Basic Aspects of Full Field Digital Mammography (FFDM)

Basic Aspects of Basic Aspects of Full Field Digital Full Field Digital

MammographyMammography(FFDM)(FFDM)

FDA Approved FFDM UnitsFDA Approved FFDM Units

http://www.fda.gov/CDRH/MAMMOGRAPHY/digital.html

FFDM Units and FFDM Units and FacilitiesFacilities

http://www.acr.org/accreditation/mammography/rsna07presentation.aspx

FFDM DifferencesFFDM 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 DifferencesFFDM Differences

–Digital imagesRequire workstations

Post-processing image enhancement

Computer aided diagnosis

Archival issues (>9 Mbyte/image)

Good Digital Good Digital Mammo ResourceMammo Resource

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

AECAEC–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 DelayPrep Delay

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

Breast DoseBreast 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

Focal Spot SizeFocal Spot Size

GE Senographe 2000 D

GE Senographe

DSHologic Selenia

Siemens Mammomat Novation

Detector material

Caesium iodide /TFT

array

Caesium iodide /TFT

array

Amorphous selenium /TFT array

Amorphous selenium /TFT array

Detector type Indirect Indirect Direct Direct

Focal spot sizes (mm) .3 and .1 .3 and .1 .3 and .1 .3 and .1

Target materials Mo and Rh Mo and Rh

MoORW Mo and W

Filter materials Mo and Rh Mo and Rh

Mo and RhOR

Rh and Ag Mo and Rh


Fuji Digital Fuji Digital MammographyMammography

ClearView-CSM Reads image plate from both sides

50 micron resolution 10 lp/mm

FFDM DetectorsFFDM 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 SourceDigital 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)

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

©1994 Williams & Wilkins

Mo & Rhtargets

Mo/Rh


Mo/Mo

Rh/Rh

Spectra of W/Rh and W/Ag at 28 kVp

Slide courtesy of Hologic

X-Ray SpectraX-Ray Spectra


GE Senographe

2000 DGE Senographe

DSHologic Selenia


Grid technology Linear Linear Cellular (HTC) Linear

Grid interspcae filler Paper Paper Air Paper

Maximum field size (cm) 19 x 23 19 x 23 24 x 29 23 x 29

Maximum image matrix (pixels) 1914 x 2294 1914 x 2294 3328 x 4096 3328 x 4096

Pixel pitch (microns) 100 100 70 70

Hich contrast limiting resolution (lp/mm) 5 5 > 7 > 7



System MTF

Scattered Radiation Scattered Radiation ControlControl

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

Scattered Radiation Scattered Radiation ControlControlLinear 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).


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.


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.

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 GridHTC Grid

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

HTC GridHTC Grid


HTC GridHTC Grid


HTC GridHTC Grid



GE Senographe

2000 DGE Senographe

DSHologic Selenia


Acquisition bit depth (bits) 14 14 14 14

Image bit depth (bits) 8 8 14 14

Workstation bit depth 10 10 12 10

Maximum image size (Mbyte) 9 9 27 27Time to display image on acquisition workstation (s) 10 <15 10 to 15 40 to 50

Reject analysis No Yes Yes Yes

Stereotactic biopsy devices Yes Yes


Future of Digital Future of Digital MammographyMammography(as of 2005)(as of 2005)

GE Medical Systems: – tomosynthesis.

Hologic:– tomosynthesis – dual energy imaging – imaging with contrast media.

Siemens Medical Solutions: – tomosynthesis– increased post processing capabilities at the review workstation

– improved reporting workstation with image fusion (ultrasound, MRI, etc)

– 2nd generation CAD.


TomosynthesisTomosynthesis

http://www.hologic.com/wh/tomomov.cfm

3:00 -7:00



Breast Tomosynthesis Breast Tomosynthesis (Hologic)(Hologic)

Data acquisition– 15 discrete views– Limited arc (~50 degrees?)– 7 frames/sec– 5 second exposure

Reconstruction– 50 slices– 1 mm thick– Back projection

TomosynthesisTomosynthesis

Breast CTBreast CT

U C Davis

Breast CTBreast CT

U C Davis

Cone Beam Breast CTCone Beam Breast CT

University of Rochester

300 views 10 seconds


University of Rochester


http://www.urmc.rochester.edu/pr/current_research/Cone_Beam/video.cfm

ReferencesReferences– ©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,

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Basic Aspects of Full Field Digital Mammography (FFDM)