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.
Thallium Hot, HMPAO cold - what is it?
Tumor
Thallium cold, HMPAO cold - what is it?
Necrosis
CNS Lymphoma, toxo, bacterial abscess, cryptococcus, and TB are positive with what tracer? CNS lymphoma is also positive with what other tracer? How does this help?
Gallium, Thallium. Thallium helps differentiate CNS lymphoma with Toxoplasmosis (toxo will be cold, CNS lymphoma will be hot)
What do you look for in brain death imaging?
Absence of intracerebral perfusion
What vessel must be identified with radiotracer otherwise study is repeated?
Common carotid
Where will tracer stop in the setting of brain death?
Skull base
What is the hot nose sign?
Secondary to perfusion through the external carotid to the maxillary branches - it cant be used to call brain death though because it is only a secondary sign
Is SPECT used to dx stroke?
NO, but you can look at it
Acute stroke is what on SPECT?
Cold
Subacute stroke is what on SPECT?
Warm, from luxury perfusion (blood flow is more than dead cells need)
Chronic stroke is what on SPECT?
Cold
In ischemia, what medications are given to evaluate for cerebrovascular reserve? What is the result?
Acetazolamide (diamox) -> perfusion tracer. Image pre and post diamox; Areas already maxed on autoregulatory vasodilation are seen as hypointense (risk for ischemia), but areas that could benefit from revascularization will show worsening tracer uptake -> take to angio.
What is diamox?
Acetazolamide
Common indication for FDG brain PET?
Dementia imaging - because blood flow mimics metabolism HMPAO and ECD can also be used for dementia imaging
What area of the brain will show activity on FDG PET for the following conditions?
1) Alzheimers
2) Multi-infarct dementia
3) Dementia with lewy bodies
4) Picks/Frontotemporal Dementia
5) Huntingtons
1) Low posterior temporoparietal cortical area (identical to parkinson’s, posterior cingulate gyrus is first abnormal area)
2) Scattered areas
3) Low in lateral occipital cortex with SPARING of the cingulate gyrus (cingulate island)
4) Low in frontal lobe
5) Low activity in caudate nucleus and putamen
Condition with depressed blood flow and metabolism affecting the cerebellar hemisphere after a contralateral supratentorial insult?
Crossed Cerebellar Diaschisis
Is there pathology in the cerebelum with Crossed Cerebellar Diaschisis? Why?
NO - briefly, corticopontine-cerebellar pathway is disrupted and is shut down, pathology is in the cerebral hemisphere but affects the contralateral cerebellar hemisphere due to above pathway
What tracer is used for CSF imaging?
111 In DTPA
Explain normal CSF imaging exam + timing.
T0 = LP
T2-4 hrs - ascends and reaches basal cisterns
T4-24 hrs - flows around sylvian fissues and interhemispheric cistern
T24 hrs - clear from basilar cisterns and be over the convexities
What are some things that would be indicative of a negative CSF imaging exam?
1) tracer in lateral ventricles
2) failure to clear from the cisterns and localize over the convexities at 24 hours
What do you look for on communicating hydrocephalus (NPH = Wet wobbly wacky)?
1) early entry (4-6 hours) of tracer into lateral ventricles
2) persistence of tracer in the lateral ventricle > 24 hours
3) delay in assent to the parasaggital region > 24 hours
Can radionuclide cisternogram differentiate between communicating vs non-communicating hydrocephalus?
No - doesnt normally enter the ventricles
Differentiate NPH and non-obstructive (communicating) hydrocephalus? Hint: clinical
High opening pressure on LP with NPH
Most common sites (3) of CSF leak on cisternogram? Purpose of pledgets?
Between the cribiform plate and ethmoid sinus, from the sella turcica into the sphenoid sinus, and from the ridge of the sphenoid to the ear. Dont forget to image pledgets jammed into patient’s nose prior to exam (compare radiotracer in serum to pledgets and > 1.5 is positive)
Radiotracer for shunt patency study?
Tc DTPA
Normal shunt patency study vs abnormal?
Normal = radiotracer in peritoneum so distal end is patent, then manually occlude the distal limb to force into ventricles sp proximal end is patent Abnormal = fails to reflux into ventricles or it does but doesn't clear so proximal obstruction, or delayed tracer into the peritoneum (> 10 min) may mean partial distal obstruction
