Lecture 4: Ultrasonography, Computed Tomography, & Magnetic Resonance Imaging

What type of imaging has high frequency sound waves that penetrate tissue and bounce back to the transducer?

Ultrasonography

With ultrasonography, high frequency _____ _____ penetrate tissue and bounce back to transducer

sound waves

What does the ultrasound transducer contain that converts sound waves to electric current?

Crystals

In an ultrasound machine, what converts electric current to an image?

Computer

What are the 2 fates of the sound waves in ultrasonography?

Hint: Acoustic Impedance

1. Goes through tissues (black arrows)

2. Bounces back (gray arrows)

What is seen in #1 with least Acoustic Impedance?

• Fluid (blood)

• Solid (Stone)

• Fibrous Tissue (Diaphragm)

• Soft Tissue (liver)

Fluid (blood)

What is seen in #2 regarding Acoustic Impedance with less penetration?

• Fibrous Tissue (Diaphragm)

• Fluid (blood)

• Solid (Stone)

• Soft Tissue (liver)

Soft Tissue (Liver)

What is seen in #3 regarding Acoustic Impedance with even less penetration?

• Fibrous Tissue (Diaphragm)

• Fluid (blood)

• Solid (Stone)

• Soft Tissue (liver)

Fibrous Tissue (Diaphragm)

What is seen in #4 with highest Acoustic Impedance?

• Fibrous Tissue (Diaphragm)

• Fluid (blood)

• Solid (Stone)

• Soft Tissue (liver)

Solid (stone)

Match:

• White, Black, Gray

  • Some waves back

  • All waves back

  • No waves back

Black = no waves back

White = all waves back

Gray = some waves back

What must you keep in mind regarding tissue and wave penetration/bouncing back?

Tissue WATER content

What do ultrasounds HATE? Why?

Air! All waves bounce back & are reflective

T/F - Waves travel in a line

True

Waves traveling through the tissue depends on the tissue’s _____ ______

Water Content

Match:

• Anechoic

• Hyperechoic

• Hypoechoic

• Isoechoic

• Same/Equal

• Black

• Brighter/Lighter

• Darker

• Anechoic: Black

• Isoechoic: same/equal

• Hyperechoic: brighter/ligher

• Hypoechoic: darker

Bone and gas organ boundaries are _____

Hyperechoic

Bile and urine are _____

Hypoechoic

What ultrasound artifact cannot be seen below a structure so reflects back ALL waves?

Acoustic Shadow

ex. ribs

What ultrasound artifact causes (artificial) brightness DEEP to an anechoic structure?

Acoustic Enhancement

What ultrasound artifact has sound waves reflecting multiple times between strong reflectors?

Reverberation Artifact

Where is Reverberation Artifact most common?

Lungs

What ultrasound artifact causes the duplication of image of the opposite side of a strong reflector?

Mirror Image Artifact

Where is the Mirror Image Artifact most common?

• What medium would be the strong reflector?

Thorax/Abdomen Interface

• Diaphragm

What ultrasound artifact can be seen from imaging a 3D structure with anechoic fluid?

Slice Thickness Artifact

Where does Slice Thickness Artifact most commonly occur?

Gall Bladder and Bladder

• can see artificial sludge

What ultrasound artifact occurs when sound waves bend as they hit a curved surface tangentially?

Edge-Shadowing Artifact

• Hypoechoic lines are NOT real

What are the 2 types of ultrasound probes/transducers?

1. Linear

2. Curvilinear (sector)

What ultrasound probe is most commonly used for equine tendons?

Linear Probe

What ultrasound probe is most commonly used for LA/SA abdomen and thorax?

Curvilinear (sector) Probe

Can either linear or curvilinear probe be used for SA thorax/abdomen?

Yes

Increased frequency of probe causes greater _____ but less _____

resolution; depth

Decreased frequency - greater _____ but less _____

depth; resolution

What probe frequency would be used for this abdomen? Why?

• 3-5 mHz = 20-25 cm of depth, low resolution

• 10-12 mHz = 8 cm of depth, high resolution

3-5 mHz = 20-25 cm of depth, low resolution because of the greater depth

What probe frequency would be used for this abdomen? Why?

• Increased or Decreased frequency?

A lower frequency for a greater depth to visualize the abdomen

Any tissue with _____ _____ can be imaged

• tendons, ligaments, joints, abdomen, repro tract, heart, thorax

Water content

T/F - You can image the surface of bone and lung for irregularity

True

Why does a "core lesion" on the SDF appear dark (hypoechoic to normal)?

Due to loss of collagen fibers and inflammatory edema

What are the 2 things Real-Time Imaging (doppler mode) can do?

1. Can measure movement

   1. Ex. heartbeat

2. Can assess direction of flow

   1. valve regurgitation

What type of diagnostic imaging uses an x-ray tube in circle and rotates at predetermined speed?

Computed Tomography (CT)

_____ of an x-ray allows for differentiation of structures (like a radiograph) in CT

Intensity

In CT, what reconstructs data acquired from detectors to make a “slice” image?

• these sliced images can then be reconstructed into a 3D image

Computer

What term defines when “2D slices allow 3D location by taking MANY views”?

Tomography

What 3 areas is CT imaging in the horse generally limited to?

1. carpus/tarsus

2. digit

3. head

• The machine is NOT big enough for the whole body

What are the 4 indications for a CT?

1. Detailed evaluation of bone

   1. fracture repair planning

2. Image the head

3. Image spine

4. Image the abdomen

   1. requires injection of contrast solution to enhance contrast of soft tissues

Any imaging of ______ ______ requires injection of contrast solution to _______

• Soft tissue

• nhance contrast of soft tissues

What diagnostic imaging is described?

1. All tissues are made of H₂O = lots of hydrogen protons

2. Protons are excited when a STRONG magnet is applied due to radiofrequency pulse

3. Pulse removed → protons relax → emits signal

   1. Protons in different tissues relax differently

      1. relaxation depends on water content and proton content

MRI (Magnetic Resonance Imaging)

With what form of imaging must we remove horseshoes and use non-magnetic anesthesia equipment?

MRI

What diagnostic imaging has better contrast resolution and is superior for imaging soft tissues?

MRI

What 2 types of imaging allows for tomography and 3D reconstruction?

MRI & CT

What diagnostic imaging is superior for imaging bone because it doesn't have as much water and is superior for fracture planning?

CT

MRI uses different type of _____ and measure different types of _____ to allow for greater contrast & focus on different types structures (bone vs soft tissue)

pulses; relaxation

When is an MRI indicated in equine?

Imaging areas where ultrasound is NOT possible (foot)

• usually used in the foot and for lower limb lesions

What are 4 SA MRI indications?

1. Neuroimaging

2. Musculoskeletal

3. Tumor staging

4. Possible: abdomen and cardiac

What type of imaging is being described?

• Inject a drug that is bound to a rapidly decaying radioactive atom called radiopharmaceutical

• Gamma camera detects decay of radioactive atom

• ↑ bone formation → ↑ uptake → ↑ atoms decaying →↑ signal

Nuclear Scintigraphy

What are these indications for?

1. Fail to localize lameness with blocks

2. Localize lameness but no lesions on radiographs or ultrasound

3. Multiple limb lameness

4. Upper limb or axial musculoskeletal issue

• (Not easily accessible radiographically/Hard to block)

5. Suspect fracture not imaged on radiographs

6. Mild, intermittent lameness that precludes blocking

Equine nuclear scintigraphy indications

1. renal function

2. thyroid

3. musculoskeletal

What are the SA nuclear scintigraphy indications?

What imaging modality is associated with the following?

• Soft tissue: Minimal

• Bone: Good

• 3D: No

Radiographs

What imaging modality is associated with the following?

• Soft tissue: Excellent

• Bone: Edge only

• 3D: No

Ultrasound

What imaging modality is associated with the following?

• Soft tissue: Some, need contrast

• Bone: Excellent

• 3D: Yes

CT

What imaging modality is associated with the following?

• Soft tissue: Excellent

• Bone: Good

• 3D: Yes

MRI