Digital Mammography: Planning, Implementation, and Integration

Katherine A. Leslie, BS, RDMS, CRA, RT(R)(CT)

   ^*Radiology Projects & Applications Director, Central Oregon Radiology Assoc., P.C., Bend, Oregon. 
   Address correspondence to: Katherine A. Leslie, BS, RDMS, CRA, RT(R)(CT), Radiology Projects & Applications Director, Central Oregon Radiology Assoc., P.C., 1460 NE Medical Center Drive, Bend, OR 97701. E-mail: kleslie@cmillc.org.

Disclosure: Ms Leslie reports having no significant financial or advisory relationships with corporate organizations related to this activity.

ABSTRACT

The use of mammography in breast cancer screening and treatment has represented a critical advance in the management of this disease. Although screen-film mammography (SFM) was considered the gold standard in mammography imaging modalities until recently, full-field digital mammography (FFDM) is increasingly recognized as an attractive alternative to SFM. However, facilities are faced with important challenges in transitioning from SFM to FFDM from the perspective of acquisition costs, clinical issues, and changes in daily workflow. The transition from film-screen to digital mammography may be complicated, but the adoption of an FFDM could be attractive to many facilities that may benefit from the advanced analytic techniques made possible with digital images. This article will describe the current state of FFDM and address the challenges that facilities may encounter when transitioning to this technology.

Introduction
Breast cancer is a relatively common disease among American women and is the most common form of cancer in women aside from skin cancer.¹ The American Cancer Society predicted that approximately 178 480 new cases of invasive breast cancer would be reported and approximately 40 460 women would die from the disease in 2007.¹ Breast cancer has received a great deal of attention through targeted awareness campaigns, which has resulted in widespread screening for the disease with mammography. Through efforts like the American College of Radiology (ACR) Mammography Accreditation Program, which was instituted in 1987, the ability of mammography to detect breast cancer has improved considerably. Although the ACR program was initially voluntary, the Mammography Quality Standards Act (MQSA) required all mammography facilities in the United States to become accredited and certified by October 1, 1994. The percentage of facilities receiving accreditation on their first attempt increased from 70% between the years 1987 and 1991, to 88.3% in 2003, suggesting considerable quality improvement since the introduction of these standards.²

Although improvements have been made with time, the screen-film mammography (SFM) modality is now fully mature, and new technologies are needed to advance the ability to detect breast cancer. Prompt annual mammography has demonstrated the ability to decrease the mortality rate due to breast cancer by almost 50% in a population-based analysis that compared breast cancer death rates in 2 Swedish counties before and after the introduction of screening.³ It has been estimated that up to 20% of breast cancer is missed by mammography.⁴ Furthermore, the sensitivity of SFM decreases as breast density increases. The introduction of full-field digital mammography (FFDM) may therefore hold promise by increasing the power of mammography detection, including detection capabilities in women with dense breast tissue. This review will describe FFDM and discuss the potential pitfalls that facilities face in adopting this new modality.

Why Adopt FFDM?
This is a valid question for many facilities considering a transition from SFM to FFDM. Indeed, only 20% of mammography facilities had adopted FFDM as of May 2007.² However, the results of a recent pivotal trial may help clarify the role of FFDM for many facilities.

The DMIST Trial
The digital mammography imaging screening trial (DMIST) enrolled 49 528 women presenting for screening mammography. Enrollees underwent both FFDM and SFM procedures, and were subsequently followed to assess their likelihood of having breast cancer. Breast cancer status was determined by the results of a breast biopsy within 15 months of enrollment or a follow-up mammogram performed at least 10 months after study enrollment.⁵

The accuracy of SFM and FFDM were found to be statistically similar (P = .18) in the DMIST trial, but FFDM was significantly more accurate in detecting cancer in women aged younger than 50 years (P = .002), women with heterogeneously dense or extremely dense breast tissue (P = .003), and premenopausal or perimenopausal women (P = .002).⁵ The findings in the DMIST study have been key to the adoption of FFDM and have resulted in the widespread recognition of the value of this modality in the medical community. Whereas FFDM was not consistently reimbursed before the DMIST trial, the publication of these findings has resulted in expanded coverage policies with regard to FFDM, especially in women in whom FFDM has demonstrated the greatest value (women aged younger than 50, women with dense breast tissue, and premenopausal/perimenopausal women).

Mammographers should note that SFM provides images with better spatial resolution (17-20 line pairs/millimeters with SFM vs 5-10 line pairs/millimeters with FFDM). FFDM also requires a longer period of time for interpretation by the radiologist. The high costs associated with FFDM represent another hurdle for many institutions, especially as insurance providers are reluctant to reimburse providers at a higher rate for FFDM versus SFM, despite the higher costs associated with obtaining the equipment and staff time required to interpret the image. The Centers for Medicare and Medicaid Services (CMS) is currently one of the few organizations that is willing to reimburse organizations at a higher rate for FFDM versus their SFM rate, and CMS has suggested that their policies may change if FFDM is unable to demonstrate a consistent diagnostic advantage to SFM.

Advantages of FFDM
One of the most promising advances with FFDM is improved contrast resolution and the greater ability to image dense breast tissue. This advantage offsets the compromise of lower spatial resolution with FFDM. As mentioned previously, the DMIST study reported a significantly greater degree of accuracy with FFDM, compared with SFM, in patient populations with dense breast tissue.⁵

Other practical considerations make FFDM an attractive option for mammography facilities. The capture of digital images with FFDM means that staff can make use of digital reading tools. Also, unlike film images, digital images cannot be lost and are always available to view when needed by various specialists involved in the patient's care. There are other advantages with FFDM that should be considered, including the following:

• Improved validation of calcifications with greater contrast resolution
• Lower radiation dose
• SFM systems are fully matured; manufacturers may be reluctant to invest additional research and development into current systems
• Ability to digitally manipulate images
• SFM is the last film-based modality
• Efficiency of computer-aided detection (CAD) is possible
• Elimination of wet processing
• Ability to differentiate as a market leader
• Ability to reclaim valuable department space
• Platform for future applications

Getting Started
Mammography facilities contemplating a transition from SFM to FFDM should consider a total switch from an analog to a digital system to avoid the complications of having both, including the additional quality control (QC) measures required and the confusion that arises in determining which system should be used in imaging individual patients. For those facilities that do decide that a digital transition is right for them, the general decision-making process is summarized in the Sidebar.⁶

 

Evaluation of Current Systems and Facility Goals
It has been suggested that those involved in the planning process of transitioning a facility from SFM to FFDM should first consider the facility's existing equipment, infrastructure, capacity, and workflow. This evaluation can help planners determine the pace at which the facility can realistically convert from analog to digital imaging, and can also dictate which type of digital system best suits the needs of the facility. For instance, planners may have to decide whether their needs are best served by an existing computed radiography (CR) acquisition unit or if an upgrade to a direct digital radiography (DR) unit is warranted.⁶

The capacity of the existing picture archiving and communication system (PACS) should also be evaluated during the planning process, because the large file sizes created with FFDM will require substantially greater PACS capacity. Planners should also ensure that all aspects of the new FFDM system, including the acquisition unit and diagnostic workstations, are able to effectively communicate with the PACS. Finally, the facility's network bandwidth should be evaluated to ensure that the larger digital mammography images can be manipulated in an efficient manner. These considerations may require the facility to upgrade the PACS and systems network when transitioning to a digital environment.

Transitioning from SFM to FFDM may represent an important opportunity for a facility to evaluate its current workflow situation and determine processes that work, as well as areas for improvement. A team approach in tackling this evaluation is important, because all staff members can provide valuable feedback on current processes. All aspects of the facility's workflow should be evaluated, including patient scheduling and registration, image acquisition and processing, diagnosis, image interpretation, reporting, and billing. Processes that are effective can be transitioned to the workflow structure of the new digital environment, and processes that do not work can be phased out.⁶

The facility's goals in transitioning from SFM to FFDM should also be carefully assessed, because this could dictate the pace at which the facility transitions and the choice of system components.⁶ For instance, a facility that simply hopes to become more efficient with a digital system may have different needs than a facility that is aiming to grow its business by offering FFDM.

Computed Radiography vs Direct Digital Radiography Systems
Those choosing to adopt FFDM must first decide between a CR and DR FFDM system. The choice of FFDM system type largely depends on the patient volume of the mammography facility. The CR FFDM systems are lower in cost and can be sufficient for a low-volume facility. However, facilities experiencing larger patient volume should consider a DR FFDM system. Also, staff members should keep in mind that facilities may have trouble integrating existing CAD modalities if transitioning to CR FFDM. Other major differences exist between CR and DR that could impact a facility's decision in image acquisition technology.

Computed radiography systems require the use of a cassette for image acquisition. The image is captured in the cassette, which then requires several postprocessing steps before the resulting digital image is ready for view. In some clinical applications, a possible advantage to CR is the fact that the cassette-based system is more portable, which may increase its ease of use in imaging difficult areas.⁷ However, this is not a great concern in mammography, as opposed to imaging applications in trauma patients, for instance. Some radiologic technologists have reported repetitive motion injuries caused by handling the imaging cassettes on a daily basis.

Direct digital radiography systems digitally detect the image, which is immediately sent for view. No additional postprocessing steps are required. As a result, DR could reduce examination times and improve mammographer workflow efficiency. The use of a DR system could also reduce repetitive motion injuries that sometimes occur when technologists handle image cassettes on a regular basis over long periods of time.⁸ The higher cost of DR systems can be an important barrier to acquisition, especially for smaller facilities. However, large facilities with a high patient volume may realize economic benefits with DR as opposed to CR, despite the higher acquisition costs, due to improved efficiency, shorter examination times, and fewer repetitive motion injuries. Patients may also appreciate the reduced wait times with DR.

In terms of image quality, technologists have differing opinions as to the preferred acquisition system. Some claim that they obtain images of greater quality with CR, whereas others cite better image quality with DR.⁸ Facilities should therefore perform a careful review of their workload and anticipated growth if choosing between a CR and DR system, especially if the choice in system will have a sizable relative impact on their bottom line. Facilities should also evaluate the current state of their acquisition units, because those with older acquisition units requiring frequent service may consider an upgrade to DR an attractive option, whereas those with newer analog acquisition units may see a full overhaul to a DR system as unnecessary, especially if their patient volume is low.⁶

Vendor Evaluations
When choosing an FFDM system provider, facilities should consider the usual criteria when evaluating any equipment vendor. The evaluation process should include a site visit and an independent review of user feedback through a service, such as MD Buyline (available at http://www.mdbuyline.com/). In addition, the evaluation process should take the following factors into consideration:

• A demonstration of image quality with phantom images
• Service history with other clients
• Experience of the vendor's physicist staff
• Demonstration of interface capability, such as a digital imaging and communications in medicine conformance statement
• Image file size
• Costs of both equipment and anticipated service requirements

The facility should also carefully examine its overall goals in choosing a digital system. For instance, the goal of the facility may be to improve efficiency, create a more versatile filmless and paperless system that meshes with other existing modalities within the facility, or to grow the business and increase revenue.⁶ Once these goals have been identified, the facility planners can more effectively evaluate potential systems vendors.

Project Planning
Staff members involved in the transition from SFM to FFDM could also benefit from a comprehensive project planning document, created in a program such as Microsoft Project. This document should review all of the operational aspects of the transition and provide timelines for installation planning, the creation of appropriate interfaces and workstations, staff training, physics evaluations, and site remodeling.

The remodeling of a facility should take into account important considerations, including the placement of power outlets and network interfaces, the placement of technologist workstations, the creation of storage space for ancillary mammography equipment, laser printer interface or placement, and the aesthetics of the imaging rooms. Although heating, ventilating, and air conditioning considerations may not seem important initially, this architectural aspect can be critical due to the temperature sensitivity of the mammography equipment. In some cases, individual temperature controllers may be required in each room to avoid problems associated with temperature fluctuations.

When upgrading from an analog to a digital environment, a multidisciplinary team consisting of representatives from every relevant department is beneficial in evaluating workflow and patient capacity, 2 critical aspects of the planning process. Important workflow considerations should include patient scheduling (for both screening and diagnostic visits), patient registration, image acquisition, image processing, the existing CAD system, image interpretation, reporting, and billing in the existing analog environment.⁶

Notification of Governing Bodies
The facility must notify appropriate governing organizations when transitioning from an analog to a digital system. A room shielding plan should be in place to control the exposure of radiation outside of the imaging room. Radiation protection laws (which vary by state) should be consulted when transitioning the facility. Although lead shielding is not required for mammography suites, facilities should consult their state's guidelines, because some states require a room shielding evaluation by a physicist prior to operating mammography equipment. On the national level, the facility should ensure that ACR accreditation is maintained by submitting a New Mammography Facility Application (available at http://www.acr.org/). During the transition process, facilities must also comply with MQSA requirements. A review of the MQSA requirements in transitioning from SFM to FFDM is also available online from the ACR Web site.⁷

ACR Accreditation Process
Once the FFDM system has been installed, the accrediting body conducts a review to determine the fitness of the new facility and the ability of the staff to manage the equipment. Facilities in many states are accredited by the ACR. As part of the ACR accreditation process, the facility must undergo a detailed physics evaluation before having patients imaged with the new equipment. The facility must be prepared to print phantom images on a mammography quality laser camera during this evaluation. The facility is then responsible for sending the application fee and faxing a physics pass/fail form to the ACR to obtain accreditation. Unlike new facilities, existing facilities that are transitioning from analog to digital equipment do not need to wait 4 days before patient imaging, but they are responsible for obtaining confirmation that the ACR has received the application and that the ACR has transmitted the application to the CMS. The time frame in which the facility is up for reaccreditation dictates whether the facility is required to submit images obtained with the FFDM system.

Mammographer Readiness
Mammographer staff members who have not previously worked with digital equipment should be informed and consulted on important workflow issues during a transition to FFDM. If the new system includes a PACS, staff training will be required to familiarize mammographers with this type of interface. Mammographers should also be consulted to determine the best locations for technologist workstations. These communications could be effectively accomplished with a targeted in-service event during which the proposed setup of the new system is discussed. Training sessions provided by the systems vendor should also be scheduled for all mammographers. Although FFDM is associated with shorter examination times, facility administrators should be prepared to experience some degree of pushback from technologists if more daily appointments are scheduled compared with the scheduling required for SFM imaging.

Above all, mammographers will require structured, specialized training before using a new modality such as FFDM. Facilities should recognize that most dedicated mammographers performing SFM on a regular basis have not previously worked in a digital environment, and extensive training will be critical. Mammographers becoming familiar with FFDM will need adequate support in every step of the process to ensure that they are comfortable with the new equipment. Although the imaging system vendor frequently provides initial training services to facilities transitioning to FFDM, a dedicated staff member may be needed to provide internal support as the facility adopts the new modality.

Radiologist Efficiency
In transitioning to FFDM, facilities will also need to provide radiologist training, depending on the chosen modality for reading the studies. As with mammographers, radiologists are required to achieve at least 8 continuing medical education credits or training hours specific to FFDM before interpreting images obtained with this modality. Although radiologists may already be familiar with digital interfaces if a PACS system is already in place, they may still require training on the use of the digital reading equipment and tools. As an alternative to installing a PACS system, the facility may choose to contract with a vendor to install a soft copy workstation (SCW) to interface with the digital reading equipment in the reading room. In transitioning to a digital reading room, a cheat sheet of radiologist reading preferences is helpful to ensure an efficient use of the radiologist's time.

The handling of prior examinations and reports also needs to be addressed when transitioning to FFDM. If the facility chooses to continue to consult analog images of previous studies, a separate station will be needed to hang the analog images in the reading room. Otherwise, a CAD system equipped with the ability to digitize images can be used to digitize prior analog images, which could streamline the reading process. The radiologist's use of CAD is another important consideration. For example, planners have to determine if the CAD system design will require separate access of images or will allow for image overlay. The user-friendliness of system interface is another important consideration when installing the digital reading room. Regardless of the reading room setup, the facility should appoint a staff member, such as a technologist aid, to inspect the reading equipment each morning, make sure that prior images are available, and make sure that the CAD images are online.

Some radiologists may be reluctant to fully transition to reading digital images on a regular basis and adopt the use of electronic reading tools, as evidenced by the magnifying glasses that are still found in the reading rooms of FFDM facilities. In designing reading rooms, planners should be sure to provide radiologists with the tools that they will need to effectively manipulate and analyze the digital images. Tools to perform digital QC, including a monitor photometer, are also necessary in the reading room. Other considerations, such as labeling computer monitors according to resolution (3K vs 5K), may be helpful as radiologists familiarize themselves with the equipment and the need to view the digital images on 5K monitors.

Initially, the transition to FFDM will undoubtedly slow down the radiologist's workflow, which could contribute to their willingness to accept the new modality. The facility should therefore make every effort to understand the radiologist workflow and have resources available to maximize efficiency. This will reduce radiologists' resistance to the new system and improve overall efficiencies within the facility. To assist in the process of transitioning to FFDM and garnering staff acceptance of the new system, the lead mammographer should make an effort to understand every aspect of the imaging and diagnostic process so that they can be an internal educational resource and advocate for radiologic technologists and radiologists.

Understanding PACS Workflow
In facilities that do adopt a PACS interface, it is critical that radiologic technologists, mammographers, and radiologists understand the PACS workflow in handling images and having images move through the network. Technologist workstations may be set up to automatically send images to the PACS or reading station, and to automatically import images to the CAD system. Depending on the PACS, images and CAD may be published to the Internet for offsite viewing by referring physicians. While primary read images can currently only have lossless compression applied, different compression methods are possible for web or CAD formats. The PACS administrator should understand which method is applied when archiving images or CAD to the Internet. Depending on the PACS system, CAD may or may not be archived.

If a facility decides to transition to PACS when adopting FFDM, staff members should be careful to upgrade reading station equipment to handle the increased needs of the PACS, including greater mammography resolution and larger file sizes. This may include replacing computer hardware to increase RAM (random access memory) or replacing old monitors. Finally, systems planners should make sure that the bandwidth of the network used at the facility is sufficient to handle the increased demands of FFDM on the PACS.

Storage of Digital Images
Regardless of the PACS format, data storage becomes an important issue in mammography, as both the primary and digitized images represent large files. One digital mammography image can average in size from 40 to 60 megabytes (MB) when uncompressed,⁹ or 4 to 27 MB when compressed with a lossless format. Overall, digital mammography requires a disproportionate amount of data storage space,¹⁰ and administrators will need to address this issue in moving to a digital work environment. The storage of digital files is a much different issue than the physical storage of film images, and the PACS administrator should understand current storage needs and anticipate the additional capacity that will be needed to house files and add new storage capacity over time.

Data compression techniques have been proposed to increase the capacity of current data storage systems, including lossy (some loss of image quality) and lossless (no loss of image quality) image compression. Compression can also facilitate the sharing of files between facilities and referring physicians. Image compression has been validated as a clinically appropriate technique in radiologic applications.¹¹ In a recent study, investigators assessed the clinical utility of digitized mammography images that were compressed with the JPEG (Joint Photographic Experts Group) 2000 file compression technique. Images from 45 patients undergoing SFM were digitized and compressed in either lossless (with a compression ratio of 20:1) or lossy (with a compression ratio of 40:1) files. Radiologists were assigned to review both the original film images and digitized images in their assessment of the presence of a malignant mass. The investigators found that diagnostic accuracy was not significantly different between uncompressed images and compressed images, including lossy images compressed at a ratio of 40:1.¹² Image compression in lossy or lossless formats may therefore be a viable tool as PACS administrators face the challenges of increased storage needs in a digital environment.

Marketing a Facility with FFDM
In a competitive marketplace, it is important that mammography facilities have a marketing plan in place to communicate the availability of FFDM to referring physicians. An informational piece that describes the advantages of FFDM can be distributed to referring offices, and information about FFDM can also be included in patient communications. Breast cancer case managers and cancer treatment center managers can also be called on to communicate the advantages of FFDM. Finally, multidisciplinary professional conferences that focus on breast cancer management can be an important venue for marketing a facility that provides FFDM.

FFDM Equipment Evaluations, Annual Surveys, and QC
The US Food and Drug Administration (FDA) requires that FFDM facilities follow QC regulations as specified by the manufacturer to ensure that the equipment is functioning properly. Current FFDM manufacturers include General Electric, Lorad, Fuji, Fischer, and Siemens. As an illustration of typical QC practices, one system manufacturer dictates the following:

• Printing
  - Daily QC of laser printer, including artifact evaluation
  - Weekly printing of phantom images
• Monitor
  - Weekly evaluation of Society of Motion Picture and Television Engineers test pattern
• Weekly artifact evaluation
• Weekly evaluation of signal-to-noise ratio and contrast-to-noise ratio
• Biweekly flat field calibration
• Regular testing of compression thickness indicator
• Reading stations
  - Evaluation of phantom images
  - Photometer QC
  - QC of viewing conditions

In dictating proper QC measures, the ACR mirrors the US FDA requirements and suggests that facilities use data forms provided by the manufacturer. To comply with ACR QC requirements, a medical physicist must also complete ACR summary forms, including the MQSA Requirements for Mammography Equipment (checklist) and the Medical Physicist's Mammography QC Test Summary Form. Both of these forms are available through the ACR Web site (http://www.acr.org/).⁷

ACR Initiatives to Change QC Processes
Manufacturers currently publish system-specific QC measures because the MQSA final regulations were published in 1997 and mandated by all mammography facilities in 1999, before the introduction of FFDM. However, the ACR is currently working with systems manufacturers to publish a standardized QC manual, regardless of the system in use. According to the ACR, this process aims to "standardize and streamline QC tests, performance criteria, and frequencies across all systems."⁷ The proposed manual will apply to all manufacturers and equipment models. Prior to completion, a draft of the manual will be sent to equipment manufacturers for their input. When a final draft of the QC manual is completed, the ACR plans to apply to the US FDA for an alternative standard. Ideally, at the completion of this process, facilities will have the option of following the ACR QC manual or the manufacturer's QC guidelines to comply with MQSA regulations.

The ACR will also propose changes to QC processes that are currently dictated by most manufacturers. For example, the ACR will suggest that laser printer density consistency be tested on a monthly basis, citing ACR imaging network data demonstrating that these lasers rarely fail. Another ACR proposal is the testing of modulation transfer function/system resolution only in systems with moving parts (in CR systems) and only on a quarterly basis. The ACR will also propose an elimination of the darkroom fog test, as well as an elimination of annual testing of kilovoltage peak. As the diagnostic community becomes more familiar with FFDM, it is possible that fewer QC measures will be needed on a regular basis.

Transferring Digital Mammograms
According to ACR guidelines, a facility must be able to provide a hard copy image of final interpretation quality when transferring the image to another facility or specialist. Hard copy original images or lossless compressed electronic images are also allowed, if accepted by the receiving party. The facility may not charge for the first hard copy sent to the requesting party, but may charge for additional copies sent to the same party.

FFDM as a Platform for New Imaging Applications
Radiologists and other radiologic professionals are recognizing that FFDM may have the greatest impact as a platform for new breast imaging applications, exceeding its role in conventional mammography screening.

Digital Tomosynthesis
Digital tomosynthesis involves the collection of images as the X ray moves in an arc around the breast, creating a 3-dimensional image for analysis. The process delivers a radiation dose that is equivalent to that received during a conventional 4-view mammography examination. It is still unclear whether digital tomosynthesis will be most applicable as a screening tool or as a supplemental tool during the diagnostic workup in confirmed cases of breast cancer. Some have suggested that if digital tomosynthesis is used as a screening modality, the recall rate could be reduced by up to 40%.¹³

Despite the promise of this new imaging modality, important hurdles still exist that may impede its acceptance. One of the greatest barriers to adoption of this modality may be the file size of the resulting image, which can be as large as 1 gigabyte. Data handling and storage would become a major issue in facilities hoping to integrate digital tomosynthesis. Also, longer interpretation times may be required with the resulting images. The high costs of digital tomosynthesis will also be prohibitive to many facilities considering the technology, especially since there is currently no allowable reimbursement for these studies. However, there may be cases in which facilities using FFDM systems can upgrade to digital tomosynthesis.

Contrast-Enhanced Digital Mammography
Contrast-enhanced digital mammography may represent a further enhancement in screening options, particularly for patients with dense breast tissue. The use of a contrast enhancement agent may be useful because cancerous lesions are often associated with a higher degree of vascular activity, or angiogenesis, than the surrounding tissue. In one study of the use of contrast agent with digital imaging in patients with dense breast tissue, this modality was shown to be effective in lesion identification.¹⁴ Contrast-enhanced digital mammography has been successfully used in conjunction with digital tomosynthesis to improve the characterization of the morphology and vascular characteristics of cancerous breast lesions.¹⁵ Contrast agents have also been used in conjunction with magnetic resonance imaging to detect the angiogenesis associated with cancerous lesions.¹⁶ Additional experience will be required before contrast-enhanced digital mammography is widely adopted in clinical practice.

Dual-Energy Subtraction Mammography
Dual-energy subtraction mammography is a process by which low-energy and high-energy X-ray images are acquired and compared so that the clutter of background tissue can be canceled out, leaving a more defined image of a lesion. This method is especially promising in detecting microcalcifications, which may be obscured by surrounding tissue structures in conventional imaging studies.¹⁷ New contrast agents, such as those containing zirconium, have been investigated to improve the detection capabilities in dual-energy subtraction mammography.¹⁸ Also, a single-shot dual-energy subtraction mammography technique has also been developed that may eliminate the need for multiple exposures and reduce motion artifacts.¹⁹

Fusion of FFDM with Ultrasound and Positron Emission Tomography
Patients with dense breast tissue may also benefit from the use of ultrasound studies coupled with digital mammography.²⁰ Ultrasound has been primarily evaluated in younger women with denser breast tissue. A meta-analysis of various screening modalities found that ultrasound was more sensitive but less specific than mammography and may therefore increase the likelihood of false-positive results.²⁰ Nevertheless, ultrasound may provide additional diagnostic strength when coupled with FFDM in appropriate patients.

Positron emission tomography (PET) has also been used to stage cancer and monitor treatment response.²¹ The use of PET with fluorodeoxyglucose (FDG) has been especially promising in predicting the aggressiveness of a tumor that has been identified through mammography, and in providing additional diagnostic information in patients with ambiguous mammography results.²² In FDG-PET imaging, the amount of FDG uptake correlates with histologic grade and tumor aggressiveness, and may therefore assist in prognosis. FDG-PET is also useful in predicting lymph node involvement prior to surgery.²² The use of PET technologies in addition to FFDM has the potential to provide a more accurate clinical picture and assist in overall patient management.

CAD Subtraction
Other digital techniques are also on the horizon to improve the diagnostic capabilities of mammography. The use of CAD has already demonstrated the ability to improve the sensitivity of mammography in detecting cancer, but studies have not definitively determined that CAD offers improved specificity.²⁰ The use of CAD subtraction, which is the comparison of CAD marks on digital mammography images with those from previous digitized studies, is now being investigated. CAD subtraction and similar techniques can maximize the ability of mammography to detect cancer.

PACS and Digital Mammography Enhancements
Additional enhancements to current systems are on the horizon and will improve workflow for all mammography staff members. For instance, although digital mammography images can only be read on 5K monitors at this time, the US FDA is reviewing the use of 3K monitors to view these images by at least one PACS vendor. The US FDA is also reviewing the lossy compression of digital mammography files, which would save considerable storage space. Finally, facilities are investigating the feasibility of digitizing and discarding images from prior studies to cut down on analog storage requirements.

Conclusions
Digital mammography represents a promising new modality in the detection and management of breast cancer, especially among women with dense breast tissue. As FFDM improves with clinical experience, this technology has the potential to considerably streamline workflow and reduce physical storage requirements in mammography facilities burdened with the ongoing need to rely on hard copy film images. The availability of digital images also facilitates the use of CAD in image analysis. FFDM may still provide the greatest clinical benefits when combined with other advanced modalities, in applications such as digital tomosynthesis, contrast-enhanced digital mammography, and dual-energy subtraction mammography. The expansion of current PACS applications with digital mammography may also provide an opportunity to streamline workflow and reduce storage requirements. As other imaging technologies have transitioned from analog to digital, FFDM has the potential to eventually replace SFM as the standard of care in the screening and management of breast cancer.

Additional Resources
Professionals interested in additional information on digital mammography are encouraged to access the following resources:

National Cancer Institute: Digital vs. Film Mammography in the Digital Mammographic Imaging Screening Trial (DMIST): Questions and Answers
http://www.cancer.gov/newscenter/pressreleases/DMISTQandA

MQSA and Accreditation for Full-Field Digital Mammography—Everything You Need to Know in 1⁄2 Hour
http://www.acr.org/accreditation/mammography/rsna07presentation.aspx

Online Radiology Resources at RTstudents.com
http://rtstudents.com/

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