Comparing two techniques (Subtraction and Dual Energy CT) for functional Chest CT for patients with suspected with pulmonary embolism.

Rationale: Iodine mapping of the lung using subtraction imaging in addition to standard computed tomography pulmonary angiography (CTPA) may improve the evaluation of pulmonary embolism (PE) in the same manner as the addition of dual energy computed tomography (DECT) to CTPA.

Objective: To evaluate image quality and accuracy of detection of perfusion defects associated with pulmonary pathology on iodine maps of the lung that are created by two different CT techniques: 1. A standard of care CTPA with DECT and 2. A new technique that subtracts a low radiation dose unenhanced CT from mono-energetic CTPA (subtraction) Study design: A maximum of 375 patients will undergo a standard CTPA with DECT according to local clinical guidelines, to have 30 patients with pulmonary embolism. For the purposes of this study, patients will undergo an additional unenhanced, low-radiation dose chest CT. Standard reconstructions of all scans and DECT iodine maps will be obtained for clinical reporting and subsequent treatment decisions, according to standard clinical routine. For research purposes, selected mono-energetic images will be post-processed using a novel subtraction algorithm to create iodine maps of the lungs. The iodine maps based on the subtraction algorithm will not be used for clinical management, only the additional unenhanced scan will be used in clinical management.

Study population: Patients presenting with a clinical indication for pulmonary CT angiography because of suspected pulmonary embolism. Only adult patients (≥ 35 years) who are able to provide informed consent will be enrolled.

Main study parameters/endpoints:

Main endpoint of the study is presence of perfusion as established by an expert panel with access to all imaging information (including CTPA, subtraction and DECT) and clinical follow-up. Accuracy of DECT and subtraction is established by observers who are blinded to CTPA and clinical data. Presence of iodine density differences in perfusion defects is measured using region of interest (ROI) measurements.

Images will be evaluated for objective and subjective image quality. Patient characteristics, radiation dose, clinical diagnosis, treatment decisions and patient outcome (all cause - and PE related mortality) will be recorded.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness:

CT imaging is associated with risks related to the use of radiation and iodinated contrast administration. No additional contrast will be used as compared to standard clinical practice as patients will only undergo one CTPA scan. The CT protocol of this study has been carefully designed to have a radiation dose identical or even lower than standard CT protocols for pulmonary embolism detection. The estimated dose-length product (DLP) of standard CTPA with DECT in Meander Medical Centre is 167 mGy-cm (effective dose is 2.4 mSv, using 0,0146 mSv/mGy-cm as a conversion factor). The researchers will expose patients who participate in the study to an estimated additional DLP of 72 mGy-cm due to the unenhanced scan, resulting in an additional estimated effective dose of 1,0 mSv. This implies that the total radiation dose is within the same range as radiation doses of other scans for PE detection in the Netherlands. The additional scan is not obligatory in pulmonary embolism diagnosis, but will be used for clinical evaluation of these patients.

Inclusion Criteria:

• Patients 35 years or older and able to provide informed consent
• Clinically requested CTPA because of suspected pulmonary embolism
• Available history and physical examination.

Exclusion Criteria:

• Pregnancy
• Hemodynamic instability
• Uncooperative patients.
• Contra-indication to intravenous iodine administration.
• Inability to position the arms above the shoulders