Instrumentation and Quality Assurance

In mammography, selecting extremely low kVp values

1. reduces contrast and lowers patient dose

2. increases contrast but increases patient dose

3. reduces contrast but increases patient dose

4. increases contrast and reduces patient dose

2

The kVp controls the wavelength or the penetrating power of the beam. The kVp will therefore ultimately control the subject con-trast, exposure latitude, and image contrast.
Remember, however, that as the kVp is re-duced, the penetrating ability of the beam is also reduced leading to the use of higher mAs. Higher mAs use increases patient dose.
(Bushong p. 273; Wentz, p. 47)

What target filtration-combination provides the best penetration for dense or thick breast?

1. molybdenum target with molybdenum filtration

2. rhodium target with rhodium filtration

3. tungsten target with tungsten filtration

4. molybdenum target with appropriate
   K-edge filtration

2

All mammography units are manufactured with tungsten, molybdenum, or rhodium targets matched with the appropriate K-edge filters. These targets have different atomic numbers and therefore different emission spectrums. The characteristic energies of molybdenum are most effective for fatty breast tissue. The characteristic x-rays produced using rhodium targets with rhodium filtration are similar to those from molybdenum but, because rhodium has a slightly higher atomic number, more bremsstrahlung x-rays are produced. However, the energy of the K-characteristic x-rays will be 2-3 keV higher, which provides a better penetration of dense breast although it generally results in lower contrast images. Tungsten targets with tungsten filtration are not used because here bremsstrahlung x-rays will predominate at energies above and below the 17- to 24-keV range. The x-rays most useful in maximizing contrast in breast tissue are in the 17- to 24-keV range. (Bushong, p. 310; Wentz, p. 47)

The material used for the exit port of the mammography tube is necessary because

1. the intensity of the beam is less on the anode side than on the cathode side

2. regular glass would harden the emerging beam

3. the intensity of the beam is more on the anode side than the cathode side

4. regular glass would soften the emerging beam

(B) Mammography uses very low energy x-ray beams and it is important that the x-ray tube window does not attenuate the low-energy photons. The proper filter shapes the emission spectrum of the x-ray beam and makes it compatible with the image receptor and breast characteristics of each patient. In general, mammography units either have borosilicate or beryllium as port windows. (Bushong, p. 311)

The intensity of the x-ray beam from the cathode side of the tube is generally higher because

	(A) soft characteristic radiation emerges from the anode side
	(B) the cathode side is directed to the thickest part of the breast
	(C) the heel effect causes variation in the intensity of the x-ray beam
	D) the heel effect hardens the beam at the anode side

(D) The heel of the anode will reduce the intensity of the x-ray beam. In general, the smaller the anode angle, the larger the heel effect because there is increased absorption of the rays (Figure 2-1). (Bushong, p. 117)

The design of the lip of the compression paddle (both height and angle along the chest wall) affects all of the following EXCEPT that it

1. prevents the posterior and axillary fat from overlapping the body of the breast

2. allows uniform compression of the posterior breast tissue

3. helps to increase structural strength of the compression paddle

4. ensures even compression of the anterior breast tissue

4

Both the height and angle of the compression paddle make a difference in the final image. A compression device with a rounded or gently sloping posterior edge does not allow uniform compression of the posterior area of the breast. The height of the compression reduces the chance of chest tissue overlapping on the mammogram. The design of the lip has a lesser effect on the anterior aspect of the breast. (ACR, pp. 30-33)

The primary goal of compression is to

	(A) reduce the object-to-image receptor dis-	tance of the lesion
	(B) allow uniform penetration of structures within the breast
(C)
	reduce the possibility of motion during the exposure D) reduce the radiation dose to the breast

(C) Compression does all of these, but its primary goal is to reduce the breast thickness uniformly-(separate breast structures) and allow uniform penetration by the x-ray beam.

(ACR, pp. 30-33)

AEC failure, resulting in an underexposed film, can be caused by

1. processing deficiencies such as fluctuating developer temperature

2. improper placement of the dense breast tissue / size over the detector

3. decreased radiographic contrast

4. inadequate breast compression

2

The most common cause of failure of the
AEC is improper placement of the detector.

Processing affects the mammographic image after exposure and mammographic quality control ensures correct processing condi-tions. Decreased radiographic contrast is a result of underexposure, not the cause, and inadequate compression, although it causes uneven densities on the mammogram, does not result from AEC failure. (ACR, p. 92)

Most AEC circuitry in modern mammographic imaging has at least three detectors. Three or more detectors are recommended because

1. multiple detectors allow for maximum variations in breast size and tissue density

2. AEC detectors eliminate the guesswork in determining the proper exposure factor for each patient

3. detectors have the ability to terminate the exposure by back-up timer when a maximum exposure time or maximum mAs is reached

4. all AEC detector systems provide consistent film densities because of the high-contrast mammography films

1

The detector system of the AEC allows the unit to respond to different breast composition and various breast sizes. If the detector is placed over fatty breast tissue, the glandular tissue will be underexposed. To produce an adequate exposure, the detector must be placed over the densest or most glandular areas of the compressed breast. (Andolina, p. 183;

Bushong, p. 315)

The major difference between the general radiography grid and the grid used in mammography is that the

1. grid use in general radiography causes an increase in exposure

2. grids in general radiography have higher ratios

3. use of a grid in mammography increases patient dose

4. grids in mammography improve the ra-diographic image contrast

2

All grids result in increased exposure and patient dose, but improve contrast. The mammography grid, however, has a lower grid ratio than general radiography grids.

The grid ratio of mammography grids ranges from 3:1 to 5:1 versus the 6:1 to 16:1 ratio of grids used in general radiography. (Grid ratio = height of the lead strips/the distance between the strips [h/d]). (Carlton, p. 570;

Bushong, p. 310)

The grid ratio can vary in modern mammography units. A common grid ratio used is

(A) 7:1

(B) 6:1

(C)5:1

(D) 4:1

(D) Higher grid ratios will require too large an increase in exposure. On average, the grids used in mammography range from 3:1 to 5:1, with frequencies of 30-50 lines per centimeter. Typically, a mammography grid may have a grid ratio of 4:1, and although such a grid will double the patient dose when compared to a nongrid exposure, the increased contrast will be significant.

(Bushong, p. 315; Carlton, p. 583)

As the size of the x-ray field decreases, to maintain a constant image density the exposure will

1. increase

2. decrease

3. not change significantly

4. decrease inversely

1

Collimating or decreasing field reduces scatter and therefore improves the contrast.

However, because collimating reduces the scattered radiation density to the area, the exposure must be increased. (Bushong, p. 222;

Wentz, pp. 2-23)

The chest wall edge of the compression paddle should be aligned just beyond the chest wall edge of the image receptor to

1. avoid pushing the patient's chest away and losing breast tissue

2. properly position and compress the breast

3. permit uniform exposure and reduce patient discomfort

4. avoid projecting the chest wall edge of the paddle on the mammogram

4

The compression plate is specifically designed to properly position and compress the breast while reducing discomfort to the pa-tient. The placement of the lip, just beyond the chest wall edge of the image receptor, prevents the projection of an image of the chest wall edge of the paddle on the mam-mogram. (AEC, pp. 30-33)

Which of the following affects focal spot size?	(A) angle of the anode
	(B) a decrease in the source-to-image receptor distance
	(C) decreasing the size of the collimated	beam
	(D) changing the relationship between the OID and the SID

(A) The focal spot size is the area that electrons strike on the target. In the design known as the line-focus principle, the target is angled allowing a larger area for the electrons to strike while maintaining a small, effective focal spot. The effective focal spot size is the area projected onto the patient or image receptor. It is also the value quoted when identifying a small or large focal spot. The smaller the target angle, the smaller the focal spot size. Although the resolution and sharpness of the image are directly related to the focal spot size, changes in the SID, OID, and size of the collimated field do not affect the focal spot size. (Bushong, p. 132; Carlton, p. 402;
Wentz, pp. 19-20)

In mammography the commonly used focal spot size for routine work is

1. 0.4 mm

2. 0.3 mm

3. 0.2 mm

4. 0.1 mm

2

Mammography machines generally have two focal spot sizes. The large focal spot may be 0.4 or below (generally 0.3 mm) and the small focal spot ranges from 0.15-0.1 (gener-ally 0.1 mm). Routine work utilizes the large focal spot size. (Bushong, p. 311)

Which of the following characteristics are unique to mammography cassettes?

1. must be easy to open

2. should be durable

3. generally have a single intensifying
   screen

4. should have low absorption characteristics

3

All cassettes are easy to open, durable, and have low absorption characteristics relative to the kVp. Mammography cassettes are designed for use with a single emulsion film and are therefore matched with a single intensifying screen. (Bushong, p. 316; Wentz, p. 24)

In digital mammography both the film and cassette can be replaced by

1. a detector and electronic system

2. the CAD technology system

3. a flexible storage phosphor

4. photostimulatable plates

1

Digital mammography systems utilize a detector and electronic system instead of a cassette. CAD technology refers to computer-assisted diagnosis, a technology that can be linked to digital systems. Storage phosphors are used with computed radiography sys-tems; the imaging plates or imaging detectors are coated with storage phosphors or photostimulatable plates. X-rays will react with the imaging plate to form the latent image (Fig-ure 2-2). (Bushong, pp. 357-375; Carlton, p. 634)

The greatest difference between digital technology and conventional mammography imaging is

1. the higher resolution increases the patient dose in digital technology

2. there is no latent image formation when using digital technology

3. in digital technology, the final image can be manipulated

4. the image can never be displayed on a film in digital technology

3

With digital technology, images can be viewed at a workstation. The image at the workstation is called the soft copy image because it can be adjusted for contrast and brightness, or magnified and further enhanced (Figure 2-3). (Bushong, pp. 357-375; Carlton, p. 635)

Which of the following mammographic quality control tests is performed monthly?

1. phantom images

2. visual checklist

3. repeat analysis

4. screen cleanliness

2

The visual checklist is performed monthly, the repeat/reject analysis is performed quarterly, and screen cleanliness is performed weekly. The complete list of mammography quality control tests and frequency are listed on page 15. (ACR, p. 119)

The criteria to pass the ACR Mammography Accreditation on phantom imaging requires a minimum of

	(A) two
	(B) three
	(C) four
	(D) five

(B) The criteria for the number of objects on the phantom necessary to pass the ACR are a minimum of the four largest fibers, the three largest speck groups, and the three largest masses (Figure 2-6). In addition, the number of test objects of each group type (fibers, specks, and masses) visible in the phantom image should not decrease by more than one-half. (ACR, p. 268)

One of the two reasons towels are used in the compression test is to

1. protect the cassette holder

2. ensure that the compression is adequate

3. force slower application of compression

4. simulate 4 cm of compressed breast

1

The towels protect the cassette holder and prevent damage to the compression de-vice. The amount of automatic compression applied is a function of the unit and will not be altered by the presence or absence of a towel. However, the force of the compression device hitting the cassette holder could damage both. (ACR,

For the repeat analysis to be meaningful, a patient volume of at least ______patients is needed.

(A) 50

(B) 100

(C) 250

(D) 300

(C) The repeat analysis is used to identify problem areas within the department (Figure 2-11). However, for the analysis to be meaningful a sufficient patient volume is needed.
The MQSA recommends a meaningful volume of at least 250 patients. (ACR, pp. 202-203)

If, after examining a phantom image, the number of visualized fibers or masses has changed significantly, the next step is to

1. record the new values

2. call the medical physicist

3. call the equipment service personnel

4. check the chemistry or temperature then repeat the test

4

Whenever a test fails, the first corrective action is to verify that the equipment (both the mammographic unit and processor) is operating correctly, and then repeat the test to determine whether the change is real or not. Because the purpose of quality control testing is to ensure optimal conditions before clinical images are processed, significant changes must first be corrected. The medical physicist or the equipment service personnel should be called if the problem cannot be isolated or corrected by the mammographer.
(ACR, p. 186; Bushong, p. 324)

Repeated films are

1. films used for processor cleaning

2. films used for quality control

3. films that involve exposure to the pa-
   tient

4. all discarded films

3

Repeated films are those that had to be repeated and resulted in additional exposure to the patient, for example, double exposed films or films with motion. Rejected films are all discarded films, including repeated films.
Films used for quality control and processor cleaning are not counted as repeated films.
(ACR, p. 202)

If the patient volume at a mammography site is 200 patients per week, the repeat/reject analysis should be done every

	(A) week
	(B) 2 weeks
	(C) 2 months
	(D) 3 months

(D) Repeat analysis testing is carried out every 3 months (quarterly), unless the patient volume is less than 250 in the quarter. (ACR, p.
202)

In imaging the phantom, the technical factors used should be the same as those used clinically for a _ _ -cm-thick breast of medium
glandularity.
(A) 6.0-6.5
(B) 5.0-5.5
(C) 4.0-4.5
(D) 3.0-3.5

(C) The mammographic phantom is equivalent to a 4.2-cm-thick compressed breast consisting of 50% glandular and 50% adipose tissue. The technique used should be the same as that used clinically and the film should be processed just like a clinical mammogram. Phantom images are taken to ensure that the optical density contrast and image quality are at optimal levels (Figure 2-13). (ACR, p. 167; Bushong, p. 325)

1. Mammography facilities can receive certification from

1. the ACR
2. the FDA
3. an SAC state
(A) 1 and 2 only
(B) 2 and 3 only
(C) 1 and 3 only
(D) 1,2, and 3 only

(B) Under MOSA rules, accreditation and certification are two separate processes. Both are required by the FDA. New rules, effective May 2002, permit certification only by the FDA and SAC states. Accreditation is a process administered by an FDA-approved accreditation body, which can be a private, nonprofit organization or a state agency approved to accredit mammography facilities. In 1997 the FDA approved five accreditation bodies-the American College of Radiology (ACR) and the states of Arkansas, California, Iowa, and Texas. These five bodies all have the authority to implement the MQSA standards through the accreditation process. (Accreditation and Certification Overview)

An MQSA certificate is issued when a mammography facility has been accredited. This certification is valued for

	(A) 1 year
	(B) 2 years
	(C) 3 years
	(D) 4 years

(C) After completing the accreditation process, the FDA or SAC state will issue a certification that is valid for 3 years and can be renewed as long as the facility remains properly accredited and demonstrates that it meets the MOSA standards during annual inspections. (Accredi-tation and Certification Overview)

If any of the visual checks fail, the first step is to

1. replace the item

2. call the medical physicist

3. call the processor service

4. call the equipment service representative

1

Examples of visual checklist items are a check of mechanical locks or display lighting.
Many items are for the mammographer's convenience; some, however, are essential for patient safety and the production of quality images. Missing or broken items should therefore be replaced or repaired immedi-ately. (ACR, p. 213)