[Interstitial T1-weighted MR lymph fistulography with Gadomer-17 in an experimental animal model]. / Interstitielle T1-gewichtete MR-Lymphfistulographie mittels Gadomer-17 im Tierexperiment.

PURPOSE: To visualize and localize fistulas of the thoracic duct with interstitial T 1 -weighted MR lymphography using Gadomer-17. MATERIALS AND METHODS: In 10 domestic pigs, leaks of the thoracic duct were created surgically or interventional-radiologically. The lymphatic leakage was located within the abdominal portion of the thoracic duct in 5 pigs, within the thoracic portion of the thoracic duct in 3 pigs, and in both, abdominal and thoracic portions of the thoracic duct, in 2 pigs. Subsequently, 10 micro mol/kg KG Gadomer-17 (1.5-1.8 ml) was administered interstitially in both hind legs of the animals. MR lymphography was performed with a 1.5 T MR unit using two different 3D gradient echo sequences before and 10 - 90 minutes after administration of contrast material. RESULTS: Leaks within the abdominal portion of the thoracic duct were directly visible as opacified fistulas. Indirect signs of active lymphatic fistulas were increasing extravasations of contrast material and free abdominal fluid. The 3D gradient echo sequence with the highest planar resolution (TR = 8,7 - 8,8 ms, TE = 4,2 - 4,3 ms, FA = 40 degrees, matrix size = 327 x 512) was best suited for distinct delineation of the lymphatic system and detailed demonstration of the thoracic duct fistulas. Intrathoracic leaks could not be demonstrated by MR lymphography due to reduced lymphatic flow or extravasated contrast medium at the abdominal puncture site. CONCLUSION: Interstitial MR lymphography with Gadomer-17 allows sensitive detection and localization of abdominally located leaks of the thoracic duct.

[Interstitial T1-weighted MR lymphography with use of the dendritic contrast agent Gadomer-17 in pigs]. / Interstitielle T1-gewichtete MR-Lymphographie mit dem polymeren Kontrastmittel Gadomer-17 im Tierexperiment.

PURPOSE: To investigate the enhancement of regional lymph nodes, lymph vessels and the thoracic duct after subcutaneous administration of the dendritic contrast agent Gadomer-17. MATERIALS AND METHODS: Interstitial T(1)-weighted MR lymphography was performed in 15 domestic pigs in a 1.5 T MR scanner using the body coil. The contrast agent was injected subcutaneously at a dose of 2.5, 10 and 20 micromol gadolinium/kg/bw (1.4 - 2.3 ml) in the hind legs of 5 pigs, respectively. T(1)-weighted coronal 3D-gradient-echo images were obtained 1 to 150 minutes and 24 hours after contrast material injection. RESULTS: Inguinal lymph nodes, iliac lymph nodes and lymph vessels showed peak enhancement within 10 minutes after subcutaneous administration of the contrast agent. The enhancement of the lymphatic system decreased slowly until 150 minutes post injection. The time-response study, which was performed for inguinal and iliac lymph nodes, revealed the best lymphographic effect for Gadomer-17 at a dose of 10 micromol gadolinium/kg/bw. At this dose the paraaortic lymph nodes and the thoracic duct were also best visualized. CONCLUSION: Interstitial administration of the evaluated dendritic contrast agent Gadomer-17 is highly efficient for the performance of T(1)-weighted MR lymphography in regional lymph nodes, lymph vessels and the thoracic duct.

Interstitial T1-weighted MR lymphography: lipophilic perfluorinated gadolinium chelates in pigs.

PURPOSE: To investigate the enhancement of the regional lymph nodes, lymphatic vessels, and thoracic duct after interstitial administration of lymphotropic perfluorinated gadolinium chelates at magnetic resonance (MR) imaging. MATERIALS AND METHODS: Two perfluorinated gadolinium chelates, gadofluoramide and gadofluorine 8, were injected subcutaneously into the hind legs of 10 pigs, respectively. Both contrast media were studied at doses of 10 and 25 micromol per kilogram of body weight. T1-weighted three-dimensional gradient-echo and maximum intensity projection images were obtained at 1.5 T between 1 and 210 minutes and 24 hours after injection. The contrast agents were qualitatively compared regarding enhancement and depiction of the regional lymph nodes, lymphatic vessels, and thoracic duct. RESULTS: The inguinal and iliac lymph nodes and lymphatic vasculature enhanced substantially within 10 minutes after subcutaneous administration of both lymphotropic contrast agents. Gadofluorine 8 showed a lymphographic effect superior to that of gadofluoramide. The paraaortic lymph nodes and thoracic duct were best visualized 10--50 minutes after injection of 25 micromol/kg of gadofluorine 8. Lymphatic system enhancement diminished after 2 hours, and the liver and bowel tract enhanced within 24 hours. CONCLUSION: Interstitial administration of perfluorinated gadolinium chelates offers great potential for T1-weighted MR lymphography with positive enhancement of the lymph nodes and lymphatic vasculature.

Experimental MR imaging-guided interstitial cryotherapy of the brain.

BACKGROUND AND PURPOSE: Hyperthermal ablation techniques such as laser or RF ablation require dedicated heat-sensitive MR imaging sequences for monitoring MR imaging--guided interventions. Because cryotherapy does not have these limitations, the purpose of this study was to evaluate the feasibility of MR imaging--guided percutaneous cryotherapy of the brain. METHODS: An experimental cryoprobe with an outer diameter of 2.7 mm was inserted into the right frontal lobe of 11 healthy pigs under MR imaging control. Freezing procedures were monitored by using an interventional 1.5-T magnet and a gradient-echo sequence with radial k-space trajectories, a fast T2-weighted single-shot spin-echo sequence, and a T1-weighted single-shot gradient-echo sequence. In three animals, the procedure was also monitored by using dynamic CT. A freeze-thaw cycle with a duration of 3 minutes was repeated three times per animal. Follow-up MR images were obtained 3, 7, and 14 days after cryotherapy by using conventional MR sequences. Six animals were killed 7 days after intervention, and five animals were killed 14 days after intervention. The brains were sectioned, and the histologic findings of the lesions were compared with the MR imaging appearance. RESULTS: No artifacts due to the probe were observed on the MR images or CT scans. The ice formation (mean diameter, 12.5 mm) was very well delineated as a signal-free sphere. MR monitoring of the freezing procedure yielded a significantly higher ice:tissue contrast than did CT. The size of the ice ball as imaged by MR imaging and CT during the intervention correlated well with the MR imaging appearance of the lesions at the 14-day follow-up examination and with the histologic findings. Histologically, coagulation necrosis and gliosis were found, surrounded by a transition zone of edema and a disrupted blood-brain barrier, corresponding to a contrast-enhancing rim around the lesions on follow-up MR images. CONCLUSION: MR imaging-guided cryotherapy of the brain is possible and allows a precise prediction of the resulting necrosis. MR imaging of the freezing process does not require heat-sensitive sequences and is superior to CT for monitoring of cryoablation.

MR-guided percutaneous cryotherapy of the liver: in vivo evaluation with histologic correlation in an animal model.

The purpose of this study was to evaluate the feasibility of MR-guided percutaneous cryotherapy of the porcine liver and to correlate the resulting tissue necrosis with MR imaging and histology. Using an MR-compatible, argon-based cryotherapy system (CryoHit; Galil Medical Ltd., Israel) with 2- and 3-mm diameter tapered cryotherapy probes, MR-guided percutaneous cryotherapy was performed in seven pigs (mean body weight, 40 kg) under general anesthesia in a short-bore magnet (1.5 T ACS NT; Philips, The Netherlands) using an ultrafast T2-weighted single-shot LoLo TSE sequence and a T1-weighted gradient-echo sequence. The frozen liver tissue was depicted accurately on fast T2- and T1-weighted sequences, providing precise delineation of the ablated tissue volume. On follow-up postcontrast MR controls, the cryolesions appeared avascular. They decreased in size compared with the initially frozen volume down to 70% at a 2-week follow-up. Histologically, a coagulation necrosis with a close correlation to the MR follow-up examinations was objectified. No cryotherapy-related complications occurred. J. Magn. Reson. Imaging 2001;13:50-56.

Comparison of two stent-grafts with different porosity: in vivo studies in a sheep model.

PURPOSE: To compare two stent-grafts with a polyurethane-carbonate (PUC) polymer lining of different pore size and water permeability in the iliac arteries of sheep. MATERIALS AND METHODS: Two stent-grafts with an inner PUC-lining of normal and low water permeability (normal, 1,200 mL/min/cm2; low, 280 mL/min/cm2; pressure gradient, 20 mm Hg) were implanted in each of 16 sheep. Hoop strength was two times higher in low-permeable than in normal-permeable stent-grafts. Patency was monitored with use of angiography and intravascular ultrasound (IVUS) after 1, 3, and 6 months. The sheep were killed after 1 or 6 months. Specimens were studied histologically. IVUS and histologic data were analyzed statistically. RESULTS: IVUS measurements showed a wider patent lumen of the low- compared to the normal-permeable prostheses at all time points (P < .03). This is likely due to the greater hoop strength of the low-permeable stent-graft. After 1 month, both types of prostheses demonstrated complete transprosthetic tissue penetration and were covered with neointima and endothelium. The neointimal area was greater in low- than in normal-permeable stent-grafts (1 month, P < .005; 6 months, P < .03). CONCLUSIONS: Presumably, the higher permeability of the normal-permeable stent-grafts led to the reduced neointimal area by improving transprosthetic capillary ingrowth and endothelialization.

Quantification of horseradish peroxidase delivery into the arterial wall in vivo as a model of local drug treatment: comparison between a porous and a gel-coated balloon catheter.

PURPOSE: To quantify horseradish peroxidase (HRP) delivery into the arterial wall, as a model of local drug delivery, and to compare two different percutaneous delivery balloons. METHODS: Perforated and hydrophilic hydrogel-coated balloon catheters were used to deliver HRP in aqueous solution into the wall of porcine iliac arteries in vivo. HRP solutions of 1 mg/ml were used together with both perforated and hydrophilic hydrogel-coated balloon catheters and 40 mg/ml HRP solutions were used with the hydrogel-coated balloon only. The amount of HRP deposited in the arterial wall was then determined photospectrometrically. RESULTS: Using the 1 mg/ml HRP solution, the hydrogel-coated balloon absorbed 0.047 mg HRP into the coating. Treatment with this balloon resulted in a mean vessel wall concentration of 7.4 microg HRP/g tissue +/- 93% (standard deviation) (n = 7). Treatment with the hydrogel-coated balloon that had absorbed 1.88 mg HRP into the coating (using the 40 mg/ml HRP solution) led to a mean vessel wall concentration of 69.5 microg HRP/g tissue +/- 74% (n = 7). Treatment with the perforated balloon using 1 mg/ml aqueous HRP solution led to a mean vessel wall concentration of 174 microg/g +/- 81% (n = 7). Differences between the hydrogel-coated and perforated balloons (1 mg/g solutions of HRP) and between hydrogel-coated balloons (0.047 mg vs 1.88 mg absorbed into the balloon coating) were significant (p < 0.05; two-sided Wilcoxon test). CONCLUSIONS: The use of a perforated balloon catheter allowed the delivery of a higher total amount of HRP compared with the hydrogel-coated balloon, but at the cost of a higher systemic HRP application. To deliver 174 microg HRP per gram of vessel wall with the perforated balloon, 6.5 +/- 1.5 mg HRP were lost into the arterial blood (delivery efficiency range = 0.2%-0.3%). With 0.047 mg HRP loaded into the coating of the hydrogel balloon, 7.4 microg HRP could be applied to 1 g of vessel wall (delivery efficiency 1.7%), and with 1.88 mg HRP loaded into the coating of the hydrogel balloon, 69.5 microg HRP could be applied per gram of vessel wall (delivery efficiency 0.6%).

Magnetic resonance angiography of nonferromagnetic iliac artery stents and stent-grafts: A comparative study in sheep.

PURPOSE: To compare nonferromagnetic iliac artery prostheses in their suitability for patency monitoring with magnetic resonance angiography (MRA) using conventional angiography as a reference. METHODS: In experiment 1, three Memotherm stents were inserted into the iliac arteries of each of six sheep: two "tandem" stents on one side and a single stent on the other side. In experiment 2, four prostheses (normal and low-porosity Corvita stent-grafts, Memotherm, ZA-stent) were inserted in each of 11 sheep. Patency was monitored before and 1, 3, and 6 months after insertion with 3D phase-contrast and two 2D time-of-flight sequences (TOF-1: TR/TE = 18/6.9, TOF-2: 13/2.5) with and without contrast at 1.5 T. On 206 coronal MIP images (72 pre-, 134 post-stenting), three readers analyzed 824 iliac segments (206 x 4) for patency and artifacts. RESULTS: There was no difference in the number of artifacts between tandem and single iliac Memotherm stents. The ZA-stent induced significantly fewer artifacts than the other prostheses (p < 0.00001). With MRA, patency of the ZA-stent was correctly diagnosed in 88% of cases, which was almost comparable to nonstented iliac segments (95%), patency of the Memotherm stent in 59%, and of the Corvita stent-grafts in 57% and 55%. The TOF-2 sequence with contrast yielded the best images. CONCLUSION: MRA compatibility of nonferromagnetic prostheses depends strongly on the design of the device. MRA may be used to monitor the patency of iliac ZA-stents, whereas iliac Memotherm stents and Corvita stent-grafts appear to be less suited for follow-up with MRA.

[Experimental MRI-controlled cryotherapy of the brain with almost real-time imaging by radial k-space scanning]. / Experimentelle MR-gesteuerte Kryotherapie des Gehirns mit nahezu Echtzeitdarstellung durch radiale k-Raum-Abtastung.

PURPOSE: To test radial k-space scanning by MR fluoroscopy to guide and control MR-guided interstitial cryotherapy of the healthy pig brain. METHODS: After MR tomographic planning of the approach, an MR-compatible experimental cryotherapy probe of 2.7 mm diameter was introduced through a 5 mm burr hole into the right frontal brain of five healthy pigs. The freeze-thaw cycles were imaged using a T1-weighted gradient echo sequence with radial k-Space scanning in coronal, sagittal, and axial directions. RESULTS: The high temporal resolution of the chosen sequence permits a continuous representation of the freezing process with good image quality and high contrast between ice and unfrozen brain parenchyma. Because of the interactive conception of the sequence the layer plane could be chosen as desired during the measurement. Ice formation was sharply demarcated, spherically configurated, and was free of signals. Its maximum diameter was 13 mm. CONCLUSIONS: With use of the novel, interactively controllable gradient echo sequence with radial k-space scanning, guidance of the intervention under fluoroscopic conditions with the advantages of MRT is possible. MR-guided cryotherapy allows a minimally-invasive, precisely dosable focal tissue ablation.

Experimental treatment of early chronic iliac vein thrombosis with a modified hydrodynamic thrombectomy catheter: preliminary animal experience.

PURPOSE: To evaluate the efficacy and safety of a new hydrodynamic catheter for removal of chronic iliac vein thrombus. METHODS: Unilateral iliac vein thrombosis was induced in seven pigs by combining permanent coil and temporary balloon occlusion. Thrombectomy was performed with a new hydrodynamic catheter (10 F S.E.T.) 3 days after thrombus induction. After thrombectomy, the animals were killed and the iliac veins were examined histologically. RESULTS: Complete thrombectomy (100% thrombus removal) was achieved in three of seven animals, 75% removal in three of seven animals, and only 30% removal in one animal. The average thrombus removal was 75%. Successful re-establishment of flow was achieved in five of seven cases. Histologically, the thrombi were partially organized, meeting the histologic criteria for early chronic venous thrombosis. Minor venous wall damage caused by the thrombectomy procedure without acute hemodynamic consequences was observed in four of seven cases. CONCLUSION: The 10-F S.E.T. catheter was reasonably effective in removing chronic iliac vein thrombus with no hemodynamically significant complications.

Single and tandem stents in sheep iliac arteries: is there a difference in patency?

PURPOSE: To compare patency and neointima formation of single and tandem arterial stents. METHODS: In each of six sheep, two Memotherm nitinol stents (tandem stents) were inserted into the external iliac artery on one side and a single stent into the artery on the opposite side. The size of the iliac lumen was assessed in the proximal, middle, and distal segments of the stents by intravascular ultrasound (IVUS) before, immediately after, and 1 month after implantation when the sheep were killed. Neointimal thickness was determined in the proximal, middle, and distal segments of each stent by light microscopy. RESULTS: All stents remained patent. There was no significant difference in lumen and neointimal thickness between single and tandem stents. Cranial tandem stents showed a significantly wider lumen and smaller neointimal thickness than caudal tandem stents. In the proximal and distal segments, the lumen of the stents was significantly smaller and the neointimal thickness greater than in the middle segment; differences in neointimal thickness were significant only between the proximal and the middle segment. CONCLUSION: In an experimental setting, tandem stents did not interfere with one another with regard to patency and neointima formation when compared with a single contralateral stent. Neointimal thickening after stent insertion seems to be inversely related to the original arterial diameter.

[Real-time MRI with radial k-radial scanning technique for control of angiographic interventions]. / Echtzeit-MR mit radialer k-Raumabtastung zur Uberwachung angiographischer Interventionen.

PURPOSE: To test the feasibility of real-time MR controlled guidance of field-inhomogeneity catheters in vitro and in vivo as a first step to MR-guided angiographic interventions. METHODS: Applying a combination of radial scanning with the sliding window reconstruction technique, a frame rate of 23 low resolution images per second was achieved. Field inhomogeneity catheters were steered through a flow phantom and into the renal arteries of a pig. RESULTS: It was possible to visualize flow or, respectively, vessels and to depict catheter movements. This enabled real-time MR-guidance of the catheter into the renal arteries of the flow phantom and into those of the pig. CONCLUSIONS: The new technique yields a sufficiently high temporal resolution for MR-guidance of catheters through vessels.

[Sutureless vascular end-to-side anastomosis: an in-vivo test of a percutaneous concept in the animal model]. / Nahtfreie vaskuläre End-zu-Seit-Anastomose: in-vivo-Test eines perkutanen Konzeptes im Tiermodell.

PURPOSE: To test a percutaneous concept for creation of a sutureless terminolateral vascular anastomosis in vivo. MATERIAL AND METHOD: By creating sideholes into the middle portion of a stent and a stent graft, both implants could be arranged in a Y-shaped configuration. An arteriovenous shunt was created in 3 sheep between the left carotid artery and the left external jugular vein. A stent graft was partially inserted into the venous lumen. Axial venous patency was restored by placing a stent through the sidehole into the graft lumen from an upstream puncture site. Graft patency was maintained by placing the sidehole of the stent at the bridging point between stent graft and stent with no stent struts crossing. Arterial end-to-end anastomosis was performed by retrograde placement of a stent graft into the arterial lumen. Both anastomoses were connected by a silicone tube. RESULTS: In all cases, a venous end-to-side anastomosis was created that was blood-tight and safely secured into the vascular lumen. CONCLUSION: Y-shaped configuration of stent and stent grafts through sideholes allows creation of sutureless end-to-side anastomoses in vivo.