Reconstruction-Based Estimation of the Scatter Component in Positron Emission Tomography

以重建法估算正子電腦斷層掃描之散射事件

Habib Zaidi

《核子醫學雜誌》 14卷3期 (2001/09) Pp. 161-172

https://doi.org/10.6332/ANMS.1403.010

摘要

本文提出一種估算正子電腦斷層掃描之散射事件的新方法。此方法是採用序列子集均值最大化重建法（OSEM）以估計低頻的散射事件。我們分別使用蒙第卡羅（Monte Carlo）模擬，假體及臨床實驗來評估比方法。我們稱此方法為“統計重建之散射修正法（SRBSC）”。使用此方法的理由是因為投影資料中的散射事件所造成的影像其空間頻率幾乎是較低的，而此低頻部分在使用疊代式統計重建法如OSEM時，會比高頻部分收斂的快。另一假設是高頻部分的影像會受散射事件的影響而變模糊。我們使用蒙地卡羅模擬法而得出一種將散射事件參數化的簡單模型。我們以簡單的幾何假體及臨床上實際的活性分佈套入SRBSC法以估算出無散射事件並和由蒙地卡羅模擬所估算出的真正無散射事件做比較。我們也以各種定量分析法如對比度、絕對濃度（absolute concentration）、復原係數（recovery coefficient）和信噪比（SNR）來評估重建後的影像。我們發現SRBSC方法在3D Hoffman腦假體的大部分區域皆會有修正不足之憾，但重建後的活性值平均誤差在1%。總而言之， 我們提出的方法所得的影像相較於沒經過修正的其品質可提高且對比度也提高。因此若要做適當的散射修正就必須對散射事件做正確的模型分析。

關鍵字

正子電腦斷層掃描 ； 散射修正 ； 序列子集均值最大化重建法 ； 蒙地卡羅

並列摘要

A new method to assess the scatter component in positron emission tomography (PET) based on estimating the low-frequency component corresponding to scattered events using ordered subsets - expectation maximization (OSEM) reconstructions is proposed in this paper and evaluated using Monte Carlo simulation studies, experimental phantom measurements and clinical studies. The rationale of this method called Statistical Reconstruction-Based Scatter Correction (SRBSC) is that the image corresponding to scattered events in the projection data consists of almost low-frequency components of activity distribution and that the low-frequency components will converge faster than the high-frequency ones in successive iterations of statistical reconstruction methods such as OSEM. The second assumption is that the high-frequency components will be smeared, i.e. filtered by the scatter response kernels. A simple model has been devised to parameterize the scatter component using Monte Carlo simulations. The unscattered component estimated using SRBSC was compared to the true unscattered component as estimated by Monte Carlo simulations for simple phantom geometries and clinically realistic source distributions. Quantitative analysis was also performed on reconstructed images using simple metrics like the contrast, absolute concentration, recovery coefficient and signal-to-noise ratio. The SRBSC method tends to undercorrect for scatter in most regions of the 3D Hoffman brain phantom, but gives good activity recovery values which average within 1%. It was concluded that the proposed method improves image quality and the contrast compared to the case where no correction is applied and that an accurate modeling of the scatter component is essential for a proper scatter correction.

並列關鍵字

PET ； scatter correction ； OSEM ； Monte Carlo