Purpose
To investigate the feasibility of describing the impact of any flip angle–TR combination on the resulting distribution of the hyperpolarized xenon‐129 (HXe) dissolved‐phase magnetization in the chest using a single virtual parameter, TR90°,equiv.
Methods
HXe MRI scans with simultaneous gas‐ (GP) and dissolved‐phase (DP) excitation were performed using 2D projection scans in mechanically ventilated rabbits. Measurements with DP flip angles ranging from 6–90° and TRs ranging from 8.3–500 ms were conducted. DP maps based on acquisitions of similar radio frequency pulse‐induced relaxation rates were compared.
Results
The observed distribution of the DP magnetization was strongly affected by acquisition flip angle and TR. However, for flip angles up to 60°, measurements with the same radio frequency pulse‐induced relaxation rates, resulted in very similar DP images despite the presence of significant macroscopic gas transport processes. For flip angles approaching 90°, the downstream signal component decreased noticeably relative to acquisitions with lower flip angles. Nevertheless, the total DP signal continued to follow an empirically verified conversion equation over the entire investigated parameter range, which yields the equivalent TR of a hypothetical 90° measurement for any experimental flip angle–TR combination.
Conclusion
We have introduced a method for converting the flip angle and TR of a given HXe DP measurement to a standardized metric based on the virtual quantity, TR90°,equiv, using their equivalent RF relaxation rates. This conversion permits the comparison of measurements obtained with different pulse sequence types or by different research groups using various acquisition parameters.
COVID-19-related coagulopathy is a known complication of SARS-CoV-2 infection and can lead to intracranial hemorrhage (ICH), one of the most feared complications of extracorporeal membrane oxygenation (ECMO). We sought to evaluate the incidence and etiology of ICH in patients with COVID-19 requiring ECMO. Patients at two academic medical centers with COVID-19 who required venovenous-ECMO support for acute respiratory distress syndrome (ARDS) were evaluated retrospectively. During the study period, 33 patients required ECMO support; 16 (48.5%) were discharged alive, 13 died (39.4%), and 4 (12.1%) had ongoing care. Eleven patients had ICH (33.3%). All ICH events occurred in patients who received intravenous anticoagulation. The ICH group had higher C-reactive protein (P ¼ 0.04), procalcitonin levels (P ¼ 0.02), and IL-6 levels (P ¼ 0.05), lower blood pH before and after ECMO (P < 0.01), and higher activated partial thromboplastin times throughout the hospital stay (P < 0.0001). ICH-free survival was lower in COVID-19 patients than in patients on ECMO for ARDS caused by other viruses (49% vs. 79%, P ¼ 0.02). In conclusion, patients with COVID-19 can be successfully bridged to recovery using ECMO but may suffer higher rates of ICH compared to those with other viral respiratory infections.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.