TABLE 4.

Opportunities and Limitations of Harmonization Using EARL and ComBat

Parameter	Upfront harmonization (like EARL)	ComBat
Opportunities	Applicable without restriction on number of patients; valid for any pathology and feature	Applicable directly to calculated radiomic feature values (no need to access images); no need for phantom acquisition; applicable retrospectively; applicable prospectively if data have already been acquired for same pathology with same acquisition and analysis protocols and settings; ability to realign data to particular site
Limitations	Not applicable retrospectively; requires acquisition of phantom images, optimization of reconstruction settings, and access to machine	Requirement for minimum number of patients (∼20–30 per batch); specific transformation for each type of tissue, each type of tumor, each scanner, each material in phantom, each analysis method (e.g., segmentation approach) and each feature; not applicable prospectively if little or no previously acquired data