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Digital Breast TomosynthesisFundamentals

Digital Breast TomosynthesisFundamentals

For nearly half a century GE Healthcare has worked closely with numerous breast imagers with a single objective in mind:

To develop accurate, efficient and patient friendly breast imaging solutions to enable earlydetection & early health.With the first launch of a digital flat panel systemin the year 2000 GE Healthcare opened the doorsto a range of new technologies and tools formammography.

Digital mammography has become the new standard of care for early breast cancer detection (1,2).Despite all the advantages that have been gainedin the past years with digital mammography, thereare still some limitations in today’s approach.

It has been documented that around 22% of the malignant lesions, especially in dense breasts,are missed today (3). One possible reason for that could be that lesions or other anatomicalstructures may be hidden by superimposed tissues and could limit the radiologists’ ability to detect them.

By utilizing volumetric imaging that is alreadyused in other modalities such as CT and MR, the images produced could help to avoid theproblem of the overlapping tissue.

Digital Breast Tomosynthesis (DBT) is an exampleof a volumetric breast imaging technology.

Tomosynthesis takes a series of low dose X-rayexposures at different angles. Each exposure inthe series is called a projection image. The generated data is reconstructed and displayedas multiple images of different planes of thebreast, with all the projection images contributingto each plane.

GE Healthcare is working with numerous worldwideclinical researchers in order to evaluate the potential benefits of this technology.

Availability of GE tomosynthesis technologydepends on the ongoing clinical trials, to then proceed accordingly with the appropriate localregulatory authorities, e.g. US FDA, CE marking.

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Figure 1: In Standard 2D mammography > Lesions can be hidden by superimposed normal structures.

Normal parenchyma

Abnormal lesion

Tomosynthesis is a three-dimensional imagingtechnology (3D imaging) that uses a low dose limited angle around the standard compressedbreast, in order to generate a series of tomo-planesplanes that are virtually free of overlapping tissue.

The acquired projection images are processedelectronically in order to reconstruct a 3Drepresentation of the entire breast, formed by a set of tomo-planes.

Each plane represents a virtual cut of the compressed breast, parallel to the detector, wherethe in-plane structures are sharply rendered andthe objects from the other planes are blurred out.

Figure 2 shows two different tomo-planes, onethrough the spherical object and the second onethrough the cubic object. Both are reconstructed byshifting and adding the projection images. This describes the basic principle of digitaltomosynthesis.

Tomosynthesis Theory>

Figure 2: Objects at different planes in the compressedbreast appear differently through the projections of theimages.

Figure 3: Tomo-plane reconstruction theory.

Projection Imagesare shifted andadded, the result is an object enhancementfor a selected plane.

Tomo-plane 1 and 2.

Low dose X-ray sweep

Multiples projections

Compressed breast

Projection images

Object 1 Object 2

While the basic principle of tomosynthesis is the same for every device, the technologies that have been developed and implemented by various companies and researchers may be different, impacting the image acquisitionprocess.

It has been shown (4) that there are some key technicalparameters that have a strongeffect on the image quality oftomosynthesis:

1. Step & Shoot tube motion

2. Sweep angle range and number of projections

3. Detector performance at low dose

4. DBT anti-scatter grid

5. ASIR DBT reconstructionalgorithm and review tools

1. Step & Shoot tube motionTo preserve microcalcification’s sharpness and to avoid image blur, step and shoot tube motion isthe natural choice, with the tube making a completestop for each exposure. It was demonstrated thatstep & shoot tube motion provides higher peakcontrast for microcalcifications than the classicalcontinuous tube motion14.

2. Sweep angle range and number of projections:It is essential to determine the right parametersfor an angle aperture because a very wide anglemay produce blurs in microcalcifications, and avery narrow one will preserve microcalcificationsbut with a poor separation of glandular overlapsand masses. Investigations have demonstratedthat an angular sweep of 25 degrees and a seriesof 9 low dose exposures are well suited for SenoClaire (the brand name of GE BreastTomosynthesis) [5,6].

3. Detector performance at low dose In order to keep the patient dose as low as possiblewhen performing a Tomosynthesis examination it isnecessary to choose an efficient detector, whichhas a high DQE at low dose. GE Healthcare’s detector offers a high DQE at low dose allowing

the visualization of small objects such as microcalcifications. The resulting high SNRand the high speed read out capabilityof the detector allow the system tooperate at the same small pixel size(100µm) as in 2D digital mammography.

A lower DQE detector would require other process to overcome signal/noise limitations, such as the addition of pixelsor “binning”. The advantage in signallevel is offset by a trade-off in spatialresolution because of doubling pixelsizes, compared to 2D.

Clinical Approaches>

Figure 5: 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) (5). Based on GE internal testing.

Tube column rotates over an angle

Stationarycompressedbreast atMLO position

Figure 4

GE’s detector offers a high DQE at low dose thatdoes not require this kind of tradeoff and thereforeit allows the visualization of small objects such asmicro calcifications. In addition it offers a largeoperating temperature range. GE Healthcare’s a-Si/Csl independent conversiontechnology provides the same detector scanning at100 micron (pixel size / resolution) for both 2D and 3D.

4. DBT anti-scatter gridX-ray scatter is equally detrimental to image qualityin 2D and 3D, particularly for large breasts, as itdecreases the signal difference-to-noise ratio (SDNR)of projection views. Just as in FFDM, SenoClairecomes with an anti-scatter solution designed fortomosynthesis. The DBT compatible grid both

enhances image quality for thick breast in 3D andgreatly contributes to preserving the same dose as 2D.

5. Reconstruction algorithmGE Healthcare uses an iterative reconstructionalgorithm, called ASiR DBT. This reconstruction yieldsimages that are FFDM-like, easy to interpret, andwith reconstruction times equivalent to transfertimes. This reconstruction method has a mechanismthat positively impacts overlapping microcalcificationconspicuity versus classic Filtered Back Projection(FBP) algorithm.

Not all the tomosynthesis systems are built &designed the same way, they work in differentways, and clinical outcome may be different.

GE Hologic

Tube motion mode Step & Shoot Continuous

Stationary or moving detector stationary moving

Sweep angle 25° 15°

Number of projections 9 15

Detector a-Si/Csl Se

Resolution 100 x 100 µ 70 x 70 µ pixel binning

Tube Mo/Rh Tungsten

Tomosynthesis views 3DMLO+2DCC 3D + 2D

Factors impacting Digital Breast Tomosynthesis (DBT) Image Quality

FFDM IQ Drivers Additional DBT IQ Drivers

+Step and Shoot tube motionSweep Angle range and Number of projectionsDetector performance at low dose Distance between tomo-planes Reconstruction AlgorithmDBT anti-scatter grid

Radiation DoseBeam QualityDetector Properties2D Image ProcessingImage Display

As tomosynthesis is multiplying the number of images per view, (for a 60mm breast thicknessat one image every 0.5 mm, the total number ofimages for one view will be 120), it is extremelyimportant to evaluate and design the Workflow.

Some additional important requirements arerelated to the workflow and productivity of tomosynthesis.

• Positioning and acquisition time • Reading time • Data storage & transmission • Reimbursement

� Patient positioning and acquisition timeThe positioning of the breast in tomosynthesis is performed the same way as in today’s mammography (2D) procedure. A very efficientprocedure is the following:

• The breast is compressed in a normal MLO position.

• The tube rotates over an angle of 25 degrees around a stationary detector

• The X-ray tube applies 9 low dose exposures • The data from the 9 acquired projections are immediately transmitted to the reconstruction computer, where the breast volume is reconstructed in 0.5 mm spaced tomo-planes, which are sent to the radiologist's review workstation.

� Data storage & transmission Both the online storage capacity and the long-term storage capacity need to be evaluatedwhen performing tomosynthesis applications as the image volume is multiplied (> 10 times). The extended data set requires a fast datatransmission in order to enable an acceptablepreview and image storage time. GE tomosynthesisimages are compatible with major PACS providers(with local variability), allowing integration intoyour environment and helping you make optimaluse of your investment.

Figure 6

Summary and outlookWhile tomosynthesis clinical results indicate its potentialto enhance breast imaging, there are still many openquestions that require further investigation. For it tobe effective, usable and as safe as FFDM, some keychallenges must be addressed:

• Total patient dose• Angular sweep range and number of projections• Reconstruction time and image display• Workflow • Acceptable reading time• Storage requirements• Quality control for 3D.

Multi-center clinical studyGE Healthcare conducted a multi-center clinical trial with renowned breast radiologists, in order to evaluatethe tomosynthesis procedure.

GE Healthcare designed theSenographe with upgradabilityin mind, you can easilyexpand the system as yourneeds and capabilities grow.SenoClaire 3D breasttomosynthesis, stereotaxy, or SenoBright contrastenhanced spectral mammo-graphy are fully compatiblewith any SenographeEssential and SenographeCare. It’s an excellent balanceof precision and performance,so you can be confident inyour investment.

Normal 2D image

Figure 7: LMLO image(zoomed), Senographe2D image.

What does a tomo-plane look like?>

Tomosynthesis tomo-plane

Figure 8: LMLO image(zoomed), SenoClairetomo-plane.

Figure 9: Images from Oncological Institute of Veneto, Padova, Italy.

2D image Tomosynthesis tomo-plane (zoomed)

Figure 10

GE imagination at work

GE HealthcareChalfont St.Giles,Buckinghamshire,UK

www.gehealthcare.com

References

1.TriMark Publications, Mammography World Markets – Trends,Industry Participants, Product Overview, Market Drivers, TriMarkPublications 2005, Vol. TMRMAM05-0101.

2. Frost & Sullivan, European Women’s Healthcare Imaging Markets,H038-50, Frost & Sullivan 2005

3. Thomas M. Kolb, MD, Jacob Lichy, MD, Jeffrey H. Newhouse, MD,Comparison of the Performance of Screening Mammography,Physical Examination, and Breast US and Evaluation of Factors thatInfluence Them: An Analysis of 27,825 Patient Evaluations,Radiology 2002; 225:165–175.

4. Jeffrey W. Eberhard, Douglas Albagli, Andrea Schmitz, BernhardE.H. Claus, Paul Karson, Mitchell Goodsitt, Heang-Ping Chan, MarilynRoubidoux, Jeffrey A. Thomas, Jacqueline Osland, MammographyTomosynthesis System for High Performance 3D Imaging, DigitalMammography 8th International Workshop, IWDM 2006,Manchester, UK, June 2006, Springer-Verlag Berlin Heidelberg 2006.

5. M. J. Yaffe, L. E. Antonuk, Editors, Performance of Advanced a-Si /CsI-based Flat Panel X-ray Detectors for Mammography, MedicalImaging 2003: Physics of Medical Imaging, Proceedings of SPIE Vol.5030 (2003) © 2003 SPIE · 1605-7422/03.

6. Wu T., Stewart A., Stanton M., McCauley T., Philips W., Kopans D.B.,Moore R.H., Eberhard J.W., Opsahl-Ong B., Niklason L., Williams M.B.,Tomographic mammography using a limited number of low dosecone beam projections images, Med. Phys. 2003;30:365-80.

7. Bernhard E.H. Claus, Jeffrey W. Eberhard, Andrea Schmitz, PaulKarson, Mitchell Goodsitt, Heang-Ping Chan, Generalized FilteredBack-Projection Reconstruction in Breast Tomosynthesis, DigitalMammography 8th International Workshop, IWDM 2006,Manchester, UK, June 2006, Springer-Verlag Berlin Heidelberg 2006.

8. Daniel B.Kopans, MD., F.A.C.R. , Professor of Radiology HarvardMedical School, Senior Radiologist – Breast Division MassachusettsGeneral Hospital, Digital Breast Tomosynthesis.

9. Steven P. Poplack, Tor D. Tosteson, Christine A. Kogel, Helene M.Nagy, Digital Breast Tomosynthesis: Initial Experience in 98 Womenwith Abnormal Digital Screening Mammography, AJR 2007;189:616–623, 0361–803X/07/1893–616

10. Walter F. Good, Gordon S. Abrams, Victor J. Catullo, Denise M.Chough, Marie A. Ganott, Christiane M. Hakim, David Gur, DigitalBreast Tomosynthesis: A Pilot Observer Study, AJR 2008;190:865–869, 0361–803X/08/1904–865

11. Amarpreet S. Chawla, Joseph Y. Lo, Jay A. Baker, Ehsan Samei,Optimized image acquisition for breast tomosynthesis in projectionand reconstruction space, Med. Phys. 36, November 2009, 4859-4869

12. H. Souchay, R. Klausz, The impact of anisotropic sampling onreconstruction MTF in limited aperture tomosynthesis, Proc. SPIE2009, vol. 7258

13. R. Schulz - Wendtland, E. Wenkel, M. Lell, W. A. Bautz, T.Mertelmeier, Experimental Phantom Lesion Detectability StudyUsing a Digital Breast Tomosynthesis Prototype System, FortschrRöntgenstr 2006; 178: 1219-1223 © Georg Thieme Verlag KGStutttgart • New York, DOI 10.1055/s-2006-926933-OnlinePublication: 2006, ISSN 1438-9029

14. Eman Shaheen, Nicholas Marshall and Hilde Bosmans,"Investigation of the effect of tube motion in breast tomosynthesis:continuous or step and shoot?", Proc. SPIE 7961, 79611E (2011);doi:10.1117/12.877348

Glossary2D Two-dimensional CT Computed TomographyMR Magnetic ResonanceUS FDA US Food and Drug AdministrationCE Marking A mandatory European marking for certain

product groups to indicate conformity with the essential health and safety requirements set out in European Directives

3D Three-dimensionalDQE Detective Quantum Efficiency- A measure of the

dose efficiency of a detector SNR Signal to Noise RatioTomo-plane A cross-section in mathematical volume created

from the retro-projections of the projectionviews. They are the geometric planes for whichthe source motion and image shift compensateeach other exactly, yielding a focused imageonly from the points belonging to that plane.

FBP Filtered Back ProjectionFFDM Full Field Digital MammographyIQ Image QualityDBT Digital Breast TomosynthesisMLO Mediolateral ObliqueCC Craniocaudal

AcknowledgementsGE Healthcare would like to thank the following institutions for supplying the images included in this white paper:• Oncological Institute of Veneto, Padova, Italy

Data subject to change.Marketing Communications GE Medical SystemsSociété en Commandite Simple au capital de 85.418.040 Euros283 rue de la Minière – 78533 Buc Cedex France RCS Versailles B 315 013 359A General Electric company, doing business as GE Healthcare

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