核医学仪器与方法-4-2.ppt

Physics of PET; attenuation correction Measured attenuation correction Correctly 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 radiation exposure from transmission scan Introduces additional statistical noise since attenuation correction coefficients are the ratios of measured counts. Motion artifacts Advantages Disadvantages 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 Physics of PET; attenuation correction Positron Emission Tomography (PET) Teaching Series Attenuation Correction Physics of PET; attenuation correction Differential Attenuation(single photon) Loss (attenuation) of photons traveling an infinitesimal distance (dx) through a region who’s coefficient of attenuation is m. Physics of PET; attenuation correction Attenuation(single photon, m) Integral solution for photon attenuation in a uniformly attenuating medium Physics of PET; attenuation correction Attenuation(single photon, m(x)) Integral solution for photon attenuation in a non-uniformly attenuating medium Physics of PET; attenuation correction Path Attenuation(single photon) Ai = activity measured outside attenuating media A0 = activity at source m(x) = differential attenuation at point x (30) exp() can have values ranging from 0 to 1 Physics of PET; attenuation correction Confirm that this general form is equivalent to the m=constant form for a straight line path: (for straight line path) Attenuation(single photon, m) Physics of PET; attenuation correction Attenuation 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 to point i; its value is constrained to the range [0,1] Physics of PET; attenuation corr