Fluke Biomedical 07-647 - Manual (Page 8)

Nuclear Associates 07-647
Operators Manual
2-2
2. Verify the monitor setup
• Under fluoroscopy, verify that the low-contrast inserts are visible in both monitor adjustment
squares.
• If they are not:
- Turn both the brightness and contrast controls completely counter-clockwise.
- Adjust the brightness so that the black video blanking circle is just visible.
- Adjust the contrast knob until both inserts are visible and the appearance of the image is
not objectionable.
3. Evaluate the fluoroscopic image
• Determine the smallest mesh pattern that can be clearly resolved.
• Larger numbers correspond to smaller mesh patterns.
• Record this value.
• Determine and record the smallest low-contrast mass that can be detected.
4. Evaluate the recorded image
• Make a spot film recording of the Phantom.
• Record the resultant kVp and mAs.
•
Process the film in the usual manner.
• Evaluate the image, recording the smallest resolvable mesh pattern and low contrast mass.
• This procedure may be repeated for 105 mm film and other recording devices.
If any problems are encountered, they should be reported to the QC Technologist, Service Engineer or
Medical Physicist.
2.2 Analysis
(See pages 2-3, 2-4 and 2-5)
As with the Mammography Accreditation Phantom, the results should be plotted on a graph rather than
just recorded in a table. The graph will make it much easier to detect any trends, such as a steady but
slow change in the fluoroscopic kVp or in the radiographic mAs. Such trends are an indication of
degradation in imaging system performance.
A well-tuned fluoroscopy system should be able to resolve at least the 20 mesh at the center of the image
in the 6" mode. From image to image, the smallest mesh visible should not decrease by more than one
step and the number of masses visible should not decrease by more than one. A change larger than this
should be investigated and corrected by a qualified service engineer. The fluoroscopic tube potential
should be between 70 and 90 kVp.
The mAs for radiographic systems, and the kVp and mA for fluoro systems should remain constant to
within 10%. No trends should be observed. A trend is defined as three or more points that move in the
same direction from the prior measurement. Even if a trend does not have any points that exceed the
control parameters, its cause should be investigated and corrected, as it is an indication of potential
system performance degradation. It is also possible to observe trends that do not move consecutively in
the same direction, but instead demonstrate either upward or downward motion over a longer period of
time. Such long-term trends, as when the points exceed control limits, should be monitored closely and
the cause investigated and corrected by a qualified service engineer. Data demonstrating the trend may
prove helpful to the service engineer, when investigating the cause.