Image fusion in dual energy computed tomography: effect on contrast enhancement, signal-to-noise ratio and image quality in computed tomography angiography.
OBJECTIVE
The aim of this study was to evaluate the influence of different weighting factors on contrast enhancement, signal-to-noise ratio (SNR), and image quality in image fusion in dual energy computed tomography (DECT) angiography.


METHODS
Fifteen patients underwent a CT angiography of the aorta with a SOMATOM Definition Dual Source CT (DSCT; Siemens, Forchheim, Germany) in dual energy mode (DECT) (tube voltage: 80 and 140 kVp; tube current: 297 eff. mA and 70 eff. mA; collimation, 14 x 1.2 mm). Raw data were reconstructed using a soft convolution kernel (D30f). Fused images were calculated using a spectrum of weighting factors (0.0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0) generating different ratios between the 80- and 140-kVp images (eg, factor 0.5 corresponds to 50% image information from the 140- and the 80-kVp image). Both CT values and SNR were measured in the descending aorta (levels of celiac trunk, renal arteries, and aortic bifurcation), in the right and left common iliac artery and in paraaortal fat. Image quality was evaluated using a 5-point grading scale. Results were compared using paired t-tests and nonparametric paired Wilcoxon tests.


RESULTS
Statistically significant increases in mean CT values were seen in vessels when increasing weighting factors were used (all P <or= 0.001). For example, mean CT values derived from the aorta at the level of the celiac trunk were 273.8 +/- 25.8 Hounsfield units (HU), 304.0 +/- 24.3 HU, 361.4 +/- 22.5 HU, 418.3 +/- 25.8 HU, 477.8 +/- 32.2 HU, 536.2 +/- 41.2 HU, 564.6 +/- 45.3 HU, when the weighting factors 0.0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0 were used. The highest SNR values were found in vessels when the weighting factor 0.5 was used. The highest SNR values of the paraaortal fat were obtained for the weighting factors 0.3 and 0.5. Visual image assessment for image quality showed the highest score for the data reconstructed using the weighting factor 0.5.


CONCLUSIONS
Different weighting factors used to create fused images in DECT cause statistically significant differences in CT value, SNR, and image quality. Best results were obtained using the weighting factor 0.5, which we recommend for image fusion in DECT angiography.
Behrendt
Florian F
FF
Department of Diagnostic Radiology, University Hospital RWTH Aachen, Aachen, Germany. behrendt@rad.rwth-aachen.de
Schmidt
Bernhard
B
Plumhans
Cédric
C
Keil
Sebastian
S
Woodruff
Seth G
SG
Ackermann
Diana
D
Mühlenbruch
Georg
G
Flohr
Thomas
T
Günther
Rolf W
RW
Mahnken
Andreas H
AH
D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D000792:Angiography / Q000379:methods*; D001014:Aortic Aneurysm / Q000000981:diagnostic imaging*; D001027:Aortography / Q000379:methods*; D003287:Contrast Media; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D007472:Iohexol / Q000031:analogs & derivatives*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique; D014057:Tomography, X-Ray Computed / Q000379:methods*
D003287:Contrast Media; D007472:Iohexol; C038192:iopromide