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第位光临者，
今天是
此网叶主要是介绍SPECT仪器的质量控制技术和方法
1、 SPECT信息密度与重建函数的关系,
2、 A
new dual-isotope convolution cross-talk correction
method: a Tl-201/Tc-99m SPECT cardiac phantom study.
3、Enhancing
spot detection and reducing noise from digitized
electrophoretic gel images using area processing filters.
4、正电子发射计算机断层仪（PET）性能测试
5、FDG-SPECT(MCD)成像的若干问题
Monday 8/4/97, 1:30 pm
应用模型研究SPECT信息密度与重建参数的关系
SPECT断层图象重建的好坏受许多因素影响,其中信息量的变化影响较大,本文用实验模型探讨SPECT信息密度与断层图象重建滤波函数参数选择的关系。
实验仪器为TOSHIBA GCA-7100A SPECT,探头配带低能通用准直器(LEGP),
研究对象为充满分别2mCi,4mCi,6mCi等不同活度的放射性过锝酸盐的SPECT模型,内置不同大小的球形体,以64X64矩阵，1.0,1.5,2.0不等的放大倍数，每帧采集计数60K至280K不等的条件进行旋转360度断层采集,共18次。图象处理:1.用ROI计算断层图像的像素值、靶面积(cm2)、单位像素的计数,像素大小(mm)、帧总计数。
2. 用Butterworth进行重建前预滤波，用RAMP函数进行重建滤波。Butterworth的陡度因子为8.0,截止频率分别从0.08至0.40,间隔0.01,然后选择3张较好的重建图象,测其FWHM,选FWHM最小者对应的截止频率即为最佳截止频率。统计处理:对截止频率与各采集参数的多元相关分析及回归分析。
结果表明单位象素计数(kCP)与截止频率(Fc)的回归有显著价值，
回归方程为：Fc=0.14＋0.49×kCP，相关系数为0.99,P<0.001。其他参数与截止频率仅有简单相关关系,不能单独作为影响因素。SPECT断层重建图象的质量受许多因素的影响[1]，如：系统均匀性、
固有均匀性、系统分辨率、固有分辨率、旋转中心漂移、系统灵敏度等诸多因素,
这些因素可称之为硬因素，可通过日常质量控制达到最佳状态，在一定时期内保持相对稳定；但对于相同硬因素，SPECT断层图象质量也会不同，
我们把断层旋转半径大小、靶的信息量、重建函数及其参数大小等因素，称之为软因素，可经常变化。其中滤波函数及参数的选择对断层图象质量的影响非常明显，许多核医学工作者对ＥＣＴ重建滤波函数选择进行了大量的研究，对重建前滤波函数的选择趋向于应用Butterworth类函数[1-4]，但函数参数(fc,n)的选择各行所爱(其中
fc为截止频率,n为陡度因子)。
究竟什么因素决定了重建前滤波函数截止频率的大小，一般认为重建函数的截止频率的大小主要与仪器系统空间分辨率，注入受检者体内剂量大小及探测病变大小有关[2]，这种关系如何？未见进一步的研究。本研究在一定条件下，研究各采集参数对Butterworth截止频率大小的贡献。发现各因素与截止频率均有显著简单相关关系,P值小于0.05。但进一步统计结果显示它们的偏相关系数检验,仅单位象素计数的P值小于0.01,其余P值均大于0.05。说明单位象素计数大小与滤波截止频率大小存在直接显著正相关，而其他参数与截止频率的关系仅是间接关系，它们的改变只是通过影响单位象素计数的大小间接影响截止频率的大小。单位象素计数大小是决定SPECT
断层重建截止频率选择的直接影响因素，是影响SPECT断层图象重建好坏的重要因素。
- ABSTRACT
- Simultaneous dual-isotope SPECT imaging provides
a clear advantage in situations where two
concurrent metabolic, anatomic, or background
measurements are desired. It obviates the need
for two separate imaging sessions, reduces
patient motion problems, and provides exact image
registration between images. However, a potential
limitation of dual-isotope SPECT imaging is
contribution of scattered and primary photons
from one radionuclide into the second
radionuclide's photopeak energy window, referred
to here as cross-talk. Cross-talk in both
photopeak energy windows can significantly
degrade image quality, resolution, and
quantitation to an unacceptable level. Simple
cross-talk correction method used in
dual-radionuclide in vitro counting, even applied
on a pixel-by-pixel basis, does not
account for the differences in spatial
distribution of the photopeak and cross-talk
photons. Here a new convolution cross-talk
correction method is presented. The convolution
filters are derived from point response functions
(PRFs) for Tc-99m and Tl-201 point sources. Three
separate acquisitions were performed, each with
two 20% wide energy windows, one centered at 140
keV and another at 70 keV. The first acquisition
was done with Tc-99m solution only, the second
with Tl-201 solution only, and the third with a
mixture of Tc-99m and Tl-201. The nonuniform RH-2
thorax-heart phantom was used to test a new
correction technique. The main difficulty and
limitation of the convolution correction approach
is caused by the variation in PRF as a function
of depth. Thus, average PRF should be used in the
creation of an approximative filter.(ABSTRACT
TRUNCATED AT 250 WORDS)
Enhancing spot detection and
reducing noise from digitized electrophoretic gel images
using area processing filters
- ABSTRACT
- Twenty area processing filters and filter
combinations were evaluated in an effort to
optimize presentation of two-dimensional
electrophoretic profiles to the Laplacian spot
finder for maximal spot detection sensitivity.
Images of electrophoresis gels were obtained by
digitizing polyacrylamide gels at 1024 x 1024
picture elements (pixels) resolution with 256
grey scale levels using the charge coupled device
(CCD) camera of the Millipore Bio Image 110S
computerized imaging system. The images were
imported into an Apple Macintosh microcomputer
and selectively enhanced by applying various area
processing filters. Previously described least
squares fit, low-pass, Gaussian and median
filters were used to reduce noise in the
digitized images. These filters differ in that
during the summation process the least squares
template weighs the immediately adjacent pixels
more heavily than the Gaussian template. The
low-pass filters weigh all neighboring pixels
equally. Median filters replace the pixel
of interest with the middle (median) value of the
pixel neighborhood. An analysis of
convolution filter sizes indicated that a
7 x 7 matrix was optimal for 22 cm x 22 cm gels.
When using the median area processing procedure,
however, the 3 x 3 filter was found to be
superior to the 7 x 7 filter. The 7 x 7
least squares filter significantly
improved detection of low abundance polypeptides
while having only minimal effects on the high
abundance polypeptides. The 7 x 7 Gaussian and 3
x 3 median filters also improved detection of low
abundance polypeptides but reduced the integrated
areas of the high abundance polypeptides and thus
their integrated optical densities as
well.(ABSTRACT TRUNCATED AT 250 WORDS)
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