Mammography Physics Flashcards
Mammography which identify cancer in asymptomatic patients
Screening mammography
Assess palpable lesions or evaluate suspicious lesions
Diagnostic mammography
To differentiate cysts from solid lesions
Ultrasound
Excellent tissue contrast sensitivity and with contrast enhancement. Can be used to diagnose, stage, biopsy guidance and sometimes for screening
MRI
Utilizes Tc - 99m sestamibi evaluation of suspected breast ca in patients whom mammography is non diagnostic
Mammoscintigraphy
Mammohraphy has DUAL FILAMENTS
- 3 mm
0. 1 mm - for magnification studies to reduce geometric blurring
Operating voltage of mammography
Below 40 kV
Most common anode target material used in mammography
Molybdenum
Increase use of tungsten (W) is due to its…
Used in DIGITAL mammography
Increased xray production efficiency (due to high atomic number)
Improved heat loading (higher melting point)
Source to image receptor distance in mammography
65cm
Effective anode angle (adequate field coverage)
At least 22 degrees
0 degree - tube tilt of 24 degrees
16 degree - tube tilt of 6 degress
Positioning of patient
Cathode (kept at highest negative voltage) over the Chest wall
Anode (kept at ground potential) over the anterior portion (nipple)
Focal spot nominal sizes
Contact mammography: 0.3 to 0.4mm
Magnification imaging: 0.1 to 0.15
In order to avoid exposure of the patient’s torsos and to maximize thr amount of breast tissue near the chest wall. Mammography utilize _____ which is achieved by fixed collimation at the xray tube head
Half field
Focal spot resolvability with or without magnification is measured by imaging a high resolution bar pattern with up to
20 line pairs/mm
Conventional breast imaging: 4.5 cm above the breast support surface near the chest wall
Magnification imaging: placed 4.5 cm above the magnification palform
Tube port window in mammography
Beryllium (z=4)
Elements that have K-shell binding energies
Mo, Rh and Ag
Half value layer of a mammography xray beam
0.3 to 0.7 mm Al for the kV range
HVL for breast tissues
1 to 3 cm
X ray beam that is HARDER than optimal that results to a reduced output and poor image quality indicates
Too much filtration
Pited anode
Aged tube
Tube output
Measure of the intensity of the xray beam
Collimation of xray beam (mammography) is achieved by the use of
Fixed size metal apertures or adjustable shutters
Used for optimizing the oblique projections for subjects with smaller breasts
Field Shift
Automatic Exposure Control (AEC) employs
Radiation sensor
Charge amplifier
Voltage comparator
For cassette based image receptors where is the phototimer located
Underneath
Modifies the AEC response to permit adjustments for unusual imaging circumstances
Exposure adjustment selector (generator control panel)
An xray exposure that is not stopped by the AEC circuit and exceeds a preset time is terminated by
Back up timer
Useful guides to help determine the appropriate kV and target filter combinations for a specific tasks
Technique charts
Firm compression
Reduces overlapping anatomy
Decreased breast tissue thickness
Reduces motion of the breast
Compression force
111 to 200 newtons (25 to 44lbs)
Carries information regarding the attenuation characteristics of the breast
Primary radiation
Additive, gradually varying radiation distribution that degrades subject contrast and adds random noise
Scattered radiation
The ratio of exposure with the grid compared to to the exposure without the grid to achieve the same film optical density
Bucky Factor ( 2 to 3 in mammography)
Used to improve system resolution, typically for better visualization of microcalcidications
Geometric magnification
Screen film mammogram comprises
Cassette
Intensifying screen
Light sensitive film
Most commonly used screen phosphor (mammo)
Terbium activated gadolinium oxysulfide
Degree of the obstruction of light transmission and optical density
Film opacity
Represents the relationship between the incident xray exposure and the resulting OD in the processed film
H and D curve (Film characteristic curve)
Graph of the change of OD per unit change in the incident exposure
Gradient Graph
A device that emulates a range of incident radiation exposures by using a constant light source and calibrated optical attenuation steps to expose a mammographic film to known relative light intensities
Sensitometer
Is a device that measures the light transmission through a small area of the film and calculates the OD
Densitometer
Describes absorption of xrays in the CsI (structured cesium iodide)
Indirect conversion
Four technologies for mammography based systems
Indirect conversion
Direct conversion
Stimulated luminescence
Slot
Computer based set of algorithms that incorporates pattern recognition and uses sophisticated matching and similarity rules to flag possible findings on a digital mammographic image
Computer aided detection (CADe)
Include software that provides information BEYOND identifying suspicious findings
Computer assisted diagnosis (CADx)
Provide the capability to localize breast lesions in three dimensions and physicay sample them with a targeted biopsy instrument
Stereotactic breast biopsy
