5. Word List
17
Slit Measurement Using Digital Image
1.0B
RTI Slit Camera User’s Manual
the image of the line source.
” (From the IEC 60788
standard)
The intensity function below the slit perpendicular to the
slit. The slit represents the line source.
Magnification
factor
The MAGNIFICATION FACTOR is the ratio of the focal
spot to image distance and the focal spot to object
distance. It is denoted by ”M”.
The spatial frequency is of the MTF is calculated for a
specific magnification factor, as follows.
f = f
i
M
M - 1
where:
f
is the corrected spatial frequency.
f
i
is the spatial frequency obtained by a Fourier
transform of the LSF.
M is the magnification factor.
The different standards specifies that you should use
standard magnification factors depending on the nominal
focal spot size as shown in Table 5–1 below. If you use the
choice ”Full MTF” you can set M as you like (1-10).
Table 5–1 The standard magnification factors.
Nominal focal spot,
f
Standard magnification,
M
s
f
0,6
2
0.6
f
1.3
Penumbra
In RADIOLOGY, spatial region around the RADIATION
BEAM where the value of radiation flux is between two
specified or specific fractions of the value that is measured
in the RADIATION BEAM AXIS.
Note.- The existence of such spatial region can be due to
one or more of the following phenomena:
-
EXTRA-FOCAL RADIATION,
-
SCATTERED RADIATION,
-
absence of lateral electronic equilibrium,
-
pair production,
-
geometry of the RADIATION SOURCE and of the
BEAM LIMITING SYSTEM.
(From the IEC 788 standard)
Reference axis
”
For a RADIATION SOURCE, line in the REFERENCE
DIRECTION through the centre of the RADIATION
SOURCE.”
