ct的質(zhì)量控制ppt課件(2)(編輯修改稿)
2025-02-15 02:00 本頁(yè)面
【文章內(nèi)容簡(jiǎn)介】 認(rèn)定位光和掃描床定位正確 ? Determine doses from scanner 確定掃描劑量 ? CT Dose Fundamentals 基本原則 ? CT Dose Terminology 術(shù)語(yǔ) ? CT Dose Variations – Equipment 劑量變化 —設(shè)備 ? CT Dose Variations – Exams 劑量變化 —測(cè)試 ? CT Dose Optimization 劑量?jī)?yōu)化 CT Dose Evaluation CT計(jì)量評(píng)估 X Z Y CT Coordinates CT 坐標(biāo) Ideal World …. 理想狀態(tài) … ? Radiation delivered only to the imaged volume 輻射僅涵蓋成像部分 5 mm 0 + 5 mm Peak dose = “dose” Real World …. 現(xiàn)實(shí)情況 … ? Radiation distribution crosses the imaged volume 輻射跨越成像區(qū)域 5 mm 0 + 5 mm Peak dose “Tails” of dose distribution 劑量分布尾跡 Computed Tomography Dose Index ( CTDI ) CT劑量指數(shù)（ CTDI） ? Integral under ONE radiation dose profile 在單一劑量曲線下積分 ? Dose profile has very long ―tails‖ 劑量曲線有很長(zhǎng)的尾跡 ? FDA uses finite integration limits (177。 7 T) FDA使用定積分極限（ 177。 7 T ） ? Typically measured with TLD (laborious) 典型測(cè)量使用 TLD ? Underestimates tail dose for slices 7 mm 低估了尾跡劑量，層厚在 7mm之內(nèi) ? Ion chamber method integrates over 100 mm 電離室法積分 100mm ? CTDI100 CTDI100 ? single convenient measurement 單一實(shí)用的測(cè)試 CTDI = Integral under the radiation dose profile along the zaxis from a single axial scan of width nT. CTDI=沿 Z軸的輻射劑量曲線積分，寬度為 nT的單一軸向掃描 nT “nominal beam width” = “total nominal scan width” Z radiation dose profile 輻射劑量曲線 CTDI100 MSAD CTDIw CTDIvol DLP Effective Dose CT Dosimetry CT 劑量 100 mm Ionization Chamber 100 mm電離室 ? CTDI measurements are usually made using a 100 mm ionization chamber CTDI測(cè)量通常使用 100mm電離室進(jìn)行 ? Therefore the CTDI is defined for use with this chamber 因此，這一電離室被確定為 CTDI測(cè)試的使用工具 CTDI measurements CTDI測(cè)量 ? In phantoms 在模體中 ? Polymethyl methacrylate (acrylic) 丙烯酸 ? 32 cm diameter, ? 16 cm length (body) 頭部模體 ? 16 cm diameter, ? 14 cm length (head) 體部模體 ? At least five 1 cm holes for exposure measurements throughout FOV 至少五個(gè) 1cm測(cè)試空，暴露于全部視場(chǎng)中 ? In air 在空氣中 ? at isocenter (center of rotation) 等量點(diǎn) CTDI Phantoms CTDI模體 Typical FOV dose distributions (%) 典型視場(chǎng)劑量分布 (%) 100 100 100 100 50 Body 32 cm 100 100 100 100 100 Head 16 cm CTDIW = 83 CTDIW = 100 CTDIW CTDIW Weighted average of center and periphery doses 中心和外圍劑量的加權(quán)平均 = 2/3 CTDI100 (edge) + 1/3 CTDI100 (center) Real World …. 現(xiàn)實(shí)情況 … ? Radiation distribution crosses the imaged volume 輻射跨越成像區(qū)域 5 mm 0 + 5 mm Peak dose “Tails” of dose distribution 劑量分布尾跡 Real World …. 現(xiàn)實(shí)情況 … ? Radiation distribution crosses the imaged volume 輻射跨越成像區(qū)域 5 mm 0 + 5 mm A x ial Po s iti on (m m)Exposure (mR)0200400600800100012001400 8 0 6 0 4 0 2 0 0 20 40 60 80S i n g l e s c a n p r o f i l e M u l t i p l e s c a n p r o f i l e : 3 m m x 3 m m , 4 0 s c a n s P o s i t i o n i n s c a n p l a n e = 6 : 0 0 MSAD Multiple Scan Average Dose 多掃描平均計(jì)量 ? MSAD is the average dose over the central scan of a multiple scan exam MSAD是多掃描檢測(cè)時(shí)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(chǎng)中的位置 ? Overestimates patient dose at beginning amp。 end of scan volume 高估了病人在掃描開(kāi)始和結(jié)束時(shí)的劑量 ? Measured directly with TLD amp。 multiple scans 直接進(jìn)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(dāng)掃描被總標(biāo)稱掃描厚度分割以及所有尾跡下的劑量均被測(cè)量時(shí) MSAD = CTDI When I ? nT MSAD = nT ? CTDI
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