Development of "imageable" beads for transcatheter embolotherapy

Bench-to-bedside development of multifunctional flexible embolic agents

Transarterial chemoembolization (TACE) has been demonstrated to provide a survival benefit for patients with unresectable hepatocellular carcinoma (HCC). However, conventional TACE still faces limitations associated with complications, side effects, unsatisfactory tumor responses, repeated treatment, and narrow indications. For further improvement of TACE, additional beneficial functions such as degradability, drug-loading and releasing properties, detectability, targetability, and multiple therapeutic modalities were introduced. The purpose here is to provide a comprehensive overview of current and emerging particulate embolization technology with respect to materials. Therefore, this review systematically identified and described typical features, various functions, and practical applications of recently emerging micro/nano materials as particulate embolic agents for TACE. Besides, new insights into the liquid metals-based multifunctional and flexible embolic agents were highlighted. The current development routes and future outlooks of these micro/nano embolic materials were also presented to promote advancement in the field.

Multimodal imaging of nano-assembled microspheres loaded with doxorubicin and Cisplatin for liver tumor therapy

Currently, clinically available drug-loaded embolic microspheres have some shortcomings, such as being invisible with standard medical imaging modalities and only being able to carry positively charged drugs. The visualization of drug-loaded microspheres is very important for real-time monitoring of embolic position to improve the therapeutic effect. Meanwhile, the visualization of microspheres can enable postoperative reexamination, which is helpful for evaluating the embolization area and guiding the subsequent treatment. In addition, microspheres capable of loading different charged drugs can increase the choice of chemotherapeutic drugs and provide more possibilities for treatment. Therefore, it is of great importance to explore drug-loaded microspheres capable of multimodal imaging and loading drugs with different charges for transarterial chemoembolization (TACE) treatment of liver tumors. In our study, we designed a kind of nano-assembled microspheres (NAMs) that can realize computer X-ray tomography (CT)/magnetic resonance imaging (MRI)/Raman multimodal imaging, be loaded with positively and negatively charged drugs and test their imaging ability, drug loading and biological safety. The microspheres have strong attenuation performance for CT, high T₂ relaxation for MRI and good sensitivity for surface enhanced Raman spectroscopy (SERS). At the same time, our microspheres can also load the positively charged drug, doxorubicin (DOX), and negatively charged drug Cisplatin. One gram of NAMs can hold 168 mg DOX or 126 mg Cisplatin, which has good drug loading and sustained-release capacity. Cell experiments also showed that the nano-assembled microspheres had good biocompatibility. Therefore, as multimodal developed drug loaded microspheres, nano assembled microspheres have great potential in TACE treatment of liver cancer.

Embolization therapy with microspheres for the treatment of liver cancer: State-of-the-art of clinical translation

Embolization with microspheres is a therapeutic strategy based on the selective occlusion of the blood vessels feeding a tumor. This procedure is intraarterially performed in the clinical setting for the treatment of liver cancer. The practice has evolved over the last decade through the incorporation of drug loading ability, biodegradability and imageability with the subsequent added functionality for the physicians and improved clinical outcomes for the patients. This review highlights the evolution of the embolization systems developed through the analysis of the marketed embolic microspheres for the treatment of malignant hepatocellular carcinoma, namely the most predominant form of liver cancer. Embolic microspheres for the distinct modalities of embolization (i.e., bland embolization, chemoembolization and radioembolization) are here comprehensively compiled with emphasis on material characteristics and their impact on microsphere performance. Moreover, the future application of the embolics under clinical investigation is discussed along with the scientific and regulatory challenges ahead in the field. STATEMENT OF SIGNIFICANCE: Embolization therapy with microspheres is currently used in the clinical setting for the treatment of most liver cancer conditions. The progressive development of added functionalities on embolic microspheres (such as biodegradability, imageability or drug and radiopharmaceutical loading capability) provides further benefit to patients and widens the therapeutic armamentarium for physicians towards truly personalized therapies. Therefore, it is important to analyze the possibilities that advanced biomaterials offer in the field from a clinical translational perspective to outline the future trends in therapeutic embolization.

Intraarterial Therapies for the Management of Hepatocellular Carcinoma

Image-guided locoregional therapies play a crucial role in the management of patients with hepatocellular carcinoma (HCC). Transarterial therapies consist of a group of catheter-based treatments where embolic agents are delivered directly into the tumor via their supplying arteries. Some of the transarterial therapies available include bland embolization (TAE), transarterial chemoembolization (TACE), drug-eluting beads-transarterial chemoembolization (DEB-TACE), selective internal radioembolization therapy (SIRT), and hepatic artery infusion (HAI). This article provides a review of pre-procedural, intra-procedural, and post-procedural aspects of each therapy, along with a review of the literature. Newer embolotherapy options and future directions are also briefly discussed.

Research on the Construction of Bispecific-Targeted Sustained-Release Drug-Delivery Microspheres and Their Function in Treatment of Hepatocellular Carcinoma

Lenvatinib (LEN) is approved as one of the commonly used drugs in the treatment of hepatocellular carcinoma (HCC). It is recognized to be a novel therapeutic choice for the direct and targeted delivery of effective drugs to HCC tumor sites. The key to the proposed method lies in the requirement for efficient targeted drug delivery carriers with targeting performance to deliver effective drugs directly and safely to tumor lesions. Methods: Here, magnetic liposomes (MLs) were modified by phosphatidylinositol proteoglycan 3 (GPC3) and epithelial cell adhesion molecules (EpCAMs). Subsequently, bispecific-targeted sustained-release drug-loaded microspheres containing LEN (GPC3/EpCAM-LEN-MLs) were constructed. In addition, both cytotoxicity and magnetic resonance imaging (MRI) analyses were performed to establish a mouse model and further perform corresponding performance assessments. Results: The corresponding results showed that GPC3/EpCAM-LEN-MLs were spherical-shaped and evenly dispersed. The encapsulation and drug-loading efficiencies were 91.08% ± 1.83% and 8.22% ± 1.24%, respectively. Meanwhile, GPC3/EpCAM-LEN-MLs showed a high inhibition rate on the proliferation of HCC cells and significantly increased their apoptosis. Furthermore, MRI revealed that the system possessed the function of tracking and localizing tumor cells, and animal experiments verified that it could exert the function of disease diagnosis. Conclusions: Our experiments successfully constructed a safe and efficient bispecific-targeted sustained-release drug delivery system for HCC tumor cells. It provides a useful diagnostic and therapeutic scheme for the clinical diagnosis and targeted therapy of HCC. Moreover, it can be used as a potential tumor-specific MRI contrast agent for the localization and diagnosis of malignant tumors.

Emerging Polymer Materials in Trackable Endovascular Embolization and Cell Delivery: From Hype to Hope

Minimally invasive endovascular embolization is a widely used clinical technique used for the occlusion of blood vessels to treat various diseases. Different occlusive agents ranging from gelatin foam to synthetic polymers such as poly(vinyl alcohol) (PVA) have been commercially used for embolization. However, these agents have some drawbacks, such as undesired toxicity and unintended and uncontrolled occlusion. To overcome these issues, several polymer-based embolic systems are under investigation including biocompatible and biodegradable microspheres, gelling liquid embolic with controlled occlusive features, and trackable microspheres with enhanced safety profiles. This review aims to summarize recent advances in current and emerging polymeric materials as embolization agents with varying material architectures. Furthermore, this review also explores the potential of combining injectable embolic agents and cell therapy to achieve more effective embolization with the promise of outstanding results in treating various devastating diseases. Finally, limitations and challenges in developing next-generation multifunctional embolic agents are discussed to promote advancement in this emerging field.

Recent advances and applications of microspheres and nanoparticles in transarterial chemoembolization for hepatocellular carcinoma

Transarterial chemoembolization (TACE) is a recommended treatment for patients suffering from intermediate and advanced hepatocellular carcinoma (HCC). As compared to the conventional TACE, drug-eluting bead TACE demonstrates several advantages in terms of survival, treatment response, and adverse effects. The selection of embolic agents is critical to the success of TACE. Many studies have been performed on the modification of the structure, size, homogeneity, biocompatibility, and biodegradability of embolic agents. Continuing efforts are focused on efficient loading of versatile chemotherapeutics, controlled sizes for sufficient occlusion, real-time detection intra- and post-procedure, and multimodality imaging-guided precise treatment. Here, we summarize recent advances and applications of microspheres and nanoparticles in TACE for HCC. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

Microfluidic fabrication of imageable and resorbable polyethylene glycol microspheres for catheter embolization

Radiopaque and degradable hydrogel microspheres have a range of potential uses in medicine including proper placement of embolic material during occlusion procedures, acting as inherently embolic materials, and serving as drug carriers that can be located after injection. Current methods for creating radiopaque microspheres are either unable to fully and homogeneously incorporate radiopaque material throughout the microspheres for optimal imaging capabilities, do not result in degradable or fully compressible microspheres, or require elaborate, time-consuming preparation. We used a simple one-step microfluidic method to fabricate imageable, degradable polyethylene glycol (PEG) microspheres of varying sizes with homogenous dispersion of barium sulfate-a biocompatible, high-radiopacity contrast agent. The imageability of the microspheres was characterized using optical microscopy and microcomputed tomography as a function of barium sulfate loading. Microspheres with 20% wt/vol barium sulfate had a mean CT attenuation value of 1,510 HU, similar to that of cortical bone, which should enable visualization with soft tissue. Compared with unloaded microspheres, barium sulfate-loaded ones saw an increase in gelation and degradation times and storage modulus and decrease in swelling. Imageable microspheres retained compressibility and were injectable via catheter. The developed radiopaque, degradable PEG microspheres have various potential uses for interventional radiologists and imaging laboratories.

Reduced nontarget embolization and increased targeted delivery with a reflux-control microcatheter in a swine model

PURPOSE

To evaluate the potential differences in non-target embolization and vessel microsphere filling of a reflux-control microcatheter (RCM) compared to a standard end-hole microcatheter (SEHM) in a swine model.

MATERIALS AND METHODS

Radiopaque microspheres were injected with both RCM and SEHM (2.4-Fr and 2.7-Fr) in the kidneys of a preclinical swine model. Transarterial renal embolization procedures with RCM or SEHM were performed in both kidneys of 14 pigs. Renal arteries were selectively embolized with an automated injection protocol of radio-opaque microspheres. Ex-vivo X-ray microtomography images of the kidneys were utilized to evaluate the embolization by quantification of the deposition of injected microspheres in the target vs. the non-target area of injection. X-ray microtomography images were blindly analyzed by five interventional radiologists. The degree of vessel filling and the non-target embolization were quantified using a scale from 1 to 5 for each parameter. An analysis of variance was used to compare the paired scores.

RESULTS

Total volumes of radio-opaque microspheres injected were similar for RCM (11.5±3.6 [SD] mL; range: 6-17mL) and SEHM (10.6±5.2 [SD] mL; range: 4-19mL) (P=0.38). The voxels enhanced ratio in the target (T) vs. non-target (NT) areas was greater with RCM (T=98.3% vs. NT=1.7%) than with SEHM (T=89% vs. NT=11%) but the difference was not significant (P=0.30). The total score blindly given by the five interventional radiologists was significantly different between RCM (12.3±2.1 [SD]; range: 6-15) and the standard catheter (11.3±2.5 [SD]; range: 4-15) (P=0.0073), with a significant decrease of non-target embolization for RCM (3.8±1.3 [SD]; range: 3.5-4.2) compared to SEHM (3.2±1.5 [SD]; range: 2.9-3.5) (P=0.014).

CONCLUSION

In an animal model, RCM microcatheters reduce the risk of non-target embolization from 11% to 1.7%, increasing the delivery of microspheres of 98% to the target vessels, compared to SEHM microcatheters.

Transarterial Chemoembolization of Hepatocellular Carcinoma Using Radiopaque Drug-Eluting Embolics: Impact of Embolic Density and Residual Tumor Perfusion on Tumor Recurrence and Survival

Purpose

To evaluate the value of dual-phase parenchymal blood volume (PBV) C-arm mounted cone-beam-CT (CBCT) to enable assessment of radiopaque, doxorubicin-loaded drug-eluting embolics (rDEE) based on the visual degree of embolization, embolic density and residual tumor perfusion as early predictors for tumor recurrence after transarterial chemoembolization (TACE) of hepatocellular carcinoma (HCC).

Material and Methods

Thirty patients (50 HCCs) were prospectively enrolled, underwent cross-sectional imaging before and after TACE using 100–300 µm rDEE and had regular follow-up examinations. Directly before and after the TACE procedure, PBV-CBCT was acquired. The response was evaluated and compared to visual degree of embolization (DE) and embolic density (ED) of rDEE deposits, as well as the presence of residual tumor perfusion (RTP) derived from PBV-CBCT. Outcome was assessed by mid-term tumor response applying mRECIST and patient survival after 12 months.

Results

RTP was detected in 16 HCCs and correlated negatively with DE (p = .03*) and ED (p = .0009*). The absence of RTP significantly improved lesion-based mid-term response rates regarding complete response (CR, 30/34 (88%) vs 2/16 (12.5%), p = .0002*), lesion-based complete response rate was 75% (21/28) for DE ≥ 50% vs. 50% (11/22) for DE < 50% (p =  .08) and 82% (27/33) for ED ≥ 2 vs. 29% for ED < 2 (5/17), p =  .005*). Thirteen patients were treated with re-TACE within 12 months, 11 of which had shown RTP. 12-month survival rate was 93%.

Conclusion

Residual tumor perfusions as assessed by PBV-CBCT during rDEE-TACE proved to be the best parameter to predict mid-term response.

“Level of Evidence: Level 3”

Supplementary Information

The online version contains supplementary material available at 10.1007/s00270-021-02858-6.

Magnetic liquid metal loaded nano-in-micro spheres as fully flexible theranostic agents for SMART embolization

Transcatheter arterial chemoembolization (TACE) has become one of the preferred choices for advanced liver cancer patients. Current clinically used microsphere embolic agents, such as PVA, gelatin, and alginate microspheres, have limited therapeutic efficacy and lack the function of real-time imaging. In this work, we fabricated magnetic liquid metal nanoparticle (Fe@EGaIn NP) loaded calcium alginate (CA) microspheres (denoted as Fe@EGaIn/CA microspheres), which integrate CT/MR dual-modality imaging and photothermal/photodynamic functions of the Fe@EGaIn NP core, as well as embolization and drug-loading functions of CA microspheres. Namely, such nano-in-micro spheres can be used as fully flexible theranostic agents to achieve smart-chemoembolization. It has been confirmed by in vitro and in vivo experiments that Fe@EGaIn/CA microspheres have advantageous morphology, favorable biocompatibility, splendid versatility, and advanced embolic efficacy. Benefiting from these properties, excellent therapeutic efficiency was achieved with a tumor growth-inhibiting value of 100% in tumor-bearing rabbits. As a novel microsphere embolic agent with promising therapeutic efficacy and diagnostic capability, Fe@EGaIn/CA microspheres have shown potential applications in clinical transcatheter arterial chemoembolization. And the preparation strategy presented here provides a generalized paradigm for achieving multifunctional and fully flexible theranostics.

Ultrasound-visualized, site-specific vascular embolization using magnetic protein microcapsules

Imaging-guided vascular embolization is frequently performed on patients with advanced hepatocellular carcinoma (HCC) to alleviate symptoms and extend their survival time. Current operation procedures are not only painful for patients, but are also inaccurate in tumor targeting after the release of embolic agents from the catheter, leading to injury to healthy tissues simultaneously. In this study, we developed an ultrasound-visualized, site-specific vascular embolization strategy with magnetic protein microcapsules (MPMs). MPMs were fabricated using a rapid emulsification method, giving it a smooth surface and a core-shell structure. Their diameters could be controlled within 10 μm, allowing them to pass through capillaries. The core-shell structure and loading of magnetic Fe3O4 endowed MPMs with good contrast under ultrasound imaging and magnetically inducible targeting properties, as well as aggregation response even under flowing conditions. In vitro cytotoxicity and hemolysis evaluation demonstrated good biocompatibility of the MPMs. Furthermore, mock embolization showed that cell death could be induced by aggregation of the MPMs. Such a combination of real-time monitoring using ultrasound and control on targeted vascular embolization might be a breakthrough in the treatment of advanced HCC.

Drug-eluting embolic microspheres: State-of-the-art and emerging clinical applications

INTRODUCTION

Drug-eluting embolic (DEE) microspheres, or drug-eluting beads (DEB), delivered by transarterial chemoembolization (TACE) serve as a therapeutic embolic to stop blood flow to tumors and a drug delivery vehicle. New combinations of drugs and DEE microspheres may exploit the potential synergy between mechanisms of drug activity and local tissue responses generated by TACE to enhance the efficacy of this mainstay therapy.

AREAS COVERED

This review provides an overview of key drug delivery concepts related to DEE microspheres with a focus on recent technological developments and promising emerging clinical applications as well as speculation into the future.

EXPERT OPINION

TACE has been performed for nearly four decades by injecting chemotherapy drugs into the arterial supply of tumors while simultaneously cutting off their blood supply, trying to starve and kill cancer cells, with varying degrees of success. The practice has evolved over the decades but has yet to fulfill the promise of truly personalized therapies envisioned through rational selection of drugs and real-time multi-parametric image guidance to target tumor clonality or heterogeneity. Recent technologic and pharmacologic developments have opened the door for potentially groundbreaking advances in how TACE with DEE microspheres is performed with the goal of achieving advancements that benefit patients.

Microfluidic-prepared, monodisperse, X-ray-visible, embolic microspheres for non-oncological embolization applications

Embolotherapy using particle embolics is normally performed with exogenous contrast to assist in visualization. However, the exact location of the embolics cannot be identified after contrast washout. We developed a novel, pseudo-check valve-integrated microfluidic device, that partitions barium- impregnated alginate from crosslinking solution, thereby preventing nozzle failure. This enables rapid and continuous generation of inherently X-ray-visible embolic microspheres (XEMs) with uniform size. The XEMs are visible under clinical X-ray and cone beam CT both in vitro and in vivo. In particular, we demonstrated the embolization properties of these XEMs in large animals, performing direct intra- and post-procedural assessment of embolic delivery. The persistent radiopacity of these XEMs enables real-time evaluation of embolization precision and offers great promise for non-invasive follow-up examination without exogenous contrast. We also demonstrated that bariatric arterial embolization with XEMs significantly suppresses weight gain in swine, as an example of a non-oncological application of embolotherapy.

On-demand degradable embolic microspheres for immediate restoration of blood flow during image-guided embolization procedures

Degradable embolic agents that provide transient arterial occlusion during embolization procedures have been of interest for many years. Ideally, embolic agents are visible with standard imaging modalities and offer on-demand degradability, permitting physicians to achieve desired arterial occlusion tailored to patient and procedure indication. Subsequent arterial recanalization potentially enhances the overall safety and efficacy of embolization procedures. Here, we report on-demand degradable and MRI-visible microspheres for embolotherapy. Embolic microspheres composed of calcium alginate and USPIO nanoclusters were synthesized with an air spray atomization and coagulation reservoir equipped with a vacuum suction. An optimized distance between spray nozzle and reservoir allowed uniform size and narrow size distribution of microspheres. The fabricated alginate embolic microspheres crosslinked with Ca²⁺ demonstrated highly responsive on-demand degradation properties in vitro and in vivo. Finally, the feasibility of using the microspheres for clinical embolization and recanalization procedures was evaluated with interventional radiologists in rabbits. Digital subtraction angiography (DSA) guided embolization of hepatic arteries with these embolic microspheres was successfully performed and the occlusion of artery was confirmed with DSA images and contrast enhanced MRI. T2 MRI visibility of the microspheres allowed to monitor the distribution of intra-arterial (IA) infused embolic microspheres. Subsequent on-demand image-guided recanalization procedures were also successfully performed with rapid degradation of microspheres upon intra-arterial infusion of an ion chelating agent. These instant degradable embolic microspheres will permit effective on-demand embolization/recanalization procedures offering great promise to overcome limitations of currently available permanent and biodegradable embolic agents.

The feasibility of degradable glass microspheres as transient embolic medical devices

The deliberate occlusion of blood flow through transarterial embolization is currently being used to treat conditions ranging from hemorrhages to hypervascular tumors. Degradable, imageable high borate glass microspheres (BRS2) were developed and tested to improve lesion targeting and promote a temporary vascular occlusion which is sufficient for most embolization procedure. A 48 hour pilot study, in a swine renal model, was conducted to assess the embolization effectiveness and potential risks of this new embolic agent. Bilateral embolization of the caudal branch of the renal arteries using test and control particles were performed in 4 pigs. Embolization efficacy, recanalization and resulting ischemia were evaluated at different time frame (0, 24 and 48 hours). The primary outcomes for this study were the assessment of: (i) embolization effectiveness, and (ii) vessel recanalization. The test article was found to occlude vessels as effectively as the control microspheres, with the use of a smaller volume of microspheres. At the 24 hour time point, over 95% of the material was found to be completely degraded, although little to no recanalization was observed. This data suggests that BRS2 is an effective embolic agent, however further investigations into the method of delivery are required prior to clinical implementation.

Temperature sensitive hydrogel for preoperative treatment of renal carcinoma

Surgical resection has been suggested as an effective and first-line treatment of renal cell carcinoma (RCC). However, operation is quite difficult for the patients with stage of middle-late or hypervascularized tumors. Transarterial chemoembolization (TACE) plays an important role in decreasing the size of tumors before surgery. In this work, we prepared an injectable drug-delivery system of doxorubicin-loaded temperature sensitive hydrogel for transarterial chemoembolization in RCC. The sol-gel transition behavior and rheologic analysis showed that the doxorubicin-loaded temperature sensitive hydrogel had good temperature sensitivity. Then, The X-ray experiment of hydrogel showed excellent visibility under the digital subtraction angiography and computed tomography scans in vitro and in vivo. Moreover, the studies of embolization in beagle's right kidney showed good properties in embolizing of renal arteries. In TACE therapy studies of rabbit VX₂ renal tumors, angiography, computed tomography and histopathological analysis verified that TACE therapy of doxorubicin-loaded temperature sensitive hydrogel had excellent embolic efficiency as a result of repressing the tumor growth. This hydrogel could provide valuable option in the treatment of renal cell carcinoma before surgery.

Updates of colorectal cancer liver metastases therapy: review on DEBIRI

Colorectal cancer is a worldwide public health issue, presenting an advanced stage at diagnosis in more than 20% of patients. Liver metastases are the most common metastatic sites and are not indicated for resection in 80% of cases. Unresectable colorectal cancer liver metastases that are refractory to systemic chemotherapy may benefit from transarterial chembolization with irinotecan-loaded beads (DEBIRI). Several studies show the safety and efficacy of DEBIRI for the treatment of colorectal cancer liver metastases. The development of transarterial chembolization and the introduction of new embolics have contributed to better outcomes of DEBIRI. This article reviews the current literature on DEBIRI reporting its use, efficacy in terms of tumor response and survival and side effects.

The opacity of mineral ion-loaded bead (DC beads®) on low-keV monochromatic images from dual energy CT and T1-weighted gradient-echo MRI

PURPOSE

To evaluate the opacity of DC beads^® (DCB) loaded with mineral ions on low-keV monochromatic images from dual energy computed tomography (DECT) and T1-weighted gradient-echo (T1-GRE) MRI.

MATERIALS AND METHODS

Fe²⁺ or Ca²⁺-loaded DCBs were prepared by mixing DCBs in 100 mM FeSO₄ or CaSO₄ solution and scanned by DECT from 10 min to 27 h after mixing. The Hounsfield units (HUs) of sedimented DCBs on 40-keV monochromatic images were measured. Next, we mixed DCBs in 100, 10, 5 and 1 mM FeSO₄ solutions, and scanned these solutions from 15 to 120 min after mixing using a 3 T MR scanner. The signal-noise ratios (SNRs) of sedimented DCBs on T1-GRE were measured. Venous blood was scanned to compare with DCBs.

RESULTS

The CT values of DCBs in FeSO₄ and CaCl₂ solutions gradually increased, and were 113.3 and 43.1 HU at 27 h, respectively; that of blood was 17.8 HU. The SNR of DCB in 1 mM FeSO₄ solution increased and achieved equilibrium at 120 min, and was 120.5 and higher than in the other FeSO₄ solutions. The SNR of blood was 49.7.

CONCLUSION

Optimally Fe²⁺-loaded DCBs can be discriminated from venous blood on 40-keV monochromatic images from DECT and T1-GRE.

Transarterial Chemoembolization of Hepatocellular Carcinoma Using Radiopaque Drug-Eluting Embolics: How to Pursue Periprocedural Cross-Sectional Imaging?

PURPOSE

To compare different imaging techniques (volume perfusion CT, cone-beam CT, and dynamic gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid-enhanced dynamic contrast-enhanced MR imaging with golden-angle radial sparse parallel MR imaging) in evaluation of transarterial chemoembolization of hepatocellular carcinoma (HCC) using radiopaque drug-eluting embolics (DEE).

MATERIALS AND METHODS

MR imaging and CT phantom investigation of radiopaque DEE was performed. In the clinical portion of the study, 13 patients (22 HCCs) were prospectively enrolled. All patients underwent cross-sectional imaging before and after transarterial chemoembolization using 100-300 μm radiopaque DEE. Qualitative assessment of images using a Likert scale was performed.

RESULTS

In the phantom study, CT-related beam-hardening artifacts were markedly visible at a concentration of 12% (v/v) radiopaque DEE; MR imaging demonstrated no significant detectable signal intensity changes. Imaging obtained before transarterial chemoembolization showed no significant difference regarding tumor depiction. Visualization of tumor feeding arteries was significantly improved with volume perfusion CT (P < .001) and cone-beam CT (P = .002) compared with MR imaging. Radiopaque DEE led to significant decrease in tumor depiction (P = .001) and significant increase of beam-hardening artifacts (P = .012) using volume perfusion CT before versus after transarterial chemoembolization. Greater residual arterial tumor enhancement was detected with MR imaging (10 HCCs) compared with volume perfusion CT (8 HCCs) and cone-beam CT (6 HCCs).

CONCLUSIONS

Using radiopaque DEE, the imaging modalities provided comparable early treatment assessment. In HCCs with dense accumulation of radiopaque DEE, treatment assessment using volume perfusion CT or cone-beam CT may be impaired owing to resulting beam-hardening artifacts and contrast stasis. Dynamic contrast-enhanced MR imaging may add value in detection of residual arterial tumor enhancement.

One-step preparation of nano-in-micro poly(vinyl alcohol) embolic microspheres and used for dual-modal T1/T2-weighted magnetic resonance imaging

It is crucial to develop dual or multi-modal self-imaging embolic microspheres to evaluate the effects of transcatheter arterial embolization therapy of tumor. However, the preparation of such hybrid microspheres always involved in multiple steps or complicated conditions. Here, poly(vinyl alcohol) (PVA) hybrid microspheres with dual-modal T₁/T₂-weighted magnetic resonance imaging (MRI) have been prepared based on microfluidic technique in one step. Gd₂O₃ and Fe₃O₄ nanoparticles with a size of ~5 nm act as T₁- and T₂-weighted MRI contrast agents, respectively, which are simultaneously in-situ synthesized in the PVA matrix via the reaction of metal ions and alkali with PVA chains as a soft template. Meanwhile, these metallic-oxide nanoparticles act as cross-linker to gelatinize the PVA droplets to obtain nano-in-micro PVA microspheres in one step. This procedure is simple, economic and feasible. The obtained nano-in-micro PVA microspheres show good magnetothermal effect, enhanced T₁- and T₂-weighted MRI and embolization effect.

DEB-TACE: a standard review

Drug-eluting bead transarterial chemoembolization (DEB-TACE) is a relative new endovascular treatment based on the use of microspheres to release chemotherapeutic agents within a target lesion with controlled pharmacokinetics. This aspect justifies the immediate success of DEB-TACE, that nowadays represents one of the most used treatments for unresectable hepatocellular carcinoma. However, there is no consensus about the choice of the best embolotherapy technique. In this review, we describe the available microspheres and report the results of the main comparative studies, to clarify the role of DEB-TACE in the hepatocellular carcinoma management. We underline that there is no evidence about the superiority of DEB-TACE over conventional TACE in terms of efficacy, but there may be some benefits with respect to safety especially with the improvement of new technologies.

Computed tomography and histopathological findings after embolization with inherently radiopaque 40μm-microspheres, standard 40μm-microspheres and iodized oil in a porcine liver model

Purpose

The present study compared standard computed tomography (CT) and histopathological findings after endovascular embolization using a prototype of inherently radiopaque 40μm-microspheres with both standard 40μm-microspheres and iodized oil in a porcine liver model.

Materials and methods

Twelve pigs were divided into six study groups, of two pigs each. Four pigs were embolized with iodized oil alone and four with radiopaque microspheres; two animals in each group were sacrificed at 2 hours and two at 7 days. Two pigs were embolized with radiopaque microspheres and heparin and sacrificed at 7 days. Two pigs were embolized with standard microspheres and sacrificed at 2 hours. CT was performed before and after segmental embolization and before sacrifice at 7 days. The distribution of embolic agent, inflammatory response and tissue necrosis were assessed histopathologically.

Results

Radiopaque microspheres and iodized oil were visible on standard CT 2 hours and 7 days after embolization, showing qualitatively comparable arterial and parenchymal enhancement. Quantitatively, the enhancement was more intense for iodized oil. Standard microspheres, delivered without contrast, were not visible by imaging. Radiopaque and standard microspheres similarly occluded subsegmental and interlobular arteries and, to a lesser extent, sinusoids. Iodized oil resulted in the deepest penetration into sinusoids. Necrosis was always observed after embolization with microspheres, but never after embolization with iodized oil. The inflammatory response was mild to moderate for microspheres and moderate to severe for iodized oil.

Conclusion

Radiopaque 40μm-microspheres are visible on standard CT with qualitatively similar but quantitatively less intense enhancement compared to iodized oil, and with a tendency towards less of an inflammatory reaction than iodized oil. These microspheres also result in tissue necrosis, which was not observed after embolization with iodized oil. Both radiopaque and standard 40μm-microspheres are found within subsegmental and interlobar arteries, as well as in hepatic sinusoids.

Bench-to-clinic development of imageable drug-eluting embolization beads: finding the balance

This review describes the historical development of an imageable spherical embolic agent and focuses on work performed in collaboration between Biocompatibles UK Ltd (a BTG International group company) and the NIH to demonstrate radiopaque bead utility and bring a commercial offering to market that meets a clinical need. Various chemistries have been investigated and multiple prototypes evaluated in search of an optimized product with the right balance of handling and imaging properties. Herein, we describe the steps taken in the development of DC Bead LUMI™, the first commercially available radiopaque drug-eluting bead, ultimately leading to the first human experience of this novel embolic agent in the treatment of liver tumors.

Radiopaque nano and polymeric materials for atherosclerosis imaging, embolization and other catheterization procedures

A review of radiopaque nano and polymeric materials for atherosclerosis imaging and catheterization procedures is presented in this paper. Cardiovascular diseases (CVDs) are the leading cause of death in the US with atherosclerosis as a significant contributor for mortality and morbidity. In this review paper, we discussed the physics of radiopacity and X-ray/CT, clinically used contrast agents, and the recent progress in the development of radiopaque imaging agents and devices for the diagnosis and treatment of CVDs. We focused on radiopaque imaging agents for atherosclerosis, radiopaque embolic agents and drug eluting beads, and other radiopaque medical devices related to catheterization procedures to treat CVDs. Common strategies of introducing radiopacity in the polymers, together with examples of their applications in imaging and medical devices, are also presented.

Distribution and Detection of Radiopaque Beads after Hepatic Transarterial Embolization in Swine: Cone-Beam CT versus MicroCT

PURPOSE

To determine the true distribution of radiopaque beads (ROBs) after hepatic embolization in swine as imaged by micro-computed tomography (microCT) compared with in vivo cone-beam computerized tomography (CT) imaged at different kVp settings.

MATERIALS AND METHODS

Swine (n = 3) underwent hepatic transarterial embolization (n = 6) with the use of 70-150-μm ROBs under fluoroscopic guidance. After stasis, in vivo cone-beam CT was performed at 120, 100, and 80 kVp. The animal was euthanized, the liver resected, and microCT with 17 μm resolution performed on embolized tissue samples. The resulting cone-beam CT and microCT data were segmented and registered. Total vessel length, minimum volume-enclosing ellipsoid (MVEE), and number of independent volumes were measured. Maximum-intensity projections (MIPs) were generated for each cone-beam CT.

RESULTS

Metrics for all cone-beam CT segmentations differed significantly from microCT segmentations. Segmentations at 80 kVp presented significantly greater vessel length, MVEE, and number of independent volumes compared with 100 kVp and 120 kVp. In addition, 100 kVp segmentations presented significantly greater vessel length than 120 kVp. MIPs presented greater visualization than cone-beam CT segmentations and improved as kVp decreased.

CONCLUSIONS

The full ROB distribution was more extensive than was apparent on cone-beam CT. Quantitative measures of embolic distribution demonstrated significantly better correlation with microCT with decreasing kVp. Similarly, qualitative analysis of MIPs showed improved visualization of beads with decreasing kVp. These findings demonstrate the clinical value of 80 kVp and 100 kVp protocols in the imaging of radiopaque embolizations compared with 120 kVp. However, considerations on X-ray penetration and dose may favor use of 100 kVp imaging over 80 kVp.

Fabrication of inherently radiopaque BaSO4@BaAlg microspheres by a one-step electrospraying method for embolization

Inherently radiopaque BaSO₄@BaAlg microspheres were fabricated by a one-step electrospraying method for embolization and noninvasive examination after operations.

Transarterial chemoembolization with DC Bead LUMI™ radiopaque beads for primary liver cancer treatment: preliminary experience

Aim: Primary objectives of the study were to assess the safety of transarterial chemoembolization (TACE) using DC Bead LUMI™ for the treatment of hepatocellular carcinoma and beads distribution after TACE. Patients/methods: This was a prospective observational cohort study. The study included 44 hepatocellular carcinoma patients who were treated with TACE using DC Bead LUMI. Beads distribution was monitored 1 h after TACE by CT scan. Results: TACE had no intraprocedural complications. Observed side effects were of mild intensity and included pain in 5 (11%), fever in 4 (9%) and vomiting in 2 (5%) patients. Most patients (89%) reported no adverse event. Non-target distribution was observed in only two cases (5%). Conclusion: DC Bead LUMI allowed assessing in real time their distribution. This could prevent non-target infusion and reduce toxicity.

Review of the Development of Methods for Characterization of Microspheres for Use in Embolotherapy: Translating Bench to Cathlab

Therapeutic embolotherapy is the deliberate occlusion of a blood vessel within the body, which can be for the prevention of internal bleeding, stemming of flow through an arteriovenous malformation, or occlusion of blood vessels feeding a tumor. This is achieved using a wide selection of embolic devices such as balloons, coils, gels, glues, and particles. Particulate embolization is often favored for blocking smaller vessels, particularly within hypervascularized tumors, as they are available in calibrated sizes and can be delivered distally via microcatheters for precise occlusion with associated locoregional drug delivery. Embolic performance has been traditionally evaluated using animal models, but with increasing interest in the 3R's (replacement, reduction, refinement), manufacturers, regulators, and clinicians have shown interest in the development of more sophisticated in vitro methods for evaluation and prediction of in vivo performance. Herein the current progress in developing bespoke techniques incorporating physical handling, fluid dynamics, occlusive behavior, and sustained drug elution kinetics within vascular systems is reviewed. While it is necessary to continue to validate the safety of such devices in vivo, great strides have been made in the development of bench tests that better predict the behavior of these products aligned with the principles of the 3R's.

Characterization of a novel intrinsically radiopaque Drug-eluting Bead for image-guided therapy: DC Bead LUMI™

We have developed a straightforward and efficient method of introducing radiopacity into Polyvinyl alcohol (PVA)-2-Acrylamido-2-methylpropane sulfonic acid (AMPS) hydrogel beads (DC Bead™) that are currently used in the clinic to treat liver malignancies. Coupling of 2,3,5-triiodobenzaldehyde to the PVA backbone of pre-formed beads yields a uniformly distributed level of iodine attached throughout the bead structure (~150mg/mL) which is sufficient to be imaged under standard fluoroscopy and computed tomography (CT) imaging modalities used in treatment procedures (DC Bead LUMI™). Despite the chemical modification increasing the density of the beads to ~1.3g/cm³ and the compressive modulus by two orders of magnitude, they remain easily suspended, handled and administered through standard microcatheters. As the core chemistry of DC Bead LUMI™ is the same as DC Bead™, it interacts with drugs using ion-exchange between sulfonic acid groups on the polymer and the positively charged amine groups of the drugs. Both doxorubicin (Dox) and irinotecan (Iri) elution kinetics for all bead sizes evaluated were within the parameters already investigated within the clinic for DC Bead™. Drug loading did not affect the radiopacity and there was a direct relationship between bead attenuation and Dox concentration. The ability (Dox)-loaded DC Bead LUMI™ to be visualized in vivo was demonstrated by the administration of into hepatic arteries of a VX2 tumor-bearing rabbit under fluoroscopy, followed by subsequent CT imaging.

Nanocomposite Carriers for Transarterial Chemoembolization of Liver Cancer

The efficacy of conventional transarterial chemoembolization (TACE) approaches in liver cancer treatment is limited by the lack of effective drug carriers and/or the inability to monitor drug delivery to the targeted tumor tissues. Recent years have seen rapid advances in drug carriers for TACE. Bioabsorbable and MRI- or CT-visible microspheres that are trackable in vivo have been developed as a form of nanocomposite. Herein, we review notable progress in nanocomposite microspheres drug carriers available for TACE.

Polymeric materials for embolic and chemoembolic applications

Percutaneous transcatheter embolization procedures involve the selective occlusion of blood vessels. Occlusive agents, referred to as embolics, vary in material characteristics including chemical composition, mechanical properties, and the ability to concurrently deliver drugs. Commercially available polymeric embolics range from gelatin foam to synthetic polymers such as poly(vinyl alcohol). Current systems under investigation include tunable, bioresorbable microspheres composed of chitosan or poly(ethylene glycol) derivatives, in situ gelling liquid embolics with improved safety profiles, and radiopaque embolics that are trackable in vivo. This article reviews commercially available materials used for embolization as well as polymeric materials that are under investigation.

Multimodal Imaging of Nanocomposite Microspheres for Transcatheter Intra-Arterial Drug Delivery to Liver Tumors

A modern multi-functional drug carrier is critically needed to improve the efficacy of image-guided catheter-directed approaches for the treatment of hepatic malignancies. For this purpose, a nanocomposite microsphere platform was developed for selective intra-arterial transcatheter drug delivery to liver tumors. In our study, continuous microfluidic methods were used to fabricate drug-loaded multimodal MRI/CT visible microspheres that included both gold nanorods and magnetic clusters. The resulting hydrophilic, deformable, and non-aggregated microspheres were mono-disperse and roughly 25 um in size. Sustained drug release and strong MRI T₂ and CT contrast effects were achieved with the embedded magnetic nano-clusters and radiopaque gold nanorods. The microspheres were successfully infused through catheters selectively placed within the hepatic artery in rodent models and subsequent distribution in the targeted liver tissues and hepatic tumors confirmed with MRI and CT imaging. These multimodal nanocomposite drug carriers should be ideal for selective intra-arterial catheter-directed administration to liver tumors while permitting MRI/CT visualization for patient-specific confirmation of tumor-targeted delivery.

Long-term biocompatibility, imaging appearance and tissue effects associated with delivery of a novel radiopaque embolization bead for image-guided therapy

The objective of this study was to undertake a comprehensive long-term biocompatibility and imaging assessment of a new intrinsically radiopaque bead (LC Bead LUMI™) for use in transarterial embolization. The sterilized device and its extracts were subjected to the raft of ISO10993 biocompatibility tests that demonstrated safety with respect to cytotoxicity, mutagenicity, blood contact, irritation, sensitization, systemic toxicity and tissue reaction. Intra-arterial administration was performed in a swine model of hepatic arterial embolization in which 0.22-1 mL of sedimented bead volume was administered to the targeted lobe(s) of the liver. The beads could be visualized during the embolization procedure with fluoroscopy, DSA and single X-ray snapshot imaging modalities. CT imaging was performed before and 1 h after embolization and then again at 7, 14, 30 and 90 days. LC Bead LUMI™ could be clearly visualized in the hepatic arteries with or without administration of IV contrast and appeared more dense than soluble contrast agent. The CT density of the beads did not deteriorate during the 90 day evaluation period. The beads embolized predictably and effectively, resulting in areas devoid of contrast enhancement on CT imaging suggesting ischaemia-induced necrosis nearby the sites of occlusion. Instances of off target embolization were easily detected on imaging and confirmed pathologically. Histopathology revealed a classic foreign body response at 14 days, which resolved over time leading to fibrosis and eventual integration of the beads into the tissue, demonstrating excellent long-term tissue compatibility.

First Human Experience with Directly Image-able Iodinated Embolization Microbeads

PURPOSE

To describe first clinical experience with a directly image-able, inherently radio-opaque microspherical embolic agent for transarterial embolization of liver tumors.

METHODOLOGY

LC Bead LUMI™ is a new product based upon sulfonate-modified polyvinyl alcohol hydrogel microbeads with covalently bound iodine (~260 mg I/ml). 70-150 μ LC Bead LUMI™ iodinated microbeads were injected selectively via a 2.8 Fr microcatheter to near complete flow stasis into hepatic arteries in three patients with hepatocellular carcinoma, carcinoid, or neuroendocrine tumor. A custom imaging platform tuned for LC LUMI™ microbead conspicuity using a cone beam CT (CBCT)/angiographic C-arm system (Allura Clarity FD20, Philips) was used along with CBCT embolization treatment planning software (EmboGuide, Philips).

RESULTS

LC Bead LUMI™ image-able microbeads were easily delivered and monitored during the procedure using fluoroscopy, single-shot radiography (SSD), digital subtraction angiography (DSA), dual-phase enhanced and unenhanced CBCT, and unenhanced conventional CT obtained 48 h after the procedure. Intra-procedural imaging demonstrated tumor at risk for potential under-treatment, defined as paucity of image-able microbeads within a portion of the tumor which was confirmed at 48 h CT imaging. Fusion of pre- and post-embolization CBCT identified vessels without beads that corresponded to enhancing tumor tissue in the same location on follow-up imaging (48 h post).

CONCLUSION

LC Bead LUMI™ image-able microbeads provide real-time feedback and geographic localization of treatment in real time during treatment. The distribution and density of image-able beads within a tumor need further evaluation as an additional endpoint for embolization.

Developing an in situ forming polyphosphate coacervate as a new liquid embolic agent: From experimental design to pilot animal study

A radiopaque temporary liquid embolic agent was synthesized from polyphosphate (PP) coacervates and optimized using a design of experiments approach. Variables studied were: strontium substitution (0-15 mol%), barium substitution (0-15 mol%), PP concentration and degree of polymerization of the polyphosphate (Dp). The viscosity, radiopacity and cell viability of the resulting coacervates were measured for 60 formulations and response surface modeling was used to determine the optimum coacervate that maximized radiopacity and cell viability. The optimum coacervate made from PP with a large Dp (9.5 g NaPP/100mL, 2.2 mol% Sr, 9 mol% Ba and 3.8 mol% Ca) was taken forward to a pilot animal trial. In this rabbit model, PP embolic agent successfully occluded the central auricular artery with promising biocompatibility. Further study is required to optimize the cohesiveness and clinical effectiveness of PP as an in situ setting temporary embolic agent.

STATEMENT OF SIGNIFICANCE

This article describes the development of a new radiopaque temporary liquid embolic agent from the optimization using design of experiments to a pilot animal study. Embolization is a minimally invasive interventional radiology procedure used to block blood flow in a targeted blood vessel. This procedure is used to treat many conditions including: tumors, aneurysms and arteriovenous malformations. Currently, no inherent radiopaque embolic agents are available in the clinic, which would allow for direct imaging of the material during the procedure and follow up treatment.

Practical Tantalum Coating of Microspheres for Experimental Visualization under Fluoroscopy and CT

The present report describes a simple technique for tantalum coating of microspheres for visualization by fluoroscopy and computed tomography (CT). Spherical microspheres were soaked with Ta powder under different conditions and microscopically evaluated for Ta-coating quality by assessing bound and unbound Ta. For 100-300-µm Embosphere particles, soaking with 0.05 mL Ta powder for 30 minutes and centrifugation at 500 rpm produced optimal coating. Optimized microspheres were injected in swine renal arteries and assessed by fluoroscopy and micro-CT for the opacification of segmental, arcuate, and interlobular arteries. This practical method can be used for experimental studies with commonly available microspheres.

A Novel Inherently Radiopaque Bead for Transarterial Embolization to Treat Liver Cancer - A Pre-clinical Study

Purpose: Embolotherapy using microshperes is currently performed with soluble contrast to aid in visualization. However, administered payload visibility dimishes soon after delivery due to soluble contrast washout, leaving the radiolucent bead's location unknown. The objective of our study was to characterize inherently radiopaque beads (RO Beads) in terms of physicomechanical properties, deliverability and imaging visibility in a rabbit VX2 liver tumor model.

Materials and Methods: RO Beads, which are based on LC Bead® platform, were compared to LC Bead. Bead size (light microscopy), equilibrium water content (EWC), density, X-ray attenuation and iodine distribution (micro-CT), suspension (settling times), deliverability and in vitro penetration were investigated. Fifteen rabbits were embolized with either LC Bead or RO Beads + soluble contrast (iodixanol-320), or RO Beads+dextrose. Appearance was evaluated with fluoroscopy, X-ray single shot, cone-beam CT (CBCT).

Results: Both bead types had a similar size distribution. RO Beads had lower EWC (60-72%) and higher density (1.21-1.36 g/cc) with a homogeneous iodine distribution within the bead's interior. RO Beads suspension time was shorter than LC Bead, with durable suspension (>5 min) in 100% iodixanol. RO Beads ≤300 µm were deliverable through a 2.3-Fr microcatheter. Both bead types showed similar penetration. Soluble contrast could identify target and non-target embolization on fluoroscopy during administration. However, the imaging appearance vanished quickly for LC Bead as contrast washed-out. RO Beads+contrast significantly increased visibility on X-ray single shot compared to LC Bead+contrast in target and non-target arteries (P=0.0043). Similarly, RO beads demonstrated better visibility on CBCT in target arteries (P=0.0238) with a trend in non-target arteries (P=0.0519). RO Beads+dextrose were not sufficiently visible to monitor embolization using fluoroscopy.

Conclusion: RO Beads provide better conspicuity to determine target and non-target embolization compared to LC Bead which may improve intra-procedural monitoring and post-procedural evaluation of transarterial embolization.

DC BeadM1™: towards an optimal transcatheter hepatic tumour therapy

Clinical use of DC Bead™ loaded with doxorubicin (DEBDOX™) or irinotecan (DEBIRI™), for the treatment of primary and secondary tumours of the liver respectively, is showing great promise. Recently there has been a tendency to select smaller bead size ranges to treat tumours in an effort to allow more drug dose to be administered, improve tumoural penetration and resultant drug delivery and tumour coverage. Herein we describe the development and performance characterisation of a new DC Bead size range (DC BeadM1 (TM), 70-150 μm) capable of an increased bead delivery in the distal vasculature, corresponding to greater tumour coverage and drug dose delivered. Both unloaded and drug loaded DC BeadM1 were shown to have a greater density of distal volume of penetration although the ultimate distal level of penetration was the same as that of the 100-300 µm beads in an in vitro penetration model. Elution of doxorubicin was slower than irinotecan elution, but it was similar when comparing the same drug elution from 70 to 150 µm compared to 100-300 µm beads. Radiopaque versions of 70-150 and 100-300 µm beads were prepared in order to evaluate distribution ex vivo using µ-CT and doxorubicin distribution using epifluorescent microscopy. Liver distribution of the radiopaque versions of the beads was shown to be more distal and efficient at filling smaller vessels with the DC BeadM1 and correspondingly more beads were found per vessel histologically with a larger area of drug coverage with the smaller size range. This study indicates that the smaller (70-150 μm) beads should permit an increased dose of drug to be administered to both hypervascular and hypovascular tumours as compared to 100-300 µm beads.

Multimodality Imaging of Ethiodized Oil-loaded Radiopaque Microspheres during Transarterial Embolization of Rabbits with VX2 Liver Tumors

Purpose To assess the visibility of radiopaque microspheres during transarterial embolization (TAE) in the VX2 rabbit liver tumor model by using multimodality imaging, including single-snapshot radiography, cone-beam computed tomography (CT), multidetector CT, and micro-CT. Materials and Methods The study was approved by the institutional animal care and use committee. Fifteen VX2-tumor-bearing rabbits were assigned to three groups depending on the type of embolic agent injected: 70-150-μm radiopaque microspheres in saline (radiopaque microsphere group), 70-150-μm radiopaque microspheres in contrast material (radiopaque microsphere plus contrast material group), and 70-150-μm radiolucent microspheres in contrast material (nonradiopaque microsphere plus contrast material group). Rabbits were imaged with single-snapshot radiography, cone-beam CT, and multidetector CT. Three to 5 weeks after sacrifice, excised livers were imaged with micro-CT and histologic analysis was performed. The visibility of the embolic agent was assessed with all modalities before and after embolization by using a qualitative three-point scale score reading study and a quantitative assessment of the signal-to-noise ratio (SNR) change in various regions of interest, including the tumor and its feeding arteries. The Kruskal-Wallis test was used to compare the rabbit characteristics across groups, and the Wilcoxon signed rank test was used to compare SNR measurements before and after embolization. Results Radiopaque microspheres were qualitatively visualized within tumor feeding arteries and targeted tissue with all imaging modalities (P < .05), and their presence was confirmed with histologic examination. SNRs of radiopaque microsphere deposition increased after TAE on multidetector CT, cone-beam CT, and micro-CT images (P < .05). Similar results were obtained when contrast material was added to radiopaque microspheres, except for additional image attenuation due to tumor enhancement. For the group with nonradiopaque microspheres and contrast material, retained tumoral contrast remained qualitatively visible with all modalities except for micro-CT, which demonstrated soluble contrast material washout over time. Conclusion Radiopaque microspheres were visible with all imaging modalities and helped increase conspicuity of the tumor as well as its feeding arteries after TAE in a rabbit VX2 liver tumor model. (©) RSNA, 2015.

Stimulation of apoptotic pathways in liver cancer cells: An alternative perspective on the biocompatibility and the utility of biomedical glasses

A host of research opportunities with innumerable clinical applications are open to biomedical glasses if one considers their potential as therapeutic inorganic ion delivery systems. Generally, applications have been limited to repair and regeneration of hard tissues while compositions are largely constrained to the original bioactive glass developed in the 1960s. However, in oncology applications the therapeutic paradigm shifts from repair to targeted destruction. With this in mind, the composition–structure–property–function relationships of vanadium-containing zinc-silicate glasses (0.51SiO2–0.29Na2O–(0.20- X)ZnO– XV2O5, 0 ≤  X ≤ 0.09) were characterized in order to determine their potential as therapeutic inorganic ion delivery systems. Increased V2O5 mole fraction resulted in a linear decrease in density and glass transition temperature (Tg). 29Si MAS NMR peak maxima shifted upfield while 51V MAS NMR peak maxima were independent of V2O5 content and overlapped well with the spectra NaVO3. Increased V2O5 mole fraction caused ion release to increase. When human liver cancer cells, HepG2, were exposed to these ions they demonstrated a concentration-dependent cytotoxic response, mediated by apoptosis. This work demonstrates that the zinc-silicate system studied herein is capable of delivering therapeutic inorganic ions at concentrations that induce apoptotic cell death and provide a simple means to control therapeutic inorganic ion delivery.

Preparation of Radiopaque Drug-Eluting Beads for Transcatheter Chemoembolization

PURPOSE

To develop a simple method to produce radiopaque drug-eluting microspheres (drug-eluting beads [DEBs]) that could be incorporated into the current clinical transcatheter arterial chemoembolization workflow and evaluate their performance in vitro and in vivo.

MATERIALS AND METHODS

An ethiodized oil (Lipiodol; Guerbet, Villepinte, France) and ethanol solution was added to a lyophilized 100-300 µm bead before loading with doxorubicin. These radiopaque drug-eluting beads (DEBs; Biocompatibles UK Ltd, Farnham, United Kingdom) were evaluated in vitro for x-ray attenuation, composition, size, drug loading and elution, and correlation between attenuation and doxorubicin concentration. In vivo conspicuity was evaluated in a VX2 tumor model.

RESULTS

Lipiodol was loaded into lyophilized beads using two glass syringes and a three-way stopcock. Maximum bead attenuation was achieved within 30 minutes. X-ray attenuation of radiopaque beads increased linearly (21-867 HU) with the amount of beads (0.4-12.5 vol%; R(2) = 0.9989). Doxorubicin loading efficiency and total amount eluted were similar to DC Bead (Biocompatibles UK Ltd); however, the elution rate was slower for radiopaque DEBs (P < .05). Doxorubicin concentration linearly correlated with x-ray attenuation of radiopaque DEBs (R(2) = 0. 99). Radiopaque DEBs were seen in tumor feeding arteries after administration by fluoroscopy, computed tomography, and micro-computed tomography, and their location was confirmed by histology.

CONCLUSIONS

A simple, rapid method to produce radiopaque DEBs was developed. These radiopaque DEBs provided sufficient conspicuity to be visualized with x-ray imaging techniques.

Synthesis and characterization of image-able polyvinyl alcohol microspheres for image-guided chemoembolization

Therapeutic embolization of blood vessels is a minimally invasive, catheter-based procedure performed with solid or liquid emboli to treat bleeding, vascular malformations, and vascular tumors. Hepatocellular carcinoma (HCC) affects about half a million people per year. When unresectable, HCC is treated with embolization and local drug therapy by transarterial chemoembolization (TACE). For TACE, drug eluting beads (DC Bead(®)) may be used to occlude or reduce arterial blood supply and deliver chemotherapeutics locally to the tumor. Although this treatment has been shown to be safe and to improve patient survival, the procedure lacks imaging feedback regarding the location of embolic agent and drug coverage. To address this shortcoming, herein we report the synthesis and characterization of image-able drug eluting beads (iBeads) from the commercial DC Bead(®) product. Two different radiopaque beads were synthesized. In one approach, embolic beads were conjugated with 2,3,5-triiodobenzyl alcohol in the presence of 1,1'-carbonyldiimidazol to give iBead I. iBead II was synthesized with a similar approach but instead using a trimethylenediamine spacer and 2,3,5-triiodobenzoic acid. Doxorubicin was loaded into the iBeads II using a previously reported method. Size and shape of iBeads were evaluated using an upright microscope and their conspicuity assessed using a clinical CT and micro-CT. Bland and Dox-loaded iBeads II visualized with both clinical CT and microCT. Under microCT, individual bland and Dox loaded beads had a mean attenuation of 7904 ± 804 and 11,873.96 ± 706.12 HU, respectively. These iBeads have the potential to enhance image-guided TACE procedures by providing localization of embolic-particle and drug.

Preparation and evaluation of biocompatible long-term radiopaque microspheres based on polyvinyl alcohol and lipiodol for embolization

The aim of this work was to develop long-term radiopaque microspheres (LRMs) by entrapping lipiodol in biocompatible polyvinyl alcohol with multiple emulsions chemical crosslinking method. The high content of lipiodol (0.366 g/mL) was hardly released from LRMs in vitro and the radiopacity could maintain at least 3 months after subcutaneous injection in mice without weakening. A series of tests was performed to evaluate the feasibility of LRMs for embolization. LRMs were proved to be smooth, spherical, and well dispersed with diameter range of 100–1200 μm. Young's modulus of LRMs was 55.39 ± 9.10 kPa and LRMs could be easily delivered through catheter without aggregating or clogging. No toxicity of LRMs was found to mouse L929 fibroblasts cells and only moderate inflammatory in surrounding tissue of mice was found after subcutaneous injection of LRMs. After LRMs were embolized in renal artery of a rabbit, the distribution and radiopacity of LRMs in vivo were easily detectable by X-ray fluoroscopy and computed tomography (CT) imaging, respectively. More accurate distribution of LRMs in embolized kidney and vessels could be detected by high-revolution visualization of micro-CT ex vivo. In conclusion, the LRMs were proved to be biocompatible and provide long-term radiopacity with good physical and mechanical properties for embolization.

Composition-property relationships for radiopaque composite materials: pre-loaded drug-eluting beads for transarterial chemoembolization

The purpose of this study was to synthesize and optimize intrinsically radiopaque composite embolic microspheres for sustained release of doxorubicin in drug-eluting bead transarterial chemoembolization. Using a design of experiments approach, 12 radiopaque composites composed of polylactic-co-glycolic acid and a radiopaque glass (ORP5) were screened over a range of compositions and examined for radiopacity (computed tomography) and density. In vitro cell viability was determined using an extract assay derived from each composition against the human hepatocellular carcinoma cell line, HepG2. Mathematical models based on a D-Optimal response surface methodology were used to determine the preferred radiopaque composite. The resulting radiopaque composite was validated and subsequently loaded with doxorubicin between 0 and 1.4% (wt% of polylactic-co-glycolic acid) to yield radiopaque composite drug-eluting beads. Thereafter, the radiopaque composite drug-eluting beads were subjected to an elution study (up to 168 h) to determine doxorubicin release profiles (UV-Vis spectroscopy) and in vitro cell viability. Radiopaque composites evaluated for screening purposes had densities between 1.28 and 1.67 g.cm(-3), radiopacity ranged between 211 and 1450HU and cell viabilities between 91 and 106% were observed. The optimized radiopaque composite comprised 23 wt% polylactic-co-glycolic acid and 60 wt% ORP5 with a corresponding density of 1.63 ± 0.001 g.cm(-3), radiopacity at 1930 ± 44HU and cell viability of 89 ± 7.6%. Radiopaque composite drug-eluting beads provided sustained doxorubicin release over 168 h. In conclusion, the mathematical models allowed for the identification and synthesis of a unique radiopaque composite. The optimized radiopaque composite had similar density and cell viability to commercially available embolic microspheres. It was possible to preload doxorubicin into radiopaque composite drug-eluting beads, such that sustained release was possible under simulated physiological conditions.

"Imageable" Zinc-Silicate Glass Microspheres For Transarterial Embolization: A Renal Artery Embolization Study

Intrinsically radiopaque (imageable) microspheres for transarterial embolization (TAE) are required to enable real-time intraprocedural feedback and definition of spatial distribution patterns of embolic materials in target tissues. This pilot study evaluates acute and sub-chronic safety and efficacy of imageable zinc-silicate (Zn-Si) glass microspheres in a swine renal artery embolization (RAE) model. Eight swine were divided into two cohorts. Clinical determinants of embolization effectiveness, including imageability, deliverability and temporal/ spatial distribution of microspheres in target tissues were assessed. Subsequently, cohort I and II were used to evaluate the acute and subchronic host response against the Zn-Si microspheres versus a clinical control. The developed microspheres provide for direct intraprocedural feedback using standard diagnostic imaging techniques. Fluoroscopy correlated with ex-vivo high-resolution radiography, CT and micro-CT, demonstrating high imageability, excellent spatial distribution and packing of the Zn- Si microspheres. At follow-up, infarction of the embolized kidneys was noted without any major adverse tissue reaction. Mild recanalization was observed microscopically for both experimental and control microspheres. Zn-Si microspheres permit the definition of spatial distribution in a target tissue, consequently permitting the optimization, personalization and improvement of TAE techniques.

Nanoparticles for imaging: top or flop?

Nanoparticles are frequently suggested as diagnostic agents. However, except for iron oxide nanoparticles, diagnostic nanoparticles have been barely incorporated into clinical use so far. This is predominantly due to difficulties in achieving acceptable pharmacokinetic properties and reproducible particle uniformity as well as to concerns about toxicity, biodegradation, and elimination. Reasonable indications for the clinical utilization of nanoparticles should consider their biologic behavior. For example, many nanoparticles are taken up by macrophages and accumulate in macrophage-rich tissues. Thus, they can be used to provide contrast in liver, spleen, lymph nodes, and inflammatory lesions (eg, atherosclerotic plaques). Furthermore, cells can be efficiently labeled with nanoparticles, enabling the localization of implanted (stem) cells and tissue-engineered grafts as well as in vivo migration studies of cells. The potential of using nanoparticles for molecular imaging is compromised because their pharmacokinetic properties are difficult to control. Ideal targets for nanoparticles are localized on the endothelial luminal surface, whereas targeted nanoparticle delivery to extravascular structures is often limited and difficult to separate from an underlying enhanced permeability and retention (EPR) effect. The majority of clinically used nanoparticle-based drug delivery systems are based on the EPR effect, and, for their more personalized use, imaging markers can be incorporated to monitor biodistribution, target site accumulation, drug release, and treatment efficacy. In conclusion, although nanoparticles are not always the right choice for molecular imaging (because smaller or larger molecules might provide more specific information), there are other diagnostic and theranostic applications for which nanoparticles hold substantial clinical potential.

A case-based approach to common embolization agents used in vascular interventional radiology

OBJECTIVE

The objective of this article is to familiarize the reader with the most commonly used embolic agents in interventional radiology and discuss an approach for selecting among the different embolic agents. This article reviews their properties and uses a case-based approach to explain how to select one.

CONCLUSION

A wide variety of embolic agents are available. Familiarity with the available embolic agents and selection of the most appropriate embolic agent is critical in interventional radiology to achieve optimum therapeutic response and avoid undesired, potentially disastrous complications such as nontarget embolization.