High-resolution Molecular Imaging Research Articles

Design and development of a high resolution animal SPECT scanner dedicated for rat and mouse imaging

A dedicated small-animal SPECT system, HiReSPECT, was designed and developed to provide a high resolution molecular imaging modality in response to growing research demands. HiReSPECT is a dual-head system mounted on a rotating gantry. The detection system is based on pixelated CsI(Na) scintillator crystals coupled to two Hamamatsu H8500 Position Sensitive Photomultiplier Tubes in each head. Also, a high resolution parallel-hole collimator is applied to every head. The dimensions of each head are 50mm×100mm, enabling sufficient transaxial and axial fields-of-view (TFOV and AFOV), respectively, for coverage of the entire mouse in single-bed position imaging. However, a 50mm TFOV is not sufficient for transaxial coverage of rats. To address this, each head can be rotated by 90 degrees in order to align the larger dimension of the heads with the short body axis, allowing tomographic data acquisition for rats. An innovative non-linear recursive filter was used for signal processing/detection. Resolution recovery was also embedded in the modified Maximum-Likelihood Expectation Maximization (MLEM) image reconstruction code to compensate for Collimator-Detector Response (CDR). Moreover, an innovative interpolation algorithm was developed to speed up the reconstruction code. The planar spatial resolution at the head surface and the image spatial resolutions were 1.7mm and 1.2–1.6mm, respectively. The measurements followed by post-processing showed that the observed count rate at 20% count loss is about 42kcps. The system sensitivity at the collimator surface for heads 1 and 2 were 1.32cps/µCi and 1.25cps/µCi, respectively. The corresponding values were 1.18cps/µCi and 1.02cps/µCi at 8cm distance from the collimator surfaces. In addition, whole-body scans of mice demonstrated appropriate imaging capability of the HiReSPECT.

Photo acoustic tomography

Photoacoustic tomography (PAT), sometimes referred to as optoacoustic tomography, is defined as cross-sectional or three-dimensional (3D) imaging of a material based on the photoacoustic effect (Wang 2009). Therefore, PAT possesses spatial resolution along the depth dimension and at least one of the other two dimensions. In PAT, light is absorbed by biological tissue and converted to transient heating, which is subsequently converted into an ultrasonic wave due to thermoelastic expansion. Detection of the ultrasonic wave yields a tomographic image. Combining rich optical contrast and scalable ultrasonic resolution, PAT is the only imaging modality capable of providing multiscale high-resolution structural, functional, and molecular imaging of organelles, cells, tissues, and organs in vivo. While functional imaging measures physiological parameters, such as oxygenation and blood flow, molecular imaging senses biomarkers to identify specific cancer cells or detects gene expression products to track gene activations.

Structural Abnormalities in Bipolar Euthymia: A Multicontrast Molecular Diffusion Imaging Study

Evidence from decades of magnetic resonance imaging (MRI) research in bipolar disorder has been summarized in meta-analyses of various MRI modalities. Notably, although structural MRI studies suggest gray matter reductions are restricted to specific cortical regions, functional MRI has also shown involvement of subcortical dysfunction. Such disparity in results is open to discussion and requires further exploration with additional MRI modalities. We applied whole-brain high angular resolution molecular diffusion imaging to compare different properties of the water diffusion process in brain tissues, using different contrasts. Specifically, we looked at fractional anisotropy, mean diffusivity, probability of return to the origin, and generalized fractional anisotropy in a sample of 40 euthymic patients with bipolar disorder and 40 well-matched healthy control subjects. Convergent abnormalities were detected by contrasts in various tissue types. Apart from alterations in white matter (in corpus callosum, cingulum bundle, corona radiata, and superior fronto-occipital fasciculus) and cortical gray matter (in medial frontal cortex, left insula, Heschl's gyrus, and cerebellum), three of the contrasts (fractional anisotropy, mean diffusivity, and generalized fractional anisotropy) revealed abnormalities in subcortical structures, including the hippocampus, the thalamus and the caudate nucleus. Our findings point to a wider pattern of axonal pathology in bipolar disorder than previously thought. Although findings related to cortical gray matter are consistent with structural meta-analyses, subcortical abnormalities suggest a cytoarchitectonic basis for previously reported subcortical dysfunction. Diffusion results could be interpreted in terms of loss of tissue volume and/or altered membrane permeability, agreeing with both hypotheses of mitochondrial malfunction and neuroinflammation.

A gradient-based method for quantitative photoacoustic tomography using the radiative transfer equation

Quantitative photoacoustic tomography (QPAT) offers the possibility of high-resolution molecular imaging by quantifying molecular concentrations in biological tissue. QPAT comprises two inverse problems: (1) the construction of a photoacoustic image from surface measurements of photoacoustic wave pulses over time, and (2) the determination of the optical properties of the imaged region. The first is a well-studied area for which a number of solution methods are available, while the second is, in general, a nonlinear, ill-posed inverse problem. Model-based inversion techniques to solve (2) are usually based on the diffusion approximation to the radiative transfer equation (RTE) and typically assume the acoustic inversion step has been solved exactly. Here, neither simplification is made: the full RTE is used to model the light propagation, and the acoustic propagation and image reconstruction are included in the simulations of measured data. Since Hessian- and Jacobian-based minimizations are computationally expensive for the large data sets typically encountered in QPAT, gradient-based minimization schemes provide a practical alternative. The acoustic pressure time series were simulated using a k-space, pseudo-spectral time domain model, and a time-reversal reconstruction algorithm was used to form a set of photoacoustic images corresponding to four illumination positions. A regularized, adjoint-assisted gradient inversion using a finite element model of the RTE was then used to determine the optical absorption and scattering coefficients.

Enhancer and gene traps for molecular imaging and genetic analysis in zebrafish

Enhancer and gene trapping methods are highly effective means for the identification and functional analysis of transcriptionally active genes. With recent advances in fluorescent proteins and transposon based integration technologies, a growing family of trapping approaches has been developed in zebrafish, offering powerful tools to both visualize and functionally dissect gene networks during development. Coupled with the intrinsic advantages of the zebrafish model system, creative genetic engineering of trap vectors has enabled high-resolution molecular imaging and genetic manipulations. This review highlights the different enhancer and gene trap approaches that have been developed in zebrafish and offers insights into the strengths, limitations and experimental strategies for their application to enrich our knowledge of gene function and the cellular processes they control.

High-Resolution Optical Molecular Imaging of Changes in Choline Metabolism in Oral Neoplasia

This study was aimed at developing an optical molecular imaging approach to measure differences in uptake and intracellular retention of choline in clinically isolated tissue biopsies from head and neck cancer patients. An optically detectable analogue of choline (propargyl choline) was synthesized and evaluated in 2D and 3D models and clinically isolated paired biopsies (n = 22 biopsies). Fluorescence contrast between clinically abnormal and normal tissues based on uptake and intracellular retention of propargyl choline was measured and correlated with pathologic diagnosis. Results in 2D and 3D models demonstrated a rapid uptake of propargyl choline in cancer cells, uniform permeation in tissue models, and specific detection of intracellular entrapped propargyl choline using the click chemistry reaction with an azide-modified Alexa 488 dye. Fluorescence imaging measurements following topical delivery of propargyl choline in clinically isolated biopsies showed that the mean fluorescence intensity (MFI) of neoplastic tissues was four-fold to five-fold higher than the MFI of clinically and pathologically normal samples. This difference in fluorescence contrast was measured on the basis of comparison of paired biopsy sets isolated from individual patients as well as comparison of clinically abnormal and normal biopsies independent of anatomic locations in the head and neck cavity and across diverse patients. In conclusion, a novel imaging approach based on monoalkyne-modified choline was developed and validated using cell and tissue models. Results in clinically isolated tissue biopsies demonstrate a significant fluorescent contrast between neoplastic and normal tissues and illustrate high specificity of the optical imaging approach.

Recent advances in two-photon imaging: technology developments and biomedical applications

In the past two decades, two-photon microscopy (TPM) transforms biomedical research, allowing nondestructive high-resolution fluorescent molecular imaging and label-free imaging in vivo and in real time. Here we review the recent advances of TPM technology including novel laser sources, new image acquisition paradigms, and microendoscopic imaging systems. Then, we survey the capabilities of TPM imaging of biological relevant molecules such as nicotinamide adenine dinucleotide (NADH), flavin adenine dinucleotide (FAD), and reactive oxygen species (ROS). Biomedical applications of TPM in neuroscience and cancer detection are demonstrated.

Molecular Imaging of Experimental Abdominal Aortic Aneurysms

Current laboratory research in the field of abdominal aortic aneurysm (AAA) disease often utilizes small animal experimental models induced by genetic manipulation or chemical application. This has led to the use and development of multiple high-resolution molecular imaging modalities capable of tracking disease progression, quantifying the role of inflammation, and evaluating the effects of potential therapeutics. In vivo imaging reduces the number of research animals used, provides molecular and cellular information, and allows for longitudinal studies, a necessity when tracking vessel expansion in a single animal. This review outlines developments of both established and emerging molecular imaging techniques used to study AAA disease. Beyond the typical modalities used for anatomical imaging, which include ultrasound (US) and computed tomography (CT), previous molecular imaging efforts have used magnetic resonance (MR), near-infrared fluorescence (NIRF), bioluminescence, single-photon emission computed tomography (SPECT), and positron emission tomography (PET). Mouse and rat AAA models will hopefully provide insight into potential disease mechanisms, and the development of advanced molecular imaging techniques, if clinically useful, may have translational potential. These efforts could help improve the management of aneurysms and better evaluate the therapeutic potential of new treatments for human AAA disease.

Biomedical Imaging Instrumentation and Design in Neurological Disorder Data Acquisition

The recent introduction of high-resolution molecular imaging technology is considered by many experts as a major breakthrough that will potentially lead to a revolutionary paradigm shift in health care and revolutionize clinical practice. This paper explores the challenges and strengths of the current major imaging modalities, as well as the biophysics engineering their repertoire of capabilities. Advancements in the mechanical aspects of both PET and SPECT imaging will advance molecular imaging diagnostic capabilities and have a direct impact on clinical medicine and biomedical research practice. A better understanding of the strengths and limitations of functional imaging modalities in the context of their particular hardware and software mechanics will shed light onto how we can advance their diagnostic capabilities on a biological level. Herein, this paper demonstrates the fundamental biomechanical differences between PET and SPECT imaging, and how these fundamental differences translate into clinically relevant data acquisition for brain disorders.

Methods for in vivo molecular imaging

Visualization of single molecules and specific subsets of cells is widely used for studies of biological processes and particularly in immunological research. Recent technological advances have provided a qualitative change in biological visualization from studying of "snapshot" pictures to real-time continuous observation of cellular dynamics in vivo. Contemporary methods of in vivo imaging make it possible to localize specific cells within organs and tissues, to study their differentiation, migration, and cell-to-cell interactions, and to follow some intracellular events. Fluorescence intravital microscopy plays an especially important role in high resolution molecular imaging. The methods of intravital microscopy are quickly advancing thanks to improvements in molecular sensors, labeling strategies, and detection approaches. Novel techniques allow simultaneous detection of various probes with better resolution and depth of imaging. In this review, we describe current methods for in vivo imaging, with special accent on fluorescence approaches, and discuss their applications for medical and biological studies.

Three-dimensional molecular reconstruction of rat heart with mass spectrometry imaging

Cardiovascular diseases are the world's number one cause of death, accounting for 17.1 million deaths a year. New high-resolution molecular and structural imaging strategies are needed to understand underlying pathophysiological mechanism. The aim of our study is (1) to provide a molecular basis of the heart animal model through the local identification of biomolecules by mass spectrometry imaging (MSI) (three-dimensional (3D) molecular reconstruction), (2) to perform a cross-species validation of secondary ion mass spectrometry (SIMS)-based cardiovascular molecular imaging, and (3) to demonstrate potential clinical relevance by the application of this innovative methodology to human heart specimens. We investigated a MSI approach using SIMS on the major areas of a rat and mouse heart: the pericardium, the myocardium, the endocardium, valves, and the great vessels. While several structures of the heart can be observed in individual two-dimensional sections analyzed by metal-assisted SIMS imaging, a full view of these structures in the total heart volume can be achieved only through the construction of the 3D heart model. The images of 3D reconstruction of the rat heart show a highly complementary localization between Na(+), K(+), and two ions at m/z 145 and 667. Principal component analysis of the MSI data clearly identified different morphology of the heart by their distinct correlated molecular signatures. The results reported here represent the first 3D molecular reconstruction of rat heart by SIMS imaging.

Multispectral Opto-acoustic Tomography (MSOT) of the Brain and Glioblastoma Characterization

Brain research depends strongly on imaging for assessing function and disease in vivo. We examine herein multispectral opto-acoustic tomography (MSOT), a novel technology for high-resolution molecular imaging deep inside tissues. MSOT illuminates tissue with light pulses at multiple wavelengths and detects the acoustic waves generated by the thermoelastic expansion of the environment surrounding absorbing molecules. Using spectral unmixing analysis of the data collected, MSOT can then differentiate the spectral signatures of oxygenated and deoxygenated hemoglobin and of photo-absorbing agents and quantify their concentration. By being able to detect absorbing molecules up to centimeters deep in the tissue it represents an ideal modality for small animal brain imaging, simultaneously providing anatomical, hemodynamic, functional, and molecular information. In this work we examine the capacity of MSOT in cross-sectional brain imaging of mice. We find unprecedented optical imaging performance in cross-sectional visualization of anatomical and physiological parameters of the mouse brain. For example, the potential of MSOT to characterize ischemic brain areas was demonstrated through the use of a carbon dioxide challenge. In addition, indocyanine green (ICG) was injected intravenously, and the kinetics of uptake and clearance in the vasculature of the brain was visualized in real-time. We further found that multiparameter, multispectral imaging of the growth of U87 tumor cells injected into the brain could be visualized through the intact mouse head, for example through visualization of deoxygenated hemoglobin in the growing tumor. We also demonstrate how MSOT offers several compelling features for brain research and allows time-dependent detection and quantification of brain parameters that are not available using other imaging methods without invasive procedures.

Synthesis and Evaluation of a Peptide Targeted Small Molecular Gd-DOTA Monoamide Conjugate for MR Molecular Imaging of Prostate Cancer

Tumor extracellular matrix has an abundance of cancer related proteins that can be used as biomarkers for cancer molecular imaging. Innovative design and development of safe and effective targeted contrast agents to these biomarkers would allow effective MR cancer molecular imaging with high spatial resolution. In this study, we synthesized a low molecular weight CLT1 peptide targeted Gd(III) chelate CLT1-dL-(Gd-DOTA)(4) specific to clotted plasma proteins in tumor stroma for cancer MR molecular imaging. CLT1-dL-(Gd-DOTA)(4) was synthesized by conjugating four Gd-DOTA monoamide chelates to a CLT1 peptide via generation 1 lysine dendrimer. The T(1) relaxivity of CLT1-dL-(Gd-DOTA)(4) was 40.4 mM(-1) s(-1) per molecule (10.1 mM(-1) s(-1) per Gd) at 37 °C and 1.5 T. Fluorescence imaging showed high binding specificity of CLT1 to orthotopic PC3 prostate tumor in mice. The contrast agent resulted in improved tumor contrast enhancement in male athymic nude mice bearing orthotopic PC3 prostate tumor xenograft at a dose of 0.03 mmol Gd/kg. The peptide targeted MRI contrast agent is promising for high-resolution MR molecular imaging of prostate tumor.

SPEM: a state-of-the-art instrument for high resolution molecular imaging of small animal organs

To describe the Single Photon Emission Microscope (SPEM), a state-of-the-art instrument for small animal SPECT imaging, and characterize its performance presenting typical images of different animal organs. SPEM consists of two independent imaging devices based on high resolution scintillators, high sensitivity and resolution Electron-Multiplying CCDs and multi-pinhole collimators. During image acquisition, the mouse is placed in a rotational vertical holder between the imaging devices. Subsequently, an appropriate software tool based on the Maximum Likelihood algorithm iteratively produces the volumetric image. Radiopharmaceuticals for imaging kidneys, heart, thyroid and brain were used. The mice were injected with 74 to 148 MBq/0,3mL and scanned for 40 to 80 minutes, 30 to 60 minutes afterwards. During this procedure, the animals remained under ketamine/xilazine anesthesia. SPEM images of different mouse organs are presented, attesting the imaging capabilities of the instrument. SPEM is an innovative technology for small animal SPECT imaging providing high resolution images with appropriate sensitivity for pre-clinical research. Its use with appropriate radiotracers will allow translational investigation of several animal models of human diseases, their pharmacological treatment and the development of potential new therapeutic agents.

Optoacoustic Imaging: An Emerging Modality for the Gastrointestinal Tract

Optoacoustic Imaging: An Emerging Modality for the Gastrointestinal Tract

In vivo Bioimaging as a Novel Strategy to Detect Doxorubicin-Induced Damage to Gonadal Blood Vessels

IntroductionChemotherapy may induce deleterious effects in normal tissues, leading to organ damage. Direct vascular injury is the least characterized side effect. Our aim was to establish a real-time, in vivo molecular imaging platform for evaluating the potential vascular toxicity of doxorubicin in mice.MethodsMice gonads served as reference organs. Mouse ovarian or testicular blood volume and femoral arterial blood flow were measured in real-time during and after doxorubicin (8 mg/kg intravenously) or paclitaxel (1.2 mg/kg) administration. Ovarian blood volume was imaged by ultrasound biomicroscopy (Vevo2100) with microbubbles as a contrast agent whereas testicular blood volume and blood flow as well as femoral arterial blood flow was imaged by pulse wave Doppler ultrasound. Visualization of ovarian and femoral microvasculature was obtained by fluorescence optical imaging system, equipped with a confocal fiber microscope (Cell-viZio).ResultsUsing microbubbles as a contrast agent revealed a 33% (P<0.01) decrease in ovarian blood volume already 3 minutes after doxorubicin injection. Doppler ultrasound depicted the same phenomenon in testicular blood volume and blood flow. The femoral arterial blood flow was impaired in the same fashion. Cell-viZio imaging depicted a pattern of vessels' injury at around the same time after doxorubicin injection: the wall of the blood vessels became irregular and the fluorescence signal displayed in the small vessels was gradually diminished. Paclitaxel had no vascular effect.ConclusionWe have established a platform of innovative high-resolution molecular imaging, suitable for in vivo imaging of vessels' characteristics, arterial blood flow and organs blood volume that enable prolonged real-time detection of chemotherapy-induced effects in the same individuals. The acute reduction in gonadal and femoral blood flow and the impairment of the blood vessels wall may represent an acute universal doxorubicin-related vascular toxicity, an initial event in organ injury.

Advances of Infrared Spectroscopic Imaging and Mapping Technologies of Plant Material

Fourier Transform Infrared (FTIR) spectroscopic imaging and mapping techniques have become essential tools for the detection and characterization of the molecular components of biological tissues [1]. These modern analytical techniques enable high-resolution molecular imaging of complex botanical samples [2]. Imaging and mapping are based on the absorption of IR radiations by vibrational transitions in covalent bonds and their major advantage is the acquisition of local molecular expression profiles, while maintaining the topographic integrity of the tissue by avoiding time-consuming extraction, purification and separation steps. All IR related information is recorded in a so called „hyperspectral cube“ from which any ingredient relevant information can be selectively extracted with a resolution of 4µm and transformed into an image as depicted for e.g. Urtica dioica in Figure 1. These new techniques enable global analysis of biological samples with highest spatial resolution and provide unique chemical-morphological information about the tissue status. With these non-destructive examination methods it is possible to get qualitative and quantitative information of heterogeneous samples. In this presentation recent applications of infrared spectroscopic imaging and mapping technologies of plant material are introduced and discussed. Keywords: Phytomics, tissue, instrumentation, data processing, transmission, reflection, hyper spectral imaging Acknowledgement: Eurasia-Pacific Uninet (EPU) (Salzburg, Austria), the Ministry for Science and Research and the Ministry for Health, Family and Youth (Vienna, Austria) (Novel Analytical Tools for Quality Control in Traditional Chinese Medicine, Project No. 80855), the Leopold-Franzens University, Innsbruck (Nachwuchsforderung) for financial support.

A proton spin diffusion based solid-state NMR approach for structural studies on aligned samples.

Rapidly expanding research on nonsoluble and noncrystalline chemical and biological materials necessitates sophisticated techniques to image these materials at atomic-level resolution. Although their study poses a formidable challenge, solid-state NMR is a powerful tool that has demonstrated application to the investigation of their molecular architecture and functioning. In particular, 2D separated-local-field (SLF) spectroscopy is increasingly applied to obtain high-resolution molecular images of these materials. However, despite the common use of SLF experiments in the structural studies of a variety of aligned molecules, the lack of a resonance assignment approach has been a major disadvantage. As a result, solid-state NMR studies have mostly been limited to aligned systems that are labeled with an isotope at a single site. Here, we demonstrate an approach for resonance assignment through a controlled reintroduction of proton spin diffusion in the 2D proton-evolved-local-field (PELF) pulse sequence. Experimental results and simulations suggest that the use of spin diffusion also enables the measurement of long-range heteronuclear dipolar couplings that can be used as additional constraints in the structural and dynamical studies of aligned molecules. The new method is used to determine the de novo atomic-level resolution structure of a liquid crystalline material, N-(4-methoxybenzylidene)-4-butylaniline, and its use on magnetically aligned bicelles is also demonstrated. We expect this technique to also be valuable in the structural studies of functional molecules like columnar liquid crystals and other biomaterials.

Recent advances in submolecular resolution with scanning probe microscopy

Recently scanning probe microscopy has made tremendous progress in imaging organic molecules with high lateral resolution. Atoms and bonds within individual molecules have been clearly resolved, indicating the exciting potential of this technique for studying molecular structures, bonding within and between molecules, molecular conformational changes and chemical reactions at the single-molecule level. It turns out that the key step enabling such studies is an atomically controlled functionalization of the microscope tip. In this Perspective, the different techniques used for high-resolution molecular imaging, their implementations, advantages and limitations are described, and possible scientific areas of applications are discussed.

Brain Protection

A growing community of researchers has questioned the merits of the translational process in stroke and has championed the need for proof-of-concept studies to explain why >100 clinical stroke studies have failed.1,2 On the positive side, no published laboratory results or strong theoretical arguments have been advanced to indicate that human neurons, glia, and blood vessels are necessarily resistant to protection with drugs or devices. In fact, proof of principle has been established for many agents in cultured cells as well as in rodent and subhuman primate stroke models. Therefore, it is important to understand the reasons why an apparent disconnect exists between preclinical and clinical trial results. The answers may lie partly in shortcomings and breaches in the translational process that repeatedly compromise adequate drug testing in both preclinical and clinical arenas. On the positive side, it may be argued that a formula for human brain protection has been established, that is, by delivering in a timely manner oxygen as well as glucose and by removing wastes from ischemic tissue. That formula has met with success for reperfusion strategies in vivo and for maintaining cultured cells and brain slices in vitro. Some success has also been achieved using hypothermia to treat victims of cardiac arrest and global ischemia. The pleiotropic actions of hypothermia have taught us that protection may be better achieved by targeting multiple rather than individual death pathways as well as by reducing energy demand and energy consumption. Some of the same lessons may also apply to the promising and emerging field of preconditioning whose tissue-sparing effects appear to rely on upregulation of multiple endogenous protective mechanisms. Lessons from the transplant field are also instructive as surgeons have become increasingly sophisticated about maintaining organ viability ex vivo for many hours in the absence of a blood …