US Flashcards
What is ultrasound, and how does it differ from X-rays and CT scans?
- A diagnostic medical imaging technique that uses high-frequency sound waves to produce images of internal organs, tissues, and blood flow.
Key Differences:
- Ultrasound uses sound waves; X-rays and CT use ionizing radiation.
-Ultrasound provides real-time imaging, while X-rays and CT produce static images
What are the key features of ultrasound imaging?
- Real-time Imaging:
Captures both structure and movement (e.g., blood flow, fetal movement). - Non-ionizing:
Safe for repeated use and sensitive populations. - Portable:
Can be used at the bedside for immediate results. - Dynamic:
Excellent for guiding procedures like biopsies.
Explain the difference between compression and rarefaction in sound waves.
Compression:
- High-pressure areas where particles in the medium are pushed closer together.
Rarefaction:
- Low-pressure areas where particles are spread further apart.
How does frequency affect wavelength and image detail in ultrasound?
Frequency:
- The number of sound wave cycles that pass a point in one second.
- Measured in Hertz (Hz).
Relationship in Ultrasound:
- Higher frequency = shorter wavelength = better resolution &image detail but reduced penetration depth.
-transducers are ideal for superficial structures (e.g., muscles, tendons).
- Lower frequency = longer wavelength = deeper penetration but lower resolution and poorer image quality.
-transducers are used for deeper structures (e.g., abdominal organs).
What is amplitude, and how does it relate to the brightness of ultrasound images?
Amplitude:
- The height of the sound wave, representing its energy.
- Higher amplitude = louder sound and brighter echoes on the ultrasound image.
- Lower amplitude = quieter sound and dimmer echoes.
How does the speed of sound vary with temperature, density, and elasticity of a medium?
Temperature:
Higher temperature increases molecular energy, speeding up sound propagation.
Density:
Denser materials (e.g., bone) allow faster sound travel, provided elasticity is high.
Elasticity:
Lower compressibility (higher elasticity) enables faster sound transmission (e.g., sound travels faster in steel than rubber).
Explain the pulse-echo principle used in ultrasound imaging.
- The pulse-echo principle is the foundation of ultrasound imaging.
- The transducer emits short pulses of sound waves, which travel through the body and interact with tissues.
-When these waves encounter a boundary with different acoustic impedance:
—Some waves are reflected back to the transducer.
—–Other waves continue deeper into the body.
- The ultrasound machine measures the time taken for the echoes to return.
- It calculates the distance to the structure using the formula:
- The division by 2 accounts for the round-trip journey of the sound wave (to the tissue and back to the transducer).
- For diagnostic purposes, the speed of sound is assumed to be 1540 m/s in soft tissue.
-The pulse-echo principle allows precise localization of structures within the body by detecting and analyzing the reflected sound waves.
How does acoustic impedance (Z) affect sound wave behavior in tissues?
Acoustic impedance is the resistance a tissue offers to sound waves as they travel through the medium. It depends on two factors:
* Density of the tissue.
* Speed of sound in the tissue.
The formula for acoustic impedance is:
Z=ρc
where Z is impedance, ρ is density, and c is the speed of sound.
Differences in acoustic impedance determine how sound waves behave at tissue boundaries:
* Low Impedance Differences: When tissues have similar acoustic impedance values (e.g., fat and liver), most of the sound wave is transmitted with minimal reflection. This allows the sound wave to travel deeper and produce good-quality images at greater depths. and clarity for structures below the boundary.
* High Impedance Differences: When tissues have very different impedance values (e.g., soft tissue and bone), more of the sound wave is reflected, resulting in stronger echoes and less transmission. This reduces depth penetration and can cause shadowing behind highly reflective structures like bone.
* Air-Tissue Boundary: Air has a significantly higher impedance difference compared to soft tissue. Nearly all the sound waves are reflected, making it difficult to image air-filled structures (e.g., lungs or bowel) without a coupling medium like gel or fluid.
These variations in impedance are critical for image formation, as reflections at boundaries provide the echoes needed to construct ultrasound images.
Define and explain acoustic interfaces and acoustic windows with examples.
How do ultrasound transducers use the piezoelectric effect to produce sound waves?
What are the main types of transducers, and what are their specific applications?
Compare curvilinear, linear, phased array, and endo-transducers in terms of frequency, depth, and field of view.
What are the different ultrasound modes, and what are their applications?
Explain the key features and uses of A-Mode, B-Mode, M-Mode, and Doppler imaging.
What are the differences between power Doppler, colour Doppler, and spectral Doppler?
What is spatial resolution, and how does it differ from axial and lateral resolution?
