CH 29 Quality assurance and control
IR ESD
1,000 mGy (100rad)
To assess Specular reflectance turn off the monitor and look for illumination within a _ angle of viewing at approximately _ to _ cm.
15 degree, 30, 50
Image Display (monitors): Dead or Stuck Pixels
15(entire screen) 3(1 cm circle) 3 (adjacent) Naked eye or Magnifying glass
ACR and AAPM recommend a minimum resolution of electronically displayed images of ?
2.5 Lp/mm
Image Display (monitors): Display Resolution
2.5 Lp/mm (white/black difference) TG18-CX pattern
A 4 min fluoroscopic exam with a 1.5mA tube current results in a patient dose of _ rad?
2xminxmA = 2x4x1.5 = 12 rad
Luminance uniformity should not deviate more than _ from their average?
30 %
ESD (Entrance Skin Dose)
30 - 50 mGy/min (3-5 R/min) Shall not exceed 100 mGy/min (10R/min)
Mobile C-arm fluoroscopy units have an SSD of ?
30 cm (12 inches)
Stationary Fluoroscopic units have a source to skin distance (SSD) of _?
38 cm (15 inches)
AAMP
American Association of Physicists in Medicine
ACR
American College of Radiology
Quality Control: AEC Exposure Reproducibility
Annual +/- 1% (OD) Densitometer (phantom)
Quality Control: AEC Ion Chamber (IC) Sensitivity
Annual +/- 10 Exposure meter
Quality Control: AEC Response Capability
Annual +/- 10 % Exposure meter (lucite phantom)
Quality Control: Exposure Linearity
Annual +/- 10% Dosimeter
Quality Control: Exposure time
Annual +/- 5% Exposure meter or spinning top
Quality Control: kVp
Annual +/- 5% kVp +/- 10% kVp Bushong KVp meter
Fluoroscopic QC: Exposure Rate
Annual < 10 rad/min Exposure meter
Fluoroscopic QC: Protective Apparel
Annual No gaps or cracks Fluoroscope or film/IR @120 kVp
Fluoroscopic QC: ABC (AERC)
Annual No limits (check different attenuators) Exposure meter
Fluoroscopic QC: Resolution
Annual No limits (look for higher Lp/mm) Resolution phantom
Quality Control: Filtration/HVL
Annual ≥ 2.5 mm Al Al sheets
Quality Control: Exposure Reproducibility
Annual +/- 5% Dosimeter
Quality Control : FS size spatial resolution
Annual +/- 50% Star test pattern Slit or pinhole camera
Display noise
Any patterns or electrical fluctuations that interfere with the detection of the true signal
Image Display (monitors): Luminance (rate of light)
Better than 5% Photometer
DR detectors: Field Uniformity
Daily to Semi-annual Erase plate look for artifacts Expose detector @72" SID (or at 78")
Focal Spot Blur
Degradation of the focal spot can produce blurred structures on the radiograph.
DR detectors: Erasure Thoroughness
Erase plate look for Ghosting or Image Lag For CR - use Al step wedge
Resolution
Is Line pairs per millimeter (Lp/mm). The higher the # of line pairs the better the resolution
Collimation
Light Radiation Field Congruence (Beam Alignment) light field and radiation field must coincide
DR detectors: Spatial Resolution (blurring)
Look for distortions Wire mesh on detector or Standard Bar test
Radiographic quality control
Periodic monitoring of X-ray tube, the associated electric circuits, the accuracy of the exposure factors, and the film processor.
Two types of Image Display Monitors
Primary Secondary (Clinical)
Exposure Reproducibility
Radiation output (measured in mR) should be at the same for a series of exposures in which all technical factors are the same
Quality Control: Collimation
Semiannual or Annual +/- 2% SID Collimator test tool
Image Display (monitors): Luminance Uniformity
Should not deviate more than 30% Photometer (measure 4 corners and center)
SMPTE
Society of Motion Picture and Television Engineers
Image Display (monitors): Display Noise
TG18-AFC (view at 30 cm)
Exposure Linearity
The ability of a unit to produce a constant radiation output from various combinations
Ghosting or Image Lag
When electrical charge is trapped in amorphous silicon or selenium and released over time
Image Display (monitors): Luminance Response (brightness of light)
Within 10% SMPTE test pattern
Stuck pixels appear as _ on a solid white field
black
Luminance uniformity refers to the consistency of a single _ level displayed across a screen.
brightness
Luminance response refers to the various shades of _ from a _.
brightness, test pattern
SMPTE - designed a generic test pattern which can test for most _ qualities
image
Diffuse Reflectance is _ that is randomly _on the digital dislay
light, scattered
Specular Reflectance resorts in _ images of light sources surrounding the display monitor.
mirror
AAMP - designed a test pattern TG18-AFC to measure _ levels
noise
Luminance is the _ of light emitted from a source
rate (intensity)
Photometers
read in units of lux, lumens, or candela/m² (cd/m²)
AAPM- designed a test pattern TG18-CX to check for _on a digital screen
resolution
Dead pixels appear as _ on a solid background
white
