Mammography -A ppt bt J K PATIL, Prof,dept of radiology

ppt on introduction and detailed explanation of mammograpghy

1. MAMMOGRAPHY

2. INTRODUCTION Mammography is a technically challenging imaging modality as it requires excellent soft tissue contrast, high spatial resolution, and wide image latitude especially in denser breasts, with a low radiation burden. The sensitivity of mammography is reported to be ranging from 45% to 85%, with relatively poorer performance as the breast density increases. However, several studies have shown an improved cancer detection with digital mammography even in younger women who have dense breasts.

3. Mammography physics Tube current: As high as possible to keep exposure time short. • Target-filter combination: Molybdenum target with 0.03 mm molybdenum filter. ○ Special X-ray tubes with molybdenum or rhodium anodes: Low energy X-rays required necessary to achieve high tissue contrast. ○ Adding filters at the source of the X-ray beam: This removes the very low energy photons which are likely to be absorbed in the breast (do not contribute in the image formation). • Peak kilovoltage (kVp): Range 26–30 kV. • High spatial resolution is essential to identify microcalcifications measuring in the order of 100 μm . ○ Small focal spot of the X-ray tube (0.3 mm for routine mammography and 0.1 mm for magnification mammography). ○ High-resolution film-screen combinations

4. • Grids are used to reduce scattered radiation and to increase contrast, especially in the dense or thick breast. • Automated exposure control: Modern equipment automatically selects target/filter combination, kVp and tube current according to breast density and the thickness of the compressed breast, e.g., higher energy X-ray spectrum for large breasts for sufficient penetration. These devices also control the exposure duration so that the optimum optical density of the mammograms is maintained over a wide range of breast densities and sizes. The automatic exposure control device ( phototimer or ionization chamber) is normally positioned 3 cm posterior to the nipple, where the most dense glandular tissue is likely to be seen

5. MAMMOGRAPHY EQUIPMENT

6. Mammography basics Mammography provides image contrast by using the differences in the x-ray attenuation among the different breast tissue types, such as fat, fibroglandular tissue, and carcinoma. With lower energy x-rays used by mammography (approximately 25–28 keV), the attenuation difference between the fibroglandular tissue and carcinoma is more pronounced than on standard radiographs, which use a 50-keV x-ray. Mammography uses ionising radiation to image the breast. The risks of ionising radiation are well known and any exposure needs to be justified, with doses kept as low as possible. The radiation dose for a standard two-view examination of the breast is approximately 3 mGy . The average effective dose of radiation from mammography is equivalent to 61 days of average natural background radiation

7. BREAST COMPRESSION IN MAMMOGRAPHY It reduces geometric unsharpness by bringing the object closer to the film. • It improves contrast by reducing scatter. • It diminishes movement unsharpness by permitting shorter exposure times and immobilising the breast. • It reduces radiation dose, as a lesser thickness of breast tissue needs to be penetrated and scatter is reduced. • It achieves more uniform image density: a homogeneous breast thickness prevents overexposure of the thinner anterior breast tissues and underexposure of the thicker posterior breast tissues. • It provides more accurate assessment of the density of masses. A s cysts and normal glandular tissue are more easily compressed, the more rigid carcinomas are highlighted. • It separates superimposed breast tissues so that lesions are better seen. Compression of the breast is essential for good mammography, for the following reasons-

8. ANATOMY OF BREAST A normal breast has glandular breast elements surrounded by fat and breast stroma, which is surrounded by a honeycomb fibrous structure of thin strandlike Cooper’s ligaments. The glandular elements are composed of lactiferous ducts leading from the nipple and branch into excretory ducts, interlobular ducts, and terminal ducts that lead to acini that produce milk . The ducts are lined by epithelium composed of an outer cellular myoepithelial layer and an inner secretory cellular layer. The ducts and glandular tissue extend posteriorly in a fanlike distribution consisting of 15 to 20 lobes draining each of the lactiferous ducts, with most of the glandular tissue found in the upper outer breast near the axilla. Fatty tissue surrounds the glandular tissue. Posterior to the glandular tissue is retroglandular fat, described by Dr. Laszlo Tabar as a “no man’s land,” in which no glandular tissue should be seen. The pectoralis muscle lies behind the fat on top of the chest wall.

9. Fatty tissue is the least dense and most translucent to x-rays and appears dark on mammography. Fibroglandular tissue, muscle, and lymph nodes are more dense and radiopaque (whiter) than fatty tissue, and are white on mammography. Cancers and fluid-filled cysts may be denser and whiter than normal surrounding fibroglandular tissue. Calcifications and metals are the brightest of all structures on mammography DIFFERENT TISSUES LOOK LIKE ON MAMMO-

10. MAMMOGRAPHY PROJECTIONS The standard mammographic evaluation consists of two orthogonal images for basic imaging evaluation of each breast: (1) mediolateral oblique (MLO) view and (2) craniocaudal (CC) view. The entire breast cannot be included in any single mammographic view. More breast tissue is shown on the MLO projection than on any other view. Different Mammographic projections - 1)Mediolateral Oblique View 2)Craniocaudal View of Breast 3)Supplementary Views Rolled View Magnification View Spot Compression View Extended Craniocaudal View

11. Mediolateral Oblique View It is obtained with the tube angled at 45° to the horizontal, with compression applied obliquely across the chest wall, perpendicular to the long axis of the pectoralis major muscle.

12. Craniocaudal View of Breast It is obtained with a vertical X-ray beam. The breast is pulled up and forward, away from the chest wall and compression is applied from above It demonstrates the subareolar, medial and lateral portions of the breast; however, tissue in the posterolateral aspect of the breast may not be documented completely.

13. Rolled View These separate normal fibroglandular elements into their individual components. The breast tissue is “rolled” and compressed in the same projection in which the finding was first noted. On the rolled view, true masses will retain their shape and persist; whereas if it is separated into its normal fibroglandular components, it represents a summation shadow. Magnification View Magnification is required for analysis of microcalcifications and the margins of small mass lesions. This can be done by increasing the film-object distance, producing an “air gap”, and using a fine focal spot to increase resolution.

14. Extended Craniocaudal View This view is performed by rotating the patient's body to display the lateral or medial breast tissue better than possible with a standard CC view. When the patient is rotated medially, the lateral part of the breast and axillary tail is brought over the film and the medial portion of the breast is excluded. This well demonstrates the tissue in most posterolateral part of the breast. For medial breast lesions, the patient is rotated laterally to bring the medial part of the breast over the film and the outer breast tissue is excluded.

15. DIGITAL MAMMOGRAPHY Full-field digital mammography (FFDM) is now gradually replacing screen-film (conventional) mammography. The diagnostic yield is increased by newer applications of digital mammography like digital breast tomosynthesis (DBT) and contrast-enhanced mammography It includes the following systems- Computed Radiography Systems Digital Radiography Systems

16. Computed Radiography Systems Another approach to digital mammography is the computed radiography (CR) approach, which uses a photo- stimulable phosphor plate. The plate is used to absorb X-rays just as a screen-film cassette. However, rather than emitting light immediately after exposure through fluorescence, absorption of Xray causes electrons within the phosphor material crystal to be promoted to higher energy levels. The screen is then placed in a reader where it is scanned with the laser beam. The laser beam causes the electrons to be released and returned to their resting levels with release of higher energy (blue) light (proportional to the X-ray beam energy). The amount of blue light released is then measured by a photomultiplier tube. Problems with this system include inefficient light collection and scatter of laser light in the phosphor material resulting in loss of spatial resolution and increased noise

17. Digital Radiography Systems The digital detector converts the X-rays into digital signals and replaces the film and are of two types. Indirect digital detectors : These convert X-rays into light and then into a digital signal. These detectors use photostimulable phosphors, amorphous silicon or charge-coupled devices (CCDs). 2. Direct digital detectors : Also known as flat panel detectors, they use a photoconductive material that is able to directly convert X-ray photons into a digital image. Examples include amorphous selenium detectors and crystal silicon detectors. Selenium is an optimum mammography detector material due to its high X-ray absorption efficiency, high intrinsic resolution and low noise.

18. Advantages and Applications of the Digital Mammography • Better contrast characteristics and dynamic range. There is no loss of contrast in over or underexposed portions of the digital image and similar contrast is seen over the entire dynamic range of the detector. • Postprocessing such as manipulations of the brightness, contrast, zoom-pan and edge enhancement and adjustment of image display. • Better archival, storage and communication, i.e. picture archiving and communication system (PACS) and telemammography . When compared with the S creen Film M, major limitations of digital mammography are the cost and lower spatial resolution. Full Field DM systems have spatial resolutions from 5 to 10 lp /mm, whereas the Screen Film Mammo combinations have a line pair resolution of 18–20 lp /mm. This lower spatial resolution of FFDM is compensated by an increase in contrast resolution. The digital system has wider dynamic range and hence it can record and differentiate minor variations in contrast better than SFM.

19. DIGITAL BREAST TOMOSYNTHESIS Digital breast tomosynthesis (DBT) is a technique to improve the detection and characterization of breast lesions, especially in women with dense breasts. Multiple projection images are reconstructed to allow evaluation of the breast in thin sections thus increasing the diagnostic confidence where the lesion margins are obscured by the surrounding normal fibroglandular tissue. Technique- In conventional digital mammography, a compressed breast is exposed to ionizing radiation coming from a stationary tube and the X-rays are detected by a stationary detector. A two-dimensional image of a three dimensional breast is created, leading to overlap and obscuration. On the other hand, in DBT, the X-ray tube moves through an arc and multiple exposures are made at different angles to create several projectional images. Reconstruction algorithms are applied to this projectional data and a series of tomographic images are produced. A radiologist can interpret these as a stack of images approximately 1 mm thick and read these similar to reading the CT or MRI stack of images on a workstation.

20. BIRADS( Breast Imaging—Reporting and Data System) The American College of Radiology (ACR) has devised the Breast Imaging-Reporting and Data System(BI-RADS) for mammogram, US, and MRI. This is a standardized method to describe the morphology of breast lesions and categorize these findings in a definite report.

21. THINGS TO LOOK FOR IN A MAMMOGRAM- 1)Breast Density 2)Mass MASS SIZE SHAPE MARGIN DENSITY LOCATION 3)Calcifications. 4)Asymmetry. 5)Associated findings- Skin retraction, Nipple retraction, Skin thickening, Axillary adenopathy

22. BREAST DENSITY

23. MORPHOLOGY OF MASS

24. SHAPE

25. MARGINS

26. MASS DENSITY COMPARED TO PARENCHYMA

27. CALCIFICATIONS

28. Distribution

29. BENIGN CALCIFICATIONS

30. SUSPICIOUS CALCIFICATIONS

31. ASYMMETRY It is important to differentiate an asymmetry versus a focal asymmetry versus a mass. Asymmetry Soft tissue finding identified only on one view, without matching tissue in a similar location in the contralateral breast. Focal Asymmetry and Mass These are seen on two views at a comparable depth with similar density and shape. Mass: Consistent convex margins Focal asymmetry: It lacks convex outward borders on both views and usually confined to a small area of the breast. Global Asymmetry In a larger portion of the breast (>1 quadrant). It can be a normal variation or secondary to the effects of hormone replacement therapy (HRT). Developing Asymmetry This is a new term defined as “a focal asymmetry which is new or becomes more conspicuous over time”. Developing asymmetry is of concern because if seen at screening mammography, there is 12.8% risk for malignancy and persistence at diagnostic mammography carries a 26.7% risk for malignancy