【正文】 of the scanner 由于掃描儀調節(jié)不到位，產生很多干擾偽影 ? Loss of resolution 分辨率下降 ? Accuracy of CT numbers CT值的精度 ? Table Location 掃描床的定位 ? CT is a high dose procedure CT診斷是一個高劑量輻射的過程 It is important to know the dose for various studies and to select appropriate dose for optimal clinical performance 重要的是了解各種研究所需的劑量，從而選擇適當的量以獲得最優(yōu)的臨床表現 Clinical Technique 臨床技術 ? Once the basic dose performance of the scanner is determined, the physicist should work with physician colleagues to optimize imagequality and dose 一旦確定了掃描儀的工作劑量，物理學家就要與臨床醫(yī)師合作優(yōu)化影像質量 ? Each site should have techniques tailored to the local needs 每一個地區(qū)應當使用滿足當地需要的技術 ? Manufacturer supplied techniques may not be optimum 制造商提供的技術并不一定是最適宜的 Clinical Technique 臨床技術 ? Technique should be adjusted so that small patients have reduced dose and large patients have increased dose 應作適當的調整，根據病人的實際情況增減劑量 ? The reconstruction filter should be selected to trade noise vs resolution 應對重建濾波器進行選擇以提高分辨率、減少噪聲 ? kV, pitch and slice thickness should be selected to optimize doseimage quality 應對 kV值、螺距和層厚進行選擇以優(yōu)化劑量 影像關系 Image Uniformity 影像均一性 ? CT uses many detectors CT使用很多檢測器 ? The detectors may not be pletely uniform 檢測器并不一定完全一致 ? They may drift 它們可能漂移 ? Quality control is necessary to insure uniformity 對于均一性而言，質控是必需的 Hounsfield Number Hounsfield值 Average attenuation value for Voxel 像素的平均衰減值 Tissue Density Xray Energy 組織密度 X線能量 utissue uw uw CT number = 1000 Uniformity Checked 均一性檢測 ? Scanning Air 掃描空氣 ? ―Air Cals‖ 空氣校準 ? Scanning Water 掃描水 ? Accuracy of Hounsfield Numbers Hounsfield值精度 ? Uniformity 均一性 ? Noise 噪聲 ? Absence of Artifacts 干擾偽影的消失 Phantoms 模體 ? Scanning Water Requires 需要掃描水 ? Water filled phantom 充滿水的模體 ? Carefully made ―solid water‖ 特制的“固體水” ? Solid water has the same density and atomic number as water 固體水具有與水相同的密度和原子數 Phantoms 模體 ? Phantoms supplied by scanner manufacturer 模體由掃描儀制造商提供 ? Often designed to work with scanner specific software 通常是被設計用來與掃描儀軟件配套的 ? Software may check and adjust the scanner 軟件可以用來檢查和調整掃描儀 ? Some manufacturers use tighter specifications than others 一些制造商使用比較苛刻的技術指標 Standards 標準 ? Hounsfield values Hounsfield值 ? Depend on scanner 取決于掃描儀 ? Should be no more than +/7 應在 +/7 之內 ? Uniformity depends on scanner 均一性取決于掃描儀 ? Noise depends on technique used for scan 噪聲取決于所使用的掃描技術 ? Data should be charted so trends can be seen 應將有關數據作圖以觀察趨勢變化 8642024681 2 / 2 5 / 2 0 0 1 2 / 1 3 / 2 0 0 2 4 / 4 / 2 0 0 2 5 / 2 4 / 2 0 0 2 7 / 1 3 / 2 0 0 2 9 / 1 / 2 0 0 2 1 0 / 2 1 / 2 0 0 2CT Number Accuracy CT值精度 ? Check accuracy and constancy of known materials 檢查已知物質的精度和穩(wěn)定性 CT Numbers CT值 ? Air 空氣 1000 970 ? Polyethylene 聚乙烯 107 87 ? Water 水 7 7 ? Acrylic 丙烯酸 110 130 You need to verify which material is in the phantom. If in doubt, check with the manufacturer. 需確認模體中是何種物質，如有疑問，與制造商溝通。 Resolution 分辨率 ? Resolution Test Object 受試目標分辨率 Commercial Phantoms 商業(yè)模體 ? Variety of phantoms available 可選的模體很多 ? Accreditation program in the . requires use of phantom designed by American College of Radiology (ACR) which measures more than QC Phantoms from manufacturers 在美國，認證過程中需使用放射協會設計的模體，而不僅僅是制造商提供的質控模體 Costly 昂貴 Doesn‘t work with manufacturer?s software 不能與制造商提供的軟件一起使用 Requires annual physicist evaluation 每年需要評估 Monitor Display amp。 Film Printer Evaluation 監(jiān)視器和打印機評估 ? Monthly 每月