Upgrade to remove ads
Only $35.99/year

Test 3 study guide

Terms in this set (64)

What is the AEC and what does it do?
Measures the quantity of x rays that reach the receptor and it terminates the exposure when the
correct amount of radiation intensity is reached
How does AEC adjust for patient size and adjust to get proper density
The AEC measures the exit radiation and adjusts the exposure time to produce proper OD on the
image and adjust for patient size
How does the AEC work control panel wise and what does the technologist set?
The tech sets the kVp, mA, backup time, and photocells specific to body part
What are the 2 types of AEC's?
Ionization chamber and photodiode
Explain Ionization chambers, what they are, how are they oriented, and how they work?
They are the most common, they are flat plates placed on top of IR, ionization creates charge in
the chamber and when peak charge is reached the system stops ionization.
Explain photodiodes in AEC, what they are, how they are oriented, and how they work?
Solid state detector which is placed on the back of the IR behind a fluorescent screen, they
convert light into electrical charge and when enough charge is reached it terminates the beam.
AEC's have 3 "photocells or photo timers" which are rectangular detectors and they are chosen by
the tech specifically set for certain body parts
...
What happens when more than one cell is chosen?
The cell that receives the most radiation will have the greatest electrical signal and influence on
the density of the image
Certain body habitus' and pathologies require an addition or subtraction of density which is set by
the tech, for example pneumonectomy requires a reduction in density, and pleural effusion requires
an addition
...
In AEC what does APR stand for and what does it do?
APR stands for anatomically programmed radiography and you select the body part and it sets
the kVP, mA, backup time, and photocells for you
What are AEC backup timers and why are they important?
They act as the timer for the shutoff of the exposure in case the AEC fails to do so, it also
prevents damage to the tube and overexposure to the patient
Name advantages of AEC
Reproducibility, less repeats, flawless images, less chance of over/under exposure
What is tomography and what does it do?
It is a technique used to improve visualization of certain objects by blurring out others around it
Main advantage of tomography?
improve contrast resolution
What is the fulcrum in tomography and what does it define?
The fulcrum is the pivot point for the tube and IR and it defines the object plane
What main body parts is tomography used for? What new technique is used as an alternative to
tomography?
Kidneys (IVP), TMJ, mandible (panorex), and the new technique was a breathing technique
What is the tomographic section?
Thickness of tissue to be imaged
What is the tomographic angle?
Determines the thickness of the part to be imaged
What is the object plane and how do structures appear inside the plane and above or below the
plane?
The object plane is the plane defined by the fulcrum and inside the plane objects are sharp on
images and above or below they are blurred.
What are factors that influence image blurring?
Sectional thickness, OID, exposure angle, alignment of anatomy to tube movement, distance of
object from object plane
Section thickness defines what? And is controlled by what?
It is the width of the object plane (the anatomy that won't be blurred)
Tomographic angle determines what? And larger angles produce what and small angles produce
what?
The amount of tube and IR motion, the larger the degree of movement the smaller the cuts, the
smaller the degree of turn the larger the cuts
Magnification in tomography is used to what?
Enhance visualization of small structures
Magnification increases what and what?
It increases OID and patient dose
Cuts are measured in what?
CM/MM
What kind of grids does tomography require and in what orientation?
Parallel grids that run along the length of the table
Quality Management:
Consists of QC and QA, system designed to monitor equipment and people
Quality Assurance:
pertains to people & services
examples: pt scheduling, image interpretation, outcome analysis
QA operates by: Identifying, monitoring and resolving the problem.
Largest accrediting body for hospitals: TJC
Accrediting body for imaging facilities: ACR (American college of radiology)
Most important steps to a QA tech:
monitoring problems includes: establish criteria, perform monitoring
test, collect, analyze and evaluate data.
Examples of QA questions: Is this the right exam for the patient? Has the patient been properly informed
of the exam? Was the report distributed in a timely fashion?
Quality Control:
pertains to monitor, equipment & instrumentation maintenance
Medical Physicist:
establishes and oversees the implementation of QC
Most involved step of QC:
monitoring equipment performance
-monitors technical equipment to maintain quality standards
-covers image producing and processing equipment
Prime responsibility of an xray tech:
ensure the quality of an image
Categories of QC: 1
Acceptance testing - sets the baseline on which all subsequent data will be evaluated. For newly
installed and repaired equipment. Performed by: tech, rad physicist and hospital service personnel
Categories of QC: 2
Routine maintenance- ensures performance as expected and catches errors. Performed by: tech, rad
physicist and hospital service personnel
Categories of QC: 3
Error maintenance - done when errors occur in performance. Performed by: vendor service personnel
QC Components - Screen film
1. Filtration
(who) Tested by? Medical Physicist
(what) What is tested? Determined by HVL
(where) Film & Digital
(when)Tested? Annually
(why)Limits? Minimum of 2.5mmAl
(how)Equipment used? Dosimetry equipment and Al sheets
QC Components - Screen film 2. Collimation (xray to light field alignment)
(who) Tested by? QA personnel
(what) What is tested? Collimation. Xray field must coincide with light field.
(where) Film & Digital
(when)Tested? Semiannually
(why)Limits? Within 2% of SID
(how)Equipment used? Penny test or test object
QC Components - Screen film 3. Focal Spot Size
-measures spatial resolution of the of the xray tube
(who) Tested by? Medical Physicist
(what) What is tested? Focal spot/ resolution
(where) Film & Digital
(when)Tested? Annually (tube installed/replaced)
(why)Limits? +/- 50% of manufacturers specifications
(how)Equipment used? Pinhole camera (most difficult), slit camera (commonly used), star pattern(easy to
use but limited)
QC Components -4. kVp Calibration
-calibration is needed because 4 kVp is enough to affect image OD & contrast
(who) Tested by? Medical Physicist
(what) What is tested? kVp
(where) Film & Digital
(when)Tested? Annually
(why)Limits? Within 10% of indicated kVp (in CA 5%)
(how)Equipment used? Ion chamber or photodiode
5. QC Components -Exposure Timer
(who) Tested by? Medical Physicist
(what) What is tested? time
(where) Film & Digital
(when)Tested? Annually or after a big repair
(why)Limits? +/- 20% under 10ms or +/- 5% over 10ms
(how)Equipment used? Stopwatch or x-ray pulse counter
-AEC must be checked so that backup time never exceeds 6 seconds or 600mAs
QC Components 6. mA Linearity
-Any combo of mA + time that gives the same mAs should give the same exposure reading.
(who) Tested by? Medical Physicist
(what) What is tested? mAs
(where) Film & Digital
(when)Tested? Annually or after a big repair
(why)Limits? Within 10% error for adjacent mA stations
(how)Equipment used? Precision dosimeter
QC Components7. Reproducibility
-Errors are normally a result of kVp control
(who) Tested by? Medical Physicist
(what) What is tested? kVp
(where) Film & Digital
(when)Tested? Annually or after a big repair
(why)Limits? Within 5% for identical exposures
(how)Equipment used? Precision dosimeter
8. Intensifying Screens (screen/film contact)
(who) Tested by? QA Personnel
(what) What is tested? screen/film contact
(where) Only in film
(when)Tested? Annually or twice a year. Acute care facilities: weekly/ at least every other month.
(why)Limits? No blur in mesh
(how)Equipment used? Wire mesh test
9. Protective Apparel
(who) Tested by? QA Personnel
(what) What is tested? Leaded apparel (aprons, thyroid shields, gloves, lap shields)
(where) Film & Digital
(when)Tested? Annually
(why)Limits? Set by facility. Looking for cracks, holes or tears.
(how)Equipment used? Fluoro suite or C-arm
10. Film Illuminators
(who) Tested by? Medical Physicist
(what) What is tested? Viewboxes and monitors
(where) Only in Film
(when)Tested? Annually
(why)Limits? Intensity at least 1500 cd/m^2. +/-10% over entire surface of illuminator
(how)Equipment used? Photometer (measures light intensity)
QC Digital performance assessment standards
-developed to standardize soft copy digital display device performance standards
SMPTE:
Society of motion picture and television engineers
-recommended by ACR to evaluate resolution and luminance of digital monitor display
-In combination with a photometer (2 types)
1. Near range: Used in close proximity 2. Telescopic: used at a distance of 1m
-Luminance measured in cd/m2
AAPM TG18:
American association of physicists in medicine- task group report 18
-Set of test patterns to manage QC for digital display devices
-principal responsibility of the medical physicist
Luminance Meter:
Luminance response of monitors & luminance uniformity
-measurements require use of a properly calibrated photometer
-photometric evaluation of digital devices & ambient light is essential to digital QC
Best digital viewing is done: Straight on
QC Components - Digital display device
1. Geometric Distortion
-displayed image is geometrically different from original (has to do with image compression)
-examples: pincushion or barrel-like distortions
(who) Tested by? Medical Physicist
(what) What is tested? Monitors
(where) Digital Only
(when)Tested? Annually
(why)Limits? Acceptable distortion is 2% for primary devices, 5% for secondary
(how)Equipment used? TG18-QC, TG18-LPV, TG18-LPH Test patterns
2. Reflection
-ambient light contributes significantly to image on screen
(who) Tested by? QA Personnel
(what) What is tested? Monitors
(where) Digital Only
(when)Tested? Annually
(why)Limits? none
(how)Equipment used? Visual inspection
3. Luminance Response
Definition: The relationship between displayed luminance and input values of a standardized display system
-digital image data arrive at digital display devices as p-values transformed into digital driving levels and
viewed as luminance levels.
Displayed Luminance:
consists of light produced by the display device
(who) Tested by? Medical Physicist
(what) What is tested? Monitors
(where) Digital Only
(when)Tested? Annually
(why)Limits? Evaluated from a distance of 30cm away. Failure= 1 or 2 dark regions not seen
(how)Equipment used? TG18-CT
4. Display Resolution
Spatial resolution: measurement of the ability of the display system to produce separable images of different
points of an object with high fidelity
(who) Tested by? Medical Physicist
(what) What is tested? Monitors
(where) Digital Only
(when)Tested? Annually
(why)Limits? Uniform resolution
(how)Equipment used? TG18-CX & TG18-QC
5. Display Noise
Noise: any high frequency fluctuations or patterns that interfere with detection of the true signal
(who) Tested by? Medical Physicist
(what) What is tested? Monitors
(where) Digital Only
(when)Tested? Annually
(why)Limits? Looking for high frequency fluctuations
(how)Equipment used? TG18-AFC
6. Printers
Tested: checked daily/weekly to ensure printer is functioning properly
Equipment used: Prints from PACS or automatically prints
CQI vs. QA/QC CQI:
CQI: Continuous quality improvement
-focuses on continuously improving the totality of the system within which people function as a team
CQI vs. QA/QC QA/QC:
-Focuses on maintaining a certain level of quality by setting forth standards & protocols to be
followed/implemented
Tech responsibilities:
-cassettes: clean, erased
-printers: clean, ink, paper
-digital system: crossing over correctly
Monthly: reject analysis, reasons, errors, report problems, artifact identification
7. Data QC process from PACS
1. Save a test pattern 2. Use different compression ratios 3. Send to PACS via 4. No compression 5.
Lossless compression (2:1 compression ratio) 6. Lossy compression (your specified compression ratio) 7.
Recall patterns and compare results
*PACS Administrators setup and implement ongoing QC and training programs
2 types of reflection:
Specular: results in mirror images of light sources surrounding monitor
Diffuse: light is randomly scattered on display device
Specular: results in mirror images of light sources surrounding monitor
Diffuse: light is randomly scattered on display device
NEMA-DICOM
National electrical manufacturers association-digital imaging and communications
DIN 2001:
"Image quality assurance in xray diagnostics" Acceptance testing for image display devices
VESA
video electronics standard association
Other sets by this creator