Digital Mammography

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Mammography

For 35+ years, screen-film has been the “gold standard” for breast cancer detection

IN THE BEGINNING

Mammography technology has come a long way since

the first machine specifically designed for producing

mammograms was introduced in 1966.

The first dedicated mammography system was essentially a tripod supporting a special X-ray camera

EARLY POSITIONING AND COMPRESSION

MLO view done in reclining positionCone

Compression Pad

CC in standing position

WHAT ABOUT THIS?

• Usually done when a patient had a very large palpable mass

• Limited productivity; 4-5 patients imaged per day

• Limited to CC and MLO views; no ability to do extra diagnostic views

DEDICATED MAMMOGRAPHY SYSTEMS

• The first systems developed specifically for mammograms were released in 1966.

• Rotating C-arm allowed both CC and MLO views to be taken with patient in standing or sitting position, for better efficiency

• Additional diagnostic views enabled

• Image quality was limited due to limitations in film capabilities

THE NEXT ADVANCEXEROMAMMOGRAPHY

• First introduced in 1971• Provided better image

quality than systems using industrial film packs

• Allowed excellent visualization of chest wall

Xeroradiographs (blue and white prints), as shown above, gave adequate image quality; however, the radiation dose to the breast was much higher than current imaging methods.

AND IT APPEALED TO THE PUBLIC…

• Advertisement in Life and Glamour magazine promoting the new technology, xeromammography

Model demonstrates the latest in mammography technology and fashion. Check out the hosiery

DMIST

• Digital Mammography Imaging Screening Trial whose objective was to determine the validity of digital mammography

• Results showed digital mammography is more beneficial for women:

• under age 50 (no matter what level of breast tissue density they had)

• of any age with heterogeneously (very dense) or extremely dense breasts

• pre- or perimenopausal women of any age (defined as women who had a last menstrual period within 12 months of their mammograms).

American College of Radiology imagining Network

Improved Image Quality?

Indications

• Women under the age of 50

• Women with heterogeneously dense or extremely dense breast

• Women who are premenopausal or perimenopausal

American College of Radiology imagining Network

Advantages of Digital Imaging

• Improved image quality

• Wider dynamic range

• Reduced exam times

• Image manipulation tools

• Removes film variability

• Eliminates processing

• Minimizes retakes

Not All Digital Is Created Equal!

• Direct Capture vs. Indirect Capture

– Screen-film is an example of indirect

The Direct Capture Difference

• Direct capture convertsx-rays to electronic signals

• In indirect conversion detectors, x-rays are first converted to visible light, which is then converted to electronic signals. Light diffuses across a large distance, resulting in reduced image sharpness and loss of tissue contrast.

Image Quality Measurements

• Digital mammography has two measurements for image quality– Modulation transfer function (MTF)

• Measure of image sharpness

– Detector quantum efficiency (DQE)• Measure of dose efficiency (how well the imaging

system uses the x-ray photons that are absorbed)

Image Sharpness

• Modulation Transfer Function (MTF) is a measure of signal transfer over a range of spatial frequencies

– ∗Higher MTF = Sharper images

– ∗Higher MTF = Superior contrast resolution

Dose Efficiency

• Detective Quantum Efficiency (DQE) is a measurement of how well the x-rays are utilized

– ∗ Higher DQE = Superior image quality

– ∗ Higher DQE = Reduced patient dose

What’s a PIXEL???

Picture a cup that collects electronic signals.

Pixel Size• Pixel size of a detection system needs to be ~ 50% of the smallest

detectable signal of an object being imaged

• Microcalcifications begin to emit signals visible to the human eye at 150μm

• Acquiring at 70-75μm enables detection and characterization of smallest microcalcifications

Image acquired with indirect detector

Image acquired with 70μm direct detector

Dose Creep

• Proper exposure for FFDM is “adequate” SNR– What is “adequate” SNR?

• Technologist has no visual indication of over exposure. Using a higher technique can be a “safer” decision

• “Dose Creep” is allowing exposure to increase with no clinical benefits

Tissue seen out to the skin line

Wider Dynamic Range

Dose Comparison- 4 views

• Screen-film with MO tube - 8 mGy

• Direct Digital with MO tube- 6.4 mGy

• Direct Digital with Tungsten tube- 4.8 mGy

• Next step in the evolution of mammography

• Limitation of screen-film mammography is image cannot be altered

• Digital image is acquired as an electronic signal which is stored in a computer and displayed as film or on a monitor

Digital Exposures

• AEC—the pixels become your photocells– A preliminary mini exposure assesses tissue

density and thickness, then applies the needed exposure

• The algorithm controls your contrast vs. kVp– Adequate and appropriate kVp should still be

applied, however in digital we can now use higher kV than film, so the dose has come down

• Dose is still a factor of mAs

MO vs Tungsten

• Molybdenum is ideal for screen-film kV ranges and gray scales

• Tungsten is better for digital imaging as the kV is more for penetration as the algorithm drives contrast now

• Tungsten offers lower dose with longer scale contrast

Benefits - Digital Mammography?

• Overcomes the limitations of screen-film

• Provides diagnostic value for many patients

• Platform of future technologies i.e. breast tomosynthesis

• Uses traditional generators and tubes

• The x-ray beam is converted into digital information which can be stored electronically, transmitted, displayed, analyzed and manipulated

Review of Prior Images before procedures

• Dense tissue can be seen more clearly

• Better cancer detection in dense tissue

Side by Side

Technical Side

• The mammography image appears in the exam room on a monitor, not by darkroom processing, for quick review by the technologist

• This facilitates a quicker overall exam time for the patient

Technologist Workstation

• Review all images– Ability to magnify

– Ability to adjust contrast and density

• Manipulate image

• Give annotations

Adjustability• Physician can

– manipulate images on a computer workstation to change the ‘look’ of the mammogram to better see areas of interest

– Zoom into an area of interest

– Move or pan around to different areas on the mammogram

• The visibility of subtle mass or clusters of calcifications present in the image can be increased by adjusted the contrast.

Radiologist Station

More data captured

Dynamic Range Controlenhances skin edge

PEM Pattern EnhancementEnhances Microcalcification detection

with PEM

MFP Multi-frequency ProcessingImproves Dense Breast Visualization

Image Processing

Greater Access• The mammogram can be read where ever

the radiologist is located

• The radiologist does not need to be at the site where the exam was performed

• Also allows for physicians to consult with their peers by remote viewing

• Misplaced or lost images will not occur

• Images are stored electronically with unlimited access to the originals

• The original version can be recalled from electronic storage for review on a workstation or printed for a film copy

Consistency in Storage

Technologist Benefits

• Acquire new, compare and display priors in room

• Instant bi-directional communication with imaging staff

• Short-term storage for call backs

• Built-in QC & service tools

• Flex Monitors for increased flexibility

User-friendly Interface – Workflow

Preview image is available for QC in 8 – 14 seconds

Full Array of Technologist Tools

Quick Zoom/Pan

Full Zoom/Pan

Region of Interest

Crosshairs

Magnification

Measurement

Window/Level

Radiologist Benefits

• Image Manipulation– Zoom, annotate, measure and magnification

tools

– Adjust contrast and brightness for better visualization of fine details

• Interpret digital images and compare to scanned in prior studies

• Customized how to view

R2 CAD for Mammography

Computer-Aided Detection

Calcification Marking

The system WILL mark:

• Clusters with three or more elements within 3mm

= < 3mm square

Each element is at or within 3mm

Calcifications

• What it does not mark– Small cluster with less than 2 elements– Clusters where each element is separated by

more than 3mm– Lead skin markers or clips

• Will occasionally mark– Calcified arteries– Cluster or rim benign calcifications– Crossing linear tissue

What Calcifications are Marked?

• R2 occasionally marks:– Calcified arteries

– Cluster or rim benign calcifications

– Crossing linear tissues

What Masses are Marked?

• R2 should mark:– Regions suggestive of masses/architectural

distortions

– Dense regions

– Regions with radiating lines

Mass Marking

For Masses the system will mark:

• Dense regions and regions with radiating lines

• The algorithm will weigh the degree of spiculation and degree of density

• Look for right/left asymmetry, as well as similarity between views

Mass/ Architectural Distortion

• What it does not usually mark:– Masses greater than 2.5 cm in diameter

• Will occasionally mark:– Ducts and tissue radiating from the nipple

– Inadvertent crossing of parenchymal tissue

– Well circumscribed masses

– Vague opacities, skin thickening or nipple retraction

Multiple Finding Correlation

• R2 uses a new shape to indicate a Malc mark:– Indicates a region containing mass and

calcifications

– Highly suggestive of malignancy

– Tends to be very specific

– Should be evaluated VERY carefully!

Anatomical Correlation

R2 uses three types of anatomical correlation to improve the algorithm performance• Orthogonal view similarity

• Contra-lateral breast asymmetry

• Multiple finding correlation (malc mark)

Mass marker

Calcification marker

Malc marker

R2 CAD Marks

Calc with low-prominence features

Mass with high-prominence features

Calc with neither high nor low prominence features

PeerView™ Digital

Calcification Mass Malc

LesionMetrics™

R2 makes additional information available for each CAD mark

May help the doctor understand what caused R2 to mark the region

Quantra V1.0

•Future Software Option – Not FDA Approved

Patient Comfort

• Slim tubehead and recessed face shield facilitates positioning

• MammoPad– Softness reduces discomfort from

compression– Warms the compression surfaces for skin

comfort– Reduces discomfort by 50% in 3 out of 4

womenMarkle study. Comfort and compression. SBI 2001, The Breast Journal 2004.

• FAST Paddle enhances patient comfort and prevents over-compression at the chest wall

Lower Patient Dose

• Tungsten x-ray tube with (rhodium (Rh) and silver (Ag) filtration)

• Silver is ideal filtration for penetrating large, dense breasts

• Same image quality as molybdenum x-ray tube, demonstrated in multiple clinical studies

• Smoother grayscale in images

• 30-40 percent less dose

– Tungsten dose: 1.2 mGy

– Moly dose: 1.6 mGy

Proprietary HTC® GridHigh Transmission Cellular Grid

• Integrated into the digital detector

• Cross-hatch design reduces scatter in X & Y direction

• Allows 70-80% transmission of primary beam

QC of Digital Mammography

Image Quality In Digital Mammography and Quality Control Tests

• The quality of an image is determined by several factors. The most important are:

• Contrast: the ability to distinguish 2 objects that have different attenuation properties.

• Resolution: the ability of an imaging system to accurately reproduce all the fine details of the anatomy.

• Noise: An undesirable and unavoidable interference signal that is not part of the object being imaged.

Image Quality and the Tests

• Operators follow manufacturer’s quality control tests.• ACR is working on a QA/QC manual for digital

mammography.• FDA/MQSA approves each Quality Control manual.

Manufacture’s QC manuals need to be approved if there have been changes made to their QC tests.

Quality Control: Image QC and Equipment QC

• Measured through:– Modulation Transfer Function (MTF)– Detective Quantum Efficiency (DQE)

• MTF and DQE are more widely recognized as ‘true’ measurements.

– Line Pair Phantom = not so much.

With a new twist!

• Laser Printer Quality Control

• Softcopy Workstation Quality Control

• Artifact Evaluation: for the Laser Printer and Detector.

• Signal to Noise/Contrast to Noise

• Detector Flat Field Calibration

As with film/screen:In a facility where more than one technologist does mammography, one technologist should be assigned the responsibilities of quality control.

Other qualified individuals may perform specific QC tests, but they must be reviewed and evaluated by the designated QC technologist.

QC software programs

SoftCopy Workstation QC- WeeklyAssures consistency of brightness, contrast and image

presentation on SoftCopy Workstation (this is guided by the manufacturer’s recommendations)

Weekly Tests:•Display White Measurement•Display Black MeasurementMonthly:•Quality Level Measurement

Quarterly:•Uniformity Measurement

•Tests for gray scale visibility, uniformity and resolution characteristics.

•Print SMPTE (Society of Motion Picture and Television Engineers) Pattern

•Using densitometer, find density of:

•MD(40%)

•DD (40% - 10%)

•LD (90%)

•Plot these numbers on QC chart

Laser Printer QC: Weekly or Daily(based on manufacturer’s recommendations)

Assures consistency of printer performance

Sample SMPTE Pattern

Artifact Evaluation- WeeklyAssures the image is free of undesirable artifacts

•Image the 4 cm acrylic block (be sure it’s clean)

•No compression paddle should be installed

• Manual exposure- MoRh or Rh/Ag Filter with various kVp and mAs exposures

•Window /level to appropriate level

•Bring up Mag Box, and “roam” the image, looking for any artifacts

•Chart results

Artifact Evaluation, continued

•If artifacts are visible:

•Rotate acrylic block and repeat the test

•If the artifacts move with the block, the artifact is present in the acrylic, and does not present a problem with the system

•If the artifact persists:

•Ask a medical physicist to perform his/her artifact analysis test

•Artifacts must be eliminated prior to performing clinical patient exams

Signal to Noise/Contrast to Noise Measurements- Weekly

Assures consistency of Digital Image Receptor

•Image ACR Phantom (with acrylic disk in place)

•Center phantom at chest wall

•Compression paddle just touching

•Auto Time exposure

C

H

E

S

T

W

A

L

L

First ROI

Second ROI

• Draw an ROI inside the acrylic disk – record Mean Value

• Click on ROI Tool

• Drag the same ROI towards the chest wall, next to the disk, and record the Mean, std, and SNR

SNR/CNR, continued

SNR/CNR, continued

Logging the results:

•Plot the SNR value from beside the disk on the QC Chart

•To determine the CNR to plot on the chart:

•Subtract the Mean Value of the ROI BESIDE the disk from the Mean Value of the ROI OVER the disk (this is the Contrast)

•Divide the Contrast by the std from the ROI Beside the disk (this is the CNR)

•Plot the CNR on the QC Chart

•Some manufacturers have ‘auto’ calculations.

SNR/CNR, continued

Logging the results:

•Plot the SNR value from beside the disk on the QC Chart

•To determine the CNR to plot on the chart:

•Subtract the Mean Value of the ROI BESIDE the disk from the Mean Value of the ROI OVER the disk (this is the Contrast)

•Divide the Contrast by the std from the ROI Beside the disk (this is the CNR)

•Plot the CNR on the QC Chart

•Some manufacturers have ‘auto’ calculations.

Phantom Image - Weekly

• The Phantom Image may be printed or scored on the softcopy workstation.

• Chart results.• If printing the phantom:

– The same density rules apply to this printed Phantom as your normal film/screen Phantom

Detector Flat-Field Calibration –Weekly

To assure detector is calibrated properly

• Creates new, clean background for digital images.

• Follow on screen instructions• Be SURE there is nothing but the acrylic on

the detector during this procedure!– Any additional object would get “burned into”

the detector

Flat-Field Calibration, continued

•The system is “adjusting” the pixels to behave in the same manner

•Images are not being evaluated during this procedure

Additional QC Information

• ACR website for accreditation in digital mammography:– www.acr.org– MQSA links available– QC charts for the different vendors tests and

requirements– For now, follow manufacturer’s recommendations.

ConnectivityDICOM

Digital Imaging Communication of Medicine• Standard used for transferring images and data

among PACS devices

PACSPicture Archiving Communication System• Common storage/sending environment for images• Communication between the HIS/RIS &

Selenia… Modality Work list, pre-fetching and routing prior studies

Connectivity

CADComputer Aided Diagnosis

HL-7How hospital systems communicate• Admissions, discharges• Lab, x-ray orders• Scheduling• Mainly patient data

Some DICOM Connectivity Options

• DICOM Receive

• DICOM Query / Retrieve

• DICOM Store

• DICOM Print

• Allows display of other DICOM images

– Ultrasound, MRI, CT, CR

Putting It All Together

Approved DICOM Compatible Printer

Workflow Manager

Softcopy Workstation

DVD Archive

Transition to Digital Mammography

• Your new best friend in Mammography is no longer the Processor Service Engineer.

• IT is everything!• Complete dependence

on IT/PACS for transfer and delivery of all images, scanned documents, patient reports, orders, etc.

The Future of Tomosynthesis

Normal Mammogram

Tomosynthesis*3-D Visualization of Breast Tissue

• Multiple views reconstructed into 3D image

• Helps solve tissue overlap problems

• Lower recall rates - Improved detection

Tomosynthesis Slices

* Works-in-progress, not approved for sale in the USA.

Why Tomosynthesis?

• Elimination of overlapping structures and shadows

• Clearer lesion margins

• Potential for reduced call-backs

Incident X-rays

Objects being imaged

2-D imageImages superimposed on image

Conventional 2-D Imaging

Tomosynthesis AcquisitionImage from multiple angles

Exposure #1 Exposure #6 Exposure #11

Incident X-rays

Objects being imaged

2-D raw data images

Tomosynthesis Reconstruction

Appropriate shifting and adding of raw data reinforces objects at specific height

Height 1 Height 2