US. Physics 2 Imaging Instruments

key terms

A mode

presents depth on horizontal axis and amplitude on vertical axis.

uses echo amplitude rather than depth

Amplification

process by which small voltages are increased to larger ones.

Pre amp. can occur in the TRX

Returning voltages are too weak for imaging.

It is a gain control

Attenuation

weakening of the sound beam

decrease in amplitude and intensity with increasing distance.

A to D converter (ADC)

converts voltage amplitude to numbers

must be 2Xs the highest frequency to preserve harmonics.

“digitizer”

analog to digital

B mode

uses shades of gray

“brightness” mode

Bandpass Filter

separates harmonic echo bandwidth from the pulse bandwidth.

rejects frequencies above and below the acceptance bandwidth.

Beam Former

where the action begins

the part of the instrument that performs electronic scanning, apodization, steering, focusing, and aperture

B color (chroma)

assigns a color to the grayscale

Bistable

2 shades- black or white

high contrast / low dynamic range

Bit

multiply 2 by the number itself for every number of bits.

ex: 2 bits = 2×2

binary digit. smallest amount of computer memory

2 to the bit power

Channel

more will result in better control of beam characteristics

a single path

transmit and receive paths for phasing, steering and focusing

# of channels usually =

# of elements

Cine loop

sequential display of stored frames

Compensation

Compensates for attenuation

equals out received echo information at different depths.

TGC, DGC, swept gain

Compression

a dynamic range control

reduction in differences between small and large amplitudes.

reduces the dynamic range

Contrast resolution

ability of gray scale display to distinguish between echoes of different intensities

if gain is too high you lose contrast resolution

Demodulation (detection)

conversion of voltage pulses from radiofrequency to video

it uses less memory and is more suitable for video

D to A converter (DAC)

converts digital (numeric) info to analog info

determines the brightness of echoes on the display

Dynamic range

decreases as it propagates through the system

refers to different shades of gray, largest to smallest power that a system can handle

trx has the highest DR, a display having the narrowest dynamic range is bistable and has high contrast

Freeze Frame

constant display of one image

Gain

does not improve signal to noise ratio. it is the ratio of amplitude output to input electronic power.

overall brightness, amplification: treats all echoes the same

gain too high = saturation which decreases contrast res.

Gray scale

shades of gray

Harmonic imaging

improves SNR, reduces grating lobes, side lobes, and reverb.

Image memory

where the information is stored

Image processor

after data is seen in image processor, it goes to the memory, then to the image

prepares images for visual display

(scan converter, persistence, cine loop, post processing, preprocessing, panoramic, spatial compounding, 3D, grayscale, D to A converter)

Imaging depth

penetration

Instrument

part of the system that drives the TRX, receives the echoes, and presents them

Lateral Gain Compensation (LGC)

adjusts image brightness across the image making the image more uniform.

M mode

motion mode

Cardiac

Magnification

Zoom

write before read

write: better resolution, preprocessing, before storage

read: poor resolution, postprocessing, after storage

Depth x # of focal zones

X LPF X FR

Noise

voltages that do not relate to input

Output

transmit power

bioeffects

Panoramic imaging

widest FOV

imaging created by manually sweeping the trx across the area of interest.

Persistence

frame averaging.

smoother image, less grainy

(averaging of sequential frames for a smoother image and reduces noise.)

Pixel

picture element

it contains 4 bits

Pixel interpolation

preprocessing

fills in the missing pixels

Post processing

image processing done after memory

Pre processing

image processing done before memory.

(interpolation, persistence, panoramic imaging, spatial compounding, write magnification, edge enhancement, magnification)

PRF

#of pulses per second. Inverse to PRP. increases with a decrease in depth, increasing PRF would increase FR.

The frequency of the voltage pulse determines the frequency of the acoustic pulse

PRP

time from the start of one pulse to the next.

Inverse to PRF

Pulser

controls the signals sent to the transducer.

“drives the transducer”

Real time

rapid frame sequencing to show motion

Receiver

receives the echoes.

echoes = receiver function.

(amplification, compensation, compression, and demodulation)

Reject

receiver function that allows the sonographer to control whether low level gray information appears on an image

can take out low level gray

Saturation

grayscale: turning up gain will saturate the image = poor contrast resolution.

if the overall image is too bright turn down the power to reduce patient exposure.

relative to gain

Scan converter

digital electronic device that reformats echo information into an image form

scan converter→ memory→ display

echo data is stored in memory, then it goes to display

Temporal Resolution

time resolution. Improves with an increase in frame rate.

depends on penetration depth, lines per frame, no. of FZs

Time Gain Compensation (TGC)

accounts for attenuation. Equals out echo information

also called:swept gain or DGC

Transducer

a device that converts energy from one form to another.

in US: converts electrical energy to acoustic during transmission and during reception converts acoustic to electric

T/R switch (transmit/recieve switch)

protects instrument receiver from high voltages. Directs the voltages to pulse in transmit and directs the echoes to amplification in receive.