38 S. H. Eriksson et al. Figure 5. Zoomed PROPELLER image of the left temporal lobe (a) with corresponding histopathological sections for patient 4. All hippocampal subﬁelds are available in the histopathological sections. The myelinated tissue in the strata moleculare, lacunosum, and radiatum is clearly seen on the LFB stained section (b, red arrow indicates the corresponding area of low signal on the PROPELLER images). Sections immunolabeled for GFAP (c) show the abrupt transition to gliosis in CA1 (black arrow). This corresponds to signal increase on PROPELLER images (white arrow). The neuronal loss can be seen on sections immunolabeled for NeuN (d, black arrow) with good preservation of nerve cells in subiculum and some nerve cells also preserved in CA3. Section immunolabeled for dynorphin shows mossy ﬁber sprouting (e). Epilepsia C ILAE clearly show the internal structures of the hippocampus. Ex vivo 9.4T scans have shown detailed images of formalin- fixed cerebral tissue, including the hippocampus (Fatter- pekar et al., 2002). Such scanning requires very high field strength and long scan times (e.g., 14 h) and is hence not feasible in patients. PROPELLER images have the advantage of being rapid, taking approximately half the time needed for the T1-volume scan, but still providing greater anatomical detail. The sequence used for this study did, however, not cover the whole brain and could not be prescribed in an oblique coronal plane, so patients had to tilt their heads forward during the scan, which precluded some other patients from having this sequence. There were no overt head movements in the patients in the current study. Subtle head movements during MRI scans can occur even in motivated control subject (Forbes et al., 2001). Previous results from studies of the PRO- PELLER sequence show improved contrast and image quality in volunteers or patients asked to keep still dur- ing the scan on both 1.5 and 3T scanners (Forbes et al., 2001; Wintersperger et al., 2006). Improved image quality has also been shown in volunteers asked to move during the scan (Forbes et al., 2001) as well as patients who were unable to keep still (Forbes et al., 2003; Wintersperger et al., 2006). This suggests that the PROPELLER sequence could be used to study brain structures in detail even in pa- tients more prone to movement, for example patients with Epilepsia, 49(1):33–39, 2008 doi: 10.1111/j.1528-1167.2007.01277.x learning difficulties or neurodegenerative disorders includ- ing Alzheimer’s disease. A previous study comparing PROPELLER to a single- shot Fast Spin Echo sequence noted more susceptibility artifacts, particularly metallic, on PROPELLER images (Forbes et al., 2003). None of our patients had any metal- lic implants and no artifacts were seen with either image sequence used. PROPELLER images showed a good correlation with the histopathological sections, confirming that this MRI se- quence could distinguish between different strata and sub- fields of the hippocampus. There was some discrepancy in the details of the morphology of internal hippocam- pal structures between in vivo MRI and histopathologi- cal sections. This is expected (Eriksson et al., 2005) and is due to tissue distortions after resection when the hip- pocampus is no longer supported by surrounding cerebral tissue. The main features, however, were clearly identifi- able and comparable between in vivo PROPELLER MRI and histopathology. The severe gliosis seen on GFAP im- munohistochemistry was mirrored by a signal increase on PROPELLER images in the same hippocampal areas. Both histopathological sections and PROPELLER images showed the abrupt transition between the relatively normal- appearing subiculum and the severely atrophic and gliotic CA1. The band of tissue with low signal stretching from the parahippocampal gyrus into the hippocampus was also