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SLAC National Accelerator Laboratory

The Elements of Stroke
SSRL Science Summary - September 2012

Figure 1.
Correlation between XRF iron maps and MR imaging. Ischemic lesions are outlined.

Rapid diagnosis and treatment is essential to limiting stroke damage. Yet, despite decades of research into the causes and effects of this devastating disease, stroke is still the fourth leading cause of death in the United States and drains the national economy of more than 50 billion dollars per year. Now the Synchrotron Medical Imaging Team, a group of Canadian, US, and European scientists (including scientists from the Stanford Synchrotron Radiation Lightsource) are using SSRL's x-ray facilities as well as the Canadian Light Source to answer key questions that affect the health and recovery of stroke patients.

There are actually two major categories of stroke: hemorrhagic, caused by a broken artery or vein leaking blood into the brain tissue, and ischemic, in which a blockage in a blood vessel starves part of the brain of oxygen. Clinical imaging of the brain is an important tool in diagnosing both types of stroke and following changes in the damaged area over time. For example, the collaborators used SSRL's x-ray fluorescence (XRF) rapid scanning Beam Line 10-2 in parallel with magnetic resonance imaging (MRI) at Wayne State University to map and quantify iron and calcium on the same slices of human brain, thus confirming which MR sequences could best distinguish the excess iron associated with small hemorrhages. SSRL's XRF imaging Beam Lines 2-3 and 10-2 are also being used to determine if that excess iron, caused by the breakdown of hemoglobin has a role in disrupting the delicate chemical balance that keeps brain cells alive.

Ischemic stroke, caused by a clot or a narrowing that prevents the flow of blood through a vessel, also disturbs normal brain chemistry, but in different ways. While specific neurons in the brain are susceptible to ischemia, the chemistry behind this vulnerability is unknown. The SMI team used Beam Lines 10-2 and 2-3 to integrate XRF mapping of sulfur and other key elements like zinc and potassium with traditional biochemical and histological methods, to paint a clearer neurochemical "picture" of the biochemical pathways through which therapies for ischemic stroke could minimise brain damage.

Finally, SSRL Beam Line 4-3 was used to determine the speciation of sulfur within the brain; one finding demanding further investigation is that levels of taurine (an abundant amino acid for which the neurological role remains unknown) correlate to neuron density within specific brain regions. However, this trend is only observed when flash-frozen, unfixed brain tissue is analyzed, highlighting sample preparation as a crucial aspect for studying chemical speciation and distribution within the brain. Future work at BL 4-3 will focus on identifying alterations in the distribution of taurine, as well as other sulfur species (for example, thiols and disulfides), as a consequence of ischemic stroke.


Primary Citation

W. Zheng, E. M. Haacke, S. M. Webb and H. Nichol, "Imaging of Stroke: A Comparison between X-ray Fluorescence and Magnetic Resonance Imaging Methods", Magn. Reson. Imaging (published online, July 11, 2012) doi: 10.1016/j.mri.2012.04.011

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Sam Webb (SSRL) and Helen Nichol (University of Saskatchewan)

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