Magnetic resonance (MR) imaging of periodic engorgement of the erectile tissue surrounding the turbinates in the beagle dog yields remarkably quiet data that are well fitted by a single sinusoidal wave form. This observation holds in spite of right-left asymmetries in the distribution of the MR signal. The nasal cycle also occurs normally in humans. Judging from the clarity of its MR representation in the dog, it is possible that this phenomenon could be confused in human MR with upper respiratory congestion associated with pathological processes.

Animals↗

PubMedDate not supplied

A simple model combining quantum noise and anatomical variation in radiographs.

A model is presented for the detection of uniform lesions by means of an ideal photon detector. The difference of observed photons between an area overlaying the embedded lesion and an adjacent reference area of equal size constitutes the signal to be detected. Application of ROC analysis reveals that the exact probability distribution of this photon count difference can be approximated well by a Gaussian, on condition that modulation less than 0.1 and signal-to-noise ratio (SNR) greater than 1. Moreover, within these constraints, SNR emerged as the more salient parameter characterizing detection performance. It is shown that in the absence of anatomical variation, lesions of arbitrarily small size may be detected at any prescribed level of confidence, provided one is willing to accept the required high photon exposure. The effect of anatomical variation on detection performance is conveniently demonstrated in a graph of SNR versus exposure. There, two global regions are identified, each characterized by an asymptote, corresponding to either photon-limited or photon-saturated imaging. Under the first condition, quantum fluctuations are dominating the noise, and thus, detection performance is influenced by the photon exposure. Under the second, anatomical variations limit the SNR to an upper value, irrespective of exposure magnitude. Data obtained from dental radiographs demonstrate that anatomical variation is amenable to experimental measurement, and that it sets the upper limit for the SNR achievable in the diagnostic task of detecting incipient carious lesions.

Elementary Particles↗

PubMedDate not supplied

An optimal synthetic aperture for circular tomosynthesis.

In circular tomosynthesis obtained from a sufficient number of radiographs with projection directions forming a single cone, object detail at a distance from the plane of interest is blurred according to the zero order Bessel function. The main lobe of this window function defines slice thickness, while its ringing side lobes are undesirable because they permit further outlying structures to "leak" through. Using the orthogonality of Bessel functions, a sampling scheme consisting of multiple, concentric projection cones was designed to synthesize by a finite Fourier-Bessel series a slice window with superior side lobe suppression. The window that concentrates the most "energy" within a finite slice, and can be realized by a limited number of sampling cones, is the zero order circular prolate spheroidal function. Its application to tomosynthesis of 3 mm thick slices with a characteristic detail size of 0.5 mm, concentrated 95% of the total series expansion to only 3 concentric circular scans, yielding a theoretical suppression of the first side lobe of -38 dB, to be compared to -8 dB achieved with the Bessel function. Experimental implementation of this optimal sampling scheme using 3, 8, and 14 projection views, distributed over cones with opening half-anges of 1.92, 4.39, and 6.88 degrees, respectively, resulted in a side-lobe attenuation of at least -20 dB. This attenuation reduced significantly artifacts arising from out-of-plane detail of high spatial frequency (e.g., edges) in tomosynthetic images of clinical interest in dentistry.

Humans↗

PubMedDate not supplied

Effect of metal surface treatment on the masking power of opaque porcelain.

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Dental Bonding↗

PubMedDate not supplied

Shot impact test for dental amalgam.

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Dental Amalgam↗

PubMedDate not supplied

Radiographic spatial frequencies essential to the diagnosis of incipient interproximal lesions.

The effects of fixed pattern noise on the interpretation of dental radiographs containing known lesions suggest that reliable detection of incipient interproximal caries is influenced by the spatial frequency of information visibly displayed. Frequencies less than the limiting resolution of existinta also permit demonstration that significantly less resolution is required horizontally than vertically to achieve a criterion level of diagnostic accuracy. These findings are consistent with the notion that accurate diagnosis may be possible with less resolution than is currently produced by conventional bitewing radiographic techniques. If this is trut means for radiographically detecting caries can be developed that require less exposure of the patient to ionizing radiation.

Dental Caries↗

PubMedDate not supplied

Pain and the diagnostic process: conceptions and misconceptions.

Pain may be considered a diagnostic alarm that acknowledges but usually fails to determine the etiology of a particular clinical problem. Diagnosis thus involves the extraction of additional information from a patient in order to determine rational bases for treatment. The process is ill-defined and fraught with error unless the diagnostician is aware of all and only the relevant diagnostic alternatives. This list of alternatives plus an appreciation of the likelihood of each possible diagnostic outcome determines the fastest rate that diagnostic information can be processed by any system in the absence of unpredictable events called noise. Human diagnosticians must be fluent in the "language" used to convey the desired information if performance is to be optimized. In general this involves restructuring the diagnostic task into smaller pieces which are easier to digest perceptually. One way to accomplish this is to ignore or eliminate patterns which are either irrelevant or occur so rarely (or so commonly) that they usually have negligible impact on diagnostic performance. The utility of a diagnosis is determined ultimately by the degree to which it influences the health and well-being of both the patient and society at large. Hence, the consequence of a particular disease may offset the low diagnostic yield per examination resulting from a low or high prevalence of the disease. When diagnostic patterns are limited by ignorance to only signs and/or symptoms such as pain, the diagnostic process loses its meaning and treatment decisions are compromised necessarily by uncertainty.

Diagnosis, Differential↗