• 沒有找到結果。

低對比度探測

第二章 文獻查證

3.2 研究方法

3.2.3 低對比度探測

在圖 27 中分別對於原點及 12 點和 3 點框出位置,並取得 ROI 標準差,如果 12 點與 3 點對於原點的標準差相減小於 0 ± 3 內,在圖上顯示"均勻度通過測 試"。

取得原點的ROI 的標準差在 3.2 ± 0.3 之內,顯示"Noise 在範圍內”。[14]

圖27

3.2.4 雜訊與均勻度

在圖 28 中分別對於原點及 12 點和 3 點框出位置,並取得 ROI 標準差,如果 12 點與 3 點對於原點的標準差相減小於 0 ± 3 內,在圖上顯示"均勻度通過測 試"。

取得原點的ROI 的標準差在 3.2 ± 0.3 之內,顯示"Noise 在範圍內”。[14]

圖28

3.2.5 雷射定位線的準確度

在圖 29 中,透過 Matlab 程式運算取得假體的實際中心點,這時候再與影像的 中心點比較;並且在圖片上顯示該影像實際位移距離,顯示"水平位移 xx 公 分,垂直位移xx 公分”。

圖29

10B

3.2.6 Modulation Transfer Function (MTF)

按照下列步驟依序計算出 MTF 值,並記錄起來。依序算出1.6 mm ,1.3 mm , 1.0 mm ,0.8 mm ,0.6 mm ,0.5 mm 的 MTF 值。

並畫出MTF 與 Lp/cm 的圖。然後透過內插法算出 MTF50及外插法算出MTF10

的值。最後與該機型的 MTF 值比較,誤差在 ± 10%。

圖30

將所得出MTF (f) 與 Spatial Frequency 繪出一份圖表 M( f ) = ( M’ 2 – N2 ) 1/2

N2 =

2 NB2 + NC2

M

0

= mean

c

– mean

b 2

A

B C

MTF( f ) = Π 2½ 4

M( f ) M0

MTF

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

0 2 4 6 8 10 12

Spatial Frequency (Lp/cm)

MTF

圖31

再用內插法算出MTF50的數值;用外插法算出MTF10的數值。[20]

3.2.7 ACR Phantom CT Number Accuracy 運算

圖32

在圖上五個相關位置摽出圓框,測量ROI 平均值。將各平均值與下表比較,符 合範圍內,標註”CT Number Accuracy 正確”。[10]

3.2.8 進行低對比度分辨率運算

在圖 35 中進行 ROI 值運算,並分別標出位置,如果每個孔的 ROI()平均 值與孔上方的 ROI(Pixelglass) 平均值在一定誤差範圍內,表示該洞無法看到。依 序判斷其他洞,然後顯示"可以看見X mm”。[10]

圖34

3.2.9 進行雷射定位線的準確度運算

透過Matlab 程式運算取得假體的實際中心點,這時候再與影像的中 心點比較;並且在圖片上顯示該影像實際位移距離,顯示"水平位移xx 公 分,垂直位移xx 公分”。

圖 35

第四章

表 2 GE QA Phantom

4.3 低對比度探測分析與結果

4.4 雜訊與均勻度分析與結果

均勻度分析

4.5 雷射定位線的準確度分析與結果

4.6 MTF 分析與結果

透過程式計算,得出 MTF50與 MTF10,並且與該機型的 MTF 值比較,得出下 表與標準值的誤差程度。標準值的 MTF50為 4.0 ± 10%.,標準值的 MTF10為 6.5 ± 10%.

12 GE QA Phantom

MTF50 MTF10

Hospital A 4.27 6.82

Hospital B 4.82 6.55

Hospital C 3.96 5.90

Hospital D 4.25 7.10

Hospital E 3.88 5.90

Hospital F 4.42 6.57

分析上述數據,透過程式計算 MTF 在標準值範圍內。

4.7 操作時間分析

第五章

第六章

Phantom[30]、gammex RMI 465 & 467 Phantom,都有原廠提供相關特定參 數。屆時可以依據這些資料修改本程式的相關參數供各廠牌 CT 測試及校正使 用。

參考資料

英文文獻

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