2490. Virtual Non-Iodine Algorithm for Photon Counting Based Calcium Scoring: Impact of Virtual Monoenergetic and Quantum Iterative Reconstruction
Authors* Denotes Presenting Author
Nicola Fink *;
Medical University of South Carolina; University Hospital, LMU Munich
Emese Zsarnoczay;
Medical Imaging Centre, Semmelweis University; Medical University of South Carolina
U. Joseph Schoepf;
Medical University of South Carolina
Jim O' Doherty;
Siemens Healthcare USA
Elias Wolf;
Medical University of South Carolina; University Medical Center of the Johannes Gutenberg University Mainz
Akos Varga-Szemes;
Medical University of South Carolina
Tilman Emrich;
Medical University of South Carolina; University Medical Center of the Johannes Gutenberg University Mainz
Objective:
It has been demonstrated that photon counting detector (PCD) CT-based virtual non-iodine (VNI) reconstructions significantly underestimate coronary artery calcium scoring (CACS) compared to true noncontrast (TNC) images. The aim of this study was to investigate the impact of virtual monoenergetic image (VMI) and quantum iterative reconstructions (QIR) on the accuracy of in vitro and in vivo CACS using this VNI algorithm on a clinical first-generation PCD-CT.
Materials and Methods:
CACS was evaluated in three chest phantoms simulating three different patient sizes and in 21 patients (64.3 +/- 9.3 years; 61.9 % men) undergoing nonenhanced as well as contrast-enhanced, ECG-gated, cardiac PCD-CT. All reconstructions were performed using a VNI algorithm at different VMI levels from 55 to 80 keV and at different QIR levels from strength 1 to 4. In vitro and in vivo TNC reconstructions at 70 keV without VNI postprocessing and the lowest QIR level (“off”) served as reference.
Results:
In both phantoms and patients, and at every evaluated VMI and QIR level, CACS using VNI reconstructions showed strong correlation (r > 0.9, p < 0.001 for all) and excellent agreement (ICC > 0.9 for all) with CACS using TNC reconstructions. In vitro and in vivo VNI-CACS significantly increased with decreasing keV levels (in vitro: from 475.2 +/- 26.3 at 80 keV up to 652.5 +/- 42.2 at 55 keV; in vivo: from 140.2 [5.8/685.7] at 80 keV up to 254.7 [27.4/1048] at 55 keV; p < 0.001 for all), up to an overestimation of VNI-CACS at 55 keV in some cases compared to TNC-CACS (in vitro TNC-CACS: 625.8 +/- 24.4, in vivo TNC-CACS: 235.2 [19.8/826.2]). Phantom CACS values increased with increasing QIR at low VMI levels. Patient CACS values were significantly higher at QIR 1 than QIR 4 only at 80 keV (157.2 [8.8/710.5] vs. 140.2 [5.8/685.7]; p < 0.001). VNI-CACS closest to TNC-CACS was obtained at 60 keV, QIR 2 (+0.1 %) in the small, at 55 keV, QIR 1 (+/- 0%) in the medium, 55 keV, QIR 4 (-0.1 %) in the large phantom, and at 55 keV, QIR 4 (+2.3 %) in patients.
Conclusion:
CACS using VNI reconstructions can significantly be adjusted with VMI reconstructions which can be used to counteract an underestimation compared to CACS using TNC reconstructions. The impact of different QIR levels is less consistent and further studies should investigate on which factors QIR effects depend.
