Ultrasound

Ultrasound – What is it? Ultrasound Sound waves beyond the limit of human hearing Frequency of Diagnostic Ultrasound Non-invasive diagnostic tool used to compliment other imaging forms

Uses and Benefits of Diagnostic Ultrasound Image the heart in motion and its valves Image the liver and its internal structure Image the Urinary bladder and measure its thickness Look at the kidneys Intestines in motion Measure the thickness of the intestines Do pregnancy checks and check the fetuses Etc……

Uses and Benefits of Diagnostic Ultrasound Pain free procedure Generally no anesthetic needed No harmful side effects Able to see through the skin and look at organs See organs in motion Can measure the size of the chambers and valves of the heart as it beats Etc…..

Sound Waves Wave of energy must be transmitted through a medium Travel through medium while transferring energy They travel back to the transducer, are analyzed, and are displayed on the screen

Sound waves Described by their Frequency Wavelength Velocity

Physical Properties - How do sound waves work? Frequency 2-15 MHz in ultrasound

Physical Properties - How do sound waves work? Wavelength

Physical Properties - How do sound waves work? Frequency and Wavelength Inverse relationship Affects the choice of frequency used in each patient High frequency Low frequency

Physical Properties - How do sound waves work? Velocity Time required for a wavelength to pass a given point Independent of the frequency Changes depending on the medium it is traveling through

Physical Properties - How do sound waves work? Velocity - continued Eg: velocity of sound is 331 m/sec in air and 4,080 m/sec in bone Within soft tissue of the body it is steady at 1,540 m/sec This medium - dependent variation affects the ultrasound image produced Velocity (m/sec) = Frequency (cycles/sec) x Wavelength (m)

Image Production Piezoelectric effect Explains how ultrasound is generated from ceramic crystals in the transducer An electric current passes through a cable to a transducer and is applied to the crystals causing them to vibrate This vibration produces the ultrasound beam The frequency of the ultrasound waves produced is determined by the crystals in the transducer

Image Production Pulse-echo Principle Explains how the image is generated Between pulses, the ultrasound beam enters the patient and is bounced back to the transducer The crystals vibrate and produce an electrical signal that is converted to an image on the monitor

Interaction with tissues Ultrasound produced by the transducer interacts with different tissues in a variety of ways Attenuation Refraction

Interaction with tissues Attenuation Caused by Reflection Scattering Absorption of sound waves Compensated for by use of specific controls

Interaction with tissues Attenuation Reflection (echo) Occurs when ultrasound waves are bounced back to the transducer for image generation The portion reflected is determined by the difference in acoustic impedance between adjacent structures

Acoustic impedance Describes the ability of sound to penetrate a material Related to density Speed of the sound (velocity) Fraction that is reflected how different the 2 materials are More difference in impedance = more sound reflected Air vs water Very different impedance Almost entirely reflected Only a small amount of sound waves enter the water

Interaction with tissues Attenuation Scattering The redirection of ultrasound waves as they interact with small, rough, or uneven structures Occurs inside the organs, and is responsible for Increases with higher frequency transducers

Interaction with tissues Attenuation Absorption Occurs when the energy of the ultrasound beam is converted to heat Only process that directly removes energy from the ultrasound waves

Interaction with tissues Refraction Occurs when the ultrasound beam hits a structure at an oblique angle The change in tissue density produces a change in velocity causing the beam to bend or refract Altering the beams direction This type of tissue interaction causes artifacts Distinct shadow appears below lateral edges of fluid filled structures

Interaction with tissues Refraction – generates several artifacts Edge shadowing Distance enhancement

Terminology Echogenicity Anechoic Hyperechoic – more echoes Hypoechoic – fewer echoes Isoechoic

Least echogenic to most echogenic Renal medulla Liver Renal cortex Spleen Prostate Renal sinus fat

Artifacts Reverberation Shadowing Acoustic enhancement Refraction/edge artifact Mirror-image artifact

Reverberation Occurs when beam hits a highly reflective tissue interface Entire beam is reflected back to transducer and it gets reflected back into patient Hits interface again and repeats Appears as a set of bright parallel lines

Acoustic Shadowing Occurs because of inadequate penetration by the sound beam In a highly reflective or sound-absorptive substance Area of darkness Occurs deep to dense material

Refraction/edge artifact Hypoechoic band at the margin of a curved structure Bending of the sound beam due to oblique angle Edge artifact helpful in ID smooth round structures Early pregnancy vesicles

Distance enhancement When beam passes through an area with low attenuation

Display Modes Information generated from an ultrasound examination can be displayed in a variety of ways, called modes. The mode used for display depends on the type of ultrasound unit used, the information to be obtained, and the organ being examined.

Display Modes A (Amplitude) Mode Used in ophthalmology Not used much anymore

Display Modes B (Brightness) Mode Echoes are represented as dots on a line that form the basis for a two-dimensional image The returning echo’s location on the axis is based on the amount of time it takes for the ultrasound wave to be transmitted and reflected Echoes in the near field (close to the transducer) take less time than those far away

Display Modes Real-time B (Brightness)Mode Allows a complete, two-dimensional, cross-sectional image to be generated by using multiple B-mode lines The transducer sweeps many times a second producing a new complete image Several sweeps are performed each second producing a “real time” image

Display Modes M (Motion) Mode Used in echocardiography Allows the sonographer to measure the heart to assess cardiac function and chamber size Uses a single B-mode line

Doppler Echocardiography Assesses turbulence and velocity of red blood cells within a vessel by measuring the doppler shift Color is added to better detect subtle abnormalities Evaluates pulmonic, aortic, mitral, and tricuspid valvular insufficiencies Evaluates stenosis and congenital heart defects such as VSD and PDA

Image optimization Transducers – classified according to the arrangement (array) of the crystals and the shape of the imaging field produced on the monitor Linear Sector

Image optimization Linear transducer Provide superior resolution of near-field structures Commonly used in equine reproduction and tendon examinations Limited use in cardiac and abdominal studies

Image optimization Sector transducer Curvilinear array Produces a fan-shaped image Narrow near-field, broad far-field Helpful in imaging deeper structures Useful in small animals and cardiac exams

Image optimization Convex/microconvex Compromise between linear and sector Good resolution, pie shaped field

Image optimization To obtain the best resolution, it is recommended to use the highest-frequency transducer that will penetrate to the desired depth. In general, a 3.5-MHz probe will be needed in large dogs, a 5.0-MHz probe in medium dogs, and a 7.5- to 10-MHz probe in small dogs and cats, depending on the type of study being conducted.

Image optimization Care of transducer If using in large animal use protective covering

Unit Controls Power control Alters the intensity of the ultrasound beam Alters the amount of voltage that is delivered to the crystals

Unit Controls Gain Control Alters the brightness of all the echoes on the monitor Ultrasound waves are attenuated If didn’t have this control there would be a light to dark gradient from near to far field Gain Compensation Control Allows the sonographer to adjust the amplification at various depths

Unit Controls Depth Control Controls the depth of the image display Scale on 1 side of screen that measure depth in cm

Abdominal ultrasound Patient prep NPO both food and water Ingesta causes more gas

Abdominal Ultrasound Patient Prep Full urinary bladder is ideal for scanning bladder and prostate Clip hair coat – costal arch, flank, caudally to the bladder Apply coupling gel Ventrodorsal or lateral recumbancy

Abdominal Ultrasound Liver and Biliary Tract Survey radiographs are superior to ultrasound for assessing liver volume Indications for liver scanning – hepatomegaly or a mass seen on survey, elevations in liver enzymes, ascites, suspected hepatic mets Ultrasound guided biopsy often performed

Abdominal Ultrasound Spleen Indications for scanning – mass, diffuse enlargement, abnormal position identified on survey radiographs, also abdominal trauma with hemorrhage, acute abdominal pain, signs of anemia and collapse

Abdominal Ultrasound Pancreas Pancreatitis is the most common reason for scanning Neoplasm, cysts and abscesses are rare

Abdominal Ultrasound Gastrointestinal Tract Difficult due to gas and feces Used to identify GI mural masses, foreign bodies, to confirm intussusception String in intestine

Abdominal Ultrasound Kidneys and adrenal glands Used to identify kidneys not seen on survey Characterize a mass seen on survey Assess enlarged kidneys Determine location of mineralizations Confirm fluid accumulations in the kidneys Adrenals – determine enlargement

Abdominal Ultrasound Prostate Indicated in Prostatomegaly Signs of urinary tract disease Constipation Caudal abdominal pain U/S guided biopsy to determine BPH from neoplasia/infection Full bladder helps to visualize

Abdominal Ultrasound Urinary Bladder Tumors Calculi Blood clots

Abdominal Ultrasound Reproductive tract Pregnant uterus Optimal time for detection of pregnancy is 25-30 days after last breeding Equine 13-14 days Non-pregnant uterus Pyometra Stump granuloma Ovarian neoplasia

Ultrasound of the Eye After application of topical anesthetic directly on the cornea Evaluates Cornea Anterior chamber Ciliary body and lens Vitreous chamber Optic disc Optic nerve Extraocular muscle Retrobulbar fat

Echocardiography Allows rapid assessment of functional compromise Detection of chamber size abnormalities Pleural and pericardial effusion Cardiac masses Congenital abnormalities Valvular motion (M-mode)

Extremities Most useful in the equine limb Traumatic injury Infection Inflammation