The Russell H. Morgan Department of Radiology and Radiological Sciences, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
Phys Med Biol. 2010 Feb 21;55(4):1069-81. doi: 10.1088/0031-9155/55/4/011. Epub 2010 Jan 28.
As an aid to evaluating image reconstruction and correction algorithms in positron emission tomography, a phantom procedure has been developed that simultaneously measures image noise and spatial resolution. A commercially available (68)Ge cylinder phantom (20 cm diameter) was positioned in the center of the field-of-view and two identical emission scans were sequentially performed. Image noise was measured by determining the difference between corresponding pixels in the two images and by calculating the standard deviation of these difference data. Spatial resolution was analyzed using a Fourier technique to measure the extent of the blurring at the edge of the phantom images. This paper addresses the noise aspects of the technique as the spatial resolution measurement has been described elsewhere. The noise measurement was validated by comparison with data obtained from multiple replicate images over a range of noise levels. In addition, we illustrate how simultaneous measurement of noise and resolution can be used to evaluate two different corrections for random coincidence events: delayed event subtraction and singles-based randoms correction. For a fixed number of iterations of the maximum-likelihood expectation-maximization algorithm, the singles-based correction gave rise to higher noise than delayed event subtraction. However, when noise and resolution were measured simultaneously it was shown that singles-based randoms correction gave rise to lower noise than delayed event subtraction for a fixed spatial resolution. The proposed method of simultaneously measuring image noise and spatial resolution is useful for evaluating reconstruction algorithms and may aid standardization of data collection between centers.
为了评估正电子发射断层扫描中的图像重建和校正算法，我们开发了一种同时测量图像噪声和空间分辨率的体模方法。将一个市售的（68）Ge 圆柱体模（直径 20cm）放置在视野中心，然后连续进行两次相同的发射扫描。通过确定两幅图像中对应像素之间的差异，并计算这些差异数据的标准差来测量图像噪声。通过傅里叶技术分析空间分辨率，以测量体模图像边缘的模糊程度。本文主要介绍该技术的噪声方面，因为空间分辨率的测量已在其他地方进行了描述。通过与在不同噪声水平下获得的多个重复图像数据进行比较，验证了噪声测量的有效性。此外，我们还说明了如何同时测量噪声和分辨率，以评估两种不同的随机符合事件校正方法：延迟事件减法和基于单计数的随机校正。对于最大似然期望最大化算法的固定迭代次数，基于单计数的校正方法会导致更高的噪声，而延迟事件减法则会导致更高的噪声。然而，当同时测量噪声和分辨率时，我们发现对于固定的空间分辨率，基于单计数的随机校正方法产生的噪声比延迟事件减法低。同时测量图像噪声和空间分辨率的方法有助于评估重建算法，并可能有助于中心之间的数据采集标准化。
