  Background: Object detection in radiograph computer vision has largely
benefited from progress in deep convolutional neural networks and can, for
example, annotate a radiograph with a box around a knee joint or intervertebral
disc. Is deep learning capable of detect small (less than 1% of the image) in
radiographs? And how many radiographs do we need use when re-training a deep
learning model?
  Methods: We annotated 396 radiographs of left and right carpi dorsal 75
medial to palmarolateral oblique (DMPLO) projection with the location of
radius, proximal row of carpal bones, distal row of carpal bones, accessory
carpal bone, first carpal bone (if present), and metacarpus (metacarpal II,
III, and IV). The radiographs and respective annotations were splited into sets
that were used to leave-one-out cross-validation of models created using
transfer learn from YOLOv5s.
  Results: Models trained using 96 radiographs or more achieved precision,
recall and mAP above 0.95, including for the first carpal bone, when trained
for 32 epochs. The best model needed the double of epochs to learn to detect
the first carpal bone compared with the other bones.
  Conclusions: Free and open source state of the art object detection models
based on deep learning can be re-trained for radiograph computer vision
applications with 100 radiographs and achieved precision, recall and mAP above
0.95.
