Fluke Biomedical 84-317 - Manual (Page 10)

Nuclear Associates 84-317 & 84-317-7000
Operators Manual
2-2
2) The echoscope and scanning apparatus under test are adjusted with non-specific controls such
as focus, brightness, etc., set in known repeatable positions typically used in practice. The
transducer size, nominal (manufacturer's) working frequency, and serial number should be
recorded. The transducer is a major variable in these procedures. A completely new set of
measurements should be made if the transducer is changed.
3) A correctly matched and calibrated attenuator is desirable, preferably between the pulse
generator and transducer, but it may be between the transducer and receiver.
B. Depth Calibration
Depth Calibration is to be performed with the vertical group of rods to the left of the center line of
the Phantom. All targets should be displayed simultaneously. If scanning is required, the rods
should be scanned linearly (i.e., without rotation of the transducer), perpendicular to the plane of
the targets.
1) Measure displayed distances “y” from the recording with distance markers on the illuminated
graticule or directly from the display.
2) Plot y values as a function of true distance x, which is 10 mm.
3) Fit a straight line to these points. This line can be described by the equation y = ax + b.
From this the following can be determined:
a. Error in zero calibration E
O
= b (mm). This parameter is important only for mechanically
operated scanners.
b. Percent error in sound velocity calibration E
V
= 100 (1-a).
c. Maximum deviation from linearity ðy (mm), where ðy is the largest y distance from the
straight line to any point (x, y).
d. A more rapid, but less precise, check of calibration can be made by aligning the displayed
echoes to the display markers or graticule.
C. Resolution Measurement
Axial or depth resolution and transverse resolution are measured at two distances, simultaneously,
with the two resolution groups. Measurements at two other distances are made from the other end
of the phantom. The measurement's distances are 3, 8, 13, and 18 cm.
The transducer axis shall be parallel to the plane of the centerline of the phantom and normal to the
target filaments or rods. In all modes, the transducer should be scanned linearly across this group
of targets (nylon rods) to measure resolution.
Resolution is the spacing of the two closest rods in the group that can be resolved. Echoscope
sensitivity should be noted in accordance with the AlUM standard. This measurement should be
repeated at several sensitivities, and at several distances, for a complete characterization of the
system. Note that resolution will, in general, be best when the resolution group is at or near the
transducer focal point.
D. Dead Zone Measurement
The dead-zone or "ring-down" distance is measured with the top group of rods. The transducer is
positioned 1 mm from the uppermost rod in the group. The distance from the transducer face to the
first rod whose echo is resolved from the reverberation is the length of the dead zone. All rods
further than this must also be resolved for this to be quoted as the dead-zone measurement. If the 6
mm rod and all succeeding ones are resolved, the dead zone will be quoted as "less than 6 mm."
E. Lateral Resolution Measurement (Beam Width)
Lateral resolution may also be measured approximately with the vertical group of rods used for
depth calibration. A linear scan is made parallel to the plane of the rods, (across the top of the
phantom). The rods will generally be displayed as lines rather than points. The lengths of these
lines, transverse to the direction of ultrasound propagation, show the beam width as a function of
distance from the transducer. The line length is also approximately equal to the transverse
resolution at each depth. Two reflectors at that distance apart will appear as two lines of this length
centered on the rods, so that the proximal ends of these lines will just meet or just fail to meet.