THERMOPLASTIC ELASTOMER ULTRASOUND TRAINING MODELS

Ultrasound imaging has rapidly become one of the most commonly used diagnostic methods of modern medicine over the last several decades.  The image shown below is reproduced from a radiology information website for patients.  Ultrasound imaging uses sound waves to produce images of the inside of the body.  It is used to help diagnose the causes of pain, swelling, and infection in the body’s internal organs, to examine a baby in pregnant women, and to examine the brain and hips in infants.  It is also used to help guide biopsies, diagnose heart conditions, and assess damage after a heart attack.  It is, therefore, used in many different medical specialties, to test for conditions involving most parts of the human anatomy.  It is safe and noninvasive, and it does not use ionizing radiation.

The rapidly rising demand for ultrasound imaging in recent decades has produced an increasing need for training in ultrasound imaging methods.  It has been difficult to meet this need by using only live human models as test subjects while training ultrasound imaging technicians and other medical professionals.  This situation has led to the development of artificial ultrasound simulators through polymer materials science.

The first criterion that a material needs to satisfy to be a realistic candidate for use in manufacturing artificial ultrasound simulators is that its hardness must match the hardness range of human tissues.  Durometer Shore hardness testers are widely used to assess hardness.  Each type of durometer is used to differentiate between samples of slightly different hardness in the same general range.  Different durometers are used for classes of materials that differ greatly in hardness.  Human and other animal tissues are very soft materials for which the use of a Type OO durometer is the most appropriate choice.

It is not surprising, therefore, that ultrasoft thermoplastic elastomers, with hardness in the Type OO durometer range, have been identified as the materials of choice for constructing anatomically realistic ultrasound training models for medical personnel. 

In addition to needing to match the softness range of human tissue, there are two other indispensable criteria that a material needs to satisfy to be a realistic candidate for use in manufacturing artificial ultrasound simulators.  One of these additional criteria is that models constructed by using the material must match the acoustic properties of human tissue to be useful in training medical personnel in ultrasound imaging.  The other additional criterion is that the material must be durable so that its use can be cost-effective. 

The development of increasingly better ultrasoft thermoplastic elastomer formulations that meet this demanding combination of requirements is an area at the frontiers of materials research and development.  Great success has been achieved already, as will be described below.  Further improvements may be anticipated with continuing work.

Several companies manufacture and sell ultrasound training models.  CAE Healthcare is one of the leaders in this technology area.  Its Blue Phantom ultrasound training models are available for many medical specialties, to help train medical professionals in the application of ultrasound imaging for as a diagnostic tool for a vast range of conditions involving most parts of the human anatomy.  A few Blue Phantom products are shown below as examples.

It is seen from the pricing of such products that use in the fabrication of ultrasound training models is an exceptionally high-value application for thermoplastic elastomer formulations that can meet the stringent performance and durability requirements summarized above.  For example, the price of the FAST Exam Real Time Ultrasound Training Model was U.S. $ 27,040, and even the much smaller and simpler Breast Biopsy Ultrasound Training Model had a price tag of $ 415, on the date of creation of this post.  Upon considering the factors affecting price discussed in the post titled PERFORMANCE VERSUS PRICE (created 08 November 2018), it is seen that an ultrasoft thermoplastic elastomer suitable for use in this application can command an exceptionally high price premium over otherwise similar thermoplastic elastomers that fall short of meeting the demands of this application.

The CAE Vimedix ultrasound simulator facilitates engaging and intuitive learning in cardiac, lung, abdominal, and Ob/Gyn ultrasound, all on one common platform.  With its state-of-the-art manikin-based system and innovative software tools, CAE Vimedix accelerates the development of essential psychomotor and cognitive skills for ultrasound probe handling, image interpretation, diagnosis, and clinical decision-making.

Two recently published experimental studies have shown that there are no statistically significant differences between the educational outcomes obtained by using only live human models (as had been the only option until the advent of ultrasound simulators) and by using ultrasound simulators.  Hence these studies lead to the conclusion that the use of an ultrasound simulator is indeed a suitable alternative method for ultrasound education.

• Focused assessment with sonography for trauma (FAST) is a commonly used and life-saving tool in the initial assessment of trauma patients in emergency medicine (EM). Bentley et al., Are Live Ultrasound Models Replaceable? Traditional versus Simulated Education Module for FAST Exam (2015), compared the test, survey, and performance of ultrasound between 39 EM students being trained on FAST on an ultrasound simulator and 54 students being trained on FAST via the traditional hands-on patient format.  No differences in knowledge-based ultrasound test scores, survey of comfort levels with ultrasound, and ability to perform and interpret FAST on human models were found between the group trained on human models and the group trained on a simulator.
• Silva et al., Randomized study of effectiveness of computerized ultrasound simulators for an introductory course for residents in Brazil (2016), assessed the educational outcomes for internal medicine residents without ultrasound experience, taking an introductory point-of-care ultrasound course, by comparing the experimental group using an ultrasound simulator with the control group undergoing hands-on training using live models alone. Forty participants, 21 of whom were in the experimental group and 19 of whom were in the control group, completed the course and all testing.  As can be seen from Figure 2, reproduced below from this article, there was no statistically significant difference between the two groups in either the written exam or the practical exam (image acquisition test) at the end of the course.