1.0 INTRODUCTION: In our today’s country, radiation protection has turned out to be one of the most alarming issues in majority of our radiological diagnostic centres. Though radiography is gaining wide acceptance in nearly all part of the continent, it is equally important that the radiation protection of staffs and patients is taken into consideration and this is the sole responsibility of the radiographer operating the x-ray equipment. For this reason, quality control was considered one of the tools in optimizing best practice in the area of radiation protection of both the patient and the staff and also in maintaining the production of consistently high-quality diagnostic radiographs. (Martin, 2007). According to ICRP (1991), there are two basic principles of radiological protection. There are; justification of the practice and optimization of protection. In the area of optimization of protection, there is considerable scope for reducing doses to patient without any loss of diagnostic information, but the extent to which the measures available are used varies widely. Optimization of radiation protection does not necessarily mean the reduction of doses to the patient or by operating in the absence of a demonstrable threshold for stochastic effects but by trade-off between the benefits of dose reduction and the costs of achieving these reductions. A number of factors facilitate this trade-off. One of such factors is the quality control 1
This Document is a guide for Radiographers wishing to instigate and implement a good Quality Control System in the x-ray department.
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1.0 INTRODUCTION:
In our today’s country, radiation protection has turned out to be one of
the most alarming issues in majority of our radiological diagnostic centres.
Though radiography is gaining wide acceptance in nearly all part of the
continent, it is equally important that the radiation protection of staffs and
patients is taken into consideration and this is the sole responsibility of the
radiographer operating the x-ray equipment. For this reason, quality control
was considered one of the tools in optimizing best practice in the area of
radiation protection of both the patient and the staff and also in maintaining
the production of consistently high-quality diagnostic radiographs. (Martin,
2007).
According to ICRP (1991), there are two basic principles of radiological
protection. There are; justification of the practice and optimization of
protection. In the area of optimization of protection, there is considerable
scope for reducing doses to patient without any loss of diagnostic
information, but the extent to which the measures available are used varies
widely. Optimization of radiation protection does not necessarily mean the
reduction of doses to the patient or by operating in the absence of a
demonstrable threshold for stochastic effects but by trade-off between the
benefits of dose reduction and the costs of achieving these reductions. A
number of factors facilitate this trade-off. One of such factors is the quality
control measurements and practices of the department. (Saure and
Hagemann, 1995).
This quality control as noted by Maccia and Moores (1997), involves a
quantitative and qualitative measurements and test of the performance of x-
ray equipments, programs and practices of that diagnostic centre. Hence, in
instituting a good quality control system in our x-ray department, a quality
control program which will monitor the basic components of the imaging
process at a low cost through the use of simple, inexpensive tools and
minimal staff time must be put in place. This quality control will now
determine their adequacy in terms of production of high-quality diagnostic
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radiographs and also evaluates their contribution to all the radiation
protection practices therefore outlining their role in the optimization of the
radiation protection of that centre.
2.0 DEFINITION OF TERMS
Quality Control (QC): These are specific actions designed to keep
measurable aspects of the process involved in manufacturing a product or
providing a service within specified limits. These actions typically involve
measurement of a process variable, checking the measured value against a
limit, and performing corrective action if the limit is exceeded. (CRCPD Pub.,
2001).
Quality Assurance (QA): These are planned and systematic actions that
provide adequate confidence that a diagnostic x-ray facility will produce
consistently high quality images with minimum exposure of the patients and
healing arts personnel. The determination of what constitutes high quality
will be made by the facility producing the images. Quality assurance actions
include both quality control techniques and quality administration
procedures. (CRCPD Pub., 2001).
Quality Control Program: allows a facility with limited resources and
personnel to monitor the basic components of the imaging process at a low
cost through the use of simple, inexpensive tools and minimal staff time.
Quality Assurance Program: Is an organized entity designed to provide
quality assurance for a diagnostic radiology facility. The nature and extent of
this program will vary with the size and type of the facility, the type of
examinations conducted, and other factors. (CRCPD Pub., 2001).
Optimization: Optimization in the field of diagnostic radiology simply
means any process or procedure which ensures that doses due to
appropriate medical exposure for radiological purposes are kept as low as
reasonably achievable (ALARA) consistent with obtaining the required
diagnostic information, taking into account economic and social factors.
(IAEA Pub., 2004).
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Cost-Effectiveness: Chesney (1981) defined Cost-Effectiveness as “the
ratio of spending to the efficiency of production that follows the result”. It
compares the relative expenditure (costs) and outcome (effects) of two or
more courses of action.
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3.0 AIMS AND OBJECTIVES:
The main aim and objective of this colloquium is to promote awareness
creation about the practical implementation of quality control protocols and
image quality evaluation by consistently implementing simple and
inexpensive actions such as the use of appropriate screen/film combination,
use of secondary radiation grids when necessary, etc.
It also aims to create pools of expertise in the area of radiation
protection of patients, hence alleviating the dangerous practices of
unnecessary irradiation of our patients.
A further objective of this research seminar is to offer assistance and
guidance to an imaging scientist implementing and operating a quality
assurance program any in diagnostic radiology department across the globe.
4.0 SIGNIFICANCE OF QUALITY CONTROL:
All medical facilities using x-ray equipment, from a simple intra-oral
dental unit to an image intensified special procedure system, will benefit
from adopting a good quality control program because;
I. It will monitor the imaging process from start to finish revealing
potential problems that may otherwise go unrecognized and
achieving reduction of dose to patient and consistent production of
high-quality diagnostic radiographs.
II. It will also form a learning process for those taking part and will also
provide them with tools and practical protocols which can be used
in the implementation of a national quality control program in
diagnostic radiology in future.
III. Another most important benefit of a close control of the x-ray
department can be summarized by saying that, the overall cost-
effectiveness of the department will be improved. (Chesney, 1981).
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Some details which add up to improved cost-effectiveness includes;
a. The number of repeated radiographs is reduced.
b. The rate of flow of patients through the department is improved.
c. The department’s ability to meet the demands made upon its
services is raised.
d. Quality of radiograph produced is higher.
e. Standardization of the radiographic results is achieved and
maintained.
f. The reliability efficiency of automatic processors and of x-ray
equipment is improved.
5.0 QUALITY CONTROL PROGRAM
According to Stewart (1993), essentially, three steps are involved in a
quality control program. There are;
i. Acceptance Testing : These are test conducted on every new x-
ray facilities e.g. the x-ray machine, cassettes, intensifying screens,
grids, to name but a few. This test is carried out prior to it clinical
usage to show if the equipment is performing within the
manufacturer’s specification. This test must be done by someone
other than the manufacturer or his representative.
ii. Routine Performance Evaluation : With use, these x-ray
equipments deteriorate. This necessitates the periodic quality
control evaluation of these equipments. That is, these are the
quality control tests conducted on these equipments to see if the
equipment will meet predestined requirements.
iii. Error Corrections : When these equipment performances are not
optimal or do not meet predetermined requirements, or errors
found after the quality control test has been conducted, actions are
taken to effect corrections on them.
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5.1 General Consideration:
An adequate quality control program for any individual facility will
depend on a number of factors which include, but may not necessarily be
limited to, items such as the type of procedures performed, type of
equipment utilized, and patient workload. This program is developed under
the guidance and supervision of a medical physicist qualified in this area of
expertise by education, training, and experience.
5.2 Equipment Log:
An individual equipment log should be maintained on each x-ray unit in
the department. This equipment log must be kept at some convenient
location where anyone using the facility (physicians, technologists,
physicists, service engineer, etc.) can get ready access. The log should
contain;
1. Equipment Data Specifications
a. Technical specifications, including tube loading charts.
b. Equipment operating instructions.
c. Detailed identification of major components of the system
including name, serial number, and date of installation.
2. An outline of the applicable quality control program.
3. A log of the quality control test results.
4. A record of service on the equipment including a description of
system
malfunctions and description of what service was carried out. The
service record should also include identification of the individual
performing the service and the date.
5.3 Recording Test Data:
All quality control test data should be recorded on standardized forms. It
is suggested by AAPM (1981), that each institution develops its own forms
suitable to its own needs.
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1. The use of standardized forms will assure that all of the required data
will be obtained.
2. Forms should be filed as part of the room log.
3. The charting of trend data is a recommended procedure which will
allow easy identifications of variation with time. This is of particular
value in the case of film processors.
5.4 Conditions of the X-Ray Equipment:
5.4.1Mechanical Integrity: As noted in ICRU Report 54 (1996), a general
observation of the diagnostic system should be made. Key items to
look for are the presence of loose or absent screws, bolts, or other
structural elements that may have been improperly installed or have
worked loose due to use. The functioning and operation of meters,
dials, and other indicators like the pilot lights should be checked.
5.4.2Mechanical Stability: To obtain a diagnostic quality radiograph, it is
important to minimize patient motion. The availability and adequacy of
patient support devices such as the table or immobilizing devices
should also be checked. ICRP Pub. 60 (1991) added that, it is equally
important to check the reproducibility of positioning of the source and
image receptor that may be indicated or controlled by physical marks
or detents. A check of the accuracy of angulations scale should also be
made.
5.4.3Electrical Integrity: The external condition of the high voltage cables
should also be observed. Check to make sure that the retaining rings
at the termination points are tight and that there are no breaks in the
insulation. (ICRU Report 54, 1996). It is important to observe the "lay"
of the cables, how they are being hanged, so that they don’t interfere
with tube positioning.
5.4.4Alignment and SID: Source to image receptor distance (SID)
indicators should be checked. The consistency between multiple SID
indicators (indicators on the tube support and the collimator) should be
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verified. The accuracy of these indicators should also be verified with a
tape measure. Verification of proper grid installation should be made.
This check should also include a verification of the alignment of the x-
ray source and the center of the grid.
5.5 The Radiograph As A Quality Control Tool:
Patient’s radiographs are also considered one of the quality control
tools of which they are being checked on periodic basis and should be
factored into any departmental evaluation program.
5.5.1Rejected Films Analysis: Rogers (2008) defined Film Reject as “a
film deemed useless and discarded with another film being taken” and
A Repeat Film as “a film retaken to provide extra/missing diagnostic
information sent with the original for reporting”.
Film Reject Analysis according to Suleiman and Showalter (1984)
are periodic assessment and checks on rejected films as well as the
accepted ones usually on monthly intervals so as to identify the
problem, determine it cause and find solutions to it, all aiming at
reduction of film reject rate.
The causes of rejection of films are analyzed according to the
following;
- Too dark, too light (under/over exposure)
- Positioning/Collimation errors
- Patient movement
- Processing errors
- Others
Reference data should also be assigned to this analysis e.g. date/time,
operator ID code, room, exam type, reject or repeat, etc.
5.5.2Accepted Films Analysis: Good practice should always question the
adequacy of radiographs of less than optimal quality for their
acceptability in making a diagnosis. Repeating a procedure to get a
film of optimal quality is often not necessary and should be evaluated
in terms of the radiation exposure and cost of the retake. Since one
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should expect to find films of less than optimal quality in a
departmental file, an analytic review of these films should be made on
a regular basis.
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6.0 FACTORS IN OPTIMIZATION OF CONVENTIONAL RADIOGRAPHY
The formation of image of the body involves interplay between many
different factors. To achieve the correct balance between patient dose and
image quality, it is necessary to understand the way in which images are
formed, and to know the factors that influence the image quality and the
radiation dose received by the patient, so that appropriate options can be
selected. These factors include;
6.1 Screen/Film Combination:
The most important factor in the optimization of conventional
radiography is the choice of screen/film combination. (Martin, 2006). For a
screen-film typed film, the x-ray film is sandwiched between two screens
inside a light-tight cassette. Each screen has a layer of a fluorescent
phosphor, such as calcium tungstate or gadolinium oxysulphide, which
converts x-ray photons into visible light photons. The spectral emission of
the phosphor must be matched to the sensitivity of the film. This therefore
means that the wavelength of light emitted by the phosphor of the
intensifying screens must be within the range of wavelengths of light to
which the films is sensitive to and will record as latent image. (Maccia,
1995). Hence, blue light and green light emitting phosphors must be used
with monochromatic and orthochromatic films respectively.
Martin (2006) continued that, the thickness chosen for the phosphor
layer is a compromise between radiation dose and image quality. That is, a
thick film will have high efficiency in the conversion of x-rays to light but with
blurred image. But thin screens results in better resolution but requires
higher radiation exposure.
Hence, in choosing a screen/film combination, factors such as; the
spectral sensitivity of the film, the sensitivity of screen/film which is
quantified in terms of speed index, image contrast and range of exposure
levels to be produce; etc must be put into consideration. (Gray and Winkler,
1983).
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6.2 Exposure Control:
To produce an image on a film with an acceptable level of contrast, the
exposure must be within a relatively narrow range of doses. This is to say
that all exposures must be as low as reasonably achievable. (ICRP Pub. 60,
1990).
Two major factors according to Martin and McKenzie (1993) are
involved in the quantity of radiation produced by the tube. These are; the
tube potential difference (kVp) and the beam filtration. They also noted that,
the exposure factors used will be optimized through the experience of the
radiographers and exposure charts employed for each X-ray unit. The charts
provide a guide to the best factors for different examinations for a patient of
standard build. But however, adjustments will need to be made for patients
of different sizes.
To achieve a consistent exposure level, an automatic exposure control
(AEC) device is usually employed in fixed radiographic imaging facilities. This
comprises a set of X-ray detectors behind the patient that measure the
radiation incident on the cassette. The detectors are usually thin ionization
chambers. Exposures are terminated when a pre-determined dose level is
reached, thereby ensuring that similar exposures are given to the image
receptor for imaging patients of different sizes. The important parameter
involved in radiographic image formation is optical density, so film is used in
setting up the AEC to give a constant optical density. (Shrimpton and Jones,
1984).
6.3 Scattered Radiation And Use Of Low Attenuation Components:
Scattered radiations are produced when x-rays are attenuated at
angles different from the incident rays by the body tissue. These scatter is
increased with increase thickness of body part examined, e.g. skull, pelvis,
lumbar spine examinations.
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As noted in IAEA Publication (1995), radiation scatter has adverse
effects on our radiographs which are;
i. Decreases the light transmitting ability of our film.
ii. Decreases slightly the sharpness of the recorded detail.
iii. Increases the random background noise of the film and all these
will result in
iv. a reduction in the contrast of the film.
The amount of scattered radiation can be reduced by means of an anti-
scatter
grid. (Bauer, 1998). The grid consist of a plate containing thin strips of lead
lying perpendicular to the plated surface, which are sandwiched between a
low attenuation inter-space material which are radiolucent materials made of
either aluminium or polyester. X-ray photons are more likely to be
attenuated by the lead strips. (Sandborg and Carisson, 1993).
Secondary radiation grids are not used for examination of the body
parts but only parts intended to produce scatter maybe as s result of
increase in the tube potential difference (kVp).
6.4 Beam Collimator and X-Ray Projection:
Collimation of the X-ray beam is an important factor in optimization.
Good collimation will both minimize the dose to the patient and improve
image quality, because the amount of scattered radiation will increase if a
larger volume of tissue is irradiated.
Hart and Shrimpton (2000) noted that, collimation is particularly
important in pediatric radiography since the patient’s organs are closer
together and larger fields are more likely to include additional radiosensitive
organs. Collimation in most cases depends on the technique of the
radiographer, but regular quality control by checking that the X-ray beam
and the field from the light beam diaphragm are accurately aligned is
important, particularly for mobile equipment.
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6.3 Film Processing :
The final stage in the production of a radiograph is processing the film.
If processing conditions are not optimal, the film will require a higher
radiation dose in order to provide an acceptable film density. Chemicals
should be changed regularly, and the processing conditions, such as
temperature and development time should be carefully optimized. A system
of quality control that involves checking temperatures of processing
chemicals and carrying out sensitometry, involving development of a test
strip of film exposed to a range of light levels ensures optimal performance.
(BIR Pub. 2001). These checks should be carried out daily to monitor
performance in terms of film density, contrast and background fog level. The
performance levels of processors that have a relatively low workload need to
be monitored carefully.
Gray and Winkler (1983) noted that, film processing affects the film
density; therefore, it influences the speed index. Thus, the measurements of
the characteristic curve for a film will also reveal problems with processing. If
a film is taken with optimized processing, it can be considered the reference
standard. Checks can then be made by comparing future results with the
reference standard to identify any deterioration.
7.0 RECOMMENDED QUALITY CONTROL TESTS
This section describes the recommended quality control tests that
should be carried out in a radiological diagnostic centre. The frequency and
brief procedure of the test is also described in this section.
To successfully carry out a good quality control tests on our x-ray
equipments, many test tools and equipments of which some could be made
by the user are required. Such items include; test phantoms, mesh patterns,
alignment fixtures and timing tools, densitometers, etc. Other test tools,
such as the test cassette, require calibration and adjustment which is
feasible only when a quantity can be made.
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According to CRCPD Pub. 01-5 (2001), the recommended guidelines
and steps on implementing a good quality control test on our x-ray facilities
are as follows;
7.1 Processor Quality Control (Sensitometry):
Objective: The objective of this test is to determine if the processor is
working optimally.
Frequency: This test should be carried out daily, prior to processing patient
films
Required Equipment: Includes; a) Sensitometer b) Dedicated box of
control film c) Densitometer.
Steps:
1. Expose the control film with the sensitometer.
2. Develop the film.
3. Determine the average optical density of the mid-density step and record
it on a form.
4. Determine the average optical density difference and record.
5. Measure the background optical density (base + fog) and record. Verify
that the measured values are within a suggested optimal performance
criteria.
Corrective Action:
The tests should be repeated if the values are outside the performance
criteria. If, after repeating, the results are still out of limits, look for
processing problems and contact the processor service supplier.
7.2 System Constancy Test :
Objective: To assure that the radiographic system is operating consistently.
Suggested Performance Criteria: Optical density on test film within 1
step of comparison film.
Frequency: This test should be carried out monthly and after service of the
equipment
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Required Equipment: Include; Aluminum step wedge, quality control
cassette, film, densitometer
Steps:
1. Set the x-ray unit to the technique factors and source-to-image distance
2. Place the step wedge on the loaded QC cassette on the table top and
center the x-ray beam to the step wedge.
3. Collimate to the edges of the step wedge.
4. Make an exposure of the step wedge and process normally.
5. Using the densitometer, compare the optical densities for Steps 4 through
8 with the comparison film.
6. Record your results on the monthly quality control checklist.
Evaluation: Compare the current film with the comparison film. If the
densities are not within 1 step of the comparison film, constancy has not
been maintained and clinical images should not be taken until the problem
has been identified and corrected.
Corrective Action: Repeat the test to confirm results. Verify that the
processor is in control. Contact your x-ray and processor service engineers.
7.3 Daily And Weekly Darkroom Quality Control
Objective: To keep the darkroom clean and processing optimized.
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