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  • Name: AN EVALUATION OF THE STATUS OF LIGHT BEAM DIAPHRAGM IN SOME GOVERNMENT AND PRIVATE RADIOLOGY DEPARTMENTS IN ENUGU STATE
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ABSTRACT

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 OF CONTENTS

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

CHAPTER ONE: INTRODUCTION

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

CHAPTER TWO: THEORETICAL BACKGROUND

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

  • Beam Limiting Devices………………………….………………….… 26
  • Principles of Light Beam Diaphragm……….…….….……………….. 34
  • Care of Light Beam Diaphragm………………………………………. 38
  • Changing a Light Bulb .….……………………….….………………… 40
  • Light Beam Diaphragm Accuracy Test…………………..……………. 40
    • Equipment/Material Required………………………………………….. 41
    • Procedure……………………………………………………………….. 41
    • Measurement Of Misalignment………………………………………… 42

CHAPTER THREE: RESEARCH METHODOLOGY

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

CHAPTER FOUR: DATA ANALYSIS AND PRESENTATION

4.1 Data presentation…………………………..……………………….…… 49

4.2 Data analysis………………………………..…………………………… 52

CHAPTER FIVE: DISCUSSION, SUMMARY OF FINDINGS, RECOMMENDATIONS, AREAS OF FURTHER STUDY, CONCLUSION AND LIMITATIONS OF STUDY

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

REFERENCES ……..…………………………………………………………. 64

APPENDIX ………………………………………..……………………..……. 71

 

CHAPTER ONE

   INTRODUCTION

  • BACKGROUND OF STUDY

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.

 

  • STATEMENT OF PROBLEMS
  1. It has been observed that radiographs taken by experienced radiographers often come out off-centered in this locality.
  2. It has also been observed that radiographers often do not apply collimation while working to avoid cut-off.
  3. How often light beam diaphragm test is conducted by hospitals has not been established in this locality.

1.3     PURPOSE OF STUDY

  1. To assess light beam diaphragm status in x-ray equipments in selected radiology departments in Enugu state.
  2. To assess if misalignment increases with increase in field size.
  3. To assess percentage misalignment of light beam in all the centers studied.
  4. To assess if radiographers in Enugu state apply collimation as a form of radiation protection measure.
  5. To assess how often light beam diaphragm test is conducted in radiology departments in Enugu state.

1.4   SIGNIFICANCE OF STUDY

  1. This study will define the status of light beam diaphragm of x-ray equipments in Enugu state.
  2. This study will show the compliance of radiographers in Enugu state towards the application of collimation.
  3. The study will define how often radiology departments carryout Quality assurance test on their machines.

1.5     SCOPE OF STUDY

This research work is limited to selected x-ray and diagnostic centers within Enugu state.

1.6     LITERATURE REVIEW

In general all equipments work efficiently within a specific period, after which some care and routine maintenance need to be administered for continuous efficiency; but if this care and maintenance are not done, certain errors and minor faults are noticed which if not corrected could advance to permanent equipment breakdown. In the radiology department, x-ray equipments follow the same trend, and so it is incumbent upon practitioners of medical imaging to understand the basic principle employed in x-ray equipment and its accessories and also be aware of any undesirable conditions that may develop from them.

It has been reported 12 and as is common in daily radiographic practice, that radiographers and other users of the final product of x-ray images often encounter radiographs which are off-centered even when proper radiographic techniques are applied. This is due to misalignment of the light field and x-ray field. Loss of alignment could be attributed to degree of utility, susceptibility to knocks and other mechanical problems; with loss of accuracy increasing with increase in field size13. The relevance of this light and x-ray field identity to radiation protection is supported by data from the 1970 x-ray exposure study of the US public health service which showed that genetically significant dose could be reduced by 21% if the beam size were reduced to the film size with such reduction also reducing the amount of scatter radiation 12. Furthermore, the US bureau of radiological health reported that genetically significant dose to people from medical diagnostic x-ray can be reduced from 55 millirads per exposure to 19 millirads per exposure if the size of the x-ray beam in the plane of the film is limited by collimation to the film size 13. Excessive beam size has been identified as the principal cause of unnecessary patient exposure in diagnostic radiology14.

According to Lloyd 7, the LBD provides the radiographer with an easy, accurate method of controlling the size of the x-ray field and placing it over the area of interest, thus reducing the radiation dose to the patient and improving the quality of radiographic image. Chesney 3, 15, describes the LBD as a common radiographic accessory and employs a mechanism that collimates and indicates the radiation field by optical means. The mirror is placed approximately at an angle of  45° to the lamp and to the focal spot of the x-ray tube occasionally goes out of alignment so that the light field and x-ray field no longer coincide 3, 16.

According to Ian 2, the light beam might have insufficient brightness which results in improper alignment to the x-ray beam. This may be due to several causes, some of which may combine to give an overall drop in light level:

  1. Dirt or dust builds up on the inside of the transparent exit cover of the collimator.
  2. The globe having some metal evaporation on the inside of the globe.
  3. The voltage supply of the lamp is too low. This is due to wiring resistance causing the voltage to drop between 2-5 volts on load hence; it is good to allow 5 volts addition during installation. He also identified two version of quartz iodide globe often used in the LBD appear similar: one with start pins to hold the filament while the other has long pins. If the wrong version is installed, there is large error the light field and x-ray field resulting in misalignment.

In a research work carried out by Ikasmaise et al 17, it was discovered that 93.28% of the 134 radiographs that were examined in the University of Calabar Teaching Hospital (UCTH) indicated inadequate collimation which could be as a result of misalignment. Some areas of the patient which were not exposed by the light field are eventually exposed by the radiation field, resulting in the production of scatter radiation and as a result, poor image contrast and geometric cut-off which cold necessitate repeat exposures with higher doses to the patient, resulting in wastage of film material, risk to the tube due to overload.

Egbe et al 9 carried out a research on the LBD of diagnostic centers in Calabar, Nigeria in 2003. They employed the LBD accuracy test which is one of the Quality assurance test in the radiology department, using six diagnostic centers. The results of this work reveal that values exceeding the allowed 2% were obtained in some centers, while others were closely approaching the mark. Hence, most (95%) of the light beam diaphragms were unable to maintain the relationship between the light field and the x-ray field. There is also increase in total misalignment with increase in field size, though it is obviously only the light field that is altered. This shift in the light field leaves the x-ray field unaffected and in its normal path. This manifests on radiographs as geometric cut-off, sometimes with sufficient loss of information to warrant repeats and therefore increase the incidence of radiation effects. The misalignment values were inhomogeneous, with the greatest misalignment values given as 7.9% and 5.6% along and across the cassette respectively while on the other hand, the least misalignment values along and across the cassette were 0.3% and 1.1% respectively. The total increase in misalignment only alters the light field while the x-ray field is unaltered. This manifests on the radiographs as geometric cut-off, sometimes with sufficient loss of information to warrant repeats and therefore increase the incidence of radiation effects 18. The measured misalignment values was poor and unacceptable when compared with Environmental Protection Agency and World Health Organization Standard – The percentage misalignment of the x-ray and light field must not exceed 2% 6, 7, 19.

In a study carried out by Okeji et al 20 to evaluate the X-ray beam collimation practice, among radiographers, as a measure of radiation protection for patients undergoing radio-diagnostic investigations, Light beam misalignment/malfunction test was carried out on the functional x-ray machines at the time of the study. A total of six x-ray machines (5 static and 1 mobile units) were evaluated for x-ray beam alignment. Four static x-ray machines showed positive misalignment, which ranged from mild to marked while one static and mobile unit showed normal beam alignment with the light beam diaphragm.

In a research work carried out by Nzotta and Anyanwu 10, the status of 18 LBDs in 5 radiological centers was studied using alignment tool test and loaded cassettes. The range of misalignment measured for the centers are 0.6cm to 5.4cm and 0.8cm to 6.0cm along and across the cassette respectively. This showed a high disparity when compared to the recommended value based on the European protection agency criteria of 0.0 to 2.0cm range of misalignment and also percentage difference greater than 2.0% in either direction is considered abnormal and requires remedy. Ten centers representing 55.5% had a percentage difference greater than 2% for both across and along the cassette. Six centers had below 2% misalignment along and across while two centers had misalignment greater than 2.0% along and across. The highest misalignment is 5.4% and 6.0% along and across the cassette respectively and the lowest misalignment is 0.6%and 0.8% along and across respectively. This result shows that any increase in light field produces a corresponding increase in misalignment along and across the cassette. This conforms to the work of Egbe 9. The result shows that newer x-ray equipments have lower degrees of misalignment. This probably is due to irregular control checks and measurement done on older equipments.

Harvest 21 performed a study of diagnostic x-ray equipments in Malawi. There  were 8 hospitals where Radiographers in- charge said they conduct the beam alignment and collimation test and actual Quality Control test results from 8 (100%) hospitals had their x-ray tube misaligned to the light field. Centering of x-ray tube to the mid-point resulted in 5 (62%) out of 8 having good centering point. From four hospitals that did not mark the test to be done, all 4 (100%) had the x-ray beam misaligned to the light field. On the centering of the x-ray tube from these 4 hospitals, 3 (75%) had their x-ray tubes off-centered. This means that even though the test is said to be conducted in some hospitals not much is done to ensure the beam alignment is corrected in the hospitals or the interpretation of the tests are not accurate. The results of the test from those that said they do not do the test are also poor. Unless the X-ray tube is correctly centered to the mid-point the images produced become distorted as emphasized by Carroll 1. The beam alignment and collimation test resulted in all 12 hospitals showing misalignment of the X-ray tube to the light field. In checking the centering point of the x-ray beam in relation to the light field exposure, in 6 hospitals, the x-ray beam was not centered to the midpoint as shown by light field but was correctly centered in the other 6 hospitals. These results show that the beam limiting devices are not functioning correctly. As stipulated by Carroll, for the production of quality radiographs, beam limiting devices help in reducing radiation exposure to the patient and staff and increase the contrast of radiographic image. When the light field is not aligned and centered to the X-ray tube, then the beam limiting device is not serving its purpose. This needs serious attention to ensure that the x-ray tubes are correctly aligned to the light field to ensure there is no cut-off or over collimation of the area of interest which leads to repeat radiographs when x-raying patients.

Esu 11 in her work to check the beam alignment and collimator accuracy of the x-ray equipment, results showed an increase in misalignment of the x-ray field with an increase in light field. The greatest misalignments were 3.9% and 1.0% along and across the cassette respectively. On the other hand, the least misalignment along and across the cassette were 2.0% and 0.9% respectively. Left sided misalignment was noted in all the LBDs tested. This indicated an unacceptable status of LBD in the 3 hospitals used, and the implication of this on image quality and radiation protection is noted as an undesirable development as it evitably contributes an unwelcome quantity to the radiation dose to the patient.

In a study by Aliyu Sa’ida 22 on the quality evaluation of diagnostic radiology departments in Zaria, light beam diaphragm test was conducted in 5 hospitals. Out of the 5 hospitals, hospitals A, E, and L have adjustable diaphragm while hospital G has a fixed diaphragm attached to it. Hospital G has the highest misalignment with 3cm on x-axis and 1.2cm on the y-axis that is 3cm and 1.2 cm along and across the cassette respectively, while hospital C has the least mismatch with 1.2cm and 1.0cm along and across the cassette respectively. All hospitals except in Hosp. H, produces satisfactory results with perpendicularity of X -ray beam Alignment. They have misalignments of 0.4cm, 0.2cm, 2.0cm, 1.5 and 0.8 in Hosp. A, E, G, and L respectively and Hosp. H has 2.4 above the tolerance value. The misalignment of light beam with X-ray beam in all the hospitals were above the tolerance limit. The misalignment was also noted to be more to the right than the left. His mismatch of the beams is all more than the accepted limit of 0.5cm on each axis as quoted by the British Institute of Radiology 23. Ideally the two should superimpose but a misalignment of up to 0.5cm in practice is allowable. From these results it implies that there is need for immediate repairs of the LBD to reduce unnecessary dose that would be received. The doses that were received in the surveyed hospitals were large considering the implication of 1cm error in misalignment. This normally occurs 2-3 times in a year by a single machine 24. Hence there is need to carry out this test quarterly so that quick repair can be made if the misalignment exceeds the acceptable limit. The principal cause of unnecessary patient exposure in diagnostic radiology was also shown to be excessive beam size and it can result in gonadal dose many times that which could be delivered by properly collimated x-ray beam25, 26.

Brian 27 in a research conducted in Northern Ireland reported that there were cases of LBD becoming detached during use which occasionally led to patient injury. He related the causes to the method of attachment to the x-ray tube; some manufacturers attach them ordinally to the x-ray tube without any safety devices to prevent them from complete detachment. According to him the causes of detachment during use include:

  1. Incorrect, missing or poorly adjusted attachment screws.
  2. Fitting an inappropriate ‘rotating flange’ between the x-ray tube and the LBD, where subsequent repositioning of the LBD has led to its detachment.
  3. The inappropriate use of attachment screws to make LBD to x-ray field adjustments.

Some of the precautions according to Brian to avoid LBD detachment include:

  1. The notice should be brought to the attention of all appropriate managers, staffs and users.
  2. LBDs should be used in accordance with the manufacturer’s instructions for use. Vigilance should be maintained for signs which could indicate an increase attachment, such as a loose fit or rattle, and gross misalignment between light and x-ray fields.
  3. It is recommended that frequent periodic checks are carried out on units where the LBD is more likely to be damaged through impact, such as mobile equipment.
  4. Where there is evidence, or it is suspected that a LBD may be insecure, the x-ray equipment should be removed from use until it has been checked by a suitably qualified person.
  5. Following installation, servicing or maintenance, service agents should be asked to confirm that the x-ray tube and LBD are compactable, correctly attached and that any adjustments made have been in accordance with the instructions provided by the equipment manufacturers.

Yesaya et al 28 carried out a study on diagnostic x-ray facilities as per Quality control performances in Tanzania. They were of the opinion that without appropriate Quality control (QC) and preventive maintenance (PM) measures for x-ray machines in place, the benefits of reduced dose to the patient and early diagnosis will not be realized. The aim of their work is to report on the current status of the diagnostic x-ray machines in Tanzania in order to produce the data needed to formulate Quality Control and Preventive maintenance practices and strategies are needed to ensure that patients received the lowest possible radiation risk and maximum health benefits from x-ray examination. Of the four Quality control test performed, beam alignment and collimation was tested on 80 units of which 60% failed the beam alignment test.

Quality assurance in radiology department of any hospital as a procedure has attracted the attention of professionals in various fields within and outside the hospital setting because every individual wants to adopt the principle of “first time right” – doing the right radiological investigation properly the first time as stated by Ekpeyong 29. According to Steve 30, Quality assurance is very important in the radiological department and should be aimed at providing high quality health care services at a very low cost according to Russell 31, 32.

Quality assurance is defined as an overall management programme put in place to ensure that equipment works effectively in its day-to-day activities 1, 7. It is divided in to 3 stages:

  1. Type testing
  2. Acceptance testing
  3. On-going quality assurance test

Type testing is the test done in the manufacturing site/company to check the equipment specification and used in the categorization of the equipment according to the quality with regards to some important parameters. The specification includes: electrical output, imaging quality and radiation output. The test is done by engineers.

Acceptance testing is the test done before the final handover of the equipment to the purchasing department. It is done to ascertain the equipment installed complies with advertised specifications. It involves confirmation and documentation of measured parameters as a basis of performance. It is done by engineer, medical physicist and the radiographer.

Ongoing quality assurance test are all those planned and systemic actions necessary to ensure that the equipment is performing effectively in its day-to-day activities. Usually after the acceptance test, the baseline parameters measured are kept for reference. In the ongoing assurance test, the values of the test are compared with that of the acceptance testing to know how far the equipment has deteriorated. It could be carried out in days, months, weeks or annually. It is done by the medical physicist and radiographer.

The light beam diaphragm accuracy test is one of the ongoing assurance tests in the radiology department. According to Fitzgerald and Courades 33, radiation protection technical and quality control when existing in a center have patient and radiation protection among their functions, at least theoretically; although in the majority of centers, this task is not effectively fulfilled with regards to diagnostic radiology. Kotre and Colin 34, reviewed faults and the relevance of Quality assurance in the x-ray equipment. They reported that 28% of the x-ray faults results from LBD misalignment. They further said that the percentage of faults appear to be greater in the older x-ray units.

Based on European guidelines for radiation protection and criteria for radiological equipment acceptability 35, once the performance of equipment gets to the remedial level, action should be taken for quality control. Remedial level is the level of performance of equipment at which repair actions needs to be initiated. The execution of remedial actions will be based on formal assessment of the equipment performance. Following this assessment, agreement should be reached on a reasonable time scale for corrective action (withdrawal or replacement or repair of equipment). Additional thorough and accurate measurement may be needed to determine the causes of the change in performance.

According to Evans 36, software has been written for the calculation, interpretation and presentation of quality control measurement of x-ray machines. This provides an efficient system of data storage and enables the ready analysis and application of result.

During the course of this research work, it was discovered by the researcher from the consulted literatures that only very few of such works have been documented in the area under study (Enugu state) and in Nigeria as a whole.

 

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