100 research outputs found
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Theoretical aspects of motion sensitivity and compensation in echo‐planar imaging
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In-plane flow velocity quantification along the phase encoding axis in MRI
In-plane flow quantification in MRI offers the potential for assessing vessel patency, and both volume flow rate and flow velocity. These techniques will have definite future impact on MR angiography. The method used in this paper employs motion artifact suppression technique (MAST
™) gradients to refocus spins travelling along any of the three imaging axes while encoding the velocity component along the phase encoding axis.
4,5,7,9 This method has several advantages over in-plane flow quantification along the read axis.
11,12 Primarily, flow voids due to complete spin dephasing can be eliminated (or reduced), wider velocity limits can be measured, and gradients can be designed which are sensitive to only velocity along the phase axis with no additional effect from higher order derivatives, or motion along the read axis. Flow phantom studies, carried out on 19 mm inside diameter glass tubes, have produced accurate results for flow rates ranging from 0.6 gallons per minute (GPM) to 2.5 GPM, corresponding to a mean velocity range from 13.2 cm/sec to 55.3 cm/sec. Reynolds numbers varied from 2,700 to 11,500. Errors were less than or equal to 8% over the range of flow rates studied
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Analysis of imaging axes significance in motion artifact suppression technique (MAST ™): MRI of turbulent flow and motion
Recently, a new technique has been demonstrated which effectively refocusses the dephasing effects of spins moving during application of MR imaging gradients. This paper presents an analysis of imaging axes significance in spin dephasing for motion occurring along the slice select, read and phase-encoding directions. A flow phantom under constant flow conditions in all experiments was used to provide complete spin dephasing when “traditional” imaging gradients were used. The MAST
™ technique was used to refocus along various combinations of imaging axes, and variable number of terms from the Taylor expansion of motion along them. Results indicate that motion along any imaging axis can be refocussed effectively when MAST gradients are used along only the slice select and read axis
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Use of superparamagnetic contrast media to suppress signal from flowing spins: Preliminary experience
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Analytical resolution and noise characteristics of linearly reconstructed magnetic resonance data with arbitraryk‐space sampling
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