Radionuclide Angiography

= 1^st-line test for cerebral perfusion; can be performed at the ICU bed site

Indication:

1. Prior to organ harvest
2. Hypothermia / drug intoxication interfering with clinical + EEG assessment of brain activity
3. Brain death as a possible result of criminal activity

Pathophysiology: increased intracranial pressure above systemic arterial pressure results in markedly decreased cerebral perfusion → thrombosis → total cerebral infarction

Path: severe brain edema, diffuse liquefactive necrosis

Agent:

• nondiffusable hydrophilic ^99mTc pentetic acid (^99mTc-DTPA)
  • Absence of effective cerebral perfusion at planar scintigraphy does NOT equate with brain death as blood flow to brainstem cannot be adequately assessed with ^99mTc pentetic acid!
• diffusible brain imaging agents that cross the normal blood brain barrier
  • lipophilic ^99mTc bicisate (^99mTc-ECD)
  • lipophilic ^99mTc exametazime (^99mTc-HMPAO)
• activity stops abruptly at the skull base = lack of activity in distribution of anterior and middle cerebral arteries + superior sagittal sinus (SSS) during 1^st pass (= angiographic phase):
  • NO / faint activity in SSS on static image with ^99mTc pentetic acid
  • absence of activity in cerebrum on delayed images with ^99mTc bicisate / ^99mTc exametazime
• sagittal sinus not visualized

N.B.:

• common carotid arteries must be clearly visualized on 1^st pass which confirms a good technically adequate bolus
• activity in face (“hot nose” sign) / scalp must not be mistaken as focal brain activity

False negative:

decrease in intracranial pressure may allow continuous flow through intracranial arteries and has been observed in

1. extensive liquefactive brain necrosis
2. incompletely ossified skull in child
3. open head injury in adults