Physical performance of diagnostic imaging modalities.
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Decision Making↗
Biomedical subjects
R F Wagner
Publications and source records attributed to R F Wagner.
Classifier design for computer-aided diagnosis: effects of finite sample size on the mean performance of classical and neural network classifiers.
Classifier design is one of the key steps in the development of computer-aided diagnosis (CAD) algorithms. A classifier is designed with case samples drawn from the patient population. Generally, the sample size available for classifier design is limited, which introduces variance and bias into the performance of the trained classifier, relative to that obtained with an infinite sample size. For CAD applications, a commonly used performance index for a classifier is the area, Az, under the receiver operating characteristic (ROC) curve. We have conducted a computer simulation study to investigate the dependence of the mean performance, in terms of Az, on design sample size for a linear discriminant and two nonlinear classifiers, the quadratic discriminant and the backpropagation neural network (ANN). The performances of the classifiers were compared for four types of class distributions that have specific properties: multivariate normal distributions with equal covariance matrices and unequal means, unequal covariance matrices and unequal means, and unequal covariance matrices and equal means, and a feature space where the two classes were uniformly distributed in disjoint checkerboard regions. We evaluated the performances of the classifiers in feature spaces of dimensionality ranging from 3 to 15, and design sample sizes from 20 to 800 per class. The dependence of the resubstitution and hold-out performance on design (training) sample size (Nt) was investigated. For multivariate normal class distributions with equal covariance matrices, the linear discriminant is the optimal classifier. It was found that its Az-versus-1/Nt curves can be closely approximated by linear dependences over the range of sample sizes studied. In the feature spaces with unequal covariance matrices where the quadratic discriminant is optimal, the linear discriminant is inferior to the quadratic discriminant or the ANN when the design sample size is large. However, when the design sample is small, a relatively simple classifier, such as the linear discriminant or an ANN with very few hidden nodes, may be preferred because performance bias increases with the complexity of the classifier. In the regime where the classifier performance is dominated by the 1/Nt term, the performance in the limit of infinite sample size can be estimated as the intercept (1/Nt= 0) of a linear regression of Az versus 1/Nt. The understanding of the performance of the classifiers under the constraint of a finite design sample size is expected to facilitate the selection of a proper classifier for a given classification task and the design of an efficient resampling scheme.
Computer Simulation↗
Uncertainties in estimates of lesion detectability in diagnostic ultrasound.
Statistical properties of estimates of focal lesion detectability for medical ultrasonic imaging systems are investigated. Analytic forms for bias and variance of estimates of detectability of a lesion consisting of fully developed speckle embedded within a speckle background are derived. Bias and variance of estimates of detectability are investigated using a computer simulation and experiments on tissue-mimicking phantoms. This work offers a systematic methodology for interpreting measurements on phantoms in order to assess lesion detectability. In addition, it provides useful results which may be used to improve design of phantoms and experiments for imaging-system performance assessment.
Computer Simulation↗
Beach holiday sunburn: the sunscreen paradox and gender differences.
A survey about sunbathing practices was performed on a summer holiday weekend at a Galveston beach. The likelihood of sunburn increased with increasing duration of sun exposure, with 100% of subjects experiencing sunburn after exposure > or = 4.5 hours. Men exhibited a significantly higher frequency of sunburn, employed fewer sun-protective measures, and demonstrated less knowledge concerning sun safety information and skin cancer than women. This information suggests a need for greater educational efforts directed toward changing public attitudes about preventing sunburn, especially those of men, that currently lead to high-risk sunbathing behavior.
Adolescent↗
Asymptomatic swelling of a man's ear. Auricular pseudocyst.
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Adult↗
Mohs micrographic surgery.
Mohs micrographic surgery (MMS) is a specialized type of minimal marginal surgery that offers cure rates superior to other options in the treatment of contiguous skin cancers in selected settings. Developed by Dr. Frederic E. Mohs, the technique originally required in situ tissue fixation before excision. Most Mohs micrographic surgeons now use the fresh tissue technique exclusively. Horizontal frozen histologic sections of the excised tumor permit more complete microscopic examination of the surgical margin than traditional methods. Residual tumor is graphically mapped and malignant extensions are pursued with staged excisions until the tumor is removed. Maximum sparing of tumor-free adjacent tissue is achieved with histologic mapping of the tumor boundaries, thus optimizing subsequent wound reconstruction. The history, techniques, indications, cure rates, and current controversies of MMS are reviewed.
Carcinoma↗
Tumor remnants within giant cells following irradiation of cutaneous squamous cell carcinoma.
BACKGROUND: The histopathologic effects of curative doses of radiation therapy on cutaneous squamous cell carcinoma (SCC) have not been well described in the dermatologic literature. OBJECTIVE: To understand the histopathologic process of cutaneous SCC involution following radiation treatment. METHODS: Hematoxylin-eosin stain and immunoperoxidase stains for keratin were performed on tissue from the site of a primary cutaneous SCC 2 months after completion of fractionated radiation therapy (7000 cGy total) but prior to clinical involution. RESULTS: Histopathological examination of the irradiated SCC revealed dermal keratin pearls and keratinocytic necrosis resembling apoptosis as well as inflammation and foreign body giant cell reaction. Immunoperoxidase staining for keratin revealed cellular remnants of cutaneous SCC without intact keratinocytic nuclei within giant cells. CONCLUSION: Complete clinical resolution of the SCC over the next several weeks without recurrence after 15 months confirmed the histopathologic findings of tumor destruction by primary radiation therapy.
Aged↗
Metastatic basal cell carcinoma presenting as unilateral lymphedema.
BACKGROUND: Metastatic basal cell carcinoma (MBCC) is rare, occurring in only 0.0028-0.55% of all basal cell carcinomas (BCCs). Patients with MBCC may present with a variety of findings, related to the site of metastasis. OBJECTIVE: Clinical presentation of a MBCC that became symptomatic due to unilateral lymphedema and a review of the relevant literature. METHODS: Case report with literature review. RESULTS: Patients may present with lymphadenopathy, ulcerations, anemia, bone pain, or muscle weakness related to the site of metastasis. In this reported case, MBCC presented as unilateral lymphedema. Risk factors for MBCC include radiation, large and invasive tumors, and a history of recurrence. The average survival time for localized lymph node metastasis in BCC is 3.6 years. This patient is currently 2 years since MBCC presentation and is currently without evidence of recurrence. CONCLUSION: To our knowledge, we report the first case of MBCC that presented as unilateral lymphedema.
Aged↗
Dermatologists' attitudes toward independent nonphysician electrolysis practice.
BACKGROUND: Dermatologists' attitudes toward independent electrolysis practice by nonphysicians has historically ranged from the critical to the praiseworthy. It is hypothesized that dermatologists' attitudes toward independent electrolysis practice by nonphysicians is related to physicians' perception of licensing requirements for independent nonphysician electrologists (INE). METHODS: Nine hundred and thirty-seven fellows of the American Academy of Dermatology (AAD) residing in the Southern United States were anonymously surveyed about independent electrolysis practice by nonphysicians. The results of the survey were analyzed using the Pearson chi-square test. RESULTS: Dermatologists who perceived that licensing was required for INE were significantly more likely to refer patients to INE for hair removal (P = 0.001) and prescribe EMLA cream (lidocaine 2.5% and prilocaine 2.5%) to patients requesting it for electrolysis performed by INE (P = 0.001). However, those dermatologists who had electrolysis services available in their practice settings (15.1%) were significantly less likely to refer patients to INE (P = 0.001) and to prescribe EMLA cream to patients seeking electrolysis from INE (P = 0.034). Only 5.7% of responding dermatologists supported the use of hair removal lasers by INE. CONCLUSION: Dermatologists' attitudes toward INE generally appear to be positively related to perceived licensure requirements for INE, but these positive attitudes do not extend to independent laser use by nonphysician electrologists for hair removal.
Allied Health Personnel↗
[Effect of subjective theories on the coping with illness process--exemplified by patients with chronic pancreatitis].
The concept of locus of control, as a basic aspect of subjective self-perception and world perception, has turned out to be an important construct in the area of psychosomatic medicine for the explanation and prediction of illness-relevant behaviour. This study investigates the influence of illness-specific locus of control on the course of the disease in patients suffering from chronic pancreatitis. While most investigations in this area of research are methodologically restricted to paper-and-pencil questionnaires, the present study registered the concept of locus of control within the metatheoretical framework of "research programme subjective theories". This programme focuses on the capacity of patients to create their own models of their relationship with the world. The procedure involves two stages of research: In the first phase of communicative validation the patient is interviewed about the possibility to influence the course of his disease. A few days later, in a second session, the patient models together with the interviewer a structure of his subjective theory. In the second stage, the phase of explanatory validation, this model will be tested using empirical methods for validation. Compared to a paper-and-pencil questionnaire this procedure means more expenditure for research. On the other hand the results are detailed and specified. Hence, it can be shown that patients dispose over a set of subjective theories on how to influence the course of their illness. These subjective theories determine the patients' coping styles. Methodological and theoretical consequences for coping research and treatment of chronic diseases are discussed.
Adaptation, Psychological↗
Emergency department management of sunburn reactions.
The medical records of fifteen patients presenting to the emergency department of a university hospital for sunburn were reviewed. Patients with sunburn had a mean age of 27 years and injury was most likely to occur in July. Six patients had blisters secondary to the ultraviolet injury. Treatment with nonsteroidal anti-inflammatory drugs was used for nine of fifteen patients. Although eight instances of patient education about the primary prevention of future sunburn were documented in the medical records, only one patient record had documentation of her being warned about her increased risk for skin cancer.
Adolescent↗
Unusual patterns of chronic photodamage through clothing.
Recent cancer statistics estimate that the yearly incidence of cutaneous malignancies in the United States is similar to the incidence of all other cancers combined. Ultraviolet radiation-induced photodamage of the skin plays a large role in the growth of these skin cancers. The case of a 47-year-old white man with peculiar patterns of actinic skin damage on the anterior chest and back is presented, and the relationship of these findings with his choice of clothing is reviewed. The transmission of ultraviolet radiation through clothing fabrics is addressed, with recommendations for the use of clothing as an effective form of photoprotection.
Basal Cell Carcinoma↗
Images in clinical medicine. Black hairy tongue.
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Aged↗
Revisiting the Michel/Green controversy of 1879: was Carron du Villards the first to use probe/needle electrolysis for permanent hair destruction?
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Dermatologic Surgical Procedures↗
Khite: a non-Western technique for temporary hair removal.
BACKGROUND: Khite (also known as fatlah in Egypt) is a manual technique of temporary vellus hair removal that is widely performed in the Middle East. METHODS: The technique of khite is reviewed as illustrated. RESULTS: Khite is an effective method of removing unwanted vellus hairs. CONCLUSIONS: Dermatologists in all parts of the world should be familiar with khite, because the ease of international travel may bring patients to their attention who have khite-association complications such as erythema, folliculitis, and secondary pigmentary changes.
Hair Removal↗
[The clientel of a psychotherapeutic polyclinic in the light of a documentation base].
A documentation system for use during the diagnostical process with psychotherapy outpatients is outlined, and sociodemographic, medical and psychosocial data of newly admitted patients of a university psychotherapy outpatient department are presented. The population structure is described on the basis of data collected during the first 18 months of the implementation of the assessment system. Data are compared with those of other psychotherapeutical institutions that differ with regard to setting (outpatient vs. inpatient), health care sector (acute care vs rehabilitation) and geographic region. Sociodemographic and medical data are given. Patients' mean age is 33.5 years. Two-thirds of the patients are female. The majority is single and has higher formal education. Slightly more than half of the patients are working. Modes of admittance, somatic and psychological complaints and aspects of illness behaviour are described. Pertaining to diagnostical classification, affective disorders (34%), somatoform disorders (15%) and anxiety disorders (11%) are most frequent. Mean duration of symptoms is 6 years. However, only few patients had prior psychological treatment. Treatments most frequently selected at the time of assessment were psychodynamic psychotherapy (41%), behavioural therapy (24%), and group therapy (10%). When comparing the study population with those of other institutions, differences showed up especially in contrast to rehabilitation clinics, where older, male, and working persons as well as those with somatoform disorders and longer durations of illness are more frequent.
Adult↗
Beachfront screening for skin cancer in Texas Gulf coast surfers.
Skin cancer screening programs may attract the "worried well," while those at greatest risk for skin cancer are less likely to attend. Our purpose was to compare the results of skin cancer screening examinations between persons participating in the 1992 American Academy of Dermatology-sponsored free skin cancer screening and surfers participating in a free beachfront skin cancer screening held in conjunction with a regional surfing competition. The hypothesis was that screening an at-risk population (ie, surfers) would be more productive in terms of incidence of clinically diagnosed malignant skin lesions. Surfers were significantly younger and predominantly male. The incidence of basal cell carcinoma was significantly greater in the surfing population than in the self-selected population with similar ages. This study indicates that directed skin cancer screening of an at-risk population was more productive in finding skin cancer than screening of a self-selected population. Future efforts to identify individuals with skin cancer should be broadened to include high-risk populations such as daytime outdoor athletes and high-risk occupational groups, since they may not be reached by current screening efforts.
Adolescent↗
Statistical properties of estimates of signal-to-noise ratio and number of scatterers per resolution cell.
Elementary theory underlying the relationship between the number of scatterers per resolution cell (N) and echo intensity signal-to-noise ratio (SNR) is reviewed. A relationship between the probability density functions for estimates of N and SNR2 is derived. This relationship is validated using a computer simulation. Phantom and in vitro experiments are described. In one set of experiments on phantoms, empirical distributions of estimates of N and SNR2 are measured and compared to theoretical predictions. The utility of SNR2 for discrimination of phantoms with different values for N is assessed using receiver operating characteristic (ROC) analysis. In another set of experiments, the frequency dependence of the SNR2 estimate is investigated for a two-component phantom and for excised dog kidney. It is shown that the frequency dependence of the SNR can help to identify the presence of two or more scattering components that are spatially mixed. With regard to kidney data, measurements performed both parallel and perpendicular to the predominant nephron orientation are reported. The observed anisotropy is compared to the anisotropy of backscatter coefficient encountered in previous investigations.
Animals↗