WEEK 9--IMAGE QUALITY Flashcards
Image Quality
• Is the _______ of the representation of the patient’s anatomy
• An image that accurately represents structure and tissue is identified as a high-‐quality radiograph
•The most important characteristics of radiographic
quality are:
–Spatial Resolution
–Contrast Resolution
–Noise
–Artifacts
exactness
Resolution
• Is the ability to image two separate objects
and visually dis?nguish one from the other.
• _________ __________ is the ability to image
small objects that have high subject contrast.
– Ex: bone-‐soft tissue interface
• Conventional radiography has excellent spatial
resolution
SPATIAL RESOLUTION
RESOLUTION TEST TOOLS
Line pairs/mm – Depicts how well you can see the distinguish two adjacent structures
More lines=more _________
detail
Focal Spot
- ______ x-‐ray beam width will produce a sharper image.
- Small focal spot = _______ detail
Smaller
Fine
Contrast Resolution
1 • Is the ability to distinguish anatomic structures of ________ subject contrast
–Ex: (liver/spleen) or (gray matter/white matter)
2• Magnetic Resonance Imaging has the _______
contrast resolution
–Computed Tomography is excellent as well
–Radiography is not nearly as good
similar
highest
_______ Contrast –Is the product of image receptor contrast and subject contrast
Radiographic
Noise
• Borrowed from electrical engineering
• Audio noise = hum or fluUer heard from a stereo
• Video noise = “snow” on a TV
• Radiographic noise = random fluctua?on in the OD of the image.
–Scatter is the principle source of radiographic noise
–Other sources:
• _____________ ______________
• Patient motion
• Parallax
QUANTUM MOTTLE
Quantum Mottle
•Contributes to image noise
• An image produced with just a few x-‐rays will
have ________ quantum motte.
• The use of very ‘high speed’ imaging system will _________ quantum mottle
***Not enough _______ – can create a mottled or grainy image
more
increase
PHOTONS
QUANTUM MOTTLE
– With a fast system you’ll get an image, but it will look very _________
– With a slow system you’ll get the same image, but it cost you more and as a result your resolution is very good.
pixelated.
SPEED
1. \_\_\_\_\_\_\_ image receptors have: –Higher Noise –Lower spatial resolution –Lower contrast resolution –Lower patient radiation dose
2. \_\_\_\_\_\_\_ image receptors have: –Lower Noise –Higher spatial resolution –Higher contrast resolution –Higher patient radiation dose
Fast
Slow
Image Receptor Factors
Characteristic curve (AKA: H&D curve)
–Is used to describe the relationship between OD
and _________ exposure
radiation
Image Receptor Speed
The ability of an image receptor to respond to
an x-‐ray exposure is a measure of its sensitivity and is referred to as the image _____
.
Speed
The LATTITUDE of an image receptor is the exposure range over which it responds with diagnostically useful OD.
- Different image receptors and imaging systems will have different latitudes.
- Latitude can also be thought of as the margin of error in technical factors.
- Latitude and contrast are _________ proportional
inversely
Patient Motion
• Can be voluntary or involuntary • Best controlled by: –\_\_\_\_\_\_\_ exposure times –Use of careful instructions to the patient –Suspension of patient \_\_\_\_\_\_\_\_\_\_\_\_ –Immobilization devices
short
respiration
Artifacts
1 • Any ________ on an image that is NOT caused by proper shadowing of tissue by the primary x-‐ray beam.
2 • Are undesirable optical densities or blemishes
on a radiograph.
3 • Can be very interesting at times. You become
the detective
What caused that? STUDY SCREEN 32!!!
irregularity
Exposure artifacts
- Exposure artifacts are generally associated with the manner in which the radiographer conducts the examination:
–incorrect screen-‐film matching
–poor screen-‐film contact
–warped cassettes
–improper positioning of the grid
–improper patient position/patient motion
–double exposure
–incorrect radiographic technique (mAs, kVp, etc.) - These represents the largest cause for repeat exposure!!
know this bullshit
Exposure Artifacts
3 • _______ ________ is essential for producing
artifact-‐free images.
4 • Artifacts on or worn by the patient are often
concealed by clothing –ex. surgical hardware and keys, hair, jewelry, patient clothing,
5. ________ exposure –Forgetting to remove and process film before taking another image.
6. Accidentally pressing the button twice for one exposure
7. Lack of contact between film and________ can cause
blurring of the image
Patient preparation
Double
cassette
Exposure Artifacts
- Dust/dirt in imaging plate/cassette
–Causes areas of ___________ optical density.
–Can mimic foreign bodies
–Seen in both digital and film/screen radiograph - Pathology: NOT An Artifact !!!
decreased
Processing Artifacts
1 • Often caused by pressure.
–Pressure artifacts typically INCREASE OD(_______)
–Scratches or scrapes that remove emulsion appear
as DECREASED OD (___________)
2 • Roller Marks, Pi lines, Dirty rollers, Chemical fog
blacker
whiter
Processing Artifacts
- Guide shoe marks
–Caused by ________ positioning or springing of guide shoes in turnaround assembly. - Pi Lines –Occur at 3.1416 inch intervals.
–As a result of 1 inch diameter rollers
improper
Processing Artifacts
- Drops of developer
–Circular artifacts of increased optical density.
–As a result of over exposure from the developer - Drops of fixer
–Circular artifacts of decreased optical fixer
– As a result of ________ exposure from the fixer.
(Can also occur with other acidic liquids)
.
under
Handling & Storage Artifacts
• Image fog –temperature, humidity, radiation, light • Pressure marks –film being stacked improperly • Kink marks • Static • Hypo Retention
know
Handling Artifacts
Scratches from improper handling
–Result in removal of the emulsion layer.
–And areas of ___________ optical density
decreased
Handling & Storage Artifacts
- Discolored film due to hypo (fixer) retention.
- Chemicals NOT washed off = Over time will turn film _______
- Kink Marks
–Caused by rough handling of film before _______
–Characteristic “fingernail-‐shaped”
–Artifact of INCREASED optical density. = DARKER!!
–Kink marks can mimic ___________
brown
processing.
fractures
Handling & Storage Artifacts
- Static electricity
–Caused by _____ humidity environments and discharge of light from electrical shock.
–Artifact of INCREASED optical density. = DARKER!! - Light fog
•This is what happens when _______ leaks into the dark room or into the light-‐proof cassette.
•Results in an INCREASE in the optical density = DARKER
low
light
