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Overview of medical imaging: Focusing on Neuroimaging

Overview of medical imaging: Focusing on Neuroimaging. Medical imaging. Using the Electromagnetic Spectrum Visible light X-ray , Fluoroscopy, CT, & Angiography gamma rays - PET (positron emission tomography) Radio waves from nuclear spin – MRI Sound waves - ultrasound.

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Overview of medical imaging: Focusing on Neuroimaging

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  1. Overview of medical imaging: Focusing on Neuroimaging

  2. Medical imaging • Using the Electromagnetic Spectrum • Visible light • X-ray, Fluoroscopy, CT, & Angiography • gamma rays - PET (positron emission tomography) • Radio waves from nuclear spin – MRI • Sound waves - ultrasound

  3. Electromagnetic wave (could use photon picture b/c wave-particle duality) one wavelength

  4. Wave Particle duality of electromagnetic radiation

  5. Electromagnetic Spectrum

  6. Guiding Questions What is the energy used? How does the energy interact with tissues? How is the image produced? What is represented in the image?

  7. Visible Electromagnetic Spectrum

  8. Visible Endoscopy Laparoscopy - ovary

  9. X-RAYs Roentgen : 1895 Discovered X-rays 1901 Nobel Prize • Advantages of X-Ray • cheap • fast • good diagnostic value for many things • Disadvantages • ionizing radiation • - contrast is just density differences

  10. X-RAYs Electromagnetic Spectrum

  11. How X-rays work Simple Fit Number of protons Roughly Proportional to mass

  12. X-ray Radiography - 2D (ie Chest) Advantage very fast high resolution Disadvantage ionizing radiation xray contrast

  13. X-ray Radiography - 2D 100KVp

  14. X-ray Radiography - 2D Compton Scattering (Photoelectric effect) [everything going digital now]

  15. X-ray Radiography - 2D Mammography Low energy X-ray b/c all tissue Bone healing study on rats

  16. “Pretty pictures, but they will never replace radiographs” –Neuroradiologist 1972 (X-ray) CT – computed tomography – 3D Godfrey Hounsfield 1972 (nobel prize 1979) Advantage high resolution1mm x0.4mm x 0.4mm 3D Disadvantage ionizing radiation xray contrast Axial - abdomen Axial - head

  17. What is tomography Red dots are areas of high density Peaks are number of Xrays absorbed (note : normally would do axially and not sagittally)

  18. (X-ray) CT – computed tomography – 3D Axial - head Axial - abdomen Why is water in brain dark compared to brain tissue? Houndsfield Units

  19. (X-ray) CT – computed tomography – 3D CT: What does the image represent? hyperdensity hypodensity isodensity

  20. (X-ray) CT – computed tomography – 3D CT: What does the image represent? Image Feature Property Sample tissues

  21. (X-ray) CT – computed tomography – 3D CT: What does the image represent?

  22. (X-ray) CT – computed tomography – 3D CT: What does the image represent?

  23. (X-ray) CT – computed tomography – 3D CT - Hemmorage

  24. (Xray) Flouroscopy – 2D Xray Realtime Imaging Heart Blood Flow Surgery advantage : disadvantage: high radiation dose

  25. (Xray) CONTRAST – Radiograph, CT, or Flouroscopy Barium Swallow Injection (Iodine Compound) Angiogram

  26. (X-ray) CT – computed tomography – 3D

  27. (X-ray) CT – computed tomography – 3D Advantages better resolution (smaller detectors source closer to detector) Disadvantage small :} 13um resolution mouse placenta vasculature mouse microCT/PET

  28. PET – positron emission tomography Electromagnetic Spectrum

  29. PET – positron emission tomography Inject Patient with Radioactive Drug Late 1960’s Drug travels to metabolically active sites (many tumors have high metabolic activity) Drug emits (+) positrons (basically a positively charged electron) FDG - Fluorodeoxyglucose (most common drug) (F18 – + emitter – two hour half-life) Advantage functional imaging Disadvantage some ionizing radiation low resolution (4mm x 4mm x 4mm) need to make/buy FDG (cyclotron)

  30. PET/CT - together CT PET (Xray) CT

  31. PET – positron emission tomography • β+ decay, positron travels several mm and collides with an electron • produce a pair of annihilation photons (511kev, 180o) • simultaneous detection 180o apart

  32. PET – positron emission tomography Abnormal FDG collection Treated Tumor growing again on periphery

  33. PET – positron emission tomography functional brain activity (mostly done with MRI now)

  34. PET/CT - together

  35. PET/CT - together CT PET PET/CT PET

  36. microPET/CT– positron emission tomography Advantages better resolution (smaller detectors source closer to detector) Disadvantage small :} signal to noise good bad physics note: signal on expanding sphere drops as 1/R2 (surface area of sphere), therefore closer is better

  37. Ultrasound Electromagnetic Spectrum Discovered (Norris) 1952, clinical 1962 Sound waves 1-15MHz (ear 20 – 20KHz) Echos (reflections) from different density interfaces are recorded Image soft tissue and blood flow (Doppler) Advantages: high resolution (mm) cheap real time imaging safe Disadvantages: skilled technician & interpretation small field of view (~20cm) bone and air problematic

  38. Ultrasound Typical ultra sound – sound reflections off surface Fetocopsy Image Example probe Arterial Blood Flow

  39. MRI – Magnetic Resonance Imaging Electromagnetic Spectrum

  40. MRI – Magnetic Resonance Imaging Mansfield and Lauterbur nobel prize 1978 first images 1st published MRI images of abdomen First brain MR Modern T2 image “Interesting images, but will never be as useful as CT” neuroradiologist, 1982 3 Tesla MRI Scanner

  41. MRI AdvantagesDisadvantages safe expensive great soft tissue contrast long time many contrast options bad for bones mediocre resolution

  42. 3 Tesla Magnetic Field (60,000 times Earths field) MRI B0 B0

  43. 3 Tesla magnet field MRI Not all the protons line up – thermal energy Protons (hydrogen nuclei act like little magnets) B0 Collective Magnetic Moment of Protons

  44. end start Collective Magnetic Moment of Protons MRI Stage I Excite Radio Waves B0

  45. MRI Stage II listen Make image based on Protons loosing energy Make image based on Protons dephasing start Fat and water loose energy and dephase at different rates Slow Precession end Fast Precession T1 (energy lose time constant) Imaging T2 (dephasing time constant) Imaging Axial MRI Head Water Fat bright dark bright dark

  46. CT versus MRI MRI +Excellent grey/white matter contrast & spatial resolution +Better for old hemorrhage (and new with Diffusion?) -Long scan time -Pts cannot have metal devices -Claustrophobia, obesity problems +No radiation - expensive CT +Excellent bone imaging +Excellent new acute hemorrhage detection +Skull fracture, calcified lesion +Short scan time, metal devices allowed -Poor contrast and resolution -Radiation

  47. MRI: “Normal” Anatomy corpus callosum fornix thalamus midbrain pons medulla

  48. MRI: “Normal” Anatomy superior frontal g. precuneus cingulate g. cuneus lingual g. g. rectus

  49. MRI: Imaging deep structures(thalamus and basal ganglia) Putamen & globus pallidus Caudate nucleus thalamus

  50. MRI Disease Tumor (can be combination of Edema and tumor tissue characteristics) Multiple Sclerosis – Active Lessions (basically edema – water)

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