Wilson J M, Turkington T G
Graduate Program in Medical Physics, Duke University, Durham, NC 27710, USA.
Phys Med Biol. 2008 Jun 21;53(12):3267-78. doi: 10.1088/0031-9155/53/12/013. Epub 2008 May 27.
PET image quality measurements of lesion detectability frequently use a small, radioactive sphere in a larger phantom. The typical analysis of a small single sphere in background has several shortcomings as a measure for detectability and quantitation: the measurement has low statistical power; the region of interest (ROI) is susceptible to large pixel-to-pixel fluctuations; only a single point in the axial and transaxial field of view is analyzed; background noise measurements in regions away from the signal sphere may bias the detectability measurement and user-placed ROIs can cause inconsistent measurements. For a more robust measurement and repeatable analysis of small lesion detectability in PET images, a multisphere phantom and analysis algorithm were developed. The multisphere phantom consists of a collection of 50 1.0-cm spheres, mounting rods and a gridded plate. A PET/CT study is presented where 29 spheres with a 4:1 sphere-to-background radioactivity ratio were acquired for multiple frame durations and reconstructed. An analysis algorithm was implemented and applied to the acquired PET/CT that detects the contrast-enhanced spheres in a CT, places ROIs on the spheres and their respective proximal background, applies the ROIs to the PET and performs quantitation. Results are presented that show the impact of increasing number of signal spheres and of different background ROI placement methods on the image quality measurement. Increasing the number of spheres reduced the variability in the image quality measurements, but only up to a point, beyond which increasing the number of spheres did not considerably reduce the variability. A phantom with numerous spherical inserts increases several measurement aspects: the flexibility of sphere placement during setup, the number of radioactivity concentrations that can be used during a single study and the statistical power of measurements. Additionally, an automated algorithm that localizes spheres, places ROIs and performs quantitation will increase reliability and reproducibility of image quality assessment, in addition to simplifying the analysis.
正电子发射断层扫描（PET）图像中病变可检测性的质量测量通常在较大的体模中使用一个小的放射性球体。对背景中单个小球体进行的典型分析作为一种可检测性和定量测量方法存在几个缺点：测量的统计功效较低；感兴趣区域（ROI）容易受到像素间大波动的影响；仅分析了轴向和横向视野中的单个点；远离信号球体区域的背景噪声测量可能会使可检测性测量产生偏差，并且用户放置的ROI可能导致测量结果不一致。为了对PET图像中小病变的可检测性进行更稳健的测量和可重复分析，开发了一种多球体体模和分析算法。多球体体模由50个1.0厘米的球体、安装杆和一个带网格的板组成。本文介绍了一项PET/CT研究，其中采集了29个球体与背景放射性比值为4:1的多帧持续时间的图像并进行重建。实施了一种分析算法，并将其应用于采集的PET/CT图像，该算法在CT中检测对比度增强的球体，在球体及其各自的近端背景上放置ROI，将ROI应用于PET并进行定量分析。给出的结果显示了增加信号球体数量以及不同背景ROI放置方法对图像质量测量的影响。增加球体数量可降低图像质量测量的变异性，但仅在一定程度上如此，超过这一点后增加球体数量并不能显著降低变异性。具有众多球形插入物的体模在几个测量方面有所改进：设置过程中球体放置的灵活性、单次研究中可使用的放射性浓度数量以及测量的统计功效。此外，一种能够定位球体、放置ROI并进行定量分析的自动化算法，除了简化分析外，还将提高图像质量评估的可靠性和可重复性。
