Kalra et al. Table 1. Statistical Correlation of Weight and Abdominal Dimensions with Image Quality Score Anthropometric Features Weight Abdominal wall thickness Anteroposterior diameter Transverse diameter Circumference Cross-sectional area Root-mean-square dimension Co-efficient of Correlation 0.46 0.47 0.47 0.58 0.56 0.54 0.56 p-value 0.003 0.002 0.002 0.0001 0.0002 0.0004 0.0002 weight, anterior abdominal fat thickness anteroposterior and transverse diameter, circumference, and cross-section- al area (p < .01). With standard protocol abdominal CT studies, the transverse diameter of the patients had the strongest negative correlation with subjective image quali- ty (p =.0001). A negative linear correlation of 0.56 be- tween subjective image quality and root mean square di- mension and circumference of abdomen was found (p < .002). DISCUSSION More than 80% of man-made sources of radiation are ac- counted by diagnostic and therapeutic ionizing radiation and radionuclides (3). Increased clinical utilization of diag- nostic radiological studies is responsible for the increase in radiation doses to society. Though CT constitutes about 5% of all radiological procedures, it contributes more than 30% of radiation exposure from medical x-ray sources (4). Contrary to other x-ray based examinations, scanning pa- rameters in CT studies are uniform for most patients and not appropriately modulated depending on patient size, body part being examined and indication of the study (5). Various technical advances to decrease radiation dose from CT have been evaluated (7 10). Prior studies have suggested that it is possible to reduce tube currents based on the part of the body being scanned and weight of the patient without jeopardizing image quality (11 13). Diverse approaches have been utilized to address the issue of radiation dose optimization such as limiting CT scans to carefully identified indications, restricting multiphase pro- tocols to obtain specific clinical information, judicious use of repeat and follow-up studies, and appropriate adjust- ments in scanning parameters (6). Tube voltage, tube cur- rent, scanning time, slice thickness, pitch and scan volume are important major scanning parameters that influence ra- diation dose on CT (6). Several studies have implied that increasing pitch decreases radiation dose by reducing the 236 scan time (14, 15). However, higher pitch can result in le- sions being missed due to slice broadening and consequent volume averaging effects. Tube current settings are often not appropriately modulated according to patient body habitus, weight, and body part to be examined (6). Some clinical investigations have actively advocated use of pa- tients’ weight for optimizing scan parameters and reducing radiation dose without compromising image quality (16, 17). In a study of 4881 subjects, Han et al. reported that waist (abdominal) circumference was the best predictor of ab- dominal fat and had greater correlation with regional fat distribution than both weight and body mass index (weight (kg)/ height (m2)) (18). Based on this large patient cohort study, we assumed that the distribution of fat and regional constitution (muscle and other tissue bulk) might reflect more accurately in the regional anthropometric dimensions than in the overall weight of the subject. Consequently, we also anticipated that a subject with height of 145 cm might have weight equivalent to a subject with height of 165 cm, and as a result, the cross-sectional abdominal dimensions of patients would be more reliable for prediction of scan- ning protocols. Therefore, we investigated association be- tween image quality and the aforementioned abdominal dimensions. Indeed, we found a statistically significant neg- ative correlation between subjective image quality and pa- tients’ abdominal dimensions and weight. Transverse diam- eter, circumference, cross-sectional area, and root-mean- square dimension had greater correlation with image quali- ty than weight, anteroposterior diameter, and anterior ab- dominal fat thickness. In view of the fact that the beam at- tenuation and thus, image quality is determined by body distance traversed by the x-ray beam, our presumption that thickness of the body portion rather than weight cor- relates better with image quality was proven to be valid (12, 13). Consequently, our findings support the con- tention of Haaga who has strongly advocated that patient diameter is a better predictor of the milliampere-second re- quirement than body weight because diameter better cor- relates with the distance of the pathway traversed by the X-ray beam (13). In our study, maximum transverse diam- eter of abdomen had greatest correlation with image quali- ty. In addition, these cross-sectional dimensions, i.e. maxi- mum transverse diameter, circumference, cross-sectional area, and root-mean-square dimension are also representa- tive of accurate regional abdominal constitution and can be used to predict the image quality at given CT scanning pa- rameters. Thus, if modulation of scanning parameters to optimize radiation dose in individual patient is to be con- sidered, the modification should be made with reference to findings of this study. Though we measured these dimen- Korean J Radiol 4(4), December 2003