Bontrager Chapter 1- Part 2

Analog Imaging

-analog images provide a two dimensional image of anatomic structure

- the image device is a film screen system that consists of a pair intensifying screens with a film in between them.

hard copy image

also referred to as the film image

- is composed of a deposit of metallic silver on a polyester base and is permanent; it cannot be altered.

analog image receptors are best described as

self regulating systems with a limited dynamic range.

-they are also described using the term exposure latitude.

what are exposure factors also known as?

technique factors

What are the exposure factors?

Kilovoltage (kV)

Milliamperage (mA)

Exposure time (ms)

What is kilovoltage?

Controls the energy ( penetrating power) of the X-ray beam.

-can also be referred to as kilovoltage peak (kVp)

What is the kilovoltage peak? kVp

-The maximum electrical potential used to create the X-ray photons within the tube.

-(the penetrator)

-kilovoltage peak

What is milliamperage?

Controls the number of X-rays produced

What is exposure time?

Controls the duration of the exposure usually exposed in milliseconds

What are the four image quality factors?

Density/brightness

Contrast/adjacent shades

Resolution/detail

Distortion

What is density?

The amount of blackness on the processed radiograph.

-when an image with high density is viewed, less light is transmitted through the image.

If your image is too dark?

1/2 the mass or decrease the KV by 15%

if your image is too light?

double the mass or increase the KV by 15 %

15 % change rule in KV example:

80 KV x .15= 12 kv

12+80=90KV

What is the primary controlling factor of film density?

mAs

It controls density by controlling the quantity of X-rays emitted from the tube and the duration of the exposure.

What is SID?

Source to image receptor distance

What is the general rule for under or over exposed repeat images?

Minimum of 25-30% change in mAs is required to make a visible difference.

* sometimes even doubling mAs is necessary

Examples of over/under exposed

Example of over/under exposed

What is the anode heel effect?

The intensity of radiation emitted from the cathode end of the tube is greater than that emitted at the anode end.

-greater attenuation or absorption of xrays occurs at the anode because of the angle of the anode.

Application: the patient is positioned so that the thicker parts are under the cathode of the tube and the thinner parts are under the anode.

Angle of anode

xrays are emitted from deeper within the anode and must travel through more anode material before exiting.

How should you position the patient using the anode heel effect?

The thicker portion of the part should be positioned at the cathode, thinner part under anode.

anode heel effect image

summary of anode heel effect application

look at chart on page 40

What is a compensating filter?

It filters out a portion of the primary beam toward the thin or less dense part of the body that is being imaged.

wedge filter

-mounts on the collimator; thicker portion of the wedge is placed toward the least dense part of the anatomy to even out the densities.

-thicker part under the toes for a foot

-numeric applications: most common include the AP foot, AP thoracic spine, and axiolateral hip

trough filter

-mounts on the collimator and is used for chest imaging

-has a filter on both sides

-the thicker portions of the filter are placed to correspond to anatomically less dense lungs

-the thinner portions of the filter correspond to the mediastinum

Boomerang filter

placed behind the patient and is used primarily for a shoulder and upper thoracic spine

-it improves visualization of soft tissues

What is radiographic contrast?

Differences in density level between adjacent structures of a radiographic image.

Controlling factor is kV

-can be referred to as long scale or short scale contrast referring to the total range of optical densities from the lightest to the darkest part of the radiographic image

When the density difference is large the contrast is what?

High contrast - short scale

When the density difference is small the contrast is what?

Low contrast -long scale

Why is radiographic contrast important?

It allows you to see anatomic detail. It allows you to visualize a quality image.

primary controlling factor for contrast in film based imaging is:

kV

-kV controls the energy or penetrating power of the xray beam

high kV produces less attenuation resulting in ______?

lower contrast

When is it recommend that you use a grid?

On any body part that is thicker than 10 cm. Grid absorbs scatter radiation

-it is positioned between the patient and the IR and absorbs much of the scatter radiation before it hits the IR.

Compton scattering

Interaction with matter in which a higher energy photon strikes a loosely bound outer electron, removing it from its shell, and the remaining energy is released as a scattered photon

-the scattering we as techs protect ourselves from

grid cutoff

incorrect use of grids resulting in loss of density across all or part of the radiographic image

4 causes of grid cut off

1. off-center grid

2. off-level grid

3. off-focus grid

4. upside-down grid

off center grid

-The CR must be centered along the center axis of the grid.

-if it is not lateral decentering is said to occur

-the more the CR is off center the greater the cutoff

results in overall decrease in image density

off-level grid

-with angling, the CR must be angled along the long axis of the lead strips.

-transverse tilted grid, results in overall decrease of image density

off focus grid

-a focused grid must be used at a specific SID if grid cutoff is to be prevented

-grids usually have a min and max SID called the focal range

-the focal range is determined by the grid frequency and grid ratio

upside down focused grid

-each grid is labeled to indicate the side that must be positioned to face the x ray tube

-the lead strips are tilted or focused to allow the xray beam to pass unimpeded

-if the grid is positioned upside down the image will show severe cutoff (grid not correctly placed; the right side is not up)

What is spatial resolution?

-Recorded sharpness of structures on the image.

-resolution is known as detail, image sharpness, or definition (being able to see the smallest of things)

-lack of visible sharpness or resolution is known as blur or unsharpness

Spatial resolution is controlled by what?

Geometric factors

Film screen system

Motion

What is the greatest deterrent to image sharpness?

Motion.

Voluntary and involuntary

Voluntary motion vs. involuntary

-Voluntary-motion in which the patient can control; motion from breathing or movement of body parts during exposure can be prevented or minimized by controlled breathing and patient immobilization such as tape, sponges, sandbags.

-Involuntary motion: includes peristaltic action, tremors, or the chills and is almost impossible to control.

what is the best way to reduce voluntary motion on a radiograph?

give the patient a thorough explanation of the procedure with well explained instructions.

what is the best way to control voluntary motion on a radiograph?

short exposure time

Voluntary motion image

Involuntary motion image

4 ways to control image quality

1) small focal spot- use whenever possible to improve detail

2) short exposure time- used to control voluntary and involuntary motion

3) SID- use longer SID to improve resolution

4) OID- use shorter OID to improve resolution

What do you need to get the best image?

1- small focal spot

2- long SID (increase SID)

3- short OID (decrease OID)

small focal spot

results in less geometric unsharpness or (penumbra)

- makes a clear image; with greater detail

large focal spot

results in more geometric unsharpness or (penumbra)

-makes a fuzzy or blurry image

penumbra

unsharp edges in the projected image

What is distortion?

a misrepresentation of object size and shape

two types:

1. size distortion (magnification)

2. shape distortion

central ray

the center point of the x ray beam

What are the 4 primary controlling factors of distortion?

1) source image receptor distance (SID)

2) object image receptor distance (OID)

3) object image receptor alignment

4) central ray alignment

1.) SID

-less magnification occurs at a greater SID than at a shorter SID

-this is the reason chest x rays are performed at 72 inches instead of 40 inches because of less magnification

2. OID

the closer the object being radiographed is to the IR, the less are the magnification and shape distortion and better is the resolution.

3. Object image receptor alignment

the alignment or plane of the object that is being x rayed in relation to the plane of the IR.

-if the object is not parallel to the plane of the IR it causes distortion.

4. central ray alignment

the least possible distortion occurs at the Central ray.

It is important to have correct positioning

How is a digital image formed?

By a matrix of pixels.

Pixel is the smallest unit, they make up rows and colums which forms the matrix.

The higher number of pixels you have makes what better?

Resolution!

mA

controls the number of x rays produced

mAs (mAx time)

refers to the number of xrays and the duration of exposure.

kV

controls the penetrating power of x-rays

What are the image quality factors in digital radiography?

1- brightness

2- contrast resolution

3- spatial resolution

4- distortion

5- exposure indicator

6- noise

What is brightness?

Intensity of light representing individual pixels in an image

What are the controlling factors for brightness?

in contrast to the linear relationship between mAs and density in film-screen imaging changes in mAs do not have a controlling effect on digital image brightness

pixels and bit depth

The greater the bit depth of a system, the greater is the contrast resolution (ie, the greater is the number of possible shades of gray that a pixel can have)

What is contrast resolution?

Differences in brightness between light and dark areas of an image

spatial resolution

in digital imaging is defined as the recorded sharpness or detail of structures on the image.

-controlling factors: pixel size (inherent to the IR. the smaller the pixel size the greater the spatial resolution)

-resolution is controlled by the display matrix (depends on the capabilities of the monitor)

What is distortion in digital radiography?

Misrepresentation of object shape or size.

What are the controlling factors for distortion?

SID

OID

CR alignment

*same as analog

What is an exposure indicator?

A numeric value that is representative of the exposure the image receptor received.

-may be inversely or directly proportional to radiation striking the IR

- key in verifying optimal digital image is obtained with least dose to patient

How do you find out if your exposure indicator number is valid?

Each institution will have a chart that your number must fall between to be an acceptable image. Varies on who makes the equipment

What is noise?

Random disturbance that obscures or reduces image clarity.

-A high SNR is desirable in imaging, in which the signal is greater than the noise so that low contrast soft tissue images can be demonstrated.

- a low SNR is undesirable in imaging, a low signal with accompanying high noise obscures soft tissue detail and produces a grainy mottled image.

What is post processing?

Changing or enhancing the electronic image to improve diagnostic quality.

-Algorithms applied to improve diagnostic quality of image.

-post-processing cannot improve a low SNR image

What are post processing options?

1- windowing

2- smoothing

3- magnification

4- edge enhancement

5- equalization

6- subtraction

7- image reversal

8- annotation

windowing

two types of adjustment are possible:

1. window width: controls the contrast of the image

2. window level: controls the brightness of the image

smoothing

specific image processing is applied to reduce the display of noise in an image.

magnification

all or part of an image is magnified

subtraction

background anatomy can be removed to allow visualization of contrast media-filled vessels (used in angiography)

image reversal

The dark and light pixel values of an image are reversed-the x-ray image reverses from a negative to a positive

annotation

text may be added to images

What was one of the first applications of computers in radiography?

Computed tomography

PSP photostimulable storage phosphor

-was the first widely implemented digital imaging system for general radiography; commonly called computed radiography

-may be cassette based or cassette less

technologist work station

-includes a bar code reader, a monitor to display the image, a keyboard with a mouse

Application for using Computed Radiography or Digital systems

1. collimation- close and accurate collimation helps reduce the amount of radiation exposure to the patient

2. Accurate centering of part and IR- the body part should be centered to the IR and properly displayed.

3. use of lead masks- use of lead masks or a blocker is recommended when a cassette based CR is used

4. use of grids- use a grid for body parts thicker than 10 cm

direct radiography (DR) (Flat-Panel detector with thin-film transistor)

1. direct radiography is the second type of digital imaging system

2. commonly referred to as direct radiography or direct digital radiography

What does PACS stand for?

What is it?

Picture- digital medical images

Archiving- electronic storage of images

Communication- routing and displaying of images

System- specialized computer network that manages the complete system.

What does PACS do?

Sends images to different areas of the hospital

-an electronic storage system for patient information and pictures

what are the advantages of PACS?

1. elimination of less efficient traditional film libraries and their inherent problem of physical space requirements for hard copy images

2. convenient search and retrieval of images

3. rapid transfer of images with hospital

4. ease in consulting outside specialists

5. viewing images at multiple locations

6. elimination of misplaced or damaged films

what does PACS stand for?

Picture Archiving Communication System

What is DICOM?

The current standard that ensures all manufactures and types of equipment are able to communicate and transmit images effectively.

what does HIS stand for?

Hospital Information System

what does HL7 stand for?

Health Level 7

What does RIS stand for?

Radiology Information System

What does IP stand for?

image plate