Arterial Spin Labeling MRI for Noninvasive Monitoring of Treatment Response in Acute Pulmonary Embolism

Purpose To evaluate perfusion imaging with arterial spin labeling (ASL) MRI for monitoring the effects of antithrombotic therapy in participants with pulmonary embolism (PE). Materials and Methods Between November 2020 and December 2022, participants with suspected PE were enrolled in this prospective study and underwent lung perfusion imaging using electrocardiographically triggered pseudocontinuous ASL MRI with balanced steady-state free precession image acquisition at 1.5 T. Of these, participants with confirmed PE underwent follow-up ASL MRI after a median of 174 days after treatment. In participants with PE, perfusion defects were assessed lobe-wise using a five-point scale: grade I, 0%; grade II, 25% or less; grade III, 26%-50%; grade IV, 51%-75%; and grade V, more than 75%. Lung parenchyma was segmented using a Gaussian mixture model, and perfusion was quantified through histogram analysis. Association between clinical parameters and MRI results was also assessed. Results A total of 107 participants were enrolled; 15 participants (median age, 55 years [IQR, 39.5-72.5 years]; eight female) with confirmed PE underwent follow-up ASL MRI. A matched cohort of 15 participants without PE and 10 healthy volunteers also underwent ASL MRI. Perfusion defects were observed in all included participants with PE, affecting 59 lobes: grade II, five lobes; grade III, 10 lobes; grade IV, 17 lobes, and grade V, 27 lobes. On follow-up, defects persisted in eight participants, involving 25 lobes: grade II, seven lobes; grade III, eight lobes; grade IV, six lobes, and grade V, four lobes (<i>P</i> = .002). Lung perfusion significantly improved after treatment in all participants (mean increase, 52%; <i>P</i> < .001). There was no evidence of a difference in perfusion values after treatment from those of participants without PE or healthy controls. The presence of residual perfusion defects was significantly associated with persistent dyspnea (<i>P</i> = .008). Conclusion ASL MRI could detect changes in lung perfusion after antithrombotic therapy in participants with PE. <b>Keywords:</b> MR Perfusion, MRI, Thrombolysis, Pulmonary, Lung, Embolism, Thrombosis German Clinical Trials Register (DRKS00023599) <i>Supplemental material is available for this article.</i> © RSNA, 2025.