Two-Dimensional Imaging - Diagnostic Images and Phasing Techniques

Chapter 12: Two-Dimensional Imaging

Diagnostic Images: Introduction

  • The process of creating diagnostic images involves a series of steps where a system sends a voltage pulse to specific crystals, which in turn generates signals that can be processed into an image.
Steps Involved in Imaging:
  1. The system sends a voltage pulse to the crystals.
  2. The crystals are energized in response to the pulse.
  3. The energized crystals send a thin pulse down a designated scan line.
  4. The pulse returns to the machine after hitting the target.
  5. The entire process is repeated with a scan line angled slightly differently than the previous one.
Terminology: Phasing
  • This sequential adjustment of angles in imaging is known as Phasing.
  • It is crucial to note that only Array transducers are capable of utilizing phasing techniques, whereas Mechanical transducers equipped with only one PZT (Piezoelectric Transducer) are incapable of this method.

Phased Arrays:

  • Phased arrays consist of multiple crystals that are interconnected to the imaging system via wires, allowing for a more sophisticated handling of imaging data compared to single PZT systems.
Functions on Transmission and Reception:
  1. The system can excite individual or groups of PZTs simultaneously.
  2. Each crystal generates a small voltage that is sent to a receiver.
Phasing Technique:
  • An electronic method is utilized to excite specific crystals with the following purposes:
    a. Create the beam: Forming the ultrasound beam necessary for imaging.
    b. Steer the beam: Adjusting the direction of the ultrasound beam dynamically.
    c. Focus the beam: Concentrating the beam at a specific depth to enhance image quality.
Phased Delays:
  • Steering:
    • Involves time differences in exciting various PZTs to steer or focus the ultrasound beam.
    • This allows alteration of the beam angle without the need to physically move the probe.
  • Beam Angles:
    • Straight Beam:
      • Voltages reach crystals simultaneously, producing a straight beam.
    • Angled Left:
      • Voltages reach crystals at different times, producing a beam angled to the left.
    • Angled Right:
      • Voltages reach crystals at different times, generating a beam angled to the right.
Focusing Techniques:
  • Focusing:
    • The technique of altering the timings of the pulse sent to the crystals to modify the intensities and clarity of the image.
  • Transmit Focusing:
    • Involves directing voltages to outer crystals first, followed by inner crystals to focus the beam.
  • Multiple Transmit Focusing:
    • A technique where multiple pulses are sent down a single scan line to improve the quality of the image.
  • Dynamic Receive Focusing:
    • The application of time delays during the reception of signals, allowing for enhanced detail and resolution in the final image.