Using Near-Infrared Light to Better Understand Peripheral Artery Disease

Inclusion Criteria: * Cases, Aim 1 1. 18 or older 2. willing to participate under the conditions described in the informed consent form (ICF) 3. eligible to sign the ICF 4. established diagnosis of PAD confirmed by a physician 5. able to comply with the study requirements * Cases, Aim 2 1\) completed Aim 1 * Controls 1) asymptomatic, with no history or diagnosis of peripheral artery disease Exclusion Criteria: * Cases, Aim 1 1. Ankle-Brachial Index \>0.9 or \<0.4 2. isolated disease in aorta/iliac vessels 3. unstable angina or myocardial infarction in past 12 months 4. orthopedic or other physical limitations which would prevent data collection 5. contraindications to MRI, including presence of a Pacemaker, presence of bone growth/ bone fusion stimulators, presence of tissue expander, presence of cochlear implants, unable to ambulate for 10 feet, receiving continuous Oxygen therapy, pregnancy, permanent Jewelry (screened using MRI safety screening form and verbal screening by MRI operator * Cases, Aim 2 1. unstable angina or myocardial infarction in past 12 months 2. orthopedic or other physical limitations which would prevent data collection 3. contraindications to MRI, including presence of a pacemaker, presence of bone growth/ bone fusion stimulators, presence of tissue expander, presence of cochlear implants, unable to ambulate for 10 feet, receiving continuous Oxygen therapy, pregnancy, permanent Jewelry (screened using MRI safety screening form and verbal screening by MRI operator). * Controls 1) history of peripheral artery disease 2) overt cardiovascular disease (e.g. heart failure) 3) known pulmonary disease (excluding mild asthma) 4) current tobacco use 5) orthopedic or other physical limitations which would prevent data collection, 6) BP \>150/90 mmHg at screening 7) contraindications to MRI, including presence of a pacemaker, presence of bone growth/ bone fusion stimulators, presence of tissue expander, presence of cochlear implants, unable to ambulate for 10 feet, receiving continuous Oxygen therapy, pregnancy, permanent Jewelry (screened using MRI safety screening form and verbal screening by MRI operator).