Short-T₂ imaging for quantifying concentration of sodium (²³ Na) of bi-exponential T₂ relaxation

Purpose: This work intends to demonstrate a new method for quantifying concentration of sodium (²³ Na) of bi-exponential T₂ relaxation in patients on MRI scanners at 3.0 Tesla.

Theory and methods: Two single-quantum (SQ) sodium images acquired at very-short and short echo times (TE = 0.5 and 5.0 ms) are subtracted to produce an image of the short-T₂ component of the bi-exponential (or bound) sodium. An integrated calibration on the SQ and short-T₂ images quantifies both total and bound sodium concentrations. Numerical models were used to evaluate signal response of the proposed method to the short-T₂ components. MRI scans on agar phantoms and brain tumor patients were performed to assess accuracy and performance of the proposed method, in comparison with a conventional method of triple-quantum filtering.

Results: A good linear relation (R² = 0.98) was attained between the short-T₂ image intensity and concentration of bound sodium. A reduced total scan time of 22 min was achieved under the SAR restriction for human studies in quantifying both total and bound sodium concentrations.

Conclusion: The proposed method is feasible for quantifying bound sodium concentration in routine clinical settings at 3.0 Tesla. Magn Reson Med 74:162-174, 2015. © 2014 Wiley Periodicals, Inc.