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<p> Medical diagnosis is a complex task, that requires integrating several sources and types of information: a patient's description of their symptoms, lab results, and perhaps even 'gut feelings' regarding potential diagnoses. From a cognitive psychology perspective, diagnosis is a type of categorization and as such has been typically divided into processes that are deliberate, rule oriented, and available to conscious control (often called analytic processing) and processes that are rapid, outside of conscious awareness, and typically based on similarity (often referred to as non-analytic processing).</p> <p> Traditionally, similarity has referred to whole-case similarity between a current and previously encountered case. However, this pattern matching to an entire previous case does not differentiate between diagnostic and non-diagnostic information, a distinction that is made clear in the rules taught to medical professionals. Since medicine does rely extensively on diagnostic rules, the research presented in this thesis will examine the effect of similarity of features relevant to the application of a diagnostic rule as well as the effect of similarity from patient identity, which is mnemonically salient but diagnostically irrelevant.</p> <p> The work presented in this thesis specifically examines the role of similarity in the categorization, or diagnostic decisions of novices. Medical students start training with the best available rules, standard diagnostic rules likely to be used in future practice. In the experiments reported in this thesis, participants are trained to competence on diagnostic rules using prototypical written case vignettes of simplified psychiatric diagnoses. Participants then evaluate cases in which clinical information supports two possible diagnoses, but in which either diagnostic features or diagnostically irrelevant identity information is similar to those seen in training. The results of these experiments indicate a strong reliance on familiar of rule-relevant symptom descriptions (i.e. similarity within the application of a diagnostic rule), supporting an adaptive role of similarity within the application of an analytical decision rule. Further, the influence of familiar diagnostically irrelevant information (i.e. similarity within the context of patient identity) demonstrates the maintenance of non-diagnostic information within memory, and the possibility of matching to a previous exemplar on rule-irrelevant features. Familiarity, whether diagnostically relevant or not, increases the probability that clinically relevant features are mentioned in support of a diagnosis, which may indicate the disambiguation of features following previous experience with that feature, and a strong influence of familiar but non-diagnostic information on the interpretation of features.</p> <p> This thesis supports a model of medical decision making in which there is an effect of similarity to previous instantiations of clinically relevant features. That is, similarity is a basic component of decision making that is not limited to matching on entire previous instances. Previous research has suggested that analytic and non-analytic reasoning are competing or fundamentally separate processes, whereas the demonstration of similarity within the application of a diagnostic rule suggests that not only is similarity an adaptive strategy for learners, but the differentiation between similarity based and rule based processes may be less clear than previously suggested.</p> / Thesis / Doctor of Philosophy (PhD)

Thesis (M. Med. Sc.)--University of Queensland, 2001. / Includes bibliographical references.

Alpha-melanotropin (alpha-melanocyte stimulating hormone, α-MSH) exerts its biological action by binding to specific receptors on the outer cell membranes of its target tissues with a high degree of affinity and specificity. Current evidence suggests that this takes place both in vitro and in vivo in both normal and malignant melanocytes. Thus, if it were possible to attach a radioisotope (e.g., ¹²⁵I) to α-MSH, or a suitable analogue, without interfering with the receptor affinity of the hormone, then a radioreceptor assay could be developed which would allow hormone-receptor interaction to be studied in detail. In addition, this radio-labeled melanotropin might be expected to accumulate in melanoma tumors in vivo thus facilitating tumor localization by nuclear imaging methods as has been successfully accomplished for thyroid tumors. The present studies were initiated to develop a radioactive melanotropin with full, or nearly full, biological activity. This labeled melanotropin must be of sufficient specific radioactivity to be suitable as a tracer in a radioreceptor assay and ultimately as a marker for in vivo tumor localization. The studies described herein provide information concerning: chloramine T induced iodination, lactoperoxidase catelyzed iodination, and iodogen induced iodination of α-MSH and certain structural analogues. Radio-labeled derivatives of various melanotropins were prepared using a variety of iodination techniques. Under conditions commonly used for the iodination of other peptides a substantial loss of biological activity of the native hormone (α-MSH) was observed. This loss of hormonal activity was primarily a consequence of oxidation of methinonine and occurred regardless of the oxidant used (chloramine T, lactoperoxidase-hydrogen perioxide, or iodogen). Under similar iodination conditions using 4-norleucine-alpha-melanotropin ([Nle⁴]-α-MSH), satisfactory incorporation of label into the peptide was accomplished without significant loss of biological activity. Data are presented suggesting that this peptide is far superior to α-MSH for use in the preparation of a radioactive melanotropin. Although some success was achieved using [Nle⁴]-α-MSH with all three iodination methods, the simplest and most consistent method involved the use of iodogen followed by purification of the labeled product using high performance liquid chromatography (HPLC). This importance of these studies in the development of a tracer for a radio-receptor assay and for in vivo localization of melanoma tumors is discussed.

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Formulas for predicting the absolute X-ray intensity spectra from both Bremsstrahlung and K characteristic X-rays have been developed. These formulas cover a wide range of target materials and target geometry conditions (incident and emission angle) and tube voltage range from 20 to 200kV. For the Bremsstrahlung Intensity Spectrum:vskip 3.5cm Where U tube voltage(kV); J tube current(mA); n&61 1.6; <i>P</i> &61 1.08x10^-6(<i>A/Z</i>^2.5;<i>k_{s}</i> &61 0.32; <i>k</i> &61 <i>K_{m}Z</i>²/<i>A; K</i> = <i>k</i>3/511. The theoretical value of <i>K_{m}</i> is 4.73x10¹⁴<i>keV/mAs.sr.keV</i>. For a Fluency with a Total Filtration of <i>d_{Al} g/cm</i>² Al: <i>F(E)dE = I(E)E^{-1}e^{-μAldAl}dEphotons/keV.mAs.sr</i>. This formula can be used at various incident angles (θi) andemission anglesfor different target material (A, Z, μ) for <i>U</i> from 20-200kV. The angular distribution <i>f</i>(θ) (defined = 1 when θ = 90^o and varies with <i>U</i>) requires definition by experimental measurements. According to this formula the Photon Fluency spectra at different tube voltages, different target angles and different emission directions are calculated and illustrated as spectral curves. There is a good agreement between the formula results and spectra measured by other authors. For K-Characteristic X-ray fluency:vskip 1.5cm Where n&61 1.61; <i>P</i> &61 1.08x10^-6(<i>A/Z</i>)^2.5; k is a factor of 1.0-2.5, which represents the effective depth of K photo production and increases with Z; θ<i>_{i}</i> and θ<i>_{r}</i> the electron incident and X-ray emission angles; Ψ(θ<i>_{i}</i>) &61 <i>cos</i>(7.89x10^-4θ2.6_i) an empirical angle function; <i>N(E_{i}</i>) the fluency of <i>E_{i}</i> characteristic X rays per mAs per solid angle; <i>E_{k}</i> the binding energy of the K sell; <i>F</i>_k the efficiency constant depends on Z; <i>f(E_{i}</i> the fractional emission of the <i>E_{i}</i> characteristic X rays; <i>J</i> the tube current; <i>U</i> the tube voltage. The recommended value of <i>F</i>_Kα, based on measured data, is 3.8-4.7x10^11<i>photon/mAs.sr</i> for values of Z from 25 to 50. The relationship between the target attentuation factor and different target materials, angles and voltages are discussed. This formula can be used at much wider situations and has good agreement with the measured data.

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