Abstract
Objective
To evaluate the feasibility of in vivo 23Na imaging of the corticomedullary 23Na gradient and to measure 23Na transverse relaxation times (T2*) in human kidneys.
Methods
In this prospective, IRB-approved study, eight healthy volunteers (4 female, 4 male; mean age 29.4 ± 3.6 years) were examined on a 7-T whole-body MR system using a 23Na-only spine-array coil. For morphological 23Na-MRI, a 3D gradient echo (GRE) sequence with a variable echo time scheme (vTE) was used. T2* times were calculated using a multiecho 3D vTE-GRE approach. 23Na signal-to-noise ratios (SNR) were given on a pixel-by-pixel basis for a 20-mm section from the cortex in the direction of the medulla. T2* maps were calculated by fitting the 23Na signal decay monoexponentially on a pixel-by-pixel basis, using least squares fit.
Results
Mean corticomedullary 23Na-SNR increased from the cortex (32.2 ± 5.6) towards the medulla (85.7 ± 16.0). The SNR increase ranged interindividually from 57.2 % to 66.3 %. Mean 23Na-T2* relaxation times differed statistically significantly (P < 0.001) between the cortex (17.9 ± 0.8 ms) and medulla (20.6 ± 1.0 ms).
Conclusion
The aim of this study was to evaluate the feasibility of in vivo 23Na MRI of the corticomedullary 23Na gradient and to measure the 23Na T2* relaxation times of human kidneys at 7 T.
Key Points
• High field MR offers new insights into renal anatomy and physiology.
• 23 Na MRI of healthy human kidneys is feasible at ultra-high field.
• Renal 23 Na concentration increases from the cortex in the medullary pyramid direction.
• In vivo measurements of renal 23 Na-T2* times are demonstrated at 7.0 T.
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Acknowledgments
This study was supported by funding from the Vienna Clinical Imaging Centre (VIACLIC) project as part of the Vienna Spots of Excellence (VSOE) Program and by Siemens Healthcare. This study was supported non-financially by the Proof-of-Concept program of Euro-BioImaging.
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Haneder, S., Juras, V., Michaely, H.J. et al. In vivo sodium (23Na) imaging of the human kidneys at 7 T: Preliminary results. Eur Radiol 24, 494–501 (2014). https://doi.org/10.1007/s00330-013-3032-6
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DOI: https://doi.org/10.1007/s00330-013-3032-6