Radiofrequency Enhancer to Recover Signal Dropouts in 7 Tesla Diffusion MRI
Varun Subramaniam,
Andrew Frankini,
Ameen Al Qadi,
Mackenzie T. Herb,
Gaurav Verma,
Bradley N. Delman,
Priti Balchandani,
Akbar Alipour
Affiliations
Varun Subramaniam
Department of Diagnostic, Molecular and Interventional Radiology, BioMedical Engineering and Imaging Institute (BMEII), Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
Andrew Frankini
Department of Diagnostic, Molecular and Interventional Radiology, BioMedical Engineering and Imaging Institute (BMEII), Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
Ameen Al Qadi
Department of Diagnostic, Molecular and Interventional Radiology, BioMedical Engineering and Imaging Institute (BMEII), Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
Mackenzie T. Herb
Department of Diagnostic, Molecular and Interventional Radiology, BioMedical Engineering and Imaging Institute (BMEII), Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
Gaurav Verma
Department of Diagnostic, Molecular and Interventional Radiology, BioMedical Engineering and Imaging Institute (BMEII), Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
Bradley N. Delman
Department of Diagnostic, Molecular and Interventional Radiology, BioMedical Engineering and Imaging Institute (BMEII), Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
Priti Balchandani
Department of Diagnostic, Molecular and Interventional Radiology, BioMedical Engineering and Imaging Institute (BMEII), Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
Akbar Alipour
Department of Diagnostic, Molecular and Interventional Radiology, BioMedical Engineering and Imaging Institute (BMEII), Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA
Diffusion magnetic resonance imaging (dMRI) allows for a non-invasive visualization and quantitative assessment of white matter architecture in the brain by characterizing restrictions on the random motion of water molecules. Ultra-high field MRI scanners, such as those operating at 7 Tesla (7T) or higher, can boost the signal-to-noise ratio (SNR) to improve dMRI compared with what is attainable at conventional field strengths such as 3T or 1.5T. However, wavelength effects at 7T cause reduced transmit magnetic field efficiency in the human brain, mainly in the posterior fossa, manifesting as signal dropouts in this region. Recently, we reported a simple approach of using a wireless radiofrequency (RF) surface array to improve transmit efficiency and signal sensitivity at 7T. In this study, we demonstrate the feasibility and effectiveness of the RF enhancer in improving in vivo dMRI at 7T. The electromagnetic simulation results demonstrated a 2.1-fold increase in transmit efficiency with the use of the RF enhancer. The experimental results similarly showed a 1.9-fold improvement in transmit efficiency and a 1.4-fold increase in normalized SNR. These improvements effectively mitigated signal dropouts in regions with inherently lower SNR, such as the cerebellum, resulting in a better depiction of principal fiber orientations and an enhanced visualization of extended tracts.
