Week 6c Chapter 19 & 20 Quality & technique

Week 6c Chapter 19 & 20 Quality & technique...

Info iconThis preview shows pages 1–16. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 19 & 20 Image Quality There are three geometric factors that affect radiographic quality. Magnification Distortion Focal Spot Blur We have explored these factors in the laboratory.
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Magnification All objects on the radiograph are larger that their actual size. This is called magnification. The magnification factor is the image size divided by the object size. At 40” (100 cm) factor is 1.1 At 72” (180 cm) factor is 1.05
Background image of page 2
Magnification Usually we do not know the size of the object so we must determine the magnification factor another way. Image size S0D MF = ----------------= ------------ Object Size SID
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Minimizing Magnification Large SID: Use the less divergent beam. Chest X-rays are done at 72” SID to minimize magnification. Lateral C-spine done at 72” Small OID: Get patient as close to the film as possible. Basic principle for positioning.
Background image of page 4
Distortion Distortion is the misrepresentation of the true size and shape of the object being radiographed. The amount of distortion depends upon the thickness, position and shape.
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Thickness Thick objects are more distorted than thin objects because of the greater change in Object Image Distance.
Background image of page 6
Thickness The position of the object relative to the central axis will cause greater distortion with thick and/or irregular shaped objects.
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Object Position If the object plane and image plane are parallel the image will not be distorted. If the object plane and image plane are not parallel, distortion will occur.
Background image of page 8
Spatial Distortion When multiple objects at different OID’s occur, we get spatial distortion due to unequal magnification. Two arrows appear as one. When shifted laterally more distortion occurs
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Object Shape Distortion When the object plane is not parallel to the image plane as when inclined, shape distortion occurs. This will result in foreshortening.
Background image of page 10
Focal Spot Blur Focal spot blur is caused by the effective size of the focal spot, which is larger at the cathode side. Focal spot blur is the most important factor in determining spatial resolution.
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Focal Spot Blur Focal spot blur is impacted by the Object to Image Distance.
Background image of page 12
Focal Spot Blur Heel Effect There is more to the heel affect than just the attenuation of the beam by the anode. The focal spot blur is smaller at the anode side and larger at the cathode side.
Background image of page 13

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Taking advantage of the Anode Heel Effect Exam Toward Cathode Toward Anode AP Full spine Abdomen Neck Chest Abdomen Neck AP T-spine Abdomen Neck Lat T-spine Neck Abdomen Humerus Shoulder Elbow
Background image of page 14
If the tube is mounted correctly for the AP Full spine, Chest and A-P Thoracic Spine, the patient must stand on his head for the lateral thoracic spine!!!! For erect radiography, the use of the
Background image of page 15

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 16
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 79

Week 6c Chapter 19 & 20 Quality & technique...

This preview shows document pages 1 - 16. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online