Neuroimaging Flashcards
Combines continuous gantry rotation with table motion
Helical CT
The density in a CT is expressed in
Hounsfield units
Intermediate density similar to the brain
Isodense
Better than CT for a subtle area of tumor, infarct, or demyelination
MRI
Which is better for a fresh hemorrhage, CT or MRI?
CT
Which is better for an old hemorrhage, CT or MRI?
MRI
Fast, can scan large areas of the body quickly, and is less costly than an MRI
-Very sensitive to hemorrhage
CT
Most effectively used for intracranial hemorrhage, acute trauma, stroke, fractures, and sinusitus
CT
CT contrast contains
Iodine
Do not use contrast when the concern is an
Intracranial hemorrhage (especially subarachnoid)
On CT, hyperdense in sulci, cisterns, and fissures
-ill defined and “whispy”
Subarachnoid Hemorrhage
Aneurysmal subarachnoid hemorrhage leads to
Hydrocephalus
Collection of blood in potential space b/w skull inner table and dura mater
-Lense shaped
Epidural Hematoma
Epidural hematomas do not cross
Sutures
Common when an epidural hematoma is present (85-95%)
Skull fractures
What fraction of patients with an epidural hematoma have neurological deterioration after the lucid interval?
1/3
Thromboembolic events are principal causes of ischemic stroke leading to vascular insufficiency
Acute cerebellar infarct
Leads to low density on CT
-Low density takes approximately 4-6 hours to develop
Acute cerebellar infarct
In an acute cerebellar infarct, edema peaks at
3-7 days
All current MRI techniques based on receiving and processing signals from
Protons
At the core of all MRIs is a homogenous
Magnetic Field
The magnetic field strength in an MRI is referred to in units of
Tesla
1 Tesla = 10,000 Gauss units. The Earth’s magnetic field =
0.5 Gauss
A sequence is a particular set of parameters used to generate a specific type of
Image
Dependent on characteristics and strength of energy released by hydrogen ions
T1 and T2 weighting
Depends mainly on differences in hydrogen ions in fat and water
MRI contrast
For T1W images, what is the intensity of
- ) Water (CSF)
- ) Edema
- ) White matter (fat)
- ) Gray matter
- ) Hypointense
- ) Hypointense
- ) Hyperintense
- ) Isointense
For T2W images, what is the intensity of
- ) Water (CSF)
- ) Edema
- ) White matter (fat)
- ) Gray matter
- ) Hyperintense
- ) Hyperintense
- ) Hypointense
- ) Isointense
Are similar to T2W, but CSF is HYPOintense
Fluid Attenuation Inversion Recovery (FLAIR)
Allows for exquisite evaluation of white matter adjacent to ventricles
-I.e. as in multiple sclerosis
FLAIR
Primary sequence for detection of ischemic (not hemorrhagic) infarct
Diffusion Weighted Image (DWI)
Hyperintensity on DWI with acute or subacute
Infarcts (up to 14 days old)
Used as contrast for MRI
-Produces hyperintensity in vessels and areas of blood brain barrier breakdown
Gadolinium
Gives an exquisite delineation of anatomy and is excellent for the detection of small lesions
MRI
Excellent for evaluation of posterior fossa structures such as brainstem and cerebellum (CT fraught with artifact)
MRI
MRIs are contraindicated for patients with a
Pacemaker
Can be primary or metastatic to the brain
Intracranial Lymphoma
Caused by HSV-1 infection
-Bilateral and asymmetric
Herpes Encephalitis
Benign tumor that shows as an extra-axial mass
- Dural based
- Arise from the meninges
Meningioma
More prominent in female than males
Meningioma
Cytotoxic edema that conforms to vascular territories
Acute infarct
Autoimmune mediated demyelination
MS
Loss of myelin with preservation of neurons early, but loss of neurons late
MS
What are the location of foci for MS?
Periventricular, corpus callosum, and brainstem
Inferior descent of cerebellar tonsil through foramen magnum > 5mm
Chiari I Malformation
Associated with cervical cord syrinx, skeletal anomalies (fusion anomalies, skull base flattening, congenital elevation of scapula), syndromes
Chiari I malformation
apitalizes on creating intensity differences between flowing blood in vessels and stationary tissues
MRI angiography
Flowing blood or even CSF –> produce signal depending on velocity and imaging parameters
MRI angiography
Used to image intracranial vessels (COW + venous sinuses), carotid vasculature, vertebral arteries, venous anatomy of neck
MRI angiography
Vascular malformation with arteriovenous shunting (no intervening capillary bed)
Parieto-Occipital AVM
Round or lobulated outpouching from COW
-Rupture results in “worst headache of life”
Basilar Tip Aneurysm
Measures brain neurotransmitters and biochemicals
-Interrogates chemical environment of brain noninvasively
Magnetic Resonance Spectroscopy (MRS)
Used to measure: Amino acids, Lipid, lactate, NAA, Choline, Creatine, and Myoinositol
MRS
Aids in evaluation of brain tumors, radiation necrosis, infections, metabolic disease
MRS
Allows assessment of white matter tracts based on water diffusion characteristics along these tracts of axons
Diffusion Tensor Imaging (DTI)
Used for evaluation of neurodegenerative disease, epilepsy, traumatic brain injury, multiple sclerosis
DTI
Assess brain metabolic activity (indirect measure of neuronal discharge) and therefore specific areas of function
Functional MRI
Uses BOLD (blood oxygen level dependent) imaging
-When brain is activated by a task, increase of blood flow we get a signal
Functional MRI
Catheter inserted via femoral artery and directed into Aorta under fluoroscopy
-Iodinated contrast material injected to visualized vasculature
Catheter Angiography
Minimally invasive treatment treatment options for conditions involving brain, H + N, and spine
Interventional Neuroradiology
Used for endovascular treatment and embolization of IC aneurysms, AVMs, dAVFs
Interventional Neuroradiology
