neuroradiology and sectional anatomy neuroradiology and sectional anatomy

Neuroradiology and Sectional Anatomy

Neuroradiology and Sectional Anatomy

Introduction

Objectives:

1. Understand basic types of brain imaging techniques

2. Understand the benefits of different brain imaging techniques

3. Be able to identify basic brain structures in MR images.

Introduction

Topics covered:

1. Computerized tomography

2. Magnetic resonance imaging (MRI)

3. Functional imaging techniques

4.Angiography

5.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 (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

CT Scans (axial plane). Red arrow - Skull fracture

*** You will NOT be responsible to know the HU numbers for different brain components


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:

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)

A B


Computerized tomography:

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)

A B

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:

1.Density of protons in tissue

2.Proton relaxation state (T1 and T2)

(Blumenfeld Neuroanatomy through Clinical Cases)


Magnetic resonance imaging (MRI) - Types

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)

T1 T2



T1-weighted (left) and T2-weighted MRIs of a patients with a glioma. (http://emedicine.medscape.com)

(*You do not need to know for exam)



Axial T1-weighted MR image with intravenous gadolinium contrast(Blumenfeld Neuroanatomy through Clinical Cases)

T1 T2

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.


CT vs MRI


Functional imaging

Functional imaging techniques

T1 T2

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


T1 T2

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])

http://en.wikipedia.org/wiki/Positron_emission_tomography

PET PET/MRI

Functional imaging


T1 T2

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

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.

con

Neuro-Angiography



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.

Neuro-Angiography


MRA

http://emedicine.medscape.com

CTA

Sectional anatomy in MRI images

Sectional Anatomy

Self-study with:

1. Purves Neuroscience. “Atlas” pages 846-853

2. MRIs in Sylvius4

3. 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.


Be able to identify the following structures in MR images:

AmygdalaAngular gyrusAnterior commissureCalcarine sulcusCaudate nucleusCentral sulcusCerebellar peduncles, superiorCerebellar peduncle, middleCerebellar peduncles, inferiorCerebellumCerebral aqueductCerebral pedunclesCingulate gyrusCorpus callosum, genuCorpus callosum, spleniumCorpus callosum, bodyCuneus gyrusFornixFourth ventricle

Globus pallidusHippocampusHypothalamusInferior colliculusInferior frontal gyrusInferior temporal gyrusInsular lobe (insular gyri)Internal capsule, anterior limbInternal capsule, posterior limbLateral ventriclesLingual gyrusLongitudinal fissureMedulla oblongataMidbrain Middle frontal gyrusMiddle temporal gyrusOptic chiasmOptic nerveOrbital gyri

Parietooccipital sulcusPonsPostcentral gyrusPrecentral gyrusPutamenSpinal cordSuperior colliculusSuperior frontal gyrusSuperior temporal gyrusSupramarginal gyrusThalamus


T1-weighted MRIUnstained brain T2-weighted MRI

Basal ganglia:Caudate nucleusGlobus pallidusPutamen

Cortical features:Inferior, middle, superior frontal gyriInferior, middle, and superior temporal gyriCingulate gyriInsular gyri (lobes)Longitudinal fissure

Ventricles:Lateral ventriclesThird ventricle

Axon tracts:Corpus Callosum, bodyAnterior commissureInternal capsule, anterior limbOptic chiasm

Other:Amygdala

Purves Digital NADigital NA


T1-weighted MRIUnstained brain T2-weighted MRIPurves Digital NADigital NA

Basal ganglia:Caudate nucleus

Cortical features:Inferior, middle, superior frontal gyriInferior, middle, and superior temporal gyriCingulate gyriInsular gyri (lobes)Longitudinal fissureParahippocampal gyrus


Axon tracts:Corpus Callosum, bodyInternal capsule, posterior limbCerebral peduncle (crus cerebri)

Other:ThalamusHippocampusPons


T1-weighted MRIUnstained brainPurvesDigital NA

Cortical features:Cingulate gyriCalcarine sulcusParieto-occipital sulcusCuneus gyrusLingual gyrus

Axon tracts:Corpus Callosum(body, genu, spleium)FornixSuperior and inferior cerebellar peduncles

Dienchephalon:ThalamusHypothalamus

Brainstem:MidbrainInferior colliculusSuperior colliculusPonsMedulla oblongata

Ventricles:Lateral ventriclesFourth ventricle Spinal cord

Cerebellum


Cortical features:Superior frontal gyriMiddle frontal gyriPrecentral gyriPostcental gyriCentral sulcusLongitudinal fissure

T1-weighted MRIPurves


Cortical features:Insular gyriParieto-occipital sulcusCuneus gyriSupramarginal gyriAngular gyri

Axon tracts:Corpus callosum, spleniumInternal capsule, anterior limbInternal capsule, posterior limb


T1-weighted MRIUnstained brainPurvesDigital NA

Subcortical:Caudate nucleusGlobus pallidusPutamenThalamus


Cortical features:Orbital gyriSuperior temporal gyrusMiddle temporal gyrusCuneus gyrusLingual gyrusCalcarine sulcusLongitudinal fissure Axon tracts:

Optic nerveOptic chiasmCerebral peduncle

Ventricles:Lateral ventricles

T1-weighted MRI

Other:AmygdalaHippocampus

Purves

Midbrain:Superior colliculusCerebral aqueductCerebral peduncle


T1-weighted MRI

PonsCerebellumMiddle cerebellar peduncleInferior cerebellar peduncleFourth ventricle

PurvesA B B

A


The structure marked by the tip of the arrow is the:

A.Caudate nucleus

B.Internal capsule, posterior limb

C.Globus pallidus

D.Putamen

E.Internal capsule, anterior limb



A.Insular gyrus

B.Orbital gyri

C.Amygdala

D.Hippocampus

E.Parahippocampal gyrus



A.Superior colliculus

B.Superior cerebellar peduncle

C.Pons

D.Inferior colliculus

E.Middle cerebellar peduncle

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