Chapter 20, 21, 22 Bioeffects & Quality Assurance Flashcards
Name the causes of Artifacts
Assumption violation ~prop velocity, resistence, beam change Physics happens refraction, grading lobes, specular reflection Operator error ~Oblique angle, distance to ROI
Name the artifact reflection errors.
Reflection not real Reflection missing from image Incorrect shape Incorrect location Incorrect brightness
What are some Assumptions?
‘Sound traveling in a straight line’
The sound beam will travel straight back’
‘Sound travels at a constant speed in tissues (1540m/s
The reflection travel from the main beam axis only
Amount of reflection related to tissue characteristics
What is Reverbration?
Sound beam bouncing between 2 strong reflectors, bounce between them like a ping-pong ball. This creates multiple parallel line echos one posterior to the other, but only 1 or 2 of the lines are real. This is seen in such places as the diaphragm or the gallblader.
What is comet tail?
it is a type of reverbertion artifact, caused by 2 closely placed reflectors, appearing as a echogenic line reaching posteriorly “reverberation as a solid line stretching anterior to posterior”
Give some examples of comet tail.
Tissue,
gas
lung
Comet tail is caused by natural tissue
Ring Down what is it?
Another type of reverberation artifact, closely resembling comet tail, only is caused by abnormal objects not normal considered part of the body, with a distinct base on the structure image.
What are some structures that cause Ring down?
- Calcified structures, -surgical tips,
- needle tip
Shadowing, what causes it?
A highly attenuating structure (shows up as something very echogenic on US) such as bone or stones, causing a shadow posterior to it.
How can shadowing be helpfule?
Helps characterize a tissue
What is edge shadow?
Refraction causing a decrease in beam intensity, it normally happens when an echo hits the edge of a curved object, causing hypoechoic regions posterior along the edge of a refractor.
What is enhancement?
It is a hyperechoic area caused by being behind a structure with low attenuation ( not cause by a difference in propagational speed ) it is the opposite of shadowing and aluminate deeper structures. Examples: GB, cystic structures Adipose, UB.
What is Focal Banding?
It looks like TGCs are off, and is caused by the focusing of the beam, making a brighter focus area because of reflected echoes.
Mirror image what is it?
The beam bounces off structures and images area outside the beam’s path, and received as signal, creating a false structure, a little deeper then the true structure. Happen in 2D and Doppler
Speed Error is …?
Caused by echoes not traveling the assumed speed of 1540m/sec. This makes structures appear at the wrong depth, can be seen in a step-down in image.
What happens when the speed error is higher then the assumed speed?
⬇️ In round trip time = Image of structure is too shallow
What happens when the speed error is lower then the assumed speed?
⬆️ In roundtrip time = Image of structure to deep.
What are lobe artifacts?
Far lateral aspects of the beam hits a strong reflecture, but returning echo is weak but strong enough to registry resulting in a second copy of the reflector right beside it, requiring multiple angles to distinguish real one.
How do we correct lobe artifact?
by….
Subdicing: A large element (crystals) divied into smaller elements
Apodization: reducing the voltage to the far lateral crystals on a transducer
What kind of artifact does Refraction cause?
Second copy of reflector next to the true reflecture.
What causes Slice thickness artifacts?
Happens when the object is thinner then our beam thickness (elevation). this causes small areas that are suppose to be anechoic to be filled in, such as the neck of GB, small cysts, fetal N/L.
What kink of artifact is associated with lateral resolution?
Unable to see two objects as seporate, espieshally in far field.
What kink of artifact is associated with lateral resolution?
Unable to distingish structure anterior/posterior to eachother, seeing two structures as one big object.
What is multipath?
Sound reflecting off of multiple reflectores before returning to transducer, the effect veries due to reflector and beam path
What defines a curved/oblique reflectors?
This is what causes edge shadowing, echoes at the edge of the artifact do not come back, it may not be noticable until resolved.
What is Speckle?
Caused by the constructive and destructive interference of sound waves making irregular tissue texture
- seen as course tissue, such as in thyroid - can reduce/eliminate
What is quality assurance?
Routine, periodic, regular evaluation of ultrasound equipment to ensure optimal image quality
Requirements for quality assurance?
Assess system components
Repair problems
Preventative maintenance
Record keeping
Goals of Quality assurance?
Proper operation of equipment Detect gradual changes Minimize downtime (unused machines don’t make money!) Reduce non-diagnostic exams Reduce repeat scans
Tools of the trade?
AIUM 100mm test object
Tissue phantom
Doppler phantom
Beam profile/thickness phantom
What is a AIUM Phntom?
Used to calabrate the US’
Resolution with predetermined distenced objects, set in a ‘V’ pattern, getting closer and closer together unit utile US precieve them as one.
Registration: are the determine weather a beam is symetricle/equal by equally spaced pins, to measure with calapers
Contrast/tissue: to determined the gray scale of mechien is suffient.
What are ways AIUM 100mm test obects test, luid, speed and pin orientation?
Fluid/ “tissue” with pins or string at certain distances No attenuation Developed for A mode and static scanning Speed of transmission exactly 1540m/s SPI- Know which face being scanned! Pin orientation Parallel to beam = AR “V” across beam Perpendicular to beam = LR “V” down beam Dead Zone = area proximal to transducer
HOW DOES TISSUE PHANTOMS WORK and what do they evaluat?
They are used for registrasion and gray scale charecteriscics
- attenuation
- scatters beam
- mimics real life applications
How does the doppler phantom evaluate?
By vibrating a string, moving belt or pump to creat flow.
What is Sensitivity?
Ability of system to display low-level echoes
Minimum- assessing weakest echo displayed
-Flat TGCs, increasing gain until low level FF rod displayed
Normal- assessing all echoes in phantom
-Power, 2D and TGCs increased until all echoes seen
Maximum- assessing max visualization depth
-All settings at max, increase depth to maximum displayed
What does the Calorimeter do?
Measures total power of sound beam through absorbtion
Thermocouple?
Cine thermometer that measures the tempreture in the beam, to alert if there is a posibility for bioeffects.
What are liquid Crystals?
Thermal active crystals which changes color like mood rings in responce to temprature changes.
What must we consider Conserning bioeffects?
-Benifits must outweigh the risks
What is Dosimetry?
Study of measuring beam characteristics that have the potential to produce bioeffects:
- In Vivo- resurch conducted within living tissue - In Vitro resurch conducted outside the living tissue
What is there to be weary of with in-vitro bioeffects?
bioeffects that it claims happen should be taken with a grain of rice
What are the 2 approches to bioefect resurch?
Mechanistic approach- searches for relationships between cause and effect
Eating ice cream makes NYs violent
Empirical approach-searches for a relationship between exposure and response
Lets feed NYs ice cream and see what happens
What is thermal Bioeffects?
Increase in tissue tempreture caused by attenuation, which alters cell activity.
What are Cavitation bioeffects?
⬆️ in gaseous bubbles ithin tissues
What is the thermal index?
Is a unitless number that prodicts tempreure increases due to bioeffects inside tissues: TI 1 = 1 degree temp increase expected TIS= Soft tissue TIB= bone TIC = Cranial Bone
How are Mechanistic and empiricle resurch approach thermal findings?
Mechanistic-
There is a relationship between exposure and increases in tissue temperature
Empirical-
Prolonged temp elevation can damage tissue
Temp elevation related to output and tissue characteristics
2-4 degree rise in testicular temp can cause infertility
According to Empirical reaserch what tissue is greatly effected by Temp. change?
Fetal tissues are less tolerant that adult tissues. Many fetal tissue defects have resulted from increased temperatures. None have been observed at 39 degrees or less
Fetal bone absorbs a high amount of acoustic energy.
What is Microstreaming?
Is the circulation of fluid with in tissues due to temp. change, which can lead to cavitation. The fluid around cells puts shear stress on surrounding cells.
What is considered Stable Cavitation?
This has a low MI level, where bubbles shrink and expand, but due not bust and cause tissue damage. These bubbles absorbs acoustic energy.
What is transient Cavitasion?
This is with a Higher MI, where the bubbles expand and burst causing tissue damage, and makes a shock wave that exerts presser on neighboring cells.
What does ALARA stand for?
As Low As Reasonably Achievble.
What is Coded Excitation?
Coded Excitation- digital codes used by beam former to alter pulse duration, results in multiple frequencies within one pulse, produces distinct/recognizable pulses
- Improves Signal to Noise - Multi Fs used on other processing techinques
What is frequency compounding?
Compares data from two mini bandwidth taken from the one original returning bandwth, allow the US to multitask.
- this reduces speckle - improves contrast resolution
What is Persistence/frame averaging?
Averages frames per time, both Color and 2D
Short term events can get removed, long term events can be exaggerated
•Newer frames given priority to older frames
What is color priority?
Displays pixel with color info vs 2D/brightness info when increased
-Compromised spatial resolution
-No effect on temporal resolution
Improves color at the expence of spatial resolution
What is compound imaging?
areas scanned at slightly different angles and data is averaged together
- Reduced reverberation artifact - Improved signal to noise
Spatial Averaging?
Breaks up larger images up into smaller sections and averages areas of missing data with the neighboring areas
-reduces noise but no improvement to signal detection.
What is Parallel Processing?
one transmit beam out and two smaller beams are processed at the same time from big beam. transmit together and process separately.
It saves time and so improves temporal resolution
-done automatically
(like cutting a carrot in half and cutting them up side by side to cut it faster.)
What is Interpolation?
it uses data from other amplitudes to fill in missing data, ⬆️ # of scan lines
- degrades temporal resolution - but goo for static images needing high detail
