Noninvasive Measurement and Quantitation of Brain Iron in Parkinson’s Disease Using Adiabatic T2ρ and T1ρ High Field MRI Techniques

Abstract

Postmortem demonstration of increased iron in the substantia nigra (SN) is a well- appreciated finding in Parkinson’s disease (PD). It is thought that this iron may facilitate the generation of free radicals which are thought to play a role in dopamine neuronal loss. To date, however, researchers have been unable to confirm an in vivo difference of iron between those with PD and control subjects using magnetic resonance imaging (MRI). This may be due to the limitations of T1 and T2: two conventional MRI techniques that have been employed. Here, novel T2ρ and T1ρ MRI relaxation methods were used for the measurement of iron load and distribution [1] , [2] , [3] . T2ρ measurements are indicative of tissue iron content and distribution and measure molecular motion in local susceptibility gradients. T1ρ measurements, on the other hand, can be used to assess cellular loss. When applied at high magnetic fields these two methods may provide a noninvasive and reliable handle on iron accumulation and neuronal loss in PD. In our 4 Tesla magnet study, we found a significant change of the T1ρ and T2ρ relaxation time constants (both the distribution and absolute values) in the PD group versus controls. Relaxogram analysis of the T2ρ and T1ρ measurements demonstrated increased water and iron content, as well as changes in iron distribution in the SN. Therefore, high resolution MRI with T2ρ and T1ρ provide unique information in Parkinson’s disease patients as compared to conventional T1 and T2 measurements. This information may prove useful in evaluating the pathogenesis and severity of PD. Future studies are underway to correlate T1ρ, T2ρ, and Τ2 findings with simultaneous spectroscopy measurements of absolute concentration of NAA [4] to further assess iron accumulation and neuronal loss in controls and those with PD.