Whole-brain MR-registered cryo-imaging of a porcine-human glioma model to compare contrast agent biodistributions.

As rapidly accelerating technology, fluorescence guided surgery (FGS) has the potential to place molecular information directly into the surgeon's field of view by imaging administered fluorescent contrast agents in real time, circumnavigating pre-operative MR registration challenges with brain deformation. The most successful implementation of FGS is 5-ALA-PpIX guided glioma resection which has been linked to improved patient outcomes. While FGS may offer direct in-field guidance, fluorescent contrast agent distributions are not as familiar to the surgical community as Gd-MRI uptake, and may provide discordant information from previous Gd-MRI guidance. Thus, a method to assess and validate consistency between fluorescence-labeled tumor regions and Gd-enhanced tumor regions could aid in understanding the correlation between optical agent fluorescence and Gd-enhancement. Herein, we present an approach for comparing whole-brain fluorescence biodistributions with Gd-enhancement patterns on a voxel-by-voxel basis using co-registered fluorescent cryo-volumes and Gd-MRI volumes. In this initial study, a porcine-human glioma xenograft model was administered 5-ALA-PpIX, imaged with MRI, and euthanized 22 hours following 5-ALA administration. Following euthanization, the extracted brain was imaged with the cryo-macrotome system. After image processing steps and non-rigid, point-based registration, the fluorescence cryo-volume and Gd-MRI volume were compared for similarity metrics including: image similarity, tumor shape similarity, and classification similarity. This study serves as a proof-of-principle in validating our screening approach for quantitatively comparing 3D biodistributions between optical agents and Gd-based agents.

Magnetic nanoparticle biodistribution following intratumoral administration.

Recently, heat generated by iron oxide nanoparticles (IONPs) stimulated by an alternating magnetic field (AMF) has shown promise in the treatment of cancer. To determine the mechanism of nanoparticle-induced cytotoxicity, the physical association of the cancer cells and the nanoparticles must be determined. We have used transmission electron microscopy (TEM) to define the time dependent cellular uptake of intratumorally administered dextran-coated, core-shell configuration IONP having a mean hydrodynamic diameter of 100-130 nm in a murine breast adenocarcinoma cell line (MTG-B) in vivo. Tumors averaging volumes of 115 mm3 were injected with iron oxide nanoparticles. The tumors were then excised and fixed for TEM at time 0.1-120 h post-IONP injection. Intracellular uptake of IONPs was 5.0, 48.8 and 91.1% uptake at one, 2 and 4 h post-injection of IONPs, respectively. This information is essential for the effective use of IONP hyperthermia in cancer treatment.

Nearly complete regression of tumors via collective behavior of magnetic nanoparticles in hyperthermia.

One potential cancer treatment selectively deposits heat to the tumor through activation of magnetic nanoparticles inside the tumor. This can damage or kill the cancer cells without harming the surrounding healthy tissue. The properties assumed to be most important for this heat generation (saturation magnetization, amplitude and frequency of external magnetic field) originate from theoretical models that assume non-interacting nanoparticles. Although these factors certainly contribute, the fundamental assumption of 'no interaction' is flawed and consequently fails to anticipate their interactions with biological systems and the resulting heat deposition. Experimental evidence demonstrates that for interacting magnetite nanoparticles, determined by their spacing and anisotropy, the resulting collective behavior in the kilohertz frequency regime generates significant heat, leading to nearly complete regression of aggressive mammary tumors in mice.

Ultrasound monitoring of a novel microwave ablation (MWA) device in porcine liver: lessons learned and phenomena observed on ablative effects near major intrahepatic vessels.

BACKGROUND: Microwave ablation (MWA) is postulated to have several advantages over other thermoablative modalities in the treatment of hepatic tumors. Herein, we use an in vivo porcine model to determine the effect of hepatic blood flow on a novel MWA applicator. METHODS: Four 100-kg pigs underwent hepatic MWA (2,450 MHz, 100 W, 4 min) using a 5.7-mm diameter applicator (Microsulis Americas, Sulis V) inserted near large intrahepatic blood vessels. Real-time monitoring was performed using 3, 5, and 12 MHz diagnostic ultrasound transducers. The ablated zones were sectioned for gross and histological processing. RESULTS: Ablation zones were uniform in shape and size (3-4 cm) and related to power deliver only. Gross and microscopic examination revealed direct extension of ablation zones to the margin of major hepatic blood vessels and occasionally beyond the intended target. Of note, a momentary acoustic white-out occurred around the probe at 25 +/- -1 s in every ablation. DISCUSSION: The Sulis V MWA applicator produced uniform zones of ablation that remain unaffected by convective heat loss. The applicator induced a reproducible but temporary event as seen by ultrasound. Further study is warranted to define the physics, benefits, limits, and clinical safety of this new MWA technology.

Matrix metalloproteinase-1 promotes breast cancer angiogenesis and osteolysis in a novel in vivo model.

Matrix metalloproteinase-1 (MMP-1) is critical for mediating breast cancer metastasis to bone. We investigated the role of MMP-1 in breast cancer invasion of soft tissues and bone using human MDA MB-231 breast cancer cells stably transfected with shRNAs against MMP-1 and a novel murine model of bone invasion. MMP-1 produced by breast cancer cells with control shRNA facilitated invasion of tumors into soft tissue in vivo, which correlated with enhanced blood vessel formation at the invasive edge, compared to tumors with silenced MMP-1 expression. Tumors expressing MMP-1 were also associated with osteolysis in vivo, whereas tumors with inhibited MMP-1 levels were not. Additionally, tumor-secreted MMP-1 activated bone-resorbing osteoclasts in vitro. Together, these data suggest a mechanism for MMP-1 in the activation of osteoclasts in vivo. We conclude that breast cancer-derived MMP-1 mediates invasion through soft tissues and bone via mechanisms involving matrix degradation, angiogenesis, and osteoclast activation.

An in vivo transmission electron microscopy study of injected dextran-coated iron-oxide nanoparticle location in murine breast adenocarcinoma tumors versus time.

Investigators are just beginning to use hyperthermia generated by alternating magnetic field (AMF) activated iron oxide nanoparticles (IONPs) as a promising avenue for targeted cancer therapy. An important step in understanding cell death mechanisms in nanoparticle AMF treatments is to determine the location of these nanoparticles in relation to cellular organelles. In this paper, we report on transmission electron microscopy (TEM) studies designed to define the position of 100 nm diameter dextran-coated iron oxide nanoparticles in murine breast adenocarcinoma (MTG-B)and human colon adenocarcinoma tumors propagated in mice. METHODS: Iron oxide nanoparticles (5 mg/g tumor) were injected into intradermal MTG-B flank tumors on female C3H/HEJ mice and into HT-29 flank tumors on female Nu/Nu mice. The IONPs were allowed to incubate for various times. The tumors were then excised and examined using TEM. RESULTS: In the MTG-B tumors, most of the nanoparticles reside in aggregates adjacent to cell plasma membranes prior to three hours post-injection. By four hours post injection, however, most of the nanoparticles have been endocytosed by the cells. At time periods after four hours post injection, few visible extracellular nanoparticles remain and intracellular nanoparticles have densely aggregated within endosomes. In the HT-29 tumor, however, endocytosis of nanoparticles has not progressed to the same extent as in the MTG-B tumors by four hours post injection. CONCLUSIONS: The time at which most of the nanoparticles transition from being extracellular to intracellular in the MTG-B system appears to be between two and four hours. The HT-29 cells, however, display different and delayed uptake pattern. These data show that there are IONP uptake differences between tumor types (cell lines) and that, based on known uptake kinetics, nanoparticle hyperthermia can be employed as an extracellular or intracellular modality. These data will be important in guiding future nanoparticle hyperthermia cancer treatments.

Synthesis and heating effect of iron/iron oxide composite and iron oxide nanoparticles.

Fe/Fe oxide nanoparticles, in which the core consists of metallic Fe and the shell is composed of Fe oxides, were obtained by reduction of an aqueous solution of FeCl3 within a NaBH4 solution, or, using a water-in-oil micro-emulsion with CTAB as the surfactant. The reduction was performed either in an inert atmosphere or in air, and passivation with air was performed to produce the Fe/Fe3O4 core/shell composite. Phase identification and particle size were determined by X-ray diffraction and TEM. Thermal analysis was performed using a differential scanning calorimeter. The quasistatic magnetic properties were measured using a VSM, and the specific absorption rates (SARs) of both Fe oxide and Fe/Fe3O4 composite nanoparticles either dispersed in methanol or in an epoxy resin were measured by Luxtron fiber temperature sensors in an alternating magnetic field of 150 Oe at 250 kHz. It was found that the preparation conditions, including the concentrations of solutions, the mixing procedure and the heat treatment, influence the particle size, the crystal structure and consequently the magnetic properties of the particles. Compared with Fe oxides, the saturation magnetization (MS ) of Fe/Fe3O4 particles (100-190 emu/g) can be twice as high, and the coercivity (HC ) can be tunable from several Oe to several hundred Oe. Hence, the SAR of Fe/Fe3O4 composite nanoparticles can be much higher than that of Fe oxides, with a maximum SAR of 345 W/g. The heating behavior is related to the magnetic behavior of the nanoparticles.

In-Vitro Investigations of Nanoparticle Magnetic Thermotherapy: Adjuvant Effects and Comparison to Conventional Heating.

Thermotherapy, particularly magnetic nanoparticle hyperthermia, is a promising modality both as a direct cancer cell killing and as a radiosensitization technique for adjuvant therapy. Dextran-coated iron oxide nanoparticles were mixed with multiple tumor cell lines in solution and exposed to varying magnetic field regimes and combined with traditional external radiotherapy. Heating of cell lines by water bath in temperature patterns comparable to those achieved by nanoparticle hyperthermia was conducted to assess the relative value of nano-magnetic thermotherapy compared with conventional bulk heating techniques and data.

Basic principles of thermal dosimetry and thermal thresholds for tissue damage from hyperthermia.

This paper is one of several in this Special Issue of the International Journal of Hyperthermia that discusses the current state of knowledge about the human health risks of hyperthermia. This special issue emanated from a workshop sponsored by the World Health Organization in the Spring of 2002 on this topic. It is anticipated that these papers will help to establish guidelines for human exposure to conditions leading to hyperthermia. This comprehensive review of the literature makes it clear that much more work needs to be done to clarify what the thresholds for thermal damage are in humans. This review summarizes the basic principles that govern the relationships between thermal exposure (temperature and time of exposure) and thermal damage, with an emphasis on normal tissue effects. Methods for converting one time-temperature combination to a time at a standardized temperature are provided as well as a detailed discussion about the underlying assumptions that go into these calculations. There are few in vivo papers examining the type and extent of damage that occurs in the lower temperature range for hyperthermic exposures (e.g. 39-42 degrees C). Therefore, it is clear that estimation of thermal dose to effect at these thermal exposures is less precise in that temperature range. In addition, there are virtually no data that directly relate to the thermal sensitivity of human tissues. Thus, establishment of guidelines for human exposure based on the data provided must be done with significant caution. There is detailed review and presentation of thermal thresholds for tissue damage (based on what is detectable in vivo). The data are normalized using thermal dosimetric concepts. Tables are included in an Appendix Database which compile published data for thresholds of thermal damage in a variety of tissues and species. This database is available by request (contact MWD or PJH), but not included in this manuscript for brevity. All of the studies reported are for single acute thermal exposures. Except for brain function and physiology (as detailed in this issue by Sharma et al) one notes the critical lack of publications examining effects of chronic thermal exposures as might be encountered in occupational hazards. This review also does not include information on the embryo, which is covered in detail elsewhere in this volume (see article by Edwards et al.) as well as in a recent review on this subject, which focuses on thermal dose.

Hyperthermia induced pathophysiology of the central nervous system.

This review is focused on the pathophysiology of the central nervous system (CNS) associated with mild-to-moderate hyperthermia (body temperature > 37 degrees C but <40 degrees C) induced thermal stress in Human cases as well as whole body hyperthermia (WBH) in animal studies. Pathological changes can be observed in the nerve cells and glial cells in Humans following mild-to-moderate thermal exposure. On the other hand, morphological changes in the axons, nerve cells, glial cells and vascular endothelium is seen at the cellular and the molecular levels in rats subjected to heat exposure at 38 degrees C for 4 h (body temperature > 40 degrees C but <42 degrees C). This effect depends on the age of the animals and their prior thermal experiences. Taken together, heat stress induced hyperthermia, once believed to be non-toxic in the mammalian CNS, do produce specific alterations in the CNS that may have long-term behavioural, physiological and neuropathological consequences. The probable mechanism(s) underlying hyperthermia induced brain pathology is discussed.

Transjugular intrahepatic portosystemic shunt with an autologous vein-covered stent: results in a swine model.

PURPOSE: To investigate the feasibility, safety, and efficacy of an autologous vein-covered stent (AVCS) to prevent shunt stenosis in a porcine transjugular intrahepatic portosystemic shunt (TIPS) model. MATERIALS AND METHODS: TIPS were created with an AVCS in 12 healthy domestic swine and with a bare stent in 10 additional swine. Tissue response was compared with use of venography, histology, and computerized morphometry analysis 2 weeks after implantation. Differences between AVCS and noncovered stents (established by a t-test), as well as regional differences within a single stent (established by an f test), were considered significant at P <.05. RESULTS: Twenty of 22 TIPS procedures were technically successful. Ten of 12 shunts with an AVCS (83%) and two of 10 with bare stents (20%) remained patent (<50% diameter narrowing) at euthanasia 2 weeks later (P <.01). Histologic evaluation of harvested bare stents showed marked intimal hyperplasia (IH), composed of smooth muscle cells, myofibroblasts, and fibroblasts. In contrast, the AVCS were remarkably free of IH and thromboses. In patent TIPS in both groups, endothelial coverage of the luminal surface was present histologically. IH accounted for 57% (26.27/45.79) of total stent cross-sectional lumen area in the control group and 21% (8.34/39.54) in the AVCS group (P <.01), with no intrashunt differences (P >.05). CONCLUSION: Based on short-term follow-up, AVCS significantly improved TIPS patency by prevention of both IH and in-stent thrombosis. TIPS created with an AVCS was feasible and safe in our porcine model.

Comparison of photosensitizer (AIPcS2) quantification techniques: in situ fluorescence microsampling versus tissue chemical extraction.

A noninvasive in situ fluorescence-based method for the quantification of the photosensitizer chloroaluminum disulfonated phthalocyanine was compared to the highly accurate but nonreal time ex vivo spectrofluorometry method. Our in vivo fluorescence technique is designed to allow real-time assessment of photosensitizer in tumor and normal tissues and therefore temporally optimal light delivery. Laser-induced fluorescence was used to measure photosensitizer concentration from multiple microscopic regions of tissue. Ex vivo chemical extraction was used to quantify photosensitizer concentration in the same volume of tissue. The amount of photosensitizer in the vascular and/or parenchymal compartments of skeletal muscle and liver was determined by quantifying fluorescent signal in vivo, ex vivo and after blood removal. Confocal microscopy was used to spatially document photosensitizer localization 30 min and 24 h after delivery. While a linear correlation can exist between the fluorescence intensity measured by our fiber-optic bundle system and actual tissue concentration, temporal changes to this calibration line exist as the photosensitizer changes its partitioning fraction between the blood (vasculature) and the tissue parenchyma. In situ photosensitizer fluorescence microsampling (dosimetry) systems can be performed in real time and linearly correlated to actual tissue concentration with minimal intertissue variance. Tissue-specific differences may require temporal alterations in the calibration.

Comparison of a new stent and Wallstent for transjugular intrahepatic portosystemic shunt in a porcine model.

AIM: To evaluate a new balloon-expandable stainless steel stent (Cordis stent) in a transjugular intrahepatic portosystemic shunt (TIPS) porcine model and compared with Wallstent. METHODS: TIPS was performed in 26 normal domestic pigs weighing 20 kg-30 kg using a Cordis stent or Wallstent (13 pigs in each stent). All pigs were sacrificed at the 14th day after TIPS. The stent deployment delivery system, stent patency, and stent recoil after placement were evaluated. Proliferative response in representative histological sections from the center,hepatic and portal regions of the two stent designs were quantified. RESULTS: The shunt was widely patent in 4 pigs in the Cordis stent group (4/12, premature dead in 1 pig), and in 5 pigs in the Wallstent group (5/13). All remaining stents of both designs were occluded or stenotic. The mean quantified proliferation including thickness of the proliferation and the ratio of proliferation: total area in three assayed regions in Cordis stent and Wallstent was 2.18 mm:2.00 mm, and 59.18 mm2:51.66 mm2, respectively (P > 0.05). The delivery system and mechanical properties of the Cordis stent functioned well. CONCLUSION: The new Cordis stent is appropriate for TIPS procedure.

Microwave thermal keratoplasty for myopia: keratoscopic evaluation in porcine eyes.

PURPOSE: Microwave thermal keratoplasty applies microwave energy to elevate the temperature of the paracentral stroma of the cornea to its thermal shrinkage temperature of about 60 degrees C. A suitable pattern of shrinkage in the paracentral cornea can flatten the central cornea. A surface cooling system preserves the epithelium during the procedure. METHODS: Fourteen enucleated porcine eyes were treated with a prototype microwave thermal keratoplasty applicator that heated in a ring pattern with inner diameter of 3.2 mm and width of 0.7 mm. The change in corneal power was quantified by a videokeratoscope. Slit-lamp microscope examinations and histological assessments were made. RESULTS: The 3-mm simulated keratometry reading showed an average of 6.60+/-6.00 D (standard deviation) of flattening. The region of opacity associated with shrinkage extended to 62% (+/-26%) of the corneal thickness. The epithelium was intact in all eyes. CONCLUSIONS: Microwave thermal keratoplasty applied in the paracentral cornea may flatten the central cornea.

Postnatal development of corneal curvature and thickness in the cat.

OBJECTIVE: To evaluate the postnatal development of central corneal curvature and thickness in the domestic cat. Animals studied Six Domestic Short-haired (DSH) kittens starting at 9 weeks of age and 6 adult cats. PROCEDURES: Kittens were evaluated biweekly to monthly for a 12-month period, starting at age 9 weeks. Corneal development was monitored by hand-held keratometry and ultrasound biomicroscopy. Standard regression analysis using a nonlinear least squares method was used to generate a formula that would predict corneal curvature as a function of age. RESULTS: Mean keratometry (K) values for the 9-week-old cats were 54.51 (+/-1.02) diopters (D) and these values steeply declined over the next 3 months to 44.95 (+/-0.90) D. Thereafter, K-values gradually decreased to reach a plateau by 12-15 months of age of 39.90 (+/-0.42) D. Because K-values still appeared to be slightly diminishing at this point, six other > 2-year-old cats were evaluated by keratometry and were found to have K-values of 38.99 (+/-0.81). Two to four diopters of astigmatism was common in young kittens whereas adult cats had a low mean degree of astigmatism (< 1 D). A formula that predicted keratometry values in diopters (K) as a function of age in weeks (w) was established as follows: K = 39.83 + 26.87 exp(-0.074 w). The central cornea increased in thickness primarily during the first 4 months of life with 9 week-old kittens having values of 0.379 (+/-0.012) mm; 16-week-old kittens, 0.548 (+/-0.021) mm and 67 week-old cats, 0.567 (+/-0.012) mm. CONCLUSIONS: The maturation process of the feline cornea proceeds over the first 1-2 years of life to attain an adult status that is characterized by a roughly spherical state of approximately 39 D corneal curvature, substantially flatter than the human cornea, and a central thickness similar to the human cornea. Research studies of the refractive or optical properties of the cornea in which cats are used as experimental animals should be conducted on animals greater than 18 months of age.

In vivo modeling of interstitial pressure in the brain under surgical load using finite elements.

Current brain deformation models have predominantly reflected solid constitutive relationships generated from empirical ex vivo data and have largely overlooked interstitial hydrodynamic effects. In the context of a technique to update images intraoperatively for image-guided neuronavigation, we have developed and quantified the deformation characteristics of a three-dimensional porous media finite element model of brain deformation in vivo. Results have demonstrated at least 75-85 percent predictive capability, but have also indicated that interstitial hydrodynamics are important. In this paper we investigate interstitial pressure transient behavior in brain tissue when subjected to an acute surgical load consistent with neurosurgical events. Data are presented from three in vivo porcine experiments where subsurface tissue deformation and interhemispheric pressure gradients were measured under conditions of an applied mechanical deformation and then compared to calculations with our three-dimensional brain model. Results demonstrate that porous-media consolidation captures the hydraulic behavior of brain tissue subjected to comparable surgical loads and that the experimental protocol causes minimal trauma to porcine brain tissue. Working values for hydraulic conductivity of white and gray matter are also reported and an assessment of transient pressure gradient effects with respect to deformation is provided.

Trauma and inflammation modulate lymphocyte localization in vivo: quantitation of tissue entry and retention using indium-111-labeled lymphocytes.

OBJECTIVE: Determine the in vivo localization pattern of indium-111-labeled lymphocytes after a standardized extremity injury or standardized laparotomy and after sterile inflammation of the central nervous system. DESIGN: Prospective animal study with concurrent controls. SETTING: Animal research laboratory. SUBJECTS: Male Lewis rats weighing 150-175 g. INTERVENTIONS: Indium-111-labeled splenic lymphocytes were injected into animals after a standardized hind limb trauma or laparotomy and after induction of sterile central nervous system inflammation. MEASUREMENTS AND MAIN RESULTS: Lymphoid and non-lymphoid organs were removed at fixed intervals after lymphocyte injection and the proportion of injected lymphocytes/gram of tissue was determined using a quantitative radionuclide calculation. Results from treated animals were compared with results from untreated control animals. Muscle injury caused early localization of lymphocytes to injured hind limbs, liver, and spleen compared with controls, whereas laparotomy decreased lymphocyte localization in the thymus and colon. Encephalitis increased localization to the central nervous system with no effect on other tissues. CONCLUSIONS: These results identify a sensitive method to track in vivo leukocyte localization and specifically demonstrate that lymphocyte localization is altered in both traumatic and nontraumatic models of inflammation.

In vivo quantification of a homogeneous brain deformation model for updating preoperative images during surgery.

Clinicians using image-guidance for neurosurgical procedures have recently recognized that intraoperative deformation from surgical loading can compromise the accuracy of patient registration in the operating room. While whole brain intraoperative imaging is conceptually appealing it presents significant practical limitations. Alternatively, a promising approach may be to combine incomplete intraoperatively acquired data with a computational model of brain deformation to update high resolution preoperative images during surgery. The success of such an approach is critically dependent on identifying a valid model of brain deformation physics. Towards this end, we evaluate a three-dimensional finite element consolidation theory model for predicting brain deformation in vivo through a series of controlled repeat-experiments. This database is used to construct an interstitial pressure boundary condition calibration curve which is prospectively tested in a fourth validation experiment. The computational model is found to recover 75%-85% of brain motion occurring under loads comparable to clinical conditions. Additionally, the updating of preoperative images using the model calculations is presented and demonstrates that model-updated image-guided neurosurgery may be a viable option for addressing registration errors related to intraoperative tissue motion.

Visualization of intravenously administered contrast material in the CSF on fluid-attenuated inversion-recovery MR images: an in vitro and animal-model investigation.

BACKGROUND AND PURPOSE: The FLAIR (fluid-attenuated inversion-recovery) pulse sequence has been shown to be sensitive to abnormalities of the subarachnoid space. Our clinical experience led us to investigate whether intravenously injected contrast material can affect the appearance of the subarachnoid space on FLAIR MR images. METHODS: After noting unexplained high signal in the subarachnoid space on FLAIR images in a patient, we studied two dogs with sequential FLAIR MR imaging after i.v. administration of contrast material. A third dog was studied with a 6-hour delayed FLAIR sequence after triple-dose (0.3 mmol/kg) i.v. contrast administration. CSF was obtained from two animals for measurement of gadolinium concentration. A phantom was developed to determine the lowest concentration at which the effects of gadolinium were evident on FLAIR images in vitro. RESULTS: In all three animals, the appearance of the CSF in the ventricles or subarachnoid space was modified after administration of i.v. contrast. This was most evident on delayed images. The CSF samples showed a gadolinium concentration of 0.007 mmol/L in the dog who received the 0.1 mmol/kg dose and 0.02 mmol/L in the dog who received a triple dose. In our in vitro phantom experiments, gadolinium effects were evident on FLAIR images at a concentration four times lower than those on T1-weighted images. CONCLUSION: I.v. contrast material can cross into the CSF in sufficient concentration to alter the appearance of the subarachnoid space on FLAIR images in normal dogs. Although we encountered two patients with CNS disease in whom enhancement of the CSF was seen on postcontrast FLAIR images, additional investigation is needed in humans to determine whether enhancement may occur at triple dose in healthy subjects.

The biological behavior of autologous collagen-based extracellular matrix injected into the rabbit bladder wall.

Endoscopic techniques are providing a minimally invasive approach to the treatment of vesicoureteral reflux and urinary incontinence. Bovine collagen has been used, but potential degradation over time and sensitivity reactions have limited its usefulness. We evaluate the use of an autologous collagen-based extracellular matrix preparation injected within the rabbit bladder submucosa and compare it to the stability of bovine collagen-injected similarly. Of 28 New Zealand white rabbits, 12 underwent injection of autologous collagen-based extracellular matrix, 12 bovine collagen, and four normal saline sham injections into the anterior bladder submucosa. Twelve collagen specimens were iodinated with iodine 125 ((125)I) paraaminobenzoate reagent. The (125)I-labeled rabbits were monitored with a gamma camera to assess the level of decay of radioactivity over 12 weeks. All animals were killed 12 weeks post-injection. Assessment of radioactivity showed minimal difference in radioisotope labeling between the autologous and bovine collagen (total counts and decay kinetics). Compared to bovine collagen, the autologous collagen- based extracellular matrix implants histologically showed increased fibroblastic and vascular infiltration focally. The most significant histologic difference was the marked inflammatory response associated with the bovine collagen implants. These data suggest that in the short term, autologous and bovine collagen appear to have similar stability. The response to autologous collagen-based extracellular matrix may increase longevity of the implant, primarily by reducing immunologic rejection and improving biocompatibility within the host tissue. Further long-term studies are necessary to assess the long-term stability of autologous collagen-based extracellular matrix. Neurourol. Urodynam. 18:487-495, 1999.