The effect of tryptophan on dopa-oxidation by melanosomal tyrosinase

1. Tryptophan has been shown to inhibit dopa-oxidation by melanosomal tyrosinase. 2. The inhibition is of mixed-type with Ki = 1.6 x 10(-3) M. 3. Tryptophan does not interact with the oxidation product of the dopa-oxidase reaction. 4. Neither oxygen nor hydroxyl radicals are involved in the inhibition found in presence of tryptophan. 5. Tryptophan, like dopa, also inhibits tyrosine hydroxylase and dopa-oxidase activity of melanosomal tyrosinase and its inhibitory mechanism differs from inhibition due to non-substrate type compounds like cysteine, ascorbic acid. 6. These experiments together with previous findings suggest that the status of tryptophan may be similar to that of dopa in relation to regulation of melanogenesis.

Cord blood diazepam: clinical effects in neonates of eclamptic mothers

Diazepam used in the treatment of eclampsia crosses the placental barrier readily, and may cause various clinical effects in the neonates. Twenty-five (25) live born babies of eclamptic mothers receiving diazepam were studied and cord blood diazepam concentration was estimated. Effect of low dose of diazepam is minimal apart from lowering of rectal temperature and the effects lasted for a period of 12 hours. But high dose (> 30 mg) of diazepam and prolonged duration of diazepam therapy in mothers causes significant depression of the newborn and the effects lasted for a period of 36-48 hours. As the clinical condition of the newborn is not related to the diazepam concentration in cord blood, the cord blood estimation is not helpful in the assessment of clinical effects of the drug in newborn. The tissue storage of the drug in newborn appears to be responsible for the clinical effects.

Hydroquinone simultaneously induces indole amine 2,3 dioxygenase (IOD) and inhibits tyrosinase in Bufo melanostictus

Hydroquinone administration in Bufo melanostictus causes an induction of indole amine 2,3-dioxygenase in skin and liver while simultaneously inhibiting tyrosinase in these organs. The result is discussed with the reports of higher urinary excretion of abnormal indole metabolites including derivatives of anthranilic acid in vitiliginous subjects (Roychoudhury and Chakraborty, Clinica. Chim. Acta 22, 298, 1968; Kurbanov and Berezov, Vopr. Med. Khim. 22, 683, 1976).

Bone mineral densitometry with x-ray and radionuclide sources: a theoretical comparison

Two methods of dual-photon absorptiometry (DPA) utilizing an x-ray tube instead of a radionuclide source have recently been introduced. In one method kVp switching is employed and two transmitted intensities at each pixel are determined. In the other method, K-edge filtration combined with a single kVp spectrum is used, but photons in two energy windows are counted. We present a theoretical analysis of the two methods, focusing on a figure of merit which is essentially the exposure efficiency (the precision for a given entrance exposure) and tube loading. We also compare their exposure efficiencies to theoretical limits that no DPA system can exceed. Our study indicates that the K-edge-filtered method is more exposure efficient by about a factor of 2. The switched-kVp method requires less heat units per scan by about a factor of 3. A hybrid K-edge switched-kVp method is suggested which achieves the same exposure efficiency as the K-edge-filtered method at lesser tube loading. Our theoretical model is based on published x-ray spectra and attenuation coefficients and is in good agreement with other simulation work. It is of interest that a point source of Gd-153 would be even more exposure efficient, achieving about 90% of the theoretical limit. However, in practice, the Gd source is of finite size and limited strength, and consequently the radionuclide method cannot achieve as good a precision as either x-ray method in similar scan times.

Semiempirical model for generating tungsten target x-ray spectra

A semiempirical model for generating tungsten target x-ray spectra is presented. This model extends earlier work in two significant areas. First, both bremsstrahlung and characteristic x-ray production are assumed to occur at varying depths within the target. Second, optimal parameters for the model were determined from experimental spectra utilizing nonlinear least-squares techniques. As a result, good agreement is obtained between calculated and measured x-ray tube spectra and output for different target angles and a wide range of x-ray tube potentials. Such is not the case with previously published models.

The digital imaging workstation

Picture archiving and communication systems (PACS) are expected to convert film-based radiology into a computer-based digital environment, with associated cost savings and improved physician communication. The digital workstation will be used by physicians to display these "soft-copy" images; however, difficult technical challenges must be met for the workstation to compete successfully with the familiar viewbox. Issues relating to image perception and the impact on physicians' practice must be carefully considered. The spatial and contrast resolutions required vary according to imaging modality, type of procedure, and class of user. Rule-based software allows simple physician interaction and speeds image display. A consensus appears to be emerging concerning the requirements for the PACS workstation. Standards such as the American College of Radiology/National Electrical Manufacturers' Association Digital Imaging and Communication Standard are facilitating commercial applications. Yet much careful study is needed before PACS workstations will be fully integrated into radiology departments.

Free-response methodology: alternate analysis and a new observer-performance experiment

The authors review the recently introduced method for analyzing free-response receiver operating characteristic (FROC) observer-performance experiments. These experiments allow multiple abnormalities and observer responses per image and require correct localization for true-positive events. A fundamental plot, the alternative FROC (AFROC), is emphasized, the area under which is a natural index of performance for measuring FROC observer performance. The authors show that it is possible to analyze free-response data in more general ways. The first method, AFROC analysis, involves scoring FROC images in a different way. The second method involves a new observer-performance experiment, the free-response forced error (FFE) experiment. FROC and AFROC analysis was applied to several FROC data sets, and simultaneous FROC-AFROC-FFE experiments were performed with several radiologist observers to test the three methods. The methods were found to be in good agreement with one another.

A comparison of dual-energy digital radiography and screen-film imaging in the detection of subtle interstitial pulmonary disease

An ROC study is described which compares the performance of three types of images--conventional screen-film, single-energy digital and dual energy bone cancelled (soft tissue) digital--in detecting subtle interstitial pulmonary disease. Marginally detectable nodular and reticulonodular patterns (12 different patterns of each) were superimposed over the lungs of a frozen human chest phantom to simulate the clinical situation. The digital images were formatted on film at full size (ie, 35 cm X 43 cm). A total of 156 images (52 of each type, of which 28 were normal and 24 had simulated pathology) were used in the study and read by five experienced chest radiologists. Using a paired t-test, the areas under the individual ROC curves were compared for three combinations of images--single-energy digital and conventional, soft tissue digital and conventional, and soft tissue and single-energy digital. No statistically significant difference was observed between the conventional and single-energy digital images. The readers performed better with both conventional and single-energy digital images than with the soft tissue digital images at statistically significant levels (P = 0.05 for conventional vs. soft tissue digital and P = 0.02 for single-energy digital vs. soft tissue digital). The results suggest that there is no advantage in employing dual-energy soft tissue images to assist in diagnosing interstitial disease in the clinical setting. They also suggest that spatial resolution requirements are less demanding in digital chest systems that obtain scatter-free images than in digital systems utilizing conventional scatter control techniques.

Maximum likelihood analysis of free-response receiver operating characteristic (FROC) data

Receiver operating characteristic (ROC) methodology is widely used in evaluating medical imaging modalities. While appropriate in some cases, it has several drawbacks when the detection task, e.g., nodule detection, involves localizing the abnormality. Free-response receiver operating characteristic (FROC) methodology offers a more natural framework to describe observer performance in such studies and has other advantages. Due to the lack of a statistical analysis procedure comparable to the maximum likelihood procedure (ROCFIT program) available for ROC studies, the FROC method has not gained widespread acceptance. This work presents and solves a two parameter model for the statistical analysis of FROC data. The model assumes that the probability density of the signal stimuli is normally distributed, as is the probability density for producing one or more false positives per image. A program (FROCFIT) is described for estimating the parameters and their uncertainties from experimental data. An index of performance is proposed to quantify observer performance in FROC experiments. Application of this methodology to several FROC data sets produced good to excellent fits.

An energy sensitive cassette for dual-energy mammography

A cassette for simultaneously acquiring dual-energy mammographic images is proposed and studied utilizing a theoretical noise analysis model. The cassette consists of a sandwich of two storage phosphor plates separated by a copper filter. The front, low atomic number, plate was assumed to be comprised of SrFBr and the rear, high atomic number, plate of commercially available BaFBr (98 mg/cm2 coating weight). Assuming a constant x-ray tube voltage of 50 kVp and a typical breast thickness, the theoretical model yielded a front SrFBr phosphor coating weight of approximately 21 mg/cm2. The study indicates that a relatively large separation in the average of x-ray photon energies absorbed in the two plates can be obtained. It also indicates that both a high-quality conventional (single energy) digital image and a tissue canceled digital image (i.e., a calcium image) can be obtained at dose levels comparable to those currently employed. The latter image could potentially improve the early detection of cancerous microcalcifications and also lends itself to computer aided diagnosis.

Chronic arsenic toxicity from drinking tubewell water in rural West Bengal

Hepatic damage caused by chronic exposure to arsenic has been frequently described. Here we report on 13 patients from West Bengal, India, who consumed large amounts of arsenic in drinking water. An epidemiological investigation of the study area showed evidence of chronic arsenical dermatosis and hepatomegaly in 62 (92.5%) of 67 members of families who drank contaminated water (arsenic level, 0.2-2 mg/l). In contrast, only six (6.25%) of 96 persons from the same area who drank safe water (arsenic level, <0.05 mg/l) had non-specific hepatomegaly, while none had skin lesions. Hepatomegaly occurred in all the 13 patients who were studied in detail, although five had splenomegaly. Biopsy of samples of liver from these patients revealed various degrees of fibrosis and expansion of the portal zone that resembled non-cirrhotic portal fibrosis (NCPF).

The case for radioprotective eyewear/facewear. Practical implications and suggestions

Numerous eyeglass lens materials have been recommended for protection of radiologists' eyes from the cataractogenic effect of radiation during fluoroscopic procedures. For the most part, these lenses coincidentally attenuate x-ray beams because they contain elements of high atomic number that are added to increase refractive index. With a bean hardened to simulate scatter, direct transmission ratios were measured for 32 commercially available lens materials. Scatter to the eye, both through and around the glass lenses and secondary scatter to the eye from the radiologist's head, was determined with lenses mounted on a head phantom and a 1-cm3 ion chamber in the position of the eye. Transmission ratios for the various lenses ranged from 3% to 98% for an 80 kVp x-ray beam (HVL = 4.5 mm Al). Measurements with the head phantom in place show that secondarily scattered radiation from the fluoroscopist's head contributes significantly to ocular exposure. Optimal radiation protection of the eyes during fluoroscopy depends not only on eyeglasses with leaded glass, but also on shielding of sufficient size and shape to reduce exposure to the surrounding head.

Image intensifier distortion correction

A method is described for determining and correcting the spatial distortion affecting images acquired with image-intensified video systems. The distortion is separated into two physically distinct components, a predominant one originating from the projection of the x-ray image onto the curved input phosphor, and a smaller component corresponding to the mapping from the input phosphor to the output phosphor and the digital image matrix. The former is determined geometrically and the latter is modeled with four empirical parameters. A method for determining the two components from calibration images of a grid phantom is presented. The model of the image intensifier distortion was found to be in good agreement with the measured distortion in the images. The correction is applicable to arbitrary angulations of the x-ray beam with respect to the image intensifier tube, and consequently is directly applicable to digital tomosynthesis. The correction allows one to obtain accurate positional information with fluorography and may also be useful in radiation therapy treatment planning and quantitative digital subtraction angiography.

Simulated pulmonary nodules: detection with dual-energy digital versus conventional radiography

Performance of a prototype dual-energy digital chest radiography unit in detecting calcified and noncalcified simulated pulmonary nodules was compared with that of a highly optimized, conventional system. Nodules ranging in size (0.5, 1.0, and 1.6 cm), in number (five to 11), and in calcium content (0-25 mg) were superimposed over the lungs of a frozen, unembalmed, human chest phantom. For each technique, six observers examined 50 posteroanterior projections with different randomized nodule locations. Detection consisted of locating and assigning a level of confidence to each perceived nodular opacity. The resulting plots of the true-positive fraction versus the mean number of false-positive calls per projection indicate that for both calcified and noncalcified nodules, the digital unit performed significantly better (P less than .01).

Digital and conventional chest imaging: a modified ROC study of observer performance using simulated nodules

A modified receiver operating characteristic (ROC) study was performed in which five readers were asked to locate multiple nodules on images of an anthropomorphic phantom obtained with a prototype digital radiographic chest unit and with a conventional chest unit. Results indicate that when nodules were projected over the lungs, a significantly greater number (significant at the 5% level) were identified on conventional radiographs, whereas for nodules projected over the mediastinum, the digital images were notably superior (difference significant at the 2% level). An error analysis of the multiple nodule problem and pseudo-ROC curves are presented. The modified ROC study does not suffer from the positional ambiguity inherent in most ROC studies and is efficient in acquiring data.

Digital subtraction angiography apparatus

An inexpensive digital subtraction angiography (DSA) apparatus that can perform live subtraction, processed subtraction, and road mapping is described. The apparatus can be used in any standard x-ray room with fluoroscopic capability, with a simple connection to the existing TV chain. It is especially useful in therapeutic neuroangiography.

Inverse relationship between melanogenesis and endogenous hydroquinone

Inhibition or stimulation of melanogenesis have been found to occur as a result of the alteration of hydroquinone levels in the body. Substances which stimulate melanogenesis are found to lower the level of hydroquinone in amphibia, and evidence for the relationship is also given by mammalian experiments.

A comparative study of tryptophan metabolism in skins and livers of black and albino rats

The skin of black rats contains less tryptophan than the skin of albino rats, possibly because the activity of tryptophan pyrrolase is higher. The opposite is found in liver, possibly because tryptophan pyrrolase activity is lower in the livers of black rats.

Temperature distributions in tumor models heated by self-regulating nickel-copper alloy thermoseeds

Needle-shaped thermoseeds have been manufactured from an alloy consisting of 70.4% nickel and 29.6% copper. The magnetic properties of the alloy were measured at various temperatures and from this the heating power produced by a thermoseed exposed to an electromagnetic induction field was computed as a function of the seed temperature. Calorimetric measurements were also performed. From these data, temperature distributions in simple tumor models assumed to be heated by an array of nickel-copper implants were computed. It was found that the nickel-copper implants produce substantially better temperature homogeneity than readily available constant power seeds, especially in tumors with unpredictable rates of blood perfusion or when the implant arrangement is not perfectly regular. Since such conditions are likely to be present in actual patients, the nickel-copper implants should be very useful in clinical hyperthermia.

Self-masking subtraction tomosynthesis

The authors tested the image quality and dose savings of self-masking subtraction tomosynthesis (SST), which combines digital tomosynthesis with subtraction of a blurred self-mask. High-quality images of the inner ear of a head phantom were obtained at moderate dose savings. Although they were taken with linear motion, they did not exhibit the streaking due to off-fulcrum objects that is characteristic of conventional linear tomography. SST could reduce patient dose by a factor of at least 12 in examinations of the inner ear, and the mechanical aspects can be implemented with moderate modifications of existing instrumentation.

Signal-to-noise ratio considerations in radiographic imaging

The methodology employed to calculate radiographic signal-to-noise ratio (SNR) for the commonly used disk-shaped test object is reviewed. Although the "matched" aperture yields the maximum SNR, its shape is difficult to achieve experimentally. On the other hand, a circular aperture having the same size as the object is much simpler to realize. We have performed a numerical analysis of the SNRs obtained with matched and circular apertures for two screen/film systems (a mammographic and a general purpose combination) for a range of test-object sizes. We find that for object sizes greater than 0.5 mm in diameter, there is a less than 4% difference between the SNRs obtained with the two apertures. The shapes of some of the matched apertures are also presented. We conclude that the SNR determined with the circular aperture is a simpler and more useful determinant of system performance for the screen/film combinations studied.