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Lower Tube Voltage Reduces Contrast Material and Radiation Doses on 16-MDCT Aortography

¹ Department of Diagnostic Radiology, Graduate School of Medical Sciences, Kumamoto University, 1-1-1 Honjo, Kumamoto 860-8556, Japan.
² Department of Radiological Technology, School of Health Sciences, Kumamoto University, Kumamoto, Japan.

View larger version (34K): [in a new window]   Fig. 1 —Bar graph shows mean CT attenuation values at initial, middle, and final levels of aorta using our two protocols. Attenuation at final level was lower in protocol 2 (90 kVp, 40 mL of contrast material) (white bars) than in protocol 1 (120 kVp, 100 mL of contrast material) (gray bars), although difference in enhancement was not statistically significant.

View larger version (60K): [in a new window]   Fig. 2A —83-year-old man weighing 55 kg who underwent abdominal CT aortography for aortic aneurysm at reduced radiation (90 kVp) and contrast material (40 mL) doses (protocol 2). CT attenuation value was 323 H at descending aorta (A). Saccular aortic aneurysm (attenuation value, 223 H) is seen at middle level of scanning (B). At final level (C), aortic bifurcation was sufficiently attenuated at 218 H.

View larger version (131K): [in a new window]   Fig. 2B —83-year-old man weighing 55 kg who underwent abdominal CT aortography for aortic aneurysm at reduced radiation (90 kVp) and contrast material (40 mL) doses (protocol 2). CT attenuation value was 323 H at descending aorta (A). Saccular aortic aneurysm (attenuation value, 223 H) is seen at middle level of scanning (B). At final level (C), aortic bifurcation was sufficiently attenuated at 218 H.

View larger version (84K): [in a new window]   Fig. 2C —83-year-old man weighing 55 kg who underwent abdominal CT aortography for aortic aneurysm at reduced radiation (90 kVp) and contrast material (40 mL) doses (protocol 2). CT attenuation value was 323 H at descending aorta (A). Saccular aortic aneurysm (attenuation value, 223 H) is seen at middle level of scanning (B). At final level (C), aortic bifurcation was sufficiently attenuated at 218 H.

View larger version (129K): [in a new window]   Fig. 2D —83-year-old man weighing 55 kg who underwent abdominal CT aortography for aortic aneurysm at reduced radiation (90 kVp) and contrast material (40 mL) doses (protocol 2). Reconstructed 3D image yields excellent visualization of entire aorta and its major branches.

View larger version (71K): [in a new window]   Fig. 3A —68-year-old man weighing 62 kg who underwent thoracic CT aortography for aortic aneurysm at reduced radiation (90 kVp) and contrast material (40 mL) doses (protocol 2). CT attenuation value was 243 H at initial level of aortic scan (A) and 155 H at final level (B). Although upper level of aorta was intensely enhanced and 3D visualization was good, image is poor at lower level of aorta (C).

View larger version (108K): [in a new window]   Fig. 3B —68-year-old man weighing 62 kg who underwent thoracic CT aortography for aortic aneurysm at reduced radiation (90 kVp) and contrast material (40 mL) doses (protocol 2). CT attenuation value was 243 H at initial level of aortic scan (A) and 155 H at final level (B). Although upper level of aorta was intensely enhanced and 3D visualization was good, image is poor at lower level of aorta (C).

View larger version (71K): [in a new window]   Fig. 3C —68-year-old man weighing 62 kg who underwent thoracic CT aortography for aortic aneurysm at reduced radiation (90 kVp) and contrast material (40 mL) doses (protocol 2). CT attenuation value was 243 H at initial level of aortic scan (A) and 155 H at final level (B). Although upper level of aorta was intensely enhanced and 3D visualization was good, image is poor at lower level of aorta (C).

View larger version (21K): [in a new window]   Fig. 4 —Graph shows reduction in mean aortic attenuation with increasing body weight. Correlation coefficients for 120 kVp () and 90 kVp (•) groups are -0.71 and -0.75, respectively. A correlation coefficient of 1.0 indicates a perfect linear relationship.

View larger version (20K): [in a new window]   Fig. 5 —Graph shows relationship between mean signal-to-noise ratio and patient body weight. Correlation coefficients for 120 kVp () and 90 kVp (•) groups are -0.56 and -0.51, respectively. A correlation coefficient of 1.0 indicates a perfect linear relationship.

View larger version (20K): [in a new window]   Fig. 6 —Graph shows relationship between mean contrast-to-noise ratio and patient body weight. Correlation coefficients for 120 kVp () and 90 kVp (•) groups are -0.51 and -0.60, respectively. A correlation coefficient of 1.0 indicates a perfect linear relationship.

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