MRI parcellation of ex vivo medial temporal lobe

Abstract

Recent advancements in radio frequency coils, field strength and sophisticated pulse sequences have propelled modern brain mapping and have made validation to biological standards - histology and pathology - possible. The medial temporal lobe has long been established as a pivotal brain region for connectivity, function and unique structure in the human brain, and reveals disconnection in mild Alzheimer's disease. Specific brain mapping of mesocortical areas affected with neurofibrillary tangle pathology early in disease progression provides not only an accurate description for location of these areas but also supplies spherical coordinates that allow comparison between other ex vivo cases and larger in vivo datasets. We have identified several cytoarchitectonic features in the medial temporal lobe with high resolution ex vivo MRI, including gray matter structures such as the entorhinal layer II 'islands', perirhinal layer II-III columns, presubicular 'clouds', granule cell layer of the dentate gyrus as well as lamina of the hippocampus. Localization of Brodmann areas 28 and 35 (entorhinal and perirhinal, respectively) demonstrates MRI based area boundaries validated with multiple methods and histological stains. Based on our findings, both myelin and Nissl staining relate to contrast in ex vivo MRI. Precise brain mapping serves to create modern atlases for cortical areas, allowing accurate localization with important applications to detecting early disease processes.

Keywords: Brodmann's area 28; Brodmann's area 35; Entorhinal; Localization; Mapping; Perirhinal.

Fig. 1

Ex vivo MRI (A), blockface (B) and Nissl stained section (C). Blockface images, collected serially during sectioning, aid in the registration between ex vivo MRI and histological slice.

Fig. 2

Steps in the ex vivo probabilistic mapping pipeline. High-resolution, high field detection of cortical architectonic fields in ex vivo MRI (A). Region of interest labeled throughout rostrocaudal extent (blue label = perirhinal area 35 as example) in (B). High resolution label transformed onto low resolution volume in (C). Note blue label in medial bank of collateral sulcus in lower resolution image.

Fig. 3

Ex vivo MRI (A), Nissl (B) and Myelin stained sections (C). Note the contrast correspondence to MRI in both the cortical graymatter in Nissl (B) and also the white matter myelinated fibers in (C).White arrowheads designate area boundaries. Abbreviations: ab = angular bundle, alv = alveus, AM = amygdala, CA1–CA3 = subfields of cornu ammonis, DG = dentate gyrus, EC = entorhinal cortex, HATA = hippocampal-amygdala transition area, ISO = isocortical Brodmann's area 36, ml = molecular layer, pp = perforant pathway, PC = perirhinal cortex, PaS = parasubiculum, PreS = presubiculum, Sub = subiculum, X = mixture of CA1 and CA2 due to an oblique plane of cut, * = unique layer in perirhinal cortex, Brodmann's area 35. Magnification bars = 0.5 cm.

Fig. 4

Left and right hemisphere averages in perirhinal (A and B) and entorhinal (C and D) cortices mapped onto a spherical template. Red and yellow reflect overlapping labels from individual cases.

Fig. 5

Optical coherence tomography images shown as an average (A) and maximum intensity projection (B). Optical coherence tomography reveals laminar detail and delineates the area 28, as well as area 35a and area 35b boundaries in the parahippocampal coronal slice.