Mammography

Question 1

This is a radiographic examination that is designed for detecting breast pathology, particularly breast cancer.

Answer 1

Mammography

Question 2

How was early x-ray mammography performed?

Answer 2

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

Question 3

What are the features characteristic of breast cancer?

Answer 3

Masses, particularly ones with irregular or spiculated margins

Clusters of microcalcifcation

Architectural distortions

Question 4

What is the purpose of screening mammography?

Answer 4

It attempts to identify breast cancer in the asymptomatc population

Mediolateral oblique and cranial views are acquired.

Question 5

What is the purpose of diagnostic mammography?

Answer 5

To assess palpable lesions or evaluate suspicious findings identifies by screening mammography.

Question 6

Modality in breast imaging that is often used to differentiate cyst from solid masses and used in biopsy needle guidance.

Answer 6

Ultrasound

Question 7

This modality in breast imaging has excellent tissue contrast sensitivity and with contrast enhancement can differentiate benign from malignant tumors.

Answer 7

MRI

Question 8

Subject contrast contrast in mammography is highest at what level of x-ray energy?

Answer 8

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.

Question 9

What are the important distinctions between mammography and conventional x-ray tube operation?

Answer 9

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.

Question 10

This is the most common anode target material used in mammography.

Answer 10

Molybdenum

Question 11

What is the major reason for choosing molybdenum as target?

Answer 11

As the number of x-rays in the optimal energy range for breast imaging are significantly increased by characteristic x-ray emission.

Question 12

With digital detectors, what material is becoming the target of choice?

Answer 12

Tungsten

Question 13

Mammography x-ray tubes have rotating anodes, with anode angles ranging from how many degrees?

Answer 13

16 to 0 degrees

Question 14

The tubes are typically positioned at a source-to-image receptor distance of about how many cm?

Answer 14

65 cm

Question 15

Where would the cathode and anode be positioned in order to achieve better uniformity of the transmitted x-rays through the breast?

Answer 15

Positioning the cathode over the chest wall of the patient and the anode over the anterior portion (nipple)

Question 16

How to reduce off-focal radiation?

Answer 16

Anode is kept at ground potential (0 voltage), and the cathode is set to the highest negative voltage

Question 17

Focal spot nominal sizes of how many mm for contact mammography?

Answer 17

0. 3 to 0.4 mm
1. 10 to 0.15 mm for magnification imaging

To reduce geometric blurring so that microcalcifications can be resolved.

Question 18

What is the consequences of using small focal spots?

Answer 18

Reduce maximal tube current and longer exposure time

Question 19

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?

Answer 19

A “half-field” geometry

Which is achieved by fixed collimation at the x-ray tube head.

Question 20

The tube port window in mammography is made from what material?

Answer 20

Beryllium

Question 21

Why is beryllium use as tube port window?

Answer 21

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

Question 22

How does added x-ray tube filtration improves the energy distribution of the mammography output spectrum?

Answer 22

By selectively removing the lowest and highest energy x-rays from the x-ray beam, while largely transmitting desired x-ray energies

Question 23

A Mo filter should never be used with a Rh target. Why?

Answer 23

Because Rh characterisitic x-rays are attenuated signifiantly as their energies are bove the Mo K-absorption edge

Question 24

The half-value layer of mammography x-ray beam ranges from how many mm Al?

Answer 24

0.3 to 0.7 mm Al

The HVL depends on the target material, kV, filter material, and filter thickness.

Question 25

Measurement of the HVL is performed how?

Answer 25

With compression paddle in the beam, using 99.9% pure Al sheets of 0.1- mm thickness.

Question 26

Why is breast compression an important part of mammography examination?

Answer 26

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.

Question 27

What happen when achieving uniform breast thickness?

Answer 27

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

Question 28

Primary radiation carried information regarding what?

Answer 28

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.

Question 29

How can scattered radiation reaching the image receptor be reduced?

Answer 29

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.

Question 30

This technique is used to improved system resolution, typically for better visualization of microcalcifications.

Answer 30

Geometric magnification

Question 31

What are the advantages of magnification?

Answer 31

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

Question 32

What comprises a mammographic screen-film detector?

Answer 32

A cassette, intensifying screen or screens, and a light-sensitive film.

Question 33

Most mammographic cassettes are made of what?

Answer 33

Made of low-attenuation carbon fiber and have a single high-definition phosphor screen used in conjunction with a single emulsion film.

Question 34

This is the most commonly used screen phosphor in mammography.

Answer 34

Terbium-activated gadolinium oxysulfide

Question 35

The scintillator of mammography emits what color of light?

Answer 35

Green light

Requiring a green-sensitive film emulson

Question 36

What determines the intensifying screen-film speeds and spatial resolution?

Answer 36

They are determined by:
Screen phosphor particle size
Number of phosphor particles per volume
Light-absorbing dyes in the phoshor matrix
Phosphor layer thickness

Question 37

This represents the relationship between the incident x-ray exposure and the resulting OD in the processed film.

Answer 37

Film characteristic curve (H and D curve)

Question 38

What are the three major sections of a film characteristic curve?

Answer 38

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

Question 39

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.

Answer 39

Gradient curve

Indicates contrast as a function of air kerma (exposure)

Question 40

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.

Answer 40

Sensitometer

Question 41

This is a deviCe that measures the light transmission through a small area of the film and calculates the OD.

Answer 41

Densitometer

Question 42

This results from variations in subject contrast translated into these OD differences according to the film’s characterisitic curve.

Answer 42

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.

Question 43

Why does high luminance needed for mammography reading?

Answer 43

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)

Question 44

Mammography view boxes should have a minimum luminance of how many cd/m²?

Answer 44

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.

Question 45

This is the luminous flux incident upon a surface per unit area, measuring in lux or lumens/m².

Answer 45

Illuminance (measures ambient light intensity)