FIVE MARKS QUESTIONS & ANSWERS

Q1. Define Quality Assurance (QA). What are the objectives and aims of QA in diagnostic radiology?

Answer:

Definition:

Quality Assurance (QA) of medical diagnostic X-ray equipment means systematic actions necessary to provide adequate confidence to the end-users that a medical diagnostic X-ray equipment will perform satisfactorily in compliance with safety standards specified by the Competent Authority.

Aim of QA:

The main aim of QA is to achieve optimum image quality of radiological procedures with minimum possible dose to the patient(s).

The Purpose of Quality Assurance and Quality Control is to:

1. Minimize the radiation dose to the patient
2. Increase the life span of the equipment
3. Provide maximum good quality images

Why QA in Diagnostic Radiology:

• To calibrate all the exposure parameters and check functional performance of X-ray equipment.
• To check radiation safety around the X-ray installation.
• To obtain the optimum quality diagnostic information at the lowest radiation risk to the patient.

Q2. What are the benefits of the QA program?

Answer:

1. Image Quality:

• Production of diagnostic image of optimum quality.

2. Equipment:

• Reduction in retakes and less wear and tear on equipment.
• Problems detected early are generally less costly to repair.

3. Patient Flow:

• Reduction in repeats and human efforts, leading to better patient management.

4. Patient Dose:

• Reduction in retakes and less wear and tear on equipment leads to less patient dose.

5. Cost Effect:

• Less repetition, less wear and tear, less wastage of resources leads to less financial wastage. Hence cost effective.

Q3. Describe the four stages of Quality Control checks for X-ray imaging equipment.

Answer:

There are four stages to the checks and measurements applicable to X-ray imaging equipment:

I. Critical Examinations

II. Acceptance

III. Commissioning

IV. Routine Performance Testing

Details of the Stages:

QA programme begins with the performance evaluation of diagnostic X-ray equipment at the manufacturing stage and then acceptance testing after the installation of X-ray equipment at the user’s institution to ensure its conformity with the specifications.

Before the final acceptance of the equipment, it is ensured that the actual performance meets the purchase specifications.

When new equipment is purchased, the facility determines the performance criteria for the equipment. These performance criteria are then reflected in the purchase specification.

The purchase specification and the records of the acceptance testing should be retained throughout the life of the equipment for comparison with monitoring results in order to assess continued acceptability of performance.

The QA tests should be carried out thereafter at regular intervals (periodicity — once in two years) and also after repairs of the equipment or when equipment malfunction is suspected.

Q4. Describe the procedure for checking Accuracy of Tube Voltage. What is the acceptance limit?

Answer:

Definition:

The maximum or peak electrical potential (kVp) across the X-ray tube affects the radiation intensity reaching the image receptor and the contrast of the final image.

Instrument Used:

Digital kVp Meter (Gammex 330 Divoltmeter)

Procedure:

1. Place the kVp Meter on the X-ray table and maintain the FFD at 40 inch or 100cm with the help of measuring tape.
2. Collimate the beam up to the specified area of the ionization chamber.
3. Keeping the mAs constant, exposures are given for different kVp values and readings are observed.

Acceptance Limit:

• Reading should be within the acceptance limit of ±5%.
• If reading is beyond this, it should be rectified by a service engineer.

Q5. Describe the procedure for Exposure Time Accuracy test with its acceptance limit.

Answer:

Definition:

• Exposure time is operator selectable on most radiographic consoles.
• The timer controls the duration of exposure — it initiates and terminates the exposure after a prefixed period of time.
• Timer accuracy is checked with the help of a Digital Timer.

Procedure:

1. Place the Digital timer on the X-ray table and reading must be on zero.
2. Set FFD to 40 inch or 100cm with the help of measuring tape.
3. Collimate the beam to the specified area of the ionization chamber.
4. Exposures are given at different timer settings and readings are recorded.

Acceptance Limit:

• Reading should be within the acceptance limit of ±10%.
• If reading is beyond this, it should be rectified by a service engineer.

Q6. Write a short note on Half Value Layer (HVL) and its evaluation.

Answer:

Definition:

• Half Value Layer (HVL) testing is used to determine the quality of an X-ray beam.
• HVL is defined as the absorber material thickness necessary to reduce the X-ray beam intensity to half of its incident intensity.

Purpose:

HVL tests are performed to determine if there is enough radiation produced by the system to produce a quality diagnostic image, while not exposing a patient to more radiation than necessary.

Evaluation Procedure:

1. The ion chamber is placed at 100cm from the focus/table top.
2. The first exposure is recorded with nothing in the path of the X-ray beam.
3. Several small sheets of Aluminum ranging from 0.1mm up to 3.0mm are placed between the tube and radiation meter.
4. A graph is plotted between absorber thickness and percentage transmission.
5. The absorber thickness at 50% transmission = half value thickness of the beam.

Key Fact:

It takes approximately 2.5mm of Aluminum to reduce the intensity to one half of its original intensity at 75kV.

Q7. Write a short note on Beam Perpendicularity test.

Answer:

Definition:

X-ray beam should be perpendicular to the image receptor, otherwise it produces geometric distortion in the image, thus deteriorating image quality.

Procedure:

1. Place the collimator test tool and beam alignment test tool on the center of the image receptor.
2. Adjust the collimator so that the edge of collimated light beam coincides with the outline of the Collimator test tool.
3. Level should be checked with a Spirit level.
4. Expose the area with appropriate exposure.
5. Shadow of two holes should coincide with each other.
6. If holes do not coincide but lie within the two concentric circles, it is within the acceptance limit.

Evaluation:

Position of Points	Shift
Both points in the inner circle	0.5°
1 point in the outer circle	1.5°
1 point outside the outer circle	3°

Tolerance / Acceptance limit = 1.5°

Q8. Write a short note on Film Screen Contact test.

Answer:

Poor contact between the intensifying screen and the radiographic film reduces the contrast and produces blurring of radiographic images if the film and cassette is not in proper contact.

This can be checked with the help of the wire mesh pattern test.

Results of the Test:

• Undistorted Image → Film and screen are in good proper contact
• Distorted Image → Film and screen are NOT in proper contact — cassette needs to be repaired or replaced

Q9. Define Preventive Maintenance and Corrective Maintenance. How do they differ?

Types of Maintenance:

Maintenance is divided into two types:

1. Preventive Maintenance
2. Corrective Maintenance

1. Preventive Maintenance:

Preventive maintenance is maintenance that is regularly performed on equipment to lessen the likelihood of its failure.

Preventive maintenance is performed while the equipment is still working, so that it does not break down unexpectedly.

There is always a danger of undesirable machine breakdown. Preventive maintenance can save a lot of time and money.

2. Corrective Maintenance:

Corrective maintenance is a maintenance task performed to identify, isolate, and rectify a fault so that the failed equipment can be restored to an operational condition within the tolerances or acceptable limits.

Maintenance Contracts:

Maintenance contracts are of two types:

1. Annual Maintenance Contract (AMC)
2. Comprehensive Maintenance Contract (CMC)

Annual Maintenance Contract (AMC):

• A manufacturer company provides the service through AMC by themselves or with the service providers.
• The contract is usually for the period of 1 year and can be extended up to three years or five years.
• Usually the service providers give only service support and would charge separately for every part under AMC.
• However, in some cases, few parts are replaced.

Comprehensive Maintenance Contract (CMC):

• It includes prompt service from the company or service providers.
• The contract is usually for the period of 1 year and can be extended up to three years or five years.
• It includes repair and replacement of faulty parts.
• Having the contracts gives the benefits such as those parts which are not part of contract being available at reduced costs.
• CMC is costlier than AMC because it includes the repair and replacement of parts.

Key Difference Between AMC and CMC:

Feature	AMC	CMC
Service	Only service support	Prompt service included
Parts	Charged separately	Repair and replacement included
Cost	Less costly	Costlier than AMC
Duration	1 year (extendable to 3 or 5 years)	1 year (extendable to 3 or 5 years)

Q10. Write a short note on Grid Alignment and its importance in conventional radiography.

Answer:

Purpose of Grid:

• The purpose of a grid is to reduce the amount of scatter radiation reaching the film.
• This greatly improves the quality of the image.

Grid Cutoff:

Grid must be properly aligned with the beam; otherwise it can lead to reduction in quality of image — this condition is called Grid Cutoff.

Procedure:

1. Place the test tool on the table top so that the central hole is at the center of the bucky table.
2. Expose each hole one by one without moving the grid alignment test tool.
3. The density on the central hole should be highest and gradually decreasing on the sides.
4. Holes on either side should have equal densities (symmetrical densities).

Evaluation:

• Uniform density from center to edges = grid properly aligned.
• Unequal density on sides = grid cutoff — realignment needed.

Q11. Write a short note on Congruence of Optical and Radiation Field.

Answer:

Definition:

This test is designed to check the centering and perpendicularity of the beam, as well as congruence (alignment) of the collimator light field and X-ray beam field.

Importance:

If the light field and X-ray beam field do not coincide, the radiographer may inadvertently expose areas outside the intended region, leading to unnecessary patient dose and poor positioning.

Procedure:

1. Beam alignment test tool is placed on the image receptor.
2. The collimator light field is adjusted to the test tool edges.
3. An exposure is made.
4. The radiation field edges are compared with the light field edges on the image.

Acceptance Limit:

Beam/light field alignment should be within ±2% of the SID (Source to Image Distance).

Q12. Describe the Annual Maintenance Contract (AMC) and Comprehensive Maintenance Contract (CMC).

Answer:

Annual Maintenance Contract (AMC):

• A manufacturer company provides the service through AMC by themselves or with the service providers.
• The contract is usually for the period of 1 year and can be extended up to three years or five years.
• Usually the service providers give only service support and would charge separately for every part under AMC.
• However, in some cases, few parts are replaced at no additional cost.

Comprehensive Maintenance Contract (CMC):

• It includes prompt service from the company or service providers.
• The contract is usually for the period of 1 year and can be extended up to three years or five years.
• It includes repair and replacement of faulty parts.
• Having the contracts gives benefits such as those parts which are not part of contract being available at reduced costs.
• CMC is costlier than AMC because it includes the cost of parts replacement in addition to service.

Q13. What are the QA tests performed in CR system? (Daily, Quarterly, Annual)

Answer:

Daily Tests:

1. Image Artifact Test — Clinical image should be free from any artefact; visually inspect for non-uniformity.
2. Reader Reboot — System is rebooted daily for proper functioning.
3. Image Reader Visual Check — Inspect imaging system for dust/dirt on or near image reception area.
4. Inspection and Cleaning — Daily secondary erasing of imaging plates; verification of system interfaces and network transmission.

Quarterly Tests:

1. Laser Jitter Test — Determines whether the mechanical motion of the image plate, laser, and optics are consistent in the transport system.
2. Imaging Plate Cleaning — Imaging plates accumulate dust, dirt, scratches; cleaned quarterly.
3. Retake Image Analysis — Analysis of repeated images to identify common causes.

Annual Tests:

1. IP Dark Noise Test — Tests background noise level of the imaging plate.
2. Uniformity Test — Checks uniformity of image over the entire imaging plate.

Q14. Describe the CR System and DR System briefly.

Answer:

CR System (Computed Radiography):

• CR technology uses an indirect conversion process using a two-stage technique.
• X-rays are captured at a storage-phosphor screen (SPS) (e.g.: BaFBr:Eu2+).
• A photodetector captures the light emitted from the SPS and converts the captured luminescence into a corresponding digital image.
• CR cassette contains a special phosphor plate called Imaging Plate (phosphor material: Eu: Barium Fluoro-halide).

DR System (Digital Radiography):

• DR detectors can use either a direct or an indirect process for converting X-rays into electric charges.
• These detectors use direct-readout by means of a TFT (Thin Film Transistor) array.

Direct-conversion detectors have an X-ray photoconductor such as amorphous selenium (a-Se), that converts X-ray photons into electric charges at only one stage.

Indirect-conversion systems use a two-stage technique — they have a scintillator such as cesium iodide (CsI) that converts X-rays into visible light first, then light is converted to electric charge by an amorphous silicon photodiode array.

Q15. What is the scope of Responsibility and Training in a QA program?

Answer:

1. Responsibility:

• It is recommended that at least one staff member at each facility is identified and responsible for ensuring quality checks are undertaken at specified times.
• The designated person(s) may include: Chief Technologist, Assistant Chief Technologist, Quality Manager, QA Technologist, Section Senior Technologist, RSO (Radiation Safety Officer).
• The designated quality manager should review non-compliance issues and provide corrective and preventative action in a timely manner.
• The quality manager is also responsible for organization, dissemination and document control of all incoming quality guidelines, policies and directives from regulatory bodies, Local Health Service, and State Departments of Health.

2. Training:

• The QA program includes the means to provide appropriate training for all personnel with QA responsibilities — especially those directly involved with QA program.
• This ensures a minimum level of competency to perform QC tests correctly and consistently.
• Medical physicist can provide seminars and training courses on How to Perform Quality Control Tests.

TEN MARKS QUESTIONS & ANSWERS

Q1. Discuss in detail the scope of activities in the Quality Assurance program for general radiology imaging systems.

Answer:

Introduction:

The contribution of radiology to better diagnosis and treatments is evident. In parallel, efforts were oriented towards the improvement and control of equipment. The importance of QA of diagnostic X-ray equipment is well recognized. Application of QA program is very important when optimization of image quality and reduction of patient exposure is desired.

The 10 Scope of Activities in QA Program:

1. Responsibility:

• At least one staff member at each facility should be identified and responsible for ensuring quality checks are undertaken at specified times.
• The designated persons may include: Chief Technologist, Assistant Chief Technologist, Quality Manager, QA Technologist, Section Senior Technologist, RSO.
• The quality manager should review non-compliance issues and provide corrective and preventative action.
• Responsible for organization and document control of all incoming quality guidelines from regulatory bodies.

2. Evaluations:

• The performance of the facility should be evaluated regularly.
• Comparison evaluation demonstrates the effectiveness of the QA program.
• Equipment monitoring results are evaluated to assess the need for correction that may indicate preventive maintenance is required.

3. Purchase Specifications:

• When new equipment is purchased, the facility determines the performance criteria for the equipment — reflected in the purchase specification.
• Before final acceptance, actual performance must meet the purchase specifications.
• Purchase specification and records of acceptance testing should be retained throughout the life of the equipment for comparison with monitoring results.

4. Standards for Image Quality:

• Standards for image quality are established for performance parameters of the X-ray system.
• If periodic equipment monitoring results show that the equipment does not meet the acceptance limits, corrective actions are needed.

5. Monitoring and Maintenance:

• Equipment monitoring and maintenance is the center of the QA program.
• At the beginning of each shift, the technologist should visually inspect the X-ray machine (X-ray control panel, tube stand, X-ray tube, collimator, table Bucky movement).
• Inspection checklist includes: checking main supply, cable conditions, indicator lights, table and Bucky tray condition, electronic locks, unusual noise, current leakage.
• Two types of maintenance: Preventive Maintenance (regular, while equipment is working) and Corrective Maintenance (after failure, to restore operation).

6. Training:

• The QA program includes means to provide appropriate training for all personnel with QA responsibilities.
• Ensures a minimum level of competency to perform QC tests correctly and consistently.
• Medical physicist can provide seminars and training courses on how to perform Quality Control Tests.

7. Committee:

• For successful establishment and implementation of QA program, it is essential to ensure good cooperation among experts — called Committee.
• Committee is responsible for: QA program and procedures, implementation of QA program, collection of data, analysis and evaluation of results, and decision on measures to correct deficiencies.
• The committee will decide appropriate corrective actions to remove deficiencies and reach the desired standards.

8. Records:

• All quality assurance test data should be recorded on standardized forms.
• Each institution should develop its own forms suitable to its needs.
• Forms should be filed as part of the room log.
• The chart of data is a recommended procedure which allows easy identification of variation with time.
• Service records should include identification of the individual performing the service and the date.

9. Manual:

• An individual equipment manual should be maintained on each X-ray unit in a facility.
• Must be kept at a convenient location where anyone can get ready access.
• The manual should contain:
  1. Equipment Data Specifications
  2. Technical specifications (including tube loading charts)
  3. Equipment operating instructions
  4. Outline of the applicable QA program
  5. Log of QA test results
  6. Service records (malfunctions and service carried out)

10. Review:

• It is essential to review QC results immediately and take action if out of tolerance.
• In some cases, it may be necessary to contact the service engineer.
• Prior to contacting, one may:
  1. Repeat the test
  2. Check correct and consistent settings (kV, mAs, test object, FFD)
  3. If artefacts are present, identify their location; clean equipment and repeat
• Example: A minor failure in X-ray to light-beam alignment could be fixed at the next service visit, but anything affecting patient dose or image quality must be addressed immediately.

Q2. Describe in detail the QC tests performed for X-ray Generators and QC for Diagnostic X-ray Tube in conventional radiography.

Answer:

Part A — QC for X-ray Generators

1. Accuracy of Tube Voltage:

The maximum or peak electrical potential (kVp) across the X-ray tube affects the radiation intensity reaching the image receptor and the contrast of the final image.

Instrument: Digital kVp Meter (Gammex 330 Divoltmeter)

Procedure:

• Place kVp Meter on X-ray table; maintain FFD at 40 inch or 100cm.
• Collimate the beam to the specified area of the ionization chamber.
• Keeping mAs constant, exposures given for different kVp values; readings observed.

Acceptance Limit: ±5% — if beyond, rectified by service engineer.

2. Linearity of mAs:

Requirements: Densitometer, Step Wedge, Lead Separator, Processor, Graph Paper.

Procedure:

• Step wedge placed on 10×12 film; half of cassette covered by lead separator.
• 3 exposures given keeping kVp and mAs constant, varying mA.
• Film processed; density measured for 2 corners and midpoint of each step.
• Mean value for each step is calculated.
• Graph plotted between density and number of steps.

Tolerance: 3 graphs should overlap.

3. Exposure Time Accuracy:

Procedure:

• Place Digital timer on X-ray table; reading must be at zero.
• Set FFD to 40 inch or 100cm.
• Collimate the beam to the specified area of the ionization chamber.
• Record exposures at different timer settings.

Acceptance Limit: ±10% — if beyond, rectified by service engineer.

Linearity of mA Loading Stations:

• Tube current (mA) = number of electrons flowing from cathode to anode per unit time.
• Exposure of beam for a given kVp and filtration is proportional to tube current.

Procedure:

• FFD = 100 cm; Radiation field size = 20cm × 20cm
• Keeping exposure time and kVp constant, radiation output measured at different mA stations.
• Readings averaged; Coefficient of Linearity (CoL) evaluated.

Formula:

Coefficient of Linearity = (X max − X min) / (X max + X min)

Tolerance: Coefficient of Linearity < 0.1

Part B — QC for Diagnostic X-ray Tube

1. Size of the Focal Spot:

Definitions:

• Actual focal spot: Area on the anode struck by electrons — determined by length of cathode filament and width of focusing cup.
• Effective focal spot: Length and width of the focal spot projected downwards.
• Small anode angle → small field of view; Large anode angle → large field of view.

Tools for Measuring Focal Spot Size:

a) Pinhole Camera:

• Uses a very small circular aperture (10 to 30 µm diameter) in a disk made of a thin, highly attenuating metal such as lead, tungsten, or gold.
• Positioned on the central axis between X-ray source and detector; image of focal spot is recorded.

b) Slit Camera:

• Consists of a plate made of a highly attenuating metal with a thin slit of 10µm wide.
• Takes two exposures — one on X-axis and second on Y-axis — and the recorded image is measured.

c) Star Test Pattern:

• Contains a radial pattern of lead spokes of diminishing width and spacing on a thin plastic disk.
• Imaged at a known magnification; distance between outermost blur patterns measured.
• Large focal spot = greater blur diameter; Small focal spot = smaller blur diameter.

d) Resolution Bar Pattern:

• Bar test pattern placed on image receptor; FFD adjusted at 18 inch.
• Exposure made with appropriate factor; focal spot size evaluated using LP/mm vs Dimension of Focal Spot table.

2. Beam Perpendicularity:

X-ray beam should be perpendicular to the image receptor; otherwise produces geometric distortion.

Procedure:

1. Place collimator and beam alignment test tool on center of image receptor.
2. Adjust collimator so edge of light beam coincides with collimator test tool outline; check level with Spirit level.
3. Expose with appropriate exposure.
4. Shadow of two holes should coincide.
5. If holes lie within two concentric circles — within acceptance limit.

Tolerance: 1.5°

3. Congruence of Optical and Radiation Field:

Tests the centering and perpendicularity of the beam and alignment of the collimator light field and X-ray beam field.

Acceptance Limit: Beam/light field alignment should be within ±2% of the SID.

4. Filtration:

• Most important characteristic of a radiographic unit is X-ray beam filtration.
• General purpose radiographic units have minimum total filtration of 2.5mm of Al.
• Filtration should be checked annually or after a change in the X-ray tube or housing.

Minimum Filtration Tolerances:

kVp Range	Minimum Al Filtration
kV < 70	1.5 mm Al
70 < kV < 100	2.0 mm Al
kV > 100	2.5 mm Al

Material Used: Aluminum filters of purity 99.99% or higher and density 2.70 g cm-3.

Q3. Describe in detail the QC for X-ray Films and Cassettes in conventional radiography.

Answer:

QC for X-ray Films and Cassettes involves four main tests:

1. Film Screen Contact:

Problem: Poor contact between the intensifying screen and radiographic film reduces contrast and produces blurring of radiographic images if the film and cassette are not in proper contact.

Method of Testing: Wire mesh pattern test.

Procedure:

• Wire mesh is placed on the cassette.
• An exposure is taken with appropriate technique.
• The resulting image is evaluated visually.
• Undistorted Image = Good contact (acceptable).
• Distorted Image = Poor contact (cassette needs repair).

2. Cassettes:

Inspection Protocol:

• Cassette should be physically inspected periodically for:
  • Wearing of the latches and hinges
  • Working of the cassette frame
  • Deterioration of the foam or felt compression material
• Testing for light leakage should also be inspected.
• Cassette should be repaired or replaced if they do not pass such inspections.

3. Radiographic Intensifying Screens:

Problem: Dirty, cracked, and torn out screens can cause radiographic artifacts — require immediate replacement.

Care Required:

• Screens must be inspected regularly for cracks, tears, and contamination.
• Any damaged screen should be replaced immediately to prevent image artifacts.

4. Grid Alignment:

Purpose:

• Grid reduces the amount of scatter radiation reaching the film.
• This greatly improves the quality of the image.
• Improper alignment leads to Grid Cutoff — unequal density distribution.

Procedure:

1. Place test tool on table top with central hole at center of bucky table.
2. Expose each hole one by one without moving the grid alignment test tool.
3. Density on the central hole should be highest and gradually decrease on the sides.
4. Holes on either side should have equal densities (symmetric distribution).

Evaluation:

• Symmetric equal density on both sides = Grid properly aligned — acceptable.
• Unequal density = Grid misaligned — Grid Cutoff — needs realignment.

Q4. Describe in detail Quality Assurance in Digital Radiography with focus on the CR system, its components, and QA tests.

Introduction:

• Development in digital detector technologies have been taking place and new digital technologies are available for clinical practice.
• Several digital systems are currently available for the acquisition of radiography.
• Digital radiography systems have been replacing traditional analogue or screen-film systems.

CR System (Computed Radiography):

Mechanism:

• CR technology uses an indirect conversion process using a two-stage technique.
• X-rays are captured at a storage-phosphor screen (SPS) (e.g.: BaFBr:Eu2+).
• A photodetector captures the light emitted from the SPS and converts the luminescence into a corresponding digital image.

DR System (Digital Radiography):

Mechanism:

• DR detectors use either a direct or indirect process for converting X-rays into electric charges.
• These detectors use direct-readout by means of a TFT (Thin Film Transistor) array.

Direct-conversion: X-ray photoconductor (amorphous selenium — a-Se) converts X-ray photons into electric charges at one stage.

Indirect-conversion: Uses a scintillator (cesium iodide — CsI) to first convert X-rays into visible light, then light is converted into electric charge by an amorphous silicon photodiode array.

Components of CR System:

1. General X-ray Equipment
2. Image Recorder (Imaging Plate)
3. Image Reader (ADC — Analog to Digital Converter)
4. Monitor / Display

Image Recorder:

• CR cassette contains a special phosphor plate called Imaging Plate.
• Phosphor material: Eu: Barium Fluoro-halide — image formed by complex electron trap mechanism.
• The imaging plate has a large dynamic range.

Image Reader (ADC):

• CR image reader is also known as Analog to Digital Converter (ADC).
• Converts the Continuous Analog Image on Imaging Plate into Digital Image.

Process inside reader:

1. Cassette enters the reader
2. Image plate removed from cassette
3. Latent image scanned by laser
4. Image plate erased with high intensity light
5. Image plate returned to cassette

Quality Control for CR System:

To ensure proper operation of CR components, it is important to develop a continuous quality control program including:

• Medical physicist’s acceptance testing of any new CR component
• Routine quality control tests by the QC technologist
• Periodic review of QC program by a qualified medical physicist

QA Tests in CR System:

Daily Tests:

Test	Purpose
Image Artifact Test	Clinical image should be free from any artefact; visually inspect for non-uniformity
Reader Reboot	System rebooted for proper functioning
Image Reader Visual Check	Inspect for dust/dirt on image reception area
Inspection & Cleaning	Daily secondary erasing of imaging plates; verification of system interfaces and network transmission

Image Artifact Test — Key Points:

• If artefacts are seen, determine if they are due to mirror, detector, or X-ray beam non-uniformity.
• To eliminate possibility of display artefact: rotate or pan the image on monitor.
  • If artefact moves with image → due to imaging system.
  • If artefact stays in same place → due to display system (monitor).

Quarterly Tests:

Test	Purpose
Laser Jitter Test	Determines whether mechanical motion of image plate, laser, and optics are consistent
Imaging Plate Cleaning	Removes accumulated dust, dirt, and scratches
Retake Image Analysis	Analysis of reasons for repeated images

Laser Jitter Test Evaluation:

• Inspect the edges of “T” in the SCALE for jagged edges.
• If jagged edges appear at both QC station AND laser film → reader should be serviced.
• If jagged edges only on hard copy but not QC station → problem with laser printer.

Imaging Plate Cleaning:

• CR image plates are sensitive to scattered and naturally occurring radiation sources.
• If left unused for long periods, they store energy from these sources.
• Damage caused by improper handling: dirty/wet hands, lotions, sanitizers, non-approved cleaners.

Annual Tests:

Test	Purpose
IP Dark Noise Test	Tests background noise level of imaging plate
Uniformity Test	Checks uniformity of image over the entire imaging plate

Inspection and Cleaning (Daily):

• System inspection for physical defects and physical inspection of display devices.
• Daily secondary erasing of imaging plates.
• Verification of system interfaces and network transmission.
• CR image plates are sensitive to scattered radiation — recommended that all CR image plates are erased before use if left unused for long periods.

Q5. Discuss in detail Quality Control in Conventional Radiography — covering QC for X-ray Generators, Diagnostic X-ray Tube, Films, and Cassettes with procedures and tolerances.

Answer:

Introduction to Quality Control:

• Quality Control (QC) is a central part of QA program, which deals with Equipment Maintenance and Monitoring.
• QA in diagnostic radiology is a means of maintaining standards in imaging and working towards minimizing patient and staff doses.
• A number of physical parameters that affect the performance of X-ray imaging systems are periodically checked.

Part 1: QC for X-ray Generators

a) Accuracy of Tube Voltage (kVp):

• kVp affects radiation intensity and image contrast.
• Instrument: Gammex 330 Divoltmeter
• Procedure: FFD 100cm, mAs constant, different kVp values tested.
• Acceptance Limit: ±5%

b) Linearity of mAs:

• Tests whether mA change produces proportional change in radiation output.
• Equipment: Densitometer, Step Wedge, Lead Separator, Processor, Graph Paper.
• 3 exposures with varying mA; density measured and graph plotted.
• Tolerance: 3 graphs should overlap.
• CoL formula: (X max − X min) / (X max + X min) < 0.1

c) Exposure Time Accuracy:

• Timer controls duration of exposure.
• Instrument: Digital Timer
• Procedure: FFD 100cm, beam collimated to ionization chamber.
• Acceptance Limit: ±10%

Part 2: QC for Diagnostic X-ray Tube

a) Size of Focal Spot:

• Tools: Pinhole Camera, Slit Camera, Star Test Pattern, Resolution Bar Pattern.
• Measured in LP/mm; higher LP/mm = smaller focal spot dimension.

b) Beam Perpendicularity:

• Beam must be perpendicular to image receptor.
• Instrument: Beam alignment test tool + collimator tool.
• Tolerance: 1.5°

c) Congruence of Optical and Radiation Field:

• Light field and X-ray beam field must align.
• Acceptance Limit: ±2% of SID

d) Filtration (HVL):

• Minimum total filtration: 2.5mm Al for general radiographic units.
• HVL measured using aluminum absorbers.
• Tolerance: 1.5 mm Al (kV<70), 2.0 mm Al (70<kV<100), 2.5 mm Al (kV>100).

Part 3: QC for X-ray Films and Cassettes

a) Film Screen Contact:

• Poor contact → image blurring.
• Tested using wire mesh pattern.
• Undistorted image = good contact; distorted = poor contact.

b) Cassettes:

• Periodically inspect latches, hinges, frame, and foam compression material.
• Test for light leakage.
• Repair or replace if not passing inspection.

c) Radiographic Intensifying Screens:

• Dirty, cracked, or torn screens cause artifacts.
• Require immediate replacement.

d) Grid Alignment:

• Grid reduces scatter radiation and improves image quality.
• Misalignment causes Grid Cutoff.
• Central hole shows highest density; sides show equal, gradual decrease.
• Unequal side densities = misalignment → correction needed.