Time-resolved high-resolution X-ray Computed Tomography (4D $μ$CT) is an imaging technique that offers insight into the evolution of dynamic processes inside materials that are opaque to visible light. Conventional tomographic reconstruction techniques are based on recording a sequence of 3D images that represent the sample state at different moments in time. This frame-based approach limits the temporal resolution compared to dynamic radiography experiments due to the time needed to make CT scans. Moreover, it leads to an inflation of the amount of data and thus to costly post-processing computations to quantify the dynamic behaviour from the sequence of time frames, hereby often ignoring the temporal correlations of the sample structure. Our proposed 4D $μ$CT reconstruction technique, named DYRECT, estimates individual attenuation evolution profiles for each position in the sample. This leads to a novel memory-efficient event-based representation of the sample, using as little as three image volumes: its initial attenuation, its final attenuation and the transition times. This third volume represents local events on a continuous timescale instead of the discrete global time frames. We propose a method to iteratively reconstruct the transition times and the attenuation volumes. The dynamic reconstruction technique was validated on synthetic ground truth data and experimental data, and was found to effectively pinpoint the transition times in the synthetic dataset with a time resolution corresponding to less than a tenth of the amount of projections required to reconstruct traditional $μ$CT time frames.

翻译：时间分辨高分辨率X射线计算机断层扫描（4D μCT）是一种成像技术，能够揭示可见光不透明材料内部动态过程的演化。传统的断层重建技术基于记录一系列代表样本在不同时刻状态的三维图像序列。这种基于帧的方法由于CT扫描所需时间，其时间分辨率相较于动态射线照相实验存在局限。此外，该方法导致数据量激增，进而需要昂贵的后处理计算来从时间帧序列中量化动态行为，且通常忽略样本结构的时间相关性。我们提出的4D μCT重建技术，命名为DYRECT，可估计样本中每个位置的独立衰减演化曲线。这产生了一种新颖的、内存高效的事件驱动型样本表示方法，仅需使用三个图像体数据：初始衰减、最终衰减及过渡时间。第三个体数据代表连续时间尺度上的局部事件，而非离散的全局时间帧。我们提出了一种迭代重建过渡时间与衰减体数据的方法。该动态重建技术在合成基准数据与实验数据上进行了验证，结果显示其能有效定位合成数据集中的过渡时间，其时间分辨率对应少于重建传统μCT时间帧所需投影数量的十分之一。