Brain[1].txt

• 1. Blood flow studies
• 2. Neuronal function
• 3. CSF dynamics

Fat soluble drugs are allowed in the brain and water soluble drugs are blocked from the brain

The drug has to be free, un ionized, and fat soluble.

• Salivary glands, gastric mucosa, thyroid, choroid plexus
• 20mCi
• Slow plasma clearance

• TcO4
• Pentetate (DTPA)
• glucepate (GH)
• Rb82 chloride

These are not used anymore because of poor anatomic resolution

• Confined in a intravascular space
• Enter the brain at sites of BBB breakdown
• normal brain is cold and lesions are hot

• Enter brain by passive diffusion through intact BBB
• Trapping occurs: HMPAO and ECD are localized
• Normal brain is hot and lesions are cold

• Exametazime (HMPAO)
• bicisate (ECD)
• N13 ammonia

It is trapped in the brain by converting unionize to ionize by glutathione, which is an intracellular reducing agent (changes lipophilic to hydrophilic)

• 1. Brain death
• 2. Epilepsy
• 3. Cerebral vascular disease
• -stroke
• - ischemia

• 1. has to cross the BBB
• 2. Brain retention long enough to acquire images
• 3. It has to remain localize

HMPAO and ECD,

because any activity reaching the brain will remain fixed in the brain which is a more sensitive study

Because the brain swells and prevents blood from entering the brain (intracranial pressure due to edema)

Shunting of blood flow to nasopharynx via external carotid arteries

Grey matter

During ictus (seizure) and it's diminished to normal brain between seizures (intraictally)

• 1. EEG monitoring
• 2. HMPAO or ECD is used during ictus because of high first pass extraction across the BBB and remain fixed at the focus
• 3. Tracer best injected within first 20 seconds of seizure onset because 60 percent of patients show hyperperfusion if tracer is injected within 100 seconds of seizure termination (post ictus)
• 4.SPECT imaging following 15-30 mCi can begin as 30-60 min and 4hrs post seizure

• Ictal: inject within 30 seconds
• Postictal: 30 seconds -5 minutes

Best to compare both because ictal or Postictal image can appear normal if read alone, but may show increased perfusion relative to hypoperfusion at the same time

• F18-FDG
• hypoperfusion is present in all patients after 100 second following a seizure; 1.shows hypometabolism (glucose metabolism is reduced at the seizure focus compared to normal brain)

2. because of the extended time required for uptake by facilitated diffusion and intracellular phosphorylation to FDG phosphate

• Hypertension
• Diabetes mellitus (DM)
• carotid artery stenosis
• AV malformations
• Aneurysms
• Thrombosis

These can lead to TIA (transient ischemic attacks) or stroke (acute cerebral vascular ischemia)

Autoregulatory response to improve blood flow by causing vasodilation as carbon dioxide accumulates do to a drop in perfusion pressure.

* non compliant regions with reduce CvR may exhibit normal blood flow at rest, but demonstrate reduce blood flow when challenge with a vasodilator

• STRESS
• 1. Give 1g acetazolamide IV over 2 minutes (elevates CO2 which dilates vessels)
• 2. After 20 minutes inject 30 mCi of HMPAO ( measures brain perfusion)

REST

• 3. give HMPAO without acetazolamide
• 4. Compare rest and stress studies

*This study the detects whether an adequate reservoir exist ( if patient loses blood flow the reservoir provides bring with emergency blood)

• F18-FDG
• -hydrophilic:facilitated diffusion

• Tl-201 Chloride
• -active transport

• Epilepsy: ictus increase; interictus decreased uptake
• Tumor regrowth: increase uptake due to tumor metabolism; decreased uptake due to differentiated tumor necrosis
• Dementias: decreased uptake

• FDG: measures altered metabolic glucose distribution
• Florbetapir (Amyvid): demonstrates increased uptake into beta amyloid plaques and neurofibrillary tangles

**Amyvid is not definitive for AD**

• -Measures dopamine synthesis
• -Enzymatic marker of dopa decarboxylase activity.
• -has decreased uptake in dopaminergic neurons as disease severity increases (Parkinson's)

Distinguishes patients with essential tremor from patients with tremor associated with dopaminergic deficit related to Parkinson's Disease

• -Measures dopamine transporter function (DAT)
• -has decreased uptake in dopaminergic neurons as Parkinson's severity increases

In-111 DTPA and Tc99m DTPA

• -show abnormal CSF dynamics, shunts, and leaks
• -hydrophilic, remains confined in CSF

• Evaluation of CSF dynamics
• -use In-111 DTPA
•   -NORMAL DISTRIBUTION:excluded from ventricles
•   -HYDROCEPHALUS: enters ventricles