Transurethral ultrasound applicators with directional heating patterns for prostate thermal therapy:<i>In vivo</i>evaluation using magnetic resonance thermometry

Diederich, Chris J.; Stafford, R. Jason; Nau, William H.; Burdette, Everette C.; Price, Roger E.; Hazle, John D.

doi:10.1118/1.1639959

Cited by 97 publications

(85 citation statements)

References 42 publications

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“…Together these three in vivo experiments consistently demonstrated these applicators are capable of fast thermal ablation ͑7.5-10 min͒ extending 12-15 mm from the applicator to the prostate boundary, with the ability to shape the angular heating pattern by appropriate sector activation and positioning. The power handling capabilities and penetration depths of these multisectored transurethral applicators are similar to previously reported values for fixed, single-sectored directional tubular transurethral devices, 24,28 but with the significant advantage of dynamic angular control.…”

Section: Discussionsupporting

confidence: 70%

“…22 Directional planar, [23][24][25] curvilinear, 26 and single-sectored tubular 27,28 ultrasound transducers have been incorporated into transurethral heating applicators. The applicators can be rotated and positioned manually or with computer controlled MR compatible motors during treatment to accurately conform heating to a predetermined target region of prostate.…”

Section: Introductionmentioning

confidence: 99%

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Transurethral ultrasound applicators with dynamic multi‐sector control for prostate thermal therapy: In vivo evaluation under MR guidance

et al. 2008

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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.

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Section: Discussionsupporting

confidence: 70%

Section: Introductionmentioning

confidence: 99%

Transurethral ultrasound applicators with dynamic multi‐sector control for prostate thermal therapy: In vivo evaluation under MR guidance

et al. 2008

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“…Similarly, the cooling system makes it possible to make a lesion of approximately the same length as the transducer in the axial direction 13,60 .…”

Section: Cylindrical Transducersmentioning

confidence: 99%

“…Diederich et al 60 therefore proposed dividing the emitting part of the device into longitudinal sectors to control the angle opening (i.e. 40°, 90°, 180° or 270°) at which tissues are heated.…”

Section: Cylindrical Transducersmentioning

confidence: 99%

Interstitial devices for minimally invasive thermal ablation by high-intensity ultrasound

Lafon

Melodelima

Salomir

et al. 2007

International Journal of Hyperthermia

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2Interstitial devices for minimally invasive thermal ablation by high intensity ultrasound AbstractInterstitial ultrasound applicators have been proposed for treating deep-seated tumors that can not be reached with extracorporeal High Intensity Focused Ultrasound. In addition, interstitial ultrasound offers several advantages compared with conventional ablation technology (radiofrequency, microwaves, cryotherapy …) in terms of penetration, speed of coagulation, ability to direct and control the thermal lesion and compatibility with image monitoring. The ultrasound source is brought as close as possible to the target in order to minimize the effects of attenuation and phase aberration along the ultrasound pathway. The present paper is a review of the interstitial applicators that were described during the last decade in the literature. It is presented in three sections. The technical aspects common to all applicators are first described. For example, most described applicators are sideview applicators which active element is water-cooled and operates at rather high frequency (above 3MHz) in order to promote heating. Then the different potential techniques for monitoring treatment administered by the interstitial route are presented and illustrated through a review of imageguided interstitial thermal ablation. Three major techniques of imaging are used for guiding interstitial treatment: MRI, ultrasound and fluoroscopy. The third section will go further in detail on diverse described medical applications.3

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“…4 Magnetic Resonance guided HIFU (MRgHIFU) has become a popular choice in a wide variety of treatment locations because it combines the noninvasiveness of HIFU, with the good soft-tissue contrast and accurate temperature measurements of MRI. Treatment targets of current research interest include breast, [5][6][7] liver, [8][9][10] kidney, 8,[10][11][12] prostate, 13,14 uterine fibroids, 15 and brain. [16][17][18][19] One of the main challenges in MRgHIFU is to achieve temperature measurements with sufficient spatial and temporal resolution over a large enough field of view (FOV) to properly monitor and control the heat deposition.…”

Section: Introductionmentioning

confidence: 99%

Sampling strategies for subsampled segmented EPI PRF thermometry in MR guided high intensity focused ultrasound

et al. 2014

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Purpose: To investigate k-space subsampling strategies to achieve fast, large field-of-view (FOV) temperature monitoring using segmented echo planar imaging (EPI) proton resonance frequency shift thermometry for MR guided high intensity focused ultrasound (MRgHIFU) applications. Methods: Five different k-space sampling approaches were investigated, varying sample spacing (equally vs nonequally spaced within the echo train), sampling density (variable sampling density in zero, one, and two dimensions), and utilizing sequential or centric sampling. Three of the schemes utilized sequential sampling with the sampling density varied in zero, one, and two dimensions, to investigate sampling the k-space center more frequently. Two of the schemes utilized centric sampling to acquire the k-space center with a longer echo time for improved phase measurements, and vary the sampling density in zero and two dimensions, respectively. Phantom experiments and a theoretical point spread function analysis were performed to investigate their performance. Variable density sampling in zero and two dimensions was also implemented in a non-EPI GRE pulse sequence for comparison. All subsampled data were reconstructed with a previously described temporally constrained reconstruction (TCR) algorithm. Results: The accuracy of each sampling strategy in measuring the temperature rise in the HIFU focal spot was measured in terms of the root-mean-square-error (RMSE) compared to fully sampled "truth." For the schemes utilizing sequential sampling, the accuracy was found to improve with the dimensionality of the variable density sampling, giving values of 0.65• C, 0.49 • C, and 0.35• C for density variation in zero, one, and two dimensions, respectively. The schemes utilizing centric sampling were found to underestimate the temperature rise, with RMSE values of 1.05• C and 1.31• C, for variable density sampling in zero and two dimensions, respectively. Similar subsampling schemes with variable density sampling implemented in zero and two dimensions in a non-EPI GRE pulse sequence both resulted in accurate temperature measurements (RMSE of 0.70• C and 0.63 • C, respectively). With sequential sampling in the described EPI implementation, temperature monitoring over a 192 × 144 × 135 mm 3 FOV with a temporal resolution of 3.6 s was achieved, while keeping the RMSE compared to fully sampled "truth" below 0.35• C. Conclusions: When segmented EPI readouts are used in conjunction with k-space subsampling for MR thermometry applications, sampling schemes with sequential sampling, with or without variable density sampling, obtain accurate phase and temperature measurements when using a TCR reconstruction algorithm. Improved temperature measurement accuracy can be achieved with variable density sampling. Centric sampling leads to phase bias, resulting in temperature underestimations.

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Transurethral ultrasound applicators with directional heating patterns for prostate thermal therapy:In vivoevaluation using magnetic resonance thermometry

Cited by 97 publications

References 42 publications

Transurethral ultrasound applicators with dynamic multi‐sector control for prostate thermal therapy: In vivo evaluation under MR guidance

Transurethral ultrasound applicators with dynamic multi‐sector control for prostate thermal therapy: In vivo evaluation under MR guidance

Interstitial devices for minimally invasive thermal ablation by high-intensity ultrasound

Sampling strategies for subsampled segmented EPI PRF thermometry in MR guided high intensity focused ultrasound

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