Distributed versus compartment models for PET receptor studies

Although distributed models are generally accepted as being more realistic than compartment models, use of simpler compartment models is pervasive in nuclear medicine applications, particularly in positron emission tomography (PET). Here, we report on comparisons made between distributed and compartment model outputs to address the question of whether differences between them are sufficient to justify distributed models for analysis of PET receptor experiments. For both two- and three-injection experiments, "data" sets were obtained by simulation using a distributed model and a wide range of parameter values. Optimal fits of the compartment model output to these "data" were achieved with three strategies in which values of different groups of parameter were estimated. Compartment model outputs yielded good fits to all the distributed model outputs and the values of the corresponding parameters were in close agreement. Given the temporal resolution typically available with PET, the use of a distributed model has no advantage over a compartment model for PET receptor quantification.     

Internally excited acoustic resonator for photoacoustic trace detection

The quantum-cascade laser can be used as an infrared source for a small portable photoacoustic trace gas detector. The device that we describe uses a quantum-cascade laser without collimating optics mounted inside an acoustic resonator. The laser is positioned in the center of a longitudinal resonator at a pressure antinode and emits radiation along the length of the resonator exciting an axially symmetric longitudinal acoustic mode of an open-ended cylindrical resonator. Experiments are reported with an 8-microm, quasi-cw-modulated, room-temperature laser used to detect N2O.     

Polymorphic New World monkeys with more than three M/L cone types

Most New World (platyrrhine) monkeys have M/L cone photopigment polymorphisms that map directly into individual variations in visual sensitivity and color vision. We used electroretinogram flicker photometry to examine M/L cone photopigments in the New World monkey Callicebus moloch (the dusky Titi). Like other New World monkeys, this species has an M/L cone photopigment polymorphism that reflects the presence of X-chromosome opsin gene alleles. However, unlike other platyrrhines in which three M/L photopigments are typical, Callicebus has a total of five M/L cone photopigments. The peak sensitivity values for these pigments extend across the range from 530 to 562 nm. The result is an enhanced array of potential color vision phenotypes in this species.     

Nanoscale deformation mechanisms in bone

Deformation mechanisms in bone matrix at the nanoscale control its exceptional mechanical properties, but the detailed nature of these processes is as yet unknown. In situ tensile testing with synchrotron X-ray scattering allowed us to study directly and quantitatively the deformation mechanisms at the nanometer level. We find that bone deformation is not homogeneous but distributed between a tensile deformation of the fibrils and a shearing in the interfibrillar matrix between them.     

Progress in medical ultrasound exposimetry

Biomedical applications of ultrasound have experienced tremendous growth over the past 50 years. Early work in thermal therapy and surgery soon was followed by diagnostic imaging and Doppler. Because patient safety was an important issue from the beginning, the study of methods for measuring exposure levels, and their relationship to possible biological effects, paralleled the growth of the various therapeutic and diagnostic techniques. The diverse conditions of use have presented a range of exposure measurement challenges, and the sensors and techniques used to evaluate ultrasound fields have had to evolve as new or expanded clinical applications have emerged. In this paper some of the more notable of these developments are presented and discussed. Topics covered include devices and techniques, methods of calibration, progress in standardization, and current problem areas, including the effects of nonlinear propagation. Some early methods are described, but emphasis is given to more recent work applicable to present and future uses of ultrasound in medicine and biology.     

Effects of gender, setting, and research productivity on intern and employment suitability ratings.

To examine possible associations between research activity and rated suitability of internship and employment, 72 counseling psychology faculty members and staff members at university counseling center intern training programs rated internship and employment suitability of applicants with differing degrees of research productivity. Three factors were studied: employment setting of raters, sex of applicant, and research productivity of applicant. Raters' perceptions of applicants' counseling performance, suitability for internship, and suitability for employment were all significantly associated with applicants' research productivity, in some instances negatively so, especially for females. (8 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

New approach to the prediction of medical specialization: Student-based Strong Vocational Interest Blank scales.

Studied longitudinal data from 1583 undergraduates in an attempt to devise means of predicting eventual specialization for medical students. Specialty membership was determined in a follow-up study 11 yr. after the SVIB was administered. SVIB scales for surgeons, obstetricians, pediatricians, and psychiatrists were developed, using the items which differentiated the specialist groups as freshmen. Senior-based scales were also tested, but predicted no better than those using freshman responses. The resulting student-based scales were reliable on retest, but on measures of distributional overlap, they did not perform as well as standard SVIB occupational scales. However, their predictive validity was superior to that of previously developed SVIB scales for medical specialists. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of prostaglandins on macromolecular transport from blood to lymph in the dog

The effect of various prostaglandins on hindlimb lymph flow and macromolecular transport was studied in dogs anesthetized with pentobarbital sodium. Lymph obtained by cannulating the popliteal lymphatics was collected at 30-min intervals and analyzed for protein and exogenously administered dextran (Dextran 110). Arterial blood was obtained at the midpoint of each collection period and similarly analyzed. Prostaglandins (E1, E2, F2alpha, and A2), the vehicle and histamine were injected subcutaneously into the paw of the dog. Prostaglandins slightly increased lymph flow (L') but the lymph-to-plasma concentration ratios (R) for total protein (T) and Dextran 110 (D) decreased. Permeability surface area products (PS) were not altered. The sieving ratios (RD/RT) were substantially less than 1 and were not altered by prostaglandins. These results indicate that selective permeability of the capillary is not impaired by prostaglandins. Timing sequences and dose-response relations were also completed for prostaglandins by subcutaneous testing in dogs injected with Evans blue (T-1824). Leakage of the T-1824-albumin complex occurred when large amounts (migrogram) of prostaglandins were administered, and the response appeared to be short lived (less than 30 min). While the prostaglandins possess vasoactive properties, as demonstrated by an increased lymph flow, they do not alter the restrictive transport of large molecules.