使用電極位移彈性影像評估組織燒灼面積：角度效應分析

Abstract

肝癌的治療方法有很多種，射頻燒灼治療為近年來新興的一種局部消除療法，為了避免在治療時波及到周圍正常的組織，必須要藉由輔助系統來評估燒灼區域，超音波影像即為一種評估的醫學影像。由於燒灼過程中，氣泡的產生與假影效應，B-mode影像很難判斷出燒灼區域，並不適合用來做術後評估，因此Ophir 等學者便提出了彈 性影像。 彈性影像(Elastography)為一種藉由組織彈性的不同來形成的超音波影像，在過去的文獻中，並沒有特別提及超音波探頭的掃描方式，而腫瘤的生長位置不一，勢必會有需要改變掃描的角度才能掃描到腫瘤，因此本文探討探頭不同的掃描角度對於彈性影像會有何影響。 在實驗中，使用自動模式來燒灼，燒灼與冷卻時間各為12 分鐘。利用豬肝來模擬人體肝臟進行燒灼，掃描時，超音波探頭與燒灼電極會有一夾角，從90 度開始掃描，每減少10 度亦做掃描，掃描至角度等於30 度時。 實驗結果顯示，掃描角度會影響燒灼區的面積大小與面積誤差，角度越小，面積越大，但面積的誤差越小，角度小於40 度時，誤差約為10~20%；建議使用彈性影像時掃描角度低於40 度，燒灼面積的評估較為準確。

Radiofrequency ablation(RFA) is an emerging therapy in recent years, RFA procedures are performed under image guidance,and ultrasound image is a medical image to assess the ablation lesion.Due to gas generation and shadow effect during ablation procedures,B-mode image can’t identify thermal leison learly. Elastography is a non-invasive method in which stiffness or strain images of soft tissue are used to detect or classify tumors.Sometimes we need to change the position or angle of probe because tumors may appear randomly. Scanning position or angle of ultrasound probe does not specifically mention in the past literature,thus,we investigate the angle effect of elastography in this study. RFA experiment was performed on the liver of a pig,and RFA of the target tissue was performed for 12 min by raising the target temperature to 100°C at a 50-W power level.Acquiring elastography when the angle of scan plane and ablation probe changed from 30 to 90 degree. Accroding to the result,thermal lesion area increased when scanning angle is decreasing.Areas measured on pathology images were compared with areas measured on elastography,and the error of area between two images is about 10% as angle is less than 40 degress. Base on this study,to evaluate thermal lesion accurately,we recommend scanning angle less than 40 degrees