Department of Electrical Engineering, Stanford University, Stanford, CA 94305, USA.
IEEE Trans Med Imaging. 2011 Feb;30(2):391-400. doi: 10.1109/TMI.2010.2080282. Epub 2010 Sep 27.
We are developing a dual panel breast-dedicated positron emission tomography (PET) system using LSO scintillators coupled to position sensitive avalanche photodiodes (PSAPD). The charge output is amplified and read using NOVA RENA-3 ASICs. This paper shows that the coincidence timing resolution of the RENA-3 ASIC can be improved using certain list-mode calibrations. We treat the calibration problem as a convex optimization problem and use the RENA-3's analog-based timing system to correct the measured data for time dispersion effects from correlated noise, PSAPD signal delays and varying signal amplitudes. The direct solution to the optimization problem involves a matrix inversion that grows order (n(3)) with the number of parameters. An iterative method using single-coordinate descent to approximate the inversion grows order (n). The inversion does not need to run to convergence, since any gains at high iteration number will be low compared to noise amplification. The system calibration method is demonstrated with measured pulser data as well as with two LSO-PSAPD detectors in electronic coincidence. After applying the algorithm, the 511 keV photopeak paired coincidence time resolution from the LSO-PSAPD detectors under study improved by 57%, from the raw value of 16.3 ±0.07 ns full-width at half-maximum (FWHM) to 6.92 ±0.02 ns FWHM ( 11.52 ±0.05 ns to 4.89 ±0.02 ns for unpaired photons).
我们正在开发一种使用 LSO 闪烁体与位置灵敏雪崩光电二极管（PSAPD）耦合的双面板乳房专用正电子发射断层扫描（PET）系统。电荷输出使用 NOVA RENA-3 ASIC 进行放大和读取。本文表明，使用某些列表模式校准可以提高 RENA-3 ASIC 的符合时间分辨率。我们将校准问题视为凸优化问题，并使用 RENA-3 的基于模拟的定时系统来校正测量数据，以纠正来自相关噪声、PSAPD 信号延迟和变化信号幅度的时间色散效应。优化问题的直接解涉及矩阵求逆，其阶数（n(3)）随参数数量的增加而增加。使用单坐标下降的迭代方法来近似求逆的阶数（n）。由于在高迭代次数下的任何增益都将低于噪声放大，因此不需要进行逆运算以达到收敛。该系统校准方法通过测量脉冲器数据以及电子符合的两个 LSO-PSAPD 探测器进行了演示。在应用该算法后，所研究的 LSO-PSAPD 探测器的 511keV 光峰对符合时间分辨率提高了 57%，从原始值 16.3±0.07ns 半最大值全宽（FWHM）提高到 6.92±0.02ns FWHM（未配对光子的 11.52±0.05ns 提高到 4.89±0.02ns）。
