UNIT 4 TECHNICAL FACTOR SELECTION study guide

When using AEC, increasing the SID will result in a shorter exposure time True or false

False

spatial frequency processing

Sharpness control

When using AEC, density settings should only be used with extreme patient conditions (ie. size/pathology). T or F?

True

amplification or high-pass filtering increases

contrast and edge enhancement -Useful for organs and soft tissue

Leveling

controls brightness -"how dark or light" -Think Bleveling for brightness + leveling (sandy taught us)

Windowing

controls contrast -"the ratio of black to white, or contrast"

Contrast-enhancement parameters

convert the digital input data to an image with appropriate density and contrast

Photomultiplier tube (PMT)

converts the light into electric current in proportion to the amount of xray exposure. -utilizes only 1 sensor

Contrast-enhancement parameters allow

enhancement of the image by controlling the steepness of the exposure gradient, density variance, and contrast amount.

When radiographing a patient with a potential bowel obstruction, what effect might this cause exposure time?

exposure time would be short -Because bowel obstruction fills the anatomy with air.

Too few mAs regardless of the kVp is will result in _____________

insufficient phosphor stimulation -which will produce a grainy image. quantum mottle or quantum noise

When using AEC, what are the components that detect the radiation exposure?

ionization chambers

variable kVp- Fixed mAs

kVp can be increased as the anatomic part size increases

Edge enhancement is accomplished by

limiting the number of pixels in a neighborhood of the matrix -Amplification of frequencies in area of interest only

Electrical capacitor

stores up electrical charge

The Nyquist theorem is applied to digital images to ensure that

sufficient signal sampling occurs so that maximum resolution is achieved

AEC definition

system used to consistently control the amount of radiation reaching the IR by terminating the length of exposure

mAs readout

the actual amount of mAs used for that image is displayed immediately after exposure

MTF refers to

the contribution of all system components to total resolution. The closer the MTF value is to 1, the better the resolution.

Collimating excessively can lead to

the exposure time would be longer than necessary

The more you manipulate a photo the greater ______

the loss of information

minimum response time (MRT)

the shortest exposure time that the system can produce

Proper patient demographic input is the responsibility of

the technologist performing the exam

Low pass filtering and smoothing are the same function in digital imaging systems. T or F?

True

Low pass filtering is useful for enhancing small anatomic structures.

True

Image manipulation

(manipulating the image post processing) -Window and level (most common controls) -Background removal or shutter -Image orientation -Image stitching -Image annotation -Magnification

Phototimers

*Not commonly used today Light paddles coated with material that when interacting with radiation produces a visable light. The light is transmitted to PMT tube (or photodiodes) that convert the light to electricity. The exposure is terminated when sufficient charge has been recieved. Summary: Xrays interact with light paddle > light is produced > Photomultiplier tube converts to electricity > triggers timer > exposure stopped.

Disadvantages of variable kVp- Fixed mAs

-Anatomic part penetration not guaranteed. -Changing kVp less effective for range of procedures -Less accurate for part size extremes

Advantages of Fixed kVp-Variable mAs

-Part measurement less critical -Increased accuracy with range of procedures -More consistent image contrast and overall quality -Part penetration assured

Image Management

-Patient demographics input -Manual send -Archive query

Patient Demographics Input issues

-Problems occur if the patient name is entered differently from visit to visit or exam to exam -Merging of files can be difficult.

Backup time

-Protects the equipment from overload & the patient from over exposure -The maximum length of time the xray exposure will continue when using the AEC

What factors should be included on a technique chart?

-kVp -mAs -Grid ratio

What are the advantages of using the 15% rule in order to reduce mAs?

-lower patient absorbed dose -less chance of motion -less heat load to the anode

What factors cannot be considered when designing a technique chart?

-patient pathology -patient condition -patient's ability to cooperate

In AEC, what is the purpose of the back up timer?

-protect the patient from overexposure -protect the tube from overheating -Cuts off the exposure in the event of an error

magnifying glass

A box is placed over a small segment of anatomy on the main image & shows a magnified version of the underlying anatomy can be made bigger or smaller

Ionization chamber

A hollow cell that contains air and is connected to the timer circuit via an electrical wire. Ionization chamber exposed to radiation and the air inside becomes ionized which creates an electrical charge. charge travels down wire to the timer. When sufficient charge is reached exposure is terminated. ** Uses 3-5 censors (cells) Summary: Radiation hits the air-filled sensors located in front of the cassette > the air becomes ionized > creates electrical current > current travels down wire > timer is tripped when sufficient amount of charge is reached > exposure is terminated.

Afterthe plate is scanned and the image location and orientation are determined ___

A value is placed on each pixel, and the histogram is generated displaying the minimum and maximum diagnostic signal (S1 & S2)

Density controls (-2, -1, N, +1 +2) or (S,M,L)

Allows radiographer to adjust the amount of preset radiation detection values for extremes in patient body habitus or pathological condition.

Anatomically programmed techniques

Allows the radiographer to to select a button on the control panel that represents an anatomical area that has pre-programmed set of exposure factors and AEC detectors to be used. These can be adjusted if needed to.

Low-pass filtering or smoothing decreases

Contrast and noise , allowing small structures to be seen. -useful for viewing small structures such as fine bone tissues

Patient Demographics Input

Demographic information about the patient: -Name -Health care facility -Patient identification number -Date of birth -Exam date -Input/linked via barcode label scans, before the start of the exam and before processing phase (CR only) -demographic information can be altered at the processing stage if needed -Proper entering of demographic information helps link patient files.

Advantages of variable kVp- Fixed mAs

Easy to construct and simple to use. At low kVp levels, small changes in kVp more effective

Two Types of Spatial Frequency Filtering

Edge enhancement & Smoothing

When using AEC, increasing the kVp will increase the exposure to the IR. True or False

FALSE. AEC terminates after a set exposure (charge) has been reached. Adjusting kVp or mAs will NOT affect exposure to the IR. Only changing density controls will change the exposure.

KvP controls radiographic contrast. True OR False

FALSE. Look up table controls contrast

Spatial frequency resolution is controlled by

FSS, OID, and computer algorithms

AEC and phototiming are one and the same. T or F ?

False

Archive Query

Function allows retrieval of images from the PACS system based on the following: -Date of exam -Patient name or number -Exam number -Pathologic condition -Anatomic area ex: you can search all chest radiographs or look up all exams on a specific date.

Which type of technique system is consistent with ALARA?

Low mAs/High kVp "as low as reasonably achievable"

Two types of Functions of the Processing System

Image manipulation and Image management

Stitching

Images are processed in computer programs that nearly seamlessly join the anatomy is used for anatomy or areas of interest too large to fit on one cassette Examples: scoliosis, bone length, extremity venograms

overexposure in digital imaging can lead to

Increase in patient exposure & can decrease contrast

Image Annotation

Information other than standard identification must be added to the image -allows selection of preset terms and/or manual text input ex: Time and date stickers & Upright/decub May not transfer to PACS

Fixed kVp-Variable mAs

Optimal kVp value for each part is indicated, and mAs is varied as a function of part thickness

Disadvantage of Fixed kVp-Variable mAs

Optimal kVp values not standardized

AEC process

Radiation is transmitted through the patient & converted into an electrical signal terminating the exposure. ***

Background Removal or Shutter

Removal of the white unexposed borders. -Results in an overall smaller number of pixels -Reduces the amount of information to be stored

Exposure technique charts

Standardized exposure factors for the typical patient so that the quality of images is consistent

masking

Suppression of frequencies -result in loss of small details -technique is useful for enhancing large structures such as organs and soft tissues but can be noisy

When using AEC, increasing the kVp will result in a shorter exposure time True OR False

TRUE. increasing kVp increases penetration from the tube to the IR. The beam is less attenuated by patient anatomy and reaches the AEC cells quicker terminating the exposure faster.

veil glare

Unexposed borders around the collimation edges allow excess light to enter the eye -Which causes oversensitization of a chemical within the eye called rhodopsin -results in temporary white light blindness

When using AEC, if the exposure needs to be adjusted, what can be done?

Utilize the density settings

two types of exposure technique charts

Variable KvP - fixed mAs & Fixed KvP - variable mAs

zoom

allows magnification of the entire image Image can be enlarged enough that only parts of it are visible on the screen

manual send

allows the quality control technologist to select one or more local computers to receive images. -quality control workstation is networked to the PACS, it also has the capability to send images to local network workstations

In digital imaging, labeling an image with text is referred to as:

annotation

In digital imaging, what controls image brightness?

automatic rescaling

Smoothing AKA low-pass filtering

averaging of the frequency of each pixel with surrounding pixel values to remove high-frequency noise -Result is a reduction of noise and contrast -useful for viewing small structures such as fine bone tissues

the only logical way to alter the resulting exposure using AEC

density controls -This readjusts the thyratron to higher or lower amounts of charges to activate when to shut off the exposure. -adjusting Ma or kVp will NOT be effective in altering the exposure

Casts and splints require a(n) ___________ in exposure factors

increase

Bariatric patients need a(n) _______________

increase in kVp and mAs - require a grid, may need to be imaged in quadrants

two types of Magnification

magnifying glass & zoom

The higher kVp, the greater amount of _______

noise

Edge Enhancement

occurs when fewer pixels in the neighborhood are included in the signal average.

High kVp/Low mAs minimizes

patient exposure

the two types of AEC are

phototimer and ionization chamber

Automatic rescaling allows

pixel display for the area of interest -regardless of the amount of exposure unless the exposure is too low or too high. In those cases, quantum mottle or contrast loss occurs

thyratron

presents the amount of charge a capacitor will hold - is responsible for actually terminating the radiation exposure when using AEC -can only be adjusted by density controls

Recognition of exposure data involves

processing only the optimal exposure range and generates a graphic representation or histogram of the optimal grayscale

Amplification AKA high-pass filtering

results in an increase of contrast and edge enhancement

masking can cause

small detail loss -Suppression of frequencies of lesser importance

underexposure in digital imaging can lead to

visibility of quantum noise & mottle