肝臟超音波掃瞄為最常見檢測肝臟病變的方式，超音波影像具有即時性及非侵入性等優點，但是其成像品質遠低於放射影像且二維影像缺乏空間資訊，在判讀上易受人為主觀影響而造成誤判。另一方面，放射影像雖然具有高成像品質，但是對人體傷害大，且肝臟會隨病人呼吸體態而有所變化，使得放射影像無法即時顯示。因此若是能結合兩種影像進行融合，並補償呼吸與體態所造成之影響，則可提升診斷與穿刺治療的精度。 本研究以肋骨作為影像對位之基準，在進行影像對位前先調整病人的體態與呼吸狀態，使其與掃瞄電腦斷層影像時一致。之後擷取肋骨超音波影像並以影像處理方式分割其邊緣特徵，並與電腦斷層影像重建之肋骨三維模型以疊代最近點(Iterative Closest Point)演算法進行曲面對應，以求出兩影像之間的座標轉換關係。 影像方位校準誤差評估以假體與真人進行測試，以超音波擷取清晰特徵邊緣資訊後，將邊緣資訊經由座標轉換後與電腦斷層影像中相對應之特徵進行比對，作為誤差評估的依據。假體實驗xy平面誤差為2.32 mm，z軸誤差為4.48mm。而人體實驗誤差約為4mm，且有明顯的角度誤差，推測誤差主因為超音波掃瞄時探頭緊壓腹部所致，若能針對緊壓的應力進行補償，將能提高系統精度。Ultrasound scan is the most common way to detect the disease of liver diseases. Ultrasound imaging is real-time and non-invasive, but its image quality is poor and lack of spatial information. Therefore, subjective interpretation of ultrasound images may cause misdiagnosis. On the other hand, computed tomography images have high quality. If CT and US images are scanned at similar respiration and posture status, the fusion of both images will be able to improve diagnosis quality and biopsy accuracy. Prior to ultrasound scan, the patient's posture and respiration are monitored and controlled to have similar status as CT scan. Then the grabbed ultrasound images of ribs are processed to find the boundary of the ribs. Using the iterative closet point algorithm, the data of boundary points are then applied to complete surface registration with reconstructed 3D model of rib’s CT images and to obtain the transformation matrix between the two image frames. Experiments of image registration error assessment are performed with an anthropomorphic phantom and a human patient. The edge information of captured characteristics ultrasound images are transformed to CT image frame and compared with the same characteristics on the CT images to calculate their position errors. The results show that position error of anthropomorphic phantom experiment at the xy plane is 2.32mm and the z axis is 4.48mm while that of human patient is approximate 4mm. Since there is clear angular error, press of ultrasound probe on the patient during ultrasound scan may be the factor caused angular error.
