overview of medical imaging: focusing on neuroimaging
TRANSCRIPT
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
Electromagnetic wave (could use photon picture b/c wave-particle duality)
one wavelength
Wave Particle duality of electromagnetic radiation
Electromagnetic Spectrum
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?
Electromagnetic Spectrum
Visible
Laparoscopy - ovaryEndoscopy
Visible
X-RAYs
Roentgen : 1895 Discovered X-rays1901 Nobel Prize
Advantages of X-Ray-cheap- fast- good diagnostic value for many things
Disadvantages- ionizing radiation- contrast is just density differences
Electromagnetic Spectrum
X-RAYs
How X-rays work
Number of protonsRoughly Proportional to mass
Simple Fit
X-ray Radiography - 2D (ie Chest)
Advantage very fast high resolution
Disadvantage ionizing radiation xray contrast
100KVp
X-ray Radiography - 2D
(Photoelectric effect)
ComptonScattering
X-ray Radiography - 2D
[everything going digital now]
X-ray Radiography - 2D
MammographyLow energy X-ray b/c
all tissue
Bone healing study on rats
(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 3DDisadvantage ionizing radiation xray contrast
What is tomography
Red dots are areas of high densityPeaks are number of Xrays absorbed(note : normally would do axially and not sagittally)
Axial - head Axial - abdomen
Substance HU
Air -1000
Fat -120
Water 0
Muscle +40
Bone +1000
HoundsfieldUnits
Why is water in brain dark comparedto brain tissue?
(X-ray) CT – computed tomography – 3D
CT: What does the image represent?
hyperdensity
hypodensity
isodensity
(X-ray) CT – computed tomography – 3D
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 Feature Property Sample tissues
(X-ray) CT – computed tomography – 3D
CT: What does the image represent?
(X-ray) CT – computed tomography – 3D
CT: What does the image represent?
(X-ray) CT – computed tomography – 3D
(X-ray) CT – computed tomography – 3D
CT - Hemmorage
(Xray) Flouroscopy – 2D
Xray
Realtime ImagingHeartBlood FlowSurgery
advantage :
disadvantage: high radiation dose
(Xray) CONTRAST – Radiograph, CT, or Flouroscopy
Barium Swallow
Injection (Iodine Compound)
Angiogram
(X-ray) CT – computed tomography – 3D
(X-ray) CT – computed tomography – 3D
13um resolution mouseplacenta vasculature
Advantages better resolution (smaller detectors source closer to detector) Disadvantage small :}
mouse microCT/PET
Electromagnetic Spectrum
PET – positron emission tomography
Inject Patient with Radioactive Drug
Late 1960’s
Drug travels to metabolically active sites (manytumors have high metabolic activity)
Drug emits (+) positrons (basically a positivelycharged electron)
FDG - Fluorodeoxyglucose (most common drug)(F18 – + emitter – two hour half-life)
Advantagefunctional imaging
Disadvantagesome ionizing radiationlow resolution (4mm x 4mm x 4mm)need to make/buy FDG (cyclotron)
PET – positron emission tomography
CT
PET/CT - together
(Xray) CT PET
• β+ decay, positron travels several mm and collides with an electron
• produce a pair of annihilation photons (511kev, 180o)
• simultaneous detection 180o apart
PET – positron emission tomography
Abnormal FDG collection
PET – positron emission tomography
Treated Tumorgrowing againon periphery
PET – positron emission tomography
functional brain activity (mostly done with MRI now)
PET/CT - together
PET/CT - together
PETPETCT PET/CT
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/R2 (surface area of sphere), therefore closer is better
signal to noisegood bad
Electromagnetic Spectrum
Ultrasound
Discovered (Norris) 1952, clinical 1962
Sound waves 1-15MHz (ear 20 – 20KHz)
Echos (reflections) from different density interfacesare recorded
Image soft tissue and blood flow (Doppler)
Advantages:high resolution (mm)
cheapreal time imagingsafe
Disadvantages:skilled technician & interpretationsmall field of view (~20cm)bone and air problematic
Ultrasound
Typical ultra sound – sound reflections off surface
Fetocopsy ImageExample
probe
Arterial Blood Flow
Electromagnetic Spectrum
MRI – Magnetic Resonance Imaging
Mansfield and Lauterbur nobel prize1978 first images
MRI – Magnetic Resonance Imaging
1st published MRI images of abdomen
3 Tesla MRI Scanner
“Interesting images, but will never be as useful as CT”neuroradiologist, 1982
First brain MR First brain MR Modern T2 imageModern T2 image
MRI
Advantages Disadvantagessafe expensivegreat soft tissue contrast long timemany contrast options bad for bones
mediocre resolution
3 Tesla MagneticField (60,000 timesEarths field)
MRI
B0
B0
3 Tesla magnet field
B0
Protons (hydrogennuclei act like littlemagnets)
Not all the protonsline up – thermal energy
MRI
Collective MagneticMoment of Protons
MRIStage IExcite
B0
Radio Waves
Collective MagneticMoment of Protons
start
end
MRIStage IIlisten
start
end
Make image based onProtons loosing energy
Make image based onProtons dephasing
Slow Precession
FastPrecession
Fat andwater looseenergy anddephase atdifferent rates
T1 (energy lose time constant)Imaging T2 (dephasing time constant)
Imaging
Axial MRI Head
Water
Fat
bright
bright dark
dark
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
MRI: “Normal” Anatomy
corpus callosum
fornix
thalamus
midbrain
pons
medulla
MRI: “Normal” Anatomy
g. rectus
cingulate g.
cuneus
lingual g.
precuneussuperior frontal g.
MRI: Imaging deep structures(thalamus and basal ganglia)
thalamus Caudate nucleus Putamen & globus pallidus
Multiple Sclerosis – Active Lessions(basically edema – water)
MRI
Tumor (can be combination ofEdema and tumor tissue characteristics)
Disease
Conventional TConventional T22 WI WI DW-EPI (advanced technique)DW-EPI (advanced technique)
Why MRI : Detection of Acute StrokeWhy 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
MRI
Brain Injury
MRA – magnetic resonance angiogram MRI
Excite Protons
Wait then Listen to Protons
Single slice from MRA
MRA (arteries)MRV (Veins) – reverseexcite and listen slices
MRIStack the slices to produce 3D image
Angiography
• Refers to imaging of blood vessels
• Several types:
•conventional x-ray angiography
•Spiral / helical CT angiography
•magnetic resonance angiography
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
Xray: Imaging Vasculature
1s
2s
3s
4s
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
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)
MR Angiography
r. Internal carotid injection
Lateral view
X-ray angiography
carotid siphon internal carotid
ophthalmic artery
ACA and branches
MCA and branches
r. Internal carotid injection
Lateral view
X-ray angiography
l. vertebral injection
Lateral view
X-ray angiography
Posterior inf. cerebellar arteryvertebral artery
basilar artery
PCA and branches
l. vertebral injection
Lateral view
X-ray angiography
Venous sinuses
Lateral view
X-ray angiography
Jugular vein & bulb
Straight sinus
Venous sinuses
Lateral view
X-ray angiography
Great cerebral vein of Galen
Superior sagittal sinus
Superior sagittal sinus
Confluence of sinuses
Anterior view
MRA
Anterior view
MRA
Basilar artery
Internal carotid
MCAACA
MCA
Carotid siphon
r. Internal carotid injection
AP view
X-ray angiography
r. Internal carotid injection
AP view
X-ray angiography
Internal carotidMCA
ACA
Carotid siphon
l. Vertebral artery injection
AP view
X-ray angiography
l. Vertebral artery injection
AP view
X-ray angiography
vertebral artery
PCA
r. Internal carotid injection
AP view
X-ray angiography
r. Internal carotid injection
AP view
X-ray angiography
Jugular vein & bulb
Superior sagittal sinus
Transverse sinus
Confluence of sinuses
Sigmoid sinus
Unused slides
Sound reflectionsSound – densitydetermines reflection
like light (E&M) – index of refractiondetermines reflection for light (E&M)
Sonar = 10 – 200KHz
Incident
Refracted (penetrated)
Reflected
Ultrasound
Doppler (frequency shift due to movement)
Heart Valve functionality
Arterial blood flow