Mammography Robert L. Metzger, Ph.D., C.H.P. Roland Wong, Sc.M., D.A.B.M.P

Mammography

Robert L. Metzger, Ph.D., C.H.P.

Roland Wong, Sc.M., D.A.B.M.P.

Introduction

Mammgraphy is a radiographic modality to detect breast pathology and cancer.

Breast cancer accounts for 32% of cancer Breast cancer accounts for 32% of cancer incidence and 18% of cancer deaths in incidence and 18% of cancer deaths in women in the United States.women in the United States.

Approximately 1 in 8 or 9 women in the US Approximately 1 in 8 or 9 women in the US will develop breast cancer over her lifetime.will develop breast cancer over her lifetime.

Introduction

Breast cancer screening programs depend on x-ray Breast cancer screening programs depend on x-ray mammography because it is a low-cost, low-radiation-mammography because it is a low-cost, low-radiation-dose procedure that has the sensitivity for early dose procedure that has the sensitivity for early detection and improved treatment.detection and improved treatment.

Recognition of breast cancer depends on Recognition of breast cancer depends on the detection of masses, particularly with irregular the detection of masses, particularly with irregular

or “spiculated” (Strands of tissue radiating out from or “spiculated” (Strands of tissue radiating out from an ill-defined mass, producing a stellate an ill-defined mass, producing a stellate appearance) margins appearance) margins

clusters of microcalcifications (specks of calcium clusters of microcalcifications (specks of calcium hydroxyapatite)hydroxyapatite)

architectural distortions of breast structuresarchitectural distortions of breast structures

Introduction

Mass with Mass with spiculated spiculated marginsmargins

Clustered Clustered heterogeneous heterogeneous microcalcificationsmicrocalcifications

Architectural Architectural distortiondistortion

c.f. Pictorial Essay : Mammographic Features of c.f. Pictorial Essay : Mammographic Features of Breast Cancer, MB Popli, Ind J Radiol Imag 2001 Breast Cancer, MB Popli, Ind J Radiol Imag 2001 11:4:175-17911:4:175-179

Introduction Mammography – Find Cancer Mammography – Find Cancer

the AMA, ACS and ACR recommends a baseline the AMA, ACS and ACR recommends a baseline mammogram by age 40, biannual examinations mammogram by age 40, biannual examinations between ages 40 and 50, and yearly examinations between ages 40 and 50, and yearly examinations after age 50 after age 50

NCI recommends women in their 40s, 50s and NCI recommends women in their 40s, 50s and older should be screened every one to two years older should be screened every one to two years with mammography with mammography

requires craniocaudal (CC) and mediolateral requires craniocaudal (CC) and mediolateral oblique (MLO) views of each breast oblique (MLO) views of each breast

Introduction

Diagnostic Mammography Diagnostic Mammography – Evaluate Abnormalities – Evaluate Abnormalities may require additional may require additional

views, magnification views, magnification views, spot views, spot compression views, compression views, stereotactic biopsy or stereotactic biopsy or other studies using other studies using other modalities other modalities

Mammographic Imaging Modalities

Ultrasound Breast Imaging Ultrasound Breast Imaging used for differentiating cysts (typically benign) from solid used for differentiating cysts (typically benign) from solid

masses (often cancerous), which have similar appearances masses (often cancerous), which have similar appearances on the mammogram on the mammogram

provides biopsy needle guidance for extracting breast tissue provides biopsy needle guidance for extracting breast tissue specimens specimens

MRI MRI has wonderful tissue contrast sensitivity has wonderful tissue contrast sensitivity useful for evaluating silicone implants useful for evaluating silicone implants accurately assess the stage of breast cancer involvementaccurately assess the stage of breast cancer involvement

Modern Mammography Breast is composed of Breast is composed of

fatty tissue, glandular fatty tissue, glandular tissue, and connective tissue, and connective tissue.tissue.

Normal and cancerous Normal and cancerous tissues in the breast have tissues in the breast have small x-ray attenuation small x-ray attenuation differences between differences between them them

Need x-ray equipment Need x-ray equipment specifically designed to specifically designed to optimize breast cancer optimize breast cancer detectiondetection

Modern Mammography Detection of minute Detection of minute

calcifications important calcifications important high correlation of high correlation of

calcification patterns with calcification patterns with disease disease

Best differential between the Best differential between the tissues is obtained at low x-tissues is obtained at low x-ray energies ray energies

Mammography equipment Mammography equipment Low contrast sensitivity Low contrast sensitivity high resolution high resolution low doselow dose

Modern Equipment Dedicated Dedicated

Mammography Mammography Equipment Equipment

Specialized X-ray Specialized X-ray Tubes Tubes

Optimized Screen/Film Optimized Screen/Film detector systemsdetector systems

Breast Compression Breast Compression DevicesDevices

X-ray Tube Design

Cathode and Filament Circuit Cathode and Filament Circuit Low operating voltage Low operating voltage

below 35 – 40 kVpbelow 35 – 40 kVp Typically 23 or 24 kVp at the lowestTypically 23 or 24 kVp at the lowest

dual filaments in a focusing cup dual filaments in a focusing cup 0.3 mm (contact) and 0.1 mm (magnification) focal spot 0.3 mm (contact) and 0.1 mm (magnification) focal spot

sizes sizes small focal spot small focal spot

minimizes geometric blurring minimizes geometric blurring maintains spatial resolution maintains spatial resolution

Typical tube currents are Typical tube currents are 100 mA (+/- 25 mA) for large (0.3 mm) focal spot 100 mA (+/- 25 mA) for large (0.3 mm) focal spot 25 mA (+/- 10 mA) for small focal spot 25 mA (+/- 10 mA) for small focal spot

X-ray Tube Design Anode Anode

rotating anode design rotating anode design Molybdenum (Mo), and dual track molybdenum/rhodium Molybdenum (Mo), and dual track molybdenum/rhodium

(Mo/Rh) targets are used (Mo/Rh) targets are used Characteristic x-ray production is the major reason for Characteristic x-ray production is the major reason for

choosing molybdenum and rhodium choosing molybdenum and rhodium For molybdenum, characteristic radiation occurs at 17.5 For molybdenum, characteristic radiation occurs at 17.5

and 19.6 keV and 19.6 keV For rhodium, 20.2 and 22.7 keVFor rhodium, 20.2 and 22.7 keV

X-ray Tube Design Anode Anode

Targets used in combination with specific tube filters to Targets used in combination with specific tube filters to achieve optimal energy spectra achieve optimal energy spectra

A source to image distance (SID) of 60 to 66 cm typically A source to image distance (SID) of 60 to 66 cm typically used used

The tube is tilted by about 25 degrees to minimize the The tube is tilted by about 25 degrees to minimize the effective focal spot size effective focal spot size

X-ray Tube Design

Heel effect - lower x-ray intensity on the anode side of Heel effect - lower x-ray intensity on the anode side of the field (attenuation through the target) the field (attenuation through the target)

Thus cathode-anode axis is placed from the chest wall Thus cathode-anode axis is placed from the chest wall (greater penetration of x-rays) to the nipple in breast (greater penetration of x-rays) to the nipple in breast imaging imaging

A more uniform exposure is achieved A more uniform exposure is achieved This orientation also minimizes equipment bulk near the This orientation also minimizes equipment bulk near the

patient’s head for easier positioning patient’s head for easier positioning

Tube Port, Tube Filtration, and Beam Quality

Monoenergetic x-rays of 15 to 25 keV are best choice, but not Monoenergetic x-rays of 15 to 25 keV are best choice, but not available available

Polychromatic spectra compromises: Polychromatic spectra compromises: High-energy x-rays in the bremsstrahlung spectrum diminish High-energy x-rays in the bremsstrahlung spectrum diminish

subject contrast subject contrast Low-energy x-rays in the bremsstralung spectrum have Low-energy x-rays in the bremsstralung spectrum have

inadequate penetration and contribute to patient dose inadequate penetration and contribute to patient dose without providing a useful image without providing a useful image

Molybdenum (Mo) and Rhodium (Rh) are used for Molybdenum (Mo) and Rhodium (Rh) are used for mammography targets and produce characteristic x-ray peaks mammography targets and produce characteristic x-ray peaks at 17.5 and 19.6 keV (Mo) and 20.2 and 22.7 keV (Rh) at 17.5 and 19.6 keV (Mo) and 20.2 and 22.7 keV (Rh)

Tube Port, Tube Filtration, and Beam Quality

1-mm thick Beryllium used as the tube port 1-mm thick Beryllium used as the tube port Beryllium provides both low attenuation and good Beryllium provides both low attenuation and good

structural integrity structural integrity

Added tube filters of the same element as the target reduce Added tube filters of the same element as the target reduce the low- and high-energy x-rays in the x-ray spectrum and the low- and high-energy x-rays in the x-ray spectrum and allow transmission of characteristic x-ray energies allow transmission of characteristic x-ray energies

Common target/filters in mammography include Common target/filters in mammography include Mo/Mo Mo/Mo Rh/Rh Rh/Rh Mo/Rh Mo/Rh

Tube Port, Tube Filtration and Beam Quality

A Mo target with Rh filter A Mo target with Rh filter are common for imaging are common for imaging thicker and denser thicker and denser breasts breasts

This combination This combination produces slightly higher produces slightly higher effective energy than effective energy than Mo/Mo Mo/Mo

Provides 20 and 23 keV Provides 20 and 23 keV leading to increased leading to increased penetration of thick penetration of thick and/or dense breastsand/or dense breasts

Tube Port, Tube Filtration and Beam Quality

Rh target with Rh filter provides the highest effective energy Rh target with Rh filter provides the highest effective energy beam beam

2 to 3 keV higher 2 to 3 keV higher useful for the thickest and densest breasts useful for the thickest and densest breasts

Tungsten (W) targets with Rh filter is used only on certain Tungsten (W) targets with Rh filter is used only on certain manufacturer’s unitmanufacturer’s unit

Half Value Layer (HVL) The HVL ranges from 0.3 to 0.45 mm Al in mammography The HVL ranges from 0.3 to 0.45 mm Al in mammography

depends on kVp, compression paddle thickness, added tube depends on kVp, compression paddle thickness, added tube filtration, target material and age of tube.filtration, target material and age of tube.

In general, HVL increases with higher kVp and higher atomic In general, HVL increases with higher kVp and higher atomic number targets and filters.number targets and filters.

Breast dosimetry relies on accurate HVL measurement Breast dosimetry relies on accurate HVL measurement The approximate HVL in breast tissue is The approximate HVL in breast tissue is ~~ 1 to 2 cm (strongly 1 to 2 cm (strongly

dependent on tissue composition: glandular, adipose and dependent on tissue composition: glandular, adipose and fibrous). fibrous). Thus a 4cm breast will attenuate 1-1/2Thus a 4cm breast will attenuate 1-1/244 0.93, or 93% of the 0.93, or 93% of the

incident primary radiation incident primary radiation [reduction in beam intensity or fraction transmitted is 1/2[reduction in beam intensity or fraction transmitted is 1/2nn

and attenuation is (1-1/2and attenuation is (1-1/2nn)])]

Collimation Fixed-size metal apertures or variable field size shutters Fixed-size metal apertures or variable field size shutters

collimate the x-ray beam.collimate the x-ray beam. The field size matches the film cassette sizes The field size matches the film cassette sizes

18 x 24 cm or 24 x 30 cm18 x 24 cm or 24 x 30 cm The x-ray focal spot and the collimator defines the radiation fieldThe x-ray focal spot and the collimator defines the radiation field The light bulb filament, the mirror, and the collimator define the The light bulb filament, the mirror, and the collimator define the

x-ray field x-ray field X-ray field – light field congruence must be within 2% of SID X-ray field – light field congruence must be within 2% of SID

for any edge for any edge The useful x-ray field must extend to the chest wall edge The useful x-ray field must extend to the chest wall edge

without field cutoffwithout field cutoff

X-ray Generator

A dedicated mammography x-ray generator is similar to a A dedicated mammography x-ray generator is similar to a standard x-ray generator in design and function. Differences standard x-ray generator in design and function. Differences exist in exist in Generator power rating is 3 kW Generator power rating is 3 kW The voltage supplied to the x-ray tube (22-40 kVp), The voltage supplied to the x-ray tube (22-40 kVp), Automatic Exposure Control (AEC) circuitry different Automatic Exposure Control (AEC) circuitry different

High-frequency generators are the standard for mammography High-frequency generators are the standard for mammography

Automatic Exposure Control (AEC)

The AEC, also called a phototimer, uses a radiation The AEC, also called a phototimer, uses a radiation sensor (or sensors), an amplifier, a voltage sensor (or sensors), an amplifier, a voltage comparator, to control the exposure comparator, to control the exposure

AEC detector is located AEC detector is located underneathunderneath the cassette in the cassette in mammography unlike conventional radiographymammography unlike conventional radiography

Automatic Exposure Control (AEC)

If the transmission of photons is insufficient to trigger the If the transmission of photons is insufficient to trigger the comparator switch, then after an extended exposure time, a comparator switch, then after an extended exposure time, a backup backup timer terminates the exposure. timer terminates the exposure.

For a retake, the operator must select a higher energy beam For a retake, the operator must select a higher energy beam for greater beam penetrability, thus permitting a shorter for greater beam penetrability, thus permitting a shorter exposure time. A higher energy is possible by selecting a exposure time. A higher energy is possible by selecting a higher kVp, a higher energy filter, a higher energy target, or higher kVp, a higher energy filter, a higher energy target, or combinations. combinations.

Technique Chart

Technique charts are useful guides to determine the Technique charts are useful guides to determine the appropriate kVp for specific imaging tasks, based on appropriate kVp for specific imaging tasks, based on breast thickness and breast composition breast thickness and breast composition posted near the consoleposted near the console

Proper kVp is essential for a reasonable exposure Proper kVp is essential for a reasonable exposure time, defined as a range from approx. 0.5 to 2.0 time, defined as a range from approx. 0.5 to 2.0 seconds, to achieve an optical density of 1.5 to 2.0seconds, to achieve an optical density of 1.5 to 2.0

Take Home Points

Breast Cancer – masses, microcalcifications and Breast Cancer – masses, microcalcifications and architectural distortions in breast architectural distortions in breast

Low energies used to optimize contrast (photoelectric Low energies used to optimize contrast (photoelectric effect) effect)

Specialized equipment needed Specialized equipment needed Improve contrast and resolution, decrease dose Improve contrast and resolution, decrease dose

kVp range 22- 40 kVpkVp range 22- 40 kVp

Take Home Points

Molybdenum and Rhodium (sometimes W) targets Molybdenum and Rhodium (sometimes W) targets used in mammography used in mammography Characteristic radiation for Mo at 17.5 and 19.6 Characteristic radiation for Mo at 17.5 and 19.6

keV keV For Rh, 20.2 and 22.7 keV For Rh, 20.2 and 22.7 keV

Heel effect due to attenuation in target Heel effect due to attenuation in target Chest wall on cathode side and nipple on anode Chest wall on cathode side and nipple on anode

side to get uniform exposure. side to get uniform exposure.

Take Home Points

Breast Cancer – masses, microcalcifications and architectural Breast Cancer – masses, microcalcifications and architectural distortions in breast distortions in breast

Low energies used to optimize contrast (photoelectric effect) Low energies used to optimize contrast (photoelectric effect) Specialized equipment needed Specialized equipment needed

Improve contrast and resolution, decrease dose Improve contrast and resolution, decrease dose kVp range 22- 40 kVp kVp range 22- 40 kVp Molybdenum and Rhodium targets used in mammography Molybdenum and Rhodium targets used in mammography

Characteristic radiation for Mo at 17.5 and 19.6 keV Characteristic radiation for Mo at 17.5 and 19.6 keV For rhodium, 20.2 and 22.7 keV For rhodium, 20.2 and 22.7 keV

Heel effect due to attenuation in target Heel effect due to attenuation in target Chest wall on cathode side and nipple on anode side to get Chest wall on cathode side and nipple on anode side to get

uniform exposure uniform exposure

Take Home Points

Common target/filters in mammography include Common target/filters in mammography include Mo/Mo (thin breasts), Mo/Rh (thicker, denser breasts), Mo/Mo (thin breasts), Mo/Rh (thicker, denser breasts),

Rh/Rh (thickest, dense breasts), Rh/Rh (thickest, dense breasts), Tungsten target available on some units but not used Tungsten target available on some units but not used

Generator similar to conventional radiography except for Generator similar to conventional radiography except for lower power rating, different AEC circuitry, low kVp used lower power rating, different AEC circuitry, low kVp used

18 x 24 and 24 x 30 cm cassettes used 18 x 24 and 24 x 30 cm cassettes used AEC detector is located AEC detector is located underneathunderneath the cassette in the cassette in

mammography unlike conventional radiography mammography unlike conventional radiography

Compression Breast compression is necessary Breast compression is necessary

it reduces overlapping anatomy and decreases it reduces overlapping anatomy and decreases tissue thickness of the breast tissue thickness of the breast

less scatter, more contrast, less geometric blurring less scatter, more contrast, less geometric blurring of the anatomic structures, less motion and lower of the anatomic structures, less motion and lower radiation dose to the tissuesradiation dose to the tissues

Compression

Compression is achieved with a low attenuating lexan paddle Compression is achieved with a low attenuating lexan paddle attached to a compression device attached to a compression device

10 to 20 Newtons (22 to 44 pounds) of force is typically used 10 to 20 Newtons (22 to 44 pounds) of force is typically used A flat, 90A flat, 90°°paddle (not curved) provides a uniform density image paddle (not curved) provides a uniform density image Parallel to the breast support table Parallel to the breast support table Spot compression uses small paddles Spot compression uses small paddles Principal drawback of compression is patient discomfortPrincipal drawback of compression is patient discomfort

Scatter Radiation Scatter radiation Scatter radiation

degrades subject degrades subject contrast contrast

The amount of scatter The amount of scatter increases with breast increases with breast thickness and breast thickness and breast area, and is relatively area, and is relatively constant with kVp (25-constant with kVp (25-35 kVp) 35 kVp)

Without scatter Without scatter rejection, only 50 to rejection, only 50 to 70% of the inherent 70% of the inherent subject contrast will be subject contrast will be detected.detected.

AntiScatter Grid

Grids are used to reject scatter.Grids are used to reject scatter. The grid is placed between the breast and the image receptor.The grid is placed between the breast and the image receptor. Linear grids with a grid ratio of 4:1 to 5:1 are typicalLinear grids with a grid ratio of 4:1 to 5:1 are typical. Cellular . Cellular

grids used by one manufacturer. grids used by one manufacturer. Higher grid ratios provide greater x-ray scatter removal but also Higher grid ratios provide greater x-ray scatter removal but also

a greater dose penalty.a greater dose penalty. Organic fiber or carbon fiber are typical interspace materials. Organic fiber or carbon fiber are typical interspace materials.

Carbon fiber is preferred because aluminum would attenuate Carbon fiber is preferred because aluminum would attenuate too many of the low-energy x-rays used in mammographytoo many of the low-energy x-rays used in mammography

AntiScatter Grids

Grid frequencies (lead strip densities) range from 30 to 50 Grid frequencies (lead strip densities) range from 30 to 50 lines/cm for moving grids and up to 80 lines/cm for stationary lines/cm for moving grids and up to 80 lines/cm for stationary grids grids

The Bucky factor is the ratio of exposure with the grid compared The Bucky factor is the ratio of exposure with the grid compared to the exposure without the grid for the same film optical to the exposure without the grid for the same film optical density. density. For mammography, Bucky factor is about 2 to 3For mammography, Bucky factor is about 2 to 3, so breast , so breast

dose is doubled or tripled, but image contrast improves by dose is doubled or tripled, but image contrast improves by 40%.40%.

Air Gaps The use of an air gap between the patient and the screen-film The use of an air gap between the patient and the screen-film

detector reduces the amount of detected scatter detector reduces the amount of detected scatter Grids not used in magnification, air gap used.Grids not used in magnification, air gap used. Reduction of the breast dose is offset by the shorter focal spot to Reduction of the breast dose is offset by the shorter focal spot to

skin distance.skin distance. Reduction of the breast dose is offset by the shorter focal spot to Reduction of the breast dose is offset by the shorter focal spot to

skin distanceskin distance

Magnification

Advantages Advantages Magnification of 1.5x Magnification of 1.5x

to 2.0x is used to 2.0x is used Increased effective Increased effective

resolution of the resolution of the image receptor by image receptor by the magnification the magnification factor factor

Small focal spot size Small focal spot size used used

Reduction of scatter Reduction of scatter

Magnification

Disadvantages Disadvantages Geometric blurring Geometric blurring

caused by the finite caused by the finite focal spot size (more on focal spot size (more on cathode side) cathode side)

High breast dose (in High breast dose (in general similar to general similar to contact mammography) contact mammography)

Long exposure times Long exposure times (small focal spot, low (small focal spot, low mA) mA)

patient motion and patient motion and blurblur

MTF in magnification mammography

c.f. Bushberg, et al. The Essential Physics of Medical c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2Imaging, 2ndnd ed., p. 211. ed., p. 211.

Screen-Film Cassettes Cassettes have a single Cassettes have a single

phosphor screen and single phosphor screen and single emulsion film emulsion film

Mammography screen-film Mammography screen-film speeds (sensitivity): speeds (sensitivity): regular (100 speed) regular (100 speed)

(12-15 mR required) (12-15 mR required) medium (150 – 190 speed) medium (150 – 190 speed)

For comparison, a For comparison, a conventional “100-speed” conventional “100-speed” screen film cassette requires screen film cassette requires about 2 mR about 2 mR


Limiting spatial Limiting spatial resolution is about resolution is about

15-20 lp/mm (0.025 15-20 lp/mm (0.025 - 0.030 mm object - 0.030 mm object size)size)

Film Processing

Film processing is a critical step in the Film processing is a critical step in the mammographic imaging chain mammographic imaging chain

Consistency in film speed, contrast, optical Consistency in film speed, contrast, optical density levels are readily achieved by density levels are readily achieved by following the manufacturer’s following the manufacturer’s recommendationsrecommendations

Film Processing A film processor quality control program is required A film processor quality control program is required

by the Mammography Quality Standards Act of 1992 by the Mammography Quality Standards Act of 1992 (MQSA) regulations, and daily sensitometric strips (MQSA) regulations, and daily sensitometric strips prior to the first clinical imagesprior to the first clinical images must verify acceptable must verify acceptable processor performance.processor performance.

Film sensitometry confirms proper film contrast, Film sensitometry confirms proper film contrast, speed and base + fog values of mammographic film speed and base + fog values of mammographic film Typical fog values are 0.17 – 0.2 OD, Dmax = 3.8 Typical fog values are 0.17 – 0.2 OD, Dmax = 3.8

– 4.0 OD and the target film OD ranges from 1.2 – – 4.0 OD and the target film OD ranges from 1.2 – 1.8.1.8.

Film Sensitometry


Film Sensitometry

Film Sensitometry


Extended Cycle Processing Not done very much anymore.Not done very much anymore. Extended cycle processing (or push Extended cycle processing (or push

processing) increases the speed of some single processing) increases the speed of some single emulsion mammography films by extending the emulsion mammography films by extending the developer immersion time by a factor of two developer immersion time by a factor of two (usually from (usually from ~~ 20 to 20 to ~~ 40 seconds). 40 seconds).

The rationale is to completely develop all latent The rationale is to completely develop all latent image centers, which does not occur with image centers, which does not occur with standard processing.standard processing.

Up to 35% to 40% decrease in required x-ray Up to 35% to 40% decrease in required x-ray exposure is obtained compared to standard exposure is obtained compared to standard processing for same OD.processing for same OD.

On conventional 90 second processor, the On conventional 90 second processor, the processing time is extended to 180 seconds.processing time is extended to 180 seconds.

Extended Cycle Processing


Viewing Conditions Optimal film viewing conditions are important in Optimal film viewing conditions are important in

detecting subtle lesions.detecting subtle lesions. Mammography films are exposed to high optical Mammography films are exposed to high optical

densities to achieve high contrast, view boxes densities to achieve high contrast, view boxes providing a high luminance are necessary.providing a high luminance are necessary.

The luminance of a mammography viewbox should The luminance of a mammography viewbox should be at least 3000 cd/mbe at least 3000 cd/m22 (nit). (nit).

In comparison, a typical viewbox in diagnostic In comparison, a typical viewbox in diagnostic radiology is about 1500 cd/mradiology is about 1500 cd/m22 (nit). (nit).

Viewing Conditions Film masking is essential for blocking clear portions Film masking is essential for blocking clear portions

of the film and the viewbox.of the film and the viewbox. The ambient light intensity in a mammography The ambient light intensity in a mammography

reading room should be low to eliminate reflections reading room should be low to eliminate reflections from the film.from the film.

A high intensity bright light to penetrate high optical A high intensity bright light to penetrate high optical

density regions of the film, such as skin line and the density regions of the film, such as skin line and the nipple area.nipple area.

Magnifiers should be available to view fine detail such Magnifiers should be available to view fine detail such as microcalcifications.as microcalcifications.

Radiation Dosimetry Risk of carcinogenesis from the radiation dose to the Risk of carcinogenesis from the radiation dose to the

breast is of concern thus monitoring of dose is important breast is of concern thus monitoring of dose is important and is required yearly by MQSA (Mammography Quality and is required yearly by MQSA (Mammography Quality Standards Act of 1992) Standards Act of 1992)

Indices used in Mammography Indices used in Mammography Entrance Skin Exposure (ESE)Entrance Skin Exposure (ESE)

the free-in-air ionization chamber measurement of the free-in-air ionization chamber measurement of the entrance skin exposure of the breast the entrance skin exposure of the breast

typical ESE values for a 4.5 cm breast are 500 to typical ESE values for a 4.5 cm breast are 500 to 1000 mR 1000 mR

Half Value Layer (HVL) Half Value Layer (HVL) Typical HVL from 0.3 to 0.4 mm Al for 25 – 30 kVpTypical HVL from 0.3 to 0.4 mm Al for 25 – 30 kVp

Dosimetry

Risk of carcinogenesis from the radiation dose to the breast is of Risk of carcinogenesis from the radiation dose to the breast is of concern thus monitoring of dose is important and is required concern thus monitoring of dose is important and is required yearly by MQSA (Mammography Quality Standards Act of 1992) yearly by MQSA (Mammography Quality Standards Act of 1992)

Indices used in Mammography Indices used in Mammography

Entrance Skin Exposure (ESE)Entrance Skin Exposure (ESE) the free-in-air ionization chamber measurement of the the free-in-air ionization chamber measurement of the

entrance skin exposure of the breast entrance skin exposure of the breast typical ESE values for a 4.5 cm breast are 500 to 1000 typical ESE values for a 4.5 cm breast are 500 to 1000

mR mR Half Value Layer (HVL) Half Value Layer (HVL)

Typical HVL from 0.3 to 0.4 mm Al for 25 – 30 kVpTypical HVL from 0.3 to 0.4 mm Al for 25 – 30 kVp

Dosimetry Factors affecting breast dose Factors affecting breast dose

Higher kVp increases beam penetrability (lower ESE Higher kVp increases beam penetrability (lower ESE and lower average glandular dose), but decreases and lower average glandular dose), but decreases inherent subject contrast.inherent subject contrast.

kVp and kVp and mAs will result in low dose because of mAs will result in low dose because of greater penetrability.greater penetrability.

Dosimetry Factors affecting breast dose Factors affecting breast dose

Increased breast thickness requires increased Increased breast thickness requires increased dose dose

Vigorous compression lowers breast dose by Vigorous compression lowers breast dose by reducing thicknessreducing thickness

Dosimetry Variables impacting breast dose:Variables impacting breast dose:

Rh/Rh combination will result in lowest average Rh/Rh combination will result in lowest average dose, followed by Mo/Rh and Mo/Mo (use Rh for dose, followed by Mo/Rh and Mo/Mo (use Rh for thicker, denser breasts).thicker, denser breasts).

Screen/film speed and film processing conditions Screen/film speed and film processing conditions (use faster screen film or digital detectors). (use faster screen film or digital detectors).

Higher OD target on film will Higher OD target on film will dose. dose. Use of a grid will Use of a grid will dose. dose. Tissue composition of the breast Tissue composition of the breast

Glandular tissue will have higher breast dose Glandular tissue will have higher breast dose due to increased attenuation, and a greater due to increased attenuation, and a greater mass of tissue at risk.mass of tissue at risk.

Dosimetry The MQSA limits the average glandular breast dose The MQSA limits the average glandular breast dose

to 3 mGy or 300 mrad per film for a compressed to 3 mGy or 300 mrad per film for a compressed breast thickness of 4.2 cm and a breast composition breast thickness of 4.2 cm and a breast composition of 50% glandular and 50% adipose tissue (using the of 50% glandular and 50% adipose tissue (using the MQSA approved mammography phantom).MQSA approved mammography phantom).

If the average glandular dose for this phantom If the average glandular dose for this phantom

exceeds 3 mGy, mammography cannot be performed. exceeds 3 mGy, mammography cannot be performed.

The average glandular dose for this phantom is The average glandular dose for this phantom is

typically 1.5 to 2.2 mGy per viewtypically 1.5 to 2.2 mGy per view or 3 to 4.4 mGy for or 3 to 4.4 mGy for two views for a film optical density of 1.5 to 2.0. two views for a film optical density of 1.5 to 2.0.

Risks and Benefits Based on AGD of 3 mGy, the increased breast cancer Based on AGD of 3 mGy, the increased breast cancer

risk from radiation is 6 per million examined women risk from radiation is 6 per million examined women This is equivalent to dying in an accident when This is equivalent to dying in an accident when

traveling 5000 miles by airplane or 450 miles by car traveling 5000 miles by airplane or 450 miles by car Screening in 1 million women is expected to identify Screening in 1 million women is expected to identify

3000 cases of breast cancer.3000 cases of breast cancer. The breast cancer mortality rate is about 50%.The breast cancer mortality rate is about 50%. Screening would reduce the mortality rate by about Screening would reduce the mortality rate by about

40%.40%. That would potentially mean 600 lives being saved due That would potentially mean 600 lives being saved due

to screening. to screening. The benefits of getting a mammogram far outweigh the The benefits of getting a mammogram far outweigh the

risks associated with the radiation due to the risks associated with the radiation due to the mammogram.mammogram.

Take Home Points Breast compression is necessary.Breast compression is necessary.

reduces overlapping anatomy, decreases tissue reduces overlapping anatomy, decreases tissue thickness of the breast, less scatter, more contrast, thickness of the breast, less scatter, more contrast, less motion and lower radiation dose to the tissues.less motion and lower radiation dose to the tissues.

Scatter reduced by gridsScatter reduced by grids 5:1 grid ratio.5:1 grid ratio. Bucky factor of 2 to 3.Bucky factor of 2 to 3.

Magnification of 1.5 to 2 times in mammographyMagnification of 1.5 to 2 times in mammography Increased resolution, decreased scatter, increased Increased resolution, decreased scatter, increased

dose, long exposure times, motion, increase in dose, long exposure times, motion, increase in geometric blur with increased magnification.geometric blur with increased magnification.

Take Home Points Single-screen and single emulsion film used.Single-screen and single emulsion film used.

15-20 lp/mm resolution.15-20 lp/mm resolution. Film processing is very important. Film processing is very important. A film processor quality control program is required by A film processor quality control program is required by

Mammography Quality Standards Act of 1992 (MQSA) Mammography Quality Standards Act of 1992 (MQSA) regulations.regulations.

The luminance of a mammography viewbox should be at The luminance of a mammography viewbox should be at least 3000 cd/mleast 3000 cd/m2 2 (nit). (nit).

Glandular tissue is sensitive to cancer induction by Glandular tissue is sensitive to cancer induction by radiation.radiation.

Take Home Points

Average glandular breast dose limited to 3 mGy or Average glandular breast dose limited to 3 mGy or 300 mrad per film for a compressed breast thickness 300 mrad per film for a compressed breast thickness of 4.2 cm, 50/50 glandular/adipose breast of 4.2 cm, 50/50 glandular/adipose breast composition.composition. Increasing kVp reduces dose.Increasing kVp reduces dose. Increased breast size increases dose. Increased breast size increases dose. Vigorous compression lowers breast dose by Vigorous compression lowers breast dose by

reducing thickness.reducing thickness. Risk of mammogram induced breast cancer is far Risk of mammogram induced breast cancer is far

less than the risk of developing breast cancer.less than the risk of developing breast cancer.

Quality Control

Regulations mandated by the MQSA of 1992 specify Regulations mandated by the MQSA of 1992 specify the operational and technical requirements necessary the operational and technical requirements necessary to perform mammography in the USA.to perform mammography in the USA.

For a facility to perform mammography legally under For a facility to perform mammography legally under MQSA, it must be certified and accredited by an MQSA, it must be certified and accredited by an accrediting body (AB) (the ACR or some states).accrediting body (AB) (the ACR or some states).

Quality Control

The accreditation body verifies that the The accreditation body verifies that the mammography facility meets standards set forth by mammography facility meets standards set forth by the MQSA such as initial qualifications, continuing the MQSA such as initial qualifications, continuing experience, education of physicians, technologists experience, education of physicians, technologists and physicists, equipment quality control etc. and physicists, equipment quality control etc.

Certification is the approval of a facility by the U.S. Certification is the approval of a facility by the U.S. FDA to provide mammography services, and is FDA to provide mammography services, and is granted when accreditation is achievedgranted when accreditation is achieved..

Radiologist Responsibilities

Responsibilities include:Responsibilities include:

Ensuring that technologists are appropriately Ensuring that technologists are appropriately

trained in mammography and perform required trained in mammography and perform required quality assurance measurements.quality assurance measurements.

Providing feedback to the technologists regarding Providing feedback to the technologists regarding aspects of clinical performance and QC issues.aspects of clinical performance and QC issues.

Radiologist Responsibilities

Responsibilities include Responsibilities include

Having a qualified medical physicist perform the Having a qualified medical physicist perform the necessary tests and administer the QC program.necessary tests and administer the QC program.

Ultimate responsibility for mammography quality Ultimate responsibility for mammography quality assurance rests with the radiologist in charge of assurance rests with the radiologist in charge of the mammography practice.the mammography practice.

The medical physicist and technologist are The medical physicist and technologist are responsible for the QC tests.responsible for the QC tests.

Mammography Phantom

Is a test object that simulates the radiographic Is a test object that simulates the radiographic characteristics of compressed breast tissues, and characteristics of compressed breast tissues, and contains components that model breast disease and contains components that model breast disease and cancer in the phantom image.cancer in the phantom image.

It is intended to mimic the attenuation characteristics It is intended to mimic the attenuation characteristics of a “standard breast” of 4.2-cm compressed breast of a “standard breast” of 4.2-cm compressed breast thickness of 50% adipose and 50% glandular tissue thickness of 50% adipose and 50% glandular tissue composition.composition.

Mammography Phantom

6 nylon fibers, 5 simulated calcification groups, 5 low contrast 6 nylon fibers, 5 simulated calcification groups, 5 low contrast disks that simulate masses disks that simulate masses

To pass the MQSA quality standards, at least 4 fibers, 3 To pass the MQSA quality standards, at least 4 fibers, 3

calcification groups and 3 masses must be clearly visible (with calcification groups and 3 masses must be clearly visible (with no obvious artifacts) at an average glandular dose of less than 3 no obvious artifacts) at an average glandular dose of less than 3 mGy mGy

c.f. Bushberg, c.f. Bushberg, et al. The et al. The Essential Essential Physics of Physics of Medical Medical Imaging, 2Imaging, 2ndnd ed., p. 228.ed., p. 228.

Mammography Phantom

Phantom Image

End Of Mammography Section

Documents

Mammography Robert L. Metzger, Ph.D., C.H.P. Roland Wong, Sc.M., D.A.B.M.P