Related Experiment Videos
Hemodynamic response changes in cerebrovascular disease: implications for functional MR imaging
Leo M Carusone1, Jayashree Srinivasan, Darren R Gitelman
1Feinberg Clinical Neuroscience Research Institute, Chicago, Illinois, USA.
Insights
Functional MR imaging (fMRI) shows altered blood oxygen level-dependent (BOLD) signals in patients with cerebrovascular disease. Event-related fMRI is sensitive to reduced vascular reactivity and delayed hemodynamic responses, impacting clinical utility.
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.
Background And Purpose:
Patients with cerebrovascular occlusive disease may develop compensatory changes in local cerebral vasculature with a resultant loss of vascular reactivity. These alterations can affect the blood oxygen level-dependent (BOLD) signal that is the basis for functional MR imaging. We investigated the BOLD signal in patients with unilateral cerebrovascular disease to ascertain the clinical utility of functional MR imaging in these patients.
Methods:
Five healthy volunteers and three patients with cerebro-occlusive disease were imaged with both a block and an event-related design of a visually cued bilateral motor task. Activation maps were calculated, and individual hemodynamic response curves were generated for left and right primary motor cortices. Vascular reserve was determined for the relevant vascular territory by using transcranial Doppler ultrasonography (US).
Results:
In the event-related data, the amplitude of the BOLD response was significantly decreased in the motor cortex ipsilateral to the stenosis and showed significant delays in the timing of the hemodynamic response. In contrast, the longer duration stimulus and longer TR of the block design showed significant decreases in the BOLD amplitude but no significant interhemispheric temporal differences. Corroborating the hemodynamic status, transcranial Doppler US analysis showed diminished vascular reserve ipsilateral to the lesion.
Conclusion:
Differences in the results between the event-related and block paradigms reflect the sensitivity to alterations in autoregulation or vascular compliance. These changes in the vasculature directly affect the BOLD contrast underlying functional MR imaging. Thus, while this technique remains a useful clinical tool, caution is warranted when studying patients with cerebrovascular disease.