Studies with PET scanning and transcranial Doppler imaging have shown that changes in cerebral blood flow, such as hypoperfusion and vasospasm, can follow penetrating head injury.[1] These changes can last for two weeks.[4] An ischemic cascade similar to the course of cellular and metabolic events that follow other head injuries may follow penetrating head injuries.[4] Sometimes in penetrating injuries, the brain releases thromboplastin, which can lead to problems with blood clotting.[5]