Ultrasound Physics 2 Exam 2

ch. 12, 13, & 15

What is the shape & how many crystals are in a mechanical transducer?

coin shaped

1 crystal

How is the beam steered in a mechanical transducer?

mechanically

How is the beam focused in a mechanical transducer?

fixed focus

What is the shape of the image produced by a mechanical transducer?

fan / sector shaped

What happens if 1 crystal gets damaged in a mechanical transducer?

entire image lost

What type of transducer has multiple crystals in a disc / ring shape?

annular phased array transducer

How is the beam steered in an annular phased array transducer?

mechanically

How is the beam focused in an annular phased array transducer?

electronically with multiple focal zones

What is the shape of the image produced by an annular phased array transducer?

fan / sector shaped

What happens if 1 crystal gets damaged in a annular phased array transducer?

horizontal line of drop out

What is another name for a linear sequential array transducer?

linear switched array transducer

What is the shape & how many crystals are in a linear sequential array transducer?

side by side

many crystals

Which transducer emits the beam through small, narrow, parallel groups of PZT firing simultaneously?

linear sequential array transducer

How is the beam steered in a linear sequential array transducer?

electronically

Which transducer type has a parallelogram image when steering?

linear sequential array transducer

How is the beam focused in a linear sequential array transducer?

electronically

Which transducer produces a rectangular shape image?

linear sequential array transducer

What happens if 1 crystal gets damaged in a linear sequential array transducer?

vertical line of drop out

What is another name for a linear phased array transducer?

vector

sector

Which transducer is the main current cardiac probe used?

linear phased array

What is the shape & how many crystals are in a linear phased array transducer?

side by side

multiple crystals

Which transducers uses phasing for beam steering & focusing?

linear phased array

vector phased array

What is phasing?

PZT impulses being sent out in a pattern in nanosecond delays

What pattern does the linear phased array transducer create for steering? What about focusing?

steering: slope

focusing: curve

What is the shape of the image produced by a linear phased array transducer?

fan / sector shaped

What happens if 1 crystal gets damaged in a linear phased array transducer?

inconsistent or erratic beam steering & focusing

What is the shape & how many crystals are in a vector phased array transducer?

side by side

multiple crystals

Which transducer produces a trapezoidal (sector w/ flat top) shape image?

vector phased array transducer

What happens if 1 crystal gets damaged in a vector phased array transducer?

inconsistent or erratic beam steering & focusing

What is another name for a curved sequenced array transducer?

convex

curvilinear

What is the shape & how many crystals are in a curved sequential array transducer?

side by side in bowed line

multiple crystals

Which transducer steers the beam by not firing the crystals simultaneously but instead in different directions?

curved sequential array transducer

How is the beam focused in a curved sequential array transducer?

electronically

Which transducer produces a curved shape image at the top & bottom?

curved sequential array

What happens if 1 crystal gets damaged in a curved sequential array transducer?

vertical line of drop out

What is unique about the capacitive micro-matched ultrasonic transducers (CMUT)?

has no PZT, uses semiconductor chips instead where 1 vibrates & the other doesn’t

portable

Which type of transducers produce side lobes?

single element transducers (mechnical)

What are side & grating lobes & what do they do?

additional areas of sound energy that extend outside of the main beam

degrades lateral resolution

Which type of transducers produce grating lobes?

array transducers

Which 2 methods can be used to reduce grating lobes?

apodization

subdicing (also used for side lobes)

What does apodization do?

makes the center of your beam stronger which increases your lateral resolution

What does subdicing do?

slices the elements & ties them together to make a stronger center which increases your lateral resolution

What is the name(s) for the beam thickness in the Z-axis?

slice thickness resolution

elevational resolution

Which axis is for objects above & below the imaging plane?

Z-axis

Which type of transducers need an acoustic lens to fix their elevational resolution?

linear & curved arrays

How does an acoustic lens improve elevational resolution?

creates thinner slices top to bottom

Which type of transducers need a 1.5 D array to fix their elevational resolution?

modern transducers

How does a 1.5 D array improve elevational resolution?

makes multiple rows of crystals into a grid to make several smaller squares

What is dynamic aperture?

method of electronic focusing to improve lateral resolution by selectively choosing crystals to create & receive sound to keep the beams narrow

What is temporal resolution?

displays structures in real time by how quickly the frames are generated

(represents time)

What is the system’s ability to create numerous frames per second called?

frame rate

What are images per second measured in?

Hertz (Hz)

When you are displaying a high number of images per second how is your temporal resolution? What about a few number of images per second?

high frame rate, good temporal resolution

low frame rate, poor temporal resolution

How many frames per second are typically used in real-time imaging?

30 - 60

Can the speed of sound in the medium be changed?

NO

What happens to your frame rate at a shallow imaging depth? What about deep imaging depth?

shallow depth: higher frame rate

deep depth: lower frame rate

What are 3 adjustments the sonographer can make to alter frame rate?

image depth

number of focal zones

number of scan lines per frame (line density)

What happens to your frame rate and resolutions with multiple focal zones? What about just one?

multiple: increased lateral resolution, decreased temporal resolution, decreased frame rate

single: decreased lateral resolution, increased temporal resolution, increased frame rate

What factors are affected with a high line density? What about low?

high: large field of view, slower frame rate, poor temporal resolution

low: small field of view, higher frame rate, good temporal resolution

Before scan converters made __ possible, images were originally __.

grayscale

bistable

What is bistable imaging?

purely black & white

narrow dynamic range

poor contrast resolution

What is gray scale imaging?

multiple levels of brightness

different shades of gray for differing echo amplitudes

increased contrast resolution

What are other names for the scan converter?

storage

memory

What does the scan converter do?

makes gray scale displays & real time imaging by storing the image data during image acquisition & converting the image into digital data for viewing

What is the smallest element of a digital 2D picture called?

pixel

What is pixel density?

the number of picture elements per inch

What factors are affected with a high pixel density? What about low?

high: many pixels per inch, smaller pixels, more detailed image, better spatial resolution

low: few pixels per inch, larger pixels, less detailed image, poor spatial resolution

What is the smallest amount of computer memory called?

bit

A binary number is the digital computer _ & is a group of _.

language

bits

What is a byte?

a group of eight bits of computer memory

What does the number of bits in the memory determine?

the number of shades of gray possible

The more bits per pixel, the more __, the better the _.

shades of gray

contrast resolution

What is the formula to determine the number of shades of gray?

2ⁿ

What does the n represent in 2ⁿ?

the number of bits

What is the analog number for 1001011?

75

What is pre-processsing?

allows altering of the reflected signals before they are stored in memory

can only be done on an active, unfrozen, live image

What is post-processing?

occurs after the echo has been stored in memory

can only be done on frozen images

What are the two types of image magnification?

write zoom

read zoom

Which magnification happens post-processing?

read magnification

Which magnification happens pre-processing?

write magnification

Which magnification decreases spatial resolution?

read magnification

Which magnification re-scans with new data?

write magnification

Which magnification has an increase in # of pixels, line density, & spatial resolution?

write magnification

What are the 4 things that improve image quality?

coded excitation

spatial compounding

frequency compounding

temporal compounding

Which qualities that improve your image qualities are built-in? Which are changeable by the sonographer?

built-in: coded excitation & frequency compounding

changeable: spatial compounding & temporal compounding

What is coded excitation?

long encoded pulses sent that are then decoded during reception as shorter pulses that keep the patient safe

What are the advantages to coded excitation?

improved signal to noise ratio

improved axial, spatial, & contrast resolution

deeper penetration

What is spatial compounding?

averages frames coming from different directions through steering that are then combined to produce a single image

What type of transducer must you use for spatial compounding?

phased array transducers

What are the advantages to spatial compounding? Disadvantages?

advantages: improved signal to noise ratio, reduced shadowing artifacts, improved spatial resolution

disadvantages: decreased frame rate & temporal resolution

What is frequency compounding?

reflected sound wave is divided into smaller groups then combined & an image is created from each part

What are the advantages to frequency compounding?

decreases noise & speckle (aka improved signal to noise ratio)

What are the other names for temporal compounding?

persistence

temporal averaging

What is temporal compounding?

superimposes (lays) current frames onto previous frames to create a smoother images from the same direction

What are the advantages to temporal compounding? Disadvantages?

advantages: improved signal to noise ratio & image quality

disadvantages: reduced frame rate & temporal resolution

When is temporal compounding most effective? What about least effective?

most effective: slowly moving structures

least effective: rapidly moving structures

What type of shaped images has scan lines that separate at increasing depths?

sector shaped images

What is fill-in interpolation?

computer program that predicts missing data in gaps using the known gray scale levels of the neighboring pixels of the missing gap

What does PACS stand for?

picture archiving & communication systems

What does DICOM stand for?

digital imaging & computers in medicine