 The investigators propose to enroll 20 volunteers in this pilot study, including males older than 20 years and postmenopausal women in two groups: Group 1: Individuals who had a gadolinium-enhanced MRI study within 1-4 weeks before participation and Group 2: Individuals who had gadolinium-enhanced MRI study within 3-6 months before enrollment. The results will inform future analyses of gadolinium retention, excretion, and potential symptoms associated with same. 