4. Ultrasonography, Computed Tomography, & Magnetic Resonance Imaging

True or false: You can literally ultrasound anything. All you have to know is your anatomy.

true

In ultrasonography, high-frequency ________ waves penetrate tissue (or don’t) and bounce back to the transducer. In order to be effective, ________/________ is needed.

sound; water/fluid

How is the electric current generated in ultrasound?

crystals in the transducer convert the sound waves to electric current

How is an image produced with ultrasound?

computer in ultrasound machine converts the electric current to an image

How does fluid appear on ultrasound?

black

How does soft tissue (liver) appear on ultrasound?

gray

How does fibrous tissue (diaphragm) appear on ultrasound?

white

How does solid material appear on ultrasound?

white line with black under it

Sound waves do not go through ________ or ________ things.

air; solid

When using ultrasound, we must think about the ________ content of the tissue.

water

Waves travel in a ________ from the ________.

straight; probe

color indicates that there are no waves back

black

color indicates that all the waves come back

white

color indicates that there are some waves back

grey

What is the orange arrow showing?

skin

What is the yellow arrow showing?

fluid

What is the purple arrow showing?

bone

Air is not ________. Therefore, ________ the waves ________ ________.

fluid; all; bounce back

black color on the ultrasound

anechoic

less black but darker than other tissues

hypoechoic

equal grey scale

isoechoic

more white / bright

hyperechoic

cannot see below a structure that reflects back all waves

acoustic shadow

What artifact is this showing?

acoustic shadow

brightness deep to anechoic structure

acoustic enhancement

What artifact is this showing?

acoustic enhancement

sound waves reflecting multiple times between 2 strong reflectors

reverberation artifact

What artifact is this showing?

reverberation artifact

Where is reverberation artifact most common?

lung

duplication of image of the opposite side of a strong reflector

mirror image artifact

What artifact is this showing?

mirror image artifact

Where is a mirror image artifact the most common to be found? What medium would be the strong reflector here?

thorax/abdomen interface; diaphragm

artifact that occurs when imaging a 3D structure with anechoic fluid

slice thickness artifact

What artifact is this showing?

slice thickness artifact

Where would a slide thickness artifact be most commonly found?

bladder and gall bladder (artificial sludge)

when sound waves bend as they hit a curved surface tangentially

edge-shadowing artifact

What artifact is this showing?

edge-shadowing artifact

What are the types of ultrasound probes (transducers)?

linear and curvilinear (sector)

Which type of ultrasound probe is most commonly used for equine tendons and gives a large footprint?

linear

Which type of ultrasound probe is most commonly used for small and large animal thorax and abdomen, and has a small footprint?

curvilinear

True or false: Quality of the transducer dictates the quality of the machine and image, and is the most valuable part of the machine.

true

Increased frequency (mHz) means ________ resolution, but ________ depth.

greater; less

Decreased frequency (mHz) means ________ resolution, but ________ depth.

less; greater

What are some indications for ultrasonography?

I
I

• image soft tissue (anything with water content)

• image surface of bone and lung for irregularity

When using ultrasound, how many planes need to be imaged? What are they?

2; transverse and longitudinal

What does the transverse plane tell us?

size of the lesion

What does the longitudinal plane tell us?

how much of the tissue (length) is involved with the lesion

True or false: Ultrasonography can be used for real-time imaging and has Doppler mode.

true

Using real-time imaging with ultrasonography, what can be assesse?

M
D

• movement

• direction of blood flow

x-ray tube in a circle that rotates at a pre-determined speed

computed tomography (CT)

What allows for the differentiation of structures in CT? What is this similar to?

the intensity of x-ray; radiographs

In computer tomography, a ________ reconstructs the data acquired from the detectors to make a “slice” image.

computer

True or false: In CT, software programs can reconstruct slices into a 3D image.

true

In tomography, ________ slices allow ________ location. In radiographs, you must take ________ views to figure this out.

2D; 3D; many

In CT, what structures cannot be seen?

soft tissue

In order to take a CT, how does the animal have to be?

anesthetized or very heavily sedated

CT imaging in a horse is generally limited to what?

C
D
H

• carpus/tarsus

• digit

• head

What are indications for CT?

D
I
I
I

• detailed evaluation of bone

• image the head

• image the spine

• image the abdomen

In CT, what does any imaging of soft tissues require?

injection of contrast solution to enhance the contrast of soft tissues

All tissues have a lot of what proton? Why?

hydrogen protons; they are made of water (H2O)

In

True or false: Protons in different tissues relax differently and there is superior contrast in tissues.

true

When using MRI, what is extremely important to remember?

R
U

• remove horseshoes

• use non-magnetic anesthesia equipment

Both MRI and CT allow for what?

tomography and 3D reconstruction

has better contrast resolution and is superior for imaging soft tissues

MRI

is superior for imaging bone because it doesn’t have as much water and is superior for fracture planning

CT

True or false: You can evaluate cartilage with MRI, but not CT, unless contrast is used.

true

In MRI, use different types of ________ and measure different types of ________ to allow for greater ________ and focus on different types of structures (bone vs. soft tissue).

pulses; relaxation; contrast

What are the indications for MRI in equine?

imaging soft tissue and bone lesions in areas where ultrasound is not possible (the foot)

True or false: In equines, there are similar limitations with MRI in structures that may be imaged as CT, since the horses have to fit in the magnet.

true

What are MRI indications in small animals?

N
M
T
P

• neuroimaging

• musculoskeletal

• tumor staging

• possible abdomen and cardiac

inject a drug (called a radiopharmaceutical) that is bound to a rapidly decaying radioactive atom and the drug has a propensity for certain tissue

nuclear scintigraphy

What is the most common radiopharmaceutical used in nuclear scintigraphy?

technetium-99m (^99mTc)

drug that has a propensity for hydroxyapatite in bone

methylene diphosphonate

By what and where is hydroxyapatite formed? What is the signal of radioactive atomy?

osteoblasts in areas of active bone formation; proportional to bone resorption

In nuclear scintigraphy, ________ camera detects decay of radioactive atoms, which can take a few minutes.

gamma

True or false: With nuclear scintigraphy, it is comparative, meaning you need to image both sides.

true

What are indications for nuclear scintigraphy in equine?

F
L
M
U
S
M

• fail to localize lameness with blocks

• localize lameness but no lesions on radiographs or ultrasound

• multiple limb lameness

• upper limb or axial musculoskeletal issue

• suspect fracture not imaged on radiographs

• mild, intermittent lameness that precludes blocking

What are indications for nuclear scintigraphy in small animals?

R
T
M

• renal function

• thyroid

• musculoskeletal