All example images were obtained via Wikimedia Commons.

Chest X-Ray images come from:
1. CC0 Universial Public Domain. Source: https://commons.wikimedia.org/wiki/File:Normal_posteroanterior_(PA)_chest_radiograph_(X-ray).jpg
2. Creative Commons Attribution-Share Alike 4.0 International. Source: https://commons.wikimedia.org/wiki/File:Chest_X-ray.jpg
3. Creative Commons Attribution 3.0 Unported. Source https://commons.wikimedia.org/wiki/File:Implantable_cardioverter_defibrillator_chest_X-ray.jpg
4. Creative Commons Attribution-Share Alike 3.0 Unported. Source: https://commons.wikimedia.org/wiki/File:Medical_X-Ray_imaging_PRD06_nevit.jpg

Heart Ultrasound Images come from:
Creative Commons Attribution-Share Alike 4.0 International. Source: https://commons.wikimedia.org/wiki/File:ProapsZCMiCh_.gif

MRI Images come from:
Public Domain. Source: https://commons.wikimedia.org/wiki/File:Multslice_short_axis.gif

Fetal head images have Creative Commons Attribution-Share Alike 3.0 Unported license.
Sources:
https://commons.wikimedia.org/wiki/File:Pregnancy_ultrasound_110328105247_1105070.jpg
https://commons.wikimedia.org/wiki/File:Pregnancy_ultrasound_110325112752_1129380.jpg
https://commons.wikimedia.org/wiki/File:Pregnancy_ultrasound_110322143039_1441530.jpg
https://commons.wikimedia.org/wiki/File:Pregnancy_ultrasound_110328105247_1054210.jpg
https://commons.wikimedia.org/wiki/File:Pregnancy_ultrasound_110322143039_1440550.jpg
https://commons.wikimedia.org/wiki/File:Pregnancy_ultrasound_110322143039_1442060.jpg