Educational Objectives Why pay special attention to mammography physics Radiation Risk/Benefit Issues The Challenge in Mammography X-ray Spectra in Mammography
Levy, Janice, Fitness Editor has reference to this Academic Journal, PHwiki organized this Journal Mammography Physics Jerry Allison, Ph.D. Department of Radiology Medical College of Georgia Augusta University Augusta, GA Educational Objectives Our educational objectives are to underst in addition to : 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).
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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 per as long as med 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 in addition to postpartum mastitis patients treated w/radiation therapy ). ©1992 RSNA Hodgkins lymphoma patients treated w/radiation therapy ©NCRP 2006 (Report 149) Risk/Benefit ©1992 RSNA
©1987 IOP Publishing The Challenge in Mammography X-ray spectral distribution is determined by: kV target/filter combination Mo/Mo, Mo/Rh, Rh/Rh as long as GE Mo/Mo, Mo/Rh, W/Rh as long as Siemens Mo/Mo, Mo/Rh or W/Rh, W/Ag as long as Hologic W/Rh, W/Ag, W/Al as long as Hologic DBT Tomo W/Rh, W/Ag, W/Cu as long as Hologic CE2D Tomo W/Rh as long as Giotto W/Rh as long as Fuji Saphire HD W/Rh, W/Ag as long as Planmed W/Al as long as Philips X-ray Spectra in Mammography X-ray spectra are variable
Compression (Redistribution) ©1994 Williams & Wilkins Scatter Geometric blurring Superposition Increases the proportion of the X-ray beam that is used to image a breast Motion Beam hardening Dose 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 as long as tomo) 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 in addition to dose as conventional linear grids Scattered Radiation Control
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 as long as visualization of calcifications in addition to 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 in addition to 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)
©1994 Williams & Wilkins Focal Spot in addition to MTF Dose Limits FDA Dose limit as long as screening mammograms 3 mGy (w/grid) Mean gl in addition to ular 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 http://www.fda.gov/Radiation-EmittingProducts/MammographyQualitySt in addition to ardsAct in addition to Program/FacilityCertification in addition to Inspection/ucm114148.htm As of December, 2016 12 Vendors 35 Models 6 CR 25 FFDM 3 DBT Not all vendors still exist Not all models actually as long as sale USA Certification statistics December 1, 2016 http://www.fda.gov/Radiation-EmittingProducts/MammographyQualitySt in addition to ardsAct in addition to Program/FacilityScorecard/ucm113858.htm 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 in addition to DBT units / Accredited FFDM/DBT units 2,948 / 4,074 Film/screen units 225 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 FFDM Technologies
Does pixel size matter As pixel size decreases: Spatial resolution improves Noise increases Signal-to-noise decreases Yet another set of imaging tradeoffs Independent (Indirect) Conversion: CsI Converter + aSi Substrate Sensor Matrix Blocking Layer 2,600+ Volts Electrode Dielectric Digital Data Electrons X-Ray Photons Selenium K-edge Fluoresence Electrons Read Out Electronics X-ray Electrode Capacitor Dependent (Direct) Conversion: aSe Converter + aSi Substrate Sensor Matrix Detector Technology Overview Courtesy: Jill Spear, GE Womens Healthcare 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 in addition to 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) http://incenter.medical.philips.com/doclib/enc/fetch/2000/4504/577242/577260/593280/593431/8477093/Photon-Counting-White-Paper.pdf%3fnodeid%3d8477094%26vernum%3d1 X-ray generates electron-hole pairs creating a short electrical signal
DQE http://www.medical.siemens.com/ 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 Per as long as mance of Advanced a-Si / CsI-based Flat Panel X-ray Detectors as long as 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) 0.1 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Spatial Frequency (lp/mm) DQE A-Se (Yorker) 70 µm pitch / 250 µm Se at 8.5 mR at 0.5 mR CsI 100 µm pitch at 8.5 mR at 0.5 mR DQE (Detective Quantum Efficiency) Courtesy: Jill Spear, GE Womens Healthcare
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