Feasibility of haemostasis in prostate using a flat trans-urethral transducer

The objective of this work is to demonstrate the feasibility of trans-urethral application of collimated high intensity ultrasound in order to coagulate blood vessels in prostate. The coagulating tool is a flat 6×10mm² transducer. It operates at a frequency of 10MHz. Doppler and conventional ultrasound imaging were performed before and after treatment. The effect of intensity, exposure duration and angular step between elementary exposures on therapeutic depth and thrombosed vessels density was studied. The therapeutic depth ranged from 6 to 10 mm. Hyperechoic spots were observed on sonograms for a few minutes right after treatment and a permanent hypoechoic zone remained in the treated zone. It corresponded in size to the histologically assessed zone of coagulation. A significant fall in Doppler signal amplitude immediately after treatment demonstrated the applicator´s ability to achieve haemostasis. The coagulation rate obtained by dividing the vessel density of the treated sample by the vessel density of the controls ranged between 51% and 99%. We demonstrated that a miniature flat ultrasound 10MHz-transducer can be used to coagulate blood vessels with a diameter less than 1 mm and located at a distance less than 1 cm from the organ surface. This makes our transducer suitable for trans-urethral application of high intensity ultrasound to coagulate prostatic tissues and vessels.