15 and 16 - Ultrasound I and II Flashcards
Diagnostic ultrasound
- Incorporates the use of high frequency sound waves emitted from a probe
- Directed into the body
- Sound waves penetrate and encounter different tissues as the waves travel through the body
Ultrasound encountering tissue
- When the ultrasound encounters tissues, the wave hits the tissue and reflects part of the wave back to the probe
- This causes a reflective pattern and this information is projected as an image
Sonography
- The ultrasound waves are inaudible to the human ear (>20,000 Hz)
- Images are created in diagnostic ultrasound when sound waves are transmitted into the foot and echoes return from various anatomical structures that reflect the transmitted sound waves
4 types of ultrasound
- A-mode
- B-mode
- M-mode
- Doppler
We will use B mode the MOST in musculoskeletal diagnosis ***
A-mode
- AKA “sonar” ultrasound
- Produced on an oscilloscope
- It measures how far the echo has traveled and how loud the echo is when it gets back
- Uses a single transducer
- Cannot determine what object looks like
B-mode
- B-mode (“Brightness Mode”): 2-dimensional picture
- Like A-mode, but adds direction, as well as, deciphers all types of echoes, both strong and weak
- Can recognize size and shape of object
- Uses a linear array of transducers
- Most commonly used type of ultrasound
M-mode
- Motion picture
- Like B-mode, but can image fetal movements, heart pumping
Doppler
Measures blood flowing using doppler physics
Colors seen in Doppler images
Color Doppler (“BART”)
- BLUE signals indicate blood flow AWAY from the probe
- RED signals indicate blood flow TOWARD the probe
Physics of ultrasound transducer (probe)
- Contains linear array of thin crystals (lead zirconate titanate) linked to the electrical system of the machine
- Machine applies a rapidly alternating electrical current to the crystals > vibration > generate sinusoidal sound wave (mechanical energy) = Piezoelectricity
The crystal’s vibration puts out sound waves
Emission of the sound wave
- Requires a medium
- Forward transmission until acoustic interface (change in the density of adjacent tissues) met
- The machine recognizes the differences in density
The signals are either reflected back or continue to progress through the body part you are examining - reflects the density of the object
In bone, less continues through, more is reflected back
In muscle, more continues through, less is reflected back
Partial reflection
- Waves transmitted back to the transducer (now a receiver)
- Sound energy transformed into electrical signal
Processes of density signal
Computer calculates amplitude , depth and time of return signal and generates 2-D black & white B-mode image of the body
Physics of musculoskeletal transducers
Musculoskeletal transducers located in the probe produce the sound at 7.5-12 Mhz (megahertz) which is then pulsed at 20 microsecond intervals
How to place the notch on the body
When doing a LONGITUDINAL (long) scan…
- The notch is placed on the PROXIMAL aspect of the structure(s)
- The proximal aspect will be on the left of the view screen.
When doing a TRANSVERSE (short) scan…
- The notch is placed on the medial aspect of the structure(s)
- The medial aspect will be on the left of the view screen.
Achilles tendon example on slide 17
Relationship of frequency and wave length of ultrasound beam
- Frequency and wavelength of the ultrasound beam are inversely related
- The higher the frequency, the lower the wavelength and vice versa
What happens when high frequency waves penetrate LESS than low frequency waves?
Higher frequency waves penetrate less than lower frequency, but resolution increases ***
*** Resolution is the ability of the ultrasound machine to distinguish two structures (reflectors or scatterers) that are close together as separate
This means we can see things in the foot BETTER than you could in the ABDOMEN
What does “good resolution” mean?
That you can see separate objects individually rather than a blurred spot together
High frequency transducers
- High frequency transducers (foot and ankle between 7.5 and 12 Mhz)
- Improved resolution
- Decreased depth of penetration
- Used on superficial structures
Low frequency transducers
- Low frequency transducers (1-6 Mhz)
- Decreased resolution
- Full depth of penetration
- Best for abdominal and pelvic imaging
What do low frequency waves do when they penetrate?
Lower frequency waves penetrate more deeply but have less well-defined images
- The deeper the signal travels into the tissue, the more it is absorbed, and the weaker the signal that is reflected back from the tissue. This is known as attenuation.
Attenuation
Attenuation results in echoes from deep tissue being displayed less intensely than those from superficial structures
High frequency transducers in musculoskleltal
- Musculoskeletal transducers are higher frequency because the structures are closer to the surface of the body
- The 7.5 transducer penetrates approximately 7 cm***
Contact of ultrasound to interface
- When the ultrasound waves contact an interface between two different media (e.g., fat and bone), part of the signal is then reflected back, whereas the rest of the wave continues to propagate deeper into the tissue.
- The greater the difference in tissue density, the more reflection will occur
Amount of reflection
- The amount of reflection is dependent upon the impedance of the tissue
- Impedance is a property of a tissue defined as density of tissue and velocity of sound in that tissue. Air is low, bone is high
Acoustic interface
- The boundary between two different surfaces is an acoustic interface
- Since there is an interface between air and skin, we need to add gel with an impedance similar to human tissue, or only 0.1% of the wave would be transmitted into the skin and 99.9% would be reflected off the skin surface
Hyperechoic structures
Hyperechoic-white-reflect majority of wave
- Bone, calcifications
- Tendon (appears striated)
- Fascia (appears non- striated)
- Ligament
- Air ***
NOTE: Air is the enemy of ultrasound. Ultrasound waves tend to reflect strongly wherever air meets biological tissue. If there is even a small bubble between the probe and the patients skin, the ultrasound waves will be reflected away instead of penetrating the skin.
Hypoechoic structures
Hypoechoic-gray-reflect some of wave
- Muscle (striated)
- Nerve (“honey-combed) ***
- Fat (with streaks of hyperechoic lines) ***
- Articular cartilage
Anechoic structures
Anechoic-black-reflect none of the wave
- Vessels
- Fluid
- Note: a skin cyst with fluid in it would appear as a round black dot
Question: Tissue that appears hyperechoic
- Bone
- Water
- Tendon
- Ligament
- Cartilage
** KNOW THIS **
- Bone
- Tendon
- Ligament
Patters of object appearance
In addition, structures are described as homogenous (uniform echo pattern) and heterogeneous (irregular echo pattern).
Near zone
Near zone (field): the region of a sound beam in which the beam diameter decreases as the distance from the transducer increases-area nearest to the transducer
Far zone
Far zone (field): the region of a sound beam in which the beam diameter increases as the distance from the transducer increases-area furthest from transducer
Question: When using US, the part of an image where the width of the beam increases as the distance from the transducer increases is called:
Far zone
Ultrasound artifacts
- Anisotropy
- Shadowing
- Posterior acoustic enhancement
- Posterior reverberation
- Refraction
Anisotropy
- Occurs when the beam is not directly perpendicular to fibrillar tissues (tendon, ligament, fascia) being examined
- Instead of looking hyperechoic, the structure becomes more hypoechoic as the angle increases, and, therefore, looks inflammed when it is not
- Less ultrasound reflected, so image is darker
Don’t assume its pathology, check you ultrasound technique
Shadowing (two types)
Occurs when ultrasound beam is reflected, resorbed, or refracted from bone or calcified object
Two types of shadowing
1 - Acoustic shadowing: false anechoic area (dark shadow) below the reflective surface
2 - Edge shadowing: dark shadow behind the edge of spherical structures when beam reflects off rounded surface
Edge shadowing
Edge of the curved surface
deflects the acoustic wave, resulting in an anechoic
image around the tendon
Slide 36 example
Posterior acoustic enhancement
- Occurs during imaging of fluid
- Deep to a fluid collection, the soft tissue will appear relatively hyperechoic compared with the adjacent soft tissues
Example on slide 38
Posterior reverberation
- Occurs when surface of object is smooth and flat (metal foreign body or surface of bone)
- Beam reflects back and forth between the surface and transducer producing a series of linear reflective echoes that extend deep to the structure
Refraction
- Depicts real structures in the wrong position
- Duplicates structures
- Caused by bending of ultrasound at interface of two materials
- Minimize by keeping beam as close to 90° to structure
Slide 42 example - duplication of the aorta and superior mesenteric artery
Improving image (“knobology”)
** KNOW THIS **
- Gain knob
- Time gain compensation
- Depth knob
- Focus knob
- Frequency knob
** KNOW THIS **
This will be what is tested from the NEXT lecture **
THREE QUESTIONS ON THESE ***
Gain knob
** KNOW THIS **
Gain Knob: Controls overall brightness of the image
More commonly used to adjust brightness and contrast of the image than the time gain compensation
Adjusts the ENTIRE picture being viewed well at all tissue levels
Time gain compensation
** KNOW THIS **
Time Gain Compensation (TGC): Allows adjustment of image brightness at selective depth
Depth knob
** KNOW THIS **
Depth Knob: Allows adjustment of the depth of field of view
Measured in cm, shown on right side of image
REMEMBER: as the depth increases, width of image gets narrower
Focus knob
** KNOW THIS **
Focus Knob: Allows focus of ultrasound beam to area of interest
Tells the machine the layer of tissue you are interested in, what will allow you to improve clarity/texture
This will diminish the areas you are not interested in
Frequency knob
** KNOW THIS **
Frequency Knob: Adjust Frequency to balance depth and resolution needs
LIMITING agent of the machine - the machine can only adjust the frequency based on the range of the probe (measure in MHz)
Ultrasound technique: gel placement
- Gel is placed onto the skin to provide a seal between the transducer and part to be examined.
- Air that may form between the probe and skin will result in parallel white line artifacts tapering down the image
Ultrasound technique: transducer placement
The transducer is placed on the foot in two different planes, longitudinal and transverse
Ultrasound technique: standoffs
Standoffs (0.5cm thick silicone) are pads attached to the transducer when imaging irregular surfaces to keep flat transducer surface in full contact with curved body surface
Ultrasound technique: longitudinal position
Longitudinal position is parallel to the long axis of the structure being examined
Ultrasound technique: transverse position
Transverse position is perpendicular to the long axis of the structure being examined
Ultrasound technique: skin and structure appearance
Skin will always be at the top of the image, and the probe reads the structures it passes through in the same order as one encounters while doing dissection (i.e., skin, to fat, to tendon, to bone)
Ultrasound technique: compression
Compression with transducer pressure can reveal important information about the composition of underlying structures
Ultrasound technique: “real time”
Ultrasound is a “real-time” study, and, as such, can be individualized for each patient based on symptom location while talking with the patient
List of examples and slide numbers
Achilles tendon
- Slide 50 example (longitudinal “long”)
- Slide 53 example (transverse “short”)
Plantar fascia
- Slide 54 example
Plantar plate
- Slide 55 example
Plantar forefoot
- Slide 56 example
Anterior ankle (tendons, arteries, nerves, talus)
- Slide 77 example
- “Tom Hates All Dicks”
Anterior tibiofibular ligament
- Slide 58 example
Anterior talofibular ligament
- Slide 59 example
Calcaneofibular ligament and peroneals
- Slide 60 example
Tarsal tunnel
- Slide 61 example
Deltoid ligament
- Slide 62 example
1st MPJ (dorsal) longitudinal image - Slide 63 example
1st MPJ (plantar) transverse image - Slide 64 example
Probe motions
- Sweep
- Slide
- Rock/tilt
- Fan
- Rotate
Sweep
Sweep: Move entire probe perpendicular to the length of the probe (like a broom)
Slide
Slide: Move entire probe in line with the length of the probe
Rock/tilt
Rock/Tilting: With the probe kept on one spot, tilt the probe along its long axis (like the leg of a rocking chair)
Fan
Fan: With the probe kept on one spot, tilt the probe along its short axis (like a fan)
Rotate
Rotate: Rotate position of probe to align with anatomy (Like hands on a clock)
