【正文】 c a n p l a n e = 6 : 0 0 MSAD Multiple Scan Average Dose 多掃描平均計量 ? MSAD is the average dose over the central scan of a multiple scan exam MSAD是多掃描檢測時中心掃描的平均劑量 ? Typically 2 4 times higher than peak doseslice 典型情況為層峰劑量的 24倍 ? Dependent on position in the Field of View (FOV) 取決于在視場中的位置 ? Overestimates patient dose at beginning amp。 multiple scans 直接進行 TLD和多掃描 When the scans are separated by the total nominal scan thickness (I = nT) and ALL dose under the tails is measured 當掃描被總標稱掃描厚度分割以及所有尾跡下的劑量均被測量時 MSAD = CTDI When I ? nT MSAD = nT ? CTDI I Volume CTDIw (CTDIvol) 體積（空間） CTDIw(CTDIvol) ? New term recently agreed upon by the IEC IEC最新使用的術(shù)語 ? CTDI100 integrates over 100 mm CTDI100積分 100mm ? CTDIw averages over x (L/R) and y (A/P) CTDIw計算 x和 y軸的平均 ? CTDIvol averages over x, y and z (C/C) CTDIvol計算 x， y和 z軸的平均 ? CTDIvol estimates the MSADw and is operationally easier to measure and pute CTDIvol估算 MSADw而且使得測試和運算更簡便 When I = NT CTDIvol = N pelvis CT 8 11 mSv (800 1100 mrem) 腹部和骨盆 CT Average . background radiation 平均本底輻射 ? mSv (360 mrem) Effective dose values (cont.) 典型的有效劑量 Stereo chest xray mSv (10 mrem) 立體胸部 X線 Low dose chest CT mSv (70 mrem) 低劑量胸部 CT Mammogram mSv (180 mrem) 乳腺 CTC (5 mm) mSv (550 mrem) CTC (5 mm) Double contrast BE mSv (750 mrem) 增強對比 BE CTC ( mm) mSv (980 mrem) CTC ( mm) CT liver perfusion 15 mSv (1500 mrem) CT肝灌注 Why is MultiSlice CT Radiation Dose of Interest? 多層 CT輻射劑量的意義何在？ ? To evaluate different MS CT systems 評估不同的 CT系統(tǒng) ? To triage applications between MS and SS CT 在多層 CT與單層 CT之間進行應用比較 ? To design and optimize MS CT Protocols 設計和優(yōu)化多層 CT應用方案 ? Tradeoff: Thinner slices vs. radiation dose 權(quán)衡：薄層 ? Increased use of CT warrants increased attention to radiation dose 良好的 CT應用需要提升對輻射劑量的關注 Why is MultiSlice dose dependent on total slice width (detector configuration)? 為何多層 CT的劑量取決于檢測器配置結(jié)構(gòu)？ ? The radiation dose profiles are larger than active detector width 輻射劑量分布大于檢測器寬度 ? Required in MultiSlice geometry to keep the penumbra off of the active detectors 就幾何形狀而言，半影區(qū)要避開檢測器 ? Size of penumbral region relatively constant 半影區(qū)的尺寸要相對恒定 ? Different percentage ―inefficiency‖ for different total scan width 對不同的掃描厚度具有不同的無效百分比 Good imaging, good physics ... 好的成像，好的物理特性 … ? Use CTDI, CTDIvol and DLP to help optimize procedures (ALARA) 運用 CTDI， CTDIvol和 DLP幫助優(yōu)化操作程序 ? low dose (increased image noise) does not mean poor image quality 低劑量并不意味著損失影像質(zhì)量 ? noise level should be appropriate for the specific diagnostic task not just to get ―pretty‖ pictures 對于特殊的診斷任務，噪聲應控制在適當?shù)乃?—不只是為得到好的畫面 ? narrow slice widths (narrow beam width) should be appropriate for the specific diagnostic task 對于某些診斷，縮窄層厚是必要的 Dose Conclusions 結(jié)論 ? MultiSlice (MS) systems have similar dose characteristics 多層 CT具有相同的劑量 ? MS dose is primarily determined by the prospective choice of detector configuration 其劑量主要取決于檢測器配置結(jié)構(gòu)的選擇 ? dose variations among detector configurations were greater than the variations among manufacturers 劑量變化更多的來源于檢測器而不是制造商 ? MS CT protocols should be carefully optimized 多層 CT應用方案應進行仔細的優(yōu)化 ? Thinner slices require narrower beam collimation, which currently leads to higher doses 較薄的層厚需要窄光束進行瞄準，這就加大了劑量 ? Thinner slices also require ? mAs to match noise 就噪聲而言，較薄的層厚也要求 mAs值增高 Summary 總述 ? ―What‘s the dose?‖ is not a simple question 劑量不是一個簡單問題 ? Know, understand, amp。 CT計量需要