Interventional MR Research Articles

Interventional MR tomography. Current status and future perspectives

The concept of MR guidance of invasive diagnostic and minimally invasive therapeutic procedures is based on the excellent morphologic and functional properties of MR imaging. Prerequisites are adequate patient monitoring and adherence to safety guidelines. Fast and ultrafast sequences, temperature quantification, visualization of intravascular devices, thermal stability of contrast media and thermosensitive contrast media are discussed. The spectrum of clinical applications includes biopsies, thermal ablation modalities, vascular applications, MR endoscopy and intraoperative MR imaging. The development of interventional MR imaging is still in its infancy. In the future, MR imaging may play an important role in interventional radiology and minimally invasive therapy.

Vascular applications of interventional MRI

The flow sensitivity inherent to the MR experiment allows for the non-invasive assessment of both the arterial and venous vasculature in any desired plane with good spatial resolution. Data can be acquired in a three-dimensional form, permitting reformating in any plane. In addition, MRI is capable of providing quantitative blood flow information with the use of phase-contrast flow-mapping techniques. Ultrafast gradient echo and echoplanar data acquisition strategies even permit imaging in near-real time. The availability of open MRI configurations now permits one to take advantage of the unique imaging features inherent to MR imaging for the purpose of guidance and control of various intravascular procedures. With the recent development of the MR tracking and MR profiling techniques, permitting visualization of guide-wires and catheters relative to their surroundings in the MR environment in real time, one of the last obstacles to 'Interventional MR angiography' has in effect been overcome. In addition, MR catheters can be modified to acquire high-resolution MR images of the vascular wall, thereby opening vast possibilities regarding characterization of atherosclerotic plaques. This review introduces the underlying techniques for catheter and guide-wire visualization in the MR environment, describes preliminary interventions in animals and humans and discusses the potential of intravascular MRI.

OPEN-CONFIGURATION MR IMAGING, INTERVENTION, AND SURGERY OF THE URINARY TRACT

The open-configuration MR imaging system provides new applications both in diagnosis and in therapy of conditions in the urinary tract. In addition to conventional imaging, the open configuration permits MR imaging of patients in many positions. This has already been shown to be useful in imaging the pelvis during voiding, where a sitting position allows urodynamic evaluation. The lithotomy position can be used for imaging the prostate, which also permits procedural access. The ultimate purpose of the interventional MR imaging suite is to integrate therapeutic tools and techniques with MR imaging. From surgical planning through specialized imaging systems with minimally invasive surgical applications, new methods are being developed and implemented. This new field of image-guided therapy will require extensive clinical development and evaluation for applications in the urinary tract. This will require a large concentrated interdisciplinary effort of surgeons, radiologists, computer scientists, engineers, and physicists. Successful integration of basic research and clinical work will result in a number of cutting-edge technologies with direct clinical application in the urinary tract. Initial projects have included biopsies, endoscopies, and real-time procedural control of high-temperature and cryogenic ablations. It is anticipated that the current surge in image-guided interventions will motivate even more research activity in this field, and will ultimately define the role of MR imaging guidance in urologic intervention and surgery.

Interventional MR-guided excisional biopsy of breast lesions.

Interventional MR (IMR) machines have produced unique opportunities for image-guided surgery. The open configuration design and fast pulse sequences allow intraoperative scanning to monitor procedures. This study was undertaken to assess the potential use of IMR for image-guided surgery. Benign breast lesion excision was chosen as an uncomplicated surgical model. Ten female patients with known benign tumors underwent excision biopsy under general anesthesia in a Signa SP10 .5-T IMR machine (General Electric Medical Systems, Milwaukee, WI). Lesions were localized with precontrast and postcontrast (intravenous gadolinium-diethylenetriamine pentaacetic acid, .2 mmol/kg) fast multiplanar spoiled gradient-recalled acquisition in the steady state (GRASS) sequences. Preoperative "real-time" fast gradient-recalled sequences were also obtained using the Flashpoint (General Electric Medical Systems, Milwaukee, WI) tracker device. The maximum dimensions of each lesion were measured from the resulting images. Excision was performed using titanium instruments and an ultrasonically activated scalpel. Intraoperative real-time scanning demonstrated the resection margin and confirmed complete excision. The maximum dimensions of the macroscopic specimens were compared with those from the MR images. All tumors were visualized with the Signa scanner and real-time imaging and the images were enhanced after intravenous contrast. Maximum dimensions on histologic examination were not significantly different from those measured from Signa (P > .17) or real-time images (P > .4). There was no significant difference between lesion size from Signa and real-time images (P > .25). All postprocedure scans demonstrated complete excision. There were six fibroadenomas, two foci of sclerosing adenosis, one area of fibrocystic disease, and one schwannoma. Intraoperative MR scanning reliably identifies palpable breast tumors and can accurately guide surgical excision. Further work using MR guidance can now be performed in other general surgical areas.

Interventional MR: A critical juncture for radiology

Interventional MR: A critical juncture for radiology

Visualization of MR-compatible catheters by electrically induced local field inhomogeneities: evaluation in vivo.

The purpose of this study was to assess the feasibility of a newly developed field inhomogeneity catheter for interventional MRI in vivo. Different prototypes of a field inhomogeneity catheter (pigtail and multipurpose configuration, balloon catheters) were investigated in pigs. The catheters were introduced in Seldinger technique via the femoral vessels over a guidewire 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 [TFE]). Catheters were introduced over a guidewire without complications in all cases. Using the field inhomogeneity concept, catheters were easily visualized in the inferior vena cava and the aorta by the fast gradient-echo technique on MR in all cases. Although aortic branches were successful cannulated, the catheters were not well displayed by the TFE technique due to the complex and tortuous anatomy. All animals survived the experiments without complications. MR-guided visualization of a field inhomogeneity catheter is a simple concept that can be realized on each MR scanner and may allow intravascular MR-guided interventions in future.

Interventional MR Imaging

Interventional MR Imaging

O-28-422 - A new frameless stereotactic system for use in the open interventional MR

O-28-422 - A new frameless stereotactic system for use in the open interventional MR

P-3-408 - Braintumor biopsies in the open interventional MR

P-3-408 - Braintumor biopsies in the open interventional MR

Design and implementation of an interventional MR imaging suite.

Design and implementation of an interventional MR imaging suite.

FUTURE DIRECTIONS IN INTERVENTIONAL PEDIATRIC RADIOLOGY

In conclusion, the explosion of interventional radiology and its impact on the pediatric patient have resulted in a completely new approach to the subspecialty of interventional pediatric radiology. The interventional radiologist has become an integral part of the management of patients and has become directly involved in the day-to-day care of patients. The use of interventional MR imaging recently has been described in clinical trial. Open-configuration magnets that allow full access to the patient and are equipped with instrument tracking systems provide an interactive environment in which biopsies, endoscopic procedures, and minimally invasive interventions or surgeries are performed. In addition, thermal ablation and image-based control of energy deposition also can be performed. Among these procedures, noninvasive MR-guided focused ultrasound ablation has the most promising future and may replace some conventional surgery. The merging of new and exciting technologies including MR, ultrasound, CT, and fluoroscopy into an environment in which both surgical and interventional radiologic procedures can be performed with image guidance is the basis of the operating room of the future. The role of the interventional radiologist as both the imager and interventionalist is central to this procedural environment; however, the interventional radiologist must accept all the responsibilities of imaging, therapy, patient care, and associated complications.

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

To assess the feasibility of a new developed field inhomogeneity catheter for interventional MR imaging in vivo. 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]). 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. 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.

Localization of MR-detected breast cancer using a prototype stereotactic guidance MR system

Abstract We report the case of an invasive tubular breast carcinoma detected solely by MR imaging, and subsequently localized for excision biopsy with an MR-compatible, spring-hook wire positioning marker using a prototype MR-guided stereotactic localization system. This report emphasises the potential of interventional MR imaging in the management of breast cancer.

Interventional MR imaging. Demonstration of the feasibility of the Overhauser marker enhancement (OMEN) technique.

The poor localization facility of interventional instruments in MR imaging has been one of the major obstacles to the popularization of interventional MR imaging. It has been suggested that the Overhauser enhancement be used to generate markers of small size and high visibility. This article studies the feasibility of a localization marker based on this method. A small Overhauser marker was constructed on the tip of a coaxial cable and comparative images were taken by a 0.23 T imager with and without electron spin irradiation. During irradiation an enhanced signal intensity from the marker was observed. The signal from the marker also exceeded the signal from a 0.25 mmol MnCl2 reference phantom. Its small size and high signal-to-noise ratio, together with immunity to most system nonlinearities and imaging errors, makes the Overhauser marker a promising localization method for the accurate positioning of interventional devices. The method may be applied at any field strength, and markers are visible in images obtained with any practical imaging sequence.

Interventional Mr imaging

Interventional Mr imaging

Will it be feasible to insert endoprostheses under interventional MRI?

Recent advances in magnetic resonance imaging (MRI) technology may provide a safer and more sensitive monitoring modality than X-ray imaging for endovascular surgical procedures. The purpose of this study was to investigate the feasibility of using MRI to monitor the insertion of endoprostheses. The endoprostheses we studied were composed of a nitinol stent encased in a polyester sheath. These were characterized with four different MRI techniques: the fast spin-echo; spin-echo; gradient-recalled echo; and the spoiled gradient-recalled echo. The deployment of the endoprosthesis into an artery was simulated in an in vitro model and viewed using a fast spin-echo MRI technique. Image artifacts produced by the nitinol framework in these endoprostheses were minimal when fast spin-echo or spin-echo imaging techniques were used, improving the visibility of the device. In in vitro tests, the catheters and endoprostheses were visualized by MRI with sufficient clarity to guide the placement of a device in the model artery. Insertion of this type of endoprosthesis under interventional MRI guidance is feasible. The convenience and improved safety provided by interventional MR systems and "real-time" imaging capabilities are expected to make this technology an attractive alternative to X-ray imaging techniques.

Will it Be Feasible to Insert Endoprostheses under Interventional MRI?

Purpose: Recent advances in magnetic resonance imaging (MRI) technology may provide a safer and more sensitive monitoring modality than X-ray imaging for endovascular surgical procedures. The purpose of this study was to investigate the feasibility of using MRI to monitor the insertion of endoprostheses. Methods: The endoprostheses we studied were composed of a nitinol stent encased in a polyester sheath. These were characterized with four different MRI techniques: the fast spin-echo; spin-echo; gradient-recalled echo; and the spoiled gradient-recalled echo. The deployment of the endoprosthesis into an artery was simulated in an in vitro model and viewed using a fast spin-echo MRI technique. Results: Image artifacts produced by the nitinol framework in these endoprostheses were minimal when fast spin-echo or spin-echo imaging techniques were used, improving the visibility of the device. In in vitro tests, the catheters and endoprostheses were visualized by MRI with sufficient clarity to guide the placement of a device in the model artery. Conclusions: Insertion of this type of endoprosthesis under interventional MRI guidance is feasible. The convenience and improved safety provided by interventional MR systems and “real-time” imaging capabilities are expected to make this technology an attractive alternative to X-ray imaging techniques.

Interactive stereotaxic interventions in superconducting, open 0.5-Tesla MRI tomography

Evaluation of an interactive, stereotactic biopsy device integrated in an open superconductive 0.5 tesla MR-scanner with a vertical gap. In addition to "in-vitro" experiments performed on a plexiglas phantom with holes of varying diameters (5-20 mm) biopsies on eleven patients (7 women, 4 men; average age 55 years) were performed in the interventional MR-system. Lesions in the abdomen (n = 6), muscle (n = 1), thyroid (n = 3) and breast (n = 1) were targeted with 18-20 G aspiration biopsy needles of 5-15 cm length. The intervention was interactively guided by a fast T1-weighted 2-D gradient echo sequence. All of the 15 and 20 mm holes of the phantom, but only 83% of the 10 and 5 mm holes were hit. No complications occurred during the MR-guided patient procedures. All lesions (mean size 3.5 cm, distance from the skin 2 cm to 10 cm) were biopsied successfully. The fast image acquisition in combination with the stereotactic technique enables interactive control of the needle. Stereotactic, interactively controlled biopsies in the interventional MR are technical feasible. However, the range of meaningful indications for MR-guided biopsies is limited.

Interventional MR imaging.

Interventional MR imaging.

Interventional MR: Successful design and use of a non-ferromagnetic needle for aspiration/biopsy

Interventional MR: Successful design and use of a non-ferromagnetic needle for aspiration/biopsy