Ralco MTR 221/A, Instruction Manual

Page: 26 / 66

MTR221/A - MTR221/A DHHS
MANUALE ISTRUZIONI / INSTRUCTION MANUAL
Modello/Model R221/A - R221/A DHHS
C
ALIBRATION
20
R22
1/A
- R221
/A DHHS -
C
alib
ration
Ralco
srl
• Set the X-ray generator to produce a density of about 50 kVp, 5 mAs.
• Make an exposure.
• Remove the cassette and process the film.
• Use the test film to check the alignments described below.
Collimator to Focal Spot Alignment (Primary Shutter Cut-Off)
Inspect the four images of the four collimator shutters which form the edges of the x-ray field.
A definitely indistinct edge indicates that the primary shutter, close to the focal spot, is the one
forming the line, rather than the outermost shutter.
To correct the condition, use the four mounting/centering adjustment screws to shift the
collimator in the direction of the indistinct line. Repeat the test film exposure after making the
adjustment.
L
IGHT
F
IELD TO
X-
RAY
F
IELD
A
LIGNMENT
Misalignment of the light field/ X-ray field in either the X (cross table) or Y (long table) direction
must not exceed 2% of the SID. In this case, it would be less than 20 mm (0.80"). If the test film
shows that the light field (shadows of the markers) matches the X-ray field (shadow of the
collimator shutters) to within the diameter of one marker and, if the diameter is less than 20 mm
(1.80"), then alignment complies with the regulations.
Greater precision than this is possible. Recommended maximum deviation is one fourth. It is
important the greatest degree of congruency possible is achieved.
If misalignment is detected in both X and Y directions, check the spacing from the focal spot to
the collimator mounting surface is 80 mm (3.14") +/- 1 mm. If spacing needs to be adjusted,
repeat the test film exposure after the adjustment.
If the collimator mount spacing is correct, but adjustment is still necessary proceed as follows:
• Place the test film on the face of the cassette over the white paper.
• Place the cassette in the position originally marked.
• Check the correct position of the film by the shadows cast by the markers.
• Using the images of the collimator shutters as the references for the shape and size of the
X-ray field, adjust the light field to match.
• If adjustment is necessary, adjust the travel of the light source. All procedures can be found
in
L
IGHT
F
IELD
A
DJUSTMENTS
in this chapter.
L
IGHT
F
IELD
A
DJUSTMENT
Longitudinal Calibration (LONG)
T
HE HEEL EFFECT WILL CAUSE THE FIELD TOWARD THE CATHODE TO BE SLIGHTLY
LESS SHARP THAN ON THE OTHER THREE SIDES
.
THIS IS NORMAL AND CANNOT BE
CORRECTED BY ADJUSTMENT
.
IN ADDITION
,
AN X
-
RAY TUBE OF
12°
OR LESS TARGET
ANGLE WILL PRODUCE AN ASYMMETRICALLY SHAPED FIELD WHEN A LARGE FIELD SIZE
IS USED AT SHORT SID
,
BECAUSE OF ANODE CUT
-
OFF EFFECT
.
THIS IS NORMAL AND
MAY NOT BE CORRECTED BY ADJUSTMENT
.
DO NOT TOUCH THE DISSIPATER WITH YOUR HANDS
;
IT COULD BE HOT
AND CAUSE SEVERE BURNS
.