicity rates were 21.4%/64.3% and 2.4%/2.4%, respectively. No grade 3 toxicities were reported. Patient-reported quality of life (QoL) showed insignificant changes in urinary, bowel, sexual, and hormonal domain scores during the follow-up period. All patients had early post-MRgSBRT biochemical responses, while biochemical recurrence (prostate-specific antigen nadir + 2 ng/mL) occurred in one patient at month 18. The early results suggested favorable treatment-related toxicities and encouraging patient-reported QoLs, but long-term follow-up is still needed. Background: Conventionally fractionated whole-pelvic nodal radiotherapy (WPRT) improves clinical outcome compared to prostate-only RT in high-risk prostate cancer (HR-PC). MR-guided stereotactic body radiotherapy (MRgSBRT) with concomitant WPRT represents a novel radiotherapy (RT) paradigm for HR-PC, potentially improving online image guidance and clinical outcomes. This study aims to report the preliminary clinical experiences and treatment outcome of 1.5 Tesla adaptive MRgSBRT with concomitant WPRT in HR-PC patients. Materials and methods: Forty-two consecutive HR-PC patients (72.5 ± 6.8 years) were prospectively enrolled, treated by online adaptive MRgSBRT (8 Gy(prostate)/5 Gy(WPRT) × 5 fractions) combined with androgen deprivation therapy (ADT) and followed up (median: 251 days, range: 20–609 days). Clinical outcomes were measured by gastrointestinal (GI) and genitourinary (GU) toxicities according to the Common Terminology Criteria for Adverse Events (CTCAE) Scale v. 5.0, patient-reported quality of life (QoL) with EPIC (Expanded Prostate Cancer Index Composite) questionnaire, and prostate-specific antigen (PSA) responses. Results: All MRgSBRT fractions achieved planning objectives and dose specifications of the targets and organs at risk, and they were successfully delivered. The maximum cumulative acute GI/GU grade 1 and 2 toxicity rates were 19.0%/81.0% and 2.4%/7.1%, respectively. The subacute (>30 days) GI/GU grade 1 and 2 toxicity rates were 21.4%/64.3% and 2.4%/2.4%, respectively. No grade 3 toxicities were reported. QoL showed insignificant changes in urinary, bowel, sexual, and hormonal domain scores during the follow-up period. All patients had early post-MRgSBRT biochemical responses, while biochemical recurrence (PSA nadir + 2 ng/mL) occurred in one patient at month 18. Conclusions: To our knowledge, this is the first prospective study that showed the clinical outcomes of MRgSBRT with concomitant WPRT in HR-PC patients. The early results suggested favorable treatment-related toxicities and encouraging patient-reported QoLs, but long-term follow-up is needed to confirm our early results.

A Novel Concept of a Phased-Array HIFU Transducer Optimized for MR-Guided Hepatic Ablation: Embodiment and First In-Vivo Studies.

PurposeHigh-intensity focused ultrasound (HIFU) is challenging in the liver due to the respiratory motion and risks of near-/far-field burns, particularly on the ribs. We implemented a novel design of a HIFU phased-array transducer, dedicated to transcostal hepatic thermo-ablation. Due to its large acoustic window and strong focusing, the transducer should perform safely for this application.Material and MethodsThe new HIFU transducer is composed of 256 elements distributed on 5 concentric segments of a specific radius (either 100, 111, or 125 mm). It has been optimally shaped to fit the abdominal wall. The shape and size of the acoustic elements were optimized for the largest emitting surface and the lowest symmetry. Calibration tests have been conducted on tissue-mimicking gels under 3-T magnetic resonance (MR) guidance. In-vivo MR-guided HIFU treatment was conducted in two pigs, aiming to create thermal ablation deep in the liver without significant side effects. Imaging follow-up was performed at D0 and D7. Sacrifice and post-mortem macroscopic examination occurred at D7, with the ablated tissue being fixed for pathology.ResultsThe device showed −3-dB focusing capacities in a volume of 27 × 46 × 50 mm3 as compared with the numerical simulation volume of 18 × 48 × 60 mm3. The shape of the focal area was in millimeter-range agreement with the numerical simulations. No interference was detected between the HIFU sonication and the MR acquisition. In vivo, the temperature elevation in perivascular liver parenchyma reached 28°C above physiological temperature, within one breath-hold. The lesion was visible on Gd contrast-enhanced MRI sequences and post-mortem examination. The non-perfused volume was found in pig #1 and pig #2 of 8/11, 6/8, and 7/7 mm along the LR, AP, and HF directions, respectively. No rib burns or other near-field side effects were visually observed on post-mortem gross examination. High-resolution contrast-enhanced 3D MRI indicated a minor lesion on the sternum.ConclusionThe performance of this new HIFU transducer has been demonstrated in vitro and in vivo. The transducer meets the requirement to perform thermal lesions in deep tissues, without the need for rib-sparing means.

Feasibility and efficacy of superconducting open-configuration magnetic resonance-guided microwave ablation of malignant liver tumors with real-time imaging sequences.

To evaluate the safety and effectiveness of open superconducting magnetic resonance (MR)-guided microwave ablation of liver tumors and explore feasibility of real-time imaging sequence-guided needle insertion technique. Medical records of December 2019-May 2021 of microwave ablations of liver tumors under MR guidance in XX University Cancer Center were reviewed. Real-time imaging-guided puncture technique refers to real-time insertion and adjusting the position of a microwave applicator under a fast imaging sequence. The safety and efficacy of the procedure among the enrolled patients were assessed. Twenty-six patients underwent 27 procedures, with 30 lesions ablated (long diameter: 1.51 ± 0.81 cm, short diameter: 1.30 ± 0.61 cm). There were 20 cases of primary liver cancer and 10 of liver metastases. All lesions were identified by MR imaging (MRI), and all procedures were successfully performed using the finger positioning method for puncture sites. Five patients underwent real-time guided needle insertion techniques. Further, the microwave applicators reached the target position at once, and the entire insertion process was completed within 3 min. The completion rate of the real-time guided needle insertion technology was 100%, and 25 (92.6%) patients had minor complications. No severe complications were observed, and the technical success rate of 30 MRI-guided lesions was 100%. Finally, the complete ablation rate of the MRI-guided ablation after the first procedure was 93.1%. Open MR-guided microwave ablation is safe and effective in treating liver tumors. Furthermore, real-time imaging sequence-guided puncture technique under MRI is feasible and efficient.

Asleep deep brain stimulation with intraoperative magnetic resonance guidance: a single-institution experience.

Deep brain stimulation (DBS) is traditionally performed on an awake patient with intraoperative recordings and test stimulation. DBS performed under general anesthesia with intraoperative MRI (iMRI) has demonstrated high target accuracy, reduced operative time, direct confirmation of target placement, and the ability to place electrodes without cessation of medications. The authors describe their initial experience with using iMRI to perform asleep DBS and discuss the procedural and radiological outcomes of this procedure. All DBS electrodes were implanted under general anesthesia by a single surgeon by using a neuronavigation system with 3-T iMRI guidance. Clinical outcomes, operative duration, complications, and accuracy were retrospectively analyzed. In total, 103 patients treated from 2015 to 2019 were included, and all but 1 patient underwent bilateral implantation. Indications included Parkinson's disease (PD) (65% of patients), essential tremor (ET) (29%), dystonia (5%), and refractory epilepsy (1%). Targets included the globus pallidus pars internus (12.62% of patients), subthalamic nucleus (56.31%), ventral intermedius nucleus of the thalamus (30%), and anterior nucleus of the thalamus (1%). Technically accurate lead placement (radial error ≤ 1 mm) was obtained for 98% of leads, with a mean (95% CI) radial error of 0.50 (0.46-0.54) mm; all leads were placed with a single pass. Predicted radial error was an excellent predictor of real radial error, underestimating real error by only a mean (95% CI) of 0.16 (0.12-0.20) mm. Accuracy remained high irrespective of surgeon experience, but procedure time decreased significantly with increasing institutional and surgeon experience (p = 0.007), with a mean procedure duration of 3.65 hours. Complications included 1 case of intracranial hemorrhage (asymptomatic) and 1 case of venous infarction (symptomatic), and 2 patients had infection at the internal pulse generator site. The mean ± SD voltage was 2.92 ± 0.83 V bilaterally at 1-year follow-up. Analysis of long-term clinical efficacy demonstrated consistent postoperative improvement in clinical symptoms, as well as decreased drug doses across all indications and follow-up time points, including mean decrease in levodopa-equivalent daily dose by 53.57% (p < 0.0001) in PD patients and mean decrease in primidone dose by 61.33% (p < 0.032) in ET patients at 1-year follow-up. A total of 205 leads were placed in 103 patients by a single surgeon under iMRI guidance with few operative complications. Operative time trended downward with increasing institutional experience, and technical accuracy of radiographic lead placement was consistently high. Asleep DBS implantation with iMRI appears to be a safe and effective alternative to standard awake procedures.

Abstract 13731: Randomized Trial of CMR Guidance for Cardiac Resynchronization Therapy: Findings in Nonischemic Cardiomyopathy From an Interim Analysis

Introduction: Cardiac resynchronization therapy (CRT) response rates in unselected cohorts are suboptimal. Cardiac magnetic resonance (CMR) provides high-quality imaging of strain and scar, and post-CRT CMR offers reliable assessment of left ventricular (LV) reverse remodeling. Hypothesis: Cardiac magnetic resonance (CMR) guidance for CRT will increase CRT response rates, particularly in nonischemic cardiomyopathy (NICM). Methods: Patients were randomized 1:1 to standard CRT or CMR guidance for CRT using circumferential strain from Displacement Encoding with Stimulated Echoes (DENSE) and scar (late gadolinium enhancement [LGE]) by CMR. The primary endpoint is the percent change in LV end-systolic volume (LVESV) calculated from CMRs before CRT and 6 months after CRT. A pre-specified interim analysis by cardiomyopathy type was performed after completion of enrollment of 45 of the projected 90 patients needed for adequate power. Results: Of 45 patients enrolled (age 65.9 +/- 10.3 years, 29% female), two patients did not undergo a CRT procedure, and the LV lead could not be placed in one patient. Of the remaining 42 patients, 26/42 had NICM and 21/42 were randomized to CMR guidance. In a linear regression model for the primary endpoint adjusted for baseline QRS duration (p=0.04) and cardiomyopathy type (p=0.01), a favorable trend for the intervention on response was noted (p=0.06). Box plots demonstrate a significant difference in the primary endpoint among NICM patients (p=0.03) and a favorable trend for QRS shortening (0.07) in NICM patients (Figure). In all patients (including ICM patients), the overall p-value for the intervention relative to the primary endpoint was 0.08. Conclusion: An interim analysis in CRT patients with NICM demonstrated a favorable effect of CMR guidance on LV reverse remodeling after CRT, as assessed with post-CRT CMRs. Enrollment is continuing to evaluate the effect of the intervention on the entire cohort and other endpoints.

A Prospective Clinical Trial Evaluating Stereotactic Magnetic Resonance Guided Adaptive Radiation Therapy (SMART) for Pancreatic Cancer

The use of ablative stereotactic body radiation therapy (SBRT) in pancreatic cancer is constrained by nearby radiation-sensitive organs. Magnetic resonance (MR)-guided adaptive radiation therapy (SMART) is an innovation that offers superior anatomical imaging during treatment allowing for daily plan adaptation based on the volumetric images prior to each treatment. We report results of a prospective phase 1 trial (NCT04115254) assessing feasibility of SMART and describe early outcomes of patients with pancreatic cancer. Secondary objectives included analysis of 90-day toxicity, local control, and patient-reported outcomes (PROMs) in patients undergoing SMART.In this prospective IRB approved study, patient eligibility criteria included: biopsy-proven diagnosis of pancreatic cancer, eligibility for SBRT, and ability to undergo and tolerate MRI imaging. Patients were ineligible if they had prior abdominal radiation, active ulcerative disease, or tumor invasion of the stomach, duodenum or bowel on endoscopy. Patients were monitored for acute and late grade ≥ 3 toxicity. PROMs included the FACT-HEP and PROMIS Physical and Mental Health batteries and were completed at baseline and during follow-up. Feasibility was defined as 1) enrolling patients and delivering SMART on the MR-Linac; 2) assessing tumor using MR guidance before, during and after MR-guided treatment and 3) generating adaptive plans.All 10 patients successfully completed SMART, receiving 40 Gy in 5 fractions with 48 of 50 fractions requiring adaptation to meet target or critical organ-at-risk metrics. The median follow up was 10.49 months (range 5.00 - 11.38). The median age was 72 (range 55 - 89), 60% were female, and 80% were white. Disease stages included 30% T1-T2, 10% T3, and 60% T4 disease, as well as 30% N0, 60% N1, 10% N2 disease, and 80% M0, 10% MX, and 10% M1. 90% of patients had other medical comorbidities. ECOG performance status was 0-1 in 90% of patients. There were no acute or late grade ≥ 3 treatment related toxicities. There were no local recurrences. The 6-month survival rate was 90% (95% CI 47.3-98.5) with two deaths due to progressive disease. The median change between baseline and follow-up within 6 months of treatment was -0.5 on FACT-HEP, -2.5 on PROMIS Physical, and -4.7 on PROMIS Mental Health (table 1).We successfully demonstrated the feasibility and safety of SMART with daily adaptation in patients with pancreatic cancer. PROMs highlight that patients tolerated treatment well with minimal toxicity. Further investigation in dose escalation in pancreatic cancer is warranted.

Deconvolution-based partial volume correction of PET images with parallel level set regularization

The partial volume effect (PVE), caused by the limited spatial resolution of positron emission tomography (PET), degrades images both qualitatively and quantitatively. Anatomical information provided by magnetic resonance (MR) images has the potential to play an important role in partial volume correction (PVC) methods. Post-reconstruction MR-guided PVC methods typically use segmented MR tissue maps, and further, assume that PET activity distribution is uniform in each region, imposing considerable constraints through anatomical guidance. In this work, we present a post-reconstruction PVC method based on deconvolution with parallel level set (PLS) regularization. We frame the problem as an iterative deconvolution task with PLS regularization that incorporates anatomical information without requiring MR segmentation or assuming uniformity of PET distributions within regions. An efficient algorithm for non-smooth optimization of the objective function (invoking split Bregman framework) is developed so that the proposed method can be feasibly applied to 3D images and produces sharper images compared to PLS method with smooth optimization. The proposed method was evaluated together with several other PVC methods using both realistic simulation experiments based on the BrainWeb phantom as well as in vivo human data. Our proposed method showed enhanced quantitative performance when realistic MR guidance was provided. Further, the proposed method is able to reduce image noise while preserving structure details on in vivo human data, and shows the potential to better differentiate amyloid positive and amyloid negative scans. Overall, our results demonstrate promise to provide superior performance in clinical imaging scenarios.

Improving image quality in transcranial magnetic resonance guided focused ultrasound using a conductive screen

Transcranial Magnetic Resonance guided Focused Ultrasound (TcMRgFUS) has been proven to be an effective treatment for some neurological disorders such as essential and Parkinson's tremor. However, magnetic resonance guidance at 3 Tesla (3T) frequencies and using the large hemispherical transducers required for TcMRgFUS results in artifactual low-signal bands that pass through key regions of the brain. The purpose of this work was to investigate the use of a circular conductive Radio Frequency (RF) screen, that is bent to have a 12 cm radius in one direction and positioned near the top or back of the head, to reduce or remove these artifactual low-signal bands in TcMRgFUS.The impact of using an RF screen to remove these low signal bands was studied in both imaging experiments and electromagnetic simulations. Hydrophone measurements of the acoustic transparency of the bronze 2 mm diameter square mesh screen used in the imaging studies were compared with temperature measurements with and without the screen in heating studies in the TcMRgFUS system.The imaging and simulation studies both show that for the different screen configurations studied in this work, RF screen removes the low-signal bands and increases both homogeneity and signal-to-noise ratio (SNR) throughout the region of the brain. Hydrophone and heating studies indicate that even a 2 mm wire mesh provides minimal attenuation to the ultrasound beam. Simulation results also suggest that a 1 cm mesh will provide adequate artifact suppression with even less ultrasound attenuation.An RF screen that disrupts the natural waveguide nature of the transducer in the 3T MR environment can change the electromagnetic field profile to reduce unwanted artifacts and provide an imaging region which has more homogeneity and higher SNR throughout the brain.