Term
| What are the main challenges for mammographic equipment. |
|
Definition
1. Increased contrast sensitivity
2. Reduced dose
3. High spatial resolution (for microcalcifications) |
|
|
Term
| Focal spot sizes used in mammo |
|
Definition
| 0.3 mm (contact) and 0.1 mm (mag mode) |
|
|
Term
| Typical tube currents in mammo |
|
Definition
100 mA for the 0.3 mm focal spot
25 mA for the 0.1 mm focal spot
200 mA and 50 mA for a W anode. |
|
|
Term
| Common anode targets in mammo |
|
Definition
Molybdenum, Mo
Rhodeum, Rh
Tungsten, W |
|
|
Term
| What is the advantage of a Tungsten anode over Mo and Rh. |
|
Definition
| Tungsten has a higher melting point, so higher tube currents can be used. Also, increased x-ray production efficiency due to its higher atomic number. |
|
|
Term
| Characteristic X-rays for Mo |
|
Definition
|
|
Term
| Characteristic X-rays for Rh |
|
Definition
|
|
Term
| Typical source to image receptor distance (SID). |
|
Definition
|
|
Term
| Effective Anode Angle, define it and give a value. Why is it this value. |
|
Definition
| Actual anode angle plus the physical tube tilt, 20-24 degrees. This large angle gives full coverage over the large FOV. |
|
|
Term
Where are the cathode and anode sides located and why?
|
|
Definition
Cathode side is over the chest wall. Anode side is over the nipple. Why - because of the heel effect.
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|
|
Term
| Large field of view (FOV) is what size? |
|
Definition
|
|
Term
| Describe "half-field" X-ray beam geometry. |
|
Definition
| Only half the potential "beam" is used, the other half is collimated out, so the central axis of the beam runs along the chest wall edge perpendicular to the detector. This eliminates unnecessary dose to the patient torso. |
|
|
Term
| Where is the nominal focal spot measured? |
|
Definition
| Along the reference axis, which bisects the x-ray field in the A-C direction. |
|
|
Term
| In which direction does the projected focal spot size change in the x-ray field? How does it change? |
|
Definition
| Along the A-C axis. It is largest at the cathode side (posterior, chest wall) and smallest at the anode side (anterior, nipple). |
|
|
Term
| Where do you get the best resolution and why? |
|
Definition
| On the anode side over the nipple because of the smaller projected focal spot size. |
|
|
Term
| Overall system resolution is measured using |
|
Definition
| a bar phantom with up to 20 lp/mm |
|
|
Term
| Where is the bar pattern placed? |
|
Definition
| 4.5 cm above the breast support surface near the chest wall. |
|
|
Term
| What typically limits the system resolution? |
|
Definition
| In magnification mammo - the focal spot size, in contact mammo - the detector element size. |
|
|
Term
| What is the tube port window made of? What is it's atomic number? |
|
Definition
|
|
Term
| Good mammo filters have k-edge energies between __ and __ keV. Elements that have this include. |
|
Definition
| 20 and 27 keV. Mo, Rh and Ag. |
|
|
Term
| What is the purpose of the k-edge filter. |
|
Definition
| To remove low energies that result in patient dose and also to remove high energies that don't result in good contrast. |
|
|
Term
| Using a filter that is the same material as the anode allows for what? |
|
Definition
| The characteristic x-rays to pass through. |
|
|
Term
| A __ filter should never be used with a Rh target. Why |
|
Definition
| Mo. The Rh characteristic x-rays are above the Mo k-edge so they would be significantly attenuated. |
|
|
Term
| Typical HVL of a mammo x-ray beam. |
|
Definition
|
|
Term
|
Definition
|
|
Term
| Minimum HVL limits are set by? Maximum HVL limits are recommended by? |
|
Definition
| minimum - MQSA regulations, maxiumum - ACR accreditation guidelines. |
|
|
Term
| Tube output rate is measured using what mAs? |
|
Definition
| 300 mAs for an exposure time > 3 seconds |
|
|
Term
| MQSA regulations require a minimum air kerma rate of _______ for screen film detectors. |
|
Definition
|
|
Term
| The x-ray field must extend to the chest wall without cutoff, but not beyond the receptor by more than ______? |
|
Definition
|
|
Term
| The light field and x-ray field must be congruent to within __________. |
|
Definition
|
|
Term
| MQSA regulations require repairs for light/x-ray field congruence, image receptor alignment, or compression paddle alignment be made within _______ days. |
|
Definition
|
|
Term
| Exposure duration is typically controlled by ____________. |
|
Definition
| AEC - Automatic Exposure Control |
|
|
Term
| AEC is set to terminate the exposure based on |
|
Definition
| a specified signal-to-noise ratio |
|
|
Term
| What are the 3 modes of operation that the AEC can have? |
|
Definition
| 1) fully automatic kV and filtration, 2) automatic kV, user set filtration, 3) user set kV and filtration |
|
|
Term
| A _______ is used if the exposure is not terminated by the AEC. |
|
Definition
|
|
Term
| How much can the AEC can be modified by the user? |
|
Definition
| There are 5 steps down and 5 steps up. Each changes the exposure by 10-15%. |
|
|
Term
| Phototimer positioning can usually be adjusted in what direction. |
|
Definition
|
|
Term
| Typical exposure times in mammo. |
|
Definition
|
|
Term
Regarding artifacts,
Too short of an exposure can result in _________.
Too long of an exposure can result in _________. |
|
Definition
too short - grid lines
too long - patient motion |
|
|
Term
| Advantages of breast compression. |
|
Definition
| Reduces overlapping anatomy, reduces motion, less scattered x-rays and lower radiation dose. |
|
|
Term
| Typical compression force. |
|
Definition
|
|
Term
| Contrast Degradation Factor |
|
Definition
| CDF = Cs/Co (contrast with scatter / contrast without scatter) = 1 / (1 + SPR) |
|
|
Term
| Scatter depends mostly on _____ and _____. |
|
Definition
breast thickness and field size.
Note: Its not really a function of kV because there is such a small range of kV used in mammo. |
|
|
Term
| How is scatter reduced in mammography? |
|
Definition
| Antiscatter grid or an air gap. |
|
|
Term
| Typical grid ratios in mammography. |
|
Definition
|
|
Term
| Bucky factor of a mammo grid. |
|
Definition
|
|
Term
| What are the consequences of using an air gap to reduce scatter. |
|
Definition
| Smaller FOV, increased magnification, and increased dose to the breast. |
|
|
Term
| Magnification in mammo is typically used for |
|
Definition
| better visualization of microcalcifications. |
|
|
Term
| Mag mode causes _________ dose to the breast. |
|
Definition
| about the same. The grid is removed which means less dose, but the breast is closer to the x-ray source which means more dose. The two effects basically cancel each other out. |
|
|
Term
| Downsides to magnification. |
|
Definition
| Increased geometric blurring. Reduced tube current means longer exposure times which can lead to patient motion blurring. |
|
|
Term
| Upsides to magnification. |
|
Definition
| Increased effective resolution, reduced image noise, and a reduction in scattered radiation. |
|
|
Term
| Biggest advantage of digital mammography. |
|
Definition
| It doesn't have the exposure latitude limitations of screen-film detectors. |
|
|
Term
| Each detector element in a flat panel array consists of what 3 things? |
|
Definition
| An electronic switch (the TFT), a charge collection electrode, and a storage capacitor. |
|
|
Term
| What is common to all flat panel TFT arrays? |
|
Definition
| An amorphous silicon circuit layer. |
|
|
Term
| An indirect detection TFT flat panel array has what on top of the amorphous silicon layer? |
|
Definition
| A CsI phosphor to convert x-rays to light and photodiodes to convert light to electrical charge. |
|
|
Term
| A direct detection TFT flat planel array has what above the amorphous silicon circuit layer. |
|
Definition
| A layer of Amorphous selenium located between two electrodes. The x-rays create electron-hole pairs in the selenium. A voltage across the electrodes causes the electrons to move. |
|
|
Term
| Which detector results in the lowest average glandular dose? The highest? |
|
Definition
| Lowest - indirect TFT detectors, Highest - cassette-based CR detectors. |
|
|
Term
| What is a typical pixel size in digital mammo? |
|
Definition
|
|
Term
| The "For Processing" image has ______ latitude and _____ contrast. |
|
Definition
| wide latitude and low contrast. |
|
|
Term
| The "For Presentation" image has _______ and _______ _________ enchancements. |
|
Definition
| contrast and spatial resolution |
|
|
Term
| The interpretation monitor should have a minimum of ______ pixels. |
|
Definition
|
|
Term
| The maximal luminance should be at least _______ cd/m2 per ACR guidelines but preferably ________ cd/m2. |
|
Definition
| at least 450, preferably 600 cd/m2 |
|
|
Term
| Computer Aided Detection (CAD) systems use the _____________ images. |
|
Definition
|
|
Term
| Stereotactic breast biopsy are generally used to target |
|
Definition
|
|
Term
| In stereotactic breast biopsy, two images are acquired at ______ degrees. |
|
Definition
|
|
Term
| What is the size of the image detector in stereotactic breast biopsy; FOV, size of the detector array and size of the detector element. |
|
Definition
| 5x5 cm2 FOV, 1000x1000 detector element matrix with each element 0.05 mm. |
|
|
Term
| In Stereotatic Breast Biopsy, the lesion distance from the detector is given by |
|
Definition
| Zdetector to lesion = shift (mm) / (2 tan(15°)) |
|
|
Term
| Breast tomosynthesis involves acquiring ___ to ____ images over _____ degrees up to _____ degrees. |
|
Definition
| 15 to 40 images over ±7.5 degrees up to ±30 degrees |
|
|
Term
| Primary advantage of breast tomosynthesis. |
|
Definition
| It reduces the overlying and underlying anatomy. |
|
|
Term
| Average glandular dose from breast tomosynthesis? |
|
Definition
|
|
Term
| Why is average glandular dose the prefered dose index in mammography? |
|
Definition
| The glandular tissue is the site of the carcinogenesis. |
|
|
Term
| What is the equation for average glandular dose? |
|
Definition
Dg = DgN x XESAK
XESAK - entrance skin air kerma
DgN - air kerma to avg. glandular dose conversion factor |
|
|
Term
| The conversion factor DgN depends on |
|
Definition
| radiation quality (kV and HVL), x-ray tube target material, filter material, breast thickness and tissue composition. |
|
|
Term
| Typical values for the conversion factor DgN. |
|
Definition
0.17 to 0.20
(mGy of AGD per mGy incident air kerma) |
|
|
Term
| What is the thickness of the accreditation phantom? |
|
Definition
|
|
Term
| The MQSA regulations limit the average glandular dose for a compressed breast of 4.2 cm thickness and a 50% glandular / 50% adipose tissue to ______. |
|
Definition
|
|
Term
| Typical dose per view for a full field digital mammo system. |
|
Definition
|
|
Term
| For a facility to legally perform mammo under MQSA, it must be both _________ and _______. Explain. |
|
Definition
Accredited and Certified
Accredited by an accreditation body like the ACR that it meets MQSA standards.
Certification is the approval of the facility by the FDA. |
|
|
Term
| What is the accreditation phantom intended to mimic? |
|
Definition
| A standard breast of 4.2 cm compressed breast thickness of 50% adipose and 50% glandular tissue composition. |
|
|
Term
| What is in the wax insert in the mammo phantom? |
|
Definition
| There are 6 nylon fibers, 5 calcification groups and 5 low contrast disks (masses). |
|
|
Term
| What is required to pass MQSA image quality standards when viewing the phantom. |
|
Definition
| You must see at least 4 fibers, 3 calcification groups and 3 masses at an average glandular dose of less than 3 mGy |
|
|
Term
| What are the main differences between a mammo system and a general radiographic system. |
|
Definition
| 1. shorter SID, 2. lower tube voltages, 3. smaller focal spots, 4. specialized targets and filters, 4. half field geometry, 5. tilted x-ray tube, 6. compression paddle, 7. magnification stands, 8. AEC after (not before) the image receptor |
|
|
Term
| How is image reconstruction performed in tomosynthesis? |
|
Definition
| The images are shifted to the selected plane and then added to create the tomograms. |
|
|
Term
| What does MQSA stand for? Where is it defined? |
|
Definition
Mammography Quality Standards Act
21 CFR 900.12 |
|
|
Term
| What are the daily and weekly QC tests? |
|
Definition
Daily - uniformity and artifact evaluation
Weekly - phantom image evaluation |
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