Optimized Magnetic Resonance T1 Mapping for Estimation of Intrathecal Contrast Concentrations in Human Brain and
Lars Magnus Valnes1,2, Trygve Holck Storås3,4, Svein Are Sirirud Vatnehol5,6
1Department of Neurosurgery, Oslo University Hospital - Rikshospitalet, Oslo, Norway.
Purpose:
Intrathecal contrast-enhanced magnetic resonance imaging (MRI), which uses a contrast agent as a cerebrospinal fluid (CSF) tracer, is an emerging technique for in vivo imaging of glymphatic function in humans. T1 mapping enables quantification of tracer concentrations; however, methodological limitations persist. This study aimed to enhance the utility of a standard Look-Locker MRI sequence for quantifying tracer concentrations in both brain parenchyma and ventricular CSF.
Methods:
Using a 3 T MRI scanner, we conducted (i) optimization of a Look-Locker T1 mapping protocol to determine T1 relaxation times in brain parenchyma and ventricular CSF, (ii) a phantom study to assess repeatability of T1 times estimation and the relaxivity constant r1 calculation, and (iii) a feasibility assessment in patients.
Results:
An optimized Look-Locker protocol for T1 mapping enabled estimation of T1 relaxation times in brain parenchyma and ventricular CSF that compare with previously reported T1 times. The phantom study demonstrated repeatability of T1 time estimations. In six patients with idiopathic normal pressure hydrocephalus, the method proved feasible for estimating CSF tracer concentrations in brain and ventricular CSF over time following intrathecal MRI contrast injection (gadobutrol, 0.5 mmol).
Conclusion:
Optimizing a standard Look-Locker T1 mapping protocol allowed for estimation of reliable T1 times in both brain parenchyma and ventricular CSF, and the subsequent determination of concentrations of intrathecal CSF tracer in the human brain, supporting its potential for studying glymphatic function. However, limitations with estimation of T1 times and the selection of relaxivity constant of the contrast agent reduce accuracy of concentration estimates.
