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Biomedical subjects

R F Wagner

Publications and source records attributed to R F Wagner.

At least 127 records · Page 7Linked to original sources
PubMed1988

Treatment of extensive extramammary Paget disease of male genitalia with Mohs micrographic surgery.

It is often difficult to accurately judge the clinical tumor margins for extramammary Paget disease. Mohs micrographic surgery was used to extirpate a tumor which clinically measured 159.5 cm2. Following Mohs micrographic surgery, it was found that the actual dimensions of the tumor had been underestimated by 97 per cent. Since the Mohs micrographic surgeon microscopically examines the entire subcutaneous margin of the resected tumor, this technique provides an accurate method of determining the depth of tumor penetration. Mohs micrographic surgery allows for maximal conservation of normal tissue and yields higher cure rates than other conventional methods of treatment. When approaching tumors of the genitalia which may display poorly defined clinical margins, Mohs micrographic surgery should be considered the technique of choice.

Aged↗
PubMed1988

Properties of acoustical speckle in the presence of phase aberration. Part II: Correlation lengths.

In recent years, analysis of the second order statistics of ultrasound speckle has led to accurate prediction and measurements of the average speckle size in the transducer focal zone. In this paper, that work has been extended to the average speckle size as determined by the normalized autocovariance in the presence of transducer phase aberrations. In general, a phase aberration causes a narrowing of the main lobe of the normalized autocovariance in the lateral direction. However, the lateral speckle autocovariance also showed significant side lobes in the presence of phase aberrations, indicating that individual speckles in a region of interest are not independent but are correlated so that less information is present for the task of signal detection when a transducer phase aberration exists. The same evidence of correlated speckle was found in the near field of a transducer in the region of fine speckle texture. This explanation satisfies the quandary of poor detectability in the near field region where the speckle is fine but the lateral resolution is quite degraded. The axial speckle in the presence of phase aberrations showed a small increase in main lobe widths and no evidence of side lobes. Beginning in 1978, the analysis of the second order statistics of speckle images for the purpose of spatial compounding led to accurate measurement and prediction of the cross-correlation curve as a function of transducer aperture translation for purposes of spatial compounding. In this paper, that work has been extended to the presence of transducer phase aberrations. The existence of transducer phase aberrations causes significant increases in the rate of decorrelation of speckle interference patterns as a transducer is translated. This indicates that spatial compounding will result in quite significant improvements in area-wise SNR and low contrast lesion detection for the case of severe random aberrators or focal point errors.

Humans↗
PubMed1988

Gray level transforms and lesion detectability in echographic images.

In search of the optimal display of echographic information for the detection of focal lesions, a systematic study was performed considering a wide range of gray level transforms (i.e., lookup tables). This range comprised power functions of the echo envelope signal (1/8 less than or equal to n less than or equal to 8), power functions of the logarithmic transform and a sigmoid function. The implications of the transforms on the first order statistics (histogram, "point signal-to-noise ratio" SNRp) and on the second order statistics (autocorrelation function) could be derived both analytically, and from the analysis of simulated and experimentally obtained echograms of homogeneously scattering tissue models. These results were employed to estimate the lesion signal-to-noise ratio SNRl, which specifies the detectability of a lesion by an ideal observer. It was found, both theoretically and practically, that the intensity display corresponds to the optimal transform (i.e., n = 2) for a low contrast lesion. When the data were first logarithmically compressed, the lesion SNR appeared to increase with increasing power (1/8 less than or equal to n less than or equal to 8). A logarithmic transform followed by a sigmoid compression did not produce much improvement. These effects of gray level transforms on the SNRl were shown to be relatively small, with the exception of powers n greater than 2 when applied to linear (i.e. amplitude) data. In the case of high lesion contrast, the sequence of log compression, followed by a square law produced the optimum SNRl. This sequence is equivalent to the processing within echographic equipment, where the TV monitor has a gamma of the order of 2.

Computer Simulation↗
PubMed1987

Multifocal recurrent basal cell carcinoma following primary tumor treatment by electrodesiccation and curettage.

Eight recurrent basal cell carcinomas and their adjacent scars, which were previously treated with electrodesiccation and curettage, were completely excised by Mohs micrographic surgery and then studied by serial vertical sections. Through the study of an average of 291 serial sections of each recurrent tumor, it was found that four of eight recurrent basal cell carcinomas contained multiple foci of unconnected tumor. It is concluded that iatrogenic multifocality of recurrent basal cell carcinoma previously treated with electrodesiccation and curettage is common. Complete excision of the recurrent basal cell carcinoma and its adjacent scar is supported in view of the high risk of multiple unconnected tumor foci.

Adult↗
PubMed1987

Statistical properties of radio-frequency and envelope-detected signals with applications to medical ultrasound.

Both radio-frequency (rf) and envelope-detected signal analyses have lead to successful tissue discrimination in medical ultrasound. The extrapolation from tissue discrimination to a description of the tissue structure requires an analysis of the statistics of complex signals. To that end, first- and second-order statistics of complex random signals are reviewed, and an example is taken from rf signal analysis of the backscattered echoes from diffuse scatterers. In this case the scattering form factor of small scatterers can be easily separated from long-range structure and corrected for the transducer characteristics, thereby yielding an instrument-independent tissue signature. The statistics of the more economical envelope- and square-law-detected signals are derived next and found to be almost identical when normalized autocorrelation functions are used. Of the two nonlinear methods of detection, the square-law or intensity scheme gives rise to statistics that are more transparent to physical insight. Moreover, an analysis of the intensity-correlation structure indicates that the contributions to the total echo signal from the diffuse scatter and from the steady and variable components of coherent scatter can still be separated and used for tissue characterization. However, this analysis is not system independent. Finally, the statistical methods of this paper may be applied directly to envelope signals in nuclear-magnetic-resonance imaging because of the approximate equivalence of second-order statistics for magnitude and intensity.

Humans↗
PubMed1986

Noise analysis of scintillation camera images: stochastic and non-stochastic effects.

An analysis of noise was performed on scintillation camera images. The analysis was performed on sets of field floods, uniform exposures over the field of view, in such a way that stochastic and non-stochastic effects were separable. Stochastic noise for the digitally acquired images was found to approach the limit of Poisson count statistics. The non-stochastic component of the calculations dominated the results at the lower spatial frequencies. These results hold true even after standard methods of uniformity correction are applied, primarily due to the effects of Compton scatter events. The noise power spectrum calculations carry information about the patterns of the noise in flood images. Examples of digitisation, photomultiplier tube mottle and edge-packing artefacts are presented.

Photography↗
PubMed1986

Late recurrent basal cell carcinoma presenting as a unilateral exophthalmos.

A late recurrent basal cell carcinoma which presented as a unilateral exophthalmos is described. Published surgical protocols of the 1960's advocated deferring further treatment for incompletely excised cutaneous basal cell carcinoma unless there was clinical evidence of tumor recurrence. Our patient demonstrates that this approach may result in late, unusual, and fatal patterns of recurrence. Complete excision of primary basal cell carcinoma is advocated.

Aged↗
PubMed1986

Solitary pigmented Bowen's disease of the scrotum.

An elderly Chinese man with solitary pigmented Bowen's disease of the scrotum is described. This disease must be distinguished from seborrheic keratoses, pigmented basal cell carcinoma, melanocytic nevus, malignant melanoma, and bowenoid papulosis.

Aged↗
PubMed1986

Pattern recognition methods for optimizing multivariate tissue signatures in diagnostic ultrasound.

Described is a supervised parametric approach to the detection and classification of disease from acoustic data. Statistical pattern recognition techniques are implemented to design the best ultrasonic tissue signature from a set of measurements and for a given task, and to rate its performance in a way that can be compared with other diagnostic tools. In this paper, we considered combinations of four ultrasonic tissue parameters to discriminate, in vivo, between normal liver and chronic active hepatitis. The separation between normal and diseased samples was made by application of the Bayes decision rule for minimum risk which includes the prior probability for the presence of disease and the cost of misclassification. Large differences in classification performance of various tissue parameter combinations were demonstrated using the Hotelling trace criterion (HTC) and receiver operating characteristic (ROC) analysis. The ability of additional measurements to increase or decrease discriminability, even measurements from other diagnostic modalities, can be evaluated directly in this manner.

Humans↗