Quantitative Susceptibility Mapping (QSM) is a promising non-invasive approach for investigating Parkinson's Disease, as several studies have reported a correlation of magnetic susceptibility with brain iron concentrations in vivo. Since QSM measures susceptibility relative to a reference value, a suitable reference region must be chosen to compare patients and the stages of the disease. Some studies using non-PD patients suggest LV as a reference with a low susceptibility of cerebrospinal fluid (CSF) that is closest to water, while others use white matter.

44 PD patients underwent baseline QSM as part of a phase II mesenchymal stem cell trial assessing a disease-modifying therapy for PD. We compared the regional mean and standard deviation of susceptibility in parts per billion in left (LH) and right hemisphere (RH) LV, WM, CP and PUT after image processing in QSMxT.

WM had the lowest susceptibility (LH mean -1.044 std 0.939, RH -1.053 std 0.950), followed by LV (LH mean 3.181 std 1.654, RH 3.167 std 1.555). The two iron-accumulating regions had higher susceptibility, with CP (LH mean 5.205 std 4.214, RH mean 6.316 std 4.404) followed by PUT (LH mean 7.069 std 4.068, RH 7.301 std 4.247). Notably, both left, and right LV susceptibility were significantly higher than left and right hemisphere WM (LH LV vs. LH WM t₍₄₃₎=14.44, p<0.001; RH LV vs. RH WM t₍₄₃₎=13.91, p<0.001).

WM is a more suitable QSM reference region than LV in PD. However, elevated susceptibility of LV CSF may be promising for future QSM analysis in PD as a correlation of iron CSF levels with disease duration has been reported.