An ultrasound contrast-detail phantom has been developed to evaluate the image quality of diagnostic ultrasound imaging systems. The phantom includes eight conical targets whose B-mode images show disk lesions such that the object contrast of each lesion relative to background is independent of the imaging device or transducer frequency/spectrum. By maintaining conditions for Rayleigh scattering and Rayleigh speckle statistics in the phantom gel, the object contrast of each lesion depends only on the scatterer concentration in the lesion relative to the scatterer concentration in the background. Experimental data confirmed this frequency independence. Results of contrast-detail performance of an ultrasound imaging system are shown, and a standard technique for error analysis of contrast-detail data is described.

Humans↗

PubMedDate not supplied

A contrast-detail analysis of diagnostic ultrasound imaging.

For diagnostic ultrasound imaging, as in computed tomography, a feature of prime importance is the detection of focal lesions of varying size and contrast (echo amplitude) from surrounding tissue. This study describes a new tissue-stimulating phantom which has been used to measure the threshold detection of varying contrast, simulated lesions. The phantom consists of a block of tissue-mimicking gelatin which contains a row of conical targets at a depth of 7 cm. Each cone contains a different tissue-mimicking material so that the echo amplitude of the cones relative to the background material covers a dynamic range of 20 dB. Cross-sectional B-scans, perpendicular to the lengths of the cones, result in images of disks of constant diameter but varying contrast. Parallel cross-sectional scans yield "lesions" varying in diameter from 20 to 1 mm. Relative contrast of the cones vs background tissue is obtained by varying scattering particle sizes from 90 to 300 microns. Ultrasound B-scans of the phantom were examined by medical physicist observers to determine threshold detection of lesions as a function of size and contrast. The results indicate that detection of high contrast targets is limited by the imaging system's spatial resolution. Detection of low contrast targets is limited by the image speckle, i.e., coherent noise.

Models, Structural↗

PubMedDate not supplied

A clinical evaluation of contrast-detail analysis for ultrasound images.

We report on the reproducibility of human observers' vanishing detection thresholds for visual targets in contrast-detail (C/D) analysis of ultrasound B-mode images. The images used in this study contain visual targets which are circular cross sections of constant-contrast conical structures in the C/D phantom. The vanishing threshold diameters for these targets vary as a function of the perceived size of the imaged target, target-to-background contrast, image noise content, and reproducibility of the decision levels of human observers for repeated observations. Our study indicates that the determination of absolute vanishing threshold diameter values for several targets of different contrast by human observers yields a high degree of error that is not predicted by existing theoretical assumptions based on a static threshold detector. We find that systematic error is introduced by the observers during the course of the experiment and that the levels of sensitivity of the observers differ widely at all times, and increase the amount of total observer error. These results suggest that, due to the large total observer error, C/D analysis may be impractical in a clinical environment, unless there is access to a team of observers specifically and extensively trained in this task. We suggest that a computer-based observer may be more reliable for the objective performance of contrast-detail analysis as a method for evaluating ultrasound image quality and comparison of imaging systems.

Humans↗

PubMedDate not supplied

In vivo cariostatic activity of actinobolin.

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Animal Feed↗

PubMedDate not supplied

Determination of selenium in urine by hydride generation atomic absorption spectrometry.

A procedure has been developed for determination of total selenium in urine by hydride generation atomic absorption spectrometry. Mineralization was performed with a nitric acid-perchloric acid mixture on a thermostated digestion block. The method was validated by comparison with the method involving mineralization in a microwave acid digestion bomb containing nitric acid and small amounts of vanadium pentoxide. Se(VI) was reduced to Se(IV) by dissolution in 7N HCl. Sample recoveries, precision studies, and analyses of a certified reference material demonstrated the reliability and accuracy of this technique. Urine samples had selenium concentrations ranging from 4.6 to 50.3 micrograms/L. These values correspond to an average of 54.9 micrograms per person per day total ingested and bioavailable Se in the daily diet.

Female↗