Passive needle guide tracking with radial acquisition and phase-only cross-correlation.

PURPOSE: Acceleration of a passive tracking sequence based on phase-only cross-correlation (POCC) using radial undersampling. METHODS: The phase-only cross-correlation (POCC) algorithm allows passive tracking of interventional instruments in real-time. In a POCC sequence, two cross-sectional images of a needle guide with a positive MR contrast are continuously acquired from which the instrument trajectory is calculated. Conventional Cartesian imaging for tracking is very time consuming; here, a higher temporal resolution is achieved using a highly undersampled radial acquisition together with a modified POCC algorithm that incorporates the point-spread-function. Targeting and needle insertion is performed in two phantom experiments with 16 fiducial targets, each using 4 and 16 radial projections for passive tracking. Additionally, targeting of eight deep lying basivertebral veins in the lumbar spines is performed for in vivo proof-of-application with four radial projections for needle guide tracking. RESULTS: The radially undersampled POCC sequence yielded in the phantom experiments a lateral targeting accuracy of 1.1 ± 0.4 mm and 1.0 ± 0.5 mm for 16 and 4 radial projections, respectively, without any statistically significant difference. In the in vivo application, a mean targeting duration of 62 ± 13 s was measured. CONCLUSION: Radial undersampling can drastically reduce the acquisition time for passive tracking in a POCC sequences for MR-guided needle interventions without compromising the targeting accuracy.

Diagnostic accuracy and safety of percutaneous MRI-guided biopsy of solid renal masses: single-center results after 4.5 years.

OBJECTIVES: To retrospectively evaluate diagnostic accuracy and complications of magnetic resonance imaging (MRI)-guided biopsy of radiologically indeterminate solid renal masses (RM). METHODS: Electronic records of all consecutive patients undergoing MRI-guided biopsy of solid RM (using free-breathing T2-BLADE and BEAT-IRTTT sequences) between April 2014 and October 2018 were reviewed; 101 patients (69 men, 32 women; median age 68 years; range 32-76) were included. Patient and RM characteristics, procedural details/complications, pathologic diagnosis, and clinical management were recorded. Diagnostic accuracy was calculated on an intention-to-diagnose basis. Diagnostic yield was also evaluated. Multi-variable analysis was performed for variables with p < .20, including patient age/sex; RM size/location/contact with vascular pedicle, RENAL score, number and total length of biopsy samples, and biopsy tract embolization, to determine factors associated with diagnostic samples, diagnostic accuracy, and complications. RESULTS: Median RM size was 2.4 cm (range 1-8.4 cm). There were 86 (85%; 95%CI 77-91%) diagnostic and 15 (15%; 95%CI 9-23%) non-diagnostic samples; 6/15 (40%) non-diagnostic biopsies were repeated with 50% malignancy rate. Sensitivity, specificity, positive predictive value, negative predictive value, and diagnostic accuracy were 96% (95%CI 89-99%), 100% (95%CI 77-100%), 100% (95%CI 95-100%), 82% (95%CI 57-96%), and 97% (95%CI 90-99%), respectively. Primary and secondary diagnostic yields were 85% (95%CI 77-91%) and 91% (95%CI 84-96%), respectively. Seven (7%; 95%CI 1-10%) complications were observed. No tested variables were associated with diagnostic samples, diagnostic accuracy, or complications. CONCLUSIONS: MRI-guided biopsy of solid RM is associated with high diagnostic accuracy and low complication rate. The technique might be helpful for inaccessible tumors. KEY POINTS: • MRI-guided biopsy of radiologically indeterminate solid renal masses (RM) appears safe, with a low rate of minor self-limiting hemorrhagic complications. • Diagnostic accuracy and primary/secondary diagnostic yield are high and appear similar to reported estimates for US- and CT-guided RM biopsy. • MRI guidance may be particularly useful for RM with poor conspicuity on US and CT, for relatively inaccessible tumors (e.g., tumors requiring double-oblique steep-angled approaches), and for young patients or those with renal failure.

Long-term MRI-guided vacuum-assisted breast biopsy results of 600 single-center procedures.

OBJECTIVES: The objective of this study is to report on the performance of the MRI-guided VABB in our center and to look at the long-term outcome of biopsies with benign histology over a period of 19 years. METHODS: In a single-center retrospective review study, data of 600 VABB procedures performed between September 1999 and March 2017 were evaluated. We collected patient demographics, histopathological diagnosis at MRI-VABB, and basic lesion characteristics (size, location). Data from the Belgian Cancer Registry was cross-referenced with our database to find out which patients with benign MRI-VABB results developed a malignant lesion over time. RESULTS: These 600 VABB procedures were performed in 558 women with a mean patient age of 51.8 years (range 18-82 years). Our technical success rate was 99.3%. We found 27.67% B5 lesions, 9.82% B3 lesions, and 0.17% B4 lesions. Of 362 benign MRI-guided VABBs, follow-up data was available for a mean follow-up period of 7.6 years (0.8-18.3). Only one (0.3%) biopsy was a false negative lesion after MRI-guided VABB during follow-up. Short-term FU-MRI provided no increase in detection rate. CONCLUSION: The accuracy of MRI-guided VABB is high with a very low false negative rate of 0.3% on long-term follow-up. The value of short-term FU-MRI for every case after MRI-guided VABB may be questioned. KEY POINTS: • MRI-guided vacuum-assisted breast biopsies yield a large portion of clinically relevant lesions (9.82% B3, 0.17% B4, and 27.67% B5 lesions). • The false negative biopsy rate of MRI-guided VABB in this study with a mean follow-up time of 7.6 years was only 0.3%. • Performing a short-term follow-up MRI after a benign MRI-guided VABB concordant to the MRI appearance may be questioned.

The Focused Ultrasound Myoma Outcome Study (FUMOS); a retrospective cohort study on long-term outcomes of MR-HIFU therapy.

OBJECTIVES: Since 2004, uterine fibroids have been treated with MR-HIFU, but there are persevering doubts on long-term efficacy to date. In the Focused Ultrasound Myoma Outcome Study (FUMOS), we evaluated long-term outcomes after MR-HIFU therapy, primarily to assess the reintervention rate. METHODS: Data was retrospectively collected from 123 patients treated with MR-HIFU at our hospital from 2010 to 2017. Follow-up duration and baseline (MRI) characteristics were retrieved from medical records. Treatment failures, adverse events, and the nonperfused volume percentage (NPV%) were determined. Patients received a questionnaire about reinterventions, recovery time, satisfaction, and pregnancy outcomes. Restrictive treatment protocols were compared with unrestrictive (aiming for complete ablation) treatments. Subgroups were analyzed based on the achieved NPV < 50 or ≥ 50%. RESULTS: Treatment failures occurred in 12.1% and the number of adverse events was 13.7%. Implementation of an unrestrictive treatment protocol significantly (p = 0.006) increased the mean NPV% from 37.4% [24.3-53.0] to 57.4% [33.5-76.5]. At 63.5 ± 29.0 months follow-up, the overall reintervention rate was 33.3% (n = 87). All reinterventions were performed within 34 months follow-up, but within 21 months in the unrestrictive group. The reintervention rate significantly (p = 0.002) decreased from 48.8% in the restrictive group (n = 43; follow-up 87.5 ± 7.3 months) to 18.2% in the unrestrictive group (n = 44; follow-up 40.0 ± 22.1 months). The median recovery time was 2.0 [1.0-7.0] days. Treatment satisfaction rate was 72.4% and 4/11 women completed family planning after MR-HIFU. CONCLUSIONS: The unrestrictive treatment protocol significantly increased the NPV%. Unrestrictive MR-HIFU treatments led to acceptable reintervention rates comparable to other reimbursed uterine-sparing treatments, and no reinterventions were reported beyond 21 months follow-up. KEY POINTS: • All reinterventions were performed within 34 months follow-up, but in the unrestrictive treatment protocol group, no reinterventions were reported beyond 21 months follow-up. • The NPV% was negatively associated with the risk of reintervention; thus, operators should aim for complete ablation during MR-guided HIFU therapy of uterine fibroids. • Unrestrictive treatments have led to acceptable reintervention rates after MR-guided HIFU therapy compared to other reimbursed uterine-sparing treatments.

Development and clinical evaluation of a 3-step modified manipulation protocol for MRI-guided high-intensity focused ultrasound of uterine fibroids.

OBJECTIVES: The clinical applicability of magnetic resonance image-guided high-intensity focused ultrasound (MR-HIFU) treatment of uterine fibroids is often limited due to inaccessible fibroids or bowel interference. The aim of this study was to implement a newly developed 3-step modified manipulation protocol and to evaluate its influence on the number of eligible women and treatment failure rate. METHODS: From June 2016 to June 2018, 165 women underwent a screening MRI examination, 67 women of whom were consecutively treated with MR-HIFU at our institution. Group 1 (n = 20) was treated with the BRB manipulation protocol which consisted of sequential applications of urinary bladder filling, rectal filling, and urinary bladder emptying. Group 2 (n = 47) was treated using the 3-step modified manipulation protocol which included (1) the BRB maneuver with adjusted rectal filling by adding psyllium fibers to the solution; (2) Trendelenburg position combined with bowel massage; (3) the manual uterine manipulation (MUM) method for uterine repositioning. A comparison was made between the two manipulation protocols to evaluate differences in safety, the eligibility percentage, and treatment failure rate due to unsuccessful manipulation. RESULTS: After implementing the 3-step modified manipulation protocol, our ineligibility rate due to bowel interference or inaccessible fibroids decreased from 18% (16/88) to 0% (0/77). Our treatment failure rate due to unsuccessful manipulation decreased from 20% (4/20) to 2% (1/47). There were no thermal complications to the bowel or uterus. CONCLUSIONS: Implementation of the 3-step modified manipulation protocol during MR-HIFU therapy of uterine fibroids improved the eligibility percentage and reduced the treatment failure rate. TRIAL REGISTRATION: Registry number NL56182.075.16 KEY POINTS: • A newly developed 3-step modified manipulation protocol was successfully implemented without the occurrence of thermal complication to the bowel or uterus. • The 3-step modified manipulation protocol increased our eligibility percentage for MR-HIFU treatment of uterine fibroids. • The 3-step modified manipulation protocol reduced our treatment failure rate for MR-HIFU treatment of uterine fibroids.

Simultaneous slice excitation for accelerated passive marker tracking via phase-only cross correlation (POCC) in MR-guided needle interventions.

OBJECTIVE: To accelerate a passive tracking sequence based on phase-only cross correlation (POCC) using simultaneous slice excitation. METHODS: For magnetic resonance (MR)-guided biopsy procedures, passive markers have been proposed that can be automatically localized online using a POCC-based tracking sequence. To accelerate the sequence, a phase-offset multiplanar (POMP) excitation technique was implemented to acquire tracking images. In a phantom experiment, the POMP-POCC sequence was tested and compared with the sequential non-accelerated version in terms of duration and accuracy. Further, technical feasibility of the POMP-POCC sequence was tested in a patient undergoing a prostate biopsy. RESULTS: The temporal resolution of the POMP-POCC tracking sequence is accelerated by 33% compared with the sequential approach. In phantom experiments, the POMP-POCC and sequential sequences yielded the same targeting accuracy of 1.6 ± 0.7 mm. Technical proof of concept of the new sequence could be demonstrated in a successful in vivo prostate biopsy. CONCLUSION: POMP-POCC tracking can substantially reduce the duration of localization of passive markers in MR-guided needle interventions without compromising targeting accuracy.

First report of robot-assisted transperineal fusion versus off-target biopsy in patients undergoing repeat prostate biopsy.

PURPOSE: To clarify the value of targeted versus off-target biopsies in men with a suspicion of prostate cancer (PC) and a visible lesion in multi-parametric magnetic resonance imaging (mpMRI) using transperineal robot-assisted biopsy. METHODS: Fifty-five consecutive men with one non-palpable suspicious lesion in mpMRI after negative 12-core transrectal ultrasound-guided biopsy were enrolled in 2014-2015. Lesions were scored using the Prostate Imaging Reporting and Data System. A robot-assisted system was utilized to collect four robot-assisted targeted transperineal biopsy cores (RA-TB) within the lesion using mpMRI-TRUS elastic fusion. Untargeted transperineal 14-core biopsy was performed only outside the lesion (RA-UB). Histological grade was compared in biopsies and available prostatectomy specimens. RESULTS: Overall, 34 of 55 patients (62%) were diagnosed with PC based on biopsy. 85% of cancers were clinically significant PC (csPC) defined as GS ≥ 7. 85% of biopsy-proven cancers were detected with RA-TB alone. RA-UB identified only one additional patient with csPC and lead to upgrading in five biopsy cases (14.7%). Pathological evaluation of 14 prostatectomy specimens showed upgrading in 2 patients (14.3%), while all other patients were correctly classified by RA-TB without need of additional RA-UB. Mean procedure duration was 43 (±6) min, and only minor complications according to Clavien-Dindo were recorded during 30-day follow-up. CONCLUSIONS: This is the first report of transperineal robot-assisted elastic mpMRI-TRUS fusion biopsy. RA-TB of positive MR lesions enabled reliable detection of csPC, while RA-UB in MRI-negative regions is of minor importance.

Assessment of irrigation dynamics in magnetic-resonance guided laser induced thermal therapy (MRgLITT).

BACKGROUND AND OBJECTIVES: Magnetic-Resonance Guided Laser-Induced Thermal Therapy (MRgLITT) is a minimally-invasive ablation procedure for treating intracranial pathology using laser energy delivered through a fiber-optic. Saline irrigation is used to cool the fiber-optic, but factors affecting irrigation efficacy are not well studied, and quantitative information regarding irrigation speed and volume during MRgLITT procedures have not been reported. Here, we aimed to characterize variables affecting irrigation efficacy in MRgLITT. METHODS: We investigated the irrigation setup of the Visualase thermal therapy system during MRgLITT procedures (Visualase Inc., Houston, TX). Using the system's peristaltic pump, irrigation flow rate was quantitated by measuring volume over five one-minute intervals. Pump settings 1-10 were assessed with and without the position-locking, resistance-imparting bone anchor in both single and double-catheter setups. Multiple tightness settings of the bone anchor were tested, and flow rates were analyzed. RESULTS: Rate of flow increased non-linearly with pump setting (F(1,4) = 2168.86; P < 0.001) in both single and double catheter setups. The lowest pump setting had a flow rate of 24 cc/min, while the highest setting was 36 cc/min. The rate of change in flow successively decreased without plateau. Tightness setting of the bone anchor affected flow in a reverse sigmoid pattern, with no impact on rate until after two quarter-turns, which produced a marked decrease in flow up to one-half of the initial rate (F(1,4) = 12818.96; P < 0.001). CONCLUSION: Flow rate through the cooling catheter in MRgLITT follows a non-linear pattern with increasing peristaltic pump speed. This rate is subject to significant changes when the bone anchor is tightened more than two quarter-turns. These findings serve as a foundation for future studies aimed at understanding the effect of irrigation speeds in achieving optimal ablation volumes.

MRI/ultrasound fusion biopsy of the prostate compared to systematic prostate biopsy - Effectiveness and accuracy of a combined approach in daily clinical practice.

PURPOSE: The aim of this study was to compare cancer detection by targeted fusion-guided biopsy with systematic biopsy, and to evaluate the value of combined biopsy, in a daily clinical practice scenario. Furthermore, we aimed to assess the influence of previous biopsies on cancer detection. METHODS: In this retrospective single-centre study, we evaluated 524 cases of combined biopsy of the prostate from October 2015 to December 2018. All men had a clinical suspicion for prostate cancer due to an elevated PSA and/or a suspicious digital rectal examination and underwent a multiparametric MRI of the prostate read by one out of 6 experienced radiologists. In all cases, fusion-guided biopsy of the prostate was consecutively followed by systematic 12-core biopsy in the same session at the same urological department performed by one out of 5 experienced urologists. RESULTS: In 270/524 (51.5%) cases, cancer was found using combined biopsy. Systematic biopsy alone detected cancer in 205/524 (39.1%) and clinically significant cancer in 137/524 (26.1%) cases. Fusion-guided biopsy alone detected 227/524 (43.3%) and clinically significant cancer in 150/524 (28.6%) cases. A histological upgrade of the Gleason score by fusion-guided biopsy was noted in 20/270 (7.4%) of all cancers found and by systematic biopsy in 31/270 (11.5%). Of all positive cases (clinically insignificant and significant cancer), 65/270 (24.1%) were detected only by fusion-guided biopsy, whereas 43/270 (15.9%) were detected only by systematic biopsy. CONCLUSIONS: Fusion-guided biopsy can detect more cases of prostate cancers than systematic biopsy alone, especially clinically significant cancer. However, the combination of both biopsy methods improves the detection rate and can help to identify clinically significant cancer.

Increased MR-guided high intensity focused ultrasound (MR-HIFU) sonication efficiency of uterine fibroids after carbetocin administration.

Purpose: We investigated whether administration of the long-acting uterus stimulant carbetocin increased intra-subject sonication efficiency during Magnetic Resonance image guided High Intensity Focused Ultrasound (MR-HIFU) treatment of uterine fibroids. Method: In this prospective cohort study, thirty women with symptomatic uterine fibroids undergoing MR-HIFU treatment were included between January 2018 and January 2019. Treatment started with three sonications on one side of the uterine fibroid. Subsequently, one ampoule of 1 mL carbetocin (100 µg/mL) was administered intravenously and treatment continued with three sonications on the other side of the uterine fibroid. We compared the intra-subject sonication efficiency, in terms of Energy Efficiency Factor (EEF), thermal dose volume and sonication time to ablate one cm3 of fibroid tissue, before and after carbetocin administration. Adverse events that occurred within 30 min after carbetocin administration were recorded. Results: Sonication efficiency improved after carbetocin administration as indicated by a significant decrease in EEF and sonication time (p = 0.006 and p = 0.001 respectively), and a significant increase in thermal dose volume reached (p = <0.001). Five women (16.7%) experienced temporary tachycardia, one women in combination with headache, within 30 min after carbetocin administration. Conclusion: Administration of the long-acting uterus stimulant carbetocin improved the MR-HIFU treatment intra-subject sonication efficiency in women with symptomatic uterine fibroids.

Systematic review of reproductive outcomes after High Intensity Focused Ultrasound treatment of uterine fibroids.

PURPOSE: Myomectomy is currently the gold standard for the treatment of uterine fibroids in women who desire pregnancy. However, this surgical fibroid removal has a long convalescence. Promising alternatives may be non-invasive High Intensity Focused Ultrasound (HIFU) under either MRI (MR-HIFU) or ultrasound guidance (USgHIFU). In this systematic review, an overview is provided of reproductive outcomes after these two relatively new ablation techniques. METHOD: A systematic literature search was performed to identify studies reporting reproductive outcomes after HIFU treatment of fibroids. Only peer reviewed, full papers were included. Outcomes included pregnancy-, live-birth- miscarriage and caesarian section rate, time to conceive, reported complications, and possible prognostic factors. RESULTS: In total 21 studies were included. Fourteen studies reported 124 pregnancies after MR-HIFU. Two placenta previas and no uterus ruptures were reported. Pregnancy rates were only retrospectively collected and ranged between 7% and 36%. Miscarriage rate in the oldest and largest prospective registry was 39%. After USgHIFU 366 pregnancies were reported with one fetal intrauterine death, six placenta previas and no uterus ruptures. The only prospective study reported a pregnancy rate of 47% and a miscarriage rate of 11%. Possible prognostic factors like age were not available in most studies. CONCLUSIONS: Based on the heterogeneous data currently available, reproductive outcomes after HIFU appear non-inferior to outcomes after the current standard of care. However, a (randomized) controlled trial comparing reproductive outcomes after HIFU and standard care is necessary to provide sufficient evidence on the preferred fibroid treatment for women with a pregnancy wish.

GantryMate: A Modular MR-Compatible Assistance System for MR-Guided Needle Interventions.

Percutaneous minimally invasive interventions are difficult to perform in closed-bore high-field magnetic resonance systems owing to the limited space between magnet and patient. To enable magnetic resonance-guided needle interventions, we combine a small, patient-mounted assistance system with a real-time instrument tracking sequence based on a phase-only cross-correlation algorithm for marker detection. The assistance system uses 2 movable plates to align an external passive marker with the anatomical target structure. The targeting accuracy is measured in phantom experiments, yielding a precision of 1.7 ± 1.0 mm for target depths up to 38 ± 13 mm. In in vivo experiments, the possibility to track and target static and moving structures is demonstrated.

Magnetic resonance-high intensity focused ultrasound (MR-HIFU) therapy of symptomatic uterine fibroids with unrestrictive treatment protocols: A systematic review and meta-analysis.

PURPOSE: Reevaluation of the effectiveness of Magnetic Resonance-High Intensity Focused Ultrasound (MR-HIFU) therapy for uterine fibroids by excluding studies with restrictive treatment protocols that are no longer used. METHODS: The National Guideline Clearinghouse, Cochrane Library, TRIP, MEDLINE, EMBASE and WHO International Clinical Trials Registry Platform (ICTRP) databases were searched from inception until the 22nd of June 2018. Keywords included "MR-HIFU", "MRgFUS", and "Leiomyoma". Only studies about MR-HIFU treatment of uterine fibroids with at least three months of clinical follow-up were evaluated for inclusion. Treatments with ultrasound-guided HIFU devices or protocols not aiming for complete ablation were eliminated. The primary outcome was the improvement in fibroid-related symptoms. Technical outcomes included screening and treatment failures, treatment time, application of bowel-interference mitigation strategies and the Non-Perfused Volume (NPV) percentage. Other secondary outcomes were the quality of life, fibroid shrinkage, safety, re-interventions, reproductive outcomes, and costs. Meta-analysis was performed using a random-effects model (DerSimonian and Laird). RESULTS: A total of 18 articles (1323 treated patients) met the inclusion criteria. All selected studies were case series except for one cross-over trial. Overall, the quality of the evidence was poor to moderate. The mean NPV% directly post-treatment was 68.1%. The use of bowel-interference mitigation strategies may lead to increased NPV%. The mean symptom reduction at 12-months was 59.9% and fibroid shrinkage was 37.7%. The number of adverse events was low (8.7%), stratification showed a difference between HIFU systems. The re-intervention percentage at 3-33.6 months follow-up ranged from 0 to 21%. Longer follow-up was associated with a higher risk at re-interventions. Reproductive outcomes and costs couldn't be analyzed. CONCLUSIONS: Treatment guidelines aiming for complete ablation enhanced the effectiveness of MR-HIFU therapy. However, controlled trials should define the role of MR-HIFU in the management of uterine fibroids.

Passive marker tracking via phase-only cross correlation (POCC) for MR-guided needle interventions: initial in vivo experience.

PURPOSE: In this work, a passive tracking sequence employing a phase-only cross correlation (POCC) algorithm was studied with a focus on the in vivo applicability of the technique. Therefore, MR-guided needle interventions were performed in a phantom and two animal experiments. METHODS: The targeting accuracy was quantified in an agarose phantom with 15 fiducials. For each fiducial, the distance between needle trajectory and target point was measured. In a first animal experiment at 3 T, the prostate of a pig was punctured under POCC guidance. Second, POCC-based tracking was performed during a laser-induced thermal therapy procedure in peripheral porcine muscle tissue at 1.5 T. RESULTS: In the phantom experiment, the 15 fiducials were penetrated with a mean accuracy of 1.5 ± 0.9 mm (mean duration for one puncture about 2 min). In the first animal experiment, the center of the pig's right prostatic lobe was accurately punctured within 15 min. In the second, targeting and insertion of the needle could be performed within 5 min and a thermal lesion was successfully created. CONCLUSION: Our initial experience with the POCC-based tracking sequence indicates that this technique has the potential as an accurate and versatile tool for in vivo MR-guided needle interventions.