Ultrasound features of low power interstitial laser hyperthermia

Low power interstitial laser hyperthermia (ILH) is a reliable means of producing in situ thermal necrosis. Ultrasonic studies have been carried out of the changes that occur in canine liver during ILH performed at laparotomy. With a single fibre delivering Nd-YAG laser at 1-1.5 W for 670 s an hyperechoic region developed at the fibre tip measuring 5-6 mm in diameter; around this developed an area of hypoechoic change (up to 500s) giving a total area of changed echogenicity of 14-16 mm. With a multiple fibre system using 4 laser fibres simultaneously the sonographic changes were a summation of the changes seen with a single fibre, the hypoechoic areas overlapping. With this four fibre system the creation of large (3.5 x 2.8 cm) areas of thermal necrosis was possible. There was good correlation between the sonographic and pathological measurements of the region of thermal change. The sonographic studies showed the extension and overlap of regions of thermal necrosis and allowed visualization and accurate measurement of the area undergoing change. The same combined technique has been successfully applied in a small number of clinical cases and may be of use in the treatment of tumours in solid organs.