Article Figures & Data
Figures
- FIGURE 1.
Findings of persistence of blood flow on blood flow study using nonlipophilic radiopharmaceutical in 22-y-old man with ruptured aneurysm of left posterior inferior cerebral artery. (A) CT scan demonstrates intraventricular and subarachnoid hemorrhage. (B) Two-second flow images (top rows) after injection of 905 MBq of 99mTc-DTPA demonstrate excellent visualization of anterior (vertical arrows) and middle (horizontal arrows) cerebral arteries, forming trident appearance indicating presence of perfusion, which progresses into visualization of intracranial venous sinuses. On immediate anterior (Ant) and right lateral (R lat) static images (bottom row), radiopharmaceutical does not cross blood–brain barrier; however, activity is noted in venous sinuses. (Reprinted from (8).)
- FIGURE 2.
Findings of persistence of blood flow on blood flow study using lipophilic radiopharmaceutical in 18-y-old man after motor vehicle accident followed by left-sided craniotomy to evacuate subdural hematoma. (A) CT indicates loss of white matter–to–gray matter differentiation in left posterior cerebral artery territory and right posterior parasagittal cortex territory. There is diffuse cerebral edema and transtentorial herniation with compression of basilar cisterns. (B) Two-second flow images (top rows) demonstrate excellent visualization of anterior (vertical arrows) and middle (horizontal arrows) cerebral arteries, resembling trident, with retention of activity within brain parenchyma, thereby indicating presence of blood flow. Anterior (Ant) and left lateral (L lat) parenchymal phase images (bottom row) demonstrate somewhat inhomogeneous though extensive brain perfusion. (Reprinted from (8).)
- FIGURE 3.
Findings of absence of blood flow on blood flow study using lipophilic radiopharmaceutical in 33-y-old man after hanging. (A) CT scan demonstrates diffuse cerebral edema with narrowing of lateral ventricles and bilateral infarction of lentiform nuclei. (B) Two-second flow images (top rows) after injection of 799 MBq of 99mTc-HMPAO demonstrate excellent visualization of common carotid arteries (arrows) but absence of flow into calvarium, consistent with brain death. Anterior (Ant) and left lateral (L lat) parenchymal phase images (bottom row) demonstrate complete lack of perfusion within boney skull (light-bulb or hollow-skull sign), including absence in posterior fossa and superior sagittal sinus. More technically demanding SPECT imaging is generally not performed in these critically ill patients. (Reprinted from (8).)
Tables
Parameter Finding Clinical prerequisites Clinical or neurologic evidence of acute central nervous system catastrophe compatible with diagnosis of brain death, with known or proximate cause of brain death identified Exclusion of confounding variables such as severe electrolyte, metabolic, endocrine, or circulatory disturbance No presence of drug intoxication or poisoning that could confound clinical assessment, including any sedative drugs administered by clinicians Core temperature maintained above 36°C (97°F), as hypothermia may suppress brain function, potentially leading to inaccurate clinical determination Systolic blood pressure maintained above 100 mg Hg and mean arterial pressure of at least 75 mm Hg for adults; in children, systolic blood pressure and mean arterial pressure should be at or above fifth percentile for age; administration of vasopressors may be needed to achieve this level Clinical findings Coma Absence of brain-originating motor response, including response to pain stimulus above neck or other brain-originating movements Absence of reflexes, including pupillary light, corneal, gag, oculocephalic (doll’s eyes), and oculovestibular reflexes (caloric responses) Absence of jaw jerk Absence of cough with tracheal suctioning Absence of sucking or rooting reflexes (in neonates) Apnea as demonstrated by apnea test Observation period Minimum of 6 h; longer periods recommended in children and for certain conditions such as after cardiopulmonary resuscitation or other severe acute brain injuries Test Diagnostic criterion Advantage Disadvantage Four-vessel conventional cerebral angiography Absence of blood flow at or beyond carotid bifurcation or circle of Willis Traditional gold standard among cerebral blood flow tests Requirement for transportation to imaging department Invasive Contrast precautions for kidneys Contrast stasis or delayed filling in intracranial arteries Radionuclide perfusion scintigraphy Absence of blood flow at or beyond carotid bifurcation or circle of Willis Sensitive for confirming brain death in presence of confounding variables Requirement for transportation to imaging department Hollow skull if using brain-specific radiopharmaceutical Potential for limitation of brain stem evaluation via planar imaging Requirement for coordination with multiple hospital personnel and nuclear pharmacy Possibility that on-call nuclear medicine staffing is not supported Restricted off-hours availability of radiopharmaceuticals Transcranial Doppler Presence of small systolic peaks without diastolic flow or reverberating flow pattern, indicating high vascular resistance and supporting diagnosis of brain death Noninvasive Requirement for technical experience Can be done at bedside Evaluation precluded by 10%–25% prevalence of temporal bone thickening No contrast medium used Reports of both false-positive and false-negative results (compared with cerebral angiography or other standard) MRI of arterial blood flow Absence of arterial blood flow Demonstration of variable degrees of cerebral edema and mass effect Requirement for transportation to imaging department Requirement for gadolinium contrast agent for improved sensitivity Requirement for patients to lie flat Possibility of short periods in which clinical monitoring is impossible CT angiography Absence of cerebral circulation perfusion Widespread availability Uncertain clinical utility of CT angiography Requirement for iodine contrast injection Administered activity (intravenous) Largest radiation dose Effective dose Radiopharmaceutical MBq mCi Organ mGy/MBq rad/mCi mSv/MBq rem/mCi 99mTc-DTPA 555–1,110 15–30 Urinary bladder wall 0.065 0.24 0.0063 0.023 99mTc-HMPAO 370–1,110 10–30 Kidneys 0.034 0.0126 0.0093 0.034 99mTc-ECD 370–1,110 10–30 Urinary bladder wall 0.05 0.18 0.0077 0.028 Administered activity (intravenous) Minimum dose Maximum dose Largest radiation dose Effective dose Radiopharmaceutical MBq/kg mCi/kg MBq mCi MBq mCi Organ mGy/MBq rad/mCi mSv/MBq rem/mCi 99mTc-DTPA 7.4 0.2 370 10 740 20 Urinary bladder wall 0.17 0.63 0.017 0.063 99mTc-HMPAO 11.1 0.3 185 5 740 20 Thyroid 0.14 0.52 0.027 0.099 99mTc-ECD 11.1 0.3 185 5 740 20 Urinary bladder wall 0.11 0.41 0.022 0.081 Fetal dose Stage of gestation mGy/MBq rad/mCi mGy rad 99mTc-HMPAO Early 0.0087 0.032 3.2–9.7 0.32–0.97 3 mo 0.0067 0.025 2.5–7.4 0.25–0.74 6 mo 0.0048 0.018 1.8–5.3 0.18–0.53 9 mo 0.0036 0.013 1.3–4.0 0.13–0.40 99mTc-DTPA Early 0.012 0.044 6.7–8.9 0.67–0.89 3 mo 0.0087 0.032 4.8–6.4 0.48–0.64 6 mo 0.0041 0.015 2.3–3.0 0.23–0.30 9 mo 0.0047 0.017 2.6–3.5 0.26–0.35 Nondiffusible, non–brain-specific radiopharmaceutical Diffusible, brain-specific radiopharmaceutical Benefit Drawback Benefit Drawback Rapid renal excretion facilitates repeat examinations if necessary Primarily planar imaging is performed Planar imaging and SPECT or SPECT/CT can be performed if patient condition allows and is needed Repeat examination on same day is often not possible because of parenchymal retention There is greater dependency on injection technique No significant redistribution occurs for several hours, making it easy to perform and interpret imaging High radiochemical stability and purity are essential to prevent false-positive interpretation Delayed images may show superior sagittal sinus activity even in presence of brain death in as many as 50% of patients. Procedure is more technically forgiving—dynamic imaging is noncritical step in image acquisition Superficial scalp blood flow interferes Parenchymal trapping appears preserved even in presence of metabolic disturbances Dynamic flow Static SPECT Anterior Anterior for blood pool images; additional static images include posterior and laterals Only if using 99mTc-HMPAO or 99mTc-ECD and only as needed 1–3 s/frame for 1–2 min 500,000–1,000,000 counts per image Time per stop and counts acquired dependent on radiopharmaceutical dose administered (e.g., 64 projections, 20–40 s/stop [200,000 counts]); use of institutional guideline for other brain SPECT studies 15%–20% window around 140-keV photopeak 15%–20% window around 140-keV photopeak 15%–20% window around 140-keV photopeak 128 × 128 matrix 128 × 128 matrix At least 128 × 128 matrix LEAP, LEHR collimators LEAP, LEHR collimators LEAP, LEHR, or UHR collimators; fanbeam or other focused collimator is needed for increased resolution and higher counting rates Zooming or magnification optional Zooming or magnification optional Zoom set to produce pixel size of 3.5 mm or less Circular or noncircular orbit with smallest radius possible Continuous or step-and-shoot LEAP = low-energy all-purpose; LEHR = low-energy high-resolution; UHR = ultrahigh resolution.
