Effect of Body Mass Index BMI on Technical Parameters (kVp and mAs) Selection in Chest X- Ray (18–45 Years) An Observational Study

Background: The tube potential (kVp) and tube current–time product (mAs) chosen for a chest radiograph determine both image quality and patient dose. Body habitus is the main patient factor that changes the exposure needed, yet in many Indian departments technique is chosen empirically and the influence of body mass index (BMI) on that choice is rarely documented. Objective: To assess how BMI influences the selection of kVp and mAs for postero-anterior (PA) chest radiography in adults aged 18–45 years. Methods: An observational cross-sectional study was conducted on 90 adults referred for PA chest radiography at a tertiary teaching hospital in Bareilly, Uttar Pradesh, India, after institutional ethics approval. Age, sex, referring department, height and weight were recorded, and BMI was classified using WHO cut-offs. The kVp and mAs used for each examination were recorded from the console. Proportions are reported with Wilson 95% confidence intervals (CIs); associations between BMI category and exposure level were tested using Fisher’s exact test, the Cochran–Armitage trend test and Spearman’s rank correlation at a significance level of 0.05. Results: Of 90 participants, 50 (55.6%) were women and 45 (50.0%) were aged 36–45 years; 84 (93.3%) were outpatients. Overall, 48 participants (53.3%; 95% CI 43.1–63.3) had a BMI of 25 kg/m2 or more, including 33 (36.7%; 95% CI 27.4–47.0) with obesity. All overweight and obese participants were exposed at 70–80 kVp and 16–18 mAs, whereas normal-weight participants were exposed at 60–65 kVp and 14–16 mAs (Fisher’s exact p below 0.001; phi coefficient 1.00). The proportion receiving high exposure factors rose across ordered BMI categories (Cochran–Armitage z = 8.66, p below 0.001; Spearman rho = 0.92, p below 0.001). On range midpoints, this corresponded to a 20.0% higher kVp, a 13.3% higher mAs and an estimated 1.63-fold higher relative tube output (kVp squared multiplied by mAs). Conclusion: BMI was strongly associated with the exposure factors chosen for adult chest radiography, and patients with a BMI of 25 kg/m2 or more received a substantially higher estimated tube output. BMI-based exposure charts, preferably combined with chest-thickness measurement and dose monitoring, are recommended to standardise technique and keep doses as low as reasonably achievable.