Mammography Systems and X-Ray Tube Design
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Questions and Answers

What is a disadvantage of extended-cycle processing?

  • Improve image quality
  • Increase film throughput
  • Reduce film throughout (correct)
  • Increase processing time

    • Why is monitoring of dose essential in radiation dosimetry?

  • To reduce the risk of radiation exposure (correct)
  • To reduce patient waiting time
  • To increase the risk of carcinogenesis
  • To improve image quality

    • What is the preferred dose index in radiation dosimetry?

  • Average organ dose
  • Average tissue dose
  • Average glandular dose (correct)
  • Average skin dose

    • What is the formula to calculate average glandular dose?

    <p>Dg = DgN × X ESE</p> Signup and view all the answers

    What is the unit of measurement for the Roentgen to dose conversion factor?

    <p>mrad/R</p> Signup and view all the answers

    What affects the value of DgN?

    <p>Radiation quality and breast thickness</p> Signup and view all the answers

    How does increasing kVp affect beam penetrability?

    <p>Increases beam penetrability</p> Signup and view all the answers

    What happens to the required dose when breast thickness increases?

    <p>The required dose increases</p> Signup and view all the answers

    What is the effect of vigorous compression on breast dose?

    <p>Reduces breast dose</p> Signup and view all the answers

    What is the effect of a Rh/Rh target/filter combination on breast dose?

    <p>Reduces breast dose</p> Signup and view all the answers

    What is the effect of a faster screen film on breast dose?

    <p>Reduces breast dose</p> Signup and view all the answers

    What is the average glandular dose limit per film for a compressed breast thickness of 4.2 cm?

    <p>3 mGy</p> Signup and view all the answers

    What is required for stereotactic breast biopsy?

    <p>Two views</p> Signup and view all the answers

    What is the purpose of measuring the shift of a lesion in stereotactic breast biopsy?

    <p>To determine the depth to insert the biopsy needle</p> Signup and view all the answers

    What is one of the essential goals of modern mammography?

    <p>To enhance low contrast detection</p> Signup and view all the answers

    What is a feature of modern mammography systems?

    <p>Special x-ray tube</p> Signup and view all the answers

    What is the purpose of the dual filaments in the cathode of the x-ray tube?

    <p>To produce a small focal spot</p> Signup and view all the answers

    What is the energy range of the k-characteristic x-ray produced by the Molybdenum target?

    <p>17.5 &amp; 19.6 keV</p> Signup and view all the answers

    Why is the x-ray tube tilted in the mammography system?

    <p>To provide adequate coverage for 60 to 70 cm typical source to image distance</p> Signup and view all the answers

    What is the 'Heal effect' in the context of mammography?

    <p>A significant drop of x-ray intensity toward the anode side</p> Signup and view all the answers

    What type of camera is used in digital mammography?

    <p>Charged coupled device (CCD) camera</p> Signup and view all the answers

    What is the dynamic range of digital mammography?

    <p>1000:1</p> Signup and view all the answers

    What is one of the advantages of digital mammography?

    <p>Ability to post-process images</p> Signup and view all the answers

    What is the purpose of computer-aided detection (CAD) in digital mammography?

    <p>To provide a second opinion</p> Signup and view all the answers

    What is required for a mammography facility to operate legally under MQSA?

    <p>Both certification and accreditation</p> Signup and view all the answers

    What is the purpose of the quality control phantom in mammography?

    <p>To test the quality of mammography images</p> Signup and view all the answers

    What is required to pass the MQSA test for the quality control phantom?

    <p>At least 4 cylinders, 3 calcification groups, and 3 masses</p> Signup and view all the answers

    What is the maximum average glandular dose allowed to pass the MQSA test?

    <p>Less than 3 mGy</p> Signup and view all the answers

    Where is the cathode placed during an X-ray procedure?

    <p>Over the chest wall of the patient</p> Signup and view all the answers

    What is the purpose of the small focal spot size (0.1mm)?

    <p>For magnification imaging</p> Signup and view all the answers

    What is the result of the line focus principle on the effective focal spot?

    <p>It decreases the effective focal spot</p> Signup and view all the answers

    What is the reason for more geometric blurring at the chest wall?

    <p>The focal spot length is greater at the chest wall</p> Signup and view all the answers

    What is the optimum x-ray energy range for achieving high subject contrast?

    <p>15-25 keV</p> Signup and view all the answers

    What is the purpose of using molybdenum and rhodium targets?

    <p>To achieve the optimum x-ray energy</p> Signup and view all the answers

    What is the advantage of using beryllium in the tube port?

    <p>It provides low attenuation and good structural integrity</p> Signup and view all the answers

    What is the purpose of added tube filters of the same element as the target?

    <p>To reduce the low and high x-ray energy in the spectrum</p> Signup and view all the answers

    Study Notes

    Modern Mammography Goals

    • The primary goals of modern mammography are to:
      • Enhance low contrast detection
      • Minimize patient dose
      • Optimize image quality

    Modern Mammography Systems

    • Modern mammography systems have:
      • Special x-ray tube
      • Breast compression devices
      • Optimized screen/film detector systems

    X-Ray Tube Design

    • The x-ray tube has:
      • Cathode with dual filaments in a focusing cup
      • Produces 0.3 mm and 0.1 mm focal spot sizes
      • Operates at low voltage (below 35 kVp)
      • Tube current: 100 ± 25 mA for 0.3 mm focal spot, 25 ± 10 mA for 0.1 mm focal spot
    • Anode:
      • Made of Molybdenum (Mo) or Rhodium (Rh) targets
      • Produces k-characteristic x-ray energies (17.5 & 19.6 keV for Mo, 20.2 & 22.7 keV for Rh)
      • X-ray tube is tilted to provide adequate coverage for 60-70 cm source to image distance

    Heel Effect

    • The heel effect causes a significant drop in x-ray intensity towards the anode side of the x-ray beam
    • The cathode is placed over the chest wall (thicker part of the breast) and the anode over the nipple part (thinner part)

    Focal Spot Considerations

    • Two focal spot sizes are used:
      • Large (0.3 mm) for routine imaging
      • Small (0.1 mm) for magnification imaging
    • The effective focal spot is smaller than the actual focal spot due to the line focus principle
    • The focal spot length at the reference axis is less than the focal spot length at the chest wall, causing more geometric blurring at the chest wall

    Tube Port, Tube Filtration, and Beam Quality

    • The optimum x-ray energy for high subject contrast is at the lowest radiation (15-25 keV)
    • The tube port is made of 1 mm thick beryllium (Z=4) for low attenuation and good structural integrity
    • Filters:
      • Added tube filters of the same element as the target reduce low and high x-ray energy in the spectrum
      • Allow characteristic x-ray energies to be transmitted

    Radiation Dosimetry

    • The risk of carcinogenesis from radiation dose to the breast is a concern
    • Monitoring of dose is essential and required yearly by MQSA
    • The average glandular dose is the preferred dose index
    • Factors affecting breast dose:
      • kVp: higher kVp increases beam penetrability but decreases inherent subject contrast
      • Breast thickness: increased breast thickness requires an increased dose
      • Compression devices: vigorous compression lowers breast dose by reducing thickness
      • Target/filter: Rh/Rh combination can significantly reduce the dose to thick breast
      • Speed of screen: faster screen film reduces the dose at the expense of spatial resolution
      • Film processing conditions: higher OD achieved on film will increase the dose
      • Antiscatter grid: increases the dose but improves image quality
      • Tissue composition of the breast: glandular tissue will have a higher breast dose due to increased attenuation and a greater tissue mass at risk

    MQSA Regulations

    • The MQSA limits the average glandular dose to 3 mGy (300 rad) per film for a compressed breast thickness of 4.2 cm and a breast composition of 50% glandular and 50% adipose tissue using the MQSA approved mammography phantom
    • The average glandular dose for this phantom is typically 1.5 to 2.2 mGy per view or 3 to 4.4 mGy for two views for a film optical density of 1.5-2

    Stereotactic Breast Biopsy

    • Biopsy systems provide the capability to localize in 3D and physically sample suspected lesions on mammograms
    • Two views are required (+15° and -15°) to measure the shift of a lesion and determine its distance from the detector
    • Charged coupled device (CCD) camera coupled to x-ray phosphor screens is used for this purpose

    Full Field Digital Mammography

    • Advantages of digital mammography:
      • Wide dynamic range (1000:1) compared with screen-film mammography (40:1)
      • Dynamic image manipulation
      • Ability to post-process
      • The soft copy read accompanied by computer-aided detection (CAD) to provide the second opinion
      • 3D imaging
    • Regulation requirements:
      • For a facility to perform mammography legally under MQSA, it must be certified and credited
      • The accreditation body verifies that the mammography facility meets the standards set forth by the MQSA

    Quality Control Phantom

    • The phantom is composed of:
      • Acrylic disk (4 mm thick, 10 mm diameter)
      • Acrylic body (mimics 4.2 cm compressed breast of 50% adipose and 50% glandular tissue composition)
      • Wax insert with 6 cylinder nylon to simulate speculations, 5 Al2O3 specks to simulate calcification, and 5 low contrast disks to simulate masses
    • A mammography phantom is a test object that simulates the radiographic characteristics of compressed breast tissues containing disease
    • To pass the MQSA test, at least 4 cylinders, 3 calcification groups, and 3 masses must be clearly visible at an average glandular dose of less than 3 mGy.

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    Description

    This quiz covers the essential goals of modern mammography, components of modern mammography systems, and the design of X-ray tubes in mammography.

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