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Neuroradiology

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

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

  2. CT Basics • Neuroradiology • The BASICS of CT • CT History • Protocol • Terminology • Contrast • Radiation Safety • Cases

  3. CT Basics • Neuroradiology • The BASICS of CT • CT History • Protocol • Terminology • Contrast • Radiation Safety • Cases

  4. CT Basics • No disclosures

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

  6. Neuroradiology • Plain Film • CT • US • MRI • Interventional • Angiography • Myelography • Biopsy • Nuclear Medicine

  7. Neuroradiology • A request for an exam is a consultation • History • Pertinent physical exam findings • Lab results • Creatinine • PT/INR • What is the question?

  8. CT Basics • Computed tomography (CT) • Computed axial tomography or computer –assisted tomography (CAT)

  9. CT Basics

  10. CT Basics • Neuroradiology • The BASICS of CT • CT History • Protocol • Terminology • Contrast • Radiation Safety • Cases

  11. CT History • Electro-Musical Instruments

  12. CT HistorySIR GODFREY N. HOUNSFIELD • 1979 Nobel Laureate in Medicine

  13. 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

  14. 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

  15. CT Basics • Neuroradiology • The BASICS of CT • CT History • Protocol • Terminology • Contrast • Radiation Safety • Cases

  16. 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.

  17. 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

  18. 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

  19. CT Protocolling • Patient Information • Is the patient pregnant? • Radiation safety • Can the patient cooperate for the exam?

  20. CT Basics • Neuroradiology • The BASICS of CT • CT History • Protocol • Terminology • Contrast • Radiation Safety • Cases (Stroke)

  21. 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

  22. 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

  23. 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

  24. CT Terminology • Voxel • Volume element • A voxel is the 2 dimensional representation of a 3 dimensional pixel (picture element). • Partial volume averaging

  25. CT Terminology

  26. CT Terminology • Window Width • Number of Hounsfield units from black to white • Level or Center • Hounsfield unit approximating mid-gray

  27. CT Terminology

  28. CT Artifacts

  29. 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

  30. 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.

  31. CT Basics • Neuroradiology • The BASICS of CT • CT History • Protocol • Terminology • Contrast • Radiation Safety • Cases

  32. Contrast • Barium • Iodinated • vascular • Biliary, Urinary • CSF • Gadolinium

  33. Contrast

  34. 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.

  35. 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

  36. 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.

  37. 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

  38. 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

  39. Contrast • Considerations in patients with renal insufficiency • Is the exam necessary? • Is there an alternative exam that can answer the question? • Decrease contrast dose

  40. 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

  41. 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

  42. CT Basics • Neuroradiology • The BASICS of CT • CT History • Protocol • Terminology • Contrast • Radiation Safety • Cases

  43. 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

  44. 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.

  45. 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

  46. 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

  47. 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.

  48. 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

  49. 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

  50. 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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