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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Computed tomography dose index ： ウィキペディア英語版 Computed tomography dose index The computed tomography dose index (CTDI) is a commonly used radiation exposure index in X-ray computed tomography and is reported by the CT manufacturers to scan personnel for each exam. The CTDI can be used in conjunction with patient size to estimate the absorbed dose. The CTDI and absorbed dose may differ by more than a factor of two for small patients such as children. ==Definitions== It is defined by the US Department of Health and Human Services (HHS) as the average dose imparted by a single axial acquisition to a standard 100-mm pencil chamber dosimeter inside a PMMA phantom over the width of 14 CT slices: $CTDI=\backslash frac\backslash int\_^$ where $n$ is the number of slices acquired, $T$ is the slice thickness and $D(z)$ is the radiation dose measured at position $z$ along the scanner's main axis. This measurement is most often made using a 100-mm standard pencil dose chamber as this is representative of a typical scan length: $CTDI\_=\backslash frac\backslash int\_^$. The absorbed dose to water $D\_(z)$ (used to refer back to patient dose) is typically measured in a cylindrical head (16 cm diameter) or body (32 cm diameter) phantom of length approximately 14–15 cm. The dose distribution imparted by a CT scan is much more homogeneous than that imparted by radiography, but is still somewhat larger near the skin than in the centre of the body. The ''weighted'' CTDI was introduced to account for this: $CTDI\_w=\backslash frac\; CTDI\_^\; +\; \backslash frac\; CTDI\_^$ using measurements acquired at central and peripheral positions in the head or body phantoms described above. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Computed tomography dose index」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.