Endoluminal ultrasound applicators for MR‐guided thermal ablation of pancreatic tumors: Preliminary design and evaluation in a porcine pancreas model

Adams, Matthew S.; Salgaonkar, Vasant A.; Plata-Camargo, Juan; Jones, Peter D.; Pascal-Tenorio, Aurea; Chen, Hsin‐Yu; Bouley, Donna M.; Sommer, Graham; Pauly, Kim Butts; Diederich, Chris J.

doi:10.1118/1.4953632

Cited by 9 publications

(20 citation statements)

References 54 publications

(48 reference statements)

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“…The performance in “liver” and “pancreas” can also be generalized as possible in other similar target tissues. Some comparisons can be drawn between the simulations of the proposed applicator assemblies and experimental evaluations of ultrasound applicators developed for endoluminal ablation of liver or pancreatic tissue, as described in literature . Collectively, these applicators had ~12 mm profiles, were placed in the stomach in in vivo porcine studies, and could create thermal lesions of ~1–2 cm maximum penetration into the target liver/pancreatic tissue .…”

Section: Discussionmentioning

confidence: 99%

“…The expanded balloon size, transducer dimensions, and transducer operating frequency all have significant impact on the predicted achievable focal gain (Figs. [6][7][8][9][10]. Increasing the balloon size resulted in greater focal gains, with large increases primarily at greater focal depths.…”

Section: B Focal Performancementioning

confidence: 97%

“…Some comparisons can be drawn between the simulations of the proposed applicator assemblies and experimental evaluations of ultrasound applicators developed for endoluminal ablation of liver or pancreatic tissue, as described in literature. 4,6,7 Collectively, these applicators had~12 mm profiles, were placed in the stomach in in vivo porcine studies, and could create thermal lesions of 1-2 cm maximum penetration into the target liver/pancreatic tissue. 4,6,7 Evidence of thermal injury to the outer stomach wall was reported for each device configuration.…”

Section: C Ablation Performancementioning

confidence: 99%

“…A wide variety of device configurations has been developed for specific endoluminal ultrasound delivery pathways . Endogastric placement of endoluminal devices along the upper GI tract (esophagus, stomach, or small intestines) has been developed to target esophageal, liver, or pancreatic tumors . Prostate tumors or benign prostate hyperplasia has been ablated using ultrasound devices placed in the urethra or in the colorectal tract .…”

Section: Introductionmentioning

confidence: 99%

“…1 Endogastric placement of endoluminal devices along the upper GI tract (esophagus, stomach, or small intestines) has been developed to target esophageal, 3 liver, 4,5 or pancreatic tumors. 6,7 Prostate tumors or benign prostate hyperplasia has been ablated using ultrasound devices placed in the urethra [8][9][10][11] or in the colorectal tract. 12,13 Endovascular devices have been developed for renal denervation 14 and pulmonary vein isolation.…”

Section: Introductionmentioning

confidence: 99%

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Integration of deployable fluid lenses and reflectors with endoluminal therapeutic ultrasound applicators: Preliminary investigations of enhanced penetration depth and focal gain

et al. 2017

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Purpose Catheter-based ultrasound applicators can generate thermal ablation of tissues adjacent to body lumens, but have limited focusing and penetration capabilities due to the small profile of integrated transducers required for the applicator to traverse anatomical passages. This study investigates a design for an endoluminal or laparoscopic ultrasound applicator with deployable acoustic reflector and fluid lens components, which can be expanded after device delivery to increase the effective acoustic aperture and allow for deeper and dynamically adjustable target depths. Acoustic and biothermal theoretical studies, along with benchtop proof-of-concept measurements, were performed to investigate the proposed design. Methods The design schema consists of an array of tubular transducer(s) situated at the end of a catheter assembly, surrounded by an expandable water-filled conical balloon with a secondary reflective compartment that redirects acoustic energy distally through a plano-convex fluid lens. By controlling the lens fluid volume, the convex surface can be altered to adjust the focal length or collapsed for device insertion or removal. Acoustic output of the expanded applicator assembly was modeled using the rectangular radiator method and secondary sources, accounting for reflection and refraction at interfaces. Parametric studies of transducer radius (1–5 mm), height (3–25 mm), frequency (1.5–3 MHz), expanded balloon diameter (10–50 mm), lens focal length (10–100 mm), lens fluid (silicone oil, perfluorocarbon), and tissue attenuation (0–10 Np/m/MHz) on beam distributions and focal gain were performed. A proof-of-concept applicator assembly was fabricated and characterized using hydrophone-based intensity profile measurements. Biothermal simulations of endoluminal ablation in liver and pancreatic tissue were performed for target depths between 2–10 cm. Results Simulations indicate that focal gain and penetration depth scale with the expanded reflector-lens balloon diameter, with greater achievable performance using perfluorocarbon lens fluid. Simulations of a 50 mm balloon OD, 10 mm transducer outer diameter (OD), 1.5 MHz assembly in water resulted in maximum intensity gain of ~170 (focal dimensions: ~12 mm length × 1.4 mm width) at ~5 cm focal depth and focal gains above 100 between 24–84 mm depths. A smaller (10 mm balloon OD, 4 mm transducer OD, 1.5 MHz) configuration produced a maximum gain of 6 at 9 mm depth. Compared to a conventional applicator with a fixed spherically-focused transducer of 12 mm diameter, focal gain was enhanced at depths beyond 20 mm for assembly configurations with balloon diameters ≥ 20 mm. Hydrophone characterizations of the experimental assembly (31 mm reflector/lens diameter, 4.75 mm transducer radius, 1.7 MHz) illustrated focusing at variable depths between 10–70 mm with a maximum gain of ~60 and demonstrated agreement with theoretical simulations. Biothermal simulations (30 s sonication, 75°C maximum) indicate that investigated applicator assembly configurations, at...

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Section: Discussionmentioning

confidence: 99%

Section: B Focal Performancementioning

confidence: 97%

Section: C Ablation Performancementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Integration of deployable fluid lenses and reflectors with endoluminal therapeutic ultrasound applicators: Preliminary investigations of enhanced penetration depth and focal gain

et al. 2017

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An endoluminal cylindrical sectored‐ring ultrasound phased‐array applicator for minimally‐invasive therapeutic ultrasound

2022

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Background The size of catheter‐based ultrasound devices for delivering ultrasound energy to deep‐seated tumors is constrained by the access pathway which limits their therapeutic capabilities. Purpose To devise and investigate a deployable applicator suitable for minimally‐invasive delivery of therapeutic ultrasound, consisting of a 2D cylindrical sectored‐ring ultrasound phased array, integrated within an expandable paraboloid‐shaped balloon‐based reflector. The balloon can be collapsed for compact delivery and expanded close to the target position to mimic a larger‐diameter concentric‐ring sector‐vortex array for enhanced dynamic control of focal depth and volume. Methods Acoustic and biothermal simulations were employed in 3D generalized homogeneous and patient‐specific heterogeneous models, for three‐phased array transducers with 32, 64, and 128 elements, composed of sectored 4, 8, and 16 tubular ring transducers, respectively. The applicator performance was characterized as a function of array configuration, focal depth, phasing modes, and balloon reflector geometry. A 16‐element proof‐of‐concept phased array applicator assembly, consisting of four tubular transducers each divided into four sectors, was fabricated, and characterized with hydrophone measurements along and across the axis, and ablations in ex vivo tissue. Results Simulation results indicated that transducer arrays (1.5 MHz, 9 mm OD × 20 mm long), balloon sizes (41–50 mm expanded diameter, 20–60 mm focal depth), phasing mode (0–4) and sonication duration (30 s) can produce spatially localized acoustic intensity focal patterns (focal length: 3–22 mm, focal width: 0.7–8.7 mm) and ablative thermal lesions (width: 2.7–16 mm, length: 6–46 mm) in pancreatic tissue across a 10–90 mm focal depth range. Patient‐specific studies indicated that 0.1, 0.46, and 1.2 cm3 volume of tumor can be ablated in the body of the pancreas for 120 s sonications using a single axial focus (Mode 0), or four, and eight simultaneous foci in a toroidal pattern (Mode 2 and 4, respectively). Hydrophone measurements demonstrated good agreement with simulation. Experiments in which chicken meat was thermally ablated indicated that volumetric ablation can be produced using single or multiple foci. Conclusions The results of this study demonstrated the feasibility of a novel compact ultrasound applicator design capable of focusing, deep penetration, electronic steering, and volumetric thermal ablation. The proposed applicator can be used for compact endoluminal or laparoscopic delivery of localized ultrasound energy to deep‐seated targets.

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Contactless Thermometry by MRI and MRS: Advanced Methods for Thermotherapy and Biomaterials

Lutz¹,

Bernard²

2020

iScience

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Control of temperature variation is of primordial importance in particular areas of biomedicine. In this context, medical treatments such as hyperthermia and cryotherapy, but also the development and use of hydrogel-based biomaterials are of particular concern. To enable accurate temperature measurement without perturbing or even destroying the biological tissue or material to be monitored, contactless thermometry methods are preferred. Among these, the most suitable are based on magnetic resonance imaging and spectroscopy (MRI, MRS). Here, we address the latest developments in this field as well as their current and anticipated practical applications. We highlight recent progress aimed at rendering MR thermometry faster and more reproducible, versatile and sophisticated, and provide our perspective on how these new techniques broaden the range of applications in medical treatments and biomaterial development by enabling insight into finer details of thermal behavior. Thus, these methods facilitate optimization of clinical and industrial heating and cooling protocols.

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Endoluminal ultrasound applicators for MR‐guided thermal ablation of pancreatic tumors: Preliminary design and evaluation in a porcine pancreas model

Cited by 9 publications

References 54 publications

Integration of deployable fluid lenses and reflectors with endoluminal therapeutic ultrasound applicators: Preliminary investigations of enhanced penetration depth and focal gain

Integration of deployable fluid lenses and reflectors with endoluminal therapeutic ultrasound applicators: Preliminary investigations of enhanced penetration depth and focal gain

An endoluminal cylindrical sectored‐ring ultrasound phased‐array applicator for minimally‐invasive therapeutic ultrasound

Contactless Thermometry by MRI and MRS: Advanced Methods for Thermotherapy and Biomaterials

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