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Most rapid form of CT
Multislice helical
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types of ct
- Multislice helical
- Single slice helical
- Multislice serial
- High Resolution Computed Tomography
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HRCT might miss
small masses because fewer slices are taken at higher resolution
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the more X-rays pass through a structure
the darker it appears
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CT vantage point
- view up ward from pts feet
- pts rt is views left
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white matter on CT
darker then grey matter due to fat content
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Units of intensity in CT
Hounsfields
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Order of intensity of tissue from least to greatest
- Air -1000
- Fat -100
- Water 0
- Tissue 100
- Calcium 200
- Bone 1000
- Dense Bone 3000
- Metal
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Makes contrast bright on imaging
iodine
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iodinated contrast on CT allows visualization of
veins and arteries
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Original contrast was more toxic because it was
ionic
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2 major side effects of contrast
- nephropathy
- anaphylactoid reaction
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Falsely associated with iodine allergy
seafood, topical iodine containing antiseptics
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Pretreatment for relative contraindication due to allergy
- corticosteroids
- anti-histamine
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Contrast induced nephropathy
increase in serum cr by 25% or 0.5mg/dl or more
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Risk factors for nephropathy
- preexisting renal insufficiency
- diabetes
- reduced intravascular volume
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used to reduce risk of contrast induced nephropathy
- non-ionic contrast
- hydrate pt well
- bicarb before and after scan
- N-acetylcysteine
- prophylactic hemodialysis
- schedule contrast inhanced CT before dialysis
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CT of Head w/o contrast is used to
- diagnose CVA and ICH
- assess hydrocephalus, mass effect, herniation, skull fracture, sinus disease
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CT with contrast is used to diagnose
tumors BUT MRI is more sensitive
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types of hemorrhagic stroke
- epidural
- subdural
- subarachnoid
- intracerebral
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Epidural hematoma
etiology
shape
- laceration of middle meningeal artery
- obey suture lines, lens shaped
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Subdural hematoma
etiology
shape
- laceration of bridging veins
- do not obey suture lines, wavy appearance against brain surface
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Subarachnoid hemorrhage
etiology
shape/location
- ruptured aneuyrsm 85% mostly in anterior circle of willis
- bleed in space between arachnoid and pia into CSF
- - midline bleeding - ACA ruptured aneursm
- - bleeding around ponds or midbrain - smile
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Subarachnoid hemorrhage diagnostic
After dx on CT then Cerebral angiography
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intracerebral hemorrhages etiology
- hypertension typically affecting deep structures
- - pons
- - thalamus
- - putamen
- amyloid angiopathy typically superficial areas
- - cortex
- - white mater
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interacerebral hemorrhages are typically located
intraparenchymal
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hydrocephalus
- abnormal CSF accumulation
- obstructive vs. communicating
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Communicating HCP on CT
Will show sharper angles on ventricles
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Obstructive HCP on CT
Ventricles will have rounder angles
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types of herniation
- subfalicial (cingulate) - midline shift
- uncal - laterally through tentorium downward
- central or transtentorial - centrally downward
- external - out of skull
- tonsillar herniation - through foramen magnum
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tPA
- given for ischemic stroke
- within 3 hrs of presentation
- but hemorragic stroke must be ruled out by CT
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major complication of tPA
hemorrhage
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contraindications to tPA
- active internal bleeding
- platlets <100
- pt on heparin or warfarin
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Intracranial hemorrhage managment
- neurosurgical consult
- strict BP control
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ischemic stroke presentation on noncontrast ct after 24hrs
- disappearing gray-white junction
- hyperdense MCA sign
- obliteration of sulci
- shifting due to edema
- hypoattenuation of lentiform nucleus
- insular ribbon sign
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