Abstract
BackgroundUltra-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.MethodsHealthy 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.ResultsThere 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).ConclusionGating 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.
Highlights
Ultra-high field magnetic resonance imaging (MR) may be used to improve intracranial blood flow measurements
For two subjects, the ECG signal was of so low quality that no signals were generated, and the comparative flow measurements were instead gated with the pulse oximetry (POX) signal
The Doppler ultrasound (DUS) scans mainly suffered from false negative triggers which were to varying degree present in four of the subjects
Summary
Ultra-high field magnetic resonance imaging (MR) may be used to improve intracranial blood flow measurements. Several new methods for cardiac synchronization have been proposed, such as self-gating [16,17,18], advanced ECG processing [9, 19], scattering of a parallel transmit RF coil [20, 21] or using acoustic [14, 22], optical [23] or magnetohydrodynamic (MHD) signals [23]. These methods require hard- or software that are difficult to implement or not readily available
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