Sound in Medicine 2024 PDF

Sound in Medicine 2024 DR.ENTIDHAR ALTAEE Topics of the Lecture Characteristics of sound wave.  Refection and transmission  Intensity level ratio.  Applications of sound in medicine  Percussion and Stethoscope Principle of Sonar US generation US Generation Production of US image ...

Sound in Medicine 2024 DR.ENTIDHAR ALTAEE Topics of the Lecture Characteristics of sound wave.  Refection and transmission  Intensity level ratio.  Applications of sound in medicine  Percussion and Stethoscope Principle of Sonar US generation US Generation Production of US image  Image quality US imaging modes  Physiological effects of US General properties of sound A sound wave is the pattern of disturbance caused by the energy traveling away from the source of the sound (waves transfer energy without transferring matter). Sound, a mechanical disturbance from a state of equilibrium that propagates through an elastic material medium with some definite velocity. In air it can be defined as a local increase (compression) or decrease (rarefaction) of pressure relative to atmospheric pressure.   A sound is a vibration that propagates through a medium in the form of a mechanical wave. The medium in which it propagates can either be a solid, a liquid or a gas. Sound travels fastest in solids, relatively slower in liquids and slowest in gases. In general, the sound speed is given by: Where : frequency λ: the wavelength of the sound waves.  The number of rarefactions and compressions that occur per unit time is known as the frequency of a sound waves. Mathematically, the frequency of a wave is denoted as follows: f=1/T  The distance between the successive compression and rarefaction is known as the wavelength of a sound wave. The wavelength is mathematically represented as follows Homework Q1: Which sound wave will have its crests farther apart from each other - a wave with frequency 100 Hz or a wave with frequency 500 Hz? Q2: If the velocity of sound is 330 meters per second (msˉ¹ what will be wavelength if the frequency is 1 KHz?  Sonic spectrum  Sonic spectrum can be classified (depending on the frequency of the wave) into three frequency ranges: infrasound, audible sound and ultrasound (rarefaction) of pressure relative to atmospheric pressure  Sonic spectrum  The human ear can hear sounds in the range of roughly 20 Hz to 20 KHz.  Infrasound: Refers to sound frequencies below the normal hearing range or less than 20Hz. It is produced by natural phenomena like earthquake waves and atmospheric pressure changes. Infrasonic effect on human body: It can travel long distances without losing much power due to its low absorption and large wavelength and also, it can travel through most media, making its effects difficult to minimize. Hence, Intense infrasonic noise is observed to produce clear symptoms including respiratory impairment and aural pain. Other effects may include Fear, Visual Hallucinations, chills.  Infrasonic may also be used in the study of heart mechanical function, revealed by the seismocardiogram (is the measure of the micro-vibrations which are signals in the infrasonic range produced by the heart contraction and blood ejection into the vascular tree.  Ultrasound; Is the frequency range above 20KHz. Ultrasound is used clinically in a number of specialties. It often gives more information than an X-ray and it is less hazardous for the fetus.  Intensity of a Sound Wave  The intensity I of a sound wave is the energy carried by the wave per unit area and per unit time (in units W/). It may be expressed by the maximum change in pressure; as following: Z acoustic impedance of the medium. Acoustic impedance (Z) =  Sound Intensity Level [Ratio] The absolute value of sound intensity (I) cannot be measured, instead we can compare it with a reference intensity; (I ) Where 0 Intensity ratio=  Effect the nature of sound on human hearing The human ear can distinguish two characteristics of sound.  Loudness: (or volume) is the degree of sensation of sound produced in the ear. It depends on its intensity.  Pitch: The pitch of a sound refers to whether it is high (sharp).  Sound Reflection and transmission: When the sound wave is applied in a perpendicular way on the interface between two media which have different acoustic impedance (Z1 and Z2) a portion of this wave will pass through and another one reflect (large difference in Z → high reflection ratio. The ratio of reflected; Iref (or transmitted; Itran) and the incident waves (Iin) can be measured as following, If Z1 = Z2 There is no reflected wave and transmission to the second medium is complete. If Z2 ˂ Z1 The sign change indicates a phase change of reflected wave. If ∆Z large High reflection &low transmission Mismatching. Application s of audible sound in medicine https://youtu.be/1JKXf5osCHE  :Stethoscope.2 Stethoscopes are diagnostic instruments that amplify sounds made by the body from the heart, lungs, or other body sites. Modern stethoscope consists of, bell which closed by a thin diaphragm, tubing and earpieces. The bell serves as impedance matcher between body and the air in the tube. This requires that the frequency of the sounds must resonate in the bell membrane. The natural frequency Fres of the bell depends on diameter(d) and tension T of the diaphragm as following: To selectivity pick up certain frequency ranges (low frequency heart murmur, high frequency lung sounds) the appropriate bell size and diaphragm tension must be chosen. Ultrasound waves Ultrasound is sound with a frequency 20kHz to 1GHZ (for medical applications). It is greater than the upper limit of human hearing.  SONAR (SOund NAvigation and Ranging)-  US Generation Piezoelectric principle  The ultrasound signal is generated and detected by the sensor. The transducer based on piezoelectric principle. Many crystals can be used so that AC voltage (electrical energy) across the crystal will produce a vibration of the crystal (mechanical energy), thus generating an ultrasound wave and vice versa.  In clinical application the piston is represented by the transducer, when an electric potential difference is applied between the faces of a piezoelectric crystal, the crystal will respond by expanding or contracting. The push– pull action of the transducer causes regions of compression and rarefaction, pass out from the transducer face into the tissue. SONAR - It is a device that uses an US waves to generate an image of a particular soft tissue structure in the body. Transducers Types Transducer - Converts electrical energy to mechanical (ultrasound) energy and vice versa. There are many types of transducers which are different in frequency and foot print:  Basic Principle of SONAR  In medical diagnosis, ultrasound pulses are transmitted into the body by placing the US transducer in close contact with the skin, using water or a jelly paste to eliminate the air and create a good impedance matching between the transducer and skin. The backed echoes are detected as a weak signal amplified and displayed on an oscilloscope.  US Image Production Three concepts that are affects US image production:  1. Focal zone  2. Acoustic impedance  3. Refraction Focal zone Acoustic impedance When an ultrasound wave encounters a boundary between two tissues with different values of Z, a certain fraction of the wave energy is backscattered (or reflected) towards the transducer, with the remainder being transmitted through the boundary is common deeper intoathe to use bodyliquid (jelly) thick between the transducer and the patients skin. The thick liquid helps to keep away air bubbles and allows easy passage of the ultrasound waves (small Az). Refraction It is a change in direction of the sound wave as it passes from one tissue to a tissue of higher or lower sound velocity. To minimize refraction the artifacts (errors) in US US transducer should be image due to the change in perpendicular to the the US wave path. interface between the two media.  Quality of ultrasound imaging The quality of ultrasound imaging is determined by the interaction of the acoustic wave with the body tissue, these interactions includes: spatial resolution, attenuation and reflection and transmission. spatial -1 resolution Quality of ultrasound imaging Attenuation: of the ultrasound beam as it propagates through tissue is the sum of absorption and scattering from small structures. Attenuation is characterized by an exponential decrease in both the pressure and intensity of the ultrasound beam as a function of its propagation distance, z, through tissue: It is the reduction in intensity (I) of US wave as it passes through the tissue (x). Image Quality The choice of the ultrasound is determined by a compromise between good resolution and deep penetration. Reflection Perpendicular reflection originates the echo signal, while non-perpendicular reflection causes an intensity loss in echo signal, as shown in the figure. Smooth surface → low scattering → good image Rough surface → high scattering → bad image  Type of US Image Modes A-Mode (1D) : It is used to obtain diagnostic information about the depth of structure (image with 1-dimention).  In this mode an US waves send into the body and measure the time required to receive the reflected sound (echoes) from the interface between the different tissues. The depth of the interface recorded is proportional to the time it takes for the echo to return. Depth= Velocity x time  Using a sound velocity of 1540 m/sec in average soft tissue, the echo takes 13 µsec at a depth of 1 cm  A-mode is used to detect the brain tumors and eye diseases.  :Applications of A- mode scan A.Echo encephalography: It is used in the detection of brain tumors.  Pulses of ultrasound are sent to a thin region of the skull above the ear and the echoes from different structures are displayed on the oscilloscope.  Compare the echoes from the left side of the head to the right side, and find the shift in the middle structure: - If the shift > 3 mm for an adult (abnormal) If the shift > 2 mm for a child (abnormal)  :Opthalmology  Application of A scan in ophthalmology can be divided into two areas:-  The first one is concerned with obtaining information for diagnosis of the eye disease.  Second :It is used in biometry (measurement of distance in the eye such as the lens thickness, depth from cornea to lens, the distance to the retina and the thickness of the vitreous tumor. It is used ultrasound frequencies of up to 20 MHz, this high frequency is used because: produce better resolution since there is no bone to absorb most of the energy and absorption is not significant because the eye is small US Image Modes B-Mode (2D) It is used to obtain 2D images of the body. The principle is the same as in A-mode except that transducer is moving. A storage oscilloscope is usually used to form the image. B-mode is providing information about the internal structure of the body, such as size, location and change with time of the eye, liver, breast, heart, and fetus.  US Image Modes M- Mode (2D +motion) It is used to study motion such as that of heart and heart valves (image with 2D + motion). M-mode combines between features of A- and B-mode. The transducer is held stationary as in A-mode and the echoes appear as dots as in B-mode. It is used in diagnostic information about the heart (mitral valve) and US Image Modes D- Mode (3D + motion; or 4D): D- Mode takes 3-dimentionanl US images and adds the element of time to the process (image with 3D with motion).  Physiological effects of ultrasound in therapy Various physiological and chemical effects occur when ultrasonic waves pass through the body, and they can cause physiological effects. The magnitude of physiological effects depends on the frequency and amplitude of the sound.  Low intensity US (~ 0.01 W/cm²) → no harmful effects are observed → used for diagnostic work (as in the sonar). Continues US (~1 W/cm²) → deep heating effect (diathermy) → temperature rise due to the absorption of acoustic energy in the tissue. Continues US (1-10 W/cm²) → sound moves through→ region of compression and rarefactions → pressure differences in adjacent regions of tissues (micromassage). Continues US (~ 35 W/cm²) →tissue destroying effect → rupture DNA molecules. Continues and focused US (~ 10³ W/cm²) → selective destroying of deep tissue using a focused ultrasound beam.