Thein vivorelationship between cross-sectional area and CT dose index in abdominal multidetector CT with automatic exposure control

Abstract

The relationship between patient cross-sectional area and both volume CT dose index (CTDI) and dose length product was explored for abdominal CT in vivo, using a 16 multidetector row CT (MDCT) scanner with automatic exposure control. During a year-long retrospective survey of patients with MDCT for symptoms of abdominal sepsis, cross-sectional areas were estimated using customised ellipses at the level of the middle of vertebra L3. The relationship between cross-sectional area and the exposure parameters was explored. Scans were performed using a LightSpeed 16 (GE Healthcare Medical Systems, Milwaukee, WI) operated with tube current modulation. From a survey of 94 patients it was found that the CTDI increased with the increase in patient cross-sectional area. The relationship was logarithmic rather than linear, with a least-squares fit to the data (R(2) = 0.80). For abdominal CT the cross-sectional area gave a measure of patient size based on the region of the body to be exposed. Exposure parameters increased with increasing cross-sectional area and the greater radiation exposure of larger patients was partly a consequence of their size. Given increasing obesity levels we believe that cross-sectional area and scan length should be added to future dose surveys, allowing patient size to be considered as a factor of relevance when examining population doses.

Body composition determinants of radiation dose during abdominopelvic CT

“…Our findings therefore advance previous knowledge that has established that patients with an elevated body weight [ 6 ], body mass index [ 4 ] or cross-sectional area [ 5 , 7 ] receive larger doses of ionising radiation during abdominopelvic CT with ATCM. Our results indicate that, of the many body tissues that constitute a patient’s BMI or cross-sectional area, it is a patient’s total abdominal/pelvic adipose tissue that is the strongest predictor of radiation dose during abdominopelvic CT.…”

“…The challenges that obese patients present to radiology departments, particularly in relation to dose reduction, are now increasingly recognised [ 15 ] because more than 30% of US adults and almost 20% of European adults have a body mass index of greater than 30 kg/m 2 [ 16 , 17 ]. Although the shielding effects of visceral and subcutaneous adipose tissue result in over 50% less radiation dose to organs deep within the abdomen in morbidly obese individuals [ 18 ], ATCM results in logarithmic increases in tube current with increasing patient size [ 7 ] and abdominopelvic organ doses in obese patients are consequentially higher [ 6 ]. Furthermore, an effective dose to the skin and more superficial organs is proportionally increased with increasing patient size because of the increased tube current and reduced distance between the patient and the x-ray source [ 18 ].…”

“…It is well recognised that patients with a larger body habitus are exposed to significantly larger doses of ionising radiation during abdominopelvic CT when automated tube current modulation (ATCM) is employed [ 4 – 7 ]. Previous studies have examined the influence of variables such as body weight [ 6 ], body mass index [ 4 ], patient cross-sectional area [ 5 , 7 ] and patient AP diameter [ 8 ] on imparted dose during abdominopelvic CT with ATCM. However, the abdominal compartment houses many structures of varying volume and density, which impact these indices.…”

The associated factors for radiation dose variation in cardiac CT angiography

“…It is logical that since the routine CT scanning protocol is usually fixed in a given CT centre, the variation in scanning protocols including exposure factor selection and scan length across centres as well as differences in patient physical characteristics may be responsible for the wide dose variations noted between the centres using a similar technology. 11 However, results show that the scan length for CCTA is short and generally consistent across the centres surveyed (mean 15 ± 2 cm). Thus, scan length may have had the minor influence on DLP in the current work.…”

“…10 It is important to note that obese individuals do not necessarily have a large chest diameter, and people of normal weight may have a large chest diameter. 11 Research conducted by Zarb et al 12 showed that the correlation between the chest diameters [anteroposterior (AP) and transverse] and CT dose is stronger than the relationship between weight and CT dose. However, current DRLs methodologies rely on average weight as the only indicator of body size, whereas size measurements such as cross-sectional area (CSA) of the chest are not widely used.…”