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Reduction of vibration‐induced signal loss by matching mechanical vibrational states: Application in high b ‐value diffusion‐weighted MRS
Author(s) -
Weidlich Dominik,
Zamskiy Mark,
Maeder Marcus,
Ruschke Stefan,
Marburg Steffen,
Karampinos Dimitrios C.
Publication year - 2020
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.28128
Subject(s) - diffusion , imaging phantom , signal (programming language) , nuclear magnetic resonance , diffusion mri , materials science , vibration , effective diffusion coefficient , optics , laser , biomedical engineering , acoustics , physics , chemistry , magnetic resonance imaging , computer science , medicine , radiology , thermodynamics , programming language
Purpose Diffusion encoding gradients are known to yield vibrations of the typical clinical MR scanner hardware with a frequency of 20 to 30 Hz, which may lead to signal loss in diffusion‐weighted MR measurements. This work proposes to mitigate vibration‐induced signal loss by introducing a vibration‐matching gradient (VMG) to match vibrational states during the 2 diffusion gradient pulses. Theory and Methods A theoretical description of displacements induced by gradient switching was introduced and modeled by a 2‐mass‐spring‐damper system. An additional preceding VMG mimicking timing and properties of the diffusion encoding gradients was added to a high b ‐value diffusion‐weighted MR spectroscopy sequence. Laser interferometry was employed to measure 3D displacements of a phantom surface. Lipid ADC was assessed in water–fat phantoms and in vivo in the tibial bone marrow of 3 volunteers. Results The modeling and the laser interferometer measurements revealed that the displacement curves are more similar during the 2 diffusion gradients with the VMG compared to the standard sequence, resulting in less signal loss of the diffusion‐weighted signal. Phantom results showed lipid ADC overestimation up to 119% with the standard sequence and an error of 5.5% with the VMG. An 18% to 35% lower coefficient of variation was obtained for in vivo lipid ADC measurement when employing the VMG. Conclusion The application of the VMG reduces the signal loss introduced by hardware vibrations in a high b ‐value diffusion‐weighted MRS sequence in phantoms and in vivo. Reference measurements based on laser interferometry and mechanical modelling confirmed the findings.