Kerrin Pine

Field-cycling NMR relaxometry with spatial selection

Fast field‐cycling MRI offers access to sources of endogenous information not available from conventional fixed‐field imagers. One example is the T1 dispersion curve: a plot of T1 versus field strength. We present a pulse sequence that combines saturation‐recovery/inversion‐recovery T1 determination with field cycling and point‐resolved spectroscopy localization, enabling the measurement of dispersion curves from volumes selected from a pilot image. Compared with a nonselective sequence, our method of volume selection does not influence measurement accuracy, even for relatively long echo times and in the presence of radiofrequency field nonuniformity. The measured voxel profile, while not ideal, corresponds with that expected from the image slice profile. On a whole‐body fast field‐cycling scanner with 59‐mT detection, the sensitivity of the experiment is sufficient to reveal distinctive “quadrupole dips” in dispersion curves of protein‐rich human tissue in vivo. Magn Reson Med, 2010.

In vivo field-cycling relaxometry using an insert coil for magnetic field offset.

The T1 of tissue has a strong dependence on the measurement magnetic field strength. T1‐dispersion could be a useful contrast parameter, but is unavailable to clinical MR systems which operate at fixed magnetic field strength. The purpose of this work was to implement a removable insert magnet coil for field‐cycling T1‐dispersion measurements on a vertical‐field MRI scanner, by offsetting the static field over a volume of interest.

Rapid multi-field T(1) estimation algorithm for Fast Field-Cycling MRI.

Fast Field-Cycling MRI (FFC-MRI) is an emerging MRI technique that allows the main magnetic field to vary, allowing probing T1 at various magnetic field strengths. This technique offers promising possibilities but requires long scan times to improve the signal-to-noise ratio. This paper presents an algorithm derived from the two-point method proposed by Edelstein that can estimate T1 using only one image per field, thereby shortening the scan time by a factor of nearly two, taking advantage of the fact that the equilibrium magnetisation is proportional to the magnetic field strength. Therefore the equilibrium magnetisation only needs measuring once, then T1 can be found from inversion recovery experiments using the Bloch equations. The precision and accuracy of the algorithm are estimated using both simulated and experimental data, by Monte-Carlo simulations and by comparison with standard techniques on a phantom. The results are acceptable but usage is limited to the case where variations of the main magnetic field are fast compared with T1 and where the dispersion curve is relatively linear. The speed-up of T1-dispersion measurements resulting from the new method is likely to make FFC-MRI more acceptable when it is applied in the clinic.