3 acceptance criteria – Fluke Biomedical 07-591 User Manual
Page 6
Nuclear Associates 07-591
Operators Manual
1-2
If desired, a similar test may be used for the large focal spot in many systems, by using an empty
cassette in the spot film device and setting the timer for fixed factors of approximately 3 to 5 mAs and
making the exposure. In most systems having spot film devices over the table, the focal spot of the x-ray
tube is 18” below the surface of the table.
The distance from the pattern to the film is 6”. The
distance from the source to the pattern must be 18”
for the table of results to be valid. As long as the
source-to-pattern distance is 3 times the pattern-to-
film distance, the table is valid.
If, for example, the source-to-pattern distance is
24”, the pattern-to-film distance must be adjusted to
8” by a spacer, perhaps of foam rubber.
1.3 Acceptance Criteria
A group of three bars is said to be resolved when exactly three bars may be seen clearly in the x-ray
image on the film. If two or four bars are seen, or if the image is just a blur, the image is said to be
unresolved. Both groups of bars (at right angles to one another) must be resolved.
Obviously, larger focal spot tubes should resolve only the larger groups. Reference to Table 1-1 indicates
what should be expected of focal spots of given sizes. For example, a 2 mm rated focal spot must
resolve 5 groups; 1.5 mm must resolve 8 groups; 1.3 mm must resolve 10 groups; 1.0 mm must resolve
11 groups; 0.8 must resolve 13 groups; 0.7 mm and 0.6 mm must resolve 13 groups.
Table 1-1 Expected Focal Spots of Given Sizes
Group
2
lp/mm
Diameter
in mm
Focal Spot
1
(Nominal)
Focal Spot
(Actual)
1 0.63 6.69
2.0
2.60
x
3.64
2 0.7 5.71
2.0
2.60
x
3.64
3 0.79 4.82
2.0
2.60
x
3.64
4 0.89 4.70
2.0
2.60
x
3.64
5 1.00 4.00
2.0
2.60
x
3.64
6 1.12 3.50
1.8
2.34
x
3.28
7 1.26 3.42
1.8
2.34
x
3.28
8 1.41 2.86
1.5
1.95
x
2.73
9 1.59 2.25
1.3
1.95
x
2.73
10 1.78 2.46
1.3
1.50
x
2.18
11
2.00
2.00
1.0
1.4 x 1.96
12 2.24 1.65
0.8
1.12
x
1.57
13 2.52 1.60
0.8
1.12
x
1.57
1
In the plane of the focal spot.
2
Acceptance Level; i.e., 1.8 mm rated focal spot must resolve groups 1, 2, 3, 4, 5, 6, 7.
NOTE