Fluke Biomedical 84-317 - Manual (Page 11)

Operation
Procedure For Using Models 34-317 and 34-317-7000
2
2-3
Echoscope sensitivity should be noted in accordance with the AlUM Standard. This measurement
should be repeated at several sensitivities for a complete characterization of lateral resolution.
F. Time-Gain Characteristics
Time-gain (or equivalently, distance-gain) characteristics can be determined with the vertical target
group. With the TGC switch off and the transducer acoustic axis fixed in the plane of the targets,
the attenuator settings required to display each rod at the Standard Echo Display level are
recorded.
The test is repeated with the TGC on at a known, repeatable position. The difference between the
two attenuator settings for each rod, as a function of distance, is the time-gain characteristic.
In equipment where one or more TGC parameters
are variable, several tests should be made with the
values of these parameters recorded.
G. Display Characteristics
1) A-Mode Linearity Measurement
An echo from an isolated rod of the test target is to be displayed at Standard Echo Display level
with the transducer fixed in place. The attenuation is then decreased in 3 dB steps (x), the
display level (y) measured, and the results are plotted. The maximum deviation from linearity E
A
equals ðy, where ðy is the largest y distance from the best-fit straight line to any point (x, y).
2) B-Mode
Using an isolated single echo as above, the attenuator is adjusted to provide an echo intensity
just below that which can be recorded photographically with brightness controls at normal
operating position. The spot is recorded, the attenuation decreased by 1.5 db, and the display
position control is changed to place the spot in new positions. This process is repeated to form
a row of spots on the recording, similar to an optical density step wedge and covering the entire
gray scale. Where a two-level storage tube is used, the effect of increased signal on displayed
spot size is indicated.
H. Scanned B-Mode Alignment
The phantom is scanned at normal settings from at least three angles and several distances.
Echoes from individual rods should superimpose subject-to-beam width characteristics at these
distances. The area enclosed by various echoes from a given rod is then a measure of the smallest
resolution element of the system.
I. Cyst-Like and Tumor-Like Objects
The purpose of these objects is to determine the smallest of them which is visible. This can be done
at various distances by scanning from different surfaces. Because contrast between the objects and
the background material is not great, varying the gain may improve their visibility.
The small group in the lower corner should be viewed with short-focal-Iength transducers, such as
those meant for eye and thyroid scanning or pediatric use. Some or all of these targets may be
visible, depending on scanner characteristics.
The single cyst-like object (Bounded Lo-S) with a relatively high impedance boundary, surrounding
it is usually easily visualized, except perhaps from the most distant viewing surface. Since it
represents deeply buried body structures such as the gall bladder or the major blood vessels (i.e.,
the aorta or the inferior vena cava) that are normally fluid-filled, this object allows the user to
simulate the normal appearance (and the normal scanner settings) for such structures.
J. Sector Scanner Errors
NOTE