Does the amount of tagged stool and fluid significantly affect the radiation exposure in low-dose CT colonography performed with an automatic exposure control?
OBJECTIVE
To determine whether the amount of tagged stool and fluid significantly affects the radiation exposure in low-dose screening CT colonography performed with an automatic tube-current modulation technique.


METHODS
The study included 311 patients. The tagging agent was barium (n = 271) or iodine (n = 40). Correlation was measured between mean volume CT dose index (CTDI (vol)) and the estimated x-ray attenuation of the tagged stool and fluid (ATT). Multiple linear regression analyses were performed to determine the effect of ATT on CTDI (vol ) and the effect of ATT on image noise while adjusting for other variables including abdominal circumference.


RESULTS
CTDI (vol) varied from 0.88 to 2.54 mGy. There was no significant correlation between CTDI (vol) and ATT (p = 0.61). ATT did not significantly affect CTDI (vol) (p = 0.93), while abdominal circumference was the only factor significantly affecting CTDI (vol) (p < 0.001). Image noise ranged from 59.5 to 64.1 HU. The p value for the regression model explaining the noise was 0.38.


CONCLUSIONS
The amount of stool and fluid tagging does not significantly affect radiation exposure.
Lim
Hyun Kyong
HK
Department of Radiology, Seoul National University Bundang Hospital, Bundang-gu, Seongnam-si, Gyeonggi-do, 463-707, Korea.
Lee
Kyoung Ho
KH
Kim
So Yeon
SY
Kim
Kil Joong
KJ
Kim
Bohyoung
B
Lee
Hyunna
H
Park
Seong Ho
SH
Yanof
Jeffrey H
JH
Hwang
Seung-Sik
SS
Kim
Young Hoon
YH
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001464:Barium; D001822:Body Burden; D001826:Body Fluids / Q000737:chemistry; D023881:Colonography, Computed Tomographic / Q000706:statistics & numerical data*; D004733:Enema; D005243:Feces / Q000737:chemistry; D005260:Female; D006801:Humans; D017613:Iodine Compounds; D008297:Male; D008875:Middle Aged; D011829:Radiation Dosage; D011835:Radiation Protection; D011874:Radiometry / Q000706:statistics & numerical data*; D056910:Republic of Korea / Q000453:epidemiology; D018570:Risk Assessment; D012307:Risk Factors
D017613:Iodine Compounds; D001464:Barium