Mammography Flashcards
This is a radiographic examination that is designed for detecting breast pathology, particularly breast cancer.
Mammography
How was early x-ray mammography performed?
With direct exposure film (intensifying screens were not used), required high radiation doses, and produces images of low contrast and poor diagnostic quality.
Momograhy Quality Standards Act was enacted in 1992
What are the features characteristic of breast cancer?
Masses, particularly ones with irregular or spiculated margins
Clusters of microcalcifcation
Architectural distortions
What is the purpose of screening mammography?
It attempts to identify breast cancer in the asymptomatc population
Mediolateral oblique and cranial views are acquired.
What is the purpose of diagnostic mammography?
To assess palpable lesions or evaluate suspicious findings identifies by screening mammography.
Modality in breast imaging that is often used to differentiate cyst from solid masses and used in biopsy needle guidance.
Ultrasound
This modality in breast imaging has excellent tissue contrast sensitivity and with contrast enhancement can differentiate benign from malignant tumors.
MRI
Subject contrast contrast in mammography is highest at what level of x-ray energy?
Highest at low x-ray energies (10 to 15 keV) and reduced at higher energies (greater than 30 keV)
Low x-ray energies provide best differential attenuation between the tissues, however, high absorption results in higher radiation doses and long exposure times.
What are the important distinctions between mammography and conventional x-ray tube operation?
Low operating voltage, below 40 kV
Filament current is restricted to limit the tube current, typically to 100 mA for the large (0.3 mm) focal spot and 25 mA for the small (0.1 mm) focal spot so as to not overheat the Mo or Rh targets due to the small interaction areas.
This is the most common anode target material used in mammography.
Molybdenum
What is the major reason for choosing molybdenum as target?
As the number of x-rays in the optimal energy range for breast imaging are significantly increased by characteristic x-ray emission.
With digital detectors, what material is becoming the target of choice?
Tungsten
Mammography x-ray tubes have rotating anodes, with anode angles ranging from how many degrees?
16 to 0 degrees
The tubes are typically positioned at a source-to-image receptor distance of about how many cm?
65 cm
Where would the cathode and anode be positioned in order to achieve better uniformity of the transmitted x-rays through the breast?
Positioning the cathode over the chest wall of the patient and the anode over the anterior portion (nipple)
How to reduce off-focal radiation?
Anode is kept at ground potential (0 voltage), and the cathode is set to the highest negative voltage
Focal spot nominal sizes of how many mm for contact mammography?
- 3 to 0.4 mm
- 10 to 0.15 mm for magnification imaging
To reduce geometric blurring so that microcalcifications can be resolved.
What is the consequences of using small focal spots?
Reduce maximal tube current and longer exposure time
In order to avoid exposure of the patients’ torso and to maximize the amount of breast tissue near the chest wall that is imaged, all dedicated mammography systems utilize what geometry?
A “half-field” geometry
Which is achieved by fixed collimation at the x-ray tube head.
The tube port window in mammography is made from what material?
Beryllium
Why is beryllium use as tube port window?
The low atomic number (4) of beryllium and the small thickness of the window (0.5 to 1 mm) allow the transmission of all but the lowest energy (less than 5 keV) bremsstrahlung x-rays
How does added x-ray tube filtration improves the energy distribution of the mammography output spectrum?
By selectively removing the lowest and highest energy x-rays from the x-ray beam, while largely transmitting desired x-ray energies
A Mo filter should never be used with a Rh target. Why?
Because Rh characterisitic x-rays are attenuated signifiantly as their energies are bove the Mo K-absorption edge
The half-value layer of mammography x-ray beam ranges from how many mm Al?
0.3 to 0.7 mm Al
The HVL depends on the target material, kV, filter material, and filter thickness.
Measurement of the HVL is performed how?
With compression paddle in the beam, using 99.9% pure Al sheets of 0.1- mm thickness.
Why is breast compression an important part of mammography examination?
It reduces overlapping anatomy, decreases tissue thickness, and reduces inadvertent motion of the breast.
It results in fewer scattered x-rays, less geometric blurring of anatomic structures, and lower radiation dose to the breast.
What happen when achieving uniform breast thickness?
It lessens exposure dynamic range and allows the use of higher contrast film, or allows more flexibility in image processing enhancement of the digital image
Primary radiation carried information regarding what?
Regarding the attenuation characteristics of the breast and delivers the maximum possible subject contrast to the detector.
Scattered radiation is an additive, gradually varying radiation distribution that degrades subject contrast and adds random noise.
How can scattered radiation reaching the image receptor be reduced?
It can be greatly reduced by the use of an antiscatter grid or air gap.
Mammography grid transmit about 60 to 70% of primary x-rays and absorb 75 to 85% of the scattered radiation.
This technique is used to improved system resolution, typically for better visualization of microcalcifications.
Geometric magnification
What are the advantages of magnification?
A. increased effective resolution of the image receptor by the magnification factor
B. reduction of image noise relative to the objects being rendered
C. reduction of scattered radiation
What comprises a mammographic screen-film detector?
A cassette, intensifying screen or screens, and a light-sensitive film.
Most mammographic cassettes are made of what?
Made of low-attenuation carbon fiber and have a single high-definition phosphor screen used in conjunction with a single emulsion film.
This is the most commonly used screen phosphor in mammography.
Terbium-activated gadolinium oxysulfide
The scintillator of mammography emits what color of light?
Green light
Requiring a green-sensitive film emulson
What determines the intensifying screen-film speeds and spatial resolution?
They are determined by: Screen phosphor particle size Number of phosphor particles per volume Light-absorbing dyes in the phoshor matrix Phosphor layer thickness
This represents the relationship between the incident x-ray exposure and the resulting OD in the processed film.
Film characteristic curve (H and D curve)
What are the three major sections of a film characteristic curve?
Toe - has a low OD that changes very little with incident exposure up to a threshold
Linear section - represents increasing OD with increasing incident exposure , with subject contrast mapped as optical densities that render the radiographic contrast
Shoulder - represents saturation of the film, where increases in incident exposure do not significantly increase the OD
This is a graph of the change in OD per unit change in the incident exposure, as a function of the logarithm of the relative exposure.
Gradient curve
Indicates contrast as a function of air kerma (exposure)
This is 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 intesities.
Sensitometer
This is a deviCe that measures the light transmission through a small area of the film and calculates the OD.
Densitometer
This results from variations in subject contrast translated into these OD differences according to the film’s characterisitic curve.
Radiographic contrast (OD differences on the developed film)
Best recording of subject contrast occurs on parts of the film where the exposures correspond to the toe and shoulder segments of the curve.
Why does high luminance needed for mammography reading?
Since mammography films are exposed to high optical densities to achieve high contrast, view boxes in the mammography read area provide high luminance (a measure of brightness)
Mammography view boxes should have a minimum luminance of how many cd/m²?
Should have at least 3,000 cd/m², luminance exceeding 6,000 are common
In comparison, the luminance of a view box in diagnostic radiolog is typically about 1,500 cd/m².
This is the luminous flux incident upon a surface per unit area, measuring in lux or lumens/m².
Illuminance (measures ambient light intensity)
