Low contrast- and low radiation dose protocol for cardiac CT of thin adults at 256-row CT: usefulness of low tube voltage scans and the hybrid iterative reconstruction algorithm

Abstract

To evaluate the effect on image quality of a low contrast and radiation dose protocol for cardiac computed tomography (CT) using a low tube voltage, the hybrid-iterative reconstruction algorithm, and a 256-row CT scanner. Before clinical study, we performed phantom experiments to evaluate the hybrid iterative reconstruction technique. We randomly assigned 68 patients undergoing cardiac CT to one of two protocols; 33 were scanned with our conventional 120 kVp protocol, the contrast material (370 mgI/kg body weight) was delivered over 15 s. The other 35 patients underwent scanning at a tube voltage of 80 kVp; the contrast dose, reduced by 50 % (185 mgI/kg), was delivered at the same fractional dose (24.7 mgI/kg/s). The 80 kVp images were post-processed with the 60 % hybrid-iterative reconstruction technique. We evaluated the effective dose (ED), image noise, mean attenuation, and contrast-to-noise ratio (CNR) of each protocol. The hybrid-iterative reconstruction technique offers almost same spatial resolution and noise-power-spectrum curve as compared with filtered back projection reconstruction. There were no decrease in spatial resolution and no shift of spatial frequency in noise power spectrum. The average ED was 74 % lower with the 80- than the 120 kVp protocol (1.4 vs 5.4 mSv). Dunnett's test showed that there were no significant differences in the image noise, mean attenuation, and CNR between hybrid-iterative-reconstructed 80 kVp scans and 120 kVp scans (28.6 ± 6.5 vs 25.3 ± 4.5, p = 0.18; 475.0 HU ± 87.0 vs 445.3 HU ± 67.7, p = 0.20; 17.1 HU ± 3.5 vs 17.8 HU ± 3.1, p = 0.53). The low kVp scan and hybrid-iterative reconstruction algorithm can dramatically decrease the radiation dose and contrast dose with adequate image quality at cardiac CT of thin adults using a 256-row CT scanner.

Low contrast and radiation dose coronary CT angiography using a 320-row system and a refined contrast injection and timing method

“…Nakaura et al 25 found that with a 256-row scanner and 80 kVp plus IR, the CM dose could be decreased by 50% (to 185 mgI/kg; mean CM dose, 29.4 AE 6.1 mL) at CCTA and that contrast enhancement in the ascending aorta was sufficient. Komatsu et al, 26 who used a 64-row CT scanner, two 80-kVp protocols, and a mean CM dose of 10 AE 4 or 15 AE 7 mL, reported that the image quality was acceptable.…”

Current and Novel Imaging Techniques in Coronary CT

“…The use of these algorithms can also lead to reduced tube current or tube voltage (if necessary, with somewhat increased tube current), both of which reduce radiation dose without increasing image noise (Fig 2). The combination of iterative reconstruction and a low-tube voltage scan allows a decrease in the dose of intravenous contrast medium with preservation of image quality (28). On the basis of data from a prospective multicenter study, investigators have suggested that the use of adaptive statistical iterative reconstruction can reasonably reduce tube current and lower radiation dose (44% reduction in median dose) compared with filtered backprojection (27,29).…”

The Role of Iterative Reconstruction Techniques in Cardiovascular CT

“…High-resolution acquisitions are becoming more feasible as IR tempers the negative effects of photon starvation [49][50][51]. Contrast material dose reductions may also be possible without prohibitive degradation of image quality [22]. Novel IR algorithms are also emerging that should expand IR applications.…”