Emerging Techniques for Dose Optimization in Abdominal CT

Abstract

Recent advances in computed tomographic (CT) scanning technique such as automated tube current modulation (ATCM), optimized x-ray tube voltage, and better use of iterative image reconstruction have allowed maintenance of good CT image quality with reduced radiation dose. ATCM varies the tube current during scanning to account for differences in patient attenuation, ensuring a more homogeneous image quality, although selection of the appropriate image quality parameter is essential for achieving optimal dose reduction. Reducing the x-ray tube voltage is best suited for evaluating iodinated structures, since the effective energy of the x-ray beam will be closer to the k-edge of iodine, resulting in a higher attenuation for the iodine. The optimal kilovoltage for a CT study should be chosen on the basis of imaging task and patient habitus. The aim of iterative image reconstruction is to identify factors that contribute to noise on CT images with use of statistical models of noise (statistical iterative reconstruction) and selective removal of noise to improve image quality. The degree of noise suppression achieved with statistical iterative reconstruction can be customized to minimize the effect of altered image quality on CT images. Unlike with statistical iterative reconstruction, model-based iterative reconstruction algorithms model both the statistical noise and the physical acquisition process, allowing CT to be performed with further reduction in radiation dose without an increase in image noise or loss of spatial resolution. Understanding these recently developed scanning techniques is essential for optimization of imaging protocols designed to achieve the desired image quality with a reduced dose.

CT imaging of congenital lung lesions: effect of iterative reconstruction on diagnostic performance and radiation dose

“…Multiple prior studies have shown that iterative reconstruction techniques allow for dose reduction while preserving image quality in the adult populations undergoing abdominal or thoracic CT imaging [11][12][13][14]. Based on the existing literature, MBIR has allowed greater dose reductions than ASiR in both children and adults [7,[15][16][17].…”

Does Iterative Reconstruction Improve Image Quality and Reduce Dose in Computed Tomography?

“…6,12,13 In addition, IR algorithms can help reduce artifacts caused by metallic implants, as well as those resulting from photon starvation and beam-hardening effects. 1 It is therefore essential to understand how IR algorithms work in general, since it provides the basis to comprehending why IR algorithms are able to offer these advantages.…”

“…The output is the resultant volumetric image after the termination of the iterative cycle. 1,6,9 The entire iterative reconstruction process is illustrated in Figure 2. A comparison of images reconstructed using the FBP and IR algorithms is shown in Figure 3.…”

“…5 Several techniques, such as automatic tube current modulation, automatic tube voltage selection and dynamically adjustable z-axis beam collimation, have been employed to reduce CT-associated radiation dose, but the amount of dose reduction is limited if the FBP algorithm is used for image reconstruction. 6,7 The FBP algorithm has been the standard algorithm for im-age reconstruction in CT for many years, but it poses the limitation of producing possible streak artifacts and a notable increase in image noise level if radiation dose is reduced exceedingly. 8 The re-emergence of IR techniques in CT recently offers a potential alternative that allows a reduction in radiation dose while preserving image quality.…”

“…1,9 Several studies done between 2012 and 2015 have shown that the use of IR algorithms do indeed aid in reducing radiation dose and improving image quality in CT examinations when compared to the FBP algorithm. 6,10 However, there has yet to be any known review published on related studies to establish if this is a shared consensus within the medical imaging community, and whether the outcomes differ for different types of CT examinations and patients. This is especially crucial, as most of these studies often employ the use of IR algorithms from only one or two CT manufacturers, with the focus on a single specific type of CT examination.…”