10.2 Diagnostic ultrasound

• Ultrasound waves have a frequency higher than 20 kHz
• What happens to image resolution as the frequency of ultrasound waves increases?

  Increases
• What is the speed of sound in water?

  ~1480 m/s
• Ultrasound waves have a frequency range above 20 kHz.


  True
• The frequency of ultrasound waves is typically above 20 kHz.

  True
• What is acoustic impedance a measure of?

  Resistance to sound flow
• Which tissue has the highest acoustic impedance?

  Bone
• Bone allows high transmission of ultrasound waves due to its high acoustic impedance.

  False
• Steps leading to attenuation of ultrasound waves

  1️⃣ Absorption of wave energy

  2️⃣ Conversion of energy into heat

  3️⃣ Scattering of waves

  4️⃣ Loss of wave intensity
• What is the frequency range of ultrasound waves used in medical imaging?

  Above 20 kHz
• Ultrasound waves can be refracted when passing through interfaces between different media.


  True
• The speed of sound in air is approximately 343 m/s.
• Arrange the media in order of increasing speed of sound:

  1️⃣ Air

  2️⃣ Water

  3️⃣ Soft tissue
• Bone has high acoustic impedance, leading to high reflection and attenuation of ultrasound waves


  True
• Tissues with higher acoustic impedance reflect more of the ultrasound wave, while tissues with lower impedance allow more transmission
• The transducer acts as both a transmitter and a receiver
• Steps in ultrasound image formation

  1️⃣ Transmission: The transducer generates a pulse of high-frequency ultrasound waves.

  2️⃣ Reflection: The waves encounter tissue interfaces and are partially reflected back.

  3️⃣ Reception: The transducer detects the reflected waves and converts them into electrical signals.

  4️⃣ Processing: The electrical signals are processed to determine the time of flight and create the image.
• What determines the degree of reflection and refraction of ultrasound waves at tissue interfaces?

  Acoustic impedance
• What type of wavelengths do ultrasound waves have compared to audible sound waves?

  Shorter
• Higher acoustic impedance differences between tissues result in more reflection of the ultrasound wave.


  True
• What are the two primary causes of attenuation in ultrasound waves?

  Absorption and scattering
• What is the primary cause of attenuation in ultrasound waves?

  Absorption and scattering
• Ultrasound waves have shorter wavelengths and higher frequencies than audible sound waves.


  True
• What are the applications of ultrasound waves?

  Diagnostic imaging and therapy
• Attenuation of ultrasound waves is caused by absorption and scattering
• Match the property of sound waves with its characteristic:

  Frequency range ↔️ > 20 kHz for ultrasound

  Use in medical imaging ↔️ Yes for ultrasound

  Tissue penetration ↔️ Good for ultrasound
• Order the following media from lowest to highest speed of sound:

  1️⃣ Air

  2️⃣ Water

  3️⃣ Soft tissue
• Why are ultrasound waves used extensively in medical imaging?

  High-frequency and tissue penetration
• The speed of sound in air is approximately 343 m/s
• Attenuation of ultrasound waves limits the depth at which imaging can be performed effectively.
• Attenuation of ultrasound waves is caused by absorption and scattering
• What is the acoustic impedance of soft tissues?

  Low
• Which tissue has very high attenuation of ultrasound waves?

  Air
• Scattering of ultrasound waves deflects them in various directions.

  True
• The frequency of ultrasound is typically above 20 kHz, beyond the upper limit of human hearing


  True
• The degree of reflection and refraction depends on the acoustic impedance
• Higher-frequency ultrasound waves attenuate faster
• Match the property of ultrasound with its corresponding characteristic:

  Frequency Range ↔️ > 20 kHz

  Use in Medical Imaging ↔️ Yes

  Tissue Penetration ↔️ Good

  Energy Levels ↔️ Safe for diagnostic use
• The time of flight of an ultrasound wave is used to determine the depth of the reflecting structure


  True
• The transducer in ultrasound acts as both a transmitter and a receiver of high-frequency waves.


  True