Hemodynamic response changes in cerebrovascular disease: implications for functional MR imaging

Area of Science:

• Neuroimaging
• Cerebrovascular Medicine
• Functional Magnetic Resonance Imaging

Background:

• Cerebrovascular occlusive disease can cause compensatory vascular changes, leading to reduced reactivity.
• These vascular alterations can significantly impact the blood oxygen level-dependent (BOLD) signal used in functional MR imaging (fMRI).

Purpose of the Study:

• To investigate the BOLD signal in patients with unilateral cerebrovascular disease.
• To assess the clinical utility of fMRI in this patient population.

Main Methods:

• fMRI was performed on healthy volunteers and patients using block and event-related designs during a motor task.
• Hemodynamic response curves were generated, and vascular reserve was assessed using transcranial Doppler ultrasonography.

Main Results:

• Event-related fMRI revealed decreased BOLD signal amplitude and delayed hemodynamic responses in the motor cortex ipsilateral to cerebrovascular stenosis.
• Block design fMRI showed decreased BOLD amplitude but no significant temporal differences.
• Transcranial Doppler ultrasonography confirmed diminished vascular reserve ipsilateral to the lesion.

Conclusions:

• Event-related and block fMRI paradigms differ in sensitivity to cerebrovascular alterations.
• Changes in vascular autoregulation and compliance directly affect the BOLD contrast essential for fMRI.
• fMRI is a valuable clinical tool, but results in patients with cerebrovascular disease require careful interpretation.