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Basic Principles of Ultrasound Imaging Components of an ultrasound machines
i. Ultrasound waves are generated by a transducer that contains piezoelectric crystals.
ii. These crystals convert electrical energy into sound waves and also act as receivers to detect the returning echoes.
ii. Mechanical Effects: Includes cavitation (formation of gas bubbles) and radiation force. These effects are negligible at diagnostic levels.
☺At extreme intensities, ultrasound can induce mechanical and thermal damage.
Threshold: A temperature rise above 41°C for extended periods can cause damage.
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ii. These crystals convert electrical energy into sound waves and also act as receivers to detect the returning echoes.
i. The transducer sends ultrasound waves into the body.
ii. These waves travel through tissues at different speeds depending on their density and elasticity.
iii. When the waves encounter a boundary between different tissues (e.g., fluid and soft tissue, or soft tissue and bone), part of the wave is reflected back to the transducer while the rest continues traveling deeper.
iii. When the waves encounter a boundary between different tissues (e.g., fluid and soft tissue, or soft tissue and bone), part of the wave is reflected back to the transducer while the rest continues traveling deeper.
☺The transducer detects the reflected waves (echoes) and sends this information to a
computer.
☺The time taken for echoes to return helps determine the depth of the structure.
☺The intensity (strength) of the reflected waves determines the brightness of the image.
☺The time taken for echoes to return helps determine the depth of the structure.
☺The intensity (strength) of the reflected waves determines the brightness of the image.
Different tissues have different acoustic properties, leading to varying shades of gray in the ultrasound image.
Anechoic (dark/black): Fluids (e.g., blood, cysts).
Hypoechoic (gray/darker): Soft tissues like muscles.
Hyperechoic (bright/white): Dense structures like bone, calcifications, or fat.
Anechoic (dark/black): Fluids (e.g., blood, cysts).
Hypoechoic (gray/darker): Soft tissues like muscles.
Hyperechoic (bright/white): Dense structures like bone, calcifications, or fat.
☺Doppler ultrasound is used to measure the motion of blood or tissues by detecting changes in frequency due to movement.
☺It helps assess blood flow direction, speed, and abnormalities like blockages.
M-mode (Motion mode): Used for moving structures like the heart.
Doppler mode: Evaluates blood flow dynamics.
3D/4D ultrasound: Provides volumetric imaging, often used in obstetrics.
☺It is considered safe for routine use, including in pregnancy.
☺It helps assess blood flow direction, speed, and abnormalities like blockages.
M-mode (Motion mode): Used for moving structures like the heart.
Doppler mode: Evaluates blood flow dynamics.
3D/4D ultrasound: Provides volumetric imaging, often used in obstetrics.
☺It is considered safe for routine use, including in pregnancy.
A. Diagnostic Ultrasound
Diagnostic ultrasound (such as fetal imaging, echocardiography, and musculoskeletal scans) operates at low intensities and is considered safe. Organizations like the FDA and AIUM (American Institute of Ultrasound in Medicine) have set guidelines to limit exposure.
i. Thermal Effects: Diagnostic ultrasound produces minimal heating of tissues. The rise in temperature is typically below 1°C and considered safe for biological tissues.ii. Mechanical Effects: Includes cavitation (formation of gas bubbles) and radiation force. These effects are negligible at diagnostic levels.
B. Therapeutic Ultrasound
☺Therapeutic ultrasound is used in physiotherapy, cancer treatment, and high-intensity
focused ultrasound (HIFU) for tumor ablation.
☺Higher intensities generate significant heat, which can be used for therapeutic effects but must be carefully controlled to avoid tissue damage.
☺Cavitation effects (microbubble formation and collapse) can be beneficial (e.g., drug
☺Cavitation effects (microbubble formation and collapse) can be beneficial (e.g., drug
delivery) but may also cause cellular damage if uncontrolled.
C. Industrial and Other Applications
☺High-intensity ultrasound is used in cleaning, welding, and non-destructive testing.☺At extreme intensities, ultrasound can induce mechanical and thermal damage.
A. Thermal Effects
Heat Generation: Ultrasound absorption by tissues leads to localized heating. Sensitive tissues like the eyes and developing fetal tissues are more susceptible.Threshold: A temperature rise above 41°C for extended periods can cause damage.
B. Mechanical Effects
☺Cavitation: Formation of gas bubbles in tissues, which can oscillate (stable cavitation) or collapse (inertial cavitation).
☺Stable cavitation is generally safe.
☺Inertial cavitation can cause cell damage if high-intensity ultrasound is used.
☺At therapeutic levels: Can cause controlled cell damage for treatment purposes (e.g.,
☺Stable cavitation is generally safe.
☺Inertial cavitation can cause cell damage if high-intensity ultrasound is used.
➤Types of Cavitation in Ultrasound
1. Stable Cavitation
☺Bubbles oscillate in response to the ultrasound waves but do not collapse.
☺Causes microstreaming, which can enhance fluid movement and increase cellular permeability.
☺Generally safe at diagnostic ultrasound levels.
☺Can be beneficial in therapeutic applications (e.g., breaking kidney stones in lithotripsy).
☺At high intensities, it can damage cells and blood vessels.
☺Radiation Force: Exerts small forces on cells, which may influence biological activity.☺Generally safe at diagnostic ultrasound levels.
2. Inertial (Transient) Cavitation
☺Bubbles grow and collapse violently, releasing energy.
☺Produces high temperatures and strong shock waves, which can cause tissue damage.☺Can be beneficial in therapeutic applications (e.g., breaking kidney stones in lithotripsy).
☺At high intensities, it can damage cells and blood vessels.
D. Biological Responses
☺At diagnostic levels: No confirmed long-term effects on tissues.☺At therapeutic levels: Can cause controlled cell damage for treatment purposes (e.g.,
breaking kidney stones, tumor ablation).
- Follow ALARA Principle: (As Low As Reasonably Achievable) to minimize exposure.
- Monitor Thermal and Mechanical Indices: The TI (Thermal Index) and MI (Mechanical Index) help assess risks.
- Avoid Prolonged Exposure: Especially in fetal imaging.
- Use Trained Operators: Ensuring proper settings and avoiding unnecessary exposure.
