Biomedical subjects

Ralph Myers

Publications and source records attributed to Ralph Myers.

5 recordsLinked to original sources

PubMed2007

Statistical neuroanatomy of the human inferior frontal gyrus and probabilistic atlas in a standard stereotaxic space.

We manually defined the inferior frontal gyrus (IFG) on high-resolution MRIs in native space in 30 healthy subjects (15 female, median age 31 years; 15 male, median age 30 years), resulting in 30 individual atlases. Using standard software (SPM99), these were spatially transformed to a widely used stereotaxic space (MNI/ICBM 152) to create probabilistic maps. In native space, the total IFG volume was on average 5%, and the gray matter (GM) portion 12% larger in women (not significant). Expressed as a percentage of ipsilateral frontal lobe volume (i.e., correcting for brain size), the IFG was an average of 20%, and the GM portion of the IFG 27%, larger in women (P < 0.005). Correcting for total lobar volume yielded the same result. No asymmetry was found in IFG volumes. There were significant positional differences between the right and left IFGs, with the right IFG being further lateral in both native and stereotaxic space. Variability was similar on the left and right, but more pronounced anteriorly and superiorly. We show differences in IFG volume, composition, and position between sexes and between hemispheres. Applications include probabilistic determination of location in group studies, automatic labeling of new scans, and detection of anatomical abnormalities in patients.

Adult↗

PubMed2004

Evolution of microglial activation in patients after ischemic stroke: a [11C](R)-PK11195 PET study.

We obtained [11C](R)-PK11195 PET scans in six patients at different time points between 3 and 150 days after onset of ischemic stroke in order to measure the time course of microglial activation. Increased [11C](R)-PK11195 binding around the lesion was observed as early as 3 days. Scans at later time points showed ongoing changes in the distribution of the [11C](R)-PK11195 signal, involving the area of the primary lesion and areas distant from the primary lesion site. Our data suggest that [11C](R)-PK11195 PET can be used to investigate both the primary lesion and remote pathological changes following Wallerian degeneration.

Adult↗

PubMed2003

Three-dimensional maximum probability atlas of the human brain, with particular reference to the temporal lobe.

Probabilistic atlases of neuroanatomy are more representative of population anatomy than single brain atlases. They allow anatomical labeling of the results of group studies in stereotaxic space, automated anatomical labeling of individual brain imaging datasets, and the statistical assessment of normal ranges for structure volumes and extents. No such manually constructed atlas is currently available for the frequently studied group of young adults. We studied 20 normal subjects (10 women, median age 31 years) with high-resolution magnetic resonance imaging (MRI) scanning. Images were nonuniformity corrected and reoriented along both the anterior-posterior commissure (AC-PC) line horizontally and the midsagittal plane sagittally. Building on our previous work, we have expanded and refined existing algorithms for the subdivision of MRI datasets into anatomical structures. The resulting algorithm is presented in the Appendix. Forty-nine structures were interactively defined as three-dimensional volumes-of-interest (VOIs). The resulting 20 individual atlases were spatially transformed (normalized) into standard stereotaxic space, using SPM99 software and the MNI/ICBM 152 template. We evaluated volume data for all structures both in native space and after spatial normalization, and used the normalized superimposed atlases to create a maximum probability map in stereotaxic space, which retains quantitative information regarding inter-subject variability. Its potential applications range from the automatic labeling of new scans to the detection of anatomical abnormalities in patients. Further data can be extracted from the atlas for the detailed analysis of individual structures.

Adult↗

PubMed2002

Small animal PET.

Positron emission tomography (PET) has well-established strengths which are commonly exploited in human clinical research. Not least of these are its dynamic and quantitative capabilities. The recent growth in small animal PET, spurred on by technological developments and an interest in the application of imaging to the field of genomics in mice, has seen impressive improvements in image spatial resolution. The availability of commercial small animal PET scanners has meant a broadening of the user base away from PET development environments and into experimental laboratories. This paper will review these developments and assess the impact on overall data quality.

Animals↗

PubMed2002

The application of PET-MR image registration in the brain.

The coregistration in three-dimensional space of positron emission tomography (PET) and magnetic resonance (MR) image volumes has, over the last decade, become a matter of routine in the analysis of brain PET studies. The ability to objectively localize small regions of interest in PET using images more closely correlated to tissue structure has itself improved the effective resolution of PET. There are a number of highly effective software packages for image coregistration available in the public domain. Voxel-by-voxel coregistration, involving little or no intervention from the user can, on today's computing hardware, provide fast and accurate registration with little or no pre-processing and algorithms based on mutual information measures now seem to be the mathematical method of choice. Registration may be applied in a number of ways. Rigid body registration is used to match a single subject's brain scanned using either different imaging modalities or as serial scans with the same modality. Increasingly, this technique is being extended to studies of disease involving regional atrophy, where location and extent of tissue loss can be identified. Non-linear registration can be used to warp a subject's brain onto a template, atlas or other standardized guide. While numerous examples are available of the added value produced by image registration in the brain, similar examples are not yet available from registration in the torso, where the problem is much more complex. It is here that newly emerging hardware such as combined PET/CT scanners may prove their worth.

Algorithms↗