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T Pfammatter

Publications and source records attributed to T Pfammatter.

70 records · Page 4Linked to original sources
PubMed1996

[Virtual intravascular endoscopy in the renal arteries: a new way of observing 3-D-MIR angiography data sets].

PURPOSE: To determine the potentials and limitations of a recently developed algorithm for virtual intravascular endoscopy (VIE) based on 3-dimensional (3-D) magnetic resonance (MR) data sets. METHOD: The data from 6 patients derived from gadolinium-enhanced MR angiography of the renal arteries were reviewed. All patients had unilateral or bilateral renal arterial pathologies (stenoses n = 2, aneurysms n = 4). Imaging was performed on a 1.5-T scanner using a 3-D gradient-echo MR sequence. The imaging parameters were as follows: TR/TE/flip angle 3.9/1.9/40 degrees, matrix 256 x 192, slice thickness 1.5 to 2 mm, FOV 32 cm, and 48 slices. Image acquisition time was 28 seconds under apnoeia conditions. A total of 60 ml 0.5 molar Gd-DTPA was injected during the scan. RESULTS: 3-D data sets could be obtained in all patients and postprocessed for VIE. The intraluminal vessel wall was depicted with high clarity in all cases. All pathologies that were not intraparenchymal could be easily seen. Limitations to the technique include the image quality of the original data set, use of the ideal threshold to minimise intraluminal artifacts, and a complicated prescription sequence. CONCLUSIONS: We have shown that VIE can be consistently performed in the renal arteries using MR data sets acquired with a contrast enhanced 3-D gradient-echo technique. It provides a hitherto unused approach to viewing 3-D vascular MR data sets.

Adolescent↗
PubMed1996

Breath-hold, contrast-enhanced, three-dimensional MR angiography.

Breath-hold gadolinium-enhanced three-dimensional magnetic resonance (MR) angiography was performed with a high-performance gradient MR imaging system in 10 volunteers with no history of vascular abnormalities (breath-hold interval, 28 seconds; repetition time, 4.0 msec; echo time, 1.9 msec; 0.4 mmol gadoterate meglumin per kilogram of body weight). High-resolution three-dimensional time-of-flight angiograms of the aorta, renal arteries, pulmonary arteries, pelvic arteries, and portal venous system were successfully acquired in all cases.

Adolescent↗
PubMed1990

[MR pelvimetric reference values].

Complete pelvimetry can be easily performed via MR. As shown by comparing the measurements of 4 observers its reproducibility is acceptable. The reference diameters obtained on 53 patients by MR are in 7 out of 9 dimensions larger than those of anatomical and obstetrical textbooks, which have not changed in the last 100 years. Hence, with the general increase in population size an increase in pelvic diameters has taken place.

Adolescent↗
PubMed1989

[Pelvimetry with magnetic resonance tomography].

Magnetic resonance imaging (MRI) in the mediosagittal and transverse planes was used to measure the antero-posterior and transverse diameters of the minor pelvic cavity. The measurements for the diameters were larger than those usually found in the literature. The antero-posterior pelvic inlet diameter, the most important measurement for obstetrics, was on average 11.9 cm in contrast to the generally accepted length of 11.0 cm.

Adolescent↗
PubMedDate not supplied

Alveolar echinococcosis of the liver: sequelae of chronic inferior vena cava obstructions in the hepatic segment.

BACKGROUND: The clinical pattern and long-term course of chronic inferior vena cava (IVC) obstructions are variable and depend on the underlying cause, the segment involved, and the extension of secondary thrombosis. Pertinent data on IVC obstructions in well-defined series of patients are lacking. We report the sequelae of chronic IVC obstructions in the hepatic segment in 11 consecutive patients derived from a cohort of 104 patients with alveolar echinococcosis of the liver. METHODS: Based on the results of computed tomography scans, 11 patients (7 men, 4 women; mean age, 53.4 years) with IVC obstructions were selected from an ongoing prospective long-term chemotherapy trial comprising 104 patients with alveolar echinococcosis studied at yearly intervals according to a protocol. Obstruction of the IVC in the 11 patients existed for a mean duration of 8.6 years. In these patients, magnetic resonance imaging was performed to assess the morphologic features and extension of the IVC obstruction, as well as the collateral venous pathways. Patency and valvular function of the femoropopliteal veins were analyzed by color-coded duplex ultrasonography. RESULTS: Total occlusions of the IVC were evident in 8 patients (73%) and subtotal stenoses in 3 patients (27%). Only 4 patients (36%) exhibited signs and symptoms of chronic venous insufficiency of the lower extremities; 2 (18%) of the 4 had a history of swelling in the lower extremity. Seven patients (64%) had no lower extremity symptoms. One patient had a history of pulmonary embolism. Abdominal collateral veins were documented in 5 patients (45%) by using magnetic resonance imaging; however, they were clinically evident in only 3 patients (27%). In the 8 patients with IVC occlusion, thrombosis ended at the confluence of the hepatic veins. Obstruction of the IVC was limited to the hepatic segment in 2 patients (18%) and extended to the distal IVC or the iliofemoral veins in 6 patients (54%). Chronic venous insufficiency was present only if the femoropopliteal veins had been involved in the thrombotic process, showing residual venous obstruction, valvular incompetence, or both. Bilateral renal vein thrombosis with moderate proteinuria was observed in 2 patients (18%). The main collateral drainage was achieved through the ascending lumbar, azygos, and hemiazygos veins. CONCLUSIONS: In patients with alveolar echinococcosis, obstruction of the IVC in the hepatic segment often develops asymptomatically and rarely leads to the impairment of renal function. The collateral circulation fully compensates for obstruction of the IVC. Thrombotic involvement and valvular incompetence of the femoropopliteal veins seems to determine the development of chronic venous insufficiency of the lower extremities.

Adult↗
PubMedDate not supplied

Optimization of contrast timing for breath-hold three-dimensional MR angiography.

The purpose of this study was to determine the influence of various factors (age, weight, breathing, saline flush) on the contrast kinetics of a test bolus injection for the purpose of calculating the scan delay for optimized contrast-enhanced three-dimensional MR angiography. Initially, the test bolus administration was optimized by evaluating the influence of breathing (breathing versus breath-hold) and the administration of a saline flush after the contrast injection (no flush versus flush) on the kinetics of a 4-ml Gd-DTPA test bolus injection in three healthy volunteers. Subsequently, in 33 patients referred for three-dimensional MR angiography of the renal arteries, test bolus kinetics were correlated to age, weight, and heart rate. In addition, the image quality of the three-dimensional MR angiograms was assessed on a four-point scale with regard to vessel visibility. The administration of a saline flush after the contrast injection significantly shortened the first appearance time (14 versus 16 seconds, P < .05), as well as the time to maximal signal intensity (SI) (6 versus 10 seconds, P < .05) and increased both maximum (67 versus 151 seconds, P < .05) and the SI slope (6.4 versus 20.5 seconds, P < .05). Breath-holding was shown to have no significant affect on the test bolus kinetics. No correlation was found between physiologic parameters and test bolus kinetics in the patient group. Image quality was graded as sufficient for diagnostic purposes in 32 of 33 patients. The contrast travel time from injection site to the vascular system under consideration cannot be predicted based on physiologic parameters. This time interval can be reliably and accurately determined by a test bolus injection of a small volume of contrast agent followed by a saline flush during normal breathing.

Adult↗
PubMedDate not supplied

Value of image subtraction in 3D gadolinium-enhanced MR angiography of the renal arteries.

The objective of this study was to evaluate quantitatively and qualitatively the effect of image subtraction on the image quality of three-dimensional (3D) gadolinium-enhanced MR angiograms of the renal arteries. Breath-hold 3D gadolinium MR angiography (MRA) as well as conventional contrast angiography of the renal arteries was performed on 20 patients with suspected renovascular hypertension. MR angiograms were acquired before and during dynamic infusion of gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA). Contrast-enhanced images were compared with images that had undergone voxel-by-voxel signal intensity subtraction of contrast-enhanced data from precontrast data. One false positive finding for significant renal artery stenosis was recorded with MRA using conventional angiography as the gold standard. Image subtraction did not alter the diagnosis at MRA in any case. The mean contrast-to-noise ratio (CNR) was significantly higher (P < .05) on the subtraction MR angiograms compared to the nonsubtracted MR angiograms. There was no significant difference in the signal-to-noise ratio (SNR). Qualitative analysis revealed a significant improvement in image quality after image subtraction with respect to visualization of the distal renal arteries. In conclusion, image subtraction improves the quality of renal MRA in terms of both CNR and visualization of the distal renal arteries.

Adult↗
PubMedDate not supplied

MR versus fluoroscopic guidance of a catheter/guidewire system: in vitro comparison of steerability.

Our purpose in this study was to evaluate the steerability of a combined catheter guidewire system with MR tracking in an open-configuration .5T MR system and compare it with fluoroscopic guidance. Experiments were performed with an aorta-shaped glass phantom with different-size branches connected to a roller flow pump to simulate pulsatile flow. A .035" guidewire was used in conjunction with a 5F Cobra 2-shaped catheter. For active MR guidance, a small RF coil was incorporated into the tips of all devices. In addition to fluoroscopic guidance, we used MR tracking devices to selectively catheterize all branches in the .5T open magnet (Signa SP, GEMS). Time requirements for the latter were compared with those needed under conventional angiographic conditions using standard catheters and guidewires. Active MR tracking permitted the simultaneous real time (4 updates/sec) guidance of both guidewire and catheter. Under MR guidance, all branch vessels were successfully catheterized. We found no significant differences in time requirements between guidance with the MR tracking device and fluoroscopic guidance. However, cannulation under fluoroscopic guidance with standard angiography devices required significantly less time (P < .05). Selective catheterization of small branch vessels is possible with active MR tracking of a combined catheter/guidewire system. Limitations of MR tracking device material and design result in a considerable lengthening of the cannulation procedures.

Aorta↗
PubMedDate not supplied

Carbon dioxide gas as a venous contrast agent to guide upper-arm insertion of central venous catheters.

PURPOSE: Evaluate in a prospective randomized study carbon dioxide (CO2) gas compared to iodinated contrast agent for image-guided placement of peripherally inserted central venous catheters (PICCs). METHODS: The upper-arm approach to the central vein was used for placement of PICCs in 74 patients requiring intermediate or long-term central venous access. Fluoroscopy was used to obtain venous access during peripheral injection of CO2 (n = 41) or low osmolar contrast material (Omnipaque 240 mgI/ml) (n = 33). RESULTS: Placement of PICCs was accomplished in 88% of the CO2 group and in 100% of the contrast group, with a mean venipuncture of two in both groups. Venous access was unsuccessful in five patients with CO2 due to a small vein, venous spasm, or technical failure. The mean and range of procedure times were 22.8 min (13-64 min) with CO2 and 23.2 min (12-60 min) with contrast material. The average and range of CO2 and nonionic contrast volumes injected during the procedure were 35.4 ml (5-300 ml) and 27.8 ml (8-120 ml), respectively. Vital signs and oxygen saturation did not change significantly during or after injection of CO2. There was no incidence of adverse reaction following CO2 injection. CONCLUSION: CO2 gas is a useful contrast agent to guide upper-arm insertion of PICCs and may be a safe alternative in patients with renal insufficiency and/or allergy to iodinated contrast material.

Adolescent↗
PubMedDate not supplied

MR-guided cholecystostomy: assessment of biplanar, real-time needle tracking in three pigs.

PURPOSE: To demonstrate the feasibility of magnetic resonance (MR)-guided cholecystostomy using active, real-time, biplanar MR tracking in animal experiments. METHODS: Experiments were performed on three fully anesthetized pigs in an interventional MR system (GE open). The gallbladder was displayed in two orthogonal planes using a heavily T2-weighted fast spin-echo sequence. These "cholangio roadmaps" were displayed on LCD monitors positioned in front of the interventionalist. A special coaxial MR-tracking needle, equipped with a small receive-only coil at its tip, was inserted percutaneously into the gallbladder under continuous, biplanar MR guidance. The MR-tracking sequence allowed sampling of the coil (needle tip) position every 120 msec. The position of the coil was projected onto the two orthogonal "cholangio roadmap" images. RESULTS: Successful insertion of the needle was confirmed by aspiration of bile from the gallbladder. The process of aspiration and subsequent instillation of Gd-DTPA into the gallbladder was documented with fast gradient-recalled echo imaging. CONCLUSION: Biplanar, active, real-time MR tracking in combination with "cholangio roadmaps" allows for cholecystostomies in an interventional MRI environment.

Animals↗
PubMedDate not supplied

MR-guided percutaneous angioplasty: assessment of tracking safety, catheter handling and functionality.

PURPOSE: Magnetic resonance (MR)-guided percutaneous vascular interventions have evolved to a practical possibility with the advent of open-configuration MR systems and real-time tracking techniques. The purpose of this study was to assess an MR-tracking percutaneous transluminal angioplasty (PTA) catheter with regard to its safety profile and functionality. METHODS: Real-time, biplanar tracking of the PTA catheter was made possible by incorporating a small radiofrequency (RF) coil in the catheter tip and connecting it to a coaxial cable embedded in the catheter wall. To evaluate potentially hazardous thermal effects due to the incorporation of the coil, temperature measurements were performed within and around the coil under various scanning and tracking conditions at 1.5 Tesla (T). Catheter force transmission and balloon-burst pressure of the MR-tracking PTA catheter were compared with those of a standard PTA catheter. The dilatative capability of the angioplasty balloon was assessed in vitro as well as in vivo, in an isolated femoral artery segment in a swine. RESULTS: The degree of heating at the RF coil was directly proportional to the power of the RF pulses. Heating was negligible with MR tracking, conventional spin-echo and low-flip gradient-echo sequences. Sequences with higher duty cycles, such as fast spin echo, produced harmful heating effects. Force transmission of the MR-tracking PTA catheter was slightly inferior to that of the standard PTA catheter, while balloon-burst pressures were similar to those of conventional catheters. The MR-tracking PTA catheter functioned well both in vitro and in vivo. CONCLUSION: The in vivo use of an MR-tracking PTA catheter is safe under most scanning conditions.

Angioplasty, Balloon↗
PubMedDate not supplied

Virtual MR angioscopy of the pulmonary artery tree.

An optimized, contrast-enhanced 3D MR angiography sequence is combined with image postprocessing to render interior views of the pulmonary arteries. Virtual angioscopy was successfully demonstrated on both a healthy volunteer and a pulmonary embolism patient. By targeting selected pulmonary artery branches, virtual angioscopy has the potential to become a powerful adjunct to the use of reformatted sections and maximum intensity projections in the assessment of pulmonary embolism.

Angioscopy↗
PubMedDate not supplied

Primary angiosarcoma of the pulmonary arteries: dynamic contrast-enhanced MRI.

PURPOSE: Our goal was to assess the MR appearance and histologic correlation of primary pulmonary artery angiosarcoma. METHOD: Four patients with tumorous masses in the pulmonary arteries were evaluated by dynamic contrast-enhanced MRI using T1- and T2-weighted SE images, GE images, as well as coronal 3D MRA in breath-hold technique. The percentage of tumor enhancement was determined by measuring regions of interest before and after Gd-DTPA administration on the 2D multiplanar spoiled GRE images. RESULTS: All four masses showed some contrast enhancement on the dynamically acquired GRE images. The degree of contrast enhancement correlated with the degree of tumor differentiation, content of myxoid matrix, and associated thrombus. Contrast-enhanced 3D MRA was useful for preoperative delineation of the peripheral pulmonary arteries to the subsegmental order. CONCLUSION: Dynamic contrast-enhanced 3D MRA of the pulmonary arteries can be used to delineate pulmonary arterial angiosarcomas preoperatively. Considerable variability of contrast agent uptake reflects the wide histologic behavior of these masses in differentiation from central pulmonary embolism.

Adult↗