核医学仪器与方法-4-2课件

1、正电子发射断层扫描仪(PET)原理应用及进展赵书俊郑州大学生物物理与医学工程研究所郑州大学物理工程学院 内 容 引言 基本工作原理与过程 临床应用 国外PET研究发展现状 国内外市场概况 国内PET研究发展现状Positron Emission Tomography (PET) Teaching SeriesAttenuation CorrectionPhysics of PET; attenuation correctionDifferential Attenuation(single photon)Loss (attenuation) of photons traveling an inf

2、initesimal distance (dx) through a region whos coefficient of attenuation is m.Physics of PET; attenuation correctionAttenuation(single photon, m)Integral solution for photon attenuation in a uniformly attenuating mediumPhysics of PET; attenuation correctionIntegral solution for photon attenuation i

3、n anon-uniformly attenuating medium (m(x)Attenuation - differentialderivation for m(x) formPhysics of PET; attenuation correctionAttenuation - differentialderivation for m(x) formPhysics of PET; attenuation correctionConfirm that this general form is equivalent to the m=constant form for a straight

4、line path:(for straight line path)Attenuation(single photon, m)Physics of PET; attenuation correctionAttenuation correction(single photon) A0 = activity at source Ai = activity measured at point i whose source is A0. m(x) = attenuation at point x ti = probability of photon transmission from origin t

5、o point i; its value is constrained to the range 0,1Physics of PET; attenuation correctionAttenuation correction(coincidence photons) Ai = activity measured at point m from a source of photons (A0) traveling to point i. ti = probability of photon transmission for photons traveling from origin to poi

6、nt i (tis are independent probabilities). Ac = total PET COINCIDENCE activity measured between path points 1 and 2.Physics of PET; attenuation correctionAttenuation correction factor(coincidence photons) a = attenuation correction factor ti = transmission probability of gs traveling path 1 to 2 Ac =

7、 total PET COINCIDENCE activity measured Physics of PET; attenuation correctionSinogram formation revisitedCPET; Buffalo, NY m = uniform attenuation coefficient a = attenuation correction factor |x2-x1| = distance between points x2 and x1Calculated attenuation correction(uniform m)Physics of PET; at

8、tenuation correctionCalculated attenuation correction(uniform m)The PET camera records the number of coincidence events occurring along a large number of lines of response (LORs).If m is a constant of known value, and you can measure the path distance through the attenuating medium (|x2-x1|) for eac

9、h LOR, you can calculate the correction which needs to be applied to the number of measured photons in these LORs which will yield the actual number of photons at the source.Physics of PET; attenuation correctionCalculated attenuation correction(uniform m)A0 somewhere along this lineAc = # of photon

10、s measured by coincidence detectors positioned at X1 and X2Physics of PET; attenuation correctionCircular cylinder sinogram90deg0deg180deg0det192detPhysics of PET; data acquisitionCalculated attenuation correction(uniform m)2nd reconstruction(calculated attenuation correction)1st reconstruction(no a

11、ttenuation correction)uniform cylindrical flood phantomPhysics of PET; attenuation correctionCalculated attenuation correctionDoesnt require additional scanFaster - more throughputLess radiation exposureNo counting statistic problemsAssumes uniform attenuation within modeled regionssinus cavityvaria

12、ble bone thicknesshead holderOperator positioned ellipseAutomated method may not identify scalpMotion artifactsAdvantagesDisadvantagesPhysics of PET; attenuation correctionApplying attenuation correctionAcaA0*=measured emission dataattenuation correctioncomputed originalactivityCPET; Buffalo, NYMeas

13、ured attenuation correctionBlank ScanTransmission ScanEmission Scan(blackboard illustration)Physics of PET; attenuation correctionBlank sinogram samples (3 planes)Physics of PET; data acquisitionTransmission & attenuation correction sinogramsPhysics of PET; data acquisitionMeasured Attenuation Corre

14、ction (short axis heart)Physics of PET; attenuation correctionMeasured Attenuation Correction (zoomed short axis heart)uncorrectedcorrectedPhysics of PET; attenuation correctionMeasured attenuation correctionCorrectly accounts for variable m(x) throughout the scanned region.Quantitatively more accurate than calculated attenuation correction in human subjects.More table time for subject to acquire the transmission scan.Additional radiat