Key Terms Week1/Lecture2 Flashcards
Dynamic Range
method of describing the extent to which a signal can vary and still maintain accuracy
units: decibels(dB)
It is a comparison, a relative measurement, or ratio, between the largest and smallest signals that are measured accurately
component dynamic range transducer 120dB reciever 100-120dB scan converter 40-50dB display 20-30dB archive 10-30dB
Switch
found in the beam former
protects the sensitive electrical components in the receiver from the high voltages created during transmission
Beam Former
receives the single electrical spike from the pulser and distributes it to the numerous active elements of an array transducer
creates and distributes the delay patterns for array transducers during transmission
Receiver
transforms the electrical signals from the transducer(produced by the reflected sound) into a form suitable for display on the system’s monitor
Five functions must be completed in this order: 1)amplification 2)compensation 3)compression 4)demodulation 5)reject
Amplification
all signals are treated identically
entire image gets brighter or darker
It is adjustable (Gain/Overall Gain Knob)
Gain/Overall Gain(amplification)
controls the degree of echo amplification, or brightness of the image
measured indB
too much gain-image is too bright
too little gain-image is too dark
Compensation
creates an image of uniform brightness from top to bottom of the image
compensates for the sound wave as it weakens(attenuates) as it travels
operator controlled
AKA-TGC(time gain compensation), DGC(depth gain compensation)
TGC(time gain compensation)
DGC(depth gain compensation)
compensates for the loss of energy through attenuation of the sound beam as it passes through the tissue
structure will be the same brightness regardless what depth it is
Compression
keeps the image’s grayscale content within the range of detection of the human eye (aprox 20 shades of gray)
keeps the electrical signal level within the accuracy range of the system’s electronics
units: dB
operator controlled
AKA-log compression or dynamic range(DR)
Decibels
a relative unit that compares one signal to another
important in quantifying the strength of the sound beams, electrical strength, and brightness of the image
notation is logarithmic
Demodulation
two part process that changes the electrical signals in the receiver into a form more suitable for the CRT monitor
rectifies and smooths the electrical signal
cannot be adjusted by sonographer
CRT Monitor
displays the receiver’s info from the returning electrical signal
2 users controls: contrast and brightness
Reject
controls whether low level signals will be displayed on the image
low level echoes can be diagnostic or noise
Persistence
frame averaging function that allows echo info to be accumulated over a longer period of time
Increasing persistance-subtle tissue texture differences will be enhanced
decreasing persistence-user is able to evaluate moving structures more easily
Zoom(magnification)
allows image magnification by increasing the pixel size-results in image degradation
two type: read and write
Read Zoom
occurs after image data is stored in scan converter
number of pixels is same as original image-results in blurry image
Write Zoom(RES)
scanning in real time, the box is placed on image and image is expanded
no degradation occurs
calipers
markers available to measure distance
can be linear, ellipsoid, and trace
annotation
allows labeling of the image
may be a keyboard or preprogrammed keys
may be voice activated
Dual Image/Quad Image
allows the screen to be split in two or four
able to compare the anatomy of the abnormal side with the normal side
Acoustic Power/Transmit Power
varies the amount of energy the transducer transmits to the patient
power should be used at the lowest level consistent with satisfactory image quality
ALARA(As Low As Reasonably Achievable)
when modifications to the output power of the receiver gain need to be made to improve the quality of the image, the first and best choice is the one that minimizes the patient’s exposure
image too dark-increase receiver gain first, no increase to patient’s exposure
image too bright-decrease output power first, decreases patient’s exposure
Pulser
creates electrical signals that excite the transducer’s PZT crystals(elements) to create the sound beams
Pulser only functions during the transmission
operator controlled
ranges from near 0-500 volts
Important in bioeffects
TI(Thermal Index)
MI(Mechanical Index)
attempts to standardize transducer output have resulted in these two measurements being seen on the monitor
TI-useful predictor of max temp increase under most clinically relevant conditions
MI-related to the likelihood of harmful bioeffects from cavitation
Noise
random and persistant degrading of the ultrasound image
unwanted low-level echoes
output power is increased-signal to noise ratio is increased
image quality improves as the signal dominates the image, and the noise disappears
