Ultralow contrast medium doses at CT to diagnose pulmonary embolism in patients with moderate to severe renal impairment: a feasibility study.

Objectives: To analyse 80-kVp 16-MDCT in patients with clinically suspected pulmonary embolism (PE) and diminished renal function after a reduction in dose of contrast medium (CM) from 200 to 150 mg I/kg.
Methods: Fifty patients with suspected PE and glomerular filtration rate (GFR) less than 50 mL/min underwent 80-kVp 16-MDCT with 150 mg I/kg. Mean density/image noise (1 standard deviation) was measured in a region of interest in the left pulmonary artery (LPA) and a lower lobe segmental artery (LLSA), and the contrast-to-noise ratio (CNR) was calculated. The values of LPA and LLSA were averaged.
Results: Median values/2.5-97.5 percentiles were: age 84/67-96 years, weight 65/43-84 kg, GFR 36/21-45 mL/min, CM dose 9.6/6.4-12 g of iodine, PA density 353/164-495 HU and CNR 11/4.4-20. PE incidence was 16%, and 8% and 12% of the examinations were regarded suboptimal by observer 1 and 2, respectively. Density/CNR values were within ranges reported for common 120-kVp MDCT protocols. None of 32 patients with plasma-creatinine follow-up within 1 week experienced a rise of more than 44.2 mumol/L and none of 50 patients had oliguria/anuria or dialysis. None of 40 patients with a negative CT/no anticoagulation had thromboembolism during follow-up.
Conclusion: 80-kVp MDCT combined with individualised ultralow CM doses may provide satisfactory diagnostic quality, which should be to the benefit of patients at risk of contrast medium-induced nephropathy.