Low-dose CT with automatic tube current modulation, adaptive statistical iterative reconstruction, and low tube voltage for the diagnosis of renal colic: impact of body mass index.

OBJECTIVE: The objective of our study was to evaluate the impact of body mass index (BMI) on dose, diagnostic performance, and image quality of a low-dose CT examination for renal colic. MATERIALS AND METHODS: This retrospective study included all patients who underwent a low-dose CT examination for renal colic performed during the year 2012 with automatic tube current modulation, adaptive statistical iterative reconstruction, and a low tube voltage (kV). Three readers independently reviewed all images for the presence of renal colic and evaluated diagnostic confidence and image quality. The results and doses were compared among patients grouped by body mass index (BMI) and between patients with a BMI<25 and those with a BMI≥25. RESULTS: Eighty-six patients were included in the study: 39 patients had a BMI<25 and 47 had a BMI≥25. No statistically significant difference was found between the accuracy rates for the diagnosis of renal colic when the rates of the three independent readers were averaged for both BMI groups (95.7% vs 96.4%, respectively; p=0.83). Image quality and diagnostic confidence scores were significantly better for patients with a BMI≥25 than for patients with a BMI<25 (mean image quality score, 3.7 vs 3.4, p<0.001; mean diagnostic confidence score, 2.8 vs 2.5, p<0.001). The mean radiation dose for patients with a BMI<25 was 2.4 mGy compared with 3.7 mGy for patients with a BMI≥25 (p<0.001). CONCLUSION: The diagnostic performance of our low-dose CT protocol for renal colic was excellent for all patients, and image quality and diagnostic confidence were significantly better for patients with a BMI≥25. However, our protocol also required exposure to a greater dose of radiation for these overweight and obese patients.

CT attenuation of the bronchial wall in patients with asthma: comparison with geometric parameters and correlation with function and histologic characteristics.

OBJECTIVE: The purposes of this study were to compare airway wall attenuation in subjects with asthma and subjects without asthma; to correlate this value with pulmonary function test results, standard bronchial CT parameters, and immunohistologic data; and to identify CT parameters that influence obstructive indexes. SUBJECTS AND METHODS: Bronchial airway wall attenuation was averaged over four bronchi in 27 subjects with asthma and 15 control subjects without asthma. The following five standard bronchial parameters also were assessed: lumen area, wall area, wall thickness, wall-to-lumen area ratio, and wall-to-total area ratio (wall area percentage). These parameters were compared between groups and correlated with functional data. Ability to predict patient group with these parameters was determined by comparison of receiver operating characteristic curves and areas under the curve. The influence of the parameters on obstructive indexes was assessed by multivariate analysis. Correlations between wall attenuation value and histologic data were studied in 11 patients with asthma. RESULTS: Wall attenuation value was greater in patients with asthma (-322 ± 79 HU) than in control subjects (-463 ± 69 HU). Correlation coefficients of wall attenuation value with functional obstructive parameters were significant and greater than those obtained for any other CT parameter. The area under the curve of wall attenuation value was greater than that of bronchial lumen area and bronchial wall area. In the model of multiple regression that included wall attenuation value and wall-to-total area ratio, wall attenuation value was the only measurement that significantly influenced obstructive indexes (R(2) = 0.39-0.43). Wall attenuation value correlated with mast cell infiltration. CONCLUSION: Compared with the usual bronchial CT parameters, airway wall attenuation better differentiates patients with asthma from control subjects and better correlates with obstruction.