Computational investigation of fitting for calculation of signal dynamics from hyperpolarized xenon-129 Gas MRI

Abstract

Aim: Computational fitting methods were investigated to determine the most accurate fitting approach for the calculation of dynamic hyperpolarized MRI parameters. Materials and Methods: The signal decay of a time-series Hyperpolarized xenon gas MRI phantom was fitted to Bloch equations using three methods varying the fitting parameters for calculation of flip angle, α, and longitudinal relaxation time, T 1 . The first fitting method used an initial calculation of α before the fitting process. The second and third techniques used direct fitting of signal decay equations with and without upper-lower boundaries for calculation of α, and T 1 . Wilcoxon signed-rank test was used to investigate the statistical significance of the calculated parameters. Results: The first approach was the most accurate fitting technique that allowed direct calculation of α=8.65° in agreement to the third approach α=8.73±0.78°, 8.75±0.12°, 8.67±0.05°. Additionally, the standard deviation of the calculated T 1 was lower than 1% (T 1 =103.2±0.04s) which was significantly more accurate than the second method (T 1 =90±30.2s and 135.7±10.3s) and the third method (T 1 =101.4±5.1s and 113.5±16.1s). Conclusion:The first technique provides repeatable and reliable calculation of signal decay parameters including α and T 1 from the dynamic hyperpolarized gas MR images and more accurate than direct fitting methods.