高解析平行孔洞式準直儀與扇型孔洞式準直儀搭配不同影像重組方法對單光子電腦斷層造影空間解析之影響

The Influence of the Parallel-Hole High-Resolution Collimator and Fan Beam Collimator for the Spatial Resolution of Brain SPECT

陳昌祺(Chang-Chi Chen) ； 袁小如(Shiao-Ju Yuan) ； 胡志明(Jimmy Hu) ； 林萬鈺(Wan-Yu Lin) ； 王世禎(Shyh-Jen Wang)

《核子醫學雜誌》 16卷2期 (2003/06) Pp. 73-77

https://doi.org/10.6332/ANMS.1602.004

摘要

背景：高解析平行孔洞式準直儀(parallel-hole high resolution 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。對單光子腦部電腦斷層造影，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(Jaszczakphantom)之斷層影像，再分別以Filter Backprojection(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假體内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値半寬値(Full Widthat Half Maximum,FWHM)籍以評估空間解析力。結果：三組不同放射活度線射源(0.5mCi,0.3mCi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分別爲2.98％、3.03％與3.22％：配合FBP重組得到之FWHM値分別爲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値分別爲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。

關鍵字

扇型孔洞式準直儀 ； 高解析平行孔洞式準直儀 ； Filter Backprojection(FBP) ； Ordered Subset Expectation Maximization(OSEM)

並列摘要

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 NaI(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 algonthm for brain SPECT imaging. Methods: A Jaszczak phantom was centered with three radioactive levels of(superscript 99m)Tc 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 reconstructed with both iteration reconstruction(OSEM)and filter back projection 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 FWHM 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 reconstruction method, the spatial resolution is better in the fan-beam collimator group than in the parallel-hole high-resolution collimator group.

並列關鍵字

fan beam collimator ； parallel-hole high-resolution collimator ； filter Backprojection(FBP) ； Ordered Subset Expectation Maximization(OSEM)