Assessment of relative brain iron concentrations using T₂‐weighted and T₂*‐weighted MRI at 3 Tesla

Abstract

In this paper a new method is presented for the relative assessment of brain iron concentrations based on the evaluation of T2 and T2*-weighted images. A multiecho sequence is employed for rapid measurement of T2 and T2*, enabling calculation of the line broadening effect (T2'). Several groups have failed to show a correlation between T2 and brain iron content. However, quantification of T2', and the associated relaxation rate R2', may provide a more specific relative measure of brain iron concentration. This may find application in the study of brain diseases, which cause associated changes in brain iron levels. A new method of field inhomogeneity correction is presented that allows the separation of global and local field inhomogeneities, leading to more accurate T2* measurements and hence, T2' values. The combination of T2*, and T2-weighted MRI methods enables the differentiation of Parkinson's disease patients from normal age-matched controls based on differences in iron content within the substantia nigra.

Diffusion tensor imaging of deep gray matter brain structures: Effects of age and iron concentration

“…Among them are susceptibility-weighted imaging , where the effect of magnetic susceptibility on signal phase accrual is used to estimate local iron concentrations. The difference in R 2 and R 2 * has been proposed for iron measurements (Gelman and Guinto, 1992;Ma and Wehrli, 1996;Ordidge et al, 1994). Alternatively, iron measurement has been proposed based on a parametric model of signal decay in a series of measurements with incrementally asymmetric spin-echoes, in a procedure called magnetic field correlation imaging (Jensen et al, 2006).…”

Visualization of nigrosome 1 and its loss in PD

“…23 T2*-weighted MRI provides excellent contrast in the midbrain due to its high iron content. [24][25][26] Previous magnetic resonance work has focused mostly on localizing and measuring characteristics of the whole SN [26][27][28] or distinguishing the SNpc and SNpr, 28,29 although there has been some inconsistency in the definition of boundaries and subareas of the SN in Figure 2 Nigrosome 1 in vivo in iron-(T2*-weighted) and neuromelanin-(MT-T1-weighted) sensitive 7 T MRI Example of 2 coregistered, high-resolution, in vivo images of a healthy control (HC) (49 years old) shows the substantia nigra and nigrosome 1 (white arrows). In the T2*-weighted image (left, 0.3 3 0.3 3 0.3 mm 3 voxels), the nigrosome is hyperintense due to its low iron content; in the MT-T1-weighted sequence (right, 0.6 3 0.6 3 0.6 mm 3 voxels), the nigrosome is hyperintense due to its high neuromelanin content.…”

Different Iron-Deposition Patterns of Multiple System Atrophy with Predominant Parkinsonism and Idiopathetic Parkinson Diseases Demonstrated by Phase-Corrected Susceptibility-Weighted Imaging

“…Many methods have been used to detect iron accumulation in neurodegenerative diseases. [10][11][12][13][14][15][16][17][18][19][20][21] However, these methods may be insufficient for detecting subtle changes in iron components associated with disease progression and may not be sensitive enough to detect and discriminate IPD from MSA-P. 22,23 SWI is a new technique that exploits the magnetic properties of iron content of tissues by using magnitude and phase images with a 3D fully velocitycompensated gradient-echo sequence. Compared with a standard T2* sequence, thin sections with 3D SWI are used to avoid background field T2* signal intensity loss and magnetic field variations.…”