The noise power spectrum of CT images

An expression for the noise power spectrum of images reconstructed by the discrete filtered backprojection algorithm has been derived. The formulation explicitly includes sampling within the projections, angular sampling, and the two-dimensional sampling implicit in the discrete representation of the image. The effects of interpolation are also considered. Noise power spectra predicted by this analysis differ from those predicted using continuous theory in two respects: they are rotationally asymmetric, and they do not approach zero at zero frequency. Both of these properties can be attributed to two-dimensional aliasing due to pixel sampling. The predictions were confirmed by measurement of noise power spectra of both simulated images and images from a commercial x-ray transmission CT scanner.     

Titanium particles identified by energy-dispersive X-ray microanalysis within the lungs of a painter at autopsy

A 72-year-old male painter, who complained of his "lungs burning" for 2 weeks, died suddenly. Autopsy examination revealed severe coronary atherosclerosis with plaque rupture as the cause of death. Examination of the lungs revealed emphysema, interstitial fibrosis, and multinucleated giant cells with intra- and extracellular brown-black, crystalline, polarizable foreign material. Energy-dispersive X-ray microanalysis showed the material to contain titanium, aluminum, silicon, and iron. An increased incidence of respiratory disease has been reported in professional painters. Titanium is widely used as a pigment in the manufacturing of commercial paints. Cases of pneumoconiosis and alveolar proteinosis have been described in painters in which analysis of lung tissue revealed increased levels of titanium. This case is presented as an example of a rarely reported phenomenon, which may have clinical implications for evaluation and management of lung disease in painters.     

Tumor Vascularity Is Not a Prognostic Factor for Malignant Melanoma of the Skin

Tumor vascularity has been proposed as a prognostic indicator for a number of solid tumors. Although a correlation between microvessel number and metastatic behavior has also been suggested for cutaneous melanoma, the small number of cases studied to date allows one to draw only preliminary conclusions. In this study, we have assessed tumor vascularity in cutaneous melanoma by comparing 60 cases of metastasizing and non-metastasizing tumors matched for tumor thickness, age, sex, and anatomic site. Ulex europaeus agglutinin I appeared to be the most suitable vascular marker for this study. Our results indicate that there was no statistically significant difference between the two groups with regard to tumor vascularity. Even after identifying 15 cases of thin (<1.0 mm thick) melanoma, there was no significant difference in the number of microvessels between metastasizing and non-metastasizing tumors. Comparison of patterns of vascular microarchitecture also failed to discriminate between the two groups. Thus, our results indicate that tumor vascularity may not be an independent prognostic factor for cutaneous melanoma.     

Mechanism of adenosine 3′,5′-monophosphate (cAMP)-induced increase in Ca2+ uptake by the sarcoplasmic reticulum in functionally skinned myocardial fibers

The increased rate of Ca²⁺ uptake and ATPase activity in isolated cardiac sarcoplasmic reticulum (SR) by adenosine 3,5-monophosphate (cAMP) has been shown to be activated by a cAMP-dependent protein kinase (cAMP kinase). Functionally skinned myocardial fiber preparations were used to study the mechanisms of cAMP action on the SR at the same time that tension was monitored. cAMP effects were studied on Ca²⁺-activated tension of the contractile proteins, and on Ca²⁺ uptake and release from the SR using caffeine-induced tension transients. Neither cyclic AMP (0.1–5 M) nor the catalytic subunit of cAMP kinase (0.1–1 M) (PK-C) significantly changed either the maximal or the submaximal Ca²⁺-activated tension. The areas of the tension transients were unchanged when cAMP was present in the releasing solution (release phase), and were significantly increased up to a mean of about 80% when cAMP or PK-C was present in the Ca²⁺ loading solutions (uptake phase). The increased tension transient was blocked by the heat-stable inhibitor of cAMP kinase. We conclude that cAMP-induced increases in Ca²⁺ uptake by the SR could play an important role in the positive inotropic effect. cAMP kinase could thus play a crucial role in the regulation of myocardial contractility.     

Teaching systems-based practice to residents by using independent study projects.

The changing health care marketplace requires new graduates to be familiar with complex health systems. Since 1999 the Oregon Health & Science University internal medicine residency program has offered a seminar-based health systems curriculum, but residents lacked an opportunity to actively apply learned concepts. To achieve this goal, the authors developed a second curricular component, the Health Systems Independent Study Project (HSISP). The HSISP is a self-directed assessment of a health care system or delivery issue residents complete in their third year. The curriculum was implemented in 2001 with goals of gaining a focused understanding of a health systems concept and building related skills. Residents present their study projects to all curriculum participants. Topics addressed so far include adherence to coronary artery disease guidelines in a defined population, screening strategies for lung cancer, resident burnout, and many others. Residents have found that these projects enhance their systems knowledge, help them link systems-based-practice concepts to clinical practice, and foster opportunities for networking and early career development.     

Effects of exercise cessation on lipids and lipoproteins in distance runners and power athletes

Summary The purpose of this study was to determine the effects of short-term exercise cessation on lipid and lipoprotein profile and insulin sensitivity in highly trained runners (n=12; mean age 19.9 years) and power athletes (n=12; mean age 24.4 years). Following 14 days of exercise cessation, running time to exhaustion and maximal oxygen uptake decreased by 9.2% and 4.8% (P < 0.05) in the runners, while in the power athletes one repetition maximum squat and bench press did not change (P>0.05). No changes occurred in body composition. Data from a 2-h oral glucose tolerance test revealed an impairment of the glycemic state in all athletes (P<0.05). In contrast, exercise cessation did not significantly (P>0.05) alter plasma levels of cholesterol, triglycerides, and low density (LDL) and high density lipoprotein (HDL). No changes were observed in HDL₂, HDL_2b, and HDL₃ subfractions, LDL diameter, and qualitative LDL pattern (P>0.05). These data thus suggest that despite a decrease in insulin sensitivity, short-term exercise cessation, independent of exercise mode, was insufficient to alter plasma lipid and lipoprotein profiles in well-trained athletes.     

DNA fingerprinting of Pasteurella multocida recovered from avian sources

Repetitive sequence-based PCR (rep-PCR) and amplified fragment length polymorphism (AFLP) were used to characterize a sample of 43 field isolates and 4 attenuated vaccine strains of Pasteurella multocida recovered from multiple avian species. Both rep-PCR and AFLP assays were rapid and reproducible, with high indices of discrimination. Concordance analyses of rep-PCR and AFLP with somatic serotyping indicate that, in general, somatic serotyping is a poor indicator of genetic relatedness among isolates of P. multocida. In addition, the data provide evidence of host specificity of P. multocida clones. Overall, the results of our study indicate that the rep-PCR and AFLP techniques enable rapid fingerprinting of P. multocida isolates from multiple avian species and enhance the investigation of fowl cholera outbreaks.     

Vaccination to prevent varicella and shingles

Vaccination of healthy children against varicella using the live attenuated Oka vaccine has been available in Japan and south Korea for several years. In 1996, a programme of universal vaccination of children to prevent varicella was introduced in the USA and other countries, including Canada, Germany, and Sweden, have licensed the vaccine for use in healthy children. This article reviews the origin of the Oka vaccine and the evidence for vaccine safety and efficacy in children and adults. Universal vaccination of children and targeted vaccination of groups at risk of severe varicella are discussed. The possible use of the Oka vaccine to prevent zoster is reviewed, and initiatives to develop new varicella zoster virus vaccines are outlined.     

Human observer detection experiments with mammograms and power-law noise

We determined contrast thresholds for lesion detection as a function of lesion size in both mammograms and filtered noise backgrounds with the same average power spectrum, P(f)=B/f3. Experiments were done using hybrid images with digital images of tumors added to digitized normal backgrounds, displayed on a monochrome monitor. Four tumors were extracted from digitized specimen radiographs. The lesion sizes were varied by digital rescaling to cover the range from 0.5 to 16 mm. Amplitudes were varied to determine the value required for 92% correct detection in two-alternative forced-choice (2AFC) and 90% for search experiments. Three observers participated, two physicists and a radiologist. The 2AFC mammographic results demonstrated a novel contrast-detail (CD) diagram with threshold amplitudes that increased steadily (with slope of 0.3) with increasing size for lesions larger than 1 mm. The slopes for prewhitening model observers were about 0.4. Human efficiency relative to these models was as high as 90%. The CD diagram slopes for the 2AFC experiments with filtered noise were 0.44 for humans and 0.5 for models. Human efficiency relative to the ideal observer was about 40%. The difference in efficiencies for the two types of backgrounds indicates that breast structure cannot be considered to be pure random noise for 2AFC experiments. Instead, 2AFC human detection with mammographic backgrounds is limited by a combination of noise and deterministic masking effects. The search experiments also gave thresholds that increased with lesion size. However, there was no difference in human results for mammographic and filtered noise backgrounds, suggesting that breast structure can be considered to be pure random noise for this task. Our conclusion is that, in spite of the fact that mammographic backgrounds have nonstationary statistics, models based on statistical decision theory can still be applied successfully to estimate human performance.