Systems and methods for measuring a physiological parameter of blood in a patient are provided herein. An example method includes establishing with a magnetic array, an first magnetic field along tissue of the patient inserted into the magnetic array and a second magnetic field perpendicular to the tissue, emitting optical signals into further tissue of the patient during at least a first alignment of the magnetic array around the tissue, detecting characteristics of the optical signals, and identifying a value of a physiological parameter based on at least the characteristics of the optical signals.