Blood flow is most commonly measured using ultrasonic probes, with probes measuring either Doppler flowmetry or transit time in order to provide an accurate reading of blood flow, according to the National Institutes of Health. Electromagnetic sensors and probes are also commonly used to read blood flow.
Doppler flowmetry is a measurement of the Doppler shifts in a blood vessel, while a transit time measurement measures flow by basing calculations on how long an ultrasonic wave takes to move through a blood vessel.
Any sensor or probe that measures blood flow must have a number of features essential to the task. Firstly, the sensor or probe needs to be extremely accurate in over the particular flow range of the blood vessels being monitored.
In order to provide the most accurate readings possible, a probe or sensor has to be lightweight, flexible and completely inert to the biological system that is to be monitored so as to not cause disruption to blood flow.
Another way to measure blood flow in the body is by using the reference sample method. This method can be effectively employed to determine blood flow to all regions of the body, while also offering important insight into organ blood flow, much like the sensor and probe method.