Download Effect of high concentration contrast material on contrast at low

Effect of high concentration contrast material on contrast
at low-energy multi-phasic CT of the upper abdomen:
initial study evaluated with virtual monochromatic spectral
imaging obtained using single-source dual-energy CT
Poster No.:
C-1269
Congress:
ECR 2012
Type:
Scientific Exhibit
Authors:
M. Sakane, T. Kim, M. Hori, H. Onishi, A. Nakamoto, M. Tatsumi,
N. Tomiyama; Suita/JP
Keywords:
Tissue characterisation, Contrast agent-intravenous, CTQuantitative, CT, Liver, Contrast agents, Abdomen
DOI:
10.1594/ecr2012/C-1269
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Purpose
Background
The results of numerous past studies have demonstrated that administration of higherconcentration contrast materials can improve the enhancement and contrast-to-noise
ratio (CNR) of abdominal organs. On the other front, low-voltage CT ha# also received
widespread attention in abdominal imaging because it has the advantage to improve
CNR without sacrificing low-contrast detectability. Currently, single-source dual-energy
CT can take two different in-plane projection data of 80 and 140 kVp, which confirms
the ability to create the simulation image at any desired virtual monochromatic spectral
(VMS) energy from 40 to 140 keV. VMS images enable the evaluation of image quality at
high and low voltage setting from the same projection data. Lower-voltage reconstruction
may be expected to improve CNR like low-voltage CT, although there were few studies
evaluating the clinical efficacy of VMS image to our knowledge.
Purpose
To investigate the effect of high-concentration contrast material on contrast at low-energy
CT imaging of the upper abdomen enabled by virtual monochromatic spectral (VMS)
imaging obtained using dual-energy CT.
Methods and Materials
Patients Population
72 patients underwent multi-phasic dual-energy CT for known or suspected liver or
pancreas tumor from January 2010 to March 2011 (exclusion criteria: vascular invasion
of tumor, major tumor involvement of liver, too thin subcutaneous fat layer of the anterior
abdominal wall ). Patients were divided into two Groups,
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Group A: 34 patients who underwent 300 mgI/ml-concentration contrast
material injection; 22 men and 12 women; mean age, 65 years (20 - 90);
mean body weight, 60.6 kg (40 - 86)
Group B: 38 patients who underwent 350 mgI/ml-concentration contrast
material injection; 21 men and 17 women; mean age, 65 years (33 - 84);
mean body weight, 61.9 kg (40 - 89)
Dual-energy MDCT Technique
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Multiphasic CT was performed by using fast kVp switching dual-energy 64-section MDCT
scanner.
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CT scanner: Discovery 750 HD (GE Healthcare, Milwaukee, WI)
Tube voltage: Fast switching between 80 and 140 kVp
Tube current: automatically preset at 600 mA
FOV: 34.5 - 40.0 cm2
Detector configuration: 64 × 0.625 mm
Rotation time: 0.5 second-Pitch: 1.375
Collimation: 0.625×64 slices
Reconstruction slice thick: 5mm
Timing of early arterial phase scan was determined by bolus tracking
program (SmartPrep)
Automatically reconstructed 140 kVp conventional CT images
Infusion Protocols
All patients received intravenous injection of 600 mgI/kg total iodine load per weight of
non-ionic contrast material.
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Group A: 300 mgI/ml-concentration contrast material with injection duration
of 30 seconds (0.067 mL/sec/kg and 20 mgI/sec/kg )
Group B: 350 mgI/ml-concentration contrast material with injection duration
of 25 seconds (0.069 mL/sec/kg and 24 mgI/sec/kg )
Scan Protocols
The early arterial, late arterial, and portal venous phasic CT scanning was started 8, 20
and 50 seconds respectively after the trigger (threshold level: increase of 100 HU over
baseline CT number of abdominal aorta).
Post-processing of Dual-Energy Data
The dual-energy projection data were also transferred to the workstation (Advantage
Workstation, GE Medical Systems). VMS images at 50 keV and 65 keV for each phase on
the workstation using a software. 50 keV and 65 keV VMS images were approximated to
the representative keV of conventional CT images at 80 kVp and 120 kVp, respectively.
One patient had two image sets for each of three phases (early arterial, late arterial, and
portal venous phases).
Quantitative Analyses
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Attenuation of the aorta, portal vein, hepatic parenchyma, paraspinal muscle and
subcutaneous fat tissue in the anterior abdominal wall was measured by manually placing
the circular or oval ROI cursor. The contrast to noise ratio (CNR) for each organ was
calculated by using the following equation.
CNR = (ROIo - ROIm) / SDn
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ROIo: attenuation of each organ
ROIm: attenuation of the paraspinal muscle
SDn: average standard deviation of subcutaneous fat tissue (or the image
noise)
Qualitative Analyses
Image quality (image contrast, overall image quality, and image noise) was evaluated by
two radiologists. Image contrast and overall image quality were rated on a 4-point scale.
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1, unacceptable
2, acceptable
3, good
4, excellent
Image noise were graded similarly.
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1, severe image noise present and unacceptable
2, moderate image noise present and interfering
3, mild image noise not interfering with depiction of structures
4, no image noise
Results
Result 1: attenuation of the organs (Fig.1)
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The mean attenuation values increased in order of the 140-kVp conventional,
65-keV VMS, and 50-keV VMS images in any phases in each patient group.
The attenuation of the organs at 50 keV VMS images were significantly higher
than those at 65 keV VMS images (p<0.01), in any phases in each patient
group.
Results 2: image noise (Fig.2)
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In any phases in each group, the mean image noise on the 50-keV VMS
images was significantly higher than that on the 65-keV VMS images (p<0.01).
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Result 3: CNR (Fig.3)
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The CNR for the organs increased in order of the 140-kVp conventional, 65keV VMS, and 50-keV VMS images in any phases in each patient group with
the exception of the CNR for the hepatic parenchyma in the early arterial phase
in each group.
The CNRs for the aorta in the early arterial phase on the 50-keV VMS images
was not significantly high compared with that on the 65-keV images in each
patient group.
However, the CNRs for the aorta in the early arterial phase for Group B were
significantly (p<0.01) higher than those for Group A at each voltage setting.
Result 4: qualitative analysis (Fig.4 - 6)
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On 50 keV VMS images, image contrast was improved but image noise and
overall image nose deteriorated in comparison with 65 keV images.
Images for this section:
Fig. 1: Attenuation of the organs
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Fig. 2: Image noise
Fig. 3: CNR of the organs
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Fig. 4: Score of qualitative analysis
Fig. 5: Case1; 60 YRS F, BW 50 kg, Group A (300 mgI/ml)
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Fig. 6: Case 2; 53 YRS F, BW 50 kg, Group B (350 mgI/ml)
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Conclusion
Discussion
Use of high-concentration contrast material is considered to be effective only for
improving arterial contrast. Both low-voltage CT and use of high-concentration contrast
material improve arterial enhancement in the early arterial phase, although use of highconcentration contrast material is more effective than low-voltage CT to improve arterial
enhancement. Besides, the combined use of high concentration contrast material and
low-voltage CT for CT arteriography is expected to 130% increase in CNR for the artery.
In the qualitative evaluation, image noise and overall image quality on 50-keV VMS
images were worse than those on 65-keV and 140 conventional images, but they were
acceptable.
Conclusion
Use of high-concentration contrast material is effective only for improving arterial contrast
in the early arterial phase, but more effective than low-voltage CT. The combined use of
high concentration contrast material and low-voltage CT for CT arteriography is expected
to 130% increase in CNR for the artery.
References
[1] Nakayama Y, Awai K, Funama Y, et al. Abdominal CT with low tube voltage:
preliminary observations about radiation dose, contrast enhancement, image quality, and
noise. Radiology 2005; 237(3):945-51.
[2] Huda W, Scalzetti EM, Levin G. Technique factors and image quality as functions of
patient weight at abdominal CT. Radiology 2000; 217(2): 430-5.
[3] Matsumoto K, Jinzaki M, Tanami Y, et al. Virtual monochromatic spectral imaging with
fast kilovoltage switching: improved image quality as compared with that obtained with
conventional 120-kVp CT. Radiology 2011; 259(1):257-62.
[4] Xiaoye Wu, David A. Langan, Dan Xu, et al. Monochromatic CT image representation
via fast switching dual kVp. Proc SPIE. 2009; 7258: 725845
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