Second Flashcards
Automatic collimators that sense the size of
the image receptor & adjust the collimating
shutters to that size
It must be evaluated for all possible receptor
sizes
The x-ray beam must not be larger than the
image receptor
Positive Beam-Limiting Collimators (PBL)
It principally determines the spatial
resolution of a radiographic imaging system
Focal-Spot Size (FSS)
Three Tools Used To Measure FSS:
o PSS
Pinhole Camera, Star Pattern & Slit
Camera
It is difficult to use
It requires excessive exposure time
Pinhole Camera
It is easy to use
Significant Limitation: focal-spot sizes less
than 3 mm
Star Pattern
The standard for measurement of focal-spot
size
Slit Camera
Specification of Focal-Spot Size
Depends on the ____ of the tube
Depends on the ___ of the electron
beam
geometry
focusing
An acceptable alternative to focal-spot size
measurement
It determines limiting spatial frequency
Line-Pair Test Tool
The x-ray generator must be properly
calibrated
kVp Calibration
Kvp Calibration Devices used based on filtered __& ___
Ion chamber photodiodes
___% Variation in kVp: necessary to affect
image OD & radiographic contrast
4
The measured kVp should be within ___% of
the indicated kVp!
10%
Exposure Timer Accuracy
____: responsible for patient dose
& OD
Devices Used:
o Based on irradiation time of an ion
chamber
o Based on irradiation time of
photodiode assembly
Frequency:
o Annually
o More frequently
Exposure Time
__% Accuracy: acceptable for exposure
times of 10 ms or less
20
Exposure timer accuracy should be within __%
of the indicated time for exposure times
greater than 10 ms!
5
Designed to provide a constant OD
regardless of tissue thickness, composition
or failure of the reciprocity law
It also must be evaluated
Evaluate By:
o Exposing an IR through various
thicknesses of aluminum or acrylic
o Regardless of material thickness &
absolute exposure time, OD of the
image must be constant
Automatic Exposure Control (AEC)
ability of a radiographic unit to produce
a constant radiation output for various
combination of mA & exposure time
Linearity
Exposure linearity must be within __% for
adjacent mA stations!
10
ability of a radiographic unit to produce
a precisely the same radiation exposure
when all the techniques are changed &
returned to previous value
Reproducibility
Sequential radiation exposure should be
reproducible to within ± __%!
5
Film Illuminators
It should be analyzed photometrically
Frequency: annually
Device Used: ___
photometer
: measures light intensity at
several areas of the illuminator
Photometer
