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Evaluation of various diagnostic x-ray measuring devices

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Title: Evaluation of various diagnostic x-ray measuring devices


1
Evaluation of various diagnostic x-ray measuring
devices
  • MDCH Radiation Safety Section
  • Don Parry, CHP

2
Evaluation of X-ray Measuring Devices
  • Evaluation Criteria (Don)
  • Accuracy
  • Reliability
  • Range of Application
  • Durability
  • Ease of Use
  • Cost

3
Evaluation of X-ray Measuring Devices
  • Evaluation Criteria (Dons Bosses)
  • Cost
  • Durability
  • Reliability
  • Range of Application
  • Accuracy
  • Ease of Use

4
Evaluation of X-ray Measuring Devices
  • Evaluation Criteria (Dons Staff)
  • Ease of Use
  • Reliability
  • Range of Application
  • Durability
  • Accuracy
  • Cost

5
Evaluation of X-ray Measuring Devices
  • Types of Devices
  • Ion Chambers
  • Solid State Detectors

6
Evaluation of X-ray Measuring Devices
  • Ion chambers
  • Advantages
  • Flat Energy Response
  • History of Reliability
  • Disadvantages
  • Weight
  • Chambers can be fragile

7
Evaluation of X-ray Measuring Devices
  • Solid State Detectors
  • Advantages
  • Small and lightweight
  • Detectors are more robust
  • Disadvantages
  • More energy dependant
  • Generally not as simple to use

8
Evaluation of X-ray Measuring Devices
  • Application of X-ray Measuring Devices
  • Dental X-ray ( 50 90 kVp)
  • Medical X-ray (45 150 kVp)
  • Mammography (24 35 kVp)

9
Evaluation of X-ray Measuring Devices - Accuracy
  • Ion Chambers Medical and Dental
  • Tested at four x-ray beam codes
  • M50 (50 kVp 1.0 mm Al HVL)
  • L80 (80 kVp 1.8 mm Al HVL)
  • L-100 (100 kVp 2.8 mm Al HVL)
  • M-100 (100 kVp 5.0 mm Al HVL)
  • MoMo 25 (25 kVp, Moly target 0.30 mm Al HVL)
  • MoMo 30 (30 kVp, Moly target 0.35 mm Al HVL)

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Evaluation of X-ray Measuring Devices
  • Solid State Detectors Medical and Dental
  • Tested at three x-ray beam codes
  • L80 (80 kVp 1.8 mm Al HVL)
  • L-100 (100 kVp 2.8 mm Al HVL)
  • M-100 (100 kVp 5.0 mm Al HVL)

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Evaluation of X-ray Measuring Devices
  • Comparison
  • Ion Chambers vs. Solid State Detectors
  • Do not use any detector outside its specified
    energy range

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All the solid state detectors showed under
response at low energies
21
Evaluation of X-ray Measuring Devices
  • Ion Chambers and Solid State Detectors In
    Mammography
  • Tested at two beam codes
  • MoMo 25 (25 kVp, Moly target 0.30 mm Al HVL)
  • MoMo 30 (30 kVp, Moly target 0.35 mm Al HVL)

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Evaluation of X-ray Measuring Devices
  • Some Mammography Machines now use beams with
    higher energies
  • NIST currently does not provide calibration
    standards for these beams
  • Since the energy response is typically flat for
    ionization chambers, no additional corrections
    should be needed.
  • Solid state instruments, however, may require
    appropriate corrections obtained from the
    instrument manufacturer.

28
Evaluation of X-ray Measuring Devices
  • Ion Chambers Reliability
  • Ion chamber calibrations have historically been
    very stable.
  • Ion chambers can be fragile and require
    appropriate handling by field staff

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Evaluation of X-ray Measuring Devices
  • Solid State Detectors Reliability
  • While reliability has been good, radiation
    response has drifted or failed on some sensors
  • Detectors appear more robust and are less often
    damaged by misuse

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Evaluation of X-ray Measuring Devices - Range of
Applicability
  • Field Data IC 1 versus SS 3

Type IC 1 mR SS 3 mR diff
Dental 190.9 197.9 3.7
Podiatrist 7.2 7.3 1.4
Medical 49.8 47.7 -4.2
Mammo 287.2 296.1 3.1
33
Evaluation of X-ray Measuring Devices Ease of
Use
  • IC1- IC3
  • Care needed in connecting probes
  • SS1
  • Set up difficult when used on some machines
  • SS2
  • Detector cable fixed to base
  • SS3
  • Some felt it was not as simple to use

34
Evaluation of X-ray Measuring Devices Our
Conclusions
  • Ion chambers exhibit good energy response over a
    wide range of beam qualities new chambers are
    lighter and smaller
  • SSDs can be designed to have acceptable energy
    responses in the diagnostic x-ray range, but know
    your instruments limitations
  • Field staff like the small size and light weight
    of SSD detectors

35
Evaluation of X-ray Measuring Devices Our
Conclusions
  • Send equipment to an accredited calibration lab
    annually to ensure radiation response remains in
    specification
  • We use SSD for equipment with known limits on the
    energy range
  • We use ion chambers for mammography beams and on
    x-ray beams in which beam qualities can vary
    significantly from machine to machine.
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