RAD136 Chap 21 Line Focus and Heel Effect

What is the line focus principle?

• Angling of the anode to increase the target area while keeping the effective focal spot size small.

• The use of large tube angles to reduce the anode heel effect

• A.The effect of tube angulation on the tube target

• A.The need to keep the tube angle as small as possible

If the focal spot is very much larger than the anatomy or pathology of interest, the image of the anatomy can be caused to:

• magnify in gross size

• increase the penumbra

• “burn out” from excessive exposure

• disappear

What image quality is affected by the focal spot size?

• Sharpness of recorded detail

• Contrast

• Brightness

• Magnification

Which of the following positioning would take advantage of the anode heel effect?

• AP Chest: Patient’s head to anode

• AP T-Spine: Patient’s head to cathode

• AP Femur: Patient’s head to anode

• AP Humerus: Patient’s head to anode

With the line focus principal, the effective focal spot size will decrease with decreasing

• target angle

• rotor speed

• window thickness

• space charge

The heel effect is caused when radiation passes through the

• stator windings

• anode

• filament

• focusing cup

In imaging, the heel effect is minimized when using

1. using smaller field sizes
2. using larger fields sizes
3. using longer SID

• 1 and 2 only

• 2 and 3 only

• 1 and 3 only

The line focus principle

• makes the focal spot appear larger than it really is

• makes use of an angled cathode structure

• produces x-ray lines

• spreads the heat over a larger part of the anode

Reduce target angle will

• decrease the heel effect

• increase the heel effect

• result in no change in the heel effect

• increase the effective focal spot

The heel effect is worsened with:

• Longer field sizes

• Larger focal spots

• Shorter SIDs

• All of the above

• None of the above