Neuroradiology

Dr Mohamed El Safwany, MD.

Intended learning outcome

• The student should learn at the end of this lecture neuroradiological Imaging.

Neuroradiology

• 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

– Protocol– Terminology– Contrast– Radiation Safety

CT Basics

• Neuroradiology• The BASICS of CT

– 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

– 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– 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

• 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

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

– 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?– 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

– 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

– 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

• 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.

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

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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