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Lecture 7 Cross sectional imaging nuclear med.ppt

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Lecture 7 Cross sectional imaging nuclear med.ppt Presentation Transcript

  • 1. Cross Sectional Imaging Nuclear Medicine Dr. LeeAnn Pack Dipl. ACVR
  • 2. Computed Tomography (CT)
  • 3. Cross Sectional Imaging
    • No superimposition of structures
    • Excellent contrast resolution – can see the difference between 2 similar tissues
    • For CT – scan can be performed in one plane (usually transverse) and reformatted in the others (sag, dorsal)
    • CT – good for bone and soft tissue
    • MRI – better for soft tissue
  • 4. Computed Tomography
    • Uses X-rays, X-ray tube, detectors, collimators – very similar to radiography in how it works.
    • Patient placed in gantry
    • Multiple samples are taken from around the patient and then reconstruction can occur to make a slice
  • 5. CT Generations Helical and Multislice CT’s are used now Generation configuration detectors beam min scan time First translate-rotate 1~2 pencil thin 2.5 min Second translate-rotate 3~52 narrow fan 10 sec Third Rotate-rotate 256~1000 wide fan 0.5 sec Fourth Rotate-fixed 600~4800 wide fan 1 sec Fifth electron beam 1284 detectors wide fan electron beam 33 ms
  • 6. How It Works
    • Scout image is made first to pick the area to scan
    • Parameters set on the computer
    • Scan begins
    • Linear attenuation coefficient of tissues
    • Houndsfield units calculated
    • Shade of grey assigned to a CT number
  • 7. CT Principles
    • The image is divided into small areas called pixels
      • Each pixel has a location
      • Each pixel has an attenuation value
    • Using this information and very complex math formulas, the computer constructs the image
  • 8. CT numbers
    • High CT number = white because of increased attenuation
    • Low CT number = black because of decreased attenuation
    • Houndsfield scale
      • Water is zero, air is –1,000 and bone is 1,000
    • 256 shades of grey
  • 9. Windowing
    • Level
      • Center portion of the Houndsfield scale that is being used
        • Should be near the tissue of interest
    • Width
      • How much of the Houndsfield scale is used
        • Values within the window will be various shades of grey - rest black or white
  • 10. Level and Width
  • 11. Windowing - Use
    • Narrow window – enhance contrast of the tissues
      • Brain
    • Wide window – area with high inherent contrast
      • Lungs
    • Soft tissue window
    • Bone window
    • Reformatting – can not be better than original slice – decreased spatial resolution
  • 12. CT Terminology
    • Density
      • Hypodense
      • Isodense
      • Hyperdense
    • IV Contrast can also be administered – then contrast enhancing, ring enhancement etc can be used
  • 13. Soft Tissue Bone
  • 14. Choroid Plexus Tumor
  • 15. Fibrosarcoma Cat Back
  • 16. Multilobular Osteochondrosarcoma
  • 17. CT images
  • 18. Bone Lysis Nasal Tumor
  • 19. Nasal Adenocarcinoma
  • 20. Retrobulbar Mass
  • 21. Pituitary Tumor
  • 22. Magnetic Resonance Imaging (MRI)
  • 23. Magnetic Resonance Imaging
    • Does not involve ionizing radiation
    • Uses magnetic field and radiofrequency pulses
    • Hydrogen proton on tissues (water)
    • Water = like tiny magnets
    • When placed into magnetic field H protons line up along field
  • 24. MRI
    • Radiofrequency pulse passed through patient
    • Protons flip and spin
    • Pulse turned off and H protons return to normal state = relaxation
    • T1
    • T2
  • 25.  
  • 26.  
  • 27. Meningioma Hydrocephalus
  • 28. MRI
    • Tissues that have little H protons have little signal and are black
      • Air, bone, moving blood
    • Good for soft tissue imaging though
    • Paramagnetic contrast agent – Gad
    • No reformat – must scan all planes
      • Thus much longer scan than CT
    • Transverse, sagittal, dorsal
  • 29. T1 vs. T2
  • 30. MRI Machines
    • Can vary from .3 Tesla to 3 Tesla for routine working machines
    • Many are superconducting – use helium
    • Magnet is always on and must be contained in a Faraday cage (blocks stray radiofrequency signals)
    • Open and closed magnets
  • 31. MRI Terminology
    • Intensity
      • Hyperintense
      • Isointense
      • Hypointense
    • Contrast enhancing with Gadolinium
  • 32. MRI Safety
    • Augment T waves on EKG
    • Light flashes – Mild skin tingling
    • Involuntary muscle twitching
    • Increased body temperature
    • Projectile effects
    • Effects on surgical implants – ferrous
    • Magnetic foreign bodies
    • Life support devices
  • 33. MRI Contraindications
    • Pacemaker
    • Intra-cranial implants, clips
    • Metallic foreign bodies
    • Implanted electrical pumps, mechanical devices
  • 34. Nuclear Scintigraphy (Nuc Med)
  • 35. The Basics
    • Radionuclides (radioisotopes) are used
      • Injected, oral, per rectal etc. administration
      • They undergo decay over time
      • Linked to a radiopharmaceutical
        • Determines the area of distribution
    • Gamma rays come from the patient
      • Radioactive – ionizing radiation is involved
    • Gamma camera detects the radiation
    • Good for physiologic function stuff
    • Does not provide a good anatomical info
  • 36. The Ideal Radionuclide
    • Technetium 99m
    • Short half life = 6 hours
    • Binds to radiopharmaceuticals
    • Cheap to purchase
  • 37. The Gamma Camera
    • The gamma rays produce scintillations
    • They are converted to electrical signals and multiplied by photomultiplier tubes
    • The computer records the strength and location of the scintillation events
  • 38. Types of Scanning
    • Static
      • Images are acquired os structures at a single point in time
    • Dynamic
      • Images are acquired of a structure over a period of time
        • Provides functional activity
        • Time activity curves
          • Activity in a region is followed over time and a graph made
  • 39. Bone Scans
    • One of the most common scans we do
      • Equine
    • 3 phases:
    • Vascular phase
    • Soft tissue phase
    • Bone phase
  • 40. Items to Consider
    • Age of the animal
      • Young animals – physis
      • Older animal – longer time to distribution of radiopharmaceutical
    • Must scan both limbs etc even if only one is suspected of being abnormal
        • Symmetry is your friend
    • Animals are radioactive for a time after the scan
  • 41. Normal Equine Bone Scan
  • 42. Bone Scans
  • 43. Equine Head
  • 44. Thyroid Scintigraphy
    • Technetium 99m Pertechnetate
    • Uptake in thyroid glands is compared to uptake in salivary glands – should be equal
    • Hyperthyroid – Benign adenoma
      • Thyroid glands exceed salivary glands
    • Functional thyroid tumors
      • Patchy irregular inconsistent pattern
  • 45. Thyroid Scintigraphy Scans
  • 46. Portosystemic Shunts
    • Technetium 99m is placed in the rectum and dynamic images every 4 seconds are acquired over 2-3 minutes
    • Non invasive, quick, accurate, quantitative
    • Liver then heart = normal
    • Heart then liver = abnormal (shunt)
    • Time Activity Curves - important
  • 47. Time Activity Curve – Portosystemic Shunt
  • 48. Shunt vs. No Shunt
  • 49. Other Scan Types
    • Renal Scans
      • To determine GFR and ERPF
    • Cardiac Scans
    • Hepatobiliary Scans
      • Hepatocyte function, function of the reticuloendothelial system, biliary function
    • Gastrointestinal scans
    • Lung Scans
    • Infection and tumor imaging
  • 50. Nuc Med Safety
    • Higher energy radiation
      • Especially before injection
    • Urine from horses
    • Bedding
    • Isolation
    • Lead for workers – not work
      • Wear plastic gloves to keep off hands
    • Wear monitoring badges, rings
  • 51. Release Protocol
    • Isolation of the animals is necessary
    • Limited contact with the animal
      • Very sick animals may not be best to inject
    • Bedding must be monitored
    • Animal must be released after scanning with Geiger counter