Keep Imaging Simple: An Introduction To Neuroimaging Meghan Elkins, OD, FAAO Please silence all mobile devices and remove items from chairs so others can sit. Unauthorized recording of this session is prohibited.
Disclosure Statement: Nothing to disclose
COURSE OBJECTIVES Brief radiation introduction Brief review of how X-rays, CTs, and MRIs work Recognize anatomic structures for normal patients Examples of pathologic and incidental findings
RADIATION
RADIATION Ionizing Radiation: DNA damage d/t high energy wavelengths Natural occurring sources: sun, radon Millisieverts (msv) NOT measured by Geiger counter Quantity of radiation dose Milligray (mgy) Approximate dose of radiation absorbed
RADIATION RISKS msv Comparisons Chest X-Ray 0.06 7 Hour Flight 0.1 Lumbar Spine X-Ray 1.5 Head CT 2 Chest CT 5 Angiogram 16 Potential for increased cancer risk if multiple CT scans http://www.xrayrisk.com/calculator/calculator.php
X-RAYS!
INDICATIONS qhistory of metal in/around eyes qused prior to MRI
EXAMPLES!
EXAMPLES!
COMPUTED TOMOGRAPHY CT
INDICATIONS Trauma Exophthalmos Acute CVA Cellulitis Sinus Visualization And many more!
CT STRATEGY Utilizes x-rays and computer algorithms to visualize bone and organ structures Best for blood and bone Black and white images: Tissue density White à High density à bone Black à Low density à air
CT REPORTS Technique Slice size Location Method DLP: Dose Length Product Required by law Total energy into pt Findings Impression
CONTRAST Iodine based Required for CTA Contraindications: Allergy Asthma Kidney Issues Pregnancy Children Blocks or attenuates x-rays Anywhere contrast goes, enhancement follows Hyperdense Brighter
CONTRAST Not needed for imaging of high density structures Hemorrhagic stroke Bony structures Metallic Foreign bodies Wood = contrast helps BUN/Creatinine GFR > 60 = okay < 30 = not okay
NO CONTRAST CONTRAST
MAGNETIC RESONANCE IMAGING MRI
BACKGROUND Uses magnets! CT is good for bones and blood MRI is good for anatomy and soft tissue Depends on hydrogen nuclei which release energy absorbed from short electromagnetic pulsations
BACKGROUND Two main imaging sequences T1 T2 Weighting: measurement of excited proton relaxation time after magnet turned off Specific tissues have different relaxation times viewed best in either T1or T2
CONTRAINDICATIONS Metal unless manufactured approved Tattoos https://www.discovery.com/tv-shows/mythbusters/videos/exploding-tattoominimyth BUSTED in 2004 Claustrophobia (relative) 350+ lbs (relative)
CONTRAINDICATIONS Metal unless manufactured approved Tattoos https://www.discovery.com/tv-shows/mythbusters/videos/exploding-tattoo-minimyth BUSTED in 2004 Claustrophobia (relative) 350+ lbs (relative)
T1-WEIGHTED Normal anatomy highlighted Recovery time < 1000 msec Vitreous will help you determine which type of scan you are looking at (CSF will, too) DARK Vitreous = HYPOintense = T1 Utilize T1 images with contrast to compare enhancements
T2-WEIGHTED Pathologies highlighted: water and edema are Recovery time > 1000 msec Bright CSF/Vitreous = HYPERintense = T2 Blood = black
T1 VS T2 CHART Tissue T1 T2 CSF Dark Bright Muscle Gray Dark Gray Fat Bright Light Gray Air Very Dark Very Dark Inflammation Dark Bright Adapted from http://casemed.case.edu/clerkships/neurology/web%20neurorad/mri%20basics.htm. Accessed: 01/29/2018.
MRI WITH CONTRAST Gandolinium based Blood-brain barrier T1 images Enhanced images = Tumors Inflammation BUN/Creatinine à Calculate GFR Omniscan > 60 Prohance 30 60 Contrast Contraindicated < 30 Less adverse events than iodine
FAT SUPPRESSION Suppresses bright signal from fat: Better visualizes orbital structures Tumors Inflammation Vascular Malformations Short T1 Inversion Recovery: best for optic neuritis Optic nerve enhancement post-contrast Must have fat suppression
FLUID ATTENUATION INVERSION RECOVERY Recovery time > 1000 msec Suppresses bright CSF on T2 Vitreous is also dark Remember: T2 should have a bright vitreous VERY useful for demyelination (periventricular plaques) Useful for pathology near sinuses
DIFFUSION WEIGHTED IMAGING Acute infarcts! = BAD Significant artifacts Poorer resolution Typically T2-weighted May have T2 shine-through ADC Map Post-processing used in conjunction with DWI Dark = Bad
OTHER OPTIONS MRA Contrast not needed Blood moves through vessels producing dark signal but bright on MRA d/t series of images processed Circle of Willis! MRV Example: venous sinus thrombosis No contrast
OTHER OPTIONS Orbital CT No need for fat suppression Fat is inherently dark on CT Orbital MRI Must use fat suppression technique Supposedly: cannot do in open MRI
T2 T1 FLAIR T2 FLAIR DWI ADC EXAMPLES Many more strategies!
ANATOMIC REVIEW
ANATOMIC REVIEW Axial Sagittal
AXIAL SCANS 3 1. Medulla 2. Cerebellum 3. Maxillary Sinus 4. Masseter Muscle 5. Semicircular Canals 1 2 5 4
AXIAL SCANS 3 1. Pons 2. Fourth Ventricle 3. Ethmoid Sinus 4. Basilar Artery 5. Internal Carotid Artery 6. Temporal Lobe 7. Sphenoid Sinus 7 5 4 1 2 6
AXIAL SCANS 1. Pons Almost Midbrain! 2. Superior Cerebral Peduncle 3. Tegmentum 4. Temporal Lobe 5. Cavernous Sinus 5 1 2 3 4
AXIAL SCANS 6 1. Midbrain 2. Cerebral Aqueduct 3. Cerebellum 4. Straight Sinus 5. Occipital Lobe 6. Optic Nerve 3 1 2 4 5
AXIAL SCANS 1. Higher Midbrain 2. Inferior Colliculus 3. Pituitary Stalk 4. Optic Tract 5. Optic Chiasm 6. Mammillary Bodies 7. Occipital Lobe 4 3 5 6 1 2 7
AXIAL SCANS 1. Superior Colliculus 2. Superior Sagittal Sinus 3. Occipital Lobe 4. Temporal Lobe 5. Third Ventricle 5 1 4 2 3
AXIAL SCANS 4 5 1. Corpus Callosum 2. Septum Pellucidum 3. Lateral Ventricles 4. Superior Sagittal Sinus 5. Frontal Lobe 6. Parietal Lobe 1 2 3 4 6
CORONAL SCANS
SAGITTAL SCANS 1
FUN FINDINGS CT MRI
CALCIFICATIONS Pineal Gland Choroidal Plexus
ISCHEMIC STROKE T2 FLAIR T2
ORBITAL INFLAMMATION
BRAIN ABSCESS
ORBITAL FRACTURE (CT)
WHAT DOES AN INTRAOCULAR FOREIGN BODY LOOK LIKE?
IDIOPATHIC INTRACRANIAL HYPERTENSION
T1 post MENINGIOMA 60-something wm No complaints Incidental finding: pseudopapilledema vs papilledema MRIs ordered STAT Patient came back to eye clinic to await results T1 Pre T2 Pre
GENERALIZED ATROPHY
RETINAL CALCIFICATIONS
CHOROIDAL MELANOMA T1 FLAIR Fat Sat T1 FLAIR
AV MALFORMATION
SOURCES 1. Radiation risk from medical imaging. https://www.health.harvard.edu/cancer/radiation-risk-from-medical-imaging. Published: October 2010. Accessed: 4 October 2018. 2. The millisievert and milligray as measures of radiation dose and exposure. https://www.mun.ca/biology/scarr/radiation_definitions.html. Accessed: 4 October 2018. 3. Mettler FA, et al. "Effective Doses in Radiology and Diagnostic Nuclear Medicine: A Catalog," Radiology (July 2008), Vol. 248, pp. 254 63. 4. Tiny FB picture: https://webeye.ophth.uiowa.edu/eyeforum/cases-i/cases/iofbxray_08232004.jpg 5. Cat picture: http://i.dailymail.co.uk/i/pix/2012/10/02/article-2211701-154e7360000005dc-858_634x543.jpg 6. Magnetic Resonance Imaging (MRI) of the Brain and Spine: Basics. http://casemed.case.edu/clerkships/neurology/web%20neurorad/mri%20basics.htm. Accessed: 01/29/2018. 7. Korchi, AM, et al. Imaging of the cavernous sinus lesions. Diagnostic and Interventional Imaging. (95)9: 849-859. September 2014. This lecture could not have been possible without the assistance of Dr. Amina Tariq, Staff Radiologist, Huntington VAMC.
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