Biomedical subjects

J J van Vaals

Publications and source records attributed to J J van Vaals.

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↗

PubMed2002

Real-time-MR guidance for placement of a self-made fully MR-compatible atrial septal occluder: in vitro test.

PURPOSE: This in vitro study investigated the feasibility to visualize the placement of three different atrial septal occluder systems using real-time MR control. METHODS: The experiments were performed on an interventional 1.5 T high field whole body system. Real-time MR imaging was achieved by radial or spiral k-space filling in conjunction with the sliding window reconstruction technique yielding an imaging speed of 15 frames per second. The CardioSeal, Amplatzer Septal Occluder and a specially designed MR-compatible closure device were tested in a water bath. A punctured plastic wall served as model for the atrial septal defect. RESULTS: The delivery systems of the CardioSeal and Amplatzer Occluder were ferromagnetic and caused substantial artifacts, making the device placement impossible, even if the magnetic forces would have been acceptable. The self-made prototype caused only minor susceptibility artifacts allowing its visualization on the MR images. The MR imaging techniques applied enabled real-time control of the occluder including steering through the artificial septal foramen and visualization of the occluder deployment. CONCLUSION: Real-time MR imaging allows for guidance and placement of an MR-compatible septal occluder in vitro suggesting the feasibility to perform atrial septal occlusion under MR-guidance in vivo as well.

Heart Atria↗

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

[Differentiation of serous and purulent fluids in vitro and in vivo by means of diffusion-weighted MRI].

AIM: The aim of this study was to test the feasibility for differentiation of serous fluid collections and abscess fluid with diffusion-weighted imaging and to compare three different diffusion sequences. MATERIAL AND METHODS: Thirteen puncture samples (6 serous, 7 purulent) and 19 patients with either serous fluid collections (n = 12) or abscesses (n = 7) were examined with diffusion-weighted spin-echo (SE), stimulated-echo (STE), and fatsuppressed SE (SE-SPIR) sequences. For in vitro studies 4 different b-factors (0, 87, 355, 798 s/mm2 in SE and SE-SPIR and 0, 51, 204, 460 s/mm2 in STE) were chosen and the apparent diffusion coefficient (ADC) was calculated. For in vivo measurements identical sequences with two b-factors (0.598 s/mm2 in SE and SE-SPIR and 0.360 s/mm2 in STE) were applied and the normalized signal attenuation was calculated. A navigator-echo technique and peripheral pulse triggering was used for motion artifact reduction. RESULTS: The in vitro study yielded an ADC of serous fluid, which was close to that of free water, whereas for purulent fluid a significantly lower ADC was calculated. During in vivo examinations, serous fluids showed a strong signal attenuation (down to 22-32% of basic value) compared to a minor signal attenuation in purulent fluids (down to 86-94% of basic value) (p < 0.05). CONCLUSIONS: In summary, with all three investigated diffusion schemes serous and purulent fluids can be clearly differentiated.

Abscess↗

PubMed2001

Improved in-stent magnetic resonance angiography with high flip angle excitation.

RATIONALE AND OBJECTIVES: To optimize the intraluminal signal intensity of a nitinol stent by performing contrast-enhanced three-dimensional magnetic resonance angiography (CE-MRA) with varying flip angles (FAs). METHODS: Contrast-enhanced magnetic resonance angiography at 1.5 T and FAs of 30 degrees, 100 degrees, and 150 degrees was performed on five sheep with 10 iliac nitinol stents (Memotherm-FLEXX). Maximum-intensity projections (MIPs) and composite images of MIPs were performed and compared. RESULTS: Reconstructed MIPs at an FA of 150 degrees showed a slightly disturbed lumen visibility inside the stent accompanied by low-grade lumen visibility outside the stent and vice versa for an FA of 30 degrees. Composite images of a 30 degrees MIP added to a 150 degrees MIP resulted in improved image quality compared with the standard MIP of a single FA. CONCLUSIONS: Signal loss due to radiofrequency shielding inside nitinol stents imaged by CE-MRA can be reduced by applying high FAs. Composite MIP images allow simultaneous visualization of the lumen inside as well as outside the stent.

Alloys↗

PubMed2001

Diffusion-weighted MR imaging for differentiation of benign fracture edema and tumor infiltration of the vertebral body.

OBJECTIVE: The aim of this study was to investigate diffusion-weighted MR imaging for differentiation of benign fracture edema and tumor infiltration with and without accompanying fracture. SUBJECTS AND METHODS: In 10 volunteers, diffusion-weighted spin-echo, fat-suppressed spin-echo, and stimulated-echo sequences were optimized on a clinical 1.5-T scanner. In 34 patients, MR imaging with and without diffusion-sensitizing gradients (b = 598 sec/mm(2) in spin-echo and fat-suppressed spin-echo, b = 360 sec/mm(2) in stimulated-echo) was performed. Thirty-five lesions were analyzed, with 18 caused by acute (< or =10 days old) osteoporotic or traumatic fractures and 17 caused by untreated malignant vertebral infiltration including nine fractures. Signal attenuation in diffusion-weighted images and contrast-to-noise ratio were calculated. The diffusion-weighted images were analyzed by two radiologists. RESULTS: Images from three of 34 patients were excluded because of motion artifact. In osteoporotic and traumatic fractures, a strong signal attenuation of bone marrow edema was seen. In contrast to this, malignant-tumor infiltration caused only minor signal attenuation (p < 0.05), independent of accompanying pathologic fracture. All sequences showed identical changes of signal intensities. In four patients, initial diagnosis was changed by the findings in the diffusion-weighted images. CONCLUSION: Diffusion-weighted spin-echo, fat-suppressed spin-echo, and stimulated-echo sequences are equally suitable for imaging of the spine. Calculation of signal attenuation and observation of signal characteristics allowed differentiation of benign fracture edema and tumor infiltration and provided excellent distinction between benign and malignant vertebral fractures in our series.

Adult↗

PubMed2001

Thermal therapies in interventional MR imaging. Focused ultrasound.

MR image-guided focused ultrasound (FUS) provides an entirely noninvasive approach for local thermal therapies. MR imaging allows target definition and continuous temperature mapping. Therefore, the heating procedure can be controlled spatially and temporally based on automatic feedback to the FUS apparatus. Phased-array ultrasound technology will further help the development. MR imaging/FUS may be applied not only for tissue ablation, but also for local drug delivery, gene therapy, and drug activation.

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

[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↗

PubMed1999

Accuracy of MR phase mapping for temperature monitoring during interstitial laser coagulation (ILC) in the liver at rest and simulated respiration.

The chemical shift or proton-resonance frequency (phase mapping) can be used to measure temperature changes. As a subtraction technique, it requires scans at exactly the same location, making it prone to respiration-induced artifacts. The accuracy of magnetic resonance (MR) phase mapping for temperature monitoring of interstitial laser coagulation (ILC) was therefore investigated in two ex vivo models with simulated respiration. MR temperatures were calibrated to interstitially measured temperature. Gradual cooling of a homogenous medium (gel) was monitored for four starting temperatures (room temperature, 40 degrees C, 50 degrees C, and 60 degrees C) during 30 min. Temperature increases were measured during ILC in ex vivo porcine liver with Nd:YAG for 6 min with 5 Watt. Experiments were performed at rest and with simulated respiratory motion (both n = 5). In liver, accuracy did not decrease with respiration simulation (P = 0.32), whereas a significant decline was found in the gel model (P = 0.002). In all experiments a small drift over time was observed between temperature determined with MR and thermoprobes. Correction for temperature-independent phase-shift at a reference location did not enhance agreement. Temperatures could be determined correctly by MR in the moving liver within a range of +/-3.5 degrees C after 6 min of laser application (95% confidence interval), justifying further pre-clinical studies.

Analysis of Variance↗

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↗

PubMed1998

[A new MR-(and CT-) compatible bone biopsy system: first clinical results].

PURPOSE: To describe the development and clinical evaluation of a new, hand-powered or alternatively motor-driven, MRI and CT compatible percutaneous bone biopsy system. MATERIALS AND METHODS: A new coaxial drill system (Cook Europe A/S) was designed for percutaneous, MR-guided bone biopsies and powered either by hand or an optional motor (10-250 rotations/minute using 6 bar [88.2 PSI] compressed air). The system has been used in 23 patients. Fourteen procedures were performed in a 1.5 T MR scanner (Philips-Gyroscan ACS-NT) which has an attached C-arm (Philips-BV 212-Angio) in case fluoroscopy is required, and 9 procedures in a CT scanner (Siemens-Somatom Plus). RESULTS: Driven by hand or by the pneumatic motor unit, the system achieved safe and accurate MR-guided access to all of the lesions and was even able to penetrate osteosclerotic lesions. MR- or CT-guided percutaneous biopsy yielded a correct diagnosis in all but 5 cases. No procedural complications occurred. CONCLUSION: MR-guided percutaneous bone biopsy performed with the new coaxial drill system was found to be safe and reliable, and suitable for obtaining histological specimens from skeletal lesions even when covered with thick cortical or sclerotic bone.

Biopsy↗

PubMed1998

[Real-time MRI with radial k-radial scanning technique for control of angiographic interventions].

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.

Angiography↗

PubMed1998

[Stent placement with real time MRI guidance: initial animal experiment experiences].

PURPOSE: The aim of this study was to test the feasibility of iliac artery stent placement under MR guidance with real-time MR radial scanning in an animal model. MATERIALS AND METHODS: The experiments were performed on three pigs in a 1.5 T scanner. Radial scanning with a gradient echo technique (TR 8.4 ms, TE 3.6 ms, flip angle 10 degrees) was used. A dedicated backprojector performed the reconstruction of the raw data in real-time. The resulting MR-images were displayed on LCD screens beside the magnet. The sliding window reconstruction technique allowed image acquisition at a frame rate of 16 images per second. MR-compatible self-expanding stents with a diameter of 8 mm and a length of 3 cm were placed into the left iliac artery. Their positions were verified by digital subtraction angiography (DSA) and compared to MRI. RESULTS: All stents were successfully placed. Stent positions as monitored by real-time MR were identical to those seen on DSA images. The time needed for exact positioning of the scan plane ranged from 15 to 30 minutes. Stent placement itself took 8 minutes on average. CONCLUSION: Radial scanning applied together with the sliding window reconstruction technique allows placement of stents in iliac arteries under real-time MR control.

Angioplasty, Balloon↗

PubMed1998

Image guidance of endovascular interventions on a clinical MR scanner.

Magnetic resonance imaging (MRI) offers potential advantages over conventional X-ray techniques for guiding and evaluating vascular interventions. Image guidance of such interventions via passive catheter tracking requires real-time image processing. Commercially available MR scanners currently do not provide this functionality. This paper describes an image processing environment that allows near-real-time MR-guided vascular interventions. It demonstrates 1) that flexibility can be achieved by separating the scanner and the image processing/display system, thereby preserving the stability of the scanner and 2) that sufficiently rapid visualization can be achieved by low-cost workstations equipped with graphics hardware. The setup of the hardware and the software is described in detail. Furthermore, image processing techniques are presented for guiding the interventionalist through simple vascular anatomy. Finally, results of a phantom balloon angioplasty experiment are presented.

Angioplasty, Balloon↗

PubMed1997

Catheter visualization using locally induced, actively controlled field inhomogeneities.

A new technique for visualization of interventional devices using MR is presented. A prototype catheter was equipped with a thin copper wire loop, leading from the proximal end to the tip and back. A small current (10-150 mA) through these two parts of a wire induces a local magnetic field along the catheter. Introduction of this catheter into the main magnetic field of the MR imager locally disturbs the homogeneity of the magnetic field. Image locations within the locally induced fields appear dark due to signal loss, and the extent of this effect can be varied during the procedure by simply adjusting the current. Different dedicated wire configurations allow visualization of the catheter in its whole length or in parts, i.e., with markers for balloons. Fast gradient echo sequences that provide a bright signal from inflowing blood are used for rapid imaging.

Animals↗

PubMed1997

[Catheter visualization in MR-tomography: initial experimental results with field-inhomogeneity catheters].

PURPOSE: To assess the feasibility of a new developed field inhomogeneity catheter for interventional MR imaging in vivo. MATERIALS AND METHODS: Three different prototypes of a field inhomogeneity catheter were investigated in 6 pigs. The catheters were introduced in Seldinger technique via the femoral vessels over a guide wire on an interventional MR system (Philips Gyroscan NT combined with a C-arm fluoroscopy unit [Philips BV 212]). Catheters were placed in veins and arteries. The catheter position was controlled by a fast gradient echo sequence (Turbo Field Echo [TEE]). RESULTS: Catheters were introduced over a guide wire without complications in all cases. Using the field inhomogeneity concept, catheters were easily visualised in the inferior vena cava and the aorta by the fast gradient echo technique on MR in all cases. Although aortic branches were successfully cannulated, the catheters were not displayed by the TFE technique due to the complex and tortuous anatomy. All animals survived the experiments without complications. CONCLUSION: MR guided visualization of a field inhomogeneity catheter is a simple concept which can be realised on each MR scanner and may allow intravascular MR guided interventions in future.

Animals↗