Biomedical subjects

A Glowinski

Publications and source records attributed to A Glowinski.

At least 19 recordsLinked to original sources

PubMed2003

[MR-guided coil embolisation of renal arteries in an animal model].

PURPOSE: To test the feasibility of MR-guided coil embolization with passive visualization in an animal model. MATERIALS AND METHODS: All experiments were performed on a 1.5 T interventional MR-scanner (Gyroscan ACS-NT, Philips, Netherlands). A gradient echo sequence was combined with radial k-space acquisition and sliding window reconstruction technique to calculate the raw data with a specially designed back projector, yielding a frame rate of 20 images per second. The images were directly displayed on LCD-screens next to the MR scanner. A multipurpose catheter with dysprosium markers was placed into the renal arteries of two pigs under MR guidance, and a nitinol coil and platinum coil each were deployed. The position of the coils was verified with magnetic resonance angiography and conventional angiography. RESULTS: MR-guided catheterization of renal arteries with subsequent coil embolization was successfully carried out but the configuration of the coils could not be visualized on the MR images. CONCLUSION: MR-guided coil embolization of renal arteries is feasible. Exact guidance of coil deployment is not attainable with passive visualization.

Angiography, Digital Subtraction↗

PubMed2001

Comparison of aerosolized gadoteridol and gadopentetate dimeglumine for magnetic resonance ventilation imaging of the lung.

The purpose of this study was to compare aerosolized gadoteridol and gadopentetate dimeglumine in regard to homogeneity of aerosol distribution and relative pulmonary signal intensity (SI) changes after a 10-min mechanical ventilation period. Twenty experimental procedures were performed in 10 intubated domestic pigs that were mechanically aerosolized with the nebulized contrast medium. Images were obtained by using a respiratory-gated T(1)-weighted TSE sequence. Pulmonary SI increase for the right and left lung was 26% +/- 25% and 25% +/- 12%, respectively, for gadopentetate dimeglumine, and 45% +/- 12% and 43% +/- 10%, respectively, for gadoteridol. Aerosol distribution was rated homogeneous in all cases by two readers. It is concluded that both contrast agents in aerosolized form are capable of depicting pulmonary ventilation in healthy animals with lung capacities comparable to those of humans. SI differences between gadoteridol and gadopentetate dimeglumine are explained by their considerable difference in viscosity.

Aerosols↗

PubMed2001

MR-guided percutaneous drainage of abdominal fluid collections in combination with X-ray fluoroscopy: initial clinical experience.

The aim of this study was to examine the feasibility of a hybrid interventional MR system, which combines a closed bore magnet with a C-arm fluoroscopy unit for percutaneous drainage of abdominal fluid collections. During the past 2 years, we have performed four drainage procedures in four patients (mean age 47 years). Three patients had abscesses (psoas muscle, kidney, subphrenic location) and the fourth patient had a recurrent splenic cyst. All procedures were performed on an interventional MR system consisting of a 1.5-T ACS-NT scanner combined with a specially shielded C-arm. The drainages were guided by T1-weighted fast gradient-echo images, T2-weighted single-shot turbo spin-echo images or both. A standard 18 G (1.2 mm) nonferromagnetic stainless steel needle with a Teflon sheath was used for the punctures following which a 0.89 mm nitinol guidewire was inserted into the fluid collection. Thereafter, the patient was positioned in the immediate adjacent fluoroscopy unit and a drainage catheter was placed under fluoroscopic control. All drainage catheters were successfully placed into the fluid collections, as proven by fluid aspiration and resolution of the collection. The mean time needed for the entire drainage procedure (MR and fluoroscopy) was 110 min. No procedure-related complications occurred. It is feasible to perform drainage procedures on a closed-bore MR scanner. The multiplanar imaging capabilities of MR are particularly helpful for fluid collections in the subphrenic location.

Abdominal Abscess↗

PubMed2001

Real-time MR Guidance for inferior vena cava filter placement in an animal model.

It was the aim of this study to examine the feasibility of real-time magnetic resonance (MR) imaging for MR-guided placement of inferior vena cava (IVC) filters, which were placed in five pigs via a femoral approach. The introducer sheath and dilator were marked with Dysprosium rings. The procedures were performed under MR guidance with use of a 1.5-T ACS-NT imager. Radial filling of k-space in conjunction with the sliding window reconstruction technique achieved real-time MR imaging with a frame rate of 20 images/sec. Simultaneous real-time visualization of the vascular anatomy and interventional instruments was achieved under real-time conditions and allowed correct placement of IVC filters in all five cases as confirmed by radiographic angiography.

Animals↗

PubMed2001

Mechanical delivery of aerosolized gadolinium-DTPA for pulmonary ventilation assessment in MR imaging.

RATIONALE AND OBJECTIVES: To evaluate a new technique with mechanical administration of aerosolized gadolinium (Gd)-DTPA for MR visualization of lung ventilation. METHODS: Ten experimental procedures were performed in six domestic pigs. Gd-DTPA was aerosolized by a small-particle generator. The intubated animals were mechanically aerosolized with the nebulized contrast agent and studied on a 1.5-T MR imager. Respiratory gated T1-weighted turbo spin-echo images were obtained before, during, and after contrast administration. Pulmonary signal intensity (SI) changes were calculated for corresponding regions of both lungs. Homogeneity of aerosol distribution was graded independently by two radiologists. RESULTS: To achieve a comparable SI increase as attained in previous trials that used manual aerosol ventilation, a ventilation period of 20 minutes (formerly 30 minutes) was sufficient. Mean SI changes of 116% were observed after that duration. Contrast delivery was rated evenly distributed in all cases by the reviewers. CONCLUSIONS: The feasibility of applying Gd-DTPA as a contrast agent to demonstrate pulmonary ventilation in large animals has been described before. The results of this refined technique substantiate the potential of Gd-based ventilation MR imaging by improving aerosol distribution and shortening the nebulization duration in the healthy lung.

Aerosols↗

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↗

PubMed2000

Real-time MR fluoroscopy for MR-guided iliac artery stent placement.

The purpose of this study was to test the feasibility of real-time magnetic resonance (MR) guidance of iliac artery stent placement. Radial scanning together with the sliding window reconstruction technique was implemented on a 1.5 T magnet, yielding a frame rate of 20 images per second. Seven prototype nitinol ZA stents were deployed in iliac arteries of living pigs under MR control. All stents were well visualized on the radial MR images, allowing depiction of the mounted stents as well as stent deployment without anatomy-obscuring artifacts. Stent placement was sucessful in all cases and took 6 minutes on average. The position of the stents was correctly visualized by real-time radial MR scanning, as proved by digital subtraction X-ray angiography. Combined radial scanning and the sliding window reconstruction technique allow real-time MR-guided stent placement in iliac arteries.

Alloys↗

PubMed2000

Social phobia in a population-based female adolescent twin sample: co-morbidity and associated suicide-related symptoms.

BACKGROUND: This report attempted to replicate and extend prior work examining social phobia (SP), co-morbid psychiatric illnesses, and the risk of suicidal ideation and suicide attempts incurred by their adolescent sufferers. METHODS: SP, alcohol dependence (ALD) and major depressive disorder (MDD) diagnoses, and suicide-related symptoms, were assessed in a population-based adolescent female twin sample. The differentiation of risks as a function of co-morbidity was explored. A trivariate model was fitted to estimate sharing of genetic and environmental vulnerability between SP and co-morbid disorders. RESULTS: The lifetime prevalence of SP was 16.3 %. Significant risk for co-morbid MDD (OR = 3.2) and ALD (OR = 2.1) was observed. Strong evidence for shared genetic vulnerability between SP and MDD (respective heritabilities 28%, 45%; genetic r = 1.0) was observed with moderate support noted for similar sharing between SP and ALD (genetic r = 0.52, heritability for ALD 63%). SP with co-morbid MDD was associated with elevated risk for ALD and for suicide-related symptoms. CONCLUSIONS: SP is a common illness often followed by co-morbid MDD and ALD. SP with comorbid MDD predicts a substantially elevated risk of ALD and suicide-related symptoms, stressing the need for early SP detection.

Adolescent↗

PubMed2000

[Radial k-scanning for real-time MR imaging of central and peripheral pulmonary vasculature].

PURPOSE: To depict the central and peripheral pulmonary vessel anatomy with real-time radial MR scanning without respiratory control. METHODS: Three healthy volunteers and one patient with pulmonary embolism proven by spiral CT angiography were studied with a 1.5 T MR imaging system. First, a breath-hold, contrast-enhanced MR angiography was performed for comparison of accuracy. Gradient echo images (TR 16 ms, TE 4 ms, flip angle 18 degrees) were obtained applying a combination of radial scanning and the sliding window reconstruction technique. A dedicated back-projector allowed data reconstruction in real-time with a frame rate of 20 images per second. Scanning was performed during free breathing. RESULTS: The described technique depicted the central and peripheral portions of the normal pulmonary anatomy with comparable image quality as the 3D contrast-enhanced angiography. Visualization of the pulmonary emboli as demonstrated by spiral CT was possible. CONCLUSION: Real-time radial scanning allows promising image acquisition of the pulmonary vasculature without respiratory control. Further technical improvements and clinical trials are required to evaluate its role in the diagnosis of vascular pathologies.

Adult↗

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↗

PubMed2000

A perspective on needle artifacts in MRI: an electromagnetic model for experimentally separating susceptibility effects.

A thorough understanding of artifacts caused by metallic instruments is essential for the guidance of interventional procedures by magnetic resonance imaging (MRI), because the accurate localization of each instrument is mandatory for this. In the past, this problem has been addressed by several groups, using theoretical, as well as experimental approaches. The artifacts associated with MRI are caused by geometry distortion and intravoxel dephasing. Usually, both effects mingle in the image, and depending on the pulse sequences and its parameters used for data acquisition, these effects are reflected in the image with different magnitude. In this paper we shortly present the well-known mathematical background of the two underlying effects. Mathematically, both can be treated separately. Here, we propose a new electromagnetic model which also allows to experimentally separate the effects better than by comparing spin-echo and gradient-echo images of the same object. With this new model, both effects-geometry distortion and intravoxel dephasing-are demonstrated separately using the same gradient-echo pulse sequence for all scans and adjusting the fields of the model properly. Furthermore, as this model allows to adjust both effects independently, it is used to study different weightings of both effects when they appear simultaneously in the image.

Artifacts↗

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

[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

[Interventional MR tomography: equipment concepts].

Interventional MRI is one of the most recent developments of clinical MR imaging. Because of the development of open MR systems and very compact high-field systems, a number of interventional procedures are already possible today under MR control and will be tested in experimental and clinical investigations. The currently commercially available systems differ with respect to their static magnetic field strength, their gradient systems and patient access. In addition, there are differences concerning their space requirements and costs. All systems have components facilitating interventional procedures. In this article we discuss the advantages and shortcomings of these commercially available systems and look at future developments in interventional MR equipment.

Equipment Design↗

PubMed1998

[MR-micturating cystourethrography using radical k-space sampling].

PURPOSE: To investigate the feasibility of micturating cystourethrography (MCU) by means of real-time MR imaging with radial k-space sampling. METHODS: The MR-MCU was performed in 7 adult male patients subsequent to a gadolinium(Gd)-DTPA-enhanced excretory MR-urography. The Gd-enhancement of the urethra was visualized by MR-fluoroscopy using a T1-weighted gradient-echo-sequence with radial k-space sampling and a slice thickness of 10 mm. RESULTS: The proposed technique allowed in all 7 patients a dynamic realtime imaging of the Gd-flow inside the urethra during micturition. The normal anatomy of the entire course of the urethra was demonstrated in each patient, while simultaneously the relation to the prostate and pelvic floor became visible. Furthermore, the urinary bladder could be assessed by interactive repositioning of the slice orientation in any preferred direction. The ureters could also be visualized due to the persisting Gd-enhancement of the upper urinary tract after the preceding MR-urography. CONCLUSIONS: MR-MCU using Gd-DTPA and radial k-space data acquisition is a novel imaging modality for a real-time visualization of the urethra during micturition without radiation exposure. This method also allows the assessment of the bladder, the pelvic floor, and the Gd-filled upper urinary tract which suggests a potential for the diagnosis of vesicoureteral reflux and urinary incontinence.

Adult↗