Image Production - Acquisition & Technical Evaluation

DEL Pitch

the distance from the center of one DEL to the center of the next

DEL Pitch vs Pixel Pitch

-DEL Pitch -> in detector

-Pixel Pitch -> in monitor

Quantization

takes electrical signal and turns them into digital bits of info. Occurs during ADC. Displays a specific brightness on screen

Bit depth

total number of possible brightness levels (shades of gray) that can be assigned to any individual pixel in the image

Detective Quantum Efficiency (DQE)

how efficient a system converts a input signal into a useful output image (measure QUALITY of digital image)

What has the highest DQE?

Direct DR (only 2 steps)

8 bits = ____ possible values for the density of each pixel

256

10 bits = ____ possible values for the density of each pixel

1024

Histogram

-graphical display of the pixel intensity distribution for a digital image

-frequency of recorded exposure values

histogram analysis

A process in which a computer analyzes the histogram using an algorithms and compares it with a pre-established histogram specific to the anatomic part being imaged

____ determine the range of the histogram data set that should be included in the display image

VOI - value of interest

Look up table (LUT)

a series of mathematical equations that are used for image processing in radiography

LUT is the controller of what?

digital contrast

Rescaling

A digital processing technique that is used to modify an overexposed or underexposed image

Dead pixel

Pixel w/ a malfunction or sensor error

Dead pixel correction

using a software technique, dead pixels are identified in the matrix and then removed from all subsequent images

flat fielding

dead pixels are removed from the matrix by making a mask of the dead pixels

edge enhancement

increases the contrast along the edges of the structure

edge enhancement helps improve _________ _______. Excessive use can cause "_______ ________".

-visibiity of details

-halo artifact

equalization

process by which soft tissue and bone are enhanced so all the information within a region of interest can be seen

smoothing: what does it do? what are other names for smoothing?

-used to mask the quantum noise in an image.

-noise supression, low pass filtering

windowing

Ability to alter the brightness and contrast of a digital image, following processing

window level

Adjusts brightness of the displayed image.

window width

adjusts contrast of the digital image

Wider the width, ______ the contrast

lower (long/more gray shades)(wide grey elephant)

narrow width, _____ the contrast

higher (short scale - more B&W) (short b&W penguin getting high)

shuttering

postexposure image manipulation that adds a black background to the original collimation edges

image inversion

Make white-black and black-white (used to view lines)

image subtraction

technique used in IR to clearly visualize blood vessels in a bony or dense soft tissue environment - removes bones

PACS (Picture Archival and Communication System in Medicine)

allows user to acquire, transmit, store, retrieve and modify digital images taken in all modalities of the radiology department

DICOM (Digital Imaging and Communications in Medicine)

-enables integration of scanners, workstations, printers

HIS (Hospital Information System)

patient information stored in hospital database

RIS (Radiology Information System)

radiology specific database

EMR (electronic medical record)

an electronic document that contains patient health information, gathered from different sources

geometric factors

Factors that affect the information recorded on the radiographic image receptor.

spatial resolution

ability of an imaging system to display two closely spaced objects as separate

Distortion

misrepresentation of the true size or shape of an object (size or shape)

why do we use a 72" SID for lateral C-spine?

reduces OID

size distortion = ___________. Controlled by OID & SID.

Magnification

_______ is the main controlled of magnification

OID

What SID helps reduce magnification? Examples of anatomical positioning that helps reduce magnification?

-72"

-PA Chest - reduces heart size

-PA skull - reduces magnification of orbits

Shape distortion= _____________& ______________. Controlled by what?

-elongation & foreshortening

-IR , X-ray tube, anatomical part

Magnification Factor formula: MF=

-SID/SOD (SOD = SID-OID)

Formula for calculation for object size or image size

image size/ object size = MF

Elongation - part will appear _____. Results from angling the _____ & ____.

-longer

-tube & IR

Foreshortening - the part appears __________. Results from angulation of the ________.

-shorter

-anatomy/part

Elongation used with what two projections to help visualize anatomy?

-AP Towne Skull

-axial calcaneus

what would be used to minimize size distortion?

Decrease OID & Increase SID

3 multiple choice options

If OID is decreased, what is the effect on spatial resolution? what is their relationship?

-Spatial resolution increases

-inverse relationship

IF SID is increased, what is the effect on spatial resolution? what is their relationship?

-Spatial resolution will increase

-direct relationship

If the FSS is decreased, what is the effect on spatial resolution? What is their relationship?

-increased spatial resolution

-inverse relationship

Penumbra

unsharpness or blurring at the edges of an object

Penumbra more significant at what SID? (40" or 72")

40"

what is voluntary motion? how is it reduced?

-Motion under the control of the patient (breathing)

- effective communication

what is involuntary motion? how is it reduced?

-motion patient is unable to control (cardiac)

-short exposure times

Why would an increase in pt size decrease spatial resolution?

-larger pt = larger OID

-larger OID = magnification

-larger pt = increased thickness/size = scatter

Tube, part or IR angulation will result in a form of distortion. If you decrease the angle of the part, what happens to spatial resolution?

-spatial resolution increased

Increasing Pixel size does what to Spatial resolution?

decreases

Increasing DEL size does what to Spatial resolution?

decreases

Increasing PSP plate (CR plate) size does what to Spatial resolution?

decreases

When using CR its important to select the ________ IR possible for the part. Why?

-smallest

-improves spatial resolution

Increasing Sampling frequency (done by laser in CR equipment) does what to Spatial resolution?

increases

Increasing matrix does what to Spatial resolution?

increases

Nyquist frequency

Relationship between sampling frequency and Spatial resolution

minimum of ____ lp/mm for diagnostic image quality

2.5

spatial resolution is _____ limited in DR

pixel

What is Modulator Tranfer Function (MTF)? Best measurement of what?

-ability of a system to record available spatial frequencies

-spatial resolution

contrast

difference in brightness levels between adjacent structures

Digital image contrast is primarily controlled by the _______________

Look up table (LUT)

Receptor exposure

amount of radiation passing through the patient and hitting the IR (both primary & secondary radiation)

Receptor exposure primarily controlled by ____

mAs

Short scale contrast

-mainly B&W

-low kVp

-High contrast

-"Short b&w penguin likes to get high"

Long scale

-lots of grays

-high KVp

-low contrast

-"Gray big elephant"

9 factors affecting subject contrast

1.kVp

2.Pt size

3.Part density

4.Pathology

5.Contrast media

6.Grids

7.OID

8.Filtration

9.Collimation

kVp has an _______ relationship with absorption

inverse

as kVp increases, ______ ________ decreases

differential absorption

increasing kVp results in increased ______

scatter

high scatter = _______ contrast

low (more gray)

attenuation

The reduction in the intensity of the x-ray beam as it passes through matter, as a result of absorption, scatter and divergence

differential absorption

different objects absorb radiation differently

actors that affect attenuation

-differential absorption

-thickness of the body part

-type of tissue (Atomic #)

-kVp

Additive disease: examples and how do we adjust technique?

-Pleural effusion

-Ascites

-osteopetrosis

-osteoscleoris

-Edema

-Increase technique

-*Fluid is heavier*

Destructive disease: examples and how do we adjust technique?

-Atrophy

-Pneumothorax

-Osteoporosis

-Decrease technique

-*air less dense*

Types of contrast agents:

positive and negative

Positive contrast agent

-Barium

-higher atomic #

-appears white

-absorbs more photons

Negative contrast agents

-air

-lower atomic #

-appears black

-less absorption

Technique that is typically changed is ______

mAs

Grids improve contrast by blocking _______ from reaching the IR

scatter

The higher the grid ratio, the _____________ the patient dose

higher

stationary grid

table top or mobile/portable radiography

crossed grid

-crosshatch pattern using 2 parallel grids

-used in specials

parallel grid

A grid with strips that are parallel to each other, rather than focused.

Focused grids

-lead strips angled to coincide w/ divergence of beam

-Focal range - specific SID

Grid ratio

the ratio of the height of the lead strips to the distance between them

grid ratio formula=

height/distance between them

grid frequency

The number of grid lines per inch or centimeter

most common error in the use of grids is

improper positioning

upside down grid error

severe grid cutoff on both sides of the image - usually happens w/ focused grids

which grid error results in grid cut off and loss of exposure on the outside edges of the IR?

incorrect SID w/ focused grid

angulation grid error

overall lowering of receptor exposure over the entire image