Biomedical subjects

Saeid Taheri

Publications and source records attributed to Saeid Taheri.

3 recordsLinked to original sources

PubMed2007

Quantitative evaluation of the effect of propylene glycol on BBB permeability.

PURPOSE: To establish the blood-brain barrier (BBB) blocking property of propylene glycol (PG) using the (14)C sucrose technique, quantitatively evaluate the effect of PG on BBB permeability using an MRI technique based on graphical analysis, and demonstrate the sensitivity of MRI for testing newer investigational drugs. MATERIALS AND METHODS: Brain uptake of sucrose was measured in treated (PG+) and untreated (PG-) rats using a (14)C sucrose technique in rat brains (N = 10) that had undergone two hours of middle cerebral artery occlusion (MCAO) and three hours of reperfusion. Another group of PG+ and PG- rats (N = 8) underwent MRI. T2-weighted (T2W) and diffusion-weighted (DW) images were acquired on a 4.7T MR system. A rapid T1 mapping protocol was implemented to acquire a baseline data set followed by postinjection data sets at regular intervals. The data were postprocessed pixelwise to generate permeability coefficient color maps. RESULTS: A significant (P < 0.05) reduction in (14)C sucrose space was observed on the ischemic side of PG+ rats only. Permeability coefficient estimates obtained by MRI from the ipsilateral hemisphere in PG+ rats were significantly lower than those in PG- rats (P < 0.05). There was no significant change on the contralateral side in PG+ rats. The results show that PG protects the BBB in ischemic stroke, and MRI measurements are sufficiently sensitive to noninvasively detect small drug effects. CONCLUSION: MRI is useful for evaluating the BBB blocking effect of PG in an ischemic stroke model of rat brain. The results from the MR experiment agree well with findings from the (14)C sucrose technique.

Analysis of Variance↗

PubMed2006

Kalman filtering for reliable estimation of BBB permeability.

INTRODUCTION: The blood-brain barrier (BBB) plays an important role in the pathophysiology of a number of central nervous system disorders. In the past, a number of laboratory techniques have been proposed to quantify permeability coefficient ki, an important index of barrier function. Recently, magnetic resonance imaging (MRI) has been used to estimate ki based on graphical plot technique. The MR technique was found to be in good agreement with the gold standard, quantitative autoradiography (QAR). However, a reduced image signal-to-noise ratio, among other factors such as partial volume effects, did not allow reliable estimation of permeability coefficients. This proof-of-principle study proposes the use of Kalman filter as a filtering technique for a reliable estimation of permeability coefficients. The results are compared to those obtained using the Wiener filter technique. MATERIALS AND METHODS: MRI experiments were performed in Wistar rats (N=2) using a 4.7-T Bruker Biospec MR system (Bruker Biospin, Billerica, MA). After acquiring localizer images, T2-weighted diffusion-weighted imaging images were acquired. Finally, a rapid T1 mapping protocol was implemented to acquire one pre-gadolinium diethylenetriamine pentaacetic acid baseline data set followed by postinjection data sets at 3-min intervals for 45 min. Data were postprocessed with and without the application of Kalman and Wiener filters to obtain an estimate of ki. RESULTS AND DISCUSSION: Comparing T1 maps, Patlak plots and permeability maps with and without the Kalman filtering presented several interesting observations. Kalman-filtered Patlak plots, compared to nonfiltered plots, showed that discrete data points on the plot were closer to the line fit. The number of time points used for the construction of the graphical plot had no effect on permeability coefficient estimates when the Kalman filter was used. A box-and-whiskers plot showed longer Y-error bars for nonfiltered and Wiener data compared to Kalman-filtered data. These observations suggest that it may be possible to obtain reliable permeability coefficient estimates in a short study time by applying the Kalman filter to the data. Future work involves investigating the application of this filter on a large-sample-size animal study and evaluating the role of partial volume effects on BBB permeability estimation.

Animals↗

PubMed2005

Spin-lock MRI with amplitude- and phase-modulated adiabatic waveforms: an MR simulation study.

INTRODUCTION: Image contrast between tissue types can be generated based on their T1/T2 ratio using spin-lock MRI techniques. An interesting application of such a concept would be to generate contrast in tissue with tissue relaxation times modified using exogenous contrast agents. An amplitude-modulated adiabatic waveform has been shown in the past to perform spin-lock MRI. However, implementation of this waveform may not prove to be efficient and practical in research or a clinical setup due to high radiofrequency power deposition. Recent advancement in software and hardware MR technology allows implementation of amplitude- and phase-modulated adiabatic waveforms on MR systems. The aim of this work was to explore role of adiabatic waveforms in performing rho imaging and demonstrate that amplitude- and phase-modulated waveforms [e.g., hyperbolic secant, B1 independent rotation-4 (BIR-4) waveforms] can be used to distinguish materials that differ in T1/T2 ratio. METHODS AND RESULTS: MR simulation was performed using computer routines implemented in MATLAB environment (Mathworks, Natick, MA). Modified Bloch equations with trapezoidal, hyperbolic secant and BIR-4 waveforms were used to perform MR simulation. Trapezoidal waveforms were only used for comparison to other waveforms. Gadolinium DTPA (Gad-DTPA) (T1/T2 approximately 1) and manganese chloride (MnCl(2)) (T1/T2 approximately 10) were used as examples of contrast agents due to their routine use in clinical and research setups and more importantly because they provide good examples of materials differing in T1/T2 ratios. Results of spin locking using trapezoidal waveform agree very well with the previously published results, thereby validating the computer routines used in this MR simulation. Plots of M(rho) (magnetization vector in rho domain) vs. offset frequency show distinct curves for these materials differing in T1/T2 for the three waveforms. BIR-4 waveform demonstrated a 40% difference in M(rho) ( approximately 150 Hz) for the materials. Rate of spin lock with hyperbolic secant waveform was rapid compared to other waveforms. DISCUSSION: MR simulation using contrast agents Gad-DTPA and MnCl(2) provided a useful way to demonstrate that amplitude- and phase-modulated adiabatic waveforms can be used to perform spin-lock imaging. Future work involves implementation of these waveforms on MR scanners and performing in vivo imaging to generate tissue contrast based on relaxation times ratio.

Computer Simulation↗