petct基本原理和應(yīng)用

1、PET/CT基本原理和應(yīng)用,陳澤龍,Medical Imaging Center,Fuzhou General Hospital,PET/CT Basic Principle and Applications,Outline,Overview 功能與解剖成像PET系統(tǒng)的發(fā)展歷史PET物理學(xué)基礎(chǔ) 符合探測 “混合”事件 分辨率和噪聲

2、衰減校正PET主機(jī)的組成和工作原理計(jì)算機(jī)圖象處理質(zhì)量控制,Medical Imaging Center,Fuzhou General Hospital,Tracing life's processes,與CT、MR的解剖成像不同，PET可對代謝過程的生理和生化改變進(jìn)行評價(jià)，而組織功能的改變往往預(yù)示著結(jié)構(gòu)的改變。,PET使用放射性藥物進(jìn)行示蹤，示蹤劑采用如C、N、O、F等組成生命的基本元素的核素作為示蹤原子。,Medical

3、 Imaging Center,Fuzhou General Hospital,因此，相對于其他成像模式而言，PET往往能夠在分子水平上揭示疾病的代謝狀態(tài)。,Medical Imaging Center,Fuzhou General Hospital,PET Application,Medical Imaging Center,Fuzhou General Hospital,Applications in Oncology,Lung

4、Cancer,Medical Imaging Center,Fuzhou General Hospital,Applications in Oncology,Breast Cancer,Medical Imaging Center,Fuzhou General Hospital,Applications in Oncology,Recurrent Colorectal Cancer,Medical Imaging Center,F

5、uzhou General Hospital,Applications in Oncology,TumorTherapyMonitoring,Medical Imaging Center,Fuzhou General Hospital,Overview 功能與解剖成像PET系統(tǒng)的發(fā)展歷史PET物理學(xué)基礎(chǔ) 符合探測 “混合”事件 分辨率和噪聲

6、 衰減校正PET主機(jī)的組成和工作原理計(jì)算機(jī)圖象處理質(zhì)量控制,Outline,Medical Imaging Center,Fuzhou General Hospital,History,1953年 Brownell G.L. 等人進(jìn)行正子發(fā)射核素探測1975年 Ter-Pogossian M.M.、Phelps M.E.、Hoffman E.J. 發(fā)展出正電子斷層掃描儀1975年 Muehllehner G. 提出

7、兩平行雙探頭配以符合探測電路進(jìn)行正電子掃描1992年 van Lingen A. 提出以平行相對的雙探頭單光子發(fā)射掃描儀配上 511 keV 的高能準(zhǔn)直器可以進(jìn)行正子發(fā)射斷層掃描1999年 Thomas Beyer 等人開發(fā)出PET/CT 掃描儀2001年 PET/CT用于臨床,Medical Imaging Center,Fuzhou General Hospital,BNL ring, c. 1964,Medical Ima

8、ging Center,Fuzhou General Hospital,First Installation in Zurich March 2001,Medical Imaging Center,Fuzhou General Hospital,Medical Imaging Center,Fuzhou General Hospital,Medical Imaging Center,Fuzhou General Hospital,Med

9、ical Imaging Center,Fuzhou General Hospital,Outline,Overview 功能與解剖成像PET系統(tǒng)的發(fā)展歷史PET物理學(xué)基礎(chǔ) 符合探測 “混合”事件 分辨率和噪聲 衰減校正PET主機(jī)的組成和工作原理計(jì)算機(jī)圖象處理質(zhì)量控制,Medical Imaging Cent

10、er,Fuzhou General Hospital,正電子的物理特性,正電子發(fā)現(xiàn)于1934年正電子帶一個(gè)單位正電荷正電子有一定的能量和射程正電子只能瞬間存在正電子由β+衰變產(chǎn)生正電子與負(fù)電子結(jié)合產(chǎn)生湮滅輻射,Medical Imaging Center,Fuzhou General Hospital,Positron Annihilation,,,,,,,,,,,,b+,,b-,~1-3mm,511KeV,,,,511KeV

11、,,,? Positron travels 1-3mm (depending on energy) before annihilation.? Annihilation process conserves:- Energy (photons are 511KeV).- Momentum (photons are almost exactly colinear).? Simultaneous detection of two 5

12、11KeV photons --> event along line between detectors.,Medical Imaging Center,Fuzhou General Hospital,Coincidence Detection,,,,,,,,,,,Pulse Processing,,,,Pulse Processing,,,,,,,AND,,,Events occurring anywhere on line b

13、etween detectors contribute coincidence counts to detector pair.Recorded counts are proportional to line integral of activity between the detectors.,DET 1,DET 2,Medical Imaging Center,Fuzhou General Hospital,Coincidence

14、 Events,單一事件（Single Events）真實(shí)符合事件（True Coincidence Events ）散射符合事件（Scattered Coincidence Events ）隨機(jī)符合事件（Random Coincidence Events ）,Medical Imaging Center,Fuzhou General Hospital,Single Events,Medical Imaging Center,Fu

15、zhou General Hospital,True Coincidence Events,Medical Imaging Center,Fuzhou General Hospital,Scattered Coincidence Events,Medical Imaging Center,Fuzhou General Hospital,Random Coincidence Events,Medical Imaging Center,Fu

16、zhou General Hospital,Nuclear Medicine Camera,Medical Imaging Center,Fuzhou General Hospital,Resolution Limits,e+,e-,,Effects of Positron Range ~1-3mm - Function of emitted positron energy. - 18F images (Emax=0.6MeV)

17、 have better resolution than 15O (Emax=2.1MeV).,Point Source,Medical Imaging Center,Fuzhou General Hospital,Multiplane and 3D Imaging,Multiple Ring Imaging“Cross planes” formed by adjacent rings.N rings --> 2N-1 ima

18、ging planes.Each plane processed independently by 2D algorithm.Septa added to reduce off-plane photons.Volume (3D) ImagingRemove septa.Big increase in system sensitivity, even bigger increase in scatter.Reconstruc

19、tion algorithm not separable into planes --> requires a 3D algorithm.,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,Medical Imaging Center,Fuzhou General Hospital,Noise in PET Images,PET圖像的噪聲大小由符合事件的計(jì)數(shù)決定

20、。在圖像重建過程中采用濾波或平滑處理可以減少圖像噪聲，但同時(shí)降低圖像分辨率。,Medical Imaging Center,Fuzhou General Hospital,衰減校正,與CT透射型掃描不同PET探測的是發(fā)射型掃描，采用符合探測，有效計(jì)數(shù)量低，介質(zhì)的影響不能忽略， 需要進(jìn)行衰減校正 。,Medical Imaging Center,Fuzhou General Hospital,外置棒源68Ge的衰減校正——正電子顯像的標(biāo)

21、準(zhǔn)衰減校正方法X-CT衰減校正,Medical Imaging Center,Fuzhou General Hospital,Outline,Overview 功能與解剖成像PET系統(tǒng)的發(fā)展歷史PET物理學(xué)基礎(chǔ) 符合探測 “混合”事件 分辨率和噪聲 衰減校正PET主機(jī)的組成和工作原理計(jì)算機(jī)圖象處理質(zhì)量控制

22、,Medical Imaging Center,Fuzhou General Hospital,整套PET系統(tǒng)包括PET主機(jī)和回旋加速器及配套的化學(xué)合成裝置三大部分。PET主機(jī)配置有掃描機(jī)架、主機(jī)柜、檢查床、主輔工作站等幾個(gè)部分。機(jī)架是最大部分，其中最主要的是探頭部分，包括探測器環(huán)和中隔、多晶體、光電倍增管、前置電子線路、符合線路、分類器、電子準(zhǔn)直線路、透射源及各種電子學(xué)儀器線路等。,Medical Imaging Center,F

23、uzhou General Hospital,Medical Imaging Center,Fuzhou General Hospital,Medical Imaging Center,Fuzhou General Hospital,Medical Imaging Center,Fuzhou General Hospital,Detector Requirements,GoalRequirementHigh Spatial

24、ResolutionSmall Detector Elements High SensitivityHigh Stopping PowerLow Scatter Fraction Good Energy ResolutionLow RandomsGood Timing ResolutionLow Deadtime Fas

25、t Event Handling Small Channel Size Limited MultiplexingLow CostNone of the Above,Medical Imaging Center,Fuzhou General Hospital,Detector Materials,High DensityOverall detection effi

26、ciency is proportional to the product of the detection efficienciesHigh Effective Atomic NumberHigh photopeak fraction (photopeak vs Compton) allows high discriminator setting for scatter rejectionFast Decay TimeThe

27、primary speed of the detector has a big effect on count rate Otherslight output, wavelength, and index of refraction are other properties that are important,Medical Imaging Center,Fuzhou General Hospital,Detector Mater

28、ials,NaI(Tl)BGOGSO(Ce)LSO(Ce),STOPPHOTONS,PRODUCELIGHT,GROWCRYSTALS,m(cm-1) 0.37 0.95 0.670.89Photonfraction ~15% ~40% ~35%~30%,Light Output 100 20-25 3575Decay Constant 230 300 6550,Radioa

29、ctiveNONONOYESMelting Point 650 1050 >2000>2000Furnace Platinum IridiumIridiumCost $5/cc $10/cc $20/cc>$25/cc ??,Medical Imaging Center,Fuzhou General Hospital,Detector Assemblies,1-to-1

30、CouplingExcellent livetime characteristics, but expensive, and limited in size to smallest available PMT (~1cm2).,Block DetectorIndividual crystals “pipe” light to detectors.More complex, but required with low light o

31、utput--BGO.,Anger CameraLight from scintillator is distributed among several PMT’s; measured distribution determines location.Poor livetime, but can have good resolution with enough light output--NaI(Tl).,Medical Imagi

32、ng Center,Fuzhou General Hospital,Medical Imaging Center,Fuzhou General Hospital,Medical Imaging Center,Fuzhou General Hospital,探測器塊的部件,Medical Imaging Center,Fuzhou General Hospital,Six Detector Blocks（module),,One Bloc

33、k,,DetectorCassette,,18 Rings,18環(huán)探測器的組成,Medical Imaging Center,Fuzhou General Hospital,Medical Imaging Center,Fuzhou General Hospital,Block Detector,,A,,B,,C,,D,Compute total energy, centroid of light distribution:E =

34、A+B+C+DX = (B+D)/EZ = (C+D)/E,Medical Imaging Center,Fuzhou General Hospital,Medical Imaging Center,Fuzhou General Hospital,Medical Imaging Center,Fuzhou General Hospital,操作臺(tái)及輔助設(shè)施,操作臺(tái)檢查床 床板采用高強(qiáng)度和低射線吸收率最佳的碳素纖維材

35、質(zhì)，不會(huì)對圖像數(shù)據(jù)造成影響；還配備腦斷層頭托，更好的固定頭位傾斜驅(qū)動(dòng)器 屬于機(jī)架部分，并非所有機(jī)型都有,Medical Imaging Center,Fuzhou General Hospital,Outline,Overview 功能與解剖成像PET系統(tǒng)的發(fā)展歷史PET物理學(xué)基礎(chǔ) 符合探測 “混合”事件 分辨率和噪聲

36、 衰減校正PET主機(jī)的組成和工作原理計(jì)算機(jī)圖象處理質(zhì)量控制,Medical Imaging Center,Fuzhou General Hospital,輔助設(shè)備PET掃描機(jī),主機(jī)柜,存儲(chǔ)器,軟件包 CPU功能鍵控制臺(tái),輸入,輸出,外存設(shè)備光盤、軟盤 顯示 打印,,,,,,,,,工 作 站,PET計(jì)算機(jī)框圖

37、,Medical Imaging Center,Fuzhou General Hospital,軟件結(jié)構(gòu)和分類,系統(tǒng)軟件 操作系統(tǒng)部分、系統(tǒng)應(yīng)用程序、調(diào)試和故障檢測程序、語言處理程序應(yīng)用軟件 PET數(shù)據(jù)采集、圖像重建、量化分析和自編 程序數(shù)據(jù)庫,Medical Imaging Center,Fuzhou General Hospital,Medical Imaging Center,Fuzhou Ge

38、neral Hospital,2D和3D采集,2D是在有柵隔板準(zhǔn)直狀態(tài)下采集3D是在撤除柵隔板的狀態(tài)下采集,Medical Imaging Center,Fuzhou General Hospital,PET的2D和3D采集模式,2D采集時(shí)探頭環(huán)與環(huán)之間放置柵隔（septa）柵隔由鉛或鎢等重金屬屏蔽材料制成，防止錯(cuò)環(huán)符合事件發(fā)生3D采集收進(jìn)環(huán)間柵隔，系統(tǒng)會(huì)記錄探測器之間任何組合的符合事件,Medical Imaging Cent

39、er,Fuzhou General Hospital,PET的2D和3D采集模式,屏蔽柵隔的存在減少隨機(jī)和散射符合計(jì)數(shù)(30%)。,Medical Imaging Center,Fuzhou General Hospital,PET的2D和3D采集模式,2D采集： 信噪比高，隨機(jī)符合和散射符合計(jì)數(shù)較小 圖像校正和圖像重建簡單，定量處理準(zhǔn)確 軸向FOV均勻性較好 靈敏度較低，采集時(shí)間較長3D采集：

40、 靈敏度較高，節(jié)省采集時(shí)間 隨機(jī)符合和散射符合計(jì)數(shù)較高 圖像校正和圖像重建復(fù)雜，定量精度很差 軸向FOV均勻性較差,Medical Imaging Center,Fuzhou General Hospital,2D采集適合腫瘤探測和全身掃描，適合精確定量分析3D采集適合神經(jīng)系統(tǒng)、腦掃描采用3D顯像，腦內(nèi)結(jié)構(gòu)顯示細(xì)膩，圖像質(zhì)量好,Medical Imaging Center,Fuzhou General Hospi

41、tal,圖像重建,濾波反投影重建迭代重建 ML-EM算法 基于極大似然估計(jì)的期望最大算法 OSEM算法 有序子集加速算法 RAMLA算法二維傅立葉變換法,Medical Imaging Center,Fuzhou General Hospital,Outline,Overview 功能與解剖成像PET系統(tǒng)的發(fā)展歷史PET物理學(xué)基礎(chǔ) 符合

42、探測 “混合”事件 分辨率和噪聲 衰減校正PET主機(jī)的組成和工作原理計(jì)算機(jī)圖象處理質(zhì)量控制,Medical Imaging Center,Fuzhou General Hospital,校準(zhǔn)（Calibration ）,Blank Scan: 20min~30min, dailySingles /update gain adjustment: 1hr

43、,weeklyCoincidence Timing Calibration:5min,weeklyNormalization Calibration: 12hr or more,quarterlyWell Counter Calibration: quarterly,Medical Imaging Center,Fuzhou General Hospital,Pin source,Ge-68；半衰期：271days高活度源（4

44、00MBq），2根低活度源（60MBq），1根,Medical Imaging Center,Fuzhou General Hospital,Blank Scan,在探頭之間只有空氣介質(zhì)的情況下，用外源性棒源進(jìn)行的一種掃描。,（1） 用于計(jì)算病人體內(nèi)組織的衰減因子（2）了解Scanner 能否正常工作（如：晶體的狀況）,Medical Imaging Center,Fuzhou General Hospital,,Crystal

45、Failure,Blank Scan 正弦圖,Medical Imaging Center,Fuzhou General Hospital,Blank Scan 示意圖,Medical Imaging Center,Fuzhou General Hospital,Coincidence Timing Calibration (CTC),Purpose: – Adjust for timing channel prop

46、agation(spread) delays so events from all blocks are timestamped equivalently.Method: – Coincidence acquisition of orbiting rod source. – CPM passes through timing difference information instead of crystal I

47、D. – Timing spectra histogrammed, analyzed to determine delay line settings.Output: – One value per block (336 total).Dependencies and Effects on Other Calibrations – CTC is independent of other calib

48、rations and is fundamentally a property of the electronics channels themselves. Re-done every time a pre-CPM electronics component is changed.,Medical Imaging Center,Fuzhou General Hospital,Singles /update gain adjustmen

49、t,Position adjustment:晶體模擬位置圖Energy adjustment: 晶體能量閾值的校準(zhǔn)Default gain : 每個(gè)晶體塊（block)的4個(gè)PMT通道增益的校準(zhǔn),晶體圖,能量圖300~650Kev,PMT Gain,Medical Imaging Center,Fuzhou General Hospital,Normalization Calibration,探測器歸一化校準(zhǔn)，用以校正發(fā)射顯像資料

50、 探頭歸一化也稱為探測器靈敏度校正。 對PET數(shù)據(jù)進(jìn)行圖像重建時(shí)，基本假設(shè)是符合投影線靈敏度一致。探測器參數(shù)的差異，符合投影線與探測器表面夾角不同，都會(huì)造成靈敏度的差異。 對這些造成探測靈敏度差異的因素，進(jìn)行校正的過程稱為探測 器歸一化。 對每一條符合投影線來說，都應(yīng)有一個(gè)歸一化因子low-activity pin source(60MBq), constantly rotating12hr

51、or more,Medical Imaging Center,Fuzhou General Hospital,Well Counter Calibration（WCC）,Radiotracer+Water,,目的：用以計(jì)算SUV,Medical Imaging Center,Fuzhou General Hospital,Thank You!,Medical Imaging Center,Fuzhou General Hospital,