An apparatus includes a sensor body, a circuit board, a cable, at least one light emitting device, and at least one photodetector. The circuit board is enclosed within the sensor body and includes at least one conductive trace and at least one aperture. The cable is coupled to the at least one conductive trace. The cable includes a shield conductor and a signal conductor. The at least one light emitting device is coupled to the circuit board and is configured to emit light into a tissue. The at least one photodetector includes a planar active area coupled to the circuit board and is configured to provide an output signal based on light detected by the active area. The planar active area is aligned with the aperture. The output signal is coupled to the cable.
