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A genetic algorithm-optimized hetero-nuclear polarization transfer pulse sequence for metabolic imaging

Vencel Somai^1,2, Felix Kreis³, Adam Gaunt¹, and Kevin M Brindle^1,4
¹Cancer Research UK Cambridge Institute, University of Cambridge, Li Ka Shing Centre, Robinson Way, Cambridge, United Kingdom, ²Department of Radiology, University of Cambridge, School of Clinical Medicine Box 218, Cambridge Biomedical Campus, Cambridge, United Kingdom, ³Department of Information Technology and Electrical Engineering, ETH Zurich, Rämistrasse 101, Zurich, Switzerland, ⁴Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge, United Kingdom

The proposed method produced a ΔB₀ and B₁ insensitive pulse sequence that required ~2 times lower peak B₁ than the BINEPT sequence. The performance was tested on a [¹⁵N₂]urea phantom, where it transferred more polarization than the BINEPT sequence and could also be used for partial transfer.

(A) Discretized shaped pulses on ¹H and ¹⁵N channels. The color-coding and the height of the bars represent the phase (Φ_i) and the amplitude of the pulse points respectively. The length of the pulse points (τ_i) is also an optimization variable. (B) Pulse amplitude on proton channel for the ¹H to ¹⁵N full transfer. (C) Pulse amplitude on the ¹⁵N channel. Despite the rapidly varying waveforms the predicted behavior was well preserved.

Time course for ¹⁵N to ¹H partial polarization transfer in a hyperpolarized [¹⁵N₂]urea phantom. The broad urea peak is the result of the degraded magnetic field homogeneity caused by injection of the hyperpolarized urea. The residual water peak is due to insufficient water suppression