Breast Imaging Essentials

Transcription

1 Breast Imaging Essentials Module 9 Transcript 2016 ASRT. All rights reserved.

2 Breast Imaging Essentials Module 9 Breast Ultrasound 1. ASRT Animation 2. Welcome Welcome to Module 9 of Breast Imaging Essentials Breast Ultrasound. This module was written by Liana Watson, DM, R.T.(R)(M)(S)(BS), RDMS, RVT, FASRT. 3. License Agreement 4. Objectives After completing this module, you will be able to: Define the basic principles of ultrasound physics. Explain the physical principles of ultrasound production as they apply to breast imaging. Use sonographic terminology as it applies to breast imaging. Describe the role of ultrasound in characterizing breast pathology. List the steps of the ultrasound examination. Recognize benign and malignant breast pathology. 5. Diagnostic Medical Sonography Diagnostic medical sonography is the term used to describe the medical imaging modality that uses sound waves to produce diagnostic medical images. Additional terms used by the medical community for diagnostic medical sonography include ultrasound, sonography, ultrasonography and echocardiography, which is a special type of ultrasound exam of the heart. Sonography produces medical images of soft tissue in the body by measuring the differences in the intensity of sound waves that are sent into and reflected back from different structures. 6. Sound Waves In nature, a wave is anything that carries or transports energy from 1 point to another; examples include heat, light, or sound. Acoustics, or sound, is a branch of physics. The physical principles of ultrasound are based on the properties of acoustic physics as opposed to the principles of x-ray generation, which are based on electromagnetic physics. Transportation of energy occurs when the particles in the substance the wave is traveling through are displaced from their normal or resting state. As soon as the energy has moved through the substance, the particles return to their normal state. There are 2 types of waves found in nature: mechanical waves and electromagnetic waves. 7. Mechanical Waves In order to transport energy, mechanical waves require a medium to travel through such as a solid, liquid, or gas. Energy is transported when the molecules in the substance vibrate, bumping into adjacent molecules causing them to vibrate. Energy is transferred as long as the molecules vibrate enough to bump into each other. When molecules are located farther from the source of the wave they are disturbed less than those located closer to the wave s source. Because all mechanical waves require a medium to transport energy, the speed or velocity of the wave is highly dependent on the properties of the medium. Mechanical waves also cannot travel in a vacuum. Examples of mechanical waves found in nature include sound waves, water waves, and seismic waves. 8. Electromagnetic Waves In comparison, electromagnetic waves are generated by the attraction of electrons and protons. The vibration caused by the attraction of the positively charged protons and the negatively charged electrons produces a magnetic field in the space around the electron. All electromagnetic waves travel at the speed of light and, unlike mechanical waves, do not require a medium to transport energy. Because electromagnetic waves don t require a medium to transport energy, the speed or velocity that these

3 waves travel is always the same the speed of light and these waves can travel in a vacuum. Examples of electromagnetic waves are X-rays, light, and microwaves. 9. Waves Transport Energy The energy in a wave can be transported in 2 different ways. In transverse waves, the particles or molecules in the substance vibrate at right angles to the direction of the wave. When the wave moves in the horizontal plane, the molecules vibrate in the vertical plane and vice versa. An example of a transverse wave is an ocean wave. A boat or other object floating in the water bounces up and down while the water moves toward and away from the shore. Other examples of transverse waves include x- rays, light, and radio waves. In longitudinal waves, the particles or molecules in the substance vibrate parallel to the direction the wave travels. If the wave moves in a horizontal plane, the molecules vibrate in a horizontal plane, and if the wave moves in a vertical plane, the molecules vibrate in a vertical plane. The movement of the wave causes the molecules in the substance to come closer together and farther apart as the wave moves through the medium. Waves that move through fluid, like a liquid or gas, are always longitudinal. An example of a longitudinal wave is the motion of a slinky. The slinky moves when there is enough energy to make the springs move closer together and farther apart. 10. Knowledge Check 11. Knowledge Check 12. What Is Sound? Because sound travels as a longitudinal wave, the movement of molecules causes changes in molecular position in relation to surrounding molecules. Compression occurs when the sound wave causes molecules to move closer together. When the molecules return to their original resting position, this is called rarefaction. Sounds waves have many properties and all waves have peaks and valleys, or maximum and minimum values. If you were to pair a maximum value with a minimum value, you would have a cycle, which is one of the properties of a sound wave. A cycle is 1 repetitive periodic oscillation. 13. Frequency Another property of a sound wave, frequency, is the term used to describe the number of times in 1 second that the sound wave causes molecules in a medium to get closer together, which is referred to as compression, and to move back to their resting position, defined by the term rarefaction. Because the wave is generated outside of the medium it travels through, the frequency of the wave is determined by the wave's source. One cycle of compression and rarefaction in 1 second would be described as a frequency of 1 hertz. The frequency of sound used for diagnostic medical sonography is in megahertz, or millions of hertz. The frequency of the sound, which in sonography is controlled by the transducer, determines the wavelength of the sound. Remember, frequency is the number of cycles that occur in 1 second, and the more cycles there are, the smaller the space they occupy. If the sound wave used for imaging has a higher frequency (more cycles in a second), the amount of space for each cycle to occur (the wavelength) has to be shorter or smaller. If the sound wave used for imaging has a lower frequency, the amount of space for each cycle is longer. 14. Period Period describes the amount of time it takes for 1 cycle of compression and rarefaction to occur and is measured in seconds. Period is inversely proportional to frequency. Period influences the amount of time

4 the ultrasound equipment transmits a pulse of sound waves. A pulse contains 3 to 5 cycles of sound, and the amount of time left for the equipment to detect reflected sound waves from the body. The period of an ultrasound wave is usually less than 1 microsecond. The amount of time it takes for 1 pulse of sound to occur is called the pulse duration, and it is calculated by multiplying the period times the number of cycles in the pulse. Because the period is technically a function of frequency, it also is determined by the source of the wave. 15. Wavelength Wavelength describes the length of space of 1 cycle of compression and rarefaction, and is usually measured in millimeters. Wavelength is the limiting factor in terms of the system s ability to image very small objects, or spatial resolution. For the sound wave to be returned to the transducer, the object intersecting the wave must be larger than the wavelength; otherwise, the sound wave is not reflected. Wavelength also influences how quickly the sound wave is converted to different types of energy and attenuated by the body. The smaller the wavelength, the more the sound wave will be reflected from the body. Smaller objects result in the wavelength being reflected. The more the sound is reflected, the less sound is available to be reflected from deeper objects within the body. As a result, sound waves with smaller wavelengths are attenuated more quickly than larger wavelength sound waves. If each of these waves occurred within the same amount of time, the horizontal axis, a wave with a greater number of frequencies would have shorter wavelengths. Conversely a wave with a lower frequency would have longer wavelengths as shown by the wave at the top. 16. Amplitude Amplitude describes the degree of variance from the norm, and is determined by the source of the sound. It is the amount of variation in acoustic variables as a result of the sound wave interacting with the body s tissues. Acoustic variables include temperature, pressure, and density. The unit of measure for amplitude depends on the acoustic variable it describes. For example, temperature is measured in degrees; pressure is measured in Pascals; the measurement for density is molecules per cubic centimeter. 17. Acoustic Intensity Acoustic intensity is proportional to amplitude squared and influences the level of pressure change exerted by the sound wave. Acoustic intensity is a measure of how strong or loud the sound wave is; intensity has a direct impact on the thermal effects of ultrasound on the body's tissues. When acoustic intensity increases, the pressure applied to the molecules in the medium also increases. This means that the higher the intensity of the sound wave, the higher the displacement of the molecules from their resting position, and the higher the pressure between the molecules. When displacement and pressure are higher, there are more interactions between molecules. More molecular interactions increase the friction among the molecules, and friction produces heat, which is a bioeffect of ultrasound. For this reason, sonographers need to maintain as low as reasonably achievable, or ALARA, principle when using sonography by using the lowest intensity sound wave needed to obtain the image. 18. Propagation Speed Propagation speed, or velocity, describes how fast a wave moves through a medium. Because the movement of the wave through the medium depends on molecules within the medium vibrating enough to bump into each other, the medium determines the velocity of the sound wave. The propagation speed of sound is influenced by specific properties of the medium. These properties include elasticity, mass density, and stiffness. All diagnostic medical ultrasound equipment uses the average speed of sound in soft tissue, or 1,540 meters per second, as a constant for the speed of sound. This variable is very important to calculate the depth of an object from the sound source in diagnostic ultrasound imaging.

5 Compared to its speed through air, 330 m/sec, sound moves through soft tissues very quickly. Depending on the type of soft tissue sound is traveling through, it moves at different speeds. For example, sound travels faster through muscle, at 1,630 m/sec, than it does through brain tissue, at 1,520 m/sec. Sound passes through abdominal structures at a speed similar to its speed through the brain, but is slightly faster for the kidneys at 1,560 m/sec, and the liver at 1,570 m/sec. 19. Elasticity Elasticity is the ability of the molecules in a medium to return to their original state after being disturbed by a sound wave. The more elastic the medium, the faster the wave travels through the substance. The faster the molecules return to their original place; the sooner they are ready to receive the next wave. 20. Density The density of a substance is defined as the mass per unit volume; in the case of tissues in the body, density is the number of molecules per cubic centimeter. Remember that gases usually have fewer molecules per cubic centimeter compared with liquids, and liquids have fewer molecules per cubic centimeter than solids. Therefore, a solid has a greater density than either a liquid or a gas. Assume that each of these cylinders is a medium and the circles inside the cylinder are molecules. The substance on the right would have a greater density than the substance on the left because there are more molecules in the same amount of space. 21. Density and Propagation Speed In general, increasing the density of a substance decreases propagation speed. However, density plays a role in both increasing and decreasing sound wave propagation. For sound to be transmitted through a substance, the molecules of a medium must be close enough together for the sound wave's movement to cause the molecules to vibrate and bump into each other. This is one reason why sonography is not effective for imaging organs filled with air; the molecules are too far apart to keep the sound wave moving and they scatter the sound wave too quickly. If the molecules of a medium are too close together, the sound wave s energy causes too many molecular interactions, and friction converts the energy to heat. The resulting lack of energy can t keep the wave moving, and the sound wave is attenuated too quickly. For this reason, sonography is not good for imaging bone. 22. Stiffness The stiffness of the medium influences the propagation speed of sound more than elasticity or density. Stiffness is the resistance of molecules to the energy exerted on them; increasing stiffness increases the propagation speed of the wave. Consider how much movement occurs when you roll a marble into another marble, compared with rolling a marshmallow into another marshmallow. For a wave to move through a medium, the molecules in the substance have to be moved from their resting state. Objects that are stiff are easier to move because the energy being exerted on the object is not absorbed by the object. Objects that are compressible, or the opposite of stiff, are difficult to move because the energy exerted on them causes the objects to deform, or absorb, the energy. Considering this, sound actually travels very quickly through stiff objects in the body. 23. Knowledge Check 24. Knowledge Check 25. Frequency, Wavelength, and Propagation Speed The relationship between frequency, wavelength, and propagation speed is the foundation for how ultrasound equipment converts a sound wave into a diagnostic medical image.

6 The propagation speed is equal to the frequency times the wavelength. In ultrasound equipment, the propagation speed of sound in soft tissue is set as a constant at 1,540 meters per second and is represented by the letter c. This leaves the primary variable in the equation as the frequency of the sound, which is generated by the transducer or ultrasound probe. 26. Choosing Frequency Frequency, wavelength, and spatial resolution have the following relationships: Increasing the frequency of the sound wave decreases the wavelength. Decreasing the wavelength increases resolution. Increasing the frequency of the sound wave increases resolution because of the decreased wavelength. It appears that increasing frequency is a good thing; however, there is another factor to consider. Every time an object reflects the sound beam, it loses strength and is no longer available for imaging deeper objects in the body. An increase in frequency results in a greater volume of reflected sound waves because the smaller wavelength increases reflections from smaller objects in the body. The increased reflections closer to the transducer decrease the amount of sound left for imaging deeper structures. So as frequency increases, the depth the sound beam can penetrate, or image, decreases. Sonographers choose the transducer that can provide a sound wave that delivers enough energy to penetrate the body, and produce the best spatial resolution for the object being imaged. 27. Ultrasound The frequency of the sound waves used to produce diagnostic medical images is higher than the frequency of sound that humans can hear. The range of frequency for human hearing is between 20 and 20,000 Hz. This means that a sound wave must vibrate in the human eardrums between 20 times per second and 20,000 times per second for us to hear. Most humans cannot hear any sound wave that has a frequency higher or lower than this range. The lowest frequency used for diagnostic medical sonography is about 2 megahertz. Remember, the highest frequency humans can hear is about 20,000 Hz, which equals 20 kilohertz or 0.02 megahertz. 28. Imaging Methods Ultrasound equipment uses several different methods to produce diagnostic medical images. B-mode real time is used to perform most ultrasound imaging, including breast imaging. In B-mode real-time imaging, the ultrasound equipment measures how long it takes a pulse of sound waves transmitted into the body to return to the source of the sound, the ultrasound transducer. This measurement indicates how deep the return signal is from the sound source. The equipment also compares the intensity of the sound that was transmitted into the body and the intensity of the sound returned to the transducer to determine how brightly the return signal should be displayed on the image. M-mode is a variation of B-mode and is used in echocardiography. Doppler ultrasound measures velocity and flow. 29. Depth and Intensity The depth and intensity of the return echo are recorded on a 2-D matrix that displays them as a dot after the ultrasound equipment receives the measurements. The grayness of the dot shows the intensity of the return echo, with white being high intensity and black being no return echo. The depth corresponds to the distance from the sound source. Objects closer to the transducer are at the top of the image. The image is considered real time because the display is refreshed at a rate that is higher than what a human brain can process visually, which is about 60 times per second. 30. Transducers A transducer is an instrument that changes one form of energy into another.

7 Many different transducers are used in everyday life. For example; telephones change acoustic energy to electrical energy and electrical energy to acoustic energy. Light bulbs change electrical energy to light energy, and gas engines change fuel to mechanical energy. The ultrasound probe, or transducer, produces sound waves for diagnostic medical sonography and determines the frequency of the sound used during imaging procedures. Diagnostic medical sonography uses frequencies from 2 to 30 megahertz. Breast sonography should be performed in the 10 to 12 MHz range. 31. The Ultrasound Probe Even though most sonographers refer to the entire ultrasound probe as the transducer, the actual component that generates the sound wave is a group of manmade crystals found within the probe housing called piezoelectric crystals. The production of sound is a result of the piezoelectric effect. Piezo is a term that means pressure. An electrical wire is attached to each of the crystals in the ultrasound probe. The ultrasound equipment sends a pulse of electricity into the crystal, which causes the crystal to deform and produce a pressure wave. The pressure wave then makes the crystal ring, or produces a sound wave. When the ultrasound probe is placed on the patient, the sound wave is directed into the body. This ultrasound imaging process is actually a reversed piezoelectric effect. 32. Piezoelectric Crystals The crystals used in ultrasound equipment are manufactured specifically for use in medical imaging. The crystals usually are made from ceramic materials, such as lead zirconate titanate or a combination of ceramic materials and epoxy. The epoxy helps prevent the individual sound waves from canceling each other out when being transmitted by the ultrasound probe. Ceramic crystals must be polarized to exhibit the piezoelectric effect and produce sound waves that can be used for medical imaging. Polarization causes the molecules of the crystals to align themselves in the same direction. Heating the piezoelectric crystals to the Curie temperature, which is the temperature at which a ferromagnetic or a ferrimagnetic material becomes paramagnetic, is how the crystals are polarized. Curie temperature is different for different substances. For lead zirconate titanate Curie temperature is approximately 365 C. A high voltage then is applied to the crystal until it is cooled. Polarization can be reversed if the crystals are heated to the Curie temperature. This is the reason why ultrasound transducers should never be sterilized using heat. 33. Transducer Crystal Thickness The optimal thickness for crystals used in diagnostic medical sonography is 0.2 to 1.0 mm. The thickness of the crystal is very important because it influences the resonance frequency of the transducer. The thinner the crystal, the higher the frequency, and the thicker the crystal, the lower the frequency. This principle works the same way for guitar strings; in other words, thinner strings produce higher-pitched sounds than thicker strings. The thinner string vibrates faster or has a higher frequency, which vibrates the eardrum faster when the sound wave reaches it. The faster the eardrum vibrates, the higher the pitch of the sound. 34. Knowledge Check 35. Knowledge Check 36. Creating an Ultrasound Image To create a grayscale image, the ultrasound transducer must compare the transmitted sound wave to a reflected sound wave, which means the same crystal has to transmit and receive the sound wave. Because the crystals perform dual functions, diagnostic medical sonography uses pulses of sound rather than continuous sound to produce an image. Pulses of sound are usually 2 to 3 cycles long.

8 Most of the time, an ultrasound transducer listens for sound waves to return from the body. Individual crystals transmit sound about 0.1% of the time and wait to receive reflected sound waves 99.9% of the time. Components in the ultrasound housing help stop the crystals from ringing, a process known as damping. Damping works the same way as when someone places a hand on a ringing bell. Damping helps keep the wavelength short and short wavelengths are better to image smaller objects. Damping also keeps the pulses short, which produces a sound wave with a higher range of frequencies. 37. Diagnostic Medical Sonography To create a medical image from the sound waves transmitted by the transducer, a computer in the ultrasound equipment first sends an electrical voltage into each of the crystals in the transducer. The strength of the voltage is the baseline measurement for the intensity of the sound wave transmitted into the body. The equipment also measures the length of time between when the voltage was sent to the crystal and when another voltage is received from the crystal. This measurement indicates the depth of the object being imaged. The equipment is able to vary the times each of the crystals receives voltage so that the sonographer can focus and direct the beam. Next, the electrical voltage causes the crystals to deform and produce a pressure, or sound, wave meaning the piezoelectric effect has occurred. Each of the crystals produces an individual sound wave. The collection of individual sound waves forms the sound beam. The ultrasound probe is placed on the patient s skin so that the sound beam can be transmitted into the patient s body. The sound waves interact with tissues in the body and are either transmitted deeper, scattered, absorbed, or reflected back to the ultrasound probe. The sound waves that are reflected back to the probe are the only ones used to produce the sonographic image. 38. Sound Wave Attenuation The sound wave is attenuated as soon as it is transmitted from the transducer. In other words, the intensity of the beam decreases because the sound wave is converted into other types of energy. Remember the law of energy conservation: Energy is not created or destroyed, but changes from 1 type of energy to another. The sound wave is attenuated when it interacts with molecules within the different types of tissue. When the sound wave encounters molecules, it can be absorbed, scattered, reflected, or transmitted. 39. Sound Transmission Transmission occurs when the molecules in the tissue are not large enough to reflect or redirect the sound wave. Remember, the higher the frequency, the smaller the wavelength and the higher the attenuation because there is more reflection or redirection of the sound wave. Sound must be transmitted to an optimal depth in the area of interest in order to create an image. Sonographers consider this when choosing the transducer for the examination. The transducer selected should offer the highest frequency for providing a diagnostic quality image at the maximum depth of the structure being imaged. Deep structures, such as the liver, require a lower-frequency transducer. When imaging superficial structures, such as the breast, higher frequencies can be used. 40. Reflection For the sound wave to produce an image, it must be reflected back to the transducer. Multiple factors influence the amount of sound that is reflected to the transducer and most are beyond the scope of basic sonographic principles. However, an important concept is that the boundaries between different types of tissue serve as the primary influence on reflection or transmission of sound. Differences in acoustic impedance, or the level of difficulty a sound wave has in passing through a certain type of tissue, also influence reflection vs transmission. The higher the acoustic impedance, the higher the reflection. The smoothness of the boundary also determines the amount of sound that is reflected.

9 41. Specular Reflectors Specular reflectors are large, smooth, mirror-like interfaces that reflect waves at the angle of incidence. When the sound wave encounters a specular reflector with large acoustic impedance, the sound is reflected at the same angle at which it hit the reflector. Specular reflectors appear on the sonographic image as bright white lines. Examples of specular reflectors include the diaphragm, walls of a full urinary bladder, and walls of a breast cyst. For the sound to return to the transducer, it must be reflected in a direction that will reach the transducer. The sound wave is reflected at the same angle at which it hits the reflector, known as the angle of incidence. The optimal angle of incidence is 90 because total reflection occurs at this point. If the sound wave encounters a specular reflector at an angle other than 90, it is called an oblique incidence. In this case, the angle of incidence must be between 87 and 93 for the sound wave to reach the transducer. The rule of thumb is that the sonographer acquires the best image when the transducer is perpendicular to the area of interest. 42. Nonspecular Reflectors Nonspecular reflectors are tissue interfaces that are uneven or irregular; these reflectors are found more often in the body than specular reflectors. When the sound wave encounters a nonspecular reflector, the sound is not redirected or reflected in a straight path back to the transducer. The waves are scattered accounting for nearly 100% of the sonographic image. Scatter occurs when sound hits a nonspecular reflector. The sound is redirected, depending on the angle of incidence, to the irregular surfaces and usually bounces around before returning to the transducer. Scatter is considered beneficial in sonography because it helps complete the image; scatter makes up nearly 100% of the grayness of the sonographic image. 43. Absorption Absorption of the sound wave is primarily a conversion of the mechanical pressure wave into heat. The higher the number of interactions between molecules, the more likely that friction occurs between the molecules. Friction produces heat. Higher frequencies increase absorption because the number of molecular interactions increases. Therapeutic ultrasound, often used for physical therapy, is designed to produce heat in tissues by applying high-frequency sound waves to affected areas. Fortunately, diagnostic medical sonography does not cause a significant temperature change in the body tissues because the intensity of the sound wave is not high enough and the amount of time sound is transmitted into the body is not long enough. However, keeping the ultrasound intensity as low as reasonably achievable helps minimize heat production in the patient's tissues. 44. Ultrasound Image Orientation Ultrasound images always are displayed on the monitor in the same way. The top of the image is the surface that the ultrasound transducer is touching. The bottom of the image is the distance from the point where the transducer is touching the skin to a depth that shows the area of interest. 45. Transverse Orientation When the notch, or light, is pointed toward the patient s right side, assuming the patient's head is at the top of the bed, the transducer is oriented in the transverse plane. If the sonographer is right handed, a helpful tip is to keep the notch or light toward the thumb when scanning in the transverse plane. Doing so helps the sonographer know the orientation of the transducer and quickly determine if the image is oriented correctly on the screen. When imaging in the transverse plane, the sonographer must make sure that the left side of the patient s body is displayed on the right side of the screen and that the right side of the patient s body is displayed on the left side of the screen, much like looking in a mirror. When a sonographer first starts to scan, it s always a good idea to ensure the transducer is oriented correctly. The transverse orientation can be checked by angling the transducer to the right and making

10 sure the image on the monitor moves to the left; this can be repeated in the opposite direction by angling the transducer to the left and making sure the image moves right. 46. Longitudinal Orientation When the notch or light is pointed toward the patient s head, the transducer is oriented in the longitudinal plane. Positioning the transducer this way helps the sonographer recognize the orientation of the transducer and quickly determine if an image is oriented correctly on the screen. When imaging in the longitudinal plane, the sonographer must make sure that the body part closest to the patient s head is displayed on the left side of the screen and the body part closest to the patient s feet is displayed on the right side of the screen. When first beginning scanning, the sonographer should check that the transducer is oriented correctly. For the longitudinal orientation, the sonographer can angle the transducer toward the patient s head and make sure the image on the monitor moves to the left or angle the transducer toward the patient s feet and make sure the image on the monitor moves to the right. 47. Knowledge Check 48. Knowledge Check 49. Purpose of Sonographic Terminology When performing breast ultrasound examinations, sonographers are asked to describe what they see. The terms used to describe the images are standardized in a breast imaging-reporting and data system, or BIRADS, so the sonographer and physician interpreting the examination can discuss the findings. If physicians review reports from breast ultrasound examinations, knowing sonographic terminology helps them better understand the reported findings and often helps make the connection between the mammographic and sonographic images. Echogenicity is a structure s ability to bounce an echo or return a signal during an ultrasound examination. There are several terms to describe the echogenicity of various types of tissues. 50. Anechoic and Sonolucent The terms anechoic and sonolucent can be used interchangeably to describe a structure on the image that appears black or echo free. Anechoic means non-echoing or echo free. Sonolucent is used to describe a structure that permits ultrasound waves to pass through it without reflecting them back to their source or does not give off echoes. Structures that are filled with fluid display as anechoic or sonolucent, and therefore appear black. Examples of structures that normally are anechoic include the urinary bladder, gallbladder, blood vessels and amniotic fluid. In terms of pathology, simple cysts, display as black. 51. Echogenic Echogenic structures generate a large number of echoes and appear as light gray or white compared with surrounding tissues, which is the opposite of anechoic structures. The stronger the reflected echo from the structure, the brighter the structure s appearance. The term echogenic describes most normal anatomy, such as lobular tissue and connective tissue in the breast. However, echogenic also is used to describe many pathologic processes, such as calcifications and solid breast lesions. These might also be referred to as hyperechoic. On an ultrasound image, hyperechoic structures appear as areas where the echo is stronger than normal or is stronger than surrounding structures. These areas are bright on the image. 52. Hypoechoic and Isoechoic Hypoechoic structures appear dark gray compared with surrounding tissue. Structures that produce lowlevel echoes are described as hypoechoic. Normal structures that usually display as hypoechoic are fat

11 lobules in the breast. The term hypoechoic is typically used to describe many abnormal findings, including solid breast lesions such as fibroadenomas. An isoechoic structure has a similar grayness as the surrounding tissues, but usually can be distinguished by a capsule or when the abnormality is located within a structure of different echogenicity. A typical isoechoic structure is the kidney parenchyma compared with the liver or spleen. A breast lipoma is an example of an abnormal structure that appears isoechoic. 53. Texture Two ultrasound terms are used to describe texture. Homogeneous structures have a uniform, consistent texture throughout the structure, with no variations in the levels of gray. Normal structures that are described as homogeneous include the liver, spleen and testicle. Abnormal structures typically are not found to be homogeneous, but a possible example is a chocolate cyst. A chocolate cyst is an endometrioma of the ovary. A heterogeneous structure has an internal texture that contains different levels of gray and can be described as having mixed echoes. Most normal structures are not found to be heterogeneous except maybe a corpus luteal cyst. Abnormal structures considered heterogeneous are a diseased liver and other organs or many types of tumors. 54. Posterior Acoustic Enhancement Posterior acoustic enhancement, also referred to as through transmission, describes increased echo intensity behind a structure that does not attenuate the sound wave. Posterior acoustic enhancement is found posterior to normal fluid-filled structures such as the gallbladder and urinary bladder. It also is found behind cysts. The enhancement appears as a brighter area, when compared with the surrounding tissues. Additionally, the enhancement is detected behind an anechoic or hypoechoic structure. 55. Shadowing Shadowing describes decreased echo intensity behind a structure that highly attenuates or reflects the sound wave. Shadowing is found posterior to normal highly reflective structures such as bone or gallstones. The shadow appears as a dark or black area, when compared with the surrounding tissues, behind a structure. 56. Breast Sonography Breast sonography is not as accurate as screening mammography in detecting microcalcifications which are the early indicators of ductal carcinoma in situ, or DCIS. However, the automated breast ultrasound system, or ABUS has been approved by the FDA as an additional screening tool in combination with mammography for those women with dense breast tissue who have no symptoms of breast cancer and have had a negative mammogram. Research continues to show that sonography improves radiologists' accuracy in diagnosing benign and malignant solid breast tumors before interventional procedures such as biopsies. Whole-breast ultrasound may be warranted occasionally for special circumstances, such as nipple discharge, suspected implant leaks, multiple mammographic abnormalities, or evaluating a radiographically dense breast. Because there is significant overlap in sonographic characteristics differentiating benign from malignant disease, whole-breast ultrasound can result in unnecessary biopsies. Breast imaging centers now consider whole-breast ultrasound examinations unacceptable in most cases. The American College of Radiology, or ACR, and the National Comprehensive Cancer Network, or NCCN, have issued guidelines for the use of ultrasound in breast imaging. 57. NCCN Practice Guidelines The NCCN published practice guidelines in 2011 titled Screening for and Evaluation of Suspicious Breast Lesions. These evidence-based statements were developed through collaborative efforts of experts in breast imaging and represent currently accepted practice for breast cancer screening. The guidelines help physicians determine the appropriate imaging modalities for evaluating breast abnormalities in women.

12 Mammographic evaluation in women younger than 30 years of age is difficult because of the large amount of radiographically dense breast tissue found in women of this age group. Therefore, the NCCN practice guidelines suggests that performing breast sonography is appropriate for women who have not had a previous mammographic evaluation and those having a palpable breast lump, areas of thickening in the breast, and skin changes such as erythema. According to the NCCN guidelines, for women older than 30, sonography should be used as an adjunct to mammography for further evaluation of specific clinical abnormalities, such as a palpable breast lump or skin changes. In addition, sonography should be used for further evaluation of mammographic abnormalities categorized using the ACR BI-RADS as a 0, 3, 4 or ACR Guidelines The ACR also publishes guidelines for the performance of breast sonography that support the recommendations of the NCCN. In addition, the ACR specifically endorses the use of sonography in image-guided interventional procedures of the breast and for use in radiation therapy treatment planning for breast cancer. Also, the ACR supports the use of sonography to evaluate and characterize abnormal findings identified by other imaging studies, palpable masses or symptomatic areas and suspected problems with implants. Sonography should be the primary tool to investigate palpable masses in pregnant or lactating women and women younger than 30 years of age. 59. BI-RADS Classifications BI-RADS is a quality assurance tool developed by the ACR to standardize exam reporting, reduce confusion in breast imaging interpretation, and facilitate outcome monitoring. The BI-RADS lexicon consists of 7 categories, 0 through 6, which are used to categorize the overall interpretation of a mammogram, breast ultrasound, or breast magnetic resonance examination. Category 0 examinations often require additional imaging before a final interpretation is made. Category 4 and 5 examinations often require some type of interventional procedure such as a biopsy. 60. Knowledge Check 61. Knowledge Check 62. Sonographic Anatomy Breast evaluation in sonography differentiates and compares the echogenicity of tissues found in the breast. Sonographic breast anatomy can be divided into 3 categories based on the echogenicity of tissues: hyperechoic structures, medium echogenic structures, and hypoechoic structures. Sonography is an excellent tool for helping physicians evaluate superficial solid tissues, such as glandular tissue, fat, and other structures found in the breast. With the use of high-definition, high-frequency transducers, ultrasound imaging can easily differentiate various tissue planes in the breast, particularly when the sonographer uses proper technical factors. Fluctuations in estrogen level affect the sonographic appearance of the breast. These fluctuations might cause slight increases in the density of the breast's fibroglandular tissue when estrogen is at its highest level, during the premenstrual period. Estrogen can have the same effect in women who undergo hormone replacement therapy. Sonographers must be aware of these factors when performing breast imaging, particularly when comparing images with previous breast sonograms or mammograms. 63. Hyperechoic Structures Hyperechoic or echogenic structures appear light gray, bright, or white on sonographic images. Connective tissue such as the superficial and deep fascia, along with ribs and skin, usually appear as hyperechoic structures on breast ultrasound images. Images of an intramammary lymph node often demonstrate the hyperechoic hilus surrounded by a hypoechoic ring. 64. Medium Echogenic Structures

13 An optimized ultrasound image shows fat displayed as a medium level of gray. Because of this adjustment, the echogenicity of the breast's fatty tissue serves as the baseline for comparison with other structures in the breast. Structures that produce medium echogenic, or medium-gray images, include fat, glandular tissue, periductal and perilobular fibrous tissue, and muscle. 65. Hypoechoic Structures Hypoechoic structures appear as a darker level of gray compared with fat and anechoic structures, which display as black. The mammary ducts and blood vessels in the breast normally exhibit this appearance. A dark appearance of structures, like mammary ducts, is apparent on most ultrasound examinations of the breast tissue. 66. Mammography and Ultrasound Correlation When an abnormality is identified on a mammogram, it s important to describe precisely the location, size, shape, and characteristics of surrounding tissue. The more precise the description of the abnormality, the more targeted the ultrasound examination can be. By providing the necessary information for a highly targeted sonographic exam, the radiologist can be confident that the suspicious area has been thoroughly examined by the sonographer and the abnormality found on ultrasound is, indeed, the abnormality demonstrated on the mammogram. Several methods are used to locate a mammographic abnormality with sonography. One method is to examine the quadrant of the breast where the mammographic abnormality is detected. This is the leasttargeted exam, and in most cases, a more targeted examination should be performed. An exception is when the sonographer is trying to locate an abnormality demonstrated on only one mammographic projection. In this case, a more precise description of the lesion's location cannot be made and the entire quadrant of the breast must be examined. The most widely used method for determining an abnormality's location is in reference to a clock face which involves examining the breast from nipple to lateral or medial boundary at the clock face position. 67. Clock Face Notation When the lesion is located directly behind the nipple on the craniocaudal, or CC, mammographic projection, the clock face position is 12 o clock or 6 o clock. If the lesion is located in the extreme lateral or medial areas of the breast on the CC projection, the clock face position is 3 o clock or 9 o clock, depending on which breast is being examined. Lesions located in the areas between the nipple and medial or lateral edge are located at the remaining clock face positions. The medial lateral oblique, or MLO, projection is most beneficial in determining whether the lesion is cephalad or caudad to the nipple. By considering the position of the lesion on both the MLO and CC projections, the clock face position can be determined very accurately. To determine the depth of the lesion, the MLO projection is divided into 4 areas, which are labeled subareolar, or SA, A, B or C. Lesions can be identified as located in 1 of these 3 planes. Describing mammographic abnormalities with this method takes a little time and practice. Before performing the examination, sonographers who are not familiar with mammography should review the mammograms with the radiologists who interpret them. By learning to locate lesions on mammograms, sonographers increase their skill and confidence in performing breast sonography. In addition to describing the lesion's clock face position, the distance from the nipple, or peripheral location, and anteroposterior depth of the abnormality are determined and described before beginning the ultrasound exam. Determining the location of the abnormality with this degree of specificity allows even more precise targeting of the area to be examined, which permits better correlation between the mammogram and sonographic exam. To determine the degree of peripheral location of an abnormality in relation to the nipple, the breast is divided into 4 circumferential rings, which are described as SA 1, 2 or Scanning Technique

14 Breast ultrasound is extremely operator dependent. Many technical factors determine the usefulness of the sonographic examination, including transducer selection, dynamic range settings, time-gain compensation settings and focusing. Whenever possible, a sonographer or radiologist experienced in breast sonography should perform the examination to provide images of high diagnostic quality. 69. Transducers The ACR practice guidelines recommend that a transducer used for a sonographic examination be a high-frequency, linear transducer that is electronically focused and has a broad bandwidth. The transducer should be manufactured specifically for use in superficial imaging. The transducer's frequency should be no less than 10 MHz although 12.5 MHz or higher is preferred. The highest frequency that provides adequate tissue penetration should be used. A stand-off pad might be needed for imaging very superficial structures. A stand-off pad is made of a transparent membrane and filled with an acoustically correct gel. It provides a compliant surface for adjusting the focal zone when scanning superficial structures. Linear transducers are preferable to sector or curvilinear probes. These transducers produce ultrasound beams that diverge more quickly than a linear transducer beam, possibly resulting in technical artifacts such as increased edge shadowing. Electronically focused transducers allow the sonographer to vary the focus of the ultrasound beam, depending on the depth of the area of interest. A transducer with a broad bandwidth generates images with better contrast resolution than more narrow bandwidth transducers. 70. Time-gain Compensation Curve The time-gain compensation, or TGC, curve should be set so that fat is displayed as medium echoes, or a medium shade of gray, uniformly throughout the entire breast. This setting is important because the echogenicity of other tissues in the breast are compared with the echogenicity of fat. If the TGC is set too low, displaying fat as hypoechoic, then black, solid breast nodules, most of which are displayed as slightly hypoechoic compared with fat, may be missed. If the TGC is set too high so that fat is displayed as hyperechoic or bright, then normally hypoechoic structures, such as the blood vessels and mammary ducts, might appear to contain debris. If a breast imaging facility typically evaluates breast lesions with color Doppler, it is very important to set the Doppler parameters to detect low-flow velocities. 71. Patient Position The patient should be positioned so the area of interest is as thin as possible to minimize the imaging depth. As a rule of thumb, if the lateral portion of the breast is being examined, the patient should lie in a posterior oblique position, supported by a wedge cushion, with the breast being imaged elevated. If the medial portion of the breast is being examined, the patient should lie supine so the breast naturally falls to the lateral side. If the patient has large breasts, it might be necessary to have her positioned in a posterior oblique position with the breast being imaged resting on the exam table. The patient should extend the arm overhead on the side of the breast to be imaged. This position also helps stretch the skin and underlying muscles. 72. Transducer Orientation All breast ultrasound examinations require the sonographer to image the breast tissue in 2 planes, 90 from each other. The 2 most common scanning orientations are transverse and longitudinal or radial and antiradial. The transverse/longitudinal imaging orientation is the most commonly used imaging alignment for most sonographic examinations and requires the sonographer to image in planes that are perpendicular or parallel to the long axis of the patient. Some breast imaging experts suggest that breast abnormalities that extend along the duct are best displayed if examined parallel to or perpendicular to the radial or antiradial planes, not in the true longitudinal or transverse planes. They believe that radial/antiradial positioning in a true long or short axis allows the sonographer to minimize artifacts caused by normal breast tissue interfaces and helps to further distinguish normal from abnormal breast tissue. The radial and antiradial scans are performed in a clockwise direction in concentric circles.

15 When an abnormality is identified on an ultrasound examination, the lesion should be measured in 3 dimensions to include AP, transverse and longitudinal, and radial and antiradial. 73. Sonographic Image Documentation The ACR practice guidelines outline the minimum requirements for sonographic image documentation. The images should be labeled as precisely as possible. General information, including facility and sonographer identification, and a minimum of 2 unique patient identifiers are standard documentation for all sonographic procedures. Anatomic location of the side and area being imaged, scan plane of the transducer, clock face position, and distance from the nipple are required for all breast sonographic images. Precise labeling serves 2 purposes. First, the radiologist reading the examination knows the exact sonographic location of the lesion for comparison with the mammogram. Secondly, the radiologist and other sonographers know the exact sonographic location of the lesion in the event an interventional procedure is indicated, if the patient is referred to another institution for further evaluation, or if a follow-up ultrasound examination is recommended to monitor the abnormality. In addition, when an abnormality is located, it should be documented in 2 planes, 90 apart. All images should be archived on radiographic film or in the facility s picture archiving and communications system, or PACS. 74. Knowledge Check 75. Knowledge Check 76. Classifying Abnormalities with Sonography When a lesion is found, several scanning techniques are used to differentiate a benign pathologic process from a malignancy. If there is any suspicion of malignancy, the lesion should be biopsied so that a cytologic or histologic diagnosis can be made. Sonography is not used to downgrade a BI-RADS category 4 or 5 abnormality; rather, it is used to determine whether a category 0, 3, or 4 abnormality should be upgraded or recommended for follow-up examination. The only exception to this is the demonstration of a simple cyst by ultrasound criteria. 77. BI-RADS Ultrasound Classification The ACR suggests that all breast tumors or masses be described using the BI-RADS ultrasound classification. The classification describes lesions in terms of shape, orientation to the chest wall, margins, echo pattern, posterior acoustic features, and the appearance of surrounding tissues. In addition, the report should indicate whether calcifications were identified, and if present, classify them as microcalcifications or macrocalcifications. The characteristics of blood vessels and blood flow should be reported when evaluated. Other findings that can be part of the sonographic examination include clustered microcysts, complicated cysts, masses in or on the skin, foreign bodies, and the presence of intramammary lymph nodes or axillary lymph nodes. 78. Tumor Diagnosis Specific sonographic markers have been established to evaluate solid tumors and help determine the probability that a tumor is malignant. A negative breast ultrasound examination should not preclude biopsy of a mammographically suspicious abnormality. Recent studies have investigated the value of using specific sonographic criteria to identify solid breast lesions as benign or malignant. These studies indicated that demonstrating only 1 of the specific criteria for malignancy produces a low-to-moderate sensitivity for malignancy. However, research also indicated that most malignancies demonstrate multiple malignant characteristics, and as the number of malignant characteristics increases, the likelihood of accurately diagnosing breast cancer increases. The shape of the tumor can be described as oval, round, or irregular.