Chapter 17 Flashcards
Harmonics and Contrast Agents
____ ____ is the creation of an image from sound reflections at twice the frequency of the transmitted sound.
Harmonic imaging
____ ____ is the transmitted frequency.
Fundamental frequency
____ ____ is twice the transmitted frequency.
Harmonic frequency
What type of behavior means proportional or symmetrical - systems respond in an even manner.
Linear behavior
What type of behavior means irregular or disproportionate - systems respond in an uneven manner
Non-linear behavior
Harmonic frequency sound waves arise from ____ behavior.
Non-linear
Harmonic imaging can produce a more accurate image because harmonic frequency waves undergo less ____ than fundamental sound waves.
Distortion
As a sound wave travels in the body, a small amount of energy is converted from the ____ frequency to the ____ frequency.
Fundamental; Harmonic
Tissue harmonics to be created during ____.
Transmission
A sound wave is a series of ____ and ____.
Compressions and rarefactions
Sound travels faster through ____ and slower through ____.
Compressions; Rarefactions
During ____ ____, (no harmonics) significant amounts of artifact arise within the first few centimeters of tissue
Fundamental imaging
During ____ ____ imaging NO harmonic signals are generated at extremely superficial depths.
Tissue harmonic
As sound travels ____ in tissue, the strength of the harmonic wave becomes larger.
Deeper
____ sound beams do not create tissue harmonic.
Weak
____ strength sound beams create a tiny amount of tissue harmonics.
Intermediate
____ sound beams create significant tissue harmonics.
Strong
Side lobes and grating lobes are usually ____ so little or no harmonics are created in them.
Weak
____ ____ ____ use the distortion free harmonic reflections, while eliminating the distorted fundamental reflections.
Pulse inversion harmonics
Pulse inversion Harmonics is a more successful method of separating ____ and ____ frequencies.
Fundamental and harmonic
How does pulse inversion harmonics work?
Two pulses are transmitted down a scan line
- 1st pulse is a typical pulse
- 2nd pulse is an inverted copy (it’s opposite)
Where a compression occurs in the 1st pulse, a rarefaction occurs in the 2nd
Upon arriving back to the receiver, these pulses are combined.
____ ____ (microbubbles) are gas bubbles encased in a shell that are injected into the circulation (I.V. typically) or swallowed.
Contrast agents
Contrast agents must meet five requirements:
- Safe
- Metabolically inert –it won’t change in a biological system
- Long lasting
- Strong reflector of ultrasound
- Small enough to pass through capillaries
Constrast harmonics are created during ____.
Reflection
This expanding and shrinking when a microbubble is in a sound beam is called ____.
Resonance
What is the most important formation of contrast harmonics?
Rarefaction
When a microbubble is exposed to the high pressure component of a sound wave, the microbubble ____.
Shrinks
When a microbubble is exposed to the low pressure component of a sound wave, the microbubble ____.
Expands
____ ____ is a number that estimates the amount of contrast harmonics produced.
Mechanical index (MI)
The mechanical index increases with:
- Lower frequency sound
- Stronger sound waves
Microbubbles the size of red blood cells just so happen to resonate in the ____MHz – ____MHz range
2 MHz – 4 MHz
Two characteristics of contrast agents that are important are the ____ ____ and the ____.
Outer shell; Gas
The shell needs to be ____ so the microbubbles can change shape.
Flexible
The gas needs to be made of ____ molecules so that it remains trapped within the bubble, no leaking out!
Large
