Background: Acute pulmonary embolism (APE) is a potentially severe medical condition with blood clots obstructing the pulmonary arterial vasculature. In most cases the APE resolves without any sequelae after anticoagulation therapy. In some patients, however, the emboli do not resolve upon treatment and the remnants cause increased vascular resistance, a condition known as chronic thromboembolic pulmonary hypertension (CTEPH). Both APE and CTEPH have a non-specific clinical presentation and imaging is an important part of the diagnosis. In APE computed tomography pulmonary angiography (CTPA) is the diagnostic gold standard, although the method is not suitable for all patients. CTPA has a high specificity for CTEPH, but the sensitivity remains under debate. At present CTPA is not recommended as a first line test among patients with a clinical suspicion of CTEPH. Purpose: To investigate unestablished imaging modalities in the diagnosis of APE (Study I) and CTEPH (Study III) including learning aspects (Study II) and knowledge (Study IV) of theses among radiologists. Regarding APE we studied magnetic resonance imaging (MRI) and in CTEPH we studied CTPA. Material and methods: Studies I-II were based on a prospective collection of 70 unenhanced MRI exams with CTPA as the gold standard. In Studies III-IV we used a retrospective material based on 43 CTPA exams from patients with confirmed CTEPH referred for presurgical assessment at a specialist centre, with a matched control with suspected APE. Results: All MRI exams were of diagnostic quality. Specificity was 100% for both readers and sensitivity 90% and 93% respectively with a nearly perfect inter-reader agreement (kappa 0.97) (Study I). Residents interpreting the MRI exams within the training program reached a clinically acceptable level after approximately 50 examinations and review time was halved during the training program (Study II). The sensitivity for CTEPH on CTPA reviewed by two experts was 100% and the specificity 100% (Study III), while the sensitivity based on the original reports from the same cases was 26% (Study IV). Conclusions: Unenhanced MRI has a high sensitivity and specificity for APE (Study I) and residents can learn to interpret such exams by using a self-directed training program (Study II). Enhanced CTPA has a high sensitivity when reviewed by experienced radiologists (Study III), but among radiologists in general the sensitivity is low (Study IV). LIST OF SCIENTIFIC PAPERS I. Detection of pulmonary embolism using repeated MRI acquisitions without respiratory gating: A preliminary study.

Background Pulmonary embolism (PE) is a severe medical condition with non-specific clinical findings. Computed tomography angiography (CTA) using iodinated contrast agents is the golden standard for diagnosis, but many patients have contraindications for CTA. Purpose To investigate the diagnostic accuracy of repeated acquisitions of magnetic resonance imaging (MRI), without respiratory gating or breath holding, in diagnosing PE using CTA as the reference standard. Material and Methods Thirty-three patients with clinically suspected PE underwent MRI within 48 h after diagnostic CTA. A control group of 37 healthy participants underwent MRI and was matched with an equal number of negative CTA exams. The MRI protocol was based on free-breathing steady-state free precession producing 4.5 mm slices in axial, sagittal, and coronal planes. Instead of respiratory or cardiac gating five repetitive slices were obtained in each anatomical position to compensate for movement and artifacts. Clinical assessment including d-dimer and Well's score was performed prior to imaging. One radiologist reviewed the CTA exams and two radiologists reviewed the MRI scans. Results All 70 MRI exams were of diagnostic quality and the total acquisition time for each MRI scan was 9 min 34 s. On CTA, 29 patients were diagnosed with PE and the MRI readers detected 26 and 27 of those, respectively. Specificity was 100% for both readers. Sensitivity was 90% and 93%, respectively. Inter-reader agreement using Cohen's kappa was 0.97. Conclusion Our unenhanced MRI protocol shows a high sensitivity and specificity for PE, but further studies are required before considering it as a safe diagnostic test.

BackgroundIn recent years, magnetic resonance imaging (MRI) has been suggested as an alternative to computed tomography angiography (CTA) to diagnose pulmonary embolism (PE). In previous studies, only senior radiologists have been evaluated as reviewers.PurposeTo investigate if radiology residents can be trained to review MRI regarding PE and to determine the learning curve effects.Material and MethodsFour residents independently went through a training program consisting of 70 participants that had undergone steady-state free precession MRI. The individuals were randomized into ten training sessions. For each exam, the review time and presence or absence of embolus was recorded. After completing each session, the residents received feedback on diagnostic accuracy compared to a consensus reading by two specialists. The residents were also presented with the corresponding CTA.ResultsThe review time was nearly halved (P = 0.0002) during the training program. Comparing the first three sessions with the last three sessions for all residents, the review time decreased from 5:22 min to 2:51 min. The inter-reader agreement improved for all residents during the training program reaching a clinically acceptable level after seven sessions.ConclusionOur study suggests that radiology residents can be trained to independently review MRI investigations regarding PE within a short training program. Similar training programs could be more extensively used as effective teaching method for residents.