Abstract
Objectives: The image quality of an Ultra-Low-Dose (ULD) chest CT depends on the patient’s morphotype. We hypothesize that there is a threshold beyond which the diagnostic performance of a ULD chest CT is too degraded. This work assesses the influence of morphotype (Body Mass Index BMI, Maximum Transverse Chest Diameter MTCD and gender) on image quality and the diagnostic performance of a ULD chest CT. Methods: A total of 170 patients from three prior prospective monocentric studies were retrospectively included. Renewal of consent was waived by our IRB. All the patients underwent two consecutive unenhanced chest CT acquisitions with a full dose (120 kV, automated tube current modulation) and a ULD (135 kV, fixed tube current at 10 mA). Image noise, subjective image quality and diagnostic performance for nine predefined lung parenchyma lesions were assessed by two independent readers, and correlations with the patient’s morphotype were sought. Results: The mean BMI was 26.6 ± 5.3; 20.6% of patients had a BMI > 30. There was a statistically significant negative correlation of the BMI with the image quality (ρ = −0.32; IC95% = (−0.468; −0.18)). The per-patient diagnostic performance of ULD was sensitivity, 77%; specificity, 99%; PPV, 94% and NPV, 65%. There was no statistically significant influence of the BMI, the MTCD nor the gender on the per-patient and per-lesion diagnostic performance of a ULD chest CT, apart from a significant negative correlation for the detection of emphysema. Conclusions: Despite a negative correlation between the BMI and the image quality of a ULD chest CT, we did not find a correlation between the BMI and the diagnostic performance of the examination, suggesting a possible use of the ULD protocol in obese patients.
Highlights
Computed Tomography (CT) accounts for the large majority of medical exposures to ionizing radiation [1]
99% and an agreement rate of 74.1% for a ULD chest CT when compared to the reference FD
Despite the statistically significant negative correlation between image quality and Body Mass Index (BMI) (ρ = −0.325; p < 0.001), we did not find a negative correlation between BMI and diagnostic performance
Summary
Computed Tomography (CT) accounts for the large majority of medical exposures to ionizing radiation [1]. Is estimated at 347 mGy·cm (50th percentile) in a 2017 review of 159,909 US patients [3] Significant susceptible organs such as the breasts, lungs and thyroid are included in the field-of-view; this justifies the reduction in the radiation dose delivered to the minimum needed for adequate diagnosis [4,5]. Chest CT is an appropriate candidate to a significant radiation dose reduction, due to an overall low attenuation of the lung parenchyma resulting in a high contrast. The image quality of these Ultra-Low-Dose (ULD) chest CTs remains dependent on the patient’s morphotype, and prior studies [11,16] seldomly included patients with a Body Mass Index (BMI) greater than 30 kg·m−2. The diagnostic performance of a ULD chest CT is not well documented in obese patients [17]
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