Fortschr. Röntgenstr. 128, 4
Sequential trials with new rare-earth intensifying screens By A. de Carvaiho and J. Jørgensen 4 Figures Department of Diagnostic Radiology R, Aarhus Kommunehospital, DK-8000 Aarhus C, Denmark
Sequential analysis of identical radiographs with calcium tungstate (CaWO4) and rare-earth intensifying screens was performed in four test situations. Most preferences in the direction of rare-earth screens were due to motion unsharpness with CaWO4 screens. Better contrast was found with rare-earth screens in one test ituation in spite of low kVp exposures. Assessment of the quality of the radiographs in practical situations gave results which differed to a certain extent from what might be expected from the technical assessment of the properties of the screens.
than calcium tungstate (CaWO4) screens, which makes it possible to reduce the radiation dose (2, 3, 5, 6). In addition, the K-edge of absorption of Gd and La are found at a lower energy level than that of CaWO4, which gives an increased efficiency at the most conversion efficiency
Es wurde eine Sequenzanalyse identischer Röntgenaufnahmen mit Kalziumwolframat (CaWO4)Verstärkerbildschirmen und eben solchen Bildschirmen, die seltene Erden enthielten, in vier Testsituationen durchgeführt. In den meisten Fällen beruht die Bevorzugung der Bildschirme, die seltene Erden enthielten, auf einer Bewegungsunschärfe der Bilder, die mittels CaWO4-Bildschirmen erhalten wurden. Bei den seltenen Erden ergab sich auch ein besserer Kontrast in einer Testsituation, obwohl die kVp-Belichtung gering war. Eine Bewertung der Qualität der Röntgenaufnahmen unter Praxisbedingungen führte zu Ergebnissen, die sich zu einem gewissen Grade von den Ergebnissen unterschieden, die bei einer rein technischen Bewertung der Bildschirmeigenschaften zu erwarten gewesen wären.
Materials and methods In a number of clinical situations (Table 1), standard exposures with the commonly used calcium tungstate screens were supplemented with exposures in which terbium-
the image quality, as a short exposure tune gives less motion
activated lanthanum oxybromide screens were employed. In all cases, the same film type (Kodak X-OMAT XL1) was used; the other factors, such as focus-film distance, subject-film distance and diaphragm, were unchanged from exposure to exposure, and the time interval between the pair of corresponding exposures was as short as possible.
unsharpness, and the optimum level of 70-80 kVp should give better contrast of the radiographs. However, the lower
been over- or under-exposed.
commonly used kilovoltages, 70-80 kVp (2).
These properties also result in a certain improvement of
dose involves the disadvantage that the statistical fluctuations
in the distribution of the absorbed photons (4) lead to an increase in the quantum mottle and hence to a deterioration
of the image quality. The weight of these factors in the evaluation of the image quality depends on the situations in which the screens are used.
The purpose of the present study was to clarify the fields of work in which these screens can be used with the greatest advantage.
The first two exposures were accepted unless they had A Bucky diaphragm was used for the axial views of the proximal humerus with the beam directed through the thorax and for urography; and a stationary grid for axial views of the hip, while no grid was used for the exposures of the wrist. Each pair of exposures were compared and evaluated on the basis of conventional radiographic criteria, such as motion unsharpness, quantum mottle, contrast, image sharpness and graininess, by one of the authors (J. J.) to
Table 1
Type of exposure Immobilized wrist
Hip, axial
Humerus, axial
Cawo Universal Cawo SE4
Cawo Universal Cawo SE4
Average kilovoltage (kVp)
83
87
Relative speed
1/s
1/3
19 13
1/5 55
1/3
No. of pairs of exposures No. of preferences Direction of preferences
49 (two planes)
80
47
44
61
No difference
No difference
Ilford Tungstate
Screens compared
0340-1618/78
Cawo Universal
0432 - 0477 $ 05.00 © 1978
Georg Thieme Publishers
Cawo Universal Cawo SEA 42 (a.-p.) 44 (lateral)
Renal regions, urography
Ilford Tungstate MR 400 64
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Sequenztests mit neuen Verstärker-Bildschirmen auf der Grundlage von seltenen Erden
Fortschr. Röntgenstr. 128,4 (1978) 477-479
The new intensifying screens with the rare earths gadolinium (Gd) and lanthanum (La) offer certain advantages in radiography. These screens have a greater X-ray-to-visible-light
477
478
Fortschr. Röntgenstr. 128, 4
A. de Carvaiho and J. Jørgensen: Sequential trials with intensifying screens
ensure uniformity in the evaluation. The results were expressed in terms of preferences for either one or the
Cawo Universal
20
other type of screen in each pair of exposures. The pairs for which no preference could be given were excluded in the
'n 'n
10
final
'n
'n
o-
20
30
40
60
50
'n
L)
X
w
20
Results
Cawo SE4
Fig.
1.
20
Table 1 shows the average kilovoltages used in the four
Sequential trial of axial y ews of the hip.
Ilford Tungstate
10
60
number of preferences
10
test situations, the relative speeds of the screens, the number of pairs of exposures, the number of preferences and their directions. The decisive factor in the evaluation of the axial views of the hip was the strikingly great quantum mottle, the decision being made after 13 preferences (Fig. 1). The same factor also decided the result in the comparison of the urographie exposures (Fig. 2), but only after 61 preferences, as many
preferences pointing in the direction of the MR 400 were due to motion unsharpness of the films taken with Ilford Tungstate. In the other two tests, the two types of screens proved to be equally good. In the axial views of the proximal humerus the decision was made after 47 preferences (Fig. 3),
mainly because of a distinct reduction in the motion unsharpness of the exposures with the rare-earth screens. In the exposures of the wrist immobilized in the plaster cast,
20
MR 400
Fig. 2.
analysis. The evaluation was made by sequential
trials with a restricted design. The design used is described by P. Armitage (1) with a two-sided significance level, 2s = 0.05, and power 1-1 0.95 of detecting a value of the proportion of preferences X1 = 0.75. The same model was used in the four test situations.
Sequential trial of urographie exposures.
there was no motion unsharpness, but the rare-earth screens
gave better contrast, which compensated for the loss in image quality referable to the greater quantum mottle and 20 'n 'n
graininess. A total of 44 preferences were required to reach the decision (Fig. 4). The rare-earth screens were also used in a number of other situations, mainly in angiography, endoscopie pancreatography and in contrast studies of the gastro-intestinal tract. However, it is very difficult to perform reliable comparisons
Cawo Universal
lo
L)
C a)
'n 'n
o-
60
-
number of preferences
in these situations, but a subjective evaluation scarcely showed any deterioration in quality when rare-earth screens were used.
10
Discussion 20 Cawa SE4
Fig. 3.
20
Sequential trial of axial views of the proximal humerus.
Cawo SE4
'n 'n
10 a)
'n
'n
û-
10
'n 'n
50
60
number of preferences
10
20
Cawo Universal
Sequential trial of exposures of the wrist immo bilis cd in a plasrer casr. Fig. 4.
The method used is deemed to be the most reliable in the evaluation of the image quality of radiographs made with rare-earth screens, as it takes into account all the factors which contribute to the final quality of the exposures and introduces a certain amount of objectivity in the comparisons. Previous studies (3) have shown that the resolving power of Cawo Universal is better than that of Cawo SE4, and that there is no definite difference between MR 400 and Ilford Tungstate, whereas the film contrast is better on Cawo SE4 than on Cawo Universal at 80 kVp, while the opposite is the case at 50 kVp. It is therefore surprising that, in a subjective evaluation, the exposures of the immobilized
wrist taken with Cawo SE4 showed a better contrast than those taken with the Cawo Universal screens. The quantum mottle within the optimum kilovoltage range was so pronounced on exposures made with rare-earth screens of the type used that the quality was definitely inferior to that of the radiographs taken with calcium rungstate screens, but, at the same time, it is worth noticing that motion unsharpness may cancel out the better quality of radiographs taken with
calcium tungstate screens. This has also been emphasized by Wagner and Weaver (7) and by Wiljasalo et al. (8).
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
10
'n 'n
number of preferences
Fortschr. Röntgenstr. 128, 4
J. Freyschrnidt u. Mitarb.: Neue Aspekte zur Belichtungstechnik
It may thus be concluded that rare-earth screens can in certain cases be used without a resultant deterioration of the quality of the radiographs. This applies, in particular, when the use of calcium tungstatc screens gives rise to pronounced motion unsharpness. The reduction in the radiation dose to the patient will then be considerable, because the motion unsharpness often necessitates repeat exposures. Furthermore, it should be pointed out that rate-earth screens can with advantage be used outside the kilovoltage ranges which the manufacturers recommend as
the most efficient. The results of the evaluation of the screens in practice deviate to some extent from what might be expected from the technical assessment of the properties
Rare-earth and calcium tungstate intensifying screens. A vom pararivc study of relative speed, radiation doses and resolving posver. Fortschr. Röntgenstr. (To he published.) Cleare, H. M., l-T. R. Splettstosser, H. E. Seemann: An experimental stttdy of the mottle produced by X-ray ititensifiyng screens. Amer. J. Roentgeito!. 88 (1962) 168
Eddleston, M. B., B. M. Moores, A. Walker: Eye dose measurements rising conventional and rare-earth screens during tomography of the
para-nasa! si in ses. Brir. J. Radio!. 50
479
Freyschmidt, J., D. Saure: Neue Verstiirkerfolien in der Kinderradiologic. Röntgen-B!. 29 (1976) 299
Wagner, R. F.,
K. E.
Weaver
Prospects for X-ray exposure reduction usi:ig rare-earth intetisifying screens. Radiology 118 (1976) 183 Wiljasaln, M., E. Tiihti, O. Korhola,
M. Valle, P. Tarkka, E. Riihimäki: Reductioti of motion u:rsharpness in coronary angiography usitig rareearth oxysulfide i:rtens:fying screens and green-sensitive X-ray film. Ann. Clin. Res. 7 (1975) 374
(1977) 266
K. A. Wickersheim: X-ray exposure reduction using rare-earth oxysulSde
Literature Armitage, P.
Sequential medical
trials. Blackwell Sc. Pub!., Oxford 1960
Buchanan, R. A., 5. 1. Finkelstein,
intensifying (1972) 185
screens.
Radiology
105
Carvalho, A. de, J. Jorgensen:
A. dc Carvaiho, Department of Dtagnosttc Radiology R, Aarhus-Kornmunehospital, DK-8000 Aarhus C
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
of the screens.
Sequential trials with new rare-earth intensifying screens By A. de Carvaiho and J. Jørgensen 4 Figures Department of Diagnostic Radiology R, Aarhus Kommunehospital, DK-8000 Aarhus C, Denmark
Sequential analysis of identical radiographs with calcium tungstate (CaWO4) and rare-earth intensifying screens was performed in four test situations. Most preferences in the direction of rare-earth screens were due to motion unsharpness with CaWO4 screens. Better contrast was found with rare-earth screens in one test ituation in spite of low kVp exposures. Assessment of the quality of the radiographs in practical situations gave results which differed to a certain extent from what might be expected from the technical assessment of the properties of the screens.
than calcium tungstate (CaWO4) screens, which makes it possible to reduce the radiation dose (2, 3, 5, 6). In addition, the K-edge of absorption of Gd and La are found at a lower energy level than that of CaWO4, which gives an increased efficiency at the most conversion efficiency
Es wurde eine Sequenzanalyse identischer Röntgenaufnahmen mit Kalziumwolframat (CaWO4)Verstärkerbildschirmen und eben solchen Bildschirmen, die seltene Erden enthielten, in vier Testsituationen durchgeführt. In den meisten Fällen beruht die Bevorzugung der Bildschirme, die seltene Erden enthielten, auf einer Bewegungsunschärfe der Bilder, die mittels CaWO4-Bildschirmen erhalten wurden. Bei den seltenen Erden ergab sich auch ein besserer Kontrast in einer Testsituation, obwohl die kVp-Belichtung gering war. Eine Bewertung der Qualität der Röntgenaufnahmen unter Praxisbedingungen führte zu Ergebnissen, die sich zu einem gewissen Grade von den Ergebnissen unterschieden, die bei einer rein technischen Bewertung der Bildschirmeigenschaften zu erwarten gewesen wären.
Materials and methods In a number of clinical situations (Table 1), standard exposures with the commonly used calcium tungstate screens were supplemented with exposures in which terbium-
the image quality, as a short exposure tune gives less motion
activated lanthanum oxybromide screens were employed. In all cases, the same film type (Kodak X-OMAT XL1) was used; the other factors, such as focus-film distance, subject-film distance and diaphragm, were unchanged from exposure to exposure, and the time interval between the pair of corresponding exposures was as short as possible.
unsharpness, and the optimum level of 70-80 kVp should give better contrast of the radiographs. However, the lower
been over- or under-exposed.
commonly used kilovoltages, 70-80 kVp (2).
These properties also result in a certain improvement of
dose involves the disadvantage that the statistical fluctuations
in the distribution of the absorbed photons (4) lead to an increase in the quantum mottle and hence to a deterioration
of the image quality. The weight of these factors in the evaluation of the image quality depends on the situations in which the screens are used.
The purpose of the present study was to clarify the fields of work in which these screens can be used with the greatest advantage.
The first two exposures were accepted unless they had A Bucky diaphragm was used for the axial views of the proximal humerus with the beam directed through the thorax and for urography; and a stationary grid for axial views of the hip, while no grid was used for the exposures of the wrist. Each pair of exposures were compared and evaluated on the basis of conventional radiographic criteria, such as motion unsharpness, quantum mottle, contrast, image sharpness and graininess, by one of the authors (J. J.) to
Table 1
Type of exposure Immobilized wrist
Hip, axial
Humerus, axial
Cawo Universal Cawo SE4
Cawo Universal Cawo SE4
Average kilovoltage (kVp)
83
87
Relative speed
1/s
1/3
19 13
1/5 55
1/3
No. of pairs of exposures No. of preferences Direction of preferences
49 (two planes)
80
47
44
61
No difference
No difference
Ilford Tungstate
Screens compared
0340-1618/78
Cawo Universal
0432 - 0477 $ 05.00 © 1978
Georg Thieme Publishers
Cawo Universal Cawo SEA 42 (a.-p.) 44 (lateral)
Renal regions, urography
Ilford Tungstate MR 400 64
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
Sequenztests mit neuen Verstärker-Bildschirmen auf der Grundlage von seltenen Erden
Fortschr. Röntgenstr. 128,4 (1978) 477-479
The new intensifying screens with the rare earths gadolinium (Gd) and lanthanum (La) offer certain advantages in radiography. These screens have a greater X-ray-to-visible-light
477
478
Fortschr. Röntgenstr. 128, 4
A. de Carvaiho and J. Jørgensen: Sequential trials with intensifying screens
ensure uniformity in the evaluation. The results were expressed in terms of preferences for either one or the
Cawo Universal
20
other type of screen in each pair of exposures. The pairs for which no preference could be given were excluded in the
'n 'n
10
final
'n
'n
o-
20
30
40
60
50
'n
L)
X
w
20
Results
Cawo SE4
Fig.
1.
20
Table 1 shows the average kilovoltages used in the four
Sequential trial of axial y ews of the hip.
Ilford Tungstate
10
60
number of preferences
10
test situations, the relative speeds of the screens, the number of pairs of exposures, the number of preferences and their directions. The decisive factor in the evaluation of the axial views of the hip was the strikingly great quantum mottle, the decision being made after 13 preferences (Fig. 1). The same factor also decided the result in the comparison of the urographie exposures (Fig. 2), but only after 61 preferences, as many
preferences pointing in the direction of the MR 400 were due to motion unsharpness of the films taken with Ilford Tungstate. In the other two tests, the two types of screens proved to be equally good. In the axial views of the proximal humerus the decision was made after 47 preferences (Fig. 3),
mainly because of a distinct reduction in the motion unsharpness of the exposures with the rare-earth screens. In the exposures of the wrist immobilized in the plaster cast,
20
MR 400
Fig. 2.
analysis. The evaluation was made by sequential
trials with a restricted design. The design used is described by P. Armitage (1) with a two-sided significance level, 2s = 0.05, and power 1-1 0.95 of detecting a value of the proportion of preferences X1 = 0.75. The same model was used in the four test situations.
Sequential trial of urographie exposures.
there was no motion unsharpness, but the rare-earth screens
gave better contrast, which compensated for the loss in image quality referable to the greater quantum mottle and 20 'n 'n
graininess. A total of 44 preferences were required to reach the decision (Fig. 4). The rare-earth screens were also used in a number of other situations, mainly in angiography, endoscopie pancreatography and in contrast studies of the gastro-intestinal tract. However, it is very difficult to perform reliable comparisons
Cawo Universal
lo
L)
C a)
'n 'n
o-
60
-
number of preferences
in these situations, but a subjective evaluation scarcely showed any deterioration in quality when rare-earth screens were used.
10
Discussion 20 Cawa SE4
Fig. 3.
20
Sequential trial of axial views of the proximal humerus.
Cawo SE4
'n 'n
10 a)
'n
'n
û-
10
'n 'n
50
60
number of preferences
10
20
Cawo Universal
Sequential trial of exposures of the wrist immo bilis cd in a plasrer casr. Fig. 4.
The method used is deemed to be the most reliable in the evaluation of the image quality of radiographs made with rare-earth screens, as it takes into account all the factors which contribute to the final quality of the exposures and introduces a certain amount of objectivity in the comparisons. Previous studies (3) have shown that the resolving power of Cawo Universal is better than that of Cawo SE4, and that there is no definite difference between MR 400 and Ilford Tungstate, whereas the film contrast is better on Cawo SE4 than on Cawo Universal at 80 kVp, while the opposite is the case at 50 kVp. It is therefore surprising that, in a subjective evaluation, the exposures of the immobilized
wrist taken with Cawo SE4 showed a better contrast than those taken with the Cawo Universal screens. The quantum mottle within the optimum kilovoltage range was so pronounced on exposures made with rare-earth screens of the type used that the quality was definitely inferior to that of the radiographs taken with calcium rungstate screens, but, at the same time, it is worth noticing that motion unsharpness may cancel out the better quality of radiographs taken with
calcium tungstate screens. This has also been emphasized by Wagner and Weaver (7) and by Wiljasalo et al. (8).
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
10
'n 'n
number of preferences
Fortschr. Röntgenstr. 128, 4
J. Freyschrnidt u. Mitarb.: Neue Aspekte zur Belichtungstechnik
It may thus be concluded that rare-earth screens can in certain cases be used without a resultant deterioration of the quality of the radiographs. This applies, in particular, when the use of calcium tungstatc screens gives rise to pronounced motion unsharpness. The reduction in the radiation dose to the patient will then be considerable, because the motion unsharpness often necessitates repeat exposures. Furthermore, it should be pointed out that rate-earth screens can with advantage be used outside the kilovoltage ranges which the manufacturers recommend as
the most efficient. The results of the evaluation of the screens in practice deviate to some extent from what might be expected from the technical assessment of the properties
Rare-earth and calcium tungstate intensifying screens. A vom pararivc study of relative speed, radiation doses and resolving posver. Fortschr. Röntgenstr. (To he published.) Cleare, H. M., l-T. R. Splettstosser, H. E. Seemann: An experimental stttdy of the mottle produced by X-ray ititensifiyng screens. Amer. J. Roentgeito!. 88 (1962) 168
Eddleston, M. B., B. M. Moores, A. Walker: Eye dose measurements rising conventional and rare-earth screens during tomography of the
para-nasa! si in ses. Brir. J. Radio!. 50
479
Freyschmidt, J., D. Saure: Neue Verstiirkerfolien in der Kinderradiologic. Röntgen-B!. 29 (1976) 299
Wagner, R. F.,
K. E.
Weaver
Prospects for X-ray exposure reduction usi:ig rare-earth intetisifying screens. Radiology 118 (1976) 183 Wiljasaln, M., E. Tiihti, O. Korhola,
M. Valle, P. Tarkka, E. Riihimäki: Reductioti of motion u:rsharpness in coronary angiography usitig rareearth oxysulfide i:rtens:fying screens and green-sensitive X-ray film. Ann. Clin. Res. 7 (1975) 374
(1977) 266
K. A. Wickersheim: X-ray exposure reduction using rare-earth oxysulSde
Literature Armitage, P.
Sequential medical
trials. Blackwell Sc. Pub!., Oxford 1960
Buchanan, R. A., 5. 1. Finkelstein,
intensifying (1972) 185
screens.
Radiology
105
Carvalho, A. de, J. Jorgensen:
A. dc Carvaiho, Department of Dtagnosttc Radiology R, Aarhus-Kornmunehospital, DK-8000 Aarhus C
This document was downloaded for personal use only. Unauthorized distribution is strictly prohibited.
of the screens.
