Patient Weight and Cross-Sectional Dimensions versus Subjective Image Quality at Standard Abdominal CT age range of 65 to 88 years (mean age of 71 years). Informed consent was obtained from all participating sub- jects. All studies were performed with multislice helical CT scanner (LightSpeed, QX/i, General Electric Medical Services, Waukesha, WI) with four-detector rows. Following standard contrast enhanced CT study, a set of four additional images was obtained in the equilibrium phase, centered at the upper pole of right kidney. The im- ages were obtained as per the standard scanning protocol at tube voltage (140 kVp) and tube current (240 280 mA). The images were acquired in a single breath-hold, with 2.5 mm detector configuration, table speed of 15 mm/gantry rotation based on 6:1 non-overlapping slice- pitch and 0.8 seconds tube rotation time. Five millimeter thick contiguous slices were reconstructed with standard soft tissue algorithm for image analysis. Weights of all patients were recorded just prior to the study. Cross-sectional abdominal area, circumference, an- teroposterior and transverse diameters of abdomen were measured with PACS diagnostic workstation software (AGFA Impax RS 3000 1K review station, AGFA Technical Imaging Systems, Richfield Park, NJ, U.S.A.). Average anterior abdominal wall fat thickness was estimat- ed from the measurements of anterior abdominal wall fat thickness at three different sites (midline and 10-cm lateral to the midpoint on both sides) at the level of upper pole of right kidney. Root mean square dimension was calculated as the root of the sum of squares of the maximum perpen- dicular anteroposterior and transverse diameters of ab- domen. Two subspecialty radiologists with expertise in ab- dominal imaging evaluated image sets qualitatively on a PACS diagnostic workstation with a standard five-point scale at a fixed window level and window width. The im- ages were presented to the readers in random order. Qualitative image quality scores were given on the basis of image noise, soft-tissue contrast and sharpness of organ boundaries for the liver, adrenals, kidneys, pancreas, and abdominal wall. Image quality was scored as 1 = not accept- able; 2 = substandard; 3 = acceptable; 4 = above average; 5 = excellent. Non-parametric correlation (Spearman) analysis was per- formed using SAS/STAT software (SAS Institute Inc., Cary, NC), to determine correlation of image quality at standard dose radiation with patient weight and cross-sec- tional abdominal dimensions. Confidence level of statistical association was determined by p-value of less than 0.01 (99% confidence limit). Cohen’s Kappa test was performed to determine interobserver concordance using SAS/STAT software (SAS Institute Inc., Cary, NC). Weighted kappa co-efficient values for interobserver agreement were con- sidered as slight, < 0.2; fair, = 0.21 0.40; moderate, = 0.41 0.60; substantial, = 0.61 0.80; or almost perfect, = 0.81 1.00. RESULTS In the randomized review, mean scores and standard er- ror of means for image quality of the CT studies by readers 1 and 2 were 3.8 0.05 and 3.75 0.05, respectively. There was moderate interobserver agreement in the image quality scores as determined by weighted kappa coefficient of 0.57 (p < 0.05). The range of patients’ weights in our study was 41.77 to 102.15 kg (median weight = 77.18 kg) (Fig. 1). The range of cross-sectional transverse abdominal diameters was 25 to 42 cm with average diameter of 33 cm (Fig. 2). The range of measurements for the average anterior abdominal fat thickness, anteroposterior diameter, circumference and cross-sectional area of abdomen were 0.1 3.2 cm (aver- age = 1.77 cm), 15.5 34.2 cm (average = 25.86 cm), 72 125 cm (average = 97.57 cm) and 386 1187 cm2 (average = 727.33 cm2), respectively. Data documenting correlation between image quality and patients’ abdominal dimensions are summarized in table 1. Significant negative correlation was found between image quality and patients’ Fig. 1. Scatter graph depicting distribution of patients’ weight. Korean J Radiol 4(4), December 2003 Fig. 2. Scatter graph depicting distribution of patients’ transverse diameter. 235