Optical Density Range Research Articles

Digital mammography—the comparative evaluation of film digitizers

To study the potential of the computer interpretation of digital mammograms it is necessary to use digitized conventional films because at the present time insufficient resolution may be achieved using computed radiography. For example, the automatic detection of very small subtle calcifications requires digitization at 50 μm or smaller with at least 8 bits of grey level (Chan et al, 1987; Dance, 1993). In this paper we present a simple and practical method to evaluate and compare the technical performance of three film digitizers. These all cost about £20 000 and are being assessed as possible methods for obtaining digital mammograms for a national database (Astley, 1993). The digitizers investigated are a drum scanning microdensitometer, a laser scanning densitometer and a CCD camera. According to manufacturers' specifications, each has a high resolution sampling pixel size (50 μm or less) and is capable of digitizing to a grey level of at least 8 bits over the complete range of diffuse optical densities (0–3 or higher) typically found in a mammogram. The digitizers have been compared by measuring the modulation transfer function (MTF), noise and linearity of each system at a pixel resolution of 50 μm with an 8 bit grey scale. Measurement of these properties provides a means of comparison of important parameters such as resolution and dynamic range. Yin et al (1992) have recently presented an evaluation of the imaging properties of a laser film digitizer using a different approach from that described in this paper.

Low loss HEMA/EMA copolymer waveguides with a range of wetting and optical properties

AbstractHomopolymers and copolymers of optical grade hydroxyethyl methacryiate (HEMA) and ethyl methacrylate (EMA) were synthesized with bulk copolymer compositions of 0, 10, 43, 75, 86, 89, and 100 mol % HEMA. Attenuated total reflection IR (ATR‐IR) and X‐ray photoelectron (XPS) spectroscopies showed an unhydrated surface composition that varied insignificantly from the bulk. Polymer surface wettability, percent swelling of the copolymers in water, and the bulk refractive index increased with increasing HEMA content. High‐quality thin‐film integrated optical waveguides (IOW) were spun cast from copolymer solutions with propagation losses of < 1 dB/cm. Waveguide refractive indices determined from coupling angle measurements agreed closely with the bulk measurements. These results show that HEMA/EMA copolymers that form transparent films produce polymer IOWs with a range of bulk swellabilities, surface wettabilities, and optical densities. © 1993 John Wiley & Sons, Inc.

Gel-Based Phantoms for Diagnostic Radiology

Tissue-equivalent phantoms are desirable for evaluation of image quality and dose in diagnostic radiology. A simple and inexpensive method for fabricating tissue-equivalent phantoms simulating soft tissues for use in radiologic imaging is presented. The tissue-equivalent materials are based on the combination of three basic constituents whose quantity, within limits, can be independently adjusted. Protein is supplied by the use of gelatin (collagen) mixed with water to form a gel, and lipid can be supplied using one of a variety of animal or vegetable fats. CT phantoms have been constructed with simulated tumours in a liver background. Contrast down to 0.1% can be reliably produced. Mammographic phantoms have been produced simulating compressed breasts. A gel step wedge is used to measure image contrast. Simulated tumours with a spiculated border are cast into individual steps to assess tumour visability over a range of optical densities.

Gel-Based Phantoms for Diagnostic Radiology

Tissue-equivalent phantoms are desirable for evaluation of image quality and dose in diagnostic radiology. A simple and inexpensive method for fabricating tissue-equivalent phantoms simulating soft tissues for use in radiologic imaging is presented. The tissue-equivalent materials are based on the combination of three basic constituents whose quantity, within limits, can be independently adjusted. Protein is supplied by the use of gelatin (collagen) mixed with water to form a gel, and lipid can be supplied using one of a variety of animal or vegetable fats. CT phantoms have been constructed with simulated tumours in a liver background. Contrast down to 0.1% can be reliably produced. Mammographic phantoms have been produced simulating compressed breasts. A gel step wedge is used to measure image contrast. Simulated tumours with a spiculated border are cast into individual steps to assess tumour visability over a range of optical densities.

Use of an Ivory Wedge as a Test Phantom in Analysing the Influence of Scattered Radiation and Tube Potential on Radiographic Contract in Intraoral Dental Radiology

Contrast, noise and spatial resolution are fundamental physical concepts used to describe image quality. Contrast is one of the most important parameters in conventional film radiography. To facilitate the analysis of the radiographic contrast over a wide range of optical densities, an ivory wedge representative of objects with marked tissue discontinuities has been constructed. It can be used either separately or included within a PMMA phantom representing the middle face to simulate realistic scatter conditions. It is thus possible to investigate how radiographic contrast may be influenced by kV setting, beam filtration, type of generator (constant potential or single pulse) and type of film. The phantom has been used in optimising image quality relative to radiation risk, with the radiographic contrast being determined both theoretically and experimentally in terms of type of film (D and E speed), radiation and object contrast. The importance of controlling physical parameters when investigating image quality and how to achieve this using a well defined phantom is clearly demonstrated.

Novel monochromatic optical density meter

A novel monochromatic optical density meter is described for use with radiographic films. The principles of the instrument are outlined together with a brief description of the construction of a prototype model. The calibration of the meter shows high accuracy ( r = 0.9999) in the optical density range 0–1.5 OD when compared to standard neutral density filters.

Noise in D- and E-speed radiographic film

The purpose of this investigation was to compare image noise in D- and E-speed radiographic film and to establish a basis for choosing a particular speed of film for study of trabecular changes in alveolar bone. Eleven D-speed and 11 E-speed radiographs were made at varying exposures and developed along with unexposed film of each type to produce uniform optical densities that range from approximately 0.05 to 2.5. Profiles (scan lines) were made of each film at a spatial resolution of 0.02 mm. Noise was quantified for each profile using three measures: the standard deviation of the profile pixel intensity, I(x), about the mean, I(x) ; the coefficient of variation of I(x) about I(x) ; and Wiener spectral analysis. Results indicate that the average magnitude of noise for D- and E-speed film over this range of optical densities exceeds 4% and 6%, respectively; the average noise content of E-speed film was 25% to 35% greater than D-speed; and noise energy of both films is concentrated at low spatial frequencies and low optical densities.

Doping dependence of the ultrafast thermalization and relaxation of highly photoexcited carriers in bulk polar semiconductors

Subpicosecond luminescence and transmission spectroscopy for a broad range of doping and optical excitation densities are used for a systematic study of thermalization and energy relaxation of highly photoexcited electrons and holes in bulk intrinsic, n- and p-doped GaAs and InP at room temperature. The measurements are complemented by an ensemble-Monte-Carlo analysis, including non-equilibrium phonons and plasmons as well as electron degeneracy.

Validity of western immunoblot band patterns in the serodiagnosis of Lyme borreliosis

Serodiagnosis of Lyme disease is hampered by low specificity of the standard assays currently used. The Western immunoblot has therefore been proposed as a potential confirmatory test. For the present report, the method was evaluated by testing sera from patients with clinically defined early- and late-stage borreliosis. In early-stage borreliosis, the 41,000-molecular-weight flagellin protein (41K) of Borrelia burgdorferi was the major antigen detected by antibodies in sera, but the specificity of the reaction pattern was dependent on the intensity of the band. The evaluation of different interpretation rules based on a semiquantitative record of band intensities showed the highest specificity (96%) and a corresponding sensitivity of 78% if there was at least one distinct (optical density range, 0.2 to 0.4) immunoglobulin G and immunoglobulin M reaction with the 41K band. Blots of B. burgdorferi proteins were also probed with sera from patients who were diagnosed by clinical criteria as having stage III Lyme borreliosis and with a control group of sera from asymptomatic persons with positive antibody titers against B. burgdorferi in the standard assays. Reaction patterns were recorded densitometrically. Statistical analysis and graphical marker analysis revealed significant discriminating capacities and relatively high specificities, respectively, for the 94K, 30K, and 21K bands, whereas the 41K and 60K bands were not discriminative between the symptomatic and asymptomatic groups and were specific only at high intensity values. Different multiple-band rules were evaluated, revealing a low specificity for positivity definitions of the type "four or five bands present" if the rules were not confined to known major bands.

A contribution to the testing and classification of industrial radiographic films

The equivalent penetrameter sensitivity (EPS) according to ASTM E 746-87 was determined for Agfa D3, D4, D5 and D7 and Azo (Rumania) G1, G2 and G3 films. The optical density range studied was between 1.0 and 4.0. A linear dependence between EPS, average silver grain size and signal-to-noise ratio was found. The crack detectability index determined with slit-type IQIs can be used to obtain quantitative estimates of crack detection in industrial radiography. On the basis of these results an eight-class classification of radiographic films is proposed.

A contribution to the testing and classification of industrial radiographic films

The equivalent penetrameter sensitivity (EPS) according to ASTM E 746-87 was determined for Agfa D3, D4, D5 and D7 and Azo (Rumania) G1, G2 and G3 films. The optical density range studied was between 1.0 and 4.0. A linear dependence between EPS, average silver grain size and signal-to-noise ratio was found. The crack detectability index determined with slit-type IQIs can be used to obtain quantitative estimates of crack detection in industrial radiography. On the basis of these results an eight-class classification of radiographic films is proposed.

Dose anisotropy around an Au‐198 seed source

For interstitial implants with radioactive Au-198 seeds, the dosimetric calculations usually ignore the finite source size and employ a point source approximation, resulting in a computed isotropic dose distribution. However, the measured radiation fluence from Au-198 seeds is reported to be anisotropic, suggesting some amount of dose anisotropy in tissue. We have measured this dose anisotropy around Au-198 seeds (2.5 X 0.8 mm2) using Kodak X-OMAT XV-2 films placed in contact with individual seeds in a phantom. Autoradiographs obtained for various exposure times were digitized and studied with an image analysis computer network. The network's overall spatial resolution was about 0.01 cm. The optical isodensity contours around the seed were obtained. The useful range of optical density (OD) for the system was found to be 1 to 2 OD units. Within this range, the shape of an optical isodensity contour would be identical to an isodose contour. Proximal to the source, the contours were elliptical in shape, elongated along the seed axis. However, further away, the elongation was in the direction normal to the seed axis. This was in agreement with the reported data on the radiation fluence around Au-198 seeds. It was concluded that measurable dose anisotropy existed around Au-198 seeds. However, it was too small to be of any clinical significance.

Thermal damage and haematoporphyrin-derivative-sensitized photochemical damage in laser irradiation of rabbit retina

In photodynamic therapy of solid tumours, 630 nm light is used to activate the photosensitizer haematoporphyrin derivative (HpD) in vivo, resulting in photochemical toxicity. This form of treatment has been used in a wide range of tumour types and sites, including ocular tumours such as malignant melanoma and retinoblastoma. In addition to HpD-sensitized photochemical effects, direct thermal damage may occur if the light exposure is sufficiently high. In this study, the thresholds for immediate and delayed thermal damage to the normal rabbit retina have been measured for a range of incident optical power and energy densities. HpD-sensitized photochemical damage has been demonstrated at light levels below these thermal thresholds. Thus, with appropriate selection of light power levels and exposure times, photodynamic response can be achieved without accompanying thermal damage.

Characteristic curves of dental x-ray film

The characteristic curves of the dental x-ray films Ultra-Speed, Ekta-Speed, Defilux, Dentus, and Phil-X30, all of which are used in Finland, and the absorption of radiation in the films with their protective wrappers were determined at the x-ray laboratory of the Institute of Radiation Protection. The most sensitive film (Ekta-Speed) was found to be almost three times more sensitive than the least sensitive film (Defilux). In the usable optical density range, the gradient of the characteristic curve obtained with the three most sensitive film types—Ekta-Speed, Dentus and Ultra-Speed—was roughly the same, whereas Phil-X30 was far more gentle. All film types gave a resolution better than 10 lp/mm. The grain size used in the most sensitive film was slightly larger than that used in the less sensitive films. The films provided with lead backing foil transmitted 10% to 20% of the radiation, whereas the film type without lead backing foil (Phil-X30) transmitted 70% to 80%.

Quantitative film autoradiography for tritium: Methodological considerations

The details of quantitative film autoradiography for tritium using tritium plastic standards were examined with respect to 3 issues: (1) tritium tissue equivalent (TE) calibration; (2) correction of autoabsorption differences for gray and white matter; and (3) the use of carbon-14 standard sources as a method for quantifying tritium tissue images. Both 3H-tissue and 3H-plastic sources produced linear log-log relationships of 3H-concentration (nCi/mg source weight) vs source optical density (OD) over a reproducible OD range (0.080–0.800). The curves for both 3H-tissue and 3H-plastic were parallel; uncalibrated 3H-plastic standards exhibited a 4-fold higher autoabsorption over 3H-tissue sources for OD values in the linear range. Using chloroform extraction of brains from rats treated with either [ 14H]deoxyglucose ([ 14C]DG) or [ 3H]deoxyglucose ([ 3H]DG), we found neither isotope loss nor redistribution after defatting (30% reduction of tissue dry weight). After chloroform extraction, the OD values from both gray and white matter structures containing carbon-14 were unaltered. Gray matter OD values increased by 28.7 ± 5.6% (mean±S.D.) in structures containing tritium; white matter structures containing tritium exhibited a 115.9 ± 29.3% increase in OD after chloroform extraction. The increase in OD after chloroform extraction was a fixed percent for any given tritium OD value from unextracted tissue when the value was within the linear range of 0.080–0.800 OD units. The magnitude of the higher white matter autoabsorption for tritium was confirmed using tritium impregnated cow brain pastes of variable gray/white mixtures. Chloroform extraction of tissue from [ 3H]DG treated rats was therefore a suitable procedure for direct correction of regionally heterogeneous autoabsorption of tritium. Finally, the rates of image generation for tritium and carbon-14 sources were compared. The rate of increase of OD with increasing exposure time was found to be equal for 3H-tissue and 3H-plastic images; sources of carbon-14 in plastic, however, exhibited more accelerated rates of image generation when compared to tritium sources (i.e. 3H- and 14C-images did not covary with exposure time). The effect of non-covariance on tritium TE calibrated standards was the overestimation of OD values for 14C-plastic standards with increasing times of exposure (comparison of 4 week images to 1 week images showed errors of 35–40%). Use of carbon-14 sources to quantify tritium-generated images therefore required recalibration of 14C-plastic for all exposure times of interest.

Grain protein variability among species of Triticum and Aegilops: quantitative SDS-PAGE studies

Total proteins were extracted from degermed seeds of various species of Triticum and Aegilops with solutions containing sodium dodecyl sulfate (SDS) and mercaptoethanol. The reduced, dissociated proteins were fractionated according to molecular weight (MW) by high-resolution polyacrylamide gel electrophoresis in buffers containing SDS (SDS-PAGE). Stained SDS-PAGE patterns were measured by densitometric scanning over a suitable range of optical density. The data were normalized to equivalent total areas for each of the densitometric scans by means of a computer program that also permitted the construction of patterns of hypothetical amphiploids by averaging patterns of two or three diploid species. The grain proteins of most species examined had distinctive qualitative and quantitative aspects that were characteristic of the species even though nearly every accession or cultivar of a species exhibited at least minor differences in pattern from other accessions or cultivars. The main protein components (probably prolamins) of Triticum monococcum ssp. monococcum, T. monococcum ssp. boeoticum, T. urartu, and Aegilops squarrosa had MW's in the range 29-36 X 10(3) whereas the most important components of Ae. speltoides, Ae. longissima, and Ae. searsii had MW's in the range 37-55 × 10(3). Changes in the quantitative expression of particular genes, especially those coding for storage protein components, may have been associated with speciation. The strong predominance of proteins with MW's in the range 29-36 × 10(3) in some accessions of AB genome tetraploids, such as T. turgidum ssp. dicoccoides, may indicate contributions to the B genome of these tetraploids by T. monococcum ssp. boeoticum, T. urartu, or Ae. squarrosa.

Extension of the dynamic range of the intracavity method of measuring optical densities

A technique was developed for the measurement of a wide range of optical densities of materials. This technique utilizes a laser with a three-mirror resonator and obviates the need for similar optical densities of the sample and calibration material. The method was tested using a helium–neon laser for nonphototropic materials and plasmas, and using an organic dye laser with selective losses introduced into the resonator.

Equilibrium gel permeation: a single-photon counting spectrophotometer for studies of protein interaction.

When a small column or flow cell packed with gel particles is completely saturated with a solution containing molecular species of interest, the average cross-sectional area occupied by the solute (partition cross section) is conveniently and precisely determined by direct optical scanning. For a mixture of interacting solutes this equilibrium gel permeation measurement yields the weight average of the species partition cross sections and the variation of this quantity with solute concentration permits determination of the solute interaction parameters (stoichiometry, equilibrium constants). We have developed a computer-controlled single-photon counting spectrophotometer for these measurements. The instrument exhibits high precision over a wide range of optical density. With counting times in the range of 10-1000 s the standard deviations on optical densities of protein solutions measured at 220 nm are typically 0.0006 at 1 OD, 0.002 at 2 OD, 0.005 at 4 OD. Beer's law tests show that deviations from linearity are less than these precision limits. Partition cross-section measurements for proteins can be made with an accuracy of better than 0.001 and information can be obtained with protein solutions at least as low as 1 mug/ml.

Rapid melting apparatus for studying thermal denaturation of polynucleotides

A spectrophotometer attachment is described which allows complete thermal denaturation of heating/cooling cycles (0 to 90 to 0°C) of polynucleotides to be obtained in less than 5 min. Solutions with a wide range of optical densities (0.15 to 500) can be studied and several examples are given to demonstrate the performance and application of the device.

Extension of a Jouan circular dichroism spectrometer with an optical absorption device

A Jouan circular dichroism spectrometer has been modified to measure low temperature magnetic circular dichroism (MCD) and optical absorption spectra. The apparatus has been fitted for the measurement of MCD mainly by adding a superconducting magnet with magnetic fields up to 6.5 T. To obtain higher resolutions, the standard hydrogen and tungsten lamps were replaced by a xenon arc. A device for the measurement of optical absorption spectra in the optical density range 0-2 was developed, which enabled the scanning of MCD and absorption successively under the same circumstances.