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Overview of medical imaging: Focusing on Neuroimaging.

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Presentation on theme: "Overview of medical imaging: Focusing on Neuroimaging."— Presentation transcript:

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 1. What is the energy used? 2. How does the energy interact with tissues? 3. How is the image produced? 4. What is represented in the image?

7 Electromagnetic Spectrum Visible

8 Laparoscopy - ovary Endoscopy Visible

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 Electromagnetic Spectrum X-RAYs

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

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

13 100KVp X-ray Radiography - 2D

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

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

16 (X-ray) CT – computed tomography – 3D Godfrey Hounsfield 1972 (nobel prize 1979) “Pretty pictures, but they will never replace radiographs” – Neuroradiologist 1972 Axial - head Axial - abdomen Advantage high resolution 1mm x0.4mm x 0.4mm 3D Disadvantage ionizing radiation xray contrast

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 Axial - head Axial - abdomen SubstanceHU Air-1000 Fat-120 Water0 Muscle+40 Bone+1000 Houndsfield Units Why is water in brain dark compared to brain tissue? (X-ray) CT – computed tomography – 3D

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

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

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

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

23 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 13um resolution mouse placenta vasculature Advantages better resolution (smaller detectors source closer to detector) Disadvantage small :} mouse microCT/PET

28 Electromagnetic Spectrum PET – positron emission tomography

29 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) (F 18 –  + 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) PET – positron emission tomography

30 CT PET/CT - together (Xray) CTPET

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

32 Abnormal FDG collection PET – positron emission tomography 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 CTPET/CT

36 microPET/CT – positron emission tomography Advantages better resolution (smaller detectors source closer to detector) Disadvantage small :} physics note: signal on expanding sphere drops as 1/R 2 (surface area of sphere), therefore closer is better signal to noise good bad

37 Electromagnetic Spectrum Ultrasound 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 Electromagnetic Spectrum MRI – Magnetic Resonance Imaging

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

41 MRI AdvantagesDisadvantages safeexpensive great soft tissue contrastlong time many contrast optionsbad for bones mediocre resolution

42 3 Tesla Magnetic Field (60,000 times Earths field) MRI B0B0 B0B0

43 3 Tesla magnet field B0B0 Protons (hydrogen nuclei act like little magnets) Not all the protons line up – thermal energy MRI Collective Magnetic Moment of Protons

44 MRI Stage I Excite B0B0 Radio Waves Collective Magnetic Moment of Protons start end

45 MRI Stage II listen start end Make image based on Protons loosing energy Make image based on Protons dephasing Slow Precession Fast Precession Fat and water loose energy and dephase at different rates T1 (energy lose time constant) Imaging T2 (dephasing time constant) Imaging Axial MRI Head Water Fat 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 g. rectus cingulate g. cuneus lingual g. precuneus superior frontal g.

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

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

51 Conventional T 2 WI DW-EPI (advanced technique) 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 Sodium ion pumps fail, water goes in cells and can not diffuse. MRI

52 Brain Injury

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

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

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 1s 2s 3s 4s

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

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

61

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

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

64 l. vertebral injection Lateral view X-ray angiography

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

66

67 Venous sinuses Lateral view X-ray angiography

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

69

70 Anterior view MRA

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

72

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

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

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

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

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

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

79 Unused slides

80

81

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

83

84 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 Ultrasound Doppler (frequency shift due to movement) Heart Valve functionality Arterial blood flow


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