An Evaluation Of The Status Of Light Beam Diaphragm In Some Government And Private Radiology Departments In Enugu State

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An Evaluation Of The Status Of Light Beam Diaphragm In Some Government And Private Radiology Departments In Enugu State


This study was designed to evaluate the status of light beam diaphragm in government and private radiology departments in Enugu state. This was conducted using questionnaire and a quality assurance test method to check the beam alignment and collimator accuracy of x-ray equipment in radiology centers in Enugu state. The main objectives were to assess the status of LBDs, to assess if misalignment increases with increase in field size, to assess if radiographers in Enugu state apply collimation and to assess how often light beam diaphragm test is conducted. A sample of 19 radiology departments and 19 questionnaires were used for the study. The result showed that 21% have a percentage misalignment value below 2% in both AC and AL, while 79% had misalignment either across or along or in both directions greater than 2%. The greatest percentage misalignment across and along the film were 10.6% and 5.8% respectively. On the other hand, the least percentage misalignment across and along the film were 0.8% and 0.4% respectively. Results also showed an increase in misalignment of the x-ray field and light field with an increase in the light field. This was correlated using inferential statistics. A majority of the radiographers apply collimation as a form of radiation protection while there is a poor practice of Quality assurance in this area with majority (74%) not conducting the test at all. This indicates unacceptable status of LBDs in enugu and the implication of this in image quality and radiation protection is noted as an undesirable development as it evidently contributes an unwelcome quantity to the radiation dose to the patient population.

Table 1: Summary of results with percentage values for AC and AL
Table 2: One-way anova test of the percentage misalignment across (AC %) and along (AL %) cassette for the of 15 × 15cm light beam sizes.
Table 3: One sample t-test of the percentage misalignment for the light beam field size of 15 × 15 cm between the radiological departments and the standard value.
Table 4: One sample t-test of the percentage misalignment for the light beam field size of 20 × 20 cm between the radiological departments and the standard value.
Table 5: The distribution of what often is the problem when LBD becomes faulty
Table 6: The observation of the application of collimation practice during x-ray examinations in all the centers.
Table 7: The distribution of the response of how often quality assurance test it is carried out.

Figure 1: An Arrangement of two pairs of movable leaves of metal in an adjustable diaphragm seen from the direction of the focus of the x-ray tube.
Figure 2: An Arrangement of two pairs of movable leaves of metal in an adjustable diaphragm showing how the pairs are arranged in a near relationship.
Figure 3: Principal components of the Light Beam Diaphragm
Figure 4: Arrangement of setup for exposure using the “eight pennies method”.
Figure 5: Arrangement of setup for exposure using the L- shaped radio-opaque markers.
Figure 6: Measurement of misalignment.
Figure 7: Pie chart representing collimation practices observed in all the radiology departments.
Figure 8: Pie chart representing how often quality assurance is carried out in all the radiology departments

Title page I
Approval Page II
Certification III
Dedication IV
Acknowledgement V
List of tables VI
List of figures VII
Abstract VIII
Table of Contents IX
1.1 Background of study 1
1.2 Statement of problem 5
1.3 Purpose of study 5
1.4 Significance of study 5
1.5 Scope of study 6
1.6 Literature review 6
2.1 Radiation Protection in Radiological Practice 18
2.1.1 X-Ray Production 18
2.1.2 Biological Effects of X-Ray Radiation 20
2.1.3 The “ALARA” Principle 22
2.1.4 Minimizing radiation doses 23
2.2 Beam Centering Devices 24
2.3 Beam Limiting Devices 26
2.4 Principles of Light Beam Diaphragm 34
2.5 Care of Light Beam Diaphragm 38
2.6 Changing a Light Bulb 40
2.7 Light Beam Diaphragm Accuracy Test 40
2.7.1 Equipment/Material Required 41
2.7.2 Procedure 41
2.7.3 Measurement Of Misalignment 42
3.1 Design of Study 45
3.2 Population of Study 45
3.3 Sample Size 45
3.4 Source of Data 45
3.5 Method of Data Collection 46
3.6 Method of Measurement of Misalignment 47
3.7 Method of Data Analysis 48
4.1 Data presentation 49
4.2 Data analysis 52
5.1 Discussion 57
5.2 Summary of findings 59
5.3 recommendations 61
5.4 Area of further studies 61
5.5 Conclusion 62
5.6 Limitations of study 62

The field of medical imaging provides opportunities for a physical foundation in the understanding of the proper utilization of instruments and equipments applied in the imaging, diagnosis and treatment of human diseases and also how imaging scientists can be active participants in enhancing the opportunities offered by their use. It is incumbent upon the practitioners of medical imaging to understand the basic principles employed in instruments that image human anatomy and to be aware of any undesirable conditions that may arise from their use. Practical use and function of diagnostic x-ray equipment is affected inevitably in its construction by the need to employ x-ray beam which is optimally useful in production of images, with minimum input from deleterious influences of secondary radiation which often contributes to high patient doses 1.
The standard x-ray unit is made up of the x-ray tube and housing, transformer assembly and control panel assembly. Most x-ray tubes incorporate beam restrictors and filters. Beam restrictors are Lead obstacles placed near the anode of the x-ray tube and are used to control the field size of x-ray beam allowed to pass through the patient on to the film. These restrictors are important as they keep the patient exposures as low as reasonably achievable. The more basic types of restrictors include the Aperture diaphragms, collimators and shutters. The reduction in the beam field reduces the radiation dose to the patient and improves image quality. Therefore the reduction of radiation doses to the patient and the effect of secondary radiation on the image contrast are achieved by the use of x-ray beam collimators. The effectiveness of collimation by the beam collimators is strongly dependent on the accuracy with which the x-ray beam is centered to the anatomical area of interest.
In most x-ray machines, there is a lamp and a suitable optical mechanism to allow projection on the patient’s area of interest to be irradiated. This mechanism is known as the Light Beam Diaphragm (LBD) which is the best form of restrictors2. The purpose of the light beam diaphragm system is to allow more accurate centering to the area of interest, to produce optimum field size and radiation protection to the patient and invariably to the radiographer. The alignment of the light beam and x-ray beam must be ensured else, the function and basic goals are hindered 3.
The LBD is attached to the x-ray tube head through a rotating flange and screwed. Situations arise where the LBD is misaligned making the light beam not to coincide with the x-ray beam, and an exposure with improper collimation and centering. After processing the exposed film, an off-centered radiograph is produced. Off-centering is a technical term in radiography used to describe a situation where the central ray does not pass through the anatomical area of interest thereby cutting off structures of interest or including unwanted areas. When this occurs, the radiographer often makes such statements such as “but I collimated properly” 3. This situation shows the radiographers are often not aware when this misalignment occurs, and the only way to prove is by conducting the Light beam diaphragm accuracy test.
It is important that the light field is congruent at all times as any misalignment may result in poor radiographic images. Misalignment may be caused by a shift in the light bulb filament inside the LBD, mirror position, collimator position on the tube or anode focal spot 4.Some of the implications of the LBD misalignment include; suboptimal patient positioning as it may be difficult to centre accurately, off-centered radiographs where area of interest may be cut off and/or unwanted areas included, increase radiation dose to the patient from repeated examination, increase films reject which invariably affects the economy of the x-ray department, increase stress on the radiographer repeating the examination, increase strain on the x-ray machine due to repeat examinations, patient inconvenience and time wastage.
Certain level of misalignment are acceptable and above which the x-ray machine used should be suspended until corrected; if the misalignment of the x-ray field edges or Bucky centre to x-ray beam is greater than 1cm (0.5cm for pediatric units), the LBD is to be adjusted but if it is greater than 3cm, the equipment should be removed from service until corrected 5. The misalignment values acceptable vary with individual country’s regulation and often expressed in percentage 6, 7.
Beam alignment and collimation test ensures that there is adequacy of the diaphragms and congruency of the light to the radiation field as occasionally the mirror of a LBD goes out of alignment so that the light and x-ray field no longer coincide. Even after wise precautions are carried out to lessen these failures because they could still occur hence regular checks are recommended after repairs or maintenance work on the x-ray equipment for quality assurance 8.
Doing this study in Enugu state will check the incidence of off-centered radiographs and will also aim at suggesting possible solutions as regards reduction of radiation dose to the patient from repeat examinations due to fault from the light beam diaphragm.
An increase in light field which produces a corresponding increase in misalignment along and across the cassette was the most common observation noted in most studies 9, 10, 11. In Nigeria for example similar works have been carried out and documented especially in the south-south geographical area. Some of the works carried out in this area are those of Egbe et al 9 and Esu 11. Similar works have also been carried out by Nzotta and Anyanwu10 and Aliyu Sa’ida 11 but in the area under study, very little of such related works have been documented such as that by Okeji et al 12. The recommendation of regular checks after installation, repairs, or maintenance work on the x-ray equipment for quality assurance is not a common practice in the area under study.


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