10/19/2006
ENGG 167
MEDICAL IMAGING
Lecture 5: Oct. 9
Chapter 8: Mammography
Chapter 9: Fluoroscopy
References: Bushberg text
The physics of medical imaging, Webb
Introduction to radiological physics and radiation dosimetry, Attix
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Mammography - Bushberg Chapter 8
Mammography: significant changes have occurred within
The last 10 years.
Ref: Bushberg
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Attenuation and soft tissue contrast
- low attenuation leads to low contrast at high keV
- higher contrast achieved at lower keV
- issues to consider are, dose, contrast, tissue thickness
exposure time, scatter, special sources and detectors
Ref: Bushberg
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Ref: Webb
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Contrast of calcifications
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Mammography systems
-
Ref: Bushberg
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Mammography systems – the tube and focal spot
-
Ref: Bushberg
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Mammography systems – the tube and focal spot
Heel Effect
Anode attenuates the distal part of the beam, incident near the
breast nipple, thereby reducing the number of photons there
(see Fig. 8-5 in text).
Grounded Anode design
Anode maintained at ground voltage, while cathode set to high
negative voltage. This design allows capture of many off focus electrons
within the housing and reduces off focus radiation.
Focal Spot size varies across the image plane
The angle of orientiation of the tube relative to the breast causes a
Smaller focal spot apparent at the nipple relative the chest wall.
Ref: Bushberg
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Mammography systems target and filter compostion
-
Options:
Molybdenum (Mo)
Ruthenium (Ru)
Rhodium (Rh)
Palladium (Pd)
Silver (Ag)
Cadmium (Cd)
Ref: Bushberg
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Mammography systems target and filter compostion
-
Ref: Bushberg
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Molybdenum (Mo) and Rhodium (Rh) targets with filtering
- filtering reduces the x-ray energy photons below the K-shell edge
providing a transmission window for characteristic x-rays.
typical values – Mo target with 0.03 mm Mo filter (Mo/Mo)
- Rh target with 0.025 mm Rh filter (Rh/Rh)
- Mo target with Rh filter
- note: cannot use Rh target with Mo filter!
Ref: Bushberg
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Tungsten targets
HVL versus kVp
Ref: Bushberg
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Automatic exposure control in mammography
Ref: Bushberg
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Compression and spot magnification
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Ref: Bushberg
ACR recommendations and FDA regulations
Ref: Bushberg
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Scatter induced in the breast, vs. thickness and spot size
Ref: Bushberg
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Antiscatter grids – reduce detected scatter
Ref: Bushberg
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Dose in Mammography
Ref: Bushberg
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Screen-Film cassettes used in Mammography
Ref: Bushberg
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MTFs of Mammography Systems
Newer curve has higher
slope and transition
is at lower exposure
Ref: Bushberg
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Mammography guided biopsy
Ref: Bushberg
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Mammography guided biopsy
Ref: Bushberg
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Ref: Bushberg
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Quality Control phantom
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QC
Ref: Bushberg
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Ref: Bushberg
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QC
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Fluoroscopy – Bushberg Chapter 9
Ref: Bushberg
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Ref: Bushberg
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Fluoroscopy Image Intensifier
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Tube photocathode
X-ray Æ optical photon Æ electrons
Ref: Bushberg
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Ref: Bushberg
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Normal and Magnification Modes
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Automatic brightness control
Ref: Bushberg
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Ref: Bushberg
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MTF in Fluoroscopy
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Radiography and Angiography with Fluoroscopic units
Ref: Bushberg
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Ref: Bushberg
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Entrance Skin Exposure (ESE)
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Dose to Radiologist
Ref: Bushberg
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Dose errors in Fluoroscopy can be very bad…
Ref: Bushberg
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