足部的結構對於站立及行走是非常重要的，不正常的足部會造成體感覺傳入的異常，進而導致平衡的失調。對於足弓(Foot arch)外型之評估，足印分析是一種非輻射且可信度高的一種二維的臨床評估方法，但是缺乏有效率及自動量測的工具；瞭解站立時之足弓立體結構，更有助於瞭解其與平衡之間的關係，而對於平衡功能之評估，可由感覺整合測試(Sensory Organization Test, SOT)來測試，藉由壓力中心（Central of Pressure, COP）的晃動軌跡變化，可間接表示平衡控制的能力。

　　本實驗設計一套整合足印擷取分析、足弓立體形狀重構以及虛擬實境靜態平衡評估的系統，結構為一可移動式平台，其上鑲有兩片相鄰排列的透明強化玻璃，每塊玻璃的四個角落各有一個荷重元（Load cell）以組成壓力板。測試者雙腳分開站在壓力板上，並將裝有藍色液體壓克力盒子放在足部及壓力板之間，使影像對比增強；當兩塊壓力版的重量相同時，數位相機立即捕捉位於壓力板底下鏡子的足底映像。經由影像分析技術，可得出足印輪廓及臨床分析常用的幾項數據；再透過已知高度的白色壓克力梯子以及用純白伸縮膜封住盒子所得出的足底映像，根據其與梯子灰階值之相關性，即可重組足弓的立體形狀；而壓力中心可透過荷重元之承重及相對位置計算，在測試平衡時，給予受測者不同的本體感覺及虛擬實境的視覺刺激並以軌跡的搖晃方向及面積，作為平衡功能評估的依據。

　　神經系統對於平衡的影響，已有廣泛的討論，但骨骼肌肉系統在平衡上扮演的角色，仍不清楚。所以我們收集共65位幼稚園及小學三、四年級足底影像以及在8種不同的情形下，靜止站立時的壓力中心變化，藉此討論足印二維、三維參數與平衡之間的關係，進而瞭解足弓高度對平衡之影響；結果顯示對於神經系統未完全發育的4、5歲小朋友，當處於本體感覺干擾及視覺幻象或閉眼時，其足弓的高度與靜止站立平衡功能有統計學上顯著的負相關，亦即足弓愈高，搖晃面積愈大。

　　綜觀上述功能，本系統可提供快速及量化的足印參數，並重構站立時的足弓立體形狀，有助於電腦輔助設計及製造鞋墊，以及評估靜止站立時之平衡功能，而虛擬實境可被用來評估較依賴視覺來控制平衡的受測者。

　Foot architecture is very important for standing and walking. Abnormality is expected to result in balance dysfunction because of inappropriate somatosensory inputs. For geometric study, footprint analysis is a non-radiation and better viable one- and two-dimensional method for clinical assessment of the medial longitudinal arch of the foot compared to the X-ray approach, but lack of automatic and efficient tool for measurement. For functional survey, monitoring central of pressure (COP) under Sensory Organization Test is a good way to evaluate postural control ability.

　In this study, we have designed a system integrating the function of digital footprint acquisition, foot arch reconstruction, and virtual reality (VR) balance evaluation. It is a portable platform consists of a digital camera and two pieces of glass, which has load cells under each corner. When the subject stands still on the transparent force plates, the digital camera is triggered, photographing the soles of the feet at the moment when both feet bear approximately at the same weight for 3 seconds. Blue water is placed between the foot and the force plate to enhance the contrast between sole and background. Contour and several parameters of footprint are acquired by image analysis techniques. Besides, by a stair with known height in each step and adding a white elastic membrane on the box, the three-dimensional (3D) structure of the arch can be reconstructed based on the relationship between the brightness of the image and the depth of the water, which can provide more representative information than a conventional ink footprint with its low resolution and easy smearing. Furthermore, with force plate, the system is also able to record the sequential changes of COP during still standing under different somatosensory and VR visual conflict conditions and derive several parameters for the balance function evaluation.

　It is well investigated in the impact of the neurological impairment on the postural control. However, little attention had been paid to the role of the bony alignment for the balance. Hence we collected the footprint image and sequential changes of COP in different SOT conditions from 65 children of a kindergarten and elementary school. As the result, the arch height is significantly negatively related with the postural control ability while standing under somatosensory and visual conflict for the children aged 4-5 years, whose neurological system are under developed.

　It is expected that this system could provide a reliable quantitative approach for 2D footprint analysis, 3D surface reconstruction of the sole under weight-bearing condition for further understanding the characteristics of the arches and insole fabrication with computer-aided-design computer-aided-manufacture (CAD-CAM) technique, and evaluation of the standing postural control ability

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