Abstract
BackgroundThe contrast agent (CA) dose for abdominal computed tomography (CT) is typically based on patient total body weight (TBW), ignoring adipose tissue distribution. We report on our experience of dosing according to the lean body weight (LBW).MethodsAfter Ethics Committee approval, we retrospectively screened 219 consecutive patients, 18 being excluded for not matching the inclusion criteria. Thus, 201 were analysed (106 males), all undergoing a contrast-enhanced abdominal CT with iopamidol (370 mgI/mL) or iomeprol (400 mgI/mL). LBW was estimated using validated formulas. Liver contrast-enhancement (CEL) was measured. Data were reported as mean ± standard deviation. Pearson correlation coefficient, ANOVA, and the Levene test were used.ResultsMean age was 66 ± 13 years, TBW 72 ± 15 kg, LBW 53 ± 11 kg, and LBW/TBW ratio 74 ± 8%; body mass index was 26 ± 5 kg/m2, with 9 underweight patients (4%), 82 normal weight (41%), 76 overweight (38%), and 34 obese (17%). The administered CA dose was 0.46 ± 0.06 gI/kg of TBW, corresponding to 0.63 ± 0.09 gI/kg of LBW. A negative correlation was found between TBW and CA dose (r = -0.683, p < 0.001). CEL (Hounsfield units) was 51 ± 18 in underweight patients, 44 ± 8 in normal weight, 42 ± 9 in overweight, and 40 ± 6 in obese, with a significant difference for both mean (p = 0.004) and variance (p < 0.001). A low but significant positive correlation was found between CEL and CA dose in gI per TBW (r = 0.371, p < 0.001) or per LBW (r = 0.333, p < 0.001).ConclusionsThe injected CA dose was highly variable, with obese patients receiving a lower dose than underweight patients, as a radiologist-driven ‘compensation effect’. Diagnostic abdomen CT examinations may be obtained using 0.63 gI/kg of LBW.
Highlights
The contrast agent (CA) dose for abdominal computed tomography (CT) is typically based on patient total body weight (TBW), ignoring adipose tissue distribution
Factors impacting on contrast enhancement in single-energy computed tomography (CT) include concentration and dose of the iodinated contrast agent (CA), injection rate, scanning delay time, saline-solution flushing, and cardiac output [1,2,3]
Dosing according to TBW is reasonably effective, but it can lead to overdosing obese patients or underdosing patients with high contribution of the lean body weight (LBW) over the TBW, such as athletes
Summary
The contrast agent (CA) dose for abdominal computed tomography (CT) is typically based on patient total body weight (TBW), ignoring adipose tissue distribution. The CA dose, expressed in gI/kg, is one of the most important factors determining the parenchymal liver contrast enhancement (CEL) [4]. Since 2000, several studies have demonstrated smaller variations in CEL when CA is dosed on the patient total body weight (TBW) instead of administering a fixed amount [8,9,10,11,12,13,14]. Dosing according to TBW is reasonably effective, but it can lead to overdosing obese patients or underdosing patients with high contribution of the lean body weight (LBW) over the TBW, such as athletes. A large proportion of TBW of obese patients consists of poorly perfused adipose tissue, where the CA poorly distributes [2, 10, 15, 16], as 99% of metabolic processes take place in the LBW [17, 18]
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