All you need is data preparation: A systematic review of image harmonization techniques in Multi-center/device studies for medical support systems

Artificial intelligence (AI) models trained on multi-centric and multi-device studies can provide more robust insights and research findings compared to single-center studies. However, variability in acquisition protocols and equipment can introduce inconsistencies that hamper the effective pooling of multi-source datasets. This systematic review evaluates strategies for image harmonization, which standardizes appearances to enable reliable AI analysis of multi-source medical imaging. A literature search using PRISMA guidelines was conducted to identify relevant papers published between 2013-2023 analyzing multi-centric and multi-device medical imaging studies that utilized image harmonization approaches. Common image harmonization techniques included grayscale normalization (improving classification accuracy by up to 24.42%), resampling (increasing the percentage of robust radiomics features from 59.5% to 89.25%), and color normalization (enhancing AUC by up to 0.25 in external test sets). Initially, mathematical and statistical methods dominated, but machine and deep learning adoption has risen recently. Color imaging modalities like digital pathology and dermatology have remained prominent application areas, though harmonization efforts have expanded to diverse fields including radiology, nuclear medicine, and ultrasound imaging. In all the modalities covered by this review, image harmonization improved AI performance, with increasing of up to 24.42% in classification accuracy and 47% in segmentation Dice scores. Continued progress in image harmonization represents a promising strategy for advancing healthcare by enabling large-scale, reliable analysis of integrated multi-source datasets using AI. Standardizing imaging data across clinical settings can help realize personalized, evidence-based care supported by data-driven technologies while mitigating biases associated with specific populations or acquisition protocols.