Brief Article
Copyright ©2012 Baishideng Publishing Group Co.
World J Radiol. Mar 28, 2012; 4(3): 102-108
Published online Mar 28, 2012. doi: 10.4329/wjr.v4.i3.102
Table 1 Patient size, computed tomography numbers and quantitative image noise at different magnitude and direction of off-centering (mean±SD)
Distance (#patients)Direction (#patients)BMI (kg)Weight (mGy)AP diameter (cm)CTDIvolaHUpHULivHUaSDpSDLivSD
0-5 mm (n = 75)Ideal centering27 (18-59)77 (31-181)28 (17-52)13.4 (5.2-48.3)-97.5 ± 27.2 (-117~-45)-92.8 ± 14.9 (-121~-34)117.0 ± 43.4 (63~153)9.9 ± 4.9 (5~45)11.8 ± 4.3 (4~33)17.0 ± 3.7 (9~15)
6-10 mm (n = 47)A (n = 20)28 (20-38)76 (54-107)27 (17-33)14.1 (9.0-33.0)-98.2 ± 9.3 (-115~-78)-90.9 ± 9.5 (-106~ -71)114.0 ± 20.0 (55~153)11.0 ± 2.6 (6~18)12.3 ± 3.0 (7~16)17.8 ± 3.4 (10~30)
B (n = 27)28 (21-40)79 (54-127)29 (20-53)13 (7.2-23.4)-95.1 ± 13.1 (-115~-60)-88.7 ± 19.3 (-109~-59)117.6 ± 26.9 (80~167)9.7 ± 2.3 (6~15)13.4 ± 4.01 (8~23)17.4 ± 5.2 (13~23)
11-20 mm (n = 125)A (n = 47)30 (19-51)88 (54-130)31 (23-40)15.4 (9.2-42.2)-96.9 ± 13.4 (-116~-45)-93.3 ± 14.0 (-114~-44)109.9 ± 22.5 (63~158)11.0 ± 3.6 (5~22)12.6 ± 3.7 (7~23)18.1 ± 4.9 (11~31)
B (n = 78)27 (17-49)74 (35-136)28 (15-44)13.2 (5.8-34.5)-97.1 ± 13.1 (-115~-53)-92.9 ± 11.8 (-124~63)119.3 ± 25.2 (31~175)9.5 ± 2.4 (6~18)11.9 ± 3.2 (8~21)17.9 ± 4.3 (11~29)
21-30 mm (n = 85)A (n = 22)29 (20-37)89 (46-129)32 (19-53)13.9 (6.2-26.7)-96.5 ± 10.9 (-112~-74)-89.0 ± 12.8 (-118~-56)107.4 ± 26.31 (40~142)12.4 ± 3.31 (7~20)13.6 ± 3.91 (9~24)18.7 ± 3.81 (6~20)
B (n = 63)26 (15-35)73 (40-109)27 (17-38)12.7 (5.9-23.5)-94.6 ± 13.7 (-113~-44)-85.3 ± 13.01 (-110~-43)122.3 ± 25.1 (55~177)10.4 ± 2.8 (6~23)13.3 ± 3.71 (6~22)17.9 ± 4.9 (11~34)
³31 mm (n = 63)A (n = 10)36 (22-52)96 (65-141)34 (28-46)14.2 (10.1-21.1)-94.3 ± 7.4 (-103~-80)-89.1 ± 16.6 (-100~-77)116.6 ± 24.8 (81~153)16.4 ± 7.01 (9~29)14.0 ± 5.0 (8~24)26.7 ± 4.01 (21~38)
B (n = 53)26 (19-38)74 (49-118)27 (19-36)14.1 (6.1-42.6)-94.1 ± 13.7 (-129~-68)-87.1 ± 13.5a (-113~-61)125.0 ± 24.8a (63~167)9.4 ± 2.5 (6~18)13.5 ± 4.7a (8~30)17.2 ± 4.0 (11~30)
aImplies significant statistical difference (P < 0.05). Off-centering distance and direction had a greater effect on image noise as compared to the mean computed tomography (CT) numbers. Numbers in parentheses are ranges. A: Superior off-centering; B: Inferior off-centering; aHU: Mean CT numbers in the anterior abdominal wall; pHU: Mean CT numbers in the posterior abdominal wall; LivHU: Mean CT numbers in liver, aSD: Quantitative noise in the anterior abdominal wall; pSD: Quantitative noise in the posterior abdominal wall; LivSD: Quantitative noise in the liver.
Table 2 Computed tomography numbers and quantitative image noise for ideally centered and off-centered patients (mean ± SD)
DirectionaHUpHULivHUaSDpSDLivSD
Ideal centering-97.5 ± 15.9-92.8 ± 15.1117.0 ± 21.59.9 ± 4.911.8 ± 4.317.0 ± 3.7
A-96.9 ± 11.5 (0.4)-91.4 ± 12.5 (0.25)111.1 ± 24.3 (0.05)11.8 ± 4.1 (0.004)a12.8 ± 3.8 (0.045)a18.8 ± 5.3 (0.003)a
B-95.5 ± 14.4 (0.16)-89.1 ± 14.5 (0.03)a121.0 ± 24.5 (0.1)9.8 ± 2.6 (0.33)12.8 ± 3.9 (0.03)a17.6 ± 4.3 (0.09)
aImplies significant statistical difference (P < 0.05). Numbers in parentheses are P values. A: Superior off-centering; B: Inferior off-centering; aHU: Mean computed tomography (CT) numbers in the anterior abdominal wall; pHU: Mean CT numbers in the posterior abdominal wall; LivHU: Mean CT numbers in the liver; aSD: Quantitative noise in the anterior abdominal wall: pSD: Quantitative noise in the posterior abdominal wall; LivSD: Quantitative noise in the liver.