MR Imaging Anatomy in Neurodegeneration: A Robust Volumetric Parcellation Method of the Frontal Lobe Gyri with Quantitative Validation in Patients with Dementia
B. Iordanovaa,
D. Rosenbauma,
D. Normana,
M. Weinera and
C. Studholmea
a From the Department of Radiology, Magnetic Resonance Unit, San Francisco Veterans Affairs Medical Center and the University of California, San Francisco, Calif
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Fig 1. A screen capture showing the general layout of the tracing software used, with overlay, outline, and surface views. The user can scroll through planes along any of the 3 main axes, use crosshairs for precise multiplanar viewing, zoom in and out, and rotate the view. The surface-rendering can be aligned or oriented independently to the section displays, and a common reference point at the crosshairs can be maintained.
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Fig 2. A view of the frontal pole showing the frontal marginal sulcus (right arrow, red line) and lateral orbital sulcus (left arrow, blue line) used as borders between the lateral and the ventral part of the frontal lobe. The SFG is in blue on the left and in green on the right.
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Fig 3. A medial view of the SFG (in green) showing an interruption of the cingulate sulcus, for which we defined the border as a straight line connecting the anterior (brown) and posterior (yellow) parts.
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Fig 4. The frontal marginal sulcus defining the anterior border of the SFG is easily identifiable on anterior coronal sections (arrows, indicating this sulcus on the left and right hemisphere).
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Fig 5. The SFG on the right hemisphere of this subject ramifies into 2 branches (left panel), and we defined the region of the gyrus to include both branches, taking into account its natural pattern. The point of ramification is indicated by the arrow. The surface-rendering on the right panel shows the posterior border of this gyrus—the PreCS marked with a white line.
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Fig 6. The IFS is marked here with a red line on the surface-rendering. It separates the IFG (brown) from the MFG (purple), and in cases of its interruption, we connected the separate pieces to form a continuous line. The arrow shows the insula and the relative position of the IFG and the insula. The sagittal plane is most useful for distinguishing the border between these 2 structures.
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Fig 7. The PreCS (shown with a blue line on the left panel) defines the posterior border of the MFG (in red). The left panel shows an example of this sulcus segmented into 2 pieces; the arrow indicates the exact location of the interruption. In such cases, we connected the segments with a line following the natural course of the sulcus.
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Fig 8. SOCs computed for the same rater who marked 5 subjects twice show the intra-rater variability for each individual scan and region. Bars are grouped by left and right brain region, and subjects are color-coded.
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Fig 9. SOCs for the 2 different raters show the spatial overlap across all 5 subjects, averaged for the marked regions left and right. The different subjects are color-coded.
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Fig 10. A comparison of the markings of the SFG by the same rater (rows 1 and 2) and the second rater (row 3). The first column shows high rater agreement. The second column (last panel) shows a relative overestimation of the inferior extent of the SFG.
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Fig 11. Results on 2 subjects (left and right). The segmentation of the subject in the first column shows good spatial overlap between raters. The tracing on the subject in the second column shows significant variability in the definition of the depth of the left IFG.
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