Low-dose CT Angiography in the Detection of Acute Pulmonary Embolism: Validation in an Obese Population

Overview

Pulmonary embolism is a common pathology in the general population, whose suspicion is based on the clinical and dosage of D-dimers in particular. The key examination for the diagnosis of pulmonary embolism is chest CT angiography (negative predictive value of 98%). The evolution of machines in recent years allows a reduction of possible kilovoltage up to 80 kV, different computer algorithms (iterative reconstructions) to reconstruct the images and thus reduce the irradiation dose with equal image quality (Evaluation of dose CT and adaptive statistical reconstruction with the same group of patients, Qi et al, 2012; Impact of iterative reconstruction on the diagnosis of acute pulmonary embolism (PE) on reduced-dose chest CT angiograms, Pontana et al , 2015) in patient populations with a weight of less than 100 kilos. However, obesity is a risk factor for pulmonary embolism and the obese population is increasing, thus requiring optimal management regarding irradiation. Few studies have evaluated the quality of low dose CT angiography in obese patients. One study showed the possibility of performing low-dose thoracic CT angiography (100 kV) in patients up to 125 kg, without loss of subjective quality (but with an impact on objective quality), without the use of current iterative reconstruction techniques (Diagnostic confidence and image quality of CT pulmonary angiography at 100 kVp in overweight and obese patients, Megyeri et al, 2015). The study seek to prove that in the obese patient, with a low dose examination (voltage of the tube at 100 kV) and the current iterative reconstructions, the thoracic angioscanner is not less efficient than in the non obese patient, that the qualities objective and subjective analyzes are maintained. The main purpose is to evaluate and compare thoracic CT angiography with weight and BMI, with identical CT parameters (same voltage, computer reconstruction techniques and same contrast injection protocol), by evaluating the objective and subjective diagnostic quality of the opacification of the pulmonary arteries.

The study is monocentric, realised in University Hospital of Clermont-Ferrand, France, using the CT GE Revolution dedicated to the emergency service. For each patient with suspicion of pulmonary embolism, regarding the inclusion and exclusion criteria (explained later), investigators realise the same protocol. Patients are divided into 2 groups of weight : \<30 kg/m2, \> 30 kg/m2. There is no change in the management of patients, who benefit from an angioscan for pulmonary embolism, with an optimized protocol for patients under 100 kg and validated by the literature (Megyeri et al. , 2015) for patients over 100 kilos, with no loss of diagnostic chance and with an improvement over the irradiation compared to the usual protocols used (over-irradiation in the obese, up to 140 kV). Concerning the CT protocol, a voltage of 100 kV is applied (irradiation 40% lower than a 120 kV test), with a modulation of the intensity of the current according to the Z axis and use of different levels of iterative reconstructions on images obtained to improve diagnostic performance. Regarding the injection protocol, the same product with high concentration of iodine is injected to all patients (IOMERON 400), with a quantity relative to the weight of 1 mL / kg of patient weight, a maximum of 90 mL, a rate of 4 mL / s and rinsing with 30 mL of saline solution at 3 mL / sec The session physician first carries out diagnostic work by searching for pulmonary embolism or an alternative diagnosis to explain the symptoms. Secondly, the research work is carried out and the analyzed data with evaluation of the objective diagnostic quality, placing regions of circular interest or ROI (for regions of interest), in the pulmonary arteries, up to the sub-segmental branches. The subjective quality is evaluated by two double-blind readers by a subjective quality scale. The different elements are then compared according to two different groups of weights and BMIs. Intermediate statistical analyzes are planned for all 30 patients. The study started on March 21st, for an estimated duration of 6 months initially. 65