胸腔X光檢測一直是放射診斷的主要項目之一，可以診斷出肋骨及鎖骨骨折情形、瀰漫性肺浸潤或感染、氣胸、血胸、肺炎、、、等。在醫學診斷治療上，可說是應用非常廣泛。目前胸腔X光影像偵測，已經由傳統類比的底片，進步到數位平板偵檢器。但是放射診斷拍攝條件，很多醫院可能沿襲傳統照射條件，峰值管電壓（kVp）及管電流（mAs）與影像品質，並未做有系統的探討，甚至照射時人體所接受的有效劑量，也沒有加以評估。

本研究主要應用新竹馬偕醫院放射部門設備儀器Revolution XR/d型全數位X光機系統進行評估研究，該系統為美國奇異公司所生產。內含新發展的數位平板偵檢器，有別於傳統類比式X光底片。將影像以數位式儲存，不僅可永久保存，而且能應用發展日趨成熟的影像處理技巧來增進影像品質，輔助放射診斷的精確判斷。

本實驗主要採用Nuclear Associates公司生產的胸部品質控制假體，在自動曝照控制模式下，以62 kVp至132 kVp不同峰值管電壓從事胸腔X光照相。在肺臟、心臟及腹腔各等效區內取得該區訊雜比作為影像品質指標，並引進優值數，其值為訊雜比平方除以有效劑量，用以評估劑量與影像品質之最佳化。有效劑量係利用PHOTKOEF程式產生的X光能譜配合BodyBuilder程式所合成的數學假體人以MCNP4C蒙地卡羅程式計算求得。

本研究所建立之模式，不僅可用在胸腔X光診斷系統之劑量與影像品質最佳化條件評估，並且可應用於不同胸腔X光診斷系統特性之比較，未來更可進一步用來比較不同醫院所採購之胸腔X光診斷系統之優劣。

Chest radiography is one of the major items for medical diagnostic examination. It is able to diagnose out the fracture of the ribs, clavicles and spine, the diffuse pulmonary infiltration or infection, the pneumothorax, the hemothorax, the pneumonia, …etc. Especially in medical diagnostic therapy, its applications are quite extensive and popular. Nowadays the image recording of chest radiography has been improved from the traditional film to the flat panel detector. Many hospitals get used to operate the radiography processes in the conventional X-ray tube conditions. Neither the relations among the image quality, peak tube voltage and tube current have been systematically explored nor has the effective dose of patient been evaluated.

This study uses the medical Revolution XR/d full digital X-ray radiography system, which is the equipment of the radiology department in Hsinchu Macay Hospital and produced by the GE Company, to research. Extremely different from the traditional medical radiography image recorded by the X-ray film, the system equipped with the new developed flat panel detector to record the image in digital method which is able to reserve the image permanently and also to improve the image quality by through the well-developed image processing techniques to aid the radiography diagnosis precisely.

Under AEC (Automatic Exposure Control) mode, the experiment adopted the chest quality control phantom to process the chest X-ray radiography under peak tube voltage from 62 kVp to 132 kVp. The calculated SNR (Signal to Noise Ratio) from the lung, heart and subdiaphragm equivalent areas is used as the image quality index. The FOM (Figure of Merit) defined as SNR2/Effective Dose is suggested to evaluate the optimization of dose and image quality. The effective dose is calculated from Monte Carlo Code program MCNP4C combined with the X-ray spectrum produced by the PHOTKOEF program and with the mathematical phantom produced by the BodyBuilder program.

This research aims to establish the standard not only for evaluating the optimization of dose-image quality in chest radiography but for comparing the characteristic from the different chest X-ray diagnostic systems. Furthermore, it could be used as a standard to compare the chest X-ray diagnostic systems in different hospitals.

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