Ultra high resolution PET imaging using a collimator insert

描述(由申请人提供)：这项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。这种准直插入物可能在小动物成像和/或临床成像的规模上有用，因此它将在两个规模上进行研究。准直会降低PET的效率，因为准直器会吸收一些发射的511keV伽马。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在减小散射分数的同时减小响应线的宽度。特别是，通过在任何时间覆盖每个晶体的横轴方向的一半，分辨率将提高近两倍。准直器的穿透等因素将阻止分辨率的两个提高的充分因素。由于需要两个晶体才能形成重合，而且每个晶体有两次不同的曝光，因此在采样方面将有四倍的改进，通过在扫描过程中重新定位准直器或患者来实现。准直仪的设计将允许在扫描仪视野的一小部分范围内测量所有新的响应线。这一比例取决于准直器的接受角，这也决定了穿透量。对于小型动物扫描仪，这一部分可能会包括一只小鼠或大鼠，对于全身扫描仪，可能会包括一个直径约20厘米的中心区域。当使用准直的床位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，并且通常是单床位置的应用包括大脑、乳房和前列腺成像。放射治疗计划还可以通过提高分辨率来辅助，例如，如果可以对EF5等缺氧剂进行成像，以确定肿瘤的核心是否缺氧，这可能会影响治疗计划。该建议的具体目标包括：(1)开发具有穿透性的灵敏度和分辨率的精确模型；(2)通过开发适当的安装和定位硬件以及适当的与扫描器同步的软件，为小动物扫描器设计、建造和集成实验原型准直器，以获得4倍的采样线增长；(3)开发迭代重建，精确地模拟准直器的灵敏度和分辨率；以及(4)在小动物扫描器上对原型准直器进行实验评估，并对全身扫描器进行详细的模拟。如果成功，准直可以作为现有扫描仪的升级，或者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时间分辨率，不太可能导致晶间散射，可以以更低的成本用于制造。未来的努力还可能包括准直，以提高轴向分辨率或用于特定用途的设备。 与公众健康相关：该项目开发了一种新的准直技术，以降低收集效率为代价，提高了PET的空间分辨率。小动物成像和临床成像都有可能具有优势。准直可能在临床上对乳房、前列腺和大脑的成像以及放射治疗计划最有利，因为改进的空间分辨率预计将改善细节和清晰度，并且因为感兴趣区域位于单床位置内，从而允许使用更长的扫描恢复计数统计数据。

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. PUBLIC HEALTH RELEVANCE: This project develops a new collimation technique for improving spatial resolution in PET at the cost of reduced collection efficiency. Advantages are likely for both small-animal and clinical imaging. It is likely that collimation may be clinically most beneficial for imaging the breast, prostate, and brain, and for radiotherapy planning, since improved spatial resolution is expected to improve the detail and clarity and because the region of interest is within a single bed position to allow for recovering count statistics with a longer scan.