Imagine techniques 2 lab 2

scatter

incident photon interacts with a loosely bound outer shell electron and is bounced in a new direction at a lower energy level

secondary

any xray photon not produced at target

-stem or off focus radiation

-photoelectric interaction

interactions of xrays with matter which produce scatter/secondary radiation

scatter: Compton interactions

secondary: photoelectric innteraction

as kVp increases, scatter ?

scatter increases

as thickness or density increases, scatter ?

scatter increases

as grid efficiency increases, scatter reaching IR ?

scatter reaching IR decreases

as collimation increases, scatter ?

scatter decreases

as SID increases, scatter ?

SID doesn’t affect scatter

As OID increases, scatter reaching IR ?

scatter reaching IR decreases

as scatter increases, patient dose ?

patient dose decreases, when increase kVp

as scatter increases, image quality ?

image quality decreases

as scatter increases, occupational exposure ?

occupational exposure increases

as kVp increases, what happens to scatter and secondary radiation?

scatter increases, secondary decreases

Purpose of grids

improve contrast

Components of grids

lead foil strips and interspace material

construction of grids

canting: angle to accommodate divergence of beam

interspace material: organic material or aluminum

types of grids

linear: used in radiology

cross hatch: used in nuclear medicine

Focal distance

distance from target to the grid

focal range

tolerance limits from the focal distance that can be varied without excessive loss of primary radiation (buffer zone)

convergent line

where the angled lead strips of a focused grid would meet if extended upward

Ratio (grids)

R = H/d

Frequency (grids)

number of lines/inch or cm

kVp increases, grid ratio must ?

grid ratio must increase

how big must the part be to use a grid

greater than 10cm

What should distance be for grids

in focal range

Where should beam alignment be for grids

along convergent line

Positioning latitude must be what for grids?

must be at the center of the grid

Exposure latitude and grids

exposure latitude decreases due to higher contrast

Grid cut off definition

When grid lines project wider than they actually are, resulting in loss of primary radiation.

Grid cutoff factors

must have accurate tube-part alignment

Far focus artifact

target above focal range

Near focus artifact

target below focal range

Off center artifact

target lateral to convergent line

Off level artifact

Grid is angled laterally

Upside down focused grid artifact

dramatically dark in center, light on edges, wont happen

Tube angle artifact

with grid lines but not against