Gordon Center for Medical Imaging

Importance: Application of deep learning algorithms to whole-slide pathology images can potentially improve diagnostic accuracy and efficiency. Objective: Assess the performance of automated deep learning algorithms at detecting metastases in hematoxylin and eosin-stained tissue sections of lymph nodes of women with breast cancer and compare it with pathologists' diagnoses in a diagnostic setting. Design, Setting, and Participants: Researcher challenge competition (CAMELYON16) to develop automated solutions for detecting lymph node metastases (November 2015-November 2016). A training data set of whole-slide images from 2 centers in the Netherlands with (n = 110) and without (n = 160) nodal metastases verified by immunohistochemical staining were provided to challenge participants to build algorithms. Algorithm performance was evaluated in an independent test set of 129 whole-slide images (49 with and 80 without metastases). The same test set of corresponding glass slides was also evaluated by a panel of 11 pathologists with time constraint (WTC) from the Netherlands to ascertain likelihood of nodal metastases for each slide in a flexible 2-hour session, simulating routine pathology workflow, and by 1 pathologist without time constraint (WOTC). Exposures: Deep learning algorithms submitted as part of a challenge competition or pathologist interpretation. Main Outcomes and Measures: The presence of specific metastatic foci and the absence vs presence of lymph node metastasis in a slide or image using receiver operating characteristic curve analysis. The 11 pathologists participating in the simulation exercise rated their diagnostic confidence as definitely normal, probably normal, equivocal, probably tumor, or definitely tumor. Results: The area under the receiver operating characteristic curve (AUC) for the algorithms ranged from 0.556 to 0.994. The top-performing algorithm achieved a lesion-level, true-positive fraction comparable with that of the pathologist WOTC (72.4% [95% CI, 64.3%-80.4%]) at a mean of 0.0125 false-positives per normal whole-slide image. For the whole-slide image classification task, the best algorithm (AUC, 0.994 [95% CI, 0.983-0.999]) performed significantly better than the pathologists WTC in a diagnostic simulation (mean AUC, 0.810 [range, 0.738-0.884]; P < .001). The top 5 algorithms had a mean AUC that was comparable with the pathologist interpreting the slides in the absence of time constraints (mean AUC, 0.960 [range, 0.923-0.994] for the top 5 algorithms vs 0.966 [95% CI, 0.927-0.998] for the pathologist WOTC). Conclusions and Relevance: In the setting of a challenge competition, some deep learning algorithms achieved better diagnostic performance than a panel of 11 pathologists participating in a simulation exercise designed to mimic routine pathology workflow; algorithm performance was comparable with an expert pathologist interpreting whole-slide images without time constraints. Whether this approach has clinical utility will require evaluation in a clinical setting.

ADVERTISEMENT RETURN TO ISSUEPREVReviewSmall Heterocycles in Multicomponent ReactionsBenjamin H. Rotstein†‡, Serge Zaretsky†, Vishal Rai†§, and Andrei K. Yudin*†View Author Information† Davenport Research Laboratories, Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, Ontario Canada, M5S 3H6‡ Division of Nuclear Medicine and Molecular Imaging, Massachusetts General Hospital, and Department of Radiology, Harvard Medical School, 55 Fruit Street, Boston, Massachusetts 02114, United States§ Department of Chemistry, Indian Institute of Science Education and Research (IISER) Bhopal, Indore By-pass Road, Bhauri, Bhopal 462 066, MP India*E-mail: [email protected]Cite this: Chem. Rev. 2014, 114, 16, 8323–8359Publication Date (Web):July 17, 2014Publication History Received29 October 2013Published online17 July 2014Published inissue 27 August 2014https://pubs.acs.org/doi/10.1021/cr400615vhttps://doi.org/10.1021/cr400615vreview-articleACS PublicationsCopyright © 2014 American Chemical SocietyRequest reuse permissionsArticle Views12974Altmetric-Citations779LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose SUBJECTS:Aldehydes,Aziridines,Ethers,Inorganic carbon compounds,Reactivity Get e-Alerts

Substantial data indicate that microRNA 21 (miR-21) is significantly elevated in glioblastoma (GBM) and in many other tumors of various origins. This microRNA has been implicated in various aspects of carcinogenesis, including cellular proliferation, apoptosis, and migration. We demonstrate that miR-21 regulates multiple genes associated with glioma cell apoptosis, migration, and invasiveness, including the RECK and TIMP3 genes, which are suppressors of malignancy and inhibitors of matrix metalloproteinases (MMPs). Specific inhibition of miR-21 with antisense oligonucleotides leads to elevated levels of RECK and TIMP3 and therefore reduces MMP activities in vitro and in a human model of gliomas in nude mice. Moreover, downregulation of miR-21 in glioma cells leads to decreases of their migratory and invasion abilities. Our data suggest that miR-21 contributes to glioma malignancy by downregulation of MMP inhibitors, which leads to activation of MMPs, thus promoting invasiveness of cancer cells. Our results also indicate that inhibition of a single oncomir, like miR-21, with specific antisense molecules can provide a novel therapeutic approach for "physiological" modulation of multiple proteins whose expression is deregulated in cancer.

IMPORTANCE: Positron emission tomography (PET) imaging now allows in vivo visualization of both neuropathologic hallmarks of Alzheimer disease (AD): amyloid-β (Aβ) plaques and tau neurofibrillary tangles. Observing their progressive accumulation in the brains of clinically normal older adults is critically important to understand the pathophysiologic cascade leading to AD and to inform the choice of outcome measures in prevention trials. OBJECTIVE: To assess the associations among Aβ, tau, and cognition, measured during different observation periods for 7 years. DESIGN, SETTING, AND PARTICIPANTS: Prospective cohort study conducted between 2010 and 2017 at the Harvard Aging Brain Study, Boston, Massachusetts. The study enrolled 279 clinically normal participants. An additional 90 individuals were approached but declined the study or did not meet the inclusion criteria. In this report, we analyzed data from 60 participants who had multiple Aβ and tau PET observations available on October 31, 2017. MAIN OUTCOMES AND MEASURES: A median of 3 Pittsburgh compound B-PET (Aβ, 2010-2017) and 2 flortaucipir-PET (tau, 2013-2017) images were collected. We used initial PET and slope data, assessing the rates of change in Aβ and tau, to measure cognitive changes. Cognition was evaluated annually using the Preclinical Alzheimer Cognitive Composite (2010-2017). Annual consensus meetings evaluated progression to mild cognitive impairment. RESULTS: Of the 60 participants, 35 were women (58%) and 25 were men (42%); median age at inclusion was 73 years (range, 65-85 years). Seventeen participants (28%) exhibited an initial high Aβ burden. An antecedent rise in Aβ was associated with subsequent changes in tau (1.07 flortaucipir standardized uptake value ratios [SUVr]/PiB-SUVr; 95% CI, 0.13-3.46; P = .02). Tau changes were associated with cognitive changes (-3.28 z scores/SUVR; 95% CI, -6.67 to -0.91; P = .001), covarying baseline Aβ and tau. Tau changes were greater in the participants who progressed to mild cognitive impairment (n = 6) than in those who did not (n = 11; 0.05 SUVr per year; 95% CI, 0.03-0.07; P = .001). A serial mediation model demonstrated that the association between initial Aβ and final cognition, measured 7 years later, was mediated by successive changes in Aβ and tau. CONCLUSIONS AND RELEVANCE: We identified sequential changes in normal older adults, from Aβ to tau to cognition, after which the participants with high Aβ with greater tau increase met clinical criteria for mild cognitive impairment. These findings highlight the importance of repeated tau-PET observations to track disease progression and the importance of repeated amyloid-PET observations to detect the earliest AD pathologic changes.

There is a wealth of new fluorescent reporter technologies for tagging of many cellular and subcellular processes in vivo. This imposed contrast is now captured with an increasing number of available imaging methods that offer new ways to visualize and quantify fluorescent markers distributed in tissues. This is an evolving field of imaging sciences that has already achieved major advances but is also facing important challenges. It is nevertheless well poised to significantly impact the ways of biological research, drug discovery, and clinical practice in the years to come. Herein, the most pertinent technologies associated with in vivo noninvasive or minimally invasive fluorescence imaging of tissues are summarized. Focus is given to small-animal imaging. However, while a broad spectrum of fluorescence reporter technologies and imaging methods are outlined, as necessary for biomedical research, and clinical translation as well.

OBJECTIVE: To examine region- and substrate-specific autoradiographic and in vitro binding patterns of positron emission tomography tracer [F-18]-AV-1451 (previously known as T807), tailored to allow in vivo detection of paired helical filament-tau-containing lesions, and to determine whether there is off-target binding to other amyloid/non-amyloid proteins. METHODS: We applied [F-18]-AV-1451 phosphor screen autoradiography, [F-18]-AV-1451 nuclear emulsion autoradiography, and [H-3]-AV-1451 in vitro binding assays to the study of postmortem samples from patients with a definite pathological diagnosis of Alzheimer disease, frontotemporal lobar degeneration-tau, frontotemporal lobar degeneration-transactive response DNA binding protein 43 (TDP-43), progressive supranuclear palsy, corticobasal degeneration, dementia with Lewy bodies, multiple system atrophy, cerebral amyloid angiopathy and elderly controls free of pathology. RESULTS: Our data suggest that [F-18]-AV-1451 strongly binds to tau lesions primarily made of paired helical filaments in Alzheimer brains (eg, intraneuronal and extraneuronal tangles and dystrophic neurites), but does not seem to bind to a significant extent to neuronal and glial inclusions mainly composed of straight tau filaments in non-Alzheimer tauopathy brains or to lesions containing β-amyloid, α-synuclein, or TDP-43. [F-18]-AV-1451 off-target binding to neuromelanin- and melanin-containing cells and, to a lesser extent, to brain hemorrhagic lesions was identified. INTERPRETATION: Our data suggest that [F-18]-AV-1451 holds promise as a surrogate marker for the detection of brain tau pathology in the form of tangles and paired helical filament-tau-containing neurites in Alzheimer brains but also point to its relatively lower affinity for lesions primarily made of straight tau filaments in non-Alzheimer tauopathy cases and to the existence of some [F-18]-AV-1451 off-target binding. These findings provide important insights for interpreting in vivo patterns of [F-18]-AV-1451 retention.

Activating KRAS mutations and p16(Ink4a) inactivation are near universal events in human pancreatic ductal adenocarcinoma (PDAC). In mouse models, Kras(G12D) initiates formation of premalignant pancreatic ductal lesions, and loss of either Ink4a/Arf (p16(Ink4a)/p19(Arf)) or p53 enables their malignant progression. As recent mouse modeling studies have suggested a less prominent role for p16(Ink4a) in constraining malignant progression, we sought to assess the pathological and genomic impact of inactivation of p16(Ink4a), p19(Arf), and/or p53 in the Kras(G12D) model. Rapidly progressive PDAC was observed in the setting of homozygous deletion of either p53 or p16(Ink4a), the latter with intact germ-line p53 and p19(Arf) sequences. Additionally, Kras(G12D) in the context of heterozygosity either for p53 plus p16(Ink4a) or for p16(Ink4a)/p19(Arf) produced PDAC with longer latency and greater propensity for distant metastases relative to mice with homozygous deletion of p53 or p16(Ink4a)/p19(Arf). Tumors from the double-heterozygous cohorts showed frequent p16(Ink4a) inactivation and loss of either p53 or p19(Arf). Different genotypes were associated with specific histopathologic characteristics, most notably a trend toward less differentiated features in the homozygous p16(Ink4a)/p19(Arf) mutant model. High-resolution genomic analysis revealed that the tumor suppressor genotype influenced the specific genomic patterns of these tumors and showed overlap in regional chromosomal alterations between murine and human PDAC. Collectively, our results establish that disruptions of p16(Ink4a) and the p19(ARF)-p53 circuit play critical and cooperative roles in PDAC progression, with specific tumor suppressor genotypes provocatively influencing the tumor biological phenotypes and genomic profiles of the resultant tumors.

The determination of brain tumor margins both during the presurgical planning phase and during surgical resection has long been a challenging task in the therapy of brain tumor patients. Using a model of gliosarcoma with stably green fluorescence protein-expressing 9L glioma cells, we explored a multimodal (near-infrared fluorescent and magnetic) nanoparticle as a preoperative magnetic resonance imaging contrast agent and intraoperative optical probe. Key features of nanoparticle metabolism, namely intracellular sequestration by microglia and the combined optical and magnetic properties of the probe, allowed delineation of brain tumors both by preoperative magnetic resonance imaging and by intraoperative optical imaging. This prototypical multimodal nanoparticle has unique properties that may allow radiologists and neurosurgeons to see the same probe in the same cells and may offer a new approach for obtaining tumor margins.

We report the implantation of patient-derived midbrain dopaminergic progenitor cells, differentiated in vitro from autologous induced pluripotent stem cells (iPSCs), in a patient with idiopathic Parkinson's disease. The patient-specific progenitor cells were produced under Good Manufacturing Practice conditions and characterized as having the phenotypic properties of substantia nigra pars compacta neurons; testing in a humanized mouse model (involving peripheral-blood mononuclear cells) indicated an absence of immunogenicity to these cells. The cells were implanted into the putamen (left hemisphere followed by right hemisphere, 6 months apart) of a patient with Parkinson's disease, without the need for immunosuppression. Positron-emission tomography with the use of fluorine-18-L-dihydroxyphenylalanine suggested graft survival. Clinical measures of symptoms of Parkinson's disease after surgery stabilized or improved at 18 to 24 months after implantation. (Funded by the National Institutes of Health and others.).

Passive targeting of large nanoparticles by the enhanced permeability and retention (EPR) effect is a crucial concept for solid tumor targeting in cancer nanomedicine. There is, however, a trade-off between the long-term blood circulation of nanoparticles and their nonspecific background tissue uptake. To define this size-dependent EPR effect, near-infrared fluorophore-conjugated polyethylene glycols (PEG-ZW800s; 1-60 kDa) are designed and their biodistribution, pharmacokinetics, and renal clearance are evaluated in tumor-bearing mice. The targeting efficiency of size-variant PEG-ZW800s is investigated in terms of tumor-to-background ratio (TBR). Interestingly, smaller sized PEGs (≤20 kDa, 12 nm) exhibit significant tumor targeting with minimum to no nonspecific uptakes, while larger sized PEGs (>20 kDa, 13 nm) accumulate highly in major organs, including the lungs, liver, and pancreas. Among those tested, 20 kDa PEG-ZW800 exhibits the highest TBR, while excreting unbound molecules to the urinary bladder. This result lays a foundation for engineering tumor-targeted nanoparticles and therapeutics based on the size-dependent EPR effect.

Endothelial vascular adhesion molecule-1 (VCAM-1) is a critical component of the leukocyte-endothelial adhesion cascade, and its strict temporal and spatial regulation make it an ideal target for imaging and therapy. The goal of this study was to develop novel VCAM-1-targeted imaging agents detectable by MRI and fluorescence imaging using phage display-derived peptide sequences and multimodal nanoparticles (NPs). We hypothesized that VCAM-1-mediated cell internalization of phage display-selected peptides could be harnessed as an amplification strategy to chaperone and trap imaging agents inside VCAM-1-expressing cells, thus improving target-to-background ratios. To accomplish our goal, iterative phage display was performed on murine endothelium under physiological flow conditions to identify a family of VCAM-1-mediated cell-internalizing peptides. One specific sequence, containing the VHSPNKK motif that has homology to the alpha-chain of very late antigen (a known ligand for VCAM-1), was shown to bind VCAM-1 and block leukocyte-endothelial interactions. Compared with VCAM-1 monoclonal antibody, the peptide showed 12-fold higher target-to-background ratios. A VHSPNKK-modified magnetofluorescent NP (VNP) showed high affinity for endothelial cells expressing VCAM-1 but surprisingly low affinity for macrophages. In contrast, a control NP without VCAM-1-targeting sequences showed no affinity for endothelial cells. In vivo, VNP successfully identified VCAM-1-expressing endothelial cells in a murine tumor necrosis factor-alpha-induced inflammatory model and colocalized with VCAM-1-expressing cells in atherosclerotic lesions present in cholesterol-fed apolipoprotein E apoE-/- mice. These results indicate that: (1) small peptide sequences can significantly alter targeting of NPs, (2) the used amplification strategy of internalization results in high target-to-background ratios, and (3) this technology is useful for in vivo imaging of endothelial markers.

Despite the development of new glioma therapies that allow for tumor-targeted in situ delivery of cytotoxic drugs, tumor resistance to apoptosis remains a key impediment to effective treatment. Mounting evidence indicates that microRNAs (miRNA) might play a fundamental role in tumorigenesis, controlling cell proliferation and apoptosis. In gliomas, microRNA-21 (miR-21) levels have been reported to be elevated and their knockdown is associated with increased apoptotic activity. We hypothesized that suppression of miR-21 might sensitize gliomas for cytotoxic tumor therapy. With the use of locked nucleic acid (LNA)-antimiR-21 oligonucleotides, bimodal imaging vectors, and neural precursor cells (NPC) expressing a secretable variant of the cytotoxic agent tumor necrosis factor-related apoptosis inducing ligand (S-TRAIL), we show that the combined suppression of miR-21 and NPC-S-TRAIL leads to a synergistic increase in caspase activity and significantly decreased cell viability in human glioma cells in vitro. This phenomenon persists in vivo, as we observed complete eradication of LNA-antimiR-21-treated gliomas subjected to the presence of NPC-S-TRAIL in the murine brain. Our results reveal the efficacy of miR-21 antagonism in murine glioma models and implicate miR-21 as a target for therapeutic intervention. Furthermore, our findings provide the basis for developing combination therapies using miRNA modulation and cytotoxic tumor therapies.

In humans, the pathways of memory and effector T cell differentiation remain poorly defined. We have dissected the functional properties of ex vivo effector-memory (EM) CD45RA-CCR7- T lymphocytes present within the circulating CD8+ T cell pool of healthy individuals. Our studies show that EM T cells are heterogeneous and are subdivided based on differential CD27 and CD28 expression into four subsets. EM(1) (CD27+CD28+) and EM(4) (CD27-CD28+) T cells express low levels of effector mediators such as granzyme B and perforin and high levels of CD127/IL-7Ralpha. EM(1) cells also have a relatively short replicative history and display strong ex vivo telomerase activity. Therefore, these cells are closely related to central-memory (CD45RA-CCR7+) cells. In contrast, EM(2) (CD27+CD28-) and EM(3) (CD27-CD28-) cells express mediators characteristic of effector cells, whereby EM(3) cells display stronger ex vivo cytolytic activity and have experienced larger numbers of cell divisions, thus resembling differentiated effector (CD45RA+CCR7-) cells. These data indicate that progressive up-regulation of cytolytic activity and stepwise loss of CCR7, CD28, and CD27 both characterize CD8+ T cell differentiation. Finally, memory CD8+ T cells not only include central-memory cells but also EM(1) cells, which differ in CCR7 expression and may therefore confer memory functions in lymphoid and peripheral tissues, respectively.

Near-infrared (NIR) fluorescence light has been widely utilized in clinical imaging by providing surgeons highly specific images of target tissue. The "NIR window" from 650 to 900 nm is especially useful due to several special features such as minimal autofluorescence and absorption of biomolecules in tissue, as well as low light scattering. Compared with visible wavelengths, NIR fluorescence light is invisible, thus allowing highly sensitivity real-time image guidance in human surgery without changing the surgical field. The benefit of using NIR fluorescence light as a clinical imaging technology can be attributed to its molecular fluorescence as an exogenous contrast agent. Indeed, whole body preoperative imaging of single-photon emission computed tomography (SPECT) and positron emission tomography (PET) remains important in diagnostic utility, but they lack the efficacy of innocuous and targeted NIR fluorophores to simultaneously facilitate the real-time delineation of diseased tissue while preserving vital tissues. Admittedly, NIR imaging technology has been slow to enter clinical use mostly due to the late-coming development of truly breakthrough contrast agents for use with current imaging systems. Therefore, clearly defining the physical margins of tumorous tissue remains of paramount importance in bioimaging and targeted therapy. An equally noteworthy yet less researched goal is the ability to outline healthy vital tissues that should be carefully navigated without transection during the intraoperative surgery. Both of these paths require optimizing a gauntlet of design considerations to obtain not only an effective imaging agent in the NIR window but also high molecular brightness, water solubility, biocompatibility, and tissue-specific targetability. The imaging community recognizes three strategic approaches which include (1) passive targeting via the EPR effect, (2) active targeting using the innate overall biodistribution of known molecules, and (3) activatable targeting through an internal stimulus, which turns on fluorescence from an off state. Recent advances in nanomedicine and bioimaging offer much needed promise toward fulfilling these stringent requirements as we develop a successful catalog of targeted contrast agents for illuminating both tumors and vital tissues in the same surgical space by employing spectrally distinct fluorophores in real time. These tissue-specific contrast agents can be versatile arsenals to physicians for real-time intraoperative navigation as well as image-guided targeted therapy. There is a versatile library of tissue-specific fluorophores available in the literature, with many discussed herein, which offers clinicians an array of possibilities that will undoubtedly improve intraoperative success and long-term postoperation prognosis.

Magnetic resonance imaging (MRI) allows noninvasive and three-dimensional visualization of whole organisms over time, and, therefore, would be ideally suited to monitor cell trafficking in vivo. Until now, systemically injected cells had been difficult to visualize by MRI because of relatively inefficient labeling methods. We developed a novel, biocompatible, and physiologically inert nanoparticle (highly derivatized cross-linked iron oxide nanoparticle; CLIO-HD) for highly efficient intracellular labeling of a variety of cell types that now allows in vivo MRI tracking of systemically injected cells at near single-cell resolution. CD8+ cytotoxic T lymphocytes labeled with CLIO-HD were detectable via MRI with a detection threshold of 2 cells/voxel in vitro and approximately 3 cells/voxel in vivo in live mice. Using B16-OVA melanoma and CLIO-HD-labeled OVA-specific CD8+ T cells, we have demonstrated for the first time high resolution imaging of T-cell recruitment to intact tumors in vivo. We have revealed the extensive three-dimensional spatial heterogeneity of T-cell recruitment to target tumors and demonstrated a temporal regulation of T-cell recruitment within the tumor. Significantly, our data indicate that serial administrations of CD8+ T cells appear to home to different intratumoral locations, and may, therefore, provide a more effective treatment regimen than a single bolus administration. Together, these results demonstrate that CLIO-HD is uniquely suited for quantitative repetitive MRI of adoptively transferred cells and that this approach may be particularly useful for evaluating novel cell-based therapies in vivo.

The single biggest challenge facing in vivo imaging techniques is to develop biocompatible molecular beacons that are capable of specifically and accurately measuring in vivo targets at the protein, RNA, or DNA level. Our efforts have focused on developing activatable imaging probes to measure specific enzyme activities in vivo. Using cathepsin D as a model target protease, we synthesized a long-circulating, synthetic graft copolymer bearing near-infrared (NIR) fluorochromes positioned on cleavable substrate sequences. In its native state, the reporter probe was essentially nonfluorescent at 700 nm due to energy resonance transfer among the bound fluorochromes (quenching) but became brightly fluorescent when the latter were released by cathepsin D. NIR fluorescence signal activation was linear over at least 4 orders of magnitude and specific when compared with scrambled nonsense substrates. Using matched rodent tumor models implanted into nude mice expressing or lacking the targeted protease, it could be shown that the former generated sufficient NIR signal to be directly detectable and that the signal was significantly different compared with negative control tumors. The developed probes should find widespread applications for real-time in vivo imaging of a variety of clinically relevant proteases, for example, to detect endogenous protease activity in disease, to monitor the efficacy of protease inhibitors, or to image transgene expression.

Abstract Positron emission tomography (PET) is a molecular imaging technology that provides quantitative information about function and metabolism in biological processes in vivo for disease diagnosis and therapy assessment. The broad application and rapid advances of PET has led to an increased demand for new radiochemical methods to synthesize highly specific molecules bearing positron‐emitting radionuclides. This Review provides an overview of commonly used labeling reactions through examples of clinically relevant PET tracers and highlights the most recent developments and breakthroughs over the past decade, with a focus on 11 C, 18 F, 13 N, and 15 O.

In vivo imaging of treatment responses at the molecular level could have a significant impact on the speed of drug discovery and ultimately lead to personalized medicine. Strong interest has been shown in developing quantitative fluorescence-based technologies with good molecular specificity and sensitivity for noninvasive 3D imaging through tissues and whole animals. We show herein that tumor response to chemotherapy can be accurately resolved by fluorescence molecular tomography (FMT) with a phosphatidylserine-sensing fluorescent probe based on modified annexins. We observed at least a 10-fold increase of fluorochrome concentration in cyclophosphamide-sensitive tumors and a 7-fold increase of resistant tumors compared with control studies. FMT is an optical imaging technique developed to overcome limitations of commonly used planar illumination methods and demonstrates higher quantification accuracy validated by histology. It is further shown that a 3-fold variation in background absorption heterogeneity may yield 100% errors in planar imaging but only 20% error in FMT, thus confirming tomographic imaging as a preferred tool for quantitative investigations of fluorescent probes in tissues. Tomographic approaches are found essential for small-animal optical imaging and are potentially well suited for clinical drug development and monitoring.

Alzheimer's disease (AD) is characterized by two hallmark molecular pathologies: amyloid aβ 1–42 and Tau neurofibrillary tangles. To date, studies of functional connectivity MRI (fcMRI) in individuals with preclinical AD have relied on associations with in vivo measures of amyloid pathology. With the recent advent of in vivo Tau-PET tracers it is now possible to extend investigations on fcMRI in a sample of cognitively normal elderly humans to regional measures of Tau. We modeled fcMRI measures across four major cortical association networks [default-mode network (DMN), salience network (SAL), dorsal attention network, and frontoparietal control network] as a function of global cortical amyloid [Pittsburgh Compound B (PiB)-PET] and regional Tau (AV1451-PET) in entorhinal, inferior temporal (IT), and inferior parietal cortex. Results showed that the interaction term between PiB and IT AV1451 was significantly associated with connectivity in the DMN and salience. The interaction revealed that amyloid-positive (aβ + ) individuals show increased connectivity in the DMN and salience when neocortical Tau levels are low, whereas aβ + individuals demonstrate decreased connectivity in these networks as a function of elevated Tau-PET signal. This pattern suggests a hyperconnectivity phase followed by a hypoconnectivity phase in the course of preclinical AD. SIGNIFICANCE STATEMENT This article offers a first look at the relationship between Tau-PET imaging with F 18 -AV1451 and functional connectivity MRI (fcMRI) in the context of amyloid-PET imaging. The results suggest a nonlinear relationship between fcMRI and both Tau-PET and amyloid-PET imaging. The pattern supports recent conjecture that the AD fcMRI trajectory is characterized by periods of both hyperconnectivity and hypoconnectivity. Furthermore, this nonlinear pattern can account for the sometimes conflicting reports of associations between amyloid and fcMRI in individuals with preclinical Alzheimer's disease.

To determine the feasibility of MR imaging of magnetically labeled cells, different cell lines were labeled with monocrystalline iron oxide (MION) particles. Phantoms containing MION labeled cells were then assembled and imaged by MR at 1.5 T using T1-weighted and T2-weighted pulse sequences. MION uptake ranged from 8.5 x 10(4) to 2.9 x 10(5) particles/cell for tumor cells (9L and LX1, respectively) to 1.5 x 10(6) to 4.8 x 10(8) particles/cell for "professional phagocytes" (J774 and peritoneal macrophages, respectively). On the T1-weighted images, cell-internalized MION appeared hyperintense relative to agar and similar to MION in aqueous solution. On T2-weighted images, signal intensity varied according to concentration of MION within cells. Cell-internalized MION caused similar MR signal changes of cells as did free MION; however, at a dose that was an order of magnitude lower, depending on the pulse sequence used. The detectability of MION within cells was approximately 2 ng Fe, which corresponded to 10(5) tumor cells/well or 5 x 10(3) macrophages/well. We conclude that a variety of cells can be efficiently labeled with MION by simple incubation. Intracellular labeling may be used for MR imaging of in vivo cell tracking.