Spin-echo MRI underestimates functional changes in microvascular cerebral blood plasma volume using exogenous...

Area of Science:

• Neuroimaging
• Biophysics
• Vascular Biology

Background:

• Functional MRI (fMRI) commonly uses gradient-echo (GE) signals for detecting brain activity.
• Spin-echo (SE) imaging is an alternative but often shows lower sensitivity.
• Understanding the comparative detection power of GE and SE imaging with exogenous contrast agents is crucial for optimizing fMRI studies.

Purpose of the Study:

• To compare the detection power of spin-echo (SE) and gradient-echo (GE) imaging for functional changes in microvascular cerebral blood plasma volume (CBV) using exogenous contrast agents in fMRI.
• To investigate the influence of basal CBV levels on the ratio of functional changes between GE and SE methods.
• To determine the optimal imaging method for contrast-enhanced fMRI.

Main Methods:

• In vivo functional MRI experiments were conducted on rat brains using both GE and SE sequences with an exogenous contrast agent.
• Measurements of functional changes in cerebral blood plasma volume (fCBV) were compared between GE and SE signals.
• The relationship between basal CBV values and the GE to SE ratio of fCBV was analyzed.

Main Results:

• SE methods systematically underestimated functional CBV changes compared to GE methods.
• In vivo SE-CBV responses were approximately 40% smaller than GE-CBV responses at low basal CBV.
• Higher basal CBV correlated with larger vessel sizes and a decreased GE to SE ratio of fCBV, suggesting the presence of large, less reactive vessels.

Conclusions:

• Gradient-echo (GE) imaging is generally the preferred method for contrast-enhanced fMRI due to its higher sensitivity in detecting functional CBV changes.
• Spin-echo (SE) methods may offer a more spatially linear representation of neural activity, particularly in regions with high basal CBV like the cortical surface.
• The choice between GE and SE imaging in fMRI depends on the specific research question and the characteristics of the brain regions being studied.