Figure 1: SNR/anatomic merged data for a patient with an arteriovenous malformation (AVM) lesion in the brain. Top (A)- The AVM is indicated by a white arrow. Bottom (B)- BOLD sensitivity map of the same slice.
Figure 2: BOLD signal changes and corresponding colors.
The signal detected in functional magnetic resonance imaging (fMRI) is on the order of a one percent signal change. Time series data with a high signal-to-noise ratio (SNR) is required to reliably detect these changes. This project is developing a model to determine the minimum required signal-to-noise ratio necessary for detecting the expected signal change.
The immediate benefits are clinical, addressing the neurosurgeon’s need to know if a region of brain near a lesion is active. Knowing the signal-to-noise characteristics allows one to make a more informed decision about the derived functional maps, which is of use to neuroscientists as well.
The result is a blood oxygen level dependent (BOLD) sensitivity map that depicts the minimum BOLD signal level that can be detected given the experimental parameters and statistical requirements.
In Figure 1, the colored image (B) represents the minimum detectable BOLD signal change, a BOLD sensitivity map. The colors correspond to different BOLD signal changes as seen in the Figure 2 chart. Notice that in the region of the lesion, a larger signal change is required. In this brain tissue, the BOLD signal changes may not meet this requirement. The implication is that these regions cannot be investigated with the stringent statistical threshold.
For more information, read The Impact of Signal to Noise on Functional MRI (Printer friendly PDF version – 1.27 MB) by Todd B. Parrish, Darren R. Gitelman, Kevin S. LaBar, and M. Marsel Mesulam.