Medical Biophysics Lecture Notes PDF

MEDICAL BIOPHYSICS DR. MAHMOUD ISMAIL LECTURE : SOUND IN MEDICINE PART 1  Sound is a mechanical wave (Cannot travel through Vacuum) that results from the back and forth vibration of the particles of the medium through which the sound wave is moving.  FACTS  Sound is a fo...

MEDICAL BIOPHYSICS DR. MAHMOUD ISMAIL LECTURE : SOUND IN MEDICINE PART 1  Sound is a mechanical wave (Cannot travel through Vacuum) that results from the back and forth vibration of the particles of the medium through which the sound wave is moving.  FACTS  Sound is a form of energy produced by vibration.  Sound travels in longitudinal waves.  Sound travels faster through solids than liquids, gases.  Velocity of sound is temperature dependent. VELOCITY OF THE SOUND  Velocity of the sound is given by : V=λf f= frequency of vibration of the sound wave. λ=wave length of the sound wave.  * The velocity of the sound differs from medium to medium because of the freedom of motion of the molecules in the medium.  The higher the density, the higher is the velocity of the sound. SOUND INTENSITY  The intensity I of a sound wave is the energy passing through 1m2/sec, or watts per square meter. For a plane wave I is given by  Where ρ is the density of the medium; v is the velocity of sound; f is the frequency; ω is the angular frequency, which equals 2πf.  A is the maximum displacement amplitude of the atoms or molecules from the equilibrium position; and Z, is the acoustic impedance.  The intensity can also be expresses as:  Where Po is the maximum change in pressure. TYPES OF SOUND WAVES ULTRASOUND  Ultrasound is sound with a frequency over 20,000 Hz, which is the upper limit of human hearing.  The basic principles and properties are same as that of audible sound  Frequencies used for diagnostic ultrasound are between 1 to 20 MHz  WIDE APPLICATIONS OF ULTRASOUND Principal reasons for its wide application are:  its ease of use,  the relatively low cost of the instrumentation,  and the lack of ionizing radiation. HOW IS ULTRASOUND IMAGING DONE? PIEZOELECTRIC EFFECT  Crystals of tourmaline, quartz, topaz, cane sugar, and Rochelle salt have the ability to generate an electric charge in response to applied mechanical stress  “Piezoelectricity" after the Greek word Piezein, which means to squeeze or press.  Ultrasound gel is a conductive medium that creates a bond between the skin and the ultrasound transducer.  The ultrasound sound waves have a hard time traveling through air, so the gel prevents any extra air space between the probe and your skin in order to create a clear image of the fetus. “FROM SOUND TO IMAGE” BASIS FOR THE USE OF ULTRASOUND IN DIAGNOSIS  It must be remembered that the basis for the use of ultrasound in medicine is the partial reflection of sound at the surface between two media that have different acoustical properties.  The amount of the reflection depends primarily upon the difference in the acoustical impedances of the two materials and the orientation of the surface with respect to the beam.  ULTRASOUND FOR DEEP HEATING (THERAPY)  Ultrasonic heating is used for reliving tightness and scarring occurring in joint disease.  It greatly aids joint that have limited motion.  It can dispose more heat in bones, as bones are better absorber for ultrasonic energy than soft tissue.