  Medical imaging analysis has witnessed remarkable advancements even
surpassing human-level performance in recent years, driven by the rapid
development of advanced deep-learning algorithms. However, when the inference
dataset slightly differs from what the model has seen during one-time training,
the model performance is greatly compromised. The situation requires restarting
the training process using both the old and the new data which is
computationally costly, does not align with the human learning process, and
imposes storage constraints and privacy concerns. Alternatively, continual
learning has emerged as a crucial approach for developing unified and
sustainable deep models to deal with new classes, tasks, and the drifting
nature of data in non-stationary environments for various application areas.
Continual learning techniques enable models to adapt and accumulate knowledge
over time, which is essential for maintaining performance on evolving datasets
and novel tasks. This systematic review paper provides a comprehensive overview
of the state-of-the-art in continual learning techniques applied to medical
imaging analysis. We present an extensive survey of existing research, covering
topics including catastrophic forgetting, data drifts, stability, and
plasticity requirements. Further, an in-depth discussion of key components of a
continual learning framework such as continual learning scenarios, techniques,
evaluation schemes, and metrics is provided. Continual learning techniques
encompass various categories, including rehearsal, regularization,
architectural, and hybrid strategies. We assess the popularity and
applicability of continual learning categories in various medical sub-fields
like radiology and histopathology...
