Fluid flow measurement systems and methods

A system comprising:

• a catheter assembly including an intravascular measuring device comprising an intravascular ultrasound imaging probe having a measurement module configured to emit and receive energy and generate ultrasound measurement data, the catheter assembly configured to introduce a quantity of fluid into a vessel of a patient;
• and
• a measurement engine in communication with the intravascular measuring device comprising at least one processor, the measurement engine configured to:
• receive the ultrasound measurement data from the intravascular measuring device;
• generate, using the at least one processor, a speckle density value based on the ultrasound measurement data, the speckle density value corresponding to a concentration of structure in the vessel that is too small to be resolved by the intravascular ultrasound imaging probe, wherein when the quantity of fluid is introduced into the vessel the speckle density value is relatively high compared to the speckle density value when the intravascular ultrasound imaging probe is surrounded by the quantity of fluid;
• determine a fluid flow travel start time associated with an introduction of the quantity of fluid into a predetermined portion of the vessel;
• determine a fluid flow travel end time as being when the speckle density crosses a first predetermined speckle density threshold using the at least one processor;
• calculate, using the at least one processor, an elapsed fluid flow travel time based on the fluid flow travel start time and the fluid flow travel end time;
• and
• calculate, using the at least one processor, a flow rate of the quantity of fluid through the vessel based on the elapsed fluid flow travel time and a travel distance of the quantity of fluid during the elapsed fluid flow travel time.