General Radiography QC

What is the goal of SC35?

Protect all individuals who may be exposed to radiation derived from X-ray equipment

The three principal objectives of SC35

1. Minimize patient exposure

2. Ensure X-ray workers are protected

3. Protection of the public in areas where X-rays are present

What does a quality assurance program include?

• Policies and procedures

• Education and training

• Departmental guidelines

• Radiation safety

• Preventative maintenance

• Quality control

What are the levels of QC testing and who completes which?

• Noninvasive/simple: technologist

• Noninvasive/complex: QC technologist

• Invasive/complex: Engineer or physicist

When is acceptance testing performed? What is the purpose?

All new or repaired equipment, establish a baseline for future QC

When is routine testing performed? What is the purpose?

After a predetermined amount of time has elapsed, diagnose any changes in performance before an issue presents itself

What is quality management?

The act of overseeing all activities and tasks needed to maintain a desired level of excellence

The responsibilities of which personnel are outlined in SC35? (7)

• Owner

• User

• Operator

• Medical physicist/radiation safety officer

• Referring physician

• Information systems specialist

• Repair & maintenance personnel

What are the medical physicist/radiation safety officers responsibilities?

• Establish safe working conditions

• Ensure procedures are being followed

• Perform routine checks on equipment

• Record radiation surveys

What are the referring physician/practitioner’s responsibilities?

• Ensure imaging is justified

• Use experience, judgement and common sense

• Consider alternative options (MRI, US)

What is the annual body dose limit for the technologist?

20 mSv

What is the annual body dose limit for the public?

1 mSv

What is the annual eye dose limit for the technologist?

150 mSv

What is the annual skin dose limit for the technologist?

500 mSv

What is the annual hand dose limit for the technologist?

500 mSv

What is the annual organ dose limit for the technologist?

500 mSv

What is the annual organ dose limit for the public?

50 mSv

What is the annual eye dose limit for the public?

15 mSv

Precision vs accuracy

Precision: consistency to create the same results after multiple tests

Accuracy: ability to measure what is meant to be measured

3 parts of a QC program for radiographic equipment

• Visual inspection

• Environmental inspection

• Performance testing

What are the daily visual inspection tasks?

• Look for loose or broken components

• Cleanliness

• Check for vibration or motion

What are the weekly visual inspection tasks?

• Look for dust and dirt in reception area

• CR and laser scanning digitizer

• DR and fluoroscopic systems

What is included in an environmental inspection?

• Mechanical and electrical safety

• Cable coverings

• Equipment grounding

  • Tube lubrication

What is the SC35 equipment warmup recommendation?

• Follow manufacturers recommendation

• Repeat warm-up after an extended period of time with no imaging

What type of detectors are used in QC radiation measurment?

• Ion chamber

• Proportional counter

• Geiger-muller counter

What does an ion chamber do?

Measures ion pairs created within a gas caused by incident radiation

What voltage are ion chambers used?

100-300V

What is kVp accuracy?

Determining any variation between stated kVp and actual kVp

What can cause discrepancies in kVp?

• Line voltage

• Faulty cables

• Tungsten vaporization

• Autotransformer issue

• kVp selection circuitry

kVp accuracy acceptance limit SC35

±10%

kVp accuracy testing frequency SC35

Annual

What is HVL?

The amount of filtration needed to reduce the exposure by 50%

With no filtration, skin dose can increase by __%

90%

How is HVL tested?

Exposures are made at 70 kVp

1mm aluminum filters are gradually added until until exposure is halved

SC35 HVL acceptance limit

2.5mmAL or more at 70 kVp

SC35 HVL testing frequency

Annual

What is reproducibility of exposure?

Ability of a radiographic unit to produce the same exposure throughout a short period

SC35 reproducibility of exposure limits

• Coefficient of variation within 0.05

• Of 10 measurements, none may differ more than 15% of the mean

SC35 reproducibility of exposure testing frequency

Annual

What is mAs linearity?

Production of a constant amount of radiation for different combinations of mA and time

How is mAs linearity testing performed?

Several exposures are taken with increasing mAs and compared to the previous

SC35 mAs linearity acceptance limits

Adjacent exposures must not differ by more than 10% of their sum

SC35 mAs linearity testing frequency

Annual

SC35 timer accuracy

• Must automatically terminate if a predetermined amount of x-ray pulses have been detected

• Operator must be able to terminate at any time

• Must automatically reset to zero if exposure is terminated

• Irradiation is not possible at zero, off or unmarked settings

SC35 AEC consistency with varying kVp acceptance limit

0.15 variation in optical density

SC35 AEC consistency with varying part thickness acceptance limit

0.2 variation in optical density

SC35 AEC reproducibility acceptance limit

0.10 variation in optical density

SC35 collimation acceptance limit

• Misalignment within ±2%

• Size of field within 3% of SID

• Total misalignment must not exceed 4% of SID

SC35 light field/radiation field alignment acceptance limits

±2% of SID

SC35 Image receptor / radiation field alignment acceptance limit

Within 3% of SID

SC35 Beam perpendicularity acceptance limits

Within 2% of SID

What is focal spot blooming?

The increase in focal spot size with age, use and high mA station use

What does focal spot size determine?

Spatial resolution and detail

What QC tests evaluate focal spot blooming?

• pinhole camera

• focal spot test tool

Lead aprons must me what thickness at 100 kV or less, 100 to 150 kV and 150 kV or more

• >100: 0.25mmPb

• 100-150: 0.35mmPb

• 150+: 0.5mmPb

How often should lead be inspected?

Annually

SC35 lead defect acceptance limits

• Total defect area greater than 670mm2

• Defect in the thyroid or gonad area greater than 5mm in diameter

What should lead thickness be in interventional procedures?

• 0.5mm Pb in the front

  • 0.25mm Pb in the back

Thyroid shield Pb thickness

0.5 mm

Gonadal shield thickness

• minimum 0.25mm

• minimum 0.50mm at 150 kV

Lead glove thickness

0.25mm Pb

Rolly shield thickness

0.50mm Pb

SC35 recommended repeat rate

Less than 5%

Bit depth

Number of bits in a pixel = shades of grey

Bit depth formula

2^n
(n=number of bits)

How are electronic display devices tested?

SMPTE test pattern or AAMP TG-18-QC test pattern

What type of distortion is this?

Barrel

What type of distortion is this?

Pincushion

What is this?

AAPM TG-18 test pattern

What is this?

SMPTE test pattern

At what distance should test patterns be viewed?

30 cm

How often should an imaging plate be cleaned?

Monthly