Dosisreduktion in der pulmonalen CT-Angiografie – Evaluation des Konzepts „hohe Jodeinbringrate – geringe mAs“

Coronary CT Angiography with Knowledge-Based Iterative Model Reconstruction for Assessing Coronary Arteries and Non-Calcified Predominant Plaques

Objective

To assess the effects of iterative model reconstruction (IMR) on image quality for demonstrating non-calcific high-risk plaque characteristics of coronary arteries.

Materials and Methods

This study included 66 patients (53 men and 13 women; aged 39–76 years; mean age, 55 ± 13 years) having single-vessel disease with predominantly non-calcified plaques evaluated using prospective electrocardiogram-gated 256-slice CT angiography. Paired image sets were created using two types of reconstruction: hybrid iterative reconstruction (HIR) and IMR. Plaque characteristics were compared using the two algorithms. The signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the images and the CNR between the plaque and adjacent adipose tissue were also compared between the two reformatted methods.

Results

Seventy-seven predominantly non-calcified plaques were detected. Forty plaques showed napkin-ring sign with the IMR reformatted method, while nineteen plaques demonstrated napkin-ring sign with HIR. There was no statistically significant difference in the presentation of positive remodeling, low attenuation plaque, and spotty calcification between the HIR and IMR reconstructed methods (all p > 0.5); however, there was a statistically significant difference in the ability to discern the napkin-ring sign between the two algorithms (χ² = 12.12, p < 0.001). The image noise of IMR was lower than that of HIR (10 ± 2 HU versus 12 ± 2 HU; p < 0.01), and the SNR and CNR of the images and the CNR between plaques and surrounding adipose tissues on IMR were better than those on HIR (p < 0.01).

Conclusion

IMR can significantly improve image quality compared with HIR for the demonstration of coronary artery and atherosclerotic plaques using a 256-slice CT.

Impact of Knowledge-Based Iterative Model Reconstruction in Abdominal Dynamic CT With Low Tube Voltage and Low Contrast Dose

OBJECTIVE

The purpose of this study was to compare iterative model reconstruction (IMR) and hybrid iterative reconstruction (HIR) of 80-kVp abdominal dynamic CT scans obtained with a low-dose contrast agent.

SUBJECTS AND METHODS

A group of 27 consecutively registered patients underwent abdominal dynamic CT with an 80-kVp protocol and a low dose of contrast agent (300 mg I/kg). Another 27 patients who had previously undergone a 120-kVp protocol with filtered back projection (FBP) and a standard contrast dose (600 mg I/kg) acted as control subjects. Effective dose, image noise, CT number, and contrast-to-noise ratio were compared between the 120-kVp and 80-kVp images with FBP, HIR, and IMR. Image contrast, image noise, image sharpness, noise texture, and overall image quality were evaluated for the four protocols.

RESULTS

The effective dose of the 80-kVp protocol was lower than that with the 120-kVp protocol. The 80-kVp protocol with HIR and IMR decreased image noise by 45% and 70% compared with the 80-kVp protocol with FBP. The contrast-to-noise ratio of the 80-kVp protocol with IMR was higher than that of the 120-kVp protocol. Qualitatively, the 80-kVp protocol with IMR improved image noise more than the 120-kVp protocol did, but noise texture was worse. HIR and the 120-kVp protocol yielded similar subjective image quality.

CONCLUSION

Use of the 80-kVp protocol with HIR allowed an approximately 50% reduction in contrast dose and an approximately 40% reduction in radiation dose compared with use of the 120-kVp protocol while preserving image quality. IMR reduced image noise more than HIR with this protocol but worsened noise texture.

Change in portal vein hemodynamics after chemoembolization for hepatocellular carcinoma: evaluation through multilevel dynamic multidetector computed tomography during arterial portography

OBJECTIVE

This study aimed to clarify the effect of embolization with lipiodol on portal vein hemodynamics.

METHODS

Time-density curves of the main portal vein on multilevel dynamic multidetector computed tomography during arterial portography were used to analyze peak computed tomography value (PV), time to PV (TPV), arrival time of contrast medium at the main portal vein (ATMPV), slope [(PV - 150) / (TPV - ATMPV)], and slope ratio (slope after embolization / slope before embolization).

RESULTS

In 20 patients with hepatoma, ATMPV and TPV were significantly prolonged and the time-density curve slope was significantly less after embolization. The difference in TPV increased (P = 0.02) and the slope ratio decreased with increasing embolized volume rate (P < 0.001). Strong correlation (R = -0.86) was found between the slope ratio and the embolized volume rate.

CONCLUSIONS

Time-density curves revealed significant portal vein flow delay after embolization; the degree of which was correlated with the extent of the embolized volume.