Toxicity of MRI and CT contrast agents

Shape-dependent cellular behaviors and relaxivity of iron oxide-based T1 MRI contrast agents

Recent research efforts about iron oxide nanoparticles has focused on the development of iron oxide-based T₁ contrast agents for magnetic resonance imaging (MRI), such as ultrasmall iron oxide nanospheres (USNPs <4 nm) and ultrathin nanowires (NW, diameter <4 nm). In this paper, we report the cellular uptake behaviors of these two types of ultrasmall scale nanostructures on HepG2 cells. Both these two nanostructures were functionalized with tannic acid and their physical and chemical properties were carefully analyzed before cellular tests. Both USNPs and NWs exhibited strong paramagnetic signals, a property suitable for T₁ MRI contrast agents. The distinct shapes also caused much difference in their cellular uptake behaviors. Specifically, the uptake of USNPs was five times higher than that of NWs after 72 hours incubation. The shape-dependent cellular uptake can potentially lead to different blood circulation times, and subsequently different applications of these two types of ultrasmall nanostructures.

Heart involvement in systemic lupus erythematosus: a systemic review and meta-analysis

Cardiovascular diseases are one of the most important causes of the disability and mortality in patients with systemic lupus erythematosus (SLE). The present study examined the cardiac abnormalities in patients with SLE by echocardiography. Case-control studies were obtained by searching PubMed MEDLINE, Embase, and MD Consult. Systemic review and meta-analysis were performed to assess the cardiac abnormalities based on the changes in the echocardiography in patients with SLE. Twenty-two studies including 1117 SLE patients and 901 healthy controls were enrolled into this study. We found that patients with SLE developed the pericardial effusion (odds ratio (OR) (95 % confidence interval (CI)) 30.52 (9.70-96.02); p < 0.00001) and the combined valvular alterations (OR (95 %CI) 11.08 (6.98-17.59); p < 0.00001). In addition, SLE patients also exhibited an increase in the left atrial diameter (LAD) (WMD-weighted mean difference (95 %CI) 0.18 (0.06-0.29); p = 0.002), the left ventricular internal diameter in diastole (LVDd) (WMD (95 %CI) 0.07 (0.02-0.12); p = 0.01), and the left ventricular mass index (LVMI) (WMD (95 %CI) 5.69 (2.69-8.69); p = 0.0002). In contrast, the left ventricular systolic function (WMD (95 %CI) -1.22 (-1.69 to -0.75); p < 0.00001) and diastolic function including E/A ratio and E/E' ratio (WMD (95  % CI) -0.13 (-0.24 to -0.01); p = 0.04; WMD (95  % CI) 1.71 (0.43 to 2.99); p = 0.009) were decreased in SLE patients. Patients with SLE are associated with significant alterations in cardiac structure and function as demonstrated by echocardiography. Data from this study suggest that echocardiographic assessment should be considered as a part of routine examinations for SLE patients clinically.

Yield of CT Pulmonary Angiography in the Emergency Department When Providers Override Evidence-based Clinical Decision Support

Purpose To determine the frequency of, and yield after, provider overrides of evidence-based clinical decision support (CDS) for ordering computed tomographic (CT) pulmonary angiography in the emergency department (ED). Materials and Methods This HIPAA-compliant, institutional review board-approved study was performed at a tertiary care, academic medical center ED with approximately 60 000 annual visits and included all patients who were suspected of having pulmonary embolism (PE) and who underwent CT pulmonary angiography between January 1, 2011, and August 31, 2013. The requirement to obtain informed consent was waived. Each CT order for pulmonary angiography was exposed to CDS on the basis of the Wells criteria. For patients with a Wells score of 4 or less, CDS alerts suggested d-dimer testing because acute PE is highly unlikely in these patients if d-dimer levels are normal. The yield of CT pulmonary angiography (number of positive PE diagnoses/total number of CT pulmonary angiographic examinations) was compared in patients in whom providers overrode CDS alerts (by performing CT pulmonary angiography in patients with a Wells score ≤4 and a normal d-dimer level or no d-dimer testing) (override group) and those in whom providers followed Wells criteria (CT pulmonary angiography only in patients with Wells score >4 or ≤4 with elevated d-dimer level) (adherent group). A validated natural language processing tool identified positive PE diagnoses, with subsegmental and/or indeterminate diagnoses removed by means of chart review. Statistical analysis was performed with the χ² test, the Student t test, and logistic regression. Results Among 2993 CT pulmonary angiography studies in 2655 patients, 563 examinations had a Wells score of 4 or less but did not undergo d-dimer testing and 26 had a Wells score of 4 or less and had normal d-dimer levels. The yield of CT pulmonary angiography was 4.2% in the override group (25 of 589 studies, none with a normal d-dimer level) and 11.2% in the adherent group (270 of 2404 studies) (P < .001). After adjustment for the risk factor differences between the two groups, the odds of an acute PE finding were 51.3% lower when providers overrode alerts than when they followed CDS guidelines. Comparison of the two groups including only patients unlikely to have PE led to similar results. Conclusion The odds of an acute PE finding in the ED when providers adhered to evidence presented in CDS were nearly double those seen when providers overrode CDS alerts. Most overrides were due to the lack of d-dimer testing in patients unlikely to have PE. ^© RSNA, 2016.

Mathematical Models of Contrast Transport Kinetics for Cancer Diagnostic Imaging: A Review

Angiogenesis plays a fundamental role in cancer growth and the formation of metastasis. Novel cancer therapies aimed at inhibiting angiogenic processes and/or disrupting angiogenic tumor vasculature are currently being developed and clinically tested. The need for earlier and improved cancer diagnosis, and for early evaluation and monitoring of therapeutic response to angiogenic treatment, have led to the development of several imaging methods for in vivo noninvasive assessment of angiogenesis. The combination of dynamic contrast-enhanced imaging with mathematical modeling of the contrast agent kinetics enables quantitative assessment of the structural and functional changes in the microvasculature that are associated with tumor angiogenesis. In this paper, we review quantitative imaging of angiogenesis with dynamic contrast-enhanced magnetic resonance imaging, computed tomography, and ultrasound.

Gd-Si Oxide Nanoparticles as Contrast Agents in Magnetic Resonance Imaging

We describe the synthesis, characterization and application as contrast agents in magnetic resonance imaging of a novel type of magnetic nanoparticle based on Gd-Si oxide, which presents high Gd3+ atom density. For this purpose, we have used a Prussian Blue analogue as the sacrificial template by reacting with soluble silicate, obtaining particles with nanorod morphology and of small size (75 nm). These nanoparticles present good biocompatibility and higher longitudinal and transversal relaxivity values than commercial Gd3+ solutions, which significantly improves the sensitivity of in vivo magnetic resonance images.

Analysis of polyvinyl alcohol microbubbles in human blood plasma using capillary electrophoresis

Recently, a new type of ultrasound contrast agent that consists of air-filled microbubbles stabilized with a shell of polyvinyl alcohol was developed. When superparamagnetic nanoparticles of iron oxide are incorporated in the polymer shell, a multimodal contrast agent can be obtained. The biodistribution and elimination pathways of the polyvinyl alcohol microbubbles are essential to investigate, which is limited with today's techniques. The aim of the present study was, therefore, to develop a method for qualitative and quantitative analysis of microbubbles in biological samples using capillary electrophoresis with ultraviolet detection. The analysis parameters were optimized to a wavelength at 260 nm and pH of the background electrolyte ranging between 11.9 and 12. Studies with high-intensity ultrasonication degraded microbubbles in water showed that degraded products and intact microbubbles could be distinguished, thus it was possible to quantify the intact microbubbles solely. Analysis of human blood plasma spiked with either plain microbubbles or microbubbles with nanoparticles demonstrated that it is possible to separate them from biological components like proteins in these kinds of samples.

Magnetic Nanoparticles: Material Engineering and Emerging Applications in Lithography and Biomedicine

We present an interdisciplinary overview of material engineering and emerging applications of iron oxide nanoparticles. We discuss material engineering of nanoparticles in the broadest sense, emphasizing size and shape control, large-area self-assembly, composite/hybrid structures, and surface engineering. This is followed by a discussion of several non-traditional, emerging applications of iron oxide nanoparticles, including nanoparticle lithography, magnetic particle imaging, magnetic guided drug delivery, and positive contrast agents for magnetic resonance imaging. We conclude with a succinct discussion of the pharmacokinetics pathways of iron oxide nanoparticles in the human body -- an important and required practical consideration for any in vivo biomedical application, followed by a brief outlook of the field.

The design of a multifunctional dendrimer-based nanoplatform for targeted dual mode SPECT/MR imaging of tumors

A multifunctional dendrimer-based nanoplatform labeled with ^99mTc can be synthesized for targeted SPECT/MR dual mode imaging of tumors.

Gold Nanotheranostics: Proof-of-Concept or Clinical Tool?

Nanoparticles have been making their way in biomedical applications and personalized medicine, allowing for the coupling of diagnostics and therapeutics into a single nanomaterial—nanotheranostics. Gold nanoparticles, in particular, have unique features that make them excellent nanomaterials for theranostics, enabling the integration of targeting, imaging and therapeutics in a single platform, with proven applicability in the management of heterogeneous diseases, such as cancer. In this review, we focus on gold nanoparticle-based theranostics at the lab bench, through pre-clinical and clinical stages. With few products facing clinical trials, much remains to be done to effectively assess the real benefits of nanotheranostics at the clinical level. Hence, we also discuss the efforts currently being made to translate nanotheranostics into the market, as well as their commercial impact.

Evaluation of Tongue Cancer Using High-Resolution Sonography: Comparison With Magnetic Resonance Imaging

OBJECTIVES

To evaluate the role of sonography in assessing tongue cancer compared with magnetic resonance imaging (MRI).

METHODS

A randomized prospective study was performed on 40 cases of tongue cancer. Magnetic resonance imaging and sonography of the tongue were performed, tumor spreading to particular sites was recorded in all cases. Sonographic and MRI findings were correlated with histopathologic findings in 18 operable cases. In 22 inoperable cases, sonography was compared only with MRI.

RESULTS

In operable patients, sonography achieved sensitivity of 61.1%, whereas MRI achieved sensitivity of 94.4%. The difference was statistically significant (P < .05). The results for detection of individual site involvement on sonography and MRI were as follows: intrinsic muscles only, 0 and 6, respectively; tongue base, 5 and 5; genioglossus muscle, 34 and 34; mylohyoid muscle, 9 and 8; sublingual space, 12 and 14; sublingual neurovascular bundle, 12 and 12; submandibular gland, 3 and 3; spread across the lingual septum, 17 and 17; and alveolar involvement, 0 and 1. There was no significant difference (P> .05) between sonography and MRI in detecting involvement of the above-mentioned sites except for cases with only intrinsic muscles and alveolar involvement. Tumors involving intrinsic tongue muscles only were not visualized on sonography. They all underwent surgery, resulting in reduced sensitivity of sonography in operable cases.

CONCLUSIONS

Even though small tumors were difficult to visualize, sonography can play an important role in assessment of tumor extension in large growths, especially when MRI is unavailable, contraindicated, or unaffordable, and for posttreatment follow-up.

Clinical Translation of an Albumin-Binding PET Radiotracer 68Ga-NEB

Suitably labeled Evans blue dye has been successfully applied to evaluate cardiac function, vascular permeability, and lymphatic imaging in preclinical settings. This study documented the first-in-human application of 68Ga-1,4,7-triazacyclononane-N,N',N″-triacetic acid (NOTA)-NEB.

METHODS

The NOTA-conjugated truncated form of Evans blue, NEB, was labeled with 68Ga and tested in BALB/C mice for dynamic PET and ex vivo biodistribution studies. Three healthy volunteers (2 men and 1 woman) underwent 90-min whole-body dynamic PET. The absorbed doses for major organs and whole body were calculated using OLINDA/EXM software. Eleven patients with focal hepatic lesions diagnosed by enhanced CT or MR imaging were subjected to whole-body PET/CT acquisitions at 30 min after intravenous injection of 111-148 MBq (3-4 mCi) of 68Ga-NEB.

RESULTS

NEB dye was labeled with 68Ga (half-time, 68 min) with high yield and purity. After intravenous injection, 68Ga-NEB formed a complex with serum albumin, thus most of the radioactivity was retained in blood circulation. The tracer was demonstrated to be safe in both healthy volunteers and recruited patients without side effects or allergies. Among the 11 patients, hemangiomas showed much higher 68Ga-NEB signal intensity than the surrounding normal hepatic tissues, whereas no apparent difference between lesions and hepatic tissues was identified on 18F-FDG PET. All other focal hepatic lesions including hepatocellular carcinoma, hepatic cysts, and neuroendocrine tumor liver metastases showed negative 68Ga-NEB contrast to hepatic tissues.

CONCLUSION

As a blood-pool imaging agent, 68Ga-NEB is safe to use in the clinic, and our preliminary studies demonstrate the value of differentiating hepatic hemangioma from other benign or malignant focal hepatic lesions. Easy labeling with different positron emitters of various half-lives, excellent pharmacokinetics, and imaging quality warrant further clinical applications of NEB-based PET tracers.

Rapid 3D dynamic arterial spin labeling with a sparse model-based image reconstruction

Dynamic arterial spin labeling (ASL) MRI measures the perfusion bolus at multiple observation times and yields accurate estimates of cerebral blood flow in the presence of variations in arterial transit time. ASL has intrinsically low signal-to-noise ratio (SNR) and is sensitive to motion, so that extensive signal averaging is typically required, leading to long scan times for dynamic ASL. The goal of this study was to develop an accelerated dynamic ASL method with improved SNR and robustness to motion using a model-based image reconstruction that exploits the inherent sparsity of dynamic ASL data. The first component of this method is a single-shot 3D turbo spin echo spiral pulse sequence accelerated using a combination of parallel imaging and compressed sensing. This pulse sequence was then incorporated into a dynamic pseudo continuous ASL acquisition acquired at multiple observation times, and the resulting images were jointly reconstructed enforcing a model of potential perfusion time courses. Performance of the technique was verified using a numerical phantom and it was validated on normal volunteers on a 3-Tesla scanner. In simulation, a spatial sparsity constraint improved SNR and reduced estimation errors. Combined with a model-based sparsity constraint, the proposed method further improved SNR, reduced estimation error and suppressed motion artifacts. Experimentally, the proposed method resulted in significant improvements, with scan times as short as 20s per time point. These results suggest that the model-based image reconstruction enables rapid dynamic ASL with improved accuracy and robustness.

Cancer stratification by molecular imaging

The lack of specificity of traditional cytotoxic drugs has triggered the development of anticancer agents that selectively address specific molecular targets. An intrinsic property of these specialized drugs is their limited applicability for specific patient subgroups. Consequently, the generation of information about tumor characteristics is the key to exploit the potential of these drugs. Currently, cancer stratification relies on three approaches: Gene expression analysis and cancer proteomics, immunohistochemistry and molecular imaging. In order to enable the precise localization of functionally expressed targets, molecular imaging combines highly selective biomarkers and intense signal sources. Thus, cancer stratification and localization are performed simultaneously. Many cancer types are characterized by altered receptor expression, such as somatostatin receptors, folate receptors or Her2 (human epidermal growth factor receptor 2). Similar correlations are also known for a multitude of transporters, such as glucose transporters, amino acid transporters or hNIS (human sodium iodide symporter), as well as cell specific proteins, such as the prostate specific membrane antigen, integrins, and CD20. This review provides a comprehensive description of the methods, targets and agents used in molecular imaging, to outline their application for cancer stratification. Emphasis is placed on radiotracers which are used to identify altered expression patterns of cancer associated markers.

Patient characteristics influencing the variability of distributed parameter-based models in DCE-CT kinetic analysis

Kinetic parameter variability may be sensitive to kinetic model choice, kinetic model implementation or patient-specific effects. The purpose of this study was to assess their impact on the variability of dynamic contrast-enhanced computed tomography (DCE-CT) kinetic parameters. A total of 11 canine patients with sinonasal tumours received high signal-to-noise ratio, test-double retest DCE-CT scans. The variability for three distributed parameter (DP)-based models was assessed by analysis of variance. Mixed-effects modelling evaluated patient-specific effects. Inter-model variability (CV_inter ) was comparable to or lower than intra-model variability (CV_intra ) for blood flow (CV_inter :[4-28%], CV_intra :[28-31%]), fractional vascular volume (CV_inter :[3-17%], CV_intra :[16-19%]) and permeability-surface area product (CV_inter :[5-12%], CV_intra :[14-15%]). The kinetic models were significantly (P<0.05) impacted by patient characteristics for patient size, area underneath the curve of the artery and of the tumour. In conclusion, DP-based models demonstrated good agreement with similar differences between models and scans. However, high variability in the kinetic parameters and their sensitivity to patient size may limit certain quantitative applications.

Accuracy of diagnosis of salivary gland tumors with the use of ultrasonography, computed tomography, and magnetic resonance imaging: a meta-analysis

OBJECTIVE

To compare ultrasonography (US), computed tomography (CT), and magnetic resonance imaging (MRI) for clinical differential diagnosis in patients with salivary gland tumor (SGT).

STUDY DESIGN

Six databases were used to search the literature published between 1982 and 2013. Histologic diagnosis was required as standard diagnosis. Pooled estimate for sensitivity, specificity, summary receiver-operating characteristic curve (SROC) and area under curve (AUC) were calculated and compared using STATA and Meta-Disc statistical software.

RESULTS

Nineteen articles were included. Pooled sensitivity for US, CT, and MRI was 0.629 (95% confidence interval [CI] 0.52-0.73), 0.830 (95% CI 0.74-0.90), and 0.807 (95% CI 0.73-0.87), respectively; pooled specificity for US, CT, and MRI was 0.920 (95% CI 0.89-0.94), 0.851 (95% CI 0.79-0.90), and 0.886 (95% CI 0.85-0.92), respectively. The AUC under SROC for US, CT, and MRI was 0.934 ± 0.058, 0.912 ± 0.889, and 0.903 ± 0.045, respectively.

CONCLUSIONS

CT is recommended, as it is an effective imaging tool for differential diagnosis in patients with primary SGT, and MRI is suggested for differential diagnosis between benign and malignant GSTs because of its highest sensitivity and specificity.

Contrast enhancement in X-ray phase contrast tomography

We demonstrate phase contrast enhancement of X-ray computed tomography derived from propagation based imaging. In this method, the absorption and phase components are assumed to be correlated, allowing for phase retrieval from a single image. Experimental results are shown for liquid samples. Signal-to-noise ratio is greatly enhanced relative to pure attenuation based imaging.

In silico evaluation of gadofosveset pharmacokinetics in different population groups using the Simcyp® simulator platform

Purpose

Gadofosveset is a Gd-based contrast agent used for magnetic resonance imaging (MRI). Gadolinium kinetic distribution models are implemented in T1-weighted dynamic contrast-enhanced perfusion MRI for characterization of lesion sites in the body. Physiology changes in a disease state potentially can influence the pharmacokinetics of drugs and to this respect modify the distribution properties of contrast agents. This work focuses on the in silico modelling of pharmacokinetic properties of gadofosveset in different population groups through the application of physiologically-based pharmacokinetic models (PBPK) embedded in Simcyp® population pharmacokinetics platform.

Methods

Physicochemical and pharmacokinetic properties of gadofosveset were introduced into Simcyp® simulator platform and a min-PBPK model was applied. In silico clinical trials were generated simulating the administration of the recommended dose for the contrast agent (i.v., 30 mg/kg) in population cohorts of healthy volunteers, obese, renal and liver impairment, and in a generated virtual oncology population. Results were evaluated regarding basic pharmacokinetic parameters of Cmax, AUC and systemic CL and differences were assessed through ANOVA and estimation of ratio of geometric mean between healthy volunteers and the other population groups.

Results

Simcyp® predicted a mean Cmax = 551.60 mg/l, a mean AUC = 4079.12 mg/L*h and a mean systemic CL = 0.56 L/h for the virtual population of healthy volunteers. Obese population showed a modulation in Cmax and CL, attributed to increased administered dose. In renal and liver impairment cohorts a significant modulation in Cmax, AUC and CL of gadofosveset is predicted. Oncology population exhibited statistical significant differences regarding AUC when compared with healthy volunteers.

Conclusions

This work employed Simcyp® population pharmacokinetics platform in order to compute gadofosveset’s pharmacokinetic profiles through PBPK models and in silico clinical trials and evaluate possible differences between population groups. The approach showed promising results that could provide new insights regarding administration of contrast agents in special population cohorts. In silico pharmacokinetics could further be used for evaluating of possible toxicity, interpretation of MRI PK image maps and development of novel contrast agents.

Self-microemulsifying drug delivery system (SMEDDS)--challenges and road ahead

Self-microemulsifying drug delivery system (SMEDDS) has emerged as a vital strategy to formulate poor water soluble compounds for bioavailability enhancement. However, certain limitations are associated with SMEDDS formulations which include in vivo drug precipitation, formulation handling issues, limited lymphatic uptake, lack of predictive in vitro tests and oxidation of unsaturated fatty acids. These limitations restrict their potential usage. Inclusion of polymers or precipitation inhibitors within lipid based formulations helps to maintain drug supersaturation after dispersion. This, thereby, improves the bioavailability and reduces the variability on exposure. Also, formulating solid SMEDDS helps to overcome liquid handling and stability problems. Usage of medium chain triglycerides (MCT) and suitable antioxidants to minimize oxidation of unsaturated fatty acids are few of the steps to overcome the limitations associated with SMEDDS. The review discussed here, in detail, the limitations of SMEDDS and suitable measures that can be taken to overcome them.

Current and future lymphatic imaging modalities for tumor staging

Tumor progression is supported by the lymphatic system which should be scanned efficiently for tumor staging as well as the enhanced therapeutic outcomes. Poor resolution and low sensitivity is a limitation of traditional lymphatic imaging modalities; thus new noninvasive approaches like nanocarriers, magnetic resonance imaging, positron-emission tomography, and quantum dots are advantageous. Some newer modalities, which are under development, and their potential uses will also be discussed in this review.

Bimodal Imaging Using Neodymium Doped Gadolinium Fluoride Nanocrystals with Near-Infrared to Near-Infrared Downconversion Luminescence and Magnetic Resonance Properties

Here we report the synthesis, characterization and application of a multifunctional surface functionalized GdF3:Nd3+ nanophosphor that exhibits efficient near infrared (NIR) fluorescence as well as magnetic properties, which can be utilized for bimodal imaging in medical applications. The nanoparticles are small with an average size of 5 nm and form stable colloids that last for several weeks without settling, enabling the use for several biomedical and photonic applications. Their excellent NIR properties, such as nearly 11 % quantum yield of the 1064 nm emission, make them ideal contrast agents and biomarkers for in vitro and in vivo NIR optical bioimaging. The nanophosphors which were coated with poly(maleic anhydride- alt-1-octadicene) (PMAO) were implemented in cellular imaging and show no significant cellular toxicity for concentrations up to 200 μg ml-1. Furthermore, the incorporation of Gd into the nanocrystalline structure supplies exceptional magnetic properties, making them ideal for use as magnetic resonance imaging (MRI) contrast agents. The utility of these NIR emitting nanoparticles in infrared bioimaging and as contrast agent in magnetic resonance imaging was demonstrated by confocal imaging, magnetic resonance and tissue experiments.

Nanosized contrast agents to noninvasively detect kidney inflammation by magnetic resonance imaging

Several molecular imaging methods have been developed that use nanosized contrast agents to detect markers of inflammation within tissues. Kidney inflammation contributes to disease progression in a wide range of autoimmune and inflammatory diseases, and a biopsy is currently the only method of definitively diagnosing active kidney inflammation. However, the development of new molecular imaging methods that use contrast agents capable of detecting particular immune cells or protein biomarkers will allow clinicians to evaluate inflammation throughout the kidneys and to assess a patient's response to immunomodulatory drugs. These imaging tools will improve our ability to validate new therapies and to optimize the treatment of individual patients with existing therapies. This review describes the clinical need for new methods of monitoring kidney inflammation and recent advances in the development of nanosized contrast agents for the detection of inflammatory markers of kidney disease.

Magnetic iron oxide nanoparticles for multimodal imaging and therapy of cancer

Superparamagnetic iron oxide nanoparticles (SPION) have emerged as an MRI contrast agent for tumor imaging due to their efficacy and safety. Their utility has been proven in clinical applications with a series of marketed SPION-based contrast agents. Extensive research has been performed to study various strategies that could improve SPION by tailoring the surface chemistry and by applying additional therapeutic functionality. Research into the dual-modal contrast uses of SPION has developed because these applications can save time and effort by reducing the number of imaging sessions. In addition to multimodal strategies, efforts have been made to develop multifunctional nanoparticles that carry both diagnostic and therapeutic cargos specifically for cancer. This review provides an overview of recent advances in multimodality imaging agents and focuses on iron oxide based nanoparticles and their theranostic applications for cancer. Furthermore, we discuss the physiochemical properties and compare different synthesis methods of SPION for the development of multimodal contrast agents.

Diagnosis and therapy of atheromatous renal artery stenosis

Atheromatous renal artery stenosis (ARAS), a lesion of systemic atherosclerotic disease, is the leading cause of stenotic lesions in the renal artery, followed by fibromuscular dysplasia, a primary abnormality of the renal artery. As a result of several clinical trails, which failed to show an additional benefit of renal revascularization to medical therapy in ARAS, the treatment of ARAS has shifted, and renal revascularization is less commonly performed for ARAS. However, it is recognized that renal revascularization benefits some patients with ARAS. Advances in imaging modalities would allow more frequent detection of ARAS in a society with a growing elderly population, a group with an increased prevalence of systemic atherosclerotic disease. Therefore, it is imperative to identify the patients with ARAS who could benefit from renal revascularization. This review presents a strategy for the treatment of ARAS based on the results of our analysis.

PET/MR: a paradigm shift

More than a decade ago, multimodality imaging was introduced into clinical routine with the development of the positron emission tomography (PET)/computed tomography (CT) technique. Since then, PET/CT has been widely accepted in clinical imaging and has emerged as one of the main cancer imaging modalities. With the recent development of combined PET/magnetic resonance (MR) systems for clinical use, a promising new hybrid imaging modality is now becoming increasingly available. The combination of functional information delivered by PET with the morphologic and functional imaging of MR imaging (e.g., diffusion-weighted imaging, dynamic contrast-enhanced MR imaging and MR spectroscopy) offers exciting possibilities for clinical applications as well as basic research. However, the differences between CT and MR imaging are fundamental. This also leads to distinct differences between PET/CT and PET/MR not only regarding image interpretation but also concerning data acquisition, data processing and image reconstruction. This article provides an overview of the principal differences between PET/CT and PET/MR in terms of scanner design and technology, attenuation correction, speed, acquisition protocols, radiation exposure and safety aspects. PET/MR is expected to show advantages over PET/CT in clinical applications in which MR is known to be superior to CT due to its high intrinsic soft tissue contrast. However, as of now, only assumptions can be made about the future clinical role of PET/MR, as data about the performance of PET/MR in the clinical setting are still limited. The possible future clinical use of PET/MR in oncology, neurology and neurooncology, cardiology and imaging of inflammation is discussed.

Diagnostic bedside EUS in the intensive care unit: a single-center experience

BACKGROUND

The knowledge of bedside diagnostic EUS in critically ill patients is limited.

OBJECTIVE

To investigate the indications, feasibility, safety, and clinical utility of diagnostic EUS in the intensive care unit (ICU).

DESIGN

Retrospective.

SETTING

Tertiary-care referral teaching hospital.

PATIENTS

All consecutive patients who had EUS done in the ICU within a 6-year period.

INTERVENTION

Bedside EUS and EUS-guided FNA.

MAIN OUTCOME MEASUREMENTS

EUS indications, complications, and impact on management.

RESULTS

A total of 64 EUS procedures were performed in 63 patients (38 men, 25 women; age range 27-78 years); 1 patient underwent 2 separate EUS procedures. EUS was performed while the patients were mechanically ventilated in 70% (45/64) of cases. Indications for EUS included jaundice (n = 24), mass of unknown etiology (n = 25), unexplained pancreatitis (n = 7), and staging of known cancer (n = 3). In 5 cases, EUS was used as an alternative to other imaging modalities because of morbid obesity (n = 3) or contraindication to intravenous contrast material (n = 2). Complications included reversible oxygen desaturation (n = 4), nonsustained ventricular tachycardia (n = 1), and transient hypotension (n = 1). Overall, EUS influenced management in 97% (62/64) of cases.

LIMITATIONS

Retrospective, single-center study.

CONCLUSION

ICU-based EUS can be performed with few intraprocedural complications and can be a valuable diagnostic modality in the ICU setting. It appears to be particularly useful for determining the etiology of jaundice, masses of unknown etiology, and pancreatitis. It may have particular value as a diagnostic technique on selected patients with unstaged cancer and when morbid obesity or the inability to use intravenous contrast material precludes the use of other imaging modalities in the critically ill patient.

Microcapsules with intrinsic barium radiopacity for immunoprotection and X-ray/CT imaging of pancreatic islet cells

Microencapsulation is a commonly used technique for immunoprotection of engrafted therapeutic cells. We investigated a library of capsule formulations to determine the most optimal formulation for pancreatic beta islet cell transplantation, using barium as the gelating ion and clinical-grade protamine sulfate (PS) as a new cationic capsule cross-linker. Barium-gelated alginate/PS/alginate microcapsules (APSA, diameter = 444 ± 21 μm) proved to be mechanically stronger and supported a higher cell viability as compared to conventional alginate/poly-l-lysine/alginate (APLLA) capsules. Human pancreatic islets encapsulated inside APSA capsules, gelated with 20 mm barium as optimal concentration, exhibited a sustained morphological integrity, viability, and functionality for at least 3-4 weeks in vitro, with secreted human C-peptide levels of 0.2-160 pg/ml/islet. Unlike APLLA capsules that are gelled with calcium, barium-APSA capsules are intrinsically radiopaque and, when engrafted into mice, could be readily imaged in vivo with micro-computed tomography (CT). Without the need of adding contrast agents, these capsules offer a clinically applicable alternative for simultaneous immunoprotection and real-time, non-invasive X-ray/CT monitoring of engrafted cells during and after in vivo administration.

Molecular Imaging and Contrast Agent Database (MICAD): evolution and progress

The purpose of writing this review is to showcase the Molecular Imaging and Contrast Agent Database (MICAD; www.micad.nlm.nih.gov ) to students, researchers, and clinical investigators interested in the different aspects of molecular imaging. This database provides freely accessible, current, online scientific information regarding molecular imaging (MI) probes and contrast agents (CA) used for positron emission tomography, single-photon emission computed tomography, magnetic resonance imaging, X-ray/computed tomography, optical imaging and ultrasound imaging. Detailed information on >1,000 agents in MICAD is provided in a chapter format and can be accessed through PubMed. Lists containing >4,250 unique MI probes and CAs published in peer-reviewed journals and agents approved by the United States Food and Drug Administration as well as a comma separated values file summarizing all chapters in the database can be downloaded from the MICAD homepage. Users can search for agents in MICAD on the basis of imaging modality, source of signal/contrast, agent or target category, pre-clinical or clinical studies, and text words. Chapters in MICAD describe the chemical characteristics (structures linked to PubChem), the in vitro and in vivo activities, and other relevant information regarding an imaging agent. All references in the chapters have links to PubMed. A Supplemental Information Section in each chapter is available to share unpublished information regarding an agent. A Guest Author Program is available to facilitate rapid expansion of the database. Members of the imaging community registered with MICAD periodically receive an e-mail announcement (eAnnouncement) that lists new chapters uploaded to the database. Users of MICAD are encouraged to provide feedback, comments, or suggestions for further improvement of the database by writing to the editors at micad@nlm.nih.gov.

Risk of nephrogenic systemic fibrosis in liver transplantation patients

OBJECTIVE

The purpose of our study was to evaluate the exposure of our institution's liver transplantation population to gadolinium-based contrast agents and assess the rate of nephrogenic systemic fibrosis (NSF) within this unique group.

MATERIALS AND METHODS

Institutional review board approval was obtained for a retrospective review of medical records of patients who had undergone liver transplantation at our institution between 1997 and 2008. Informed consent was not required. Demographic information, history of gadolinium-based contrast agent exposure, stage of chronic kidney disease (CKD), and evidence of NSF were recorded.

RESULTS

A total of 2142 patients who had undergone liver transplantation at our institution between 1997 and 2008 were identified. Of this total, 33% (709/2142) had documented gadolinium-based contrast agent exposure peritransplantation. Patients in CKD1 and 2, CKD3, CKD4, and CKD5 comprised 50% (352/709), 28% (200/709), 8% (60/709), and 14% (97/709), respectively. Of patients in CKD5, 76% (74/97) required dialysis. Thorough review of all patients' medical records identified one biopsy-confirmed case of NSF in the 709 patients. This patient was also in CKD5 and required dialysis.

CONCLUSION

Within our institution, only 0.1% (1/709) of all liver transplantation patients exposed to gadolinium-based contrast agents or 1.4% (1/74) of CKD5 patients requiring dialysis had biopsy proof of NSF. This incidence is consistent with the rate of NSF in all patients exposed to gadolinium-based contrast agents regardless of liver transplantation reported in the literature. Therefore, liver transplantation may not be an independent risk factor in development of NSF in patients exposed to gadolinium-based contrast agents.

Gold-silver alloy nanoshells: a new candidate for nanotherapeutics and diagnostics

We have developed novel gold-silver alloy nanoshells as magnetic resonance imaging (MRI) dual T1 (positive) and T2 (negative) contrast agents as an alternative to typical gadolinium (Gd)-based contrast agents. Specifically, we have doped iron oxide nanoparticles with Gd ions and sequestered the ions within the core by coating the nanoparticles with an alloy of gold and silver. Thus, these nanoparticles are very innovative and have the potential to overcome toxicities related to renal clearance of contrast agents such as nephrogenic systemic fibrosis. The morphology of the attained nanoparticles was characterized by XRD which demonstrated the successful incorporation of Gd(III) ions into the structure of the magnetite, with no major alterations of the spinel structure, as well as the growth of the gold-silver alloy shells. This was supported by TEM, ICP-AES, and SEM/EDS data. The nanoshells showed a saturation magnetization of 38 emu/g because of the presence of Gd ions within the crystalline structure with r1 and r2 values of 0.0119 and 0.9229 mL mg-1 s-1, respectively (Au:Ag alloy = 1:1). T1- and T2-weighted images of the nanoshells showed that these agents can both increase the surrounding water proton signals in the T1-weighted image and reduce the signal in T2-weighted images. The as-synthesized nanoparticles exhibited strong absorption in the range of 600-800 nm, their optical properties being strongly dependent upon the thickness of the gold-silver alloy shell. Thus, these nanoshells have the potential to be utilized for tumor cell ablation because of their absorption as well as an imaging agent.

Advances in lymphatic imaging and drug delivery

Cancer remains the second leading cause of death after heart disease in the US. While metastasized cancers such as breast, prostate, and colon are incurable, before their distant spread, these diseases have invaded the lymphatic system as a first step in their progression. Hence, proper evaluation of the disease state of the lymphatics which drain a tumor site is crucial to staging and the formation of a treatment plan. Current lymphatic imaging modalities with visible dyes and radionucleotide tracers offer limited sensitivity and poor resolution; however, newer tools using nanocarriers, quantum dots, and magnetic resonance imaging promise to vastly improve the staging of lymphatic spread without needless biopsies. Concurrent with the improvement of lymphatic imaging agents, has been the development of drug carriers that can localize chemotherapy to the lymphatic system, thus improving the treatment of localized disease while minimizing the exposure of healthy organs to cytotoxic drugs. This review will focus on the use of various nanoparticulate and polymeric systems that have been developed for imaging and drug delivery to the lymph system, how these new devices improve upon current technologies, and where further improvement is needed.

Translational imaging endpoints to predict treatment response to novel targeted anticancer agents

Response Evaluation Criteria in Solid Tumors (RECIST) and World Health Organization (WHO) Criteria have been traditionally used for the evaluation of therapeutic response to chemotherapeutic treatment regimens. They determine anatomic criteria for patients response to anti-cancer therapy based on morphological measurements of each target lesion. While this assessment is justified for cytotoxic (chemotherapeutic) drugs, it is now recognized that morphological imaging protocols are poorly suited to the evaluation of the efficacy of novel signal transduction inhibitors (STIs) which exhibit cytostatic rather than cytotoxic properties. New imaging technologies are now designed to evaluate, in a functional manner, modifications in tumor metabolic activity, cellularity, and vascularization before a reduction in tumor volume can be detected. Introduction of physiological imaging end-points, derived from dynamic contrast-enhanced (DCE) imaging protocols--including magnetic resonance imaging (MRI), computed tomography (CT) and ultrasound (US)--allow for early assessment of disruption in tumor perfusion and permeability for targeted anti-angiogenic agents. Diffusion-weighted MRI (DWI) provides another physiological imaging end-point since tumor necrosis and cellularity are seen early in response to anti-angiogenic treatment. Changes in glucose and phospholipid turnover, based on metabolic MRI and positron emission tomography (PET), provide reliable markers for therapeutic response to novel receptor-targeting agents. Finally, novel molecular imaging techniques of protein and gene expression have been developed in animal models followed by a successful human application for gene therapy-based protocols.

Correlation between CA-125 serum level and response by RECIST in a phase III recurrent ovarian cancer study

OBJECTIVES

To evaluate in a large phase III recurrent ovarian cancer trial (OVA-301): 1) the concordance between CA-125 level vs. best overall response (OR) and progression-free survival (PFS) determined by radiological assessment 2) the impact of early CA-125 changes over the subsequent radiological response, and 3) the prognostic value of CA-125 response and CA-125 PFS to predict radiological response and PFS.

METHODS

Assessment of response in the entire randomized population was performed by the Response Evaluation Criteria in Solid Tumors 1.0 (RECIST) and modified Rustin criteria for CA-125 determination.

RESULTS

Most CA-125 decreases were observed in RECIST responders (82% of patients treated with the combination and 74% in the PLD alone). CA-125 progression preceded RECIST progression in 35% of patients with a median lead time of 8.4 weeks. A high concordance rate between CA-125 PFS status at 4 months (PFS4) and CA-125 response as a predictor of PFS4 (87%) and radiological response (79%) was found in the combination, with high positive predictive value for radiological PFS4 (92%) and high negative predictive value for OR (90%). An early CA-125 decrease was predictive for the ultimate response since it was found in a high rate of RECIST responders.

CONCLUSION

Radiological response was preceded by a favorable predictive CA-125 decrease in a high proportion of patients, suggesting that CA-125 evaluation may be an appropriate tool for tumor assessment in patients with ovarian cancer.

Protein Nanospheres: Synergistic Nanoplatform-Based Probes for Multimodality Imaging

No single clinical imaging modality has the ability to provide both high resolution and high sensitivity at the anatomical, functional and molecular level. Synergistically integrated detection techniques overcome these barriers by combining the advantages of different imaging modalities while reducing their disadvantages. We report the development of protein nanospheres optimized for enhancing MRI, CT and US contrast while also providing high sensitivity optical detection. Transferrin protein nanospheres (TfpNS), silicon coated, doped rare earth oxide and rhodamine B isothiocyanate nanoparticles, Si⊂Gd(2)O(3):Eu,RBITC, (NP) and transferrin protein nanospheres encapsulating Si⊂Gd(2)O(3):Eu,RBITC nanoparticles (TfpNS-NP) were prepared in tissue-mimicking phantoms and imaged utilizing multiple cross-sectional imaging modalities. Preliminary results indicate a 1:1 NP to TfpNS ratio in TfpNS-NP and improved sensitivity of detection for MRI, CT, US and fluorescence imaging relative to its component parts and/or many commercially available contrast agents.