Therapeutic applications of acoustic and electromagnetic energy

Abstract

This thesis focuses on techniques based on electromagnetic and acoustic energy for treatment of a variety of diseases, including development of new techniques as well as improvement and evaluation of existing techniques. The subjects treated are:

Provocation of heat generated thrombi in pigs. A bipolar RF-catheter was introduced in the vessel of interest where 6 W of RF-energy was applied through the catheter for 30 seconds. Subsequently the vessel was occluded for 15 minutes. With this protocol, 100 % (n = 11) of the vessels were occluded with an associating thrombotic mass completely filling the entire lumen. Using a static dose may cause severe or insufficient damage to the vessel wall because of varying blood flow in the in-vivo situation. The behaviour of the electrical impedance during exposure in different tissues was therefore studied to create a more standardised injury to the vessel wall independent of blood flow.

Trans Urethral Microwave Thermotherapy (TUMT), with the ECP-system. Between 1991 and 1999, 371 patients were treated with TUMT at Karolinska Hospital, Sweden. Seventy-six percent of the patients subjectively benefited from the TUMT treatment and 22 %judged they were fully cured. IPSS and Quality of Life score decreased approximately 40 % and 30 % respectively. Forty-one percent of the patients with CAD (cathéter A demeure) before the treatment became permanently or temporarily catheter free after the treatment. Furthermore, the cross-coff elation between output power and rectal temperature was studied during 15 in vivo treatments to assess if catheter dislocations could be automatically detected as a change in the crosscorrelation. The sampled in-vivo data showed no detectable cross correlation, preventing the realisation of this automatic technique.

Variation in electrical tissue admittivity after exposure to acoustic energy. The effects of three modes of acoustic energy on in-vitro electrical admittivity were studied. Thirty-four muscle tissue samples were irradiated with either extra corporeal shock wave lithotripsy (ESWL) or high intensity focused ultrasound (HIFU) in pulsed or continuous wave. Significant changes in magnitude of admittivity were detected only during continuous HIFU when temperatures over 44 degrees C were generated. The admittivity decreased by 35 % during these protocols. The phase angle of impedivity increased during all our protocols. The increase was approximately 50-70 % depending on the temperature elevation and the mode of delivery. We conclude that both thermal and non-thermal effects have an impact on the phase angle of the target tissue.

Treatment of breast cancer with a cooled monopolar RF-system. Initially, a complete RFAsystem was developed on which the power distribution around the needle was mapped. Subsequently, treatment on in-vitro breast tissue with tumour was performed, showing that ductal breast cancer was well suited for RF-ablation. Interestingly, thin tumour strips extending from the core tumour were also killed. The surrounding fat was however unaffected. Hence, the heat pattern appears to be drawn to the tumour. The origin of this focusing effect was studied using Finite Element Method (FEM) analysis. The dissimilarity of mainly the electrical properties in tumour and fat is capable of focusing the heating to the tumour. The degree of this differentiating effect depends on tumour shape and placement relative to the electrode. However, the observed differentiating effect between tumour and fat in the in-vitro studies were more pronounced, indicating that additional effects might be involved in the tumour targeting.