Ultra high resolution PET imaging using a collimator insert

描述（由申请人提供）：本提案的长期目标是开发一种用于正电子发射断层扫描（PET）扫描仪的准直插件，以提高空间分辨率和量化。该准直插入物在小动物成像和/或临床成像的规模上可能是有用的，因此将在两个规模上对其进行研究。准直会降低PET的效率，因为准直器会吸收一些发射的511 keV伽马射线。然而，检测到的伽马将具有更好的空间分辨率，因为准直将被设计为减小响应线的宽度，同时还减小散射分数。特别地，通过在任何时间在横轴方向上覆盖每个晶体的一半，将寻求几乎两倍的分辨率改进。诸如准直器穿透等因素将阻止分辨率中的两个增益的全因子。由于需要两个晶体来形成重合，并且每个晶体具有两个不同的曝光，因此通过在扫描期间重新定位准直器或患者来实现采样的四倍改进。准直器设计将允许在扫描仪视场的一小部分内测量所有新的响应线。该分数取决于准直器的接收角，这也决定了穿透量。小动物扫描仪可能包括一只小鼠或大鼠，全身扫描仪可能包括一个直径约20厘米的中心区域。当对于使用准直的床位置的较长扫描时间可以克服一些灵敏度损失时，或者当感兴趣的结构尺寸小于扫描仪的分辨率能力时，准直也可能是最有用的。分辨率增强将是有益的并且通常是单个床位置的应用包括脑、乳房和前列腺成像。放射治疗计划也可以通过提高分辨率来辅助，例如，如果缺氧剂如EF 5可以成像以确定肿瘤的核心是否缺氧，这可能影响治疗计划。该提案的具体目标包括：（1）开发具有穿透性的灵敏度和分辨率的精确模型;（2）通过开发用于安装和定位的适当硬件以及用于与扫描仪同步的适当软件，设计、构建和集成用于小动物扫描仪的实验原型准直器，这是获取4倍增加的采样线所需的;（3）开发精确模拟准直的灵敏度和分辨率的迭代重建;以及（4）在小动物扫描仪上实验性地评估原型准直器，并对全身扫描仪进行详细模拟。如果准直成功，可以作为现有扫描仪的升级或直接集成到未来的设计中。准直也有可能改变未来扫描仪的设计，因为更大的晶体具有更好的能量和定时分辨率，并且不太可能导致晶间散射，可以以更低的成本用于制造。未来的努力还可能涉及准直，以提高轴向分辨率或用于特定应用的设备。

DESCRIPTION (provided by applicant): The long-term objective of this proposal is to develop a collimating insert for positron emission tomography (PET) scanners for improving spatial resolution and quantification. This collimating insert may be useful at the scale of small-animal imaging and/or clinical imaging, so it will be studied at both scales. Collimation will reduce the efficiency of PET since the collimator will absorb some of the emitted 511-keV gammas. However, the detected gammas will have better spatial resolution since the collimation will be designed to reduce the widths of the lines of response while also decreasing the scatter fraction. In particular, a resolution improvement of almost a factor of two will be sought by covering half of each crystal in the transaxial direction at any time. Factors such as penetration of the collimator will prevent the full factor of two gains in resolution. Since two crystals are needed to form a coincidence and each crystal has two different exposures, there will be a factor of four improvements in sampling, achieved by repositioning the collimator or patient during the scan. The collimator design will allow all of the new lines of response to be measured for a fraction of the scanner's field of view. That fraction depends on the acceptance angle of the collimator, which also determines the amount of penetration. It is likely the fraction will encompass a mouse or rat for the small-animal scanner and about a 20-cm diameter central region for the whole-body scanner. It is also likely that the collimation may be most useful when some of the sensitivity loss can be overcome by a longer scan time for the bed positions that use collimation or when the structure size of interest is smaller than the scanner's resolution capabilities. Applications where the resolution enhancement would be beneficial and that are often a single bed position include brain, breast, and prostate imaging. Radiotherapy planning may also be aided by improved resolution, for example, if hypoxia agents such as EF5 can be imaged to determine if the tumor's core is hypoxic, which may affect the treatment plan. The specific aims of this proposal include (1) developing accurate models of sensitivity and resolution with penetration; (2) designing, building, and integrating an experimental prototype collimator for the small-animal scanner by developing the appropriate hardware for mounting and positioning and the appropriate software for synchronizing with the scanner, which is needed in order to acquire the 4-fold increase in sampled lines; (3) developing iterative reconstruction that accurately models the sensitivity and resolution of the collimation; and (4) evaluating the prototype collimator experimentally on the small-animal scanner and with detailed simulations for the whole-body scanner. Collimation, if successful, could be used as an upgrade to existing scanners or be directly integrated in future designs. It is also possible that collimation could change the design of future scanners since larger crystals, which have better energy and timing resolution and are less likely to result in inter-crystal scatter, could be used in fabrication at reduced cost. Future efforts could also involve collimation to improve axial resolution or for application-specific devices.