Clinical molecular imaging

Label-Free Chemically and Molecularly Selective Magnetic Resonance Imaging

Biomedical imaging, especially molecular imaging, has been a driving force in scientific discovery, technological innovation, and precision medicine in the past two decades. While substantial advances and discoveries in chemical biology have been made to develop molecular imaging probes and tracers, translating these exogenous agents to clinical application in precision medicine is a major challenge. Among the clinically accepted imaging modalities, magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) exemplify the most effective and robust biomedical imaging tools. Both MRI and MRS enable a broad range of chemical, biological and clinical applications from determining molecular structures in biochemical analysis to imaging diagnosis and characterization of many diseases and image-guided interventions. Using chemical, biological, and nuclear magnetic resonance properties of specific endogenous metabolites and native MRI contrast-enhancing biomolecules, label-free molecular and cellular imaging with MRI can be achieved in biomedical research and clinical management of patients with various diseases. This review article outlines the chemical and biological bases of several label-free chemically and molecularly selective MRI and MRS methods that have been applied in imaging biomarker discovery, preclinical investigation, and image-guided clinical management. Examples are provided to demonstrate strategies for using endogenous probes to report the molecular, metabolic, physiological, and functional events and processes in living systems, including patients. Future perspectives on label-free molecular MRI and its challenges as well as potential solutions, including the use of rational design and engineered approaches to develop chemical and biological imaging probes to facilitate or combine with label-free molecular MRI, are discussed.

Synergistic Theranostics of Magnetic Resonance Imaging and Photothermal Therapy of Breast Cancer Based on the Janus Nanostructures Fe3O4-Aushell-PEG

Background

Satisfactory prognosis of breast cancer (BC) is limited by difficulty in early diagnosis and insufficient treatment. The combination of molecular imaging and photothermal therapy (PTT) may provide a solution.

Methods

Fe₃O₄-Au_shell nanoparticles (NPs) were prepared by thermal decomposition, seeded growth and galvanic replacement and were comprehensively characterized. After conjugated to PEG, NPs were used as MRI and PTT agents in vitro and in vivo.

Results

Fe₃O₄-Au_shell NPs which had uniform Janus-like morphology were successfully synthesized. The Fe₃O₄ had a size of 18 ± 2.2 nm, and the Au_shell had an outer diameter of 25 ± 3.3 nm and an inner diameter of 20 ± 2.9 nm. The NPs showed superparamagnetism, a saturation magnetization of 36 emu/g, and an optical absorption plateau from 700 to 808 nm. The Fe₃O₄-Au_shell NPs were determined to possess good biocompatibility. After PEG coating, the zeta potential of NPs was changed from −23.75 ± 1.37 mV to −13.93 ± 0.55 mV, and the FTIR showed the characteristic C–O stretching vibration at 1113 cm⁻¹. The NPs’ MR imaging implied that the T₂ can be shortened by Fe₃O₄-Au_shell NPs in a concentration-dependent manner, and the Fe₃O₄-Au_shell NPs coated with PEG at the molar ratio of 160 (PEG: NPs) showed the highest transverse relaxivity (r₂) of 216 mM⁻¹s⁻¹. After irradiation at 0.65 W/cm² for 5 min, all cells incubated with the Fe₃O₄-Au_shell-PEG160 NPs (Fe: 30 ppm, Au: 70 ppm) died. After administrated intratumorally, Fe₃O₄-Au_shell-PEG160 notably decreased the signal intensity of tumor in T₂WI images. Under the same irradiation, the temperature of tumors injected with Fe₃O₄-Au_shell-PEG160 quickly rose to 54.6°C, and the tumors shrank rapidly and were ablated in 6 days.

Conclusion

Fe₃O₄-Au_shell-PEG NPs show good r₂ and PTT performance and are promising synergistic theranostic agents of MRI and PTT for BC.

Multivalent Probes in Molecular Imaging: Reality or Future?

The rapidly developing field of molecular medical imaging focuses on specific visualization of (patho)physiological processes through the application of imaging agents (IAs) in multiple clinical modalities. Although our understanding of the principles underlying efficient IAs design has increased tremendously, many IAs still show poor in vivo imaging performance because of low binding affinity and/or specificity. These limitations can be addressed by taking advantage of multivalency, in which multiple copies of a ligand are employed to strengthen the interaction. We critically address specific challenges associated with the application of multivalent compounds in molecular imaging, and we give directions for a stepwise approach to the design of multivalent imaging probes to improve their target binding and pharmacokinetics (PK) for improved diagnostic potential.

Musculoskeletal trauma imaging in the era of novel molecular methods and artificial intelligence

Over the past decade rapid advancements in molecular imaging (MI) and artificial intelligence (AI) have revolutionized traditional musculoskeletal radiology. Molecular imaging refers to the ability of various methods to in vivo characterize and quantify biological processes, at a molecular level. The extracted information provides the tools to understand the pathophysiology of diseases and thus to early detect, to accurately evaluate the extend and to apply and evaluate targeted treatments. At present, molecular imaging mainly involves CT, MRI, radionuclide, US, and optical imaging and has been reported in many clinical and preclinical studies. Although originally MI techniques targeted at central nervous system disorders, later on their value on musculoskeletal disorders was also studied in depth. Meaningful exploitation of the large volume of imaging data generated by molecular and conventional imaging techniques, requires state-of-the-art computational methods that enable rapid handling of large volumes of information. AI allows end-to-end training of computer algorithms to perform tasks encountered in everyday clinical practice including diagnosis, disease severity classification and image optimization. Notably, the development of deep learning algorithms has offered novel methods that enable intelligent processing of large imaging datasets in an attempt to automate decision-making in a wide variety of settings related to musculoskeletal trauma. Current applications of AI include the diagnosis of bone and soft tissue injuries, monitoring of the healing process and prediction of injuries in the professional sports setting. This review presents the current applications of novel MI techniques and methods and the emerging role of AI regarding the diagnosis and evaluation of musculoskeletal trauma.

Hot spot 19 F magnetic resonance imaging of inflammation

Among the preclinical molecular imaging approaches, lately fluorine (¹⁹ F) magnetic resonance imaging (MRI) has garnered significant scientific interest in the biomedical research community, due to the unique properties of fluorinated materials and the ¹⁹ F nucleus. Fluorine is an intrinsically sensitive nucleus for MRI-there is negligible endogenous ¹⁹ F in the body and, thus, no background signal which allows the detection of fluorinated materials as "hot spots" by combined ¹ H/¹⁹ F MRI and renders fluorine-containing molecules as ideal tracers with high specificity. In addition, perfluorocarbons are a family of compounds that exhibit a very high fluorine payload and are biochemically as well as physiologically inert. Perfluorocarbon nanoemulsions (PFCs) are well known to be readily taken up by immunocompetent cells, which can be exploited for the unequivocal identification of inflammatory foci by tracking the recruitment of PFC-loaded immune cells to affected tissues using ¹ H/¹⁹ F MRI. The required ¹⁹ F labeling of immune cells can be accomplished either ex vivo by PFC incubation of isolated endogenous immune cells followed by their re-injection or by intravenous application of PFCs for in situ uptake by circulating immune cells. With both approaches, inflamed tissues can unambiguously be detected via background-free ¹⁹ F signals due to trafficking of PFC-loaded immune cells to affected organs. To extend ¹⁹ F MRI tracking beyond cells with phagocytic properties, the PFC surface can further be equipped with distinct ligands to generate specificity against epitopes and/or types of immune cells independent of phagocytosis. Recent developments also allow for concurrent detection of different PFCs with distinct spectral signatures allowing the simultaneous visualization of several targets, such as various immune cell subtypes labeled with these PFCs. Since ligands and targets can easily be adapted to a variety of problems, this approach provides a general and versatile platform for inflammation imaging which will strongly extend the frontiers of molecular MRI. This article is categorized under: Diagnostic Tools > in vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Emerging Technologies Therapeutic Approaches and Drug Discovery > Nanomedicine for Cardiovascular Disease.

Optical diagnosis of actinic cheilitis by infrared spectroscopy

Actinic cheilitis (AC) is considered a potentially malignant disorder of the lip. Biomolecular markers study is important to understand malignant transformation into squamous cell carcinoma. Fourier transform infra red (FT-IR) spectroscopy was used to analyze AC in this study.

OBJECTIVES

The aim of the study was to evaluate if FT-IR spectral regions of nucleic acids and collagen can help in early diagnosis of malignant transformation.

METHODS

Tissues biopsies of 14 patients diagnosed with AC and 14 normal tissues were obtained. FT-IR spectra were measured at five different points resulting in 70 spectra of each. Analysis of Principal components analysis (PCA) and linear discrimination analysis (LDA) model were also used. In order to verify the statistical difference in the spectra, Mann-Whitney U test was performed in each variable (wavenumber) with p-value <0.05.

RESULTS

After the Mann-Whitney U test the vibrational modes of CO (Collagen 1), PO2 (Nucleic Acids) and CO asymmetric (Triglycerides/Lipids) were observed as a possible spectral biomarker. These bands were chosen because they represent the vibrational modes related to collagen and DNA, which are supposed to be changed in AC samples. Based on the PCA-LDA results, the predictive model corresponding to the area under the curve was 0.91 for the fingerprint region and 0.83 for the high wavenumber region, showing the greater accuracy of the test.

CONCLUSIONS

FT-IR changes in collagen and nucleic acids could be used as molecular biomarkers for malignant transformation.

Molecular imaging for theranostics in gastroenterology: one stone to kill two birds

Molecular imaging in gastroenterology has become more feasible with recent advances in imaging technology, molecular genetics, and next-generation biochemistry, in addition to advances in endoscopic imaging techniques including magnified high-resolution endoscopy, narrow band imaging or autofluorescence imaging, flexible spectral imaging color enhancement, and confocal laser endomicroscopy. These developments have the potential to serve as "red flag" techniques enabling the earlier and accurate detection of mucosal abnormalities (such as precancerous lesions) beyond biomarkers, virtual histology of detected lesions, and molecular targeted therapy-the strategy of "one stone to kill two or three birds"; however, more effort should be done to be "blue ocean" benefit. This review deals with the introduction of Raman spectroscopy endoscopy, imaging mass spectroscopy, and nanomolecule development for theranostics. Imaging of molecular pathological changes in cells/tissues/organs might open the "royal road" to either convincing diagnosis of diseases that otherwise would only be detected in the advanced stages or novel therapeutic methods targeted to personalized medicine.

Academic radiology in the new health care delivery environment

RATIONALE AND OBJECTIVES

Ongoing concerns over the rising cost of health care are driving large-scale changes in the way that health care is practiced and reimbursed in the United States.

MATERIALS AND METHODS

To effectively implement and thrive within this new health care delivery environment, academic medical institutions will need to modify financial and business models and adapt institutional cultures. In this article, we review the expected features of the new health care environment from the perspective of academic radiology departments.

CONCLUSIONS

Our review will include background on accountable care organizations, identify challenges associated with the new managed care model, and outline key strategies-including expanding the use of existing information technology infrastructure, promoting continued medical innovation, balancing academic research with clinical care, and exploring new roles for radiologists in efficient patient management-that will ensure continued success for academic radiology.

Imaging of intratumoral inflammation during oncolytic virotherapy of tumors by 19F-magnetic resonance imaging (MRI)

Background

Oncolytic virotherapy of tumors is an up-coming, promising therapeutic modality of cancer therapy. Unfortunately, non-invasive techniques to evaluate the inflammatory host response to treatment are rare. Here, we evaluate ¹⁹F magnetic resonance imaging (MRI) which enables the non-invasive visualization of inflammatory processes in pathological conditions by the use of perfluorocarbon nanoemulsions (PFC) for monitoring of oncolytic virotherapy.

Methodology/Principal Findings

The Vaccinia virus strain GLV-1h68 was used as an oncolytic agent for the treatment of different tumor models. Systemic application of PFC emulsions followed by ¹H/¹⁹F MRI of mock-infected and GLV-1h68-infected tumor-bearing mice revealed a significant accumulation of the ¹⁹F signal in the tumor rim of virus-treated mice. Histological examination of tumors confirmed a similar spatial distribution of the ¹⁹F signal hot spots and CD68⁺-macrophages. Thereby, the CD68⁺-macrophages encapsulate the GFP-positive viral infection foci. In multiple tumor models, we specifically visualized early inflammatory cell recruitment in Vaccinia virus colonized tumors. Furthermore, we documented that the ¹⁹F signal correlated with the extent of viral spreading within tumors.

Conclusions/Significance

These results suggest ¹⁹F MRI as a non-invasive methodology to document the tumor-associated host immune response as well as the extent of intratumoral viral replication. Thus, ¹⁹F MRI represents a new platform to non-invasively investigate the role of the host immune response for therapeutic outcome of oncolytic virotherapy and individual patient response.

CD44-specific supramolecular hydrogels for fluorescence molecular imaging of stem-like gastric cancer cells

We describe a near-infrared-sensitive molecular imaging probe based on hydrogel complexes that can target a stem-like gastric cancer cell marker (CD44, a marker that often correlates with a poor prognosis in patients). Thus, CD44-targetable and near-infrared-sensitive supramolecular hydrogels (NIRSHs, Cy5.5-conjugated polyethyleneimine/hyaluronic acid polyplexes) were fabricated by polyplexing in an aqueous medium. NIRSHs demonstrated good water-stability, biocompatibility, and specificity to CD44-expressing stem-like gastric cancer cells. Furthermore, NIR-sensitive in vivo imaging potentials of CD44-targetable NIRSHs for heterotopic/orthotopic xenograft mouse models were investigated.

Biomedical nanomaterials for imaging-guided cancer therapy

To date, even though various kinds of nanomaterials have been evaluated over the years in order to develop effective cancer therapy, there is still significant challenges in the improvement of the capabilities of nano-carriers. Developing a new theranostic nanomedicine platform for imaging-guided, visualized cancer therapy is currently a promising way to enhance therapeutic efficiency and reduce side effects. Firstly, conventional imaging technologies are reviewed with their advantages and disadvantages, respectively. Then, advanced biomedical materials for multimodal imaging are illustrated in detail, including representative examples for various dual-modalities and triple-modalities. Besides conventional cancer treatment (chemotherapy, radiotherapy), current biomaterials are also summarized for novel cancer therapy based on hyperthermia, photothermal, photodynamic effects, and clinical imaging-guided surgery. In conclusion, biomedical materials for imaging-guided therapy are becoming one of the mainstream treatments for cancer in the future. It is hoped that this review might provide new impetus to understand nanotechnology and nanomaterials employed for imaging-guided cancer therapy.

PET Imaging of Integrin Positive Tumors Using F Labeled Knottin Peptides

Purpose: Cystine knot (knottin) peptides, engineered to bind with high affinity to integrin receptors, have shown promise as molecular imaging agents in living subjects. The aim of the current study was to evaluate tumor uptake and in vivo biodistribution of ¹⁸F-labeled knottins in a U87MG glioblastoma model.

Procedures: Engineered knottin mutants 2.5D and 2.5F were synthesized using solid phase peptide synthesis and were folded in vitro, followed by radiolabeling with 4-nitrophenyl 2-¹⁸F-fluoropropionate (¹⁸F-NFP). The resulting probes, ¹⁸F-FP-2.5D and ¹⁸F-FP-2.5F, were evaluated in nude mice bearing U87MG tumor xenografts using microPET and biodistribution studies.

Results: MicroPET imaging studies with ¹⁸F-FP-2.5D and ¹⁸F-FP-2.5F demonstrated high tumor uptake in U87MG xenograft mouse models. The probes exhibited rapid clearance from the blood and kidneys, thus leading to excellent tumor-to-normal tissue contrast. Specificity studies confirmed that ¹⁸F-FP-2.5D and ¹⁸F-FP-2.5F had reduced tumor uptake when co-injected with a large excess of the peptidomimetic c(RGDyK) as a blocking agent.

Conclusions: ¹⁸F-FP-2.5D and ¹⁸F-FP-2.5F showed reduced gallbladder uptake compared with previously published ¹⁸F-FB-2.5D. ¹⁸F-FP-2.5D and ¹⁸F-FP-2.5F enabled integrin-specific PET imaging of U87MG tumors with good imaging contrasts. ¹⁸F-FP-2.5D demonstrated more desirable pharmacokinetics compared to ¹⁸F-FP-2.5F, and thus has greater potential for clinical translation.

Relationship between diffusion-weighted magnetic resonance imaging and histological tumor grading of hepatocellular carcinoma

BACKGROUND

Intrahepatic and extrahepatic recurrence remains a significant problem for hepatocellular carcinoma (HCC). The aim of this study was to determine the usefulness of diffusion-weighted magnetic resonance imaging (DWI) for histological tumor grading and preoperative prediction of early HCC recurrence within 6 months of operation.

METHODS

A total of 44 patients who had undergone hepatic resection for HCC (50 nodules) were reviewed retrospectively. DWI was performed within 30 days before hepatectomy, and apparent diffusion coefficients (ADCs) were measured using 2 methods: mean ADC and minimum-spot ADC. Relationships between ADCs and histological differentiation and between ADCs and early recurrence of HCC were analyzed.

RESULTS

Mean ADC was significantly lower in poorly differentiated HCC (n=18, 1.07±0.15×10(-3) mm2/s) than in moderately differentiated HCC (n=29, 1.29±0.21×10(-3) mm2/s; P<.05). Minimum-spot ADC was significantly lower in poorly differentiated HCC (n=18, 0.69±0.19×10(-3) mm2/s) than in well-differentiated HCC (n=3, 1.15±0.10×10(-3) mm2; P<.01) or in moderately differentiated HCC (n=29, 0.98±0.18×10(-3) mm2/s; P<.0001). Of 34 patients who were able to be observed for >6 months after resection, 9 showed early recurrence. Minimum-spot ADC was significantly lower in patients with early recurrence (n=9, 0.64±0.24×10(-3) mm2/s) than in patients without early recurrence (n=25, 0.88±0.19×10(-3) mm2/s; P<.05). On multivariate analysis, minimum-spot ADC was a significant risk factor for early recurrence (P<.05).

CONCLUSION

Quantitative measurement of ADC of HCC with magnetic resonance diffusion weighted imaging is a promising functional imaging tool in the prediction of histological grade and early recurrence before treatment.

Pediatric oncology and the future of oncological imaging

The future of pediatric oncology will be influenced by changes in drug design and treatment strategy, with genomic medicine and molecular-based diagnostics and therapeutics playing increasingly important roles. The role of imaging as a means of measuring response to therapy has also evolved, with the development of new technologies and higher sensitivity means of detecting tumors. Conventional anatomical imaging techniques are being increasingly supplemented with functional techniques, including FDG-PET imaging and diffusion-weighted MR imaging. The risk-adapted treatment regimens of the past, which led to improved event-free and overall survival in many pediatric cancers, have paved the way for new response-based treatment paradigms. Response-based approaches seek to identify patients with a high likelihood of cure, treating them less aggressively, while those not responding to therapy are identified early and redirected into more aggressive therapeutic regimens. These advances will require concurrent development of imaging biomarkers as surrogates of early response to therapy. Incorporating these techniques into new response-directed treatment algorithms will be crucial as personalized medicine and molecular-targeted, tumor-specific therapies gain acceptance for the treatment of children with cancer.

Preliminary evaluation of a nanotechnology-based approach for the more effective diagnosis of colon cancers

AIM

The goal of this research was to develop and preliminarily test a novel technology and instrumentation that could help to significantly increase the diagnostic yield of current colon cancer screening procedures. This technology is based on a combined fluorescence-optical coherence tomography (OCT) imaging, and topical delivery of a cancer-targeting agent.

MATERIALS & METHODS

Gold colloid-adsorbed poly(ε-caprolactone) microparticles were labeled with a near-infrared dye, and functionalized with argentine-glycine-aspartic acid (RGD peptide) to effectively target cancer tissue, and enhance fluorescence-imaging contrast. The RGD peptide recognizes the α(v)β(3)-integrin receptor, which is overexpressed by epithelial cancer cells. OCT was used under fluorescence guidance to visualize tissue morphology and, thus, to serve as a confirmatory tool for cancer presence.

RESULTS

A preliminary testing of this technology on human colon cancer cell lines, a mouse model of colon cancer, as well as human colon tissue specimens, was performed. Strong binding of microparticles to cancer cells and no binding to cells that do not significantly express integrins, such as mouse fibroblasts, was observed. Preferential binding to cancer tissue was also observed. Strong fluorescence signals were obtained from cancer tissue, owing to the efficient binding of the contrast agent. OCT imaging was capable of revealing clear differences between normal and cancer tissue.

CONCLUSION

A dual-modality imaging approach combined with topical delivery of a cancer-targeting contrast agent has been preliminarily tested for colon cancer diagnosis. Preferential binding of the contrast agent to cancer tissue allowed the cancer-suspicious locations to be highlighted and, thus, guided OCT imaging to visualize tissue morphology and determine tissue type. If successful, this multimodal approach might help to increase the sensitivity and the specificity of current colon cancer-screening procedures in the future.

Optimization of ultrasound contrast agents with computational models to improve selection of ligands and binding strength

Diagnosis of cardiovascular disease is currently limited by the testing modality. Serum tests for biomarkers can provide quantification of severity but lack the ability to localize the source of the cardiovascular disease, while imaging technology such as angiography and ultrasound can only determine areas of reduced flow but not the severity of tissue ischemia. Targeted imaging with ultrasound contrast agents offers the ability to locally image as well as determine the degree of ischemia by utilizing agents that will cause the contrast agent to home to the affected tissue. Ultrasound molecular imaging via targeted microbubbles (MB) is currently limited by its sensitivity to molecular markers of disease relative to other techniques (e.g., radiolabeling). We hypothesize that computational modeling may provide a useful first approach to maximize microbubble binding by defining key parameters governing adhesion. Adhesive dynamics (AD) was used to simulate the fluid dynamic and stochastic molecular binding of microbubbles to inflamed endothelial cells. Sialyl Lewis(X) (sLe(x)), P-selectin aptamer (PSA), and ICAM-1 antibody (abICAM) were modeled as the targeting receptors on the microbubble surface in both single- and dual-targeted arrangements. Microbubble properties (radius [R(c)], kinetics [k(f), k(r)], and densities of targeting receptors) and the physical environment (shear rate and target ligand densities) were modeled. The kinetics for sLe(x) and PSA were measured with surface plasmon resonance. R(c), shear rate, and densities of sLe(x), PSA, or abICAM were varied independently to assess model sensitivity. Firm adhesion was defined as MB velocity <2% of the free stream velocity. AD simulations revealed an optimal microbubble radius of 1-2 µm and thresholds for kf(in) ( >10(2) s(-1)) and kr(o) (<10(-3) s(-1)) for firm adhesion in a multi-targeted system. State diagrams for multi-targeted microbubbles suggest sLe(x) and abICAM microbubbles may require 10-fold more ligand to achieve firm adhesion at higher shear rates than sLe(x) and PSA microbubbles. The AD model gives useful insight into the key parameters for stable microbubble binding, and may allow flexible, prospective design, and optimization of microbubbles to enhance clinical translation of ultrasound molecular imaging.

Clinical application of FTIR imaging: new reasons for hope

In the 1990s, Fourier transform infrared (FTIR) imaging arrived as an analytical tool for the biological sciences. However, major limitations have appeared with respect to modern techniques of clinical imaging; slow acquisition of data, diffraction limitations, inability to image living biosystems, and weak sensitivity of detectors. Recent technological developments have demonstrated that FTIR imaging can be used to image living biosamples at the surface of specific crystals, lateral resolution can reach 100 nm without diffraction limits, and real-time imaging is accessible. These analytical improvements, in conjunction with industrial efforts in providing a new generation of high photon flux IR sources and more sensitive detectors, will give FTIR imaging a 'second chance' to be introduced into the clinic.

Cancer stem cells in solid tumors

According to the cancer progression model, several events are required for the progression from normal epithelium to carcinoma. Due to their extended life span, stem cells would represent the most likely target for the accumulation of these genetic events but this has not been formally proven for most of solid cancers. Even more importantly, cancer stem cells seem to harbor mechanisms protecting them from standard cytotoxic therapy. While cancer stem cells have been demonstrated to be responsible for therapy resistance in glioblastoma and pancreatic cancer, further evidence now points to similar mechanisms in colon cancer stem cells. Therefore, it appears reasonable to conclude that there is sufficient evidence now for the existence of cancer stem cells in several epithelial tumors and that these cancer stem cells pose a significant threat via their resistance to standard therapies. Accumulating evidence suggests, however, that novel approaches targeting cancer stem cells are capable of overcoming these resistance mechanisms. To further foster our understanding of in vivo cancer stem cell biology, novel imaging modalities in conjunction with clinically most relevant cancer stem cell models need to be developed and utilized. These studies will then pave the way to better elucidate the underlying regulatory mechanisms of cancer stem cells and develop platforms for targeted theragnostics, which may eventually help improving the prognosis of our patients suffering from these deadly diseases.

Molecular imaging: a primer for interventionalists and imagers

The characterization of human diseases by their underlying molecular and genomic aberrations has been the hallmark of molecular medicine. From this, molecular imaging has emerged as a potentially revolutionary discipline that aims to visually characterize normal and pathologic processes at the cellular and molecular levels within the milieu of living organisms. Molecular imaging holds promise to provide earlier and more precise disease diagnosis, improved disease characterization, and timely assessment of therapeutic response. This primer is intended to provide a broad overview of molecular imaging with specific focus on future clinical applications relevant to interventional radiology.

The evolving role of nuclear molecular imaging in cancer

BACKGROUND: Novel therapies targeted to specific tumor pathways are entering the clinic. The need for in vivo monitoring of resulting molecular changes, particularly with respect to the tumor microenvironment, is growing. Molecular imaging is evolving to include a variety of imaging methods to enable in vivo monitoring of cellular and molecular processes. OBJECTIVES: This article reviews the emerging role of molecular imaging in the development of improved therapeutic strategies that provide better patient selection for therapeutic personalization (i.e. determine which therapies have the greatest chance of success given the individual patient's disease genetic, and phenotypical profile). METHODS: In order to illustrate the utility of integrating molecular imaging into therapy development strategies, current and emerging applications of nuclear molecular imaging strategies will be compared with conventional strategies. Proposed methods of integrating molecular imaging techniques into cancer therapeutic development and limitations of these techniques will be discussed. RESULTS/CONCLUSION: Molecular imaging provides a variety of new tools to accelerate the development of cancer therapies. The recent drive to develop molecular imaging probes and standardize molecular imaging techniques is creating the scaffolding for the evolving paradigm shift to personalized cancer therapy.

In vivo monitoring of inflammation after cardiac and cerebral ischemia by fluorine magnetic resonance imaging

BACKGROUND

In this study, we developed and validated a new approach for in vivo visualization of inflammatory processes by magnetic resonance imaging using biochemically inert nanoemulsions of perfluorocarbons (PFCs).

METHODS AND RESULTS

Local inflammation was provoked in 2 separate murine models of acute cardiac and cerebral ischemia, followed by intravenous injection of PFCs. Simultaneous acquisition of morphologically matching proton ((1)H) and fluorine ((19)F) images enabled an exact anatomic localization of PFCs after application. Repetitive (1)H/(19)F magnetic resonance imaging at 9.4 T revealed a time-dependent infiltration of injected PFCs into the border zone of infarcted areas in both injury models, and histology demonstrated a colocalization of PFCs with cells of the monocyte/macrophage system. We regularly found the accumulation of PFCs in lymph nodes. Using rhodamine-labeled PFCs, we identified circulating monocytes/macrophages as the main cell fraction taking up injected nanoparticles.

CONCLUSIONS

PFCs can serve as a "positive" contrast agent for the detection of inflammation by magnetic resonance imaging, permitting a spatial resolution close to the anatomic (1)H image and an excellent degree of specificity resulting from the lack of any (19)F background. Because PFCs are nontoxic, this approach may have a broad application in the imaging and diagnosis of numerous inflammatory disease states.

Diagnostic imaging tests and microbial infections

Despite significant advances in the understanding of its pathogenesis, infection remains a major cause of patient morbidity and mortality. While the presence of infection may be suggested by signs and symptoms, imaging tests are often used to localize or confirm its presence. There are two principal imaging test types: morphological and functional. Morphological tests include radiographs, computed tomography (CT), magnetic resonance imaging, and sonongraphy. These procedures detect anatomic, or structural, alterations produced by microbial invasion and host response. Functional imaging tests reflect the physiological changes that are part of this process. Prototypical functional tests are radionuclide procedures such as bone, gallium, labelled leukocyte and fluorodeoxyglucose (FDG)-positron emission tomography (PET) imaging. In-line functional/morphological tomographic imaging systems, PET/CT and single photon emission tomography (SPECT)/CT, have revolutionized diagnostic imaging. These devices consist of a functional imaging device (PET or SPECT) joined together with a CT scanner. The patient undergoes both tests sequentially without leaving the examination table. Images from each study can be viewed separately and as fused images, providing precisely localized anatomic and functional information. It must be noted, however, that none of the current morphological or functional tests, either alone or in combination, are specific for infection and the goal of finding such an imaging test remains elusive.

Molecular imaging programs in the United States: results of a national survey

RATIONALE AND OBJECTIVES

We sought to identify and describe the characteristics of molecular imaging (MI) programs in the United States and to determine the factors considered critical for their future.

MATERIALS AND METHODS

In a cross-sectional study, a validated survey was sent to members of the Society of Chairmen in Academic Radiology Departments (SCARD) in the United States, and 26 variables were studied.

RESULTS

The response rate was 40.3%; 67.9% of the departments surveyed have an MI program. The main focus of 47.4% of departments is oncology. The number of radiologists working for the department was the only variable found to be significantly positively correlated with (1) number of researchers in the MI program, (2) number of MI modalities available, (3) total number of grants, and (4) having ongoing MI clinical trials. These four variables plus the number of federal grants and the space used by MI programs were independent of the geographical region, hospital size (number of beds), and department size (number of radiological examinations per year). All the MI programs received grants during 2005. Only 16.1% have no alliances with industry. Among all the departments, 82% identified staff training and recruitment as the keys for success; 78.57% considered oncology the most important future application of MI and cancer management the hospital service most affected by MI.

CONCLUSION

MI programs are starting to be more widespread throughout the United States, and the trend is for more academic radiology departments to become engaged in MI activities; their development is independent of department characteristics. Radiology departments strongly agreed about the key components for success of MI initiatives and the areas that will be most affected by MI applications.

Analysis of type I and IV collagens by FT-IR spectroscopy and imaging for a molecular investigation of skeletal muscle connective tissue

Many muscular diseases result from abnormal organization of connective tissue and/or collagen network formation. Only a few molecular imaging techniques are able to analyze this collagen network by differentiating collagen types. In this study, FT-IR spectroscopy was used to analyze type I and IV collagens, the most important compounds of which are perimysium and endomysium, respectively. Secondary structure of collagen types was determined by curve-fitting the 1,700-1,480 cm(-1) spectral interval. Type I collagen could be differentiated from type IV by its higher amounts of triple helix and alpha-helix, but lower amounts of beta-sheets (P < 0.01). FT-IR imaging was then used to determine structural features of perimysium and endomysium collagen network in bovine Flexor carpi radialis muscle. Secondary structure of proteins contained in perimysium and endomysium was found to be very close to type I and IV collagens, respectively. FT-IR spectroscopy and imaging are thus analytical tools that might be used for investigating biodistribution and assembly of collagen types in connective tissues.

Molecular Imaging: A Primer for Interventionalists and Imagers

The characterization of human diseases by their underlying molecular and genomic aberrations has been the hallmark of molecular medicine. From this, molecular imaging has emerged as a potentially revolutionary discipline that aims to visually characterize normal and pathologic processes at the cellular and molecular levels within the milieu of living organisms. Molecular imaging holds promise to provide earlier and more precise disease diagnosis, improved disease characterization, and timely assessment of therapeutic response. This primer is intended to provide a broad overview of molecular imaging with specific focus on future clinical applications relevant to interventional radiology.

Chemical mapping of tumor progression by FT-IR imaging: towards molecular histopathology

Fourier-transform infrared (FT-IR) spectro-imaging enables global analysis of samples, with resolution close to the cellular level. Recent studies have shown that FT-IR imaging enables determination of the biodistribution of several molecules of interest (carbohydrates, lipids, proteins) for tissue analysis without pre-analytical modification of the sample such as staining. Molecular structure information is also available from the same analysis, notably for protein secondary structure and fatty acyl chain peroxidation level. Thus, several cancer markers can be identified from FT-IR tissue images, enabling accurate discrimination between healthy and tumor areas. FT-IR imaging applications are now able to provide unique chemical and morphological information about tissue status. With the fast image acquisition provided by modern mid-infrared imaging systems, it is now envisaged to analyze cerebral tumor exereses in delays compatible with neurosurgery. Accordingly, we propose to take FT-IR imaging into consideration for the development of new molecular histopathology tools.

Molecular imaging of hepatocellular carcinoma

Molecular imaging may be defined as spatially localized and/or temporally resolved sensing of molecular and cellular processes in vivo. An imageable molecular event may be the result of the overexpression of a gene that produces a specific messenger RNA. The overexpressed protein could be an enzyme or could be incorporated into cell-surface transporters or receptors. Any step of this process is a potential target for molecular imaging. Current molecular imaging modalities include magnetic resonance imaging, nuclear imaging, ultrasound, and optical imaging. Nuclear medicine has been at the forefront of molecular imaging because of the relatively high sensitivity to detect nanomolar or picomolar quantities of the radiolabeled imaging probe. Imaging has had a central role in the diagnosis of hepatocellular carcinoma (HCC), which is considered the fifth most frequent malignancy worldwide. Nuclear imaging was one of the earlier modalities used for liver imaging. Traditional tracers included technetium 99m ( 99m Tc) sulfur colloid, gallium 67, and 99m Tc iminodiacetate acid analogues. Other less traditional probes include 99m Tc diethylenetriamine pentaacetic acid-galactosyl-human serum albumin for evaluation of functional liver volume and 99m Tc-labeled tetrofosmin and methoxisobutylisonitrile for detecting drug resistance. Fluorodeoxyglucose is the most widely used probe for positron emission tomography (PET) tumor imaging; however, carbon 11-labeled acetate appears to show improved sensitivity and specificity for HCC. Oxygen 15 PET imaging allows for the measurement of hepatic and tumor blood flow. Difficulties developing specific imaging methods for HCC are caused by the lack of obvious specific molecular targets, problems with drug delivery, and poor contrast-to-noise. No magic molecular imaging method exists today to accurately detect, characterize, and monitor HCC in vivo.