Introduction to Ultrasound PDF

Basic Ultrasonography Shona McIntyre BVMS MRCVS Learning Outcomes To understand the generation and delivery of ultrasound and the difference between the standard probes To be able to describe an ultrasonographic image in terms of image quality and positioning in relation to tissues of int...

Basic Ultrasonography Shona McIntyre BVMS MRCVS Learning Outcomes To understand the generation and delivery of ultrasound and the difference between the standard probes To be able to describe an ultrasonographic image in terms of image quality and positioning in relation to tissues of interest To describe potential imaging faults and the means to avoid, identify and account for such faults Discuss the relative advantages and disadvantages of abdominal ultrasound and radiography 2 Basic Ultrasound Principals Ultrasound uses transmission of sound waves through tissue to produce an image A current is applied to the piezo-elements in the transducer This causes the crystals to change shape and oscillate, producing an ultrasound wave Returning sound waves are received at the transducer, causing compression of the crystals and thus an electric voltage This signal is then amplified, converted, and displayed as a dot on the screen 3 Interaction with tissues 1. Reflection – a wave is reflected back to the transducer and called an echo 2. Refraction - the change in direction of a wave due to differing velocities of tissues 3. Diffraction – change in direction of a wave through an opening or around a barrier. Allows sound waves to be detected around a corner 4. Attenuation – loss of energy of the wave due to scatter or absorption 4 Interaction with tissues Reflection Refraction 5 Interaction with tissues Diffraction Scatter 6 Ultrasound Probes Linear Array Curved Array Phased Array Crystals in a line Crystals in a curve Crystals in a line Rectangular image Fan shaped image Fan shape – greater depth No near field Some near field Steered artefact artefact electronically Large footprint Smaller footprint Smaller footprint 7 Basic Ultrasound Principles Frequency High Frequency Low Frequency Good axial resolution Poor axial resolution More rapid beam Less rapid beam attenuation attenuation Poor penetration Better penetration Axial resolution The ability to determine two points along the path of the beam 8 Axial Resolution 9 Basic Ultrasound Principles Depth 10 Basic Ultrasound Principles Gain Changes the overall brightness of the image If Gain too high – Increase in “noise” 11 Basic Ultrasound Principles Time Gain Compensation Echoes from deeper tissues are weaker due to attenuation TGC controls brightness at different levels though the tissue 12 Basic Ultrasound Principles Focus / Focal Zone Area where image is optimised by focusing the sound wave Most often shown by triangular marker Keep region interest in focal zone Improves lateral resolution Lateral Resolution The ability to determine 2 points perpendicular to the beam Determined by beam width Narrow beam = better lateral resolution 13 Lateral resolution 14 Ultrasound Artefacts Reverberation Cause parallel bright lines Mirror Image At curved reflective surface Acoustic Enhancement Caused by lack attenuation, i.e. through fluid Bright area deep to fluid structure Poor Probe Contact Often insufficient clipping or not enough gel 15 Ultrasound Artefacts Reverberation Mirror Image 16 Ultrasound Artefacts Acoustic Enhancement 17 Ultrasound Artefacts Acoustic Shadowing If meet highly reflective interface get complete reflection and distal shadow (if gas get a comet tail) Edge Shadowing Acoustic shadow distal to lateral aspect cystic structure Slice thickness Part of beam is wider than a cystic structure Mimics tissue interface 18 Ultrasound Artefacts Distal acoustic shadow Slice thickness 19  Describing an ultrasound image Echogenicity Normal organs and tissues are displayed as shades of grey Isoechoic - structures the same shade of grey Hypoechoic - Describes a structure that is a darker shade of grey Hyperechoic - Describes a structure that is a lighter shade of grey Anechoic - Describes a structure that is black 20 Describing an ultrasound image Echotexture The image is made up of large (coarse) or small (fine) dots. These contribute to echotexture Homogeneous - a uniform distribution of grey shade (echogenicity) or dot size (echotexture) Heterogeneous - a non uniform distribution of grey shade (echogenicity) or dot size (echotexture) 21 Describing an ultrasound image Describing a lesion Roentgen Signs Number Size Shape Margin Location Echogenicity and echotexture Artefacts LEMONS Location, Echotexture, Measurements, Outline, Number, Size 22 Abdominal Ultrasound 23 Abdominal Ultrasound Indications Elective Any condition involving an abdominal organ Identifying and describing abdominal tumours Staging of neoplasia Intra-abdominal biopsy System specific investigation – Reproductive tract 24  Abdominal Ultrasound Indications Emergency POCUS scan Used to identify free fluid, often following trauma Where to scan: DH: diaphragmatic hepatic HR: hepato-renal SR: spleno-renal CC: cysto-colic 25 Benefits of Abdominal Ultrasound Non-invasive and safe General anaesthesia not required Excellent morphological information and good resolution Information from all major organs Real-time sampling of tissues possible Relatively inexpensive 26 Disadvantages of Abdominal Ultrasound Limited functional information Diffuse disease more difficult to detect Sampling required to classify disease Patient needs to be clipped Sedation often required Gas interferes with sound transmission Technically demanding to get good results Images cannot be interpreted by a specialist as taken in real-time 27 Patient Preparation Withhold food – ideally 8 hours – allow water to drink Extensive clipping Wash patient down to remove stray hairs Apply liberal amounts coupling gel Sedation as required Lateral recumbency 28 Patient Preparation Allow plenty of time for examination Use a darkened, quiet room Ensure table at correct height Vet bed or similar for comfort of patient Sufficient assistance from nurses 29  Abdominal Ultrasound A systematic approach is required so as not to miss anything Right lateral recumbency Left lateral recumbency Left Liver Right liver Gastric fundus and body Biliary system Spleen Pylorus Left limb pancreas Duodenum Left kidney and adrenal Right pancreas Small intestine Right kidney and adrenal Colon Urinary bladder (+/- prostate) 30  Abdominal ultrasonography Ultrasound Guided Techniques Ultrasound guidance improves target acquisition Abdominocentesis Cystocentesis – providing sterile sample for C&S Needle + FNA, Trucut mass, liver, spleen Syringe Transducer Tissue Samples can be obtained for cytology and histology Must aseptically prepare skin Mass lesion Ultrasound Apply spirit to skin beam Protect probe in glove with copious gel 31 Echocardiography 32 Echocardiography Indications Heart murmurs ECG abnormalities Radiography abnormalities Hypertension Dyspnoea Syncope Arterial thromboembolism Identification phenotypically normal animals prior to breeding 33  Patient Preparation Clip right and left side over the apex beat Patient in lateral recumbency on a table with a cut out Heart falls towards thoracic wall to allow visualisation through lung window R side 3rd to 6th intercostal space L side 5th to 7th intercostal space 34 Echocardiography Standard Views Right parasternal long axis view Right parasternal short axis view Papillary muscle Chordae tendinae Mitral valve Aortic valve Subcostal view Left apical 4 and 5 chamber view 35 Echocardiography Right parasternal Long Axis view 36 Echocardiography B mode M Mode Doppler - Colour flow doppler Pictures courtesy of A. Denning 37 Thoracic ultrasound Arrow = Normal lung surface. Smooth hyperechoic line * = Rib. Hyperechoic line with distal acoustic shadow Images courtesy of BSAVA Manual of canine and feline ultrasonography 38 TFAST Thoracic Focused Assessment with Sonography for Trauma Used to examine for pleural space disease and pericardial effusions. 5-point scan Chest tube site (CTS) (x2) Pericardial site (PCS) (x2) Diaphragmaticohepatic view (DH) Fluid = hypoechoic effusion present Air = absence of the ‘glide sign’ 39  Vet BLUE assessment - assessment of pulmonary parenchyma Evaluation of the thorax in 4 areas Caudodorsal lung lobe region (cdll) Middle lung lobe region (mdll) Perihilar lung lobe region (phll) Cranial lung lobe region (crll) Cole,L. Pivetta,M. Humm,K. JSAP (2021) 62,178-186 40 41 Summary Understand basic ultrasonographic principles Recognise commonly encountered artefacts Patient preparation Benefits of abdominal ultrasound over radiography Have a basic understanding of use of ultrasound in thorax 42