Neuroradiology and Sectional Anatomy

Understand basic types of brain imaging techniques Introduction Objectives: Understand basic types of brain imaging techniques Understand the benefits of different brain imaging techniques Be able to identify basic brain structures in MR images.

Computerized tomography Magnetic resonance imaging (MRI) Introduction Topics covered: Computerized tomography Magnetic resonance imaging (MRI) Functional imaging techniques Angiography Sectional anatomy in MRI images

Computerized Tomography Computerized tomography (CT): CT scans measure the density of tissue (hyperdense, hypodense, isodense) Like a conventional X-Ray image, but the X-Ray beam is rotated around a patients head capturing images from multiple planes (TOMOGRAPHY) Multiple images are ‘reconstructed’ into a single image (COMPUTERIZED)

Computerized Tomography Computerized tomography (CT): hyperdense, hypodense, isodense Hyperdense: Bone - WHITE Hypodense: Cerebral spnal fluid (CSF) - DARK GRAY Fat tissue, air - BLACK Isodense: Brain tissues - GRAY Scout Image (X-Ray) CT Scan (axial plane)

Computerized Tomography Density in CT scans measured in Hounsfield Units (HU) Air --- -1000 to -600 HU Fat --- -100 to -60 HU CSF --- 8-18 HU White matter --- 30-34 HU Gray matter --- 37-41 HU Freshly congealed blood --- 50-100 HU Bone --- 600-2000 HU *** You will NOT be responsible to know the HU numbers for different brain components CT Scans (axial plane). Red arrow - Skull fracture

Computerized Tomography Density in CT scans measured in Hounsfield Units (HU) Air --- -1000 to -600 HU Fat --- -100 to -60 HU CSF --- 8-18 HU White matter --- 30-34 HU Gray matter --- 37-41 HU Freshly congealed blood --- 50-100 HU Bone --- 600-2000 HU Other information obtained from CT scans: Mass effect - anything that distorts normal brain anatomy CT Scans (axial plane). Black arrow - left frontal acute epidural hematoma. White arrows - displaced midline (http://emedicine.medscape.com)

Computerized Tomography B Other information obtained from CT scans: Cerebral infarctions: Usually cannot be detected by CT scans in the first 12 hours. Subsequent cell death and edema lead to hypodensity. Neoplasms: Can be hyper-, hypo- or isodense depending on the type, location, etc. CT Scans (axial plane). A. Middle cerebral artery infarction with mild mass effect after 24 hrs (red arrow). B. Glioblastoma multiforme with mass effect (GBM). (http://emedicine.medscape.com)

Computerized Tomography B Specialized types of CT scans: CT with intravenous contrast: -material injected is denser than brain and will therefore appear hyperdense (white). Example -- iodine CT myelography: -iodinated injected material delivered into CSF. -allows visualization of impingements of spinal CSF space or nerve roots Subdural hematoma (red arrows). CT Scans obtained at the same level with or without intravenous contrast (axial plane). A. Without contrast B. With intravenous contrast. Green arrow is an enhanced vein. Blue arrow highlights border of hematoma. (http://emedicine.medscape.com)

Magnetic resonance imaging Magnetic resonance imaging (MRI) A technique in which atomic nuclei are placed in a static electric field and then pulsed with magnetic energy - the electric field aligns most of the protons atomic spin - a pulse of magnetic energy flips some protons spin against the electric field - after the pulse of energy ‘flipped’ protons ‘relax’ back into alignment with the electric field and release energy Determinants of MRI signal: Density of protons in tissue Proton relaxation state (T1 and T2) (Blumenfeld Neuroanatomy through Clinical Cases)

Magnetic resonance imaging Magnetic resonance imaging (MRI) - Types T2 T1 Axial T1-weighted, T2-weighted, and FLAIR (fluid attenuation inversion recovery) MR images at the same level in the same patient. (Blumenfeld Neuroanatomy through Clinical Cases)

Magnetic resonance imaging Magnetic resonance imaging (MRI) - Types (*You do not need to know for exam) T1-weighted (left) and T2-weighted MRIs of a patients with a glioma. (http://emedicine.medscape.com)

Magnetic resonance imaging Magnetic resonance imaging (MRI) - Types Specialized types of MRI scans: MRI with intravenous contrast: -paramagnetic material is injected to enhance vasculature. Example -- gadolinium Magnetic resonance spectroscopy: -measures abundance of brain neurotransmitters or other biochemicals. Diffusion tensor imaging (DTI): -permits the sensitive assessment of white matter tracts. T2 T1 Axial T1-weighted MR image with intravenous gadolinium contrast (Blumenfeld Neuroanatomy through Clinical Cases)

Magnetic resonance imaging CT vs MRI (Blumenfeld Neuroanatomy through Clinical Cases)

Functional imaging techniques Functional imaging techniques capitalize on detecting differential levels of blood flow and/or metabolism. Regions of high brain activity = regions with high levels of blood flow/metabolism

Functional imaging techniques Positron emission tomography (PET) Scans: -Short-lived radio-active isotopes (typically conjugated to biological agents, such as glucose analogs [eg. fluorodeoxyglucose]) are delivered into the blood stream -Isotopes undergo positron emission decay and emit 2 gamma photons at 180˚ from each other allowing localization. -Images of isotope density within tissues are generated like CT Scans (A similar technique is Single-Photon Emission Computerized Tomography [SPECT]) T2 T1 PET PET/MRI http://en.wikipedia.org/wiki/Positron_emission_tomography

Functional imaging techniques Functional MRIs (fMRI or blood oxygen level-dependent [BOLD] fMRI): Predicated on the principle that differences in hemoglobin levels distort magnetic resonance properties of tissues. No radioactivity required Non-invasive

Neuro-Angiography Conventional angiography: An invasive technique that delivers iodinated contrast material into the vasculature and detects it with X-rays Interventional angiography: Wada test: Injection of amobarbital instead of (or with) contrast material. (Blumenfeld Neuroanatomy through Clinical Cases) con (Blumenfeld Neuroanatomy through Clinical Cases)

Neuro-Angiography Magnetic resonance angiography (MRA): A less invasive technique that takes advantage of changes in magnetic resonance signals that occur as a result of blood flow. Gadolinium may be used to enhance contrast. CT angiography (CTA): A rapid injection of iodinated contrast material is injected and CT scans are quickly obtained. MRA (Blumenfeld Neuroanatomy through Clinical Cases) CTA http://emedicine.medscape.com

Sectional anatomy in MRI images Self-study with: Purves Neuroscience. “Atlas” pages 846-853 MRIs in Sylvius4 Chapter 6 of “Digital Neuroanatomy” on the eCurriculum website ***A list of structures to identify is in your syllabus. Be able to identify these structures in axial, coronal and sagital MRI images.

Sectional anatomy in MRI images Be able to identify the following structures in MR images: Amygdala Angular gyrus Anterior commissure Calcarine sulcus Caudate nucleus Central sulcus Cerebellar peduncles, superior Cerebellar peduncle, middle Cerebellar peduncles, inferior Cerebellum Cerebral aqueduct Cerebral peduncles Cingulate gyrus Corpus callosum, genu Corpus callosum, splenium Corpus callosum, body Cuneus gyrus Fornix Fourth ventricle Globus pallidus Hippocampus Hypothalamus Inferior colliculus Inferior frontal gyrus Inferior temporal gyrus Insular lobe (insular gyri) Internal capsule, anterior limb Internal capsule, posterior limb Lateral ventricles Lingual gyrus Longitudinal fissure Medulla oblongata Midbrain Middle frontal gyrus Middle temporal gyrus Optic chiasm Optic nerve Orbital gyri Parietooccipital sulcus Pons Postcentral gyrus Precentral gyrus Putamen Spinal cord Superior colliculus Superior frontal gyrus Superior temporal gyrus Supramarginal gyrus Thalamus

Sectional anatomy in MRI images Unstained brain T1-weighted MRI T2-weighted MRI Digital NA Purves Digital NA Cortical features: Inferior, middle, superior frontal gyri Inferior, middle, and superior temporal gyri Cingulate gyri Insular gyri (lobes) Longitudinal fissure Ventricles: Lateral ventricles Third ventricle Axon tracts: Corpus Callosum, body Anterior commissure Internal capsule, anterior limb Optic chiasm Basal ganglia: Caudate nucleus Globus pallidus Putamen Other: Amygdala

Sectional anatomy in MRI images Unstained brain T1-weighted MRI T2-weighted MRI Digital NA Purves Digital NA Axon tracts: Corpus Callosum, body Internal capsule, posterior limb Cerebral peduncle (crus cerebri) Cortical features: Inferior, middle, superior frontal gyri Inferior, middle, and superior temporal gyri Cingulate gyri Insular gyri (lobes) Longitudinal fissure Parahippocampal gyrus Ventricles: Lateral ventricles Third ventricle Other: Thalamus Hippocampus Pons Basal ganglia: Caudate nucleus

Sectional anatomy in MRI images Unstained brain T1-weighted MRI Digital NA Purves Cortical features: Cingulate gyri Calcarine sulcus Parieto-occipital sulcus Cuneus gyrus Lingual gyrus Axon tracts: Corpus Callosum(body, genu, spleium) Fornix Superior and inferior cerebellar peduncles Brainstem: Midbrain Inferior colliculus Superior colliculus Pons Medulla oblongata Ventricles: Lateral ventricles Fourth ventricle Dienchephalon: Thalamus Hypothalamus Spinal cord Cerebellum

Sectional anatomy in MRI images T1-weighted MRI Purves Cortical features: Superior frontal gyri Middle frontal gyri Precentral gyri Postcental gyri Central sulcus Longitudinal fissure

Sectional anatomy in MRI images Unstained brain T1-weighted MRI Digital NA Purves Cortical features: Insular gyri Parieto-occipital sulcus Cuneus gyri Supramarginal gyri Angular gyri Subcortical: Caudate nucleus Globus pallidus Putamen Thalamus Ventricles: Lateral ventricles Third ventricle Axon tracts: Corpus callosum, splenium Internal capsule, anterior limb Internal capsule, posterior limb

Sectional anatomy in MRI images T1-weighted MRI Purves Cortical features: Orbital gyri Superior temporal gyrus Middle temporal gyrus Cuneus gyrus Lingual gyrus Calcarine sulcus Longitudinal fissure Other: Amygdala Hippocampus Axon tracts: Optic nerve Optic chiasm Cerebral peduncle Ventricles: Lateral ventricles Midbrain: Superior colliculus Cerebral aqueduct Cerebral peduncle

Sectional anatomy in MRI images T1-weighted MRI A A B Purves B Pons Cerebellum Middle cerebellar peduncle Inferior cerebellar peduncle Fourth ventricle

Sectional anatomy in MRI images The structure marked by the tip of the arrow is the: Caudate nucleus Internal capsule, posterior limb Globus pallidus Putamen Internal capsule, anterior limb

Sectional anatomy in MRI images The structure marked by the tip of the arrow is the: Insular gyrus Orbital gyri Amygdala Hippocampus Parahippocampal gyrus

Sectional anatomy in MRI images The structure marked by the tip of the arrow is the: Superior colliculus Superior cerebellar peduncle Pons Inferior colliculus Middle cerebellar peduncle