Nonuniform collimator sensitivity: improved precision for quantitative SPECT.
Nonuniform collimator sensitivity: improved precision for quantitative SPECT.
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发表时间：
1997
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通讯作者：
M. Kijewski;S. Müller;S. Moore
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作者：
M. Kijewski;S. Müller;S. Moore
未标记的光子衰减会降低SPECT图像的准确度和精度;衰减校正算法可以校正偏差，但无法提高精度。由于光子衰减而导致的噪声增加在实体切片中的深部区域（例如大脑和腹部）中最为明显。我们已经量化的性能退化，在几个估计任务，可以归因于光子衰减，并确定在何种程度上可以提高性能的准直器与不均匀的灵敏度配置文件。方法：分析使用理想观察者模型的性能，在任务涉及估计的活动和大小的局灶性病变。该模型的基础上的Cramer-Rao下限的方差与病变的活动和大小可以估计一个公正的程序。为了量化衰减的影响，Cramer-Rao界限的值被计算为每个估计任务的功能的位置病变的圆形衰减器的半径为10和20厘米，有和没有衰减。还确定了两个不均匀的灵敏度配置文件，其中之一是为了均衡（或几乎均衡）整个图像的任务性能的界限值。结果：对于99 mTc，光子衰减使估计值的方差增加了10 cm半径衰减器的4.5倍和20 cm半径衰减器的20.0倍。具有不均匀灵敏度功能的准直器将方差降低了10 cm半径衰减器的1.8倍和20 cm半径衰减器的2.8倍。估计性能的这些增益对成像任务和与假设的衰减器尺寸和形状的偏差不敏感。结论使用具有均匀灵敏度准直器的SPECT系统图像进行估计任务的性能大大低于理论最佳值。我们已经推导出一个灵敏度函数，使用现有的技术实现，大大提高了性能。
UNLABELLED Attenuation of photons degrades both the accuracy and the precision of SPECT images; attenuation correction algorithms correct the bias but cannot improve precision. Increased noise due to photon attenuation is most pronounced in regions deep in solid body sections, such as the brain and abdomen. We have quantified the degradation in performance in several estimation tasks that can be attributed to photon attenuation and determined the degree to which performance might be improved by a collimator with a nonuniform sensitivity profile. METHODS The analysis used ideal-observer models of performance in tasks involving estimation of the activity and size of a focal lesion. The models were based on the Cramer-Rao lower bound on the variance with which lesion activity and size can be estimated by an unbiased procedure. To quantify the effects of attenuation, values of the Cramer-Rao bound were calculated for each estimation task as a function of location of the lesion in circularly-shaped attenuators of 10- and 20-cm radii, with and without attenuation. Values of the bound were also determined for two nonuniform sensitivity profiles, one of which was designed to equalize (or nearly equalize) task performance throughout the image. RESULTS For 99mTc, photon attenuation increased the variance of the estimates by factors of up to 4.5 for the 10-cm radius attenuator and up to 20.0 for the 20-cm radius attenuator. A collimator with a nonuniform sensitivity function reduced variance by factors of up to 1.8 for the 10-cm radius attenuator and up to 2.8 for the 20-cm radius attenuator. These gains in estimation performance were insensitive to the imaging task and to deviations from the assumed attenuator size and shape. CONCLUSION Performance in estimation tasks using images from SPECT systems with uniform sensitivity collimators is considerably lower than the theoretical optimum. We have derived a sensitivity function, realizable using existing technology, that improves performance substantially.