A morphometric magnetic resonance method for measuring cranial, facial and brain characteristics for application to schizophrenia: part 1

Automated analysis of craniofacial morphology using magnetic resonance images

Quantitative analysis of craniofacial morphology is of interest to scholars working in a wide variety of disciplines, such as anthropology, developmental biology, and medicine. T1-weighted (anatomical) magnetic resonance images (MRI) provide excellent contrast between soft tissues. Given its three-dimensional nature, MRI represents an ideal imaging modality for the analysis of craniofacial structure in living individuals. Here we describe how T1-weighted MR images, acquired to examine brain anatomy, can also be used to analyze facial features. Using a sample of typically developing adolescents from the Saguenay Youth Study (N = 597; 292 male, 305 female, ages: 12 to 18 years), we quantified inter-individual variations in craniofacial structure in two ways. First, we adapted existing nonlinear registration-based morphological techniques to generate iteratively a group-wise population average of craniofacial features. The nonlinear transformations were used to map the craniofacial structure of each individual to the population average. Using voxel-wise measures of expansion and contraction, we then examined the effects of sex and age on inter-individual variations in facial features. Second, we employed a landmark-based approach to quantify variations in face surfaces. This approach involves: (a) placing 56 landmarks (forehead, nose, lips, jaw-line, cheekbones, and eyes) on a surface representation of the MRI-based group average; (b) warping the landmarks to the individual faces using the inverse nonlinear transformation estimated for each person; and (3) using a principal components analysis (PCA) of the warped landmarks to identify facial features (i.e. clusters of landmarks) that vary in our sample in a correlated fashion. As with the voxel-wise analysis of the deformation fields, we examined the effects of sex and age on the PCA-derived spatial relationships between facial features. Both methods demonstrated significant sexual dimorphism in craniofacial structure in areas such as the chin, mandible, lips, and nose.

Landmark-based software for anatomical measurements: a precision study

The aim of this study was to develop a software program, called Landmarker, which would aid studies of complex anatomical morphometry by simplifying the manual identification of landmarks in 3D images. We also tested its precision on routine magnetic resonance imaging (MRI) scans. To understand human biological variation, there is a need to identify morphological characteristics from the exterior and the interior of human anatomy. MRI, as opposed to other radiographic methods (mainly based on X-ray techniques), supplies good soft tissue contrast, which allows for more complex assessments than what bony landmarks can provide. Because automation of this assessment is highly demanding, one of the primary goals for the new software was to enable more rapid identification of landmark sets in 3D image data. Repeat acquisition of head MRIs having a resolution of 0.94 x 0.94 x 1.20 mm3 were performed on 10 volunteers. Intra- and interoperator, as well as interacquisition variations of manual identification of exterior, craniofacial interior, and brain landmarks were studied. The average distances between landmarks were <1.8 mm, <2.3 mm, and <2.0 mm in the intra- and interoperator, and interacquisition evaluations, respectively. This study presents new software for time efficient identification of complex craniofacial landmarks in 3D MRI. To the best of our knowledge, no evaluation of software for rapid landmark-based analysis of complex anatomies from 3D MR data has yet been presented. This software may also be useful for studies in other anatomical regions and for other types of image data.

A pilot study of facial, cranial and brain MRI morphometry in men with schizophrenia: part 2

This pilot study applies a new 3D morphometric MR method to test the hypothesis that men with schizophrenia (vs. controls) have deviant facial shapes and landmark relations in cranio/facial/brain (CFB) regions. This constitutes Part 2 of paired articles in this issue of Psychiatry Research: Neuroimaging, in which Part 1 presents the new method in detail. MRI coordinates from CFB landmarks of 23 patients and 15 controls were identified and then aligned with the Procrustes model, leaving shape as the only unit-less geometrical information. Men with schizophrenia had significantly longer mid- and lower-facial heights, and greater lower (left) facial depth, with a tendency toward rotation along the facial midline. This supports findings from earlier anthropometric and 3D studies of the "exterior" (face). In contrast, none of the patient-control differences for the new "interior" (cranial-brain) distances reached statistical significance. These results need to be retested on a larger sample of both sexes.