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AME 60676 Biofluid & Bioheat Transfer

AME 60676 Biofluid & Bioheat Transfer. 6. Biofluid / Bioheat Transfer Measurement Techniques. Objectives. Description of different in vivo, in vitro and in silico techniques to measure the flow and thermal characteristics of blood flow. Outline. Pressure measurement

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AME 60676 Biofluid & Bioheat Transfer

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  1. AME 60676Biofluid & Bioheat Transfer 6. Biofluid/Bioheat Transfer Measurement Techniques

  2. Objectives • Description of different in vivo,in vitro and in silicotechniques to measure the flow and thermal characteristics of blood flow

  3. Outline • Pressure measurement • Blood flow measurement • Impedance measurement • Flow visualization • Ultrasound Doppler velocimetry • Laser Doppler velocimetry • Magnetic Resonance Imaging • Computational fluid dynamics • Photo-acoustics

  4. 1. Pressure Measurement Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  5. Indirect Method • Sphygmomanometer (pressure cuff method) Increase in cuff pressure Error  10 mmHg Collapse of the brachial artery, artery occlusion Cuff pressure higher than blood pressure Decrease in cuff pressure Cuff pressure lower than systolic pressure Systolic pressure Arterial blood release, turbulent flow Korotkoff sound Complete opening of artery, laminar flow Diastolic pressure Cuff pressure decreased futher Cessation of Korotkoff sound Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  6. Direct Method fluid-filled transducer • Catheterization • Transducer sensitivity: • Filling fluid: heparinized saline (prevents blood clots) • Continuous monitoring of blood pressure diaphragm (resistance R) catheter e0: output voltage E: excitation voltage Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  7. 2. Blood Flow Measurement Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  8. Blood Flow Measurement • EMF (electromagnetic flow meter) Voltage generated between electrodes: B: flux density of magnetic field l: spacing between electrodes V: mean flow velocity Volumetric flow rate: Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  9. Blood Flow Measurement • EMF (electromagnetic flow meter) • Pros: • Very accurate for in vitro testing • Cons: • Invasive in vivo technique (vessel must be exposed) • Loss of signal over long in vivo measurement periods (protein and thrombus coating) • Probe lumen area must be precisely known • EMF theory assumes flat velocity profile Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  10. Blood Flow Measurement • Transit Time Flow Meter • Speed of sound wave in fluid depends on fluid velocity • Sound wave (kHz range) transmitted through vessel along flow axis in alternate directions Flow probe with 2 emitting crystals Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  11. Blood Flow Measurement • Transit Time Flow Meter and where: Flow probe with 2 emitting crystals Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  12. Blood Flow Measurement • Transit Time Flow Meter • In vitro flow meters • In vivo flow meters Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  13. 3. Impedance Measurement Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  14. Impedance Measurement • In steady flow model: resistance • In unsteady flow model: longitudinal impedance input impedance Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  15. Impedance Measurement • Longitudinal impedance • Analogous to vascular resistance defined in steady flow • Depends on local vessel properties • Input impedance • Ratio of pressure and flow at a particular site • Depends on local and distal vessel properties longitudinal impedance input impedance Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  16. Impedance Measurement • Depend on Womersley number and elastic tube properties • Complex quantities: • Real part: resistive component • Imaginary part: reactive component • Input impedance measurement: • Simultaneous flow and pressure measurement at one point • Frequency analysis: at each frequency component n: Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  17. Impedance Measurement characteristic impedance Z0 Input impedance in aorta of a dog (left) and human (right) • Input impedance independent of frequency (except at low frequency) • Fluctuations at high frequencies (wave reflection at discontinuities in peripheral arteries, vasoconstriction) Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  18. Impedance Measurement characteristic impedance Z0 Input impedance in aorta of a dog (left) and human (right) • Fluctuation characterization: Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  19. 4. Flow Visualization Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  20. Definition and Objectives • Method: • Visible marker introduced in flow stream • Photographic record of marker movement • Purpose: • general overview of the flow field • identify fine details of flow structures (jets, separation zones, secondary motion) • characterization of the flow stability (laminar vs. turbulent) Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  21. Assumptions • Marker accurately follows the actual flow movement • Requirements: • balance between inertial, viscous, buoyant, gravitational forces acting on marker • No effect of marker on flow  small, neutrally buoyant particles Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  22. Pros / Cons • Pros: • Simple technique • Full-field, real-time information • Cons: • Optically accessible fluid (and model) • Non-quantitative technique Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  23. Pathlines, Streaklines, Streamlines • Pathline: A trajectory of a given fluid particle • Method: solid particles (small, reflective, neutral density) Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  24. Pathlines, Streaklines, Streamlines • Streakline: The locus of particles which have passed a specified (usually fixed) spatial location • Method: colored dye (not appropriate for unsteady or well-mixed flows) Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  25. Pathlines, Streaklines, Streamlines • Streamline: A line drawn tangent to the local velocity vector field at an instant of time Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  26. Other flow visualization techniques • Hydrogen bubble technique • Electrolysis (breakdown of H2O molecules into H2 at a cathode and O2 at an anode) • Pros: • No external markers • Appropriate for high-velocity flows • Cons: • Invasive technique (electrodes must be inserted in the flow) • Fluid must be electrical conductor Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  27. Other flow visualization techniques • Photochromic dye • Use of TNSB mixed into the fluid medium and converted selectively to a colored state upon laser activation • TNSB becomes opaque when exposed to ultraviolet light emitted by nitrogen laser • Pros: • Laser can be positioned at any site of the flow field • Chemical reaction is reversible (no accumulation of dye) • Cons: • TNSB soluble in hydrocarbon-based fluid (e.g., kerosene) Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  28. 5. Ultrasound Doppler Velocimetry Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  29. Principle • Doppler shift: change in frequency is proportional to relative motion between source and observer Nb of peaks received Nb of peaks intercepted Nb of peaks emitted Wave motion between a source and a moving receiver  Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  30. Practical Implementation • Use of sound wave • Transmission + reflection (twice the number of peaks intercepted) • Doppler transducer located outside the body, at an angle with respect to the flow axis • Equation carries information on both velocity magnitude and direction Practical implementation of ultrasound Doppler Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  31. Continuous-Wave Devices • Description: • Transmission of high-frequency sound wave (>1 MHz) • Use of 2 crystals (one emitting continuously and one receiving continuously) Schematic of a continuous-wave ultrasound Doppler device Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  32. Continuous-Wave Devices • Description: • Large sampling volume due to overlap between emitted and received beams • Lack of spatial resolution • Wide spectrum of shifted frequencies due to large number of particles in sampling volume ( averaging or max velocity) overlap region Schematic of a continuous-wave ultrasound Doppler device Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  33. Continuous-Wave Devices • Clinical applications: • Provides maximum velocity along the ultrasound beam (peak signal displayed at a given temporal location on the spectrum) • Maximum pressure drop across heart valves to detect potential stenosis (eliminates limitations of catheterization) • Other advantage: • no maximum velocity limit due to continuous processing MV ejection velocity Continuous-wave spectrum of patient with mitral valve stenosis Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  34. Pulse-Doppler Devices • Description: • Intermittent emission/reception of signal by a single crystal • Provides frequency shit information • Provides exact location of reflective particle (travel time for sound wave) Pulse-Doppler principle Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  35. Pulse-Doppler Devices • Spatial resolution: • depends on length of signal burst sent out • Number of cycles transmitted: n • Length of sample volume: n = n( c / f )  Increased frequency produces higher resolution Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  36. Pulse-Doppler Devices • Limitations: • Maximum range depends on time period between pulses • PRF: pulse repetition frequency (cycle/s) • Returning echo received once every (1/PRF) sec • This imposes condition on maximum detectable Doppler shift (Nyquist sampling limit) Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  37. Pulse-Doppler Devices • Limitations: • PRF imposes condition on maximum detectable Doppler shift (Nyquist sampling limit) • Nyquist criterion: (sampling rate > 2 x signal frequency) • Since  For a given flow or depth, a limited range of velocities can be accurately detected Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  38. Pulse-Doppler Devices • Clinical applications: • Pressure drop across a stenosis • Local velocity profile across a vessel • Local shear stress, wall-shear stress • Residence time • 2D implementation with large array of crystals Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  39. 6. Laser-Doppler Velocimetry Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  40. Principle • Laser light scattered by particles suspended in fluid • Frequency of light reflected from a moving object is shifted by an amount proportional to the speed of the flowing material  Frequency shit provides an estimate for flow velocity Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  41. Principle • Particles are illuminated by a known frequency of laser light • Scattered light is detected by a photomultiplier tube  generates a current in proportion to absorbed photon energy • Doppler shift = incident light frequency – scattered light frequency Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  42. Characteristics • Velocity range: 0 to supersonic • Up to three velocity components • Non-intrusive measurements • Absolute measurement technique (no calibration required) • Very high accuracy • Very high spatial resolution (small probe volume) Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  43. Overview fiber drive laser couplers transceivers Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  44. Laser Beam Generation • Bragg cell divides laser beam into 2 beams (direct + frequency shifted) • Each beam separated into 3 wavelengths Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  45. Laser Beam Generation • 2D transceiver: blue and green, 2 probe volumes • 1D transceiver: purple, 1 probe volume Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  46. Probe Volume • Each color is used for measuring one velocity component • The two probes are aligned so their intersection volumes coincide • The velocity components measured by the beams from the probes are orthogonal Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  47. Probe Volume f: beam focal length d: prefocal beam spacing : half angle of beam intersection : beam wavelength De: initial beam diameter E: beam expansion ratio Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  48. Fringe Pattern • Intersection of coherent fringes • Probe volume is a stable interference pattern characterized by alternating light and dark fringes (from optics theory) Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  49. Fringe Pattern • Moving particle  fluctuations in scattered light intensity • Particle crossing a destructive (dark) fringe: zero light intensity • particle crossing a constructive (bright) fringe: peak in the light signal Typical Doppler burst Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

  50. 7. Magnetic Resonance Imaging Pressure measurement Blood flow measurement Impedance measurement Ultrasound Doppler velocimetry Laser Doppler velocimetry Magnetic resonance imaging Computational fluid dynamics Flow visualization

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