Geometry of Projection Radiography
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Questions and Answers

What is the primary effect of projection radiography?

  • To record an image of a 2D object in 3D
  • To decrease the magnification of the object
  • To increase the spatial resolution of the image
  • To record an image of a 3D object in 2D (correct)

    • What is the result of the superposition of anatomy along each ray in projection radiography?

  • An image with increased spatial resolution
  • A 3D image of the patient
  • An image with no distortion
  • A 2D image with superposition of anatomy (correct)

    • What is the typical range of fine focal spots in radiography?

  • 0.3-1.0 mm (correct)
  • 1.0-3.0 mm
  • 3.0-5.0 mm
  • 0.1-0.3 mm

    • What is the main factor that affects the magnification of an object in projection radiography?

    <p>The OID of the object</p> Signup and view all the answers

    Why do objects appear progressively larger in a projection radiograph?

    <p>Due to their differences in position</p> Signup and view all the answers

    Why must lower mAs be used with fine focal spots?

    <p>To protect the tube from heating effects</p> Signup and view all the answers

    What is the effect of angulation on the projected length of an angled object?

    <p>It causes foreshortening of the object</p> Signup and view all the answers

    What is the formula for magnification (m) in radiography?

    <p>XF / SOD</p> Signup and view all the answers

    What is the effect of increasing the OID in magnification imaging?

    <p>Increased magnification</p> Signup and view all the answers

    What is the ideal image sharpness produced by?

    <p>A point source</p> Signup and view all the answers

    What is the main factor that limits the spatial resolution in a projection radiograph?

    <p>The image receptor factors</p> Signup and view all the answers

    What is the compromise required in choosing an appropriate focal spot size?

    <p>Between exposure time and resolution</p> Signup and view all the answers

    What depends on the focal spot size in projection radiography?

    <p>The spatial resolution of the image</p> Signup and view all the answers

    What is the result of using a very small focal spot size?

    <p>Good spatial resolution with low tube current</p> Signup and view all the answers

    What is the effect of increasing the FID on magnification imaging?

    <p>Increased magnification</p> Signup and view all the answers

    What is the effect of motion blur on magnification imaging?

    <p>Decreased spatial resolution</p> Signup and view all the answers

    What is the effect on the scatter fraction at the image receptor when increasing the OID?

    <p>It decreases substantially</p> Signup and view all the answers

    What is the consequence of increasing the OID on image sharpness?

    <p>It decreases due to geometric blur</p> Signup and view all the answers

    What is the primary consideration for choosing the kV setting in screen-film systems?

    <p>Required contrast</p> Signup and view all the answers

    What is the effect of magnification on spatial resolution?

    <p>It improves compared to contact methods</p> Signup and view all the answers

    What is the reason for increasing the mAs when increasing the OID?

    <p>To maintain the dose to the image receptor</p> Signup and view all the answers

    What is the limitation of using magnification for large body regions?

    <p>It requires a larger image receptor</p> Signup and view all the answers

    What is the consequence of increasing the OID on the SNR?

    <p>The effect on SNR is not mentioned</p> Signup and view all the answers

    What is the difference between magnification and a simple zoom of a digital image?

    <p>Magnification improves spatial resolution, but a simple zoom does not</p> Signup and view all the answers

    What is the primary source of noise in imaging?

    <p>Random arrival of photons at the image receptor</p> Signup and view all the answers

    What is the formula to determine the number of detected photons required per unit area?

    <p>N = k2/C2d2</p> Signup and view all the answers

    What is the effect of increasing contrast C on the number of photons required at the image receptor?

    <p>It reduces the number of photons required</p> Signup and view all the answers

    What is the usual value of k in Rose's expression?

    <p>5</p> Signup and view all the answers

    What is the effect of reducing kV on image quality?

    <p>It produces an image of satisfactory quality at a lower image receptor dose</p> Signup and view all the answers

    What is the effect of reducing kV on patient dose?

    <p>It increases patient dose</p> Signup and view all the answers

    How does patient dose (Ki) relate to mAs and kV?

    <p>Ki is proportional to mAs and approx to kV2</p> Signup and view all the answers

    How does penetration through the patient relate to kV?

    <p>It is proportional to kV3</p> Signup and view all the answers

    How does the total dose to the image receptor depend on kV?

    <p>It depends approximately on kV5</p> Signup and view all the answers

    What is the 15% rule in technique selection?

    <p>A reduction in kV requires an increase in mAs of at least 15%</p> Signup and view all the answers

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