3Q03 Physics Flashcards
Another term for grating lobe artifact?
Haze
Do we want a high or low SNR?
high SNR = improves contrast res
What is the cost of frame/signal averaging?
FR and temporal res are decreased
Can we control the amount of SC?
Yes we can add more angle (RES) or less with (SPD)
What is Aberration?
when the sound beam gets distorted through fat resulting in a decrease intensity of the main beam and an increase in grating lobes
How can we fix abberation?
Same way as we fix grating lobes - with harmonics (therefore harmonics is good in obese people)
Which type of harmonics is better for axial res?
Pulse inversion
Panoramic imaging is also known as:
EFOV (wide scan is not the same thing)
How does axial strain elastography show malignancies?
darker areas = more stiff = more malignant
How is tissue stiffness measured?
With young’s Modules where BM = stress/strain = change in pressure / (change in volume/volume)
How can we determine stifness/malignancy by the E number?
higher E value = stiffer = more malignant
How does shear wave elastogrophy work?
By produces shear waves into the body which are slow but travel faster the stiffer the area is aka malignant
In colour or shades of grey
it is quantifiable - E value
How to determine the E value
E =3 x p x c^2
What is the difference in shear waves compared to longitudinal sound eaves?
they are transverse, travel perpendicular to sound waves, and are a lot weaker
What can lead to inaccurate results in axial strain elastogrpahy?
In axil you are making your own compressions and if you press to high it can create non linear changes in the strain = inaccurate results
Blue tissue means
harder
What is B-flow?
displays blood flow echoes on B-mode
What are the main differences of B-flow and Doppler?
- not angle dependent
- no aliasing
- much better temporal and spatial res
What is a transducer that provides real time volume imaging?
matrix
In 3D oimagign which has the worst resolution
Z/coronal plane
What is Multiplanar resolution
shows all 3 planes at the same time and you can chose how you want to slice through
What type of scan has the WORST thermal risk?
PW SD because high PRF and large DF - not scanned across a FOV
What is the order from most risk to least of thermal bioeffect?
1. CW PW SD 2. CD/PD 3. M mode 4 Least risk if 2D B mode
What causes an icnrease in thermal effects?
increased out put power AND time
What is the max SPTA?
720 mW/cm2
What is mechanical bioeffects from?
transient cavitation - non thermal
What is the recommended MI?
if gas bodies and obstetrics and neonates <0.3
but an MI <1.9 has no confirmed bioeffects
When should each type of TI be used?
TIS - first triemster - 10 weeks
TIB - late first trimester, 2nd and 3rd
TIC - neonatal, pediatric, adult cranial, or spinal
What are the recommended TI Values?
<2.0 in adulta
less than 0.7 in fetus
What are common results of those scanned in utero?
- low birth weight
- delayed speech
- dyslexia
non right handedness in boys
