unit seven exam

ch n/a - detail and distortion

_________ and __________ ___________ are the two geometric properties of the image

distortion, spatial resolution

__________ ___________ is the number of lines per mm

spatial frequency

high spatial frequency = __________ spatial resolution

high

high spatial resolution = ________ detail

increased

___________ ____________ refers to the smallest object that can be detected in an image.

spatial resolution

The accuracy of structural lines is determined by ___________ ___________

spatial resolution

_____________ _____________ is inherent resolution on an image as a function of image acquisition time.

temporal resolution

Increasing exposure time _____________ motion unsharpness, which ______________ temporal resolution

increases, decreases

______________ ______________ expresses boundaries of an image by testing sharpness of lines point by point

point-spread function

______________ ____________ expresses boundaries of an image by testing sharpness of lines line by line. The less spread, the better the resolution

line-spread function

The less line-spread, the _________ the resolution

better

___________ ____________ ____________ (______) is also called trueness of the image

modulation transfer function (MTF)

___________ ____________ ____________ (______) is the ability of a system to record available spatial frequencies. Measures the accuracy of an image compared to the original size

modulation transfer function (MTF)

modulation transfer function (MTF) of ______ is perfect

1

________ is anything that interferes with the formation of the image; background or quantum

noise

noise is measured by _______

SNR

higher SNR = ________ nosie

lower

___________ __________ suggests that pixels need to be sampled twice in order to form a correct image

nyquist theorem

_________ is when the nyquist theorem is not met

aliasing

distortion can be classified as either _________ or _________ distortion

size, shape

____________ is the only possible size distortion in radiography

magnification

_____________ is not possible in radiography because of how the beam diverts

minification

__________ __________ is misrepresentation by unequal magnification of the actual shape of the structure

shape distortion

Which of the following factors affect distortion:

1. distances

2. direction of the angle

3. angle of the part, CR and IR

1, 2, and 3

the __________ the SID, the _________ the magnification

greater, smaller

the phosphor layer = the _________ layer

active

thin phosphor layer = ________ resolution

increased

decreased pixel size = _________ spatial resolution

increased

source = _________

target

distance ____________ the effects of OID

decreases

___________ SID can help offset OID

increased

SID has increased over time, standards for SID keep moving further back

true

_______ is the most critical distance for magnification and resolution

OID

OID is the most critical distance for ____________ and ____________

magnification, resolution

minimize OID to ___________ magnification

decrease

the larger the OID, the _________ magnification

more

parts that are _________ the IR will be magnified due to spatial distortion

further

_________ is the sharpness of an image

umbra

___________ is the unsharpness of the edges around an image

penumbra

small focal spot = _________ penumbra and _________ resolution

decreased, increased

small focal spot = ___________ detail

increased

large focal spot = ___________ penumbra

increased

SOD

source to object distance

________ refers to the distance from the x-ray source (focal spot, target) to the object being imaged

SOD

To find SOD you take ________ minus _________

SID, OID

Mag factor is the degree of ______________

magnification

A mag factor of _______ indicates no magnification

1

A mag factor of 1 indicates no magnification, this means the object is its __________ size

truest

A mag factor of 1 is almost impossible to achieve due to anatomic structures situated at __________ levels of the body

different

the mag factor expresses the ______ compared to what it actually should be

size

a mag factor of greater than one is expressed as a percentage of magnification

true

A mag factor of 1.2 means the image size is ______ percent _______ than the object size

20, larger

The formula to calculate mag factor is ________ divided by ________

SID, SOD

magnification factor permits calculation of the _______ size of an object

actual

To determine ______________, take Image size (I) and divide it by the Mag factor (M)

Object size (O)

Once the _______________ _____________ is known, the object size can be determined

magnification factor

Object size = __________ divided by _________

image size, MF

If both the object size and image size are known, the percentage of ___________________ of the object can be calculated

magnification

to find SID, add ________ and _________

SOD, OID

object of magnification = ____________ minus ____________ divided by ___________ times 100

image size, object size, object size

_______________________ = image size - object size, divided by

object size, times 100

object of magnification

______________________________ = image size/MF

object size

_________________ = SID/SOD

magnification factor

_________ = SID - OID

SOD

_________ __________ results from inaccurate central ray alignment, the part itself, or divergence of the beam

shape distortion

any misalignment of the CR from these three factors -tube, part, or IR - will alter the ________ of the part recorded

shape

___________ is when objects appear longer

elongation

____________ is when the object appears shorter

foreshortening

elongation occurs when the _______ or _______ is improperly aligned

tube, IR

foreshortening occurs when the _________ is improperly aligned

patient

___________ is the most common type of shape distortion

elongation

The only true part representation is what is directly under the CR

true

In general, shape distortion is _______________

undesirable

tube angle always causes _____________, it never will cause _____________

elongation, foreshortening

elongation is used to ________ or ________ out pathology

distort, draw

elongation is used to _____________ anatomy

un-superimpose

radiographic images are most accurate when ___________ or __________ relationships are obtained

orthogonal, right-angle

_____________ can cause or avoid shape distortion by central ray, part and IR

alignment

To avoid distortion, part and IR must always be _______ and the CR must always be ______________

parallel, perpendicular

you may use creative ___________ to ensure the part and IR are parallel and the CR is perpendicular

positioning

CR should be _____________ to the part and IR

perpendicular

If CR is not perpendicular, some degree of _________ __________ will result

shape distortion

anything not positioned at the central ray will be __________ because of ____________

distorted, divergence

the greater the distance from the CR, the ___________ the distortion

greater

The long axis of the part is to be positioned _____________ to central ray and ___________ to IR

perpendicular, parallel

____________ is caused by poor alignment of tube and/or IR

elongation

_____________ is caused by poor alignment of part

foreshortening

IR should be positioned ______________ to the CR and ___________ to the anatomical part

perpendicular, parallel

elongation will occur when the CR and IR are not _____________

perpendicular

___________ is the direction of degree the tube is moved from its normal position perpendicular to the IR

angulation

angulation can cause a controlled or expected amount of shape distortion to avoid ______________

superimposition

cephalic = ____________

toward head

caudal = ___________

toward feet

transversely = _________

roll

maintaining correct degree of rotation is important for specified exams to decrease excess ______________

distortion

Shape distortion is ___________ and can't be ______________

subjective, calculated

image appearance includes size (_____________) and shape (_______________/_____________)

magnification, elongation/foreshortening

all magnification involves a degree of loss of ____________

resolution

when magnification is increased, spatial resolution ____________

decreases

____________ ___________ is the degree of geometric unsharpness/accuracy of the structure lines recorded

recorded detail