A multi-element interstitial ultrasound applicator for the thermal therapy of brain tumors

Abstract

Interstitial thermal therapy is a minimally invasive treatment modality that has been used clinically for ablating both primary and secondary brain tumors. Here a multi-element interstitial ultrasound applicator is described that allows for increased spatial control during thermal ablation of tumors as compared to existing clinical devices. The device consists of an array of 56 ultrasound elements operating at 6 MHz, oriented on the seven faces of a 3.2 mm flexible catheter. The device was first characterized using the acoustic holography method to examine the functioning of the array. Then experiments were performed to measure heating in tissue-mimicking gel phantoms and ex vivo tissue samples using magnetic resonance imaging-based thermometry. Experimental measurements were compared with results obtained using numerical simulations. Last, simulations were performed to study the feasibility of using the device for thermal ablation in the brain. Experimental results show that the device can be used to induce a temperature rise of greater than 20 °C in ex vivo tissue samples and numerical simulations further demonstrate that tumors with diameters of greater than 30-mm could potentially be treated.

Active MR‐temperature feedback control of dynamic interstitial ultrasound therapy in brain: In vivo experiments and modeling in native and coagulated tissues

“…Delivery of high-intensity ultrasound energy from minimally invasive applicators enables accurate spatial control of the heat deposition in biological tissues, large treatment volumes, and high treatment rate under appropriate conditions. [35][36][37][38][39][40][41][42][43] Previous in vivo studies carried out in the canine model demonstrated the feasibility of using interstitial high-intensity contact ultrasound (HICU) applicators to generate thermal coagulation of in vivo brain tissue under multi-slice MRTI monitoring to control administration of thermal treatment. 44,45 Thermal ablations up to 4 cm 3 could be achieved within 25 min using an interstitial HICU applicator with 360 • directivity and stationary ultrasound exposures (no mechanical or electronic ultrasound beam scanning).…”

Magnetic resonance–guided interstitial high-intensity focused ultrasound for brain tumor ablation

“…1 In 2014, N’Djin et al conducted a study showing feasibility of spatial heating pattern prediction by using a linear ultrasound transducer in a porcine model. 23 Our lab currently utilizes Acoustic MedSystem, Inc.’s TheraVision Ultrasound Ablation System and ACOUSTx applicators, which contain multiple, cylindrical, MRI-compatible transducers that afford multidirectionality for precise shaping of the ablative field and allow for treatment of large tumors.…”

Catheter-based ultrasound technology for image-guided thermal therapy: Current technology and applications

“…This multi-faced device has an outer diameter of 3.2 mm, an integrated cooling channel, and is deployed within a 4.8 mm diameter sheath for coupling and water flow return [11]. This design, as well as the tubular-element CBUS applicators discussed earlier, can obtain angular and axial control of ablation without mechanical manipulation of the device, which can facilitate MR guidance and simplify treatment delivery.…”

“…Ablative necrosis was observed in 1.5 – 4.0 cm 3 volumes [10, 37], with good agreement between histological findings and lethal thermal dose. Controlled ablation of brain tissue was also demonstrated using multi-faced interstitial applicators in ex vivo experiments [11]. In a recent study aimed at showing initial feasibility, a 6-mm OD rotating endoluminal applicator was interstitially placed within an in vivo porcine brain to perform ablations [43] and evaluate general performance under MR thermometry feedback control, demonstrating a high degree of conformal delivery.…”

“…However CBUS technology has been or is currently under development at academic research institutions and commercial entities. Some examples of commercialized devices or those of significant commercial interest include: transurethral devices that originated in the academic domain are being further developed by companies such as Profound Medical [55] and Phillips [82]; dual-mode US arrays for percutaneous and laparoscopic applications as developed by Guided Therapy Systems [12, 25]; large split-beam HIFU devices developed by Sonacare Medical for laparoscopic ablations [124]; a 7-sided interstitial device reported by Canney et al [11] for brain ablation is of commercial interest to Carthera; HIFU-BC catheters developed by Atrionix/Johnson & Johnson [91] and ProRhythm[95, 96] to treat atrial fibrillation by ablating tissue surrounding the pulmonary vein; and Recor Medical has developed and clinically evaluated CBUS for renal denervation in the treatment of hypertension [98, 99]. Motivating factors in support of development of CBUS technology may include: has the potential to deliver fast and highly conformable volumetric ablation with short procedure times and less resource intensive than many currently used devices; devices of the type which will be in direct contact with the target tissue may be able to follow the 510k route for FDA approval for use and marketing, which requires significantly less time and expense than the alternative Pre-Market Approval (PMA); similar to HIFU, CBUS is amenable to image guidance and monitoring platforms; deployment of CBUS procedures fit closely within existing standards of practice for interventional radiologists and surgeons implementing thermal therapy.…”