FDA Guidance on Quantitative Imaging: Overview

Table of Contents

The Food and Drug Administration (FDA or the Agency), the US regulating authority in healthcare products, has published a guidance document dedicated to the technical performance assessment of quantitative imaging in radiological device premarket submissions. The document is intended to provide additional clarifications regarding the applicable regulatory requirements, as well as recommendations to be considered by medical device manufacturers and other parties involved in operations with medical devices to ensure compliance thereto. The authority also mentions that the guidance is non-binding in its legal nature. Moreover, an alternative approach could be applied, provided such an approach is in line with the existing legislation and has been agreed with the authority in advance. 

The document outlines the scope of information to be included in the premarket submission for a new medical device to ensure completeness of the information provided and facilitate the review process. 

Function Description 

According to the guidance, the premarket submission should include a technical description of the quantitative imaging function(s) included in [the] device at a level of detail sufficient for the Agency to understand the functionality. In certain cases, it will be sufficient to provide only a general description, while in complex cases the authority will expect to receive a detailed enough description to ensure the authority has sufficient information to assess all the important aspects. The document also refers to the guidance on the content of premarket submissions for the software contained in medical devices. 

In general, the authority expects the following information to be included:

• Description of the measurand (including units);
• Name, version, and relevant characteristics of the software platform;
• A detailed description of the algorithm employed, including algorithm inputs and outputs;
• For algorithms derived from physical processes (e.g., fluency correction, tomographic image reconstruction), the assumed underlying physics and its relationship to the mathematical components of the algorithm; 
• Level of automation (e.g., manual, automatic, or semi-automatic); and 
• If applicable, a summary of your algorithm training paradigm, including how algorithm parameters and thresholds were established. 

Apart from this, the applicant should also provide additional details regarding the input data (images) used by the device, including the aspects related to the target population and diseases, as well as any applicable restrictions and limitations regarding the conditions where the device will not operate as intended. 

Additionally, the submission should include information about:

• Image acceptance activities – the ones to be undertaken to ensure the input data is suitable for further processing – and also the particular way they should be performed;
• Information presented to the user about the derived values (including units); and
• The way users should interact with the device to ensure it operates properly, as well as the instructions for use to be followed. 

Technical Performance Assessment 

According to the guidance, the scope of premarket submission should also cover performance specifications for the quantitative imaging function(s) the device in question has. Under the general rule, they should correspond to the claims and statements made by the manufacturer about the product’s functionality and effectiveness. It is further stated that the appropriate performance specifications will depend on the intended use of the quantitative imagining function, the complexity of the measurement algorithm, and the availability of reference values; additionally, performance specifications may change through the operating range of the quantitative imaging function. 

Furthermore, the authority mentions that all the claims and statements regarding the performance of the device should be supported by the respective performance data. The authority additionally emphasizes the importance of determining the proper objective reference values, as this could be used when comparing the medical device in question to a similar product already placed on the market (predicate). 

As explained by the FDA, the technical performance assessment of a quantitative imaging function of the device should include the following steps: 

1. Define the quantitative imaging function, its relationship to the measurement, and the use conditions. 
2. Determine an appropriate reference standard and the performance metrics applicable to your device. At this stage, it is important to assess any bias or limitations associated with using the device. 
3. Characterize the performance of the quantitative imaging function under the conditions defined in the device labeling. 
4. Define the experimental unit (e.g., per lesion, per patient). 
5. Define the appropriate statistical estimates of performance. 
6. Define acceptance criteria based on the intended use of the quantitative imaging function and other restrictions/limitations. 
7. Specify the elements of the statistical design, the necessary data, and the statistical analysis plan, based on the selected performance metrics.
8. Collect the relevant data. 
9. Perform the statistical analysis. 
10. Compare the analysis results to the pre-defined acceptance criteria.  

The authority also mentions that the performance specifications used should also address the aspects related to uncertainty in the context of the intended use of the device in question. The authority acknowledges that the uncertainty assessment would cover not all the uncertainty-related issues that could potentially take place during the actual use of the device. According to the guidance, the authority expects the applicant to provide information describing the operating range of the device, as well as uncertainties within the said range. As it was mentioned before, any claims made by the manufacturer should be supported by the respective performance data. 

Another important aspect is related to the level of interactions with the device during its use. In particular, the authority additionally emphasizes that the fully automated devices (the ones that operate without the need for corrections to be made by the user manually) require a more rigorous assessment than the ones allowing their users to review and correct the output results. The manufacturer should also provide detailed enough information regarding the way the user will be able to understand that the output provided by the device is incorrect. The authority mentions that automated devices that make claims of improved accuracy and reproducibility compared to manual methods should be supported by studies comparing quantitative imaging values produced by the device to those of expert use. 

In summary, the present FDA guidance provides an overview of specific requirements for quantitative image function. The document highlights the most important aspects to be considered to ensure the accuracy of the results provided by the device when used for its intended purpose. 

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