Reconstruction method for extended depth-of-field optical diffraction tomography.

In the paper we present a novel method of extended depth-of-field limited-angle optical diffraction tomography, in which the change of a focal plane position is performed with a liquid focus-tunable lens. One sinogram is acquired for each state of a focus-tunable lens. After acquisition process is complete, all sinograms are independently reconstructed and stitched to form the final tomographic reconstruction. The presented solution effectively extends the applicability of the Rytov approximation to relatively thick samples and provides uniform resolution of 3D tomographic reconstructions. The method is also combined with Generalized Total Variation Iterative Constraint algorithm, which minimizes distortion of the results due to the limited angular range of acquired projections. The combined solution is dedicated to investigation of transparent and semi-transparent biological micro-structures, like cells and tissue slices.

Assembling the pieces.

Transition metals function as cofactors in specific proteins, catalyzing electron exchange reactions, binding substrates and stabilizing protein structure. Studies of human diseases and of model organisms have defined many of the molecular details of metal uptake, trafficking, and excretion. The current challenge is to integrate these details into a systematic view of metal content, speciation, localization and use within organisms and ecosystems.

The internal structure of mitochondria.

Electron microscopic (EM) tomography is providing important new insights into the internal organization of mitochondria. The standard baffle model for cristae structure, called into question years ago, has now clearly been shown to be inaccurate. Depending on source and conformational state, cristae can vary from simple tubular structures to more complex lamellar structures merging with the inner boundary membrane through tubular structures 28 nm in diameter. The structural information provided by EM tomography has important implications for mitochondrial bioenergetics, biogenesis and the role of mitochondria in apoptosis. The structural paradigm defined by EM tomography is helping in the design of new experimental approaches to mitochondrial function.

[A review of electrical impedance tomography based on MRI technique].

In this paper, a review of a new electrical impedance tomography technique-magnetic resonance electrical impedance tomography (MREIT) is presented. Some medical imaging methods are briefly introduced. The basic theory of MREIT is given as well as its realization methods and developing status. The merits and challenges of this new trend are also demonstrated.

Advanced technologies in image-guided radiation therapy.

In addition to rapid developments in the use of stationary radiographs and computed tomography scans in treatment rooms, a variety of additional technologies is on the horizon to aid in guided treatment. Some of these (fluoroscopy and tomosynthesis) are variations on the use of existing hardware, whereas others (electromagnetic localization, magnetic resonance imaging) represent significant departures from recently adopted technologic concepts. This review introduces these methods and explores their potential for initial use in guidance.

Electron cryotomography.

Electron cryotomography is an emerging technique that allows the structures of unique biological objects such as individual macromolecules, viruses, and even small whole cells to be reconstructed in their near-native states in three dimensions (3-D) to an approximate 5-nm resolution. The required instrumentation, sample preparation and limitations, data collection, typical results, and future prospects are summarized briefly.

The evolving role of structural and functional imaging in assessment of age-related changes in the body.

Aging is an extremely complex, multifactorial, and inevitable process that varies in rate from person to person and that is not fully understood at its most basic levels. Despite this complexity, knowledge of age-related changes and normal variation in organ structure and function is essential to differentiate them from alterations that are associated with pathology. Combined structural and functional imaging, which increasingly is used to assess a multitude of disorders, including cancer, cardiovascular disease, and central nervous system abnormalities, can be applied to study changes in structure and function related to aging. This article reviews the major theories of biological aging and presents our approach and rationale to study age-related changes through quantitative tomographic radiological and scintigraphic approaches. In the series of articles that follow, we have made an attempt to determine age-related changes in volume, attenuation, and function as measured by computed tomography, magnetic resonance imaging, and position emission tomography in the following organs and systems: central nervous system, head and neck, heart and major arteries, lungs, abdominal and pelvic parenchymal organs, gastrointestinal tract, genitourinary tract, breast, bone and bone marrow, joints, and skin. The population examined includes a large number of subjects in all decades of life. We have also made an effort to introduce some new concepts such as partial volume correction and measurements of global metabolic activity of the organs examined, and emphasize the importance of quantitative techniques in such applications. It is our hope that this new initiative will further enhance the role of novel imaging techniques in the management of patients with cancer and other disorders.

Problems and Possibilities of Passive Thermoacoustical Tomography.

The problems and possibilities of passive thermoacoustical tomography are discussed. Algorithms for reconstruction of internal temperature in the human body are proposed. These algorithms take into account heat transfer and blood circulation and the absorption factor, obtained previously. The results of reconstruction of deep temperature in the human hand in simulations with the medium with a heated object are reported. These results support the possibility of the correlation measurements of the thermal acoustic radiation. Such measurements allow the information on ultrasound absorption by the object under study to be obtained and open the way to the development of a passive acoustic tomography system using a priori information on the absorption factor.

Fiber optic in vivo imaging in the mammalian nervous system.

The compact size, mechanical flexibility, and growing functionality of optical fiber and fiber optic devices are enabling several new modalities for imaging the mammalian nervous system in vivo. Fluorescence microendoscopy is a minimally invasive fiber modality that provides cellular resolution in deep brain areas. Diffuse optical tomography is a non-invasive modality that uses assemblies of fiber optic emitters and detectors on the cranium for volumetric imaging of brain activation. Optical coherence tomography is a sensitive interferometric imaging technique that can be implemented in a variety of fiber based formats and that might allow intrinsic optical detection of brain activity at a high resolution. Miniaturized fiber optic microscopy permits cellular level imaging in the brains of behaving animals. Together, these modalities will enable new uses of imaging in the intact nervous system for both research and clinical applications.

Functional monitoring of peripheral nerves from electrical impedance measurements.

Medical electrical stimulators adapted to peripheral nerves use multicontact cuff electrodes (MCC) to provide selective neural interfaces. However, neuroprostheses are currently limited by their inability to locate the regions of interest to focus. Intended until now either for stimulation or recording, MCC can also be used as a means of transduction to characterize the nerve by impedancemetry. In this study, we investigate the feasibility of using electrical impedance (EI) measurements as an in vivo functional nerve monitoring technique. The monitoring paradigm includes the synchronized recording of both the evoked endogenous activity as compound action potentials (CAP) and the superimposed sine signal from the EI probe. Measurements were conducted on the sciatic nerve of rodents, chosen for its branchings towards the peroneal and tibial nerves, with both mono- and multi-contact per section electrodes. During stimulation phases, recordings showed CAP with consistent fiber conduction velocities. During coupled phases of both stimulation and sine perturbation, impedance variations were extracted using the mono-contact electrode type for certain frequencies, e.g. 2.941kHz, and were temporally coherent with the previous recorded CAP. Using a MCC, localized evoked CAP were also recorded but the signal to noise ratio (SNR) was too low to distinguish the expected associated impedance variation and deduce an image of impedance spatial changes within the nerve. The conducted in vivo measurements allowed to distinguish both evoked CAP and associated impedance variations with a strong temporal correlation. This indicates the feasibility of functional EI monitoring, aiming at detecting the impedance variations in relation to neural activity. Further work is needed to improve the in vivo system, namely in terms of SNR, and to integrate new multicontact devices in order to move towards EI tomography with the detection of spatially-localized impedance variations. Eventually, regions that are interesting to be targeted by stimulation could be identified through these means.

Clinical imaging of cancer metastasis.

Tumour imaging is an essential part of the practice of oncology, with a crucial role in screening programmes and in diagnosis and staging of established disease. Furthermore, the assessment of tumour size by imaging, usually with computer tomography (CT) scanning, is a key component in determining the tumour response to therapy both in clinical trials and in daily oncology practice. Techniques such as CT, ultrasound (US) and magnetic resonance imaging (MRI) provide high resolution anatomical images with detailed structural information. However, these imaging modalities yield limited functional information on the tumour tissues and often cannot distinguish residual disease from non-viable or necrotic tumour masses, nor can they detect minimal residual disease. In contrast, radiopharmaceutical imaging and, in particular, positron emission tomography (PET) can give some functional information about the underlying tissues. The possibility of refining these techniques and also the emergence of newer imaging modalities that can detect changes in cancers at the physiological, cellular or molecular levels, gives rise to the notion that these methods will have implications for drug development strategies and also future clinical management. In this review, we briefly discuss the current role of imaging in clinical practice, describe some of the advances in imaging modalities currently undergoing evaluation, and speculate on the future role of these techniques in developmental therapeutics programmes.

Optical biopsy using tissue spectroscopy and optical coherence tomography.

'Optical biopsy' or 'optical diagnostics' is a technique whereby light energy is used to obtain information about the structure and function of tissues without disrupting them. In fluorescence spectroscopy, light energy (usually provided by a laser) is used to excite tissues and the resulting fluorescence provides information about the target tissue. Its major gastrointestinal application has been in the evaluation of colonic polyps, in which it can reliably distinguish malignant from benign lesions. Optical coherence tomography (OCT) has been used in the investigation of Barrett's epithelium (and dysplasia), although a variety of other applications are feasible. For example, OCT could assist in the identification and staging of mucosal and submucosal neoplasms, the grading of inflammation in the stomach and intestine, the diagnosis of biliary tumours and the assessment of villous architecture. OCT differs from endoscopic ultrasound, a complementary modality, in that it has a much higher resolution but lesser depth of penetration. The images correlate with the histopathological appearance of tissues, and the addition of Doppler methods may enable it to evaluate the vascularity of tumours and the amount of blood flow in varices. Refinements in these new optical techniques will likely make them valuable in clinical practice, although their specific roles have yet to be determined.

EIT reconstruction algorithms: pitfalls, challenges and recent developments.

We review developments, issues and challenges in electrical impedance tomography (EIT) for the 4th Conference on Biomedical Applications of Electrical Impedance Tomography, held at Manchester in 2003. We focus on the necessity for three-dimensional data collection and reconstruction, efficient solution of the forward problem, and both present and future reconstruction algorithms. We also suggest common pitfalls or 'inverse crimes' to avoid.

Recent activity in ultrasonic tomography.

During the past two decades there have been significant developments in many aspects of acoustical imaging techniques for various applications. One aspect of this development has been the application of ultrasonic tomography to medical imaging and diagnosis instrumentation, and also to non-destructive evaluation of materials, to oceanographic systems for measurements of such factors as temperature and currents etc, and to seismic exploration. This paper reviews the theoretical and practical work in acoustical tomography to the present time.

Magnetic particle imaging: advancements and perspectives for real-time in vivo monitoring and image-guided therapy.

Magnetic particle imaging (MPI) is an emerging biomedical imaging technology that allows the direct quantitative mapping of the spatial distribution of superparamagnetic iron oxide nanoparticles. MPI's increased sensitivity and short image acquisition times foster the creation of tomographic images with high temporal and spatial resolution. The contrast and sensitivity of MPI is envisioned to transcend those of other medical imaging modalities presently used, such as magnetic resonance imaging (MRI), X-ray scans, ultrasound, computed tomography (CT), positron emission tomography (PET) and single photon emission computed tomography (SPECT). In this review, we present an overview of the recent advances in the rapidly developing field of MPI. We begin with a basic introduction of the fundamentals of MPI, followed by some highlights over the past decade of the evolution of strategies and approaches used to improve this new imaging technique. We also examine the optimization of iron oxide nanoparticle tracers used for imaging, underscoring the importance of size homogeneity and surface engineering. Finally, we present some future research directions for MPI, emphasizing the novel and exciting opportunities that it offers as an important tool for real-time in vivo monitoring. All these opportunities and capabilities that MPI presents are now seen as potential breakthrough innovations in timely disease diagnosis, implant monitoring, and image-guided therapeutics.

Photoacoustic tomography: fundamentals, advances and prospects.

Optical microscopy has been contributing to the development of life science for more than three centuries. However, due to strong optical scattering in tissue, its in vivo imaging ability has been restricted to studies at superficial depths. Advances in photoacoustic tomography (PAT) now allow multiscale imaging at depths from sub-millimeter to several centimeters, with spatial resolutions from sub-micrometer to sub-millimeter. Because of this high scalability and its unique optical absorption contrast, PAT is capable of performing anatomical, functional, molecular and fluid-dynamic imaging at various system levels, and is playing an increasingly important role in fundamental biological research and clinical practice. This review discusses recent technical progress in PAT and presents corresponding applications. It ends with a discussion of several prospects and their technical challenges.