[A technic of MRT-guided abdominal drainage with an open low-field magnet. Its feasibility and the initial results]

MR-guided biopsy: a review of current techniques and applications

Biopsy has become a cornerstone of modern medicine and most modern biopsies are performed percutaneously using image guidance, typically computed tomography or ultrasound. MR-guided biopsy offers many advantages over these more traditional modalities, and the recent development of interventional MR imaging techniques has made MR-guided percutaneous biopsies and aspirations a clinical reality. As the field of MR-guided procedures continues to expand and to attract more attention from radiologists, it is important to understand the concepts, techniques, applications, advantages, and limitations of MR-guided biopsy/percutaneous procedures. Radiologists should also recognize the need for their significant involvement in the technical aspects of MR-guided procedures, since several user-defined parameters can alter device visualization in the MR imaging environment and affect procedure safety. This article reviews the prerequisites, systems, and applications of MR-guided biopsy.

Feasibility of MR imaging-guided percutaneous drainage of pancreatic fluid collections

PURPOSE

To assess the feasibility and safety of magnetic resonance (MR) imaging-guided percutaneous drainage of pancreatic fluid collections in an open configuration low field MR imaging system.

MATERIALS AND METHODS

Ten patients with pancreatic fluid collections were examined prospectively. Five of the fluid collections were symptomatic pseudocysts and five were pancreatic abscesses. All percutaneous drainages were performed solely under MR imaging guidance with a 0.23-T open configuration C-arm shaped MR imaging scanner with interventional optical tracking. Every step of the procedure was monitored using balanced fast field echo sequences. In each case, the drainage of the fluid collection was performed with a MR imaging-compatible drainage kit using the Seldinger technique. The kit included an 18-gauge needle, a 0.035-inch stiff guide wire, 6-F and 8-F dilators, and an 8-F pigtail drainage catheter.

RESULTS

All drainage catheters could successfully be placed into the pancreatic fluid collections under MR imaging guidance. Visualization of the needle, dilator, and drainage catheter was excellent. However, visualization of the guide wire was suboptimal. The mean time needed for the MR-guided drainage procedure was 44 minutes. No immediate complications occurred. The clinical success rate of the percutaneous drainage was 70%; three patients were subsequently treated surgically. There were no deaths. The average duration of catheterization was 40 days.

CONCLUSION

MR imaging-guided percutaneous drainage of pancreatic fluid collections is feasible and safe. The presented technique has limitations--lack of real-time imaging control and small selection of MR imaging-compatible devices--that necessitate further technical developments before the procedure can be recommended for routine clinical use.

The Interventional MR Imaging Suite: Magnet Designs and Equipment Requirements

Soon after the introduction of MR imaging as an imaging tool, researchers began to investigate its capabilities to guide interventional minimally invasive procedures, such as biopsies. These early efforts have encouraged vendors and numerous research groups worldwide to identify clinical problems in the field of image-guided intervention, for which MR imaging is beneficial as an imaging modality, and to develop and refine soft-ware and hardware components to meet the specific requirements of interventional MR imaging. Over nearly 20 years, continuous advances in magnet and system design have accelerated the progress of MR-guided intervention.

Comparison of MR imaging sequences for liver and head and neck interventions

RATIONALE AND OBJECTIVES

To compare the appropriate pulse sequences for interventional device guidance during magnetic resonance (MR) imaging at 0.2 T and to evaluate the dependence of sequence selection on the anatomic region of the procedure.

MATERIALS AND METHODS

Using a C-arm 0.2 T system, four interventional MR sequences were applied in 23 liver cases and during MR-guided neck interventions in 13 patients. The imaging protocol consisted of: multislice turbo spin echo (TSE) T2w, sequential-slice fast imaging with steady precession (FISP), a time-reversed version of FISP (PSIF), and FISP with balanced gradients in all spatial directions (True-FISP) sequences. Vessel conspicuity was rated and contrast-to-noise ratio (CNR) was calculated for each sequence and a differential receiver operating characteristic was performed.

RESULTS

Liver findings were detected in 96% using the TSE sequence. PSIF, FISP, and True-FISP imaging showed lesions in 91%, 61%, and 65%, respectively. The TSE sequence offered the best CNR, followed by PSIF imaging. Differential receiver operating characteristic analysis also rated TSE and PSIF to be the superior sequences. Lesions in the head and neck were detected in all cases by TSE and FISP, in 92% using True-FISP, and in 84% using PSIF. True-FISP offered the best CNR, followed by TSE imaging. Vessels appeared bright on FISP and True-FISP imaging and dark on the other sequences.

CONCLUSION

In interventional MR imaging, no single sequence fits all purposes. Image guidance for interventional MR during liver procedures is best achieved by PSIF or TSE, whereas biopsies in the head and neck are best performed using FISP or True-FISP sequences.

Interventional and intraoperative magnetic resonance imaging

The goal of the Image Guided Therapy Program, as the name implies, is to develop the use of imaging to guide minimally invasive therapy. The program combines interventional and intraoperative magnetic resonance imaging (MRI) with high-performance computing and novel therapeutic devices. In clinical practice the multidisciplinary program provides for the investigation of a wide range of interventional and surgical procedures. The Signa SP 0.5 T superconducting MRI system (GE Medical Systems, Milwaukee, WI) has a 56-cm-wide vertical gap, allowing access to the patient and permitting the execution of interactive MRI-guided procedures. This system is integrated with an optical tracking system and utilizes flexible surface coils and MRI-compatible displays to facilitate procedures. Images are obtained with routine pulse sequences. Nearly real-time imaging, with fast gradient-recalled echo sequences, may be acquired at a rate of one image every 1.5 s with interactive image plane selection. Since 1994, more than 800 of these procedures, including various percutaneous procedures and open surgeries, have been successfully performed at Brigham and Women's Hospital (Boston, MA).

MR-guided core biopsies using a closed 1.0 T imager. First clinical results

OBJECTIVE

High soft-tissue contrast and multiplanar imaging capabilities of MRI may be advantageous in biopsy guidance compared to CT. We report our first results with MR-guided core biopsies using a closed 1.0 T MR imager.

METHODS AND PATIENTS

In ten patients, seven liver lesions and one lesion each in the muscle of the back, the gluteal muscle and in the breast were biopsied under MR guidance using MR-compatible needles (Tru-Cut type, 18G and 14G). For control scans T1-weighted turbo-spin-echo (TSE), gradient-echo and T2-weighted TSE sequences were used.

RESULTS

In all patients, the suspicious lesions and the biopsy needle were exactly delineated in MR control scans. In nine out of ten patients, the suspicious lesion was clarified histologically. Controls of needle position in a second plane were performed twice. Pushing the inner stylet alone resulted in a distortion of the needle in several cases in its flat area. The small diameter of the MR gantry was inconvenient for a few patients. One complication (intrahepatic bleeding) was observed, which healed up without consequences.

CONCLUSION

Using a closed 1.0 T MR imager MR-guided core biopsies can be conducted efficiently. Core biopsies should be taken by pulling and pushing the outer cannula. Advantageous compared to CT are the multiplanar imaging capabilities, while the smaller gantry is disadvantageous.

Intraoperative magnetic resonance imaging-guided drainage of nonpalpable abscesses

SUMMARY

Intraoperative magnetic resonance imaging provides the surgeon with powerful, high-resolution, real-time imaging. Procedures may be performed with minimal invasion, with the benefit of reduced tissue damage, improved wound healing, and a better cosmetic result. The authors present a case of a leukemic pediatric patient with a few large, deeply situated, nonpalpable abscesses that were drained successfully with intraoperative magnetic resonance imaging guidance. In this case, this new intraoperative imaging method enabled minimal invasiveness, with fast recovery.

Magnetic resonance image-guided biopsy and aspiration

Recent advances in magnet design and magnetic resonance (MR) system technology coupled with the development of fast gradient-echo pulse sequences have contributed to the increasing interest in interventional magnetic resonance imaging (MRI). Minimally invasive diagnostic and therapeutic image-based intervention can now be performed under near real-time MR guidance, taking advantage of the high tissue contrast, spatial resolution, vascular conspicuity and multiplanar capabilities of MRI to achieve safe and precise needle placement. This is particularly advantageous for needle navigation in regions of complex anatomy, such as the suprahyoid neck. This article discusses the theoretical concepts and clinical applications of MR for guidance for biopsy and aspiration, and highlights the technical developments that provide the foundation for interventional MRI.