Transcript Mammography Physics - Augusta University

Mammography Physics
Jerry Allison, Ph.D.
Department of Radiology
Medical College of Georgia
Augusta University
Augusta, GA
Educational Objectives
Our educational objectives are to understand:
1. Why pay special attention to mammography physics?
2. Radiation Risk/Benefit Issues
3. Physical principles of mammography
4. Physical principles of full field digital mammography
(FFDM)
5. Technical Details of Digital Breast Tomosynthesis
(DBT)
6. Technical Details of Contrast Enhanced Digital
Mammography (CEDM)
Why pay special attention
to mammography physics?
• Approximately 1 of 8 women will
develop breast cancer over a lifetime.
• 10-30% of women who have breast
cancer have negative mammograms.
• ~80% of masses biopsied are not
malignant (fibroadenomas, small
papillomas, proliferating dysplasia).
Radiation Risk/Benefit Issues
• Radiation is a carcinogen (ionizing radiation, x-radiation,
radiation: National Toxicology Program 2004)
• "No woman has been shown to have developed breast
cancer as a result of mammography, not even from
multiple studies performed over many years with doses
higher than the current dose (250 mRad)... However the
possibility of such risk has been raised because of
excessive incidence of breast cancer in women exposed to
much higher doses (100-2000 Rad: Japanese A-bomb
survivors, TB patients having chest fluoro and postpartum
mastitis patients treated w/radiation therapy ).” ©1992
RSNA
• Hodgkin’s lymphoma patients treated w/radiation therapy
Risk/Benefit
©NCRP 2006 (Report 149)
©1992 RSNA
The Challenge in Mammography
©1987 IOP
Publishing
X-ray Spectra in Mammography
• X-ray spectral distribution is determined by:
– kV
– target/filter combination
–
–
–
–
–
–
–
–
–
Mo/Mo, Mo/Rh, Rh/Rh for GE
Mo/Mo, Mo/Rh, W/Rh for Siemens
Mo/Mo, Mo/Rh or W/Rh, W/Ag for Hologic
W/Rh, W/Ag, W/Al for Hologic DBT Tomo
W/Rh, W/Ag, W/Cu for Hologic CE2D Tomo
W/Rh for Giotto
W/Rh for Fuji Saphire HD
W/Rh, W/Ag for Planmed
W/Al for Philips
X-ray spectra are variable
Compression (Redistribution?)
Scatter
Geometric blurring
Superposition
Increases the proportion of
the X-ray beam that is used
to image a breast
Motion
Beam hardening
Dose
©1994 Williams & Wilkins
Scattered Radiation Control
• Linear Grids
– Grid ratio (height of lamina/distance between
laminae): 4:1 or 5:1 w/ 30-40 lines/cm.
– Conventional grids are 8:1 to 12:1 (up to 43
lines/cm).
– Breast dose is increased by grids (Bucky Factor:
x2 to x3) w/40% improvement in contrast.
– Laminae are focused to the focal spot to prevent
grid cut off.
– Grid septa generally perpendicular to chest wall
(but can be parallel to chest wall for tomo)
Scattered Radiation Control
• High Transmission Cellular (HTC) Grids
–
–
–
–
Focused
Increased 2D absorption of scattered radiation
Increase contrast
Must move the grid a very precise distance
during exposure regardless of exposure duration
– Essentially same grid ratio and dose as
conventional linear grids
HTC Grid
http://www.hologic.com/oem/pdf/W-BI-HTC_HTC%20GRID_09-04.pdf
HTC Grid
http://www.hologic.com/oem/pdf/W-BI-HTC_HTC%20GRID_09-04.pdf
Magnification Mammography
• Magnification factor: x1.5 – x2.0
• Increases the size of the projected
anatomical structures compared
with the granularity of the image
• Valuable for visualization of
calcifications and spiculations.
©1994 Williams & Wilkins
Magnification
• Spot compression paddles
http://www.americanmammographics.com/mammopads.htm
Magnification
• Reduction of effective image noise (less
quantum noise, more photons per object
area)
• Air gap between breast and image
receptor reduces scattered radiation
without attenuating primary photons or
increasing radiation dose (no grid!)
• Small focal spot: 0.1 - 0.15mm (low mA,
long exposure times): increased motion
• Increased dose (x2-x3)
Focal Spot and MTF
©1994 Williams & Wilkins
Dose Limits

FDA Dose limit for screening
mammograms
– 3 mGy (w/grid)
 Mean
glandular dose
 Single view: CC
 4.5cm compressed breast
 Average composition
Physical Principles of Full Field
Digital Mammography (FFDM)
• FFDM Technologies
– Direct detectors
– Indirect detectors
– Computed radiography (CR)
– Slit scanning technology
FDA Approved Digital Mammo Units
• As of December, 2016
• 12 Vendors
• 35 Models
• 6 CR
• 25 FFDM
• 3 DBT
• Not all vendors still exist
• Not all models actually for sale
http://www.fda.gov/RadiationEmittingProducts/MammographyQualityStandardsActandProgram/FacilityCertificationandInspectio
n/ucm114148.htm
USA Certification statistics
December 1, 2016
• Total certified facilities / Total accredited units
• 8,747 / 16,959
• Certified facilities with FFDM only units /
Accredited FFDM only units
• 5,626 / 12,660
• Certified facilities with FFDM and DBT units /
Accredited FFDM/DBT units
• 2,948 / 4,074
• Film/screen units
• 225
http://www.fda.gov/RadiationEmittingProducts/MammographyQualityStandardsActandProgram/FacilityScorecard/ucm113858.htm
FFDM Technologies
“INDIRECT” Detectors (GE)
• Scintillating phosphor (CsI columns) on an array of amorphous silicon
photodiodes using thin-film transistor (TFT) flat panel technology (GE)
– ~100 micron pixels, ~5 lp/mm
“DIRECT” Detectors (Siemens, Hologic, Giotto, Planmed, Fuji)
• Amorphous selenium (direct conversion)
• (TFT) flat panel technology
• ~70-85 micron pixels , ~7 lp/mm
• Direct optical switching technology (Fuji Aspire HD))
• ~50 micron pixels , ~10 lp/mm
Computed radiography (Fuji, Carestream, Agfa, Konica, iCRco)
– ~50 micron pixels, ~10 lp/mm
– ~100 micron pixels, ~5 lp/mm
Slit scanning technology (Philips)
– ~50 micron pixels, ~10 lp/mm
Does pixel size matter?
• As pixel size decreases:
– Spatial resolution improves
– Noise increases
– Signal-to-noise decreases
• Yet another set of imaging tradeoffs
Detector Technology Overview
Independent (“Indirect”) Conversion:
Dependent (“Direct”) Conversion:
CsI Converter + aSi Substrate Sensor
Matrix
aSe Converter + aSi Substrate Sensor
Matrix
X-Ray Photons
X-ray
X-ray
Selenium
K-edge
Fluoresence
CsI
Light
Electrons
Photodiode
Photodiode
Blocking
Layer
Electrons
Read Out Electronics
Electrode
Digital
Data
Capacitor
Electrons
Read Out Electronics
Digital
Data
Courtesy: Jill Spear, GE Women’s Healthcare
2,600+ Volts
X-Ray Photons
Electrode
Dielectric
Fuji CR Digital Mammography
•
•
•
•
•
ClearView-CSM
Reads image plate from both sides
~50 micron resolution
~10 lp/mm
For CR, the film-screen cassette is
replaced with a photostimulable
phosphor plate cassette (Low $)
• Mammography CR units also offered
by Carestream, Agfa, Konica, iCRco
©Kanal, K, Digital Mammography Update: Design and Characteristics of
Current Systems, 2009 AAPM Annual Meeting
Slit Scanning Technology
• Philips MicroDose
• 650 installed worldwide (June 2015)
• 35 installed USA (June 2015)
Slit Scanning Technology
• Slit Scanning
Technology
(multi-slit)
• X-ray generates electron-hole pairs
creating a short electrical signal
http://incenter.medical.philips.com/doclib/enc/fetch/2000/4504/577242/577260/593280/593
431/8477093/Photon_Counting_White_Paper.pdf%3fnodeid%3d8477094%26vernum%3d1
Philips MicroDose
•
•
•
•
•
Multi-slit scanning (~ 26 slits)
Pre & post collimation
Photon counting
50 micron pixels
Silicon strip detectors (tapered toward
focal spot)
• Mean glandular dose ~50% of other FFDM
approaches
Philips Micro Dose
•
•
•
•
3-15 sec exposures
2 Mhz digitization rate per channel (15 bit)
Detectors “ready” every 2msec
~5000 electrons per pulse (noise: ~200
electrons RMS)
• Can sort photon events into high energy
and low energy (spectral imaging) for
quantitative breast density measurements
Breast Dose in FFDM
• Systems display breast dose with image
– Mean Glandular Dose < 3 mGy
– Dose recorded in DICOM image header
Entrance skin exposure and/or mean glandular dose
 Vendors use different dose calculation algorithms
• Dance
• Wu & Barnes
• U.S. Method
• As of the 3.4.2 software upgrade, Hologic “follows
the latest EUREF adopted method if the system is set
up to use EUREF dose calculation”

Technical Details of Digital Breast
Tomosynthesis (DBT)
• FDA Approved DBT Units
• Hologic Selenia Dimensions Digital Breast
Tomosynthesis (DBT) System on 2/11/11
• GE SenoClaire Digital Breast Tomosynthesis
(DBT) System on 8/26/14
• Siemens Mammomat Inspiration with
Tomosynthesis Option (DBT) System on 4/21/15
http://www.fda.gov/RadiationEmittingProducts/MammographyQualityStandardsActandProgram/FacilityCertificationandInspectio
n/ucm114148.htm
Technical Details of Digital Breast
Tomosynthesis (DBT)
• Accreditation of DBT Units is available
only through FDA via an FDA MQSA
Facility Certification Extension
http://www.fda.gov/RadiationEmittingProducts/MammographyQualityStandardsActandProgram/FacilityCertificationandInspectio
n/ucm114148.htm
Breast tomosynthesis
Intro
Figure 1A <p> Basic technologic principles of breast tomosynthesis. (a, b) Schemas show how image data are acquired from various angles as the x-ray tube
moves in an arc. Either the step-and-shoot method (a) or the continuous exposure method (b) may be used, and the detector may be moving or stationary
during image acquisition. The 3D image data are subsequently reconstructed as conventional mammographic projections (craniocaudal, mediolateral oblique,
and mediolateral views). (c, d) Diagrams show how different 3D image data acquired from different angles (c) are reconstructed to provide separate depiction
of two overlapping structures located in different planes (d). </p>
Published in: "Breast Tomosynthesis: Present Considerations and Future Applications1"
Park et al.
RadioGraphics Vol. 27, No. suppl_1: S231-S240
©RSNA, 2007
One PowerPoint slide of each figure may be downloaded and used for educational, non-promotional purposes by an author for slide presentations only. The
RSNA citation line must appear in at least 10-point type on all figures in all presentations. Pharmaceutical and Medical Education companies must request
permission to download and use slides, and authors and/or publishing companies using the slides for new article creations for books or journals must apply for
permission. For permission requests, please contact the Publisher at [email protected].
Figure 1B <p> Basic technologic principles of breast tomosynthesis. (a, b) Schemas show how image data are acquired from various angles as the x-ray tube
moves in an arc. Either the step-and-shoot method (a) or the continuous exposure method (b) may be used, and the detector may be moving or stationary
during image acquisition. The 3D image data are subsequently reconstructed as conventional mammographic projections (craniocaudal, mediolateral oblique,
and mediolateral views). (c, d) Diagrams show how different 3D image data acquired from different angles (c) are reconstructed to provide separate depiction
of two overlapping structures located in different planes (d). </p>
Published in: "Breast Tomosynthesis: Present Considerations and Future Applications1"
Park et al.
RadioGraphics Vol. 27, No. suppl_1: S231-S240
©RSNA, 2007
One PowerPoint slide of each figure may be downloaded and used for educational, non-promotional purposes by an author for slide presentations only. The
RSNA citation line must appear in at least 10-point type on all figures in all presentations. Pharmaceutical and Medical Education companies must request
permission to download and use slides, and authors and/or publishing companies using the slides for new article creations for books or journals must apply for
permission. For permission requests, please contact the Publisher at [email protected].
Figure 1C <p> Basic technologic principles of breast tomosynthesis. (a, b) Schemas show how image data are acquired from various angles as the x-ray tube
moves in an arc. Either the step-and-shoot method (a) or the continuous exposure method (b) may be used, and the detector may be moving or stationary
during image acquisition. The 3D image data are subsequently reconstructed as conventional mammographic projections (craniocaudal, mediolateral oblique,
and mediolateral views). (c, d) Diagrams show how different 3D image data acquired from different angles (c) are reconstructed to provide separate depiction
of two overlapping structures located in different planes (d). </p>
Published in: "Breast Tomosynthesis: Present Considerations and Future Applications1"
Park et al.
RadioGraphics Vol. 27, No. suppl_1: S231-S240
©RSNA, 2007
One PowerPoint slide of each figure may be downloaded and used for educational, non-promotional purposes by an author for slide presentations only. The
RSNA citation line must appear in at least 10-point type on all figures in all presentations. Pharmaceutical and Medical Education companies must request
permission to download and use slides, and authors and/or publishing companies using the slides for new article creations for books or journals must apply for
permission. For permission requests, please contact the Publisher at [email protected].
Figure 1D <p> Basic technologic principles of breast tomosynthesis. (a, b) Schemas show how image data are acquired from various angles as the x-ray tube
moves in an arc. Either the step-and-shoot method (a) or the continuous exposure method (b) may be used, and the detector may be moving or stationary
during image acquisition. The 3D image data are subsequently reconstructed as conventional mammographic projections (craniocaudal, mediolateral oblique,
and mediolateral views). (c, d) Diagrams show how different 3D image data acquired from different angles (c) are reconstructed to provide separate depiction
of two overlapping structures located in different planes (d). </p>
Published in: "Breast Tomosynthesis: Present Considerations and Future Applications1"
Park et al.
RadioGraphics Vol. 27, No. suppl_1: S231-S240
©RSNA, 2007
One PowerPoint slide of each figure may be downloaded and used for educational, non-promotional purposes by an author for slide presentations only. The
RSNA citation line must appear in at least 10-point type on all figures in all presentations. Pharmaceutical and Medical Education companies must request
permission to download and use slides, and authors and/or publishing companies using the slides for new article creations for books or journals must apply for
permission. For permission requests, please contact the Publisher at [email protected].
Breast tomosynthesis
Hologic Selenia Dimensions
http://www.hologic.com/data/WP-00007_Tomo_08-08.pdf
http://www.hologic.com/data/WP-00007_Tomo_08-08.pdf
Cone Beam Breast CT



University of Rochester
300 views
10 seconds
Breast tomosynthesis
©www.hologic.com/data/W-BI-001_EmergTech_08-06.pdf
Breast tomosynthesis
http://www.hologic.com/data/WP-00007_Tomo_08-08.pdf
DQE in Breast Tomosynthesis
• Mean glandular dose (MGD) for tomosynthesis
is expected to be the same as for projection
mammography (< 300 mRad)
• Since breast tomosynthesis requires several
exposures (e.g.15), low exposure DQE
performance of digital detectors used in breast
tomosynthesis is important
• A grid MIGHT not be used in breast
tomosynthesis, which reduces dose (x2 – x3)
• GE uses a grid
Characteristics: DBT Breast Tomo
• Tiling of very large breasts (more than one view to
cover very large breasts) may not work since tissue
outside of FOV can cause artifacts
Characteristics: Hologic DBT Breast Tomo
Modes/ views:
•2D: one conventional FFDM image
•3D Tomo: 15 views used to reconstruct tomographic
slices
• 15 projection images
• Stack of tomographic slices (1 mm thick)
•Combo: acquisition of both 2D and 3D tomo (still <
3 mGy total)
•Synthetic view (C-View): reconstruction of a pseudo
projection mammogram from a stack of tomographic
images
Characteristics: Hologic C-View
• C-View
• Uses DBT dataset to generate one 2D mammogram
• In C-View images, DBT slices having detectable calcifications
and/or masses are weighted more heavily that other DBT slices
• Creates a 2D image with no additional exposure
• C-View image appears similar to and serves the same purpose as
2D digital mammogram
• C-View images MUST be interpreted in combination with a DBT
dataset
Characteristics: Hologic C-View
http://appliedradiology.com/articles/the-benefits-of-using-synthesized-2d-c-view-images-inbreast-tomosynthesis-exams
Characteristics: Hologic DBT Breast Tomo
• Data acquisition (tomo)
– 15 discrete views (exposures)
– Limited arc (± 7.5 degrees)
– 4 sec
• Anode
– Tungsten
Characteristics: Hologic DBT Breast Tomo
• Filters
– Rh: for 2D only
– Ag: for 2D only
– Al: for 3D tomo only
• Density control
– None
• No grid during tomo
• No MAGnification in tomo
Characteristics: Hologic DBT Breast Tomo
• Pixel binning
– In 3D tomo mode, pixels are “binned” into groups
of 2x2 pixels (140 micron pitch)
• Reconstruction
– 1 mm thick
– Number of tomo images: (compressed breast
thickness/ 1mm => 40 – 80)
• Interpretation
– 1mm tomographic slices
– 15 individual projection views (good for motion
detection)
– May also have a conventional 2D view and/or
synthetic view
Hologic DBT MGD
• 2D:
1.2 mGy
• 3D Tomo:
• Combo*:
1.45 mGy
2.65 mGy
*Combo: 2D and 3D tomo of the same
breast view (e.g. MLO)
Characteristics: DBT Breast Tomo
DBT System
Type of geometry
Detector type
Detector material
Detector element size
(μm)
Focal plane pixel size
X-ray tube motion
Target
Filter
Angular range
Number of projection
images
Source to detector
distance (mm)
Distance between
detector and centre of
rotation (mm)
Reconstruction
algoorithm
Grid used for tomo
Detector binning for
tomo
General
Hologic
Siemens
Electric
Selenia
Mammomat
Essential Dimensions Inspiration
Full-field
Full-field
Full-field
Energy
Energy
Energy
integrating integrating integrating
CsI-Si
a-Se
a-Se
100
100
Step-and
shoot
Mo/Rh
Mo: 30μm
Rh: 25 μm
25
70
95-117
85
85
Continuous Continuous
W
W
Al: 700 μm
15
Rh: 50 μm
50
9
15
25
660
700
655
40
0
47
Iterative
Filtered back
projection?
yes
no
Analytic
no (scatter
correction
software)
no
yes
?
Hologic Contrast Enhanced Digital
Mammography (CEDM)





CEDM (Hologic: CE2D) is contrast enhanced dual energy
imaging.
CE2D consists of contrast administration and two 2 images, taken
in sequence and in the same breast compression.
IV non-ionic CT contrast agent
Imaging 2 – 6 minutes after contrast injection
The first image is a standard 'low energy' image.
– 25 to 33 kVp
– Rh or Ag filter

The second image is a ’high energy' image.
– 45 to 49 kVp
– Cu filter
Hologic Contrast Enhanced Digital
Mammography (CEDM)






Weighted subtraction of low energy image from the high
energy image.
The low energy image together with the subtracted image is
used clinically.
Adjunct following mammography and/or ultrasound to
localize a known or suspected lesion.
Hologic I-View software provides 2D contrast information
for both 2D and 3D MAMMOGRAPHY™ for CE2D
Imaging.
GE also has an implementation
Siemens?
Hologic Contrast Enhanced Digital
Mammography (CEDM)

Two infiltration ductal carcinomas
http://appliedradiology.com/articles/contrast-enhanced-mammography-successful-
clinical-experience
References
– ©NCRP 2006
NCRP Report 149, “A Guide to Mammography and Other
Breast Imaging Procedures” National Council on Radiation
Protection and Measurements, 2004
– ©1994 Williams & Wilkins
Bushberg, JT, Seibert, JA, Leidholdt, EM Jr., Boone, JM, ”The
Essential Physics of Medical Imaging” Williams & Wilkins,
Baltimore, Maryland, 1994
– ©1993 RSNA
Haus, AG, Yaffe, MJ, Eds., “Syllabus: A Categorical Course
in Physics Technical Aspects of Breast Imaging”, 2nd
Edition, RSNA, 1993
– ©1992 RSNA
Haus, AG, Yaffe, MJ, Eds., “Syllabus: A Categorical Course
in Physics Technical Aspects of Breast Imaging”, RSNA,
1992
– ©1987 IOP Publishing
Johns, PC, Yaffe, MJ, “X-Ray characterisation 675-695
of normal and neoplastic breast tissues”, Phys Med Biol, 1987,
32,
Breast tomosynthesis
GE SenoClaire
http://www3.gehealthcare.com/en/products/categories/mammogr
aphy/senoclaire_3d
Characteristics: GE DBT Breast Tomo
• 3D Tomo:
• 9 views (± 12.5 degrees)
• Step and shoot (versus continuous motion)
• No detector binning
• Tomo grid is used
• Iterative reconstruction (versus filtered backprojection)
• 3D dose same as 2D dose
• GE has a new FFDM unit (Pristina)
• Not yet approved for DBT
Characteristics: GE DBT Breast Tomo
• V-Preview 3: a 2D image generated from the raw DBT
projection data that helps the user get an overview of the entire
stack, before examining the DBT planes
• http://www3.gehealthcare.com/en/products/categories/mammography/seno
claire_3d#tabs/tab0A5E89E4B6F442DE962349399E6B384D
Breast tomosynthesis
Siemens Inspiration
http://usa.healthcare.siemens.com/siemens_hwem-hwem_ssxa_websites-contextroot/wcm/idc/groups/public/@us/documents/download/mda1/mjuz/~edisp/tomo_approved_
brochure-02166193.pdf
Characteristics: Siemens DBT Breast Tomo
• 3D Tomo:
• 25 views (± 25 degrees)
• Scan time: ~ 25 sec
• Tomo grid is not used (software based scatter
correction)
• Analytic reconstruction (iterative?)
FFDM Image Characteristics
• MTF
• DQE
• Dynamic Range
Modulation Transfer Function (MTF):
• Detector’s ability to transfer
modulations in the pattern of photons
that enter the detector to modulations
in the detector output (the image)
MTF comparison
•
•
•
•
a-Se detector (~70 micron pixels)
Screen-film
CsI detector (~100 micron pixel)
CR (~50 micron pixels)
www.hologic.com/data/W
-BI-CR_11-06.pdf
Dynamic range
Figure 3. Limitations of SFM in imaging a breast composed of a wide range of tissues
Mahesh M Radiographics 2004;24:1747-1760
©2004 by Radiological Society of North America
Figure 2. Typical response curves for SFM and digital mammography
Mahesh M Radiographics 2004;24:1747-1760
©2004 by Radiological Society of North America
Detector response
S/F
FFDM
~50mAs
~100mAs
~200mAs
©2004 by Radiological Society of North America, Mahesh M Radiographics 2004;24:1747-1760
Detective Quantum Efficiency (DQE)
• DQE is often quoted for image quality
in FFDM
Ratio of SNR (signal-to-noise ratio) at
the detector output to SNR at the
detector input
Who has the best DQE?
• It– spatial
depends:
frequency (lp/mm)
–
–
–
–
–
kV
Target
Filter
breast phantom used
EXPOSURE!!!!!
DQE
http://www.medical.siemens.com/
DQE (Detective Quantum Efficiency)
1.0
CsI
0.9
at 8.5 mR
at 0.5 mR
A-Se (Yorker)
100 µm pitch
0.8
µm pitch / 250 µm Se
0.7
8.5 mR
0.5 mR
0.6
DQE
70
at
at
0.5
0.4
0.3
0.2
0.1
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
Spatial Frequency (lp/mm)
The significant advantage in the electronic noise factor allows the CsI-based detector to maintain its high DQE even at ultra low exposure
levels (0.5 mR).
(From Performance of Advanced a-Si / CsI-based Flat Panel X-ray Detectors for Mammography, Medical Imaging 2003: Physics of
Medical Imaging, M. J. Yaffe, L. E. Antonuk, Editors, Proceedings of SPIE Vol. 5030 (2003) © 2003 SPIE · 1605-7422/03)
Courtesy: Jill Spear, GE Women’s Healthcare