Focal pair merging for contrast enhancement of single particles

A common technique in transmission electron microscopy is the collection of a focal pair, in which the first, close to focus image contains higher resolution information at lower contrast, and the second, far from focus image has high contrast but less reliable high-resolution information. Typically these second micrographs are used for purposes of particle selection, orientation estimate or micrograph evaluation. We introduce a technique for merging the information from both images, including signal to noise ratio weighting, contrast transfer function correction, and optional Weiner filtration. This produces a composite image with reduced contrast transfer function artifacts and optimized contrast. This technique is useful in numerous cases where low-contrast images are produced, such as small particles, proteins solubilized in detergent or projects with high-resolution goals when the first image is taken very close to focus.     

Molecular imaging with targeted contrast ultrasound

Molecular imaging with contrast ultrasound relies on the detection of targeted microbubbles or other acoustically active nanoparticles. These microbubbles are retained in diseased tissue where they produce an acoustic signal because of their resonant properties in the ultrasound field. Targeting is accomplished either through manipulating the chemical properties of the microbubble shell or through conjugation of disease-specific ligands for the targeted molecule to the microbubble surface. As microbubbles cannot leave the intravascular space, the disease process must be characterized by molecular changes in the vascular compartment to be imaged. Inflammation, angiogenesis and thrombus formation are central pathophysiologic processes in many disease states and produce phenotypic changes in the vascular compartment. Thus, targeted contrast ultrasound in the future could aid in the diagnosis of such diverse diseases as atherosclerosis, transplant rejection and tumor-related angiogenesis.     

Accuracy of colour Doppler ultrasound velocity measurements in small vessels

Colour Doppler ultrasound offers the possibility of imaging small vessels not visible by B-mode alone. The colour Doppler image of velocities allows the course of small vessels to be imaged in the X-Y plane of the scan provided the Doppler frequency shift is of sufficient magnitude. This permits alignments of the Doppler cursor, allowing angle correction to provide true velocity measurements from the Doppler shift obtained. Before attempting to make velocity measurements, however, it is essential to be aware of the possible error in the Z plane caused by the thickness of the Doppler sample volume. To quantify this source of error, hydrophone and flow-rig measurements were performed on an Acuson 128 colour Doppler scanner with both 5 MHz linear-array and 3.5 MHz phased-array transducers. Measurements of the transmitted pulses using a point hydrophone showed that both probes employ approximately 3.5 MHz Doppler pulses (in both colour and pulsed Doppler modes). The two transducers have the same axial resolution. In colour Doppler mode the axial length of the sample volume increases automatically with depth by up to 0.5 mm. Measurements of colour and pulsed Doppler signal strength were obtained in a controlled flow rig. Both transducers produced accurate colour flow images of the phantom at their optimum depths; flow velocity errors due to Z-plane thickness are < 5%. There was, however, substantial error outside these optimum conditions (up to 20%).     

Targeted contrast agents for magnetic resonance imaging and ultrasound

The development of contrast agents that can be localized to a particular tissue or cellular epitope will potentially allow the noninvasive visualization and characterization of a variety of disease states. Recent advances have been made in the field of molecular imaging with magnetic resonance imaging and ultrasound and varied approaches have been devised to overcome the high background tissue signal. The types of agents and applications developed include gadolinium-conjugated targeting molecules for imaging of fibrin, superparamagnetic iron oxide particles for stem-cell tracking, multimodal perfluorocarbon nanoparticles for visualization of angiogenesis, liposomes for targeting atheroma components, and microbubbles for imaging transplant rejection.     

Paramagnetic oligonucleotides: contrast agents for magnetic resonance imaging with proton relaxation enhancement effects

An antisense paramagnetic oligonucleotide analogue targeted to a model macromolecular receptor (5S rRNA) was prepared. The paramagnetic agent's relaxivity (dependence of the relaxation rate on paramagnetic agent concentration) in the presence and absence of the macromolecular receptor was measured at 1.5 and 6.3 T. The relaxivity of the targeted agent increased specifically in the presence of the macromolecular receptor (16% at 6.3 T and 15% at 1.5 T). This effect was specific for a paramagnetic oligonucleotide targeted to the receptor and was larger than the relaxivity enhancement due simply to receptor-induced viscosity differences. Maximizing this relaxivity enhancement of tumor targeted paramagnetic oligonucleotides will aid in contrast agent development for magnetic resonance imaging.     

An interventional magnetic resonance imaging technique for the molecular characterization of intraprostatic dynamic contrast enhancement

The biological characterization of an individual patient's tumor by noninvasive imaging will have an important role in cancer care and clinical research if the molecular processes that underlie the image data are known. Spatial heterogeneity in the dynamics of magnetic resonance imaging contrast enhancement (DCE-MRI) is hypothesized to reflect variations in tumor angiogenesis. Here we demonstrate the feasibility of precisely colocalizing DCE-MRI data with the genomic and proteomic profiles of underlying biopsy tissue using a novel MRI-guided biopsy technique in a patients with prostate cancer.     

Vasa vasorum and molecular imaging of atherosclerotic plaques using nonlinear contrast intravascular ultrasound

There is increasing evidence that presence and location of neovascular vasa vasorum play an important role in atherosclerotic plaque pathogenesis and stability. This paper describes a method to detect vasa vasorum with high contrast and high spatial resolution. It uses second harmonic or subharmonic intravascular ultrasound, in combination with ultrasound contrast agents. The same technology in combination with targeted contrast agents is suited for molecular imaging. The potential for vasa vasorum imaging is illustrated using an atherosclerotic animal model and the potential for molecular imaging is illustrated using phantom experiments.     

Accurate memory for colour but not pattern contrast in chicks

The visual displays of animals and plants often look dramatic and colourful to us, but what information do they convey to their intended, non-human, audience [1] [2]? One possibility is that stimulus values are judged accurately - so, for example, a female might choose a suitor if he displays a specific colour [3]. Alternatively, as for human advertising, displays may attract attention without giving information, perhaps by exploiting innate preferences for bright colours or symmetry [2] [4] [5]. To address this issue experimentally, we investigated chicks' memories of visual patterns. Food was placed in patterned paper containers which, like seed pods or insect prey, must be manipulated to extract food and their patterns learnt. To establish what was learnt, birds were tested on familiar stimuli and on alternative stimuli of differing colour or contrast. For colour, birds selected the trained stimulus; for contrast, they preferred high contrast patterns over the familiar. These differing responses to colour and contrast show how separate components of display patterns could serve different roles, with colour being judged accurately whereas pattern contrast attracts attention.     

Tailoring the size distribution of ultrasound contrast agents: possible method for improving sensitivity in molecular imaging

Encapsulated microbubble contrast agents incorporating an adhesion ligand in the microbubble shell are used for molecular imaging with ultrasound. Currently available microbubble agents are produced with techniques that result in a large size variance. Detection of these contrast agents depends on properties related to the microbubble diameter such as resonant frequency, and current ultrasound imaging systems have bandwidth limits that reduce their sensitivity to a polydisperse contrast agent population. For ultrasonic molecular imaging, in which only a limited number of targeted contrast agents may be retained at the site of pathology, it is important to optimize the sensitivity of the imaging system to the entire population of contrast agent. This article presents contrast agents with a narrow size distribution that are targeted for molecular imaging applications. The production of a functionalized, lipid-encapsulated, microbubble contrast agent with a monodisperse population is demonstrated, and we evaluate parameters that influence the size distribution and demonstrate initial acoustic testing.     

The use of submicroscopic gold particles combined with video contrast enhancement as a simple molecular probe for the living cell

We describe a new approach to probe the molecular biology of the living cell that uses small colloidal gold particles coupled to specific ligands. They are visualized in cells by bright-field, video enhanced contrast microscopy. We describe the basic aspects of the technique and provide examples of applications to intracellular motility, cell membrane dynamics, receptor translocation, internalization, and intracellular routing. We also provide examples of the use of this approach in immunospecific labelling of cells and tissue sections.     

Digital imaging for colour measurement in ecological research

Traditional methods for colour quantification are complicated by the fact that colours change depending on illumination, and that different observers often perceive colours differently. Here we describe a new affordable method, which improves methods relying on human observers, to quantify patterns and colour variations. The procedure combines customized software with the use of digital cameras and commercial photofinishing software. The computer routines correct unavoidable illumination changes during image capturing, making all images comparable. Colours are quantified in a continuous scale of the conventional colour models developed for the human vision system, such as HSB, RGB, CMYK, or Lab, amenable for statistical analyses. We illustrate the use of this technique showing a previously unknown sexual dimorphism in the red-legged partridge, Alectoris rufa , undetectable with the unaided human eye. We also demonstrate that the digital system provides a finer discrimination than human observers for scoring the plumage of partridges belonging to two different subspecies. This method has potential applications in behavioural ecology, physiology, genetics, evolutionary biology, and taxonomy.