It is also a valid option for patients who present in a delayed fashion after head trauma (eg, gradual decline after a fall due to subacute or chronic subdural hematoma). Head Trauma CTA Head and Neck There is no relevant literature to support the use of CTA in the initial imaging evaluation of subacute or chronic head trauma with unexplained cognitive or neurologic deficit(s) unless there is also suspected intracranial vascular injury (see Variants 8 and 9 when suspected). FDG-PET/CT Brain FDG is the most widely used PET radiopharmaceutical and is a glucose analog. Glucose is the primary energy source for the brain; therefore, FDG uptake on PET is a marker of local metabolism, which is closely coupled to local neuronal activity and can be quantified as the cerebral metabolic rate of glucose [18]. In normally functioning brain tissue, local metabolism is also closely coupled to perfusion; therefore, findings on metabolic PET imaging will often (but not always) parallel findings on perfusion SPECT imaging [32]. In acute severe TBI with brain contusion, FDG-PET has found both pericontusion and distant/global hypometabolism, whereas in chronic mild TBI, FDG-PET has found regional hypometabolism that may correlate with cognitive and behavioral impairments [18]. One study in combat veterans with chronic postconcussive syndrome found hypometabolism in the infratentorial and medial temporal regions, which may be unique to blast exposures [44]. Aside from FDG, other research studies have used oxygen (15O), neuronal ([11C] flumazenil), inflammation ([11C] PK11195), amyloid ([11C] PiB), and tau ([18F] T807) radiopharmaceuticals [18]. Despite the promise of molecular imaging for advancing our understanding of TBI pathophysiology, there is insufficient evidence to support the routine clinical use of PET at the individual patient level [45].
Head Trauma PCAs. It is also a valid option for patients who present in a delayed fashion after head trauma (eg, gradual decline after a fall due to subacute or chronic subdural hematoma). Head Trauma CTA Head and Neck There is no relevant literature to support the use of CTA in the initial imaging evaluation of subacute or chronic head trauma with unexplained cognitive or neurologic deficit(s) unless there is also suspected intracranial vascular injury (see Variants 8 and 9 when suspected). FDG-PET/CT Brain FDG is the most widely used PET radiopharmaceutical and is a glucose analog. Glucose is the primary energy source for the brain; therefore, FDG uptake on PET is a marker of local metabolism, which is closely coupled to local neuronal activity and can be quantified as the cerebral metabolic rate of glucose [18]. In normally functioning brain tissue, local metabolism is also closely coupled to perfusion; therefore, findings on metabolic PET imaging will often (but not always) parallel findings on perfusion SPECT imaging [32]. In acute severe TBI with brain contusion, FDG-PET has found both pericontusion and distant/global hypometabolism, whereas in chronic mild TBI, FDG-PET has found regional hypometabolism that may correlate with cognitive and behavioral impairments [18]. One study in combat veterans with chronic postconcussive syndrome found hypometabolism in the infratentorial and medial temporal regions, which may be unique to blast exposures [44]. Aside from FDG, other research studies have used oxygen (15O), neuronal ([11C] flumazenil), inflammation ([11C] PK11195), amyloid ([11C] PiB), and tau ([18F] T807) radiopharmaceuticals [18]. Despite the promise of molecular imaging for advancing our understanding of TBI pathophysiology, there is insufficient evidence to support the routine clinical use of PET at the individual patient level [45].