west test 4 chapt 16

Image quality definition

The Fidelity, with which the anatomy under investigation is rendered on the image receptor

The four interrelated categories of image quality are

Spatial resolution, contrast resolution, geometric factors, subject factors

High-quality images should always

Demonstrate structure and tissues

The scriptures/characteristics of image quality

Spatial resolution, contrast resolution, noise, artifacts, speed

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

Define resolution

The ability to image, small objects that have high subject contrast, such as a bone-soft tissue interface, a breast microcalcification, or a calcified lung nodule

Spatial resolution definition

The ability to image, small objects that have high subject contrast, such as a bone, soft tissue interface, a breast microcalcification, or a calcified lung nodule

Spatial resolution improves with decreased

Pixel size, focal spot size on patient, motion

Can you image an object smaller than the size of a pixel?

No

Contrast resolution is considered

More important than spatial resolution for most imaging modalities

Define contrast resolution

The ability to distinguish anatomical structures of similar subject contrast

High subject contrast can image smaller objects than low

Subject contrast

Contrast resolution is improved by

tight collimation, lowering kVp, patient compression

With x-ray imaging

Contrast resolution improves at lower KVP

With nuclear medicine

Contrast resolution improves with increased metabolic activity

With MRi

It's considered to have the best contrast resolution

Noise is the

Random fluctuation of x-ray interaction on the IR

With lower noise

You get improved contrast resolution

Quantum mottle

refers to the random nature by which x-rays interact with the IR

Quantum Mottle

Is the principal contributor to image noise?

To reduce quantum mottle

high mAs

low kVp

slower IR

Radiator port

To reduce patient dose of radiation

How do you reduce the dose?

Use high KVP low MAS and high speed IR

Quantum mottle

To reduce QM or noise

What does speed refer to?

To how the IR response to a quantity of radiation

What does speed influence?

Spatial resolution, contrast resolution, and noise

Slow speed IR gives

High contrast images

First IRS have

High noise and low contrast resolution

Low noise accompanies

Slow IRS and high contrast resolution

Magnification definition

When objects appear larger than they actually are

What two factors decide magnification

Sid and oid

Distortion definition

When object size and shapes are different than they actually are

Blur definition

Focal spot blur occurs because the focal spot is not a point

Magnification factor formula

image size/object size = SID/SOD

SOD=

Sid - oid

When minimizing magnification what do you need?

Large Sid and small OID

What is distortion in radiographic imaging?

It refers to unequal magnification of different portions of the same object

What does distortion depend on?

1. object thickness

2. object position

3. object shape

Thick objects are more

Distorted than thin objects

If the object plane and the image plane are not parallel

distortion occurs

What are the two types of distortion

Elongated and four shortened

elongated distortion is

When the object in the image appears longer than it actually is

Foreshortened distortion is

When the object in the image appear shorter than it actually is

Distortion is also

Misrepresentation of an anatomic structure on an image receptor in terms of size and shape

Spatial resolution/recorded detail is

The sharpness of anatomic structures displayed on an image receptor

X-rays are produced on a ________ shape area on the focal track

Rectangular

Focal spot blur is smaller on the

Anode side and larger on the cathode side of the IR

To minimize focal spot blur

-use small focal spots

-use short OID

-use longer SID

Patient related factors that affect medical image quality are

Subject factors

What are the subject factors

•Subject contrast

•Patient thickness

•Tissue mass density

•Z #

•Object shape

Radiographic contrast

It's the difference between adjacent densities mathematically it's represented as D2-D1

Radiographic contrast ranges from

White to various shades of grey and black

Rad contrast is the

Product of image contrast x. Subject contrast.

What makes up radiographic

Subject contrast and ir contrast

The formula for rad contrast

Subject contrast x ir contrast

Subject contrast is

The range of differences in the x-ray beam after attenuates the subject

What is subject contrast dependent on

KVP, patient thickness, type of material radiated, effective atomic number of the tissue, object shape

IR contrast definition

The range densities that the image receptor is capable of recording

What are examples of low subject contrast

Abdomen and breast

What is an example of high subject contrast

Chest, involves high kvp and low MAs to add grays

What are the types of opacity

Radiopaque and radiolucent

What is radiopaque

It absorbs X-rays and has high effective atomic number

What is radiolucent

It attenuates few x rays and appears white and has low atomic number

When can blur occur

The patient or x-ray tube moves during an exposure

Patient motion is most usual

Cause of motion blur

What are the two types of motion blur

voluntary and involuntary

How to reduce motion blur

Use the shortest possible exposure time

Tools for improved image quality

Patient positioning, image receptors, and selection of technique factors

Proper patient positioning

Place body close to ir, use short oid and long Sid, and immobilize patient

What is density

Overall blackness on the radiograph

What is contrast

The difference in density of adjacent areas on a radiograph

mason

Milliamperage per second, quantity of radiation

Kccl

Kvp controls contrast and quality of radiation

Receptor exposure definition

The amount of radiation striking the ir, it directly determines the quality of the digital image

No amount of MAs can compensate for

inadequate kVp

High kvp has

Short wavelength, more penetrability, long scale, low contrast, many shades of gray, wide latitude

Low kvp

Long wavelength, less penetrability, short scale contrast, high contrast, few shades of grey, narrow latitude

Kvp controls

Quality, controls scale of contrast ,penetrating ability

MAs

Controls quantity, density

High contrast

Fewer shades of gray, increased contrast, low kvp, short scale contrast, improved contrast, narrow latitude

Low contrast

Many shades of gray, decreased contrast, hi KVP, long scale contrast, not improved contrast, wide latitude

Radiography

The medical science of using x-rays as a probe sent through the body to obtain information about the patient state of health

Remnant radiation exits the patient and carries the information to the

Ir

Radiograph

External display of patient information displayed on a view box

Latent image

Invisible image on film after exposure prior to processing with chemicals or read with an image reader

Manifest image

Visible image on radiograph after processing or image on monitor

15 percent rule for object density

To double od increase kvp 15% and don't touch mass and for decreased of decrease kvp and don't touch mass