1. Overview of medical imaging: Focusing on Neuroimaging

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

3. (could use photon picture b/c wave-particle duality)
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 How does the energy interact with tissues?
What is the energy used?
How does the energy interact with tissues?
How is the image produced?
What is represented in the image?

7. Electromagnetic Spectrum
Visible
Electromagnetic Spectrum

8. Visible
Endoscopy
Laparoscopy - ovary

9. X-RAYs Advantages of X-Ray Disadvantages 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. Electromagnetic Spectrum
X-RAYs
Electromagnetic Spectrum

11. Roughly Proportional to mass
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. Low energy X-ray b/c all tissue Bone healing study on rats
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 resolution 1mm 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. Why is water in brain dark compared to brain tissue?
(X-ray) CT – computed tomography – 3D
Axial - head
Axial - abdomen
Substance HU
Air
-1000
Fat
-120
Water
Muscle
+40
Bone
+1000
Why is water in brain dark compared
to brain tissue?
Houndsfield
Units

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

20. CT: What does the image represent?
(X-ray) CT – computed tomography – 3D
CT: What does the image represent?
Image Feature
Property
Sample tissues
Hypodensity (dark)
Not much x-ray absorbed
Air, fat, water, CSF
Hyperdensity (bright)
Lots of x-ray absorbed
Bone, newly congealed blood
Isodensity (gray)
Some x-ray absorbed
Gray matter, white matter

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

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

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

24. Realtime Imaging (Xray) Flouroscopy – 2D Xray advantage : 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. Electromagnetic Spectrum
PET – positron emission tomography
Electromagnetic Spectrum

29. Inject Patient with Radioactive Drug
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. Electromagnetic Spectrum
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 Fetocopsy Image Example
Typical ultra sound – sound reflections off surface
Fetocopsy
Image
Example
probe
Arterial Blood Flow

39. Electromagnetic Spectrum
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 Advantages Disadvantages 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. MRI Stage I Excite B0 Radio Waves end start Collective Magnetic
Moment of Protons
start
end

45. MRI Stage II listen Make image based on Protons loosing energy
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 CT
+Excellent bone imaging
+Excellent new acute hemorrhage detection
+Skull fracture, calcified lesion
+Short scan time, metal devices allowed
-Poor contrast and resolution
-Radiation
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

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

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

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

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

51. Why MRI : Detection of Acute Stroke
“Diffusion Weighted Imaging (DWI) has proven to be the most effective
means of detecting early strokes” Lehigh Magnetic Imaging Center
Conventional T2 WI
DW-EPI (advanced technique)
Sodium ion pumps fail, water goes in cells and can not diffuse.

52. MRI
Brain Injury

53. MRI Excite Protons Wait then Listen to Protons
MRA – magnetic resonance angiogram
Single slice from MRA
Excite Protons
Wait then Listen to
Protons

54. MRI Stack the slices to produce 3D image MRV (Veins) – reverse
excite and listen slices
MRA (arteries)

55. Angiography Refers to imaging of blood vessels Several types:
conventional x-ray angiography
Spiral / helical CT angiography
magnetic resonance angiography

56. X-Ray Angiography
inject pt. With contrast agent (e.g. sodium iodide)
take series of images at intervals following injection (e.g. 1-second intervals)
early images show arteries; later images show veins

57. Xray: Imaging Vasculature

58. Xray: Imaging Vasculature
1. Obtain scout
4. Take second image
5. Subtract second image from mask
2. Reverse image of scout = “mask”
3. Inject contrast

59. MR Angiography
often don’t need contrast agent
pulse sequences accentuate flowing tissues and minimize contrast from stationary ones
usually both arteries and veins are shown together (but can be separated)

60. MR Angiography

62. r. Internal carotid injection
Lateral view
X-ray angiography

63. r. Internal carotid injection
Lateral view
X-ray angiography
MCA and branches
ACA and branches
ophthalmic artery
carotid siphon
internal carotid

64. l. vertebral injection
Lateral view
X-ray angiography

65. Posterior inf. cerebellar artery
l. vertebral injection
Lateral view
X-ray angiography
PCA and branches
basilar artery
Posterior inf. cerebellar artery
vertebral artery

67. Venous sinuses
Lateral view
X-ray angiography

68. Superior sagittal sinus
Venous sinuses
Lateral view
X-ray angiography
Superior sagittal sinus
Superior sagittal sinus
Great cerebral vein of Galen
Straight sinus
Confluence of sinuses
Jugular vein & bulb

70. Anterior view
MRA

71. Anterior view
MRA
ACA
MCA
MCA
Internal carotid
Carotid siphon
Basilar artery

73. r. Internal carotid injection
AP view
X-ray angiography

74. r. Internal carotid injection
AP view
X-ray angiography
ACA
Carotid siphon
MCA
Internal carotid

75. l. Vertebral artery injection
AP view
X-ray angiography

76. l. Vertebral artery injection
AP view
X-ray angiography
PCA
vertebral artery

77. r. Internal carotid injection
AP view
X-ray angiography

78. Superior sagittal sinus
r. Internal carotid injection
AP view
X-ray angiography
Superior sagittal sinus
Confluence of sinuses
Transverse sinus
Sigmoid sinus
Jugular vein & bulb

79. Unused slides

82. Sound reflections Sound – density determines reflection
like light (E&M) – index of refraction
determines reflection for light (E&M)
Sonar = 10 – 200KHz
Incident
Reflected
Refracted (penetrated)

84. AMNIOCENTESIS-diagnostic / therapeutic C V S
Ultrasound
Doppler (frequency shift due to movement)
Arterial blood flow
Heart Valve functionality
AMNIOCENTESIS-diagnostic / therapeutic
C V S
CORDOCENTESIS-sampling / transfusion
BIOPSY- fetal skin / liver
SHUNTS-vesicoamniotic / thoracoamniotic
FETOSCOPY -usg guided
FETAL GENE Rx- stem cell transplants