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

Abstract

Catheter-based ultrasound (CBUS) is being applied to deliver minimally invasive thermal therapy to solid cancer tumors, benign tissue growth, vascular disease, and tissue remodeling. Compared to other energy modalities used in catheter-based surgical interventions, unique features of ultrasound result in conformable and precise energy delivery with high selectivity, fast treatment times, and larger treatment volumes. Here, a concise review of CBUS technology being currently utilized in animal and clinical studies or being developed for future applications is presented. CBUS devices have been categorized into interstitial, endoluminal and endovascular/cardiac applications. Basic applicator designs, site specific evaluations and possible treatment applications have been discussed in brief. Particular emphasis has been given on ablation studies that incorporate image-guidance for applicator placement, therapy monitoring, feedback control, and post-procedure assessment. Examples of devices included here span the entire spectrum of development cycle from preliminary simulation based design studies to implementation in clinical investigations. The use of CBUS under image guidance has the potential for significantly improving precision and applicability of thermal therapy delivery.

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

“…Endoluminal catheter‐based ultrasound applicators provide a minimally invasive option for delivering localized and spatially precise thermal therapy to tissue targets that are adjacent to body cavities or lumens. Compared to other commonly used energy sources for thermal ablation, such as radiofrequency (RF), laser, or microwave, ultrasound provides a high degree of control over the spatial deposition of energy and heating, and improved penetration for targeting deeper tissues . Extracorporeal high intensity focused ultrasound (HIFU) uses large focused transducer arrays (0.5–1.5 MHz) to deliver ultrasound through the body to target depths of 10–15 cm, but when applied in abdominal and pelvic sites requires a clear acoustic window between the transducer and target site for safe and effective treatment, devoid of gas‐containing tissues (lungs, bowel) or other significant tissue interfaces (e.g., soft tissue‐bone) where off‐target reflection, preferential absorption, and heating can occur .…”

“…Extracorporeal high intensity focused ultrasound (HIFU) uses large focused transducer arrays (0.5–1.5 MHz) to deliver ultrasound through the body to target depths of 10–15 cm, but when applied in abdominal and pelvic sites requires a clear acoustic window between the transducer and target site for safe and effective treatment, devoid of gas‐containing tissues (lungs, bowel) or other significant tissue interfaces (e.g., soft tissue‐bone) where off‐target reflection, preferential absorption, and heating can occur . Catheter‐based ultrasound, while more invasive than external HIFU, can be used to target sites with limited external acoustic access and provides better volumetric energy localization …”

“…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 .…”

Thermal therapy of pancreatic tumours using endoluminal ultrasound: Parametric and patient-specific modelling

“…Significant advantages of this ultrasound-based approach for thermal therapy include the high degree of control over the spatial distribution of energy as compared to other modalities, direct localization of the energy source and therapy adjacent to the target zone, as well as compatibility with diagnostic ultrasound or MR guidance techniques for possible real-time treatment monitoring and feedback control [20,21]. Specific applicator configurations for placement in the upper gastrointestinal (GI) tract have been applied clinically for endoluminal ablation of esophageal and biliary tumors [22,23].…”

Ultrasound: The versatile energy source

“…Although ultrasonically induced thermal ablation by ultrasound is now in clinical use [12,13] there is still much work to be done in optimising treatment delivery and monitoring, both in terms of improving the ultrasound transducers being used [14,15], in overcoming the problems of organ motion [16] and in improving of thermometry and of techniques for imaging tissue effects [17,18].…”