Alkaline brain pH shift in rodent lithium-pilocarpine model of epilepsy with chronic seizures

Evaluation of Brain Impairment Using Proton Exchange Rate MRI in a Kainic Acid-Induced Rat Model of Epilepsy

PURPOSE

Proton exchange rate (Kex) is a valuable biophysical metric. Kex MRI may augment conventional structural MRI by revealing brain impairments at the molecular level. This study aimed to investigate the feasibility of Kex MRI in evaluating brain injuries at multiple epilepsy stages.

PROCEDURES

Six adult rats with epilepsy induced by intra-amygdalae administration of kainic acid (KA) underwent MRI experiment at 11.7 T. Two MRI scans, including T1 mapping and CEST imaging under three B1 amplitudes of 0.75, 1.0, and 1.5 μT, were conducted before and 2, 7, and 28 days after KA injection. Quasi-steady-state analysis was performed to reconstruct equilibrium Z spectra. Direct saturation was resolved using a multi-pool Lorentzian model and removed from Z spectra. The residual spectral signal (ΔZ) was used to construct the omega plot of (1-ΔZ)/ΔZ as a linear function of 1/ ω 1 2 , from which Kex was quantified from the X-axis intercept. One-way ANOVA or two-tailed paired student's t-test was employed with P < 0.05 as statistically significant.

RESULTS

All animals exhibited repetitive status epilepticus with IV to V seizure stages after KA injection. At day 28, Kex values in the hippocampus and cerebral cortex at the surgical hemisphere with KA injection were significantly higher than that at the time points of control and/or day 2 in the same regions (P < 0.01). Moreover, the values were significantly higher than that in respective contralateral regions at day 28 (P < 0.02). No substantial changes of Kex were seen in bilateral thalamus or contralateral hemisphere among time points (all P > 0.05).

CONCLUSIONS

Kex increase significantly in the cerebral cortex and hippocampus at the surgical hemisphere, especially at day 28, likely due to substantial alterations at chronic epilepsy stage. Kex MRI is promising to evaluate brain impairment, facilitating the diagnosis and evaluation of neurological disorders.

3D CEST MRI with an unevenly segmented RF irradiation scheme: A feasibility study in brain tumor imaging

PURPOSE

To integrate 3D CEST EPI with an unevenly segmented RF irradiation module and preliminarily demonstrate it in the clinical setting.

METHODS

A CEST MRI with unevenly segmented RF saturation was implemented, including a long primary RF saturation to induce the steady-state CEST effect, maintained with repetitive short secondary RF irradiation between readouts. This configuration reduces relaxation-induced blur artifacts during acquisition, allowing fast 3D spatial coverage. Numerical simulations were performed to select parameters such as flip angle (FA), short RF saturation duration (Ts2), and the number of readout segments. The sequence was validated experimentally with data from a phantom, healthy volunteers, and a brain tumor patient.

RESULTS

Based on the numerical simulation and l-carnosine gel phantom experiment, FA, Ts2, and the number of segments were set to 20°, 0.3 s, and the range from 4 to 8, respectively. The proposed method minimized signal modulation in the human brain images in the kz direction during the acquisition and provided the blur artifacts-free CEST contrast over the whole volume. Additionally, the CEST contrast in the tumor tissue region is higher than in the contralateral normal tissue region.

CONCLUSIONS

It is feasible to implement a highly accelerated 3D EPI CEST imaging with unevenly segmented RF irradiation.

Numerical simulation-based assessment of pH-sensitive chemical exchange saturation transfer MRI quantification accuracy across field strengths

Chemical exchange saturation transfer (CEST) MRI detects dilute labile protons via their exchange with bulk water, conferring pH sensitivity. Based on published exchange and relaxation properties, a 19-pool simulation was used to model the brain pH-dependent CEST effect and assess the accuracy of quantitative CEST (qCEST) analysis across magnetic field strengths under typical scan conditions. First, the optimal B1 amplitude was determined by maximizing pH-sensitive amide proton transfer (APT) contrast under the equilibrium condition. Apparent and quasi-steady-state (QUASS) CEST effects were then derived under the optimal B1 amplitude as functions of pH, RF saturation duration, relaxation delay, Ernst flip angle, and field strength. Finally, CEST effects, particularly the APT signal, were isolated with spinlock model-based Z-spectral fitting to evaluate the accuracy and consistency of CEST quantification. Our data showed that QUASS reconstruction significantly improved the consistency between simulated and equilibrium Z-spectra. The residual difference between QUASS and equilibrium CEST Z-spectra was, on average, 30 times less than that of the apparent CEST Z-spectra across field strengths, saturation, and repetition times. Also, the spinlock fitting of the QUASS CEST effect significantly reduced the residual errors 9-fold. Furthermore, the isolated APT amplitude from QUASS reconstruction was consistent and higher than the apparent CEST analysis under nonequilibrium conditions. To summarize, this study confirmed that QUASS reconstruction facilitates accurate determination of the CEST system under different scan protocols across field strengths, with the potential to help standardize CEST quantification.

Electrophysiological characterization of a Cav3.2 calcium channel missense variant associated with epilepsy and hearing loss

T-type calcium channelopathies encompass a group of human disorders either caused or exacerbated by mutations in the genes encoding different T-type calcium channels. Recently, a new heterozygous missense mutation in the CACNA1H gene that encodes the Cav3.2 T-type calcium channel was reported in a patient presenting with epilepsy and hearing loss-apparently the first CACNA1H mutation to be associated with a sensorineural hearing condition. This mutation leads to the substitution of an arginine at position 132 with a histidine (R132H) in the proximal extracellular end of the second transmembrane helix of Cav3.2. In this study, we report the electrophysiological characterization of this new variant using whole-cell patch clamp recordings in tsA-201 cells. Our data reveal minor gating alterations of the channel evidenced by a mild increase of the T-type current density and slower recovery from inactivation, as well as an enhanced sensitivity of the channel to external pH change. To what extend these biophysical changes and pH sensitivity alterations induced by the R132H mutation contribute to the observed pathogenicity remains an open question that will necessitate the analysis of additional CACNA1H variants associated with the same pathologies.

Demonstration of fast multi-slice quasi-steady-state chemical exchange saturation transfer (QUASS CEST) human brain imaging at 3T

PURPOSE

To combine multi-slice chemical exchange saturation transfer (CEST) imaging with quasi-steady-state (QUASS) processing and demonstrate the feasibility of fast QUASS CEST MRI at 3T.

METHODS

Fast multi-slice echo planar imaging (EPI) CEST imaging was developed with concatenated slice acquisition after single radiofrequency irradiation. The multi-slice CEST signal evolution was described by the spin-lock relaxation during saturation duration (T_s ) and longitudinal relaxation during the relaxation delay time (T_d ) and post-label delay (PLD), from which the QUASS CEST was generalized to fast multi-slice acquisition. In addition, numerical simulations, phantom, and normal human subjects scans were performed to compare the conventional apparent and QUASS CEST measurements with different T_s , T_d, and PLD.

RESULTS

The numerical simulation showed that the apparent CEST effect strongly depends on T_s , T_d , and PLD, while the QUASS CEST algorithm minimizes such dependences. In the L-carnosine gel phantom, the proposed QUASS CEST effects (2.68 ± 0.12% [mean ± SD]) were higher than the apparent CEST effects (1.85 ± 0.26%, p < 5e-4). In the human brain imaging, Bland-Altman analysis bias of the proposed QUASS CEST effects was much smaller than the PLD-corrected apparent CEST effects (0.03% vs. -0.54%), indicating the proposed fast multi-slice CEST imaging is robust and accurate.

CONCLUSIONS

The QUASS processing enables fast multi-slice CEST imaging with minimal loss in the measurement of the CEST effect.