MRI methods have become increasingly relied upon by pulmonary medicine and cardiovascular medicine to help diagnose pulmonary hypertension and monitor the effects of therapy on the right ventricle. Recently selected sites have begun using MRA for the primary diagnosis of pulmonary embolism. This symposium will discuss the highlights and difficulties in the use of MRI for the diagnosis and follow up of pulmonary vascular diseases.

Group 1: Pulmonary Arterial Hypertension (PAH). – Etiologies include idiopathic PAH, heritable PAH, Drug and Toxin-Induced PAH, persistent hypertension on the newborn, pulmonary veno-occlusive disease.

Group 2: Pulmonary hypertension owing to left heart disease – Etiologies include systolic and diastolic dysfunction and valvular disease. •

Group 3: Pulmonary hypertension owing to lung disease and/or hypoxia. – Etiologies include as COPD, interstitial lung disease. •

Group 4: Chronic Thromboembolic Pulmonary Hypertension (CTEPH).

Group 5: Pulmonary Hypertension with unclear multi-factorial mechanisms – Etiologies include hematologic, systemic, and metabolic disorders.

Appropriateness Criteria: Pulmonary MRA for the primary diagnosis of PE is most effective when used in patients with the following criteria: (A) a low to intermediate pretest probability for venous thromboembolic disease; (B) patients with iodinated contrast allergies; (C) female subjects less than 30 years of age that are potentially at slightly higher risk from medical radiation; (D) borderline renal function patients wherein the use of Ferumoxytol as an MRA contrast agent may be considered.² This test is not recommended for ill patients with significant dyspnea at high risk for PE, as the MRI room is not suitable environment for cardiopulmonary resuscitation.

Choice of MRA contrast agent: There is limited data on the use of non contrast MRA methods in the clinical setting of PE. Currently available GBCA's are all potentially of use for this procedure, however, those agents with higher relaxivity are preferred to maximize the intraluminal signal intensity. When the patient is unable to hold their breath, purely intravascular agents that have a long residence time are helpful to obtain exams during free breathing. For those patients that are in renal failure, the use of Ferumoxytol 2 is an option. Technique: There has been some work showing an advantage for an initial perfusion examination which is then followed by a higher resolution MRA.3 Another important feature to consider is the length of time for the bolus administration. We have found that having contrast administered for the entire length of the acquisition limits artifacts.

Direct findings of Pulmonary Embolism at MRA: (1) Occlusive intraluminal filling defect with a vessel “cutoff sign”, (2) non-occlusive intraluminal filling defect, (3) non-occlusive filling defect with dilation of the affected pulmonary artery, (4) webs of non-occlusive clot from resolving PE, (5) double bronchus sign (wherein the hypointense occlusive thrombus next to a bronchus creates a double barrel shotgun in cross-section appearance) (6) high T1 signal intensity from met-hemoglobin intralumenally before IV contrast administration.

Indirect findings of PE: Pulmonary infarction, atelectasis, pleural effusion, White-black-white sign of a focal perfusion defect (black) surrounded on both sides by enhancing lung (white) high signal intensity draining pulmonary vein, perfusion defect, enhancing pleural surfaces.

Indirect findings of elevated pulmonary artery pressure: enlarged pulmonary trunk (>3.0 cm),

Direct finding of Right ventricular dysfunction: increased right ventricular short axis/ left ventricular short axis ratio (RV/LV). Indirect findings of right ventricular dysfunction: Inferior vena cava reflux in centimeters, Oval shape of the Inferior vena cava, Bowing of interatrial septum towards the left atrium.

Mimics/Pitfalls of PE diagnosis at MRA: Gibbs truncation artifact and the use of the Bannas ⁴ 50% signal dropout rule, truncation artifact ringlets, Maki artifact ⁵ from bolus timing error, “Pseudo PE” appearance from unenhanced venous inflow (Transient interruption of the bolus and extra cardiac venous shunts (Glenn and Fontan)).

The use of MRI is complementary to the use of CT for the diagnosis of the many possible causes of pulmonary vascular disease. Often, MRI is the study of choice for the baseline metrics and follow-up of those pulmonary vascular diseases caused by congenital heart disease while CT is still the gold standard for characterizing those diseases that are due to lung parenchymal pathology. There is currently no single test for the diagnosis all of the causes of pulmonary vascular disease.Pulmonary MRA is an off-label use of Gadolinium based contrast agents (GBCA's) and the Ferumoxytol.