Transcript basics

Neuroradiology
Dr Mohamed El Safwany, MD.
Intended learning outcome
• The student should learn at the end of this
lecture neuroradiological Imaging.
Neuroradiology
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Plain Film
CT
US
MRI
Interventional
– Angiography
– Myelography
– Biopsy
• Nuclear Medicine
CT Basics
• Computed tomography (CT)
• Computed axial tomography or computer –
assisted tomography (CAT)
CT Basics
CT Basics
• Neuroradiology
• The BASICS of CT
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Protocol
Terminology
Contrast
Radiation Safety
CT Basics
• Neuroradiology
• The BASICS of CT
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Protocol
Terminology
Contrast
Radiation Safety
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
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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
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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
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Protocol
Terminology
Contrast
Radiation Safety
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.
– Volume of images
– Ability to manipulate and reconstruct images
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
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Protocol
Terminology
Contrast
Radiation Safety
Contrast
• Iodinated
• Water
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
• 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
Contrast
• Pretreatment for anaphylaxis
– 50 mg Oral Prednisone 13, 7 and 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?
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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
• Contrast induced renal failure
– Elevated creatinine 24-48 hours after contrast
which resolves over 7-21 days.
– Can require dialysis
CT Basics
• Neuroradiology
• The BASICS of CT
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Protocol
Terminology
Contrast
Radiation Safety
Radiation Safety
– Diagnostic CT Scans: Assessment of Patient,
Physician, and Radiologist Awareness of
Radiation Dose and Possible Risks
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
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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
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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
• 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.
Text Book
• David Sutton’s Radiology
• Clark’s Radiographic positioning and
techniques
Assignment
• Two students will be selected for
assignment.
Question
• Describe variables in CT protocoling?
Thank You
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