Bilateral gradient-echo spectroscopic imaging with correction of frequency variations for measurement of fatty acid composition in mammary adipose tissue.

PURPOSE: To develop a simultaneous dual-slab three-dimensional gradient-echo spectroscopic imaging (GSI) technique with frequency drift compensation for rapid (<6 min) bilateral measurement of fatty acid composition (FAC) in mammary adipose tissue. METHODS: A bilateral GSI sequence was developed using a simultaneous dual-slab excitation followed by 128 monopolar echoes. A short train of navigator echoes without phase or partition encoding was included at the beginning of each pulse repetition time period to correct for frequency variation caused by respiration and heating of the cryostat. Voxel-wise spectral fitting was applied to measure the areas of the lipid spectral peaks to estimate the number of double-bond (ndb), number of methylene-interrupted double-bond (nmidb), and chain length (cl). The proposed method was tested in an oil phantom and 10 postmenopausal women to assess the influence of the frequency variation on FAC estimation. RESULTS: The frequency drift observed over 5:27 min during the phantom scan was about 10 Hz. Phase correction based on the navigator reduced the median error of ndb, nmidb, and cl from 9.7%, 17.6%, and 3.2% to 2.1%, 9.5%, and 2.8%, respectively. The in vivo data showed a mean ± standard deviation frequency drift of 17.4 ± 2.5 Hz, with ripples at 0.3 ± 0.1 Hz. Our reconstruction algorithm successfully separated signals from the left and right breasts with negligible residual aliasing. Phase correction reduced the interquartile range within each subject's adipose tissue of ndb, nmidb, and cl by 18.4 ± 10.6%, 18.5 ± 13.9%, and 18.4 ± 10.6%, respectively. CONCLUSION: This study shows the feasibility of obtaining bilateral spectroscopic imaging data in the breast and that incorporation of a frequency navigator improves the estimation of FAC.

Quantitative sodium imaging and gliomas: a feasibility study.

PURPOSE: Recent advances in sodium brain MRI have allowed for increased signal-to-noise ratio, faster imaging, and the ability of differentiating intracellular from extracellular sodium concentration, opening a new window of opportunity for clinical application. In gliomas, there are significant alterations in sodium metabolism, including increase in the total sodium concentration and extracellular volume fraction. The purpose of this study is to assess the feasibility of using sodium MRI quantitative measurements to evaluate gliomas. METHODS: Eight patients with treatment-naïve gliomas were scanned at 3 T with a homemade 1H/23Na head coil, generating maps of pseudo-intracellular sodium concentration (C1), pseudo-extracellular volume fraction (α2), apparent intracellular sodium concentration (aISC), and apparent total sodium concentration (aTSC). Measurements were made within the contralateral normal-appearing putamen, contralateral normal-appearing white matter (NAWM), and solid tumor regions (area of T2-FLAIR abnormality, excluding highly likely areas of edema, cysts, or necrosis). Paired samples t test were performed comparing NAWM and putamen and between NAWM and solid tumor. RESULTS: The normal-appearing putamen demonstrated significantly higher values for aTSC, aISC, C1 (p < 0.001), and α2 (p = 0.002) when compared to those of NAWM. The mean average of all solid tumors, when compared to that of NAWM, demonstrated significantly higher values of aTSC and α2 (p < 0.001), and significantly lower values of aISC (p = 0.02) for each patient. There was no significant difference between the values of C1 (p = 0.19). CONCLUSION: Quantitative sodium measurements can be done in glioma patients and also has provided further evidence that total sodium and extracellular volume fraction are increased in gliomas.