Evaluation of Hand-held Strain Imaging for Guiding HIFU Ablation: in vivo Results Compared with MR-images.

A 256 element toroidal piezocomposite transducer with a diameter of 70 mm and a radius of curvature of 70 mm working at 3MHz was used. A 7.5 MHz ultrasound imaging probe was integrated to the centre of the HIFU transducer. This paper discusses the interest in using real-time hand held elastography to guide a HIFU treatment. 16 lesions were produced and imaged intra-operatively in vivo in 4 pigs. Strain images were obtained and displayed at a frame rate identical to that of the sonograms (23 frames/s) using the ultrasound imaging probe placed in the centre of the HIFU device. The compression was applied manually. At the end of the procedure the liver was removed and imaged using a 1.5 T MR-scanner. The dimensions of the coagulated volumes measured on gross pathology were 22.1 mm (average diameter) and 19.8 mm (average depth). The contrast between ablated and untreated liver was higher on strain images (23dB) than on the B-Mode (3dB), T1-weighted (3dB) and T2-weighted images (13dB). The correlation between dimensions measured on gross pathology and dimensions measured on B-mode images, strain images, T1-weighted and T2-weighted images were r = 0.51, r = 0.68, r = 0.72 and r = 0.74 respectively. The correlation between dimensions measured on strain images and dimensions measured on T1-weighted and T2-weighted images were r = 0.77 and r = 0.78 respectively. In conclusion, the device presented in this study allows the creation of large ablations volumes over short periods of time. In addition, these in vivo results show that realtime hand-held strain imaging performed with an ultrasound probe integrated to the HIFU device can be used intra-operatively to visualize the dimensions of HIFU ablations with a precision similar to MRI, but with improved contrast. [ABSTRACT FROM AUTHOR]