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Sensitometric and image analysis of T-grain film
Sensitometric and image analysis of T-grain film Kavas H. Thunthy, B.D.S., M.S., M.Ed.,* LOUISIANA
STATE
UNIVERSITY
SCHOOL
and Roger Weinberg, Ph.D.,**
New Orleans, La
OF DENTISTRY
The new Kodak T-grain film is the result of a new technology that makes fast films with high image resolution. The purpose of the investigation was to determine the sensitometric properties and image quality of a T-grain film (T-Mat G) and also to compare this film with a green-sensitive orthochromatic film (Ortho G) and a blue-sensitive film (XRP). The criteria for film evaluation were relative speed, average contrast, exposure latitude, and image resolution. The results showed that the T-Mat G film is twice as fast as the X-Omat RP film and, one and one-third times as fast as the Ortho G film. T-Mat G also produces high resolution and high contrast. This is contrary to the widely held notion that speed is inversely proportional to image quality. (ORAL SURG.ORAL MED. ORAL PATHOL. 62~218-220, 1986)
I n November
1983, Eastman Kodak Company introduced a new film called T-Mat. This film is the result of a breakthrough in technology in which the silver halide grains are tabular (flat), instead of their usual pebble shape, and are oriented to face their flat surfaces to the x-ray beam. This results in the silver halide crystals exposing a large cross section of their surfaces, which increases their “light-gathering” ability. This same technology made possible the world’s fastest 35 mm color print film: Kodacolor VR 1000. The tabular grains of a T-Mat film contain green-sensitive dye, and therefore the film should be used with green-emitting intensifying screens (rare earth screens). The increased light-gathering ability of the grains reduces crossover exposure in the two emulsion layers of a film and results in improved image resolution. According to the information supplied by Kodak, T-grain films in combination with green-emitting intensifying screens (Lanex) produce increased speed and also increased resolution when compared with green-sensitive films (Ortho G and Ortho L) in combination with green-emitting intensifying screens (Lanex). The two types of Kodak T-Mat films are T-Mat G and T-Mat L. This article was presented at the American Radiology
Meeting
at Lake
of Dental
Radiology.
1984. *Professor
**Professor
218
of Biometry.
Lanier,
Academy of Dental Georgia, on October 18,
OBJECTIVE
The purpose of the investigation was to determine the sensitometric properties and image quality of a T-grain film (T-Mat G) and also to compare this film with a green-sensitive orthochromatic film (Ortho G) and a blue-sensitive film (XRP). The criteria for film evaluation were relative speed, average contrast, exposure latitude, and image resolution.‘-4 MATERIALS
AND METHOD
Kodak T-Mat G (TMG) and Kodak Ortho G (OG) films were used in combination with greenemitting Kodak Lanex regular rare earth intensifying screens. Kodak RP X-Omat (XRP) film was used with blue (ultraviolet)-emitting Kodak XOmatic regular intensifying screens.5 A specially designed cassette containing a felt cushion was used throughout the experiment to maintain intimate film-screen contact. After the cassette was loaded with a film-screen combination, it was placed at a fixed distance of 72 inches from the anode of the x-ray tube with the use of a cephalostat cassette holder. A General Electric 1000 x-ray machine with a 2.7 mm aluminum equivalent half-value layer was operated at 10 mA and 80 kVp. The machine timer was checked with a spin top and was found to be consistently accurate for all indicated times. The cassettecontaining a film-screen combination
Volume 62 Number 2
Sensitometric
I. Relative speed,contrast, latitude, and resolution of XRP, OG, and TMG films
Table
XRP Film ----OGFilm . . . . . . TMG Fi,m
Relative speed Contrast Latitude Resolution
200 2.6 1 0.67 4.6
,,...” ,:’
286 2.40 0.73 4.5
..‘.
C-e _’
Lanex regular screens OG film
219
3.5
3-
X-Omaric regular screens XRP film
and image analysis of T-grain film
___---
.*
TMG f;lm
386 2.69 0.65 6.1
was positioned in the center of the beam of xradiation and exposedfor a time period of 1 impulse. The film was then developed. The process was repeated with the same type of film-screen combination, increasing exposure times up to 90 impulses. A total of nineteen exposures were made for each film-screen combination. The films were processed under rigid processing controls. They were developed in a Litton P6 automatic processor, with Kodak RP X-Omat developer and fixer solutions at a temperature of 80” F. The processing solutions were intermittently replenished and were changed after all the films of a particular film-screen combination were developed. To eliminate the effect of the darkroom safelight, all films were handled in total darkness. Film densities were measured with a TD-502 Macbeth transmission densitometer. All recorded densities were above base and fog density. The statistical package STATPAK (Northwest Analytical, Portland, Oregon) was used on a Zenith Z-100 microcomputer to draw scatter plots of density against log-relative exposure. These scatter plots produced the graphs for the characteristic curves for the various film-screen combinations. The curves were used to derive relative speed, average contrast, and exposure latitude. To study the resolution of the film-screen combinations, an x-ray test pattern distributed by Nuclear Associates (Type 53G, Model 07-533) was x-radiated.” It consisted of lead 50 pm thickin the form of parallel lines enclosed in Plexiglas. The test pattern was attached to the exposure surface of the cassette. The exposure and processing techniques were similar to those used previously in the experiment. To measure resolution, six radiographs with densities closest to 1.50 above base and fog were selected from each of the three film-screen combinations. The density of 1.50 was chosen because it is on the straight line portion of the characteristic curves and is therefore clinically more useful than other extreme
6
014
0:8
1:2
1:6
Lag Relative Exposure
Fig. 1. Characteristic curves: XRP film with X-Omatic regular screens, OG and TMG films with Lanex regular screens.
densities. The eighteen radiographs selected were coded and randomized and then viewed by three observers who used a Kodak achromatic 5X stand magnifier under standardized conditions. Each of the three observers made his choice of the smallest resolving group in which he could count the number of lines with reasonable confidence. The mean resolution of the three observersfor each radiograph was calculated. RESULTS
The characteristic curves of the three films are shown in Fig. 1. The OG and TMG films were combined with Lanex regular screens, whereas the XRP film was combined with X-Omatic regular screens. The curve of each film-screen combination contains information on speed,contrast, and latitude for a useful density range. The speed of a film-screen combination was determined as the reciprocal of the exposure required to yield a density of 1.00 above base and fog density. The relative speedswere calculated from the characteristic curves of Fig. 1. Table I showsthat XRP film with X-Omatic regular screens has a relative speed number of 200, arbitrarily chosen as a reference to match Kodak consumer publication no. M3-138. The TMG film was the fastest with a relative speed of 386, whereas OG had a relative speed of 286. Contrast refers to the slope (steepness) of the characteristic curves. In this experiment, the average contrast was calculated for densities ranging from 0.25 to 2.00 above base and fog density. The average contrast produced by the TMG film was higher
220
Thunthy and Weinberg
OI’d Sllrg. August,
1986
than that of the XRP and OG films (Table I). Latitude refers to the range between the minimum and maximum radiation exposures,which produces a scale of densities acceptable for diagnostic purposes. In this experiment, latitude was calculated from a density of 0.25 to a density of 2.00 above base and fog density. The TMG film produced the highest contrast (Table I). Because latitude is inversely proportional to contrast, it also produced the narrowest latitude. The OG film produced the lowest contrast and therefore the widest latitude. Resolution refers to the ability of an imagerecording system to record separate structures that are close together. Table I shows that the TMG film produced the highest resolution, whereas the XRP and OG films produced nearly the same resolution.
Kodak recommendsa safelight filter, type GBX-2, with a standard frosted 15 watt bulb for use in the darkroom. However, in the experiment, all processing was done in total darkness to eliminate the effect of the safelight. This new film is one of the most important advances in dental radiography. So far, radiology textbooks and articles have stated that there is always a trade-off between film speed and image quality. This statement is no longer true with the development of the T-grain film. As the experiment shows, an orthodontist can use a fast film without sacrificing image quality. The possible use of the T-grain film in panoramic radiography needs to be investigated.
DISCUSSION
The TMG film is the result of a new technology that makes fast films with high image quality. This is contrary to the widely held notion that speed is inversely proportional to image quality. The TMG film is twice as fast as the XRP film and one and one-third times as fast as the OG film. It also produces high resolution and high contrast.
Advances in film-manufacturing technology have led to the development of faster films. These increases in film speed have resulted in decreasesin image quality. However, the new technology of TMG film produces a faster film that also has higher image-resolving power. The results of the experiment showed that the TMG film had higher speed, contrast, and resolution than the OG and XRP films. The TMG film achieves high speed without sacrificing image quality, contradicting the widely held notion that speed is inversely proportional to image quality. Many variables are involved when measuring the speed of a film-screen combination, and therefore absolute values cannot be used. Comparisons made at various densities could have different relative speedsthan the ones obtained at a density of 1.00. Similarly, comparisons of average contrast and exposure latitude, made at various density ranges, could have different results from the ones obtained at a density range of 0.25 to 2.00. Resolution was measured clinically with a stand magnifying glass. Although a sophisticated instrument or method of measurement would have increased the numeric values obtained, the relative resolutions would have been the same.
CONCLUSIONS
REFERENCES I. Arnold reciprocity
BA,
Eisenberg H, Bjarngard law failure in green-sensitive
gy lt6:493-498, 2. 3. 4. 5. 6.
BE: Measurements of x-ray films. Radiolo-
1978.
Eastman Kodak Company: Kodak tilm/screen combinations. Publication No. M3-138, Rochester, N.Y., 1980. Eastman Kodak Company: Sensitometric properties of x-ray films, Publication No. Ml-2, Rochester, N.Y., 1973. Reynolds J, Skucas J, Gorski J: An evaluation of screen-film speed characteristics. Radiology 118: 7 I 1-7 13, 1976. Skucas J. Gorski J: Application of modern intensifying screens in diagnostic radiology. Med Radiogr Photogr 56(2): 25-36, 1980. Thunthy KH, Manson-Hing LR: A study of the resolution of dental films and screens. ORAL. SURG ORAI Mto ORAL PATII~I 42(2): 255-266, 1976.
Rqvint rcyimrs 10. Kavas H. Thunthy Department of Oral Diagnosis School of Dentistry Louisiana State University Medical II00 Florida Ave. New Orleans, LA 70119-2799
Center
STATE
UNIVERSITY
SCHOOL
and Roger Weinberg, Ph.D.,**
New Orleans, La
OF DENTISTRY
The new Kodak T-grain film is the result of a new technology that makes fast films with high image resolution. The purpose of the investigation was to determine the sensitometric properties and image quality of a T-grain film (T-Mat G) and also to compare this film with a green-sensitive orthochromatic film (Ortho G) and a blue-sensitive film (XRP). The criteria for film evaluation were relative speed, average contrast, exposure latitude, and image resolution. The results showed that the T-Mat G film is twice as fast as the X-Omat RP film and, one and one-third times as fast as the Ortho G film. T-Mat G also produces high resolution and high contrast. This is contrary to the widely held notion that speed is inversely proportional to image quality. (ORAL SURG.ORAL MED. ORAL PATHOL. 62~218-220, 1986)
I n November
1983, Eastman Kodak Company introduced a new film called T-Mat. This film is the result of a breakthrough in technology in which the silver halide grains are tabular (flat), instead of their usual pebble shape, and are oriented to face their flat surfaces to the x-ray beam. This results in the silver halide crystals exposing a large cross section of their surfaces, which increases their “light-gathering” ability. This same technology made possible the world’s fastest 35 mm color print film: Kodacolor VR 1000. The tabular grains of a T-Mat film contain green-sensitive dye, and therefore the film should be used with green-emitting intensifying screens (rare earth screens). The increased light-gathering ability of the grains reduces crossover exposure in the two emulsion layers of a film and results in improved image resolution. According to the information supplied by Kodak, T-grain films in combination with green-emitting intensifying screens (Lanex) produce increased speed and also increased resolution when compared with green-sensitive films (Ortho G and Ortho L) in combination with green-emitting intensifying screens (Lanex). The two types of Kodak T-Mat films are T-Mat G and T-Mat L. This article was presented at the American Radiology
Meeting
at Lake
of Dental
Radiology.
1984. *Professor
**Professor
218
of Biometry.
Lanier,
Academy of Dental Georgia, on October 18,
OBJECTIVE
The purpose of the investigation was to determine the sensitometric properties and image quality of a T-grain film (T-Mat G) and also to compare this film with a green-sensitive orthochromatic film (Ortho G) and a blue-sensitive film (XRP). The criteria for film evaluation were relative speed, average contrast, exposure latitude, and image resolution.‘-4 MATERIALS
AND METHOD
Kodak T-Mat G (TMG) and Kodak Ortho G (OG) films were used in combination with greenemitting Kodak Lanex regular rare earth intensifying screens. Kodak RP X-Omat (XRP) film was used with blue (ultraviolet)-emitting Kodak XOmatic regular intensifying screens.5 A specially designed cassette containing a felt cushion was used throughout the experiment to maintain intimate film-screen contact. After the cassette was loaded with a film-screen combination, it was placed at a fixed distance of 72 inches from the anode of the x-ray tube with the use of a cephalostat cassette holder. A General Electric 1000 x-ray machine with a 2.7 mm aluminum equivalent half-value layer was operated at 10 mA and 80 kVp. The machine timer was checked with a spin top and was found to be consistently accurate for all indicated times. The cassettecontaining a film-screen combination
Volume 62 Number 2
Sensitometric
I. Relative speed,contrast, latitude, and resolution of XRP, OG, and TMG films
Table
XRP Film ----OGFilm . . . . . . TMG Fi,m
Relative speed Contrast Latitude Resolution
200 2.6 1 0.67 4.6
,,...” ,:’
286 2.40 0.73 4.5
..‘.
C-e _’
Lanex regular screens OG film
219
3.5
3-
X-Omaric regular screens XRP film
and image analysis of T-grain film
___---
.*
TMG f;lm
386 2.69 0.65 6.1
was positioned in the center of the beam of xradiation and exposedfor a time period of 1 impulse. The film was then developed. The process was repeated with the same type of film-screen combination, increasing exposure times up to 90 impulses. A total of nineteen exposures were made for each film-screen combination. The films were processed under rigid processing controls. They were developed in a Litton P6 automatic processor, with Kodak RP X-Omat developer and fixer solutions at a temperature of 80” F. The processing solutions were intermittently replenished and were changed after all the films of a particular film-screen combination were developed. To eliminate the effect of the darkroom safelight, all films were handled in total darkness. Film densities were measured with a TD-502 Macbeth transmission densitometer. All recorded densities were above base and fog density. The statistical package STATPAK (Northwest Analytical, Portland, Oregon) was used on a Zenith Z-100 microcomputer to draw scatter plots of density against log-relative exposure. These scatter plots produced the graphs for the characteristic curves for the various film-screen combinations. The curves were used to derive relative speed, average contrast, and exposure latitude. To study the resolution of the film-screen combinations, an x-ray test pattern distributed by Nuclear Associates (Type 53G, Model 07-533) was x-radiated.” It consisted of lead 50 pm thickin the form of parallel lines enclosed in Plexiglas. The test pattern was attached to the exposure surface of the cassette. The exposure and processing techniques were similar to those used previously in the experiment. To measure resolution, six radiographs with densities closest to 1.50 above base and fog were selected from each of the three film-screen combinations. The density of 1.50 was chosen because it is on the straight line portion of the characteristic curves and is therefore clinically more useful than other extreme
6
014
0:8
1:2
1:6
Lag Relative Exposure
Fig. 1. Characteristic curves: XRP film with X-Omatic regular screens, OG and TMG films with Lanex regular screens.
densities. The eighteen radiographs selected were coded and randomized and then viewed by three observers who used a Kodak achromatic 5X stand magnifier under standardized conditions. Each of the three observers made his choice of the smallest resolving group in which he could count the number of lines with reasonable confidence. The mean resolution of the three observersfor each radiograph was calculated. RESULTS
The characteristic curves of the three films are shown in Fig. 1. The OG and TMG films were combined with Lanex regular screens, whereas the XRP film was combined with X-Omatic regular screens. The curve of each film-screen combination contains information on speed,contrast, and latitude for a useful density range. The speed of a film-screen combination was determined as the reciprocal of the exposure required to yield a density of 1.00 above base and fog density. The relative speedswere calculated from the characteristic curves of Fig. 1. Table I showsthat XRP film with X-Omatic regular screens has a relative speed number of 200, arbitrarily chosen as a reference to match Kodak consumer publication no. M3-138. The TMG film was the fastest with a relative speed of 386, whereas OG had a relative speed of 286. Contrast refers to the slope (steepness) of the characteristic curves. In this experiment, the average contrast was calculated for densities ranging from 0.25 to 2.00 above base and fog density. The average contrast produced by the TMG film was higher
220
Thunthy and Weinberg
OI’d Sllrg. August,
1986
than that of the XRP and OG films (Table I). Latitude refers to the range between the minimum and maximum radiation exposures,which produces a scale of densities acceptable for diagnostic purposes. In this experiment, latitude was calculated from a density of 0.25 to a density of 2.00 above base and fog density. The TMG film produced the highest contrast (Table I). Because latitude is inversely proportional to contrast, it also produced the narrowest latitude. The OG film produced the lowest contrast and therefore the widest latitude. Resolution refers to the ability of an imagerecording system to record separate structures that are close together. Table I shows that the TMG film produced the highest resolution, whereas the XRP and OG films produced nearly the same resolution.
Kodak recommendsa safelight filter, type GBX-2, with a standard frosted 15 watt bulb for use in the darkroom. However, in the experiment, all processing was done in total darkness to eliminate the effect of the safelight. This new film is one of the most important advances in dental radiography. So far, radiology textbooks and articles have stated that there is always a trade-off between film speed and image quality. This statement is no longer true with the development of the T-grain film. As the experiment shows, an orthodontist can use a fast film without sacrificing image quality. The possible use of the T-grain film in panoramic radiography needs to be investigated.
DISCUSSION
The TMG film is the result of a new technology that makes fast films with high image quality. This is contrary to the widely held notion that speed is inversely proportional to image quality. The TMG film is twice as fast as the XRP film and one and one-third times as fast as the OG film. It also produces high resolution and high contrast.
Advances in film-manufacturing technology have led to the development of faster films. These increases in film speed have resulted in decreasesin image quality. However, the new technology of TMG film produces a faster film that also has higher image-resolving power. The results of the experiment showed that the TMG film had higher speed, contrast, and resolution than the OG and XRP films. The TMG film achieves high speed without sacrificing image quality, contradicting the widely held notion that speed is inversely proportional to image quality. Many variables are involved when measuring the speed of a film-screen combination, and therefore absolute values cannot be used. Comparisons made at various densities could have different relative speedsthan the ones obtained at a density of 1.00. Similarly, comparisons of average contrast and exposure latitude, made at various density ranges, could have different results from the ones obtained at a density range of 0.25 to 2.00. Resolution was measured clinically with a stand magnifying glass. Although a sophisticated instrument or method of measurement would have increased the numeric values obtained, the relative resolutions would have been the same.
CONCLUSIONS
REFERENCES I. Arnold reciprocity
BA,
Eisenberg H, Bjarngard law failure in green-sensitive
gy lt6:493-498, 2. 3. 4. 5. 6.
BE: Measurements of x-ray films. Radiolo-
1978.
Eastman Kodak Company: Kodak tilm/screen combinations. Publication No. M3-138, Rochester, N.Y., 1980. Eastman Kodak Company: Sensitometric properties of x-ray films, Publication No. Ml-2, Rochester, N.Y., 1973. Reynolds J, Skucas J, Gorski J: An evaluation of screen-film speed characteristics. Radiology 118: 7 I 1-7 13, 1976. Skucas J. Gorski J: Application of modern intensifying screens in diagnostic radiology. Med Radiogr Photogr 56(2): 25-36, 1980. Thunthy KH, Manson-Hing LR: A study of the resolution of dental films and screens. ORAL. SURG ORAI Mto ORAL PATII~I 42(2): 255-266, 1976.
Rqvint rcyimrs 10. Kavas H. Thunthy Department of Oral Diagnosis School of Dentistry Louisiana State University Medical II00 Florida Ave. New Orleans, LA 70119-2799
Center