Purpose
To explore the impact of slice profile effects on ADC mapping of hyperpolarized substrates.
Methods
Slice profile effects were simulated using a Gaussian RF pulse with a variety of flip angle schedules and b-value ordering schemes. A long T1 water phantom was used to validate the simulation results, and ADC mapping of hyperpolarized [13C,15N2]urea was performed on the murine liver to assess these effects in vivo.
Results
Slice profile effects result in excess signal after repeated RF pulses, causing bias in HP measurements. The largest error occurs for metabolites with small ADCs, resulting in up to 10-fold overestimation for metabolites that are in more restricted environments. A mixed b-value scheme substantially reduces this bias, while scaling the slice-select gradient can mitigate it completely. In vivo, the liver ADC of hyperpolarized [13C,15N2]urea is nearly 70% lower (0.99 ± 0.22 vs. 1.69 ± 0.21 × 10−3 mm2/s) when slice-select gradient scaling is employed.
Conclusion
Slice profile effects can lead to bias in hyperpolarized ADC measurements. A mixed b-value ordering scheme can reduce this bias compared to sequential b-value ordering. Slice-select gradient scaling can also correct for this deviation, minimizing bias and providing more precise ADC measurements of hyperpolarized substrates.