B - Principle factors affecting Image Quality

Question 1

Primary control of contrast is?

Answer 1

kVp

Question 2

primary control of density is?

Answer 2

mAs

Question 3

What are principle factors that could affect Radiographic Quality?

Answer 3

Resolution
Noise
Speed
Artifacts

Question 4

What are film factors that could affect Radiographic Quality?

Answer 4

Characteristic Curve
Optical Density
Film Processing

Question 5

What are Geometric factors that could affect Radiographic Quality?

Answer 5

Geometric Factors
Magnification
Distortion
Focal Spot Blur
Heel Effect

Question 6

What are subject factors that could affect Radiographic Quality?

Answer 6

Subject Contrast
Motion Blur

Question 7

What are tools that that could improve Radiographic Quality?

Answer 7

Patient Positioning
Image Receptors
Selection of Technique Factors

Question 8

What is resolution?

Answer 8

Ability to image two separate objects and visually distinguish one from the other.

Question 9

What is spatial resolution?

Answer 9

Ability to image small objects that have high subject contrast i.e. bone and soft tissue

Question 10

What is contrast resolution?

Answer 10

Ability to distinguish anatomical structures of similar contrast i.e. liver and spleen

Question 11

What is noise with regards to x-rays?

Answer 11

Random fluctuation of the optical density of the radiograph
Noise is present in all electronic systems (image processors) and can cause an irregular granular pattern and may degrade image detail
Noise can reduced by increasing the mAs

Question 12

What is speed with regards to x-rays?

Answer 12

Speed refers to the speed of the image detector in registering the quantity of radiation that reaches it
Despite this not being a factor that is evident on the radiograph, it is very closely related to the noise and resolution
Fast image receptors have high noise and low spatial resolution and contrast resolution
High spatial resolution and contrast resolution requires low noise and slow image receptors
Low noise accompanies slow image receptors with high spatial resolution and contrast resolution

Question 13

What are artefacts on an x-ray?

Answer 13

Artefacts can be represented on the radiograph through damage or foreign material being present on the receptor

Question 14

What are some examples of artefacts?

Answer 14

Scratches
Pregnancy/Foetus
Pacemaker
Jewellery
Bra straps
Piercings
Shrapnel
movement
double exposure
surgical clips
sternal wires
Abdominal Aortic Stent
Vascular Stent
Total hip replacement
Dynamic hip screw

Question 15

What is optical density?

Answer 15

Degree of blackening on radiograph (mAs

Question 16

What is shape distortion?

Answer 16

Unequal magnification of different portions of the same objects. Anatomy can be angled or image detector can be angled

Question 17

What is focal spot blur?

Answer 17

Blurred region on the radiograph over which the radiographer has little control

Question 18

What is penumbra?

Answer 18

Image blur that results from the size of the focal spot, also referred to as geometric unsharpness

Question 19

What is the heel effect?

Answer 19

Absorption of x-rays in the heel of the target, resulting in reduced x-ray intensity to the anode side of the central axis

This is also closely related to the focal spot size
Variation in focal spot size results in focal spot blur, and consequently images towards the cathode side of a radiograph have a higher degree of blur and poorer degree of spatial resolution to those on the anode side

Question 20

What is subject contrast?

Answer 20

Component of radiographic contrast determined by the size, shape and x-ray attenuating characteristics of the subject who is being examined and the energy of the x-ray beam

Question 21

What is Radiographic Contrast?

Answer 21

Radiographic Contrast = Image receptor Contrast x Subject Contrast

Question 22

Different anatomical thicknesses contribute to subject contrast. True or false?

Answer 22

True

Question 23

What is motion blur?

Answer 23

Blurring of the image that results from movement of the patient or the x-ray tube during exposure

Question 24

What are procedures for reducing motion blur?

Answer 24

Use shortest possible exposure time
Restrict patient motion by providing instruction or acceptable restraining techniques
Use a large SID
Use a small OID
Suspended Inspiration/Expiration

Question 25

What is patient positioning?

Answer 25

Proper patient positioning requires that the anatomical structure under investigation be as close to the IR as possible, with the axis of said structure in a plane that is parallel to the plane of the IR
Patient must be immobile
Central ray should be incident on the centre of the structure
Good anatomy knowledge