Detection of fully refocused polyamine spins in prostate cancer at 7 T

(1)H MRSI is often used at 1.5 or 3 T to study prostate cancer, where the ratio of choline + creatine to citrate is taken as a marker for tumour presence. Recently, the level of polyamines (mainly spermine) has been shown to improve specificity even further. However, the in vivo detection of these polyamines (at 3.1  ppm) is hampered by signal cancellation as a result of J-coupling effects and signal overlap with choline (3.2  ppm) and creatine (3.0  ppm) resonances. At higher magnetic field strengths, the chemical shift dispersion will increase, which allows the use of very selective radiofrequency pulses to refocus J-coupled spins. In this work, we added selective refocusing pulses to a semi-LASER (localisation based on adiabatic selective refocusing) sequence at 7 T, and optimised the inter-pulse timings of the sequence for fully refocused detection of spermine spins, whilst maintaining optimised detection of choline, creatine and the strongly coupled spin system of citrate.