Regarding the heel effect: a. It is more pronounced in worn-out anode

1.	Regarding the heel effect: a. It is more pronounced in worn-out anodes with a rugged surface b. It is less pronounced in tubes with rotating compared with stationary anodesc. For a given film size, it is more noticeable on images acquired with a long focus-to-film distance d. In mammography, the anode side of the tube should be directed towards the chest wall e. It is useful in spine radio graphs
Answer» a. True. The electrons penetrate deeper into the anode material and the photons produced have a greater distance to travel through it. b. False. Anode rotation does not directly affect the heel effect. However, the heel effect is of less significance in stationary anodes tubes as they tend to have larger anode angles (due to thermal factors), and the field uniformity is not as critical in the applications they are used in. c. False. With a long focus-to-film distance, only the central, more uniform part of the beam is used to produce the image and the heel effect is less noticeable. d. False. The anode side (with a lower intensity of the beam due to the heel effect) should point away from the chest wall (where the thickness of breast tissue is less). e. True. It may be used to compensate for varying patient thickness along the cranio-caudal axis. For example, antero-posterior (AP) images of the thoracic spine are normally more penetrated (darker) towards the upper vertebrae. With the anode facing cranially, more uniform images can be obtained.

Regarding the heel effect: a. It is more pronounced in worn-out anodes with a rugged surface b. It is less pronounced in tubes with rotating compared with stationary anodesc. For a given film size, it is more noticeable on images acquired with a long focus-to-film distance d. In mammography, the anode side of the tube should be directed towards the chest wall e. It is useful in spine radio graphs

Answer»

a. True. The electrons penetrate deeper into the anode material and the photons produced have a greater distance to travel through it.

b. False. Anode rotation does not directly affect the heel effect. However, the heel effect is of less significance in stationary anodes tubes as they tend to have larger anode angles (due to thermal factors), and the field uniformity is not as critical in the applications they are used in.

c. False. With a long focus-to-film distance, only the central, more uniform part of the beam is used to produce the image and the heel effect is less noticeable.

d. False. The anode side (with a lower intensity of the beam due to the heel effect) should point away from the chest wall (where the thickness of breast tissue is less).

e. True. It may be used to compensate for varying patient thickness along the cranio-caudal axis. For example, antero-posterior (AP) images of the thoracic spine are normally more penetrated (darker) towards the upper vertebrae. With the anode facing cranially, more uniform images can be obtained.

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