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Case studies

Improving accuracy of temperature measurement in ultrasound transducers

NPL has created a customised solution for use in medical devices

Case study

The need

Ultrasound is widely used for diagnostic medical imaging and is a useful way of examining many of the body's internal organs. There are two types of ultrasound procedure:

  • A non-invasive examination, performed by applying a transducer on the surface of the body over the test area, such as heart, liver or uterus.
  • An invasive examination, where the transducer is inserted inside the body, such as cardiac or transoesophageal.

When developing new equipment, medical device manufacturers need to follow the IEC 60601 standard, ensuring that the new device operates within the accepted limits. When it comes to safety and essential performance of ultrasonic diagnostic equipment, IEC 60601-2-37 standard sets the test criteria for temperature measurement.

In the case of invasive procedures, transducers need to be tested in specific conditions with the test object temperature maintained at 37 °C at least, mimicking human body temperature.

The solution

NPL came up with a bespoke solution of a temperature-controlled ultrasound phantom, whose design offered the option to elevate the temperature of the test object between room temperature and 40 °C, and keep it constant through a closed loop control.

In addition, the solution was adapted to the surface temperature test phantom, used to test compliance with the limits of ultrasound transducer surface temperature, which also included a cavity to accommodate the invasive transducer.

The impact

This solution will allow increased accuracy when monitoring the temperature of the transducer head surface, by ensuring the testing is carried out at a temperature which is as close as possible to a real environment setting.

The solution provides confidence in transducer performance in a real-world situation for use in the human body whilst remaining compliant with IEC 60601-2-37 standards.

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