Radiographic Imaging Contrast

As SID increases, what effect is seen in the IR exposure of images, and why?

IR exposure decreases because because photons slowdown and cant reach the IR

When you increase your SID what must be increased in order to maintain the same EXI# (IR exposure)?

mAs must increase when SID increases in order to keep the same EXI # (IR Exposure)

Define Radiographic Contrast

Visible difference between adjacent densities (IR exposure values) in a radiographic image

What type of contrast scale is produced by low kVp?

Short scale (less gray/more black and white)

What type of contrast scale is produced by high kVp?

Long Scale (more gray shades)

What does high contrast mean when discussing a Radiographic Image?

The differences between shades of gray in the image are increased and it looks more distictly black and white (good)

What does low contrast mean when discussing a Radiographic Image?

The differences between shades of gray in the image are decreased and it looks more less distinctly black and white (bad)

How does kVp affect IR exposure?

Higher kVp results in higher IR exposure

Does mAs affect contrast?

mAs has a negligible affect on contrast, but we may need to change the mAs number to acheive a certain EXI#

High kVp produces what energy photons

High kvp produces high energy photons

How does OID affect contrast?

More OID you have the less scatter reaches the IR and thus gives our image a higher contrast (Direct Relationship)

How does filtration impact scatter?

Filtration increases scatter because similar to kVp it increases the average energy of the photons and thus increases scatter

How do Grids affect contrast?

Increasing grid ratio absorbs scatter and thus increases contrast

How does patient thickness affect contrast?

More matter=More scatter; Increased patient thickness elevates the amount of scatter that is produced and thus decreases contrast

How does collimation affect contrast?

Collimation has direct relationship with contrast; As collimation increases the amount of space for high energy photons to land on the IR decreases, which means contrast increases as less scatter is present.

How does pathology affect contrast

Added pathology = more matter meaning that there is more scatter and decreased contrast (indirect relaionship)

How does atomic # affect contrast

Increased atomic # means more scatter and thus decreased contrast (indirect)