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Quality Assurance in Mammography
Melissa C. Martin, M.S., FACR
Sacramento Mammograpy Society Meeting
February 9, 2008
The Evolution of Mammography
What is Mammography?
• 2-D X-ray breast imaging
History of Mammography
1930:Pre compression
History of Mammography
1951:Early method ofcompression
History of Mammography
1966:First dedicatedmammographysystem
Screen-Film Mammography
For 35+ years, screen-film has been the “gold standard” for breast cancer detection
Screen Film MammographyX-ray source
Screen-film cassette
Film Processor Film viewer
State of the Art Mammography
2000: Digital mammography
X-ray source
Digital detector
Full Field Digital Mammography
Acquisition computer
Softcopy display
System Quality Control
• Pre-Acquisition• Acquisition• Image Processing and Display• Storage/Archive
The system is only as good as the weakest link-more than just the modality itself
QC Recommendations
• Daily QC checks (technologist)– System warmup
• Detector uniformity• Spatial resolution• Contrast resolution (signal to noise ratio)• Geometric accuracy• Clinical review and artifact identification
– Logging / preventive maintenance
QC Recommendations
• Each image: QC verification (technologist)– Patient positioning– Image orientation– Image markers– Processing and grayscale rendering– Artifacts (dropouts, lines, scratches, etc.)– Exposure Index- Patient Dose Estimates
FDA Approved Full-Field Digital Mammography Systems
GE Senographe 2000D- January 28, 2000
Fischer SenoScan– September 25, 2001
Lorad Selenia– October 2, 2002
GE Senographe DS– February 19, 2004
Siemens MammomatNovation DR- August 20, 2004
GE Senographe Essential - April 11, 2006
Fuji FCRm- July 10, 2006
GE 2000DGE 2000D
System Components
GE Seno DS & EssentialGE Seno DS & Essential
LoradLorad SeleniaSelenia
SiemensSiemensMammomatMammomat NovationNovationDRDR
Fischer Fischer SenoscanSenoscan
MQSA National Statistics
• Certified facilities as of 2/1/08: 8861• Certified facilities as of 10/1/2006: 8832• Total accredited units (2/1/08): 13,575• Certified facilities with FFDM units: 2743
(2/1/08) - 31% of facilities• Accredited FFDM units (2/1/08): 4132
- 30.4% of all units
MQSA National Statistics (Butler/Wilcox)
MQSA National Statistics (Butler/Wilcox)
Why Full Field Digital Mammography?Why Full Field Digital Mammography?
• Technical Reasons
• Clinical Reasons
• Practical Reasons
• Technical Reasons
• Clinical Reasons
• Practical Reasons
Why FFDM - Technical ReasonsWhy FFDM - Technical Reasons• Wider dynamic range
– 3-4 times higher• Linear detector response
– Over full range• Better low contrast resolution
– Enhanced visualization of masses• Higher DQE
– Higher absorption efficiency– Dose or SNR– Important for detector as well as entire system
• Wider dynamic range– 3-4 times higher
• Linear detector response– Over full range
• Better low contrast resolution– Enhanced visualization of masses
• Higher DQE– Higher absorption efficiency– Dose or SNR– Important for detector as well as entire system
Technical Reasons
Why FFDM- Clinical Reasons
DMIST Results
Why FFDM- Practical Reasons
Weaknesses of Digital Mammography
Dose Creep
31Butler/wilcox - RSNA 2006
Fundamentals of Digital Mammography• Theory of digital detectors• Pixel size considerations• Anti-scatter grids• Gantry system components• Acquisition system components• Softcopy workstation components• Computer aided diagnosis• Advanced applications
Digital Mammography Detector Technical Background
Direct Vs. Indirect Conversion
a-Selenium Semiconductor
TFT array
---+++
Selenia Direct Digital
CsI Scintillator
TFT array or CCD
Indirect DigitalX-ray photon X-ray photon
Line spread functions
Film
X-ray photon
Film
Phosphor
Available FFDM Systems
direct conversion TFT
MammomatNovation (DR)
•Siemens Medical
direct conversion TFT
Selenia•Hologic/Lorad
indirect conversion, slot scanning
Senoscan•Fischer Imaging(No longer available as new)
Indirect conversion TFT
Senographe 2000Dand Essential
•GE Medical Systems
Image Sharpness
Modulation Transfer Function (MTF)measures resolution∗ Higher MTF = Sharper images∗ Higher MTF = Superior detail image
contrast
0
0.2
0.4
0.6
0.8
1
0 2 4 6 8 10
Spatial Frequency (lp/mm)
Pres
ampl
ed M
TF
Modulation Transfer Function
Kodak Min-R 2000
GE Senographe 2000D
Lorad Selenia
Fischer Senoscan
* Data From PMA Submissions, European Journal Radiology
What Does Higher MTF Mean?• Higher MTF means increased image
sharpness, less blur• Sharper images of small details means
better detection• Better detection means fewer missed
cancers• Sharper microcalcifications means better
visualization of morphology & higher confidence in diagnosis
Dose EfficiencyDetective Quantum Efficiency (DQE) measures dose efficiency
∗ Higher DQE = Superior image quality
∗ Higher DQE = Reduced patient dose
0%
10%
20%
30%
40%
50%
60%
70%
0 2 4 6 8 10 12
Spatial Frequency (lp/mm)
DQ
EDetective Quantum Efficiency
Kodak Min-R 2000
GE Senographe 2000D
Lorad Selenia
Fischer Senoscan
* Data From PMA Submissions
What Does Better DQE Mean?
• Better DQE means less noise in the image• Less noise means better detection of low
contrast pathology, e.g., masses• Better detection means fewer missed
cancers• Lower noise means better visualization &
higher confidence in diagnosis• Better DQE means flexibility to reduce dose
a-Se Direct Capture Detector*
• 70 μm TFT pixel pitch • 24 cm x 29 cm active
image area
*Currently used by Hologicand Siemens
Pixel Size Considerations• Need to optimize conflicting requirements: Smaller
pixels give higher resolution, but files are larger. Monitors can’t display large FFDM images in their entirety.
• If resolution is too low, it may impair accurately imaging microcalcifications at earliest stage of formation (~ 150 μm).
• In direct conversion systems, smaller pixel sizes provides higher resolution. This may not be true for indirect conversion systems, which are scintillator limited.
System ComponentsSystem Components
Selenia Gantry
• Built on analog Lorad M-IV design
• Optimized for digital imaging
Selenia High Transmission Cellular (HTC®) Grid
• Integrated into the digital detector • Cross-hatch design reduces scatter in
X & Y direction• Allows 70-80% transmission of
primary beam• Automatic retraction mechanism
facilitates geometric magnification exams
Image Receptor Size
24 x 29 cm Detector
18 x 24 cm Detector
• Unlike film, you only get one size per system!
With 18 x 24 cm Detector Size:• >30% of women will undergo
– Double exposure of overlapping tissue– Multiple additional compressions– Extended exam times
• Radiologists will have to review a total of 7 to 8 images per exam
With 24 x 29 cm Detector Size:• Need to accommodate imaging of smaller breasts
Smart Paddle System
• Microprocessor in each Smart Paddle controls movement of collimation
• When paddle is shifted, collimation automaticallymoves to proper position
CC
LMLO
RMLO
• Integrated into Smart Paddle system
• Provides proper & consistent compression across the entire breast– Reduced motion artifacts– More uniform compression– Maximum patient comfort
Fully Automatic Self-adjusting Tilt (FAST) Paddle
Bi-Angular X-ray TubeAllows higher mA loading with smaller effective focal spot size for improved resolution, especially on magnification views
• Two modes of operation– Virtual multi-
sensor (fully automatic)
– 7 User-selectable positions
• 12.5 cm travel from chest wall– Accommodates
imaging of larger breasts
Automatic Exposure Control (AEC)
Fully Automatic Collimation• Easier & quicker workflow• Easier positioning on
magnification & spot compression views
• System selections can be overridden easily
• Collimation follows compression paddle
• Stored image size reduces with smaller paddle
Auto FiltrationMolybdenum or Rhodium is automatically selected for reduced dose & increased penetration of dense tissue
Selenia Image Acquisition Station• Integrated X-ray control • Familiar M-IV interfaces• Short-term archive• Built-in QC & service tools• DICOM 3.0 connectivity
• Flat panel display monitor
• Automatic MQSA repeat analysis report
• Small foot print
Flexible Technology InterfacesFlexible Technology Interfaces
• Fully integrated, vendor independent Display of CAD markers & results
• Compatibility with multiple vendors of reporting software
• Multiple approved DICOM compatible printers
• Fully integrated, vendor independent Display of CAD markers & results
• Compatibility with multiple vendors of reporting software
• Multiple approved DICOM compatible printers
There Are Currently Several FDAThere Are Currently Several FDA--Approved Laser Imagers for Digital Approved Laser Imagers for Digital MammographyMammography
•• Agfa DS4500MAgfa DS4500M
•• Kodak 8600 Laser ImagerKodak 8600 Laser Imager
•• Kodak 8610 Laser ImagerKodak 8610 Laser Imager
•• Kodak 8900MKodak 8900M
•• Fuji Fuji DrypixDrypix 7000 & 5000 7000 & 5000
•• Fuji Fuji DrypixDrypix FMFM--DP LDP L
•• Konica Konica DryProDryPro 793793
OD Requirements for OD Requirements for HiHi--Resolution Laser ImagersResolution Laser Imagers
DDmaxmax > 3.5 OD> 3.5 OD
MidMid--density > 1.5 ODdensity > 1.5 OD
Kodak daily sensitometryKodak daily sensitometry
Laser Processor QCLaser Processor QC
Base + FogBase + Fog
Density Difference Density Difference –– OD closest to 2.20 OD closest to 2.20 minus OD closest but not less than 0.45minus OD closest but not less than 0.45
MidMid--density density –– step closest to but not less step closest to but not less than 1.20than 1.20
DDmaxmax
Action Limits:Action Limits:
MD & DD MD & DD ++ 0.15 OD0.15 OD
B+Fog = 0.03B+Fog = 0.03
DDmaxmax ++ 0.250.25
Selenia Softcopy Workstation
Softcopy Image Review StationSoftcopy Image Review Station• Dual 5 Megapixel displays• Display 10-bit grayscale • Configurable doctor-
specific hanging protocols• Supports DICOM For-
Presentation and For-Processing
• Display For-Presentation images from other vendors and other modalities
• Supports double reading• Standard workstation
tools: window, zoom, annotation, measurement, …
Soft Copy Workstation ControlsSoft Copy Workstation Controls• User configurable workflow
– Hanging protocol and workflow defined by individual users
– Accommodates multiple users• Custom designed workflow keypad
– Places all controls at physician’s fingertips
– Allows attention to focus solelyon case review
• User configurable workflow– Hanging protocol and workflow
defined by individual users– Accommodates multiple users
• Custom designed workflow keypad– Places all controls at physician’s
fingertips– Allows attention to focus solely
on case review
High Volume ThroughputHigh Volume Throughput• Supports Screening &
Diagnostic Mammography• Sub-second delay between
cases• One softcopy workstation
supports up to 4 Selenia Acquisition Stations
• Supports optional automatic double-reading
• Supports Screening & Diagnostic Mammography
• Sub-second delay between cases
• One softcopy workstation supports up to 4 Selenia Acquisition Stations
• Supports optional automatic double-reading
Proprietary Image Processing
• Automatic image processing – Optimally enhances
each digital mammogram
• Mammography specific algorithms– Designed specifically
for direct capture Selenia images
• Automatic image processing – Optimally enhances
each digital mammogram
• Mammography specific algorithms– Designed specifically
for direct capture Selenia images
• Peripheral Contrast Enhancement (PCE)– Optimal skin line
visibility– Optimal image
contrast applied across entire breast for different tissue densities
Peripheral Contrast Enhancement (PCE)Peripheral Contrast Enhancement (PCE)
PCE Off PCE Applied
Thickness CompensationThickness Compensation
Goal: Visualize the breast from chest wall to skin line.Algorithm: 1. Estimate the thickness of the breast at all pixels2. Add a nearly-equivalent thickness [of water] to raise gray level. Original TC Processed
*Note: This is only applied near the skin line
Thickness Compensation
Digital Mammography Workflow
Technologist Workstation• TWS is the means to get the digital image to every
place you would take a film to view in the analog world.
• TWS will be used to assist with workflow in the mammography suite. – TWS used for viewing priors, in the tech area– Annotations done by the radiologist will be sent from
the SCW to the TWS for review– A notification will alert the technologist when
annotated images arrive.
Image Management
• Digital mammography images require extensive archiving space & increased bandwidth– Single system can generate 1 Terabyte of Data/year
(50 patients/day)– 2 – 3 Terabytes With Images From Prior Years
• Many PACS may be negatively impacted by demands of digital mammography– Insufficient storage space– Inadequate bandwidth to support acceptable
transmission speed
FFDM Mobile Applications
Network Connectivity to Hospital PACS
On-board Image Storage
Satellite Connection toHospital PACS
QC - Part 2 - SAMS Meeting 2/08
• QC Procedures
FFDM Quality Control
• MQSA Final Regulation– Screen-Film QA/QC– Manufacturer QA/QC for FFDM System
• Manufacturer’s FFDM QC Manual
LORAD Selenia QC TestsQC Manual tests:• Medical Physicist
– Annually• Radiologic Technologist
– Daily– Weekly– Biweekly– Monthly– Quarterly– Semiannually
Medical Physics Annual Tests• Mammographic Unit Assembly Evaluation• Collimation Assessment• Artifact Evaluation• kVp Accuracy and Reproducibility• HVL Measurement• Evaluation of System Resolution• Breast Entrance Exposure and Glandular Average Dose• Radiation Output Rate• Phantom Image Quality Evaluation• Signal-To-Noise and Contrast-To-Noise Measurements• Viewbox Luminance and Room Illuminance• Softcopy Workstation QC
QC Tests for FFDM Units:Tests and Frequencies Differ
Not requiredBi-weeklyWeeklyWeeklyLorad
MonthlyWeeklyWeeklyDailyFischer
MonthlyWeeklyMonthlyMonthlyGE
MTF/ Sys Res
Flat FieldSNRSoft Copy Display
Test
Ex: Tech Test Frequencies
LORAD Selenia FFDM System
• RT QC Tests
Technologist QC Tests
• Laser Printer Quality Control (Daily)• SNR and CNR Measurements (Weekly)• Softcopy Workstation QC (Weekly)• Phantom Image (Weekly)
Laser Printer Quality Control
• SMPTE Pattern from Acquisition Workstation (Daily)
• Measure 10%, 40% and 90% Density Patches• Daily Performance
– 40% density tracks within ±15%– (40% - 10%) density tracks within ±15%– 90% density tracks within ±15%
• NOTE: Printer uses linear LUT
SNR and CNR Measurements• ACR Accreditation Phantom with Disc
(Weekly)• Measure SNR and CNR from Image
SNR and CNR Measurements
• Passing Criteria– SNR at least equal or greater than 40– CNR should stay within ±15% of
measurement obtained during acceptance testing of system
LORAD Selenia FFDM System
• Workstation QC
Room Illuminance
• From the ACR QC Manual, 1999, the room illuminance must be below 50 lux.
• From the February 2006 version of the Medical Physicist Equipment Evaluation forms from ACR, room illuminance for soft copy displays must be below 20 lux.
Softcopy Workstation QC
• Performed Weekly– Black level measurement– White level measurement
• Performed Monthly– LUT conformance
• Performed Quarterly– White field uniformity
Softcopy Workstation QC
• Data Logged by Software• Warning Flags and Errors if Conformance
Fails
Phantom Image
• Review Weekly Phantom Image Results– Measured film densities– Phantom objects seen (printer, monitors)
• 5 fibers• 4 speck groups• 4 masses
LORAD Selenia FFDM System
• FDA Conformance Regulations
Conformance• Federal regulations, 900.12(e), specify that any
time quality control test results fall outside of the action limits for systems with image receptor modalities other than screen-film, the source of the problem shall be identified and corrective action shall be taken before any further examinations are performed.
• Full Field Digital Mammography systems are affected by this ruling
QC Alternative Standard• The majority of the required QC testing performed on
a FFDM system applies to system components other than the digital image receptor.
• Only a small portion of the quality control testing performed on an FFDM system is specific to the digital image receptor.
• Thus, alternative standards has been approved by FDA on the QC testing of several of the FFDM systems.
QC Alternative Standards for FFDM Units• Three different corrective action
categories– Action Category A– Action Category B– Action Category C
Action Category A
• Applies to performance testing of the digital image receptor
• Corrective action shall be taken before any further examinations are performed– Evaluation of System Resolution– Breast Entrance Exposure and Average Glandular Dose– Phantom Image Quality Evaluation– SNR and CNR Measurements
Action Category B• Applies to performance testing of diagnostic devices
used for mammographic image interpretation• Corrective action shall be taken before the device can
be used for mammographic image interpretation• Clinical imaging can be continued and alternative
approved diagnostic devices shall be used for mammographic image interpretation– Phantom Image Quality Evaluation– Softcopy Workstation QC– Laser Printer Quality Control
Action Category C
• Applies to performance testing of rest of the system• Corrective action shall be taken within thirty days of
the test date• Clinical imaging and mammographic image
interpretation can be continued during this period– All other tests
Siemens Novation
Phantom Image Quality Check
Fuji Digital Mammography QCTechnologist’s Tests
TESTCNR-Contrast/NoisePhantom ImagePrinter/MonitorVisual ChecklistRepeat AnalysisCompressionIP Fog
FREQUENCYWeeklyWeekly
Per ManufacturerMonthly
QuarterlySemi-annualSemi-annual
Fuji Digital Mammography QCTechnologist’s Tests
Printer TestsNo film in cassetteImaging Plate should be erased after 8
hours of non-useImaging Plate should be processed or
erased after each exposurePrinters are monitored according to the
manufacturer’s approved QC program
Fuji Digital Mammography QCTechnologist’s Tests
Phantom Images TestConfirms image quality using ACR PhantomTools required - QC Cassette & ACR PhantomMethod - AEC Exposure, process IP using the
Physics, ACR MAPP MenuVisually inspect the image. Same scoring method
as MQSACorrection Period - Before any further
examinations are performed
Fuji Digital Mammography QCTechnologist’s Tests
CNR (Contrast/Noise Ratio) TestEvaluates Noise and Contrast using a fixed x-
ray exposureTools needed - 4 cm acrylic block & 0.2 mm AlMethod - Fixed manual techniqueCNR Measurement must be within +/- 20%Correction Period - Before any further
examinations are performed
Fuji Digital Mammography QCTechnologist’s Tests
Tests in Accordance with ACR/MQSAVisual Checklist MonthlyRepeat Analysis QuarterlyCompression Test Semi-Annual
Same Action Limits and Corrective Action as MQSA
IP Fog replaces Darkroom Fog test - Semi Annual
Fuji Digital Mammography QCTechnologist’s Tests
Imaging Plate FogConfirm that the storage conditions of the exposure
room protects the IP cassettes from scatterTools required - IP CassetteMethod - Tape coin to front of cassette and place in
storage location during test exposuresVisually inspect image for visibility of coinCorrection Period - Before any further examinations
are performed
Fuji Digital Mammography QCTechnologist’s Tests
Inter-Plate Consistency - As NeededThe Inter-plate Consistency Test replaces the
Screen Speed TestMust be performed when new IPs and/or
cassettes are introducedCan be performed by the QC technologist under
Qualified Medical Physicist oversight
Fuji Digital Mammography QCTechnologist’s Tests
Inter-Plate Consistency - As NeededConfirm that Imaging Plates used in the facility
are similar in sensitivity and image qualityTools Required - new and existing IPs and
Cassettes, 4 cm acrylic blockMethod - Expose cassettes using AEC (time)
ModeAcceptable results: mAs +/- 10$, SNR +/- 15%Correction Period - Within 30 days of the test
129Butler/Wilcox - RSNA 2006
As good or better than film, but its main advantage is:
Provides ideal platform for advanced applicationsTomosynthesis (3D mammography)Contrast enhanced mammography
As good or better than film, but its main advantage is:
Provides ideal platform for advanced applicationsTomosynthesis (3D mammography)Contrast enhanced mammography
Full Field Digital Mammography (FFDM)
Future of Mammography
2008:Tomosynthesis3D mammography
What is Tomosynthesis?• 3-D X-ray mammography• Helps reduce tissue overlap (structure noise)
2-D image can obscure
lesions
Thin slices from 3-D
reduce tissue overlap
Why Tomosynthesis?
• Elimination of overlapping structures and shadows
• See through dense breasts• Clearer lesion margins• Potential for reduced call-
backs• Potential for reduced dose
Tomosynthesis Acquisition
• Limited angle tomography • X-ray tube moves in an arc across the breast• Series of low dose images are acquired at different angles• Total dose similar to single view breast exam
Digital detector
Compression plate
Breast
X-ray tube
Reconstructed planes
Conventional 2-D Imaging
Incident X-rays
Objects being imaged
2-D imageImages superimposed on image
Tomosynthesis Acquisition
Incident X-rays
Objects being imaged
2-D raw data images
Image from multiple angles
Exposure #1 Exposure #6 Exposure #11
Tomosynthesis Acquisition
• X-ray tube moves in an arc around the breast• Series of low dose images are acquired at different
angles • Total dose similar to standard breast exam
Digital Detector
Compression PlateBreast
X-ray Tube
Tube motion
Reconstructed planes
Visualization of Microcalcifications
Normalmammogram
Tomosynthesis slice
3-D Information
Normalmammogramshows 2 calcs, but what is their spatialrelationship?
Tomosynthesis slices show they are separated by17 mm.
Z = 30 mm. Z = 47 mm.
Seeing through overlying tissue
Normal mammogram Tomosynthesis slice
Improved Visualization
Normal mammogram Tomosynthesis slice
3D Digital Mammography Tomosynthesis
• Multiple views reconstructed into 3D image• Helps solve tissue overlap problems• Initial clinical trials underway
* Works-in-progress
Normal mammogram
Tomosynthesis slices
Tomosynthesis Reconstruction
Acquiring images of breast at different angles allows reconstruction of 3-D volume
Tomosynthesis ReconstructionAppropriate shifting and adding of raw data reinforces objects at specific height.
Additions improve quantum signal/noise
Height 1 Height 2
Raw Data
Data Formats
Raw data:11-21 low dosemammogramsviewing breast atslightly differentangles
Data Formats
Reconstruction:40-60 cross-sectional slices, one per mm ofcompressedbreast
TomosynthesisSystem Requirements• Rapid digital detector readout• High Detective Quantum Efficiency (DQE),
low noise detectors ~ each image low dose• Large area detectors, to image the entire
breast• Short scan times (~ seconds) to reduce
patient motion
Tomosynthesis Prototype
FFDM Gantry
Compression paddle
Breast support platform
Selenium image receptor
Tomosynthesis Dose
• Total dose similar to conventional single view mammography exposure
• Each single view low dose• Reconstruction recovers quantum
signal/noise in final image by adding the exposures
Signal to Noise Improvement• Reconstruction recovers quantum signal/noise from
sequence of low dose images• Relevant noise is structure, not quantum• Improved visibility by removal of overlapping tissues
2-Dimage
3-D Tomo image
3-D Information
Mammogramshows 2 calcs, but what is their spatialrelationship?
Tomosynthesisslices show they are separated in depth by17 mm
Z = 30 mm Z = 47 mm
Tomosynthesis
• Superior low contrast visibility compared to FFDM or film, even at lower doses
• Clinical trial is being done at matched dose to FFDM– for improved clinical efficacy
Features of Tomosynthesis• 3-D X-ray mammography• High in-plane resolution
(mammographic resolution)• Thin cross-sectional slices
(typically about 1 mm)• Same radiation dose as 2D mammography• Rapid scans in seconds• Simple modification of FFDM systems
Purposes of Tomosynthesis
• Addresses superimposed tissue problem– See small pathologies more reliably– Reduce superimposed tissues mimicking
pathology• Provides accurate 3D localization
– Helpful for biopsy
Current Clinical Status
• In clinical trials in the US and elsewhere• Several manufacturers have announced
plans• No system currently FDA approved • May change the standard of care in
mammography!
Thank You !!!
Melissa C. Martin, M.S., FACRTherapy Physics Inc.
879 West 190 St., Ste 419Torrance, CA 90248
Office Phone: 310-217-4114e-mail: [email protected]