Findings
Quantitative imaging extracts numerical values from medical data that are subject to systematic error and random variation. The utility of these values depends on well-characterized performance and sufficient user information for interpretation. Performance specifications often change throughout the operating range of a device, such as volumetric reproducibility varying by structure size. Fully automated functions require more robust analytical validation than manual or semi-automated functions because they lack the opportunity for expert user correction. While phantoms serve as high-quality reference standards for ground truth, they are simplifications that may not fully reflect clinical performance.

Recommendations
Manufacturers should provide a detailed technical description of the quantitative imaging function, including the measurand, algorithm training paradigms, and level of automation. Performance specifications should incorporate objective reference values when available to allow for comparisons between subject and predicate devices. A sensitivity analysis should be conducted to determine the impact of sources of error like patient characteristics, image acquisition protocols, and image processing. Labeling must include clear instructions for user-performed quality assurance and specify any limitations where the function has been found ineffective. For automated devices, manufacturers should help users understand scenarios where the function might generate an incorrect output that is not easily identifiable.

Regulatory Considerations
The FDA recommends following a ten-step technical performance assessment process, ranging from defining the measurand to comparing statistical results against pre-defined acceptance criteria. Premarket submissions should include performance data demonstrating that the device meets claims regarding bias, precision, linearity, and limits of quantitation. Uncertainty should be reported in units of the measurand and cover the entire operating range of the function. Manufacturers are encouraged to use the Q-Submission process to address questions regarding regulatory status or specific requirements. Software implementation details should align with existing FDA guidance for the content of premarket software documentation.