Mutational analysis reveals a noncontractile but interactive role of actin and profilin in viral RNA-dependent RNA synthesis.

As obligatory parasites, viruses co-opt a variety of cellular functions for robust replication. The expression of the nonsegmented negative-strand RNA genome of respiratory syncytial virus (RSV), a significant pediatric pathogen, absolutely requires actin and is stimulated by the actin-regulatory protein profilin. As actin is a major contractile protein, it was important to determine whether the known functional domains of actin and profilin were important for their ability to activate RSV transcription.

Basic nonlinear acoustics: an introduction for radiological physicists.

Presented is a brief introduction to nonlinear acoustics, a topic of increasing importance in modern diagnostic ultrasound. Specifically treated is shock wave and harmonic production in lossless media. We also present a description of linear attenuation mechanisms in soft tissue and finally nonlinear propagation in soft tissue.

Positronium: review of symmetry, conserved quantities and decay for the radiological physicist.

The PET-CT scanner, which overlays a high spatial resolution CT image on a relatively low resolution physiologic PET image, has greatly increased the efficacy of the PET imaging modality. With the resulting increase in the presence of PET imaging in the radiologic and medical physics communities, medical physicists can expect professional responsibilities in acceptance testing, quality assurance, radiation safety and resident teaching of this new modality. With this in mind we present a review of a subtle aspect of PET: the formation, symmetry properties and decay of positronium; the hydrogen like positron-electron complex which forms prior to annihilation.

Partial wave analysis of the ultrasound comet tail artifact.

An adaptation of linear acoustic scattering theory is used to describe the comet tail artifact which is observed in the diagnostic ultrasound imaging of small spherical masses. The calculated backscattered pressure wave is shown to correspond well with the appearance of the artifact in a variety of clinical images.