Effect of intravoxel incoherent motion on diffusion parameters in normal brain
At very low diffusion weighting the diffusion MRI signal is affected by intravoxel incoherent motion (IVIM) caused by dephasing of magnetization due to incoherent blood flow in capillaries or other sources of microcirculation. While IVIM measurements at low diffusion weightings have been frequently used to investigate perfusion in the body as well as in malignant tissue, the effect and origin of IVIM in normal brain tissue is not completely established. We investigated the IVIM effect on the brain diffusion MRI signal in a cohort of 137 radiologically-normal patients (62 male; mean ageâ€¯=â€¯50.2â€¯Â±â€¯17.8, rangeâ€¯=â€¯18 to 94). We compared the diffusion tensor parameters estimated from a mono-exponential fit at bâ€¯=â€¯0 and 1000â€¯s/mm2 versus at bâ€¯=â€¯250 and 1000â€¯s/mm2. The asymptotic fitting method allowed for quantitative assessment of the IVIM signal fraction f* in specific brain tissue and regions. Our results show a mean (median) percent difference in the mean diffusivity of about 4.5 (4.9)% in white matter (WM), about 7.8 (8.7)% in cortical gray matter (GM), and 4.3 (4.2)% in thalamus. Corresponding perfusion fraction f* was estimated to be 0.033 (0.032) in WM, 0.066 (0.065) in cortical GM, and 0.033 (0.030) in the thalamus. The effect of f* with respect to age was found to be significant in cortical GM (Pearson correlation ÏÂ =Â 0.35, pÂ =Â 3*10-5) and the thalamus (Pearson correlation Ïâ€¯=â€¯0.20, pâ€¯=â€¯0.022) with an average increase in f* of 5.17*10-4/year and 3.61*10-4/year, respectively. Significant correlations between f* and age were not observed for WM, and corollary analysis revealed no effect of gender on f*. Possible origins of the IVIM effect in normal brain tissue are discussed.
Visualizing Fluorescence: Using a Homemade Fluorescence "Microscope" to View Latent Fingerprints on Paper
We describe an inexpensive handheld fluorescence imager (low-magnification microscope), constructed from poly(vinyl chloride) pipe and other inexpensive components for use as a teaching tool to understand the principles of fluorescence detection. Optical filters are used to select the excitation and emission wavelengths and can be easily interchanged to accommodate different fluorescent samples. As a demonstration, we used the fluorescence imager to view lawsone-dyed fingerprints on paper, which fluoresce red when illuminated with green light. This emission can be seen by viewing the sample through the instrument by eye, or the fluorescence can be captured by a camera. The entire imager can be built for less than $300.
Effect of the postictal state on visual-spatial memory in immature rats
Postictal cognitive impairment following seizures can last from minutes to days and be disabling to the patient. The purpose of this study was to compare the behavioral features of seizures with postictal memory impairment in young seizure-naive rats and rats with a prior history of status epilepticus (SE) and examine the relationship between postictal EEG changes and cognitive recovery. Following training in the water maze to asymptote levels of learning, rats with a prior history of SE and seizure-naive rats had flurothyl-induced generalized seizures and time to recovery to baseline was then measured. Following generalized seizures rats had impaired performance in the water maze with the duration of the cognitive deficits exceeding the length of the seizure. There was not a close relationship between duration of cognitive impairment and either latency to onset of seizure or duration. The animal's neurological status was a factor in the duration of cognitive impairment following seizures; while there were no differences between SE and seizure-naive rats in latency to seizure onset or duration of the seizures, animals with a prior history of SE had a longer period of impairment following a seizure than animals without such a history. Postictal cognitive impairment was associated with changes in theta activity in animals with a prior history of SEs but not in seizure-naive animals. Caffeine, when administered following the seizure, reduced postictal cognitive impairment in a dose-dependent manner. This study demonstrates that duration of postictal cognitive impairment is not directly related to duration of the seizure. The neurological status of the animal is a determining factor in duration of postictal impairment.
Lack of cell loss following recurrent neonatal seizures
In the neonatal rat recurrent seizures have been associated with long-term changes in cerebral excitability and cognition. Whether recurrent seizures in the neonatal rat lead to cell loss in the cerebral cortex is not known. We counted cells in the parietal cortex, piriform cortex, and CA3 and CA1 hippocampal subfields in young adult rats that had undergone a series of 55 seizures during the first 12 days of life. There were no differences in cell counts between the controls and rats subjected to neonatal seizures. Like the hippocampus, the neonatal pririform and parietal cortex is resistant to seizure-induced cell loss.