Relationship between patient centering, mean computed tomography numbers and noise in abdominal computed tomography: Influence of anthropomorphic parameters

AIM: To determine the influence of anthropomorphic parameters on the relationship between patient centering, mean computed tomography (CT) numbers and quantitative image noise in abdominal CT. METHODS: Our Institutional Review Board approved study included 395 patients (age range 21-108, years; male: female = 195:200) who underwent contrast-enhanced abdominal CT on a 16-section multi-detector row scanner (GE LightSpeed 16). Patient centering in the gantry isocenter was measured from the lateral localizer radiograph (off center S = patient off centered superior to isocenter; off center I = patient off centered inferior to isocenter). Mean CT numbers (Hounsfield Units: HU) and noise (standard deviation of CT numbers: SD) were measured in the anterior (aHU, aSD) and posterior (pHU, pSD) abdominal wall subcutaneous fat and liver parenchyma (LivHU, LivSD) at the level of the porta hepatis. Patients' age, gender, weight, body mass index and maximal anteroposterior diameter were recorded. The data were analyzed using linear regression analysis. RESULTS: Most patients (81%; 320/395) were not correctly centered in the gantry isocenter for abdominal CT scanning. Mean CT numbers in the abdominal wall increased significantly with an increase in the off-centering distance, regardless of the direction of the off-center (P < 0.05). There was a substantial increase in pSD (P = 0.01) and LivSD (P = 0.017) with off-centering. Change in mean CT numbers and image noise along the off-center distance was influenced by the patient size (P < 0.01). CONCLUSION: Inappropriate patient centering for CT scanning adversely affects the reliability of mean CT numbers and image noise. (c) 2012 Baishideng. All rights reserved.