Chapter 10 Imaging and Digital

Question 1

Film-Screen Systems

Answer 1

Portable, lightproof case for x-ray film
Contains one or two intensifying screens which amplify the x-ray beam by converting it to light
Light is created by phosphors in the screens

Question 2

Luminescence

Answer 2

to emit visible light
Phosphorescence or Fluorescence
95% of the image is formed by light!

Question 3

Phosphorescence

Answer 3

Continues to emit light after stimulation

Question 4

Fluorescence

Answer 4

Emits light only when being stimulated

Question 5

Latent image

Answer 5

invisible image on film before processing

Question 6

Manifest image

Answer 6

visible image on the film after

processing

Question 7

Film

Answer 7

First radiographs made on glass
  Film introduced in the early 1900s
   -  used with intensifying screens
   -  screens contain phosphors that 
      fluoresce and expose the film (95%)
      rather than direct x-ray 
   -  greatly reduces patient exposure!
  Film must be developed in a processor

Question 8

Processor

Answer 8

Automatically develops x-ray film

Converts the latent image into a manifest image

Question 9

CR Photostimulable Plates (PSP)

Answer 9

Protective Layer
Photostimulable Phosphor
   - absorbs energy from x-rays
Reflective Layer
Base - polyester
Backing
Plate is read with a laser which
    releases energy in the form of light

Image is digitized and sent to computer

Question 10

Digital Radiography

Answer 10

Indirect or direct

Question 11

Indirect

Answer 11

uses a scintillator of either cesium iodide or gadolinium oxysulfide
- x-rays converted to light, light converted to an electrical charge

Question 12

Direct

Answer 12

x-rays converted directly into an electrical charge

Question 13

Advantages of Digital Imaging

Answer 13

No film or processing chemicals
Less imaging time
Post-Processing
Multi-viewing
Much less storage space required
Decrease in repeats

Question 14

Radiographic Density

Answer 14

Degree of blackening on a film
Caused by metallic silver deposited in the film emulsion
Primary controlling factor is mAs
- mA x second = mAs

Question 15

mAs is always responsible for

Answer 15

patient dose

Question 16

Inverse Square Law

Answer 16

As the distance is doubled the intensity of the beam decreases 4 times. If the distance is halved, the intensity of the beam is increased by 4 times!

Question 17

Radiographic Contrast

Answer 17

The differences between adjacent densities
Controlling factor for film is kVp
Computer processing controls contrast in digital images
kVp selection is dependent on differential absorption

Question 18

Differential Absorption of Tissue

Answer 18

Air – easy to penetrate, dark on image (radiolucent)
Fat – dark gray
Muscle – light gray
Bone – white
Contrast – Iodine and Barium 
Metal (radiopaque)

Question 19

Detail

Controlled by:

Answer 19

The degree of geometric sharpness or accuracy of the structural lines actually recorded in the image
     1.  source to image receptor
          distance (SID)
     2.  object to image receptor 
          distance (OID)
     3.  Focal Spot Size

Question 20

Distortion

Answer 20

The misrepresentation of the size or shape of the structure being examined
Size (magnification)
1. SID
2. OID**
Shape is affected by tube angle and tube-part-IR alignment

Question 21

Other Factors to Consider….

Answer 21

Beam Restriction (collimation)
- the smaller the filed size, the less exposure
Grids
- as grid ratio increases, density decreases
and contrast increases due to absorption of
scatter