Fluke 07-591 User Manual

Nuclear Associates 07-591

Focal Spot Test Tool

February 2005
Manual No. 07-591-1 Rev. 2
©2004, 2005 Fluke Corporation, All rights reserved. Printed in U.S.A.
All product names are trademarks of their respective companies

Users Manual

Fluke Biomedical

Radiation Management Services

6045 Cochran Road
Cleveland, Ohio 44139

440.498.2564

www.flukebiomedical.com/rms

Table of Contents

Section 1: General Information................................................................................... 1-1

1.1 Introduction .................................................................................................. 1-1

1.2 Instructions .................................................................................................. 1-1

1.3 Acceptance Criteria ..................................................................................... 1-2

i

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General Information

Introduction

1

Section 1

General Information

1.1 Introduction

The Focal Spot Test Tool (Model 07-591) provides a simple “pass-fail” test to determine if an x-ray tube
focal spot has been damaged. It consists of a 6” high stand with a thirteen-group test pattern. Each
group has six bars, three of which are positioned at right angles to the adjacent set. The groups diminish
in size from 0.63 line pairs/mm to 2.52 line pairs/mm. By observing the radiograph and using the chart
supplied, showing resolution vs. focal spot size, the nominal focal spot dimension (in mm) can be
determined.

Figure 1-1

1.2 Instructions

When checking overhead x-ray systems, position the focal spot of the x-ray tube 18” from the top of the
test tool. Adjust the collimator so that the x-ray field is within the dimensions of the base of the test tool.
Then set the x-ray generator between 50 and 60 kVp and between 3 and 5 mAs. Place a piece of dental
x-ray film (type BF46 or equivalent) or a non-screened film in a cardboard cassette under the cylinder of
the test tool, and make the exposure with the small focal spot. Repeat with a second piece of film for the
large focal spot.

To check fluoroscopic tubes, place the tool upside-down on the table. Place an absorber such as the
Patient Phantom/Penetrometer (Model 07-706) or the Copper Test Plate (Model 07-708) on top of the test
tool in order to protect the image intensifier. Operate the system in a fluoroscopic mode, and adjust the
fluoroscopic shutters so that they limit the beam to the dimensions of the plate. Place the non-screen film
between the absorber and the test tool. Using 80 kVp and 1 mA, expose the film for 5 to 10 seconds
using the small focal spot.

1-1

Nuclear Associates 07-591

Operators Manual

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.

NOTE

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-to­film 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

1

Group2 lp/mm

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.

Diameter

in mm

Focal Spot

(Nominal)

Focal Spot

(Actual)

1-2

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Fluke Biomedical

Radiation Management Services

6045 Cochran Road
Cleveland, Ohio 44139

440.498.2564

www.flukebiomedical.com/rms