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Optimal Adaptive Statistical Iterative Reconstruction Percentage in Dual-energy Monochromatic CT Portal Venography

Posted Feb 29, 2016 Updated Apr 10, 2023
By Liqin Zhao MD , Sebastian Winklhofer MD , Zheng-Han Yang MD , Keyang Wang MD , Wen He MD
9 min read

Rationale and Objectives

The aim of this article was to study the influence of different adaptive statistical iterative reconstruction (ASIR) percentages on the image quality of dual-energy computed tomography (DECT) portal venography in portal hypertension patients.

Materials and Methods

DECT scans of 40 patients with cirrhosis (mean age, 56 years) at the portal venous phase were retrospectively analyzed. Monochromatic images at 60 and 70 keV were reconstructed with four ASIR percentages: 0%, 30%, 50%, and 70%. Computed tomography (CT) numbers of the portal veins (PVs), liver parenchyma, and subcutaneous fat tissue in the abdomen were measured. The standard deviation from the region of interest of the liver parenchyma was interpreted as the objective image noise (IN). The contrast-noise ratio (CNR) between PV and liver parenchyma was calculated. The diagnostic acceptability (DA) and sharpness of PV margins were obtained using a 5-point score. The IN, CNR, DA, and sharpness of PV were compared among the eight groups with different keV + ASIR level combinations.

Results

The IN, CNR, DA, and sharpness of PV of different keV + ASIR groups were all statistically different ( P < 0.05). In the eight groups, the best and worst CNR were obtained in the 60 keV + 70% ASIR and 70 keV + 0% ASIR (filtered back-projection [FBP]) combination, respectively, whereas the largest and smallest objective IN were obtained in the 60 keV + 0% ASIR (FBP) and 70 keV + 70% combination. The highest DA and sharpness values of PV were obtained at 50% ASIR for 60 keV.

Conclusions

An optimal ASIR percentage (50%) combined with an appropriate monochromatic energy level (60 keV) provides the highest DA in portal venography imaging, whereas for the higher monochromatic energy (70 keV) images, 30% ASIR provides the highest image quality, with less IN than 60 keV with 50% ASIR.

Introduction

Computed tomography portal venography (CTPV) is used for the evaluation of portal-systemic collateral circulations of patients with liver cirrhosis . It provides therapeutic relevant information, such as portal vein lesions, the status of the portal-systemic collateral circulation, including the diameter, location, and extent of esophageal and gastric varicosis, spleno-renal and para-umbilical veins, as well as the underlying hepatic disease . In addition, CTPV is frequently used for the presurgical vascular evaluation of patients with upcoming liver transplantation .

However, the image quality of CTPV is commonly influenced by several factors. First, beam-hardening artifacts are frequently an obstacle to the image quality of CT angiography . Second, patients who undergo CTPV often suffer from severe hepatic disease accompanied with portal vein thrombosis, which might influence the image quality of CTPV . Furthermore, because renal dysfunction is commonly present in patients with severe hepatic disease, a reduction of contrast agent dosage is frequently required, which may result in decreased imaging conditions . In addition, the portal venous imaging quality may be affected by the cardiac function and the body mass index (BMI) of the patient, making the timing of the optimal contrast enhancement difficult .

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Material and Methods

Patient Population

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Imaging Technique

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Data Post-processing

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Objective Image Quality Assessment (Quantitative Assessment)

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Figure 1, Objective assessment on image quality of CT portal venography of 60 and 70 keV with different ASIR percentages. The patient was a 48-year-old woman (BMI > 25) with portal hypertension secondary to liver cirrhosis; enhanced axial images at portal venous phase are shown. ( a ) 60 keV + 0 ASIR; ( b ) 60 keV + 30% ASIR; ( c ) 60 keV + 50% ASIR; ( d ) 60 keV + 70%; ( e ) 70 keV + 0 ASIR; ( f ) 70 keV + 30% ASIR; ( g ) 70 keV + 50% ASIR; ( h ) 70 keV + 70%. The marked regions were ROIs in the main stem of portal vein, liver parenchyma, and subcutaneous fat.

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Subjective Image Quality Assessment (Qualitative Assessment)

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Table 1

Grading Scale for Qualitative Image Analysis of Sharpness, Image Noise, and Diagnostic Acceptability of the Portal Vein

Grading Scale Sharpness Diagnostic Acceptability 1 Blurry Unacceptable 2 Poor Suboptimal 3 Average Average 4 Better Above average 5 Sharpest Excellent

Figure 2, Subjective assessment on image quality of CT portal venography of 60 and 70 keV with different percentage ASIRs. The same patient as Figure 1 . Same slice thickness, field-of-view, and nearly identical angle were used for reconstruction of all images. ( a ) 60 keV + 0% ASIR; ( b ) 60 keV + 30% ASIR; ( c ) 60 keV + 50% ASIR; ( d ) 60 keV + 70% ASIR; ( e ) 70 keV + 0% ASIR; ( f ) 70 keV + 30% ASIR; ( g ) 70 keV + 50% ASIR; ( h ) 70 keV + 70% ASIR.

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Statistical Analysis

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Results

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Objective Scores (Quantitative Assessment)

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Table 2

Comparison of objective and subjective assessment of image quality of CT portal venography in different groups

Item_F_ Value_P_ Value CNR 36.000 <0.001 IN 91.274 <0.001 DA 50.552 <0.001 Sharpness 8.510 <0.001

CNR, contrast-to-noise ratio of portal vein to liver parenchyma; CT, computed tomography; DA, diagnostic acceptability; IN, image noise.

Figure 3, Objective image quality assessment of 60 and 70 keV images with different ASIR percentages in different BMI groups. ( a ) Contrast-noise ratio (CNR) of portal vein to liver parenchyma; ( b ) image noise of objective assessment.

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Subjective Scores (Qualitative Assessment)

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Figure 4, Subjective image quality assessment on the 60 and 70 keV images with different ASIR percentages levels in different BMI groups. ( a ) Diagnostic acceptability; ( b ) sharpness of portal vein.

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The Interobserver Agreement Results of Subjective Assessment

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Discussion

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Conclusion

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Acknowledgements

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Academic Radiology, Volume 23, Issue 3
Journals General Radiology
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