Evaluation of imaging protocol for ECT based on CS image reconstruction algorithm

Single-photon emission computerized tomography and positron emission tomography are essential medical imaging tools, for which the sampling angle number and scan time should be carefully chosen to give a good compromise between image quality and radiopharmaceutical dose. In this study, the image quality of different acquisition protocols was evaluated via varied angle number and count number per angle with Monte Carlo simulation data. It was shown that, when similar imaging counts were used, the factor of acquisition counts was more important than that of the sampling number in emission computerized tomography. To further reduce the activity requirement and the scan duration, an iterative image reconstruction algorithm for limited-view and low-dose tomography based on compressed sensing theory has been developed. The total variation regulation was added to the reconstruction process to improve the signal to noise Ratio and reduce artifacts caused by the limited angle sampling. Maximization of the maximum likelihood of the estimated image and the measured data and minimization of the total variation of the image are alternatively implemented. By using this advanced algorithm, the reconstruction process is able to achieve image quality matching or exceed that of normal scans with only half of the injection radiopharmaceutical dose.     

单柱离子色谱法测定过热器管垢和锅炉垢中铁、镁和钙的含量

首先用碱熔融法分解试样,然后加抗坏血酸将试液中的Ｆｅ３＋还原为Ｆｅ２＋,再用离子色谱法测定试液中的Ｆｅ２＋,Ｍｇ２＋和Ｃａ２＋。采用Ｓｈｉｍ－ｐａｃｋＩＣ－Ｃｌ阳离子交换柱分离样品离子,以０．２５ｍｍｏｌ／Ｌ乙二胺－０．５０ｍｍｏｌ／Ｌ柠檬酸（ｐＨ４．５０）为流动相,以ＣＤＤ－６Ａ电导检测器检测,使被测组分得到满意的分离和检测。Ｆｅ,Ｍｇ和Ｃａ的加标回收率均在９０％以上。测定结果与原子吸收光谱法测定结果相近。     

Evaluation of imaging protocol for ECT based on CS image reconstruction algorithm

Single-photon emission computerized tomography and positron emission tomography are essential med- ical imaging tools, for which the sampling angle number and scan time should be carefully chosen to give a good compromise between image quality and radiopharmaceutical dose. In this study, the image quality of different ac- quisition protocols was evaluated via varied angle number and count number per angle with Monte Carlo simulation data. It was shown that, when similar imaging counts were used, the factor of acquisition counts was more important than that of the sampling number in emission computerized tomography. To further reduce the activity requirement and the scan duration, an iterative image reconstruction algorithm for limited-view and low-dose tomography based on compressed sensing theory has been developed. The total variation regulation was added to the reconstruction process to improve the signal to noise Ratio and reduce artifacts caused by the limited angle sampling. Maximization of the maximum likelihood of the estimated image and the measured data and minimization of the total variation of the image are alternatively implemented. By using this advanced algorithm, the reconstruction process is able to achieve image quality matching or exceed that of normal scans with only half of the injection radiopharmaceutical dose.     

Respiratory motion correction with an improved demons algorithm for PET images

Respiratory motion is a major factor that affects the quality of PET images of the thoracic area. The diaphragm moves about 15-20 mm due to respiratory motion, which substantially degrades the effective spatial resolution of PET. In this paper, a gated acquisition method is used to correct the motion effects. In this method, an improved demons algorithm is proposed to align the gated images. The experimental results show that the quality of PET images is significantly improved when using our improved method and the proposed method has a faster convergence rate than the original demons algorithm.     

Preliminary study of depth of interaction measurement for a PET detector

In this work we studied the feasibility of detecting the depth of interaction (DOI) with two layers of crystal arrays of LYSO and BGO scintillators coupled to a position-sensitive photomultiplier tube (PS-PMT) R8900-C12. A front-end electronics was designed, with which we got different pulse shapes for different crystals to obtain depth information. With the double integration method, we got the DOI histogram of a divided integration ratio of two crystals as the standard to determine the layer-of-interaction. The DOI accuracy, measured by scanning a ²²Na slit source along the side of the module, was 98% for the LYSO layer and 95% for the BGO layer. The energy resolution at 511keV was 13.1% for LYSO and 17.1% for BGO. We obtained good crystal separation in 2D position histograms of both layers. These results could be useful in the manufacture of PET scanners with high spatial resolutions.     

A region segmentation based algorithm for building a crystal position lookup table in a scintillation detector

In a scintillation detector, scintillation crystals are typically made into a 2-dimensional modular array.The location of incident gamma-ray needs be calibrated due to spatial response nonlinearity. Generally, position histograms—the characteristic flood response of scintillation detectors—are used for position calibration. In this paper, a position calibration method based on a crystal position lookup table which maps the inaccurate location calculated by Anger logic to the exact hitting crystal position has been proposed. Firstly, the position histogram is preprocessed, such as noise reduction and image enhancement. Then the processed position histogram is segmented into disconnected regions, and crystal marking points are labeled by finding the centroids of regions. Finally, crystal boundaries are determined and the crystal position lookup table is generated. The scheme is evaluated by the whole-body positron emission tomography(PET) scanner and breast dedicated single photon emission computed tomography scanner developed by the Institute of High Energy Physics, Chinese Academy of Sciences. The results demonstrate that the algorithm is accurate, efficient, robust and applicable to any configurations of scintillation detector.