Comparison between intravenous and intraarterial contrast injections for dynamic 3D MRI of liver tumors in the VX2 rabbit model

Use of X-Ray Fluorescence Microscopy for Studies on Research Models of Hepatocellular Carcinoma

Introduction: TheraSphere^® microspheres containing yttrium ⁹⁰Y are among many radioembolization agents used clinically to reduce liver tumor burden, and their effects on cancer volume reduction are well-established. At the same time, concerns about off target tissue injury often limit their use. Deeper investigation into tissue distribution and long-term impact of these microspheres could inform us about additional ways to use them in practice.

Methods: Healthy rat liver and rabbit liver tumor samples from animals treated with TheraSpheres were sectioned and their elemental maps were generated by X-ray fluorescence microscopy (XFM) at the Advanced Photon Source (APS) synchrotron at Argonne National Laboratory (ANL).

Results: Elemental imaging allowed us to identify the presence and distribution of TheraSpheres in animal tissues without the need for additional sample manipulation or staining. Ionizing radiation produced by ⁹⁰Y radioactive contaminants present in these microspheres makes processing TheraSphere treated samples complex. Accumulation of microspheres in macrophages was observed.

Conclusions: This is the first study that used XFM to evaluate the location of microspheres and radionuclides in animal liver and tumor samples introduced through radioembolization. XFM has shown promise in expanding our understanding of radioembolization and could be used for investigation of human patient samples in the future.

Transcatheter Intraarterial Perfusion MRI Approaches to Differentiate Reversibly Electroporated Penumbra From Irreversibly Electroporated Zones in Rabbit Liver

RATIONALE AND OBJECTIVES

To investigate whether transcatheter intraarterial perfusion (TRIP) magnetic resonance imaging (MRI) can differentiate reversible electroporation (RE) zones from irreversible electroporation (IRE) zones immediately after IRE procedure in the rabbit liver.

MATERIALS AND METHODS

All studies were approved by the institutional animal care and use committee and performed in accordance with institutional guidelines. A total of 13 healthy New Zealand White rabbits were used. After selective catheterization of the hepatic artery under X-ray fluoroscopy, we acquired TRIP-MRI at 20 minutes post-IRE using 3 mL of 5% intraarterial gadopentetate dimeglumine. Semi-quantitative (peak enhancement, PE; time to peak, TTP; wash-in slope, WIS; areas under the time-intensity curve, AUT, over 30, 60, 90, 120, 150, and 180 seconds after the initiation of enhancement) and quantitative (K^trans, v_e, and v_p) TRIP-MRI parameters were calculated. The relationships between TRIP-MRI parameters and histological measurements and the differential ability of TRIP-MRI parameters was assessed.

RESULTS

PE, AUT₆₀, AUT₉₀, AUT₁₂₀, AUT₁₅₀, AUT₁₈₀, K^trans, and v_e were significantly higher in RE zones than in IRE zones (all P < 0.05), and AUC for these parameters ranged from 0.91(95% CI, 0.80, 1.00) to 0.99 (95% CI, 0.98, 1.00). There was no significant difference in AUC between any two parameters (Z, 0-1.47; P, 0.14-1.00). Hepatocyte apoptosis strongly correlated with PE, AUT₆₀, AUT₉₀, AUT₁₂₀, AUT₁₅₀, AUT₁₈₀, K^trans, and v_p (the absolute value r, 0.6-0.7, all P < 0.0001).

CONCLUSION

AUT₁₅₀ or AUT₁₈₀ could be a potential imaging biomarker to differentiate RE from IRE zones, and TRIP-MRI permits to differentiate RE from IRE zones immediately after IRE procedure in the rabbit liver.

Intra-procedural dual phase cone beam computed tomography has a better diagnostic accuracy over pre-procedural MRI and MDCT in detection and characterization of HCC in cirrhotic patients undergoing TACE procedure

PURPOSE

This study was directed to compare diagnostic accuracy of dual-phase cone beam computed tomography (DP-CBCT) vs pre-procedural second line imaging modality (SLIM [multidetector computed tomography and magnetic resonance imaging]) to detect and characterize hepatocellular carcinoma (HCC) in cirrhotic patients with indication for trans-arterial chemoembolization (TACE).

METHODS

This is a single centre, retrospective, and observational study. Exclusion criteria were not-assisted DP-CBCT TACE, and unavailable follow-up SLIM. We evaluated 280 consecutive patients (January/2015-Febraury/2019). Seventy-two patients were eligible. Three radiologists in consensus reviewed: pre-procedural SLIM, DP-CBCT, and SLIM at follow-up, with 4 months of interval between each reading. Hyper-vascular foci (HVF) were detected and characterized. Diameter was recorded. Radiological behaviour, according to LI-RADS criteria, of HFV throughout follow-up time was the reference standard. Diagnostic accuracy was calculated for pre-procedural SLIM and DP-CBCT and evaluated through receiver operating characteristic curve. HVF only visible on DP-CBCT (defined as occult) were analysed. Tumour diameters were compared.

RESULTS

Median time between pre-procedural SLIM and DP-CBCT and between DP-CBCT and definitive radiological diagnosis of HVF were 46.0 days (95%CI 36.5-55.0) and 30.5 days (95%CI 29.0-33.0), respectively. DP-CBCT had a better diagnostic performance than pre-examination SLIM (sensitivity 99%vs78%; specificity 89%vs85%; PPV 99%vs99%; NPV 92%vs30%; and accuracy 94%vs79%). DP-CBCT diagnosed 63 occult HVF. Occult HCC were 54/243 (22.2%). Six were occult angiomas. Three were false positive. Mean diameter was significantly higher in DP-CBCT vs pre-procedural SLIM (+7.5% [95%CI 3.7-11.3], p < 0.05).

CONCLUSIONS

DP-CBCT has a better diagnostic accuracy and NPV than pre-procedural SLIM in cirrhotic patients with indication for TACE.

Establishment of metastatic liver carcinoma model by implanting AX7 cells into rabbit liver, and its histological findings

Background: Progression of metastatic liver carcinoma from any original cancer is aggressive and the prognosis is very poor. Therefore the new model that is easily approachable to study the propagation and prognosis of metastatic liver carcinoma is necessary. The aim of this study is to confirm the tumor formation and metastatic activity of anaplastic thyroid cancer and to support the research basis for the next generation cancer treatment that is to be developed, by carrying out additional experiments like cytokine stimulation. We investigated sequential findings of immunohistochemistry of rabbit hepatic malignancy induced by AX7 cells. Methods: 13 rabbits implanted with AX7 cells directly into liver parenchyme with laparotomy were investigated by histopathology examination, immunohistochemistry, which is useful for the evaluation of metastatic cancer angiogenesis. Growing tissue at the edge of the mass was collected and placed in the petri dish filled with saline. After removing necrotic and fibrous tissue, tumor tissue was cut into pieces, placed in saline, and extracted during the experiment. Results: Tumor growth and malignancy was confirmed on the 10th day after AX7 cells were implanted into liver. Positive for VEGF staining was found in the cytoplasm or cell membrane. The scores for VEGF stained cells were moderately positive (++) on day 10, strongly positive (+++) on day 44. Ki-67-positive hepatocytes reached at 65% on day 10, at 65.78% on day 14, at 66.4% on day 30, at 67.88% on day 44. Conclusion: AX7 cells implanted into liver can be used as a new rabbit metastatic liver carcinoma model and would become useful for human metastatic liver carcinoma studies. Future studies may facilitate the establishment of an effective systemic therapy for the metastatic liver cancer.

The rabbit as a behavioral model system for magnetic resonance imaging

BACKGROUND

fMRI requires that subjects not move during image acquisition. This has been achieved by instructing people not to move, or by anesthetizing experimental animal subjects to induce immobility. We have demonstrated that a surgically implanted headbolt onto the skull of a rabbit allows their brain to be imaged comfortably while the animal is awake. This article provides a detailed method for the preparation.

NEW METHOD

We took advantage of the rabbit's tolerance for restraint to image the brain while holding the head at the standard stereotaxic angle. Visual stimulation was produced by flashing green LEDs and whisker stimulation was done by powering a small coil of wire attached to a fiber band. Blinking was recorded with an infrared emitter/detector directed at the eye with fiber-optic cabling.

RESULTS

Results indicate that a single daily session of habituation is sufficient to produce adequate immobility on subsequent days to avoid movement artifacts. Results include high resolution images in the stereotaxic plane of the rabbit.

COMPARISON WITH EXISTING METHOD(S)

We see no degradation or distortion of MR signal, and the headbolt provides a means for rapid realignment of the head in the magnet from day to day, and across subjects. The use of rabbits instead of rodents allows much shorter periods of habituation, and the rabbit allows behavior to be observed during the day while the animal is in its normal wake cycle.

CONCLUSIONS

The natural tolerance of the rabbit for restraint makes it a valuable subject for MRI studies of the brain.

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.

Application of Volumetric Modulated Arc Therapy and Simultaneous Integrated Boost Techniques to Prepare "Safe Margin" in the Rabbit VX2 Limb Tumor Model

Background

In this study, we aimed to establish the rabbit VX2 limb tumor model, and then prepare a “necrotic zone” as a safe margin by volumetric modulated arc therapy and simultaneous integrated boost (VMAT-SIB) technique applied in the areas where the tumor is located adjacent to the bone (GTV_boost area).

Material/Methods

Rabbits in the control group (n=10) were not treated, while those in the test group (n=10) were treated with the SIB schedule delivering a dose of 40Gy, 35Gy, 30Gy, and 25Gy to the GTV_boost, GTV (gross tumor volume), CTV (clinical target volume), and PTV (planning target volume) in 10 fractions. Magnetic resonance diffusion-weighted imaging (MRDWI), 3-dimensional power Doppler angiography (3D-PDA), and histological changes were observed after radiotherapy.

Results

After radiotherapy, the two groups showed a significant difference in the GTV_boost area. In the test group, the tumor necrosis showed a significantly low signal in DWI and high signal in apparent diffusion coefficient (ADC) maps. The 3D-PDA observation showed that tumor vascular structures decreased significantly. Histological analysis demonstrated that a necrotic zone could be generated in the GTV_boost area, and microscopic examination observed cell necrosis and fibroplasia.

Conclusions

This studies demonstrated the feasibility of using VMAT-SIB technique in the rabbit VX2 limb tumor model. The formation of a necrotic zone can be effectively defined as safe margin in the GTV_boost area. showing potential clinical applicability.

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.

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.

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.

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.

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).

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.

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.

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

PURPOSE

To prospectively test the hypothesis that transcatheter intraarterial first-pass perfusion (TRIP) magnetic resonance (MR) imaging can depict serial reductions in rabbit liver tumor perfusion during transcatheter arterial embolization (TAE).

MATERIALS AND METHODS

All experiments had institutional animal care and use committee approval. In four rabbits implanted with eight VX2 liver tumors, catheters were positioned in the hepatic arteries with conventional angiographic guidance. After transfer to the MR imaging suite, serial TAE was performed, with approximately 0.5 million 40-120-microm embolic particles injected at each embolic stage. TRIP MR imaging was performed at baseline and after each subsequent embolic stage (10 minutes between stages). Serial TAE and TRIP MR imaging were repeated until stasis. The first-pass time course of signal enhancement was measured in both tumors and hepatic arteries. Tumor area under the curve (AUC) and maximum upslope (MUS) values, each normalized by arterial input, were measured to assess iterative perfusion reduction. Perfusion measurements across TAE stages were compared with paired t tests and linear regression.

RESULTS

AUC decreased from a pre-TAE baseline of 0.408 (95% confidence interval [CI]: 0.330, 0.486) to 0.065 (95% CI: 0.046, 0.085) (P<.001) after TAE. MUS decreased from a pre-TAE baseline of 0.151 (95% CI: 0.121, 0.181) to 0.027 (95% CI: 0.022, 0.031) (P<.001) after TAE. Reductions to AUC and MUS after each embolic stage were statistically significant (P<.006 for each group of paired comparisons). AUC strongly correlated with MUS (r=0.966, P<.001).

CONCLUSION

TRIP MR imaging can depict serial reductions in liver tumor perfusion during TAE. TRIP MR imaging offers the potential to target functional embolic end points during TAE.