Experimental measurement of local noise power spectrum (NPS) in photon counting detector‐CT (PCD‐CT) using a single data acquisition.

Background: Accurate noise power spectra (NPS) measurement in clinical X‐ray CT exams is challenging due to the need for repeated scans, which expose patients to high radiation risks. A reliable method for single CT acquisition NPS estimation is thus highly desirable. Purpose: To develop a method for estimating local NPS from a single photon counting detector‐CT (PCD‐CT) acquisition. Methods: A novel nearly statistical bias‐free estimator was constructed from the raw counts data of PCD‐CT scan to estimate the variance of sinogram projection data. An analytical algorithm is employed to reconstruct point‐wise covariance cov(xi,xj)$\text{cov}({\bf x}_i,{\bf x}_j)$ between any two image pixel/voxel locations xi${\bf x}_i$ and xj${\bf x_j}$. A Fourier transform is applied to obtain the desired point‐wise NPS for any chosen location xi${\bf x}_i$. The method was validated using experimental data acquired from a benchtop PCD‐CT system with various physical phantoms, and the results were compared with the conventional local NPS measurement method using repeated scans and statistical ensemble averaging. Results: The experimental results demonstrate that (1) the proposed method can achieve pointwise/local NPS measurement for a region of interest (ROI) located at any chosen position, accurately characterizing the NPS with spatial structures resulting from image content heterogeneity; (2) the local NPS measured using the proposed method show a higher precision in the measured NPS compared to the conventional measurement method; (3) spatial averaging of the local NPS yields the conventional NPS for a given local ROI. Conclusion: A new method was developed to enable local NPS from a single PCD‐CT acquisition. [ABSTRACT FROM AUTHOR]