The effects of artery occlusion on temperature homogeneity during hyperthermia in rabbit kidneys in vivo

Focused Ultrasound for Dermal Applications

Focused ultrasound (FUS) is emerging as one of the most promising, non-invasive treatment techniques. The advancement of transducer technology has paved the way for dermatological applications. A comprehensive review is presented for healthcare practitioners and researchers, summarizing the effect of various operational parameters on the injury zone produced by ultrasound beams for various dermatological applications, which include skin tightening, fat reduction, hyperpigmentation and cancer treatment. In this article, we aim to highlight the efficient operational parameters of FUS to enhance pain relief during surgery and its affordability for skin treatment. Finally, a prospective future technique for efficient FUS is discussed.

Ultrasound-guided therapeutic focused ultrasound: current status and future directions

This paper reviews ultrasound imaging methods for the guidance of therapeutic focused ultrasound (USgFUS), with emphasis on real-time preclinical methods. Guidance is interpreted in the broadest sense to include pretreatment planning, siting of the FUS focus, real-time monitoring of FUS-tissue interactions, and real-time control of exposure and damage assessment. The paper begins with an overview and brief historical background of the early methods used for monitoring FUS-tissue interactions. Current imaging methods are described, and discussed in terms of sensitivity and specificity of the localisation of the FUS effects in both therapeutic and sub-therapeutic modes. Thermal and non-thermal effects are considered. These include cavitation-enhanced heating, tissue water boiling and cavitation. Where appropriate, USgFUS methods are compared with similar methods implemented using other guidance modalities, e.g. magnetic resonance imaging. Conclusions are drawn regarding the clinical potential of the various guidance methods, and the feasibility and current status of real-time implementation.

Arterial embolization hyperthermia in porcine renal tissue

BACKGROUND

Arterial embolization hyperthermia (AEH) consists of arterially embolizing tumors with ferromagnetic particles that generate hysteretic heating on exposure to an alternating magnetic field. It was the objective of this study to evaluate AEH using the kidney of a large animal as a tumor model.

METHODS

Between 50 and 400 mg of ferromagnetic microspheres (32 microm in diameter) was arterially infused into the kidneys of three pigs. Temperature probes were inserted into renal tissue, skin, and subcutaneous fat. Each subject was then exposed to an alternating magnetic field for 5 min, while under a general anesthetic. A femoral artery catheter was used to monitor the cardiac pulse. Three days after treatment the renal tissue was chemically analyzed for iron content, which was then correlated with tissue heating rates.

RESULTS

There was a linear relationship between heating rate and iron concentration (N = 18, correlation = 0.72, P < 0.001) that suggested tissue iron concentrations in the range of 1.55 to 4.05 mg/g would yield tissue heating rates of 0.5 to 1.0 degrees C/min. No temperature increases were detected in control renal tissue (N = 6). The median increase in skin temperature after 5 min of heating was 0.8 degrees C (N = 6, min = 0.7 degrees C, max = 1.3 degrees C), and that in subcutaneous fat was 1.1 degrees C (N = 6, min = 0.8 degrees C, max = 1.2 degrees C). There was no detectable stimulation of cardiac or skeletal muscle or peripheral nerves during treatment. All subjects had uneventful 3-day posttreatment survivals.

CONCLUSION

This study has shown that AEH can target deep-seated, vascularized tissue in a large animal with therapeutic temperatures (> 42 degrees C), and that the treatment is safe and well tolerated. Further assessment of treatment schedules should allow for a human trial in the near future.

Experimental examination of a targeted hyperthermia system using inductively heated ferromagnetic microspheres in rabbit kidney

It is known that significant heating can be generated by magnetic hysteresis effects in small ferromagnetic particles exposed to a rapidly alternating magnetic field. If such particles can be made to infiltrate the vascular bed surrounding a tumour by intravascular infusion then it may be possible to generate sufficient heating to destroy the tumour by hyperthermia. One of the constraints on such a technique is the limited amount of magnetic material that can be delivered to a tumour via the intravascular route and the consequent heating that can be induced by this material. Here, we report on a series of experiments in which doses of microspheres containing different amounts of ferromagnetic material were infused into rabbit kidneys via the renal artery with the aim of testing whether adequate tissue heating could be achieved using realistic concentrations of the embolised material. Heating rates were measured for each infused quantity under similar conditions with the animal alive and dead to examine the role of blood flow in the heating process. The results show that tissue temperatures above the therapeutic threshold of 42 degrees C can be readily achieved using this method with clinically relevant concentrations of microspheres in living tissue.