醫用超音波斑紋疊減與影像增強

Speckle Reduction and Image Strength in Medical Ultrasound

醫用超音波在B模式影像中，由於不均勻物質的回散射形成一種特有的雜訊稱為斑紋(speckle)，此斑紋雜訊會影響影像的判讀，因此如何去除此雜訊則成為超音波影像學上一個值得探討的問題。一般為去除雜訊和增強影像其方法多是基於非同調處理和影像後處理技術。利用合適的濾器技術處理來抑制斑紋技術是一種常用的影像後處理方法，而本研究的目的將嘗試使用影像投影重建的方法，利用雷登轉換(radon transform)來撰寫程式執行影像後處理的方法，並且與其他方法做分析比較。從研究結果中發現，不同的濾器處理可以達到不同程度的影像增強與平滑效果，在影像清晰度上，用中值濾波處理比用低通濾波處理效果還要好。而在雜訊處理上，中值濾波處理後的影像內，雜訊處理效果也較佳，而在低通濾波處理後的影像中，其雜訊還是存在，只是較模糊不明顯而已。而在經過同形濾波後，整張影像較原來的影像更清楚且較暗的地方也變得更明亮清晰。而選用雷登轉換與適當的濾器配合亦可有效使醫用超音波影像達到斑紋遞減與影像增強。

In the B-mode image of medical ultrasound, noise caused by the backscatter of uneven substance is called “speckle.” Speckle may influence the interpretation of images; removing speckle is a subject of interest among sonographers. Normally, interpretation of noise and strengthening of image are based on asynchronous processing and image aftertreatment; using proper filter technique to suppress speckle is a commonly used image aftertreatment technique. The purpose of this research was to employ the Radon transform to write an equation for image aftertreatment and then to compare this approach with other methods. We discovered that different filter processes reach different levels of image strength and smoothness. We also found that the median wave process produced better image clarity than did the low-pass wave process. Use of the Radon transform and proper filters can reduce speckle and strengthen sonographic images.