使用網格規則化追蹤超音波腎結石影像

Abstract

體外震波碎石技術和腎結石的震波聚焦能力有很大的關係。為了達到移動物體、目標的自動聚焦，必須能夠做到及時追蹤。一種具有網格式的區塊比對計算程序能夠適當的用在超音波影像的腎結石追蹤。雖有需要同時追蹤多個目摽，但是對於解決腎結石追蹤的目標物消失和影像的強度衰退，網格的追蹤計算程序能夠發揮一個制約調整的功能。 將人體軟組織視為一個彈性體，以彈簧模型來分析其應力、應變、變形能量與位移間的關係。藉由最佳化參數設計，定義區塊比對的位移初始值，最小化因位移向量造成的匹配誤差能量和變形能量的 函數，求解出網格節點的位移向量最佳值。其中，變形能量裡的剛性矩陣由有限元素法求解出。 而為了簡化剛性矩陣的計算量，我們選擇規則四邊形元素作為網格模型，以期達到及時追蹤的效果。經由最佳化參數設計的結果，改善了因區塊比對錯誤所造成的誤判率，避免碎石機對人體腎臟過多的傷害。

The efficacy of Extracorporeal Shock Wave Lithotripsy (ESWL) depends greatly on the capability to focus shock waves on renal stone. To achieve automatic focusing on moving target, the target must be under tracking. A mesh-based block matching algorithm is proposed for renal stone tracking using ultrasound image sequence. Since multiple targets are tracked together, the mesh-based tracking algorithm can provide a function of contextual regularization for solving the target missing and image degradation problems in renal stone tracking. Recorded ultrasound images of kidney during ESWL treatment are modified for demonstrating the capability of this algorithm. We regard the soft tissue of the body as elastic in order to analyze the relationship of stress, strain, deformable energy and displacement. On the basis of the optimal design, we also define the initial displacement of block-matching to minimum the function of matching error energy and the deformable energy by displacement vector to solve the optimal value of displacement of mesh grid nodes. Therein, we figure out the stiffness matrix of deformable energy by finite element method. In order to simplify the calculation, we choose a regular quadrilateral element as the mesh model to achieve the tracking of real time. According to the optimal design, we amend the performance of block-matching to avoid the damage of renal caused by stone breakers.