Saturation-transfer effects and longitudinal relaxation times of ³¹P metabolites in fibroglandular breast tissue at 7T

Purpose: To investigate longitudinal relaxation times and saturation-transfer effects of phosphorous metabolites in breast fibroglandular tissue in vivo with ³¹P MR spectroscopy at 7T. Methods: Progressive saturation with adiabatic half passage excitation was used to determine T₁ values of ³¹P metabolites in a group of six healthy volunteers. Saturation-transfer experiments were performed in seven healthy volunteers by saturating at 0 ppm and 10 ppm with sinc-Gaussian pulses (90 ms; 10-ms pulse interval; B₁ = 17 μT) prior to excitation. Localization was performed by surface coils and one-dimensional chemical shift imaging. Data were analyzed via spectral fitting with the JMRUI software package, and T₁ values were obtained by fitting the data to the signal equation. Results: The determined longitudinal relaxation time values at 7T were as follows: phosphoethanolamine, 4.0 ± 0.2 s; phosphocholine, 1.8 ± 0.2 s; inorganic phosphate, 6.1 ± 0.1 s; phosphodiesters, glycerophosphatidylethanolamine plus glycerophosphocholine, 2.1 ± 0.1, and glycerophosphatidylethanolamine, 1.5 ± 0.1s; γ-ATP, 2.1 ± 0.1 s; and α-ATP, 2.0 ± 0.1 s. Saturation-transfer measurements with saturation pulses at 0 ppm showed a significant signal reduction in the phosphodiester 2–3 ppm range, whereas the γ-ATP signal at −2.5 ppm was not affected significantly. Conclusion: Longitudinal relaxation times of phosphorous metabolites in fibroglandular tissue revealed relatively low T₁ values for phosphodiesters. Saturation-transfer measurements showed that the phosphodiester signals were the only signals that were affected significantly, possibly indicating the presence of mobile phospholipids. Magn Reson Med 76:402–407, 2016.