Radionuclide brain imaging-3

Report
Radionuclide Brain Imaging
Lecture 3
Dr Hussein Farghaly
PSMMC
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• Syllabus Contents
Cerebral Anatomy
Cerebral Perfusion Imaging
Radiopharmaceuticals
Methodology
Dosimetry
Clinical Applications
Cisternography
Radiopharmaceuticals
Methods
Pharmacokinetics
Dosimetry
Clinical Applications
Brain SPECT and PET Radiopharmaceuticals
Molecular Mechanism
FDG
PET/CT
Vascular
Tumor Cell
Glycogen
18FDG-1-P
Hexokinase
K1
18FDG
18FDG-6-
K3
18FDG
K2
Glucose
transporter
protein
K4
18FDG-6P
Glucose-6phosphatase
phosphogluconolactone
18F-fru-6-P
Glycolysis
HMP
shunt
Tomographic perfusion image of the brain
Tomographic perfusion image of the brain
Tomographic perfusion image of the brain
Tomographic perfusion image of the brain
Normal cerebral perfusion
Abnormal Patterns
 Focal decreased uptake
 Focal increased uptake
 Crossed cerebellar diaschisis
 Enlargement of white matter or midline
shift
 Structure disorder
 Abnormal distribution of the tracer
 cerebral atrophy
 Dissymmetric distribution
Clinical Indications of Brain Perfusion
Imaging
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Cerebral ischemia
Dementia
Seizures
Alzheimer diseases
psychiatric diseases
Brain death
Parkinson's Disease
Clinical Applications of Brain
Perfusion Imaging
Cerebral Vascular Diseases
• Acute CNS Ischemia/Infarction
• Transient Ischemic Attacks(TIA)
Acute CNS Ischemia/Infarction
• A focal or regional area of hypo- or absent
perfusion on SPECT images.
• Larger defects area on SPECT than those
noted on CT. The defects represent a
combination of a central zone of infarction
surrounded by a penumbra zone of ischemia but
potentially viable tissue.
Acute CNS Ischemia/Infarction(Cont.)
• Confirm the presence of cerebral infarction, monitor
the effects of acute thrombolytic therapy, and to
predict stroke outcome .
• Higher sensitive than CT in the early (first 24 hours)
detection of acute ischemia, sensitivity 88-95% vs.
20-63% for CT, MRI has a sensitivity of about 80%
for the detection of acute infarction .
Subacute Phase Infarction
• Size of the infarct may be grossly underestimated due
to luxury perfusion
• Luxury perfusion :uncoupling of flow and
metabolism following an infarct. Apparently
increased or normal tracer uptake despite the absence
of metabolism in the involved area possibly related to
either local breakdown in the blood-brain barrier or
hyperemia from local tissue acidosis
Crossed Cerebellar Diaschisis
Transient Ischemic Attacks
• It occurs in 10 to 20% of stroke patients.
One third of these patients suffer a stroke
within 5 years without treatment.
Transient Ischemic Attacks(Cont.)
• Single or multiple cerebral blood perfusion defect
or abscent
• Early detecting ischemia region with SPECT
compared to CT or MRI.
• Sensitivity is about 55-60% with SPECT, the
sensitivity declines with time.
• SPECT CBF stress test with Diamox has been
shown to increase the likelihood of detection of
residual blood flow changes after TIA.
Transient Ischemic Attacks
Epilepsy
• Epilepsy is one of the most prevalent neurological
disorders.Seizures can be classified as either
partial (focal) or generalized. Partial seizures
originate in a given area of the brain and can be
divided into simple (with no impairment of
consciousness) and complex (with impairment of
consciousness).
• About 10-20% of patients with partial complex
seizures have inadequate control on medical
treatment.Patients unresponsive to anti-convulsant
therapy may be surgical candidates which can
render the patient seizure free.
Epilepsy
(Cont.)
• Scalp EEG often fails to accurately localize the
seizure focus and although depth EEG is much
more accurate, it is also extremely invasive and
suffers from regional under sampling .
• CT and MRI have low sensitivity for seizure foci
detection, 17% and 34% respectively. The role
of brain SPECT is to localize the seizure focus.
Epilepsy
(Cont.)
• Ictal Imaging: hyperperfusion at the seizure
focus in 80 to 100% of patients. Crossed
cerebellar hyperperfusion can also be
identified in 75% of patients. Ipsilateral or
diffuse cerebellar hyperperfusion may also be
seen. Ipsilateral basal ganglia hyperperfusion
is also common.
• Ictal SPECT: sensitivities 81 to 93%. The
positive predictive value for localizing a
unilateral seizure focus can be as high as
97% (when the tracer was injected
immediately after the seizure).
Epilepsy
(Cont.)
• Inter-ictal Imaging: Inter-ictal (seizure free)
SPECT studies will demonstrate an area of
diminished tracer activity (hypoperfusion) at the
seizure focus in up to 50% of patients.
• Inter-ictal PET FDG studies demonstrate a focal
area of hypometabolism in 60 to 70% of patients
with normal MRI's. The area of hypometabolism
is often much larger than the actual area of
structural abnormality.
Epilepsy
(Cont.)
• The sensitivity for localization of the ictus site
using inter-ictal SPECT scanning ranges from
40 to 66%, which is less sensitive than postictal (70%) or ictal (80-90%) SPECT, and
inter-ictal PET FDG (70%) imaging.
PATIENT PREPARATION
Precautions
- Pregnancy is a relative contraindication especially during 1st trimester.
- Refrain from breastfeeding for 24 hrs for Tc-99m tracer and 2 hrs for FDG
Pre-arrival :
•Patients should be instructed, if possible, to avoid caffeine, alcohol or other
drugs known to affect cerebral blood flow (CBF) or glucose metabolism.
• Administration of psychoactive drugs should be avoided.
• If sedative drugs need to be considered, these should be administered not
earlier than 5 min post-injection for Tc-99m radiopharmaceuticals and 15
minutes for FDG.
•For PET-FDG imaging, patients fast for at least 6 hours to allow the
establishment of a metabolic steady state, a prerequisite for glucose
metabolism evaluation.. Free access to water is allowed. All chronic
medication should be maintained.
PATIENT PREPARATION cont.
Pre-Injection
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(a) patient cooperation. Keeping the patient informed about the whole procedure
usually improves its cooperation.
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(b) Achieve a consistent environment during tracer injection and uptake:
i. Place the patient in a quiet, dimly lit room, with ears unplugged.
ii. eyes open ,not speak and not read..
iii. Ensure that the patient is seated or reclining comfortably.
iv. Place intravenous access at least 10 min prior to injection to permit
accommodation. Simultaneously for FDG-PET study, obtain a blood sample for
determination of plasma glucose
vi. Have no interaction with the patient prior to, during or up to 5 min post-injection
for Tc-99m radiopharmaceuticals and 15 min for F-18 fluorodeoxyglucose.
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(c) Patients must be closely monitored at all times ; their neurologic deficits may
require special care and monitoring.
Relevant patient data suggested for optimal
interpretation of scans includes
● patient history, including :
any past drug use or trauma,
history of epilepsy, time and type of last seizure,
recent brain surgery
● neurological examination
● psychiatrical examination, mental status examination
● interictal EEG for epilepsy
● recent morphologic imaging studies (e.g. CT, MRI)
● current medication and when last taken.
EEG monitoring
• EEG monitoring prior to and during the study may be required
to exclude subclinical focal seizures in epileptic patients.
• Patients who are suspected to be unaware of partial seizures
(and are thus unable to report their frequency or occurrence),
require monitoring to assure that the study is indeed interictal.
• At least 20 minutes before injection and 10 minutes following
the injection, no epileptic activity should be detectable on the
EEG.
• Importantly, interictal CBF-SPECT and interictal FDGPET
should be performed after a period of at least 24 hours without
any clinical epileptic attack.
Time interval from injection to imaging
• For HMPAO and ECD, images obtained after a 20
min delay will be interpretable. For the best image
quality allow for ≥90 min delay from injection for
HMPAO and 45-60 min for ECD. For both tracers,
imaging should be completed within 4 hr postinjection if possible. Excessive delay should be
avoided.
• For FDG-PET, ≥30 min delay from injection to
imaging is required for reaching a steady state.
Common Questions??????
• Can a patient have a CT scan, diagnostic X ray
examination or MRI scan on the same day as the PET/CT
scan?
• Are there any radiation risks to other non-radiation
workers, e.g. anaesthetists, para medical staffs, nurses?
Can a patient breastfeed after a
scan?
• Some of the administered 18F-FDG might be
excreted in small amounts in breast milk. Normally,
the scan should be delayed until breast feeding has
stopped. But if the scan is needed urgently, then it is
advisable to collect milk before the scan, so that this
can be used to provide a feed after the scan.
Furthermore, milk should be collected and discarded
for 2 hours after the scan. Normal breast feeding can
resume after that.
• What if an ancillary staff member is in the early stage of
pregnancy and is exposed to a patient who has undergone
PET/CT?
There is no significant risk involved in such an exposure
• Is there significant risk to the staff taking care of these
patients?
No, there is no significant risk to the staff taking care of these patients. However,
radiation from patients undergoing other diagnostic and therapeutic radionuclide
procedures such as bone scans or radioiodine therapy may pose a risk of radiation
exposure to medical staff and does require attention. Patients undergoing PET/CT
scan would add to this radiation exposure. Following simple guidelines for reducing
contact time and increasing distance would suffice to minimize the radiation exposure
to staff. For patients with urinary catheters or incontinence, standard precautions for
dealing with biohazardous material would be sufficient to prevent undue radiation
exposure and contamination
rCBF changes during temporal lobe seizures
Epilepsy
Ictal
Inter
ictal
Interictal SPECT Brain Perfusion
Ictal SPECT Brain Perfusion
inter-ictal PET FDG
Extratemporal epilepsy
• Normal or inconclusive MRI is not unusual.
• Rapid rCBF changes. Short seizures are
common.
• Need for very early injection
• Interictal SPECT has low sensitivity (30%)
• Ictal SPECT remains highly sensitive
• Guide for invasive EEG recording
• Subtraction images or SISCOM are required
SISCOM
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Improved localization, mostly in extratemporal epilepsy.
Epileptogenic zone detected in 50% of patients with no
localizing EEG and 76% with normal MRI
Localizing SISCOM concordant with surgical site predicts
successful surgery outcome (58% vs. 18% with non-localizing
or non-concordant SISCOM).

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