RESUMO
We studied the validity of using an external signal reference for absolute quantification of brain metabolites. We chose cyclohexane as the signal standard. An expression of a perturbed magnetic field in diamagnetic cylindrical materials was first obtained by using a method of equivalent magnetic charges. Broadening of the spectrum in this perturbed magnetic field was then computed. We performed phantom studies. We measured the full width at half maximum (FWHM) of the cyclohexane and the signal ratio (SR) between water and cyclohexane in spheres of two different diameters, and in cylinders of various diameters and lengths. The observed FWHM and SR in the small cylinders had large variations in distribution, whereas those in the spheres and in the large cylinders had small variations. Specifically, in a cylinder with a diameter > 5 cm and with a length > 10 cm, the variation of the SR was < 1.0%. The diameter and the length of the cylinder preferably are large when a cylindrical material is adopted as an external signal standard.
