  State-of-the-art automated segmentation algorithms are not 100\% accurate
especially when segmenting difficult to interpret datasets like those with
severe osteoarthritis (OA). We present a novel interactive method called
just-enough interaction (JEI), which adds a fast correction step to the
automated layered optimal graph segmentation of multiple objects and surfaces
(LOGISMOS). After LOGISMOS segmentation in knee MRI, the JEI user interaction
does not modify boundary surfaces of the bones and cartilages directly. Local
costs of underlying graph nodes are modified instead and the graph is
re-optimized, providing globally optimal corrected results. Significant
performance improvement ($p \ll 0.001$) was observed when comparing
JEI-corrected results to the automated. The algorithm was extended from 3D JEI
to longitudinal multi-3D (4D) JEI allowing simultaneous visualization and
interaction of multiple-time points of the same patient.
