Improved Reconstruction of Periodic Distributions in 4D CT

Reconstructing fast dynamic phenomena captured in micro-CT scans presents a significant challenge. Fortunately, many biomedical structures, such as the lungs, heart, and auditory system, exhibit periodic motion patterns, making them well-suited for observation using 4D CT. To address this, 2D projections can be grouped according to their respective motion phases, and reconstruction can be performed for each group using conventional algorithms, treating each as though it originated from a static object. This approach, known as gating-based methodology, is the standard for periodic reconstruction, as exemplified in ECG-gated cardiac CT [1], and has been extensively developed at the TOMCAT beamline for high-frequency biomechanical systems at microtomographic spatial resolution [2].

Four-dimensional gated tomography using synchrotron radiation enables the visualization of periodically deforming objects with high temporal and spatial resolutions. However, 4D experiments on biological samples require short exposure times and low radiation doses to minimize motion artifacts and prevent sample damage. These limitations reduce the number of photons detected, thereby compromising image quality. In response to this challenge, we present an improved analytical reconstruction method based on lock-in amplification (LIA) theory [3]. Validated with experimental data from sound-stimulated fish auditory structures [4] at the TOMCAT beamline, our method effectively reduces random noise in the reconstructed images without diminishing the sharpness of the observed features.