The first invented CT scanner was a single slice CT allowing for one slice data by a single detector to be acquired for each tube rotation [
12]. To scan the target organ, a number of single scanning revolutions needs to be performed to obtain each slice, resulting in long scanning time and artifact. In the early 1980, Electron Beam Computed Tomography (EBCT) was developed [
13]. Using a large stationary x-ray tube that partially surrounds the imaging field, tube rotation assembly was not necessary, resulting a reduced scan times to 50–100 ms (depending on the imaging mode) for each slice acquisition [
13]. However, technical challenges such as poor quality images due to the limited X-ray power, limited the achievement of its widespread adoption in clinic. In the late 1980s, helical CT, or spiral CT scanners were developed and were rapidly adopted clinically. By scanning the body spirally, the target area can be evaluated in a shorter period allowing scanning time to be remarkably reduced [
14]. Furthermore, to meet the clinical expectations of wider range scanning and three-dimensional image acquisition, in 1998, multi-slice CT, or multi-detector CT, was invented [
15,
16]. Multi-slice CT has multiple rows of detectors, allowing data for multiple slices to be acquired simultaneously in each tube rotation [
15]. It enables the acquisition of three-dimensional images by layering multiple slices using various reconstruction methods, such as multi-planar reconstruction (MPR) and volume rendering. Multi-slice CT allows the acquisition of three-dimensional data of the target body part quickly [
15]. The number of the detector rows increased gradually from 2, 4, 8, 16, 64 to 256. In 2007, the number of detectors reached 320, corresponding to a total detector width of 16 cm [
17]. Because a 16 cm range can cover the majority of human organs, scanning can be performed without helical rotation in the area of interest [
17]. This repeated scanning allows for the acquisition of images over time or dynamic 3D-CT images (4D images; 3D × time).