Multicenter clinical trial of ultrasmall superparamagnetic iron oxide in the evaluation of mediastinal lymph nodes in patients with primary lung carcinoma

Advancing MRI with magnetic nanoparticles: a comprehensive review of translational research and clinical trials

The nexus of advanced technology and medical therapeutics has ushered in a transformative epoch in contemporary medicine. Within this arena, Magnetic Resonance Imaging (MRI) emerges as a paramount tool, intertwining the advancements of technology with the art of healing. MRI's pivotal role is evident in its broad applicability, spanning from neurological diseases, soft-tissue and tumour characterization, to many more applications. Though already foundational, aspirations remain to further enhance MRI's capabilities. A significant avenue under exploration is the incorporation of innovative nanotechnological contrast agents. Forefront among these are Superparamagnetic Iron Oxide Nanoparticles (SPIONs), recognized for their adaptability and safety profile. SPION's intrinsic malleability allows them to be tailored for improved biocompatibility, while their functionality is further broadened when equipped with specific targeting molecules. Yet, the path to optimization is not devoid of challenges, from renal clearance concerns to potential side effects stemming from iron overload. This review endeavors to map the intricate journey of SPIONs as MRI contrast agents, offering a chronological perspective of their evolution and deployment. We provide an in-depth current outline of the most representative and impactful pre-clinical and clinical studies centered on the integration of SPIONs in MRI, tracing their trajectory from foundational research to contemporary applications.

Metal Nanoparticles as Novel Agents for Lung Cancer Diagnosis and Therapy

Lung cancer is one of the most common malignancies worldwide and contributes to most cancer-related morbidity and mortality cases. During the past decades, the rapid development of nanotechnology has provided opportunities and challenges for lung cancer diagnosis and therapeutics. As one of the most extensively studied nanostructures, metal nanoparticles obtain higher satisfaction in biomedical applications associated with lung cancer. Metal nanoparticles have enhanced almost all major imaging strategies and proved great potential as sensor for detecting cancer-specific biomarkers. Moreover, metal nanoparticles could also improve therapeutic efficiency via better drug delivery, improved radiotherapy, enhanced gene silencing, and facilitated photo-driven treatment. Herein, the recently advanced metal nanoparticles applied in lung cancer therapy and diagnosis are summarized. Future perspective on the direction of metal-based nanomedicine is also discussed. Stimulating more research interests to promote the development of metal nanoparticles in lung cancer is devoted.

Molecular Imaging for Early-Stage Disease Diagnosis

With the development of cellular biology, molecular biology, and other subjects, targeted molecular probe was combined with medical imaging technologies to launch a new scientific discipline of molecular imaging that is a research discipline to visualize, characterize, and analyze biological process at the cellular and molecular levels for real-time tracking and precision therapy, also termed as the medical imaging in the twenty-first century. An array of imaging techniques has been developed to image specific targets of living cells or tissues by molecular probes, including optical molecular imaging (OI), magnetic resonance molecular imaging, ultrasound (US) molecular imaging, nuclear medicine molecular imaging, X-ray molecular imaging, and multi-mode molecular imaging. These imaging techniques make the early diagnosis of various diseases possible by means of visualization of gene expression, interactions between proteins, signal transduction, cell metabolism, cell traces, and other physiological or pathological processes in the living system, which bridge the gap between molecular biology and clinical medicine. This chapter will lay the emphasis on the early-stage diagnosis of fatal diseases, such as malignant tumors, cardio- or cerebrovascular diseases, digestive system disease, central nervous system disease, and other diseases employing molecular imaging in a real-time visualized manner.

Progress of Cancer Nanotechnology as Diagnostics, Therapeutics, and Theranostics Nanomedicine: Preclinical Promise and Translational Challenges

Early detection, right therapeutic intervention, and simultaneous effectiveness mapping are considered the critical factors in successful cancer therapy. Nevertheless, these factors experience the limitations of conventional cancer diagnostics and therapeutics delivery approaches. Along with providing the targeted therapeutics delivery, advances in nanomedicines have allowed the combination of therapy and diagnostics in a single system (called cancer theranostics). This paper discusses the progress in the pre-clinical and clinical development of therapeutics, diagnostics, and theranostics cancer nanomedicines. It has been well evident that compared to the overabundance of works that claimed success in pre-clinical studies, merely 15 and around 75 cancer nanomedicines are approved, and currently under clinical trials, respectively. Thus, we also brief the critical bottlenecks in the successful clinical translation of cancer nanomedicines.

USPIO-enhanced MRI of pelvic lymph nodes at 7-T: preliminary experience

Purpose

To evaluate the technical feasibility of high-resolution USPIO-enhanced magnetic resonance imaging of pelvic lymph nodes (LNs) at ultrahigh magnetic field strength.

Materials and methods

The ethics review board approved this study and written informed consent was obtained from all patients. Three patients with rectal cancer and three selected patients with (recurrent) prostate cancer were examined at 7-T 24–36 h after intravenous ferumoxtran-10 administration; rectal cancer patients also received a 3-T MRI. Pelvic LN imaging was performed using the TIAMO technique in combination with water-selective multi-GRE imaging and lipid-selective GRE imaging with a spatial resolution of 0.66 × 0.66 × 0.66mm³. T₂^*-weighted images of the water-selective imaging were computed from the multi-GRE images at TE = 0, 8, and 14 ms and used for the assessment of USPIO uptake.

Results

High-resolution 7-T MR gradient-echo imaging was obtained robustly in all patients without suffering from RF-related signal voids. USPIO signal decay in LNs was visualized using computed TE imaging at TE = 8 ms and an R₂^* map derived from water-selective imaging. Anatomically, LNs were identified on a combined reading of computed TE = 0 ms images from water-selective scans and images from lipid-selective scans. A range of 3–48 LNs without USPIO signal decay was found per patient. These LNs showed high signal intensity on computed TE = 8 and 14 ms imaging and low R₂^* (corresponding to high T₂^*) values on the R₂^* map.

Conclusion

USPIO-enhanced MRI of the pelvis at 7-T is technically feasible and offers opportunities for detecting USPIO uptake in normal-sized LNs, due to its high intrinsic signal-to-noise ratio and spatial resolution.

Key Points

• USPIO-enhanced MRI at 7-T can indicate USPIO uptake in lymph nodes based on computed TE images.

• Our method promises a high spatial resolution for pelvic lymph node imaging.

Evaluation of the diagnostic performance of apparent diffusion coefficient (ADC) values on diffusion-weighted magnetic resonance imaging (DWI) in differentiating between benign and metastatic lymph nodes in cases of cholangiocarcinoma

INTRODUCTION

Cholangiocarcinoma (CCA) is the primary tumor found in the bile duct and is associated with a high incidence of lymph node (LN) metastases and poor outcomes. The presence of metastatic lymph nodes, when shown by imaging, can influence patient treatment and prognosis. DWI is a promising, non-invasive imaging technique for differentiating between benign and malignant LNs. Many studies have shown that LN metastases have a lower apparent diffusion coefficient (ADC) value when compared to benign nodes.

OBJECTIVE

To evaluate the performance of ADC values as a basis for diagnosis of LN metastasis in cholangiocarcinoma patients.

MATERIALS AND METHODS

This was a retrospective imaging study that evaluated histopathologically proven intraabdominal LNs in cholangiocarcinoma patients who underwent a 1.5T abdomen MRI with DWI between January 2012 and July 2016. The ADC values and short-axis diameters of the LNs were measured and compared using student's t test. Receiver operating characteristic (ROC) curves were used to determine the threshold.

RESULTS

A total of 120 lymph nodes-85 benign and 35 metastatic-were included. The mean short-axis diameter of the benign LNs (8.34 mm) was significantly lesser than that of the malignant LNs (9.56 mm). Receiver operating characteristic curve analysis using a size criterion of 1 cm yielded a value of 0.63. A diagnostic size criterion of 1 cm for the short axis was applied and yielded an accuracy of 66%, sensitivity/specificity of 41%/75%, and positive/negative predictive value of 34%/80%. The mean ADC values of metastatic (1.31 × 10^-3 mm²/s) LNs were not significantly different from those of non-metastatic LNs (1.29 × 10^-3 mm²/s).

CONCLUSION

There was no difference in terms of ADC value between benign lymph nodes and those with metastatic cholangiocarcinoma. Isolated measurement of the ADC value does not contribute to a diagnosis of lymph node metastasis.

Alternatives to GBCA: Are We There Yet?

Gadolinium has been widely used as the contrast agent of choice for magnetic resonance imaging (MRI). However, gadolinium administration is not always desired due to its inherent enhancement properties and potential side effects (nephrogenic systemic fibrosis). This article reviews gadolinium alternatives, iron-, and manganese- based agents, and their current clinical usage for contrast-enhanced MRI examinations.

Emerging Role of MRI for Radiation Treatment Planning in Lung Cancer

Magnetic resonance imaging (MRI) provides excellent soft-tissue contrast and allows for specific scanning sequences to optimize differentiation between various tissue types and properties. Moreover, it offers the potential for real-time motion imaging. This makes magnetic resonance imaging an ideal candidate imaging modality for radiation treatment planning in lung cancer. Although the number of clinical research protocols for the application of magnetic resonance imaging for lung cancer treatment is increasing (www.clinicaltrials.gov) and the magnetic resonance imaging sequences are becoming faster, there are still some technical challenges. This review describes the opportunities and challenges of magnetic resonance imaging for radiation treatment planning in lung cancer.

Magnetic resonance imaging for N staging in non-small cell lung cancer: A systematic review and meta-analysis

Background

Lymph node staging in non-small cell lung cancer (NSCLC) is essential for deciding appropriate treatment. This study systematically reviews the literature regarding the diagnostic performance of magnetic resonance imaging (MRI) in lymph node staging of patients with NSCLC, and determines its pooled sensitivity and specificity.

Methods

PubMed and Embase databases and the Cochrane library were used to search for relevant studies. Two reviewers independently identified the methodological quality of each study. A meta-analysis of the reported sensitivity and specificity of each study was performed.

Results

Nine studies were included. These studies had moderate to good methodological quality. Pooled sensitivity, specificity, positive likelihood ratio (LR+), negative likelihood ratio (LR−) and diagnosis odds ratio (DOR) for per-patient based analyses (7 studies) were 74%, 90%, 7.5, 0.26, and 36.7, respectively, and those for per-lymph node based analyses (5 studies) were 77%, 98%, 42.24, 0.21, and 212.35, respectively. For meta-analyses of quantitative short time inversion recovery imaging (STIR) and diffusion-weighted imaging (DWI), pooled sensitivity and specificity were 84% and 91%, and 69% and 93%, respectively. Pooled LR+ and pooled LR− were 8.44 and 0.18, and 8.36 and 0.36, respectively. The DOR was 56.29 and 27.2 respectively.

Conclusion

MRI showed high specificity in the lymph node staging of NSCLC. Quantitative STIR has greater DOR than quantitative DWI. Large, direct, and prospective studies are needed to compare the diagnostic power of STIR versus DWI; consistent diagnostic criteria should be established.

Imaging the delivery of brain-penetrating PLGA nanoparticles in the brain using magnetic resonance

Current therapy for glioblastoma multiforme (GBM) is largely ineffective, with nearly universal tumor recurrence. The failure of current therapy is primarily due to the lack of approaches for the efficient delivery of therapeutics to diffuse tumors in the brain. In our prior study, we developed brain-penetrating nanoparticles that are capable of penetrating brain tissue and distribute over clinically relevant volumes when administered via convection-enhanced delivery (CED). We demonstrated that these particles are capable of efficient delivery of chemotherapeutics to diffuse tumors in the brain, indicating that they may serve as a groundbreaking approach for the treatment of GBM. In the original study, nanoparticles in the brain were imaged using positron emission tomography (PET). However, clinical translation of this delivery platform can be enabled by engineering a non-invasive detection modality using magnetic resonance imaging (MRI). For this purpose, we developed chemistry to incorporate superparamagnetic iron oxide (SPIO) into the brain-penetrating nanoparticles. We demonstrated that SPIO-loaded nanoparticles, which retain the same morphology as nanoparticles without SPIO, have an excellent transverse (T(2)) relaxivity. After CED, the distribution of nanoparticles in the brain (i.e., in the vicinity of injection site) can be detected using MRI and the long-lasting signal attenuation of SPIO-loaded brain-penetrating nanoparticles lasted over a one-month timecourse. Development of these nanoparticles is significant as, in future clinical applications, co-administration of SPIO-loaded nanoparticles will allow for intraoperative monitoring of particle distribution in the brain to ensure drug-loaded nanoparticles reach tumors as well as for monitoring the therapeutic benefit with time and to evaluate tumor relapse patterns.

A novel scheme for nanoparticle steering in blood vessels using a functionalized magnetic field

Magnetic drug targeting is a drug delivery approach in which therapeutic magnetizable particles are injected, generally into blood vessels, and magnets are then used to guide and concentrate them in the diseased target organ. Although many analytical, simulation, and experimental studies on capturing schemes for drug targeting have been conducted, there are few studies on delivering the nanoparticles to the target region. Furthermore, the sticking phenomenon of particles to vessels walls near the injection point, and far from the target region, has not been addressed sufficiently. In this paper, the sticking issue and its relationship to nanoparticle steering are investigated in detail using numerical simulations. For wide ranges of blood vessel size, blood velocity, particle size, and applied magnetic field, three coefficient numbers are uniquely generalized: vessel elongation, normal exit time, and force rate. With respect these new parameters, we investigated particle distribution trends for a Y-shaped channel and computed ratios of correctly guided particles and particles remaining in the vessel. We found that the sticking of particles to vessels occurred because of low blood flow velocity near the vessel walls, which is the main reason for low targeting efficiency when using a constant magnetic gradient. To reduce the sticking ratio of nanoparticles, we propose a novel field function scheme that uses a simple time-varying function to separate the particles from the walls and guide them to the target point. The capabilities of the proposed scheme were examined by several simulations of both Y-shaped channels and realistic three-dimensional (3-D) model channels extracted from brain vessels. The results showed a significant decrease in particle adherence to walls during the delivery stage and confirmed the effectiveness of the proposed magnetic field function method for steering nanoparticles for targeted drug delivery.

Does quantification of USPIO uptake-related signal loss allow differentiation of benign and malignant normal-sized pelvic lymph nodes?

Ultrasmall superparamagnetic iron oxide (USPIO) particles are promising contrast media, especially for molecular and cellular imaging besides lymph node staging owing to their superior NMR efficacy, macrophage uptake and lymphotropic properties. The goal of the present prospective clinical work was to validate quantification of signal decrease on high-resolution T(2)-weighted MR sequences before and 24-36 h after USPIO administration for accurate differentiation between benign and malignant normal-sized pelvic lymph nodes. Fifty-eight patients with bladder or prostate cancer were examined on a 3 T MR unit and their respective lymph node signal intensities (SI), signal-to-noise (SNR) and contrast-to-noise (CNR) were determined on pre- and post-contrast 3D T(2)-weighted turbo spin echo (TSE) images. Based on histology and/or localization, USPIO-uptake-related SI/SNR decrease of benign vs malignant and pelvic vs inguinal lymph nodes was compared. Out of 2182 resected lymph nodes 366 were selected for MRI post-processing. Benign pelvic lymph nodes showed a significantly higher SI/SNR decrease compared with malignant nodes (p < 0.0001). Inguinal lymph nodes in comparison to pelvic lymph nodes presented a reduced SI/SNR decrease (p < 0.0001). CNR did not differ significantly between benign and malignant lymph nodes. The receiver operating curve analysis yielded an area under the curve of 0.96, and the point with optimal accuracy was found at a threshold value of 13.5% SNR decrease. Overlap of SI and SNR changes between benign and malignant lymph nodes were attributed to partial voluming, lipomatosis, histiocytosis or focal lymphoreticular hyperplasia. USPIO-enhanced MRI improves the diagnostic ability of lymph node staging in normal-sized lymph nodes, although some overlap of SI/SNR-changes remained. Quantification of USPIO-dependent SNR decrease will enable the validation of this promising technique with the final goal of improving and individualizing patient care.

Molecular body imaging: MR imaging, CT, and US. Part II. Applications

Molecular imaging is expected to have a major impact on the early diagnosis of diseases and disease monitoring in the next decade. Traditionally, nuclear imaging techniques have been the mainstay of molecular imaging in the clinical arena. However, with continued development of molecularly targeted contrast agents for nonnuclear imaging techniques such as magnetic resonance (MR), computed tomography (CT), and ultrasonography (US), the spectrum of clinical molecular imaging applications is expanding. In the second part of this review series, an overview of applications of molecular MR imaging-, CT-, and US-based imaging strategies that show promise for clinical translation is presented, and key challenges that need to be addressed to successfully translate these promising techniques in the future are discussed. © RSNA, 2012.

Recent technological and application developments in computed tomography and magnetic resonance imaging for improved pulmonary nodule detection and lung cancer staging

This review compares the emerging technologies and approaches in the application of magnetic resonance (MR) and computed tomography (CT) imaging for the assessment of pulmonary nodules and staging of malignant findings. Included in this review is a brief definition of pulmonary nodules and an introduction to the challenges faced. We have highlighted the current status of both MR and CT for the early detection of lung nodules. Developments are detailed in this review for the management of pulmonary nodules using advanced imaging, including: dynamic imaging studies, dual energy CT, computer aided detection and diagnosis, and imaging assisted nodule biopsy approaches which have improved lung nodule detection and diagnosis rates. Recent advancements linking in vivo imaging to corresponding histological pathology are also highlighted. In vivo imaging plays a pivotal role in the clinical staging of pulmonary nodules through TNM assessment. While CT and positron emission tomography (PET)/CT are currently the most commonly clinically employed modalities for pulmonary nodule staging, studies are presented that highlight the augmentative potential of MR.

Diagnostic performance of USPIO-enhanced MRI for lymph-node metastases in different body regions: a meta-analysis

OBJECTIVES

USPIO (ultrasmall superparamagnetic iron oxide contrast agent) MRI was a promising imaging modality in the detection of lymph-node metastases. And this meta-analysis is performed to compare the diagnostic accuracy of USPIO-enhanced MRI with non-enhanced MRI, USPIO-enhanced MRI in various body regions, and postcontrast alone for diagnosis of lymph-node metastases.

METHODS

A comprehensive and systematic search was conducted in PubMed and EMBASE databases. After a systematic review of the studies, sensitivity, specificity, the Q* value and other measures of accuracy of USPIO-enhanced MRI in the diagnosis of lymph-node metastases were summarized. The overall test performance was based on summary receiver operating characteristic curves.

RESULTS

Summary of ROC curve analysis for per-lymph-node data shows a pooled sensitivity of 0.90 (95% confidential interval [CI]: 0.88-0.91) and overall specificity of 0.96 (95% CI: 0.95-0.97) for USPIO-enhanced MRI, the Q* value for USPIO-enhanced MRI is 0.9195, diagnostic odds ratio (DOR) is 162.28 (95% CI: 91.82-286.81). Non-enhanced MRI had less overall sensitivity 0.39 (95% CI: 0.34-0.43) and specificity 0.90 (95% CI: 0.89-0.91), respectively, the Q* value for USPIO-enhanced MRI was 0.6321, DOR is 5.81 (95% CI: 3.64-9.82). Postcontrast MRI alone had sensitivity 0.85 (95% CI: 0.81-0.88) and specificity 0.93 (95% CI: 0.91-0.95), respectively, the Q* value for USPIO-enhanced MRI was 0.8976, DOR is 76.92 (95% CI: 34.21-172.93). There was significant heterogeneity for studies reporting enhanced MRI and non-enhanced MRI.

CONCLUSIONS

This meta-analysis has shown that USPIO-enhanced MRI offers higher diagnostic performance than conventional MRI, and is sensitive and specific for the detection of lymph-node metastases. Postcontrast images alone can equate diagnostic performance pre- and postcontrast MRI has achieved for lymph-node characterization. And the role of USPIO-enhanced MRI in clinical practice still needs to be investigated in future studies.

Size of noncancerous hilomediastinal lymph nodes measured on coronal and sagittal reconstruction CT images

PURPOSE

To determine the sizes of hilomediastinal lymph nodes on coronal and sagittal reconstruction computed tomographic images of subjects without known malignancies.

MATERIALS AND METHODS

We evaluated 560 lymph nodes of 246 consecutive patients who underwent multidetector-row computed tomography (MDCT) of the chest, then reconstructed coronal and sagittal images on a viewer and measured short-axis diameters of lymph nodes in each station according to the American Thoracic Society (ATS) map for axial, coronal, and sagittal images.

RESULTS

On coronal images, short-axis diameters were significantly larger than on axial images in station #4R (P < 0.01). On sagittal images, short-axis diameters were significantly smaller than on axial images in stations #4L (P < 0.01), #10R (P < 0.001), and #10L (P < 0.05). On coronal and sagittal images, short-axis diameters were significantly smaller than on axial images in stations #11R (P < 0.001). In #7, diameters were significantly larger on coronal images than on axial and sagittal images (P < 0.001), and diameters were significantly smaller on sagittal images than on axial images (P < 0.01).

CONCLUSION

In stations #4R, #4L, #7, #10R, #10L, and #11R, measurements of short-axis diameters of hilomediastinal lymph nodes differed on coronal and sagittal images. On coronal and sagittal images, evaluation of hilomediastinal lymph nodes requires unique size criteria for every station.

Lymphotropic nanoparticle-enhanced MRI for independent prediction of lymph node malignancy: a logistic regression model

OBJECTIVE

The purpose of this study was to determine whether use of lymphotropic nanoparticle-enhanced MRI can improve the ability to characterize lymph nodes as benign or malignant beyond size criteria alone.

MATERIALS AND METHODS

The cases of 42 consecutively registered patients with a known primary malignant tumor of the genitourinary tract who underwent both lymphotropic nanoparticle-enhanced MRI and CT-guided biopsy of a lymph node at our institution from 2000 to 2005 were retrospectively identified. Lymphotropic nanoparticle-enhanced MRI included T2(*)-weighted gradient-recalled echo imaging before and 24-36 hours after i.v. administration of lymphotropic iron oxide nanoparticles. Two positivity criteria for lymph node malignancy were evaluated independently: lack of nanoparticle uptake at lymphotropic nanoparticle-enhanced MRI and short-axis length of 1 cm or greater. Sensitivity and specificity were calculated for each criterion with biopsy results as the standard of reference. Logistic regression analysis was used to determine the association (odds ratio) between lymphotropic nanoparticle-enhanced MRI findings and the presence of lymph node malignancy when controlling for short-axis length.

RESULTS

Metastatic lesions were detected at histologic examination in 67% (28/42) of nodes. According to the lymphotropic nanoparticle-enhanced MRI criterion, sensitivity for malignancy was 100% (28/28 nodes), and specificity was 64% (9/14 nodes). According to the short-axis criterion, sensitivity was 79% (22/28 nodes), and specificity was 21% (3/14 nodes). In multivariate analysis, when controlling for short-axis length, the finding of malignancy at lymphotropic nanoparticle-enhanced MRI was an independent predictor of the presence of malignancy (odds ratio, 61.0; 95% CI, 8.0 to infinity; p < 0.0001).

CONCLUSION

Use of lymphotropic nanoparticle-enhanced MRI may improve ability to characterize lymph nodes beyond size criteria alone. Our results emphasize the need to further assess lymphotropic nanoparticle-enhanced MRI in prospective large-scale studies with wider variation in the distribution of lymph node sizes and primary malignancies.

Detection of lymph node metastases with ultrasmall superparamagnetic iron oxide (USPIO)-enhanced magnetic resonance imaging in oesophageal cancer: a feasibility study

Aim: In this feasibility study we investigated whether magnetic resonance imaging (MRI) with ultrasmall superparamagnetic iron oxide (USPIO) can be used to identify regional and distant lymph nodes, including mediastinal and celiac lymph node metastases in patients with oesophageal cancer.

Patients and methods: Ten patients with a potentially curative resectable cancer of the oesophagus were eligible for this study. All patients included in the study had positive lymph nodes on conventional staging (including endoscopic ultrasound, computed tomography and fluorodeoxyglucose-positron emission tomography). Nine patients underwent MRI + USPIO before surgery. Results were restricted to those patients who had both MRI + USPIO and histological examination. Results were compared with conventional staging and histopathologic findings.

Results: One patient was excluded due to expired study time. Five out of 9 patients underwent an exploration; in 1 patient prior to surgery MRI + USPIO diagnosed liver metastases and in 3 patients an oesophageal resection was performed. USPIO uptake in mediastinal lymph nodes was seen in 6 out of 9 patients; in 3 patients non-malignant nodes were not visible. In total, 9 lymph node stations (of 6 patients) were separately analysed; 7 lymph node stations were assessed as positive (N1) on MRI+USPIO compared with 9 by conventional staging. According to histology findings, there was one false-positive and one false-negative result in MRI + USPIO. Also, conventional staging modalities had one false-positive and one false-negative result. MRI + USPIO had surplus value in one patient. Not all lymph node stations could be compared due to unforeseen explorations. No adverse effects occurred after USPIO infusion.

Conclusion: MRI+USPIO identified the majority of mediastinal and celiac (suspect) lymph nodes in 9 patients with oesophageal cancer. MRI+USPIO could have an additional value in loco-regional staging; however, more supplementary research is needed.

Basics of Magnetic Resonance Imaging and Magnetic Resonance Spectroscopy

In this chapter, the basic principles of magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) (Sects. 2.2, 2.3, and 2.4), the technical components of the MRI scanner (Sect. 2.5), and the basics of contrast agents and the application thereof (Sect. 2.6) are described. Furthermore, flow phenomena and MR angiography (Sect. 2.7) as well as diffusion and tensor imaging (Sect. 2.7) are elucidated.

Lymphotrophic nanoparticle enhanced MR imaging (LNMRI) for lymph node imaging

Nodal staging is an integral part of the pretreatment staging of any patient with malignancy and has therapeutic and prognostic implications. Currently used imaging techniques used for nodal evaluation are limited in accuracy because they rely on size criteria for the detection of metastases. This has led to the emergence of lymphotropic nanoparticle enhanced magnetic resonance imaging as a promising tool for nodal characterization. This article reviews the properties of lymphotropic iron oxide nanoparticles and the technique, image interpretation, and initial clinical experience with lymphotropic nanoparticle enhanced magnetic resonance imaging.

Comparison of Lymphotropic Nanoparticle-Enhanced MRI Sequences in Patients with Various Primary Cancers

OBJECTIVE

This study was performed to empirically evaluate T2-weighted fast spin-echo, moderately T2*-weighted gradient-refocused echo (GRE), and heavily T2*-weighted GRE sequences to determine which sequence is the most effective for nodal characterization on lymphotropic nanoparticle-enhanced MRI (LNMRI).

MATERIALS AND METHODS

The study included 65 patients who had proven primary cancer and were scheduled for either surgical lymph node dissection or imaging-guided lymph node biopsy. All patients underwent LNMRI using T2-weighted fast spin-echo, moderately T2*-weighted GRE, and heavily T2*-weighted GRE sequences. Unequivocal correlation of histopathology and MRI could be made in 140 nodes and only these were included in the analysis. Two blinded reviewers performed qualitative analysis of the nodes. Alternative free-response receiver operating characteristic (ROC) curves with a continuous rating scale were plotted for each sequence for both reviewers and the diagnostic accuracy of fast spin-echo T2-weighted and GRE T2*-weighted images were compared by calculating the area under the curve (A(Z)). A two-tailed Student's t test was performed to test the significance (p < 0.05) of the differences between the ROC curves derived from the three sequences.

RESULTS

Irrespective of reviewer experience, T2*-weighted sequences showed better nodal characterization when compared with T2-weighted sequences. For both reviewers, there was a statistically significant difference between the A(Z) for T2- and the two T2*-weighted sequences (p < 0.05). Neither reviewer showed a statistically significant difference between the two T2*-weighted sequences.

CONCLUSION

GRE T2*-weighted sequences are superior for nodal characterization on LNMRI to fast spin-echo T2-weighted sequences. Imaging protocols for LNMRI should include fast spin-echo T2-weighted imaging for anatomic localization, but characterization of nodes should be based on their appearance on contrast-enhanced T2*-weighted images. The T2*-weighted images acquired with dual TE values, one of which is intermediate and the other longer, improve nodal characterization.

Emerging implications of nanotechnology on cancer diagnostics and therapeutics

Nanotechnology is multidisciplinary field that involves the design and engineering of objects <500 nanometers (nm) in size. The National Cancer Institute has recognized that nanotechnology offers an extraordinary, paradigm-changing opportunity to make significant advances in cancer diagnosis and treatment. In the last several decades, nanotechnology has been studied and developed primarily for use in novel drug-delivery systems (e.g. liposomes, gelatin nanoparticles, micelles). A recent explosion in engineering and technology has led to 1) the development of many new nanoscale platforms, including quantum dots, nanoshells, gold nanoparticles, paramagnetic nanoparticles, and carbon nanotubes, and 2) improvements in traditional, lipid-based nanoscale platforms. The emerging implications of these platforms for advances in cancer diagnostics and therapeutics form the basis of this review. A widespread understanding of these new technologies is important, because they currently are being integrated into the clinical practice of oncology.

Imaging, distribution, and toxicity of superparamagnetic iron oxide magnetic resonance nanoparticles in the rat brain and intracerebral tumor

OBJECTIVE

Superparamagnetic iron oxide nanoparticle magnetic resonance imaging (MRI) contrast agents are gaining use in the central nervous system. The purpose of this study was to evaluate the imaging characteristics, distribution, time course, and neurotoxicity of the clinical agents ferumoxtran-10, ferumoxides, and ferumoxytol, and the laboratory preparation MION-46 in rat brain.

METHODS

Iron oxide agents were administered by intracerebral inoculation or intraarterially after osmotic blood-brain barrier opening in normal rats and intravenously in nude rats with intracerebral tumor xenografts. Rat brains were imaged by MRI at multiple time points and then were assessed for iron histochemistry and pathological features.

RESULTS

After intracerebral injection, MRI signal changes declined slowly over weeks to months. After transvascular delivery, transient (3 d) enhancement was seen with ferumoxtran-10 or ferumoxytol, whereas ferumoxides induced long-term (28 d) signal dropout. No pathological brain cell or myelin changes were detected after delivery of the clinical iron oxide agents to normal brains. In tumor models, ferumoxtran-10 enhanced one small-cell lung carcinoma intracerebral tumor, which correlated with iron staining in cells with macrophage morphological features at the tumor margin. Little enhancement was seen in two other models.

CONCLUSION

These studies demonstrate the safety and efficacy of iron oxide-based MRI contrast agents in the brain and provide imaging parameters and time course data for future studies in brain tumors and neurological lesions.

Minimally invasive pharmacokinetic and pharmacodynamic technologies in hypothesis-testing clinical trials of innovative therapies

Clinical trials of new cancer drugs should ideally include measurements of parameters such as molecular target expression, pharmacokinetic (PK) behavior, and pharmacodynamic (PD) endpoints that can be linked to measures of clinical effect. Appropriate PK/PD biomarkers facilitate proof-of-concept demonstrations for target modulation; enhance the rational selection of an optimal drug dose and schedule; aid decision-making, such as whether to continue or close a drug development project; and may explain or predict clinical outcomes. In addition, measurement of PK/PD biomarkers can minimize uncertainty associated with predicting drug safety and efficacy, reduce the high levels of drug attrition during development, accelerate drug approval, and decrease the overall costs of drug development. However, there are many challenges in the development and implementation of biomarkers that probably explain their disappointingly low implementation in phase I trials. The Pharmacodynamic/Pharmacokinetic Technologies Advisory committee of Cancer Research UK has found that submissions for phase I trials of new cancer drugs in the United Kingdom often lack detailed information about PK and/or PD endpoints, which leads to suboptimal information being obtained in those trials or to delays in starting the trials while PK/PD methods are developed and validated. Minimally invasive PK/PD technologies have logistic and ethical advantages over more invasive technologies. Here we review these technologies, emphasizing magnetic resonance spectroscopy and positron emission tomography, which provide detailed functional and metabolic information. Assays that measure effects of drugs on important biologic pathways and processes are likely to be more cost-effective than those that measure specific molecular targets. Development, validation, and implementation of minimally invasive PK/PD methods are encouraged.

Breast imaging. Preoperative breast cancer staging: comparison of USPIO-enhanced MR imaging and 18F-fluorodeoxyglucose (FDC) positron emission tomography (PET) imaging for axillary lymph node staging--initial findings

Magnetic resonance (MR) imaging after ultra-small super paramagnetic iron oxide (USPIO) injection and 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) for preoperative axillary lymph node staging in patients with breast cancer were evaluated using histopathologic findings as the reference standard. USPIO-enhanced MR and FDG-PET were performed in ten patients with breast cancer who were scheduled for surgery and axillary node resection. T2-weighted fast spin echo, T1-weighted three-dimensional (3D) gradient echo, T2*-weighted gradient echo and gadolinium-enhanced T1-weighted 3D gradient echo with spectral fat saturation were evaluated. MR imaging before USPIO infusion was not performed. The results were correlated with FDG-PET (acquired with dedicated PET camera, visual analysis) and histological findings. The histopathologic axillary staging was negative for nodal malignancy in five patients and positive in the remaining five patients. There was one false positive finding for USPIO-enhanced MR and one false negative finding for FDG-PET. A sensitivity (true positive rate) of 100%, specificity (true negative rate) of 80%, positive predictive value of 80%, and negative predictive value of 100% were achieved for USPIO-enhanced MR and of 80%, 100%, 100%, 80% for FDG-PET, respectively. The most useful sequences in the detection of invaded lymph nodes were in the decreasing order: gadolinium-enhanced T1-weighted 3D gradient echo with fat saturation, T2*-weighted 2D gradient echo, T1-weighted 3D gradient echo and T2-weighted 2D spin echo. In our study, USPIO-enhanced T1 gradient echo after gadolinium injection and fat saturation emerged as a very useful sequence in the staging of lymph nodes. The combination of USPIO-enhanced MR and FDG-PET achieved 100% sensitivity, specificity, PPV and NPV. If these results are confirmed, the combination of USPIO MR with FDG-PET has the potential to identify the patient candidates for axillary dissection versus sentinel node lymphadenectomy.

Lymphotropic nanoparticle enhanced MR imaging (LNMRI) technique for lymph node imaging

Accurate nodal staging is important in the management of any primary malignancy. The presence of nodal metastases has both therapeutic and prognostic implications. Lymphotropic nanoparticles are a new class of MRI contrast agents, which are promising in detecting minimal metastatic nodal disease particularly in normal sized lymph nodes. This paper discusses the technique and interpretation of lymphotropic nanoparticle enhanced MRI (LNMRI) and reviews the various trials evaluating nodal staging with ferumoxtran-10 enhanced MRI.

Diagnostic precision of nanoparticle-enhanced MRI for lymph-node metastases: a meta-analysis

BACKGROUND

At present, there is no accepted, ideal imaging modality or technique for diagnosis of lymph-node metastases. We aimed to assess the diagnostic precision of MRI with ferumoxtran-10-an ultrasmall superparamagnetic iron-oxide nanoparticle used as a contrast agent for diagnosis of lymph-node metastases, compared with that of unenhanced MRI and final histological diagnosis.

METHODS

We did a meta-analysis of prospective studies that compared MRI, with and without ferumoxtran-10, with histological diagnosis after surgery or biopsy. Sensitivity, specificity, and diagnostic odds ratio (DOR) were calculated for every study; summary receiver operating characteristic (ROC) and subgroup analyses were done; and study quality and heterogeneity were assessed. Metaregression analysis was used to analyse the effect of ferumoxtran-10 in diagnostic precision of MRI.

FINDINGS

Summary ROC curve analysis for per-lymph-node data showed an overall sensitivity of 0.88 (95% CI 0.85-0.91) and overall specificity of 0.96 (0.95-0.97) for ferumoxtran-10-enhanced MRI. Overall weighted area under the curve for ferumoxtran-10-enhanced MRI was 0.96 (SE 0.01), DOR 123.05 (95% CI 5.93-256.93). Unenhanced MRI had less overall sensitivity (0.63 [0.57-0.69]) and specificity (0.93 [0.91-0.94]), with an overall weighted area under the ROC curve of 0.84 (SE 0.11) and DOR of 26.75 (95% CI 8.48-84.42). Significant heterogeneity was noted for studies reporting enhanced MRI and unenhanced MRI. Metaregression analysis confirmed the significant effect of ferumoxtran-10 in the diagnostic precision of MRI (p=0.001).

INTERPRETATION

Ferumoxtran-10-enhanced MRI is sensitive and specific in detection of lymph-node metastases for various tumours. It offers higher diagnostic precision than does unenhanced MRI for detection of lymph-node metastases, and allows functional and anatomical definition when used as an imaging modality.

Functional Imaging in Lung Cancer

Accurate detection of the presence and extent of disease is vital in the management of non–small-cell lung cancer. While computed tomography and magnetic resonance imaging tend to be the routine diagnostic modalities used in the management of lung cancer, there have been significant advances in the field of functional and molecular imaging. In this article, we review the performance of the functional imaging techniques that are currently available for the evaluation of non–small-cell lung cancer. The techniques range from evaluation of glucose metabolism in tumors with fluorodeoxyglucose, to evaluation of proliferation with fluorothymidine and evaluation of tumor hypoxia with agents such as fluoromisonidazole. Magnetic resonance imaging with an emphasis on dynamic contrast enhancement of tumors as well as detecting of malignant lymph nodes with targeted contrast agents is discussed. Emerging technologies such as lung imaging fluorescence endoscopy are considered. The role of functional imaging in planning, predicting response to, and evaluating effects of, various therapies is explored.

Evaluation of tumoral enhancement by superparamagnetic iron oxide particles: comparative studies with ferumoxtran and anionic iron oxide nanoparticles

This study was designed to compare tumor enhancement by superparamagnetic iron oxide particles, using anionic iron oxide nanoparticles (AP) and ferumoxtran. In vitro, relaxometry and media with increasing complexity were used to assess the changes in r2 relaxivity due to cellular internalization. In vivo, 26 mice with subcutaneously implanted tumors were imaged for 24 h after injection of particles to describe kinetics of enhancement using T1 spin echo, T2 spin echo, and T2 fast spin echo sequences. In vitro, the r2 relaxivity decreased over time (0-4 h) when AP were uptaken by cells. The loss of r2 relaxivity was less pronounced with long (Hahn Echo) than short (Carr-Purcell-Meiboom-Gill) echo time sequences. In vivo, our results with ferumoxtran showed an early T2 peak (1 h), suggesting intravascular particles and a second peak in T1 (12 h), suggesting intrainterstitial accumulation of particles. With AP, the late peak (24 h) suggested an intracellular accumulation of particles. In vitro, anionic iron oxide nanoparticles are suitable for cellular labeling due to a high cellular uptake. Conversely, in vivo, ferumoxtran is suitable for passive targeting of tumors due to a favorable biodistribution.

The role of functional and molecular imaging in cancer drug discovery and development

Studies of pharmacokinetics (which is what the body does to the drug) and pharmacodynamics (which is what the drug does to the body) are essential components of the modern process of cancer drug discovery and development. Defining the precise relationship between pharmacokinetics and pharmacodynamics is critical. It is especially important to establish a well understood pharmacological "audit trail" that links together all of the essential parameters of drug action, from the molecular target to the clinical effects. The pharmacological audit trail allows us to answer two absolutely crucial questions: (1) how much gets there; and (2) what does it do? During the pre-clinical drug discovery phase, it is essential that pharmacokinetic/pharmacodynamic (PK/PD) properties are optimized, so that the best candidate can be selected for clinical development. As part of contemporary mechanistic, hypothesis-testing clinical trials, construction of the pharmacological PK/PD audit trail facilitates rational decision-making. However, PK/PD endpoints frequently require invasive sampling of body fluids and tissues. Non-invasive molecular measurements, e.g. using MRI or spectroscopy, or positron emission tomography, are therefore very attractive. This review highlights the need for PK/PD endpoints in modern drug design and development, illustrates the value of PK/PD endpoints, and emphasises the importance of non-invasive molecular imaging in drug development. Examples cited include the use of PK/PD endpoints in the development of molecular therapeutic drugs such as the Hsp90 molecular chaperone inhibitor 17AAG, as well as the development of SR-4554 as a non-invasive probe for the detection of tumour hypoxia.

Magnetic resonance molecular imaging with nanoparticles

Molecular imaging agents are extending the potential of noninvasive medical diagnosis from basic gross anatomic descriptions to complicated phenotypic characterizations based on the recognition of unique cell surface biochemical signatures. Although originally the purview of nuclear medicine, molecular imaging is now a prominent feature of most clinically relevant imaging modalities, in particular magnetic resonance (MR) imaging. MR nanoparticulate agents afford the opportunity not only for targeted diagnostic studies but also for image-monitored site-specific therapeutic delivery, much like the "magic bullet" envisioned by Paul Erhlich 100 years ago. Combining high-resolution MR molecular imaging with drug delivery will facilitate verification and quantification of treatment (ie, rational targeted therapy) and will offer new clinical approaches to many diseases.

Current state of imaging for lung cancer staging

Proper selection and interpretation of imaging studies is essential to provide optimal treatment to patients who have lung cancer. The following combines the recommendations of the American College of Chest Physicians [74] and the authors' current clinical practice guidelines: --All patients who have known or suspected lung cancer should undergo a CT of the chest and upper abdomen. --An FDG-PET study should be performed, if available. --Mediastinoscopy should be performed in all patients except those who have peripheral small (<2 cm) tumors and no evidence of N2 disease on CT or PET imaging. --MRI should be performed for tumors of the superior sulcus to define the relationship of the tumor to adjacent neurovascular structures. --Patients who have neurologic signs or symptoms should undergo a brain imaging study (CT or MRI). --Screening for extrathoracic disease is not necessary in asymptomatic patients who have clinical stage I or II disease.

Early MR lymphography with gadofluorine M in rabbits

PURPOSE

To investigate the dose and time dependency of gadofluorine M for lymph node imaging and the detection of lymph node metastases in an animal model and to compare gadofluorine M with Gadomer (both, Schering, Berlin, Germany) for lymph node enhancement.

MATERIALS AND METHODS

Enhancement of popliteal and iliac lymph nodes was studied in VX2 tumor-bearing rabbits before injection and at 5-120 minutes and 24 hours after intravenous bolus injection of 0.025, 0.05, and 0.1 mmol gadolinium per kilogram of body weight gadofluorine M (six rabbits) or 0.5 mmol/kg Gadomer (eight rabbits). Effects of treatment and time point at enhancement were evaluated with repeated measures analysis of variance. Means were separated with all-pairs comparison with Tukey-Kramer adjustment. After 1.5-T magnetic resonance (MR) imaging, lymph nodes were removed, and prepared sections were stained with hematoxylin-eosin for microscopic examination.

RESULTS

MR images in VX2 tumor-bearing rabbits revealed rapid and strong signal intensity increase in the functional lymph node tissue by 15 minutes after intravenous injection of gadofluorine M. Maximum enhancement of 165%-309% was observed 60-90 minutes after injection (enhancement with 0.05 and 0.1 mmol/kg significantly different from that with 0.025 mmol/kg, P < or =.05). Metastatic tissue showed only slight enhancement at early time points, resulting in high-contrast differentiation between functional and metastatic tissue. Intravenous injection of the blood-pool agent Gadomer induced only short and inhomogeneous lymph node enhancement (enhancement significantly lower [P < or =.05] than that with gadofluorine M).

CONCLUSION

Findings in the study showed that gadofluorine M produces rapid lymph node accumulation. Diagnosis of lymph node metastases was shown with intravenous injection of gadofluorine M with a minimum effective diagnostic dose of 0.025 mmol/kg.

MR Lymphangiography: Imaging Strategies to Optimize the Imaging of Lymph Nodes with Ferumoxtran-10

Detection of local or regional metastases to lymph nodes is clinically important in virtually any type of primary tumor. Current imaging techniques rely heavily on the size criterion for characterization of nodal disease. However, size can be an ineffective parameter for diagnosis of tumor spread to lymph nodes. Magnetic resonance (MR) imaging performed before and after administration of ferumoxtran-10 is a promising technique for characterization of lymph nodes in patients with various primary tumors. Normal homogeneous uptake of ferumoxtran-10 in nonmetastatic nodes shortens the T2 and T2*, turning these nodes dark, whereas malignant nodes lack uptake and remain hyperintense. To optimize acquisition strategies, the following factors should be considered: the timing of contrast material-enhanced imaging, the section thickness, the imaging plane, and the imaging parameters for T2*-weighted sequences. In addition, MR imaging with ferumoxtran-10 allows presurgical mapping of lymph nodes and quantitative estimation of T2*.

Rectal cancer: mesorectal lymph nodes at MR imaging with USPIO versus histopathologic findings--initial observations

PURPOSE

To compare histopathologic findings with appearances of mesorectal lymph nodes at magnetic resonance (MR) imaging with ultrasmall particles of iron oxide (USPIO) in rectal cancer.

MATERIALS AND METHODS

Mesorectal lymph nodes in 12 patients with adenocarcinoma of the rectum were evaluated with USPIO and high-spatial-resolution MR imaging. Appearance and signal intensity of lymph nodes at T2- and T2*-weighted imaging were recorded before and after USPIO administration. Two radiologists visually assessed pattern of enhancement; interobserver agreement was tested with the kappa statistic. After total mesorectal excision, MR imaging of surgical specimens was performed, and it enabled node-by-node correlation with histopathologic findings.

RESULTS

Appearances of 74 nodes at in vivo MR imaging were compared with histopathologic findings. Sixty-eight nodes were nonmalignant (34 were normal, 34 showed reactive changes); six nodes were malignant. Four patterns of USPIO uptake were demonstrated at T2*-weighted imaging: uniform low signal intensity, central low signal intensity, eccentric high signal intensity, and uniform high signal intensity. Two radiologists showed good interobserver agreement (kappa = 0.88, P <.01) in classification of nodes into these four categories. Sixty-five (96%) of 68 nonmalignant nodes showed uniform or central low-signal-intensity patterns; 16 (47%) of 34 reactive nodes showed central low-signal-intensity patterns. Compared with uniform low-signal-intensity pattern, central low-signal-intensity pattern was more commonly observed in reactive nodes (P <.01, chi(2) test; positive predictive value, 67%; 95% CI: 47%, 87%). Eccentric and uniform high-signal-intensity patterns were observed in lymph nodes that contained metastases larger than 1 mm in diameter.

CONCLUSION

Mesorectal lymph nodes can be characterized by using USPIO and T2*-weighted MR imaging. Uniform and central low-signal-intensity patterns are features of nonmalignant nodes. Reactive nodes frequently show central low signal intensity at T2*-weighted imaging.

Advances in radiological staging of non-small cell lung cancer (NSCLC)

Imaging plays a vital role in the management of non-small cell lung cancer including diagnosis, staging and follow-up. CT and magnetic resonance imaging (MRI) are used in staging and provide anatomical information but have well known limitations in differentiating reactive from malignant nodes, and fibrosis from active disease and in defining the extent of invasion. MRI with its superior soft tissue contrast provides optimal information on brachial plexus and central nervous system involvement. Functional imaging using 2-18 fluoro-deoxyglucose positron emission tomography is increasingly being used to provide unique information and when combined with anatomic imaging will provide better staging information for both local disease and the extent of metastases.

Predictability of FTY720 efficacy in experimental autoimmune encephalomyelitis by in vivo macrophage tracking: Clinical implications for ultrasmall superparamagnetic iron oxide-enhanced magnetic resonance imaging

PURPOSE

To examine the efficacy of FTY720 as a new agent to reduce inflammatory activity in an animal model of multiple sclerosis (MS) by in vivo macrophage tracking.

MATERIAL AND METHODS

FTY720 was used for treatment of rats in a model of chronic relapsing experimental autoimmune encephalomyelitis (EAE) at an oral dose of 0.3 mg/kg/day. Magnetic resonance imaging (MRI) based on in vivo tracking of macrophages labeled with ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles, immunohistological staining (IHC), and neurological readouts was used to study the burden of disease in treated and untreated animals.

RESULTS

While untreated animals showed severe paralysis of the hind paws, intense accumulation of macrophages in brain tissue, and areas of blood-brain barrier (BBB) disruption, FTY720-treated animals displayed no signs of inflammatory activity or neurological impairment. These observations were made for both acute phase and first relapse.

CONCLUSION

Tracking of macrophages by MRI provides direct evidence of the immunomodulatory efficacy of FTY720 in the EAE model and correlates well with neurological symptoms and histology.

Trafficking of superparamagnetic iron oxide particles (Combidex) from brain to lymph nodes in the rat

Central nervous system (CNS) drainage may occur via connections to the vasculature, but in animal models up to 50% occurs via perivascular, perineural and primitive lymphatic drainage to cervical lymph nodes. We evaluated efflux of particles from the brain to cervical lymph nodes in normal rats, using Combidex iron oxide-based magnetic resonance imaging (MRI) agent. After intracerebral, intraventricular, intracarotid or intravenous injection of Combidex in normal Long Evans rats, particle localization was assessed by MRI and histochemistry for iron and the dextran coat (n = 27). Intraventricular or intracerebral injection, but not intracarotid administration of Combidex (100 micro g), resulted in MRI signal changes in the deep cervical lymph nodes around the carotid artery, and, less strongly, in the superficial cervical nodes. Within 2 h of Combidex administration, iron was histologically localized in cervical lymph nodes, with patched staining of capsule and peripheral sinus consistent with delivery via multiple afferent lymphatic vessels. Lymph node staining in groups receiving CNS Combidex was significantly different from controls (P < 0.0001) and was significantly localized in the deep vs. superficial cervical lymph nodes (P = 0.0003). The trafficking of the superparamagnetic iron particles from the CNS in the rat could be visualized by MRI and histology. Combidex provides a powerful tool to rapidly assess drainage of virus-sized particles from the CNS.