Test Data AC7-04: Difference between revisions
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==Measured Data== | ==Measured Data== | ||
The data collected are magnitude and phase images proportional to the proton magnetization and are saved as DICOM (Digital Imaging and COmmunications in Medicine) files. The first post-processing step is to reordered the data and to compute the velocity field from the phase images. The resulting dataset is written as a structured grid in the VTK format (Visualisation ToolKit, Kitware, Inc, CliftonPark, NY). All post-processing steps, which will be further expanded on in the coming sections, are performed using in-house VTK-based Python scripts. | |||
==Measurement Errors== | ==Measurement Errors== | ||
==References== | ==References== | ||
Revision as of 11:40, 26 July 2021
A pulsatile 3D flow relevant to thoracic hemodynamics: CFD - 4D MRI comparison
Application Challenge AC7-04 © copyright ERCOFTAC 2021
Test Data
Overview of Tests
The experimental method presented in this section is described in detail by Puiseux et al. (2019) [2]. However, the MRI machine and sequence parameters differ. The PC-MRI scans were performed on a 1.5T scanner (Siemens MAGNETOM Sola, Siemens Medical Systems, Erlangen, Germany).
Description of Experiment
A scheme presenting the experimental setup is shown on Fig. 1. The pulsatile flow is delivered by a computer-controlled pump (CardioFlow 5000MR, Shelley Medical Imaging Technologies, London, Ontario, Canada), which allows the user to define the desired waveforms. To control the flow rate it delivers, an ultrasonic flowmeter (UF25B100 Cynergy3 components Ltd, Wimborne, Dorset, UK) is used. Futhermore to reduce the swirling motion of the fluid entering the phantom, a flow straightener is positioned downstream of the flowmeter and upstream of the phantom. Inside the scanner room, the pump is positioned outside the 5 Gauss Line for MR safety considerations.
Concerning the PC-MRI acquisitions, one acquisition was made for 4D Flow (duration of 42.6 min) and several for 2D cine PC-MRI (duration of 3.6 min each). For each acquisition, the full k-space was recorded (ie there was no parallel imaging acceleration), where the k-space refers to the complex-values Fourier transform of the MR images measured. Indeed the signal collected during the MR experiment corresponds to the Fourier transform of the transverse magnetization signal and is thus expressed in terms of spatial frequencies. The MR images are reconstructed through an inverse Fourier transform applied on this k-space. All scans were retrospectively cardiac gated, which allows to reconstruct a certain number of phases of the whole cardiac cycle. 20 phases were acquired for the 4D Flow scan and 30 for the 2D cine PC-MRI scan. Concerning the spatial resolution, isotropic voxels of 2 mm were acquired for the 4D Flow scan. For the 2D cine PC-MRI, the isotropic pixel size was 0.8 mm, with a slice thickness of 6 mm to enhance the signal-to-noise ratio.
These settings and additional MR information are given in the following table:
| 4D Flow | 2D cine PC-MRI | |
|---|---|---|
| Acquisition Duration | 42.6 min | 3.6 min |
| Cardiac Phases Number | 20 | 30 |
| Acquisition Plane | Coronal | Transverse |
| Voxel size | 2 x 2 x 2 mm | 0.78125 x 0.78125 x 6 mm |
| Flip Angle | 7° | 20° |
| VENC | 0.7 m/s (in-plane velocity) | 0.7 m/s (through-plane velocity) |
| 0.2 m/s (through-plane velocity) | 0.2 m/s (in-plane velocity) | |
| TR | 51.84 ms | 30.32 ms |
| Effective TE | 4.15 ms | 4.84 ms |
Table 1: MR sequences parameters
Boundary Data
The inlet and outlet of the phantom are both connected to the whole hydraulic circuit and care is taken to avoid any air running into it. Before the measurements, the fluid was freely running through the circuit. Besides the flowmeter measurements, the high-resolution 2D cine PC-MRI acquisitions at the inlet enable to check whether the prescribed pulsatile flow is achieved. The averaged flowrate obtained at the inlet for 2D cine PC-MRI acquisitions is displayed in Fig. 4, together with the flow rate obtained for 4D Flow at the same location.
Figure 4: Flowrate at the inlet over one cardiac cycle (duration: 1s)
Measured Data
The data collected are magnitude and phase images proportional to the proton magnetization and are saved as DICOM (Digital Imaging and COmmunications in Medicine) files. The first post-processing step is to reordered the data and to compute the velocity field from the phase images. The resulting dataset is written as a structured grid in the VTK format (Visualisation ToolKit, Kitware, Inc, CliftonPark, NY). All post-processing steps, which will be further expanded on in the coming sections, are performed using in-house VTK-based Python scripts.
Measurement Errors
References
Contributed by: Morgane Garreau — University of Montpellier, France
© copyright ERCOFTAC 2021