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

Abstract

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

Image-guided Tumor Ablation: Standardization of Terminology and Reporting Criteria—A 10-Year Update

“…Both of these terms are separate from the direct application of ultrasound energy through an applicator placed within the target tissue, which should be referred to as interstitial ultrasound ablation. We feel that this revised nomenclature provides a more concise and clear description of different methodologies being studied and more closely aligns several classifications being used in the literature (25,26).…”

“…Now, there are a wide range of applicator types, device modifications, applicator and for intracavitary (and intracardiac) devices (26). Hence, additional nomenclature is required to distinguish between these two groups.…”

Multiple applicator hepatic ablation with interstitial ultrasound devices: Theoretical and experimental investigation

“…Devices suitable for percutaneous ablation (13-14 g) have been developed and successfully evaluated in vivo for application in highly perfused organs such as the liver, [13][14][15] prostate, 16, 17 brain 18 and uterine fibroids. 19 Compared to other needle-based ablation devices, minimally invasive catheter based ultrasound devices have the unique ability to control the spatial energy deposition profile along the length of the applicator, 14,20 as well as across the angular expanse. 16,17 Ultrasound applicators for thermal therapy also offer the potential to be used as an imaging device to determine proper applicator placement as well as to monitor treatment progression.…”

Calibration and measurement issues for therapeutic ultrasound

“…For instance, the Ultracinch (Epicor Medical, Inc., Sunnyvale, California) is a commercially available system which arranges 5-7 small transducers on a belt which is wrapped around the heart to treat atrial fibrillation by ablation of some of the electrical pathways in the cardiac muscle [62]; there are numerous phased array systems under development which permit beam steering or the use of multiple beams; there are radial-firing intravascular and transurethral transducers [63]; and one of the 'holy grails' of HIFU is non-invasive transcranial treatment of brain tumours, often using a nearly hemispherical transducer to maximise the focal gain [64]. The vast majority of these geometries do not lend themselves to measurement by the radiation force technique as only a fraction of the power is travelling in the direction to which the force measuring system is sensitive.…”