Coded-aperture imaging in nuclear medicine

Coded-aperture imaging is a technique for imaging sources that emit high-energy radiation. This type of imaging involves shadow casting and not reflection or refraction. High-energy sources exist in x ray and gamma-ray astronomy, nuclear reactor fuel-rod imaging, and nuclear medicine. Of these three areas nuclear medicine is perhaps the most challenging because of the limited amount of radiation available and because a three-dimensional source distribution is to be determined. In nuclear medicine a radioactive pharmaceutical is administered to a patient. The pharmaceutical is designed to be taken up by a particular organ of interest, and its distribution provides clinical information about the function of the organ, or the presence of lesions within the organ. This distribution is determined from spatial measurements of the radiation emitted by the radiopharmaceutical. The principles of imaging radiopharmaceutical distributions with coded apertures are reviewed. Included is a discussion of linear shift-variant projection operators and the associated inverse problem. A system developed at the University of Arizona in Tucson consisting of small modular gamma-ray cameras fitted with coded apertures is described

Molecular Analysis of N6-Methyladenine Patterns in \u3cem\u3eTetrahymena thermophila\u3c/em\u3e Nuclear DNA

We have cloned two DNA fragments containing 5\u27-GATC-3\u27 sites at which the adenine is methylated in the macronucleus of the ciliate Tetrahymena thermophila. Using these cloned fragments as molecular probes, we analyzed the maintenance of methylation patterns at two partially and two uniformly methylated sites. Our results suggest that a semiconservative copying model for maintenance of methylation is not sufficient to account for the methylation patterns we found during somatic growth of Tetrahymena. Although we detected hemimethylated molecules in macronuclear DNA, they were present in both replicating and nonreplicating DNA. In addition, we observed that a complex methylation pattern including partially methylated sites was maintained during vegetative growth. This required the activity of a methylase capable of recognizing and modifying sites specified by something other than hemimethylation. We suggest that a eucaryotic maintenance methylase may be capable of discriminating between potential methylation sites to ensure the inheritance of methylation patterns

Estimating Subjective Probabilities

Subjective probabilities play a role in many economic decisions. There is a large theoretical literature on the elicitation of subjective probabilities, and an equally large empirical literature. However, there is a gulf between the two. The theoretical literature proposes a range of procedures that can be used to recover subjective probabilities, but stresses the need to make strong auxiliary assumptions or "calibrating adjustments" to elicited reports in order to recover the latent probability. With some notable exceptions, the empirical literature seems intent on either making those strong assumptions or ignoring the need for calibration. We illustrate how the joint estimation of risk attitudes and subjective probabilities using structural maximum likelihood methods can provide the calibration adjustments that theory calls for. This allows the observer to make inferences about the latent subjective probability, calibrating for virtually any well-specified model of choice under uncertainty. We demonstrate our procedures with experiments in which we elicit subjective probabilities. We calibrate the estimates of subjective beliefs assuming that choices are made consistently with expected utility theory or rank-dependent utility theory. Inferred subjective probabilities are significantly different when calibrated according to either theory, thus showing the importance of undertaking such exercises. Our findings also have implications for the interpretation of probabilities inferred from prediction markets.

Detecting early signs of depressive and manic episodes in patients with bipolar disorder using the signature-based model

Recurrent major mood episodes and subsyndromal mood instability cause substantial disability in patients with bipolar disorder. Early identification of mood episodes enabling timely mood stabilisation is an important clinical goal. Recent technological advances allow the prospective reporting of mood in real time enabling more accurate, efficient data capture. The complex nature of these data streams in combination with challenge of deriving meaning from missing data mean pose a significant analytic challenge. The signature method is derived from stochastic analysis and has the ability to capture important properties of complex ordered time series data. To explore whether the onset of episodes of mania and depression can be identified using self-reported mood data.Comment: 12 pages, 3 tables, 10 figure

Demonstration and Characterization of an Epidermal Angiogenic Factor

In this study the vasoproliferative effects of adult hamster epidermis and epidermal homogenates on the microvasculature of the hamster cheek pouch were observed. Implants of epidermis stimulated a rapid growth of new vessels both upon direct implantation and when separated from the vascular bed by a microporous filter. No significant vasoproliferation was seen with dermis, polythene, dialysis membrane, Millipore filter, with epidermis placed on or within sheets of dialysis membrane, or when the epidermis had been inactivated by heat treatment. Epidermal homogenates, Millipore filtrates, and dialysis tenates induced new vessel growth whereas similar preparations from dermis did not. Activity was found to be present in the aqueous but not the organic phase following ethyl acetate extraction and was deactivated by heating or removed by precipitation with trichloroacetic acid. Vasoproliferative activity was not affected by maintenance at 4° C for up to 7 days. These observations are interpreted as evidence for a specific, heat-labile, diffusible but nondialyzable protein “epidermal angiogenic factor.

The evaluation of cognitive function in the dementias: methodological and regulatory considerations

Impairment of cognitive function is the central feature of dementia. Although, clinically, the cognitive deficit most often manifests itself as memory problems, a number of other areas of cognition are affected, and memory is but one of the cognitive skills compromised in dementia. Dementia with Lewy bodies, for example, accounts for 15% to 25% of all dementias and does not have memory deficits as a core feature. Our cognitive facilities underlie our abilities to engage successfully in the activities of daily living (ADL) and it follows thai enhancement of cognitive function will facilitate performance of ADL The assessment and understanding of these impairments are crucial to any treatment of the disorder. Unfortunately, the principal instrument used to assess cognitive function in most of the major clinical trials of Alzheimer's disease in recent years, the Alzheimer's Disease Assessment Scale-Cognitive Subsection (ADAS-COG), primarily assesses aspects of memory, which has resulted in other important cognitive deficits in dementia being overlooked. Automated cognitive tests are now available that can identify an earlier onset of improvements in dementia in smaller samples than the ADAS, Regulatory authorities should encourage - or even require - the use of automated procedures alongside the ADAS in pivotal trials to help determine the relative utility of the instruments in the fairest way possible. Whatever the outcome, this will be of long-term benefit to patients, carers, drug developers, clinicians, and regulators in this important area

A validation study of appropriate phonological verbal fluency stimulus letters for use with Croatian speaking individuals [Fonološka verbalna fluentnost na hrvatskom uzorku: primjena testa, izbor podražaja i norme]

The aim of this study is to determine the word frequency for all thirty letters of the Croatian alphabet and to collect normative data for the letter fluency task in Croatian speakers. Ninety two healthy participants were given each of the Croatian letters, and asked to generate as many words as possible in 60 seconds for each letter. Results suggested that participants generated most frequently words starting with the letters as follows: »K«, »P«, »S« and »M«

Inferring Beliefs as Subjectively Uncertain Probabilities

We propose a method for estimating subjective beliefs, viewed as a subjective probability distribution. The key insight is to characterize beliefs as a parameter to be estimated from observed choices in a well-defined experimental task, and to estimate that parameter as a random coefficient. The experimental task consists of a series of standard lottery choices in which the subject is assumed to use conventional risk attitudes to select one lottery or the other, and then a series of betting choices in which the subject is presented with a range of bookies offering odds on the outcome of some event that the subject has a belief over. Knowledge of the risk attitudes of subjects conditions the inferences about subjective beliefs. Maximum simulated likelihood methods are used to estimate a structural model in which subjects employ subjective beliefs to make bets. We present evidence that some subjective probabilities are indeed best characterized as probability distributions with non-zero variance.