Highly directional transurethral ultrasound applicators with rotational control for MRI-guided prostatic thermal therapy (original) (raw)
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Medical Physics, 2008
The purpose of this study was to explore the feasibility and performance of a multi-sectored tubular array transurethral ultrasound applicator for prostate thermal therapy, with potential to provide dynamic angular and length control of heating under MR guidance without mechanical movement of the applicator. Test configurations were fabricated, incorporating a linear array of two multisectored tubular transducers ͑7.8-8.4 MHz, 3 mm OD, 6 mm length͒, with three 120°independent active sectors per tube. A flexible delivery catheter facilitated water cooling ͑100 ml min −1 ͒ within an expandable urethral balloon ͑35 mm longϫ 10 mm diameter͒. An integrated positioning hub allows for rotating and translating the transducer assembly within the urethral balloon for final targeting prior to therapy delivery. Rotational beam plots indicate ϳ90°−100°acoustic output patterns from each 120°transducer sector, negligible coupling between sectors, and acoustic efficiencies between 41% and 53%. Experiments were performed within in vivo canine prostate ͑n =3͒, with real-time MR temperature monitoring in either the axial or coronal planes to facilitate control of the heating profiles and provide thermal dosimetry for performance assessment. Gross inspection of serial sections of treated prostate, exposed to TTC ͑triphenyl tetrazolium chloride͒ tissue viability stain, allowed for direct assessment of the extent of thermal coagulation. These devices created large contiguous thermal lesions ͑defined by 52°C maximum temperature, t 43 = 240 min thermal dose contours, and TTC tissue sections͒ that extended radially from the applicator toward the border of the prostate ͑ϳ15 mm͒ during a short power application ͑ϳ8−16 W per active sector, 8-15 min͒, with ϳ200°or 360°sector coagulation demonstrated depending upon the activation scheme. Analysis of transient temperature profiles indicated progression of lethal temperature and thermal dose contours initially centered on each sector that coalesced within ϳ5 min to produce uniform and contiguous zones of thermal destruction between sectors, with smooth outer boundaries and continued radial propagation in time. The dimension of the coagulation zone along the applicator was well-defined by positioning and active array length. Although not as precise as rotating planar and curvilinear devices currently under development for MR-guided procedures, advantages of these multi-sectored transurethral applicators include a flexible delivery catheter and that mechanical manipulation of the device using rotational motors is not required during therapy. This multi-sectored tubular array transurethral ultrasound technology has demonstrated potential for relatively fast and reasonably conformal targeting of prostate volumes suitable for the minimally invasive treatment of BPH and cancer under MR guidance, with further development warranted.
Feasibility of a transurethral ultrasound applicator for coagulation in prostate
Ultrasound in medicine & biology, 2004
Transurethral resection of the prostate (TURP) is the surgical method routinely used in clinics to treat benign prostate hyperplasia (BPH). The purpose of this work is to demonstrate the feasibility of a transurethral ultrasound (US) applicator based on a miniature US flat transducer to coagulate prostatic tissues. Rabbit liver was found to comply well with human prostate. A significant fall in Doppler signal amplitude immediately after treatment demonstrated the applicator's ability to achieve haemostasis. The therapeutic depth extended from 6 to 10 mm, depending on conditions of exposure, and the coagulation rate ranged between 51% and 99%. The coagulated zone pinpointed on histological examination could be easily correlated to a permanent hypoechoic zone observed on B-scans of treated zones. This observation is most likely due to temperature-related changes in the acoustic attenuation of liver and, unfortunately, may not be visible in the prostate.
BJU International, 2013
• To characterise the feasibility and safety of a novel transurethral ultrasound (US)-therapy device combined with real-time multi-plane magnetic resonance imaging (MRI)-based temperature monitoring and temperature feedback control, to enable spatiotemporally precise regional ablation of simulated prostate gland lesions in a preclinical canine model. • To correlate ablation volumes measured with intra-procedural cumulative thermal damage estimates, post-procedural MRI, and histopathology. • Three dogs were treated with three targeted ablations each, using a prototype MRI-guided transurethral US-therapy system (Philips Healthcare, Vantaa, Finland). • MRI provided images for treatment planning, guidance, real-time multi-planar thermometry, as well as post-treatment evaluation of efficacy. • After treatment, specimens underwent histopathological analysis to determine the extent of necrosis and cell viability. • Statistical analyses (Pearson's correlation, Student's t-test) were used to evaluate the correlation between ablation volumes measured with intra-procedural cumulative thermal damage estimates, post-procedural MRI, and histopathology. • MRI combined with a transurethral US-therapy device enabled multi-planar temperature monitoring at the target as well as in surrounding tissues, allowing for safe, targeted, and controlled ablations of prescribed lesions.
Medical Physics, 2008
Magnetic resonance imaging ͑MRI͒-guided transurethral ultrasound therapy is a potential minimally invasive treatment for localized prostate cancer offering precise targeting of tissue within the gland, short treatment times, and the capability to quantify the spatial heating pattern delivered during therapy. A significant challenge in MRI-guided ultrasound therapy is the design and construction of MRI-compatible equipment capable of operation in a closed-bore MR imager. We describe a prototype system developed for MRI-guided transurethral ultrasound therapy and characterize the performance of the different components including the heating applicator design, rotational motor, and radio frequency electronics. The ultrasound heating applicator described in this study incorporates a planar transducer and is capable of producing high intensity ultrasound energy in a localized region of tissue. Results demonstrated that the heating applicator exhibits excellent MRI-compatibility, enabling precise MR temperature measurements to be acquired as close as 6 mm from the device. Simultaneous imaging and rotational motion was also possible during treatment using a motor based on piezoelectric actuators. Heating experiments performed in both phantoms and in a canine model with the prototype system verified the capability to perform simultaneous MR imaging and therapy delivery with this system. Real-time control over therapy using MR temperature measurements acquired during heating can be implemented to achieve precise patterns of thermal damage within the prostate gland. The technical feasibility of using the system developed in this study for MRI-guided transurethral ultrasound therapy in a closed-bore MR imager has been demonstrated.
The Journal of urology, 2007
Preclinical experiments were performed in an acute canine model to analyze the spatial pattern of thermal damage generated in the prostate gland following treatment with a prototype magnetic resonance imaging guided transurethral ultrasound heating system. In particular the boundary of tissue coagulation was analyzed to quantify the treatment margin resulting from this technology. A heating device incorporating a planar 20 x 3.5 mm transducer operated at 9.1 MHz was used to deliver ultrasound energy to targeted regions in the prostate gland in 7 animals monitored with magnetic resonance imaging thermometry during heating. The animals were sacrificed approximately 45 minutes after treatment. The thermal damage pattern was evaluated using contrast enhanced magnetic resonance imaging, vital tissue staining, and whole mount hematoxylin and eosin stained histological sections. An image warping technique enabled quantitative comparison of these data. Regions of thermal fixation, coagulati...
Surgical Applications of Energy, 1998
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Treatment of localised prostate cancer with transrectal high intensity focused ultrasound
European journal of ultrasound : official journal of the European Federation of Societies for Ultrasound in Medicine and Biology, 1999
With the advent of PSA dosing, an increasing number of prostate cancers are being detected at a local stage. Since 1989, our group has been developing a research project with the aim of establishing treatment of localised prostate cancer by means of HIFU. The treatment is performed transrectally, using ultrasound imaging guidance only. The quality of HIFU treatment depends on four factors: the intensity of the transmitted pulse, the exposure time, the signal frequency, and the time between two firing bursts. The lesions are created by a thermal effect. Their slightly conical form is due to the absorption of ultrasound by tissue, enhanced by cavitation bubbles. Results obtained since 1993 demonstrate that transrectally administered HIFU treatment achieves local control of localised prostate cancer in 80% of cases, with 70% complete success and 30% partial response. The use of an annular array probe with variable focus and frequency should significantly improve results in the future. ...
Medical Physics, 2018
In this study, the efficacy of transurethral prostate ablation in the presence of silica-shell ultrasound-triggered phase-shift emulsions (sUPEs) doped with MR contrast was evaluated. The influence of sUPEs on MR imaging assessment of the ablation zone was also investigated. Methods: sUPEs were doped with a magnetic resonance (MR) contrast agent, Gd 2 O 3 , to assess ultrasound transition. Injections of saline (sham), saline and sUPEs alone, and saline and sUPEs with Optison microbubbles were performed under guidance of a prototype interventional MRI navigation platform in a healthy canine prostate. Treatment arms were evaluated for differences in lesion size, T 1 contrast, and temperature. In addition, non-perfused areas (NPAs) on dynamic contrast-enhanced (DCE) MRI, 55°C isotherms, and areas of 240 cumulative equivalent minutes at 43°C (CEM 43) dose or greater computed from MR thermometry were measured and correlated with ablated areas indicated by histology. Results: For treatment arms including sUPEs, the computed correlation coefficients between the histological ablation zone and the NPA, 55°C isotherm, and 240 CEM 43 area ranged from 0.96-0.99, 0.98-0.99, and 0.91-0.99, respectively. In the absence of sUPEs, the computed correlation coefficients between the histological ablation zone and the NPA, 55°C isotherm, and 240 CEM 43 area were 0.69, 0.54, and 0.50, respectively. Across all treatment arms, the areas of thermal tissue damage and NPAs were not significantly different (P = 0.47). Areas denoted by 55°C isotherms and 240 CEM 43 dose boundaries were significantly larger than the areas of thermal damage, again for all treatment arms (P = 0.009 and 0.003, respectively). No significant differences in lesion size, T 1 contrast, or temperature were observed between any of the treatment arms (P > 0.0167). Lesions exhibiting thermal fixation on histological analysis were present in six of nine insonations involving sUPE injections and one of five insonations involving saline sham injections. Significantly larger areas (P = 0.002), higher temperatures (P = 0.004), and more frequent ring patterns of restricted diffusion on ex vivo diffusion-weighted imaging (P = 0.005) were apparent in lesions with thermal fixation. Conclusions: T 1 contrast suggesting sUPE transition was not evident in sUPE treatment arms. The use of MR imaging metrics to predict prostate ablation was not diminished by the presence of sUPEs. Lesions generated in the presence of sUPEs exhibited more frequent thermal fixation, though there were no significant changes in the ablation areas when comparing arms with and without sUPEs. Thermal fixation corresponded to some qualitative imaging features.