TH‐E‐17A‐02: High‐Pitch and Sparse‐View Helical 4D CT Via Iterative Image Reconstruction Method Based On Tensor Framelet

Abstract

Purpose:4D CT is routinely performed during radiation therapy treatment planning of thoracic and abdominal cancers. Compared with the cine mode, the helical mode is advantageous in temporal resolution. However, a low pitch (∼0.1) for 4D CT imaging is often required instead of the standard pitch (∼1) for static imaging, since standard image reconstruction based on analytic method requires the low‐pitch scanning in order to satisfy the data sufficient condition when reconstructing each temporal frame individually. In comparison, the flexible iterative method enables the reconstruction of all temporal frames simultaneously, so that the image similarity among frames can be utilized to possibly perform high‐pitch and sparse‐view helical 4D CT imaging. The purpose of this work is to investigate such an exciting possibility for faster imaging with lower dose.Methods:A key for highpitch and sparse‐view helical 4D CT imaging is the simultaneous reconstruction of all temporal frames using the prior that temporal frames are continuous along the temporal direction. In this work, such a prior is regularized through the sparsity transform based on spatiotemporal tensor framelet (TF) as a multilevel and high‐order extension of total variation transform. Moreover, GPU‐based fast parallel computing of X‐ray transform and its adjoint together with split Bregman method is utilized for solving the 4D image reconstruction problem efficiently and accurately.Results:The simulation studies based on 4D NCAT phantoms were performed with various pitches (i.e., 0.1, 0.2, 0.5, and 1) and sparse views (i.e., 400 views per rotation instead of standard >2000 views per rotation), using 3D iterative individual reconstruction method based on 3D TF and 4D iterative simultaneous reconstruction method based on 4D TF respectively.Conclusion:The proposed TF‐based simultaneous 4D image reconstruction method enables high‐pitch and sparse‐view helical 4D CT with lower dose and faster speed.