Ultrasonography - Radiology - Lecture Notes, Study notes of Radiology

Download Ultrasonography - Radiology - Lecture Notes and more Study notes Radiology in PDF only on Docsity! ULTRASONOGRAPHY In today’s veterinary practice, the use of Ultrasonography (US) is becoming much more common place. In the past, US has only been available in larger practices or universities. As owners are now well aware of US, they often expect it will be available for their pet. US is non-invasive and does not use radiation so its quite safe. Ultrasonography vs. Radiography • They complement each other • Both have strengths and weaknesses • Cost concerns  correct selection – if cost is a concern, think about what specifically you are looking for and need to rule out. If you are worried about an obstruction of the GI tract for example, this might be better visualized on radiographs compared to US. • All patients should receive abdominal radiographs before Ultrasonography – this is what we shoot for on each case – but it doesn’t always work out as noted above. – Get all the information – May eliminate need for ultrasound – sometimes the diagnosis can be made from radiographs and US is not needed. Strengths of Ultrasonography • Determining origin of an abdominal mass – on radiographs, it may not be definitive which organ is affected • Evaluation of organ parenchyma – Liver, spleen, kidneys, adrenals, pancreas, intestines, prostate, bladder, heart – radiographs just provide an image of the silhouette of the organ – US lets you see inside • Fetal viability – heart beats of the fetus can be seen with US • Real time scanning – see movement/motion – this is great for hearts, like to evaluate contractility in a dilated cardiomyopathy case, or see the left ventricle in action in a hypertrophic cardiomyopathy kitty. Intestinal peristalsis can also be evaluated. • Performing fine needle aspiration/ biopsy – Cells or tissue NOT images ultimately give us the definitive diagnosis for neoplasia, etc. – Ultrasound does not provide a histopathologic diagnosis – different diseases can appear very similar on US so and FNA or biopsy might be needed. Weaknesses of Ultrasonography • Ultrasound can’t penetrate gas or bone – lungs, free air in abdomen, ribs etc make evaluation difficult – we can use gas and bone however to diagnose things – such as cystic calculi docsity.com • Difficult to evaluate liver size, kidney size in dogs – size is subjective on US • Can’t assess intestinal gas patterns • Can’t evaluate some extra abdominal structures (i.e. spine) • Equipment can be expensive – though this is becoming much less of an issue • Diagnostic success is user dependent – trash in = trash out. It takes a long time to become proficient at US. A weekend course using someone else’s machine wont cut it. You must know how to use YOUR machine. The best option in my opinion is to get a radiologist to work with you on your machine to become comfortable. Also it would be useful to select a person you could send CDs to which are in movie mode for a specialist to view. This way they can help you improve your scanning and also aid in the diagnosis. Interpretation often is best left to a very experienced sonographer. • Must know anatomy very well – it is again looking at anatomy in a different light – essentially cross sectionally. Why do you need both? • Examples – Prostatic adenocarcinoma seen on ultrasound • Has it spread to lumbar vertebrae? – Coughing patient with mitral regurgitation on echo • Does the patient have pulmonary edema? – Enlarged liver on radiographs • Can get a guided FNA with ultrasound Basic Ultrasound Physics • Transducer (probe) – produces the ultrasound beam A transducer is a device that can convert one form of energy into another. Ultrasonic transducers are used to convert an electrical signal into ultrasonic energy that can be transmitted into tissues and to convert ultrasonic energy reflected back from the tissues to an electrical signal. The most important component in the transducer is the piezoelectric crystal element. As the sound pulse passes through the body, echoes reflect back toward the transducer from each tissue interface. These echoes carry energy and transmit their energy to the transducer causing physical compression of the crystal elements – Piezoelectric crystal • Emit sound after electric charge applied • Sound reflected from patient • Returning echo is converted to electric signal- grayscale image on monitor • Echo may be reflected, transmitted, or refracted • Transmit 1% receive 99% of the time docsity.com Reverberation refers to the production of spurious echoes due to two or more reflectors in the sound path; the first reflector is usually the skin transducer interface. Internal reflectors such as bone or gas are also common causes of reverberation. Classic examples of this artifact are the internal echoes created by superficially located gas-filled bowel segments and the contact artifact created by interposition of a highly reflective interface (air) between the probe and the patient. The sound is entirely reflected back from the gas and then bounces back and forth between the probe and the gas, creating multiple echoes from one ultrasound pulse. The numerous lines represent several reflectors encountered by the sound beam. The number of reverberation images depends on the penetrating power of the beam and the sensitivity of the probe. Reverberation differs depending on the size, location, nature and number of reflectors encountered. Comet tail artifacts are produced by small, highly reflective interfaces such as metal objects or discrete gas bubbles. This artifact is easily recognized by its regular arrangement of bright continuous echoes. – Mirror image – liver diaphragm GB – when echoes bounce back and forth between 2 interfaces the return to the transducer time is extended. Therefore, a second image of the structure is placed deeper than it really is. – Comet tail – gas bubble – multiple bright streaks/bands deep to the reflective structure – Ring down – skin transducer surface • Acoustic shadowing – failure of the US beam to pass through an object because of reflection and or absorption of the beam. See a black area beyond the surface of the reflector. Bone, cystic calculus, lung. Shadowing is an artifact manifested as a hypointense signal area distal to an object. The low signal is caused by high attenuation, strong reflection or refraction of the beam. Highly attenuating objects such as bones or kidneys stones will manifest a low intensity streaking in the image. When u/s is incident on a curved surface, much of the incident beam is reflected or refracted away, resulting in dark streaks distal to the curved surfaces. - Area of low amplitude echoes created by structures of high attenuation - due to near total reflection or absorption - Gas "dirty shadow" due to reflection or reverb or both - more beam reflected - Bone "clean shadow" no reverb - mineral - more beam absorbed - Calculus must be near focal zone and at least as wide as beam to create a shadow Acoustic shadowing appears as an area of low amplitude echoes created by structures of high attenuation. Acoustic shadowing occurs as a result of nearly complete reflection or absorption of the sound. It can be produced by gas or bone. In gas-tissue interfaces ~99% of the sound is reflected. In bone-tissue interfaces 2/3 of the sound is reflected and a significant portion is absorbed. There are no reverberations and a uniformly black shadow is formed. Urinary calculi and gallstones tend to behave similarly to bone. Barium in a segment of bowel also appears as a clean shadow and produces attenuation of the sound due to reflection. docsity.com • Acoustic enhancement Enhancement is opposite of shadowing and occurs distal to objects with very low attenuation, such as fluid filled cavities (bladder and cyst). Hyperintense signal areas relative to the adjacent tissues not under the cavities occurs, because of the much greater attenuation of the intervening tissues. - Localized area of increase echo amplitude distal to a structure of low attenuation - Echoes past structure is attenuated less Acoustic enhancement is also known as through transmission. It represents a localized increase in echo amplitude occurring distal to a structure of low attenuation. The enhancement is seen as an area of increased brightness distal to the gallbladder or urinary bladder. This artifact is helpful in differentiating cystic structures from solid, hypoechoic masses. • Edge enhancement – Border of kidney Side Lobe and Slice Thickness Artifacts Lateral displacement of structures not aligned with the sound beam - Produced by minor beams traveling in different directions from the primary beam (side lobes) - If a side lobe of sufficient intensity interacts with a highly reflective interface the returning echoes will be erroneously placed along the path of the main beam - Curved surfaces and highly reflective interface - Less intense than real echoes from main beam - will disappear with lower instrument settings Lateral displacement of structures not aligned with the sound beam is called side-lobe artifact. Side lobe artifacts are produced by minor beams of sound traveling out in different directions than the primary ultrasound beam. The beam is composed of a main lobe and numerous secondary or side lobes of various intensities. When side lobes of sufficient intensity interact with a highly reflective interface, the returning echoes are erroneously placed on the path of the main ultrasound beam even though they did not originate within the main beam. Curved surfaces such as the diaphragm, bladder or gallbladder and a highly reflective interface such as with air are common conditions in which side-lobe artifacts occur. Slice thickness artifact In the bladder and gallbladder, a variant of the side-lobe artifact is the slice thickness artifact, which mimics the presence of sediment in the gallbladder or bladder also called pseudosludge. It is similar to the partial volume effect described in CT and occurs when part of the ultrasound beam’s width (thickness) is outside a cystic structure. Echoes originating from this part of the beam are erroneously displayed within the cystic structure on the image. The echoes disappear when the entire beam width is placed in the cystic structure. True sediment usually has a flat interface, whereas the surface of pseudosediment is curved. Changing the position of the animal will change the location of the sediment to the dependent portion of the bladder or gallbladder. The pseudo- docsity.com sediment interface remains perpendicular to the incident beam while true sediment interface changes with position. Ultrasound Terminology • Never use dense, opaque, lucent • Anechoic – No returning echoes= black (acellular fluid) • Echogenic – high or low can be use to qualify – Regarding fluid--some shade of grey d/t returning echoes – Echogenicity can also be called mixed – if both white and dark areas are noted. • Relative terms – Comparison to normal echogenicity of the same organ or other structure – * Hypoechoic = a structure which is of low echogenicity - it will appear blacker * Isoechoic = structure which is of equal echogenicity * Hyperechoic = a structure which is of higher echogenicity – it will appear whiter. • Spleen should be hyperechoic to liver Describing findings in terms of focal or diffuse, echogenicity, size, shape, margination and position should be used. Patient Positioning – Prep If the stomach or GIT is of interest, withholding food for 12 hours might be useful. Placing water in the stomach can help visualize the stomach wall and pancreas area just before the exam. Gas in the GIT can be very annoying and can limit visualization of abdominal organs. It is best to view the bladder under moderate distension. If the bladder is empty, a mass can be missed. If sedation is needed to perform the US exam, it should be noted than GI transit for example can be altered. • Dorsal recumbency – this is the way I prefer to scan – it is very similar anatomy wise to performing surgery from a ventral approach • Lateral recumbency – can be used if the patient is having difficulty breathing • Standing – large dogs like Danes that are hard to place on their backs. Urinary bladder calculi can also be imaged this way as well to see if they “are gravity dependent” • Clip hair – Be sure to check with owners (show animals) – the US beam can not penetrate air and air gets trapped in the hair of the patient. • Apply ultrasound gel – acoustic coupling gel • Alcohol can be used – esp. in horses Image Orientation and Labeling • Must be consistent – so if you can the animal one time and on recheck someone else scans they can look at your images and know what you saw. • Symbol on screen ~ dot on transducer docsity.com