SIMPLE PROCEDURES FOR IMAGE QUALITY ASSURANCE AND DOSE REDUCTION IN MAMMOGRAPHY

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SIMPLE PROCEDURES FOR IMAGE QUALITY ASSURANCE AND
DOSE REDUCTION IN MAMMOGRAPHY

• Dr. Nabil Maalej
• Physics Dept., KFUPM
• 28-3-2005

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Outline

• Introduction
• Image Quality
• Contrast
• Resolution
• Quality Control
• Breast Dose
• Entrance Skin Exposure
• Mean Glandular Dose
• Dose Reduction

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Breast Cancer (Highest)

• For the total Saudi population, the most common
  ten cancers are (1994-1996 Cancer Registry)
• Female breast cancer (8.8),
• Liver cancer (7.5),
• Leukemia (7.5),
• Non-Hodgkin's lymphoma (7.3)
• Colo-rectum cancer (5.5).
• Thyroid cancer (5.2),
• Lung cancer (4.7)
• Nervous system cancer (3.9)
• Stomach cancer (3.8) and
• Urinary bladder cancer (3.5)

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US Mammography Quality Standards Act (MQSA)

• The Mammography Quality Standards Act (MQSA) of
  1992 requires that all mammography facilities in
  the United States be (1) accredited by an
  approved body, (2) certified by the U.S.
  Department of Health and Human Services (HHS),
  and (3) receive an on-site inspection by a state
  agency acting on behalf of the HHS (or by HHS
  inspectors).

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US Mammography Quality Standards Act (MQSA)

• Radiologist, Technologist and Medical Physicist
  Qualifications (initial, continuing,
  reestablished)
• Reporting and Record Keeping Standard
• Equipment Standards
• Quality Assurance Schedule

http//www.fda.gov/cdrh/mammography
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IMAGE QUALITY
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Mammography Machine
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Imaging Setup
X-ray Source
X-ray Beam
Compression Paddle
Compressed Breast
Table
Chest Wall
Grid
Image Detector
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Imaging Quality Parameters
CONTRAST
RESOLUTION
NOISE
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Contrast

• Image Contrast is a measure of difference between
  regions in an image
• Good image contrast is particularly important
  when imaging low-contrast objects such as breast
  tumors

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Resolution

• Spatial resolution of an imaging system can be
  defined in terms of the smallest spacing between
  two objects that can be imaged clearly

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Measurement of Resolution
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IMAGE QUALITY CONTROL
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ACR Accreditation Phantom (RMI 156 )
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RMI 156 Phantom
ACR minimum score is 4 visible fibers, 3 speck
groups and 3 masses
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RMI 156 Phantom
ACR minimum score is 4 visible fibers, 3 speck
groups and 3 masses
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Importance of Image Quality
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Dose to The Breast
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Entrance Skin Exposure

• The entrance skin exposure is the amount of
  radiation delivered to the patient skin at the
  entrance point of the X-ray

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SETUP For Entrance Skin Exposure Measurement
X-Ray Beam
Compression Paddle
Ionization Chamber
Breast Equivalent Phantom
Table
Film
Film
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Entrance Skin Exposure Measurement
Dosimeter Mammography Phantom
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Mean Glandular Dose

• The mean, or average, dose to the glandular
  tissue within the breast
• The federal and ACR dose limit for an
  average-size patient is 3 mGy (300 mrad) per view

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Conclusion

• Using the ACR phantom allows the evaluation of
  image quality
• Using the simple measurement of the entrance skin
  exposure the breast mean glandular dose can be
  determined
• Government agencies and hospitals in the region
  should implement Quality Assurance standards to
  reduce the chances of misdiagnosis while
  maintaining safe levels of radiation exposure to
  mammography patients

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THANK YOU
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Equipment Standards (MQSA)

• Maximum compression force for initial power drive
  must be between 111 N and 200 N
• Automatic Exposure Control Maintain film optical
  density within 0.15 of mean optical density
• Focal spot condition only evaluated by
  determining system resolution
• Radiation output goes from 513 mR/sec to 800
  mR/sec

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Equipment Standards (MQSA)

• Image receptor sizes 18 x 24 cm and 24 x 30 cm
  with moving grid mechanisms
• Light fields illumination of 160 lux at 100 cm
• Magnification at least one magnification in the
  range of 1.4 to 2.0
• Collimation assessment
• Exposure reproducibility

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Equipment Standards (MQSA)

• Beam quality (HVL) measurement
• Dose calculation for a cranio-caudal view
• Processor evaluation
• Darkroom fog
• Phantom image quality evaluation

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How Can We Reduce Scatter?

• Use an Anti-Scatter Grid
• Use and Air Gap between the breast and the
  detector
• Line Scanning System
• Capillary optics

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Anti-scatter grid
breast
leadsepta
detector
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Contrast Detail Analysis

• Contrast detail analysis an observer reports the
  size of the smallest object he or she can
  perceive at a certain contrast level and with a
  given noise level in the image.

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Measuring Contrast Detail Curve
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Measuring Contrast Detail Curve
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Measuring Contrast Detail Curve
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Contrast Degradation with Scatter
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Scattered Reduces Contrast
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Risk of Radiation Induced Breast Cancer
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Survey of MammographyFacilities in KSA (Not
Published)

• A site visit survey of 12 hospitals showed
• 6 institutions fail in the image quality assessed
  by the ACR accreditation phantom
• Only 2 of the institution do the image quality
  test weekly