| 摘要: | 醫學影像為現今輔助診斷病灶不可或缺的一個工具，在研究核子醫學
影像中，建構更高空間解析度的影像擷取設備或是重建出更清晰的物體 影
像為重要的研究方向。本研究以單光子放射顯微鏡 Single Photon Emission
Microscope, SPEM 作為研究儀器，此為單光子放射電腦斷層掃描系統
Single Photon Emission Computed Tomography, SPECT) 的一個分支，擁有較
高的空間解析度，專門用於小動物造影。本論文將利用 傅立葉串擾矩陣
(Fo urier Crosstalk Matrix, FCM 分析影像系統矩陣的空間解析度，再以多針
孔取樣完整性分析此影像系統矩陣的物空間取樣，並以不同軌道 的取樣進
行物體影像重建。
影像系統的成像矩陣將三維物空間的單位體素點透過成像系統計算找
到該體素在偵測器上面的投影點，稱為影像系統矩陣 H 矩陣 ))，他的特性會
是決定這套系統成敗的關鍵，該系統的點響應函數 Point R e sponse Function,
PRF 是否過寬，調制傳遞函數 Modulation Transfer Function, MTF) 會不會太
低，將會影響此影像系統的空間解析度。本研究以 F ourier Crosstalk Matrix
分析 單光子放射顯微鏡系統的影像系統矩陣的 P R F 與 MTF 並取得矩 陣的
混疊，分析在重建時是否產生取樣不足。並將透過圓形軌道、單螺旋軌道與
雙螺旋軌道的取樣方式進行比較。
取樣完整性分析方法為過去本實驗室針對
SPEM 系統所開發的針孔設
計分析方法，在製作針孔擋板前提早取得最佳針孔的分布位置，以利降低開
發成本。本研究中將以影像系統矩陣開發的環境回推物體的空間取樣，比較
單螺旋軌道與圓形軌道取樣的差異，以及在相同取樣角度下雙螺旋與單螺
旋軌道的取樣差異。;Medical imaging
has now become an i ndispensable tool for assisting in the
diagnosis of diseases or physical problems In researching of nuclear medicine
imaging, getting higher spatial resolution devices or reconstructing clearer object
images are important research directions. This study uses the Single Photon
Emission Microscope (SPEM) system as the research equipment. SPEM is a high
resolution branch of Single Photon Emission Computed Tomography (SPECT)
systems specifically designed for imaging small animals. We used the F ourier
Crosstalk Matrix to analyze the characteristics of the imaging system matrix, used
the s ampling completeness coeffici ent (SCC) to analyze the object space sampling,
and finally reconstructed the object images with different imaging orbits.
The imaging system matrix, also called the
H matrix, contains the point
source response on the detector of each voxel in the three di mensional object
space. It characterizes the spatial resolution of the imaging system, whether the
point response function (PRF) is narrow or wide and the m odulation transfer
function (MTF) is high or low. Therefore, the study analyzed the imaging system
m atrix of SPEM through the Fourier Crosstalk Matrix to find the equivalent MTF
and to compare the aliasing characteristics of circular orbit and single helical orbit.
The
S CC analysis was developed by this laboratory for the SPEM system
before, aimed at fin ding the best pinhole distribution before starting experiments
to reduce the development cost. This study utilized SCC to compare the sampling
completeness between the circular orbit, single helical orbit, and double helical
orbit.
Finally, we used phantom
reconstructions to assess the imaging performance
of SPEM, including a three point phantom and Defrise phantoms. All images
were reconstructed by 20 iterations of Ordered Subset Expectation Maximization
(OSEM). The three point phantom is to validate the c orrectness of the H matrix
of double helical orbit, which was rewritten from the H matrix of circular orbit
In Defrise phantom reconstructions, we designed three different phantoms.
The first one occupies a cylinder of 20 mm diameter and 20 mm height, and the
circular disks are 2 mm thick with 2 mm separation. The second one occupies a
cylinder of 31 mm diameter and 31 mm height, and the circular disks are 2 mm
thick with 2 mm separation. The third one occupies a cylinder of 20 mm diameter
and 20 mm height , and the circular disks are 1 mm thick with 1 mm separation.
The size of the second phantom, 31 mm, is the Field of view (FOV) size o f the
circular orbit H matrix. The reconstruction results of the second phantom showed
that with the same number of projec tions, a single helical orbit complemented the
sampling incompleteness of the circular orbit and got better reconstruction images,
and a double helical orbit further improved the sampling uniformity |
