Preclinical Development and Validation of Translational Temperature Sensitive Iodized Oil Emulsion Mediated Transcatheter Arterial Chemo-Immuno-Embolization for the Treatment of Hepatocellular Carcinoma.

Herein a practical strategy for augmenting immune activation in transcatheter arterial chemoembolization (TACE) of hepatocellular carcinoma (HCC) is presented. Pluronic F127 (PF127) is incorporated with Lipiodol (LPD) to achieve safe and effective delivery of therapeutic agents during transcatheter intra-arterial (IA) local delivery. Enhanced emulsion stability, IA infusion, embolic effect, safety, pharmacokinetics, and tumor response of Doxorubicin loaded PF127-LPD (Dox-PF127-LPD) for TACE in both in vitro and in vivo preclinical VX2 liver cancer rabbit model and N1S1 HCC rat model are demonstrated. Then, transcatheter arterial chemo-immuno-embolization (TACIE) combining TACE and local delivery of immune adjuvant (TLR9 agonist CpG oligodeoxynucleotide) is successfully performed using CpG-loaded Dox-PF127-LPD. Concurrent and safe local delivery of CpG and TACE during TACIE demonstrate leveraged TACE-induced immunogenic tumor microenvironment and augment systemic anti-tumor immunity in syngeneic N1S1 HCC rat model. Finally, the broad utility and enhanced therapeutic efficacy of TACIE are validated in the diethylnitrosamine-induced rat HCC model. TACIE using clinically established protocols and materials shall be a convenient and powerful therapeutic approach that can be translated to patients with HCC. The robust anti-cancer immunity and tumor regression of TACIE, along with its favorable safety profile, indicate its potential as a novel localized combination immunotherapy for HCC treatment.

Yttrium-90 Radioembolization in the VX2 Rabbit Model: Radiation Safety and Factors Influencing Delivery Efficiency.

The purpose of this study was to define the optimal infusion parameters and operator radiation exposure for yttrium-90 (90Y) radioembolization in the VX2 rabbit model of liver cancer. Forty-one rabbits with VX2 were treated with glass microspheres with vial sizes of 1, 3, and 5 GBq. The mean administered activity was 51.5 MBq (95% CI, 39.1-63.9). Delivery efficiency improved with 1 GBq versus with 3 GBq (residual 11.0% vs 46.4%, respectively; P = .0013) and improved with 1 GBq versus with 5 GBq (residual 11.0% vs 33.8%, respectively; P = .0060). The mean operator extremity exposure was 41.7 µSv/infusion. The optimal minimum infusion volume and rate was 49 mL and 21 mL/min, respectively. Fecal elimination occurred with microsphere uptake in the gallbladder at 1 and 2 weeks. 90Y radioembolization can be safely and efficiently performed in the VX2 rabbit model. Methodological considerations as a "how-to" for the setup of a preclinical 90Y laboratory are included to support future translational research.

Yttrium-90 Radioembolization and Tumor Hypoxia: Gas-challenge BOLD Imaging in the VX2 Rabbit Model of Hepatocellular Carcinoma.

RATIONALE AND OBJECTIVES: To use a rapid gas-challenge blood oxygen-level dependent magnetic resonance imaging exam to evaluate changes in tumor hypoxia after 90Y radioembolization (Y90) in the VX2 rabbit model. MATERIALS AND METHODS: White New Zealand rabbits (n = 11) provided a Y90 group (n = 6 rabbits) and untreated control group (n = 5 rabbits). R2* maps were generated with gas-challenges (O2/room air) at baseline, 1 week, and 2 weeks post-Y90. Laboratory toxicity was evaluated at baseline, 24 hours, 72 hours, 1 hours, and 2 weeks. Histology was used to evaluate tumor necrosis on hematoxylin and eosin and immunofluorescence imaging was used to assess microvessel density (CD31) and proliferative index (Ki67). RESULTS: At baseline, median tumor volumes and time to imaging were similar between groups (p = 1.000 and p = 0.4512, respectively). The median administered dose was 50.4 Gy (95% confidence interval:44.8-55.9). At week 2, mean tumor volumes were 5769.8 versus 643.7 mm3 for control versus Y90 rabbits, respectively (p = 0.0246). At two weeks, ΔR2* increased for control tumors to 12.37 ± 12.36sec-1 and decreased to 4.48 ± 9.00sec-1 after Y90. The Pearson correlation coefficient for ΔR2* at baseline and percent increase in tumor size by two weeks was 0.798 for the Y90 group (p = 0.002). There was no difference in mean microvessel density for control versus Y90 treated tumors (p = 0.6682). The mean proliferative index was reduced in Y90 treated tumors at 30.5% versus 47.5% for controls (p = 0.0071). CONCLUSION: The baseline ΔR2* of tumors prior to Y90 may be a predictive imaging biomarker of tumor response and treatment of these tumors with Y90 may influence tumor oxygenation over time.

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.

Correlation and Agreement of Yttrium-90 Positron Emission Tomography/Computed Tomography with Ex Vivo Radioembolization Microsphere Deposition in the Rabbit VX2 Liver Tumor Model.

PURPOSE: To demonstrate a stronger correlation and agreement of yttrium-90 (90Y) positron emission tomography (PET)/computed tomography (CT) measurements with explant liver tumor dosing compared with the standard model (SM) for radioembolization. MATERIALS AND METHODS: Hepatic VX2 tumors were implanted into New Zealand white rabbits, with growth confirmed by 7 T magnetic resonance imaging. Seventeen VX2 rabbits provided 33 analyzed tumors. Treatment volumes were calculated from manually drawn volumes of interest (VOI) with three-dimensional surface renderings. Radioembolization was performed with glass 90Y microspheres. PET/CT imaging was completed with scatter and attenuation correction. Three-dimensional ellipsoid VOI were drawn to encompass tumors on fused images. Tumors and livers were then explanted for inductively coupled plasma (ICP)-optical emission spectroscopy (OES) analysis of microsphere content. 90Y PET/CT and SM measurements were compared with reference standard ICP-OES measurements of tumor dosing with Pearson correlation and Bland-Altman analyses for agreement testing with and without adjustment for tumor necrosis. RESULTS: The median infused activity was 33.3 MBq (range, 5.9-152.9). Tumor dose was significantly correlated with 90Y PET/CT measurements (r = 0.903, P < .001) and SM estimates (r = 0.607, P < .001). Bland-Altman analyses showed that the SM tended to underestimate the tumor dosing by a mean of -8.5 Gy (CI, -26.3-9.3), and the degree of underestimation increased to a mean of -18.3 Gy (CI, -38.5-1.9) after the adjustment for tumor necrosis. CONCLUSIONS: 90Y PET/CT estimates were strongly correlated and had better agreement with reference measurements of tumor dosing than SM estimates.

Yttrium-90 Portal Vein Radioembolization in Sprague-Dawley Rats: Dose-Dependent Imaging and Pathological Changes in Normal Liver.

PURPOSE: Portal vein embolization (PVE) is an established neoadjuvant method to induce future liver remnant hypertrophy prior to surgical resection of hepatic tumors. The purpose of our study was to examine the feasibility of PVE with glass 90Y microspheres (Y90 PVE) in Sprague-Dawley rats. We tested the hypothesis that increased doses of Y90 PVE would increase target lobe fibrosis and atrophy. METHODS: Twenty-two rats were assigned to four groups for Y90 PVE to the right median lobe: very high- (273.8 MBq; n = 2), high- (99.9 MBq; n = 10), medium- (48.1 MBq; n = 5), and low-dose (14.8 MBq; n = 5). An untreated control group included seven rats. 90Y PET/CT of 90Y distributions confirmed lobar targeting. MRI volumes were measured at baseline, 2-, 4-, 8- and 12-weeks. Explanted hepatic lobes were weighed, sectioned, and stained for H&E and immunohistochemistry. Digitized slides allowed quantitative measurements of fibrosis (20 foci/slide). RESULTS: Ex vivo measurements confirmed 91-97% activity was localized to the target lobe (n = 4). The percent growth of the target lobe relative to baseline was - 5.0% (95% CI - 17.0-6.9%) for high-, medium dose rats compared to + 18.6% (95% CI + 7.6-29.7%) in the low-dose group at 12-weeks (p = 0.0043). Radiation fibrosis increased in a dose-dependent fashion. Fibrotic area/microsphere was 22,893.5, 14,946.2 ± 2253.3, 15,304.5 ± 4716.6, and 5268.8 ± 2297.2 µm2 for very high- (n = 1), high- (n = 4), medium- (n = 3), and low-dose groups (n = 5), respectively. CONCLUSION: Y90 PVE was feasible in the rat model, resulted in target lobe atrophy, and dose-dependent increases in hepatic fibrosis at 12 weeks. The onset of imaging-based volumetric changes was 8-12 weeks.

Feasibility of Combination Intra-arterial Yttrium-90 and Irinotecan Microspheres in the VX2 Rabbit Model.

PURPOSE: To evaluate the combination of 90Y radioembolization (Y90) and drug-eluting bead irinotecan (DEBIRI) microspheres in the VX2 rabbit model. MATERIALS AND METHODS: An initial dose finding study was performed in 6 White New Zealand rabbits to identify a therapeutic but subcurative dose of Y90. In total, 29 rabbits were used in four groups: Y90 treatment (n = 8), DEBIRI treatment (n = 6), Y90 + DEBIRI treatment (n = 7), and an untreated control group (n = 8). Hepatic toxicity was evaluated at baseline, 24 h, 72 h, 1 week, and 2 weeks. MRI tumor volume (TV) and enhancing tumor volume were assessed baseline and 2 weeks. Tumor area and necrosis were evaluated on H&E for pathology. RESULTS: Infused activities of 84.0-94.4 MBq (corresponding to 55.1-72.7 Gy) were selected based on the initial dose finding study. Infusion of DEBIRI after Y90 was technically feasible in all cases (7/7). Overall, 21/29 animals survived to 2 weeks, and the remaining animals had extrahepatic disease on necropsy. Liver transaminases were elevated with Y90, DEBIRI, and Y90 + DEBIRI compared to control at 24 h, 72 h, and 1 week post-treatment and returned to baseline by 2 weeks. By TV, Y90 + DEBIRI was the only treatment to show statistically significant reduction at 2 weeks compared to the control group (p = 0.012). The change in tumor volume (week 2-baseline) for both Y90 + DEBIRI versus control (p = 0.002) and Y90 versus control (p = 0.014) was significantly decreased. There were no statistically significant differences among groups on pathology. CONCLUSION: Intra-arterial Y90 + DEBIRI was safe and demonstrated enhanced antitumor activity in rabbit VX2 tumors. This combined approach warrants further investigation.

Pickering-Emulsion for Liver Trans-Arterial Chemo-Embolization with Oxaliplatin.

PURPOSE: Biodegradable polylactic-co-glycolic acid (PLGA) nanoparticles can adsorb at the water/oil interface to stabilize the emulsion (forming Pickering-emulsion). The purpose of this study was to compare the release profiles of oxaliplatin from Pickering-emulsion and Lipiodol-emulsion. MATERIALS/METHODS: Pickering-emulsions and Lipiodol-emulsions were both formulated with oxaliplatin (5 mg/mL) and Lipiodol (water/oil ratio: 1/3). For Pickering-emulsion only, PLGA nanoparticles (15 mg/mL) were dissolved into oxaliplatin before formulation. In vitro release of oxaliplatin from both emulsions was evaluated. Then, oxaliplatin was selectively injected into left hepatic arteries of 18 rabbits bearing VX2 liver tumors using either 0.5 mL Pickering-emulsion (n = 10) or 0.5 mL Lipiodol-emulsion (n = 8). In each group, half of the rabbits were killed at 1 h and half at 24 h. Mass spectrometry was used to quantify drug pharmacokinetics in blood and resulting tissue (tumors, right, and left livers) oxaliplatin concentrations. RESULTS: Pickering-emulsion demonstrated a slow oxaliplatin release compared to Lipiodol-emulsion (1.5 ± 0.2 vs. 12.0 ± 6% at 1 h and 15.8 ± 3.0 vs. 85.3 ± 3.3% at 24 h) during in vitro comparison studies. For animal model studies, the plasmatic peak (Cmax) and the area under the curve (AUC) were significantly lower with Pickering-emulsion compared to Lipiodol-emulsion (Cmax = 0.49 ± 0.14 vs. 1.08 ± 0.41 ng/mL, p = 0.01 and AUC = 19.8 ± 5.9 vs. 31.8 ± 14.9, p = 0.03). This resulted in significantly lower oxaliplatin concentrations in tissues at 1 h with Pickering-emulsion but higher ratio between tumor and left liver at 24 h (43.4 vs. 14.5, p = 0.04). CONCLUSION: Slow release of oxaliplatin from Pickering-emulsion results in a significant decrease in systemic drug exposure and higher ratio between tumor and left liver oxaliplatin concentration at 24 h.

Immunomodulatory Magnetic Microspheres for Augmenting Tumor-Specific Infiltration of Natural Killer (NK) Cells.

The purpose of this research is to develop magnetic resonance imaging (MRI) visible immunomodulatory microspheres (IMM-MS) for efficient image guided cancer immunotherapy. IMM-MS composed of recombinant interferon gamma (IFN-γ), iron oxide nanocubes (IONC), and biodegradable poly(lactide-co-glycolide) (PLGA) were successfully prepared via a double-emulsion method. The prepared IMM-MS exhibited a sustained IFN-γ release and highly sensitive MR T2 contrast effects. Finally, in an orthotopic liver tumor VX2 rabbit model, successful hepatic intra-arterial (IA) transcatheter delivery of IMM-MS to liver tumors was confirmed with MR images. The deposition of IMM-MS significantly increased NK-cell infiltration into the liver tumor site.

An empirical method for reducing variability and complexity of myocardial perfusion quantification by dual bolus cardiac MRI.

PURPOSE: Myocardial perfusion can be quantified using the "dual bolus" technique, which uses two separate contrast boluses to avoid signal nonlinearity in the blood pool. This technique relies on knowing the precise ratio of contrast concentrations between the two boluses. In this study, we investigated the variability found in these ratios, as well as the error it introduces, and developed a method for correction. METHODS: Five dogs received dual bolus myocardial perfusion MRI scans. Perfusion was calculated separately using assumed contrast dilution ratios and empirically determined contrast ratios. Perfusion was compared with reference standard fluorescent microspheres. The same technique was then applied to a cohort of six patients with no significant coronary artery stenosis by cardiac catheterization. RESULTS: Assumed contrast dilution ratios were 10:1 for all animal and patient scans. Empirically derived contrast ratios were significantly different for animal (8.51:1 ± 1.53:1, P < 0.001) and patient scans (7.32:1 ± 2.27:1, P < 0.01). Incorporating empirically derived ratios for animal scans improved correlation with microspheres from 0.84 to 0.90 (P < 0.05). CONCLUSION: Variability in dual bolus contrast concentration ratios is an important source of experimental error, especially outside of a carefully controlled laboratory setting. Empirically deriving the correct ratio is feasible and improves the accuracy of quantitative perfusion measurements. Magn Reson Med 77:2347-2355, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

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.

A Comparison of Theory-Based and Experimentally Determined Myocardial Signal Intensity Correction Methods in First-Pass Perfusion Magnetic Resonance Imaging.

OBJECTIVES: To evaluate the impact of correcting myocardial signal saturation on the accuracy of absolute myocardial blood flow (MBF) measurements. MATERIALS AND METHODS: We performed 15 dual bolus first-pass perfusion studies in 7 dogs during global coronary vasodilation and variable degrees of coronary artery stenosis. We compared microsphere MBF to MBF calculated from uncorrected and corrected MRI signal. Four correction methods were tested, two theoretical methods (Th1 and Th2) and two empirical methods (Em1 and Em2). RESULTS: The correlations with microsphere MBF (n = 90 segments) were: uncorrected (y = 0.47x + 1.1, r = 0.70), Th1 (y = 0.53x + 1.0, r = 0.71), Th2 (y = 0.62x + 0.86, r = 0.73), Em1 (y = 0.82x + 0.86, r = 0.77), and Em2 (y = 0.72x + 0.84, r = 0.75). All corrected methods were not significantly different from microspheres, while uncorrected MBF values were significantly lower. For the top 50% of microsphere MBF values, flows were significantly underestimated by uncorrected SI (31%), Th1 (25%), and Th2 (19%), while Em1 (1%), and Em2 (9%) were similar to microsphere MBF. CONCLUSIONS: Myocardial signal saturation should be corrected prior to flow modeling to avoid underestimation of MBF by MR perfusion imaging.

Poly(lactide-co-glycolide) microspheres for MRI-monitored delivery of sorafenib in a rabbit VX2 model.

Transcatheter arterial embolization and chemoembolization are standard locoregional therapies for hepatocellular carcinoma (HCC). However, these can result in tumor hypoxia, thus promoting tumor angiogenesis. The anti-angiogenic agent sorafenib is hypothesized to improve outcomes; however, oral administration limits patient tolerance. Therefore, the purpose of this study was to fabricate poly(lactide-co-glycolide) microspheres for local sorafenib delivery to tumors during liver-directed embolotherapies. Iron oxide nanoparticles (IONP) were co-encapsulated for magnetic resonance imaging (MRI) of microsphere delivery. Microspheres were fabricated using a double emulsion/solvent evaporation method and characterized for size, sorafenib and IONP content, and MRI properties. MRI was performed before and after intra-arterial microsphere infusions in a rabbit VX2 liver tumor model. The microspheres were 13 microns in diameter with 8.8% and 0.89% (w/w) sorafenib and IONP, respectively. 21% and 28% of the loaded sorafenib and IONP, respectively, released within 72 h. Rabbit VX2 studies demonstrated that sorafenib microspheres normalized VEGFR 2 activity and decreased microvessel density. Quantitative MRI enabled in vivo visualization of intra-hepatic microsphere distributions. These methods should avoid systemic toxicities, with MRI permitting follow-up confirmation of microsphere delivery to the targeted liver tumors.

Percutaneous ultrasound guided implantation of VX2 for creation of a rabbit hepatic tumor model.

Creation of a VX2 tumor model has traditionally required a laparotomy and surgical implantation of tumor fragments. Open surgical procedures are invasive and require long procedure times and recovery that can result in post-operative morbidity and mortality. The purpose of this study is to report the results of a percutaneous ultrasound guided method for creation of a VX2 model in rabbit livers. A total of 27 New Zealand white rabbits underwent a percutaneous ultrasound guided approach, where a VX2 tumor fragment was implanted in the liver. Magnetic resonance imaging was used to assess for tumor growth and necropsy was performed to determine rates of tract seeding and metastatic disease. Ultrasound guided tumor implantation was successful in all 27 rabbits. One rabbit died 2 days following the implantation procedure. Two rabbits had no tumors seen on follow-up imaging. Therefore, tumor development was seen in 24/26 (92%) rabbits. During the follow-up period, tract seeding was seen in 8% of rabbits and 38% had extra-hepatic metastatic disease. Therefore, percutaneous ultrasound guided tumor implantation safely provides reliable tumor growth for establishing hepatic VX2 tumors in a rabbit model with decreased rates of tract seeding, compared to previously reported methods.

Leakage and water exchange characterization of gadofosveset in the myocardium.

PURPOSE: To determine the compartmentalization of the blood pool agent gadofosveset and the effect of its transient binding to albumin on the quantification of steady-state fractional myocardial blood volume (fMBV). METHODS: Myocardial vascular fraction measurements were simulated assuming the limiting cases (slow or fast) of two-compartment water exchange for different contrast agent injection concentrations, binding fractions, bound and free relaxivities, and true cardiac vascular fractions. fMBV was measured in five healthy volunteers (4 males, 1 female, average age 33) at 1.5T after administration of five injections of gadofosveset. The measurements in the volunteers were retrospectively compared to measurements of fMBV after three serial injections of the ultra-small, paramagnetic iron oxide (USPIO) blood pool agent ferumoxytol in an experimental animal. The true fMBV and exchange rate of water protons in both human and animal data sets was determined by chi square minimization. RESULTS: Simulations showed an error in the measurement of fMBV due to partial binding of gadofosveset of less than 30%. Measured fMBV values over-estimate simulation predictions, and approach cardiac extracellular volume (22%), which suggests that the intravascular assumption may not be appropriate for the myocardium, although it may apply to more distal perfusion beds. In comparison, fMBV measured with ferumoxytol (5%, with slow water proton exchange across vascular wall) agree with published values of myocardial vascular fraction. Further comparison between myocardium relaxation rates induced by gadofosveset and by other extracellular and intravascular contrast agents showed that gadofosveset behaves like an extracellular contrast agent. CONCLUSIONS: The distribution of the volunteer data indicates that a three-compartment model, with slow water exchange of gadofosveset and water protons between the vascular and interstitial compartments, and fast water exchange between the interstitium and the myocytes, is appropriate. The ferumoxytol measurements indicate that this USPIO is an intravascular contrast agent that can be used to quantify myocardial blood volume, with the appropriate correction for water exchange using a two-compartment water exchange model.

Absolute quantification of myocardial blood flow with constrained estimation of the arterial input function.

PURPOSE: To evaluate the performance of the constrained alternating minimization with model (CAMM) method for estimating the input function from the myocardial tissue curves. MATERIALS AND METHODS: Myocardial perfusion imaging was performed on seven canine models of coronary artery disease in 15 imaging sessions. In each session, stress was induced with intravenous infusion of adenosine and a variable occluder created coronary artery stenosis. A dual bolus protocol was used for each acquisition, and input functions were then estimated using the CAMM method with data acquired from the high dose scan following each imaging session. For each acquisition, myocardial blood flow was measured by injected microspheres. RESULTS: The dual bolus and CAMM-derived flows were not significantly different (P = 0.18), and the correlation between the two methods was high (r = 0.97). The correlation between the dual bolus and CAMM methods and microsphere measurements was lower than that for the two MR methods (r = 0.53; r = 0.43, respectively). CONCLUSION: The CAMM method presented here shows promise in estimating myocardial blood flow in patients with coronary artery disease at stress with a single injection and without any specialized acquisitions. Further work is needed to validate the approach in a clinical setting.

Off-resonance positive contrast imaging of a passive endomyocardial catheter in swine.

The use of off-resonance methods in interventional MRI may be valuable since active devices that provide positive signal enhancements are currently not approved for human use. This study investigated the capacity of a low flip angle steady-state free precession (FLAPS) method for generating off-resonance positive contrast surrounding a susceptibility-shifted endomyocardial Stiletto catheter in excised swine hearts and in live swine. Consistent with theory, discernable positive contrast surrounding the interventional device was visualized under ex-vivo (CNR of 24 +/- 2.1 in the left ventricular (LV) chamber and 18 +/- 2.7 in LV myocardium) and in-vivo conditions (CNR of 22 +/- 3.9 in aorta, 16 +/- 4.1 in the LV chamber and 13 +/- 0.9 in LV myocardium). The findings show that off-resonance imaging with the FLAPS method may be used for passive device visualization with positive contrast. Further studies are necessary prior to clinical translation.

Comparison of two different methods for inoculating VX2 tumors in rabbit livers and hind limbs.

PURPOSE: To compare two methods to (a) propagate VX2 cell strain in rabbit hind limbs and (b) inoculate liver parenchymal tumors in rabbits. MATERIALS AND METHODS: One hundred forty-two New Zealand white rabbits were used for this study (60 with hind limb tumor [donors] and 82 with liver tumors [recipients]). In the donor group, nine rabbits received frozen VX2 cell suspension and 51 were injected with freshly prepared VX2 cell suspension. In the recipient group, 32 rabbits were injected with VX2 tumor cells and 50 were implanted with a small tumor fragment in the liver parenchyma. Success rates in terms of tumor growth were compared by using chi(2) or Fisher exact tests, with alpha = .05. RESULTS: Hind limb and liver tumors were successfully grown in 48 of the 60 rabbits in the donor group (80%) and 57 of the 82 rabbits in the recipient group (70%). The success rate of growing hind limb tumors increased from 33% (three of nine rabbits) to 88% (45 of 51 rabbits) when fresh VX2 cells instead of frozen were injected percutaneously (P < .0011). Similarly, the success rate for VX2 liver tumors almost doubled from 47% (15 of 32 rabbits) to 84% (42 of 50 rabbits) when a tumor fragment instead of VX2 cell suspension was used (P < .00036). This also significantly reduced the frequency of metastasis (P < .005). CONCLUSIONS: The authors recommend (a) the use of fresh VX2 cell suspension for percutaneous injection in the hind limbs of rabbits to maintain the VX2 cell strain and (b) the surgical implantation of freshly harvested VX2 tumor fragment into the liver parenchyma to establish liver tumors.

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.

Rabbit VX2 tumors as an animal model of uterine fibroids and for uterine artery embolization.

PURPOSE: To determine the suitability of the rabbit VX2 tumor animal model for uterine fibroids and uterine artery embolization (UAE). MATERIALS AND METHODS: The authors implanted and grew one uterine VX2 tumor per rabbit in six rabbits. UAE was performed by using 100-300 microm embolic particles and confirmed with x-ray digital subtraction angiography, magnetic resonance (MR) imaging, and necropsy. Unenhanced and contrast medium-enhanced MR images of VX2 tumors were obtained before and after UAE. Relative MR signal-to noise-ratio (SNR) was measured in the uterine VX2 tumor and in normal uterine tissue before and after UAE and compared by using a paired t-test (P = .05). RESULTS: VX2 uterine tumors were successfully grown, and both VX2 tumor presence in the uterus and UAE were seen angiographically and confirmed with necropsy in all six rabbits. Statistically significant reductions in relative SNRs were measured in tumors (SNR before UAE, 15.3 +/- 5.15; SNR after UAE, 3.84 +/- 3.94; P < .0001). No statistically significant decrease in SNR was measured in normal uterine tissue before and after UAE (P = .63 for the right uterine horn and P = .93 for the left uterine horn). CONCLUSION: Rabbit VX2 uterine tumors may be a suitable animal model of uterine fibroids and UAE.