Test-time augmentation-based active learning and self-training for
  label-efficient segmentation
Bella Specktor-Fadida Anna Levchakov Dana Schonberger Liat Ben-Sira Dafna Ben-Bashat Leo Joskowicz
Deep learning techniques depend on large datasets whose annotation is
time-consuming. To reduce annotation burden, the self-training (ST) and
active-learning (AL) methods have been developed as well as methods that
combine them in an iterative fashion. However, it remains unclear when each
method is the most useful, and when it is advantageous to combine them. In this
paper, we propose a new method that combines ST with AL using Test-Time
Augmentations (TTA). First, TTA is performed on an initial teacher network.
Then, cases for annotation are selected based on the lowest estimated Dice
score. Cases with high estimated scores are used as soft pseudo-labels for ST.
The selected annotated cases are trained with existing annotated cases and ST
cases with border slices annotations. We demonstrate the method on MRI fetal
body and placenta segmentation tasks with different data variability
characteristics. Our results indicate that ST is highly effective for both
tasks, boosting performance for in-distribution (ID) and out-of-distribution
(OOD) data. However, while self-training improved the performance of
single-sequence fetal body segmentation when combined with AL, it slightly
deteriorated performance of multi-sequence placenta segmentation on ID data. AL
was helpful for the high variability placenta data, but did not improve upon
random selection for the single-sequence body data. For fetal body segmentation
sequence transfer, combining AL with ST following ST iteration yielded a Dice
of 0.961 with only 6 original scans and 2 new sequence scans. Results using
only 15 high-variability placenta cases were similar to those using 50 cases.
Code is available at: https://github.com/Bella31/TTA-quality-estimation-ST-AL