Relationship Between Planned And Coagulative Necrosis Volume Under Ultrasonography-Guided HIFU

OBJECTIVEAs a new non-invasive technique to treat solid tumors, High-intensity focused ultrasound (HIFU) has been used in clinic. It has several advantages such as non-invasion, safety,quick-revive post-treatment, no ionising radiation, no radiation damage, and has an considerable clinical application. At present HIFU has been used to ablate hysteromyoma, hyperplasia of prostate gland , tumor of prostate, hepatocarcinoma , breast cancer , bone tumor, soft tissue sarcoma and other solid tumors.HIFU can not only destroy the pathological area, but also lead to damage to the adjacent normal tissue quickly. Many specialists pay close attention to the safe and effective use of HIFU. It has been confirmed that there are close relations of hyperechoic change of targeted region in US images and coagulation necrosis, and we can compare images before and after treatment to judge coagulation necrosis qualitative. But there is none of study on quantization relationship between the gray scale change and coagulation necrosis, and no gray scale change to guide the HIFU treatment . In primary experiment, the positive correlation between the volume of tissue necrosis and the gray scale change when it varied from the threshold of gray scale change to the best value of gray scale change was confirmed. In this part, the relationship of the tissue coagulation necrosis and the gray scale change will be quantificated. Analysis gray scale change within the planned irradiated volume and the real necrosis volume to find an optimal B-ultrasound gray scale change for monitoring HIFU treatment. It ensure that the real necrosis volume is not smaller than the planned irradiated volume, and they may be very near. In addition, the quantification of the planned irradiated tissue and the real necrosis will be researched. The relationship between the planned irradiated area, the maximum area of histologically documented coagulation necrosis and maximum area of hyperechoic region on US imaging was investigated.METHODS1.Study of the optimal B-mode ultrasound gray scale change.Twenty-five Nanjiang goats were randomly divided into five groups according to different gray scales change which are 7 to 18, 19 to 26, 27 to 34, and 43 to 50. Two samples on each thigh were treated with HIFU irradiation monitored by different gray scale change. The instrumental parameters were a Power of 200W and a frequency of 0.8MHz. All the planned irradiance volumes were 1㎝×1㎝×1㎝, and compared with the real necrosis volumes to find an optimal gray scale change to guide the treatment. Under the optimal gray scale change, Complete coagulation necrosis which near but not smaller than the planned necrosis took place.2.The relationship between the planned irradiated region and the real necrosis region guiding by the optimal gray scale change.(1)The relationship between the planned irradiance volume and the real coagulation necrosis volume guiding by the optimal gray scale change .Twenty-five Nanjiang goats were randomly divided into five groups according to different planned irradiance volumes which are 1cm×1cm×1cm,1.5cm×1cm×1cm,2cm×1cm×1cm,3cm×1cm×1cm,2cm×2cm×1cm,and were treated with HIFU guiding by the optimal gray scale change. The acoustics parameters were the same as that in part one.(2)The relationship between the planned irradiance area, the maximum area of histologically documented coagulation necrosis and the maximum area of hyperechoic region on the real-time US image. Twenty Nanjiang goats were randomly divided into four groups according to different planned irradiance areas which are 1cm×1cm, 1.5cm×1cm,2cm×1cm,3cm×1cm, and the acoustics parameters were the same as that in part one.RESULTS1.The real necrosis volumes increased with raising the gray scale target region. There was a positive correlation between the gray scale change and the real coagulation necrosis (r=0.8460). Below the gray scale change from 35 to 42, there were some incomplete coagulation necrosis on samples. Above the gray scale change from 35 to 42, the coagulation necrosis volume were larger than the planned one. When the gray scale change from 35 to 42, complete coagulation necrosis which near but not smaller than the planned necrosis took place in every sample. So the gray scale change from 35 to 42 was regared the optimal B-mode ultrasound gray scale change.2.The real necrosis volumes increased with raising the planned irradiance volumes and had no phenomenons of necrosis volumes saturation. There was a positive correlation between the planned irradiance volume and the real necrosis volume (r=0.98776).The real necrosis volume was approximately 1.31 times than the planned irradiance volume.3.There was significant difference between the planned irradiation area and the maximum area of hyperechoic region (P<0.05), the difference between the planned necrotic area and the real necrotic area was also significant (P<0.05). However, the maximum area of hyperechoic region was not significantly different from the maximum cross-sectional area of histologically documented coagulation necrosis (P>0.05). There was a positive correlation between the planned irradiance area and the maximum cross-sectional area of histological coagulation necrosis (r=0.942), and also a positive correlation between the planned irradiance area and the maximum area of hyperechoic region (r=0.946).CONCLUSIONThe gray scale change from 35 to 42 was the optimization to monitor muscle tissue ablation by HIFU. The real necrosis volume was approximately 1.31 times than the planned irradiance volume guiding by the gray scale change from 35 to 42.And monitoring by the optimal gray scale change, the maximum area of hyperechoic region of US image was not significantly different from the real histological necrosis area. We may observe the area of hyperechoic region of US imaging to monitor and evaluat the HIFU treatment in clinic.