Finding the optimal dose reduction and iterative reconstruction level for coronary calcium scoring.
OBJECTIVE
To assess the maximally achievable computed tomography (CT) dose reduction for coronary artery calcium (CAC) scoring with iterative reconstruction (IR) by using phantom-experiments and a systematical within-patient study.


METHODS
Our local institutional review-board approved this study and informed consent was obtained from all participants. A phantom and patient study were conducted with 30 patients (23 men, median age 55.0 (52.0-56.0) years) who underwent 256-slice electrocardiogram-triggered CAC-scoring at four dose levels (routine, 60%, 40%, and 20%-dose) in a single session. Tube-voltage was 120 kVp, tube-current was lowered to achieve stated dose levels. Data were reconstructed with filtered back-projection (FBP) and three IR levels. Agatston, volume and mass scores were determined with validated software and compared using Wilcoxon signed ranks-tests. Subsequently, patient reclassification was analyzed.


RESULTS
The phantom study showed that Agatston scores remained nearly stable with FBP between routine-dose and 40%-dose and increased substantially at lower dose. Twenty-three patients (77%) had coronary calcifications. For Agatston scoring, one 40%-dose and six 20%-dose FBP reconstructions were not interpretable due to noise. In contrast, with IR all reconstructions were interpretable. Median Agatston scores increased with FBP from 26.1 (5.2-192.2) at routine-dose to 60.5 (11.6-251.7) at 20% dose. However, IR lowered Agatston scores to 22.9 (5.9-195.5) at 20%-dose and strong IR (level 7) with Agatston reclassifications in 15%.


CONCLUSIONS
IR allows for CAC-scoring radiation dose reductions of up to 80% resulting in effective doses between 0.15 and 0.18 mSv. At these dose-levels, reclassification-rates remain within 15% if the highest IR-level is applied.
Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands. Electronic address: m.j.willemink@gmail.com.
Martin J
MJ
Willemink
Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
Annemarie M
AM
den Harder
Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
Wouter
W
Foppen
Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
Arnold M R
AM
Schilham
Department of Cardiology, University Medical Center Utrecht, Utrecht, The Netherlands.
Rienk
R
Rienks
Department of Cardiology, University Medical Center Utrecht, Utrecht, The Netherlands.
Eduard M
EM
Laufer
Department of Cardiology, Erasmus Medical Center, Rotterdam, The Netherlands; Department of Radiology, Erasmus Medical Center, Rotterdam, The Netherlands.
Koen
K
Nieman
Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
Pim A
PA
de Jong
Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands; Department of Radiology, Erasmus Medical Center, Rotterdam, The Netherlands.
Ricardo P J
RP
Budde
Department of Cardiology, University Medical Center Utrecht, Utrecht, The Netherlands.
Hendrik M
HM
Nathoe
Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands.
Tim
T
Leiner
D000465:Algorithms; D017023:Coronary Angiography / Q000379:methods*; D003324:Coronary Artery Disease / Q000000981:diagnostic imaging*; D004307:Dose-Response Relationship, Radiation; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011829:Radiation Dosage; D000069079:Radiation Exposure / Q000032:analysis / Q000517:prevention & control*; D011835:Radiation Protection / Q000379:methods; D011856:Radiographic Image Enhancement / Q000379:methods*; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D059629:Signal-To-Noise Ratio; D014057:Tomography, X-Ray Computed / Q000379:methods*; D061205:Vascular Calcification / Q000000981:diagnostic imaging*
Agatston score; Computed tomography; Coronary artery calcifications; Iterative reconstruction