Whole-body tissue stabilization and selective extractions via tissue-hydrogel hybrids for high-resolution intact circuit mapping and phenotyping

To facilitate fine-scale phenotyping of whole specimens, we describe here a set of tissue fixation-embedding, detergent-clearing and staining protocols that can be used to transform excised organs and whole organisms into optically transparent samples within 1–2 weeks without compromising their cellular architecture or endogenous fluorescence. PACT (passive CLARITY technique) and PARS (perfusion-assisted agent release in situ) use tissue-hydrogel hybrids to stabilize tissue biomolecules during selective lipid extraction, resulting in enhanced clearing efficiency and sample integrity. Furthermore, the macromolecule permeability of PACT- and PARS-processed tissue hybrids supports the diffusion of immunolabels throughout intact tissue, whereas RIMS (refractive index matching solution) grants high-resolution imaging at depth by further reducing light scattering in cleared and uncleared samples alike. These methods are adaptable to difficult-to-image tissues, such as bone (PACT-deCAL), and to magnified single-cell visualization (ePACT). Together, these protocols and solutions enable phenotyping of subcellular components and tracing cellular connectivity in intact biological networks

Poor Correlation Between Perihematomal MRI Hyperintensity and Brain Swelling After Intracerebral Hemorrhage

BACKGROUND AND PURPOSE: The perihematomal hyperintensity is commonly interpreted to represent cerebral edema following ICH, but the accuracy of this interpretation is unknown. We therefore investigated the relationship between changes in PHH and changes in hemispheric brain volume as a measure of edema during the first week after ICH. METHODS: Fifteen individuals aged 66±13 with baseline hematoma size of 13.1 mL (range 3–43) were prospectively studied with sequential MRI 1.0±0.5, 2.6±0.9, and 6.5±1.0 days after spontaneous supratentorial ICH. Changes in hemispheric brain volume were assessed on MPRAGE using the Brain-Boundary Shift Integral. Hematoma and PHH volumes were measured on T2-weighted images. RESULTS: Brain volume increased a small but statistically significant amount (6.3±8.0 mL, 0.6±0.7%) between the first and second scans relative to 10 normal controls (−0.9±4.1 mL, p=0.02) and returned toward baseline at the third scan (1.5±9.5 mL vs. controls 0.9±4.0 mL, p=0.85). There were no significant differences in the volume changes between the two hemispheres at scan 2 or scan 3. At both scan 2 (p=0.04) and scan 3 (p=0.004), the change in PHH was significantly greater than and poorly correlated with the change in ipsilateral hemispheric volume. There were no significant correlations between change in NIHSS and change in PHH, ipsilateral, or total brain volume at scan 2 or scan 3 (all p> 0.05). CONCLUSIONS: In patients with small-to-moderate-sized hematomas, change in PHH was a poor measure of brain edema in the first week following ICH. A small degree of bihemispheric brain swelling occurred but was of little clinical significance