New automated tomography imaging process speeds up whole-brain mapping

January 18, 2012
STP tomography

STP tomography (credit: Timothy Ragan et al./CSHL)

Serial Two-Photon Tomography (STP tomography), a new technology developed by neuroscientists at Cold Spring Harbor Laboratory (CSHL) and MIT, significantly speeds up the process of acquiring highly detailed anatomical images of whole brains. Until now, the process has been painstakingly slow and available only to a handful of highly specialized research teams.

“The new technology should greatly facilitate the systematic study of neuroanatomy in mouse models of human brain disorders such as schizophrenia and autism,” says CSHL Assoc. Prof. Pavel Osten.

Tomography refers to any process (including the familiar CAT and PET scans used in medical diagnostics) that images an object section by section, by shooting penetrating waves through it.  Computers then produce a 3D rendering (of the brain, in this case). Two-photon imaging is used in biology laboratories in conjunction with fluorescent biomarkers to illuminate specific cell types or other anatomical features. The two-photon method allows deeper optical penetration into the tissue being sampled than conventional confocal microscopy.

STP tomography achieves high-throughput fluorescence imaging of whole mouse brains via robotic integration of the two fundamental steps — tissue sectioning and fluorescence imaging. At 10x magnification of brain tissue samples, the researchers were able to achieve fast imaging at a resolution sufficient to visualize the distribution and morphology of green-fluorescent protein-labeled neurons, including their dendrites and axons, Osten reports.

A full set of data, including final images, could be obtained by the team in 6.5 to 8.5 hours per brain, depending on the resolution.  These sets each were comprised of 260 top-to-bottom (coronal) slices of mouse brain tissue, which were assembled by computer into 3D renderings capable of a wide range of “warping” to reveal hidden structures and features.

“The technology is a practical one that can be used for scanning at various levels of resolution, ranging from 1 to 2 microns to less than a micron,” Osten says.  Scans at the highest resolution level take about 24 hours to collect.  This makes possible an impressive saving of time, Osten says, compared to methods that are now in use, which would take an experienced technician about a week to collect a set of whole-brain images at high resolution.

“What is most exciting about this tool is its application in the study of mouse models of human illness, which we are already doing in my lab,” Osten says.  “We are focusing on making comparisons between different mouse models of schizophrenia and autism.  Many susceptibility genes have been identified in both disorders. Dr. Alea Mills at CSHL has published a mouse model of one genetic aberration in autism — a region on chromosome 16 — and soon we will have tens of models, each showing a different aberration.”

The researchers  conclude that STP tomography is sufficiently mature to be used in whole-brain mapping efforts such as the ongoing Allen Mouse Brain Atlas project. “We will want to compare these mice, and that is essentially why we designed STP tomography — to automate and standardize the process of collecting whole-brain images in which different cell-types or circuit tracings have been performed.  This makes possible comparisons across different mouse models in an unbiased fashion.”

Ref.: Timothy Ragan et al., Serial two-photon tomography: an automated method for mouse brain imaging, Nature Methods, 2012 [doi: 10.1038/nmeth.1854]