Chapter 8 - Mammography Flashcards
Most simple advantage of digital mammography
Ability to overcome the exposure latitude limitations of screen-film detectors AND produce better image quality at lower doses
(In digital mammo) describes the absorption of X-rays in the CsI; the production of secondary light photons directed to a photodiode, and the generation of the charge, which is stored on the storage capacitor in the detector element
Indirect conversion
Refers to the direct generation of charge by X-rays within the photoconductor and capture by the electrode without intermediate signals
Direct conversion
A process where electrons fall to a lower energy state with the emission of light
Stimulated luminescence
4 technologies used in digital mammo
A. Indirect X-ray conversion TFT flat panel array receptor
B. Direct X-Ray conversion TFT detector
C. Cassette-based dual side readout CR photostimulable storage phosphor (PSP) imaging plate detector and reader system
D. Charge-coupled-device (CCD) detector array
Strongly recommended display monitor specification for digital mammo
Must have a minimum of 5 million pixels (5MP)& a calibrated,sustained maximal luminance of at least 450 cd/m2
(Per ACR guidelines for digital mammography), but preferably at 600 cd/m2
A method which acquires multiple low-dose images at Several angular positions as the X-ray tube moves in an arc about the breast to reduce superimposition
Breast Digital Tomosynthesis
Preferred dose index in the breast’s glandular tissue (site of carcinogenesis)
Average glandular dose
3 Major factors affecting breast dose
- Speed of the screen-film receptor
- Film OD
- Digital detector SNR level
The MQSA regulations limit the average glandular dose for a compressed breast thickness of 4.2 cm and a breast composition of 50% glandular and 50% adipose tissue to _____
3mGy per film or digital image (6mGy for two films or images)
Breast QC standard category specific to the digital acquisition system(system resolution, breast dose, image quality evaluation, SNR/CNR,flat-field calibration and compression)
Category A QC
Breast QC standard category specific to the performance of a diagnosis device used for mammographic interpretation including the review workstation and laser film printer
Category B QC
Breast QC standard category which evaluate performance of components other than the digital image receptor or diagnostic devices for interpretation(collimation assessment, artifact evaluation, kV accuracy, HVL assessment,AEC performance and reproducibility, radiation output rate, compression thickness indicator)
Category C QC
To pass the MQSA image quality standards for screen film mammo (mammo accreditation phantom)
At least FOUR fibers , THREE calcification groups and THREE masses must be clearly visible (with no obvious artifacts) at an average glandular dose of less than 3 mGy
Two breast imaging views used in screening mammography
Mediolateral oblique view and craniocaudal view
Attempts to identify breast cancer in the asymptomatic population
Screening mammography
Procedures performed to assess palpable breast lesions or evaluate suspicious findings identified by screening mammography
Diagnostic mammography
Breast modality that is used to differentiate cysts(typically benign) from solid masses (often cancerous) and is also used when possible for biopsy needle guidance
Breast ultrasound
Breast modality with excellent tissue contrast sensitivity and with contrast enhancement can differentiate benign from malignant tumors; used for diagnosis, staging, biopsy guidance, and in some cases, screening.
Breast MRI
Breast modality that utilizes Tc-99m sestamibi in the evaluation of suspected breast cancer in patients for whom mammography is nondiagnostic, equivocal, or difficult to interpret (e.g. Presence of scar tissue, mammographically dense breast tissue, implants or severe dysplastic disease)
Mammoscintigraphy
Most common anode target material used in mammo
Molybdenum
Major reason for choosing Mo and Rh targets in mammo
Characteristic X-ray production
with digital detectors, W is becoming the target of choice
Actual anode angle plus physical tube tilt
Effective anode angle (at least 22 degrees in mammo)
X-ray intensity is greater at the cathode side of the projected field than the intensity on the anode side
Heel effect
- chest wall side of the breast (over the cathode)
- anterior side of the breast (over the anode)
Improves the energy distribution of the mammography output spectrum
Added xray tube filtration
Tube port window in mammo is made up of____.
Beryllium
A Mo filter should _______ with a Rh target
NEVER BE USED
*Rh characteristic X-rays are attenuated significantly as their energies are above the Mo K-absorption edge
Half value layer of a mammo X-ray beam ranges from ____
0.3 to 0.7 mm
A measure of the intensity of the X-ray beam, typically normalized to mAs or to 100 mAs, at a specified distance from the source (focal spot)
Tube output
Determined from the known SID, breast platform to detector distance and compressed breast thickness
Source-to-breast surface distance
Air Kerma rate at a specified distance from the X-ray focal spot and is a function of the X-ray tube current achievable for an extended exposure time
Tube output rate
Phototimer sensor is located ____ the cassette and consists of a single ionization chamber or an array of three or more semiconductor diodes
UNDERNEATH
An X-ray exposure that is not stopped by the AEC circuit and exceeds a preset time (e.g.greater than 5s) is terminated by a _____
Backup timer
The resultant OD is < would be predicted by the amount of radiation delivered to the screen-film cassette; consequently, insufficient film OD results and extension of the exposure time is added to compensate
Reciprocity law failure
Carries informations regarding the attenuation characteristics of the breast and delivers the maximum possible subject contrast to the detector
Primary radiation
An additive gradually varying radiation distribution that degrades subject contrast and adds random noise
Scattered radiation
Main adverse effect of scatter in digital mammo
Add random noise(thus, degrading the signal to noise ratio)
X-ray scatter _______ with increasing breast thickness and breast area
Increases
Cause of most grid-line artifacts
Insufficient grid motion
Ratio of the exposure with the grid compared to the exposure without the grid to achieve the same film optical density
Bucky factor
3 consequences of using a air-gap
- Reduced field of view
- Increased breast magnification
- Increases breast dose
Used to improve system resolution, typically for better visualization of MICROCALCIFICATIONS
Geometric magnification
Most commonly used screen phosphor in mammo
Terbium-activated gadolinium oxysulfide (Gd2O2S:Tb)
Intensifying screen is positioned in the ____ of the cassette so that X-Rays travel through the cassette cover and the film before interacting with the phosphor
Back
Degree of the obstruction of light transmission(the inverse of transmittance)
Film opacity
Equal to the base ten logarithm of the opacity
Optical density (OD)
An indication of the amount of the incident radiation required to achieve a specified OD on the film
Film speed
The rate of change of OD for a known difference in incident radiation
Film contrast
If developer temperature is too low, film speed and film contrast will be ________
Reduced
If the developer temperature is too high or immersion time too long film speed will _____ while film contrast will ____
Increased….
Reduced…because the film fog and quantum mottle are increased
Represents the relationship between the incident X-ray exposure and the resulting OD in the processed film; graph of the OD as a function of the logarithm of the relative exposure
Film characteristic curve(H and D curve)
3 major sections of a film characteristic curve
- Toe (has a low OD)
- Linear section (has increasing OD w/ increasing incident exposure)
- Shoulder (represents film saturation)
Graph of the change of OD per unit change in the incident exposure, as a function of the logarithm of the relative exposure
Gradient curve
Rate of change of the characteristic curve
Gradient (film contrast)
A device that emulates the 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
A range of numbered OD steps produced by developing a film
Film sensitometric strip
A device that measures light transmission through a small area of the film and calculates the OD
Densitometer
The one whose OD is closest to, but does not exceed 0.2
Mid-density step
Those whose ODs are closest to but not exceeding 0.45 and closest to 2.20
Density difference steps
A measure of brightness
Luminance
Mammo view boxes should have minimum luminances of at least ________, and luminances exceeding ______ are common
3,000 cd/m2
6,000 cd/m2
(Note: the luminance of 1 cd/m2 is approx. the luminous intensity of the sky at the western horizon on a clear day, 15 min. after sunset)
The luminance of the view box in diagnostic radiology is typically about ________.
1,500 cd/m2
Blocking clear portions of the film and areas of the view box that are not covered by film
Film masking
*prevents extremely bright light from degrading the radiologist’s visual adaptation to the range of luminances displayed by the images)
Luminous flux incident upon a surface per unit area measured in lux or lumens/m2
Illuminance
- 1 lux (1 full moon in a clear night sky)
- 100 to 1000 lux (normal room lighting)
- ** 20-40 lux, acceptable for viewing and interpretation of mammograms (subdued room lighting)
