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BASICS IN NEUROIMAGING: CT, MRI AND PET

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Pramod Krishnan

This document discusses the use of computerized tomography (CT) and positron emission tomography (PET) in evaluating the central nervous system. CT is useful for imaging many neurological conditions such as trauma, tumors, strokes, and infections. It provides anatomical details quickly and is widely available, but MRI generally provides better soft tissue contrast. PET combined with CT or MRI provides functional imaging of brain metabolism and is useful for conditions like Alzheimer's disease, Parkinson's disease, seizures, and cancers. Both CT and PET have advantages and limitations and are generally used together with other clinical information for diagnosis and management of neurological diseases.

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Footer1 IMAGING IN NEUROLOGICAL SCIENCES Computerised Tomography and Positron Emission Tomography Dr Pramod Krishnan Consultant Neurologist, Epileptologist and Sleep specialist, Manipal Hospital, Bangalore.
Footer2 CENTRAL NERVOUS SYSTEM CT and PET are useful in the study of CNS
Footer3 INTRODUCTION CNS is made up of millions of neurons and supporting cells Impulses transmitted through ion exchanges. Why? Where? When? ?How- still largely unknown.
Footer4 INTRODUCTION Peculiarities of the CNS:  Regeneration is minimal or absent.  Almost completely enclosed by bone.  Standard surgical principles do not apply.  Incomplete understanding of pathology and recovery processes.  Functions of various CNS areas is yet to be defined.  Clinical examination is often inadequate to plan specific approaches like surgery.
Footer5 INTRODUCTION  Neurological disorders can be structural or functional or both.  Diagnosis and treatment often requires multi-specialty inputs.  Clinical history and examination guide the investigation.  Investigative findings should always be correlated with the patient’s clinical features.  Investigations only supplement and do not substitute a thorough patient interview and examination.
Footer6 DISEASE PROCESSES  Neoplasms/mass lesions  Vascular disorders  Degenerative disorders  Congenital defects  Infections  Non-infective inflammatory disorders  Toxic/ metabolic/nutritional  Trauma
Footer7 UNCOMFORTABLE PARADOX Neuroimaging is least useful in the most common neurological disorders. It is of limited use in the following disorders:  Headaches- especially migraine  Seizures and epilepsy.  Trigeminal neuralgia  Bells palsy.  Neuropathies.  Myopathies.
Footer8 COMPUTERISED TOMOGRAPHY
Footer9 NORMAL BRAIN ANATOMY ON CT
Footer10 CT CONTRAST • Improves detection and characterization of intra cranial lesions. • Opacifies blood vessels and detects areas of abnormal BBB break down. • Normal renal function is a pre- requisite. • Ionic vs non-ionic contrast.
Footer11 NEUROTRAUMA  Gold standard  Can be done rapidly.  Easily available.  Minimum patient preparation.  Repeatability.  Can be done in uncoooperative patients and ICU patients.  Highly sensitive for blood.  Bony details are well visualized and hence useful for detecting fractures.
Footer12 EXTRADURAL HEMORRHAGE
Footer13 SUBDURAL HEMORRHAGE Acute SDH Chronic SDH
Footer14 COMPLEX FRACTURES CT reconstruction of complex maxillo facial and skull fractures.
Footer15 TRAUMATIC CONTUSIONS
Footer16 DIFFUSE AXONAL INJURY MRI brain showing acute axonal injury. CT brain showing multiple small areas of hemorrhage consistent with diffuse axonal injury.
Footer17 TUMORS Calcified tumor with perilesional edema, probably a meningioma. Solitary lesion with contrast enhancement with significan tperilesionaledema and mass effect: glioblastoma/ brain abscess.
Footer18 TUMORS • CT is excellent in imaging calcified tumors and for detecting intra-tumor bleeds. • However, in all other aspects CT is far inferior to MRI which is the preferred imaging modality for tumors. • MRI is often diagnostic and obviates the need for biopsy in many cases. MRI brain allows accurate estimation of the size, relation to surrounding structures and also nature of the lesion using MRS.
Footer19 HYDROCEPHALUS CT brain with contrast is an excellent test for evaluation of hydrocephalus.
Footer20 HYDROCEPHALUS • MRI is the investigation of choice for hydrocephalus. • It can identify the type, severity, cause and quantify the obstruction far more accurately than CT scan. • In NPH, MRI can determine the CSF flow velocity across the obstruction and prognosticate surgical outcome.
Footer21 STROKE Evolved left MCA territory infarct more than 24 hours old. Evolving left MCA territory infarct of 16 hours duration.
Footer22 CT VS MRI IN STROKE CT brain on the left shows very subtle loss of grey-white differentiation in the left frontal region. This is easily made out on MRI diffusion. CT angiogram and CT perfusion can together provide excellent imaging of brain circulation but is more expensive, requires longer scan time and higher radiation exposure.
Footer23 DIFFICULT SITUATIONS IN THROMBOLYSIS “Maximum benefit with minimum complications” “Correct patient selection” Denial of treatment or inappropriate use= malpractice/negligence. • Time of onset not clear. • Deceptive time of onset. • Stroke with fall. • Cause of paralysis in the past is not clear- Stroke Vs Hemorrhage. • Estimation of size of infarct.
Footer24 CTA and CTP STUDIES in STROKE • CTA and CTP can be performed immediately after conventional CT scan, requiring only 5-10 minutes of additional time. It can be done in the same examination, with separate contrast boluses. • Allows detection of occlusion of large vessels and assessment of perfusion status of brain parenchyma. • Can help in deciding between intravenous and intra-arterial thrombolysis.
Footer25 CTA in CAROTID DISEASE • Provides an anatomic depiction of the carotid lumen and allows imaging of adjacent soft tissue and bony structures. • 3D reconstruction provides accurate measurements of the lumen diameter unlike MRA which tends to overestimate stenosis. • Especially useful in difficult situations like short neck, severe kinking, severe calcification or high bifurcation. • Sensitivity for carotid occlusion is between 97-99 % compared to DSA. • Sensitivity for severe carotid disease is 77% and specificity is 95%. • Preferred modality of imaging to plan for intervention.
Footer26 INTRACEREBRAL HEMORRHAGE
Footer27 CTA in SUBARACHNOID HEMORRHAGE CTA brain showing a small right ACA aneurysm. 3D Reconstruction using CTA showing large aneurysm in right MCA.
Footer28 CTA IN SUBARACHNOID HEMORRHAGE • Investigation of choice in the initial evaluation of SAH. • Can identify aneurysms as small as 3-5 mm. • Sensitivity compared to DSA is 83-98% and improving constantly. • Sensitivity is 97% with multidetector machines. • Preferred over MRA and even conventional angiography because of speed and reliability.
Footer29 INFECTIONS CT brain with contrast showing a right cerebellar ring- enhancing lesion. CT brain plain showing numerous calcified lesions of neurocysticercosis.
Footer30 INFECTIONS CT brain with contrast showing tuberculoma of the left frontal region with perilesional edema and mass effect with midline shift. CT brain with contrast showing enhancing meninges with basal exudates with hydrocephalus.
Footer31 LIMITATIONS OF CT • CT is practically useless in identifying demyelinating disorders like Multiple sclerosis. • It has poor sensitivity for chronic ischemic and toxic, metabolic disorders. • It is very poor at identifying degenerative diseases like Alzheimer's disease, progressive supranuclear palsy. Comparison of CT (left) and MRI (right) brain scans in multiple sclerosis. CT looks almost normal whereas MRI shows marked abnormalities.
Footer32 ADVANTAGES • Best preliminary neuroimaging test, especially in emergencies. • Cheap, easily available, with readily available expertise. • Adequate for routine decision making. • Repeatability. • 3D reconstruction provides valuable additional information. • Can be performed in patients who are uncooperative, critically ill, with prosthesis and those with pacemaker and other electronic devices. • Has reduced need for invasive imaging techniques. • Excellent for bone and blood imaging.
Footer33 DISADVANTAGES •Involves radiation •Inferior to MRI in resolution, contrast and in diagnostic yield. •Inferior to MRI in acute stroke, demyelinating disease, epilepsy, neuroinfection, degenerative diseases among others. •Affected by bony artifacts. •Posterior fossa structures are poorly visualised. •Not useful in spinal cord imaging. •Cannot be used in pregnant women. •CT Contrast is more toxic than MRI contrast.
Footer34 FUNCTIONAL BRAIN IMAGING POSITRON EMISSION TOMOGRAPHY COMBINED WITH CT SCAN
Footer35 TECHNIQUE • PET relies on the detection of positrons emitted during the decay of a radionuclide that has been injected into a patient. • Most commonly used moiety is fluoro-deoxy glucose. • Multiple images of glucose uptake activity are obtained after 45-60 min. • Images reveal differences in regional glucose metabolism among normal and pathological brain structures. • PET-CT or PET-MRI refers to functional imaging superimposed on high resolution of CT or MRI scans and provide more precise anatomical and functional diagnosis.
Footer36 ALZHEIMER’S DISEASE
Footer37 DEMENTIAS Centre images show bilateral parieto- temporal areas of hypometabolism in patients with AD, corresponding to the atrophy seen on MRI. Right sided images show bilateral fronto- temporal areas of hypometabolism in patients with FTD corresponding to the atrophy seen on MRI.
Footer38 PARKINSON’S DISEASE DaTscan (phenyltropane): Top panel: a normal scan. Middle panel: abnormalities in the putamen (reduced uptake) in a patient with Parkinson’s disease. Lower panel: a return to an almost normal scan following the introduction of levodopa.  
Footer39 FDG PET shows decreased uptake in the left temporal lobe in a lady with refractory seizures, suggesting the location of the epileptogenic focus.
Footer40 SCHIZOPHRENIA FDG PET comparing patients with schizophrenia (left) with normal subjects (right) shows increased metabolism in the stratum and medial prefrontal cortex in schizophrenia patients.
Footer41 CEREBRAL METASTASIS Treated case of melanoma of the toe. Focus of intense FDG uptake is seen in the midline anterior to the third ventricle on axial PET (a) and fused PET/CT images (b) suggesting the diagnosis of cerebral metastasis.
Footer42 Operable case of lung cancer for preoperative staging for brain metastases. Contrast enhanced T1 W axial MRI (a) shows a well-defined enhancing metastatic lesion in the pons (arrow). Lesion is not appreciated on axial PET and fused PET/CT images (b and c)
Footer43 GLIOMA
Footer44 THANK YOU

More Related Content

BASICS IN NEUROIMAGING: CT, MRI AND PET

  • 1. Footer1 IMAGING IN NEUROLOGICAL SCIENCES Computerised Tomography and Positron Emission Tomography Dr Pramod Krishnan Consultant Neurologist, Epileptologist and Sleep specialist, Manipal Hospital, Bangalore.
  • 2. Footer2 CENTRAL NERVOUS SYSTEM CT and PET are useful in the study of CNS
  • 3. Footer3 INTRODUCTION CNS is made up of millions of neurons and supporting cells Impulses transmitted through ion exchanges. Why? Where? When? ?How- still largely unknown.
  • 4. Footer4 INTRODUCTION Peculiarities of the CNS:  Regeneration is minimal or absent.  Almost completely enclosed by bone.  Standard surgical principles do not apply.  Incomplete understanding of pathology and recovery processes.  Functions of various CNS areas is yet to be defined.  Clinical examination is often inadequate to plan specific approaches like surgery.
  • 5. Footer5 INTRODUCTION  Neurological disorders can be structural or functional or both.  Diagnosis and treatment often requires multi-specialty inputs.  Clinical history and examination guide the investigation.  Investigative findings should always be correlated with the patient’s clinical features.  Investigations only supplement and do not substitute a thorough patient interview and examination.
  • 6. Footer6 DISEASE PROCESSES  Neoplasms/mass lesions  Vascular disorders  Degenerative disorders  Congenital defects  Infections  Non-infective inflammatory disorders  Toxic/ metabolic/nutritional  Trauma
  • 7. Footer7 UNCOMFORTABLE PARADOX Neuroimaging is least useful in the most common neurological disorders. It is of limited use in the following disorders:  Headaches- especially migraine  Seizures and epilepsy.  Trigeminal neuralgia  Bells palsy.  Neuropathies.  Myopathies.
  • 10. Footer10 CT CONTRAST • Improves detection and characterization of intra cranial lesions. • Opacifies blood vessels and detects areas of abnormal BBB break down. • Normal renal function is a pre- requisite. • Ionic vs non-ionic contrast.
  • 11. Footer11 NEUROTRAUMA  Gold standard  Can be done rapidly.  Easily available.  Minimum patient preparation.  Repeatability.  Can be done in uncoooperative patients and ICU patients.  Highly sensitive for blood.  Bony details are well visualized and hence useful for detecting fractures.
  • 14. Footer14 COMPLEX FRACTURES CT reconstruction of complex maxillo facial and skull fractures.
  • 16. Footer16 DIFFUSE AXONAL INJURY MRI brain showing acute axonal injury. CT brain showing multiple small areas of hemorrhage consistent with diffuse axonal injury.
  • 17. Footer17 TUMORS Calcified tumor with perilesional edema, probably a meningioma. Solitary lesion with contrast enhancement with significan tperilesionaledema and mass effect: glioblastoma/ brain abscess.
  • 18. Footer18 TUMORS • CT is excellent in imaging calcified tumors and for detecting intra-tumor bleeds. • However, in all other aspects CT is far inferior to MRI which is the preferred imaging modality for tumors. • MRI is often diagnostic and obviates the need for biopsy in many cases. MRI brain allows accurate estimation of the size, relation to surrounding structures and also nature of the lesion using MRS.
  • 19. Footer19 HYDROCEPHALUS CT brain with contrast is an excellent test for evaluation of hydrocephalus.
  • 20. Footer20 HYDROCEPHALUS • MRI is the investigation of choice for hydrocephalus. • It can identify the type, severity, cause and quantify the obstruction far more accurately than CT scan. • In NPH, MRI can determine the CSF flow velocity across the obstruction and prognosticate surgical outcome.
  • 21. Footer21 STROKE Evolved left MCA territory infarct more than 24 hours old. Evolving left MCA territory infarct of 16 hours duration.
  • 22. Footer22 CT VS MRI IN STROKE CT brain on the left shows very subtle loss of grey-white differentiation in the left frontal region. This is easily made out on MRI diffusion. CT angiogram and CT perfusion can together provide excellent imaging of brain circulation but is more expensive, requires longer scan time and higher radiation exposure.
  • 23. Footer23 DIFFICULT SITUATIONS IN THROMBOLYSIS “Maximum benefit with minimum complications” “Correct patient selection” Denial of treatment or inappropriate use= malpractice/negligence. • Time of onset not clear. • Deceptive time of onset. • Stroke with fall. • Cause of paralysis in the past is not clear- Stroke Vs Hemorrhage. • Estimation of size of infarct.
  • 24. Footer24 CTA and CTP STUDIES in STROKE • CTA and CTP can be performed immediately after conventional CT scan, requiring only 5-10 minutes of additional time. It can be done in the same examination, with separate contrast boluses. • Allows detection of occlusion of large vessels and assessment of perfusion status of brain parenchyma. • Can help in deciding between intravenous and intra-arterial thrombolysis.
  • 25. Footer25 CTA in CAROTID DISEASE • Provides an anatomic depiction of the carotid lumen and allows imaging of adjacent soft tissue and bony structures. • 3D reconstruction provides accurate measurements of the lumen diameter unlike MRA which tends to overestimate stenosis. • Especially useful in difficult situations like short neck, severe kinking, severe calcification or high bifurcation. • Sensitivity for carotid occlusion is between 97-99 % compared to DSA. • Sensitivity for severe carotid disease is 77% and specificity is 95%. • Preferred modality of imaging to plan for intervention.
  • 27. Footer27 CTA in SUBARACHNOID HEMORRHAGE CTA brain showing a small right ACA aneurysm. 3D Reconstruction using CTA showing large aneurysm in right MCA.
  • 28. Footer28 CTA IN SUBARACHNOID HEMORRHAGE • Investigation of choice in the initial evaluation of SAH. • Can identify aneurysms as small as 3-5 mm. • Sensitivity compared to DSA is 83-98% and improving constantly. • Sensitivity is 97% with multidetector machines. • Preferred over MRA and even conventional angiography because of speed and reliability.
  • 29. Footer29 INFECTIONS CT brain with contrast showing a right cerebellar ring- enhancing lesion. CT brain plain showing numerous calcified lesions of neurocysticercosis.
  • 30. Footer30 INFECTIONS CT brain with contrast showing tuberculoma of the left frontal region with perilesional edema and mass effect with midline shift. CT brain with contrast showing enhancing meninges with basal exudates with hydrocephalus.
  • 31. Footer31 LIMITATIONS OF CT • CT is practically useless in identifying demyelinating disorders like Multiple sclerosis. • It has poor sensitivity for chronic ischemic and toxic, metabolic disorders. • It is very poor at identifying degenerative diseases like Alzheimer's disease, progressive supranuclear palsy. Comparison of CT (left) and MRI (right) brain scans in multiple sclerosis. CT looks almost normal whereas MRI shows marked abnormalities.
  • 32. Footer32 ADVANTAGES • Best preliminary neuroimaging test, especially in emergencies. • Cheap, easily available, with readily available expertise. • Adequate for routine decision making. • Repeatability. • 3D reconstruction provides valuable additional information. • Can be performed in patients who are uncooperative, critically ill, with prosthesis and those with pacemaker and other electronic devices. • Has reduced need for invasive imaging techniques. • Excellent for bone and blood imaging.
  • 33. Footer33 DISADVANTAGES •Involves radiation •Inferior to MRI in resolution, contrast and in diagnostic yield. •Inferior to MRI in acute stroke, demyelinating disease, epilepsy, neuroinfection, degenerative diseases among others. •Affected by bony artifacts. •Posterior fossa structures are poorly visualised. •Not useful in spinal cord imaging. •Cannot be used in pregnant women. •CT Contrast is more toxic than MRI contrast.
  • 35. Footer35 TECHNIQUE • PET relies on the detection of positrons emitted during the decay of a radionuclide that has been injected into a patient. • Most commonly used moiety is fluoro-deoxy glucose. • Multiple images of glucose uptake activity are obtained after 45-60 min. • Images reveal differences in regional glucose metabolism among normal and pathological brain structures. • PET-CT or PET-MRI refers to functional imaging superimposed on high resolution of CT or MRI scans and provide more precise anatomical and functional diagnosis.
  • 37. Footer37 DEMENTIAS Centre images show bilateral parieto- temporal areas of hypometabolism in patients with AD, corresponding to the atrophy seen on MRI. Right sided images show bilateral fronto- temporal areas of hypometabolism in patients with FTD corresponding to the atrophy seen on MRI.
  • 38. Footer38 PARKINSON’S DISEASE DaTscan (phenyltropane): Top panel: a normal scan. Middle panel: abnormalities in the putamen (reduced uptake) in a patient with Parkinson’s disease. Lower panel: a return to an almost normal scan following the introduction of levodopa.  
  • 39. Footer39 FDG PET shows decreased uptake in the left temporal lobe in a lady with refractory seizures, suggesting the location of the epileptogenic focus.
  • 40. Footer40 SCHIZOPHRENIA FDG PET comparing patients with schizophrenia (left) with normal subjects (right) shows increased metabolism in the stratum and medial prefrontal cortex in schizophrenia patients.
  • 41. Footer41 CEREBRAL METASTASIS Treated case of melanoma of the toe. Focus of intense FDG uptake is seen in the midline anterior to the third ventricle on axial PET (a) and fused PET/CT images (b) suggesting the diagnosis of cerebral metastasis.
  • 42. Footer42 Operable case of lung cancer for preoperative staging for brain metastases. Contrast enhanced T1 W axial MRI (a) shows a well-defined enhancing metastatic lesion in the pons (arrow). Lesion is not appreciated on axial PET and fused PET/CT images (b and c)