In vivo K-edge imaging with synchrotron radiation.

We present in this paper two imaging techniques using contrast agents assessed with in vivo experiments. Both methods are based on the same physical principle, and were implemented at the European Synchrotron Radiation Facility medical beamline. The first one is intravenous coronary angiography using synchrotron radiation X-rays. This imaging technique has been planned for human studies in the near future. We describe the first experiments that were carried out with pigs at the ESRF. The second imaging mode is computed tomography using synchrotron radiation on rats bearing brain tumors. Owing to synchrotron radiation physical properties, these new imaging methods provide additional information compared to conventional techniques. After infusion of the contrast agent, it is possible to derive from the images the concentration of the contrast agent in the tumor area for the computed tomography and in any visible vessel for the angiography method.     

The role of magnetic resonance imaging in the management of vascular malformations of the trunk and extremities

Vascular malformations can usually be diagnosed on clinical grounds. They have a well-defined appearance on magnetic resonance imaging, which can effectively determine their tissue and flow characteristics. However, the role of cross-sectional imaging in the management of vascular malformations is not well defined. Most reviews suggest that magnetic resonance imaging should be reserved for cases in which the extent of the lesion cannot be estimated on physical examination. However, to date no group has compared the accuracy of physical examination alone to that of magnetic resonance imaging in determining this extent. A review was performed of all the patients evaluated for vascular malformations at the New York University Trunk and Extremity Vascular Anomalies Conference between July of 1994 and August of 1999. Patients who underwent magnetic resonance evaluation at other institutions and whose images were not available for review were excluded. All study patients either underwent magnetic resonance imaging examination at New York University Medical Center or had outside films reviewed at the center. The physical examination findings were compared with the magnetic resonance findings and the surgeon and radiologist made a joint decision about whether there was a correlation between the magnetic resonance and physical examination findings. Fifty-eight patients met the study criteria, 44 (76 percent) of whom were found to have more extensive disease on magnetic resonance examination than appreciated on physical examination. Of the 51 patients with low-flow vascular malformations (venous vascular malformations, lymphatic malformations, and capillary malformations), 39 (76 percent) had more extensive disease on magnetic resonance examination than on physical examination. Of the seven patients with high-flow arteriovenous malformations, five had more extensive disease on magnetic resonance. In all of the 44 patients whose magnetic resonance imaging findings did not correlate with those of the physical examination, therapeutic decision making was affected. Contrary to the conventional wisdom of published reviews, physical examination findings significantly underestimated the extent of vascular malformations in the majority of cases. Magnetic resonance imaging should be performed in all patients with vascular malformations of the trunk and extremities before therapy is planned. In an age when physicians are asked to justify their decisions, especially where the use of expensive diagnostic modalities is concerned, the situations in which these tests are indispensable must be clearly defined or else patients will be denied access to them.     

宝石能谱CT的功能特点及心血管检查的临床应用

宝石能谱CT拥有一系列独特的技术,包括宝石探测器、高压发射器、ASIR重组技术、能谱栅技术等,使其具有低剂量高清成像、能谱成像和动态500排成像特点,实现了全身0.23mm的极限空间分辨率和类MRI的软组织低密度分辨率,为心脏能量成像、斑块性质的鉴别及金属伪影的消除提供了全新有效的手段。其特有的高纯度和高通透性的物理学特性,再加上影像链中采样率的增高,专有的高清算法,使得宝石能谱CT能够在更低的剂量下,获得更为清晰的图像质量,达到目前业内最高的空间分辨率和密度分辨率;同时,其独有的能谱栅成像技术,将CT诊断从形态学带入功能学领域,因此也被称为"显微CT,病理CT,绿色CT",宝石能谱CT代表了目前CT发展的趋势,它用准确的绝对CT值的单能量成像(keV)诊断和基物质成像诊断来取代传统的相对CT值的混合能量(kVp)成像诊断,用多参数CT成像诊断来代替传统的单参数CT成像诊断,而"三同"(同时、同源、同向)的物理基础保证了其能谱成像的准确性,使CT能谱成像真正走入了临床诊断的第一线,从而提高了心血管疾病诊断的准确性和安全性。为CT在心脏疾病的诊断方面开拓了新领域和新方法。     

New methods and uses for fast optical scanning

Advanced optical imaging techniques used in neurobiology commonly employ fluorescent molecules for studying the structure and function of neural tissue. To obtain adequate spatio-temporal resolution, sophisticated scanning schemes are used to manage the excitation light going to and emission light coming from objects under observation. Although the fundamental principles of these techniques remain the same, such as scanning point illumination and point detection for confocal imaging, their physical implementation is the subject of technological advance, for example, the advent of inertia-free discontinuous scanning schemes. In general, the aims of these technological advances are to improve the spatio-temporal resolution of and/or reduce potential photodamage caused by optical imaging in live neural tissue. The number of recent advances in scanning methods indicates their increasing importance in imaging techniques.     

Fluorescence lifetime imaging.

We describe a new fluorescence imaging methodology in which the image contrast is derived from the fluorescence lifetime at each point in a two-dimensional image and not the local concentration and/or intensity of the fluorophore. In the present apparatus, lifetime images are created from a series of images obtained with a gain-modulated image intensifier. The frequency of gain modulation is at the light-modulation frequency (or a harmonic thereof), resulting in homodyne phase-sensitive images. These stationary phase-sensitive images are collected using a slow-scan CCD camera. A series of such images, obtained with various phase shifts of the gain-modulation signal, is used to determine the phase angle and/or modulation of the emission at each pixel, which is in essence the phase or modulation lifetime image. An advantage of this method is that pixel-to-pixel scanning is not required to obtain the images, as the information from all pixels is obtained at the same time. The method has been experimentally verified by creating lifetime images of standard fluorophores with known lifetimes, ranging from 1 to 10 ns. As an example of biochemical imaging we created life-time images of Yt-base when quenched by acrylamide, as a model for a fluorophore in distinct environments that affect its decay time. Additionally, we describe a faster imaging procedure that allows images in which a specific decay time is suppressed to be calculated, allowing rapid visualization of unique features and/or regions with distinct decay times. The concepts and methodologies of fluorescence lifetime imaging (FLIM) have numerous potential applications in the biosciences. Fluorescence lifetimes are known to be sensitive to numerous chemical and physical factors such as pH, oxygen, temperature, cations, polarity, and binding to macromolecules. Hence the FLIM method allows chemical or physical imaging of macroscopic and microscopic samples.     

Characterization of vascular strain during in-vitro angioplasty with high-resolution ultrasound speckle tracking

Background

Ultrasound elasticity imaging provides biomechanical and elastic properties of vascular tissue, with the potential to distinguish between tissue motion and tissue strain. To validate the ability of ultrasound elasticity imaging to predict structurally defined physical changes in tissue, strain measurement patterns during angioplasty in four bovine carotid artery pathology samples were compared to the measured physical characteristics of the tissue specimens.

Methods

Using computational image-processing techniques, the circumferences of each bovine artery specimen were obtained from ultrasound and pathologic data.

Results

Ultrasound-strain-based and pathology-based arterial circumference measurements were correlated with an R² value of 0.94 (p = 0.03). The experimental elasticity imaging results confirmed the onset of deformation of an angioplasty procedure by indicating a consistent inflection point where vessel fibers were fully unfolded and vessel wall strain initiated.

Conclusion

These results validate the ability of ultrasound elasticity imaging to measure localized mechanical changes in vascular tissue.     

Anaphylaxis Imaging: Non-Invasive Measurement of Surface Body Temperature and Physical Activity in Small Animals

In highly sensitized patients, the encounter with a specific allergen from food, insect stings or medications may rapidly induce systemic anaphylaxis with potentially lethal symptoms. Countless animal models of anaphylaxis, most often in BALB/c mice, were established to understand the pathophysiology and to prove the safety of different treatments. The most common symptoms during anaphylactic shock are drop of body temperature and reduced physical activity. To refine, improve and objectify the currently applied manual monitoring methods, we developed an imaging method for the automated, non-invasive measurement of the whole-body surface temperature and, at the same time, of the horizontal and vertical movement activity of small animals. We tested the anaphylaxis imaging in three in vivo allergy mouse models for i) milk allergy, ii) peanut allergy and iii) egg allergy. These proof-of-principle experiments suggest that the imaging technology represents a reliable non-invasive method for the objective monitoring of small animals during anaphylaxis over time. We propose that the method will be useful for monitoring diseases associated with both, changes in body temperature and in physical behaviour.     

Interstitial fluid pressure as an emerging biomarker in solid tumors

The physical microenvironment of cancer is characterized by elevated stiffness and tissue pressure, the main component of which is the interstitial fluid pressure (IFP). Elevated IFP is an established negative predictive and prognostic parameter, directly affecting malignant behavior and therapy response. As such, measurement of the IFP would allow to develop strategies aimed at engineering the physical microenvironment of cancer. Traditionally, IFP measurement required the use of invasive methods. Recent progress in dynamic and functional imaging methods such as dynamic contrast enhanced (DCE) magnetic resonance imaging and elastography, combined with numerical models and simulation, allows to comprehensively assess the biomechanical landscape of cancer, and may help to overcome physical barriers to drug delivery and immune cell infiltration. Here, we provide a comprehensive overview of the origin of elevated IFP, and its role in the malignant phenotype. Also, we review the methods used to measure IFP using invasive and imaging based methods, and highlight remaining obstacles and potential areas of progress in order to implement IFP measurement in clinical practice.     

Characterizing Organelles in Live Stem Cells Using Label-Free Optical Diffraction Tomography

Label-free optical diffraction tomography (ODT), an imaging technology that does not require fluorescent labeling or other pre-processing, can overcome the limitations of conventional cell imaging technologies, such as fluorescence and electron microscopy. In this study, we used ODT to characterize the cellular organelles of three different stem cells—namely, human liver derived stem cell, human umbilical cord matrix derived mesenchymal stem cell, and human induced pluripotent stem cell—based on their refractive index and volume of organelles. The physical property of each stem cell was compared with that of fibroblast. Based on our findings, the characteristic physical properties of specific stem cells can be quantitatively distinguished based on their refractive index and volume of cellular organelles. Altogether, the method employed herein could aid in the distinction of living stem cells from normal cells without the use of fluorescence or specific biomarkers.     

Electrical impedance tomography imaging using a priori ultrasound data

Background  

Different imaging systems (e.g. electrical, magnetic, and ultrasound) rely on a wide variety of physical properties, and the datasets obtained from such systems provide only partial information about the unknown true state. One approach is to choose complementary imaging systems, and to combine the information to achieve a better representation.     

Quantitative comparison of the sensitivity of detection of fluorescent and bioluminescent reporters in animal models

Bioluminescent and fluorescent reporters are finding increased use in optical molecular imaging in small animals. In the work presented here, issues related to the sensitivity of in vivo detection are examined for standard reporters. A high-sensitivity imaging system that can detect steady-state emission from both bioluminescent and fluorescent reporters is described. The instrument is absolutely calibrated so that animal images can be analyzed in physical units of radiance allowing more quantitative comparisons to be performed. Background emission from mouse tissue, called autoluminescence and autofluorescence, is measured and found to be an important limitation to detection sensitivity of reporters. Measurements of dual-labeled (bioluminescent/fluorescent) reporter systems, including PC-3M-luc/DsRed2-1 and HeLa-luc/PKH26, are shown. The results indicate that although fluorescent signals are generally brighter than bioluminescent signals, the very low autoluminescent levels usually results in superior signal to background ratios for bioluminescent imaging, particularly compared with fluorescent imaging in the green to red part of the spectrum. Fluorescence detection sensitivity improves in the far-red to near-infrared, provided the animals are fed a low-chlorophyll diet to reduce autofluorescence in the intestinal region. The use of blue-shifted excitation filters is explored as a method to subtract out tissue autofluorescence and improve the sensitivity of fluorescent imaging.     

Imaging for lung physiology: what do we wish we could measure?

The role of imaging as a tool for investigating lung physiology is growing at an accelerating pace. Looking forward, we wished to identify unresolved issues in lung physiology that might realistically be addressed by imaging methods in development or imaging approaches that could be considered. The role of imaging is framed in terms of the importance of good spatial and temporal resolution and the types of questions that could be addressed as these technical capabilities improve. Recognizing that physiology is fundamentally a quantitative science, a recurring emphasis is on the need for imaging methods that provide reliable measurements of specific physiological parameters. The topics included necessarily reflect our perspective on what are interesting questions and are not meant to be a comprehensive review. Nevertheless, we hope that this essay will be a spur to physiologists to think about how imaging could usefully be applied in their research and to physical scientists developing new imaging methods to attack challenging questions imaging could potentially answer.     

Ultrasound radiation force modulates ligand availability on targeted contrast agents

Radiation force produced by low-amplitude ultrasound at clinically relevant frequencies remotely translates freely flowing microbubble ultrasound contrast agents over distances up to centimeters from the luminal space to the vessel wall in order to enhance ligand-receptor contact in targeting applications. The question arises as to how the microbubble shell might be designed at the molecular level to fully take advantage of such physical forces in targeted adhesion for molecular imaging and controlled therapeutic release. Herein, we report on a novel surface architecture in which the tethered ligand is buried in a polymeric overbrush. Our results, with biotin-avidin as the model ligand-receptor pair, show that the overbrush conceals the ligand, thereby reducing immune cell binding and increasing circulation persistence. Targeted adhesion is achieved through application of ultrasound radiation force to instantly reveal the ligand within a well-defined focal zone and simultaneously bind the ligand and receptor. Our data illustrate how the adhesive properties of the contrast agent surface can be reversibly changed, from stealth to sticky, through the physical effects of ultrasound. This technique can be combined with any ligand-receptor pair to optimize targeted adhesion for ultrasonic molecular imaging.     

Multiphoton microscopy for the in-situ investigation of cellular processes and integrity in cryopreservation

In this study we demonstrate a new noninvasive imaging method to monitor freezing processes in biological samples and to investigate life in the frozen state. It combines a laser scanning microscope with a computer-controlled cryostage. Nearinfrared (NIR) femtosecond laser pulses evoke the fluorescence of endogenous fluorophores and fluorescent labels due to multiphoton absorption.The inherent optical nonlinearity of multiphoton absorption allows 3D fluorescence imaging for optical tomography of frozen biological material in-situ. As an example for functional imaging we use fluorescence lifetime imaging (FLIM) to create images with chemical and physical contrast.     

Myocardial Hypertrophy in Athletes: Physiology or Pathology?

This paper includes data from the 11th century to the present day on athlete’s heart and its most controversial trait, myocardial hypertrophy. Four historical stages in the evolution of the concept of athlete’s heart are considered: physical, electrocardiographic, echocardiographic, and magnetic resonance imaging stages.     

Monte Carlo method for bioluminescence tomography

Bioluminescence imaging plays an important role in the areas of cancer biology, cell biology, gene therapy, and so on. The 2D planar bioluminescent imaging has been transformed into a 3D framework by bioluminescence tomography (BLT) that enables bioluminescent source reconstruction in a mouse using a modality fusion approach. To solve this BLT problem, a geometrical model of the mouse is usually built from a CT/micro-CT/micro-MRI scan, which facilitates the assignment of optical parameters to various anatomical regions in the model. This optical model is then used to facilitate BLT. The forward model is based on Monte Carlo simulation to calculate the diffuse light flux on the surface of the mouse. The forward model data are used to define the imaging system and perform the BLT reconstruction. In this paper, we report the reconstruction of sources inside a heterogeneous highly scattering physical phantom to demonstrate the feasibility of this Monte Carlo based BLT method.     

Nondestructive quantum dot-based intracellular serotonin imaging in intact cells

In recent years, quantum dots (Qdot), with their unique physical, chemical, and optical properties, have been used extensively as probes to visualize several cell membrane receptors and extracellular biomolecules. However, Qdot-based intracellular imaging has always been associated with vital lacunas. High affinity between quantum dots may induce serious aggregation in the cytoplasm; as a result, quantum dot aggregates are usually misinterpreted as quantum dot-probed intracellular molecules. Moreover, due to the more viscous nature of the cytoplasm versus the extracellular aqueous media, aggregation issues become more severe during intracellular studies. In this work, we suggest direct nondestructive serotonin imaging in an intact cell using the quantum dot-based immunoassay with a rapid tunable multicolor imaging system based on the acousto-optic tunable filter. Any false-positive intracellular serotonin molecules that appeared due to the aggregation of quantum dots could be completely discriminated from the real intracellular serotonin granules through multicolor cellular imaging. The developed method is quick and has wide applicability in targeting various intracellular proteins, coenzymes, and micronutrients.     

The clinical diagnosis of splenomegaly.

Assessing for the presence of splenomegaly is an important component of the physical examination. Although several methods of palpation and percussion of the spleen have been described, until recently they have not been validated by noninvasive imaging techniques such as ultrasonography, radionuclide scanning, and computed tomography that offer objective means to assess splenomegaly. We review the literature comparing various physical examination techniques with noninvasive imaging modalities and conclude that palpation and percussion of the spleen are complementary but frequently insensitive and that further studies are needed to evaluate the efficacy of specific diagnostic methods.     

Bioluminescence imaging: looking beyond the light

Bioluminescence imaging (BLI) enables in vivo imaging of molecular and cellular processes. It has gained in popularity over the past decade because of its easy translation from in vitro to in vivo experiments, its sensitivity, and its ease of use. However, experience in applying BLI in living subjects is still limited, and many researchers have encountered unexpected or biased BLI readout and reported important influencing factors. In this review, we summarize both the biological and physical effects that occur at the enzyme level or during light propagation towards the camera. The knowledge and detection of such factors, together with the development of new strategies and better BLI compounds, will improve the accuracy of the technique in the future.