Fluke Biomedical 84-317 - Manual (Page 9)

Operation
Functions
2
2-1
Section 2
Operation
2.1 Functions
A. Standard Echo Display Level
1) A-Mode
The standard echo display level is an arbitrarily chosen pulse height on the oscilloscope
display. It is for reference only, but should be the same for subsequent tests and should be
recorded. For example, a 4 cm pulse height on an 8 cm high display might be used.
2) B-Mode and M-Mode Including Gray Scale Displays
The standard echo display level is an intensity level equivalent to an arbitrary number of gray
levels above the zero display level. The level should be consistent and recorded. For example,
a 3 dB level above the display zero or threshold might be used, but in any case the system
should be well below the saturation level. Any scanning motion should be specified, e.g., sector
scan with an effective linear speed of n cm/sec or an M-mode time sweep of n cm/sec.
Low gain settings can be used to image targets
with minimum scattering. Higher gain settings will
increase scattering effects and allow system
performance evaluation at "clinical" settings.
B. Resolution
1) A-Scope
Two targets are said to be resolved if the amplitude between the two echoes decreases below
0.7 of the maximum amplitude of the weaker echo, which should be adjusted to the Standard
Echo Display Level. If the amplitude drops below 0.3 between the echoes, the targets are said
to be completely resolved.
2) Video Display
Two targets are said to be resolved if the display intensity between the two echoes decreases
more than two 1.5 db gray-levels below the weaker of the echoes, which should be set to the
Standard Echo Display Level.
3) Dead Zone
The dead zone of a transducer is defined as the distance corresponding to the time
immediately after the transmitted pulse in which transducer reverberation and/or amplifier
overloading causes or necessitates significantly reduced sensitivity or otherwise seriously alters
the echo patterns received.
2.2 Procedure for Using Models 34-317 and 34-317-7000
A. Requirements
1) The Time-Varying Gain Control (TGC) is normally switched off or set to a minimum for these
tests.
NOTE