Impact of Hybrid Iterative Reconstruction on Agatston Coronary Artery Calcium Scores in Comparison to Filtered Back Projection in Native Cardiac CT

Abstract

Purpose: To investigate whether the effects of hybrid iterative reconstruction (HIR) on coronary artery calcium (CAC) measurements using the Agatston score lead to changes in assignment of patients to cardiovascular risk groups compared to filtered back projection (FBP). Materials and Methods: 68 patients (mean age 61.5 years; 48 male; 20 female) underwent prospectively ECG-gated, non-enhanced, cardiac 256-MSCT for coronary calcium scoring. Scanning parameters were as follows: Tube voltage, 120 kV; Mean tube current time-product 63.67?mAs (50???150?mAs); collimation, 2???128???0.625?mm. Images were reconstructed with FBP and with HIR at all levels (L1 to L7). Two independent readers measured Agatston scores of all reconstructions and assigned patients to cardiovascular risk groups. Scores of HIR and FBP reconstructions were correlated (Spearman). Interobserver agreement and variability was assessed with ?-statistics and Bland-Altmann-Plots. Results: Agatston scores of HIR reconstructions were closely correlated with FBP reconstructions (L1, R?=?0.9996; L2, R?=?0.9995; L3, R?=?0.9991; L4, R?=?0.986; L5, R?=?0.9986; L6, R?=?0.9987; and L7, R?=?0.9986). In comparison to FBP, HIR led to reduced Agatston scores between 97?% (L1) and 87.4?% (L7) of the FBP values. Using HIR iterations L1???L3, all patients were assigned to identical risk groups as after FPB reconstruction. In 5.4?% of patients the risk group after HIR with the maximum iteration level was different from the group after FBP reconstruction. Conclusion: There was an excellent correlation of Agatston scores after HIR and FBP with identical risk group assignment at levels 1 - 3 for all patients. Hence it appears that the application of HIR in routine calcium scoring does not entail any disadvantages. Thus, future studies are needed to demonstrate whether HIR is a reliable method for reducing radiation dose in coronary calcium scoring. Key Points: ??Agatston-Scores showed excellent correlation between HIR and FBP. ??The higher the HIR Level, the more Agatston scores deviated to lower values. ??No change in risk group assignment using Level 1???3. ??Change in risk group assignment when using HIR compared to FBP in 1.5?% (Level?4), 5.4?% (Level 5???7). Citation Format: ??Obmann VC, Klink T, Heverhagen JT et?al. Impact of Hybrid Iterative Reconstruction on Agatston Coronary Artery Calcium Scores in Comparison to Filtered Back Projection in Native Cardiac CT. Fortschr R?ntgenstr 2015; 187: 372???379

Iterative reconstruction can permit the use of lower X-ray tube current in CT coronary artery calcium scoring

“…28 A further study has recently shown the excellent correlation of clinical risk groups between FBP and hybrid IR at full-dose scanning. 29 In the present study, there remained excellent agreement of absolute and percentile risk scores with the reference technique (FBP at normal dose settings) when using AIDR-3D mild at a tube current as low as 25%. The patients who were reclassified with AIDR-3D mild were the result of small absolute changes in Agatston scores in patients who were either on the borderline between categories or relatively young, so that a small absolute change resulted in reclassification.…”

False-Positive Calcifications and Radiation Dose in Coronary Artery Calcium Scoring Using Iterative Reconstruction on The Basis of a Noise Threshold

“…Phantom studies also showed a trend towards lower Agatston scores using IR [8,13,21]. The results of patient studies comparing FBP and IR in standard dose CAC scoring are equivocal with significant reduction in Agatston scores and only slight reduction of Agatston scores, respectively [11,12,15,16,22]. The noise related over-blooming effect in calcifications causes overestimation of the score values.…”

“…At present, an iterative reconstruction (IR) technique is able to reduce image noise [8,9]. Some phantom studies as well as patient studies have shown comparable Agatston scores comparing IR with the standard filtered backprojection (FBP) technique using identical image data [10][11][12]. In contrast, other studies have indicated minor differences or significant differences with underestimation of Agatston scores and calcium volume scores, respectively [8,[13][14][15].…”

In vitro evaluation of a new iterative reconstruction algorithm for dose reduction in coronary artery calcium scoring

“…Several previous publications, all using multi-row single source CT, have discussed the benefits and pitfalls of different IR algorithms for noise and dose reduction in CAC evaluation. In particular, the publications on hybrid IR algorithms and model-based IR (iDose4 and IMR, Phillips Healthcare, Best, The Netherlands), as well as adaptive iterative dose reduction algorithms (AIDR 3D, Toshiba Corp. Medical Systems, Tokyo, Japan) attract attention (6,10,22–24). IR algorithms allow for a significant reduction in image noise and could allow for substantial reduction in radiation dose while maintaining diagnostic accuracy as has been previously shown for other vendors than the one in the present study (22,25,26).…”