Quality assurance

QUALITY ASSURANCE AND QUALITY CONTROL FOR
DIAGNOSTIC X RAY EQUIPMENTS
PRESENTED BY:
KHURSHEED AHMAD GANIE
COURSE: MRIT 2nd SEM.

CONTENTS
• DEFINITION OF QA & QC
• AIM OF QUALITY ASSURANCE
• THREE BASIC RULES OF QA PROGRAM
• QUALITY ASSURURANCE TESTS FOR DIAGNOSTIC X RAY EQUIPMENTS
- CONGRUENCE OF RADIATION AND OPTICAL FIELDS
- CENTRAL BEAM ALIGNMENT
- FOCAL SPOT SIZE
- TUBE VOLTAGE

- TIMER CHECK
- TOTAL FILTRATION
- LINEARITY OF mA LOADING STATION
- TIMER LINERAITY
- OUT PUT CONSISTENCY
- TUBE HOUSING LEAKAGE
. SUMMARY OF QA TESTS

DEFINITION
• Quality assurance (QA) deals primarily with personnel and their interactions
with the patient and other staff. It is the term used to maintain high quality
imagining. It is many step process that involves identifying goals, implementing
The plans, evaluating the success of the program. Quality assurance also includes
outcomes analysis, such as how often the radiologists report agrees with the
patient condition.
Quality control (QC) refers to the measurement and evaluation of radiographic
equipment, together with identification and correction of problems associated
with the equipment.

AIM/ OBJECTIVES OF QUALITY ASSURANCE TESTS
- Optimum image quality
- Minimum radiation exposure
- Minimum cost
BASIC RULES OF QA PROGRAM
The QA program should adhere to three basic rules viz…
- Tests that make up the program must be performed on regular basis.
- results of all quality control must be documented in consistent format.
- QC test should indicate whether the test parameter is within specific
guidelines.

• Congruence of Radiation and Optical Fields
- The X-ray field must be aligned with the
light field so that the operator can accurately
position the body part to be imaged. If the
optical field and radiation field are not congruent,
the area of clinical interest may be missed in the
radiograph leading to retakes and unnecessary
radiation exposure to patients.
- Collimator test tool are used with screen film
cassette .
- FFD kept 100cm to obtain shift in terms of FFD
percentage.
- Shift (x, x*, y, y*) should be within 2% of FFD
- (x + x*,y + y*) within 3% FFD.

Central Beam Alignment: - If the x-ray beam is not perpendicular to the image
receptor, the image may be distorted. If grid is used, the distortion will be
magnified resulting in complete loss of minute details. Beam alignment test can be
done simultaneously with the test for congruence of optical and radiation field
• Beam alignment test tool is used for this.
• If image two steel balls overlap CR beam within 0.5°
• if image of top ball falls within inner circle central ray lies within 1.5°
• If it falls B/w images of inner and outer circle, CR lies within 1.5°-3°
Tolerance Central beam alignment < 1.5°

• Effective Focal Spot Size measurements:- Ability of resolving smallest in an
image depends on Focal spot. Its size change with time hence can be checked
periodically.
. Focal spot test tool with non- screen film cassette is used.
Effective Focal Spot Size Measurements: Tools used for effective focal spot size
measurements:
• Pinhole camera
• Slit camera
• Star pattern
• Resolution bar pattern
Tolerance: for f < 0.8 mm +0.5 f for 0.8 ≤f≤1.5 mm +0.4 f
for f > 1.5 mm +0.3f

• ACCELERATING TUBE VOLTAGE
- Kvp affects quality & quantity of x ray beam.
- if there is variation in Kvp setting , it affects image quality hence it is necessary to
check the Kvp settings periodically.
- test tool: Kvp meter is used.
- frequency: once in 3 years.
- beam centered on marked area on the top of the Kvp meter proper distance is
selected b/w the focus and meter and exposed for given Kvp, mA and time settings.
- Kvp meter reading is noted.
- similar measurements are taken for different Kvp settings and variation b/w the
set Kvp and measured Kvp is found.

• Accuracy of Exposure Timer
If the exposure time of the x-ray unit is not in order, the radiograph can be under
exposed or overexposed. For this, absolute timer method is adopted by measuring
set and measured time with digital timers.
- Test tool: spinning top test tool.
- It consists of rotating circular brass disc with a small hole at its periphery.
- To check the timer spinning top is placed on cassette , loaded with film and for a
set time, the unit is energized, while top is rotating and repeated to cover entire
range of timer.
- Pulses pass through the hole and produce density pattern on the film & space
b/w the pattern depends on speed of rotation of spinning top.

- time = no. of density pattern on the film/pulse frequency
- Frequency of test:
once in 3 months.
- Tolerance:
Accuracy of exposure timer % Error ± 10 %

• Total Filtration of X-ray tube
Total filtration of the x ray tube is evaluated by determining HVT of beam by using
pocket dosimeter. HVT is measured for maximum operating potential of the tube.
- The absorber thickness for 50 % transmission will be the half value thickness of
the x-ray beam.
Material Used: Aluminum filters of purity 99.99% or higher and density 2.70 g cm-3
Tolerance: 1.5 mm Al for kV equal or less than 70
2.0 mm Al for 70kV- 100kv
2.5 mm Al for kV greater than 100kV
Aluminum Equivalence of table top (Couch) ≤ 1.2 mm

Linearity of mA loading stations:- The tube current (mA) is equal to the
number of electrons flowing from the cathode to the anode per unit time. The
exposure of the beam for a given kVp and filtration is proportional to the tube
current. This test is carried out to check the linearity of radiation output with
respect to change in tube current (mA) stations by keeping timer station
constant at a particular kV station.
- FFD=100 cm Radiation field size = 20 cm x 20 cm
- Test tool: charged pocket dosimeter
- Measurement for mA loading station is to be repeated for a number of times
each to eliminate statistical errors. Radiation output readings of each mA loading
station readings are averaged and the coefficient of linearity (CoL) is evaluated
from average mR/mAs or mGy/mAs as follows:
- Coefficient of linearity = (X max -Xmin) /(Xmax + X min)
- Tolerance: Coefficient of Linearity less than 0.1

• Linearity of timer :- The exposure time is the duration of X-ray production.
- Keeping the kVp and mA constant, radiation output is measured at different timer
stations and Coefficient of Linearity is evaluated.
- This test is carried out to check the linearity of radiation output with respect to
change in timer stations by keeping mA station constant at a particular kV station.
- The pocket dosimeter is exposed to 50Kvp, 200mA and 0.5 s and reading is noted
and measurement is repeated 5 times.
- Similar measurements are made at different times keeping Kvp & mA constant.
- For each measurement avg. and X (mR/mAs) is calculated:
Coefficient of linearity = (X max -Xmin) /(Xmax + X min)
Tolerance: Coefficient of timer linearity < 0.1

• Output Consistency:- To check the constancy of radiation output, Keeping fixed
mA and time, radiation output is measured at various available kV stations.
Average(X) of (mR/mAs) or (mGy/mAs) is calculated. Consistency at each kV
station is checked by evaluating the coefficient of variation.
Coefficient of variation (COV) = 1/ X x [( ∑ (Xi- X)2 ) /(n-1)] ½
Tolerance: Coefficient of Variation <0.05
.Radiation Leakage Levels from Tube housing
- The radiation leakage measurement is carried with an ionization
chamber/semiconductor based radiation survey meter.
- collimators are fully closed and tube is energized to its maximum.
- Max leakage from tube housing =
mA- min in one hour X ----Max. leakage radiation level (mR/hr)
60 min X ----- mA used for measurement

• Tolerance limit:
1. Radiation Leakage at 1 m distance from the focus < 1 mGy in one hour
( for Radiography/Radiography & Fluoroscopy/C-Arm/Interventional Radiology/
dental OPG and dental CBCT equipment)
2. Radiation Leakage limit at 5cm from the external surface of mammography unit
< 0.02 mGy in one hour
3. Radiation Leakage limit at 1m distance from the focus of dental (intra-oral) unit
< 0.25 mGy in one hour
• Table Top Dose Rate (Fluoroscopy)
- The air kerma rate, measured in air at the position where the central of the
useful beam enters the patient, shall be less than 5cGy/min for units without
automatic brightness control (ABC) and less than 10 cGy/min for units with ABC.
- The focus-to-table top distance shall be not less than 30 cm for fluoroscopy
equipment.

Quality assurance

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