Mauro Costagli: “Imaging magnetic susceptibility with magnetic resonance: a tool to study neurodegenerative diseases”
CiNet 1F Conference Room
Laboratory of Medical Physics and Magnetic Resonance Technologies
IRCCS Stella Maris / Imago7 Foundation, PISA (Italy)
Host: Ichiro Fujita (PI)
Magnetic susceptibility χ describes the response of a substance when it is placed in an external magnetic field. Conventional Magnetic Resonance Imaging (MRI) techniques, such as T2*-weighted imaging, offer valuable information that reflect physical properties of biological tissues, as they provide imaging contrast weighted by local field homogeneity. More recent techniques, namely Susceptibility-Weighted Imaging, enhance this information by combining the conventional T2* signal amplitude with signal phase.
We have optimized Susceptibility-Weighted ANgiography (SWAN), a technique based on 3D gradient-recalled multi-echo acquisition, to target the mesencephalon on a 7T whole-body MRI system, and we described, with excellent anatomical detail in-vivo, a three-layered organization of the substantia nigra (SN) formed by the pars reticulata, pars compacta dorsalis and pars compacta ventralis. Patients with Parkinson Disease (PD) don’t present such anatomical architecture in SWAN imaging, which allowed discriminating between PD patients and healthy subjects with excellent sensitivity and specificity, suggesting that 7T susceptibility-weighted imaging could be used in diagnosis.
With a similar approach we targeted the primary motor cortex (M1) in patients with amyotrophic lateral sclerosis (ALS). We demonstrated that signal hypointensity of M1 deep layers correlated with clinical scales of upper motor neuron impairment and with disease progression rate.
We also implemented Quantitative Susceptibility Mapping (QSM), a novel MRI technique that allows quantifying χ, and demonstrated that, in a group of healthy subjects, the measured values of χ correlated with the expected concentration of iron in different regions of the cerebral cortex. In ALS patients, significant increases in magnetic susceptibility colocalized with T2* hypointensity observed in the deep layers of M1. The magnetic susceptibility, hence iron concentration, of the deep cortical layers of patients' M1 subregions corresponding to Penfield's areas of the hand and foot significantly correlated with the clinical scores of impairment of the corresponding limbs. QSM, which therefore appears to reflect the presence of iron deposits related to neuroinflammatory reaction and cortical microgliosis, might prove useful as a possible radiological sign of severe upper motor neuron burden in ALS patients.