Doppler ultrasound cardiac gating of intracranial flow at 7T
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Doppler ultrasound cardiac gating of intracranial flow at 7T Karin Markenroth Bloch1* , Fabian Kording2,3 and Johannes Töger4
Abstract Background: Ultra-high field magnetic resonance imaging (MR) may be used to improve intracranial blood flow measurements. However, standard cardiac synchronization methods tend to fail at ultra-high field MR. Therefore, this study aims to investigate an alternative synchronization technique using Doppler ultrasound. Methods: Healthy subjects (n = 9) were examined with 7T MR. Flow was measured in the M1-branch of the middle cerebral artery (MCA) and in the cerebral aqueduct (CA) using through-plane phase contrast (2D flow). Flow in the circle of Willis was measured with three-dimensional, three-directional phase contrast (4D flow). Scans were gated with Doppler ultrasound (DUS) and electrocardiogram (ECG), and pulse oximetry data (POX) was collected simultaneously. False negative and false positive trigger events were counted for ECG, DUS and POX, and quantitative flow measures were compared. Results: There were fewer false positive triggers for DUS compared to ECG (5.3 ± 11 vs. 25 ± 31, p = 0.031), while no other measured parameters differed significantly. Net blood flow in M1 was similar between DUS and ECG for 2D flow (1.5 ± 0.39 vs. 1.6 ± 0.41, bias ± 1.96SD: − 0.021 ± 0.36) and 4D flow (1.8 ± 0.48 vs. 9 ± 0.59, bias ± 1.96SD: − 0.086 ± 0.57 ml). Net CSF flow per heart beat in the CA was also similar for DUS and ECG (3.6 ± 2.1 vs. 3.0 ± 5.8, bias ± 1.96SD: 0.61 ± 13.6 μl). Conclusion: Gating with DUS produced fewer false trigger events than using ECG, with similar quantitative flow values. DUS gating is a promising technique for cardiac synchronization at 7T. Keywords: Ultra-high field MRI, Flow quantification, Cardiac synchronization, Neurovascular, Doppler ultrasound, ECG Background For many magnetic resonance imaging (MRI) applications, it is necessary to synchronize the MR data acquisition to the cardiac rhythm, either to investigate motion due to the heartbeat, or to avoid artifacts or image blurring caused by the pulsation. Examples relevant for MRI neuroimaging at 7T are neurovascular flow and velocity mapping [1–3], arterial pulsation measurements [4] and cardiac gated functional magnetic resonance imaging (fMRI). In clinical practice, cardiac synchronization is *Correspondence: [email protected] 1 The Swedish National 7T Facility, Lund University Bioimaging Center, Lund University, Klinikgatan 32, BMC D11, 22242 Lund, Sweden Full list of author information is available at the end of the article
done with electrocardiogram (ECG) or pulse oximetry (POX), techniques that through continuous technical development work well at both 1.5 T and 3 T [5]. However, at high field strengths such as 7T, ECG-based methods become unreliable due to the magnetohydrodynamic effect (MHD) [6, 7]. Several studies find that ECG gating at 7T fails in 10–20% of examinations, and is suboptimal in another 20–30%, leading to prolonged scan time or reacq
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