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RESEARCH PRODUCT

The effects of linearly increasing flip angles on 3D inflow MR angiography

Dirk PetersenThomas NägeleUwe KloseWolfgang GroddJaroslav Tintera

subject

Materials scienceInflowsymbols.namesakeNuclear magnetic resonanceHumansPopliteal ArteryRadiology Nuclear Medicine and imagingSaturation (magnetic)Fourier AnalysisModels CardiovascularMr angiographyReproducibility of ResultsPulse durationRangingArteriesImage EnhancementMagnetic Resonance ImagingComputational physicsTibial ArteriesFourier transformFibulaRegional Blood FlowBlood CirculationsymbolsSlabBlood VesselsArtifactsAlgorithmsBlood Flow VelocityExcitation

description

As recently demonstrated, spin saturation effects in 3D time-of-flight (TOF) MR angiography (MRA) can be reduced by using RF pulses with linearly increasing flip angles (ramp pulses) in the main direction of flow. We developed a model for calculating the signal distribution of proton flow within the excitation volume (slab) for different ramp slopes and compared the results with the measured distribution for the lower-leg arteries. The ramp pulses were generated using the Fourier transformation of the desired excitation profiles. With a bandwidth of 6 kHz and a pulse length of 2.56 ms satisfactory ramps with variable slopes were generated and applied in a standard flow-compensated 3D FISP sequence. The effects on the signal distribution in the resulting angiograms of the lower limbs revealed a considerable reduction of saturation losses in agreement with the calculations. Calculated optimal ramp slopes are provided for flow velocities ranging from 5 to 50 cm/s and excitation volumes ranging from 5 to 25 cm.

yearjournalcountryeditionlanguage
1994-05-01Magnetic Resonance in Medicine
https://doi.org/10.1002/mrm.1910310515