三維超音波成像法對於偵測肝臟組織變異之應用

Abstract

肝臟是人體最大的器官，位於人體的右上腹部，其功能相當複雜，除了儲存能量、製造膽汁外，它還可以排除多種人體代謝後所產生的毒素。醫學上常用的肝病診斷方法：<1>血液檢查-肝功能試驗、<2>肝臟超音波檢查、<3>肝組織切片檢查。目前醫院所使用的超音波影像大多是屬於B-mode影像，而B-mode成像是一種二維的人體橫切面影像，對於沒有經過專業訓練的人，或是經驗不夠的醫生，B-mode影像提供的資訊實在很少。在肝病變發生時，我們比較感興趣的是肝臟內部的軟組織異化過程。對於肝臟軟組織的特性，我們希望能發展新的三維超音波成像方式，以視覺的方式及統計的方法將變異的肝組織辨識出來。 本論文的實驗目的是希望能夠辨識肝臟組織的變異，我們把實驗仿體(豬肝葉)用浸泡酒精的方式來使肝組織產生變異。在肝臟剛浸泡酒精時就放入水槽內，使用三維步進馬達來進行掃描，然後再將肝臟靜置於水槽中每隔一段時間再掃描一次。這個研究是以立體成像法為工具，利用光線投擲的原理把三維的超音波訊號資料投影在二維平面上成像。在本論文中也討論到立體成像法所該選取最適當的投影路徑長度，再利用所找到的投影路徑長分析第二次的實驗。 實驗結果主要是超音波的強度影像與中心頻率影像在浸泡酒精前後進行比對，強度影像對於組織變異可以比較容易觀察到，就是影像整體強度增加，而中心頻率的影像資訊非常的豐富，跟強度影像比起來並不會受到血管的影響，可以把肝臟軟組織的資訊顯示出來，但是對於組織變異較不容易觀察。因為中心頻率影像不容易觀察到肝臟組織變異，我們把影像做Histogram再求出其mean值，可以發現到中心頻率在浸泡酒精後有向下偏移的趨勢。看到浸泡酒精後中心頻率有變低的趨勢，我們又把中心頻率的影像相減，看到了影像的變化並非一致的往下掉，所以又做了一個短時間掃描的實驗來提高時間上的解析度，結果發現在短時間內中心頻率還是有變動，而且比強度上的變動還要快很多。

Liver is the biggest organ in human body, it lies in the right upper abdomen of human body. The function of liver is quite complicated. Besides storing energy and making bile, it can also get rid of the toxin that produced after metabolism. The diagnosis methods for liver diseases include: 1. Liver function test - Check by blood, 2. Ultrasound, 3. Biopsy. For ultrasound, B-mode image is the mostly used method in hospital, and it is a kind of 2D human cross section image. B-mode image offers really few information to a person who doesn’t undergo professional training or even doctors who don’t have enough of experience. When the liver pathological changes takes place, what we are relatively interested in is the variation process of soft tissue within the liver. We hope that we can develop a new 3D ultrasonic image to distinguish the variation of liver tissue by the way of vision and the method of statistics.o distinguish the variation of the liver which has been affected by alcohol is the experimental works done in this thesis. In order to make the characteristics of liver tissue change, we soak the pork liver in the alcohol. The liver is put into water tank while soaking in the alcohol, and use a 3D-controlled step-motor to scan. Then keep the liver in the water tank and scan once again at a regular period. This research uses volume rendering as a tool, and the method used is ray casting. Volume rendering projects the 3D ultrasonic signal data on a 2D plane to form the image. In this thesis, how to choose the most proper length of projection route is discussed also. We use the length of projection route that we find to analyze the experimental data.he experimental result is compared to find the difference before and after soaking the pork liver in the alcohol using the intensity image and central frequency image. Through the increasing of image intensity, the intensity image is apter to observe the variation of liver tissue. The information of the central frequency image is very abundant, and it is not influenced by blood vessel like the intensity image. The central frequency image can show the information of soft tissue, but it is not apter to observe the variation of liver tissue. Because the central frequency image is difficult to observe the variation of liver tissue, we use histogram to quantify the image. We can find that there is trend of downward skew in the central frequency after the pork liver is soaked in alcohol. We ckeck the change of the central frequency image in time, then it is found that the change is not unanimous. So we make the images scanned in short time to improve the analysis. We found finally that the central frequency may change in short time, and the change on the central frequency is swifter than the change on the intensity