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Neuroradiology. Dr. Grant J. Linnell Fellow Montreal Neurological Hospital McGill University. 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

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Neuroradiology

Dr. Grant J. Linnell

Fellow

Montreal Neurological Hospital

McGill University


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CT Basics

  • Neuroradiology

  • The BASICS of CT

    • CT History

    • Protocol

    • Terminology

    • Contrast

    • Radiation Safety

    • Cases


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CT Basics

  • Neuroradiology

  • The BASICS of CT

    • CT History

    • Protocol

    • Terminology

    • Contrast

    • Radiation Safety

    • Cases


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CT Basics

  • No disclosures


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Neuroradiologist

  • A consultant in imaging and disease of the brain, spinal cord, head, neck, face and peripheral nerves


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Neuroradiology

  • Plain Film

  • CT

  • US

  • MRI

  • Interventional

    • Angiography

    • Myelography

    • Biopsy

  • Nuclear Medicine


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Neuroradiology

  • A request for an exam is a consultation

    • History

    • Pertinent physical exam findings

      • Lab results

        • Creatinine

        • PT/INR

    • What is the question?


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CT Basics

  • Computed tomography (CT)

  • Computed axial tomography or computer –assisted tomography (CAT)



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CT Basics

  • Neuroradiology

  • The BASICS of CT

    • CT History

    • Protocol

    • Terminology

    • Contrast

    • Radiation Safety

    • Cases


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CT History

  • Electro-Musical Instruments


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CT HistorySIR GODFREY N. HOUNSFIELD

  • 1979 Nobel Laureate in Medicine


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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


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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


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CT Basics

  • Neuroradiology

  • The BASICS of CT

    • CT History

    • Protocol

    • Terminology

    • Contrast

    • Radiation Safety

    • Cases


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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.


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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


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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


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CT Protocolling

  • Patient Information

    • Is the patient pregnant?

      • Radiation safety

    • Can the patient cooperate for the exam?


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CT Basics

  • Neuroradiology

  • The BASICS of CT

    • CT History

    • Protocol

    • Terminology

    • Contrast

    • Radiation Safety

    • Cases (Stroke)


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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


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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


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CT Terminology

  • What we can see

    • The brain is grey

      • White matter is usually dark grey (40)

      • Grey matter is usually light grey (45)

      • CSF is black (0)

      • Things that are brite on CT

        • Bone or calcification (>300)

        • Contrast

        • Hemorrhage (Acute ~ 70)

        • Hypercellular masses

        • Metallic foreign bodies


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CT Terminology

  • Voxel

    • Volume element

      • A voxel is the 2 dimensional representation of a 3 dimensional pixel (picture element).

    • Partial volume averaging



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CT Terminology

  • Window Width

    • Number of Hounsfield units from black to white

  • Level or Center

    • Hounsfield unit approximating mid-gray




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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


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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.


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CT Basics

  • Neuroradiology

  • The BASICS of CT

    • CT History

    • Protocol

    • Terminology

    • Contrast

    • Radiation Safety

    • Cases


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Contrast

  • Barium

  • Iodinated

    • vascular

    • Biliary, Urinary

    • CSF

  • Gadolinium



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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.


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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


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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.


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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


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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


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Contrast

  • Considerations in patients with renal insufficiency

    • Is the exam necessary?

    • Is there an alternative exam that can answer the question?

    • Decrease contrast dose


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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


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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


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CT Basics

  • Neuroradiology

  • The BASICS of CT

    • CT History

    • Protocol

    • Terminology

    • Contrast

    • Radiation Safety

    • Cases


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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


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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.


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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


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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


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Radiation Safety

  • Effects of X rays.

    • 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.


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Radiation Safety

  • 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


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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


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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 studyBMJ, Jan 2004; 328: 19 - 0.


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Radiation Safety

  • 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.


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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.


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Radiation Safety

  • Hiroshima and Nagasaki

    • Most victims with high doses died

    • Victims with low doses despite their large numbers are still statistically insignificant.


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Radiation Safety

Comparison of Image Quality Between Conventional and Low-Dose Nonenhanced Head CT

Mark E. Mullinsa, et al.

AJNR April 2004.

Reduction of mAs from 170 to 90


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Radiation Safety

  • What does all this mean?

    • 1 CXR approximates the same risk as:

      • 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


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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.


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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


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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


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CT Basics

  • Neuroradiology

  • The BASICS of CT

    • CT History

    • Protocol

    • Terminology

    • Contrast

    • Radiation Safety

    • Cases




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Normal CTOlder person



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Case 1

  • 55 yo female with sudden onset of worst headache of life




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Case 1

  • What do I do now?





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Case 1

  • Subarachnoid Hemorrhage

    • Most common cause is trauma

    • Aneurysm

    • Vascular malformation

    • Tumor

    • Meningitis

    • Generally a younger age group


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Case 2

  • 82 yo male with mental status change after a fall



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Case 2

  • Subdural hematoma

  • Venous bleeding from bridging veins

  • General presentation

    • Older age group

    • Mental status change after fall

    • 50% have no trauma history



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Case 3

  • 44 yo female with right sided weakness and inability to speak



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Case 3

  • Acute ischemic left MCA stroke


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MCA Stroke“Dense MCA”


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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.



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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.


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Case 5

  • 71 yo male who initially complained of incoordination of his left hand and subsequently collapsed



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Case 5

  • Intraparenchymal hemorrhage

    • Hypertensive

    • Amyloid angiopathy

    • Tumor

    • Trauma


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Case 6

  • 62 yo female acute onset headache

    • Hemiplegic on the right and unable to speak


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Case 6

  • Add htn image here


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Case 6

  • Hypertensive hemorrhage

    • Clinically looks like a large MCA stroke

    • Generally younger than amyloid angiopathy patients


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Chronic Ischemic change =Encephalomalacia


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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


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Case 7

  • 53 y.o. male

  • Sudden onset of ataxia loss of consciousness proceeding rapidly to coma


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Case 7

  • Probable basilar occlusion with cerebellar and brainstem infarction


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Case 8

  • 52 yo male with right sided weakness




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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



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Case 9

  • 59 yo female with multiple falls over last weekend



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Case 9

  • Stroke involving caudate head, anterior limb internal capsule and anterior putamen.

  • What is the artery?

  • Recurrent artery of Heubner


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Case 10

  • 42 yo male found in coma



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Case 10

  • Global ischemia



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Case 11

  • 24 yo male with siezures



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Case 11

  • Heterotopia


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Case 12

  • 34 y.o. female

  • Severe H/A,nausea

  • Taking oral contraceptives




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Case 12

  • Transverse sinus thrombosis