CNS Imaging Flashcards
Goal of brain imaging in NM?
Evaluate function - think of sz and ischemia, FDG brain for demential, cisternograms/shunt series etc.
What 3 agents are commonly used in CNS nukes? How are they separated?
Extracted (can be used for parenchymal imaging - SPECT): HMPAO, ECD NOT extracted (not used for parenchymal imaging): DTPA
What property of HMPAO and ECD allow them to cross BBB? Why is this important? What do they accumulate proportional to?
Neutral and lipophilic - they accumulate in the brain and can be used with SPECT to look at brain blood flow which mimics metabolism. Accumulate in cortex proportional to blood flow (gray > white matter).
What is the main difference between HMPAO and ECD?
HMPAO washout it fast. ECD washout is slow (more rapid clearance from blood pool with ECD).
Where does uptake favor in HMPAO and ECD, respectively?
Frontal lobe, thalamus, cerebellum - HMPAO
Parietal and occipital lobes - ECD
What property of DTPA allows it to stay in the blood?
Lipophobic - it stays in the blood or CSF if you put it there. Doesnt cross BBB.
What is the advantage of DTPA over HMPAO and ECD?
It can be repeated without delay.
What is the main utility for DTPA?
Shunt studies, NPH, brain death
Why do NM studies for seizure? Findings?
To localize seizure focus. Will be hot during ictal state, and cold interictal. Plan for surgery.
Describe properties of 201-Thallium. Decay type, half life, emissions.
Decay - electron capture
Half life - 3 days (73 hours)
Major emissions via characteristics x-rays of the daughter product Mercury 201 @ 69 kEV and 81 kEV
Usually given with chloride so it can be rapidly removed from blood
How does thallium behave? What conditions increase uptake?
Like potassium - crosses membranes via Na+/K pump. Tumors and inflammatory conditions increase the uptake of the tracer. Need living cell to transport it (tissue viability)
Normal distribution of 201-Thallium?
Thyroid, salivary glands, lung, heart, skeletal muscle, liver, spleen, bowel, kidneys, and bladder - muscle twitching is hot
Positive or Negative in the following:
1) Toxoplasma infxn
2) Lymphoma
3) Kaposi Sarcoma (gallium?)
4) Tumor
5) Necrosis
1) Negative
2) Positive
3) Positive (gallium negative)
4) Positive
5) Negative
What tracers are used for brain tumor SPECT?
201 Ti more commonly, and Sestamibi less commonly.
Do inflammatory conditions show up with 201 Ti SPECT?
Yes, but not as intense as tumor. Higher tumor grade = higher activity.
What is control for thallium study?
Scalp uptake. Abnormalities have greater uptake.
Can you use Thallium in conjunction with HMPAO?
Yes.