Small cylindrical ultrasound sources for induction of hyperthermia via body cavities or interstitial implants

Abstract

In this study, small (outside diameter 1 mm) cylindrical ultrasound sources were investigated for induction of hyperthermia in tumours. These ultrasound transducers could be placed in small-diameter body cavities, or they could be used interstitially in brachytherapy catheters. The ultrasound field measurements showed that the field is fairly uniform as a function of the length of the applicator except at the ends where sharp peaks were located. However, there were significant field variations as a function of rotation angle around the transducers. The degree of these non-uniformities varied from transducer to transducer, and also as a function of frequency. The temperature measurements in vitro perfused kidneys showed that therapeutic temperature elevations could be induced in perfused tissues. The radial extent of the therapeutic zone could be increased by circulating water around the applicators, thus avoiding high temperatures on the applicator surface. It was also shown that some control over the temperature distribution along the length of the applicator could be achieved by using a two-element applicator. An array of four applicators implanted in a square pattern with the spacing of 25 mm between the catheters, was able to heat the tissue volume inside of the implant. The results showed that these small ultrasound applicators may offer significant improvement over existing techniques by increasing the penetration depth and the control over the power deposition pattern.

Ultrasound hyperthermia control system for deep-seated tumours: Ex vivo study of excised tumours, modeling of thermal profile and future nanoengineering aspects

“…When heat is applied to the tumour, vital nutrients and oxygen are cut off from the tumour cells. This results in a collapse of the tumour's vascular system and destruction of the cancer cells [5][6][7][8]. Hyperthermia is a low and smooth temperature elevation, with long exposure times.…”

“…In addition, segmented systems can be built, thus allowing longitudinal and angular control, giving them a potential advantage over microwaves [8][9][10][11][12][13][14][15][16][17][18][19][20].…”

“…However, if the patient recovers, some abnormality is developed. Focussed ultrasound modality has been tried recently and is found effective [1][2][3][4][5][6][7][8][9][10]. Ultrasonic vibrations are orderly oscillatory motions generated by an external source.…”

Interstitial devices for minimally invasive thermal ablation by high-intensity ultrasound

“…Angle resolution is then limited to each applicator which is specially designed for a given angle opening. Some authors have also proposed using two or three transducers (sectorial or not) placed along an axis to obtain dynamic axial control of heat deposit 61,56 . It would then be possible to adjust the shape and axial dimensions of coagulation necroses by modulating the power emitted by each transducer.…”

Principles and results of high-intensity focused ultrasound for localized prostate cancer

“…The lesion formation is also related to the firing duration: the lesion starts at the transducer focus and progresses toward the transducer during the firing sequence (Figure 1c). [6][7][8] HIFU was initially applied for the treatment of glaucoma and then on different models of animal liver, kidney, and bladder tumours. The prostate gland is the ideal candidate for HIFU treatment because of its location adjacent to the anterior aspect of the rectal wall.…”