Final answer:
Magnetic Resonance Imaging (MRI) is the test that detects subtle changes and shows detailed images of brain injuries, offering more contrast than other imaging techniques like CT scans, X-rays, and PET scans.
Step-by-step explanation:
The diagnostic test done to detect subtle changes in brain tissue and show more specific details of a brain injury is Magnetic Resonance Imaging (MRI). Unlike CT scans, X-rays, and PET scans, an MRI uses a magnetic field to generate detailed images of the brain without exposing the patient to ionizing radiation. CT scans provide good detail, but an MRI offers better contrast between different types of soft tissues, which makes it more effective for diagnosing many types of brain injuries. PET scans show brain activity and functionality but do not provide as much anatomical detail as an MRI.
When discussing safe imaging techniques during pregnancy, the least invasive and safest option is an ultrasound, as it does not use ionizing radiation and can effectively monitor fetal development.