A Beginner’s Guide to Ultrasound Technology

The Importance of Ultrasound

Diagnostic ultrasound, or sonography, is a common, noninvasive method for taking real time images from inside your body. The first thing that may come to mind when you think about ultrasound is probably pregnancy. This makes sense, as ultrasound is a bit of a gold standard for obstetrics and gynecology. Safe and gentle, routine scanning for pregnant women can aid in preventing perinatal and maternal mortality due to complications such as prematurity, birth asphyxia and congenital malformations1. Sonography was introduced to OB/GYN beginning in 19582, with early abdominal ultrasound images. These paved the way for the eventual development of equipment and scanners that could be used to locate the placenta and later conduct fetal biometry2. The technology took off through the rest of the 20th century as scientists improved upon scanning systems and probes that displayed its robust range of capabilities such as detecting placenta location, observing the heartbeat, identifying the presence of twins and monitoring high risk pregnancies. By the year 2000, medical professionals offered real-time scanning and 3D images with high resolution abdominal and endovaginal transducers2. With all of its modern capabilities, sonography is on the rise in other areas of medicine such as cardiology, emergency point of care, sports medicine and even ophthalmology.

How it Works

Ultrasound probes generally utilize piezoelectric crystalsto transmit high frequency soundwaves into the body through a transducer. Ultrasonic frequencies differ from others in that they cannot be heard by the human ear (above 20,000 Hz), with typical scanners operating in a range of 2 to 18 megahertz3. Rapidly applying and removing voltage to said crystals causes them to expand and contract, producing the ultrasonic waves. As the waves travel some are absorbed, and others are reflected back.  Modern methods use a sonar-like principle to register the pulse reflected off of the boundary between two tissues with differing acoustic resistance3. The acoustic resistance is simply the resistance to the flow of sound through a given surface. These echoes travel back to the crystal and generate a different voltage depending on the wave intensity. The transducer sends these signals to the ultrasound machine to be converted to an image.

There are four primary modes3 for scanning tissue:

  • A-mode or amplitude mode, which uses a single transducer to scan a line through the body and plot the echoes as a function of depth.
  • B-mode or 2D mode, uses a linear array of transducers (phased array) to scan a plane through the body and generate a 2D image.
  • M-mode or motion, employs a rapid sequence of B-mode scans in sequence to view range of motion.
  • Doppler mode, chiefly used to measure and visualize blood flow using the doppler effect.

Common Probe Types

Different devices tune the sound waves to focus on particular depths, either through controlled pulses from the machine or by utilizing differently shaped probes. Some common probe types include linear, curvilinear, phase array and endocavity4,5. Numerous probe types allow for diverse imaging applications:

  • Linear probes are used for imaging structures near the surface as well as vascular imaging and guided procedures. High frequency waves offer better resolution, but cannot penetrate as deep.
  • Curvilinear or convex probes use lower frequency waves in order to gain deeper penetration and have a wider field depth. They can be general purpose and are commonly used for abdominal imaging.
  • Phased Array probes have a smaller contact area and are primarily used for intercostal imaging of the liver between the ribs and for cardiac scans.
  • Endocavity or Intracavity probes are designed to image inside the body cavity and have a longer, slim design.

Challenges

Despite numerous benefits, traditional cart-based ultrasound equipment is expensive and difficult to maneuver. Ultrasound units can cost anywhere between $10,000 and $200,0006 depending on the machine, and may require more budget for additional probes and maintenance. Components such as piezoceramics tend to be expensive, though recent progress in fabrication of capacitive micromachined transducers could eventually reduce the cost as well as advance current technology 7. Another pitfall is the need for a trained operator as experience is generally necessary to obtain quality images and for making a correct diagnosis. Detailed user training courses can cost providers an additional $1000-$6000 6, consuming valuable time and resources. Portable scanners are an emerging technology targeted at addressing some of these issues. Conventional ultrasound machines require higher voltages to drive their transducers7, and early scaled-down applications struggled to compete at first. However, recent advances in computing and batteries have allowed for the development of new, smaller equipment that can image on a similar level to cart based systems.

The Benefits of Portable Ultrasound

Easy-to-use handheld ultrasound systems present a cost effective solution for diagnostic imaging on the go as well as reducing the learning curve for operators. The VistaScan software shrinks your typical carted ultrasound machine into a conveniently sized cell phone or tablet, in addition to being 20 times less expensive. This mobile health innovation makes it possible for clinicians to capture and save images and video loops at the touch of a button with choice of four different types of probes. USB probes can conveniently be swapped out to adapt to a doctor’s needs even out of the hospital or in rural areas. Those seeking a second opinion or assistance in diagnosing a patient are able to send an image through the platform and receive a diagnosis report back within minutes. By reducing the time and cost to diagnose patients, VistaScan helps people receive treatment faster and feel better sooner.

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References

[1] Amo Y, T. A, T. E. The Role of Obstetric Ultrasound in Reducing Maternal and Perinatal Mortality. Ultrasound Imaging – Medical Applications. August 2011. doi:10.5772/22847.

[2] Campbell S. A short history of sonography in obstetrics and gynaecology. Facts Views Vis Obgyn. 2013;5(3):213-29.

[3] Carovac A, Smajlovic F, Junuzovic D. Application of ultrasound in medicine. Acta Inform Med. 2011;19(3):168-71.

[4] Szabo, T. L. and Lewin, P. A. (2013), Ultrasound Transducer Selection in Clinical Imaging Practice. Journal of Ultrasound in Medicine, 32: 573-582. doi:10.7863/jum.2013.32.4.573

[5] Stanford Medicine 25. (2019). Bedside Ultrasound. [online] Available at: https://stanfordmedicine25.stanford.edu/the25/ultrasound.html [Accessed 1 Feb. 2019].

[6]Costowl.com. (2019). 2019 Average Ultrasound Machine Prices: How Much Does an Ultrasound Machine Cost?. [online] Available at: https://www.costowl.com/healthcare/healthcare-ultrasound-machine-costs.html [Accessed 1 Feb. 2019].

[7]J. M. Baran and J. G. Webster, “Design of low-cost portable ultrasound systems: Review,” 2009 Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Minneapolis, MN, 2009, pp. 792-795. doi: 10.1109/IEMBS.2009.5332754