1. RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY
Part No...., Module No....Lesson No
Module title
IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
RADIATION PROTECTION IN DIAGNOSTIC AND INTERVENTIONAL RADIOLOGY
Part 15.5: Optimization of protection in radiography
Practical exercise - focal spot
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to: …
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

2. Part No...., Module No....Lesson No
Module title
Contents
Subject matter : quality control of general radiography system
Step by step procedure to be followed to implement the considered QC test
Interpretation of results
Explanation or/and additional information
Instructions for the lecturer/trainer
15.5: Optimization of protection in radiography
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

3. Part 15.5: Optimization of protection in radiography
Part No...., Module No....Lesson No
Module title
IAEA Training Material on Radiation Protection in Diagnostic and Interventional Radiology
Part 15.5: Optimization of protection in radiography
Focal spot size measurement
(star pattern method)
Part …: (Add part number and title)
Module…: (Add module number and title)
Lesson …: (Add session number and title)
Learning objectives: Upon completion of this lesson, the students will be able to: …
. (Add a list of what the students are expected to learn or be able to do upon completion of the session)
Activity: (Add the method used for presenting or conducting the lesson – lecture, demonstration, exercise, laboratory exercise, case study, simulation, etc.)
Duration: (Add presentation time or duration of the session – hrs)
Materials and equipment needed: (List materials and equipment needed to conduct the session, if appropriate)
References: (List the references for the session)
IAEA Post Graduate Educational Course in Radiation Protection and Safe Use of Radiation Sources

4. What Minimum Equipment is Needed?
Focal spot tool : star pattern
Radiographic film
Non-screen cassette
Roll of removable tape
15.5: Optimization of protection in radiography

5. Focal spot size (star pattern) (1)
The focal spot size measurement is intended to determine its effective dimensions at installation or when resolution has markedly decreased. For routine quality control the evaluation of spatial resolution is considered adequate
A magnified X-ray image of the test device is produced using a non-screen cassette
This can be achieved by placing the film to be exposed between two sheets of opaque film (optical density greater than 3.0) inside of the cassette.
Alternatively, a mammography screen-film system can be used.
15.5: Optimization of protection in radiography

6. Focal spot size (star pattern) (2)
Select the focal spot size, 70 kV and an mAs to obtain an optical density between 0.80 and 1.40 above base-plus-fog (measured in the central area of the image)
Tape the star pattern to the bottom of the collimator with it centered using the collimator cross hairs and the quadrants aligned parallel and perpendicular to the anode-cathode axis.
15.5: Optimization of protection in radiography

7. Focal spot size (star pattern) (3)
Place the cassette on the table top
Make an exposure and process the film
For digital systems the procedure is the same except that measurements are made on a digital image
15.5: Optimization of protection in radiography

8. Focal spot size (star pattern) (4)
The magnification is determined as the ratio of the diameter of the test pattern image to the diameter of the physical test pattern.
The focal spot dimensions can be estimated from the 'blurring diameter' on the of the star pattern
The distance between the outermost blurred regions is measured in two directions: perpendicular and parallel to the tube axis
15.5: Optimization of protection in radiography

9. Focal spot size (star pattern) (5)
The focal spot size is calculated using: p q x D
blur f = x
180 ( M - 1 )
star
where :
q : the angle of the radiopaque spokes (1° or °),
Dblur : the diameter of the blur.
Mstar : the magnification factor determined by measuring the diameter of the star pattern on the acquired image (Dimage) and the diameter of the device itself (Dstar), directly on the star
15.5: Optimization of protection in radiography

10. Focal spot size (star pattern) (6)
According to the IEC Standard:
a nominal 0.8 focal spot should not exceed 1.2 mm in width and 1.6 mm in length.
A nominal 1.2 focal spot should not exceed 1.7 mm in width and 2.4 mm in length.
15.5: Optimization of protection in radiography

11. Where to Get More Information
Quality Control in Diagnostic Imaging, Gray JE, Winkler NT, Stears J, Frank ED. Available at no cost.
15.3: Optimization of protection in radiography