A new venographic imaging method has been developed to probe brain function. The method relies on the changes induced in the MR signal in venous blood caused by the blood oxygenation level dependent (BOLD) effect from the presence of de-oxyhemoglobin. These changes cause a signal loss in the MR images due to the cancellation of venous blood with surrounding brain parenchyma. When this signal loss is examined as a function of echo time it reveals a unique signature, a non-exponential decay, indicative of the state of oxygen saturation and venous blood volume in the tissue. In this proposal, we plan to use a high resolution 3D version of this BOLD venographic (HRBV) method to cover a large region of interest in the brain. Specifically, we wish to understand the roles of intravascular and extravascular effects in causing this signal loss as a function of vessel size, oxygen saturation and field strength. Given this knowledge, we will attempt to predict both venous oxygen saturation and venous blood volume. This capability will be used under a number of physiologically challenged states in the brain using oxygen, and diamox. It is expected that a robust 3D methodology will be developed and validated to make this approach generally viable for clinical utility in the future. As part of this goal, we will revisit the quantification of oxygen saturation and blood volume measurements using a T1 reducing contrast agent. This will lead to higher quality images and improved accuracy and precision. Finally, we will test a new approach to functional brain imaging which offers the advantage of having a reduced sensitivity to field distortion and its associated signal loss when very long echo times are used. Today, refined techniques exist to handle many of the key experimental issues needed to accomplish these goals. The success of this research may offer a better means to evaluate brain function in fMRI experiments, to diagnose occult venous lesions, to study tumors and other vascular related diseases.
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