Prospective randomised comparison of diagnostic confidence and image quality with normal-dose and low-dose CT pulmonary angiography at various body weights

Objectives: To find a threshold body weight (BW) below 100kg above which computed tomography pulmonary angiography (CTPA) using reduced radiation and a reduced contrast material (CM) dose provides significantly impaired quality and diagnostic confidence compared with standard-dose CTPA. Methods: In this prospectively randomised study of 501 patients with suspected pulmonary embolism and BW <100kg, 246 were allocated into the low-dose group (80kVp, 75ml CM) and 255 into the normal-dose group (100kVp, 100ml CM). Contrast-to-noise ratio (CNR) in the pulmonary trunk was calculated. Two blinded chest radiologists independently evaluated subjective image quality and diagnostic confidence. Data were compared between the normal-dose and low-dose groups in five BW subgroups. Results: Vessel attenuation did not differ between the normal-dose and low-dose groups within each BW subgroup (P = 1.0). The CNR was higher with the normal-dose compared with the low-dose protocol (P < 0.006) in all BW subgroups except for the 90-99kg subgroup (P = 0.812). Subjective image quality and diagnostic confidence did not differ between CT protocols in all subgroups (P between 0.960 and 1.0). Conclusions: Subjective image quality and diagnostic confidence with 80kVp CTPA is not different from normal-dose protocol in any BW group up to 100kg. Key Points : • 80kVp CTPA is safe in patients weighing <100kg • Reduced radiation and iodine dose still provide high vessel attenuation • Image quality and diagnostic confidence with low-dose CTPA is good • Diagnostic confidence does not deteriorate in obese patients weighing