Pulmonary Perfusion by Iodine Subtraction Mapping CT Angiography in Acute Pulmonary Embolism (PASEP)

Pulmonary Perfusion by Iodine Subtraction Mapping CT Angiography in Acute Pulmonary Embolism: a Diagnostic Accuracy Study Versus Pulmonary Perfusion SPECT.

Pulmonary embolism (PE) is a diagnostic and therapeutic challenge. The risk of death of untreated PE is approximately 25%. On the other hand, anticoagulant treatment is associated with a haemorrhagic risk (2% of major haemorrhagic accidents per year, of which 10% are fatal). A diagnostic accuracy is therefore necessary. Two approaches are available to diagnose PE: A functional approach, represented by pulmonary ventilation / perfusion scintigraphy (V / P), which looks for the functional consequences of PE. The main disadvantage of this approach is that there is a high rate of non-diagnostic examinations. On the other hand, it allows a mapping of pulmonary perfusion at the microcapillary scale, and thus allows the quantification of the vascular obstruction index, which would be an independent risk factor of PE recurrence. A morphological approach, represented by CT pulmonary angiography (CTPA), which allows the visualisation of the clot itself. This approach is currently the most used but has some limitations, including a risk of over-diagnosis of pulmonary embolism and the inability to reliably quantify the index of vascular obstruction. Lung subtraction iodine mapping CT is a new technique allowing, during the realization of a CTPA, without additional irradiation, to provide a mapping of the iodine. This mapping of iodine could potentially be used to evaluate pulmonary perfusion. It would then be possible to obtain, during a single examination, in addition to the anatomical information of the thoracic angioscan, information on the pulmonary perfusion and thus to assess the functional consequences of PE. No study to date has evaluated the performance of the pulmonary subtraction CT for the evaluation of pulmonary perfusion in the context of acute pulmonary embolism suspicion.

Included patients with a diagnosis of acute PE on CTPA and who had a subtraction iodine mapping CT will undergo a SPECT/CT within 24 hours. Each lung subtraction iodine mapping CT will be interpreted blindly by 3 radiologists. Each of the 20 lung segments will be interpreted as normoperfused or hypoperfused. Each perfusion SPECT will be interpreted blindly by 3 nuclear medicine physicians. Each of the 20 lung segments will be interpreted as normoperfused or hypoperfused.

The included patients will benefit from pulmonary tomoscintigraphy within 24 hours after the diagnosis of pulmonary embolism. Each tomoscintigraphy will be interpreted blindly by 3 nuclear physicians. Each of the 20 lung segments will be interpreted as normoperfused or hypoperfused.

The sensitivity of iodine mapping by subtraction technique for the detection of perfusion defects in pulmonary embolism is evaluated with using pulmonary perfusion tomoscintigraphy as a reference standard .

The specificity of iodine mapping by subtraction technique for the detection of perfusional defects in acute pulmonary embolism is determinated with using pulmonary perfusion tomoscintigraphy as reference standard.

Thé correlation between the pulmonary vascular obstruction index measured by iodine mapping by subtraction technique and that obtained by perfusion tomoscintigraphy is evaluating

The concordance between the morphological abnormalities visualized at the thoracic angioscanner (visualization of an endoluminal defect within the pulmonary arterial network) is evaluated.

The concordance between the morphological abnormalities on CTPA (visualization of an endoluminal defect within the pulmonary arterial network) is evaluated.

The interobserver reproducibility of subtraction technique versus pulmonary tomoscintigraphy in reported as normal or abnormal lung perfusion at a segmental level.

Inclusion Criteria: All patients who have been diagnosed with acute pulmonary embolism on the Aquilion One Genesis scan (Toshiba, Medical System, Tokyo, Japan) at the Brest University Hospital, and who have had a mapping of the iodine derived from the subtraction images. Exclusion Criteria: Tomoscintigraphy not feasible within 24 hours. Massive pulmonary embolism or with signs of gravity Pregnant or lactating women Minor patient Protected adults Incapacity / refusal to give consent Hypersensitivity to pertechnetate (99m Tc) Hypersensitivity to human albumin