4 Not penetrate through BBB Brain Imaging AgentsNot penetrate through BBB99mTcO4-99mTc-GH201Tl99mTc-DTPA
5 Brain Imaging Agents (Cont.) Penetrate through BBBPerfusion99mTc-ECD99mTc-HMPAO123I-IMPMetabolic18F-FDGReceptor and Transporter11C-NMSP99mTc-TRODAT-1
6 Requirements for penetrating through BBB Small moleculeNone electronically chargedLipophilic
7 Brain Perfusion Imaging The injected tracer is freely diffusible from the blood pool into the brain.There is complete extraction of the tracer by the brain.Once taken up by the brain, the tracer is “trapped”, or that efflux from the brain is accounted for.Following the initial tracer uptake, there is no subsequent redistribution.
13 Abnormal Patterns Focal decreased uptake Focal increased uptake Crossed cerebellar diaschisisEnlargement of white matter or midline shiftStructure disorderAbnormal distribution of the tracercerebral atrophyDissymmetric distribution
19 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.
20 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 % for CT, MRI has a sensitivity of about 80% for the detection of acute infarction .
21 Subacute Phase Infarction Size of the infarct may be grossly underestimated due to luxury perfusionLuxury 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
22 Crossed Cerebellar Diaschisis Crossed cerebellar diaschisis (CCD): decreased cerebellar perfusion contralateral to the cortical infarct during the acute and subacute phases of middle cerebral artery territory strokes.Mechanism: loss of axons interconnecting the infarcted cortical regions with other brain structuresintact vascular reserve: activity increase in these areas following the administration of diamox due to the increased perfusion to these areas.
24 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.
25 Transient Ischemic Attacks(Cont.) Single or multiple cerebral blood perfusion defect or abscentEarly 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.
28 Alzheimer's DementiaDementia affects 10% of people over the age of 60 years and Alzheimer's accounts for roughly 50% of these cases. Alzheimer's disease (AD) has a prevalence of 0.3% in patients aged years, but increases to nearly 11% in year olds . The mental degeneration associated with Alzheimer's is insidious and progressive memory loss is the most important symptom.
29 Alzheimer's Dementia(cont.) Very early stage: normal CBF perfusionEarly stage: unilateral or bilateral temporoparietal perfusion defectModerate to severe stage:bilateral temporoparietal perfusion defectAdvanced stage: bilateral temporoparietal and frontal lobe perfusion defect
31 Alzheimer's Dementia(Cont.) A correlation has been described between the severity of these defects, and the severity of the patient's dementia .The cerebellum, primary visual areas, and primary sensorimotor areas along the central sulcus remain relatively intact.SPECT perfusion imaging has a sensitivity of 63%, a specificity of 82%, a positive predictive value of 81%, a negative predictive value of 65%, and an accuracy of 71% for the diagnosis of Alzheimer's .
32 Multi-infarct Dementia Multi-infarct dementia (MID) is characterized clinically by multiple cerebral infarcts that occur sporadically and produce a step-wise deterioration in intellectual function. MID is the second most common cause of dementia in the elderly.
33 Multi-infarct Dementia (Cont.) multiple, bilateral, and randomly distributed cortical perfusion defects that follow vascular territories. The basal ganglia, motor, and sensory cortices may also be involved (spared in Alzheimer's).
34 Pick's Disease (Frontal lobe dementia) A rare frontal dementiaSymptoms usually include the gradual onset of confusion with respect to place and time, anomia, slowness of comprehension, loss of tact, and changes in personality and behavior.SPECT images demonstrate bilateral, diffuse decreased frontal lobe perfusion extending to the cingulate gyrus.
35 EpilepsyEpilepsy 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.
36 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.
37 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).
38 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.
39 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 post-ictal (70%) or ictal (80-90%) SPECT, and inter-ictal PET FDG (70%) imaging.
41 Brain DeathLack of intracranial arterial flow: the carotid arteries are visualized in the neck, but there is an abrupt cut-off of activity at the skull baseSagittal/Venous sinuses are not visualized on subsequent static imagesThe "hot nose" sign: due to increased flow in the external carotid circulation.SPECT imaging in patients with brain death demonstrates no cerebral or cerebellar accumulation of the radiotracer
42 Brain Death (dynamic)Normal perfusionBrain Death
43 Brain Death (30 Min)Normal perfusionBrain Death
44 CNS TraumaSPECT is more sensitive than CT or MRI in detecting post traumatic CNS abnormalities both in the acute and remote stages. In the setting of acute trauma, small, non-focal frontal or occipital defects are associated with a favorable prognosis. Large or multifocal defects involving the parietal or temporal lobes, the cerebellum, or the brainstem are associated with an unfavorable prognosis.
46 Psychiatric Disorders Schizophreniahypofrontality on both PET FDG and SPECT perfusion images (i.e., relative decreased frontal perfusion/metabolism).Improved cortical activity in this region is seen following effective therapy
47 Drug abuseCocaine abuser: multiple small perfusion defect in brain cortexChronic alcoholics:reversible decreasing frontal lobe flow that reverts to normal with abstinence
48 Stress TestVarious stress methods which help to detect mild or latent abnormality.
59 Parkinson's DiseaseParkinson's is a progressive neurodegenerative disorder resulting from the progressive death of dopaminergic neurons in the nigrostriatal pathway.Symptoms consist of rigidity, bradykinesia, difficulty in initiating and stopping movement, and a resting tremor
60 Parkinson's Disease(Cont.) perfusion pattern in these patients is non-specific and demonstrates either normal or mild global cortical deficits. A pattern of bilateral posterior parietal/temporal defects indistinguishable from Alzheimer's may be observed in patients with Parkinson's disease with dementia.
64 Brain TumorsPET can play a role in grading of tumors, predictive of prognosis, differentiation of recurrent tumor from radiation necrosis.Most high-grade neolpasm are hypermetabolism, low-grade tumors are hypometabolism.Radiation necrosis are hypometabolism, recurrence are hypermetabolism.
65 Brain Tumor High Grade recurrence post RT PET FDG TRANSAXIALT-1 POST Gd