Surti S, Shore Adam R, Karp Joel S
Department of Radiology at the University of Pennsylvania, Philadelphia, PA 19104 USA (phone: 215-662-7214; fax: 215-573-3880).
Formerly with the Department of Radiology at the University of Pennsylvania, Philadelphia, PA 19104 USA.
IEEE Trans Nucl Sci. 2013 Jul 2;60(5). doi: 10.1109/TNS.2013.2265605.
Current state-of-art whole-body PET scanners achieve a system spatial resolution of 4-5 mm with limited sensitivity. Since the reconstructed spatial resolution and image quality are limited by the count statistics, there has not been a significant push for developing higher resolution whole-body PET scanners. Our goal in this study is to investigate the impact of improved spatial resolution together with time-of-flight (TOF) capability on lesion uptake estimation and lesion detectability, two important tasks in whole-body oncologic studies. The broader goal of this project is the development of a new state-of-art TOF PET scanner operating within an MRI while pushing the technology in PET system design. We performed Monte Carlo simulations to test the effects of crystal size (4 mm and 2.6 mm wide crystals), TOF timing resolution (300ps and 600ps), and 2-level depth-of-interaction (DOI) capability. Spatial resolution was calculated by simulating point sources in air at multiple positions. Results show that smaller crystals produced improved resolution, while degradation of resolution due to parallax error could be reduced with a 2-level DOI detector. Lesion phantoms were simulated to measure the contrast recovery coefficient (CRC) and area under the LROC curve (ALROC) for 0.5 cm diameter lesions with 6:1 activity uptake relative to the background. Smaller crystals produce higher CRC, leading to increased ALROC values or a reduction in scan time. Improved timing resolution provides faster CRC convergence and once again leads to an increase in ALROC value or reduced scan time. Based on our choice of timing resolution and crystal size, improved timing resolution (300ps) with larger crystals (4 mm wide) has similar ALROC as smaller crystals (2.6 mm wide) with 600ps timing resolution. A 2-level DOI measurement provides some CRC and ALROC improvement for lesions further away from the center, leading to a more uniform performance within the imaging field-of-view (FOV). Given a choice between having either an improved spatial resolution, improved timing resolution, or DOI capability, improved spatial or timing resolution provide an overall higher ALROC relative to a 2-level DOI detector.
当前最先进的全身正电子发射断层扫描（PET）扫描仪实现了4 - 5毫米的系统空间分辨率，但灵敏度有限。由于重建的空间分辨率和图像质量受计数统计限制，因此在开发更高分辨率的全身PET扫描仪方面一直没有重大进展。我们在本研究中的目标是研究提高空间分辨率以及飞行时间（TOF）能力对病变摄取估计和病变可检测性的影响，这是全身肿瘤学研究中的两项重要任务。该项目的更广泛目标是开发一种在磁共振成像（MRI）环境中运行的新型最先进的TOF PET扫描仪，同时推动PET系统设计技术的发展。我们进行了蒙特卡罗模拟，以测试晶体尺寸（4毫米和2.6毫米宽的晶体）、TOF时间分辨率（300皮秒和600皮秒）以及两级相互作用深度（DOI）能力的影响。通过在空气中多个位置模拟点源来计算空间分辨率。结果表明，较小的晶体可提高分辨率，而两级DOI探测器可减少因视差误差导致的分辨率下降。模拟病变体模以测量直径为0.5厘米、相对于背景具有6:1活性摄取的病变的对比度恢复系数（CRC）和LROC曲线下面积（ALROC）。较小的晶体产生更高的CRC，导致ALROC值增加或扫描时间减少。改进的时间分辨率提供更快的CRC收敛，并再次导致ALROC值增加或扫描时间减少。基于我们对时间分辨率和晶体尺寸的选择，具有300皮秒改进时间分辨率的较大晶体（4毫米宽）与具有600皮秒时间分辨率的较小晶体（2.6毫米宽）具有相似的ALROC。两级DOI测量为离中心较远的病变提供了一些CRC和ALROC的改善，从而在成像视野（FOV）内实现更均匀的性能。在提高空间分辨率、提高时间分辨率或DOI能力之间进行选择时，相对于两级DOI探测器，提高空间或时间分辨率可提供总体更高的ALROC。
