Increased heating efficiency of hyperthermia using an ultrasound contrast agent: A phantom study

Abstract

It is known that there are large temperature elevations in proximity to air bubbles during US (ultrasound) heating. The existence of tiny air bubbles in the target tissue may enhance the temperature elevation in US hyperthermia. To examine this hypothesis, phantom tissue experiments using an US contrast agent consisting of tiny air bubbles surrounded by a 5% (w/v) human albumin shell (Alb) were performed. As a phantom tissue, a 2 cm cube of beef was used. The phantom tissue was heated with or without the US contrast agent by an US hyperthermia device for 3 min. The heating device was operated at 1.5 MHz with the US intensity of 0.9 W/cm2. Physiological saline solution, iodized oil, and ethanol were used for control experiments. The effect of multiple needle punctures to the beef phantom was also examined. The temperature elevation rate (TER) was defined as the ratio of temperature elevation by heating with Alb or control materials to the temperature elevation by US heating alone. The TER of Alb was 1.7, whereas the TERs of the control materials and of the multiple needle punctures were approximately 1. The administration of Alb significantly increased the temperature in US hyperthermia. In addition, the heating efficiency of Alb was compared to the effect of an increase in the US intensity. Phantom tissue was heated at various US intensities. When the US intensity was increased from 0.9 to 1.8 W/cm2, the temperature elevated by approximately 1.7-fold. Thus, the effect of the administration of Alb was almost equivalent to the effect of increase in US power intensities from 0.9 to 1.8 W/cm2 in the present experimental settings. The results suggest that the US contrast agent can be a potential enhancer in US hyperthermia.

Contrast-agent-enhanced ultrasound thermal ablation

“…In general, increasing the US intensity or the ablation duration will enlarge the lesion, but these methods may also overheat the surrounding normal tissue. Previous research shows that the presence of bubbles near the HIFU focus can result in a larger lesion (Fujishiro et al 1998;Yu et al 2004;Kaneko et al 2005). The administration of contrast microbubbles can effectively reduce the treatment time or the required US intensity (Tran et al 2003).…”

Microbubble Contrast Agent with Focused Ultrasound to Create Brain Lesions at Low Power Levels: MR Imaging and Histologic Study in Rabbits

“…Major drawbacks of using cavitation are the high power requirements and the unpredictability of lesion formation (10,14). If preformed microbubbles (such as ultrasonographic [US] contrast agents) are introduced, they act as cavitation nucleation sites, and the pressure amplitudes required for enhanced heating and lesion creation are greatly reduced (19)(20)(21)(22)(23)(24)(25).…”

Investigation of bubble dynamics and heating during focused ultrasound insonation in tissue-mimicking materials

“…Wu studied the heating due to a kind of contrast agent using a disk model [53]. Fujishiro et al [54] investigated the enhanced tissue damage due to micro-bubble based contrast agents in a beef liver. They reported an increase in the measured temperature rise by a factor of 1.7 in the presence of a micro-bubble based contrast agents, as compared to control samples.…”