Overall system layout illustrating the main components of our MRI microvelocimetry system.
Dimensions and the components of the H-shaped permanent magnetic configuration are labeled in the top figure with a photo of the assembled magnet at the bottom. The four adjustment bolts allow adjusting the width of the air gap and the parallelism of the pole faces.
Layout of the three gradient coils with the orientation of the capillary tube and rf coil are shown.
Simulated current path configurations for the (a) Maxwell and (b) rectangular loop gradient coils. Only the cross-sectional view of the gradient coils is shown.
Simulation results of for case 1 in Fig. 4(a): (a) magnetic field contours; (b) gradient field strength and linearity with and without the presence of a ferromagnetic pole in the vicinity of the coils.
Triaxial gradient assembly: (a) schematic of the top half, (b) after assembling and before applying epoxy, and (c) fabrication process of the gradient coils.
Machined enclosure and the components of the probe are shown. The dimensions of the probe enclosure are . See Fig. 6(b).
Block diagram of the rf system for excitation and detection of MR signals.
Gradient strength vs the drive current of the gradients , , and . The bandwidth BW was measured from the spectrum of the MR signal as shown in the inset. The gradient sensitivity of , , and are 0.086, 0.069, and , respectively.
Static 2D cross-sectional image of a 1.67 mm diameter capillary filled with water. A second capillary (column guard) with an inner diameter of and wall thickness of that is also filled with water is inserted inside the first capillary. The wall of the smaller capillary is clearly visible in this figure.
Simplified SE pulse sequence for 1D imaging of fast flow.
Measured velocity profile (TOF method) inside a 1.67 mm capillary tube at average flow velocities of 200 and 410 mm/s using this MRI prototype. The nominal in-plane spatial resolution is .
Measured phase-encoded velocity profile inside the capillary tube at average flow velocities of 5, 7, and 10 mm/s. The nominal in-plane spatial resolution is .
Performance results from simulation for the gradient coil configurations shown in Fig. 4.
Dimensions of the gradient coils and their simulated performance in absence of the ferromagnetic poles. Each coil consists of three turns where each conductor is 1.5-mm-wide and -thick.
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