The Role of Phantoms in Diagnostic Ultrasound Quality Assurance
For sensitive medical equipment, including ultrasound probes, rigorous quality assurance (QA) is necessary to ensure instruments perform as expected. This is especially true over time, as probes rack up hours of use in the field, where they’re subject to wear and tear. Tissue-mimicking phantoms (TMP) are a critical component in probe testing and calibration.
How do TMPs work, and what role do they play in quality assurance over the serviceable life of an ultrasound probe?
An overview of TMPs
In diagnostic imaging, phantoms are physical objects or simulations used to test and calibrate ultrasound equipment. The phantom is a known and controlled medium for the imaging equipment to scan, which allows sonographers and repair technicians to benchmark and assess equipment performance. There are several types of ultrasound phantoms used for QA, including:
- Tissue-mimicking phantoms to simulate the acoustic properties of muscle, fat, or bone
- Lesion-mimicking phantoms to copy pathology such as cysts, tumors, and calcifications
- Doppler phantoms to mimic blood flow and Doppler shift
- Elastography phantoms to simulate the mechanical properties of biological tissue
- Flow phantoms to mimic blood flow, vessel walls, and tissue motion
- 3D/4D phantoms to simulate tissue properties in three or four dimensions
Accurate representation of a real-world application
Procedures for phantom QA testing may vary depending on the type of phantom and the imaging technology being tested, but most processes involve the following basic steps:
- Position the phantom correctly for the imaging modality.
- Run the test like a patient examination.
- Analyze the images to evaluate quality and accuracy.
- Compare actual results to expected results.
- Record the results for future comparison.
Measuring the efficacy of probe function
Phantoms are useful for testing imaging equipment throughout its life cycle. By using the same phantom for regular QA testing, it’s possible to compare the results from one test to the next and determine if there has been any change or degradation in the performance of the equipment.
Phantoms are useful for assessing critical probe function because they simulate various properties of biological tissue. The ability to test speed of sound, attenuation, relative contrast, thermal properties, mechanical properties, and other variables provides critical insight into the efficacy of the probe relative to expectations. If probe performance falls short in TMP testing, it’s bound to fall short in the field. Likewise, passing TMP tests often indicates a field-ready probe.
Advantages of using phantoms for QA
Using phantoms to mimic human tissue, bone, muscle, and fat allows clinicians to make more accurate observations for proper diagnosis and treatment. Benefits of using phantoms include capabilities for:
- Providing a consistent and controlled environment for testing and calibrating imaging equipment
- Accurate simulation of a wide range of tissue properties
- Evaluating the performance of different imaging algorithms and software
- Testing and evaluating new imaging technologies before they’re deployed
- Training medical professionals on the use and interpretation of imaging technologies
Disadvantages of using phantoms for QA
Nothing works perfectly 100% of the time, but there’s little room for error in medical diagnostics. As useful as existing phantoms are, they do present some challenges for QA testing, including difficulties with:
- Perfectly mimicking the complexity and variability of real biological tissue
- Simulating all the tissue properties for a particular imaging modality
- Mimicking the measurement sensitivity of clinical diagnostics
- Maintaining their properties over time with consistent handling
Using phantoms is one way to determine if your equipment is faulty, but they’re not infallible, and they can only determine if a probe is defective and to what relative degree. Responsible evaluation also includes additional testing methods, such as with the Advantage. This system tests ultrasound probes to verify the accuracy with a frequency range of 2.25 to 10 MHz. Beyond simply recognizing the existence of a problem, Advantage testing helps to quantify it, thus enabling proper service or repair.
Testing ensures reliability
Thorough ultrasound probe testing and repair guarantees proper function in the field. Beyond ensuring the integrity of the probe housing and the efficacy of its critical electrical components, service providers must also make sure the images generated by a probe meet the expectations essential to its application. Phantoms mimic the real-world conditions of an ultrasound scan, which makes them critical for testing probe function and guaranteeing quality.