Transcript RAD 354 Chapt. 16 Image QUALITY

RAD 354 Chapt. 16 Image QUALITY
• “Finite” Radiographic quality
– Noise
– Resolution
• Spatial resolution
– Contrast resoultion
– Noise
Film/Screen Factors
• Speed of the “system”
• Characteristic Curve
– Digital vs Film/screen
• Optical Density
– Factors directly and indirectly effecting density
Log Relative Exposure
sensitivity of the human eye
Contrast
•
•
•
•
•
•
Image contrast
Subject contrast
How to compensate for subject contrast
Film/screen contrast
Image receptor/film screen contrast
Film/receptor processing
Geometric factors
• Magnification
– Direct vs distortion
– Mag factor vs mag ratio
•
•
•
•
Distortion
Focal spot blur
Sid – Oid relationships
Heel effect
RAD 354 Chapt. 17 Image Artifacts
• Usually TECHNOLOGIST dependant
• Patient Preparation
– Clothes left on (zippers, jewelry, dentures)
• Positioning errors (patient, tube, bucky,
receptor)
• Wrong screen-film combination
• Upside down film casstte/receptor
Processing Artifacts
• Roller marks
– Cascading (curtain effect/run down)
– Guide shoe lines
– Pi lines
– Dirty rollers
– Chemical fog
– “Wet-pressure sensation” varied amount of
pressure on the rollers = uneven film “splotches”
Handling Artifacts
• Light/Radiation Fog
– Sensitivity prior and after exposure
• Kink marks
• Static (Tree, smudge are the most common)
• Hypo retention (test is mandatory for
mammo)
RAD 354 Chapt. 18 Quality Control
• Quality Assurance is a JCAHO required 10 step
PEOPLE process
• Quality Control is an imaging intrumentation
and equipment process
QC- 3 Step Process
• Acceptance testing
• Routine performance monitoring
• Maintenance
Radiography QC
• Filtration – annually
• Collimation – semiannually (+/-2% of the SID)
• F.S. size Annually (+/-50%) Frequently MISSED
parameter!
• kVp calibration – annually (+/-10%)
• Exp. Timer Accuracy – annually (based on ms
used – more leeway with longer exposures)
• Linearity – annually (+/-10%) of same mAs with
differing mA/times – but SAME mAs
• Exp. Reproducibility – Same cont./Dens., etc
when exposures are repeated
Focal Spot Check Tools/Frequency
• Annually
• Pin hole camera (somewhat hard to use)
• Star Pattern (down to .3 mm sizes)
• Slit camera – easiest to use/preferred method
Other RAD QC
•
•
•
•
•
•
•
•
Filtration
Collimation (PBL)
kVp/Timer
Exposure Linearity (same mAs with varied mA
and times)
Intensifying screens
Protective apparel
Film illuminators
Computer station monitors
Fluoro QC
• Exposure rate
• Spot film exposures
• Automatic Exposure System (ABS – AEC)
Tomo QC
• Tube travel/Arc
• Fulcrum level
• Pt. Expossure
Processor QC
• See table 18-8 (p. 313) for QC for RAD
Processor items/intervals
• Processor Maintenance
– Scheduled maintenance
– Preventative maintenance
– Non-scheduled maintenance
Processor Monitoring
• Temperatures
• Replenishment
• Sensitometry/Densitometry