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Biomedical subjects

J Tacke

Publications and source records attributed to J Tacke.

At least 37 records · Page 2Linked to original sources
PubMed2001

Nephron-sparing percutaneous ablation of a 5 cm renal cell carcinoma by superselective embolization and percutaneous RF-ablation.

PURPOSE: To report on the nephron-sparing, percutaneous ablation of a large renal cell carcinoma by combined superselective embolization and percutaneous radiofrequency ablation. MATERIALS AND METHODS: A 5 cm renal cell carcinoma of a 43-year-old drug abusing male with serologically proven HIV, hepatitis B and C infection, who refused surgery, was superselectively embolized using microspheres (size: 500 - 700 microm) and a platinum coil under local anesthesia. Percutaneous radiofrequency ablation using a 7 F LeVeen probe (size of expanded probe tip: 40 mm) and a 200 Watt generator was performed one day after transcatheter embolization under general anesthesia. RESULTS: The combined treatment resulted in complete destruction of the tumor without relevant damage of the surrounding healthy renal tissue. The patient was discharged 24 hours after RF ablation. No complications like urinary leaks or fistulas were observed and follow up CT one day and 4 weeks after the radiofrequency intervention revealed no signs of residual tumor growth. CONCLUSION: The combined transcatheter embolization and percutaneous radiofrequency ablation of renal cell carcinoma has proved technically feasible, effective, and safe in this patient. It may be offered as an alternative treatment to partial or radical nephrectomy under certain circumstances.

Adult↗
PubMed2001

[Gadolinium-enhanced T(1)-weighted MR urography versus T(2)-weighted (HASTE) MR urography in children].

PURPOSE: To evaluate gadolinium-enhanced T(1)-weighted excretory MR urography (EMRU) versus T(2)-weighted (HASTE) MR urography in children with upper urinary tract abnormalities. PATIENTS AND METHODS: In a prospective study 63 children, aged from 3 weeks to 15 years, underwent MR urography in a 1.5-T scanner. Before and after an intravenous injection of 0.05 mg/kg body weight of furosemide, respiratory-triggered HASTE images were obtained for T(2)-weighted MR urography. EMRU was performed subsequent to i. v. gadolinium injection with respiratory-gated, coronal 3 D-gradient-echo sequences. RESULTS: Compared to T(2)-weighted (HASTE) MR urography, gadolinium-enhanced MR urography revealed a superior diagnostic accuracy in non-dilated collecting systems (horseshoe kidneys, ectopic kidneys, duplex systems, single ectopic ureters, ureteroceles). EMRU and T(2)-weighted (HASTE) MRU turned out to be equivalent in the assessment of obstructed but normal functioning upper urinary tracts (UPJ obstructions, megaureters). Non-functioning dilated collecting systems and multicystic dysplastic kidneys were best visualized with use of T(2)-weighted (HASTE) MR urography. CONCLUSION: Respiratory-gated gadolinium-enhanced T(1)-weighted MRU allows accurate evaluation of most upper urinary tract abnormalities. T(2)-weighted (HASTE) MRU complements GMRU in the evaluation of non-functioning renal units and cystic disease of the kidneys.

Adolescent↗
PubMed2001

Prototype percutaneous thrombolytic device: preclinical testing in subacute inferior vena caval thrombosis in a pig model.

PURPOSE: To develop an animal model of subacute inferior vena caval (IVC) thrombosis and apply this model in evaluating the safety and efficacy of a prototype percutaneous thrombolytic device for restoring patency. MATERIALS AND METHODS: In 11 pigs, a stent with a ligature in the middle was placed in the IVC. Thrombin was injected to induce thrombosis. Hemostasis was achieved by using an occlusion balloon. The stent was ligated to prevent thrombus migration. Five to 8 days after thrombus induction, the ligature was broken and the stent fully deployed. In 10 animals, thrombectomy was performed by using the percutaneous thrombolytic device. A vena caval filter was inserted at the beginning of each declotting procedure. Thrombus removal percentage was estimated and pulmonary angiograms obtained to detect embolism before and after thrombectomy. The IVC was analyzed histologically. To determine thrombus composition, one animal was sacrificed without thrombectomy. Concerning procedural safety, failure of the stent delivery system, stent migration, and venous perforation due to balloon inflation and the stent placement or thrombectomy procedure were evaluated. RESULTS: Thrombus creation was successful in all animals. Fragmentation led to 75%--100% thrombus removal with flow restoration in all cases. There were no episodes of stent delivery failure, stent migration, or venous perforation. No significant pulmonary embolism was observed. In one case, a vessel dissection was identified at histologic examination. CONCLUSION: In this animal model of IVC thrombosis, the percutaneous thrombolytic device is effective and safe for clot removal.

Animals↗
PubMed2001

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.

Animals↗
PubMed2001

Thermal therapies in interventional MR imaging. Cryotherapy.

Cryotherapy of the brain is an old and well-established technique of functional and resective neurosurgery. With the use of modern imaging techniques such as MR imaging, which is ideally suited for diagnosis, planning, and monitoring of an ablation procedure, cryotherapy can become a modern alternative to other ablation techniques. In contrast to hyperthermal ablation tools such as laser or radiofrequency ablation, cryotherapy has specific potentials. First and most importantly, the freezing process ideally can be precisely monitored by MR imaging during the procedure without any specific temperature-sensitive pulse sequence. As shown in the experimental study, several techniques including conventional gradient echo sequences, ultrafast subsecond MR sequences, and MR fluoroscopy, are suited for monitoring the freezing process. Furthermore, the volume of the damaged tissue, as imaged by MR imaging, does not increase after completion of the ablation procedure. The extension of the ice corresponds well to the final, histologically confined necrosis and allows a high predictability of the resulting necrosis. Although not yet in clinical use, the combination of minimally invasive modern cryotherapy devices and ultrafast interventional MR techniques offer a promising alternative to other ablation techniques. In addition, it holds great promise for minimally invasive neurologic procedures in the near future. Further technical modifications and clinical studies, however, are necessary to establish the potential of this new treatment option.

Brain↗
PubMed2000

[Interventional magnetic resonance imaging--non-invasive imaging for interventions].

As a prerequisite for MR-guidance of interventional procedures, instruments have to be well depicted in the MR image without obscuring or distorting the underlying anatomy. For non-vascular interventions the imaging speed has to be in the range of seconds while control of vascular interventions requires real time imaging speed. The imaging contrast has to be maintained as well as a high spatial resolution. Furthermore, sufficient patient access has to be provided by the MR scanner. Neither an ideal magnet nor the optimal single sequence are available to fulfill the above-mentioned criteria. The type of sequence--gradient echo versus spin echo--together with changing of the echo time and phase encoding direction will ensure an appropriate size of the artifact and thereby of the appearance of the instrument in the MR image. The feasibility of non-vascular MR-guided interventions has been proved at field strengths ranging from 0.064 T to 1.5 T. Bone biopsies, soft tissue biopsies, drainages, and control of interstitial thermo- and cryotherapy have been reported. For vascular interventions, different real time MR strategies are currently under investigation. The development of dedicated catheters and guide wires has enabled MR-guided dilatations, stenting, placement of vena cava filters, and TIPS procedures. Considering the fast progress being made in this field, there can be no question that interventional MRI will become a well-accepted clinical tool offering potential advantages such as excellent soft tissue contrast, multiplanar imaging, flow measurements, high resolution imaging of vessel walls, and lack of ionizing radiation.

Artifacts↗
PubMed2000

[Aerosolized gadolinium-DTPA for demonstration of pulmonary ventilation in magnetic resonance tomography].

PURPOSE: Magnetic resonance assessment of lung ventilation with aerosolized Gd-DTPA. METHODS: Eleven experimental procedures were carried out in a domestic pig model. The intubated pigs were aerosolized for 30 minutes with an aqueous formulation of Gd-DTPA. The contrast agent aerosol was generated by a small particle aerosol generator. Imaging was performed on a 1.5 T MR imager using a T1-weighted turbo spin echo sequence with respiratory gating (TR 141 ms, TE 8.5 ms, 6 averages, slice thickness 10 mm). Pulmonary signal intensities before and after ventilation were measured in peripheral portions of both lungs. RESULTS: Immediately after ventilation with aerosolized Gd-DTPA, the signal intensity in both lungs increased significantly in all animals with values up to 237% above baseline (mean 139% +/- 48%), but with in some cases considerable regional intra- and interindividual intensity differences. Distinctive parenchymal enhancement was readily visualized in all eleven cases with good spatial resolution. CONCLUSION: The presented data indicate that Gd-DTPA in aerosolized form can be used to demonstrate pulmonary ventilation in large animals with lung volumes comparable to man. Further experimental trials are necessary to improve reproducibility and to define the scope of this method for depicting lung disease.

Aerosols↗
PubMed2000

MRI of the inner ear: comparison of axial T2-weighted, three-dimensional turbo spin-echo images, maximum-intensity projections, and volume rendering.

RATIONALE AND OBJECTIVES: To compare the ability of axial T2-weighted, three-dimensional, turbo spin-echo (3D TSE) images, targeted maximum-intensity projections (MIPs), and 3D volume reconstructions to depict anatomic details of the labyrinth. METHODS: In 24 volunteers, 3D TSE images were obtained. MIPs and 3D volume reconstructions were performed from the acquired data. All images were evaluated by three radiologists independently regarding the visualization of the different anatomic structures. RESULTS: In the axial slices, most anatomic details were visible in comparison with observations by the other modalities. The 2.5 windings of the cochlea were best depicted on the MIPs. Volume reconstructions rendered excellent spatial information regarding the vestibule and semicircular canals and were the only technique that demonstrated all three ampullae in all cases. CONCLUSIONS: Axial TSE images, MIPs, and 3D volume reconstructions are complementary modalities that provide different information. Our results suggest that improved diagnostic information can be obtained by applying these volume visualization reconstruction techniques.

Adult↗
PubMed1999

Preoperative assessment of mortality risk in hepatic resection by clinical variables: a multivariate analysis.

Hepatic resection is a chance for cure for primary and secondary liver tumors and a variety of benign diseases. Despite advances in surgical technique and patient care, preoperative and postoperative morbidity in patients undergoing liver resection remains high. Because a high morbidity represents a risk factor contributing to a fatal outcome of the surgical procedure, our study aimed to investigate the contribution of different risk factors to a fatal outcome and if mortality can be predicted by the presence of certain risk factors. Two hundred fifty-seven patients undergoing hepatic resection (curative and palliative) were analyzed preoperatively, immediately after surgery, and 10 days after surgery for 60 potential risk factors. Survivors (n = 238) and nonsurvivors (n = 19) were compared univariately. The analysis identified 14 variables to differentiate between groups. These variables were processed by multivariate logistic regression analysis. Three models to estimate 30-day mortality were identified, tested for statistical accuracy, and assessed for their receiver-operated characteristics (ROCs). The variables in the multivariate models were as follows: preoperatively, age, number of comorbid factors, and presence of cirrhosis; immediately after surgery, age, number of comorbid factors, and percentage of resected liver; and 10 days after surgery, age, hours of ventilation, and number of adverse events. Goodness of fit was 0. 863, 0.912, and 0.966, respectively. Areas under the ROC curves were 83.6%, 85.7%, and 98.0%. The specificity (probability to identify survivors correctly) was greater than 90% for all models, although sensitivity (probability to identify nonsurvivors correctly) was greater than 90% only for 10 days after surgery. We conclude that logistic regression is appropriate to assess the importance of risk factors in the course of hepatic resection and to identify patient groups at high risk.

Female↗
PubMed1999

Imaging of interstitial cryotherapy--an in vitro comparison of ultrasound, computed tomography, and magnetic resonance imaging.

RATIONALE AND OBJECTIVES: To evaluate the imaging capabilities of ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI) in monitoring interstitial cryotherapy and to compare them with visual control. METHODS: An experimental MR-compatible, vacuum-insulated and liquid nitrogen-cooled cryoprobe was inserted under in vitro conditions into a porcine liver, which was kept at a temperature of 37 +/- 1 degrees C, in a water bath with continuous stirring. The freezing procedure was controlled macroscopically, by US (Toshiba Sonolayer, 7.5-MHz linear array transducer), by CT (Siemens Somatom Plus, slice thickness 2-8 mm, 165-210 mA at 120 kV), and by MRI (Philips Gyroscan ACS-NT, FFE TR/TE/FA = 15/5.4/25 degrees, T1-SE 550/20, T2-TSE 1800/100) after the iceball reached its maximum size. RESULTS: The maximum iceball diameter around the probe tip was 12.0 mm by visual control, 12.4 mm by US, 12.7 mm by CT, and within 12.8 mm by spin echo sequences and 11 mm by gradient echo sequence. Due to the nearly signal-free appearance of the frozen tissue on MR images, the ice/tissue contrast on T1-weighted and gradient echo images was superior to T2-weighted images and CT images. Sonographically, the ice formation appeared as a hyperechoic sickle with nearly complete acoustic shadowing. CONCLUSION: Due to the better ice/tissue contrast, T1-weighted or gradient echo MR images were superior to CT and US in monitoring interstitial cryotherapy. Gradient echo sequences generally underestimated the ice diameter by 15%.

Animals↗
PubMed1999

Interventional MR imaging: percutaneous abdominal and skeletal biopsies and drainages of the abdomen.

Since the introduction of open magnets and short-bore closed magnets, and the availability of fast imaging sequences, MR imaging has become a tool for guidance and control of percutaneous nonvascular and vascular procedures. In general, percutaneous biopsies or drainages require no specific hardware or software modifications. For lesion localization and control of the needle track, simple fast imaging sequences such as fast T1-weighted gradient-echo techniques or fast single-shot T2-weighted spin-echo sequences are sufficient and can be applied depending on the best tissue-to-lesion contrast. Typical scan times range from 1 to 3 s. Different types of biopsy needles are commercially available, allowing sampling of sufficient amounts of tissue. For drainage procedures non-ferromagnetic materials, such as nitinol wires, should be preferred to minimize image distortion by metallic artifacts. Indications for percutaneous biopsies include subdiaphragmatic liver lesions, lesions poorly visible on ultrasound or contrast-enhanced computed tomography, and lesions of the bone marrow characterized by an unspecific bone marrow edema. For percutaneous drainages, subdiaphragmatic lesions appear to be a good indication. With some experience the procedure time is not longer than that under CT or US guidance.

Abdomen↗
PubMed1999

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.

Animals↗
PubMed1999

[MR defecography at 1.5 Tesla with radial real-time imaging and reduced image field].

PURPOSE: To evaluate a new technique for MR defecography with real-time imaging using radial k-space profiles. MATERIALS AND METHODS: A catheter-mounted condom was inserted into the rectum of 16 patients and filled in situ by a mixture of Nestargel and Gadolinium. After multiplanar imaging of the pelvis by high resolution T2-weighted turbo-spin echo sequences, defecation was imaged by a gradient echo sequence with radial k-space filling using a reduced field of view (rFOV) in real-time. The documentation was performed on an S-VHS recorder. RESULTS: At a constant background signal, radial k-space filling yields a real-time impression. An interactive software allowed the operator to modify the slice thickness, slice plane, flip angle and slice angulation during scanning, resulting in an optimum imaging quality of the defecation. CONCLUSIONS: This new imaging technique allows real-time MR defecography in a high-field scanner and provides all anatomical und functional information of the defecation.

Adult↗
PubMed1999

[A smooth pneumatic motion device for dynamic MRI imaging of the cervical spine].

PURPOSE: To develop and evaluate a new, pneumatically operated motion apparatus for the dynamic functional MR examination of the cervical spine. MATERIALS AND METHODS: A metal-free, pneumatically operated motion apparatus for functional dynamic MR imaging of the cervical spine was developed with respect to the geometry of a short-bore, superconducting high-field MR system. The examination protocol included a T2-weighted multi-slice turbospin echo sequence (T2-TSE, TR/TE = 2610/115, matrix 254/512) and a dynamic T2-weighted single-shot sequence (T2-TSE, TR/TE = 1110/110, matrix 255/256, acquisition time 1 s) in a sagittal plane. In order to evaluate the new motion apparatus and the examination protocol, 10 healthy subjects and 10 patients were examined. RESULTS: The new motion apparatus allowed us to perform a passive stepless inclination and reclination motion of the patient's cervical spine within the MR scanner without leaving the magnet bore. The maximum motion degrees of the cervical spine were within -35 degrees (reclination) and 30 degrees (inclination). Due to the T2-contrast and the high spatial resolution of the dynamic sequence, the myelon, the surrounding cerebrospinal fluid and the discoligamental structures were imaged with a good contrast and allowed a sufficient evaluation of the cervical spinal channel in all functional positions. CONCLUSIONS: This new motion apparatus allows a standardized and stepless dynamic functional MR examination in a short-bore high-field MR scanner. By the use of fast T2-weighted spin echo sequences it has been shown to be of high value for the evaluation of the cervical myelon, the anterior and posterior cerebrospinal fluid and the discoligamental structures.

Biomechanical Phenomena↗
PubMed1999

[Magnetic-field-based navigation system for ultrasound-guided interventions].

PURPOSE: To describe a new magnetic field-based navigation system for ultrasound-guided interventional procedures. METHODS: The navigation system supports biopsies either in plane or out of plane. To evaluate the accuracy of the system, targets in four standard silicone phantoms were punctured. Six cystic and six solid lesions were present in every phantom. The success of the puncture was controlled by aspiration of the content of the lesions, which was coloured. Furthermore, liver lesions of different sizes (2-6 mm) and depths (3-6 cm) were produced by injecting a viscous fluid and punctured in three swine carcasses. Functions of the gallbladder and nephrostomies were carried out as well. RESULTS: All 48 targets were successfully punctured using the in plane and out of plane modus in the phantom. In the carcasses all 16 lesions were reached in plane. In the out of plane modus two 6 cm deep lesions were not reached. All other 14 biopsies were successful. Nephrostomy of the not dilated renal pelvis and punction of the gallbladder were successfully carried out. CONCLUSIONS: The described navigation system is a promising tool for fast and safe performance of ultrasound-guided interventional procedures.

Biopsy↗
PubMed1999

[Experimental MRI-controlled cryotherapy of the brain with almost real-time imaging by radial k-space scanning].

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.

Animals↗
PubMed1998

MR-guided interstitial cryotherapy of the liver with a novel, nitrogen-cooled cryoprobe.

The purpose of the study was to test a newly developed, MR-compatible, liquid nitrogen-cooled cryoprobe. The probe has an outer diameter of 3.5 mm and was specifically developed for percutaneous, MR-guided, interstitial cryotherapy. The probe was inserted percutaneously into the livers of 10 rabbits. The cryotherapy procedure was monitored with a surface coil in a 1.5 Tesla magnet using a gradient echo sequence. Follow-up examinations were performed 3 and 7 days after the freezing procedure using T1- and T2-weighted spin echo sequences. At 7 days the animals were sacrificed and the cryolesions were examined histologically. The cryoprobe enabled artifact-free MR imaging of the "iceball" formation during freezing of the rabbit liver. After 1 min of freezing, the iceball at the tip of the probe showed an average maximum diameter of 10.8 mm. No bleeding complications were observed during or after the freezing procedure. Histologic examination 7 days after cryotherapy confirmed that the liver lesions were the same size as had been predicted by the images of the acute iceball. This new, percutaneously inserted, MR-compatible, liquid-nitrogen cooled cryoprobe allows accurate, artifact-free MR imaging of interstitial cryotherapy.

Animals↗