Imaging Chapter 16- powerpoint, penguins, book questions

image quality

the degree or exactness of the anatomy under investigation and how it is rendered on the image receptor

high-quality image

a medical image that faithfully reproduces structure and tissues

resolution

the ability to image 2 separate objects and visually distinguish one from the other

spatial resolution

the ability to image small objects that have high subject contrast

spatial resolution improves with

small pixel size

spatial resolution is influenced by

focal spot size

contrast resolution

the ability to distinguish anatomical structures of similar subject contrast

contrast improves with

lower kVp

MRI is considered

the best contrast resolution

radiographic noise is

the random fluctuation of xray interaction on the image receptor

the goal of noise =

low noise

the IR will have

inherent electronic noise

quantum mottle

principal contributor to image noise

quantum mottle is random nature by which

xrays interact with the IR

smaller quantity of xrays=

more quantum mottle

faster IR=

more quantum mottle

what helps to improve quantum mottle

high mAs, low kVp, and slower image receptors

fast IR =

high noise, low contrast resolution

low noise =

slow IR, high contrast

spatial resolution is limited to

pixel size

what are the 3 geometric factors

-magnification

-distortion

-focal spot blur

MF =

image size/object size

SID/SOD

what 2 factors affect MF

SID and OID

object thickness

-santa claus

-thick objects are more than thin

object position

more irregular objects off CR show more distortion, such as the human body

object shape

foreshortening, elognation

distortion is

unequal magnification of different portions of the same object

spatial distortion

misrepresentation of an object

xrays are not emitted or made from a specific point,

but an area

the focal spot is not a point, but

more of a rectangular area

focal spot blur is

undesireable

focal spot blur =

(effective focal spot) X (OID/SOD)

focal spot blur equations

SOD/OID = effective focal spot/focal spot blur

or

focal spot blur = (effective focal spot) OID / SOD

to minimize small focal spots

position patient so anatomical part is close to IR, large SID

the focal spot you choose is determined by

anode heat capacity than spatial resolution

heel effect

radiation intensity across the xray field in the anode-cathode direction

heel effect is caused by

attenuation of the xrays in the heel of anode

focal spot blur is larger on the

cathode side of the tube

subject contrast includes what 5 things

-subject thickness

-patient thickness

-tissue mass density

-effective atomic number

-object shape

image receptor contrast is selectable with post processing and

depends on bit depth and window/level selection by technologist

post processing is more important for

radiographic contrast

the degree of subject contrast is directly related to

the number of xrays leaving the body

the effect on subject contrast is a direct result in

the differences in attenuation in the body

different sections of the body can have equal thickness and

they can have different mass densities

when effective atomic number is different of adjacent tissues

the subject contrast is high

structures that coincide with xray beam have

maximum contrast

other anatomical structures have

reduced subject contrast

motion blur

movement of patient of xray equipment during an exposure

-voluntary vs involuntary

how to improve image quality with patient positioning

-anatomical structures being investigated as close to the IR as you can

-CR on center of structure

-reduce motion blur

how to improve image quality using the IR

-extremity and soft tissue, small pixel size (higher dose)

-larger pixel size (lower patient dose)

how to improve image quality with selection of technique factors

-shortest time as possible

-best generator possible

-high kVp, lower patient dose (allows to reduce mA), more xrays to IR, loss of contrast

increase in patient thickness

-increase patient dose

-increase magnification

-increase focal spot blur

-increase motion blur

-increase absorption blur

-decrease image contrast

increase in field size

-increase patient dose

-no change in magnification

-no change in focal spot blur

-no change in motion blur

-no change in absorption blur

-decrease image contrast

increase in use of contrast media

-no change in patient dose

-no change in magnification

-no change in focal spot blur

-no change in motion blur

-no change in absorption blur

-increase in image contrast

increase in focal spot size

-no change in patient dose

-no change in magnification

-increase in focal spot blur

-no change in motion blur

-no change in absorption blur

-no change in image contrast

increase in SID

-decrease patient dose

-decrease magnification

-decrease focal spot blur

-decrease motion blur

-no change in absorption blur

-no change in image contrast

increase in OID

-no change in patient dose

-increase in magnification

-increase in focal spot blur

-increase in motion blur

-no change in absorption blur

-increase image contrast

increase in mAs

-increase patient dose

-no change in radiographic magnification

-no change in focal spot blur

-no change in motion blur

-no change in absorption blur

-may increase or decrease image contrast

increase in time

-increase patient dose

-no change in magnification

-no change in focal spot blur

-increase in motion blur

-no change in absorption blur

-may increase or decrease image contrast

increase in kVp

-increase patient dose

-no change in magnification

-no change in focal spot blur

-no change in motion blur

-no change in absorption blur

-decrease in image contrast

increase voltage ripple

-increase patient dose

-no change in magnification

-no change in focal spot blur

-increase in motion blur

-no change in absorption blur

-increase image contrast

increase total filtration

-decrease patient dose

-no change in magnification

-no change in focal spot blur

-no change in motion blur

-no change in absorption blur

-decrease image contrast

spatial resolution improves with

smaller pixel size

radiographic noise is

the random fluctuation of xray interaction on the image receptor

the use of high mAs, low kVp, and slower image receptors

reduce quantum mottle

digital image quality rules

-fast image receptors have high noise and low contrast resolution

-low noise accompanies slow image receptors and high contrast resolution

-spatial resolution is limited to pixel size

sharpness in this shadow context is

spatial resolution

magnification factor 1

MF= image size/object size

magnification factor 2

MF = SID/SOD

magnification factor 3

MF = image size/object size = SID/SOD

object size = image size x (SID/SOD)

two factors affect image magnification

SID and OID

minimizing magnification

-large SID

-small OID: place object as close to IR as possible

magnification is

the ratio of image size to object size of SID to SOD

magnification of an object positioned off the CR is

the same as that of an object on the CR if the objects are in the same plane

IR factors that affect digital image quality

-pixel size

-dynamic range

-intensity response

-signal to noise

-postprocessing

geometric factors that affect digital image quality

-distortion

-magnification

-blur

subject factors that affect digital image quality

*contrast

-thickness

-density

-atomic number

*motion

unequal magnification of different portions of the same object is called

distortion

distortion can interfere with

diagnosis

three conditions contribute to image distortion

-object thickness

-object position

-object shape

what objects are more distorted

thick objects are more distorted than thin objects

when can distortion occur

when the object plane and the image plane are not parallel

focal spot blur occurs because

the focal spot is not a point

Focal-spot blur is relatively unimportant for determining spatial resolution.

pixel size is most important

focal spot blur equation

SOD/OID = effective focal spot/focal spot blur

or

focal spot blur = (effective focal spot) OID / SOD

Focal-spot blur is _______ on the anode side and _______ on the cathode side of the image receptor

small; large

subject contrast equation

radiographic contrast = IR contrast x subject contrast

what is usually the cause of motion blur

patient motion

keep exposure time

as short as possible

define contrast resolution

The ability to distinguish between and to image similar tissues.

define superimposition

The placement of one thing above or on top of another.

define image distortion

Unequal magnification of different portions of the same object is called distortion.

define focal spot blur

An undesirable loss of spatial resolution that is caused by a large effective focal spot, a short SID, and a long OID; the most important factor in determining spatial resolution.

define magnification radiography

When magnification is desirable and carefully planned into the radiographic examination.

define geometric factors

Factors that apply to the production of high-quality images.

define motion blur

Loss of spatial resolution that is the result of movement of the patient, the x-ray tube, or the image receptor.

define image noise

A grainy or uneven appearance of an image caused by an insufficient number of primary x-rays

define quantum mottle

The random nature in which x-rays interact with the image receptor; too few photons to cover the image receptor uniformly

define spatial resolution

Ability to image small objects that have high subject contrast

what principally determines radiographic spatial resolution?

focal spot size