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Neuroradiology
CT Basics
• Neuroradiology
• The BASICS of CT
– CT History
– Protocol
– Terminology
– Contrast
– Radiation Safety
– Cases
CT Basics
• Neuroradiology
• The BASICS of CT
– CT History
– Protocol
– Terminology
– Contrast
– Radiation Safety
– Cases
CT Basics
• No disclosures
Neuroradiologist
• A consultant in imaging and disease of the
brain, spinal cord, head, neck, face and
peripheral nerves
Neuroradiology
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Plain Film
CT
US
MRI
Interventional
– Angiography
– Myelography
– Biopsy
• Nuclear Medicine
Neuroradiology
• A request for an exam is a consultation
– History
– Pertinent physical exam findings
• Lab results
– Creatinine
– PT/INR
– What is the question?
CT Basics
• Computed tomography (CT)
• Computed axial tomography or computer –
assisted tomography (CAT)
CT Basics
CT Basics
• Neuroradiology
• The BASICS of CT
– CT History
– Protocol
– Terminology
– Contrast
– Radiation Safety
– Cases
CT History
• 1972 – First clinical CT scanner
– Used for head examinations
– Water bath required
– 80 x 80 matrix
– 4 minutes per revolution
– 1 image per revolution
– 8 levels of grey
– Overnight image reconstruction
CT History
• 2004 – 64 slice scanner
– 1024 x 1024 matrix
– 0.33s per revolution
– 64 images per revolution
– 0.4mm slice thickness
– 20 images reconstructed/second
CT Basics
• Neuroradiology
• The BASICS of CT
– CT History
– Protocol
– Terminology
– Contrast
– Radiation Safety
– Cases
CT Protocolling
• What happens when an exam is requested?
– A requisiton is completed.
– The requested exam is protocolled according to history,
physical exam and previous exams.
– The patient information is confirmed.
– The exam is then performed.
– Images are ready to be interpreted in …
• Uncomplicated exam – 5-10 minutes after completion
• Complicated exams with reconstructions take at least 1 hour but
usually 1-2 hours.
CT Protocolling
• CT head protocols
– With or Without contrast
– CT Brain
– CT Brain with posterior fossa images
– CT Angiogram/Venogram
– CT Perfusion
– CT of Sinuses
– CT of Orbit
– CT of Temporal bones
– CT of Mastoid bones
– CT of Skull
– CT of Face
CT Protocolling
• Variables
– Plain or contrast enhanced
– Slice positioning
– Slice thickness
– Slice orientation
– Slice spacing and overlap
– Timing of imaging and contrast administration
– Reconstruction algorhithm
– Radiation dosimetry
CT Protocolling
• Patient Information
– Is the patient pregnant?
• Radiation safety
– Can the patient cooperate for the exam?
CT Basics
• Neuroradiology
• The BASICS of CT
– CT History
– Protocol
– Terminology
– Contrast
– Radiation Safety
– Cases (Stroke)
CT Terminology
• Exams using Ionizing radiation
– Plain film
– CT
• 1/10 of all exams
• 2/3 OF RADIATION EXPOSURE
– Fluoroscopy
• Angiography, barium studies
– Nuclear medicine
• V/Q scan, bone scan
CT Terminology
• Attenuation
– Hyperattenuating (hyperdense)
– Hypoattenuating (hypodense)
– Isoattenuating (isodense)
• Attenuation is measured in Hounsfield units
– Scale -1000 to 1000
• -1000 is air
• 0 is water
• 1000 is cortical bone
CT Terminology
• What we can see
– The brain is grey
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White matter is usually dark grey (40)
Grey matter is usually light grey (45)
CSF is black (0)
Things that are brite on CT
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Bone or calcification (>300)
Contrast
Hemorrhage (Acute ~ 70)
Hypercellular masses
Metallic foreign bodies
CT Terminology
• Voxel
– Volume element
• A voxel is the 2 dimensional representation of a 3
dimensional pixel (picture element).
– Partial volume averaging
CT Terminology
CT Terminology
• Window Width
– Number of Hounsfield units from black to white
• Level or Center
– Hounsfield unit approximating mid-gray
CT Terminology
CT Artifacts
CT Terminology
• Digital reading stations are the standard of
care in interpretation of CT and MRI.
• Why?
– Volume of images
– Ability to manipulate and reconstruct images
– Cost
CT Terminology
• DICOM
– Digital Imaging and Communications in
Medicine
– DICOM provides standardized formats for
images, a common information model,
application service definitions, and protocols for
communication.
CT Basics
• Neuroradiology
• The BASICS of CT
– CT History
– Protocol
– Terminology
– Contrast
– Radiation Safety
– Cases
Contrast
• Barium
• Iodinated
– vascular
– Biliary, Urinary
– CSF
• Gadolinium
Contrast
Contrast
• Types of iodinated contrast
– Ionic
– Nonionic - standard of care
• No change in death rate from reaction but number of
reactions is decreased by factor of 4.
• If an enhanced study is needed, patient needs
to be NPO at least 4 hours and have no
contraindication to contrast, ie allergy or
renal insufficiency.
Contrast
• What are the risks of iodinated contrast?
– Contrast reaction
• 1 in 10,000 have true anaphylactic reaction
• 1 in 100,000 to 1 in 1,000,000 will die
– Medical Issues
• Acute renal failure
• Lactic acidosis in diabetics
» If on Glucophage, patient must stop Glucophage for 48
hours after exam to prevent serious lactic acidosis
• Cardiac
– Extravasation
Contrast
• Who is at risk for an anaphylactic reaction?
– Patients with a prior history of contrast reaction
– Patients with a history asthma react at a rate of 1
in 2,000
– Patients with multiple environmental allergies, ie
foods, hay fever, medications
Amin MM, et al. Ionic and nonionic contrast media: Current status and controversies.
Appl Radiol 1993; 22: 41-54.
Contrast
• Pretreatment for anaphylaxis
– 50 mg Oral Prednisone 13, 7 and 1 hour prior to
exam
– 50 mg oral Benedryl 1 hour prior to exam
– In emergency, 200 mg iv hydrocortisone 2-4
hours prior to exam
Contrast
• What are the risk factors for contrast induced acute
renal failure?
– Pre-existing renal insufficiency
– Contrast volume
– Dehydration
– Advanced age
– Drugs
– Multiple myeloma
– Cardiac failure
Contrast
• Considerations in patients with renal
insufficiency
– Is the exam necessary?
– Is there an alternative exam that can answer the
question?
– Decrease contrast dose
Contrast
• Pretreatment for renal insufficiency
– Hydration
– Mucomyst
• 600 mg po BID the day before and day of study
Prevention of radiographic-contrast-agent-induced reductions in renal function by
acetylcysteine.
Tepel M, et al. N Engl J Med 2000 Jul 20;343(3):180-4
Contrast
• Contrast induced renal failure
– Elevated creatinine 24-48 hours after contrast
which resolves over 7-21 days.
– Can require dialysis
Mehran, R. et al. Radiocontrast induced renal failure:Allocations and outcomes.
Reviews in Cardiovascular Medicine Vol. 2 Supp. 1 2001
CT Basics
• Neuroradiology
• The BASICS of CT
– CT History
– Protocol
– Terminology
– Contrast
– Radiation Safety
– Cases
Radiation Safety
•Diagnostic CT Scans: Assessment of Patient,
Physician, and Radiologist Awareness of
Radiation Dose and Possible Risks
–Lee, C. et al. Radiology 2004;231:393
Radiation Safety
• Deterministic Effects
– Have a threshold below which no effect will be
seen.
• Stochastic Effects
– Have no threshold and the effects are based on
the dose x quality factor.
Radiation Safety
• Terminology
– Gy = Gray is the absorbed dose (SI unit)
• The equivalent of 1 joule/kg of tissue
• Rad = radiation absorbed dose
– Sv = Sievert is the dose equivalent (SI unit)
• Absorbed dose multiplied by a quality factor
• Rem = radiation equivalent man
Radiation Safety
• Relative values of CT exam exposure
– Background radiation is 3 mSv/year
• Water, food, air, solar
• In Denver (altitude 5280 ft.) 10 mSv/year
– CXR = 0.1 mSv
– CT head = 2 mSv
– CT Chest = 8 mSv
– CT Abdomen and Pelvis = 20 mSv
-The equivalent of 200 CXR
Radiation Safety
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Effects of X rays.
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Absorption of photons by biological material
leads to breakage of chemical bonds.
The principal biological effect results from
damage to DNA caused by either the direct or
indirect action of radiation.
Radiation Safety
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Tissue/Organ radiosensitivity
– Fetal cells
– Lymphoid and hematopoietic tissues; intestinal
epithelium
– Epidermal, esophageal, oropharyngeal epithelia
– Interstitial connective tissue, fine vasculature
– Renal, hepatic, and pancreatic tissue
– Muscle and neuronal tissue
Radiation Safety
• Estimated Risks of Radiation-Induced Fatal
Cancer from Pediatric CT
– David J. Brenner, et al. AJR 2001; 176:289-296
• Additional 170 cancer deaths for each year of head CT in the
US.
– 140,000 total cancer deaths, therefore ~ 0.12% increase
– 1 in 1500 will die from radiologically induced cancer
Radiation Safety
• 3094 men received radiation for
hemangioma
– Those receiving >100 mGy
– Decreased high school attendance
– Lower cognitive test scores
Per Hall, et al. Effect of low doses of ionising radiation in infancy on cognitive function
in adulthood: Swedish population based cohort study
BMJ, Jan 2004; 328: 19 - 0.
Radiation Safety
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Hiroshima and Nagasaki
– There has been no detectable increase in genetic
defects related to radiation in a large sample
(80,000) of survivor offspring, including:
congenital abnormalities, mortality (including
childhood cancers), chromosome aberrations, or
mutations in biochemically identifiable genes.
William J Schull, Effects of Atomic Radiation: A Half-Century of Studies from
Hiroshima and Nagasaki, 1995.
Radiation Safety
• Hiroshima and Nagasaki
– However, exposed individuals who survived the
acute effects were later found to suffer increased
incidence of cancer of essentially all organs.
William J Schull, Effects of Atomic Radiation: A Half-Century of Studies from
Hiroshima and Nagasaki, 1995.
Radiation Safety
• Hiroshima and Nagasaki
– Most victims with high doses died
– Victims with low doses despite their large
numbers are still statistically insignificant.
Radiation Safety
Comparison of Image Quality
Between Conventional and LowDose Nonenhanced Head CT
Mark E. Mullinsa, et al.
AJNR April 2004.
Reduction of mAs from 170 to 90
Radiation Safety
• What does all this mean?
– 1 CXR approximates the same risk as:
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1 year watching TV (CRT)
1 coast to coast airplane flight
3 puffs on a cigarette
2 days living in Denver
– 1 Head CT is approximately 20 CXR
Health Physics Society on the web--http://hps.org
Radiation Safety
• The pregnant patient
– Can another exam answer the question?
– What is the gestational age?
– Counsel the patient
• 3% of all deliveries have some type of spontaneous
abnormality
• The mother’s health is the primary concern.
Radiation Safety
• "No single diagnostic procedure results in a radiation dose
that threatens the well-being of the developing embryo and
fetus." -- American College of Radiology
• "Women should be counseled that x-ray exposure from a
single diagnostic procedure does not result in harmful fetal
effects. Specifically, exposure to less than 5 rad has not
been associated with an increase in fetal anomalies or
pregnancy loss." -- American College of Obstetricians and Gynecologists
Conclusion
• Neuroradiologists are consultants
• Garbage in ------- Garbage out
• CT Terminology
– Attenuation (density) in Hounsfield units
– Digital interpretation is standard of care
• CT has risks
– Contrast
– Radiation exposure
CT Basics
• Neuroradiology
• The BASICS of CT
– CT History
– Protocol
– Terminology
– Contrast
– Radiation Safety
– Cases
Normal
CT
1 day
1 year
2 years
Normal CT
Older person
Normal Enhanced CT
Case 1
• 55 yo female with sudden onset of worst
headache of life
Case 1
Case 1
Case 1
• What do I do now?
CTA
Normal Angiography
Diagnostic Angiography
Case 1
• Subarachnoid Hemorrhage
– Most common cause is trauma
– Aneurysm
– Vascular malformation
– Tumor
– Meningitis
– Generally a younger age group
Case 2
• 82 yo male with mental status change after a
fall
Case 2
Case 2
• Subdural hematoma
• Venous bleeding from bridging veins
• General presentation
– Older age group
– Mental status change after fall
– 50% have no trauma history
Subdural Hematoma
Case 3
• 44 yo female with right sided weakness and
inability to speak
Case 3
Case 3
• Acute ischemic left MCA stroke
MCA Stroke
“Dense MCA”
Case 4
• 50 yo male post head trauma.
• Pt was initially conscious but now 3 hours
post trauma has had a sudden decrease in his
neurological function.
Case 4
Case 4
• Epidural hematoma
– Typical history is a patient with head trauma who
has a period of lucidity after trauma but then
deteriorates rapidly.
– Hemorrhage is a result of a tear through a
meningeal artery.
Case 5
• 71 yo male who initially complained of
incoordination of his left hand and
subsequently collapsed
Case 5
Case 5
• Intraparenchymal hemorrhage
– Hypertensive
– Amyloid angiopathy
– Tumor
– Trauma
Case 6
• 62 yo female acute onset headache
– Hemiplegic on the right and unable to speak
Case 6
• Add htn image here
Case 6
• Hypertensive hemorrhage
– Clinically looks like a large MCA stroke
– Generally younger than amyloid angiopathy
patients
Chronic Ischemic change =
Encephalomalacia
Thrombolysis:
• Intravenous
– 3 hours
• Intra-arterial
– 6 hours ICA territory
– 24 hours basilar territory
• CT head plain shows no established stroke
nor hemorrhage
• CT perfusion shows a salvagable penumbra
Case 7
• 53 y.o. male
• Sudden onset of ataxia loss of consciousness
proceeding rapidly to coma
Case 7
• Probable basilar occlusion with cerebellar
and brainstem infarction
Case 8
• 52 yo male with right sided weakness
Case 8
Case 8
Case 8
• Acute lacunar infarction
– Cannot reliably differentiate this finding on CT
from remote lacune without clinical correlation.
– MRI with diffusion is the GOLD STANDARD
– A word on TIA
Chronic Small Vessel Disease
Case 9
• 59 yo female with multiple falls over last
weekend
Case 9
Case 9
• Stroke involving caudate head, anterior limb
internal capsule and anterior putamen.
• What is the artery?
• Recurrent artery of Heubner
Case 10
• 42 yo male found in coma
Case 10
Case 10
• Global ischemia
Angiographic Brain Death
Case 11
• 24 yo male with siezures
Case 11
Case 11
• Heterotopia
Case 12
• 34 y.o. female
• Severe H/A,nausea
• Taking oral contraceptives
Case 12
Case 12
Case 12
• Transverse sinus thrombosis