Abstract:The purpose of this thesis is to serve as a general introduction to the blood flow physics and blood flow measuring methods, and as a comparative study and analysis for these methods. Blood flow is an important concept in medical field; it represents the function of the heart and the blood vessels of the body. Any abnormality in the heart or blood vessel will be expressed as change in the blood flow velocity from the assumed normal value. Many methods are used to measure the blood flow, some measure the blood flow velocity, some measure the blood perfusion, and some only indicate the presence or absence of blood flow. In this thesis, three blood flow measuring methods were considered to compare between them regarding their medical applications, basic concepts, data analysis, techniques, and mathematical models are done, these methods are Doppler ultrasound flowmeter, Electromagnetic blood flowmeter, and laser Doppler perfusion Flowmeter. A practical study and calculations were done on the Doppler ultrasound system as it is the most available and widely used system. Blood flow velocity was measured in five different blood vessels; the effect of change in transmitter receiver angle on the flow velocity was studied as well as the effect of changing the transmitted ultrasonic wave frequency on the measured velocity. In the electromagnetic blood flowmeter the effect of change in the blood flow velocities in two large arteries on the calculated potential difference of the voltage was studied and discussed, as well as the effect of changing the magnetic field strength on the potential difference; the effect of change in vessel diameter, as in diseased blood vessels, on the measured potential difference and on the flow velocity was also studied and discussed. The electrical circuit was designed for the instrumentation amplifier with a passive low pass filter of the electromagnetic blood flowmeter using MULTISUM (version 7.0) by electronic workbench, the instrumentation amplifier is composed of five fundamental op-amps.The circuit was simulated by entering input voltage and measuring the output voltage, the effect of changing the passive low pass filter frequency on the output signal was studied and discusse d. The last system in the thesis was the Laser Doppler perfusion system, voltage out, which represents the blood perfusion, was calculated and its relation with the shifted Doppler frequency of the laser light was studied and discussed in normal and diseased blood vessels and was compared. All calculations were made using MATLAB package (version 6.5). and the results from this study for these three systems, reveal that Doppler ultrasound system and the Laser Doppler perfusion system depend on the Doppler shift technique, and they are non invasive, but laser Doppler perfusion is limited to the microcirculations, unlike the Doppler ultrasound which can measure any type of blood vessels but need certain transmitting angle. The electromagnetic flowmeter depends on the potential difference, and its use is limited to the arteries around the heart mainly, as any collapse in vessel wall will alter the readings. It is used intra-operatively (i.e. invasive) when patient is under general anesthesia.