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In the liver, the efficacy of radiofrequency or HIFU ablation is impaired by blood perfusion. This can be overcome by hepatic inflow occlusion using a Pringle manoeuver. Here we report the in vivo evaluation of ablations performed in the liver using a surgical toroidal High Intensity Focused Ultrasound (HIFU) device used during an open procedure with and without hepatic inflow occlusion. The HIFU device was composed of 256 toroidal-shaped emitters working at 3 MHz and an integrated ultrasound imaging probe working at 7.5 MHz. Using an Intermittent Pringle Manoeuver (IPM), thermal ablations were created in three pigs with hepatic inflow occlusion (IPM Group) and in three pigs with normal perfusion (NoIPM Group). The ablations were studied on sonograms, macroscopically and microscopically fourteen days after the treatment. In the NoIPM group, the average coagulated volume obtained after a 40 s total exposure was 7.4 ± 3.8 cm3 (2.2 - 16.6). In the IPM group, the average ablated volume was 6.3 ± 2.9 cm3 (2.6 - 12.1). There was no significant difference between the two groups in terms of ablated volume (p=0.25), diameter (p=0.37), or depth (p=0.61). The data from the present study demonstrated that there is no significant influence of hepatic vascular flow on the size and shape of ablations created with the toroidal-shaped HIFU device that has been used. The HIFU approach presented in this study is characterized by the brevity of the treatment (40 seconds for one ablation of 7 cm3), which makes it possible to reduce treatment dependence on blood perfusion. Ablations obtained with or without a Pringle manoeuver were homogeneous in both groups and were not significantly different in terms of diameter, depth and volumes in the IPM group compared with the NoIPM group. [ABSTRACT FROM AUTHOR]

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]

In a large number of applications, high intensity focused ultrasound (HIFU) treatments are guided using ultrasound imaging. The purpose of this study was to use an in vivo tumor-mimic model for guiding HIFU ablation in the liver. Tumor-mimics were created in in vivo porcine livers by injecting a mixture of agarose, cellulose, glycerol and methylene blue, which formed 1 cm hyperechoic discrete lesions on sonograms. In vivo experiments were then conducted in 10 pigs for 30 days. Four tumor-mimics were created in each animal using an open approach to evaluate if they are well tolerated. Lesions were characterized sonographically, examined pathologically and using histopathologic analysis with reproducible dimensions (0.92 ± 0.25 cm3) and similar to those measured on the sample removed during surgery. The mean difference between macroscopic measurements and ultrasound measurements is 0.19 ± 0.06 cm3 for 1 cm3 injections. Target creation took a few minutes per tumor-mimic and 80% of injections were successful. Ablations in normal liver tissue and in tumor-mimic were performed in vitro on 20 samples using a HIFU probe (working frequency: 3 MHz) with an integrated ultrasound imaging probe (working frequency: 7.5 MHz). Ablation sizes were not significantly different for controls and tumor-mimics. The agarose-based tissue-mimic creates realistic sonographic targets in vivo and in vitro for learning ultrasound-guided open HIFU ablation in an in vivo model. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]