Arndt Glowinski

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. J. Magn. Reson. Imaging 2000;12:616–622.

Interventional magnetic resonance. Initial clinical experience with a 1.5-tesla magnetic resonance system combined with c-arm fluoroscopy.

RATIONALE AND OBJECTIVES The authors evaluate the feasibility of performing magnetic resonance (MR) procedures on a 1.5-tesla (T) system combined with conventional c-arm fluoroscopy. METHODS A 1.5-T MR imaging system was combined with a conventional c-arm fluoroscopy unit in one room. The two systems were connected via a floating table top. Twenty-six interventional procedures (biopsies, MR-portography, percutaneous alcohol injection, laser ablation, fluid aspiration, and breast marking) were performed in 22 patients under MR, fluoroscopic control, or both. For MR guidance, fast gradient echo sequences were used, initiated from a panel at the front of the magnet. Images were displayed on an liquid crystal display screen positioned on the magnet. RESULTS All MR-guided procedures were performed successfully without complications. The addition of c-arm fluoroscopy was useful for bone interventions and MR-portography. All diagnostic biopsies yielded sufficient amounts of tissue for histologic diagnosis. In breast lesions, the target identified on dynamic MR imaging was marked correctly in each case. In interstitial laser thermotherapy the laser effect could be visualized, and in percutaneous ethanol injection the distribution of the alcohol could be seen. Both imaging systems worked without image distortions and high-quality MR images were obtained. CONCLUSIONS The combination of a 1.5-T MR imager with a c-arm fluoroscopy system seems to be a promising technical solution for performing interventional MR procedures.

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.

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

Haage P, Adam G, Karaagac S, et al. Mechanical delivery of aerosolized gadolinium-DTPA for pulmonary ventilation assessment in MR imaging. Invest Radiol 2001;36:240-243. 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.

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

Abstract 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.

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.

Gadolinium-enhanced magnetic resonance fluoroscopy used as micturating cystourethrography: experiences in adult male patients.

Rationale and Objective:To approach the concept of magnetic resonance (MR) imaging-monitored micturating cystourethrography (MRMCU) by using gadolinium-enhanced real-time MR fluoroscopy. Methods:MRMCU was performed in 21 male patients (27–76 years) subsequent to gadolinium excretory MR urography. Patients were examined in supine position at 1.5 T. For MR fluoroscopy of the urethra during micturition, we used a T1-weighted single-slice gradient-echo sequence with continuous radial k-space acquisition. Image reconstruction was obtained with the sliding-window technique reaching a frame rate of 25/s. The image plane was guided interactively through the urethra, the bladder and the ureters without stopping the scan. Results:Two patients were unable to void in supine position. With MR fluoroscopy, the flow of gadolinium-enhanced urine through the urethra was visualized in 19 patients, in 14 of whom with complete demonstration of the urethral anatomy subdivided into 5 segments. Four urethral segments were identified in 1 patient, 3 segments in 2 patients, 2 segments in 3 patients, and 1 segment in 1 patient. MRMCU demonstrated changes in the urethral anatomy and the urine flow in 2 patients with a neobladder and in 1 patient with hypertrophy of the prostate. Subject to the limitation of antegrade gadolinium application, interactive MRMCU allowed to determine whether the ureters were enhanced by gadolinium or not. Conclusion:Gadolinium-enhanced MR fluoroscopy using radial k-space acquisition has achieved complete demonstration of the segmental anatomy of the urethra in 74% of the male adult patients who were able to accomplish micturition. Although MR fluoroscopy was able to visualize the gadolinium-enhanced ureters, the current data do not permit to conclude that MRMCU can demonstrate vesicoureteral reflux, especially in children.

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 T1‐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. Magn Reson Med 46:803–806, 2001.

Interventional MR tomography: equipment concepts

SummaryInterventional 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.ZusammenfassungDie interventionelle MRT ist die jüngste Entwicklung der klinischen Magnetresonanztomographie. Durch die Entwicklung offener Kernspintomographen und sehr kompakter Hochfeldgeräte sind bereits heute eine Reihe interventioneller Eingriffe unter MR-Kontrolle möglich und werden in experimentellen und klinischen Untersuchungen erprobt. Die Geräte unterscheiden sich bezüglich ihrer statischen Magnetfeldstärke (0,2 bis 1,5 T), der Gradientensysteme und den Zugangsmöglichkeiten zum Patienten sowie in dem benötigten Raumbedarf und den Anschaffungskosten. In allen Geräten wurden sinnvolle Bauteile realisiert, die Interventionen unter MR Kontrolle erleichtern. Die Vor- und Nachteile der derzeit existierenden Gerätekonzepte für die interventionelle MR werden gegenübergestellt und diskutiert sowie ein Ausblick auf mögliche Weiterentwicklungen gegeben.