The regional distribution of T2-relaxation times in MR images of the substantia nigra and crus cerebri

Abstract

When scanning the size of the substantia nigra (SN), for example in Parkinson's disease, it is important to precisely locate its true anatomic location. The hypointense areas on T2-weighted magnetic resonance images (T2w) at the level of the upper midbrain are usually labeled as the SN. Recent studies showed that the line of demarcation between the SN and the crus cerebri (CC) in T2w images seems not to be clear. The purpose of our study was to evaluate the depiction of the SN and the CC on calculated R2 maps by analyzing the regional distribution of T2 values in both regions. In 36 healthy subjects, triple echo turbo spin echo were obtained at 1.5 T and R2 maps calculated. Proton density-weighted turbo spin echo images (PDw) were used as reference. The CC and SN were manually traced on PDw sections (CCP and SNP) and also the hyperintense areas on the R2 maps, suggestive of the SN (DT2). The obtained volumes were evaluated in terms of total size, intersections size, and residual areas, as well as the corresponding T2 values. DT2 corresponded to anterolateral parts of the SNP and showed an extension to anteromedial part of the CC. The intersections between DT2 and CCP and DT2 and SNP presented both decreased but different T2 values (102 +/- 5 and 95 +/- 4 ms). An exact differentiation of the SN from the CC is not possible on the basis of T2w images but rather on the basis of the underlying calculated T2 values from the triple echo sequence.