Central Nervous System Dr. Dalia Ahmed MD Assistant Prof. Of Nuclear Medicine NMT 473

Role of Nuclear medicine in CNS Nuclear medicine has in general a limited role in the central nervous system disorders. CT and MRI have a more important role in imaging CNS. In certain conditions nuclear medicine can provide more reliable information that cannot be obtained from other imaging modalities.

Role of Nuclear medicine in CNS Early diagnosis of Alzheimer disease and the differential diagnosis of dementia. Confirming brain death Preoperative localization of seizure foci. Cerebrovascular insufficiency: Location, size, and prognosis of cerebral ischemia and stroke. Evaluation of brain tumor recurrence. Evaluation and follow-up of certain cerebrospinal fluid disorders

Radiopharmaceuticals Several radiopharmaceuticals are used for imaging central nervous system. These include 99mTc HMPAO. 99mTc ECD. F-18 FDG . less commonly In111 DTPA.

Projection views transaxial slices

Normal 99mTc-HMPAO study

Normal brain perfusion study using 99mTc-HMPAO showing adequate and uniform activity in different areas

Dementia Dementia can be broadly categorized as resulting from vascular disease or from a progressive degenerative process. Brain SPECT imaging using regional cerebral blood flow (rCBF) tracers is useful to distinguish these two classes of dementia.

Alzheimer’s disease Alzheimer’s disease (the most common progressive degenerative dementia) is characterized by low global blood flow with accentuation of the diminution in the posterior temporal parietal lobes ,relative sparing of the thalamus and corpus striatum, as well as the somatomotor sensory cortex, and late involvement of the frontal lobes.

Brain Death Death is an irreversible, biological event that consists of permanent cessation of the critical functions of the organism as a whole. It implies permanent absence of cerebral and brainstem functions. It then qualifies as death (as brain is essential for integrating critical functions of the body).

Brain Death

Brain Death In patients with deep coma, it is important to be sure of brain death, especially if organ transplant is needed. Scan pattern show no blood flow to the brain which is sure sign of death compared to EEG.

Diagnosis of brain death The specific criteria necessary to make the diagnosis of brain death are as follows: The patient must be in deep coma with total absence of brainstem reflexes or spontaneous respiration. The clinical findings of brain death must be present for a defined period of observation (6-24 hours). The cause of the brain dysfunction must be diagnosed(e.g., trauma, stroke). Potentially reversible causes such as drug intoxication, metabolic derangement, or hypothermia must be excluded.

Brain death: No intracranial activity is seen on planar (a) or SPECT (b). Compare to where activity is present indicating no brain death

No tracer uptake in the brain parenchyma indicates brain death . This study is increasingly used as an alternative to cerebral angiography. Imaging is done using a radioactively labeled substance that readily crosses the blood–brain barrier such as 99mTc-HMPAO.

60 year, Patient with right hemiparesis, Which seen as hypoperfusion in left temproparietal region in Tc-ECD

Left hemispheric stroke.

Epilepsy Epilepsy is a disorder in which repeated episodes of seizures occur with or without an identifiable primary brain disease. Epilepsy affects about 0.5% of the population and usually begins in childhood, but it can affect people at any age.

Seizure Localization Seizures result when a focus of neuronal discharge is propagated indiscriminately within the brain by an abnormal neuronal electrochemical process. This process can be detected as electrical activity by an electroencephalograph (EEG). The use of Tc-99m-HMPAO in epilepsy patient during the ictal state or PET FDG during interictal phase is valuable in localizing detecting and epileptic foci in difficult cases where other modalities cannot provide accurate localization.

Brain Tumor The current therapy of malignant high-grade tumor is suboptimal, partly because of the difficulty in distinguishing recurrent viable tumor from cerebral necrosis resulting from effective therapy or radiation therapy. Conventional CT or MRI shows mass effect, edema, and contrast enhancement in both cases.

Brain Tumor Metabolic imaging can assist to differentiate these processes since effective therapy results in decreased tumor growth and metabolism, while suboptimal treatment will result in tumor regrowth and increased uptake of radionuclide markers of metabolism . PET has been successful in differentiating post-therapy changes from tumor recurrence . Additionally it has also been successful in determining the prognosis as it can more accurately predict the degree of malignancy than CT and MRI.

Cerebrospinal Fluid Abnormalities The cerebrospinal fluid (CSF), with a total volume of 150 mL, provides a mechanical buffer to the central nervous system. It is produced by the choriod plexus at a rate of 500 mL per day. The CSF drains into the sagittal sinus through absorption by the arachnoid villi. Mechanical obstruction of the brain ventricular system or absorption failure of the CSF at the granules leads to dilatation of the ventricular system called hydrocephalus with associated clinical disturbances.

Cerebrospinal Fluid Abnormalities These abnormalities can be studied by Introducing radiotracers intrathecally via a lumbar puncture and following their fate by scintillation imaging (Radionuclide Cisternoscintigraphy).

Radionuclide Cisternoscintigraphy This study is used to diagnose: • Normal pressure hydrocephalus • Hydrocephalus due to obstruction of the ventricular and duct system • Cerebrospinal fluid leak (rhinorrhea or otorrhea) • Evaluation of ventricular shunt patency

Radionuclide Cisternoscintigraphy Abnormalities of CSF drainage can be corrected by the placement of artificial shunting from the lateral ventricle to the peritoneal cavity. Other similar devices are used for drug delivery in CNS tumors. Radionuclide shunt studies are valuable also in monitoring the patency of these devices.