Mammography Physics Jerry Allison Ph D Department of

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 m. Rad). . . 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: – k. V – 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 CE 2 D 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: x 2 to x 3) 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 2 D 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%20 GRID_09 -04. pdf

HTC Grid http: //www. hologic. com/oem/pdf/W-BI-HTC_HTC%20 GRID_09 -04. pdf

Magnification Mammography • • • Magnification factor: x 1. 5 – x 2. 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. 15 mm (low m. A, long exposure times): increased motion Increased dose (x 2 -x 3)

Focal Spot and MTF © 1994 Williams & Wilkins

Dose Limits FDA Dose limit for screening mammograms – 3 m. Gy (w/grid) Mean glandular dose Single view: CC 4. 5 cm 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/Radiation. Emitting. Products/Mammography. Quality. Standards. Actand. Program/Facility. Certificationand. Inspectio n/ucm 114148. 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/Radiation. Emitting. Products/Mammography. Quality. Standards. Actand. Program/Facility. Scorecard/ucm 113858. htm

FFDM Technologies “INDIRECT” Detectors (GE) • Scintillating phosphor (Cs. I 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, i. CRco) – ~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: Cs. I Converter + a. Si Substrate Sensor Matrix Dependent (“Direct”) Conversion: a. Se Converter + a. Si Substrate Sensor Matrix X-Ray Photons X-ray Selenium K-edge Fluoresence Cs. I Light Photodiode Electrons Blocking Layer 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 • • • Clear. View-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, i. CRco

©Kanal, K, Digital Mammography Update: Design and Characteristics of Current Systems, 2009 AAPM Annual Meeting

Slit Scanning Technology • Philips Micro. Dose • 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%3 fnodeid%3 d 8477094%26 vernum%3 d 1

Philips Micro. Dose • • • 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 2 msec ~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 m. Gy – 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 Seno. Claire 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/Radiation. Emitting. Products/Mammography. Quality. Standards. Actand. Program/Facility. Certificationand. Inspectio n/ucm 114148. 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/Radiation. Emitting. Products/Mammography. Quality. Standards. Actand. Program/Facility. Certificationand. Inspectio n/ucm 114148. htm

Breast tomosynthesis Intro

Figure 1 A <p> Basic technologic principles of breast tomosynthesis. (a, b) Schemas show 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 3 D image data are subsequently reconstructed as conventional mammographic projections (craniocaudal, mediolateral oblique, and mediolateral views). (c, d) Diagrams show different 3 D 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 Applications 1" Park et al. Radio. Graphics Vol. 27, No. suppl_1: S 231 -S 240 ©RSNA, 2007 One Power. Point 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 permissions@rsna. org.

Figure 1 B <p> Basic technologic principles of breast tomosynthesis. (a, b) Schemas show 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 3 D image data are subsequently reconstructed as conventional mammographic projections (craniocaudal, mediolateral oblique, and mediolateral views). (c, d) Diagrams show different 3 D 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 Applications 1" Park et al. Radio. Graphics Vol. 27, No. suppl_1: S 231 -S 240 ©RSNA, 2007 One Power. Point 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 permissions@rsna. org.

Figure 1 C <p> Basic technologic principles of breast tomosynthesis. (a, b) Schemas show 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 3 D image data are subsequently reconstructed as conventional mammographic projections (craniocaudal, mediolateral oblique, and mediolateral views). (c, d) Diagrams show different 3 D 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 Applications 1" Park et al. Radio. Graphics Vol. 27, No. suppl_1: S 231 -S 240 ©RSNA, 2007 One Power. Point 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 permissions@rsna. org.

Figure 1 D <p> Basic technologic principles of breast tomosynthesis. (a, b) Schemas show 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 3 D image data are subsequently reconstructed as conventional mammographic projections (craniocaudal, mediolateral oblique, and mediolateral views). (c, d) Diagrams show different 3 D 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 Applications 1" Park et al. Radio. Graphics Vol. 27, No. suppl_1: S 231 -S 240 ©RSNA, 2007 One Power. Point 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 permissions@rsna. org.

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_Emerg. Tech_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 m. Rad) • 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 (x 2 – x 3) • 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: • • 2 D: one conventional FFDM image 3 D Tomo: 15 views used to reconstruct tomographic slices • 15 projection images • Stack of tomographic slices (1 mm thick) • • Combo: acquisition of both 2 D and 3 D tomo (still < 3 m. Gy 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 2 D mammogram In C-View images, DBT slices having detectable calcifications and/or masses are weighted more heavily that other DBT slices Creates a 2 D image with no additional exposure C-View image appears similar to and serves the same purpose as 2 D 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-2 d-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 2 D only – Ag: for 2 D only – Al: for 3 D tomo only Density control – None No grid during tomo No MAGnification in tomo

Characteristics: Hologic DBT Breast Tomo • • • Pixel binning – In 3 D tomo mode, pixels are “binned” into groups of 2 x 2 pixels (140 micron pitch) Reconstruction – 1 mm thick – Number of tomo images: (compressed breast thickness/ 1 mm => 40 – 80) Interpretation – 1 mm tomographic slices – 15 individual projection views (good for motion detection) – May also have a conventional 2 D view and/or synthetic view

Hologic DBT MGD • 2 D: 1. 2 m. Gy • 3 D Tomo: Combo*: 1. 45 m. Gy 2. 65 m. Gy • *Combo: 2 D and 3 D tomo of the same breast view (e. g. MLO)

Characteristics: DBT Breast Tomo

Hologic Contrast Enhanced Digital Mammography (CEDM) CEDM (Hologic: CE 2 D) is contrast enhanced dual energy imaging. CE 2 D 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 k. Vp – Rh or Ag filter The second image is a ’high energy' image. – 45 to 49 k. Vp – 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 2 D contrast information for both 2 D and 3 D MAMMOGRAPHY™ for CE 2 D 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”, 2 nd 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 Seno. Claire http: //www 3. gehealthcare. com/en/products/categories/mammogr aphy/senoclaire_3 d

Characteristics: GE DBT Breast Tomo • • 3 D Tomo: • 9 views (± 12. 5 degrees) • Step and shoot (versus continuous motion) • No detector binning • Tomo grid is used • Iterative reconstruction (versus filtered backprojection) • 3 D dose same as 2 D dose GE has a new FFDM unit (Pristina) • Not yet approved for DBT

Characteristics: GE DBT Breast Tomo • V-Preview 3: a 2 D 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: //www 3. gehealthcare. com/en/products/categories/mammography/seno claire_3 d#tabs/tab 0 A 5 E 89 E 4 B 6 F 442 DE 962349399 E 6 B 384 D

Breast tomosynthesis Siemens Inspiration http: //usa. healthcare. siemens. com/siemens_hwem-hwem_ssxa_websites-contextroot/wcm/idc/groups/public/@us/documents/download/mda 1/mjuz/~edisp/tomo_approved_ brochure-02166193. pdf

Characteristics: Siemens DBT Breast Tomo • 3 D 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 Cs. I 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 ~50 m. As ~100 m. As ~200 m. As © 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 depends: – spatial frequency (lp/mm) – – – k. V Target Filter breast phantom used EXPOSURE!!!!!

DQE http: //www. medical. siemens. com/

DQE (Detective Quantum Efficiency) 1. 0 Cs. I 0. 9 at 8. 5 m. R at 0. 5 m. R A-Se (Yorker) 70 µm pitch / 250 µm Se at 8. 5 m. R at 0. 5 m. R 100 µm pitch 0. 8 0. 7 DQE 0. 6 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 Cs. I-based detector to maintain its high DQE even at ultra low exposure levels (0. 5 m. R). (From Performance of Advanced a-Si / Cs. I-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