Korean J Radiol.  2012 Apr;13(2):152-164. 10.3348/kjr.2012.13.2.152.

80-kVp CT Using Iterative Reconstruction in Image Space Algorithm for the Detection of Hypervascular Hepatocellular Carcinoma: Phantom and Initial Clinical Experience

• Hur S
• Lee JM
• Kim SJ
• Park JH
• Han JK
• Choi BI

• KMID: 1245379
• DOI: http://doi.org/10.3348/kjr.2012.13.2.152

Abstract

OBJECTIVE
To investigate whether the low-tube-voltage (80-kVp), intermediate-tube-current (340-mAs) MDCT using the Iterative Reconstruction in Image Space (IRIS) algorithm improves lesion-to-liver contrast at reduced radiation dosage while maintaining acceptable image noise in the detection of hepatocellular carcinomas (HCC) in thin (mean body mass index, 24 +/- 0.4 kg/m2) adults.
SUBJECTS AND METHODS
A phantom simulating the liver with HCC was scanned at 50-400 mAs for 80, 100, 120 and 140-kVp. In addition, fifty patients with HCC who underwent multiphasic liver CT using dual-energy (80-kVp and 140-kVp) arterial scans were enrolled. Virtual 120-kVP scans (protocol A) and 80-kVp scans (protocol B) of the late arterial phase were reconstructed with filtered back-projection (FBP), while corresponding 80-kVp scans were reconstructed with IRIS (protocol C). Contrast-to-noise ratio (CNR) of HCCs and abdominal organs were assessed quantitatively, whereas lesion conspicuity, image noise, and overall image quality were assessed qualitatively.
RESULTS
IRIS effectively reduced image noise, and yielded 29% higher CNR than the FBP at equivalent tube voltage and current in the phantom study. In the quantitative patient study, protocol C helped improve CNR by 51% and 172% than protocols A and B (p < 0.001), respectively, at equivalent radiation dosage. In the qualitative study, protocol C acquired the highest score for lesion conspicuity albeit with an inferior score to protocol A for overall image quality (p < 0.001). Mean effective dose was 2.63-mSv with protocol A and 1.12-mSv with protocols B and C.
CONCLUSION
CT using the low-tube-voltage, intermediate-tube-current and IRIS help improve lesion-to-liver CNR of HCC in thin adults during the arterial phase at a lower radiation dose when compared with the standard technique using 120-kVp and FBP.

Keyword

Hepatocellular carcinoma; Low tube voltage; Iterative reconstruction; 80-kVp; Computed tomography; Image quality

MeSH Terms

*Algorithms
Analysis of Variance
Carcinoma, Hepatocellular/*blood supply/*radiography
Contrast Media/diagnostic use
Female
Humans
Iohexol/analogs & derivatives/diagnostic use
Liver Neoplasms/*blood supply/*radiography
Male
Middle Aged
Phantoms, Imaging
Radiographic Image Interpretation, Computer-Assisted/*methods
Regression Analysis
Retrospective Studies
Tomography, X-Ray Computed/*methods

Figure

• 

  Fig. 1 Axial CT image of phantom at tube voltage of 100 kVP and 150 mAs. Fifth tube was selected as target lesion to simulate subtle hypervascular HCC nodules.

• 

  Fig. 2 Flow chart of study population enrollment based on recommended standards for reporting diagnostic accuracy and proof of tumor burden. *Follow-up was performed with multidetector CT, MR imaging, or both after minimum of 6 months. AASLD = American Association for Study of Liver Disease

• 

  Fig. 3 Axial contrast-enhanced multidetector CT images obtained by using preset soft-tissue window (window width, 300 HU; window level, 40 HU) in 61-year-old man with HCC nodule in left lobe of liver. Images obtained during late arterial phase with (A) protocol A (linearly blended virtual 120 kVp, FBP), (B) protocol B (80 kVp, FBP), and (C) protocol C (80 kVp, IRIS) show substantially reduced image noise with protocol C compared to image noise with protocol B. Note reduced conspicuity of hypervascular liver tumors in due to decreased iodine attenuation at higher tube voltage settings compared with tumor conspicuity in B and C.

• 

  Fig. 4 Axial contrast-enhanced multidetector CT images obtained in 45-year-old man during late arterial phase with (A) protocol A (linearly blended virtual 120 kVp, FBP), (B) protocol B (80 kVp, FBP), and (C) protocol C (80 kVp, IRIS), which show ROIs manually drawn on HCC nodule (ROI 1), aorta (ROI 2), liver (ROIs 3-6), pancreas (ROIs 7, 8), paraspinal muscle (ROI 9, 10), and subcutaneous fat of anterior abdominal wall (ROI 11). Another ROI was drawn in other axial image (not shown) to measure attenuation value of pancreatic head. For all measurements, size, shape, and position of ROIs were kept constant among three protocols by applying copy-and-paste function at workstation.

• 

  Fig. 5 Relationship of CNR versus effective dose. (A) Scatterplots and non-linear regression of lesion-to-background CNR versus effective dose at each kVp and reconstruction method in phantom study. The non-linear regression fit is represented by following equation, CNR = √(FOM × ED). Regression analysis resulted in FOM values from 0.03 to 0.58 for each condition with p values of less than 0.001. (B) Imaginary graphs of lesion-to-liver CNR versus effective dose for three CT protocols in patient study by following equation of CNR = √FOM × ED, which were proven in phantom study. Lesion-to-liver CNR can be increased in protocol C moreso than in protocols A or B at constant effective dose. Alternatively, effective dose can be reduced in protocol C moreso than in protocols A or B.

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