New Technological Advancements in Breast Imaging

Karen S. Bubb, AS, BSRT, RT(R), RVT, RDMS

   ^*Manager, Outpatient Ambulatory Imaging Center, Oklahoma City, Oklahoma.
    Address correspondence to: Karen S. Bubb, AS, BSRT, RT(R), RVT, RDMS, Manager, Outpatient Ambulatory Imaging Center, 1111 N Lee, Suite 334, Oklahoma City, OK 73103. E-mail: KarensBubb@cox.net.

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

ABSTRACT

New technological advancements in breast imaging modalities are improving image quality and enhancing the diagnostic accuracy of breast cancer detection, staging, and treatment. The American Cancer Society's most recent breast cancer screening guidelines recommend an overlapping approach for high-risk patients by using dual modalities in the screening process. Studies indicate that using a redundancy approach to breast cancer screening in high-risk patients by incorporating dual modalities in the screening process has proven beneficial in improving early detection and long-term survival rates. The addition of new technological advancements in each imaging modality include breast tomosynthesis in mammography, sonoelastography and computer-aided detection in ultrasound, diffusion-weighted and apparent diffusion coefficient magnetic resonance imaging, nuclear medicine scintimammography, positron emission tomography combined with computed tomography (CT), dynamic CT perfusion, and cone beam breast CT. A brief overview of breast cancer, the existing breast imaging modalities, and the new technological advancements are presented.

Introduction
Breast cancer is the most common cancer that affects women; however, it is not exclusive to women. Men can develop breast cancer as well. According to the American Cancer Society (ACS), the incidence rates of invasive breast cancer began to decrease for the first time in the year 2000. Conversely, the incidence rates for noninvasive breast cancers increased. The change in statistics is attributed, in part, to the increase in the availability of mammography and subsequent increase in the number of patients who consistently participated in yearly screening mammography examinations. As the number of screening mammograms increased, the result was favorable for earlier detection of noninvasive breast cancers prior to tumor invasion. The overall death rate from breast cancer has been declining since 1990 largely due to early detection and improvements in breast cancer staging and treatment.¹

Recent technological advancements in breast imaging modalities are continuing to improve image quality to enhance the diagnostic accuracy of breast cancer detection, staging, and treatment. The ACS recently updated their breast screening guidelines by recommending an overlapping approach for high-risk patients using dual modalities in the screening process. Breast screening typically begins with mammography and can be expanded to ultrasonography and/or magnetic resonance imaging (MRI) in high-risk situations. Once breast cancer is detected, further imaging with nuclear medicine, positron emission tomography (PET), and computed tomography (CT) can be used as needed. Many facilities are accumulating a robust collection of breast imaging equipment to enhance diagnostic, staging, and therapeutic accuracy. A brief overview of breast cancer, the existing breast imaging modalities, and the new technological advancements in each modality is presented below. It is important to note that the information presented is a basic overview. The specific aspects of each type of breast cancer, the existing breast imaging modalities, and the newest technological advancements are far beyond the scope of the information provided here. Further information can be found in the references provided.

Breast Cancer and Precancerous Conditions
In order to appreciate the rationale behind the fervent quest for improved breast imaging technology, it is important to grasp a basic knowledge about the most common types of breast cancer, including precancerous conditions and high-risk markers. This information will provide a better understanding about the challenges each cellular classification can present in the imaging arena.

Breast cancer develops when epithelial and/or myoepithelial cells in the breast change and grow abnormally forming a tumor. There are several different cellular classifications of breast cancer and each one presents its own diagnostic challenge. Certain cellular types are much more difficult to detect with current conventional imaging modalities, which is why some breast cancers seem to be more elusive than others. For this reason, researchers continue to develop more methods to improve breast imaging and subsequent breast cancer detection and treatment.

Once breast cancer is diagnosed, determining the extent of breast cancer invasion is very important in breast cancer staging and management. Multicentric breast disease indicates the breast cancer has spread to other areas of the breast and additional tumors have been located at least 5 cm from the primary tumor or it has extended to different quadrants of the same breast. Multifocal breast disease indicates that additional tumors have been located within the same quadrant and/or ductal system and are less than 5 cm from the primary cancer.² Multifocal lesions are also referred to as tandem lesions when they present in a chain or row pattern with small tumor bridges connecting them. Contralateral extension indicates that the breast cancer has spread and has invaded the opposite breast.

Ductal carcinoma in situ (DCIS), also called intraductal carcinoma, is the most common noninvasive type of breast cancer. It makes up approximately 80% of noninvasive breast cancers.¹ DCIS originates in the lactiferous (milk) ducts of the breast. The term "in situ" indicates that the cancer has not spread outside of the basement membrane where it originated; therefore, it is considered noninvasive. DCIS is categorized into histologic subtypes based on architectural pattern, nuclear grade, and necrosis. The 2 most common subtypes are comedocarcinoma and noncomedocarcinoma (cribriform, micropapillary, and solid types).³ Typically, DCIS is non-palpable (cannot be felt) in its early stages.⁴ A hallmark sign of DCIS is the formation of certain patterns of microcalcifications, which can be detected on a mammogram in women older than 50 years more than 90% of the time. For this reason, screening mammography plays a very important role in early the detection of DCIS prior to tumor invasion and mass formation.⁵

Lobular carcinoma in situ (LCIS), also called lobular neoplasia, is an abnormal growth of cells found in the milk producing lobules of the breast. It is different from DCIS because DCIS is found in the ducts of the breast rather than the lobules. LCIS is considered to be a high-risk indicator or marker for potential development of invasive breast cancer later in life.⁶ A more severe form of LCIS called pleomorphic LCIS is considered to be a noninvasive breast cancer, comparable to DCIS in breast cancer staging. The term pleomorphic indicates that similar cells have taken on distinctly different forms.⁷ LCIS is less prevalent than DCIS and comprises less than 10% of high-risk or noninvasive breast cancers.¹ LCIS is an elusive neoplasm and is often not detected by conventional mammography, sonography, or even MRI. It is most often diagnosed by the pathologist microscopically as an incidental finding from a biopsy that was conducted for another reason.⁸ The ACS indicates that once LCIS is diagnosed, the patient has a 20% to 40% chance of developing a future invasive breast cancer. Therefore, close monitoring of the patient is advised. Some patients are prescribed a medication called tamoxifen that can reduce the risk of developing an invasive breast cancer later in life by 50%, whereas other patients choose prophylactic bilateral mastectomies to try to circumvent a future occurrence.⁹

Invasive ductal carcinoma (IDC), also called infiltrating ductal carcinoma, is the most common invasive form of breast cancer, representing approximately 80% of all invasive breast cancers. The term "invasive" indicates that the breast cancer has spread into the surrounding tissues beyond the basement membrane of the duct in which it originated. Once it becomes invasive, it has the potential to metastasize (spread) to other parts of the body through the lymph system or bloodstream.¹⁰ Early IDC lesions may or may not be palpable. For this reason, routine screening mammography is highly recommended. When an IDC lesion is palpated during a clinical breast examination (CBE) or breast self examination (BSE), it often presents as a firm, non-mobile mass. Skin changes, such as skin dimpling, discoloration in certain areas, and skin thickening, may also be apparent.¹¹ Mammographic signs of IDC lesions usually include architectural distortion, dense spiculated masses (masses with multiple spiked edges), and groups or clusters of microcalcifications.¹² Patients with dense breast tissue on mammography pose a significant imaging challenge due to the potential risk of the dense breast tissue camouflaging a small cancer.

Invasive lobular carcinoma (ILC) represents less than 15% of invasive breast cancers.¹³ Early ILC lesions are often not palpable during CBEs or BSEs and are often occult (not detected or visualized) by screening mammography alone. Even when an ILC nodule is palpable during a CBE or BSE, in some cases the ILC lesions can resemble normal fibroglandular tissue on mammography and sonography.¹⁴ Microcalcifications are often not observed in ILC lesions. For this reason, statistical analyses indicate that mammography's sensitivity to detect ILC ranges from less than 60% to 80%, whereas sonographic sensitivity for detecting ILC is less than 70%. Dynamic MRI of ILC typically demonstrates heterogeneous enhancement and a specific mass formation may or may not be visible.¹³ When ILC lesions are eventually identified and diagnosed, they are usually larger than other types of breast cancers. Because they are found at a later stage, the result is often a poorer prognosis. ILC is more likely to metastasize to the contralateral breast.

There are some rare and uncommon histologic subtypes of invasive breast cancer, such as tubular, mucinous (colloid), papillary, medullary, and inflammatory. Each histologic subtype provides important prognostic and predictive data for breast cancer management.¹⁵  

The presence of precancerous, proliferative breast disease is also very important to understand. The presence of ductal and/or lobular epithelial and/or myoepithelial hyperplasia indicates that there is an increased presence of multiple cells with mild irregularities in their shape. When these structural irregularities progress to display various characteristics that are similar to the cells seen in a carcinoma in situ, they are classified as atypical hyperplasia and should be considered high-risk markers for the potential development of breast cancer.¹⁶

Papillomatosis is classified as a benign condition in which epithelial cells in the lactiferous ducts grow on small stalk-like strands of connective tissue forming nodules similar to a wart. An overgrowth of abnormal epithelial cells growing on the stalks can lead to atypical hyperplasia and/or carcinoma in situ. A standard symptom of benign papillomatosis is the occurrence of spontaneous clear or cloudy nipple discharge. More worrisome symptoms, such as bloody nipple discharge, can indicate the manifestation of atypical hyperplasia or even DCIS.¹⁶ Juvenile papillomatosis, also termed "Swiss cheese disease," is characteristically found in women aged 20 years or younger. It is usually limited to a small area of the breast and can lead to atypical ductal hyperplasia and/or carcinoma later in life.¹⁷

Phyllodes tumor or cystosarcoma phyllodes is a leaf-shaped tumor composed of connective tissue (stroma) and epithelial tissue. They typically present as rapidly growing breast nodules, with the majority occurring in patients between the ages of 40 to 50 years. Phyllodes tumors can be classified as benign, borderline, or malignant depending on the margins of the tumor and the connective tissue characteristics. Sharp margins with minimal stromal atypia indicate a benign phyllodes tumor, whereas malignant tumors are characterized as having poorly defined, infiltrating borders with marked stromal atypia and overgrowth.¹⁸

There are several factors that can elevate a person's risk of developing breast cancer. These risk factors include age, race, gender, menstrual cycle history, hormone status, parity related to childbirth, genetic predisposition (the presence of BRCA1 and BRCA2 mutated genes), family history, personal history of certain breast conditions or breast cancer, exposure to certain drugs and/or radiation, alcohol consumption, obesity, diet, and physical activity. All risk factors should be taken into consideration by the patient's clinician when determining appropriate breast cancer screening procedures for each patient. In 2007, the ACS updated their breast cancer screening recommendations. The ACS now recommends that a woman aged 40 or older with a lifetime risk of less than 15% should have a screening mammogram every year. Women with a lifetime risk greater than 20% should have a screening mammogram and screening breast MRI every year.¹⁹

Imaging Modalities
Mammography
Mammography is an imaging modality of the breasts using low-dose X rays. Conventional analog mammography (also called film-screen mammography) is performed using special screened cassettes containing X-ray film. The breasts are compressed in different mammographic views, such as the craniocaudal and mediolateral oblique projections. Compression of the breast is essential to reduce tissue overlap and improve image resolution. The end result is a small stack of X-ray films. Because age, race, hormonal status, and surgical intervention, such as implants and such, all play a role in the challenge of breast imaging, drawbacks in the diagnostic accuracy of conventional film-screen mammography emerged. Younger patients, premenopausal or perimenopausal, with radiographically dense breasts posed a significant diagnostic challenge. The dense breast tissue obscured underlying tumors, which often resulted in false-negative and false-positive results. For this reason, full-field digital mammography (FFDM) was introduced.

Full-field digital mammography was first approved by the US Food and Drug Administration (FDA) on January 31, 2000.²⁰ Similar to the film-screen mammography method, in FFDM the breast tissue is also compressed and various mammographic views are obtained. However, rather than using an X-ray screened cassette and processing a film in the darkroom, FFDM uses computerized technology to acquire an image. The mammography machine is equipped with an image receptor connected to a computer, which converts the X-ray photons into a digital picture during image acquisition. The digital images are displayed on a high-resolution monitor. Because the image is in a digital format, the interpreting physician is able to manipulate the image by enlarging it, reversing the image, or adjusting the contrast and brightness levels to gather more diagnostic information. Image archive, storage, and retrieval using FFDM are drastically improved. Film is no longer needed, which reduces the need for large storage spaces. Because the images are archived digitally, image retrieval is much faster and there are no X-ray films to file, carry, fumble with, or lose.

The question of image quality between the 2 mammographic methods has been researched extensively. According to the American College of Radiology Imaging Network (ACRIN) Digital Mammography Trial (DMIST), it was concluded that breast cancer detection was diagnostically superior with digital mammography images when compared to conventional analog mammography images in younger women, premenopausal women, perimenopausal women, and all women with heterogeneously dense breast tissue (Figure 1).²¹

Although FFDM has improved the diagnostic accuracy of mammography of the dense breast, challenges still remain. Even though the breasts are compressed to obtain a more uniform tissue density, a major challenge that remains is the superimposition or overlapping of dense breast tissue above and below an area of interest. This superimposition can obscure visualization of a possible cancer. For this reason, researchers have developed a new and promising imaging method called breast tomosynthesis that improves tissue differentiation.  

Breast tomosynthesis is a new technology that uses an imaging technique called tomography (slice-imaging) that is similar to other types of tomography. Unlike traditional mammography, in breast tomosynthesis the breast is compressed only enough to hold it stationary and reduce patient motion. In most cases, the images are acquired in the craniocaudal and mediolateral oblique projections. Once the patient is in position, the mammography X-ray tube moves in an arc above the breast acquiring images or slices with low-dose exposures at different angles in a rapid sequence. The overall exposure dose is comparable to a routine mammographic examination. Once the images are acquired they are digitally reconstructed and the resulting images can be viewed individually or displayed as a 3-dimensional image.²²

Recent studies indicate that the image quality of breast tomosynthesis was rated as superior in image quality by nearly 70% when compared to digital mammography (Figure 2). In some instances, microcalcifications were better visualized with digital mammography due to blurring artifacts.²³ Recent research addressed the blurring dilemma by developing an algorithm called "point-by-point back projection correction" to reduce microcalcification blurring. Using this method, microcalcifications are better delineated with tomosynthesis.²⁴ Breast tomosynthesis has drastically increased the confidence level of the interpreting physician by providing greater image clarity brought about by eliminating tissue superimposition. This new technology is currently pending final approval by the US FDA and should be released for clinical use in the first quarter of 2009.

Sonography (Ultrasound or Ultrasonography)
For many years the primary role of breast ultrasonography was to evaluate areas of concern in the breast that were either discovered on a mammogram or presented as a palpable abnormality during a CBE or BSE. In an ultrasound examination, high-frequency sound waves (≥7 MHz) are directed into the soft tissue. As the sound waves bounce off of structures, they are reflected back to the transducer and an image is acquired based on the travel time and intensity of the sound beam as it reflects off of different structures. Conventional targeted breast sonography focused on specific areas of concern and did not include imaging of the whole breast. However, according to the recent ACRIN study 6666, breast sonography is playing a new role in breast cancer screening. Rather than targeting small portions of the breast for imaging, whole breast sonography screening allows imaging of the entire breast. The study concluded that in high-risk patient populations, the cancer detection rate increased from 7.6 cancers per 1000 patients with mammography alone to 11.8 cancers per 1000 patients when whole breast sonography screening was added to mammography screening.²⁵

Breast sonography screening is very useful in the younger patient population (aged 39 or younger), who typically have very dense breast tissue. Dense breast tissue lowers the sensitivity of mammography in detecting invasive breast cancers to approximately 85%. However, breast sonography is not affected by dense breast tissue and is much more reliable (99%) at detecting invasive breast cancers. It is important to note that sonography is less reliable than mammography at detecting noninvasive cancers, such as DCIS, because of the decreased sensitivity of detecting microcalcifications.²⁶    

The disadvantage of adding breast sonography to the screening process is the potential for higher false-positives that may lead to more biopsies. Because of the potential for higher false-positives, breast sonoelastography is coming to the forefront as the newest innovation in breast sonography.

Breast sonoelastography, also called tissue elastography or E-Mode, measures the breast tissue's elasticity (tissue softness vs hardness) and categorizes the result into an elasto-strain-ratio measurement. The E-Mode technique is a fairly simple process consisting of attaching a small compression plate to the ultrasound transducer. Very light, even compression (much less than that required for normal scanning) is manually applied as the sonoelastography software acquires the image data. The elasto-strain-ratio measurement characterizes breast lesions as either benign or malignant by measuring the tissue strain of a lesion and comparing it to normal fatty breast tissue, resulting in a "fat-to-lesion ratio." Tissue elasticity can range from very soft with lots of strain comparable to surrounding breast tissue, indicating a benign process, to very hard with little to no strain, which is highly suggestive of a malignancy (Figures 3 and 4).²⁷ Most sonoelastography procedures will add approximately 5 to 10 additional minutes to the sonographic examination.²⁸

Sonoelastography scores are not hindered by tissue thickness, tissue echogenicity (brightness), or lesion depth. Lesion sizes of 5 to 15 mm provide the most accurate elasticity scores. Statistical analyses of sonoelastography scores indicate an overall sensitivity of 80%, reaching 90% in lesions that are 5 mm in size or less.²⁹ Incorporating this technology when a suspicious mass is detected on conventional B-mode screening sonography will help to lower the number of false-positives and reduce unnecessary biopsies. Sonography is relatively inexpensive, easy to perform, and tolerable to the patient; therefore, adding sonoelastography hardware and software will improve diagnostic accuracy with minimal change to work flow. 

Breast ultrasound computer-aided detection (CAD) is another technology that is gaining popularity. It is a tool that can be used as a second opinion to help the interpreting physician evaluate breast ultrasound images in order to determine whether a biopsy is indicated. Breast ultrasound CAD categorizes the lesions using standardized descriptors based on the American College of Radiology Ultrasound Breast Imaging and Reporting Data System (BI-RADS^®) lexicon.³⁰ Breast ultrasound CAD is most helpful in distinguishing between a BI-RADS 3 (probably benign) and a BI-RADS 4 (suspicious abnormality) category.³¹

After acquiring digital ultrasound images of a breast lesion or lesions, the CAD software evaluates the sonographic appearance of the lesion. The user selects the area or lesion in question. This area in question is traced manually or through an automated process, and certain image characteristics are identified that help differentiate between benign and malignant features.³² The primary characteristics evaluated are the lesion's "orientation, shape, boundaries, margins, posterior acoustic features, and echo patterns." Other features such as "calcifications, vascularity, and the integrity of the surrounding tissue" are also evaluated (Table).³³ After all characteristics are evaluated and identified, the CAD software calculates a BI-RADS category and automatically generates a report for the interpreting physician's consideration. Breast ultrasound CAD was given US FDA 510(k) clearance in 2005 and is currently available for commercial use in the United States. It can be used as a stand alone workstation or can be added to most existing sonography equipment or Digital Imaging and Communications in Medicine workstations.³⁴

 

Magnetic Resonance Imaging
Now more than ever, breast MRI plays a vital role in breast care management. As mentioned previously, the ACS recommends that women aged 40 and older with a lifetime risk greater than 20% should have a screening mammogram and screening breast MRI every year.¹⁹ MRI is very useful in evaluating benign conditions, such as assessing the integrity of breast implants. It also serves as an adjunct screening modality for the detection of certain types of mammographically or sonographically occult breast cancers in high-risk patients. Once an initial diagnosis of breast cancer is made, breast MRI plays a secondary, but vital role in staging by assessing tumor size and determining the extent of disease, such as multicentric, multifocal, or contralateral extension. In the recent breast MRI ACRIN trial 6667, statistical analyses revealed that the sensitivity of MRI in detecting contralateral breast cancer was 91%.³⁵

Magnetic resonance imaging consists of using magnetic fields used to produce cross-sectional images of the patient's anatomy.¹ Conventional T1- and T2-weighted breast MRI consists of using a dedicated breast unit or coil with a recommended minimum field strength of 1.5 Tesla to allow for the performance of chemical fat suppression (Figure 5).³⁶ Because the majority of breast cancers form primitive blood vessels that shunt blood to the tumor bed (termed angiogenesis), most breast cancers demonstrate an increased vascularity when compared to the surrounding tissue. When an MRI contrast agent is administered during a fast dynamic imaging sequence, malignant lesions will collect more of the contrast agent due to their increased vascularity, causing the tumor to enhance when compared to the surrounding breast tissue.¹³

The limitation of conventional T1- and T2-weighted breast MRI is the potential for false-positives due to the enhancement of some benign vascular lesions that mimic cancers.³⁷ To help reduce the number of false-positives, diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) measurements are being added to conventional breast MRI studies. Rather than relying on contrast enhancement alone, DWI is a process in which the diffusion of water molecules is measured during specific pulse sequences. Positional change of the water molecules or the lack of positional change of the water molecules help to differentiate between benign and malignant lesions. Molecules that show no or very little positional change are considered to have restricted diffusion, whereas molecules that show various positional changes are considered to have unrestricted diffusion. Restricted diffusion typically indicates a malignancy whereas unrestricted diffusion typically indicates a benign process. The ADC is a measure of the amount of signal drop in a mass during diffusion imaging. Statistical analyses conducted by Kelcz and Musack revealed that ADCs greater than 1.2 indicate a benign process and ADCs less than 1.2 indicate a malignancy (sensitivity and specificity of 100%). The drawback of DWI is image noise, which necessitates imaging with thicker slices. Thicker slices make comparison and correlation to the conventional MRI difficult.³⁸  

Nuclear Medicine
For many years the role of nuclear medicine in breast imaging has predominately been lymphoscintigraphy, which is used to detect sentinel lymph nodes (SLNs). An SLN is the first lymph node in a chain of lymph nodes located along a lymphatic drainage pathway. If breast cancer metastasizes through the lymphatic system, microscopic tumor cells (micrometastases) will accumulate in the SLN first. Absence or presence of tumor cells in the SLN is an accurate staging predictor for the status of the remaining lymph nodes in the region. If there are no tumor cells present in the SLN, the need to dissect the remaining lymph nodes in the region (called an axillary lymph node dissection) is reduced significantly. This helps to minimize patient morbidity.³⁹

Lymphoscintigraphy is performed before surgery by injecting a radiocolloid into multiple sites of the breast. The most common injection techniques are perilesional, retroareolar, and/or intradermal. Once the breast is injected, the radiocolloid disperses through the lymphatic channels and can be detected by gamma cameras for imaging (called scintigraphy; Figure 6) and by operative gamma probes in the surgical suite to assist the surgeon in removing SLNs.³⁹

Recently, the role of nuclear medicine in breast care has expanded. Scintimammography, also called molecular breast imaging, is a new advancement in nuclear medicine imaging of the breast in which a radioactive substance composed of technetium-99M-sestamibi is injected intravenously. After injection, the patient is positioned similar to mammographic craniocaudal and mediolateral oblique projections (with no to very minimal compression). A high-resolution breast specific gamma camera acquires images to record the uptake of the radioactive tracer that was injected intravenously. Uptake is categorized with scores of normal (1), benign (2), probably benign (3), probably abnormal (4), and abnormal (5).⁴⁰ Statistical analysis of scintimammography indicates a sensitivity of approximately 86% for detecting breast lesions smaller than 1 cm.⁴¹ High sensitivity in detecting non-palpable lesions, axillary lymph node metastasis, and mammographically occult lesions in the ipsilateral (same breast) and contralateral (opposite breast) have also been reported. The drawbacks reported are false-negatives due to high uptake found in some fibroadenomas, inflammatory processes, and post-surgical changes.^42,43

Scintimammography can be used as an adjunct imaging modality to compliment mammography. High-risk patients, patients with dense breast tissue, and those who cannot undergo an MRI procedure for medical reasons or due to lack of MRI availability, may benefit from scintimammography as an effective secondary alternative.  

Positron Emission Tomography
Positron emission tomography is a nuclear medicine imaging study that detects metabolic activity in different cells. It is very useful in detecting axillary lymph node involvement of breast cancer. A radioactive isotope, fluorodeoxyglucose (FDG), is injected into the patient intravenously. Because most malignant tumor cells have higher metabolic rates than the surrounding tissue, they will absorb (uptake) more of the FDG. As the radioisotope decays inside the tumor cells, positrons are emitted, which produce photons that are detected during image acquisition and appear as "hot spots" of high metabolic activity.⁴⁴

Positron emission tomography combined with CT is becoming a useful diagnostic and staging tool for the management of breast cancer. The predominant role of PET/CT in breast care is to identify axillary metastasis by detecting regional lymph node involvement. It can also detect distant metastasis beyond the lymph nodes. CT provides the ability to view cross-sectional anatomy and correlate the pathologic metabolic uptake from PET with the precise anatomical location of the activity.⁴⁵

Statistical analyses of noninvasive PET/CT at detecting axillary lymph node involvement indicate 94% sensitivity, 86% specificity, and 89% accuracy. When a PET-positive result is obtained confirming axillary lymph node involvement, surgical SLN biopsy using conventional lymphoscintigraphy can be avoided and axillary lymph node dissection should be performed instead. However, patients with PET-negative results pose a challenge. Although the statistical data indicate high diagnostic accuracy, the decision on whether or not to proceed with lymphoscintigraphy and subsequent SLN biopsy for axillary staging must be made.⁴⁶

Computed Tomography
Computed tomography is an X-ray imaging study in which an X-ray tube rotates 360° around an anatomical structure acquiring data. These data are reconstructed to form cross-sectional images that typically demonstrate tissue morphology. Several rotations or slices are made in specified slice thickness increments in order to obtain multiple cross-sectional images in a sequence. Each image can be viewed individually or as a volumetric image for interpretation. There are numerous types of CT devices available for different imaging needs. Until recently, the role of CT in breast imaging typically consisted of evaluating post-surgical lumpectomy sites for breast conservation planning and/or to aid in breast cancer staging. However, new CT technology is expanding the role of CT in breast imaging.

Computed tomography perfusion (CTp) research using dynamic multidetector imaging is being conducted to determine whether a differentiation can accurately be made between tumor invaded lymph nodes versus inflamed lymph nodes. This new technology provides functional (physiologic) data based on the perfusion (blood flow) in a lymph node. Comparisons made between malignant angiogenesis indicating tumor perfusion and benign inflammatory response revealed that blood flow in malignancies was higher than that found in inflammatory conditions. These finding suggest that CTp has the potential to provide accurate noninvasive staging for breast cancer.⁴⁷ CTp may enhance PET/CT imaging by improving lymph node staging capabilities. 

Cone beam breast CT (CBBCT) was recently unveiled at the Radiological Society of North America in 2006. This new technology combines digital X-ray technology and CT technology to produce exceptional 3-dimensional "isotropic" imaging of the breast (Figure 7). The term isotropic indicates that the physical characteristics do not change regardless of image direction, thus providing a true anatomical depiction. The apparatus is ergonomically designed to allow the patient to comfortably lie prone on the imaging table and suspend the breast being imaged through a special opening in the table. During image acquisition, a specially designed X-ray tube located beneath the table rotates 360° around the suspended breast.⁴⁸ Complete image acquisition of the breast takes approximately 10 to 50 seconds (depending on the imaging protocol) and requires no breast compression, which significantly improves patient comfort during the examination. The radiation exposure is comparable to a standard mammographic examination.⁴⁹ In a recent feasibility study conducted by Yang et al, CBBCT was found to consistently produce high-quality images with outstanding tissue contrast and yield the potential for a marked reduction of breast examination time.⁵⁰ This new technology is pending US FDA approval and is currently available for research purposes in the United States.⁴⁸

Conclusions
Using a redundancy approach to breast cancer screening in high-risk patients by incorporating dual imaging modalities in the screening process has proven beneficial in improving early breast cancer detection and subsequent long-term survival rates. The newest technological advancements in breast imaging, such as breast tomosynthesis, breast sonoelastography, breast ultrasound CAD, diffusion-weighting and ADC breast MRI, scintimammography, PET/CT, CTp, and CBBCT, are improving image quality and enhancing the diagnostic accuracy of breast cancer detection, staging, and treatment.

However, there are challenges with the acceptance and utilization of the newest technology. Researchers and developers are faced with the challenges of meeting strict government specifications and regulations. Once the regulations are met and the new technology is made available for clinical use, cost becomes a large factor in the equation. Many imaging facilities must follow strict budgets making it very difficult to obtain, install, educate, and use the newest breast imaging advancements. Unless the facilities propose a projected return on their investment, many imaging facilities are faced with the inability to substantiate the purchase of the equipment. Many third-party payers are reluctant to accept the new breast imaging technology and screening guidelines, and subsequently may deny reimbursement, making the return on investment goal even more difficult to attain.

Equipment utilization is an equally challenging factor stemming from the imaging professionals themselves and is manifested in their reluctance to accept the new technological innovations and ACS breast cancer screening guidelines. The learning curve is steep with much of the new equipment, and complacency or lack of time for training to master the technology is hindering progress.

It is important to overcome these obstacles in order to focus on the universal goal of improving early breast cancer detection and subsequent treatment. The benefits of the newest technological innovations have propelled breast imaging further down the path of early detection than ever before. Each emerging technology has the potential of becoming part of a new multimodality paradigm shift in breast imaging.

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