背景:高解析平行孔洞式準直儀 (parallel-hole high resolu-tion collimator) 具有較優之解析度，而扇型孔洞式準直儀(fan beam collimator) 因孔洞走向，使用較多的碘化鈉晶體而提高影像計數量。對單光予腦部電腦斷層造影，兩種準直儀各有其優點，若再搭配不同的影像重組方法，則會產生不同的影響。本研究即以高解析平行孔洞式準直儀與扇型孔洞式準直儀分別攝取Jaszczak假體 (Jaszczak phantom) 之斷層影像，再分別以 Filter Backproiecti (FBP) 與Ordered Subset Expectation Maximization (OSEM)方法重組，目的在找出何種組合具有最佳之空間解析度。
方法：Jaszczak假體內分別放置不同放射活度之鎝-99m線射源(line source)，分別以高解析平行孔洞式準直儀及扇型孔洞式準直儀攝取Jaszczak假體之斷層影像，並分別以FBP與OSEM方法重組計算影像之全值半寬值 (Full Widthat Half Maximum,FWHM)藉以評估空間解析力。
結果:三組不同放射活度線射源 (0.5 mCi、0.3 mCi與0.014 mCi)，使用高解析平行孔洞式準直儀取像配合OSEM重組得到之FWHM分別為2.98％、3.03％與3.22％；配合FBP重組得到之FWHM值分別為3.8％、3.88％與3.88％。使用扇型孔洞式準直儀取像配合FBP重組得到之FWHM值分別為3.65％、3.79％與3.39％。
結論:高解析平行孔洞式準直儀配合OSEM重組獲得SPECT影像之FWHM優於扇型孔洞式準直儀配合FBP重組之表現。使用相同的影像重組方法時，扇型孔洞式準直儀的空間解析力優於高解析平行孔洞式準直儀

Background: The spatial resolution of imaging with parallel-hole high-resolution collimator is superior to that with parallel-hole general-purpose collimator. The increased sensitivity with fan-beam collimator is due to its hole direction and using more Nal (TI) crystals to interact with the photons emitted from object. The purpose of this study is to optimize the combination of collimator and image reconstruction algorithm for brain SPECT imaging.
Methods: A Jaszczak phantom was centered with three radioactive levels of 99mTc line sources, and was filled with water to simulate the scatter medium. The planar data of line source were acquired with parallel-hole high-resolution collimators and fan-beam collimators on a dual-head SPECT system, respectively. The image data were recon-structed with both iteration reconstruction (OSEM) and filter backprojection reconstruction (FBP). The spatial resolution of each combination was evaluated by its full-width-of-half-maximum (FWHM) value.
Results: The FWHM values for imaging three line sources (0.5 mCi, 0.3 mCi and 0.014 mCi, respectively) were calculated as follows. By using parallel-hole high-resolution collimators, they were 2.98%, 3.03% and 3.22%, respectively, with OSEM reconstruction, and were 3.8%, 3.88% and 3.88%, respectively, with FBO algorithm. The F'WHM for FBP and OSEM were 3.8% and 2.98%, respectively. With a combination of fan-beam collimators and FBP algorithm, the FWHM were 3.65%, 3.79% and 3.39%, respectively.
Conclusions: The spatial resolution for SPECT images using parallel-hole high-resolution collimator and OSEM reconstruction is better than that using fan beam collimator and BPF reconstruction. When using the same recon- struction method, the spatial resolution is better in the fan-beam collimator group than in the parallel-hole high-reso-lution collimator group.