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 it’s 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 a 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
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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
– 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
Acoustic Impedance
• The velocity of sound in a tissue and tissue density = determine acoustic
impedance – acoustic impedance allows differentiation of separate structures
in an US image. This is because different soft tissues for example have
slightly different acoustic impedances.
• Most soft tissues = 1400-1600m/sec
• Bone = 4080, Air = 330
– Sound will not penetrate – gets reflected or absorbed
• Travel time – dot depth – the time interval between transmission of the sound
beam and the reception of the echo that returns
Attenuation = removal of energy from the sound wave as it travels through tissue.
• Absorption = energy is captured by the tissue then converted to heat
• Reflection = occurs at interfaces between tissues of different acoustic
properties
• Scattering = beam hits irregular interface – beam gets scattered
Basic Ultrasound Physics
• Sound waves are measured in Hertz (Hz)
• Diagnostic ultrasound typically
– 1-20 MHz
• As frequency increases, resolution improves
• As frequency increases, depth of penetration decreases
Transducers
• Sector scanner – fan shaped beam
– Small surface require for contact
• Linear scanner – rectangle beam
– Large contact area required
– New ones are curvi-linear
• These scan heads are much smaller with wide field of view
Basic Ultrasound Physics
• Monitor and computer – many now are the size of a lap top computer and
many use the windows XP platform
– Convert signal to an image/ archive
– Tools for image manipulation
• Gain – amplification of returning echoes
– Overall brightness – this is usually a single knob
• Time gain compensation (curve)
– Adjust brightness at different depths – this is usually multiple
structures placed in a slide fashion – I usually place mine on a
diagonal. The curve can be seen on the monitor image along the
side.
• Freeze
• Depth
– Zoom in superficial, or zoom out for wide view
– Depth limited by frequency
• Focal zone
– Optimal resolution wherever focal zone is
Modes of Display
• A mode
– Spikes – where precise length and depth measurements are needed –
ophtho
• B mode (brightness) – used most often
– 2 D reconstruction of the image slice
• M mode – motion mode – function of time on a horizontal axis
– Moving 1D image – cardiac mainly
Doppler – used to identify the presence or absence of flow. The direction and
velocity of flow can be visualized and calculated and turbulence can also be
seen.
Artifacts
• Improper machine settings – gain
Excessive TGC can result in an acceptable image in the far field but the near
field will be too bright. Inadequate TGC can result in an acceptable image in the
near field but the far field will be too dark.
• Reverberation – time delays due to bouncing back and forth
– 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.
• Acoustic enhancement
• Edge enhancement
– Border of kidney
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 echogencity * Hyperechoic
= a structure which is of higher echogencity – 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 cannot
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 scan 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
• “dot” to head and “dot” to patients right
• “dot” lateral for transverse and proximal for longitudinal images of limbs
For distance – use from the accessory carpal or calcaneal bones – such as
lesion located 5 cm distal to the ACB
• Label label label
Indications for Abdominal Ultrasonography
• Same as with abdominal radiographs
• Should have some idea of what you are looking for—not just a fishing
expedition
• Further investigate a radiographic finding
• ***If clinical signs or history indicate abdominal ultrasound, then it should be
performed even if radiographs are normal!!!
Ultrasound-guided FNA/ biopsies
• NORMAL ABD U/S FINDINGS DO NOT MEAN ORGANS ARE NORMAL!!!
***Do FNA if suspect disease
• Abnormal u/s findings nonspecific
– Benign and malignant masses identical
– Bright liver may be secondary to Cushing’s disease or lymphoma
• Aspirate abnormal structures (with few exceptions)!!!
– Obtain owner approval prior to exam
– Warn owner of risks
– +/- Clotting profile
• Risks of FNA’s
– Fatal hemorrhage
– Pneumothorax w/ pulmonary masses
– Seeding of tumors
• TCC
– Sepsis
• Abscesses
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• I Routinely aspirate
– Liver (masses and diffuse disease)
– Spleen (nodules and diffuse disease)
– Gastrointestinal masses
– Enlarged lymph nodes
– Enlarged prostate
– Pulmonary/ mediastinal masses (usually don’t biopsy due to risk of
pneumothorax
• I Occasionally aspirate
– Kidneys (esp. if enlarged)
– Pancreas
– Urinary bladder masses
• I Never aspirate
– Adrenals
– Gall bladder
• Non-aspiration Technique
– 22g 1.5in needle
– 6 cc syringe
– Short jabs into organ
– Spray onto slide, smear, and check abd for hemorrhage
• Aspiration technique
– Same set up as with non-aspiration technique
– With needle in structure, pull back plunger vigorously several times
– Remove needle, fill syringe with air
– Spray onto slide and smear
Ultrasound-guided Core Biopsies
• Use a special biopsy “gun”
– 14-20g
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Insert thru small skin incision
• Much more representative sample
– Tissue not just cells
– Sometimes it is necessary to get the answer
– But…. MUCH MORE LIKELY TO BLEED!
Common Applications of Abdominal Ultrasonography
• Liver
– Nodules, masses, cysts
– Infiltrative disease
• Lymphoma
– Diffuse dz
• Hepatitis
– Biliary obstruction
– Portosystemic shunts
• Spleen
– Nodules, masses, hematomas
– Infiltrative disease
Splenic hemangiosarcoma, hematoma, and nodular hyperplasia all look alike!
• Pancreas
– Pancreatitis
– Masses, cysts
• Gastrointestinal tract
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May be limited by gas, ingesta, feces
Dilation
Motility
Masses
Intussusceptions
Inflammatory/ infiltrative dz
• Adrenals
– Adrenomegaly
• Bilateral vs. unilateral enlargement
– Masses
• Kidneys
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Chronic renal disease
Infarcts
Hydronephrosis/ pyelectasia
Pyelonephritis
Calculi
PKD
• Urinary bladder
– Cystitis
– Neoplasia
– Calculi
• All types are visible
• Reproductive tract
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Pregnancy (fetal viability), pyometra
Ovarian/ testicular masses
Prostatic disease
– Hyperplasia
– Neoplasia
– Prostatitis/ abscesses
– Prostatic/ paraprostatic cysts
• Lymph nodes
– Lymphoma, metastasis, reactive nodes
• Mesenteric
• Aortic
• Sublumbar (medial iliac, hypogastric)
• Organ specific nodes
• Peritoneum
– Abdominocentesis with small volumes
Echocardiography
• Contractility, chamber size, wall thickness
• Septal defect and other anomalies
• Valvular abnormalities
• Pericardial effusion/ pericardiocentesis
• Heart base, myocardial tumors
Non-cardiac Thoracic Ultrasonography
• Mediastinal masses
• Pulmonary/ pleural masses
• Diaphragmatic hernia
• Thoracocentesis for small volume pleural effusion
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Head
– Ocular
• Cataracts
• Retinal detachment
• Intraocular masses
• Retrobulbar masses
– Brain
• If have open fontanelle
• Hydrocephalus
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Neck
– Thyroid and parathyroid gland
• Adenomas, adenocarcinomas
– Carotid a. and jugular v.
Musculoskeletal
• Tendons and ligaments
– Trauma
• Tendonitis
• Desmitis
– Joint or tendon sheath effusion
• Bone
– Limited value with U/S
– Sometimes to find area to FNA
Final Notes
• Know your limitations
– Lack of expertise
– $15,000 vs. $150,000 machine depending on bells and whistles selected
• For abd or thx, do radiographs first
• If safe and reasonable, do FNA’s of all suspected abnormal structures based
on history, clinical signs, or the ultrasound exam
– Abnormal structures can look normal
– Of the structures that do look abnormal, benign and malignant processes
can be identical
• Documentation – save images in some fashion