Ultrasound Physics and Instrumentation - MRD535

Ultrasound Physics and Instrumentation - MRD535

• The course covers ultrasound physics, instrumentation, accessories, and image recording in ultrasonography.
• It also explains the principles of ultrasonography, including ultrasound physics.
• Topics also include image optimization, image orientation, and brightness control.

Image Optimization

• Output power: Measures energy per unit time (mW/cm²). Increasing it increases the amplitude of voltage pulses across crystals, affecting crystal vibration strength, and ultimately, image brightness.
• Gain: Adjusts the displayed amplitude of returning signals, boosting the brightness of the entire ultrasound image by amplifying electrical signals in the receiver. It does not change the pulse strength sent into the body or output power.
• Total Gain Compensation (TGC): Boosts signals differently at various image depths, addressing beam attenuation, which is more significant in deeper interfaces. TGC corrects for attenuation, meaning the loss of sound wave strength as it travels further into tissue, ensuring uniform brightness across the image. However, it does not affect the strength of the pulse sent into the body.

Brightness Control

• There are three primary brightness controls:
  • Output power: Controls the energy of the sound wave.
  • Gain control: Boosts the signal strength reflected from tissues.
  • Total Gain Compensation (TGC): Adjusts signal strength based on depth.

Transmission/Output Power

• Transmission power (output power) describes the energy per unit time (mW/cm²).
• Higher output power leads to stronger sound waves, resulting in stronger returning echoes and uniformly brighter images.
• Output power adjustments modify brightness levels by adjusting the sound pulse strength sent into the body.

Time Gain Compensation (TGC)

• TGC boosts signals from different depths within an image to account for beam attenuation (signal weakening).
• Attenuation is greater for deeper interfaces.
• TGC corrects for the loss of signal strength as the sound wave travels further into the tissue.
• TGC doesn't alter the strength of the initial pulse.

ALARA (As Low As Reasonably Achievable)

• When improving images and adjusting controls, prioritize patient impact.
• Adjusting TGC first, then Gain, Frequency, Focal zones, and lastly output power.

Frequency

• Wider bandwidth transducers allow selection of higher or lower frequencies:
  • Higher frequencies: Improve detail resolution, but may reduce penetration.
  • Lower frequencies: Improve penetration, but lower resolution.
• Transducer frequency is calculated by dividing the speed of sound by wavelength (f = c / λ).
• High frequencies mean shorter wavelengths, and shorter wavelengths mean improved resolution.
• Operators can select between high-frequency, general, or low-frequency (penetration) modes.

Focal Zone

• The focal zone is the area in the ultrasound beam with the narrowest diameter. Beam diameter widens as it moves toward and away from the focus point.
• A thicker layer width (compared to a thinner focal zone) decreases image resolution.
• The focal zone should be set at or just above the level of the structure of interest.

Zoom

• Zoom enlarges a specific section of an ultrasound image on the monitor.
• Zoom does not affect depth penetration.
• Increasing zoom concentrates scan-line density, leading to improved resolution.

Sector Width

• Sector width is the area of tissue interrogated by the ultrasound beam.
• Narrowing the sector width improves lateral (side-to-side) resolution by reducing the acoustic window.
• Decreasing sector width improves frame rate by scanning fewer lines.

Dynamic Range

• The range of echo strengths a system can display.
• Adjusting dynamic range only changes how the signals are displayed, not their amplitude.
• Higher dynamic range shows more detail and a wider range of gray values.
• Lower dynamic range produces a more "black-and-white" image style with higher contrast.

Frame Rate

• Frame rate means how many times per second an ultrasound image is updated.
• It's important for assessing moving body parts (e.g., in cardiac imaging).
• Frame rate is affected by factors like imaging frequency, depth, sector width, and focus.
• Increased depth or higher frequencies/resolution may reduce the frame rate.

Image Recording Options

• Thermal paper: Heat-sensitive paper used for immediate image visualization. Does not use ink. Can last up to 7-10 years if stored properly.
• Film: Conventional film recording method.
• CD: Optical storage medium for image storage.
• PACS (Picture Archiving and Communication System): A digital system for storing and transmitting medical images, replacing conventional film.