Ultrasound Artifacts PDF

ULTRASOUND ARTIFACTS Lesson 6 Lesson Objectives 1. Define ultrasound artifacts. 2. Identify the different types of ultrasound artifacts. 3. Describe the different types of ultrasound artifacts. 4. Discuss how the different types of ultrasound artifacts affects ultrasound scans. ARTI...

ULTRASOUND ARTIFACTS Lesson 6 Lesson Objectives 1. Define ultrasound artifacts. 2. Identify the different types of ultrasound artifacts. 3. Describe the different types of ultrasound artifacts. 4. Discuss how the different types of ultrasound artifacts affects ultrasound scans. ARTIFACTS Unwanted marks in the radiograph. Artifacts can obscure important anatomical details, potentially leading to misdiagnosis or the need for repeat imaging. ARTIFACTS IN ULTRASOUND Part of an ultrasound image which does not represent or directly correlate to the actual anatomic structures being evaluated. An additional, missing or distorted image which does not conform to the real image of the part being examined. Ultrasound artifacts are commonly encountered, and familiarity is necessary to avoid false diagnoses. Artifacts in Ultrasound In some cases, specific artifacts can even offer valuable diagnostic information. For instance, some artifacts may be indicative of certain pathologies. FRIEND or FOE? Different Forms of Ultrasound Artifacts Structures that are not actually present Objects that should be represented but are missing from the image Structures that are misregistered Different Forms of Ultrasound Artifacts The following descriptions represents some typical artifacts encountered in diagnostic ultrasound. ACOUSTIC ENHANCEMENT Acoustic enhancement also called posterior enhancement or enhanced through transmission, refers to the increased echoes deep to structures that transmit sound exceptionally well. This is characteristic of fluid-filled structures such as cysts, the urinary bladder and the gallbladder. The fluid only attenuates the sound less (low attenuating objects) than the surrounding tissue. ACOUSTIC ENHANCEMENT ACOUSTIC ENHANCEMENT ACOUSTIC SHADOWING Acoustic shadowing (posterior acoustic shadowing. Characterized by the apparent lack of signal deep to an imaged tissue interface, due to all of the transmitted sound wave being reflected back to the transducer or absorbed by the tissue. It commonly occurs when an area of interest contains a high Z/solid tissue (e.g. calcified gallstone or bone) or at an interface with high acoustic impedance mismatch (e.g. soft tissue /air). ACOUSTIC SHADOWING Diagnostic Significance Limits the examination of body regions behind gas or bone. Useful in diagnosing stones, calcifications or foreign bodies. ACOUSTIC SHADOWING ACOUSTIC SHADOWING EDGE SHADOWING Edge shadowing occurs at the edges of rounded tissue structures caused by reflection away from the beam at the boundary edge and refraction of the beam within the structure. These interactions result in an edge shadow, an example of which is shown for an internal carotid artery. EDGE SHADOWING EDGE SHADOWING CLEAN SHADOWING AND DIRTY SHADOWING Clean and dirty shadowing are common phenomena in ultrasound imaging. Clean shadowing is produced by sound- absorbing materials (ie, stones), and dirty shadowing is by sound-reflecting materials (ie, abdominal gas), but these properties are not consistent. CLEAN SHADOWING AND DIRTY SHADOWING REVERBERATION ARTIFACT Reverberation artifacts are a result of the presence of two or more strong reflecting surfaces. When the ultrasound beam reflects back and forth between the reflectors ("reverberates"), the ultrasound transducer interprets the sound waves returning as deeper structures since it took longer for the wave to return to the transducer. REVERBERATION ARTIFACT REVERBERATION ARTIFACT COMET TAIL A type of reverberation artifact. This results in a short train of reverberations from an echogenic focus which has strong parallel reflectors within it (e.g. cholesterol crystals in adenomyomatosis). With comet tail artifact, the space between the two strong parallel reflectors may be less than 1/2 the space pulse length, causing the echoes to be displayed as triangular lines (the later echoes get attenuated and have a decreased amplitude, manifesting on the display as decreased width). COMET TAIL Sm a l l r e n a l o r u r e te r ic ca l cu li Sm a l l co m m o n b i l e d u ct s to n e s A d e n o myo ma tos is o f th e g a l lb ladd er Pa n cr e a tic ca l ci f ication s o f ch r o n i c p a n c r e a titis Te s ti cula r m i cr o lith ias is ( s o m e time s ) Thy r o id co l l oid n o d u l es Id e n tif ica tion o f f o r e ig n b o d i es Su r g i cal clip s C a th e ter ti p s D e b r is / g las s / me tal COMET TAIL RING DOWN ARTIFACTS Appears as a solid streak or a series of parallel bands (ladder like) radiating away from abdominal gas collections. The artifact is only associated with gas bubbles The trapped fluid resonates, emitting a continuous signal back to the transducer. Whereas the transducer pulse is broad spectrum, the returning signal consists of one or more discrete (resonant) frequencies. "Beats" between these frequencies produce the variable appearance of the ring down. There is no "reverberation" RING DOWN ARTIFACTS RING DOWN ARTIFACTS SIDE LOBE ARTIFACTS Side lobe artifacts occur where side lobes reflect sound from a strong reflector that is outside of the central beam, and where the echoes are displayed as if they originated from within the central beam. These artifacts are caused by low energy ‘side lobes’ of the main ultrasound beam. Side lobe beam returns to the receiver and is assigned to the false location as the main beam. SIDE LOBE ARTIFACTS SIDE LOBE ARTIFACTS MIRROR IMAGE ARTIFACT Mirror image ar tifact in sonography is seen when there is a highly ref lective sur face (e.g. diaphragm) in the path of the primary beam. The primary beam ref lects from such a surface (e.g. diaphragm) but instead of directly being received by the transducer, it encounters another structure (e.g. a nodular lesion) in its path and is ref lected back to the highly ref lective sur face (e.g. diaphragm). It then again ref lects back towards the transducer. The ultrasound machine makes a false assumption that the returning echo has been ref lected once and hence the delayed echoes are judged as if being returned from a deeper structure, thus giving a mirror ar tifact on the other side of the ref lective sur face. MIRROR IMAGE ARTIFACT MIRROR IMAGE ARTIFACT  DOUBLE IMAGE ARTIFACT This ar tifact is caused by refraction of the beam and may occur in areas such as the rectus abdominis muscle on the anterior abdominal wall. In the transverse plane the edges of the muscle act as a lens and the ultrasound beam to be refracted and this causes the single structure to be interrogated by two separate refracted beams. Two sets of echoes will be returned, and these will cause display of two structures in the image. SPEED DISPLACEMENT ARTIFACT Speed displacement artifact, also known as propagation velocity artifact, is a gray scale ultrasound finding that can be identified as an area of focal discontinuity and displacement of an echo deeper than that its actual position in an imaged structure. SPEED DISPLACEMENT ARTIFACT Depth determination by an ultrasound machine is based on the principle that the average propagation velocity of sound in human tissue is 1540 m /s, and as such the time between broadcasting and detecting the returned sound wave to the transducer is multiplied by this number and halved to determine distance, regardless of tissue type. As a result, if the true propagation velocity of a tissue falls significantly below or above 1540 m /s, such as fat or bone, then the distance calculated by the machine will be false, displaying an inaccurate depth measurement. SPEED DISPLACEMENT ARTIFACT  TWINKLING ARTIFACT Twinkling artifact is seen with color flow Doppler ultrasound. It occurs as a focus of alternating colors on Doppler signal behind a reflective object (such as a calculus), which gives the appearance of turbulent blood flow. It appears with or without an associated color comet tail artifact. Twinkling artifact is more sensitive for detection of small stones (e.g. urolithiasis, cholelithiasis) than is acoustic shadowing. EQUIPMENT-GENERATED ARTIFACTS Incorrect use of the equipment controls can lead to artifacts appearing. If too much gain is applied then the electronic noise, inherent in all systems, will also be amplified. If too little gain is applied, this can lead to loss of relevant information, and incorrect diagnosis may occur.