Lecture 5, Bio Physics, HUE AHST, 2024-2025 PDF

BIOPHYSICS FIRST LEVEL 2024-2025 Prepared By Dr. Nermin Ali Dr. Enas Lotfy Lec No. 5 Course Code: FAC-104 Page 1  ULTRASOUND TERMINOLOGY The period: is the time for a sound wave to complet...

BIOPHYSICS FIRST LEVEL 2024-2025 Prepared By Dr. Nermin Ali Dr. Enas Lotfy Lec No. 5 Course Code: FAC-104 Page 1  ULTRASOUND TERMINOLOGY The period: is the time for a sound wave to complete one cycle; the period unit of measure is the microsecond (µs). Wavelength: is the length of space over which one cycle occurs; it is equal to the travel distance from the beginning to the end of one cycle. Frequency: is the number of cycles repeated per second and measured in hertz (Hz). Acoustic velocity: is the speed at which a sound wave travels through a medium. It is equal to the frequency times the wavelength.  𝟏 Speed c is determined by: 𝒄 = (𝜿/𝝆)𝟐 density (ρ): is the concentration of a medium. Stiffness (κ): is the resistance of a material to compression. Propagation speed increases if the stiffness is increased or the density is decreased. The average propagation speed in soft tissues is 1540 m/s (ranges from 1400 to 1640 m/s). Ultrasound waves have a self-focusing effect, which refers to the natural narrowing of the ultrasound beam at a certain travel distance in the ultrasonic field.  Acoustic impedance z is the degree of difficulty demonstrated by a sound wave being transmitted through a medium; it is equal to density ρ multiplied by acoustic velocity c (z = ρc). It increases if the propagation speed or the density of the medium is increased. All materials (tissues) will present an impedance to the passage of sound waves.  Interactions of Ultrasound with Tissues The attenuation coefficient: is the parameter used to estimate the decrement of ultrasound amplitude in certain media as a function of ultrasound frequency. The attenuation coefficient increases with increasing frequency; therefore, a practical consequence of attenuation is that the penetration decreases as frequency increases.  Interactions of Ultrasound with Matter Ultrasound interactions are determined by the acoustic properties of matter. As ultrasound energy propagates through a medium, interactions include reflection, refraction, scattering, and absorption. Reflection occurs at tissue boundaries where there is a difference in the acoustic impedance of adjacent materials. Refraction describes the change in direction of the transmitted ultrasound energy with non- perpendicular incidence.  Scattering occurs by reflection or refraction, usually by small particles within the tissue medium, causes the beam to diffuse in many directions, and gives rise to the characteristic texture and gray scale in the acoustic image. Absorption is the process whereby acoustic energy is converted to heat energy, whereby, sound energy is lost and cannot be recovered.  Component of US Apparatus The Ultrasound instrument consists of a high-frequency generator. This is connected to a treatment head or transducer circuit by a co-axial cable for the production of ultrasound waves.  Ultrasound is produced and detected with a transducer, comprised of one or more ceramic elements with electromechanical properties and peripheral components. The ceramic element converts electrical energy into mechanical energy to produce ultrasound and mechanical energy into electrical energy for ultrasound detection.  Interactions of Ultrasound with Tissues As the ultrasound wave travels through tissues, it is subject to several interactions. The most important features are as follows: 1. Reflection 2. Scattering 3. Refraction When ultrasound encounters boundaries between different media, part of the ultrasound is reflected and the other part is transmitted.  Medical ultrasound Ultrasound imaging (sonography) uses high-frequency sound waves to view inside the body. Because ultrasound images are captured in real-time, they can also show movement of the body's internal organs as well as blood flowing through the blood vessels. Unlike X-ray imaging, there is no ionizing radiation exposure associated with ultrasound imaging.  In an ultrasound exam, a transducer (probe) is placed directly on the skin or inside a body opening. A thin layer of gel is applied to the skin so that the ultrasound waves are transmitted from the transducer through the gel into the body.  The ultrasound image is produced based on the reflection of the waves off of the body structures. The strength (amplitude) of the sound signal and the time it takes for the wave to travel through the body provide the information necessary to produce an image.  Uses Ultrasound imaging is a medical tool that can help a physician evaluate, diagnose and treat medical conditions Common ultrasound imaging procedures include: Abdominal ultrasound (to visualize abdominal tissues and organs) Bone sonometer (to assess bone fragility) Breast ultrasound (to visualize breast tissue) Doppler fetal heart rate monitors (to listen to the fetal heart beat)  Doppler ultrasound (to visualize blood flow through a blood vessel, organs, or other structures) Echocardiogram (to view the heart) Fetal ultrasound (to view the fetus in pregnancy) Ultrasound-guided biopsies (to collect a sample of tissue) Ophthalmic ultrasound (to visualize ocular structures Ultrasound-guided needle placement (in blood vessels or other tissues of interest) Benefits/Risks  Ultrasound imaging has been used for over 20 years and has an excellent safety record. It is based on non-ionizing radiation, so it does not have the same risks as X-rays or other types of imaging systems that use ionizing radiation. Although ultrasound imaging is generally considered safe when used prudently by appropriately trained health care providers, ultrasound energy has the potential to produce biological effects on the body. Ultrasound waves can heat the tissues slightly. In some cases, it can also produce small pockets of gas in body fluids or tissues (cavitation).  The long-term consequences of these effects are still unknown. Because of the particular concern for effects on the fetus, organizations such as the American Institute of Ultrasound in Medicine External Link Disclaimer have advocated prudent use of ultrasound imaging in pregnancy. Furthermore, the use of ultrasound solely for non-medical purposes such as obtaining fetal ‘keepsake’ videos has been discouraged. Keepsake images or videos are reasonable if they are produced during a medically-indicated exam, and if no additional exposure is required. Information for Patients including Expectant Mothers For all medical imaging procedures, the FDA recommends that patients talk to their health care provider to understand the reason for the examination, the medical information that will be obtained, the potential risks, and how the results will be used to manage the medical condition or pregnancy. Because ultrasound is not based on ionizing radiation, it is particularly useful for women of child-bearing age when CT or other imaging methods would otherwise result in exposure to radiation. Expectant Mothers Ultrasound is the most widely used medical imaging method for viewing the fetus during pregnancy. Routine examinations are performed to assess and monitor the health status of the fetus and mother. Ultrasound examinations provide parents with a valuable opportunity to view and hear the heartbeat of the fetus, bond with the unborn baby, and capture images to share with family and friends.  In fetal ultrasound, three-dimensional (3D) ultrasound allows the visualization of some facial features and possibly other parts such as fingers and toes of the fetus. Four-dimensional (4D) ultrasound is 3D ultrasound in motion. While ultrasound is generally considered to be safe with very low risks, the risks may increase with unnecessary prolonged exposure to ultrasound energy, or when untrained users operate the device.  Expectant mothers should also be aware of concerns with purchasing over- the-counter fetal heartbeat monitoring systems (also called doptones). These devices should only be used by trained health care providers when medically necessary. Use of these devices by untrained persons could expose the fetus to prolonged and unsafe energy levels, or could provide information that is interpreted incorrectly by the user. Or Page 20  Thank You Course Code: FAC-104 Page 21