Physical characteristics of modern radiographic screen-film systems.

The most important characteristics that determine the performance of a screen-film system are system sensitivity (speed), slope or the average gradient of the characteristic curve, latitude of the film, system resolution (MTF) and system noise. In addition to these, one has to consider secondary characteristics such as the base plus fog level, the base tint, safelight sensitivity, reciprocity law failure and film granularity while evaluating performance. A comprehensive study of many of these characteristics has been made for a number of film-screen systems on the market. The data has been tabulated in the form of what are called "characteristic tables of radiographic film-screen systems." In these tables, characteristics such as average gradient, base plus fog level, etc. which depend on film alone, appear along the horizontal axis and MTF values which essentially depend on screens only appear along the vertical axis. The body of the table contains the absolute speeds in units of mR-1 at 80 KVP (heavy filtration) and a quantum mottle index of the various film-screen combinations tested, since these depend both on the film as well as on the screens.

Predicting femoral neck strength from bone mineral data. A structural approach.

An interactive computer program was developed to derive femoral neck geometry from raw bone mineral image data for an estimate of hip strength using single plane engineering stress analysis. The program, which we call Hip Strength Analysis (HSA), was developed as an attempt to improve the predictive value of hip bone mineral data for osteoporosis fracture risk assessment. We report a series of experiments with an aluminum phantom and with cadaver femora, designed to test the accuracy of derived geometric measurements and strength estimates. Using data acquired with both Lunar DP3 (DPA) and Hologic QDR-1000 (x-ray) scanners, HSA computed femoral neck cross-sectional areas (CSA) and cross-sectional moments of inertia (CSMI) on an aluminum phantom were in excellent agreement with actual values (r greater than .99). Using Lunar DP3 data, CSA and CSMI measurements at mid-femoral necks of 22 cadaver specimens were in good general agreement with literature values. HSA computed cross-sectional properties of three of these specimens were compared with measurements derived from sequential CT cross-sectional images. Discrepancy between the two methods averaged less than 10% along the length of the femoral neck. Finally, breaking strengths of 20 of the femora were measured with a materials testing system, showing better agreement with HSA predicted strength (r = .89, percent standard of the estimate (%SEE) = 21%) than femoral neck bone mineral density (r = .79, %SEE = 28%).

Quantum fluctuations in radiographic screen-film systems.

With the recent introduction of fast rare-earth screens into the market, the question of noise and how it influences image quality becomes particularly important. In this paper a compact formula involving familiar and measurable quantities is derived for the specification of the noise arising from the spatial fluctuations of the x-ray quanta absorbed in the screens. Experimental evidence in support of this concept is also given.

The relationship between resolution and speed of x-ray intensifying screens.

Two important physical characteristics of x-ray intensifying screens, speed and resolution, are inversely related. However, the exact mathematical relationship, if any, between them is not known. To investigate this matter, a simple model is considered, which predicts that the product of the equivalent passband Ne and the square root of the speed is constant for a given phosphor material and given film. This relationship is found to be in excellent agreement with experimental data. The papper concludes with a discussion of the generalized validity of this relationship.

Evaluation of a new x-ray film with reduced crossover.

The improvement in MTF that can be obtained by the reduction of crossover exposures is evaluated using an experimental film supplied by the 3M Company (3M XUD). It was found that image resolution, as measured by the equivalent passband (2 integral of infinity 0 [M(f)]2df), of 3M Trimax 8 screens when used with the experimental 3M XUD film was 2.9 c/mm as compared to 1.8 c/mm when used with a conventional double coated film such as Kodak Ortho G or 3M XD. On the other hand, system speed with 3M XUD film was only 1.6 mR-1 as compared to 3.2 mR-1 with 3M XD film and 2.4 mR-1 with Kodak Ortho G film. These findings were substantiated by phantom studies as well.

On optimizing the xeromammographic image.

This work undertakes a detailed system-based analysis of the xeromammographic process starting from basic considerations. Both the edge enhancement and wide-recording latitude, the two principal characteristics of xeroradiography, are shown to bear an intimate relationship to the electric-field distribution. Criteria and methods are formulated for optimizing xeromammographic image quality and a procedure is developed for calculating the white gap. Densitometric curves are derived for both positive- and negative-mode xeroradiography and found to be in excellent agreement with experiment. The question of image linearity is examined carefully and a threshold value of the electrostatic contrast is established, which sets a natural criterion for the application of Fourier analysis. Furthermore, it is shown that, in xeromammography with its inherently low-contrast structures, an optimal exposure exists which optimizes simultaneously all low-contrast edges. This last finding, coupled with experimental results, suggest immediately the possibility of an automatic exposure termination in xeromammography. Beam hardening is also investigated and it is shown that increased filtration combined with a lower bias potential leads to substantial dose reduction without significant loss of image quality. The paper concludes with a discussion of scattered radiation and how it affects xeromammographic image quality.

Xeromammographic image quality.

Xeroradiography is a diagnostic modality whose image-forming properties are fundamentally different from those of the conventional silver halide process. In this work, the xeromammographic process, representing the low-constrast limit of xeroradiography, is analyzed in detail. A step by step approach is taken, whereby th eimiting factors in the exposure and development stages are identified and quantified. The sensitivity of the Se layer is also computed and the concept of optimal exposure introduced. The paper concludes by considering a simple model for xeroradiographic noise.

Systematic errors in bone-mineral measurements by quantitative computed tomography.

Bone-mineral measurements using quantitative computed tomography (QCT) are commonly based on comparisons with solutions in water of known concentrations of K2HPO4. In this paper are described theoretical and experimental studies that have led to the conclusion that large systematic errors can arise in these measurements, depending on the soft-tissue and fat concentrations in the vertebral spongiosa. In the case of single energy scanning, such large errors have been identified to be due to the varying water content (displacement effect) in the calibration samples and the varying fat content in the region of interest (ROI) within the patient. In the case of dual energy scanning, the error arises because when normalized to that of water, the mass attenuation coefficient of fat increases with photon energy while the reverse is true for K2HPO4. Our studies have also revealed that total trabecular bone density (which includes the mineral, soft tissue, and fat) can be much more accurately determined by the dual energy QCT method than bone mineral alone. This finding is especially interesting since there have been several reports in the literature suggesting that bone density rather than bone-mineral content is a better predictor of the risk of osteoporosis-related fractures.

Emission factors of carbon monoxide and size-resolved aerosols from biofuel combustion.

This study reports emission factors of carbon monoxide and size-resolved aerosols from combustion of wood, dung cake, and biofuel briquette in traditional and improved stoves in India. Wood was the cleanest burning fuel, with higher emissions of CO from dung cake and particulate matter from both dung cake and briquette fuels. Combustion of dung cake, especially in an improved metal stove, resulted in extremely high pollutant emissions. Instead, biogas from anaerobic dung digestion should be promoted as a cooking fuel for public health protection. Pollutant emissions increased with increasing stove thermal efficiency, implying that thermal efficiency enhancement in the improved stoves was mainly from design features leading to increased heat transfer but not combustion efficiency. Compared to the traditional stove, the improved stoves resulted in the lower pollutant emissions on a kW h-1 basis from wood combustion but in similar emissions from briquette and dung cake. Stove designs are needed with good emissions performance across multiple fuels. Unimodal aerosol size distributions were measured from biofuel combustion with mass median aerodynamic diameters of 0.5-0.8 micron, about a factor of 10 larger than those from fossil fuel combustion (e.g. diesel), with potential implications for lung deposition and health risk.

Polygalacturonase: a candidate gene for the soft flesh and deciduous fruit mutation in Capsicum.

The soft flesh and deciduous fruit of pepper (Capsicum spp.) originated from the wild C. frutescens BG 2816 accession is a complete dominant trait controlled by the S gene. We constructed an F2 population from a cross of BG 2816 (SS) and the bell-type C. annuum cultivar Maor (ss) and determined that S cosegregated with the tomato fruit-specific endo-polygalacturonase (PG) gene. The soft flesh and deciduous fruit phenotypes were observed together in all F2 individuals, indicating a pleiotropic effect of PG on the two traits. We mapped S to pepper chromosome 10 in the region corresponding to that in which PG was previously mapped in tomato. Northern, RT-PCR and western analyses and enzyme activity assays, collectively, indicated that PG is not detected in green, breaker or red fruits of Maor, nor in green fruits of BG 2816. Accumulation of PG mRNA and protein was detected in the fruits of BG 2816, and it increased during ripening from breaker to red stages. The sequence analysis of partial PG cDNA isolated from BG 2816 revealed high homology (87% identity) with the tomato PG. The resemblance of the soft flesh and deciduous fruit phenotypes to PG-associated phenotypes in other fruit crops, the complete linkage between S and PG, and the greater expression of PG in the fruits of BG 2816 than in those of Maor, all strongly indicate that PG is a candidate gene for S.

Collimator misalignment in high energy therapy machines.

Measurements of the intensity distribution of a 60-Co beam revealed a significant field distortion caused by minor misalignment of the collimator assembly which was not detected by routine methods. Accurate monitoring of radiation intensity distribution and periodic visual inspection of collimators are suggested for early detection of this problem.