Liver tumors: monitoring embolization in rabbits with VX2 tumors--transcatheter intraarterial first-pass perfusion MR imaging

Experimental VX2 Rabbit Liver Tumor Model in Carbon Tetrachloride-Induced Cirrhosis of the Liver

Liver cirrhosis is a major underlying factor in the development of hepatocellular carcinoma. Currently, there is an unmet need for midsize experimental vertebrate models that would offer reproducible implantable liver tumors in a cirrhotic liver background. This study establishes a protocol for a syngeneic rabbit model of VX2 liver cancer with underlying liver cirrhosis induced using carbon tetrachloride (CCl4). Male New Zealand white rabbits (n = 3) received CCl4 by intragastric administration once weekly. Concentrations started at 5% v/v CCl4 dissolved in olive oil. CCl4 dosing was progressively increased every week by 2.5% v/v increments for the duration of treatment (16 weeks total). VX2 tumors were then orthotopically implanted into the left hepatic lobe and allowed to grow for 3 weeks. Cross-sectional imaging confirmed the presence of hepatic tumors. Gross and histopathological evaluations showed reproducible tumor growth in the presence of liver cirrhosis in all animals.

Animal Models of Hepatocellular Carcinoma for Local-Regional Intraarterial Therapies

Animal models play a crucial role in developing and testing new therapies for hepatocellular carcinoma (HCC), providing preclinical evidence prior to exploring human safety and efficacy outcomes. The interventional radiologist must weigh the advantages and disadvantages of various animal models available when testing a new local-regional therapy. This review highlights the currently available animal models for testing local-regional therapies for HCC and details the importance of considering animal genetics, tumor biology, and molecular mechanisms when ultimately choosing an animal model. Keywords: Animal Studies, Interventional-Vascular, Molecular Imaging-Clinical Translation, Molecular Imaging-Cancer, Chemoembolization, Liver © RSNA, 2022.

Evaluation of liver tumour response by imaging

The goal of assessing tumour response on imaging is to identify patients who are likely to benefit - or not - from anticancer treatment, especially in relation to survival. The World Health Organization was the first to develop assessment criteria. This early score, which assessed tumour burden by standardising lesion size measurements, laid the groundwork for many of the criteria that followed. This was then improved by the Response Evaluation Criteria in Solid Tumours (RECIST) which was quickly adopted by the oncology community. At the same time, many interventional oncology treatments were developed to target specific features of liver tumours that result in significant changes in tumours but have little effect on tumour size. New criteria focusing on the viable part of tumours were therefore designed to provide more appropriate feedback to guide patient management. Targeted therapy has resulted in a breakthrough that challenges conventional response criteria due to the non-linear relationship between response and tumour size, requiring the development of methods that emphasize the appearance of tumours. More recently, research into functional and quantitative imaging has created new opportunities in liver imaging. These results have suggested that certain parameters could serve as early predictors of response or could predict later tumour response at baseline. These approaches have now been extended by machine learning and deep learning. This clinical review focuses on the progress made in the evaluation of liver tumours on imaging, discussing the rationale for this approach, addressing challenges and controversies in the field, and suggesting possible future developments.

Quantitative MRI for Assessment of Treatment Outcomes in a Rabbit VX2 Hepatic Tumor Model

Globally, primary and secondary liver cancer is one of the most common cancer types, accounting 8.2% of deaths worldwide in 2018. One of the key strategies to improve the patient's prognosis is the early diagnosis, when liver function is still preserved. In hepatocellular carcinoma (HCC), the typical wash-in/wash-out pattern in conventional magnetic resonance imaging (MRI) reaches a sensitivity of 60% and specificity of 96-100%. However, in recent years functional MRI sequences such as hepatocellular-specific gadolinium-based dynamic-contrast enhanced MRI, diffusion-weighted imaging (DWI), and magnetic resonance spectroscopy (MRS) have been demonstrated to improve the evaluation of treatment success and thus the therapeutic decision-making and the patient's outcome. In the preclinical research setting, the VX2 liver rabbit tumor, which once originated from a virus-induced anaplastic squamous cell carcinoma, has played a longstanding role in experimental interventional oncology. Especially the high tumor vascularity allows assessing the treatment response of locoregional interventions such as radiofrequency ablation (RFA) and transcatheter arterial embolization (TACE). Functional MRI has been used to monitor the tumor growth and viability following interventional treatment. Besides promising results, a comprehensive overview of functional MRI sequences used so far in different treatment setting is lacking, thus lowering the comparability of study results. This review offers a comprehensive overview of study protocols, results, and limitations of quantitative MRI sequences applied to evaluate the treatment outcome of VX2 hepatic tumor models, thus generating a unique basis for future MRI studies and potential translation into the clinical setting. Level of Evidence: 2 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2019. J. Magn. Reson. Imaging 2020;52:668-685.

Radioembolization of Hepatocellular Carcinoma with Built-In Dosimetry: First in vivo Results with Uniformly-Sized, Biodegradable Microspheres Labeled with 188Re

A common form of treatment for patients with hepatocellular carcinoma (HCC) is transarterial radioembolization (TARE) with non-degradable glass or resin microspheres (MS) labeled with ⁹⁰Y (⁹⁰Y-MS). To further simplify the dosimetry calculations in the clinical setting, to have more control over the particle size and to change the permanent embolization to a temporary one, we developed uniformly-sized, biodegradable ¹⁸⁸Re-labeled MS (¹⁸⁸Re-MS) as a new and easily imageable TARE agent.

Methods: MS made of poly(L-lactic acid) were produced in a flow focusing microchip. The MS were labeled with ¹⁸⁸Re using a customized kit. An orthotopic HCC animal model was developed in male Sprague Dawley rats by injecting N1-S1 cells directly into the liver using ultrasound guidance. A suspension of ¹⁸⁸Re-MS was administered via hepatic intra-arterial catheterization 2 weeks post-inoculation of the N1-S1 cells. The rats were imaged by SPECT 1, 24, 48, and 72 h post-radioembolization.

Results: The spherical ¹⁸⁸Re-MS had a diameter of 41.8 ± 6.0 µm (CV = 14.5%). The site and the depth of the injection of N1-S1 cells were controlled by visualization of the liver in sonograms. Single 0.5 g tumors were grown in all rats. ¹⁸⁸Re-MS accumulated in the liver with no deposition in the lungs. ¹⁸⁸Re decays to stable ¹⁸⁸Os by emission of β^¯ particles with similar energy to those emitted by ⁹⁰Y while simultaneously emitting γ photons, which were imaged directly by single photon computed tomography (SPECT). Using Monte Carlo methods, the dose to the tumors was calculated to be 3-6 times larger than to the healthy liver tissue.

Conclusions:¹⁸⁸Re-MS have the potential to become the next generation of β^¯-emitting MS for TARE. Future work revolves around the investigation of the therapeutic potential of ¹⁸⁸Re-MS in a large-scale, long-term preclinical study as well as the evaluation of the clinical outcomes of using ¹⁸⁸Re-MS with different sizes, from 20 to 50 µm.

Liver Injury and Tumor-Inhibiting Effect of Sequential Transcatheter Arterial Chemoembolization and Portal Venous Embolization on Rabbit VX2 Liver Carcinoma

BACKGROUND The concepts of sequential transcatheter arterial chemoembolization (TACE) and portal venous embolization (PVE) were proposed to prevent the detrimental tumor growth-inducing effect of PVE and to facilitate growth of further future liver remnant (FLR). This study aimed to investigate the effect of sequential TACE and PVE on liver damage and the therapeutic effect in a rabbit VX2 liver tumor model. MATERIAL AND METHODS Rabbits bearing VX2 liver tumors were randomly divided into TACE+PVE, TACE, PVE, and Sham groups. Plasma levels of aspartate aminotransferase (AST), alanine aminotransferase (ALT), total bilirubin (TBIL), and alkaline phosphatase (ALP) at 6 h, 24 h, 3 days, and 7 days were measured by ELISA assay. Tumor diameter on day 7 was measured and the tumor sections with cleaved caspase-3 was stained and observed. RESULTS Plasma ALT, AST, and ALP levels were significantly increased at the first hours after the interventions. The TACE group had higher increases than the TACE+PVE and PVE alone groups. ALT, AST, and ALP levels decreased on day 7 and presented a trend to return to the baseline level. The TACE+PVE group showed stronger tumor-inhibiting effect than the TACE and PVE alone groups and also induced the highest level of tumor cell apoptosis. CONCLUSIONS The liver damage caused by TACE+PVE is mild and recoverable. TACE+PVE showed stronger tumor-inhibiting effect than in the TACE and PVE group and also induced the highest level of tumor cell apoptosis.

Radiological biomarkers for assessing response to locoregional therapies in hepatocellular carcinoma: From morphological to functional imaging (Review)

Many hepatocellular carcinoma (HCC) patients do not qualify for curative surgical intervention and are instead treated with locoregional therapies (LRTs) including ablative and endovascular therapies. Assessment of imaging response is essential in the management of HCC for determining efficacy of therapy and as a surrogate marker for improved survival. The established morphological image biomarkers for tumor burden measurement continue to be applied, as size measurement can easily be used in clinical practice. However, in the setting of liver-directed LRTs for HCC, simple tumor morphological changes can be less informative and usually appear later than biologic changes. Functional imaging (such as perfusion and diffusion imaging, PET-CT/MR and MR spectroscopy) has the potential to be a promising technique for assessment of HCC response to LRTs. Although promising, none of these functional imaging biomarkers have gone through all the required steps of standardization and validation and established accepted criteria for clinical practice.

Induction of VX2 para-renal carcinoma in rabbits: generation of animal model for loco-regional treatments of solid tumors

Background

Animal models of para-renal cancer can provide useful information for the evaluation of tumor response to loco-regional therapy experiments in solid tumors. The aim of our study was to establish a rabbit para-renal cancer model using locally implanted VX2 tumors.

Methods

In order to generate a rabbit model of para-renal cancer, we established four hind limb donor rabbits by using frozen VX2 tumor samples. Following inoculation, rabbits were monitored for appetite and signs of pain. Viable tumors appeared as palpable nodules within 2 weeks of inoculation. Tumor growth was confirmed in all rabbits by high-resolution ultrasound analysis and histology. Once tumor growth was established, hind limb tumors extraction was used for tumor line propagation and para-renal tumor creation. Twenty-one rabbit models bearing para-renal cancer were established by implanting VX2 tumor into the para-renal capsula. Tumors developed into discreet 2–3 cm nodules within 1–3 weeks of implantation. Serial renal ultrasonography follow-up, starting 1 week after tumor implantation, was performed. Two weeks after tumor implantation, rabbits were euthanized and tumors and other organs were collected for histopathology.

Results

Tumor growth after VX2 tumor fragment implantation was confirmed in all rabbits by high-resolution ultrasound (US) imaging examinations of the para-renal regions and was measured with digital caliper. The para-renal injection of VX2 tumor fragments, achieved tumor growth in 100% of cases. All data were confirmed by histological analysis.

Conclusions

We generated for the first time, a model of para-renal cancer by surgical tumor implantation of VX2 frozen tumor fragments into rabbit’s para-renal region. This method minimizes the development of metastases and the use of non-necrotic tumors and will optimize the evaluation of tumor response to loco-regional therapy experiments.

Functional imaging in liver tumours

Functional imaging encompasses techniques capable of assessing physiological parameters of tissues, and offers useful clinical information in addition to that obtained from morphological imaging. Such techniques may include magnetic resonance imaging with diffusion-weighted sequences or hepatobiliary contrast agents, perfusion imaging, or molecular imaging with radiolabelled tracers. The liver is of major importance in oncological practice; not only is hepatocellular carcinoma one of the malignancies with steadily rising incidence worldwide, but hepatic metastases are regularly observed with a range of solid neoplasms. Within the realm of hepatic oncology, different functional imaging modalities may occupy pivotal roles in lesion characterisation, treatment selection and follow-up, depending on tumour size and type. In this review, we characterise the major forms of functional imaging, discuss their current application to the management of patients with common primary and secondary liver tumours, and anticipate future developments within this field.

Radio-frequency ablation-based studies on VX2rabbit models for HCC treatment

Hepatocellular carcinoma (HCC) is the fifth most frequent cancer worldwide with high morbidity, mortality and increasing incidence. It is of note that the main curative therapies for HCC are hepatic resection and transplantation although the majority of patients at the time of presentation are not eligible for resection or orthotopic liver transplantation (OLT) due to the underlying cirrhosis. Currently, a variety of loco-regional therapies, including radiofrequency ablation (RFA), percutaneous ethanol injection (PEI), microwave coagulation therapy (MCT), transarterial chemoembolization (TACE) and others, have been developed as alternative treatment options for HCC. Among these techniques, RFA is currently the most widely used treatment, due to its several advantages, such as safety and efficacy. To date, the effectiveness of RFA for HCC is reduced by the presence of residual tumor as a consequence of insufficient treatment. In order to ameliorate the effects of RFA on HCC, several in vivo studies, have been performed on its application as single or in combination treatment with drugs or others loco-regional therapies, by using rabbit VX2 liver model. This represents an ideal model of liver cancers and is widely used for imaging and other experimental studies due to the rapid growth of these tumors and their similarity to human hepatocellular carcinoma. In order to elucidate the therapeutic potential of RFA with adjuvant treatments for HCC, we reviewed the latest findings on the RFA-based studies in rabbit VX2 hepatocarcinoma models.

Distribution of Iron Oxide Core-Titanium Dioxide Shell Nanoparticles in VX2 Tumor Bearing Rabbits Introduced by Two Different Delivery Modalities

This work compares intravenous (IV) versus fluoroscopy-guided transarterial intra-catheter (IC) delivery of iron oxide core-titanium dioxide shell nanoparticles (NPs) in vivo in VX2 model of liver cancer in rabbits. NPs coated with glucose and decorated with a peptide sequence from cortactin were administered to animals with developed VX2 liver cancer. Two hours after NPs delivery tumors, normal liver, kidney, lung and spleen tissues were harvested and used for a series on histological and elemental analysis tests. Quantification of NPs in tissues was done both by bulk inductively coupled plasma mass spectrometry (ICP-MS) analysis and by hard X-ray fluorescence microscopy. Both IV and IC NPs injection are feasible modalities for delivering NPs to VX2 liver tumors with comparable tumor accumulation. It is possible that this is an outcome of the fact that VX2 tumors are highly vascularized and hemorrhagic, and therefore enhanced permeability and retention (EPR) plays the most significant role in accumulation of nanoparticles in tumor tissue. It is, however, interesting to note that IV delivery led to increased sequestration of NPs by spleen and normal liver tissue, while IC delivery lead to more NP positive Kupffer cells. This difference is most likely a direct outcome of blood flow dynamics. Armed with this knowledge about nanoparticle delivery, we plan to test them as radiosensitizers in the future.

CT spectral imaging for monitoring the therapeutic efficacy of VEGF receptor kinase inhibitor AG-013736 in rabbit VX2 liver tumours

PURPOSE

The aim of this study was to evaluate the value of computed tomography (CT) spectral imaging in assessing the therapeutic efficacy of a vascular endothelial growth factor (VEGF) receptor inhibitor AG-013736 in rabbit VX2 liver tumours.

METHODS

Twenty-three VX2 liver tumour-bearing rabbits were scanned with CT in spectral imaging mode during the arterial phase (AP) and portal phase (PP). The iodine concentrations(ICs)of tumours normalized to aorta (nICs) at different time points (baseline, 2, 4, 7, 10, and 14 days after treatment) were compared within the treated group (n = 17) as well as between the control (n = 6) and treated groups. Correlations between the tumour size, necrotic fraction (NF), microvessel density (MVD), and nICs were analysed.

RESULTS

The change of nICs relative to baseline in the treated group was lower compared to the control group. A greater decrease in the nIC of a tumour at 2 days was positively correlated with a smaller increase in tumour size at 14 days (P < 0.05 for both). The tumour nIC values in AP and PP had correlations with MVD (r = 0.71 and 0.52) and NF (r = -0.54 and -0.51) (P < 0.05 for all).

CONCLUSIONS

CT spectral imaging allows for the evaluation and early prediction of tumour response to AG-013736.

KEY POINTS

• AG-013736 treatment response was evaluated by CT in a rabbit tumour model. • CT spectral imaging allows for the early treatment monitoring of targeted anti-tumour therapies. • Spectral CT findings correlated with vascular changes after anti-tumour therapies. • Spectral CT is a promising method for assessing clinical treatment response.

Quantitative assessment of angiographic perfusion reduction using color-coded digital subtraction angiography during transarterial chemoembolization

PURPOSE

The aim of this study was to develop a quantitative measurement of perfusion reduction using color-coded digital subtraction angiography (ccDSA) to monitor intra-procedural arterial stasis during TACE.

MATERIALS AND METHODS

A total number of 35 patients with hepatocellular carcinoma who had undergone TACE were enrolled into the study. Pre- and post-two-dimensional digital subtraction angiography scans were conducted with same protocol and post-processed with ccDSA prototype software. Time-contrast-intensity (CI[t]) curve was obtained by region-of-interest (ROI) measurement on the generated ccDSA image. Quantitative 2D perfusion parameters time to peak, area under the curve (AUC), maximum upslope, and contrast intensity peak (CI-Peak) derived from the ROI-based CI[t] curve for pre- and post-TACE were evaluated to assess the reduction of antegrade blood flow and tumor blush. Relationships between 2D perfusion parameters, subjective angiographic chemoembolization endpoint (SACE) scale, and clinical outcomes were analyzed.

RESULTS

Area normalized AUC and CI-Peak revealed significant reduction after the TACE (P < 0.0001). AUCnorm decreased from pre-procedure of 0.867 ± 0.242 to 0.421 ± 0.171 (P < 0.001) after completion of TACE. CI-Peaknorm was 0.739 ± 0.221 before TACE and 0.421 ± 0.174 (P < 0.001) after TACE. Tumor blood supply time slowed down obviously after embolization. A perfusion reduction either from AUCnorm or CI-Peaknorm ranging from 30% to 40% was associated with SACE level III and a reduction ranging from 60% to 70% was equivalent to SACE level IV. For intermediate reduction (SACE level III), better tumor response was found after TACE rather than a higher reduction (SACE level IV).

CONCLUSION

ccDSA application provides an objective approach to quantify the perfusion reduction and subjectively evaluate the arterial stasis of antegrade blood flow and tumor blush caused by TACE.

Biometabolic Distribution of 99mTc-3PRGD2 and Its Potential Value in Monitoring Chemotherapeutic Effects

Previous studies have reported that 99mTc-3PRGD2 is an excellent tumor imaging agent that showed a good correlation with integrin αvβ3, a main factor of tumor-induced angiogenesis. In this study, we investigated the biometabolic distribution characteristics of 99mTc-3PRGD2 with a continuous dynamic acquisition mode to explore the potential value of 99mTc-3PRGD2 in monitoring chemotherapeutic effects in VX2 tumor models. Eighteen rabbits with 27 implanted VX2 squamous cell tumors were randomly divided into a nontreated control group (NTG, n = 8; 12 tumors) and a treatment group (TG, n = 10; 15 tumors). 99mTc-3PRGD2 imaging was performed prior to cisplatin injection and repeated on days 0, 1, 7, and 14 postinjection. Continuous dynamic scanning up to 30 minutes; static imaging at 0.5 hours, 1 hour, and 3 hours; and single-photon emission computed tomography/computed tomography (SPECT/CT)-integrated imaging at 3 hours post-99mTc-3PRGD2 injection were performed. The peak time (time to reach peak in dynamic curve), tumor to normal (T/N) ratios, and their change rates relative to pretherapy were calculated. Autoradiography, hematoxylin-eosin (H&E) staining, and CD31 and integrin αv immunohistochemical staining were examined. VX2 tumors were clearly visualized at 3 hours post-99mTc-3PRGD2 injection. Tumors in the TG shrank significantly on day 7 after cisplatin administration (p < .05). The half-life (t1/2) of the radiotracer in heart, liver, and tumor in the NTG were 3.43 ± 0.94 minutes, 13.41 ± 9.17 minutes, and 70.83 ± 33.37 minutes, respectively. The peak time was delayed in the TG immediately and continuously after cisplatin administration compared to the peak time in the NTG. The T/N values and their change rates decreased significantly in the TG compared to the NTG after therapy (p < .05). The immunostained areas were significantly decreased in the TG (p < .05) compared to the NTG. 99mTc-3PRGD2 was an excellent imaging agent for demonstrating tumor angiogenesis. The peak time, T/N values, and their change rates were sensitive parameters to monitor early chemotherapeutic effects. Due to the specific target mechanism and the cost-effective value of 99mTc-3PRGD2, 99mTc-3PRGD2 SPECT imaging may have potential in detecting the therapeutic effects of anticancer therapy.

Development, growth, propagation, and angiographic utilization of the rabbit VX2 model of liver cancer: a pictorial primer and "how to" guide

The VX2 tumor is a leporine anaplastic squamous cell carcinoma characterized by rapid growth, hypervascularity, and facile propagation in the skeletal muscle. Since its introduction over 70 years ago, it has been used to model a variety of malignancies, and is commonly employed by interventional radiologists in preclinical investigations of hepatocellular carcinoma. However, despite the widespread and lasting popularity of the model, there are few technical resources detailing its use. Herein, we present a comprehensive pictorial outline of the technical methodology for development, growth, propagation, and angiographic utilization of the rabbit VX2 liver tumor model.

Rabbit hepatic arterial anatomy variations: implications on experimental design

BACKGROUND

The VX2 rabbit model of liver cancer is commonly used to evaluate the efficacy of locoregional anticancer therapy and knowledge of the hepatic arterial anatomy in the rabbit is important for catheter-directed experiments.

PURPOSE

To describe the normal anatomy and anatomic variations of the celiac axis and hepatic artery in the rabbit.

MATERIAL AND METHODS

Angiograms of 222 rabbits were retrospectively reviewed. The branching pattern of the celiac axis was classified and the diameters of the major branches were measured. Paired t-tests were used to compare the difference between the average sizes of arteries.

RESULTS

Variant celiac axis or hepatic artery anatomy was noted in 25.9% of angiograms, with the gastric branches arising from the proper hepatic artery in 23.3% of cases. The celiac axis could be successfully classified into one of five distinct branching patterns in 193 (86.9%) cases. The mean diameters of the right and left hepatic arteries were 0.67 mm (95% CI [0.64, 0.7]) and 1.25 mm (95% CI [1.19, 1.31]), respectively. The mean diameters of the medial and lateral branches of the left hepatic artery were 0.63 mm (95% CI [0.6, 0.67]) and 0.91 mm (95% CI [0.86, 0.96]), respectively. The right hepatic artery was significantly smaller than the left hepatic artery and the lateral branch of the left hepatic artery (all P values <0.0001).

CONCLUSION

Arterial variants in the rabbit are not uncommon. The proper hepatic artery often gives origin to gastric artery branches. To facilitate superselective intra-arterial intervention, the left lateral lobe of the liver should be targeted for tumor implantation because of the significant size difference between the right and left hepatic arteries.

Perfusion reduction at transcatheter intraarterial perfusion MR imaging: a promising intraprocedural biomarker to predict transplant-free survival during chemoembolization of hepatocellular carcinoma

PURPOSE

To investigate the predictive value of transcatheter intraarterial perfusion (TRIP) magnetic resonance (MR) imaging-measured tumor perfusion changes during transarterial chemoembolization on transplant-free survival (TFS) in patients with unresectable hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

This HIPAA-compliant prospective study was approved by the institutional review board. Written informed consent was obtained from all patients. Fifty-one consecutive adult patients with surgically unresectable single or multifocal measurable HCC and adequate laboratory parameters who underwent chemoembolization in a combined MR imaging-interventional radiology suite between February 2006 and June 2010 were studied. Tumor perfusion changes during chemoembolization were measured by using TRIP MR imaging with area under the time-signal intensity curve calculation. The end point of the study was TFS. The authors assessed the correlation between the percentage perfusion reduction in the tumor during chemoembolization and TFS by using univariate and multivariate analyses.

RESULTS

Fifty patients (mean age, 61 years; 39 men aged 42-87 years [mean age, 61 years] and 11 women aged 49-83 years [mean age, 62 years]) were eligible for the analysis. Patients with 35%-85% intraprocedural tumor area under the time-signal intensity curve reduction (n = 32) showed significantly improved median TFS compared with patients with an area under the time-signal intensity curve reduction outside this range (n = 18) (16.6 months [95% confidence interval: 11.2, 22.0 months] vs 9.3 months [95% confidence interval: 6.6, 12.0 months], respectively; P = .046; hazard ratio: 0.46; 95% confidence interval: 0.21, 1.00). The cumulative TFS rates in the 35%-85% and less than 35% or more than 85% perfusion reduction groups at 1, 2, and 5 years after chemoembolization were 66.4%, 42.2%, and 28.2% versus 33.8%, 16.9%, and 0%, respectively.

CONCLUSION

The study shows evidence of an association between intraprocedural tumor perfusion reduction during chemoembolization and TFS and suggests the utility of TRIP MR imaging- measured tumor perfusion reduction as an intraprocedural imaging biomarker during chemoembolization.

Novel functional magnetic resonance imaging biomarkers for assessing response to therapy in hepatocellular carcinoma

The established and adapted image biomarkers based on size for tumor burden measurement continue to be applied to hepatocellular carcinoma (HCC) as size measurement can easily be used in clinical practice. However, in the setting of novel targeted therapies and liver directed treatments, simple tumor anatomical changes can be less informative and usually appear later than biological changes. Functional magnetic resonance imaging (MRI) has a potential to be a promising technique for assessment of HCC response to therapy. In this review, we discuss various functional MRI biomarkers that play an increasingly important role in evaluation of HCC response after treatment.

Image-guided local delivery strategies enhance therapeutic nanoparticle uptake in solid tumors

Nanoparticles (NP) have emerged as a novel class of therapeutic agents that overcome many of the limitations of current cancer chemotherapeutics. However, a major challenge to many current NP platforms is unfavorable biodistribution, and limited tumor uptake, upon systemic delivery. Delivery, therefore, remains a critical barrier to widespread clinical adoption of NP therapeutics. To overcome these limitations, we have adapted the techniques of image-guided local drug delivery to develop nanoablation and nanoembolization. Nanoablation is a tumor ablative strategy that employs image-guided placement of electrodes into tumor tissue to electroporate tumor cells, resulting in a rapid influx of NPs that is not dependent on cellular uptake machinery or stage of the cell cycle. Nanoembolization involves the image-guided delivery of NPs and embolic agents directly into the blood supply of tumors. We describe the design and testing of our innovative local delivery strategies using doxorubicin-functionalized superparamagnetic iron oxide nanoparticles (DOX-SPIOs) in cell culture, and the N1S1 hepatoma and VX2 tumor models, imaged by high resolution 7T MRI. We demonstrate that local delivery techniques result in significantly increased intratumoral DOX-SPIO uptake, with limited off-target delivery in tumor-bearing animal models. The techniques described are versatile enough to be extended to any NP platform, targeting any solid organ malignancy that can be accessed via imaging guidance.

Electroporation-mediated transcatheter arterial chemoembolization in the rabbit VX2 liver tumor model

RATIONALE AND OBJECTIVES

Electropermeabilization involves the application of electrical pulses to increase cell membrane permeability. The purpose of our study was to demonstrate the potential to use electroporation-mediated transcatheter arterial chemoembolization (E-TACE) approaches to increase liver tumor drug uptake while using magnetic resonance imaging (MRI) for intraprocedural optimization of these procedures.

METHODS

Fourteen VX2 tumors were grown in the left hepatic lobes of 8 rabbits. Two tumors were grown in each of 6 rabbits (1 tumor serving as E-TACE-treated tumor and the other as nonelectroporated control), and solitary larger tumors were grown in 2 rabbits (half of the tumor treated with E-TACE, remaining half serving as control). Each rabbit was selectively catheterized under digital subtraction angiography guidance. Baseline MRI was performed to generate tumor contrast enhancement curves following catheter-directed infusion of gadopentetate dimeglumine to estimate the proper time delay between subsequent bolus infusion of cisplatin and application of electrical pulses (electrodes were used to deliver 8, 100-μs, 1300-V pulses at the selected delay interval postinfusion). Three hours after E-TACE, rabbits were euthanized, and tumors were sectioned for inductively coupled plasma mass spectroscopy measurements of platinum concentration (serving as reference standard of cisplatin uptake levels).

RESULTS

Inductively coupled plasma mass spectroscopy results demonstrated significantly increased cisplatin uptake in E-TACE-treated tumor tissues, increases of 6.0 ± 3.3-fold compared with transcatheter infusion alone (P = 0.017).

CONCLUSIONS

Our findings suggest that our E-TACE approach may significantly increase liver tumor drug uptake after targeted transcatheter infusion. MRI measurements permitted intraprocedural guidance during these catheter-directed E-TACE procedures.

Ethiodized oil uptake does not predict doxorubicin drug delivery after chemoembolization in VX2 liver tumors

PURPOSE

To investigate the accuracy of ethiodized oil as an imaging marker of chemotherapy drug delivery after liver tumor chemoembolization in an animal model of hepatocellular carcinoma.

MATERIALS AND METHODS

Eleven VX2 liver tumors (mean diameter, 1.9 cm ± 0.4) in six New Zealand White rabbits were treated with chemoembolization using ethiodized oil and doxorubicin emulsion, followed by immediate euthanasia. Postprocedure noncontrast computed tomography (CT) was used to evaluate intratumoral ethiodized oil distribution and calculate iodine content within four peripheral tumor quadrants and the tumor core at a central tumor slice (N = 55 total tumor sections). Liquid chromatography/tandem mass spectrometry (LC-MS/MS) was then used to directly measure doxorubicin concentration in the same tissue sections. Statistical correlation was performed between tissue iodine content and doxorubicin concentration by using linear regression.

RESULTS

Chemoembolization was successfully performed in all tumors via the left or proper hepatic artery. A mean of 0.9 mL ± 0.6 ethiodized oil and 1.8 mg ± 1.2 doxorubicin were injected. CT-calculated tissue iodine content averaged 335 mg/mL ± 218. Corresponding LC-MS/MS analysis yielded a mean doxorubicin concentration of 15.8 μg/mL ± 14.3 in each sample. Although iodine content (391 mg/mL vs 112 mg/mL; P = .000) and doxorubicin concentration (18.0 μg/mL vs 7.2 μg/mL; P = .023) were significantly greater along peripheral tumor sections compared with the tumor core, no significant predictable correlation was evident between these measures (R(2) = 0.0099).

CONCLUSIONS

Tissue ethiodized oil content is a poor quantitative predictor of local doxorubicin concentration after liver tumor chemoembolization. Future studies should aim to identify a better imaging marker for chemoembolization drug delivery.

Quantitative 4D transcatheter intraarterial perfusion MRI for standardizing angiographic chemoembolization endpoints

OBJECTIVE

The purpose of this study was to test the hypothesis that subjective angiographic endpoints during transarterial chemoembolization (TACE) of hepatocellular carcinoma are consistent and correlate with objective intraprocedural reductions in tumor perfusion determined with quantitative 4D transcatheter intraarterial perfusion MRI.

SUBJECTS AND METHODS

In this prospective study, 18 consecutively registered patients underwent TACE in a combined MRI-interventional radiology suite. Three board-certified interventional radiologists independently graded the angiographic endpoint of each procedure using a previously described subjective angiographic chemoembolization endpoint scale. A consensus endpoint rating was established for each patient. Patients underwent quantitative 4D transcatheter intraarterial perfusion MRI immediately before and after TACE, and mean whole tumor perfusion was calculated from the images. Consistency of subjective angiographic endpoint ratings between observers was evaluated with the intraclass correlation coefficient. The relation between the endpoint ratings and intraprocedural transcatheter intraarterial perfusion MRI changes was evaluated with the Spearman rank correlation coefficient.

RESULTS

The subjective angiographic chemoembolization endpoint rating scale showed very good consistency among all observers (intraclass correlation coefficient, 0.80). The consensus endpoint rating correlated significantly with both absolute (r = 0.54, p = 0.022) and percentage (r = 0.85, p < 0.001) reduction in intraprocedural perfusion.

CONCLUSION

The subjective angiographic chemoembolization endpoint rating scale shows very good consistency between raters and significantly correlates with objectively measured intraprocedural perfusion reductions during TACE. These results support the use of the scale as a standardized alternative method in quantitative 4D transcatheter intraarterial perfusion MRI to classify patients on the basis of embolic endpoints of TACE.

Four-dimensional transcatheter intraarterial perfusion MRI monitoring of radiofrequency ablation of rabbit VX2 liver tumors

PURPOSE

To investigate the hypothesis that four-dimensional (4D) transcatheter intraarterial perfusion (TRIP) magnetic resonance imaging (MRI) can quantify immediate perfusion changes after radiofrequency (RF) ablation in rabbit VX2 liver tumors.

MATERIALS AND METHODS

Nine New Zealand White rabbits were used to surgically implant VX2 liver tumors. During ultrasound-guided RF ablation, tumors received either a true or sham ablation. After selective catheterization of the left hepatic artery under x-ray fluoroscopy, we acquired pre- and post-RF ablation 4D TRIP MR images using 3 mL of 2.5% intraarterial gadopentetate dimeglumine. Two regions-of-interest were drawn upon each tumor to generate signal-intensity time curves. Area under the curve (AUC) was calculated to provide semiquantitative perfusion measurements that were compared using a paired t-test (α = 0.05). Ablated tissue was visually confirmed on pathology using Evans blue dye.

RESULTS

Mean AUC perfusion of VX2 tumors for the true ablation group decreased by 92.0% (95% confidence interval [CI]: 83.3%-100%), from 1913 (95% CI: 1557, 2269) before RF ablation to 76.6 (95% CI: 18.4, 134.8) after RF ablation (a.u., P < 0.001). Sham-ablated tumors demonstrated no significant perfusion changes.

CONCLUSION

4D TRIP MRI can quantify liver tumor perfusion reductions in VX2 rabbits after RF ablation. This MRI technique can potentially be used to improve tumor response assessment at the time of RF ablation.

Intraprocedural transcatheter intra-arterial perfusion MRI as a predictor of tumor response to chemoembolization for hepatocellular carcinoma

RATIONALE AND OBJECTIVES

To prospectively test the hypothesis that transcatheter intraarterial perfusion magnetic resonance imaging (TRIP-MRI) measured semiquantitative perfusion reductions during transcatheter arterial chemoembolization of hepatocellular carcinoma (HCC) are associated with tumor response.

MATERIALS AND METHODS

Twenty-eight patients (mean age 63 years; range 47-87 years) with 29 tumors underwent chemoembolization in a combined magnetic resonance interventional radiology suite. Intraprocedural tumor perfusion reductions during chemoembolization were monitored using TRIP-MRI. Pre- and postchemoembolization semiquantitative area under the time-signal enhancement curve (AUC) tumor perfusion was measured. Mean tumor perfusion pre- and postchemoembolization were compared using a paired t-test. Imaging follow-up was performed 1-3 months after chemoembolization. We studied the relationship between short-term tumor imaging response and intraprocedural perfusion reductions using univariate and multivariate analysis.

RESULTS

Intraprocedural AUC perfusion value decreased significantly after chemoembolization (342.1 vs. 158.6 arbitrary unit, P < .001). Twenty-six patients with 27 HCCs (n = 27) had follow-up imaging at mean 39 days postchemoembolization. Favorable response was present in 67% of these treated tumors according to necrosis criteria. Fifteen of 16 (94%) tumors with 25%-75% perfusion reductions showed necrosis treatment response compared to only 3 of 11 (27%) tumors with perfusion reductions outside the above range (P = .001). Multivariate logistic regression indicated that intraprocedural tumor perfusion reduction and Child-Pugh class were independent factors associated significantly with tumor response (P = .012 and .047, respectively).

CONCLUSION

TRIP-MRI can successfully measure semiquantitative changes in HCC perfusion during chemoembolization. Intraprocedural tumor perfusion reductions are associated with future tumor response.

Targeted radiofrequency field mapping using 3D reduced field-of-view-catalyzed double-angle method

PURPOSE

The aim of this study was to develop a targeted volumetric radiofrequency field (B(1)(+)) mapping technique to provide region-of-interest B(1)(+) information.

MATERIALS AND METHODS

Targeted B(1)(+) maps were acquired using three-dimensional (3D) reduced field-of-view (FOV) inner-volume turbo spin echo-catalyzed double-angle method (DAM). Targeted B(1)(+) maps were compared with full-FOV B(1)(+) maps acquired using 3D catalyzed DAM in a phantom and in the brain of a healthy volunteer. In addition, targeted volumetric abdomeninal B(1)(+) mapping was demonstrated in the abdomen of another healthy volunteer.

RESULTS

The targeted reduced-FOV images demonstrated no aliasing artifacts in all experiments. Close match between targeted B(1)(+) map and reference full-FOV B(1)(+) map in the same region was observed, with percentage root-mean-squared error <0.4% in the phantom and <0.8% in the healthy volunteer brain. The abdominal B(1)(+) maps showed small B(1)(+) variation in the kidneys and liver from the healthy volunteer.

CONCLUSION

The proposed 3D reduced-FOV catalyzed DAM provides a rapid, simple and accurate method for targeted volumetric B(1)(+) mapping and can be easily implemented for applications related to radiofrequency field mapping in small targeted regions.

Quantitative 4D transcatheter intraarterial perfusion MRI for monitoring chemoembolization of hepatocellular carcinoma

PURPOSE

To develop a fully quantitative 4D transcatheter intraarterial perfusion (TRIP) magnetic resonance imaging (MRI) technique and prospectively test the hypothesis that quantitative 4D TRIP-MRI can be used clinically to monitor intraprocedural liver tumor perfusion reductions during transcatheter arterial chemoembolization (TACE).

MATERIALS AND METHODS

TACE was performed within an x-ray digital subtraction angiography (DSA)-MRI procedure suite in 16 patients with hepatocellular carcinoma. Quantitative 4D TRIP-MRI with targeted radiofrequency field mapping and dynamic longitudinal relaxation rate mapping was used to monitor changes in tumor perfusion during TACE. First-pass perfusion analysis was performed to produce intraprocedural blood flow (Frho) maps. Mean liver tumor perfusions before and after TACE were compared with a paired t-test (alpha = 0.05).

RESULTS

Perfusion reductions were successfully measured with quantitative 4D TRIP-MRI in 22 separate tumors during 18 treatment sessions. Mean tumor perfusion Frho decreased from 16.3 (95% confidence interval [CI]: 10.7-21.9) before TACE to 5.0 (95% CI: 3.5-6.5) (mL/min/100 mL) after TACE. Tumor perfusion reductions were statistically significant (P < 0.0005), with a mean absolute perfusion change of 11.4 (95% CI: 5.6-17.1) (mL/min/100 mL) and a mean percentage reduction of 61.0% (95% CI: 48.3%-73.6%).

CONCLUSION

Quantitative 4D TRIP-MRI can be successfully performed within clinical interventional settings to monitor intraprocedural changes in liver tumor perfusion during TACE.

Four-dimensional transcatheter intra-arterial perfusion MR imaging before and after uterine artery embolization in the rabbit VX2 tumor model

PURPOSE

To test the hypothesis that four-dimensional (4D) transcatheter intra-arterial perfusion (TRIP) MR imaging can measure uterine fibroid perfusion changes immediately before and after uterine artery embolization (UAE) in the rabbit VX2 tumor model.

MATERIALS AND METHODS

Eight VX2 uterine tumors were grown in six rabbits. After positioning a catheter within the uterine artery, we performed 4D TRIP-MRI measurements with 3-mL injections of 2.5% gadopentetate dimeglumine. We used a dynamic 3D spoiled-gradient echo sequence with in vivo B(1)-field correction for improved accuracy during perfusion quantification. We performed UAE using 1 mL of gelatin microspheres (2 x 10(6) particles; diameter 40-120 mum). Two regions-of-interest were drawn within each tumor upon perfusion maps. Functional embolic endpoints were reported as the mean percent reduction in fibroid tumor perfusion. Measurements before and after UAE were compared using paired t-tests (alpha = 0.05).

RESULTS

VX2 uterine tumor perfusion decreased significantly from 27.1 at baseline to 7.09 after UAE (mL/min/100 mL of tissue, P < 0.0001). Overall perfusion reduction was 76.3% (95% confidence interval: 66.3-86.3%).

CONCLUSION

Four-dimensional TRIP MRI can objectively quantify uterine fibroid perfusion reductions during UAE in VX2 rabbits. This technique could be used clinically to potentially determine an optimal embolic endpoint with the long-term goals of improving UAE success rates and minimizing procedure-related ischemic pain.

Functional magnetic resonance imaging in an animal model of pancreatic cancer

AIM

To test the hypotheses that diffusion weighed (DW)- and transcatheter intraarterial perfusion (TRIP)-magnetic resonance imaging (MRI) can each be used to assess regional differences in tumor function in an animal pancreatic cancer model.

METHODS

VX2 tumors were implanted in pancreata of 6 rabbits. MRI and digital subtraction angiography (DSA) were performed 3 wk following implantation. With a 2-French catheter secured in the rabbit's gastroduodenal artery, each rabbit was transferred to an adjacent 1.5T MRI scanner. DW- and TRIP-MRI were performed to determine if necrotic tumor core could be differentiated from viable tumor periphery. For each, we compared mean differences between tumor core/periphery using a 2-tailed paired t-test (alpha = 0.05). Imaging was correlated with histopathology.

RESULTS

Tumors were successfully grown in all rabbits, confirmed by necropsy. On DW-MRI, mean apparent diffusion coefficient (ADC) value was higher in necrotic tumor core (2.1 +/- 0.3 mm(2)/s) than in viable tumor periphery (1.4 +/- 0.5 mm(2)/s) (P < 0.05). On TRIP-MRI, mean perfusion values was higher in tumor periphery (110 +/- 47 relative units) than in tumor core (66 +/- 31 relative units) (P < 0.001).

CONCLUSION

Functional MRI can be used to differentiate necrotic from viable tumor cells in an animal pancreatic cancer model using ADC (DW-MRI) and perfusion (TRIP-MRI) values.

Diffusion-weighted magnetic resonance imaging to predict response of hepatocellular carcinoma to chemoembolization

AIM: To investigate whether intra-procedural diffusion-weighted magnetic resonance imaging can predict response of hepatocellular carcinoma (HCC) during transcatheter arterial chemoembolization (TACE).

METHODS: Sixteen patients (15 male), aged 59 ± 11 years (range: 42-81 years) underwent a total of 21 separate treatments for unresectable HCC in a hybrid magnetic resonance/interventional radiology suite. Anatomical imaging and diffusion-weighted imaging (b = 0, 500 s/mm²) were performed on a 1.5-T unit. Tumor enhancement and apparent diffusion coefficient (ADC, mm²/s) values were assessed immediately before and at 1 and 3 mo after TACE. We calculated the percent change (PC) in ADC values at all time points. We compared follow-up ADC values to baseline values using a paired t test (α = 0.05).

RESULTS: The intra-procedural sensitivity, specificity, and positive and negative predictive values (%) for detecting a complete or partial 1-mo tumor response using ADC PC thresholds of ±5%, ±10%, and ±15% were 77, 67, 91, and 40; 54, 67, 88, and 25; and 46, 100, 100, and 30, respectively. There was no clear predictive value for the 3-mo follow-up. Compared to baseline, the immediate post-procedure and 1-mo mean ADC values both increased; the latter obtaining statistical significance (1.48 ± 0.29 mm²/s vs 1.65 ± 0.35 × 10^-3 mm²/s, P < 0.014).

CONCLUSION: Intra-procedural ADC changes of > 15% predicted 1-mo anatomical HCC response with the greatest accuracy, and can provide valuable feedback at the time of TACE.

The role of tumor vascularity in predicting survival after yttrium-90 radioembolization for liver metastases

PURPOSE

It is unclear what role pretreatment tumor vascularity plays in determining outcomes after yttrium-90 radioembolization. A hypothesis was tested that radiographic vascularity of a tumor does not affect patient survival.

MATERIALS AND METHODS

In this two-institution retrospective study, 137 patients with metastatic liver disease underwent (90)Y radioembolization. Primary sites were categorized as colon, neuroendocrine, and other. All patients underwent triphasic contrast-enhanced computed tomography (CT) or magnetic resonance imaging, as well as detailed hepatic angiography. Two board-certified interventional radiologists interpreted all images and evaluated them for the presence of enhancement. Median survival times, as well as 1- and 2-year survival rates, were compared between patients with hypervascular and hypovascular tumors on (i) cross-sectional imaging and (ii) angiography with use of the log-rank statistic (alpha = 0.05).

RESULTS

On angiography, 108 patients had hypervascular tumors and 29 had hypovascular tumors. Median survival times for the two subgroups were 300 days and 261 days, respectively (P = .95). On CT, 24 patients had hypervascular tumors and 113 had hypovascular tumors. Median survival times for these subgroups were 306 days and 284 days, respectively (P = .67). Eighty-four patients' tumors that were hypovascular on CT were hypervascular on angiography. There were no statistical differences in survival between patients with hypervascular and hypovascular tumors, regardless if vascularity was defined based on CT or angiography.

CONCLUSIONS

Radiographic vascular appearance of liver tumors, regardless of imaging modality, does not affect survival after radioembolization. Therefore, hypovascular tumors should not be considered contraindicated for radioembolization.

Development of a VX2 pancreatic cancer model in rabbits: a pilot study

PURPOSE

An animal model of pancreatic cancer that is large enough to permit imaging and catheterization would be desirable for interventional radiologists to develop novel therapies for pancreatic cancer. The purpose of this study was to test the hypothesis that the VX2 rabbit model of pancreatic cancer could be developed as a suitable platform to test future interventional therapies.

MATERIALS AND METHODS

The authors implanted and grew three pancreatic VX2 tumors per rabbit in six rabbits. Magnetic resonance (MR) imaging was performed at 2 weeks to confirm tumor growth. At 3 weeks, the authors selectively catheterized the gastroduodenal artery under guidance of x-ray digital subtraction angiography (DSA). T2-weighted anatomic imaging, diffusion-weighted MR imaging, and transcatheter intraarterial perfusion (TRIP) MR imaging were then performed. After imaging, tumors were confirmed at necropsy and histopathologically. Tumor sizes at 2 and 3 weeks were compared with a paired t test (P = .05).

RESULTS

VX2 pancreatic tumors were grown in all six rabbits. The difference between tumor sizes at 2 and 3 weeks (1.29 cm +/- 0.39 vs 1.91 cm +/- 0.50, respectively) was significant (P < .001). All tumors were confirmed to be located within pancreatic tissue via histopathologic analysis. DSA and TRIP MR imaging were successful in five rabbits. Diffusion-weighted and anatomic MR imaging were successful in all six rabbits.

CONCLUSIONS

The VX2 rabbit model of pancreatic cancer is feasible, as verified by imaging and pathologic correlation, and may be a suitable platform to test future interventional therapies.

Four-dimensional transcatheter intraarterial perfusion (TRIP)-MRI for monitoring liver tumor embolization in VX2 rabbits

Transcatheter intraarterial perfusion (TRIP)-MRI is an intraprocedural technique to iteratively monitor liver tumor perfusion changes during transcatheter arterial embolization (TAE) and chemoembolization (TACE). However, previous TRIP-MRI approaches using two-dimensional (2D) T(1)-weighted saturation-recovery gradient-recalled echo (GRE) sequences provided only limited spatial coverage and limited capacity for accurate perfusion quantification. In this preclinical study, a quantitative 4D TRIP-MRI technique (serial iterative 3D volumetric perfusion imaging) with rigorous radiofrequency (RF) B(1) field calibration and dynamic tissue longitudinal relaxation rate R(1) measurement is presented for monitoring intraprocedural liver tumor perfusion during TAE. 4D TRIP-MRI and TAE were performed in five rabbits with eight VX2 liver tumors (N = 8). After B(1) calibrated baseline and dynamic R(1) quantification, subsequent tissue contrast agent concentration time curves were derived. A single-input flow-limited pharmacokinetic model and peak gradient method were applied for perfusion analysis. The perfusion Frho reduced significantly from pre-TAE 0.477 (95% confidence interval [CI]: 0.384-0.570) to post-TAE 0.131 (95% CI: 0.080-0.183 ml/min/ml, P < 0.001).

Four-dimensional transcatheter intraarterial perfusion MR imaging for monitoring chemoembolization of hepatocellular carcinoma: preliminary results

PURPOSE

Angiographic endpoints for chemoembolization of hepatocellular carcinoma (HCC) are subjective, and optimal endpoints remain unknown. Transcatheter intraarterial perfusion (TRIP) magnetic resonance (MR) imaging, when performed in a combined MR/interventional radiology (MR-IR) suite, offers an objective method to quantify intraprocedural tumor perfusion changes, but was previously limited to two spatial dimensions. This study prospectively tested the hypothesis that a new volumetric acquisition over time, four-dimensional TRIP MR imaging, can measure HCC perfusion changes during chemoembolization.

MATERIALS AND METHODS

Seven men (mean age, 53 years; range, 42-65 y) with eight tumors (mean size, 2.5 x 2.4 cm(2); diameter range, 1.5-5.2 cm) underwent chemoembolization in an MR-IR suite between February and December 2007, with intraprocedural tumor perfusion reductions monitored with four-dimensional TRIP MR imaging. Microcatheter chemoembolization was performed with a 1:1 mixture of chemotherapy agent and emulsifying contrast agent, followed by the administration of gelatin microspheres. Pre- and post-chemoembolization time-intensity curves were generated for each tumor. Semiquantitative measures of tumor perfusion, including area under the curve (AUC), peak signal intensity (SI), time to peak SI, and maximum upslope (MUS), were calculated, and mean differences before and after chemoembolization were compared with paired t tests.

RESULTS

Four-dimensional TRIP MR imaging-monitored chemoembolization was successful in all cases. Calculated AUCs before and after chemoembolization (439 vs 221, P = .004, 50% reduction), peak SI (32 vs 19, P = .012, 41% reduction), and MUS (11 vs 3, P = .028, 73% reduction) showed significant reductions after chemoembolization. Time to peak SI did not significantly change (23 sec vs 36 sec, P = .235, 57% increase).

CONCLUSIONS

Four-dimensional TRIP MR imaging can successfully measure semiquantitative changes in HCC perfusion during MR-IR-monitored chemoembolization. Future studies may correlate changes in these objective functional parameters with tumor response.

Diffusion-weighted PROPELLER MRI for quantitative assessment of liver tumor necrotic fraction and viable tumor volume in VX2 rabbits

PURPOSE

To test the hypothesis that diffusion-weighted (DW)-PROPELLER (periodically rotated overlapping parallel lines with enhanced reconstruction) MRI provides more accurate liver tumor necrotic fraction (NF) and viable tumor volume (VTV) measurements than conventional DW-SE-EPI (spin echo echo-planar imaging) methods.

MATERIALS AND METHODS

Our institutional Animal Care and Use Committee approved all experiments. In six rabbits implanted with 10 VX2 liver tumors, DW-PROPELLER and DW-SE-EPI scans were performed at contiguous axial slice positions covering each tumor volume. Apparent diffusion coefficient maps of each tumor were used to generate spatially resolved tumor viability maps for NF and VTV measurements. We compared NF, whole tumor volume (WTV), and VTV measurements to corresponding reference standard histological measurements based on correlation and concordance coefficients and the Bland-Altman analysis.

RESULTS

DW-PROPELLER generally improved image quality with less distortion compared to DW-SE-EPI. DW-PROPELLER NF, WTV, and VTV measurements were strongly correlated and satisfactorily concordant with histological measurements. DW-SE-EPI NF measurements were weakly correlated and poorly concordant with histological measurements. Bland-Altman analysis demonstrated that DW-PROPELLER WTV and VTV measurements were less biased from histological measurements than the corresponding DW-SE-EPI measurements.

CONCLUSION

DW-PROPELLER MRI can provide spatially resolved liver tumor viability maps for accurate NF and VTV measurements, superior to DW-SE-EPI approaches. DW-PROPELLER measurements may serve as a noninvasive surrogate for pathology, offering the potential for more accurate assessments of therapy response than conventional anatomic size measurements.

Transcatheter intraarterial perfusion: MR monitoring of chemoembolization for hepatocellular carcinoma--feasibility of initial clinical translation

PURPOSE

To prospectively test the hypothesis that intraprocedural transcatheter intraarterial perfusion (TRIP) magnetic resonance (MR) imaging can be used to successfully measure reductions in perfusion to the targeted hepatocellular carcinoma (HCC) and the adjacent surrounding liver tissue during MR-interventional radiology (IR)-monitored transcatheter arterial chemoembolization (TACE).

MATERIALS AND METHODS

This HIPAA-compliant prospective study was approved by the institutional review board. An MR-IR unit was used to perform TACE in 10 patients with HCC (seven male, three female; eight younger than 69 years, two older than 69 years). Intraprocedural reductions in tumor perfusion before and after TACE were monitored with TRIP MR imaging. Time-signal intensity curves were derived, and semiquantitative spatially resolved area under the time-signal intensity curve maps of tumor perfusion before and after TACE were produced. Mean perfusion values before and after TACE for liver tumors and adjacent liver tissue were compared by using a mixed-model analysis, with alpha = .05.

RESULTS

Perfusion reductions were measured successfully with TRIP MR imaging in 18 separate tumors during 13 treatment sessions. Perfusion maps showed significant perfusion reductions for tumors (P < .013) but not for adjacent nontumorous liver tissue (P = .21). For tumors, the mean perfusion value was 193 arbitrary units (AU) +/- 223 (standard deviation) before TACE and 45.3 AU +/- 91.9 after TACE, with a mean reduction in baseline perfusion of 74.6% +/- 24.8. For adjacent liver tissue, the mean perfusion value was 124 AU +/- 93.5 before TACE and 93.2 AU +/- 72.3 after TACE, with a mean reduction in baseline perfusion of 24.2% +/- 14.5.

CONCLUSION

TRIP MR imaging can be used to detect intraprocedural changes in perfusion to HCC and surrounding liver parenchyma during MR-IR-monitored TACE.

Comparison of transcatheter intraarterial perfusion MR imaging and fluorescent microsphere perfusion measurements during transcatheter arterial embolization of rabbit liver tumors

PURPOSE

Transcatheter intraarterial perfusion (TRIP) magnetic resonance (MR) imaging is clinically used in the interventional MR imaging setting to verify distribution of injected embolic or chemoembolic material during liver-directed transcatheter therapies and to monitor reductions in perfusion. The accuracy of this technique remains unknown. In the present study, rabbit VX2 liver tumors were used to test the hypothesis that TRIP MR imaging accurately measures changes in tumor perfusion during transcatheter arterial embolization (TAE), with injection of fluorescent microspheres used as the gold-standard technique.

MATERIALS AND METHODS

Five New Zealand White rabbits were used for this study (two donor rabbits and three with VX2 liver tumors). In three rabbits with implanted VX2 liver tumors, catheters were superselectively placed under digital subtraction angiographic guidance into the left hepatic artery supplying the targeted tumor. Fluorescent microspheres were injected into each rabbit's left ventricle before and after TAE. TRIP MR images were obtained at baseline and after embolizations for all rabbits with intraarterial injections of 2.5% gadopentetate dimeglumine solution. Linear regression was used to compare relative reductions in tumor perfusion between TRIP MR imaging and fluorescent microspheres. Results were considered statistically significant at a P value less than .05.

RESULTS

There was good correlation between TRIP MR imaging and fluorescent microsphere measurements of reduction in tumor perfusion (r = 0.722, P < .012).

CONCLUSIONS

TRIP MR imaging provides accurate semiquantitative measurement of perfusion reduction during TAE in rabbit liver tumors.