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Results for “Magnetic Resonance Imaging, Interventional”

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At least 19 recordsLinked to original sources

PubMed2000

Pulse sequences for interventional magnetic resonance imaging.

Interventional magnetic resonance imaging (iMRI) is different from diagnostic magnetic resonance imaging (MRI) in its spatial, temporal, and contrast resolution requirements due to its specific clinical applications. As a result, the pulse sequences used in iMRI often are significantly different than those used in the more conventional diagnostic arena. The focus of this article is to summarize how iMRI is different from diagnostic MRI, to describe a variety of MRI pulse sequences and sequence strategies that have evolved because of these differences, and to describe some MRI sequence strategies that are in development and may be seen in future iMRI applications.

Body Temperature↗

PubMed2000

Safety, efficacy, and functionality of high-field strength interventional magnetic resonance imaging for neurosurgery.

OBJECTIVE: Interventional magnetic resonance imaging (MRI) allows neurosurgeons to interactively perform surgery using MRI guidance. High-field strength (1.5-T) imaging permits exceptional observation of intracranial and spinal pathological features. The development of this technology and its application to a variety of neurosurgical procedures are described. METHODS: We report on the first 101 cases that were treated in the interventional MRI unit (between January 1997 and September 1998). These cases included 39 brain biopsies, 30 tumor resections, 9 functional neurosurgical cases, 8 cyst drainages, 5 laminectomies, and 10 miscellaneous cases. Patients ranged in age from 14 months to 84 years (median, 43 yr); 61 patients were male and 40 were female. Intraoperative functional techniques that were used to influence surgical decision-making included magnetic resonance spectroscopy, functional MRI, magnetic resonance angiography and venography, chemical shift imaging, and diffusion-weighted imaging. All surgery was performed using MRI-compatible instruments within the 5-gauss line and conventional instruments outside that line. RESULTS: All 39 brain biopsies yielded diagnostic tissue. Of the 30 tumor resections, 24 (80%) were considered radiographically complete. The incidence of serious complications was low and was comparable to that associated with conventional operating rooms. One patient developed a Propionibacterium acnes brain abscess 6 weeks after surgery and another patient experienced Staphylococcus aureus scalp cellulitis after a brain biopsy, yielding an infection rate of less than 2%. No clinically significant hemorrhage was observed in immediate postoperative imaging scans, although one patient developed a delayed hematoma after a thalamotomy. One patient experienced a stroke after resection of a hippocampal tumor. No untoward events were associated with MRI-compatible instrumentation or intraoperative patient monitoring. CONCLUSION: High-field (1.5-T) interventional MRI is a safe and effective technology for assisting neurosurgeons in achieving the goals of surgery. Preliminary results suggest that the functional capabilities of this technology can yield data that can significantly influence intraoperative neurosurgical decision-making. The rates of serious complications, such as infection, associated with this new technology were low.

Adolescent↗

PubMed1998

High-field strength interventional magnetic resonance imaging for pediatric neurosurgery.

BACKGROUND: Interventional magnetic resonance (MR) imaging allows neurosurgeons to interactively perform surgery using MR guidance. High-field (1.5-Tesla) strength imaging provides exceptional visualization of intracranial and spinal pathology. The full capabilities of this technology for pediatric neurosurgery have not been defined or determined. MATERIALS AND METHODS: From January 1997 through June 1998, 10 of 85 cases performed in the interventional MR unit were in the pediatric population (mean age 8.3, median 8, range 2-15 years). Procedures included 2 brain biopsies, 5 craniotomies for tumor, 2 thoracic laminectomies for syringomyelia, and placement of a reservoir into a cystic brainstem tumor. The biopsies and reservoir placement were performed using MR-compatible equipment. Craniotomies and spinal surgery were performed with conventional instrumentation outside the 5-Gauss magnetic footprint. Interactive and intraoperative imaging was performed to assess the goals of surgery. RESULTS: Both brain biopsies were diagnostic for cerebral infarct and anaplastic astrocytoma and the reservoir was optimally placed within the tumor cyst. Of the 5 tumor resections, all were considered radiographically complete. One biopsy patient and 1 tumor resection patient experienced transient neurological deficits after surgery. The patient with the thoracic syrinx required reoperation when the syringosubarachnoid shunt migrated into the syrinx 3 months after initial placement. No patient sustained a postoperative hemorrhage. Tumor histologies found at craniotomy were craniopharyngioma, ganglioglioma, and 3 low-grade gliomas. No evidence of tumor progression has been seen in any of these patients at a mean follow-up of 5.3 (range 4-8) months. The goals of the procedure were achieved in all 10 cases. There were no untoward events experienced related to MR-compatible instrumentation or intraoperative patient monitoring, despite the present inability to monitor core body temperature. CONCLUSIONS: 1.5-Tesla interventional MR is a safe and effective technology for assisting neurosurgeons to achieve the goals of pediatric neurosurgery. Preliminary results suggest that surgical resection of histologically benign tumors is enhanced in the interventional MR unit. The incidence of surgically related morbidity is low.

Adolescent↗

PubMed1999

Interventional magnetic resonance imaging guided aspiration and biopsy of a cystic midbrain tumor.

Interventional magnetic resonance imaging defines the intraoperative application of magnetic resonance imaging technology, permitting the surgeon to work in an open magnetic field. The application of this technology to pediatric neurosurgery allows precise intraoperative localization of pathology, real-time assessment of the anatomical consequences of surgical and anesthetic interventions, accountability of brain shifts, confirmation of the exact site of biopsy or completeness of lesion removal, and immediate identification of some intraoperative and early postoperative complications. We present the case of a young boy with a cystic left midbrain tumor who underwent interventional magnetic resonance imaging guided aspiration and biopsy to illustrate the surgical advantages of this technology.

Astrocytoma↗

PubMed2001

Assessment of spinal kinematics using open interventional magnetic resonance imaging.

Assessment of spinal intersegmental motion has been a focus for research and has depended on radiographic techniques. Radiographic techniques are limited because of ionizing radiation exposure, magnification errors, and image quality. Interventional magnetic resonance scanners, however, allow dynamic imaging in the scanner in different positions. Twelve healthy subjects were scanned using a General Electric Signa SP10 open interventional magnetic resonance scanner. Subjects were scanned while they were in the supine position and during sitting in flexed and extended positions. Measurements of lumbar curvature and intersegmental motion were made from the sagittal images obtained. The results showed that it was possible to obtain repeatable measures of intersegmental rotation and translation from open magnetic resonance images of the spine in flexed and extended positions. These measures of motion are in agreement with previous data and suggest that the greatest motion occurs at the L4-L5 level. The use of interventional magnetic resonance imaging for assessing lumbar intersegmental mobility seems promising.

Adult↗

PubMed2005

A review of technical advances in interventional magnetic resonance imaging.

Initial research in the development of interventional magnetic resonance (MR) imaging in the late 1980s and early to mid-1990s focused on pulse sequences, devices, and clinical applications. This focus was largely a result of the limited number of areas in which the academic research community leading the development could provide innovation on the MR systems of the time. However, during the past decade, computational power, higher bandwidth graphical displays, faster computer networks, improved pulse sequence architectures, and improved technical specifications have accelerated the pace of development on modern MR systems. Today, it is the combination of multiple system factors that are enabling the future of interventional MR. These developments, their impact on the field, and newly emerging applications are described.

Animals↗

PubMed2003

Endovascular interventional magnetic resonance imaging.

Minimally invasive interventional radiological procedures, such as balloon angioplasty, stent placement or coiling of aneurysms, play an increasingly important role in the treatment of patients suffering from vascular disease. The non-destructive nature of magnetic resonance imaging (MRI), its ability to combine the acquisition of high quality anatomical images and functional information, such as blood flow velocities, perfusion and diffusion, together with its inherent three dimensionality and tomographic imaging capacities, have been advocated as advantages of using the MRI technique for guidance of endovascular radiological interventions. Within this light, endovascular interventional MRI has emerged as an interesting and promising new branch of interventional radiology. In this review article, the authors will give an overview of the most important issues related to this field. In this context, we will focus on the prerequisites for endovascular interventional MRI to come to maturity. In particular, the various approaches for device tracking that were proposed will be discussed and categorized. Furthermore, dedicated MRI systems, safety and compatibility issues and promising applications that could become clinical practice in the future will be discussed.

Blood Vessels↗

PubMed2004

Interventional magnetic resonance imaging for guiding gene and cell transfer in the heart.

BACKGROUND: Interventional magnetic resonance imaging (iMRI) has the potential for guiding interventional cardiac procedures in real time. OBJECTIVES: To test the feasibility of iMRI guided gene and cell transfer to the heart and to monitor myocardial remodelling after myocardial infarction in a rat model. METHODS: The MRI contrast agent GdDTPA, together with either Evans blue dye, or a recombinant adenovirus encoding the LacZ gene, or primary fibroblasts tagged by BrdU, were injected into the myocardium of rats under iMRI guidance. Rats were killed seven days after the injection and the hearts sectioned to identify the blue dye, LacZ expression, or fibroblast presence, respectively. In a parallel study, left ventricular area was measured before and after myocardial infarction and in sham operated rats by T1 weighted MRI and by echocardiography. RESULTS: Location of GdDTPA enhancement observed with iMRI at the time of injection was correlated with Evans blue stain, beta-gal expression, and the primary fibroblast location in histological studies. iMRI and echocardiography measured a comparable increase in left ventricular area at seven and 30 days after myocardial infarction. A good correlation was found between the iMRI and echocardiographic assessment of left ventricular area (r = 0.70; p < 0.0001) and change in left ventricular area with time (r = 0.75; p < 0.0001). CONCLUSIONS: The results show the feasibility and efficiency of iMRI guided intramyocardial injections, and the ability to monitor heart remodelling using iMRI. Genes, proteins, or cells for tissue engineering could be injected accurately into the myocardial scar under iMRI guidance.

Adenoviridae↗

PubMed2000

A clinical method for real-time dosimetric guidance of transperineal 125I prostate implants using interventional magnetic resonance imaging.

PURPOSE: The clinical utility of an interventional magnetic resonance (IMR)-guided implant technique with real-time dosimetric feedback is presented. METHODS AND MATERIALS: The work was carried out at a IMR unit at Brigham and Women's Hospital. Planning and dosimetric feedback were provided by a software system that provides an interface to the IMR images, anatomy demarcation, template registration, dose calculation engine for planning, and evaluating the implant. Planning during the procedure permits the incorporation of actual needle trajectories in the dose calculations. RESULTS: Fifteen patients were planned in the treatment position. During source placement, actual needle locations were incorporated into the dose calculations. After accounting for the observed needle trajectories of the planned needles, 14 of 15 patients (93%) required additional sources to achieve the desired coverage of the target volume. CONCLUSION: A brachytherapy implant procedure which provides clinically significant advances has been implemented. Specifically, the planning system allows dosimetric validation of the needle placement. This procedure is effective in delivering brachytherapy to the target volume and assuring that the implant is delivered in accordance with the preplan. The dosimetric feedback could be incorporated in ultrasound-guided implants.

Brachytherapy↗

PubMed1999

Brain biopsy using high-field strength interventional magnetic resonance imaging.

OBJECTIVE: Lesions within the brain are commonly sampled using stereotactic techniques. The advent of interventional magnetic resonance imaging (MRI) now allows neurosurgeons to interactively investigate specific regions, with exquisite observational detail. We evaluated the safety and efficacy of this new surgical approach. METHODS: Between January 1997 and June 1998, 35 brain biopsies were performed in a high-field strength interventional MRI unit. All biopsies were performed using MRI-compatible instrumentation. Interactive scanning was used to confirm accurate positioning of the biopsy needle within the region of interest. Intraoperative pathological examination of the biopsy specimens was performed to verify the presence of diagnostic tissue, and intra- and postoperative imaging was performed to exclude the presence of intraoperative hemorrhage. Recently, magnetic resonance spectroscopic targeting was used for six patients. RESULTS: Diagnostic tissue was obtained in all 35 brain biopsies and was used in therapeutic decision-making. Histological diagnoses included 28 primary brain tumors (12 glioblastomas multiforme, 9 oligodendrogliomas, 2 anaplastic astrocytomas, 2 astrocytomas, 1 lymphoma, and 1 anaplastic oligodendroglioma), 1 melanoma brain metastasis, 1 cavernous sinus meningioma, 1 cerebral infarction, 1 demyelinating process, and 3 cases of radiation necrosis. In all cases, magnetic resonance spectroscopy was accurate in distinguishing recurrent tumors (five cases) from radiation necrosis (one case). No patient sustained clinically or radiologically significant hemorrhage, as determined by intraoperative imaging performed immediately after the biopsy. One patient (3%) suffered transient hemiparesis after a pontine biopsy for investigation of a brain stem glioma. Another patient developed scalp cellulitis, with possible intracranial extension, 3 weeks after the biopsy; this condition was effectively treated with antibiotic therapy. Three patients were discharged on the day of the biopsy. CONCLUSION: Interventional 1.5-T MRI is a safe and effective method for evaluating lesions of the brain. Magnetic resonance spectroscopic targeting is likely to augment the diagnostic yield of brain biopsies.

Adolescent↗

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↗

PubMed1997

Generation and observation of radio frequency thermal lesion ablation for interventional magnetic resonance imaging.

RATIONALE AND OBJECTIVES: Recently, there has been increased interest in interventional magnetic resonance (MR) imaging and minimally invasive cancer therapy via radio frequency (RF) thermal ablation. In this work, we examined RF thermal lesion generation in phantoms and ex vivo bovine liver and correlated them with MR images under a variety of conditions, which begins our assessment of the role of MR imaging in this new method for cancer treatment. METHODS: Radio frequency lesions were created in gel phantoms and ex vivo bovine liver, using stationary (bovine liver) and variable speed (gel) moving electrodes to create lesions with shapes mimicking tumors. Ex vivo bovine liver lesions were made with the tissue held at room temperature (n = 4) and in a 37 degrees C saline bath (n = 3) using a 16-gauge electrode (tip temperature: 70 degrees C, 80 degrees C, and 90 degrees C; ablation time: 1-13 minutes). Electrical impedance and RF power were plotted during ablation. After ablation, RF-induced lesions were imaged with a 0.2-tesla (T) MR system using a variety of pulse sequences. RESULTS: Complex shaped lesions were created successfully in phantoms. Averaged maximum ex vivo lesion volume made at 90 degrees C ablation experiments holding the tissue temperature at 37 degrees C and at room temperature were 1.58 +/- 0.35 cm3 and 1.0 +/- 0.26 cm3 respectively (confidence interval: 90%). The aspect ratios and RF power of the lesions decreased as ablations proceeded. Impedance dropped during the first 2 minutes of the ablation. Ex vivo lesions appeared as regions of low-signal amplitude in T2-weighted MR images. CONCLUSIONS: Phantom ablation experience may be useful and applicable in thermotherapy planning. Lesions made in ex vivo bovine liver held at 37 degrees C via a saline bath are larger than those created at room temperature. Lesions shapes are ablation time dependent until thermal equilibrium is reached. Impedance reduction and lesion formation are related; 0.2-T MR systems can image RF energy-induced thermal lesions.

Animals↗

PubMed2002

Interventional magnetic resonance imaging cryotherapy of uterine fibroid tumors: preliminary observation.

OBJECTIVE: The purpose of this study was to identify alternatives to hysterectomy. We have developed a transabdominal interventional magnetic resonance imaging-guided cryoablation procedure and report this novel approach. STUDY DESIGN: This represents the preliminary and first report of a prospective Institutional Review Board-approved protocol to study interventional magnetic resonance imaging-guided cryoablation of uterine fibroid tumors. Women were selected on the basis of symptoms that were related to uterine fibroid tumors (bleeding, uterine pain, pelvic congestion, compression symptoms) and the absence of any desire for child bearing. A physical examination confirmed the presence of fibroid tumors, and magnetic resonance imaging was performed before the procedure to measure the size and number of fibroid tumors. Patients returned to the interventional magnetic resonance imaging and underwent placement of 3 to 5 probes (2-3 mm) under magnetic resonance imaging-directed guidance. Follow-up magnetic resonance imaging determined the size reduction of the lesion, and a clinical evaluation determined the change in symptoms. RESULTS: Nine patients were treated and had substantial reduction in the uterine size (average, 66% volume reduction), and their primary symptoms have either improved or resolved. CONCLUSION: This is the first reported review of interventional magnetic resonance imaging-directed cryotherapy of uterine fibroid tumors. This minimally invasive therapy produced shrinkage of the tumor in 8 of our first 9 patients.

Adult↗

PubMed2006

Interventional magnetic resonance imaging: an alternative to image guidance with ionising radiation.

At present, interventional procedures, such as stent placement, are performed under X-ray image guidance. Unfortunately with X-ray imaging, both patient and interventionalist are exposed to ionising radiation. Furthermore, X-ray imaging is lacking soft tissue contrast and is not capable of true 3-D displays of either interventional device or tissue morphology. Magnetic resonance imaging (MRI) offers excellent soft tissue contrast, 3-D acquisition techniques, as well as rapid image acquisition and reconstruction. Despite these advantages, MR-guided interventions are challenging owing to the limited access to the patient, strong magnetic and radio-frequency fields that require special interventional devices, inferior image frame rates and spatial resolution, and high MRI scanner noise. For MR-guided intravascular interventions, where access to the target organ is achieved through catheters, dedicated hardware and automated image slice positioning techniques have been developed. We illustrate that MR-guided renal embolisations can be performed in closed-bore high-field MR scanners.

Animals↗

PubMed1996

Towards active guidewire visualization in interventional magnetic resonance imaging.

Improving the visibility of interventional devices is of paramount importance if MRI-guided fluoroscopy is to become a reality. Passive visualization is problematic in that the susceptibility-induced artifacts are material- and orientation-dependent. Here a concept is presented for making interventional devices visible. It involves fitting a device with a straight-wire antenna. As the sensitivity of such an antenna is highest for signal sources in the immediate neighborhood, using the antenna for reception gives an outline image. In this manner a guidewire or other interventional device could be made MRI-visible. The image appearance of a straight-wire antenna depends on the orientation of the device with respect to the main magnetic field and imaging plane. This phenomena is discussed theoretically and documented with MR images.

Catheterization↗

PubMed1997

Interventional magnetic resonance imaging.

The development of minimally invasive surgical and interventional techniques has created a need for more accurate and sensitive image guidance and monitoring. Magnetic resonance imaging, with its superior soft tissue discrimination and multiplanar facilities, seems the obvious choice for an ideal image-guidance tool. Until recently, the employment of MRI in this role has been prevented by the physical constraints of conventional, closed-configuration machines. The problem has now been overcome by the development of an open design allowing both horizontal and vertical access to the patient in the scanner so that procedures can be performed concurrent with image acquisition. This configuration, together with the use of fast gradient echo sequences which can scan at speeds close to real time, means that a wide range of interventional procedures can be performed with on-line image guidance and monitoring. In addition, the versatility of the open design means that patients can assume physiological positions to allow dynamic joint imaging to be performed. This opens up a whole new field in the understanding of joint pathophysiology. This review article discusses these recent technological developments and their clinical applications. In particular, the potential role in guidance of biopsies, monitoring of thermal ablation techniques and applications in endoscopic surgery is outlined.

Animals↗

PubMed1996

Interventional magnetic resonance imaging of the head and neck and new imaging techniques.

The use of magnetic resonance imaging to directly guide therapy is a new area of investigation. Clinical magnetic resonance imaging has the potential to evolve from a purely diagnostic tool into a guide for invasive procedures. The idea of using magnetic resonance to guide percutaneous biopsy developed one decade ago. Magnetic resonance-guided fine-needle aspiration for head and neck lesions has become a standard technique some institutions. Once the needle reaches a lesion in the head and neck, it is natural to explore the possibility of treatment in the same setting. The concept of interventional magnetic resonance imaging has generated interest among radiologists, surgeons, and manufacturers. This article provides an overview of interventional procedures of the head and neck and other new imaging techniques that have been developed.

Head and Neck Neoplasms↗

PubMed2006

Real-time vascular interventional magnetic resonance imaging: the future of aortic stent-graft placement?

Endovascular stent-graft placement is emerging as a promising alternative to medical and surgical treatment of patients with diseases of the descending thoracic and abdominal aorta. Precise placement of the stentgraft, which is currently performed under x-ray control, remains, however, challenging as there are several shortcomings to fluoroscopic guidance beyond that related to the harmful effect of radiation exposure and nephrotoxic contrast media. While transesophageal echocardiography and intravascular ultrasound have been used as adjunct imaging modalities during endovascular stent-graft procedures to overcome the limitations of angiography, these techniques have not mitigated the need for fluoroscopy. Magnetic resonance imaging (MRI) guidance of vascular interventional procedures offers several potential advantages over fluoroscopy-guided techniques, including image acquisition in any desired orientation, superior 3D soft-tissue contrast with simultaneous visualization of the interventional device, absence of ionizing radiation, and avoidance of nephrotoxic contrast media. Magnetic resonance imaging is often used for pre-operative diagnosis of aortic disease and can provide all relevant information for the planning of endovascular stent-graft procedures as well as for accurate and immediate post-interventional evaluation. However, visualization of interventional instruments by MRI has proven to be the chief obstacle. This article will review current approaches that have been developed for depicting vascular instruments by MRI and will also discuss the first experimental experiences with MRI-guided endovascular stent-graft placement in a swine model of aortic dissection.

Aorta, Abdominal↗