Healthy Subjects

Inclusion criteria:

1. Age 18-49
2. No history of hypertension, hyperlipidemia, peripheral artery disease, prior stroke, coronary artery disease, chronic kidney disease, congestive heart failure, dementia, or current tobacco use.

Exclusion criteria:

1. Hemicraniectomy or other skull defect that would interfere with monitoring. 
2. Any other illness or condition that the investigator feels would pose a hazard to the subject from participation in the study
3. Pregnant women* and prisoners are excluded

CCOD SUBJECTS:

Inclusion Criteria:

1. Age ≥ 35
2. Unilateral carotid stenosis or occlusion, defined as any of the following:
   • Carotid ultrasound with a peak systolic velocity >230 cm/s, and either EDV>100 cm/s, or internal to common carotid artery ratio >4.0.
   • CT Angiography showing a ≥70% stenosis per NASCET criteria.
   • MR angiography showing a ≥70% stenosis per NASCET criteria.
   • Digital subtraction angiography with a ≥70% stenosis per NASCET criteria.

Exclusion criteria:

1. Contralateral carotid artery stenosis ≥70% stenosis, using the above definitions
2. Contralateral carotid artery occlusion
3. Prior history of carotid territory ischemic stroke or intraparenchymal hemorrhage at any time
4. History of dementia
5. Hemicraniectomy or other skull defect that would interfere with monitoring. 
6. Any other illness or condition that the investigator feels would pose a hazard to the subject from participation in the study
7. Pregnant women* and prisoners are excluded

SVID SUBJECTS:

Inclusion criteria:

1. Age ≥ 35
2. Cerebral small vessel disease, defined by:
   • Prior lacunar infarction, <15mm in size and with subcortical location
     • AND
   • Confluent or beginning confluent cerebral white matter hyperintensities, corresponding to Fazekas visual rating scale score of 2 or 3 in the periventricular or subcortical white matter on MRI obtained for clinical purposes prior to enrollment.

Exclusion criteria:

1. Prior history of intraparenchymal hemorrhage
2. History of dementia
3. Hemicraniectomy or other skull defect that would interfere with monitoring. 
4. Any other illness or condition that the investigator feels would pose a hazard to the subject from participation in the study
5. Pregnant women* and prisoners are excluded

* Pregnancy Testing: The MRI screening questionnaire will be administered to each patient at the time of check in for the MRI appointment.  The questionnaire will ask each female patient about their “pregnancy” status before each MRI session.  Consistent with clinical care standards, attestation of pregnancy status will be accepted at the time of MRI screening for this study.