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The non-invasive in vivo visualization of the microvasculature of the brain using ultra-high field 7.0T magnetic resonance angiography (MRA) is performed in humans. It may play a major role in the study of small vascular abnormalities, such as the early stages of a cerebral stroke.

• Stroke and Microvascular Study - First observation of the Lenticulostriate Arteries (LSAs) in vivo human

Fig. 1. (A) Anatomical sketch of LSAs, (B) an image obtained by DSA, (C) a MRA image obtained by 7.0T and (D) a MRI image obtained by 1.5T MRI. The vascular details are completely lost in the 1.5T image suggesting that high field MRI is uniquely capable of visualizing the small vascular structures like LSAs.

The 7.0T MRI has an increased T1 and decreased T2, which provides a higher contrast between blood vessel and tissue, thereby drastically increasing the direct measurement of small vessels. We have investigated whether 7.0T MRA images of the LSAs are superior to the images obtained by standard DSA(Digital Subtraction Angiography) or conventional angiography in a young patient with a history of cerebellar arteriovenous malformation (AVM; Stroke 2008; MRM 2009). The 7.0T MRA image depicted a substantially clearer and more distinct LSAs pattern compared with that of the 1.5T MRA (see Fig. 1).

Functional MRI (fMRI) is a well-known technique for the study of brain function. The source signal depends on the levels of deoxyhemoglobin, but is also affected by blood flow and volume, as well as oxygen extraction and utilization rate. In order to investigate hemodynamic responses, we have examined the brain function in vivo by directly measuring the changes of the individual blood vessels with external stimulation.An example of the experiment is shown in Fig. 2. An imaging slab was selected to investigate vascular changes during visual stimulation using a simple block design. Vascular changes were observed during visual stimulation (Neuroimage 2008). The arrows indicate the targeted vessels that supply blood to the occipital lobe, showing the maximum changes observed during the task (see Figure 2).

Fig. 2. Change of cerebral vasculature that supplies the visual cortex during visual stimulation.

• fMRA - A new high Resolution fMRI?

Fig. 3. Comparison of fMRA and fMRI. The substantially improved spatial resolution of fMRA encourages numerous applications of this technique in the area of cognitive neuroscience in the future.

We have utilized the unique advantages of ultra-high-field 7.0T MRI to visualize specific arterial changes in human brains that are concurrent with neuronal stimulation, thus resulting in “functional MR angiography” (fMRA). The results of our studies demonstrate that activation foci obtained with fMRA at 7.0T were more tightly confined to gray matter parenchymal areas when compared to conventional fMRI (Fig. 3). fMRA yields an order of magnitude superior spatial resolution when compared with the conventional fMRI at a comparable temporal resolution. The fMRA technique, therefore, could essentially provide a new method of localizing neuronal activation sites by arterial blood-weighted functional brain imaging. This technique appears to have substantially improved the spatio-temporal resolution over existing venous-weighted techniques, such as blood oxygenation level dependent (BOLD) fMRI. This fMRA, possible only with 7.0T or Ultra high field MRI, could potentially compliment the existing BOLD fMRI, providing new information hitherto unavailable.

• References

- Cho, Z.H., Kang, C.K., Han, J.Y., Kim, S.H., Kim, K.N., Hong, S.M., Park, C.W., Kim, Y.B., 2008. Observation of the Lenticulostriate Arteries in the Human Brain in-vivo using 7.0T MR Angiography. Stroke 39, 1604-1606.
- Cho, Z.H., Kang, C.K., Han, J.Y., Kim, S.H., Park, C.A., Kim, K.N., Hong, S.M., Park, C.W., Kim, Y.B., 2008. Functional MR angiography with 7.0 T Is direct observation of arterial response during neural activity possible? Neuroimage 42, 70-75.
- Kang, C.K., Park, C.W., Han, J.Y., Kim, S.H., Park, C.A., Kim, K.N., Hong, S.M., Kim, Y.B., Lee, K., Cho, Z.H., 2009. “Imaging and Analysis of Lenticulostriate Arteries using 7.0 Tesla Magnetic Resonance Angiography”. Magn. Reson. Med. 61:1:136-144..

• Research Interests

Ultra High Field 7T MR Angiography
Small Vessel Diseases
Functional MRA
Functional Venography
Brain Function