測量內測足弓高度是診斷分類扁平足的重要參數之一。就之前的研究顯示，診斷方法可分為直接以及間接測量，直接測量可分為人體測量學和放射線影像分析法，間接測量可分為相片取像分析以及常用的足印分析法。就臨床診斷而言，比起放射線影像分析法，足印分析法具有簡單、非侵入式的特點。然而，以目前的技術仍然缺乏自動診斷的機制以及三維結構的評估。本研究目的在於建立一套自動化的足印影像量化分析系統，並提供三維表面結構分析。
本系統硬體機構設計主要包含壓力板、光源及數位相機及均質特性的介質。壓力板包括四個單軸的荷重單元以偵測身體重心的偏移，目的在使兩腳站立穩定平衡實自動取像。利用影像處理技術自動分析影像，並以Convex Hull 演算法分析足印參數(footprint index)。另外藉由建立影像亮度與深度的關係曲線，做為三維表面重構的依據。再根據重構的三維模型中，衍生出新的評估參數，包括足弓部分的面積、足弓凹陷深度等。
在研究的結果方面，我們已完成一套即時的足印影像擷取分析系統。克服傳統油墨足印分析的缺點，本系統在受測者站立平衡的狀態下自動擷取負重的足印，並利用影像處理的技術分析足印參數。在三維重構方面，提供一個監測亮度分布的方法提高重溝模型的準確度到平均差異小於2 %。最後建立負重三維足弓表面模型，希望有助於電腦輔助設計製造扁平足矯形鞋墊或足部矯正輔具。

The height of the medial longitudinal arch of the foot has been one of the primary criteria for the classification of foot structure. In previous studies, direct measurement by using anthropometrics and radiographic techniques or indirect methods such as footprint and photographic analysis have been developed to certain degree of success. Compared to the X-ray approach, footprint analysis is a non-radiation and a more viable method for clinical assessment of the flatfoot. However, automatic detection scheme for footprint index and 3D measurement in characterizing the structure of the foot for diagnosing foot pathologies are still lacked in clinic. The aim of this study is to develop a footprint image acquisition system, which automatically takes the photos in the standardized foot position and balanced weight-bearing conditions. An alternative 3D reconstruction technique based on the relationship between depths and brightness was developed for estimating the 3D contour of footprint.
The system consists of four main components: force plates, reflection and light source, digital camera, and homogenous contrast medium. Two force plates consisting of transparent glass with one-axis load cell under each corner were used to acquire the weight shift of the body. Convex Hull operation was applied for detecting the tangent line of the footprint arch for conventional footprint index. To measure the 3D contour of arch, a descending stair phantom was designed to calibrate brightness to the depth of contrast medium. The 3D mapping process was carried out by interpolating the calibration curve from the stair phantom. Based on the 3-D footprint contour image, new indices for diagnosing flatfoot, such as concave arch area and 3D arch volume can be developed for flatfoot assessment.
With overcoming the disadvantages of traditional ink imprint system, our results demonstrate that convex hull is feasible technique for deriving the footprint index in the standardized foot position and balanced weight-bearing condition. The 3-D weight-bearing surface model of the arch was reconstructed with small variation less 2 % of mean error for varied slices. It is expected that the 3D contour of footprint not only can be used a new index for assessing flatfoot but also be useful for CAD-CAM approach for fabricating arch support.

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