Linear least squares compartmental-model-independent parameter identification in PET

A simplified approach involving linear-regression straight-line parameter fitting of dynamic scan data is developed for both specific and nonspecific models. Where compartmental-model topologies apply, the measured activity may be expressed in terms of: its integrals, plasma activity and plasma integrals--all in a linear expression with macroparameters as coefficients. Multiple linear regression, as in spreadsheet software, determines parameters for best data fits. Positron emission tomography (PET)-acquired gray-matter images in a dynamic scan are analyzed: both by this method and by traditional iterative nonlinear least squares. Both patient and simulated data were used. Regression and traditional methods are in expected agreement. Monte-Carlo simulations evaluate parameter standard deviations, due to data noise, and much smaller noise-induced biases. Unique straight-line graphical displays permit visualizing data influences on various macroparameters as changes in slopes. Advantages of regression fitting are: simplicity, speed, ease of implementation in spreadsheet software, avoiding risks of convergence failures or false solutions in iterative least squares, and providing various visualizations of the uptake process by straight line graphical displays. Multiparameter model-independent analyses on lesser understood systems is also made possible.

Breeding, Population Dynamics and Habitat Relationships of Sminthopsis dolichura (Marsupialia : Dasyuridae) in Semi-arid Shrublands of Western Australia

Demographic data were gathered from two populations of the little long-tailed dunnart, Sminthopsis dolichura, inhabiting semi-arid nature reserves in the Western Australian wheatbelt in order to place the ecology of this species (formerly part of the Sminthopsis murina complex) in perspective. In all respects, S. dolichura is similar to S. murina from south-eastern Australia, and, indeed, to most other species of the Sminthopsis group. High mobility and transiency rates, an extended seasonal pattern of reproduction, relatively rapid development of the young and the probable existence of polyoestry characterise the life history of S. dolichura and most other species within the group that have been studied. These attributes enable a high degree of reproductive flexibility and permit these species to opportunistically invade new habitats and ephemeral post-fire seral stages. The observed sympatry with highly seasonal monoestrous dasyurids of the genus Antechinus is postulated to occur through spatial and temporal selection of different microhabitats, but also suggests that phylogenetic factors may be at least as important as the predictability of climate and food resources in explaining the evolution of different reproductive strategies.

Differentiating benign from malignant lung lesions using "quantitative" parameters of FDG PET images

Fluorine-18 labeled deoxyglucose positron-emission tomography (FDG-PET) applications in oncology include the differential diagnosis of chest masses and single pulmonary nodules. However, FDG is not tumor-specific; rather, it also accumulates in inflammatory processes. This study was performed to identify image parameters that would improve the specificity of PET.

METHODS

Twenty-six patients who had benign and malignant lung lesions were examined retrospectively. Positron-emission tomography data were acquired in dynamic scanning mode after intravenous bolus of 250-402 MBq of FDG. Standardized uptake values (SUVs) were calculated and Patlak analyses were performed in selected regions of interest in the PET images. Positron-emission tomography results were related to histological diagnosis (N = 49) or clinical follow-up (N = 3).

RESULTS

The specificity and sensitivity of the original PET scan reports, which was based on visual image interpretation and loosely applied SUVs, was 100% and 73%, respectively. Using the SUVs with a cut-off value of 3.8 and Kpat value with a cut-off at 0.025 min-1 improved the specificity to 81% and 85%.

CONCLUSION

FDG-PET image interpretation can be facilitated by using SUV information or the accumulation rate of the radiotracer (Patlak). With additional validation, this method could have a significant cost-effective impact on the medical/surgical management of chest masses.

Human in vivo comparative study of zinc and copper transmetallation after administration of magnetic resonance imaging contrast agents

RATIONALE AND OBJECTIVES

The authors compare in vivo transmetallation of three magnetic resonance contrast agents in humans in terms of their kinetic stability.

METHODS

Blood and urine samples were taken before and after the intravenous injection of gadolinium (Gd)-HP-DO3A, Gd-DTPA, or Gd-DTPA-BMA at 0.1 mmol/kg to healthy volunteers. Serum and urine were assayed for zinc, copper, and Gd, using inductively coupled plasma atomic emission spectrometer.

RESULTS

Gadolinium-DTPA-BMA caused the highest increase in zinc excretion among the three agents. Gadolinium-HP-DO3A did not cause a significant increase in zinc excretion. In serum, although Gd-DTPA-BMA exhibited a decrease in zinc concentration, the difference between the drugs was not statistically significant.

CONCLUSIONS

The difference in observed zinc excretion among the chelates studied reflects in vivo transmetallation of the magnetic resonance contrast media and correlates with the respective kinetic inertia for transmetallation, rather than thermodynamic stability constants. Gadolinium-HP-DO3A was found to be the most kinetically inert among the three drugs tested.

Hepatic extraction efficiency and excretion rate of technetium-99m-mebrofenin in dogs

Quantitative hepatobiliary scintigraphy aids in the diagnosis of hepatic disease. Two scintigraphic parameters that have great value in discriminating between hepatocellular and biliary disease are hepatic extraction fraction (HEF), which is a measure of the hepatic extraction efficiency (HEE), and hepatic excretion rate. It is generally accepted that hepatic extraction fraction is normally 100%, but a review of the literature provided little information on the actual HEF of 99mTc-mebrofenin.

METHODS

We determined the HEE of 99mTc-mebrofenin in nine normal dogs after direct injection into the afferent hepatic vasculature using a two-compartment model. The forward and reverse rate constants for the two-compartment model were solved by a simple graphic approach and a more complex numerical approach using a nonlinear least squares algorthm. The HEEs were determined using both methods.

RESULTS

The HEE for the graphic and numerical methods of analysis were not significantly different and were calculated to be 92.2 +/- 4.75% (mean +/- s.d.) and 91.2 +/- 4.44% (mean +/- s.d.) by each method, respectively. The half-time clearance of 99mTc-mebrofenin was 19.10 +/- 4.86 min (mean +/- s.d.).

CONCLUSION

This study validates the assumption that the normal HEE of 99mTc-mebrofenin is nearly 100%, barring species differences.

Seasonal plasticity in the song nuclei of wild rufous-sided towhees

Seasonal changes in the brain nuclei that control song behavior in songbirds are among the most striking examples of plasticity in the adult vertebrate brain. Although seasonal changes in the size of these brain nuclei have been found in several species in captivity, results on seasonal changes in the song nuclei of wild songbirds have been equivocal. In the present study, I measured plasma testosterone (T) concentrations and the size of song nuclei across seasons in wild male rufous-sided towhees (Pipilo erythrophthalmus). I found seasonal changes in both T concentrations and the size of song nuclei that were as large as or larger than those observed in this species in captivity. These results demonstrate that seasonal plasticity of the song nuclei occur in wild, as well as captive, songbirds.

Use of PG-21 immunocytochemistry to detect androgen receptors in the songbird brain

The avian song control system is an excellent model in which to study the effects of gonadal steroid hormones on neural and behavioral plasticity. Several of the brain regions that control song behavior concentrate androgens and/or estrogens. Investigations of the distribution and regulation of androgen receptors have been limited by the lack of a reliable immunocytochemical method to detect androgen receptors in the songbird brain. We describe a protocol by which the PG-21 polygonal antibody to the rat androgen receptor can be used to label androgen receptor-containing cells in the songbird brain. By treating songbirds of several species with testosterone 90 min before sacrifice and by using relatively low concentrations (0.5 0.75 microg/ml) of PG-21 antibody to reduce nonspecific background staining, we were able to obtain strong specific labeling of cell nuclei in androgen-sensitive brain regions. This technique will facilitate the study of the role of androgens in mediating neural plasticity in the avian brain. Testosterone pretreatment may also facilitate the use of this antibody to label androgen receptors in tissues from a wide array of nonmammalian species.

Short-term responses to periodontal therapy in insulin-dependent diabetic patients

This investigation studied relative changes in periodontal conditions of 18 insulin-dependent diabetic patients. Measures of gingival inflammation, crevicular fluid aspartate aminotransferase (AST) levels, probing depth and attachment levels, the presence of three periodontal pathogens (Porphyromonas gingivalis, Bacteroides forsythus, and Actinobacillus actinomycetemcomitans) and serum antibody titers to these bacteria, and blood sugar levels (glycosylated hemoglobin, HbAlc) were studied before and 2 months after non-surgical debridement. Antibody titers to the same bacteria were also studied in sera from 18 sex- and age-matched periodontally healthy and non-diabetic subjects. Periodontal conditions showed significant improvement. The mean probing depth at 4 of the worst sites selected in each patient decreased from 5.7 mm to 4.8 mm (p < 0.0001). The mean full width probing depth changed from 2.9 mm (s.d. +/- 0.2) to 2.5 mm (s.d. +/- 0.3). A mean gain of 0.4 mm attachment level was recorded (P < 0.0001). The mean AST value decreased from 1009 microIU to 518 microIU (P < 0.006). Minimal differences in mean glycosylated hemoglobin values (HbAlc) were noticed before and after treatment. A. actinomycetemcomitans was never detected. P. gingivalis was present at 7% of the sites both before and after treatment. B. forsythus was found at 29% of sites (50% of patients) before and at 36% of sites (61% of patients) after treatment. Positive associations were found between the presence of B. forsythus and AST values, gingival index, probing depth, and attachment level (P < 0.05). Baseline serum IgG titers to P. gingivalis were significantly lower in the patients with diabetes (9.5 ELISA units vs. 28.5 ELISA units in the healthy controls). IgG titers to B. forsythus did not differ between diabetic and non-diabetic subjects. No changes in IgG titers occurred after treatment. Clinical improvements after mechanical non-surgical therapy in patients with insulin-dependent diabetes mellitus were modest after 2 months. Treatment did not eliminate B. forsythus and P. gingivalis and did not affect IgG titer responses. More intense therapy, and longer follow-up times, may be necessary to see more pronounced clinical and systemic effects.

Evidence that nitric oxide enhances cadmium toxicity by displacing the metal from metallothionein

Cadmium is carcinogenic in humans and rodents. Although extensive evidence indicates that the toxicity and genotoxicity of Cd is ameliorated by binding to cysteine clusters in metallothionein (MT), the factors governing Cd release at intracellular target sites remain unknown. Nitric oxide is a pollutant gas and an important intercellular messenger in the inflammatory immune response. When growing Chinese hamster ovary cells were treated for 24 h with 0.5, 0.75, or 1.0 mM CdCl2 followed by a 1-h exposure to 1.0, 1.5, or 2.0 mM 1,1-diethyl-2-hydroxy-2-nitrosohydrazine (DEA/NO), an NO-generating sodium salt, NO enhanced Cd-induced inhibition of colony forming ability without affecting Cd-induced cytolethality. In experiments designed to determine whether NO acts by displacing Cd from cellular MT, cells treated with 2.0 mM CdCl2 followed by 1.5 or 3.0 mM DEA/NO exhibited 29 and 38% reductions, respectively, in the amount of Cd bound to MT. When purified rat liver MT was used to further characterize NO-induced release of Cd from MT, dose-related increases in Cd displacement were observed at DEA/NO concentrations between 0.1 and 0.5 mM, and a plateau was reached at 3 mol of Cd displaced/mol of MT at higher DEA/NO concentrations. Compared to cells exposed to Cd or DEA/NO alone, cells treated with Cd followed by DEA/NO also exhibited a transient 2-3-fold decrease in c-myc proto-oncogene expression. Taken together, our results support the hypothesis that NO mediates Cd release from MT in vivo and suggest that intracellular generation of free Cd may induce DNA damage and force cells into a period of growth arrest. Such findings may have particular relevance with regard to the etiology of Cd-induced carcinogenesis in human populations.

Seasonal changes in song nuclei and song behavior in Gambel's white-crowned sparrows

In males of several songbird species, the morphology of forebrain nuclei that control song changes seasonally. The only seasonally breeding songbird in which seasonal changes in the structure of song control nuclei have been reported not to occur is the nonmigratory Nuttall's subspecies of white-crowned sparrow. In the present study, we manipulated photoperiod and plasma testosterone concentrations in captive male white-crowned sparrows of the migratory Gambel's subspecies. Males exposed to photoperiods and plasma testosterone concentrations typical of those experienced by wild breeding males had larger song control nuclei than males held on a winter photoperiod. We also found seasonal changes in stereotype of spectral and temporal parameters of song in wild Gambel's white-crowned sparrows. We hypothesize that seasonal changes in the song control nuclei may correlate with seasonal changes in song stereotypy.

Assessment of skeletal muscle viability by PET

We investigated the use of [18F]fluoro-2-deoxyglucose (FDG) PET scanning for assessment of skeletal muscle viability in patients with peripheral vascular disease and in patients following free-flap skeletal muscle transfer for closure of open wounds.

METHODS

We obtained 32 FDG-PET scans from 30 patients, either at the time of admission for peripheral vascular disease (n = 16) or between 1 and 15 days after surgery for skeletal muscle transfer (n = 16). Ratios between injured and contralateral limb FDG tracer activity uptake were correlated with clinical outcome at 1 mo to 3 yr follow-up.

RESULTS

Viable muscle uptake ratios ranged from 0.47 to 7.88 (mean: 2.26 +/- 1.81; n = 26), while nonviable muscle uptake ratios ranged from 0.12 to 0.46 (mean: 0.27 +/- 0.12; n = 6; p < 0.02). After skeletal muscle transfer, two patients with viable tissue, as documented by PET, required amputation due to osteomyelitis, and one patient with peripheral vascular disease who showed viable tissue by PET required amputation 3 mo after the PET scan because of recurrent ulcers.

CONCLUSION

FDG-PET scanning can determine skeletal muscle viability in patients with peripheral vascular disease and in patients following free-flap transfer.

Self-reported drinking and alcohol-related problems among early adolescents: dimensionality and validity over 24 months

OBJECTIVE

Researchers rely on adolescents' self-reports of alcohol consumption and alcohol-related problems, despite little evidence concerning their validity. We assessed the reliability and validity of adolescents' self-reports, employing collateral validation and focusing on the understudied transitional years of early adolescence.

METHOD

Subjects were 214 boys and 247 girls who participated in school-wide surveys that assessed drinking, drunkenness and alcohol-related problems each year for 3 years. These measures were validated by collateral (peer) reports and by separate, 7-day drinking calenders. Internal consistency and test-retest reliability were also assessed.

RESULTS

Results replicated findings with older adolescents that drinking/drunkenness and alcohol-related problems fall on two partially overlapping dimensions. Scales assessing each dimension had moderate to high internal consistency and high test-retest stability. Correlations with collateral reports were relatively strong for the drinking/drunkenness scale, moderate for a dichotomous variable reflecting the presence or absence of alcohol-related problems, and more modest for the alcohol-related problems scale. Correlations with diary reports of drinking behavior were strong for drinking/drunkenness. Results generally replicated across gender and over time.

CONCLUSIONS

Researchers can have some confidence in the reliability and validity of early adolescents' survey self-reports, particularly of alcohol consumption (alcohol-related problems occurred with low base rates, perhaps limiting validity coefficients). Because drinking/drunkenness and alcohol-related problems shared 30% of their variance, factors other than consumption (e.g., personality factors) apparently influenced the experience of alcohol-related problems.

Expectancy for social facilitation from drinking: the divergent paths of high-expectancy and low-expectancy adolescents

Using a 3-wave longitudinal design, adolescents were studied over a 2-year period during which many first began to drink. Covariance structure modeling showed that teens' expectancy for social facilitation from alcohol and their drinking experience influenced each other in a reciprocal, positive feedback fashion: the greater the expectancy endorsement, the higher subsequent drinking levels, and the higher the drinking levels, the greater the subsequent expectancy endorsement. This model fit the data quite well; comparison models, in which expectancy (or drinking) had no independent influence on future drinking (or expectancy), showed significantly poorer fit than the present model. Initial nondrinkers' social expectancy predicted individual differences in the rate of drinking increase over the 2 years. Results bolster the hypothesis that expectancy actively influences drinking and point to the importance of expectancy-based intervention efforts.

Crack cocaine mimicking pulmonary embolism on pulmonary ventilation/perfusion lung scan. A case report

Cocaine inhalation is associated with multiple pulmonary complications including pulmonary infiltrates, pulmonary edema, barotrauma, tracheal injury, and alveolar hemorrhage. Little has been reported about ventilation/perfusion (V/Q) lung scanning in patients who smoke cocaine. The authors report a case of inhalation cocaine abuse mimicking pulmonary embolism by V/Q scan criteria. This case report documenting perfusion abnormalities within hours of cocaine smoking which resolved within days provides the first in vivo evidence for pulmonary vasoconstriction.

Survival of adult and nestling western lon-billed corellas, Cacatua pastinator, and Major Mitchell cockatoos, C. leadbeateri, in the wheatbelt of western Australia

The western long-billed corella, Cacatua pastinator, and the Major Mitchell cockatoo, C. leadbeateri, were studied in the central wheatbelt of Western Australia from 1977 to 1983. Nestling and breeding adult birds were individually marked with patagial tags and their survival was calculated from resighting of tagged birds. Mean annual survival of adult male and female western long-billed corellas and Major Mitchell cockatoos were 94.2%, 93.2%, 92.9% and 81.3%, respectively. Survival of immature birds was less than that of adults and only 9% of male and 23% of female western long-billed corellas survived to age of first breeding at three and five years, respectively; 20% of male and 31% of female Major Mitchell cockatoos survived to age of first breeding at two and three years, respectively. The use of patagial tags had no significant effect on the survival of adult birds; the situation with immature birds is less certain, but the data suggest that any effect was small. Dispersal had only a slight negative effect on 'survival' of immature Major Mitchell cockatoos. The lower survival of immature birds was attributed to increased predation while in the locally nomadic immature flocks. Data on survival and productivity suggest that the populations should be stable or slowly increasing and this is in agreement with the data on the populations.

Arnold G, E. Steven D, T. Smith G, Atkins L, J. Viveen J, Gutter M. Biodiversity indicators in semi-arid, agricultural Western Australia

The predicted future loss of native Australian species of plants and animals, in part as a result of adverse land management strategies, has led to attempts to identify areas of high biotic richness (numbers of species). Bioindicators are measures of the physical environment, or of a subset of the plants or animals, that best predict biotic richness. Ideally, bioindicators should aim at predicting as large a component of the plant or animal fauna as is possible at minimum cost. For two contrasting vegetation types, we examined remnant area, vegetation structural diversity, species richness of plants, lizards and terrestrial arthropods, and the relative abundance of individual arthropod species, as indicators of faunal richness, using correlation, principal component regression and stepwise regression analyses. The study was carried out in gimlet Eucalyptus salubris woodlands (29 sites) and shrublands (27 sites) in semi-arid, agricultural Western Australia. Sites varied considerably in grazing history (woodland) and in farming history (shrubland). Fauna sampled were lizards (woodland), scorpions (woodland), isopods (woodland), cockroaches (woodland), termites (woodland, shrubland), earwigs (woodland), hemipterans (shrubland), beetles (woodland, shrubland), butterflies (shrubland) and ants (woodland, shrubland). None of the indicator variables in any analyses effectively predicted total faunal richness for either vegetation type (<35% of variation in total richness explained). In correlation analyses for woodlands, vegetation structural diversity and plant richness, but no fauna variable, explained a high percentage of the variation in the richness of lizards (56% explained by richness of native plants, +ve), scorpions (48%, richness of native plants, +ve), termites (55%, vegetation structural diversity, +ve) and beetles (59%, litter, –ve). The richness of the shrubland fauna was poorly predicted by all indicator variables (<25% explained). When using the total richness and abundance of ant functional groups, the abundance of a subset of species within ant functional groups, and of termite and beetle species, in principal component regressions, various ant functional groups explained 42% each of the richness of scorpions and beetles, and eight beetle species explained 50% of termite richness. When remnant area, vegetation structural diversity and the richness of native plants in woodland were tested in step-wise regressions as indicators of total faunal richness, remnant area was the only significant indicator variable, explaining 33% of total richness. The richness of native plants and vegetation structural diversity explained a total of 76% of the pooled richness of lizards + scorpions + termites. No significant indicator variable was found by regression procedures for total richness, or for a subset, of the shrubland fauna. We argue that differences in the predictive qualities of vegetation structure and plant richness between the vegetation types was due, in part, to differences in the spatial heterogeneity of biotic richness, and possibly the scale at which structure was measured. The use of structural diversity or plant richness as predictors of faunal richness for different woodland types, or those with different disturbance histories, or in different geographic or climatic regions, should not be adopted without verification of their efficiency at predicting the richness of the local fauna.

Modifying alcohol-related expectancies in grade-school children

Expectancies for reinforcement from alcohol appear to form during the grade-school years and play a causal role in problem drinking behavior. Using a sample of 268 second through fourth graders, we investigated whether children's expectancies could be modified successfully. Children were randomly assigned to one of four conditions: two experimental expectancy modification conditions (using 10-minute video interventions), one control condition involving a 10-minute video presenting facts concerning alcohol's deleterious effects, and one no-intervention control condition. Relative to controls, expectancies were increased by one experimental condition and decreased by the other; these changes were sustained at 4-week follow-up. This suggests expectancy modification should be tested as an adjunct to current prevention programs. Relations of gender and family history of problem drinking or alcoholism to expectancy endorsement are described.

Formulating clinical research hypotheses as structural equation models: a conceptual overview

Structural equation modeling is a comprehensive, flexible approach to research design and data analysis. Although in recent years there has been phenomenal growth in the literature on technical aspects of structural equation modeling, relatively little attention has been devoted to conceiving research hypotheses as structural equation models. The aim of this article is to provide a conceptual overview of clinical research hypotheses that invite evaluation as structural equation models. Particular attention is devoted to hypotheses that are not adequately evaluated using traditional statistical models.

Substance use disorder: abuse, dependence and dyscontrol

The purpose of this paper is to review the diagnostic concepts of substance abuse and substance dependence provided in DMS-III, DSM-III-R, and the forthcoming DSM-IV. The review incorporates the principles that there are no infallible criteria for identifying when a person lacks sufficient control over the usage of a drug, that dyscontrol exists on a continuum, that substance use dyscontrol shares many formal properties with behavioral dyscontrol within other domains, and that the diagnosis of a mental disorder should be free of moralistic connotations. We conclude the paper with an alternative proposal, wherein the DSM-IV diagnoses of abuse and dependence are collapsed within one diagnosis of substance dyscontrol disorder and physiological substance dependence is placed with the diagnoses of substance intoxication and substance withdrawal.

Psychological expectancy as mediator of vulnerability to alcoholism

Alcohol expectancy has proven to be a powerful predictor of drinking behavior, including alcoholism, in a wide range of groups. Three recent studies that begin to address expectancy's relation to other alcoholism vulnerability factors are reviewed. Results indicate that: (1) expectancies for reinforcement from alcohol predate teens' first drinking experiences; (2) expectancies predict subsequent drinking onset and problem drinking; (3) high initial expectancies lead to a vicious cycle of progressively more drinking and more positive expectancies during the adolescent years; (4) expectancy mediates the influence of family drinking history on adolescent drinking; and (5) as an alcohol-specific risk factor, expectancy adds to and (in women) interacts with more general, dispositional (personality) risk factors to predict problem drinking in young adults. These findings support the model of expectancy as a mediator of the original causal influences of earlier learning experiences.