CT Pulmonary Angiography > Pulmonary Embolus > Diagnostic Alternatives > MRPA

Magnetic Resonance Pulmonary Angiography (MRPA)

Magnetic resonance pulmonary angiography (MRPA), although still considered a second-line imagine technique behind CTPA, has been gaining acceptance in the evaluation of VTE. In contrast to CT, MR imaging does not expose the patient to ionizing radiation, and its main contrast agent, gadolinium chelate, shows a much lower potential for allergic reactions and nephrotoxicity than does iodinated contrast. There is however the risk of developing nephrogenic systemic fibrosis (NSF) in patients on dialysis or with renal insufficiency (reference). However, longer acquisition times and poorer spatial resolution have historically limited its applicability in the imaging of the pulmonary arterial system.

As MR techniques improve these historic limitations are slowly being overcome. The advent of more rapid imaging sequences in conjunction with parallel imaging has diminished motion artifact, allowing for improved resolution of the pulmonary vascular system. Additionally, dynamic imaging during contrast injection now offers the functional information of perfusion imaging. The systemic venous structures can be simultaneously evaluated, using MR venography (MRV), to assess for pelvic and lower extremity VTE. Recent published literature suggests that MR imaging of acute VTE (MRI, MRPA, MR perfusion, MRV) indeed may rival the accuracy of CT in the detection of VTE and PE (at least centrally). These data have yet to be validated in larger prospective studies. As it continues to evolve, MR imaging is expected to play an increased role in the future evaluation of PE.

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