To evaluate whether the lines occasionally detected on clinical magnetic resonance (MR) images are genuine
hippocampal layers, a formalin fixed hippocampal specimen was scanned using T2 weighted sequences at 7
Tesla (voxel dimensions 0.064×0.064×1 mm) and at 1.5 Tesla (voxel dimensions: 0.156×0.156×1 mm) and
compared with the results of histological examination. In addition, a healthy volunteer was scanned with a
T2 weighted sequence at 1.5 Tesla (voxel dimensions: 0.469×0.469×2 mm). On 7 Tesla images
hippocampal layers and the granule cell layer of the dentate were visible. On 1.5 Tesla images of the
specimen, the hippocampal layers were again identified, but the granule cell layer of the dentate was not
detectable. On 1.5 Tesla images of the hippocampus in vivo, 3 layers could be distinguished in the
hippocampus on some slices. These mainly represented the alveus, pyramidal cell layer and stratum
radiatum. A dark line consisting of a few pixels possibly represented the dentate gyrus. Our results show
that the lines occasionally detected on clinical MR images are likely to be real hippocampal layers. However,
the resolution currently used in clinical imaging (typically 0.469×0.469×2 mm or lower) is not sufficient for
the detection of all hippocampal layers. For the reliable detection of all hippocampal layers on MR images
an increase by a factor of approximately 20 would be necessary.