The Impact of Different Levels of Adaptive Iterative Dose Reduction 3D on Image Quality of 320-Row Coronary CT Angiography: A Clinical Trial.

PURPOSE: The aim of this study was the systematic image quality evaluation of coronary CT angiography (CTA), reconstructed with the 3 different levels of adaptive iterative dose reduction (AIDR 3D) and compared to filtered back projection (FBP) with quantum denoising software (QDS). METHODS: Standard-dose CTA raw data of 30 patients with mean radiation dose of 3.2 ± 2.6 mSv were reconstructed using AIDR 3D mild, standard, strong and compared to FBP/QDS. Objective image quality comparison (signal, noise, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), contour sharpness) was performed using 21 measurement points per patient, including measurements in each coronary artery from proximal to distal. RESULTS: Objective image quality parameters improved with increasing levels of AIDR 3D. Noise was lowest in AIDR 3D strong (p ≤ 0.001 at 20/21 measurement points; compared with FBP/QDS). Signal and contour sharpness analysis showed no significant difference between the reconstruction algorithms for most measurement points. Best coronary SNR and CNR were achieved with AIDR 3D strong. No loss of SNR or CNR in distal segments was seen with AIDR 3D as compared to FBP. CONCLUSIONS: On standard-dose coronary CTA images, AIDR 3D strong showed higher objective image quality than FBP/QDS without reducing contour sharpness. TRIAL REGISTRATION: Clinicaltrials.gov NCT00967876.

Determining the radiation dose reduction potential for coronary calcium scanning with computed tomography: an anthropomorphic phantom study comparing filtered backprojection and the adaptive iterative dose reduction algorithm for image reconstruction.

PURPOSE: This study describes a method to determine the lowest possible thresholds for volume computed tomographic dose index (CTDI(min)) and maximum tolerable pixel noise (SD(max)) values for coronary calcium scanning while maintaining accurate Agatston score values. The method was applied to a comparison between the iterative reconstruction (IR) and filtered backprojection (FBP) image reconstruction algorithms in a phantom study. MATERIALS AND METHODS: An anthropomorphic thoracic phantom with a calibration insert for the quantification of coronary calcium, containing 200, 400, and 800 mg HA/cm of calcium mass spheres of 1, 3, and 5 mm diameter (QRM GmbH, Moehrendorf, Germany), was scanned without (G1) and with (G2) an additional 2 cm-thick wrap of muscle-equivalent material. Electrocardiographically simulated volume scans were performed on a 320-row computed tomographic scanner (Aquilion ONE, Toshiba Medical Systems, Otawara, Japan) set to 120 kilovolt peak [kVp] and 10 to 580 mA variations in 21 steps. For the IR, the Adaptive Iterative Dose Reduction 3-dimensional algorithm (AIDR 3D) was used. Agatston scores were calculated semiautomatically on the computed tomographic console. Inclusion tests to assess the accuracy of the Agatston scores were performed to determine the CTDI(min) thresholds and the associated maximum pixel noise SD(max) for FBP and IR from identical raw data. The inclusion tests were as follows: (1) the semiautomatic identification of the 1 mm sphere with 800 mg HA/cm, (2) the exclusion of false-positive lesions, and (3) a statistical outlier test. Statistical differences between the Agatston score means from both image reconstruction algorithms were evaluated using the paired t test. RESULTS: All Agatston scores using both reconstruction methods were normally distributed (P > 0.49). For FBP and IR, the mean ± 1σ of Agatston score, CTDI(min), and SD(max), respectively, were determined as follows: 697.8 ± 7.7, 7.5 mGy, and 24.4 Hounsfield unit (HU) (G1-FBP); 678.8 ± 14.3, 1.5 mGy, and 20.1 HU (G1-IR); 677.0 ± 11.6, 14.5 mGy, and 27.3 HU (G2-FBP); and 643.9 ± 13.4, 2.6 mGy, and 20.0 HU (G2-IR). The mean Agatston scores obtained using IR (both with and without the additional 2 cm muscle shell) were slightly (approximately 5%) but significantly lower (P ≤ 0.001) than those obtained using FBP reconstruction. CONCLUSIONS: The Adaptive Iterative Dose Reduction algorithm AIDR 3D shows potential to reduce dose exposure by approximately 80% in comparison with the dose currently applied with FBP image processing. On the basis of phantom evaluation, a target noise of 20 HU for the application of this method in coronary calcium scanning is recommended to avoid loss in accuracy.