Optimizing iterative reconstruction for quantification of calcium hydroxyapatite with photon counting flat-detector computed tomography: a cardiac phantom study

Abstract

Purpose: Coronary artery calcium (CAC) scoring with computed tomography (CT) has been proposed as a screening tool for coronary artery disease, but concerns remain regarding the radiation dose of CT CAC scoring. Photon counting detectors and iterative reconstruction (IR) are promising approaches for patient dose reduction, yet the preservation of CAC scores with IR has been questioned. The purpose of this study was to investigate the applicability of IR for quantification of CAC using a photon counting flat-detector.Approach: We imaged a cardiac rod phantom with calcium hydroxyapatite (CaHA) inserts with different noise levels using an experimental photon counting flat-detector CT setup to simulate the clinical CAC scoring protocol. We applied filtered back projection (FBP) and two IR algorithms with different regularization strengths. We compared the air kerma values, image quality parameters [noise magnitude, noise power spectrum, modulation transfer function (MTF), and contrast-to-noise ratio], and CaHA quantification accuracy between FBP and IR.Results: IR regularization strength influenced CAC scores significantly (p < 0.05). The CAC volumes and scores between FBP and IRs were the most similar when the IR regularization strength was chosen to match the MTF of the FBP reconstruction. Conclusion:When the regularization strength is selected to produce comparable spatial resolution with FBP, IR can yield comparable CAC scores and volumes with FBP. Nonetheless, at the lowest radiation dose setting, FBP produced more accurate CAC volumes and scores compared to IR, and no improved CAC scoring accuracy at low dose was demonstrated with the utilized IR methods.

Harmonization of technical image quality in computed tomography: comparison between different reconstruction algorithms and kernels from six scanners

“…In practice, however, the diagnostic task should be considered when selecting the optimal weighting parameters (Richard et al 2012, Samei et al 2014). For illustration, for volume quantification tasks, such as coronary artery calcium scoring, the preservation of spatial resolution is crucial (Juntunen et al 2021), and consequently, the MTF could be weighted more than the NPS during the matching. In contrast, applications requiring excellent low contrast detectability, such as tumor diagnostics, may benefit from a weighting that prioritizes agreement in NPS.…”

“…The one-dimensional, radial NPS was used for the determination of noise texture. This strategy has been addressed in more depth in a number of publications (Verdun et al 2015, Juntunen et al 2021, and the reader is referred to these studies for further information. The CTP 528 contains two tungsten carbide beads with 0.28 mm diameter that act as point sources.…”

Special Section Guest Editorial: Computed tomography (CT) at 50 years

“…5 The nine research papers offer a snapshot of current technical CT research interests and span a wide and representative range of topics. In the realm of emerging hardware and techniques, we see work on system design for a head scanner using a novel x-ray source, 6 a study of phase contrast CT of the breast, 7 as well as image reconstruction for photon counting CT. 8 In a case of one form of CT helping another, we see microCT used to help characterize the performance of an emerging dedicated breast CT scanner. 9 Spectral CT is studied for both stand-alone CT 10 and as a potential source of improved attenuation correction maps for SPECT.…”