Strong exciton-plasmon coupling in dye-doped film on a planar hyperbolic metamaterial.

We experimentally demonstrate the direct strong coupling between the S0→S1 absorption transition of rhodamine 6G (R6G) dye molecules and the surface plasmon polaritons of a hyperbolic metamaterial (HMM) substrate. The surface plasmon mode was excited by a guided mode of the R6G-doped polymer thin film on the HMM. The coupling strengths of the interactions between the surface plasmon and two molecular exciton modes are greater than the average linewidths of the individual modes indicating a strong coupling regime. This is the first, to the best of our knowledge, experimental demonstration of the direct strong coupling between the resonance mode supported by the HMM and the dye molecules on the HMM surface, not embedded in the HMM structure. The study may provide the foundation for the development of novel planar photonic or electronic devices.

Molecular packing-dependent exciton dynamics in functionalized anthradithiophene derivatives: From solutions to crystals.

Understanding the impact of inter-molecular orientation on the optical properties of organic semiconductors is important for designing next-generation organic (opto)electronic and photonic devices. However, fundamental aspects of how various features of molecular packing in crystalline systems determine the nature and dynamics of excitons have been a subject of debate. Toward this end, we present a systematic study of how various molecular crystal packing motifs affect the optical properties of a class of high-performance organic semiconductors: functionalized derivatives of fluorinated anthradithiophene. The absorptive and emissive species present in three such derivatives (exhibiting "brickwork," "twisted-columnar," and "sandwich-herringbone" motifs, controlled by the side group R) were analyzed both in solution and in single crystals, using various modalities of optical and photoluminescence spectroscopy, revealing the nature of these excited states. In solution, in the emission band, two states were identified: a Franck-Condon state present at all concentrations and an excimer that emerged at higher concentrations. In single crystal systems, together with ab initio calculations, it was found in the absorptive band that Frenkel and Charge Transfer (CT) excitons mixed due to nonvanishing CT integrals in all derivatives, but the amount of admixture and exciton delocalization depended on the packing, with the "sandwich-herringbone" packing motif least conducive to delocalization. Three emissive species in the crystal phase were also identified: Frenkel excitons, entangled triplet pairs 1(TT) (which are precursors to forming free triplet states via singlet fission), and self-trapped excitons (STEs, similar in origin to excimers present in concentrated solution). The "twisted-columnar" packing motif was most conducive to the formation of Frenkel excitons delocalized over 4-7 molecules depending on the temperature. These delocalized Frenkel states were dominant across the full temperature range (78 K-293 K), though at lower temperatures, the entangled triplet states and STEs were present. In the derivative with the "brickwork" packing, all three emissive species were observed across the full temperature range and, most notably, the 1(TT) state was present at room temperature. Finally, the derivative with the "sandwich-herringbone" packing exhibited localized Frenkel excitons and had a strong propensity for self-trapped exciton formation even at higher temperatures. In this derivative, no formation of the 1(TT) state was observed. The temperature-dependent dynamics of these emissive states are reported, as well as their origin in fundamental inter-molecular interactions.

Preparation and specificities of antisera to the amino-terminal sequence of the carcinoembryonic antigen.

A tetracosapeptide (peptide-24) corresponding to the amino-terminal sequence of the carcinoembryonic antigen (CEA) was synthesized and characterized. Antisera were produced to the peptide-24, and a radioimmunoassay was developed utilizing peptide-24 with a tyrosine residue on the amino-terminal end (Tyr-peptide-24). Inhibitions of anti-peptide-24-125I-Tyr-peptide-24 complex formation were done with several preparations of CEA and the normal cross-reacting antigen. The extent of cross-reactivities was low, one CEA preparation requiring a 250-fold molar quantity greater than peptide-24 to obtain the same degree of inhibition. Attempts to degrade the CEAs and normal cross-reacting antigens in order to possibly expose the amino-terminal ends for reactivity with antibody did not result in any great increase in inhibitory capacity. It was concluded that either the conformations of the antigenic determinant(s) of the peptide-24 and of the amino-terminal end of CEA were sufficiently different to result in little cross-reacting antigen are blocked for reactivity with antibody by other portions of the molecule.

A simplified solid-phase radioimmunoassay for carcinoembryonic antigen.

A simple and rapid solid-phase radioimmunoassay for the measurement of carcinoembryonic antigen (CEA) levels in sera or plasma is described. The procedure involves perchloric acid (PCA) extraction of the samples, followed by a rapid neutralization of excess acid with alkaline buffer solution. The PCA extracts are assayed uing antibody-coated plastic tubes and radio-labeled anti-CEA antibody as a marker. The assay may be completed in one day. The solid-phase direct-binding assay demonstrated a sensitivity of 0.5 ng CEA/ml plasmin and a marked tolerance to variations in pH and ionic strength of the system. A fair correlation between the CEA levels determined by the solid-phase radioimmunoassay and zirconium phosphate gel method was observed.

Passive hemagglutination procedure for group A streptococcal polysaccharide.

A passive hemagglutination procedure for detection of antibody to group A beta-hemolytic streptococcus polysaccharide is described. The polysaccharide was conjugated to human gamma globulin and the complex adsorbed onto stabilized human erythrocytes. Antigen coated cells were used to measure antibody levels in normal human sera and in rabbit antisera.

The usefulness of a contrast agent and gradient-recalled acquisition in a steady-state imaging sequence for magnetic resonance imaging-guided noninvasive ultrasound surgery.

RATIONALE AND OBJECTIVES: The ability of magnetic resonance imaging to detect small temperature elevations from focused ultrasound surgery beams was studied. In addition, the value of a contrast agent in delineating the necrosed tissue volume was investigated. MATERIALS AND METHODS: Gradient-recalled acquisition in a steady state (GRASS) T1-weighted images were used to follow the temperature elevation and tissue changes during 2-minute sonications in the thigh muscles of 10 rabbits. The effects of the treatment on the vascular network was investigated by injecting a contrast agent bolus before or after the sonication. RESULTS: The signal intensity decreased during the sonication, and the reduction was directly proportional to the applied power and increase in temperature. The signal intensity returned gradually back to baseline after the ultrasound was turned off. Injection of the contrast agent increased the signal intensity in muscle, but not in the necrosed tissue. The dimensions of the delineated tissue volume were the same as measured from the T2-weighted fast-spin-echo images and postmortem tissue examination. CONCLUSIONS: These results indicate that magnetic resonance imaging can be used to detect temperature elevations that do not cause tissue damage and that contrast agent can be used to delineate the necrosed tissue volume.

Orbital magnetic resonance imaging.

Magnetic resonance images of the eye and orbit performed with surface coils at 1.5 tesla showed anatomic details superior to those of conventional third- and fourth-generation computed tomography.

MR imaging of the optic nerve and sheath: correcting the chemical shift misregistration effect.

The interface between soft-tissue structures and adipose tissue may be obscured by the chemical shift misregistration effect on MR images. In the orbit, this effect occurs at the edges at the optic nerve, even on high-resolution local coil images. In both phantom and clinical studies with a 1.5 T local coil imaging system, it was found that the chemical shift misregistration effect can be minimized by positioning the patient so that the optic nerve is parallel to the frequency encoding gradient. Alternatively, the effect can be corrected by using a computer program to combine "lipid" and "water" proton images. The sensitivity of MR for optic nerve lesions should be improved by these technical modifications.

Magnetic resonance imaging of the jugular foramen.

The jugular foramen in normal volunteers was studied with 1.5 T magnetic resonance (MR) systems in 3-mm-thick head- and surface-coil images. Anatomic sections through cadaver heads were correlated with the MR images to identify the jugular bulb and the course of cranial nerves IX-XI. Sagittal images were more useful than coronal or axial to show the course of these nerves through the skull base. MR demonstrates the anatomic relations of the jugular foramen (except its osseous margins) such that its primary use in evaluating this region can be anticipated.

Imaging of brain iron by magnetic resonance: T2 relaxation at different field strengths.

Soon after the advent of magnetic resonance imaging (MRI) as a diagnostic modality in the 1980s, it was recognized that some of the contrast found in brain imaging correlated with patterns of iron deposition. The presence of non-heme iron had previously been established by pathological studies on post-mortem brains. The iron concentration is highest in specific nuclei of the basal ganglia and some associated structures. It is low at birth and increases with age until a relatively constant level is reached at an age of 20-30 years. There is evidence for further increases in very elderly persons. Although iron is ubiquitous in human tissues, only in a few situations is the concentration large enough to affect MRI. Because MRI has the ability to detect, in a noninvasive fashion, the naturally occurring iron in the basal ganglia and related nuclei, it may be used to study the physiology and pathology of these important structures. Magnetic resonance imaging has confirmed the results of earlier post mortem studies of the anatomical localization and age-dependence of brain iron. Initial steps have been toward the use of MRI to study disorders of thought, movement, and behavior that are believed to be related to brain iron. However, additional understanding is required of the physical details of the contrast mechanism, the physiology of the iron accumulation, and the significance of abnormal patterns of iron deposition. In this report, data are presented on the normal variation in MRI parameters and their dependence on magnetic field strength. The potential clinical and basic science applications are briefly reviewed. Information from widely differing fields is relevant to the study of the physical and pathological significance of brain iron, and for this reason, extensive, although not exhaustive, literature references are included.

The role of magnetic susceptibility in magnetic resonance imaging: MRI magnetic compatibility of the first and second kinds.

The concept of magnetic susceptibility is central to many current research and development activities in magnetic resonance imaging (MRI); for example, the development of MR-guided surgery has created a need for surgical instruments and other devices with susceptibility tailored to the MR environment; susceptibility effects can lead to position errors of up to several millimeters in MR-guided stereotactic surgery; and the variation of magnetic susceptibility on a microscopic scale within tissues contributes to MR contrast and is the basis of functional MRI. The magnetic aspects of MR compatibility are discussed in terms of two levels of acceptability: Materials with the first kind of magnetic field compatibility are such that magnetic forces and torques do not interfere significantly when the materials are used within the magnetic field of the scanner; materials with the second kind of magnetic field compatibility meet the more demanding requirement that they produce only negligible artifacts within the MR image and their effect on the positional accuracy of features within the image is negligible or can readily be corrected. Several materials exhibiting magnetic field compatibility of the second kind have been studied and a group of materials that produce essentially no image distortion, even when located directly within the imaging field of view, is identified. Because of demagnetizing effects, the shape and orientation, as well as the susceptibility, of objects within and adjacent to the imaging region is important in MRI. The quantitative use of susceptibility data is important to MRI, but the use of literature values for the susceptibility of materials is often difficult because of inconsistent traditions in the definitions and units used for magnetic parameters-particularly susceptibility. The uniform use of SI units for magnetic susceptibility and related quantities would help to achieve consistency and avoid confusion in MRI.

MRI-guided noninvasive ultrasound surgery.

In this study, the feasibility of using magnetic resonance imaging (MRI) to detect tissue necrosis induced by focussed ultrasound beams was investigated. It was shown that lesions produced in dog's thigh muscle in vivo were clearly visible in T2-weighted images and that the lesion dimensions measured from the images correlated with the postmortem measurements of the visible tissue damage. It was also shown that the sonications can be done in the magnet and that the lesions are visible immediately after the sonications with increasing image contrast as a function of time. These results showed that MRI can be used to direct and monitor on-line noninvasive ultrasound surgery. This may have a major impact in future patient treatments.

Human exposure to 4.0-Tesla magnetic fields in a whole-body scanner.

Details are given for the design, construction, properties, and performance of a large, highly homogeneous magnet designed to permit whole-body magnetic resonance imaging and spectroscopy at 4 T. The magnet has an inductance of 1289 H and a stored energy of 33.4 MJ at rated field. The health of a group of 11 volunteers who had varying degrees of exposure to this field was followed over a 12-month period and no change that could be associated with this exposure was detected. A mild level of sensory experiences, apparently associated with motion within the field of the magnet, was reported by some of the volunteers during some of their exposures. A questionnaire regarding sensory effects associated with magnetic resonance scanners and possibly caused by the static magnetic field of these instruments, was given to nine respondents who had experience within both 1.5-T scanners and this 4-T scanner and to another group of 24 respondents who had experience only within 1.5-T scanners. For the sensations of vertigo, nausea, and metallic taste there was statistically significant (p less than 0.05) evidence for a field-dependent effect that was greater at 4 T. In addition, there was evidence for motion-induced magnetophosphenes caused by motion of the eyes within the static field. These results indicate the practicality of experimental whole-body body scanners operating at 4 T and the possibility of mild sensory effects in humans associated with motion within a static magnetic field. The results also indicate the likelihood of a wide margin of safety for the exposure of noncompromised patients to the static fields of conventional magnetic resonance scanners operated at 1.5 to 2 T and below.

Phototoxicity involving the ocular lens: in vivo and in vitro studies.

Our laboratory has demonstrated the cataractogenic potential of UV radiation and several photosensitizing drugs in laboratory animals and in humans. We have utilized lens fluorescence measurements (which we have demonstrated to be a reliable marker for pre-cataractous and early cataractous changes), NMR pulse relaxation techniques, and our recently developed magnetic resonance imaging method to measure lens T2 values in the normal and UV exposed Degus lens (in vivo and in vitro) to detect pre-cataractous changes in the lens. These approaches will permit us to employ two parameters (increased non-tryptophan fluorescence and a decrease in T2 values) to monitor for such changes months before the lens opacities become manifest by conventional slit lamp examinations.

Very-high-field magnetic resonance imaging: instrumentation and safety issues.

Because of their advantage in terms of signal-to-noise ratio, high-field magnetic resonance imaging systems have become favored in the last few years for functional magnetic resonance imaging (fMRI) applications. In many ways the conceptual development of these high-field scanners has involved more-or-less straightforward extensions of practices at lower field strengths. However, in other ways specific engineering challenges have been encountered and largely overcome in the quest for scanners capable of realizing the advantages of high-field systems. An understanding of the technical trade-offs that can be made in terms of hardware performance is useful in deciding on the optimum system for a given fMRI application. In this article the technical issues surrounding high-field scanning are reviewed in the context of a typical brain mapping protocol. In addition there is a discussion of the safety issues related to the use of these systems.

In vivo non-invasive studies on the human lens.

Progress in biophysical technology now permits us to monitor aging and precataractous changes in the human ocular lens in vivo as well as in vitro. We are employing two noninvasive techniques to measure changes in lens fluorescence and in one lens water compartment (T2) utilizing Scheimpflug lens fluorescence densitography and magnetic resonance imaging. These studies demonstrate age-related changes in the normal lens as reflected by enhanced fluorescence and longer T2 values. Precataractous changes can also be detected with this approach.

Head and body imaging by hydrogen nuclear magnetic resonance.

A hydrogen (1H) nuclear magnetic resonance (NMR) imaging study of the normal head, thorax, and limbs is reported. The images are 10 to 15 mm thick transverse slices obtained in 2 to 4 min using a two-dimensional Fourier transform technique. Spatial resolution in the imaging plane is about 2 mm, enabling the optic nerve and many small blood vessels to be observed. Thorax scans show details of the cardiac chambers, aorta wall, and lungs without artefacts arising from physiological motion.

Noninvasive imaging of the normal temporal bone. Comparison of sagittal surface coil magnetic imaging and high-resolution computed tomography.

High-resolution computed tomography (HRCT) is a noninvasive technique for evaluating the middle ear for primary and recurrent cholesteatoma. However, a limitation of HRCT is that it cannot differentiate between cholesteatoma and granulation tissue. Magnetic resonance imaging (MRI) is a noninvasive, nonradiologic technique that has been effective in demonstrating histochemical differences between various soft tissues. We present images from a normal living subject's temporal bone in the sagittal plane obtained with both HRCT and MRI. Anatomic correlates in the same cut planes are presented. The HRCT provided excellent detail of the bony landmarks within the temporal bone and was used as the reference for the MRI. The soft-tissue structures such as cranial nerves, cochlea, vestibule, and semicircular canals were identified.

In vitro simulation. Early results of stereotaxy for pedicle screw placement.

STUDY DESIGN: Frameless stereotaxy with doppler ultrasound and three dimensional computer model registration is assessed in vitro for pedicle screw placement. OBJECTIVE: To identify feasibility of pedicle screw navigation and placement using this technology. SUMMARY OF BACKGROUND DATA: Inaccurate pedicle screw placement can lead to neurovascular injury or suboptimal fixation. Present techniques in pedicle screw placement involve only confirmation of hole orientation. METHOD: Forty-four pedicle screws were placed in lumbosacral models and cadaver specimens. Accuracy was assessed with a computed tomography scan and vertebral cross sectioning. RESULTS: All screws were intrapedicular. Accuracy of anterior cortical fixation was 1.5 mm, with a range of 2.5 mm. CONCLUSION: In vitro frameless stereotaxy is accurate for pedicle screw placement. This technology adds a component of navigation to pedicle screw placement.

Quality assurance experiences within a physical therapy curriculum.

A brief description is presented of a curriculum that provides learning experiences that can lead to students' achievement of basic skills in quality assurance. The model of a system for patient care that is presented includes patient problem identification, management planning, documentation, and assessment of effectiveness of patient care. Focus of the learning experiences described is on the assessment-of-effectiveness portion of the system. Students practice management planning, documentation, and audit throughout the curriculum. Premises that guided design of experiences are given.