Lecture Outline CTMRIEEGMEGPET (LO#5 BB3)Functional neuroimaging (LO#6 BB3)Cranial Trauma (LO#6 BB2)Practical Neuoimaging: clinical examples

Exam prep-what to know!

SagittalAxial

CT/ CAT scanning:IntroductionComputerised Axial Tomography/ Computer Tomography is well accepted imaging modality for evaluation of the entire body.

Use thousands of narrow-beam X-rays to pass through the tissue at different anglesX-rays are detected forming slices of images of the tissuesCT looks at structures rather than functionsUsed to detect brain diseaseSmall structures cannot be distinguished

2D measurement are taken in a helical manner all around the patientAttenuation coefficient reflects the degree to which the X-ray intensity is reduced by the material it passes throughAttenuation data is summed up from thousands of angles used in a process called reconstructionContrast dye is sometimes used to make the internal organs more visible in the imageBone appears white (hyper-intensity) ; gases and liquids are black (hypo-intensity); tissues are gray

CT/ CAT scanning:MethodologyBasically, a narrow beam of X ray scans across a patient in synchrony with a radiation detector on the opposite side of the patient. CT scan Showing a braintumor

CT/ CAT scanning:Tomographic imagesThe tomographic image is a picture of a slab of the patients anatomyThe 2D CT image corresponds to a 3D section of the patientThe 2D array of pixels in the CT image corresponds to an equal number of 3D voxels (volumetric pixel or, more correctly, Volumetric Picture Element) in the patientEach pixel on the CT image displays the average x-ray attenuation properties of the tissue in the corresponding voxel

What is a MRI?MRI stands for magnetic resonance imaging.

A MRI scanner has a magnetic field that is frequently up to 60,000 times as strong as Earths magnetic field!MRI equipment is expensive. 1.5 tesla scanners often cost between $1 million and $1.5 million USD. 3.0 tesla scanners often cost between $2 million and $2.3 million USD. Construction of MRI suites can cost up to $500,000 USD, or more, depending on project scope.Dangers of MRI's Video: http://www.youtube.com/watch?v=_lBxYtkh4ts

MRI How does it work? The BasicsPatient is bathed in a magnetic fieldThis field causes some of the bodys nuclei to behave like tiny compasses and line upThe nuclei spins on an axis, a bit like a spinning topThe atom that the MRI uses is the hydrogen atomProtons are most strongly affected by the Magnetic field it is more likely to line up than other atomsThen the nuclei are hit by pulsing radio waves-This RF makes the protons spin at a particular frequency, in a particular direction This is the Resonance bitOnce the RF pulses stop the nuclei go back to their state induced by the magnetThe energy now released by the nuclei acts like miniature radio stations giving out a signalThe coil now picks up that excess energy and sends the signals to the computer which is the Imaging part of the scanMolecules with magnetic charges align with the strong magnetic field.A radio frequency is used to tip these molecules over.

MRI How the image is madeOften, patients are injected with a contrast dye during the scanThe dye will reach different tissues at different ratesThe image being sent back to the computer will have different strengths depending on the level of contrast dye in the tissuesApplications:Diagnosing: MS; strokes; infections of the brain/spine/CNS; tendonitisVisualizing: Injuries; torn ligaments especially in areas difficult to see like the wrist, ankle or kneeEvaluating: Masses in soft tissue; cysts; bone tumors or disc problems.

Magnetic Resonance Imaging (MRI) image of the brain

MRI:AdvantagesThe MRI does not use ionizing radiation, which is a comfort to patientsAlso the contrast dye has a very low chance of side effectsA non invasive way of diagnosing diseases and conditions-They have given doctors the chance to detect cancers earlier than ever before-a view into the body without surgeryWhile CT provides good spatial resolution (the ability to distinguish two separate structures an arbitrarily small distance from each other), MRI provides comparable resolution with far better contrast resolution (the ability to distinguish the differences between two arbitrarily similar but not identical tissues). Variable thickness, any planeMany details without I.V contrast

CT vs MRI

MRI the disadvantagesClaustrophobia. Patients are in a very enclosed space.Weight and size. There are limitations to how big a patient can be.Noise. The scanner is very noisy-gets really scaryKeeping still. Patients have to keep very still for extended periods of time.Cost. A scanner is very, very expensive, therefore scanning is also costly.Medical Contraindications. Pacemakers, metal objects in body etc.Time consumingNot easily available (long waiting list)No on-call serviceNeed to tweak sequences as per the clinical questions; hence cannot be generalisedMRI has limitations:BoneAir-Pain abdomen ? causeTime consumingExpertise!

Material to read latter-Before MRI, there is a checklist!No mobiles, no credit cards, please!Known potential safety concerns due to large static magnetic field:Internal cardiac pacemakersSteel cerebral aneurysm clips (ferromagnetic)Small steel slivers embedded in eyeLife-support equipment with magnetic steelCochlear implantsStents anywhere in the body

Material to read latter-MRI Further checklist!Malfunction: ICDs, neurostimulators, bone growth stimulators (prosthetic heart valves)Superficial burns (uninsulated wire leads)NEED sedation: infants, younger peds, agitated adults (claustrophobia)Precautions: magnetic plastic cards, watches, hearing aids, ferromagnetic steel objects (LEAVE OUTSIDE)Loud noise (long-term hearing loss)Pregnancy!

Types of MRI imagesT1WIT2WIPDWIDWIADCGEPerfusion imagesfMRIBOLD imagesMRAMRVPost-Gd imagesVolumetric imagesMR arthrogramsFLAIRSTIREtc etc etc

Types of MRI images: T1- T2-weighted

For example, with particular values of the echo time (TE) and the repetition time (TR), which are basic parameters of image acquisition, a sequence takes on the property of T1 or T2-weighting. On a T2-weighted scan, water- and fluid-containing tissues are bright and fat-containing tissues are dark. The reverse is true for T1-weighted images. Damaged tissue tends to develop edema, which makes a T2-weighted sequence sensitive for pathology, and generally able to distinguish pathologic tissue from normal tissue. With the addition of an additional radio frequency pulse and additional manipulation of the magnetic gradients, a T2-weighted sequence can be converted to a Fluid Attenuated Inversion Recovery (FLAIR) sequence, in which free water is now dark, but edematous tissues remain bright. This sequence in particular is currently the most sensitive way to evaluate the brain for demyelinating diseases, such as multiple sclerosis.

Pooley, R. A. Radiographics 2005;25:1087-1099T1-weighted contrastIn the brain T1-weighted scans provide good gray matter/white matter contrast, in other words put simply, T1 Weighted Images highlights fat deposition.Types of MRI images: T1WI

Pooley, R. A. Radiographics 2005;25:1087-1099T2-weighted contrastTypes of MRI images: T2WIT2 images are particularly well suited to edema as they are sensitive to water content (edema is characterized by increased water content). In other words, put more simply, T2 weighted images light up liquid on the images being visualized.

Magnetic Resonance Angiography (MRA) is a group of techniques based on Magnetic Resonance Imaging (MRI) to image blood vessels. MRA generates pictures of the arteries to evaluate them for stenosis (abnormal narrowing) or aneurysms (vessel wall dilatations, at risk of rupture). A variety of techniques can be used to generate the pictures, such as administration of a paramagnetic contrast agent (gadolinium, Gd).Types of MRI images: Magnetic resonance angiography (MRA)Magnetic Resonance Angiography:Maximum intensity projection of an MRA covering from the top of the heart to just below the circle of WillisMRA showing the circle of Willis in the brain.

Material to read latter-T1 vs T2 MRI: Tissue Appearance

WTFATH2OMUSCLIGBONET1BDIDDProton DensityIIIDDT2IBIDD

Material to read latter-T1 vs T2 MRI: Tissue Appearance

Spine imagingMR is the investigation of choiceConventional CT, CT myelogram and conventional myelogram are no longer performed, unless MRI is contraindicated.First line of investigation in suspected spinal infection, cord compression, cauda equina, sciaticaVirtually everyone after the age of 40 years will have at least one degenerative disc/end plate

Functional Magnetic Resonance Imaging (fMRI) Looks at functions using oxygen uptakeWith functional magnetic resonance imaging (fMRI), is based on hemoglobin (the blood protein that binds oxygen). The fMRI can measure the oxygen used by the brain, and the most active brain areas use the most oxygen. Hemoglobin is diamagnetic when oxygenated (oxyhemoglobin) but paramagnetic when deoxygenated (deoxyhemoglobin). The magnetic resonance (MR) signal of blood is therefore slightly different depending on the level of oxygenation.

fMRI scan of the brain. The red areas are the ones showing the highest level of brain activity

Electroencephalograph (EEG)Electroencephalograph is used measure brain activity, electrodes (sometimes just a few and sometimes more than a hundred) are placed on the outside of the head. These electrodes are temporarily glued in place with glue that is easy to remove with an alcohol wipe. These electrodes measure the average amount of activity at any point in time for the cells that are directly under the electrode. The main use is research into brain function, diagnosis of epilepsy, sleep disorders.No risks (unlike CT scans for example)They are not as spatially accurate as fMRI

Material to read latter-Magnetoencephalograph (MEG)A magnetoencephalograph (MEG) is similar to an electroencephalograph, but it doesnt measure electrical activity. Instead, it measures the magnetic fields that brain activity produces naturally. MEGs are very sensitive and can measure changes in the brains activity from one millisecond to another.

PETPositron Emission Tomography-nuclear medical imaging techniqueInject short half-life radioactive isotopes(tracers) into body, then detect gamma raysPET detects the radiation emitted from radioactive substances injected into the bodyGamma rays given off are detected by PETGamma rays are converted to photons of light, and electrical signalsThe signals convert into slices of imagesCan show glucose metabolism in the brain, detect cancer, detect dementia and seizures, map brain function

Wilsons diseaseDas SK and Ray K (2006) Wilson's disease: an updateNat Clin Pract Neurol 2: 482493 10.1038/ncpneuro0291Hyperintensities due to copper deposition in the bilateral basal ganglia and thalami shown by T2-weighted MRI of the brain

Radiology: Glioblastoma is usually seen as a grossly heterogeneous mass. Ring enhancement surrounding a necrotic center is the most common presentation, but there may be multiple rings. Characterized by irregular ring-enhancement surrounding a central non-enhancing region of necrosis. Note the shaggy inner-margin of the ring, and the remarkable variation in its thickness. The small foci of internal enhancement represent islands of living tumor within the regions of necrosis. Surrounding vasogenic edema can be impressive, and adds significantly to the mass effect.

Glioblastoma multiforme (GBM)Axial Gd Enhanced T1W MRIAxial T2W MRI

MRI appearance two months after whole brain radiation (small lesions gone and large lesion much smaller)Metastatic brain tumors

Structure departed from normal position due to intracranial lesionCommonly found in tumors, hematoma, infarction, abscess, etcSigns of supratentorial space-occupying Displaced or compressed ventricleNarrowing or occlusionof ipsilateral cerebral sulcus and cisternShift of midline structuresSigns of infratentorial space-occupying Deformation and shift of fourth ventricle and brainstem Ventricular dilatation caused by CSF pathway obstruction

Basic Features of Brain Lesions Mass effect

Multiple sclerosis (MS)*Axial Gd Enhanced T1W MRAxial T2W MRMRI imaging of the brain Gd enhanced helps diagnose MS. Typical MS white matter lesions are bright lesions on T2-weighted image (left image), especially in the corpus callosum and periventricular regions.T2W axialT2W sagittal

Exam prep-what to know!

Recognize the clinical neuroimaging examples from this lecture

Recognize anatomical regions of the brain on CT/MRI-re-visit normal anatomy of the brain notes at the end of this lecture as you learn from the practical and weekly anatomy lectures.

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Figure MRI of childs head*Figure Left CT scan showing intracranial tumor*Axial plane CT vs MRI of brain tumor, same subject-mri clearly has better contrast resolution.*****Dystonia caused by defect in copper excretion*WHO Grade IV Cell of Origin: ASTROCYTE Synonyms: GBM, glioblastoma multiforme, spongioblastoma multiforme Common Locations: cerebral hemispheres, occasionally elsewhere (brainstem, cerebellum, cord) Demographics: peak from 45-60 years Histology: grossly heterogeneous, degeneration, necrosis and hemorrhage are common Special Stains: GFAP varies, often present in areas of better differentiation Progression : Can't get any worse. Radiology: Glioblastoma is usually seen as a grossly heterogeneous mass. Ring enhancement surrounding a necrotic center is the most common presentation, but there may be multiple rings. Surrounding vasogenic edema can be impressive, and adds significantly to the mass effect. Signs of recent (methemoglobin) and remote (hemosiderin) hemorrhage are common. Despite its apparent demarcation on enhanced scans, the lesion may diffusely infiltrate into the brain, crossing the corpus callosum in 50-75% of cases.

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