Threshold adjusted calcium scoring using CT is less susceptible to cardiac motion and more accurate.
ABSTRACT The purpose of this paper is to investigate calcium scoring on computed tomography (CT) using an adjusted threshold depending on the maximum Hounsfield value within the calcification (HU(peak)). The volume of 19 calcifications was retrospectively determined on 64-slice multidetector CT and dual source CT (DSCT) at different thresholds and the threshold associated with the physical volume was determined. In addition, approximately 10 000 computer simulations were done simulating the same process for calcifications with mixed density. Using these data a relation between the HU(peak) and the threshold could be established. Hereafter, this relation was assessed by scanning six calcifications in a phantom at 40-110 beats per minute using DSCT. The influence of motion was determined and the measured calcium scores were compared to the physical volumes and mass. A positive linear correlation was found between the scoring threshold and the HU(peak) of the calcifications both for the phantom measurements as for the computer simulations. Using this relation the individual threshold for each calcification could be calculated. Calcium scores of the moving calcifications determined with an adjusted threshold were approximately 30% less susceptible to cardiac motion compared to standard calcium scoring. Furthermore, these scores approximated the physical volume and mass at least 10% better than the standard calcium scores. The threshold in calcium scoring should be adjusted for each individual calcification based on the HU(peak) of the calcification. Calcium scoring using an adjusted threshold is less susceptible to cardiac motion and more accurate compared to the physical values.
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ABSTRACT: To assess whether absolute mass scores are comparable or differ between identical 64-slice MDCT scanners of the same manufacturer and to compare absolute mass scores to the physical mass and between scan modes using a calcified phantom. A non-moving anthropomorphic phantom with nine calcifications of three sizes and three densities was scanned 30 times on three 64-slice MDCT scanners of manufacturer A and on three 64-slice MDCT scanners of manufacturer B in both sequential and spiral scan mode. The mean mass scores and mass score variabilities of seven calcifications were determined for all scanners; two non-detectable calcifications were omitted. It was analyzed whether identical scanners yielded similar or significantly different mass scores. Furthermore mass scores were compared to the physical mass and mass scores were compared between scan modes. The mass score calibration factor was determined for all scanners. Mass scores obtained on identical scanners were similar for almost all calcifications. Overall, mass score differences between the scanners were small ranging from 1.5 to 3.4% for the total mass scores, and most differences between scanners were observed for high density calcifications. Mass scores were significantly different from the physical mass for almost all calcifications and all scanners. In sequential mode the total physical mass (167.8 mg) was significantly overestimated (+2.3%) for 4 out of 6 scanners. In spiral mode a significant overestimation (+2.5%) was found for system B and a significant underestimation (-1.8%) for two scanners of system A. Mass scores were dependent on the scan mode, for manufacturer A scores were higher in sequential mode and for manufacturer B in spiral mode. For system A using spiral scan mode no differences were found between identical scanners, whereas a few differences were found using sequential mode. For system B the scan mode did not affect the number of different mass scores between identical scanners. Mass scores obtained in the same scan mode are comparable between identical 64-slice CT scanners and identical 64-slice CT scanners on different sites can be used in follow-up studies. Furthermore, for all systems significant differences were found between mass scores and the physical calcium mass; however, the differences were relatively small and consistent.The international journal of cardiovascular imaging 09/2009; 26(1):89-98. · 2.15 Impact Factor
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ABSTRACT: Purpose: Coronary artery calcium score, traditionally based on electrocardiography (ECG)-triggered computed tomography (CT), predicts cardiovascular risk. However, nontriggered CT is extensively utilized. The study-purpose is to evaluate the in vitro agreement in coronary calcium score between nontriggered thoracic CT and ECG-triggered cardiac CT.Methods: Three artificial coronary arteries containing calcifications of different densities (high, medium, and low), and sizes (large, medium, and small), were studied in a moving cardiac phantom. Two 64-detector CT systems were used. The phantom moved at 0-90 mm∕s in nontriggered low-dose CT as index test, and at 0-30 mm∕s in ECG-triggered CT as reference. Differences in calcium scores between nontriggered and ECG-triggered CT were analyzed by t-test and 95% confidence interval. The sensitivity to detect calcification was calculated as the percentage of positive calcium scores.Results: Overall, calcium scores in nontriggered CT were not significantly different to those in ECG-triggered CT (p > 0.05). Calcium scores in nontriggered CT were within the 95% confidence interval of calcium scores in ECG-triggered CT, except predominantly at higher velocities (≥50 mm∕s) for the high-density and large-size calcifications. The sensitivity for a nonzero calcium score was 100% for large calcifications, but 46% ± 11% for small calcifications in nontriggered CT.Conclusions: When performing multiple measurements, good agreement in positive calcium scores is found between nontriggered thoracic and ECG-triggered cardiac CT. Agreement decreases with increasing coronary velocity. From this phantom study, it can be concluded that a high calcium score can be detected by nontriggered CT, and thus, that nontriggered CT likely can identify individuals at high risk of cardiovascular disease. On the other hand, a zero calcium score in nontriggered CT does not reliably exclude coronary calcification.Medical Physics 08/2013; 40(8):081915. · 2.91 Impact Factor
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ABSTRACT: INTRODUCTION: Multi detector computed tomography (MDCT) underestimates the coronary calcium score as compared to electron beam tomography (EBT). Therefore clinical risk stratification based on MDCT calcium scoring may be inaccurate. The aim of this study was to assess the feasibility of a new phantom which enables establishment of a calcium scoring protocol for MDCT that yields a calcium score comparable to the EBT values and to the physical mass. MATERIALS AND METHODS: A phantom containing 100 small calcifications ranging from 0.5 to 2.0mm was scanned on EBT using a standard coronary calcium protocol. In addition, the phantom was scanned on a 320-row MDCT scanner using different scanning, reconstruction and scoring parameters (tube voltage 80-135kV, slice thickness 0.5-3.0mm, reconstruction kernel FC11-FC15 and threshold 110-150HU). The Agatston and mass score of both modalities was compared and the influence of the parameters was assessed. RESULTS: On EBT the Agatston and mass scores were between 0 and 20, and 0 and 3mg, respectively. On MDCT the Agatston and mass scores were between 0 and 20, and 0 and 4mg, respectively. All parameters showed an influence on the calcium score. The Agatston score on MDCT differed 52% between the 80 and 135kV, 65% between 0.5 and 3.0mm and 48% between FC11 and FC15. More calcifications were detected with a lower tube voltage, a smaller slice thickness, a sharper kernel and a lower threshold. Based on these observations an acquisition protocol with a tube voltage of 100kV and two reconstructions protocols were defined with a FC12 reconstruction kernel; one with a slice thickness of 3.0mm and a one with a slice thickness of 0.5mm. This protocol yielded an Agatston score as close to the EBT as possible, but also a mass score as close to the physical phantom value as possible, respectively. CONCLUSION: With the new phantom one acquisition protocol and two reconstruction protocols can be defined which produces Agatston scores comparable to EBT values and to the physical mass.European journal of radiology 10/2012; · 2.65 Impact Factor