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PubMed2004

Dose response characteristics of new models of GAFCHROMIC films: dependence on densitometer light source and radiation energy.

This paper presents a systematic study of the dose response characteristics of two new models and one commonly used model of GAFCHROMIC film: HS, XR-T, and MD55-2, respectively. We irradiated these film models with three different radiation sources: I-125, Ir-192, and 6 MV photon beam (6 MVX). We scanned the films with three different densitometers: a He-Ne laser with a wavelength of 633 nm, a spot densitometer with a wavelength of 671 nm, and a CCD camera densitometer with interchangeable LED boxes with wavelengths of 665 nm (red), 520 nm (green), and 465 nm (blue). We compared the film sensitivities in terms of net optical density (NOD) per unit dose in Gy. The sensitivity of each film model depends on radiation energy and the densitometer light source. Using He-Ne laser based densitometer as a reference standard, we found the sensitivities (NOD/Gy) for the red lights of wavelengths, 671 nm and 665 nm, are higher by factors of about 2.5 and 2, respectively. The sensitivities for green (520 nm) and blue (465 nm) lights are lower than that for He-Ne laser (633 nm) by factors of about 2 and 4, respectively. The energy dependence of the sensitivity varies with the film model, but is similar for all densitometer light sources. Comparing I-125 to Ir-192 and 6MVX, we note that (a) model XR-T is about eight times more sensitive, and (b) models HS and MD55-2 are about 40% less sensitive. Relative to MD55-2, XR-T is 12 times more sensitive for I-125 but comparable for Ir-192 and 6MVX, whereas HS is 2 to 3 times more sensitive in all cases. This set of results can serve as useful information for making decisions in selecting the film model and compatible densitometer to achieve the best accuracy of dosimetry in the appropriate dose range.

Densitometry↗

PubMed2006

Accurate skin dose measurements using radiochromic film in clinical applications.

Megavoltage x-ray beams exhibit the well-known phenomena of dose buildup within the first few millimeters of the incident phantom surface, or the skin. Results of the surface dose measurements, however, depend vastly on the measurement technique employed. Our goal in this study was to determine a correction procedure in order to obtain an accurate skin dose estimate at the clinically relevant depth based on radiochromic film measurements. To illustrate this correction, we have used as a reference point a depth of 70 micron. We used the new GAFCHROMIC dosimetry films (HS, XR-T, and EBT) that have effective points of measurement at depths slightly larger than 70 micron. In addition to films, we also used an Attix parallel-plate chamber and a home-built extrapolation chamber to cover tissue-equivalent depths in the range from 4 micron to 1 mm of water-equivalent depth. Our measurements suggest that within the first millimeter of the skin region, the PDD for a 6 MV photon beam and field size of 10 x 10 cm2 increases from 14% to 43%. For the three GAFCHROMIC dosimetry film models, the 6 MV beam entrance skin dose measurement corrections due to their effective point of measurement are as follows: 15% for the EBT, 15% for the HS, and 16% for the XR-T model GAFCHROMIC films. The correction factors for the exit skin dose due to the build-down region are negligible. There is a small field size dependence for the entrance skin dose correction factor when using the EBT GAFCHROMIC film model. Finally, a procedure that uses EBT model GAFCHROMIC film for an accurate measurement of the skin dose in a parallel-opposed pair 6 MV photon beam arrangement is described.

Computer Simulation↗

PubMedDate not supplied

Mammography screen-film selection: individual facility testing technique.

Variations in tube output, film processing, and radiologist's preferences affect the screen-film combination that is appropriate for any particular mammographic facility. A technique to test a variety of screen-film combinations for screening mammography is described. Films are selected for testing because of their densitometric characteristics. Dose and clinical reliability are established with phantoms before the screen-film combinations are used to image consecutive patients having bilateral examinations. The mammograms selected for evaluation are those with similar optical density ranges, and which also may be compared to available previous mammograms or which have unusual mammographic findings. All radiologists reading mammograms at a facility independently score the selected cases. Scores of "unacceptable," "acceptable," or "outstanding" are assigned to four basic imaging characteristics: sharpness, contrast, visibility of skin line, and noise. Interobserver variations by this method require normalization, unlike ROC analysis which is not applicable for this data because of the absence of proved pathologic diagnoses. The testing of 5 films and two screens using 42 patient examinations required 2 h of time from each radiologist. It took 7 h of the physicist's time to pretest the 5 films, select the 42 acceptable examinations for testing by the radiologists, and summarize the data.

Female↗

PubMed1996

Basic imaging properties of a new screen-film system for chest radiography.

To evaluate the potential clinical usefulness of a new screen-film system (advanced screen-film system; AD system) for chest radiography, its fundamental imaging properties compared with a conventional screen-film system (HR-4/HR-S) were investigated. The basic imaging properties were evaluated by measuring characteristic (H&D) curves, relative speeds, MTFs (modulation transfer functions), WS (Wiener spectra), and x-ray attenuations of screens. The detail visibilities and pathological details of various diseases in chest radiographs of patients were evaluated subjectively. The film gradient of the AD system was slightly lower at low radiographic density, and higher at high density, as compared with a conventional screen-film system. The screen speed of the AD system was 212% greater than that of the conventional system, and the film speed was 53% that of the conventional film. As the result, the total speed of the AD system was slightly higher compared with the conventional system. The spatial resolution of the AD system was comparable to or slightly lower than that of the conventional system. The noise level of the AD system was considerably lower than that of the conventional system at low (D = 0.5) and middle (D = 1.0) radiographic density levels. However, it was high at high radiographic density (D = 1.8). The radiographic densities in the underpenetrated areas with the AD system were greater than those of the conventional system when the lung densities are matched comparable. Improvement in noise level with the AD system at low and middle density levels may be useful for detection of various diseases in chest radiographs.

Equipment Design↗

PubMed2000

Using light sensitometry to evaluate mammography film performance.

The performance of commercially available light sensitometers was compared with two other methods of x-ray sensitometry to determine whether commercially available sensitometers are viable for evaluating clinical performance of mammography film. X-ray sensitometry was performed using mammography screens that were modified to accommodate a graded optical step tablet (screen sensitometry). Finally, a means for performing intensity-scale x-ray sensitometry was configured (inverse-square sensitometry). Clinical mammography x-ray exposure conditions were used and film processing quality was closely monitored during the study. Statistical results for chi-square probabilities on the resulting contrast curves yielded good agreement for most of the configurations investigated. Comparison of film gradient versus optical density curves showed good agreement for maximum contrast values and the corresponding optical density for maximum contrast for three of the four screen-film combinations used when comparing light sensitometry to screen sensitometry. A similar comparison of light sensitometers to inverse-square sensitometry showed good agreement for maximum contrast, but less agreement for the corresponding optical density of maximum contrast. Based on these results, the authors concluded that commercially available sensitometers could be used to estimate clinical film performance for the screen-film systems tested. In particular they can be used to determine the range of optical densities that provide optimal film contrast.

Biophysical Phenomena↗

PubMed2000

Radiochromic film dosimetry of a low energy proton beam.

In this work some dosimetric characteristics of MD-55-2 GafChromic films were studied in a low energy proton beam (21.5 MeV) directly in a water phantom. The nonlinearity of the optical density was quantified by a factor P(lin). A correction factor P(en), that accounts for optical density dependence on the energy, was empirically determined. The effects of detector thickness in depth dose measurements and of the film orientation with respect to beam direction were investigated. The results show that the MD-55-2 films provide dose measurements with the films positioned perpendicularly to the proton beam. A dosimetric formalizm is proposed to determine the dose to water at depth d, with films oriented perpendicularly to the beam axis. This formalism uses a calibration factor of the radiochromic film determined directly on the proton beam at a reference depth in water, and the P(lin) factor, that takes into account the nonlinearity of the calibration curve and the P(en) factor that, in turn takes into account the change of proton beam energy in water. The MD-55-2 films with their high spatial resolution and the quasiwater equivalent material are attractive, positioned perpendicularly along the beam axis, for the absolute dose determination of very small beam sizes and modulated proton beams.

Calibration↗

PubMed2003

Dosimetric comparison of extended dose range film with ionization measurements in water and lung equivalent heterogeneous media exposed to megavoltage photons.

In this study, a dosimetric evaluation of the new Kodak extended dose range (EDR) film versus ionization measurements has been conducted in homogeneous solid water and water-lung equivalent layered heterogeneous phantoms for a relevant range of field sizes (up to a field size of 25x25 cm2 and a depth of 15 cm) for 6 and 15 MV photon beams from a linear accelerator. The optical density of EDR film was found to be linear up to about 350 cGy and over-responded for larger fields and depths (5% for 25x25 cm2 at depth of 15 cm compared to a 10x10 cm2, 5 cm depth reference value). Central axis depth dose measurements in solid water with the film in a perpendicular orientation were within 2% of the Wellhöfer IC-10 measurements for the smaller field sizes. A maximum discrepancy of 8.4% and 3.9% was found for the 25x25 cm2 field at 15 cm depth for 6 and 15 MV photons, respectively (with curve normalization at a depth of 5 cm). Compared to IC-10 measurements, film measured central axis depth dose inside the lung slab showed a slight over-response (at most 2%). At a depth of 15 cm in the lung phantom the over-response was found to be 7.4% and 3.7% for the 25x25 cm2 field for 6 and 15 MV photons, respectively. When results were presented as correction factors, the discrepancy between the IC-10 and the EDR was greatest for the lowest energy and the largest field size. The effect of the finite size of the ion chamber was most evident at smaller field sizes where profile differences versus film were observed in the penumbral region. These differences were reduced at larger field sizes and in situations where lateral electron transport resulted in a lateral spread of the beam, such as inside lung material. Film profiles across a lung tumor geometry phantom agreed with the IC-10 chamber within the experimental uncertainties. From this investigation EDR film appears to be a useful medium for relative dosimetry in higher dose ranges in both water and lung equivalent material for moderate field sizes and depths.

Dose-Response Relationship, Radiation↗

PubMed2005

Dosimetric evaluation of GAFCHROMIC XR type T and XR type R films.

The high spatial resolution of radiochromic film makes it ideal for dosimetric measurements and dose distributions in regions of high dose gradient. Intensity-modulated radiation therapy, intravascular brachytherapy, and eye-plaque radiation therapy demand precise spatial dosimetric calculations. Such precision is not possible with conventional dosimeters, such as thermoluminescent dosimeters and ionization chambers. Recently, new GAFCHROMIC XR type T and type R films have been developed for radiation dosimetry, specifically in interventional radiology procedures. Dosimetric characteristics (i.e., linearity, post-exposure density growth, energy dependence, dose-rate dependence, and UV light sensitivity) of these new films were investigated. To evaluate the clinical applications of these films, their characteristics were compared with other commercially available film models. GAFCHROMIC XR type T and type R films were found to be more sensitive to low-energy doses as compared with GAFCHROMIC MD-55 films.

Dose-Response Relationship, Radiation↗

PubMed1996

Optimum processing of mammographic film.

Underprocessing of mammographic film can result in reduced contrast and visibility of breast structures and an unnecessary increase in radiation dose to the patient. Underprocessing can be caused by physical factors (low developer temperature, inadequate development time, insufficient developer agitation) or chemical factors (developer not optimized for film type; overdiluted, underreplenished, contaminated, or frequently changed developer). Conventional quality control programs are designed to produce consistent processing but do not address the issue of optimum processing. Optimum processing is defined as the level of processing that produces the film performance characteristics (contrast and sensitivity) specified by the film manufacturer. Optimum processing of mammographic film can be achieved by following a two-step protocol. The first step is to set up the processing conditions according to recommendations from the film and developer chemistry manufacturers. The second step is to verify the processing results by comparing them with sensitometric data provided by the film manufacturer.

Female↗

PubMed1989

Processing of mammographic films: technical and clinical considerations.

Sensitometrically exposed film strips and clinical mammograms from single-emulsion Kodak Ortho M SO-177 and double-emulsion Kodak T-Mat M II films were processed in separate film processors set up for standard and extended-cycle processing. For the extended-cycle method, it is necessary to use a process that is dedicated to mammographic films only. Radiation dose reductions of approximately 30% for Ortho M film and 13% for T-Mat M II film were achieved with the extended-cycle process. In the mammogram comparisons, higher-contrast images were obtained with Ortho M film in the extended-cycle process, which allowed for improved demonstration of marginal structural characteristics of soft-tissue masses and better differentiation of benign and malignant tumors. No significant differences in contrast were observed in the T-Mat M II mammograms obtained with the extended-cycle process.

Adult↗

PubMed1991

Increased radiation dose at mammography due to prolonged exposure, delayed processing, and increased film darkening.

Four single-emulsion films introduced over the past 2 years--Du Pont Microvision, Fuji MiMa, Konica CM, and Eastman Kodak OM--were compared with Eastman Kodak OM SO-177 (Min-RE) film to evaluate their varying effects on mean glandular dose of reciprocity law failure due to prolonged exposure, delayed processing, and increased film darkening as a result of increased radiation exposure to improve penetration of glandular tissue. Exposures over 1.3 seconds led to increased radiation doses of 20%-30%. Delays in processing of 6 hours decreased processing speed by 11%-32% for all films except Du Pont Microvision. Optical density increases of 0.40 required 20%-30% more skin exposure for all five films. Optimal viewing densities were also evaluated and found to be different for each of the five films. Mammographers need to be aware of these differences in mammographic films to achieve maximum contrast at mammography.

Breast↗

PubMed1984

Comparison of xeroradiographs and film for detection of periapical lesions.

Xeroradiographs and Kodak Ektaspeed film were compared with Kodak Ultraspeed film for their ability to reveal periapical lesions. Cadaver specimens containing teeth which were normal or demonstrated periapical inflammatory disease were used as the test objects. These specimens were first radiographed using xeroradiographic plates or film. Following radiography, histologic analysis revealed the true presence or absence of disease. Ten oral radiologists scored all xeroradiographic and film images of the specimens for the presence of periapical disease. In general, the observers detected about 70% of the cases with periapical disease, while simultaneously considering about 10 to 15% of the normal surfaces to be abnormal. Receiver-operating-characteristic (ROC) analysis of the radiographic decisions revealed little difference in the diagnostic performance of the observers using the various image receptors, although both types of film and low-contrast xeroradiographs viewed in transmitted light were all more useful than low-contrast xeroradiographs viewed in reflected light. In terms of patient dose, both xeroradiographic images and Ektaspeed film are preferred over Ultraspeed film.

Diagnosis, Differential↗

PubMed1991

Exposure factors and screen-film combinations in temporomandibular joint radiography.

Exposure factors and screen-film combinations providing optimal quality are identified for transcranial and transpharyngeal temporomandibular joint views, using conventional intra-oral radiographic equipment without grids. Standardized transcranial and transpharyngeal views, using a fixed whole cadaver head, were performed. Ten readily available screen-film combinations, ranging in nominal speed 20-600, were exposed over 40-100 kV. Films were blindly and independently order ranked by three observers on the basis of sharpness and contrast of cortical outline, trabecular detail, and visualization of adjacent bony structures. Preferred screen-film combinations as a function of kV, preferred kV levels for each screen-film combination, and overall ranking irrespective of kV or screen-film combination, were established. Accepting the use of the lowest radiation dose possible for diagnostically useful radiographs but imposing arbitrarily an upper limit of 20 mGy, it was found that exposures between 50 kV and 70 kV gave the optimal result for both techniques. The amount of scattered radiation in the emergent beam differs greatly between the two techniques. The most favoured combinations for the transpharyngeal technique used screens of fine resolution. Min-r/ortho M screen and film with nominal speed 40 at 60 kV gave 8.0 mGy skin dosage at 0.8 seconds exposure; the same combination at 50 kV was the most favoured, but with skin dosage calculated at 16.7 mGy for 3.0 seconds exposure. For the transcranial technique, medium speed screens providing better differentiation of scattered radiation beams and increased speeds were preferred. Most favoured for image quality was the Lanex Fine/T-Mat G combination at 60 kV giving 17.5 mGy skin radiation dose at 1.75 seconds exposure.(ABSTRACT TRUNCATED AT 250 WORDS)

Arthrography↗

PubMed1991

Influence of scattered radiation and tube potential on radiographic contrast: comparison of two different dental X-ray films.

The fundamental concept in image quality of contrast has been analysed in terms of its elements; film, radiation and object contrast, and the theoretical formula to describe their interrelationship have been evaluated. Experiments were designed to investigate the dependence of radiographic contrast on the kV, the type of generator and dental film used (D and E speed). An ivory wedge was used as the object, both alone and within a polymethyl methacrylate phantom as scattering medium. Precise definition and control of the X-ray generators were achieved by means of measurements of the primary X-ray spectra using a Compton spectrometer. D speed was found to have higher film contrast than E speed when compared at the same optical density, due to its lower base and fog and lower level of saturation in these experiments. On the other hand, E speed was found to have wider latitude. The experimental object was reproduced with the highest radiographic contrast using D-speed film and, with a given type of generator, this increased when the kV was decreased. While no difference in scatter/primary ratios was observed using the two different films, a weak dependence on kV in the range from 36 to 77 kV was found and confirmed by Monte Carlo calculations. The results indicate that the D and E speed films used had equal energy absorption properties; the difference in radiographic performance is due to their different film characteristics. The importance of controlling the physical parameters (photon energy spectrum, base and fog and optical density level) when comparing image qualities is clearly demonstrated.

Radiography, Dental↗

PubMed2004

Quality of film-based and digital panoramic radiography.

OBJECTIVES: To compare the image quality of panoramic radiographs obtained with storage phosphor plate and screen-film systems. METHODS: Panoramic radiographs were taken in 60 patients both with film and with a storage phosphor plate system (30 with DenOptix (Dentsply/Gendex) and 30 with Digora PCT). The images were obtained with either the Cranex Tome or the Scanora multimodal X-ray unit. The screen-film combination was Lanex medium/Curix Ortho HT-G. The digital images were displayed as 8-bit images with a 300 dpi resolution on a 19" monitor and the film images were placed on a light box adjacent to the screen. Ten observers evaluated diagnostic image quality by means of visual grading analysis of different anatomical structures. The structures were scored as being visualized much better (5), better (4), equal (3), worse (2) or much worse (1) in the digital images than in the film images. The mean number of patients receiving the different scores was calculated. Statistical methods used were Wilcoxon sign rank test and Mann-Whitney test. RESULTS: On average, visualization was equal in 19 of the 30 patients imaged using Digora PCT; in 10 it was worse. The corresponding values for DenOptix were 20 and 9. The difference between the film-based and the digital images was small but statistically significant (P<0.0001). The difference between the two image plate systems was not statistically significant (P>/=0.17). CONCLUSIONS: It was concluded that digital panoramic radiographs are equivalent to film-based images for most purposes.

Adult↗

PubMed2004

Comparison of the psychophysical properties of various intraoral film and digital systems by means of the perceptibility curve test.

OBJECTIVES: To compare psychophysical properties of two intraoral films and three digital systems using the perceptibility curve (PC) test. MATERIALS AND METHODS: A test object was used to determine the exposures and exposure differences between the total thickness of the test object and details consisting of holes of increasing depth. The PCs for the two intraoral films, UltraSpeed and EktaSpeed Plus, were constructed employing exposure and exposure differences from dose response functions. Integrals of the PCs were calculated to obtain the psychophysical properties of the two films. Psychophysical properties of the two films were compared with those of the three digital systems published previously (CDR, Dixel and Digora). RESULTS: The PC for the EktaSpeed Plus showed a slightly higher peak than that for the UltraSpeed. Available exposure ranges were comparable. The PC for the EktaSpeed Plus was shifted to the left of the exposure axis indicating its higher sensitivity as compared with UltraSpeed. All three digital systems had narrower but higher peaks compared with the films. The integrals for the digital systems were considerably larger than those for the two film types. CONCLUSIONS: All the three digital systems have superior psychophysical properties compared with the two tested films.

Absorptiometry, Photon↗

PubMed1990

Evaluation of radiographs developed by a new ultrarapid film processing system.

The image quality of radiographs developed by a new ultrarapid processor was evaluated to determine if faster processing causes degradation in the image. The processor used was the Konica Super-Rapid SRX-501 model. Two films designed for this processor (Konica MGH-SR and MGL-SR) were processed in 45 sec and were compared with standard rapid processing in 90 sec of corresponding conventional films (Kodak TMG and OC). Rare-earth screens (Kodak Lanex Regular and Lanex Medium) used with the new and conventional films interleaved during angiographic studies or for phantom images were assessed for image quality. The basic imaging properties of the screen-film systems were examined by measuring (1) Hurter and Driffield curves, (2) modulation transfer functions by using the slit method, and (3) noise Wiener spectra. Subjective clinical assessment showed that the images obtained with ultrarapid processing were acceptable, with increased contrast and graininess. Hurter and Driffield curve measurements confirmed higher gradients. Modulation transfer function measurements were the same as for the conventional films. Noise Wiener spectrum measurements showed a 10% increase in noise for MGH-SR vs TMG film and a 30% increase for MGL-SR vs OC film. We conclude that acceptable image quality can be obtained using ultrarapid processing, with processing time approximately 60% that of conventional rapid processing. Potential applications include all areas in which rapid availability of the radiograph for interpretation is important. Although the processor studied was the first of its kind available, our evaluation indicates that the technology is available for a new class of ultrarapid processors.

Evaluation Studies as Topic↗

PubMed2004

An in vivo evaluation of the diagnostic quality ultra-speed versus insight intraoral dental film.

Twelve sets of FMS (full mouth survey) radiographs were taken by California licensed radiology technicians. Ten of the sets of FMS radiographs were taken using Ultra-Speed "D" film on the left side of the patient and Insight "F" speed film on the right side of the patient. The remaining two sets of films were taken using Insight Film on both sides of the patient to act as a control. Ten faculty members of the Diagnostic Department were asked to evaluate the twelve sets of FMS radiographs and report whether they had a preference for the right side, left side, or no preference. Criteria for preference were diagnostic ability and clarity of the films. The results of the study showed a preference for the right side (65.7%), which was imaged with Insight Film, compared to the left side (34.3%), which was imaged with Ultra-Speed Film.

Absorptiometry, Photon↗