TAs: Süleyman Yasin Peker
Topics covered:
Introduction to Verasonics Vantage 32LE Ultrasound Research System.
Introduction to ultrasound transducers.
Introduction to ultrasound imaging modes.
Real-time data acquisition using Verasonics.
Time-of-Flight measurement of common carotid artery (cca) using ultrasound and image processing.
Flow measurement and colour doppler imaging using ultrasound.
Experiment details:
Introduction
This experiment involves the use of the Verasonics Vantage 32LE, a sophisticated ultrasound research system, to explore various aspects of ultrasound imaging and data acquisition. Participants will gain hands-on experience with different ultrasound imaging modes, including A-Mode, B-Mode, Colour Doppler, and Power Doppler, while understanding the applications of linear array, curvilinear/convex, and phased array transducers. The experiment will also cover real-time data acquisition using the Verasonics system, focusing on measuring Time-of-Flight values for echoes and analyzing the power spectrum of ultrasound signals in Doppler mode. This comprehensive approach will provide a deeper understanding of both the technical and practical aspects of ultrasound technology.
Theoretical Background
Ultrasound Transducers
A linear transducer is a straight transducer. The linear transducer’s length determines the image’s sector width and shape. A linear transducer offers detailed resolution at superficial depths. Linear transducers are most frequently used with MSK, nerve, small parts, vascular, and pediatric applications.
A convex transducer is a curved transducer. The shape of a convex transducer determines the sector width and shape of the image. A convex transducer offers a wider field of view for larger or deeper structures. Convex transducers are most frequently used for abdomen, obstetrics/gynecology (OB/GYN), urology, and some musculoskeletal (MSK) applications.
A phased array transducer has a small footprint with a sector image shape and features high temporal resolution and penetration. This allows clinicians to image structures that are moving in real-time. Phased array transducers are most frequently used with applications ranging from cardiac, transcranial, abdomen, and pediatrics.
Ultrasound Imaging Modes
The earliest ultrasound mode showed returning echoes in a one dimensional, graphical format (Figure 6). Known as amplitude or A-mode, the information could be used to measure the distance between, or thickness of, tissues. An example is examining the cornea, lens and chambers of the eye.
“B” or Brightness mode represents the amplitude peaks seen in A-mode as dots or pixels of varying brightness (Figure 6).
Using B-mode, ultrasound systems can send sequential ultrasound pulses out in different directions to form multiple image lines. This process is completed quickly and repeatedly, creating the typical ultrasound image seen on all systems.
In this display mode, Doppler data received by the ultrasound system is displayed as coloured pixels within the sample box shown on the B-mode image (Figure 7). This gives information about direction and a semi-quantitative assessment of blood flow velocities.
A variation of colour Doppler available on most systems is a power Doppler display. This mode ignores the directional information provided by Doppler shift and displays the total Doppler signal strength as shades of one colour (Figure 8). Whilst it does not display any data on flow direction, power Doppler is a useful tool for examining low velocity blood flow and is more sensitive to flow than colour doppler.
Time-of-Flight Measurement
Time-of-Fight (TOF) in ultrasound refers to the time it takes for an ultrasound pulse to travel from the transducer to a target (such as tissue or a vessel wall) and back to the transducer after being reflected. It is a critical measurement used to determine the depth of structures within the body, as the distance traveled by the ultrasound wave is directly related to the time it takes for the wave to return to the transducer.
The formula to calculate the time-of-flight for a single echo is:
where:
d is the depth of the target (the distance from the transducer to the reflecting surface),
c is the speed of sound in the medium (typically c≈1540 m/s in soft tissue),
The factor of 2 accounts for the round-trip distance (to the target and back).
Calculating Time-of-Flight for Two Echoes
When considering two echoes, the TOF for each can be calculated separately if the depths d1 and d2 are known:
To find the difference in time-of-flight between the two echoes:
Report requirements:
The report for this part is expected to include:
· Abstract and Introduction
· Procedures and Steps
· Experiment Related (Plots & Calculations)
· Discussion and Conclusion