Basic Aspects of Full Field Digital Mammography (FFDM)

FDA Approved FFDM Units http://www.fda.gov/CDRH/MAMMOGRAPHY/digital.html

FFDM Units and Facilities http://www.acr.org/accreditation/mammography/rsna07presentation.aspx

FFDM Differences Image acquisition and display are separated Wide dynamic range (versus H&D curve) Lower Dose (~20%) Same dose limits as for film-screen Higher kVp (+3 kVp) Better for dense breasts Imaging detector can be used as AEC detector Automated AEC sensor adjustment (under some AEC modes) Use of Mo/Mo, Mo/Rh, Rh/Rh, W/Rh and W/Ag targets

FFDM Differences Digital images Require workstations Post-processing image enhancement Computer aided diagnosis Archival issues (>9 Mbyte/image)

Good Digital Mammo Resource © Report 05037: Comparative Specifications of Full Field Digital Mammography Systems 2005

AEC Done with the image detector rather than discrete radiation detectors: Amorphous silicon PIN diodes (with scintillator) PM tube (with scintillator) Ion chamber System can automatically select the densest aspect of the breast for AEC “cell” positioning or the technologist can manually select the AEC “cell” position

Prep Delay Can be quite long Up to 7 seconds Especially in AEC mode Very brief for film-screen mammography

Breast Dose Systems display breast dose with image Dose recorded in DICOM image header Entrance skin exposure and/or average glandular dose Vendors use different dose calculation algorithms Dance Wu & Barnes U.S. Method

Siemens Mammomat Novation Focal Spot Size   GE Senographe 2000 D GE Senographe DS Hologic Selenia Siemens Mammomat Novation Detector material Caesium iodide /TFT array Amorphous selenium /TFT array Detector type Indirect Direct Focal spot sizes (mm) .3 and .1 Target materials Mo and Rh Mo OR W Mo and W Filter materials Rh and Ag © Report 05037: Comparative Specifications of Full Field Digital Mammography Systems 2005

Fuji Digital Mammography ClearView-CSM Reads image plate from both sides 50 micron resolution 10 lp/mm

FFDM Detectors Scintillating phosphor (CsI columns) on an array of amorphous silicon photodiodes using thin-film transistor (TFT) flat panel technology (GE) ~100 micron pixels Mo/Mo. Mo/Rh, Rh/Rh Amorphous selenium (direct conversion) using (TFT) flat panel technology (Siemens, Hologic) ~70 micron pixels Mo/Mo, Mo/Rh OR W/Rh, W/Ag for Hologic Mo/Mo, Mo/Rh, W/Rh for Siemens Computed radiography (Fuji) ~50 micron pixels Slot scanning CCD (Fischer? Fischer Medical Technologies?) ~27 micron pixels

Digital Mammography: X-ray Source Target Material and Characteristic X-ray Emission Mo (kα=17.4 keV; kβ =19.6 keV) Rh (kα=20.2 keV; kβ =22.7 keV) W (kα=58.6 keV; kβ =67.4 keV) Filter Material and K-edge (Absorption Edge) Mo (K edge = 20.0 keV) Rh (K edge = 23.3 keV) Ag (K edge = 25.5 keV) 13

X-ray spectral distribution is determined by: anode target material filter material and thickness kVp. Screen-film mammography emphasizes characteristic X-rays rather than Bremmstrahlung photons.

Spectra of Mo/Mo and Mo/Rh at 28 kVp Slide courtesy of Hologic 15

Mo & Rh targets Mo/Rh ©1994 Williams & Wilkins

Mo/Mo Rh/Rh ©1994 Williams & Wilkins

Spectra of W/Rh and W/Ag at 28 kVp Slide courtesy of Hologic 18

X-Ray Spectra

Siemens Mammomat Novation Focal Spot Size   GE Senographe 2000 D GE Senographe DS Hologic Selenia Siemens Mammomat Novation Grid technology Linear Cellular (HTC) Grid interspcae filler Paper Air Maximum field size (cm) 19 x 23 24 x 29 23 x 29 Maximum image matrix (pixels) 1914 x 2294 3328 x 4096 Pixel pitch (microns) 100 70 Hich contrast limiting resolution (lp/mm) 5 > 7 © Report 05037: Comparative Specifications of Full Field Digital Mammography Systems 2005

System MTF ©1994 Williams & Wilkins

Scattered Radiation Control Only 40-75% of the possible contrast is imaged in mammography unless scatter is controlled.

Scattered Radiation Control Linear Grids Grids preferentially remove scattered photons. Lead laminae separated by radiolucent spacers. 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).

Scattered Radiation Control Linear Grids Grids move (linearly or oscillatory L<-->R) during an exposure (20 or more grid line spacings) to blur out grid lines. Short exposures can cause gridline artifacts that result from insufficient motion. Mammography grids transmit 60-70% of primary X-rays and absorb 75-85% of the scattered X-rays.

Scattered Radiation Control Linear Grids 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.

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

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

Siemens Mammomat Novation Focal Spot Size   GE Senographe 2000 D GE Senographe DS Hologic Selenia Siemens Mammomat Novation Acquisition bit depth (bits) 14 Image bit depth (bits) 8 Workstation bit depth 10 12 Maximum image size (Mbyte) 9 27 Time to display image on acquisition workstation (s) <15 10 to 15 40 to 50 Reject analysis No Yes Stereotactic biopsy devices   © Report 05037: Comparative Specifications of Full Field Digital Mammography Systems 2005

Future of Digital Mammography (as of 2005) GE Medical Systems: tomosynthesis. Hologic: tomosynthesis dual energy imaging imaging with contrast media. Siemens Medical Solutions: increased post processing capabilities at the review workstation improved reporting workstation with image fusion (ultrasound, MRI, etc) 2nd generation CAD. © Report 05037: Comparative Specifications of Full Field Digital Mammography Systems 2005

Tomosynthesis http://www.hologic.com/wh/tomomov.cfm 3:00 -7:00

Breast Tomosynthesis (Hologic) Data acquisition 15 discrete views Limited arc (~50 degrees?) 7 frames/sec 5 second exposure Reconstruction 50 slices 1 mm thick Back projection

Tomosynthesis

Breast CT U C Davis

Breast CT U C Davis

Cone Beam Breast CT University of Rochester 300 views 10 seconds

Cone Beam Breast CT University of Rochester

Cone Beam Breast CT http://www.urmc.rochester.edu/pr/current_research/Cone_Beam/video.cfm

References ©NCRP 2006 ©1994 Williams & Wilkins ©1993 RSNA ©1992 RSNA 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,