Related Experiment Videos
Temporal and regional changes during focal ischemia in rat brain studied by proton spectroscopic imaging and
W Dreher1, B Kühn, M L Gyngell
1Universität Bremen, Germany.
Abstract:
The early development of focal ischemia after permanent occlusion of the right middle cerebral artery (MCA) was studied in six rats using interleaved measurements by diffusion-weighted NMR imaging (DWI) of water and two variants of proton spectroscopic imaging (SI), multiecho SI (TE: 136, 272, 408 ms) and short TE SI (TE: 20 ms). Measurements on a 4.7-T NMR imaging system were performed between the control phase and approximately 6 h postocclusion. In the center of the ischemic lesion of all rats, the apparent diffusion coefficient (ADC) decreased rapidly to 84.4 +/- 4.2% (mean +/- SD) of the control values approximately 2 min postocclusion. Approximately 6 h postocclusion, the ADC was reduced to 67.1 +/- 5.9%. In contrast, large differences between the animals were observed for the temporal increase of lactate (Lac) in the ipsilateral hemisphere. The maximum Lac signal was reached in four rats after 0.5-1.5 h, and in two rats was not reached even after 6 h postocclusion. Six h postocclusion, SI spectra measured at a TE of 136 ms revealed a decrease in the CH3 signal of N-acetylaspartate (NAA) to 67 +/- 13% of the control values. Differences were observed between the spatial regions of decreased NAA and increased Lac. In the lesions, a T2 relaxation time of Lac of 292 +/- 40 ms, considering a J-coupling constant of 6.9 Hz, was measured. Furthermore, a prolongation of the T2 of the CH3 signal of creatine/phosphocreatine (Cr/PCr) was observed in the lesion, from 163 +/- 22 ms during control to 211 +/- 41 ms approximately 6 h postocclusion. The experiments proved that DWI and proton SI are valuable tools to provide complementary information on processes associated with brain infarcts.
Insights
Diffusion-weighted imaging and proton spectroscopic imaging reveal early changes in brain infarcts. These techniques provide complementary information on water diffusion and metabolite levels during focal ischemia.
Area of Science:
- Neuroscience
- Medical Imaging
- Biochemistry
Background:
- Focal ischemia, such as stroke, involves rapid cellular changes.
- Understanding early events in ischemic lesions is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the early development of focal ischemia using advanced NMR imaging techniques.
- To assess the complementary information provided by diffusion-weighted imaging (DWI) and proton spectroscopic imaging (SI).
Main Methods:
- Used interleaved DWI and proton SI (multiecho and short TE) in rats with middle cerebral artery occlusion.
- Measurements were performed on a 4.7-T NMR system up to 6 hours postocclusion.
- Analyzed apparent diffusion coefficient (ADC), lactate (Lac), N-acetylaspartate (NAA), and creatine/phosphocreatine (Cr/PCr) levels.
Main Results:
- ADC rapidly decreased within 2 minutes postocclusion, further reducing by 6 hours.
- Lactate levels increased, with variable temporal profiles across animals.
- N-acetylaspartate decreased, showing spatial differences from lactate accumulation.
- T2 relaxation times of lactate and creatine/phosphocreatine were measured and showed alterations.
Conclusions:
- DWI and proton SI are valuable tools for studying early ischemic processes.
- These techniques provide complementary insights into water diffusion and metabolic changes in brain infarcts.
- The findings highlight the dynamic metabolic and diffusion changes occurring in the early stages of focal ischemia.