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P J Hoopes

Publications and source records attributed to P J Hoopes.

At least 19 recordsLinked to original sources
PubMed2001

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.

Animals↗
PubMed2001

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.

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PubMed2001

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.

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PubMed2001

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.

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PubMed2000

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.

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PubMed2000

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.

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PubMed2000

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.

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PubMed2000

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.

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PubMed1999

Application of linear circuit models to impedance spectra in irradiated muscle.

We have applied a number of modeling schemes to previously reported in vivo electrical impedance measurements on irradiated and normal muscle in the hind legs of rats. Specifically, seven-parameter parallel pathways and embedded membrane circuit models have been fit to group averages of impedance spectra measured at different doses and time points. Correlations between histologically scored tissue sections and model parameters have also been determined. The results show that both models produce good fits to the experimental observations, especially in the case of the irradiated tissues. The correlations between histology scores and circuit parameters were, however, higher with the embedded model. Trends in the spectra and the model parameters were found to agree with the expected changes in tissue pathophysiology associated with the progression of tissue injury from radiation exposure. Quantitative correlations with specific histological criteria were less conclusive, suggesting that more information may be needed to refine the model architecture if model parameters are to be explicitly related to the types and extent of tissue damage induced by radiation treatments.

Animals↗
PubMed1999

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.

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PubMed1999

A computational model for tracking subsurface tissue deformation during stereotactic neurosurgery.

Recent advances in the field of stereotactic neurosurgery have made it possible to coregister preoperative computed tomography (CT) and magnetic resonance (MR) images with instrument locations in the operating field. However, accounting for intraoperative movement of brain tissue remains a challenging problem. While intraoperative CT and MR scanners record concurrent tissue motion, there is motivation to develop methodologies which would be significantly lower in cost and more widely available. The approach we present is a computational model of brain tissue deformation that could be used in conjunction with a limited amount of concurrently obtained operative data to estimate subsurface tissue motion. Specifically, we report on the initial development of a finite element model of brain tissue adapted from consolidation theory. Validations of the computational mathematics in two and three dimensions are shown with errors of 1%-2% for the discretizations used. Experience with the computational strategy for estimating surgically induced brain tissue motion in vivo is also presented. While the predicted tissue displacements differ from measured values by about 15%, they suggest that exploiting a physics-based computational framework for updating preoperative imaging databases during the course of surgery has considerable merit. However, additional model and computational developments are needed before this approach can become a clinical reality.

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PubMed1999

In vivo electrical impedance spectroscopic monitoring of the progression of radiation-induced tissue injury.

This study evaluates the potential of electrical impedance spectroscopy (EIS) as a noninvasive technique for tracking the progression of radiation-induced damage in normal muscle tissue. Male Sprague-Dawley rats were irradiated locally to the gastrocnemius and biceps femoris muscle. Single doses were administered using a procedure that spares skin and bone. Complex impedance spectral measurements (taken at 50 frequency points between 1 kHz and 1 MHz) were made at monthly intervals using recessed disk electrodes applied to the skin. A histological scoring scheme was developed for evaluation of injury. A strong dose-dependent progression of injury evident in both spectral measurements and histological scoring has been observed. Latent time also appears to be dependent on dose with changes induced by 70 Gy evident by 2 months, changes induced by 90 Gy observed by 1 month, and dramatic changes found within 3 weeks at 150 Gy. Injury was morphologically comparable to the type of damage that occurs in response to small, fractionated doses, but on a much shorter time scale. Increased spectral shift was a consistent indicator of the extent of tissue injury at the time of measurement. The use of a large single dose resulted in an excellent model in terms of inducing a significant progression in tissue injury over a short post-treatment follow-up period in the muscle mass while also providing a consistent location for in vivo electrical impedance measurements. The results show that EIS can follow radiation-induced tissue change, suggesting that EIS has the potential to monitor the types of injury observed in late radiation damage of muscle tissue noninvasively.

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PubMed1998

In vivo gradient echo microimaging of rodent spinal cord at 7 T.

An optimization scheme was developed for gradient echo imaging using a half-birdcage RF coil at 7 T to obtain maximal contrast between gray and white matter in the spinal cord of rodents. This optimization was combined with microimaging techniques to obtain in vivo pixel sizes of 78 x 78 x 700 microm. These techniques can be implemented in an in vivo study to investigate the myelin structure within the white matter of the rodent spinal cord.

Animals↗
PubMed1998

Transjugular intrahepatic portosystemic shunt in a porcine model: histologic characteristics at the early stage.

RATIONALE AND OBJECTIVES: The authors attempted to determine the histologic processes that take place during development of stenosis after transjugular intrahepatic portosystemic shunt (TIPS) creation. MATERIALS AND METHODS: TIPS were created with metallic stents in 20 healthy domestic pigs (tantalum stents in 10, stainless steel stents in 10). The animals were sacrificed 2-16 days later. All the shunts were examined by means of venography both immediately after placement of the stents and before sacrifice. All histologic sections were assessed with modified Giemsa and basic fuchsin stains. Anti-smooth-muscle-cell alpha-actin stain was used in three specimens. The stenotic reaction was quantified by using standard planimetry techniques and a computerized image-analysis system. RESULTS: Within 16 days after TIPS placement, 15 (75%) of the 20 shunts were completely occluded, four (20%) of 20 shunts were partially occluded, and one (5%) of 20 shunts remained widely patent (animal died of unknown cause 2 days after the TIPS procedure). Stent occlusion was caused primarily by pseudointimal hyperplasia, which was similar morphologically in the portal, middle, and hepatic portions of the stent. Myofibroblastic proliferation was the most striking feature of the pseudointimal hyperplasia. The average thickness of the proliferation was 2.14 mm, which was 67% of the total diameter of the stent. A mild fibrous or lymphocytic reaction occurred around the stent wires and between the pseudointimal hyperplasia and the liver parenchyma. CONCLUSION: The histologic features of pseudointimal formation in this swine TIPS model closely resemble those in humans. This model may prove useful for evaluating stents and other devices and improving the understanding of restenosis after vascular interventions.

Animals↗
PubMed1998

Transjugular intrahepatic portosystemic shunt: effect of bile leak on smooth muscle cell proliferation.

PURPOSE: To evaluate the effect of bile on smooth muscle cell (SMC) proliferation in vitro and in vivo in a porcine transjugular intrahepatic portosystemic shunt (TIPS) model. MATERIALS AND METHODS: In vitro, SMCs explanted from porcine thoracic aorta were cultured with standard techniques. After initial pilot studies, they were subcultured in one of three groups: 1% porcine serum plus 1% bile, 10% porcine serum plus 1% bile, and 10% porcine serum. Cells were harvested at 3, 10, or 14 days, and DNA, protein, and disintegrations per minute (an indicator of proliferation) were measured. In vivo, TIPS creation was successful in 45 swine. All pigs were euthanized at 10-16 days. The proliferative response within the stent was histologically quantified and correlated for evidence of bile leak. RESULTS: In pilot studies, 2.5%-10.0% bile solutions caused 100% SMC mortality by 3 days. In the presence of 1% bile (with or without porcine serum), both DNA and protein production decreased significantly compared with that in porcine serum alone (P < .05). In vivo, 13 of 45 specimens (29%) showed bile leak at gross or microscopic examination. SMC proliferation was less overall in animals with versus those without bile leak (difference not significant). CONCLUSION: These data suggest that the proliferative response in a TIPS is not primarily due to bile leak. Bile leak may promote thrombosis, but it appears to inhibit myointimal proliferation.

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PubMed1997

MRI contrast enhanced study of cartilage proteoglycan degradation in the rabbit knee.

Early degeneration of cartilage is accompanied by a loss of proteoglycans and consequent changes in the content of water. Conventional magnetic resonance imaging (MRI) cannot reliably detect this change, since the relaxation properties of the cartilage are dominated by its collagen content. The applicability of a positively charged nitroxide as an MRI contrast agent in detection of the content of the negatively charged proteoglycans within the cartilage was investigated. The results from both MRI and electron paramagnetic resonance (EPR) spectroscopy indicate that the accumulation of the contrast agent reflects the amount of proteoglycans within the cartilage, presumably due to the electrostatic interactions between the negatively charged proteoglycans and the positively charged nitroxide. Such a contrast agent could be useful in the detection and study of early stages of the degeneration of joints.

Animals↗
PubMed1997

Histological assessment of rodent CNS tissues to EPR oximetry probe material.

The effects of the paramagnetic oxygen sensing material, lithium phthalocyanine (LiPc) and fusinite were assessed in the brain of Mongolian gerbils and the spinal columns of rats respectively, to determine if there are histologically discernible changes in the tissue surrounding the probe material. This information is essential for the evaluation of the role of EPR oximetry in the measurements of pO2 in the CNS; the technique has great potential value for such measurements because it reports on the pO2 accurately and sensitively and, after the initial placement, measurements can be made repeatedly without invasive procedures or anesthesia. Histologic assessments demonstrated the inert nature of both the fusinite and LiPc EPR probes in rodent CNS tissue over relatively long (2 month) time periods. The fusinite suspensions and LiPc crystals (size range of approximately 100-200 microns) remained well localized to the point of injection and created mild acute tissue reaction on implantation (which appeared to resolve quickly) and virtually no tissue reaction at later times. The majority of the implanted fusinite and LiPc material was present extracellularly in the brain and spinal cord. MRI provided an accurate, noninvasive assessment of probe placement and was able to investigate pathologic effects (hemorrhage, edema, necrosis) associated with the probe placement and treatment effects.

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