Lecture 3: Rad Quality and Princ. of Image Formation Flashcards
What are the 5 subject opacities in order of radio-opaque to radio-lucent?
Metal, Bone, Soft Tissue, Fat, Air
What two factors determine opaqueness?
Density (5 subject opacities) and Thickness
What are the contrast medias commonly used?
Iodine and Barium
What is the silhouetting effect/border effacement?
Two objects of the SAME SUBJECT DENSITY are in contact and essentially disappear in a radiograph
An object that is further away from the film upon shooting a radiograph will appear larger or smaller in the image?
LARGER – the larger the shadow projected
Where is the least degree of distortion in the radiographic beam?
in the center
What is the penumbra?
Where the shadows produced from xrays produced at varying points on the anode create blurring on the image
reduces spatial resolution
How can the size of the penumbra be minimized?
Increasing the TFD (tube film distance); the closer the object is to the film; Minimize the focal spot size (source of xrays)
How can you reduce motion?
Reduce the time interval of exposure
How long exposure for thoracic radiograph?
1/60th second
How long exposure for abdominal radiograph?
1/30th second
Increasing the TFD does what?
Increases amount of radiation needed to expose the film; increase mAs (need more # and intensity)
What is the inverse square law?
Intensity = original intensity * (new distance)^2/(old distance)^2
ie: Doubling the distance increases mAs by 4
How is the radiograph named?
By the direction of path of the beam as it passes through the patient
How do you view a radiograph?
ALWAYS IN THE SAME ORIENTATION: Lateral View: - Head to the LEFT - Caudal to the RIGHT - Ventral to the BOTTOM - Dorsal to the TOP DV View: - Animal right on our left
