Patent ID: 8175667

Claim:
A sensor comprising: a substantially annular housing configured to be disposed about a patient's finger, the annular housing being bisected by an imaginary line into a first semicircular region and a second semicircular region; a first source of electromagnetic radiation coupled to the first semicircular region of the annular housing, and configured to operate at a first wavelength; a second source of electromagnetic radiation coupled to the first semicircular region of the annular housing, and configured to operate at a second wavelength; a third source of electromagnetic radiation coupled to the first semicircular region of the annular housing, and configured to operate at a third wavelength, wherein the second source is positioned between the first and third sources along a circumference of the annular housing; and a photodetector coupled to the second semicircular region of the annular housing, and configured to receive electromagnetic radiation from the first, second and third sources after the electromagnetic radiation has passed through blood-perfused tissue of the patient's finger; wherein the photodetector is positioned generally opposite from the second source along the circumference of the annular housing, the first and third sources are generally symmetrically disposed about an axis that bisects the second source and the photodetector, the first, second and third sources are the only sources of electromagnetic radiation coupled to the annular housing, and the photodetector is the only detector coupled to the annular housing.