Rumiko Torigoe

Adaptive Iterative Dose Reduction in coronary CT angiography using 320-row CT: Assessment of radiation dose reduction and image quality

BACKGROUND Several methods have been developed to reduce the radiation dose in coronary computed tomography angiography (CTA). OBJECTIVE The objective of our study was to evaluate the effects of Adaptive Iterative Dose Reduction (AIDR) on objective and subjective image quality as well as the radiation dose, compared with conventional filtered back projection (FBP), in coronary CTA. METHODS We retrospectively reviewed 100 consecutive patients who underwent coronary CTA. In the first 50 patients, a higher tube current was used, and images were reconstructed with FBP. In the last 50 patients, a lower tube current was used, and images were reconstructed with AIDR. Subjective and objective image quality (noise, signal-to-noise ratio, contrast-to-noise ratio) were assessed. RESULTS The median radiation dose of the AIDR group was 22% lower than that of the FBP group (4.2 vs 5.4 mSv; P = 0.0001). No significant difference was found in subjective image quality, noise, signal-to-noise ratio, or contrast-to-noise ratio between the 2 groups. CONCLUSION AIDR reduced the tube current which resulted in reduction of radiation dose in coronary CTA while maintaining subjective and objective image quality compared with coronary CTA reconstructed with FBP.

Influence of hemodynamic parameters on coronary artery attenuation with 320-detector coronary CT angiography.

OBJECTIVES To investigate the relationship between cardiac output, end diastolic volume and the contrast enhancement in coronary CT angiography using 320-detector CT. MATERIALS AND METHODS A total of 38 patients underwent coronary CT angiography by using a 320-detector CT scanner (detector configuration, 320 × 0.5mm). The attenuation value of the ascending aorta at the level of the orifice of the left main trunk was measured. The cardiac output (CO), end diastolic volume (EDV) and stroke volume (SV) were measured by echocardiography. The EDV was normalized to the body surface area (BSA). The total blood volume injected from the left ventricle from the beginning of the contrast agent injection to the time of image acquisition was determined to be the total injected blood volume (TIV), which is a product of SV and the number of heart beats from the initiation of contrast agent injection to the scan. RESULTS There was a negative correlation between the attenuation of the ascending aorta and CO (r = -0.44, P = 0.0053). However, the negative correlation between the attenuation of the ascending aorta and TIV was stronger (r = -0.52, P = 0.0007). There was a negative correlation between the attenuation of the ascending aorta and EDV/BSA (r = -0.45, P = 0.0039). CONCLUSION In 320-detector CT, contrast enhancement in CCTA with a lesser amount of contrast medium decreases when cardiac output is high. Patients with larger EDV/BSA may also show decreased attenuation.

Effect of saline flush on enhancement of proximal and distal segments using 320-row coronary CT angiography

OBJECTIVE To investigate the effect of saline flush on coronary CT angiography of proximal, middle, and distal coronary artery segments, using 320-row CT, and to compare two injection duration protocols as to amount of contrast in the right heart chambers. METHODS This retrospective study was approved by the local ethics committee, and the requirement for informed consent to participate in this study was waived. The final study group included 108 patients who underwent coronary CT angiography. The first 36 patients received contrast medium without saline flush (group 1); the next 36 patients received contrast medium for 14s and saline flush (group 2); the last 36 patients received contrast medium for 12s and saline flush (group 3). The CT number, noise, contrast-to-noise ratio (CNR), and number of segments with a CT number greater than 325 Hounsfield units (HU) were recorded for proximal, middle, and distal segments. RESULTS The CT numbers and the CNR in groups 2 and 3 were significantly higher than that in group 1 (p<0.005); the difference between groups 2 and 3 was not significant. The proportion of segments greater than 325HU improved with saline flush (p<0.05), with a larger improvement in the distal segments. CONCLUSIONS Saline flush improves enhancement and CNR of coronary arteries, particularly of distal segments, in coronary CT angiography using 320-row CT. An average contrast medium injection of 44mL was feasible using a saline flush.

Subjective and objective evaluation of 10–30% dose reduced coronary artery phantom scans reconstructed with Forward projected model-based Iterative Reconstruction SoluTion (FIRST)

The data presented in this articles are related to the research article entitled “The feasibility of Forward-projected model-based Iterative Reconstruction SoluTion (FIRST) for coronary 320-row computed tomography angiography: a pilot study” (E. Maeda, N. Tomizawa, S. Kanno, K. Yasaka, T. Kubo, K. Ino, R. Torigoe, K. Ohtomo, 2016) [1]. This article describes subjective and objective evaluations of 2 mm–4 mm coronary artery phantom scanned with 100% dose and reconstructed with hybrid iterative reconstruction, and 90%, 80% and 70% dose reconstructed with full iterative reconstruction.

In reply to: minimizing the radiation dose in coronary CT angiography using prospective ECG-triggering, low tube voltage and iterative reconstruction technologies.

We have carefully read the letter by Dr. Saglam et al. [1] and wish to thank them for their interest in our paper. They achieved an effective radiation dose of 0.34 mSv in coronary computed tomography angiography (CTA) using 320-row CT with excellent image quality of the coronary arteries. Several methods have been developed to reduce the radiation dose of coronary CTA. These include prospective gating, noise-reduction filters, tube-potential reduction, acquisition-phase narrowing and use of iterative reconstruction methods [2]. Low tube voltage is advantageous for CTA especially in lean patients, because the increased contrast surpasses the increased noise, thus improving the contrast-to-noise ratio due to lower radiation dose, such as the case presented by Dr. Saglam et al. The average radiation dose of our study was 1.7 mSv, which was higher than in the case presented by them, because we used 120 kVp in all patients. Chen et al. [3] achieved a median radiation dose of 0.93 mSv for coronary CTA using the 320-row CT. The tube potential was 100 kVp in 90 % of the patients in their study. Reducing the tube potential to 80 kVp could further reduce the radiation dose, as Dr. Saglam et al. indicated. However, there are some concerns with using low tube potential. First, the image noise increases substantially in obese patients. Increasing tube current could reduce noise, but high tube current may not be available with earlier scanners. Second, increased image noise at low tube potential might obscure the coronary artery wall. Assessing plaque characteristics, not just assessing stenosis, is important. Patients with low-attenuation plaques are at higher risk of acute coronary syndrome compared with other patients [4]. Images with intensive noise could underestimate these high-risk plaques. Also, when the coronary artery wall is obscured, diffuse coronary artery disease might be underestimated. In conclusion, we thank Dr. Salgam et al. for sharing their experience of very-low-dose coronary CTA using 80 kVp. Although this method is feasible with lean patients, excessive dose reduction could be disadvantageous for assessing stenosis in obese patients or plaque assessment. The optimal dose necessary for coronary CTA should be investigated by further studies.

Prediction of the attenuation of the ascending aorta using bolus-tracking parameters and heart rate in coronary computed tomography angiography

OBJECTIVE The purpose of this study was to evaluate the correlation between bolus-tracking parameters and heart rate (HR) with attenuation of the ascending aorta and create a linear regression model for predicting coronary attenuation in coronary computed tomography angiography (CCTA). METHODS A total of 50 patients (31 men, 19 women; mean age, 67.2±10.8 y) underwent CCTA using a 320-detector CT scanner. A bolus-tracking scan was performed to optimize the scan timing. The average HR under normal breathing for 10s was recorded just before the bolus-tracking scan started. Attenuation values of the pulmonary artery at 7s (PA7) and 10s (PA10) after the beginning of the injection were recorded during the bolus-tracking scan and the ascending aortic attenuation (CEAAo) was measured during the diagnostic scan. RESULTS A positive correlation was observed between PA7 and CEAAo (r=0.41, P=0.003) and PA10 and CEAAo (r=0.66, P<0.0001), and weak negative correlation was observed between HR and CEAAo (r=-0.46, P=0.15). A multivariable linear regression model for predicting CEAAo was evaluated, and the residual error between the predicted and the measured CEAAo was within approximately ±100 HU. CONCLUSIONS Coronary attenuation could be predicted using HR and pulmonary artery attenuation during the bolus-tracking method.

Diagnostic Phase of Calcium Scoring Scan Applied as the Center of Acquisition Window of Coronary Computed Tomography Angiography Improves Image Quality in Minimal Acquisition Window Scan (Target CTA Mode) Using the Second Generation 320-Row CT

Objective. To compare the image quality of coronary computed tomography angiography (CCTA) acquired under two conditions: 75% fixed as the acquisition window center (Group 75%) and the diagnostic phase for calcium scoring scan as the center (CS; Group CS). Methods. 320-row cardiac CT with a minimal acquisition window (scanned using “Target CTA” mode) was performed on 81 patients. In Group 75% (n = 40), CS was obtained and reconstructed at 75% and the center of the CCTA acquisition window was set at 75%. In Group CS (n = 41), CS was obtained at 75% and the diagnostic phase showing minimal artifacts was applied as the center of the CCTA acquisition window. Image quality was evaluated using a four-point scale (4-excellent) and the mean scores were compared between groups. Results. The CCTA scan diagnostic phase occurred significantly earlier in CS (75.7 ± 3.2% vs. 73.6 ± 4.5% for Groups 75% and CS, resp., p = 0.013). The mean Group CS image quality score (3.58 ± 0.63) was also higher than that for Group 75% (3.19 ± 0.66, p < 0.0001). Conclusions. The image quality of CCTA in Target CTA mode was significantly better when the center of acquisition window is adjusted using CS.