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DIAGNOSTIC RADIOGRAPHY · NTA LEVEL 4 · SEMESTER TWO Ultrasound Physics CRT04210 · Ultrasound Imaging START READING NOTES Study Ultrasound Physics using the sections below. Use the topic navigation to continue through Ultrasound Imaging. Contents of This Topic artifacts Ultrasound artifacts are image distortions or errors that do not correspond to real anatomical structures. Advantages Detection of Pathology: Technical Feedback: Ultrasound Physics Improved Interpretation: A thorough understanding of artifact physics leads to more accurate and confident image interpretation. Disadvantages of Ultrasound Artifacts: Operator Dependency: Image Degradation: Many artifacts obscure underlying anatomy or pathology, reducing overall image quality. Operator Dependence: The appearance and severity of some artifacts can be influenced by the sonographer's technique. Increased Complexity: The presence of artifacts adds complexity to image interpretation, requiring specialized knowledge. artifacts Advantages and disadvantages Ultrasound artifacts are image distortions or errors that do not correspond to real anatomical structures. While often perceived as limitations, they can also provide valuable diagnostic clues Advantages Diagnostic Clues: Posterior Acoustic Enhancement: Bright areas behind fluid-filled structures (e.g., cysts) confirm the presence of fluid. Acoustic Shadowing: Dark areas behind calcifications (e.g., gallstones) help identify hard, reflective structures. Comet Tail Artifact: Suggests small metallic objects (e.g., surgical clips) or gas bubbles in tissues. NB: Diagnostic Clues: Certain artifacts are characteristic of specific tissues or conditions (e.g., shadowing from gallstones, enhancement behind cysts, reverberation from air). Detection of Pathology: Twinkling Artifact (Doppler): Highlights kidney stones or microcalcifications. Edge Artifact: Helps differentiate cystic from solid masses by creating refractive shadows at margins. Technical Feedback: Reverberation Artifacts: Indicate improper probe contact or gas interference (e.g., in bowel scans). Mirror Artifact: Reveals strong reflectors (e.g., diaphragm) and confirms anatomical relationships. Ultrasound Physics Differentiation: Recognizing artifacts helps distinguish them from real anatomical structures or pathology, preventing misdiagnosis. Procedural Guidance: Artifacts like reverberation can confirm the placement of needles or catheters during ultrasound-guided procedures. Confirmation: The presence or absence of certain artifacts can confirm the nature of a visualized structure (e.g., confirming gas with ring-down artifact). Cost-Effective Information: Utilizing artifact recognition can sometimes provide diagnostic information without the need for more expensive or invasive procedures. Improved Interpretation: A thorough understanding of artifact physics leads to more accurate and confident image interpretation. Technical Optimization: Recognizing artifacts can guide adjustments to ultrasound machine settings to improve image quality and minimize misleading artifacts. Real-time Problem Solving: During an examination, recognizing an artifact allows the sonographer to adjust the probe or technique to clarify the image. Educational Value: Studying artifacts enhances the understanding of ultrasound physics and image formation. Ultrasound Physics Research Opportunities: Analyzing the patterns and characteristics of artifacts can lead to advancements in ultrasound technology and image processing. Disadvantages of Ultrasound Artifacts: Misdiagnosis Risk: Mirror Artifact: Duplicates structures (e.g., liver appearing in the lung), mimicking pathology. Side Lobe/Grating Lobe Artifacts: Create false echoes (e.g., "ghost vessels") in Doppler imaging. mage Obscuration: Acoustic Shadowing: Blocks visualization of deeper structures (e.g., behind bones or stones). Reverberation: Mimics layers or debris in anechoic structures (e.g., bladder). Operator Dependency: Anisotropy: Poor probe angling in tendons/ligaments creates hypoechoic regions, mimicking tears. Slice Thickness Artifact: False echoes in cysts due to beam width, mistaken for solid components Technical Limitations: Aliasing (Doppler): Misrepresents blood flow direction/speed, requiring adjustments to PRF. Speed Error Artifact: Misplaces structures due to incorrect assumptions about tissue sound velocity (e.g., in fatty tissues) Image Degradation: Many artifacts obscure underlying anatomy or pathology, reducing overall image quality. Misdiagnosis: Misinterpreting artifacts as real structures can lead to incorrect diagnoses and unnecessary interventions. Reduced Diagnostic Confidence: The presence of numerous or confusing artifacts can lower the confidence of the interpreter. Time-Consuming Troubleshooting: Identifying and differentiating artifacts can sometimes be time-consuming during an examination. Operator Dependence: The appearance and severity of some artifacts can be influenced by the sonographer's technique. Limited Visualization: Strong artifacts (e.g., shadowing from bone or air) can completely block the visualization of deeper structures Measurement Errors: Artifacts can distort the size, shape, or location of structures, leading to inaccurate measurements. Mimicking Pathology: Some artifacts can mimic the appearance of certain diseases or abnormalities, making diagnosis challenging. Increased Complexity: The presence of artifacts adds complexity to image interpretation, requiring specialized knowledge. Potential for False Positives/Negatives: Misinterpreting or missing artifacts can lead to false positive or false negative findings. ← PREVIOUS TOPICVIEW ALL MODULE NOTESVIEW SEMESTER NOTESVIEW ALL LEVEL NOTESALL DIAGNOSTIC RADIOLOGY NOTES Need These Notes as PDF? Need a clean, well-formatted PDF copy for offline study, revision or printing? Request the complete notes directly through WhatsApp. GET WELL-FORMATTED PDF NOTES

DIAGNOSTIC RADIOGRAPHY · NTA LEVEL 4 · SEMESTER TWO Ultrasound of the Ovary and Endometrium CRT04210 · Ultrasound Imaging START READING NOTES Study Ultrasound of the Ovary and Endometrium using the sections below. Use the topic navigation to continue through Ultrasound Imaging. Contents of This Topic THE MENSTRUAL CYCLE The first menstrual cycle is termed menarche. Menarche occurs at different ages and may be influenced by environment and diet. Ultrasound of the Ovary and Endometrium THE PHYSIOLOGY OF THE OVARIAN CYCLE THE PHYSIOLOGY OF THE ENDOMETRIAL CYCLE During the first half of the menstrual cycle, the endometrium undergoes thickening as a result of estrogen stimulation. SONOGRAPHIC APPEARANCES OF THE ENDOMETRIUM This finding is referred to as the three-line sign. Following ovulation, the secretory endometrium is maintained by the DISRUPTION OF THE MENSTRUAL CYCLE BY PREGNANCY ENDOMETRIAL PATHOLOGY The endometrium will appear thin and will not measure more than 5 mm .It may also contain some intracavitary fluid. Endometrial Hyperplasia Endometrial Carcinoma ANATOMY AND PHYSIOLOGY OF THE OVARY The cells surrounding the tiny follicles produce estrogen, which stimulates the endometrium to thicken. PATHOLOGY OF THE OVARY Corpus Luteum Cysts Cystic Teratoma (Dermoid) Endometrioma (Chocolate Cyst) THE MENSTRUAL CYCLE The last menstrual period relates to the onset of menses; therefore, the first day of the menstrual cycle is said to occur on the first day of bleeding. The average menstrual cycle lasts 28 days, with ovulation typically occurring around day 14. However, some menstrual cycles may last only 25 days while others may last up to 45 days. 1 Days 1 through 5 of the menstrual cycle correlate with menses, at which time the endometrium is shed. The first menstrual cycle is termed menarche. Menarche occurs at different ages and may be influenced by environment and diet. However, if an individual does not experience menarche before age 16, she is said to have primary amenorrhea. Ultrasound of the Ovary and Endometrium Primary amenorrhea may be caused by congenital abnormalities or congenital obstructions, such as an imperforate hymen. Secondary amenorrhea may be associated with endocrinologic abnormalities or pregnancy. Secondary amenorrhea that is not associated with pregnancy is characteristically diagnosed in the postmenarchal woman who has had at least 12 months without a menstrual cycle THE PHYSIOLOGY OF THE OVARIAN CYCLE The ovarian cycle consists of two phases: the follicular phase and the luteal phase. The follicular phase of the ovarian cycle is considered to begin on day 1 and lasts until day 14, thus, in effect, ending with ovulation. During the follicular phase, the anterior pituitary gland secretes FSH, which initiates the follicular development of the ovary. Ultrasound of the Ovary and Endometrium Many follicles are produced by the ovary. While numerous follicles manifest, only one follicle will be maintained and become the graafian follicle or dominant follicle prior to ovulation. This graafian follicle, which can grow as large as 2.7 cm, contains the developing oocyte (egg) within a region called the cumulus oophorus. Ultrasound of the Ovary and Endometrium Around day 14, LH, produced by the anterior pitu itary gland, stimulates ovulation, at which time the graafian follicle, which has grown to a size of 15 to 27 mm, ruptures and expels a small amount of fluid and the ovum into the peritoneum. The ovum is picked up by the fimbria of the fallopian tube and is propelled through the tube, either to be fertilized, resorbed by the body, or passed with menstruation. Ultrasound of the Ovary and Endometrium The second phase of the ovarian cycle, days 15 to 28, is termed the luteal phase. After the graafian follicle ruptures, it is temporarily turned into an endocrine gland in the form of the corpus luteum. The corpus luteum, while producing estrogen in small amounts, primarily produces progesterone to maintain the thickness of the endometrium and prepare the endometrium for the (conceivably) fertilized ovum. All the other follicles undergo atresia. Ultrasound of the Ovary and Endometrium While the corpus luteum depends on LH to be maintained, progesterone negatively inhibits the production of LH by the anterior pituitary gland, resulting in the regression of the corpus luteum. The remaining structure of the corpus luteum is now termed the corpus albicans, which can often be seen sonographically as a small echogenic scar on the ovary.1 THE PHYSIOLOGY OF THE ENDOMETRIAL CYCLE The endometrium has two basic layers. The innermost portion, the functional layer, is the layer that changes throughout the menstrual cycle. The functional layer provides an appropriate location for implantation to occur. The outermost portion, the basal layer, is only slightly altered during the menstrual cycle. It consists of dense, cellular stroma Ultrasound of the Ovary and Endometrium The endometrial cycle consists of two phases: the proliferative phase and the secretory phase. The proliferative phase occurs after menstruation and lasts until ovulation. The endometrium is influenced by estrogen and progesterone, which are produced by the ovary. During the first half of the menstrual cycle, the endometrium undergoes thickening as a result of estrogen stimulation. Thus, proliferation of the endometrium, which is described as the multiplication of similar forms, occurs during the proliferative phase of the endometrial cycle, as the functional layer increases in thickness. Ultrasound of the Ovary and Endometrium The secretory phase of the endometrial cycle occurs after ovulation and is stimulated by progesterone. Progesterone maintains the thickness of the endometrium in preparation for implantation. Should fertilization not take place, menses begin on day 1 of the cycle, resulting from a lack of estrogen and proges terone. Ultrasound of the Ovary and Endometrium Conversely, if fertilization does occur, the en dometrial thickness is maintained by the continual production of progesterone by the corpus luteum of pregnancy SONOGRAPHIC APPEARANCES OF THE ENDOMETRIUM As the hormones produced by the ovary act upon the endometrium, the thickness of the endometrium varies. Consequently, the sonographic appearance of the endometrium changes Following menses, the endometrium appears as a thin, echogenic line Ultrasound of the Ovary and Endometrium Thus, the early proliferative endometrium appears echogenic and thin and

DIAGNOSTIC RADIOGRAPHY · NTA LEVEL 4 · SEMESTER TWO Ultrasound Of The Gallbladder CRT04210 · Ultrasound Imaging START READING NOTES Study Ultrasound Of The Gallbladder using the sections below. Use the topic navigation to continue through Ultrasound Imaging. Contents of This Topic SONOGRAPHY OF THE GALLBLADDER GALLBLADDER MEASUREMENTS NON-DISTENDED GALLBLADDER INADEQUATE FAST NON-FASTING GALLBLADDER ANATOMY OF THE GALLBLADDER GALLBLADDER FOLDS GALLBLADDER SEPTATIONS ANATOMIC VARIANT: THE PHRYGIAN CAP THE GALLBLADDER NECK CYSTIC DUCT CYSTIC DUCT AND BILE DUCT GALLSTONES SMALL CALCULI Ultrasound Of The Gallbladder FALSE GALLSTONES CALCULI OR GAS? CHECK THE CYSTIC DUCT Summary word slide SHADOW PRODUCTION EXPERIMENT WITH GALLSTONE AND FOCAL ZONE CRITICAL ANGLE SHADOWS FROM THE GALLBLADDER SHADOWS NEAR THE GALLBLADDER NON-VISUALIZATION OF THE GALLBLADDER NON-VISUALIZATION OF GB FINDING THE NON-VIZ GALLBLADDER DOUBLE ARC SHADOW SIGN FINDING THE NON-VIZUALIZED GALLBLADDER BOWEL GAS NEAR THE GALLBLADDER SHADOWS NON-SHADOWING ECHOGENIC FOCI IN GB GALLBLADDER POLYPS CHOLESTEROL POLYPS GALLBLADDER MASS ULTRASOUND OF THE GALLBLADDER SONOGRAPHY OF THE GALLBLADDER Since ultrasound is the primary imaging modality in the evaluation of the gallbladder, it is a “bread and butter” type of study. In patients with right upper quadrant symptoms, ultrasound not only evaluates the gallbladder, but adjacent structures such as liver, bile ducts, pancreas, right kidney and great vessels. SONOGRAPHY OF THE GALLBLADDER The gallbladder is an excellent organ to image by sonography, because it is a fluid-filled structure with no internal echoes. It is visualized as an anechoic pear-shaped structure outlined by a smooth thin wall. Any abnormality within the gallbladder becomes outlined by the bile and is easily seen. SONOGRAPHY OF THE GALLBLADDER As with any structure imaged by ultrasound, it must be examined in two perpendicular (orthogonal) planes in order to be able to reconstruct a proper 3-dimensional mental picture of the object and to avoid artifacts SONOGRAPHY OF THE GALLBLADDER This is a transverse section of the gallbladder. Based on its purely fluid content, the gallbladder is used as a standard of reference for fluid-containing structures in the right upper quadrant. Cysts in the liver and right kidney can be compared to the gallbladder, as long as they are at similar depths. SONOGRAPHY OF THE GALLBLADDER If the echogenicity of their contents is the same as that of the gallbladder, then they are simple cysts. If their contents is more echogenic, then the cysts contain true echoes and are not simple cysts. One should be mindful of the fact that it is possible to have a congenital duplication of the gallbladder, which is rare. Also there are structures that can mimic the gallbladder. These include omental cysts, enteric duplication cysts, choledochal cysts, aneurysms, abscesses. GALLBLADDER MEASUREMENTS The size of the gallbladder is quite variable, so that it is not a very useful indicator of disease. In general the normal gallbladder is < 5cm transversely, and < 10cm longitudinally. A gallbladder larger than this is usually abnormally enlarged, such as a Courvoisier gallbladder, which enlarges on the basis of distal extrahepatic biliary duct obstruction. NON-DISTENDED GALLBLADDER A post-prandial gallbladder cannot be differentiated from an abnormal diseased, contracted gallbladder. An empty gallbladder is difficult to scan and results are unreliable. The gallbladder should always be examined in the fasting state, when it is maximally distended. NON-DISTENDED GALLBLADDER This is accomplished by an overnight fast, usually starting by midnight before the scan. The ultrasound is usually performed in the morning, when the bowel is quiet and abdominal gas is at a minimum. If the patient has not had a proper overnight fast, fasting for approximately 8 hours is considered adequate. INADEQUATE FAST An inadequate fast may result in slight gallbladder wall contraction and mild wall thickening, which in turn may lead to incorrect diagnosis. NON-FASTING GALLBLADDER One should avoid the temptation of scanning the gallbladder without a proper fast. Even if gallstones are visualized, the complete diagnosis may be compromised because of suboptimal visualization, as in this case of a non-fasting patient with right upper quadrant pain. NON-FASTING GALLBLADDER Two gallstones are seen in the fundus (short arrows), but the potentially obstructing stone (long arrow) in the gallbladder neck was not seen until the patient underwent a proper fast. In retrospect the stone was present on the original image shown here (long arrow). ANATOMY OF THE GALLBLADDER The fundus is the rounded curved end of the gallbladder. The body is the central portion, while the neck is the tapered part. The gallbladder is connected to the biliary system by the cystic duct, which contains numerous folds called valves of Heister. Stones are easily trapped within these folds. ANATOMY OF THE GALLBLADDER After the cystic duct joins the common hepatic duct, the extrahepatic bile duct is called the common bile duct. GALLBLADDER FOLDS Folds within the gallbladders are non-pathologic. A particular fold, called the junctional fold, normally occurs in the mid to proximal end of the gallbladder, closer to the gallbladder neck (arrow). This fold may cause an acoustical shadow due to an artifact and should not be mistaken for a stone or calcification. GALLBLADDER SEPTATIONS Rarely gallbladders contain true septations. These are congenital in origin and are of no clinical significance. A gallbladder folded back upon itself may simulate septations. In fact, sometimes during different degrees of inspiration and expiration, one can observe the gallbladder folding and unfolding. This is of no known clinical consequence. ANATOMIC VARIANT: THE PHRYGIAN CAP When the fundus of the gallbladder folds over on itself, it creates the appearance of a cap, called the “phrygian cap” (arrow). Occurring in 4% of the population, this is one of the better known anatomic variants of the gallbladder. It is asymptomatic and unrelated to disease. THE GALLBLADDER NECK The gallbladder neck often has a convoluted tortuous course, which becomes a trap for calculi. The neck usually does not contain enough bile to allow for its recognition. Calculi within the neck of the gallbladder are often not imaged for this reason and this is one cause of false negative sonograms for cholelithiasis. CYSTIC DUCT The convoluted appearance of the

DIAGNOSTIC RADIOGRAPHY · NTA LEVEL 4 · SEMESTER TWO Ultrasound Beam Shape CRT04210 · Ultrasound Imaging START READING NOTES Study Ultrasound Beam Shape using the sections below. Use the topic navigation to continue through Ultrasound Imaging. Contents of This Topic ULTRASOUND BEAM SHAPE AND FOCUSING Beam shape General shape of the ultrasound beam Factors affecting shape of the beam Effect of source size Variation of fresnel zone's length and angle of divergence with source diameter Practical Implication Effect of source size: In summary Effect of beam frequency Focusing of the ultrasound beam Mechanical methods of focusing Electronic beam focusing Focus of a transducer Focal zone Classification of focusing Strong focusing Weak focusing Summary ULTRASOUND BEAM SHAPE AND FOCUSING J.J. John (DDR-CUHAS) Beam shape As a beam of ultrasound travels outwards from the surface of the transducer, the distribution in space of the ultrasonic energy undergoes change. The ultrasound beam spreads out, or undergoes divergence as it moves away from the transducer. The term "ultrasound beam shape" is commonly used to describe the manner in which the spatial distribution of the beam changes with distance from the source. Beam shape The beam shape has very significant effects on the Quality of the ultrasonic image (Image Resolution) The tissue depths that can be usefully interrogated We are going to examines the factors which influence ultrasound beam shape and the associated implications for ultrasonic imaging. General shape of the ultrasound beam The typical manner in which the ultrasound beam spreads out with increasing distance from the transducer T is shown below T- Transducer d – Beam width P – Plane/point where the beam diverge D – Lenght of near field/fresnel zone General shape of the ultrasound beam Initially, between T and the plane P along the beam path, the beam is narrow, with a small beam width d, equal to about the diameter of the piezoelectric crystal. This part of the beam is referred to as the near field, or the Fresnel zone. Near field/Fresnel zone General shape of the ultrasound beam Beyond P, the beam spreads out (diverges) over a larger and larger area, with increasing beam widths which result in a rapid deterioration of spatial resolution of the image. This part of the beam is known as the far field, or the Fraunhofer zone. Far field/Fraunhofer zone General shape of the ultrasound beam The distance from the transducer to the plane P is sometimes called the transition distance (in reference to the change from Fresnel zone to Fraunhofer zone). General shape of the ultrasound beam The length D of the Fresnel zone, and the beam width d, at a given plane across the beam, are important parameters The length of the Fresnel zone influence the practical tissue depth that can be interrogated with the beam The beam width influence the spatial resolution in the ultrasonic image. The narrow beam associated with near field is desirable for good spatial resolution. Factors affecting shape of the beam The shape of the ultrasound beam is affected by: The size and shape of the ultrasound source The beam frequency Beam focusing Effect of source size The size of the ultrasound source affects the Beam width The length of the Fresnel zone (Transition distance) Angle of divergence beyond the near field With No focusing applied,the Fresnel zone's length (D), is determined by the diameter of the Piezoelectric Crystal (d) and the wavelength of the ultrasound beam according to the relation: Where r = radius of the transducer, = wavelength, v=Velocity of the ultrasound beam and d = 2r is the diameter of the transducer. Effect of source size Within the near field, the beam width is approximately equal to the transducer diameter. The length of the Fresnel zone (D) increases rapidly as the beam width (or transducer crystal’s diameter, d) is increased. Conversely, the length of the Fresnel zone diminishes rapidly as the transducer diameter is reduced. Variation of fresnel zone's length and angle of divergence with source diameter In addition, a small transducer diameter results in a large angle of divergence beyond the near field Practical Implication An important practical implication of these observations is that: Although a narrow beam gives us good image resolution, narrow beams should not be obtained ONLY by making the transducer smaller, as this would also reduce the depth of tissue interrogation. It is for this reason that, in multicrystal transducers where many small crystal elements are used: The crystals are not pulsed individually, but in small groups of neighbouring crystals which then provide an instantaneous beam wide enough to give a sufficiently long length of the Fresnel zone. Effect of source size: In summary A small source provides a narrow beam initially, is associated with a short Fresnel zone, and the beam diverges rapidly beyond the near field. A large source provides a broader beam initially, gives a longer Fresnel zone, and the beam diverges more gradually, thus providing better resolution of deeper structure. Effect of beam frequency substituting the wavelength of the ultrasound beam by = v/f we get: From this expression, we conclude that the length of the Fresnel zone increases as the beam frequency is increased. Also, the angle of divergence beyond the near field diminishes with increasing frequency. Effect of beam frequency The effect of higher frequencies is therefore not only improved image resolution but also an increase in the length of the useful near field. In practice, however, some of this advantage is taken away by increased beam attenuation at higher frequencies Focusing of the ultrasound beam The shape of the ultrasound beam can be influenced to varying extents by applying different focusing methods In general the main methods are: Mechanical methods of focusing Electronic methods of focusing The Mechanical methods of focusing includes the use of Acoustic lenses and Shape of the crystal element while The Electronic methods of focusing archived by appllication of a pulsing programme with carefully controlled time delays between different crystal elements Mechanical methods of focusing Shape of

DIAGNOSTIC RADIOGRAPHY · NTA LEVEL 4 · SEMESTER TWO Ultrasound Artifact CRT04210 · Ultrasound Imaging START READING NOTES Study Ultrasound Artifact using the sections below. Use the topic navigation to continue through Ultrasound Imaging. Contents of This Topic ULTRASOUND ARTIFACT Artifact assumes different forms including REVERBERATION This artifact will be seen at the skin-transducer interface and behind the bowel gas ACOUSTIC SHADOWING ACOUSTIC ENHANCEMENT EDGE SHADOWING BEAM WIDTH ARTIFACT SLICE THICKNESS ARTIFACT RING-DOWN ARTIFACT COMET-TAIL ARTIFACT DUPLICATE ARTIFACT MIRROR ARTIFACT SIDE LOBE ARTIFACTS GROUP 5 MEMBERS ULTRASOUND ARTIFACT Artifact is a structure in an image which is not direct similar with the actual anatomy of the tissue being scanned Artifact assumes different forms including Structures in the image that are not actually present Objects that should be represented but are missing from the image Structures which are misregistered on the image MULTIPLE ECHO ARTIFACTS Reverberation Comet tail Ring down Mirror image Air artifact VELOCITY ERROR ARTIFACT Edge shadowing ATTENUATION ARTIFACT Acoustic shadowing enhencement TYPES OF ARTIFACTS ULTRASOUND BEAM ARTIFACT Side lobes Grating lobes Beam width artifacts Slice thickness artifact REVERBERATION This is the production of false echoes due to repeated reflections between two interface with a high acoustic impedance mismatch The echo from the interface is received by the transducer and displayed on the image The reverberation echoes will be equally spaced because the time for each additional echoes is multiple of the time of return of the first echo This artifact will be seen at the skin-transducer interface and behind the bowel gas RECTIFICATION Increase the amount of gel used Reduce the gain ACOUSTIC SHADOWING This appears as an area of low amplitude echoes behind an area of strongly attenuating tissue. It is caused by severe attenuation of a beam at an interface, resulting in very little sound being transmitted beyond The attenuation can be due to either absorption or reflection of the sound waves, or a combination of the two Acoustic shadowing will occur at interfaces with large acoustic mismatch such as soft tissue and gas and soft tissue and bone ACOUSTIC ENHANCEMENT This artifact appears as localized area of increased echo amplitude behind an area of low attenuation Acoustic Enhancement can to differentiate fluid filled structures from solid , hypoechoic masses. Can commonly be seen distal to fluid filled structures such as the Urinary bladder, Gallbladder or a Cyst EDGE SHADOWING A combination of refraction and reflection occurring at the edge of rounded structures will results in edge shadowing artifacts It arises due to refraction of beam caused by both curvature of rounded edges and difference in speed of two materials When the ultrasound beam reaches the rounded edge of the structure reflection will occur with an angle of incidence equal to angle of reflection The combination of reflection and refraction of the beam sat the edges of a rounded structure results in a thin strip of tissue behind the edge not being inso nated and causes a shadow It occurs at edges of rounded structures such as Gallbladder and Cyst BEAM WIDTH ARTIFACT When the ultrasound beam is produced from the transducer its width starts to narrow as it approaches the focal zone. the structure outside the width of the main ultrasound beam if highly reflective will generate echoes that are assumed to originate within the main ultrasound beam It maybe recognized within echo free zones or anechoic structures such as Gallbladder and Blood vessels Correct positioning of the focal zone will help to reduce this artifact SLICE THICKNESS ARTIFACT This artifact is similar to the beam width artifact but occurs due to thickness of the beam which is transverse This artifact is caused by assuming that the ultrasound beam is thin like a sheet of paper but in reality it is not thin hence it is three dimensional Therefore structures above and below the beam can be mapped into the main ultrasound beam. This artifact can be found in anechoic structures such as Gallbladder, Urinary Bladder, Cyst and Blood vessels RING-DOWN ARTIFACT This is the type of reverberation artifact It occurs as a line or series of parallel bands extended posterior to a gas correction As a sound wave encounters gas bubbles the sound waves excites the gas bubbles causing them to vibrate The vibrations creates a continuous sound wave directed backward the transducer It occurs in the posterior collections of gas, such as Portal Venous gas, Gas in abscesses and Bowels COMET-TAIL ARTIFACT This is the form of reverberation artifact As the sound wave bounces between the transducer and the strong reflector resulting in multiple lines of artifact Thus, the sequential echoes are closely spaced that individual signals are not perceivable in the image It occurs in calcifications, biopsy clip and surgical clip PREVENTION; by decreasing the TGC in the near field as well as changing the beam angle DUPLICATE ARTIFACT This artifact is caused by refraction of the beam It occurs in areas such as rectus abdominis muscle on the anterior abdominal wall In transverse plane, the edges of the muscle acts as a lens and the ultrasound beam to be refracted and this causes a single structure to interrogated by two separate refracted beam The two sets of echoes will therefore be returned and this will cause display of two structures in the image MIRROR ARTIFACT They arise due to specular reflection of the beam sat a large smooth interface An area close to a specular reflector will be emerged twice, once by the original ultrasound beam and once by the beam after it has reflect off the specular reflector It is commonly seen when scanning the liver, the diaphragm acts as a specular reflector SIDE LOBE ARTIFACTS The energy within the ultrasound beam exists as several sidelobes radiating at a number of angles from a central lobe Echoes are generated by these lobes in addition to the main lobe but all the returning echoes are assumed by the transducer to have arisen from the central axis of the main lobe