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The Food and Drugs Administration (FDA or the Agency), the US regulating authority in the sphere of healthcare products, has published a guidance document dedicated to the technical performance assessment of quantitative imaging in radiological device premarket submission. The document is intended to provide additional clarifications regarding the existing regulatory requirements, as well as recommendations to be considered by medical device manufacturers to ensure compliance thereto. At the same time, the authority additionally emphasizes that the guidance and provisions contained therein are non-binding, and are not intended to introduce new rules or impose new requirements. Moreover, an alternative approach could be applied, provided such an approach is in line with the current legislation and has been agreed with the authority in advance. 

 

Regulatory Background 

The present guidance is intended to provide recommendations to be considered by medical device manufacturers concerning the information to be included in premarket submissions related to radiological devices that include quantitative imaging functions. The scope of the guidance covers a wide range of submission pathways including, inter alia, the following ones:

• Premarket approval (PMA) applications;
• Humanitarian device exemption (HDA) applications;
• Premarket notification (510(k)) submissions;
• Investigational device exemption (IDE) applications; and 
• De Novo requests. 

The document also contains references to the Q-Submission pathway. 

According to the guidance, the authority expects the applicants to provide performance specifications for the quantitative imaging functions, supporting performance data to demonstrate that the quantitative imaging functions meet those performance specifications, and sufficient information for the end-user to obtain, understand and interpret the values provided by the quantitative imaging functions. 

As further explained by the FDA, medical imaging is a common approach for diagnosing conducted in healthcare facilities. In particular, such technologies are used to obtain images representing the internal structures of the patient’s body, which are further used in the clinical decision-making process. For this purpose, such images are to be interpreted and analyzed by healthcare professionals having the appropriate qualification and training. Apart from that, it is also possible to extract additional information from images using quantitative imaging. However, the information received in such a way could be subject to both systematic error and random variation, resulting in certain differences from the actual data, which could impact adversely the decision-making process. 

As further explained by the FDA, the utility of any quantitative imaging value is greatest when the performance of the quantitative imaging function is well-characterized and users have sufficient information to understand and interpret the quantitative values being reported. At the same time, due to the variety of ways the technology could be used, it is quite difficult to determine specific criteria to be applied when assessing the performance. 

The scope of the guidance covers any medical devices intended to generate quantitative imaging values irrespectively of a specific technology the device employs. The document is intended to provide additional clarifications and recommendations regarding the scope of information the authority expects to be provided when applying for marketing approval for such devices. The authority additionally emphasizes that all the claims and statements made by the manufacturer concerning the functionality of the device, its performance, and its characteristics should be duly supported with the respective data. In certain cases, clinical validation could be required to collect additional information related to the device. At the same time, it is stated that the types of evidence described in the guidance are not exhaustive. The authority also mentions that the regulatory matters related to clinical validation are not covered by the scope of the document as well. 

Definitions 

To assist in interpreting and following the requirements set forth under the applicable legislation, the document provides definitions of the most important terms and concepts used in the context of devices with quantitative imaging functions. As it is mentioned in the guidance, the terminology used services from the Radiological Society of North America’s (RSNA) Quantitative Imaging Biomarker Alliance (QIBA), the Biomarkers, EndpointS and other Tools (BEST) glossary, the International Vocabulary of Metrology and the appropriate guidance document dedicated to the clinical evaluation of the Software as a Medical Device (SaMD) issued by the International Medical Device Regulators Forum (IMDRF). The terms explained in the guidance include, inter alia, the following ones: 

• Accuracy – the closeness of agreement between a test result and the accepted reference value;
• Clinical Validation – the assessment and analysis of clinical data about a medical device to verify the clinical safety, performance, and effectiveness of the device when used as intended by the manufacturer;
• Linearity – the ability to provide measured quantity values that are directly proportional to the value of the measurand;
• Measurand – the quantity intended to be measured;
• Precision – the closeness of agreement between measured quantity values obtained by replicate measurements under specified conditions; 
• Technical Performance Assessment – establishing that the technical performance specifications of the quantitative imaging function correspond to the claims and uncertainty associated with the quantitative imaging function; the technical performance assessment of a quantitative imaging device is based on a specified technical protocol, which may include media collection and processing.  

Potential Sources of Measurement Error 

The document further describes the issues that could potentially result in measurement errors. As it was mentioned before, the factors impacting the accuracy and precision are systematic error and random variation. Hence, it should be acknowledged that the value obtained by the virtue of quantitative imaging differs to a certain extent from the actual value measured. As further explained by the FDA, errors may come from the acquisition of the medical images, patient characteristics, and the image processing algorithm. The authority emphasizes the importance of understanding the root cause of errors to mitigate the impact they cause on the final result.  

In summary, the present FDA guidance provides a brief overview of the applicable regulatory requirements for medical devices with a quantitative imaging function. The document highlights the most important aspects to be considered and explains the main terms and concepts. 

Sources:

https://www.fda.gov/regulatory-information/search-fda-guidance-documents/technical-performance-assessment-quantitative-imaging-radiological-device-premarket-submissions

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