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Blood-oxygen-level-dependent MRI allows metabolic description of tissue at risk in acute stroke patients
Benjamin S Geisler1, Frank Brandhoff, Jens Fiehler
1Department of Neuroradiology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany. b.geisler@uke.uni-hamburg.de
Background And Purpose:
The delineation of the "penumbra" is of particular interest in acute stroke imaging. The "mismatch concept" applying perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) appears to be an oversimplification of the underlying electrophysiological tissue status. An additional parameter reflecting the metabolic state of the threatened brain tissue would improve our ability to describe the penumbra. One candidate is deoxyhemoglobin (deoxy-Hb) as an indicator of the oxygen extraction fraction that can be visualized by T2*-based blood oxygen level-dependent (BOLD) imaging.
Methods:
We analyzed data from 32 patients with acute stroke in the territory of the middle cerebral artery. MRI included fluid-attenuated inversion recovery, DWI, PWI, time-of-flight angiography, and quantitative T2 and T2* (qT2, qT2*) imaging. Follow-up was performed on day 1 and days 5 to 8. We calculated 1/T2'=1/qT2*-1/qT2. Changes of T2', representing the deoxy-Hb effect, were analyzed by 3D regions of interest (ROIs): apparent diffusion coefficient lesion day 0 (L0), time-to-peak-lesion day 0 (T0), final infarct size days 5 to 8 (F5-8), lesion growth (LG; F5-8-L0), and surviving tissue (ST; T0-F5-8).
Results:
We observed a clear decrease of T2' in the infarcted hemisphere compared with the unaffected control ROIs. The mean value showed the most pronounced loss of T2' signal intensity in L0 (-15.7%), followed by LG (-10.5%) and ST (-8.0%).
Conclusions:
The implementation of BOLD imaging in acute stroke MRI offers a noninvasive estimation of the O2 utilization and is able to add additional information concerning the present metabolic state of the threatened brain tissue. The changes in T2' intensity are visually noticeable in the reconstructed T2' images and provide a better estimation of the real penumbra.
Insights
Blood oxygen level-dependent (BOLD) imaging using T2* can assess oxygen utilization in acute stroke. This method provides a better estimation of the penumbra, improving stroke assessment beyond traditional perfusion and diffusion imaging.
Area of Science:
- Neuroimaging
- Stroke Imaging
- Medical Physics
Background:
- The penumbra in acute stroke imaging is critical for treatment decisions.
- Current methods like perfusion-weighted imaging (PWI) and diffusion-weighted imaging (DWI) may oversimplify tissue status.
- Assessing the metabolic state of threatened brain tissue is needed.
Purpose of the Study:
- To evaluate deoxyhemoglobin (deoxy-Hb) as a marker of oxygen extraction fraction using T2*-based BOLD imaging.
- To improve the description of the penumbra in acute stroke.
- To investigate the utility of quantitative T2' imaging in stroke patients.
Main Methods:
- Analyzed MRI data from 32 acute middle cerebral artery stroke patients.
- Included fluid-attenuated inversion recovery, DWI, PWI, time-of-flight angiography, and quantitative T2/T2* imaging.
- Calculated 1/T2' and analyzed changes in T2' signal intensity in various regions of interest.
Main Results:
- Observed decreased T2' signal intensity in the infarcted hemisphere compared to controls.
- The most significant T2' signal loss was in the initial lesion (L0), followed by lesion growth (LG) and surviving tissue (ST).
- Mean T2' signal intensity changes were -15.7% in L0, -10.5% in LG, and -8.0% in ST.
Conclusions:
- BOLD imaging offers noninvasive estimation of oxygen utilization in acute stroke.
- T2' imaging provides additional information on the metabolic state of threatened brain tissue.
- Changes in T2' intensity enhance the estimation of the true penumbra.
