| Japanese |
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| Title | コーデット・アパーチャ・イメージングにおける信号対雑音比と雑音の性質 |
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| Subtitle | 原著 |
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| Authors | 田中栄一*, 飯沼武** |
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| Organization | *放射線医学総合研究所 物理研究部, **臨床研究部 |
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| Journal | 核医学 |
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| Volume | 13 |
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| Number | 2 |
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| Page | 95-102 |
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| Year/Month | 1976/4 |
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| Article | 原著 |
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| Publisher | 日本核医学会 |
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| Abstract | 「1. 緒言」近年, 核医学におけるRIイメージングにおいてコーデット・アパーチャ・イメージング(coded aperture imaging)と称する方法が注目され, 多くの研究グループが活発に研究を進めている. この方法では, まず従来のピンホール・コリメータまたは平行多孔コリメータの代りに, 特殊なパターンのアパーチャを有する鉛板を被写体(患者)とイメージ検出器の間に置いてイメージを測定する. 得られたイメージは真のRIイメージを上記のパターンでコーディング(coding)したものとなり, そのままでは人間の眼では一般に判別できないので, 適当な方法でデコーディング(decoding)して真のRI分布に近いイメージに復元する必要がある. 現在, おもに用いられているアパーチャはフレネル・ゾーンプレート(Fresnel zone plate), ランダム・マルチ・ピンホール, 疑似ランダム・マルチ・ピンホール, 円形スリット等で, なかにはアパーチャを移動しながら測定する時間変調型のものもある. |
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| Practice | 臨床医学：一般 |
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| English |
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| Title | Signal to Noise Ratio and Noise Characteristics in Coded Aperture Imaging |
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| Subtitle | Original Articles |
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| Authors | Eiichi TANAKA, Takeshi IINUMA |
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| Organization | National Institute Radiological Sciences |
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| Journal | The Japanese Journal of nuclear medicine |
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| Volume | 13 |
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| Number | 2 |
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| Page | 95-102 |
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| Year/Month | 1976/4 |
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| Article | Original article |
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| Publisher | THE JAPANESE SOCIETY OF NUCLEAR MEDICINE |
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| Abstract | [Summary] This paper presents a general method of image decoding for an arbitrary time-modulated aperture and the formulation of the noise characteristics in the decoded images. The first step of image formation is to construct a "shadow image" which is formed by accumulating the shadow of the aperture onto the object plane from each point of detection. The shadow image is further processed by a correction function, h(x, y), to yield a final image which has a point spread function, p(x, y). Then, we have : p(x, y)=j(x, y, y)*j(-x, -y, t)*h(x, y) where j(x, y, t) is the aperture function defined at the object plane, *denotes the convolution operation and - indicates the time-averaging. The auto-covariance function of noise for a locally uniform image is given by : Cov(x, y)=nB[p(x, y)*h(x, y] where nB is the count density. The variance of the noise is equal to Cov(0, 0). Assuming a constant aperture area, the signal to noise ratio in detecting a small lesion in a uniform large organ is proportional to the "figure of merit" given by : F=[A/∬p(x, y)h(x, y)dxdy]1/2 where A is the area of the shadow of the aperture onto the object plane. An analysis has been made to find an aperture yielding a large F-value. It is concluded, however, that no coded aperture has a larger F-value than that of the optimum pinhole for a given spatial resolution, and that a suitable coded aperture would provide an image having different noise characteristics which may yield a larger F-value over a certain range of resolution than a pinhole. Such a coded aperture may be expected to be suitable for observing an image with various resolution by modifying the processing function. |
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| Practice | Clinical medicine |
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