MR imaging-guided biliary drainage in an open low-field system: first clinical experiences

Hybrid Approach for Biliary Interventions Employing MRI-Guided Bile Duct Puncture with Near-Real-Time Imaging

OBJECTIVE

To assess the feasibility of a hybrid approach employing MRI-guided bile duct (BD) puncture for subsequent fluoroscopy-guided biliary interventions in patients with non-dilated (≤3 mm) or dilated BD (≥3 mm) but unfavorable conditions for ultrasonography (US)-guided BD puncture.

METHODS

A total of 23 hybrid interventions were performed in 21 patients. Visualization of BD and puncture needles (PN) in the interventional MR images was rated on a 5-point Likert scale by two radiologists. Technical success, planning time, BD puncture time and positioning adjustments of the PN as well as technical success of the biliary intervention and complication rate were recorded.

RESULTS

Visualization even of third-order non-dilated BD and PN was rated excellent by both radiologists with good to excellent interrater agreement. MRI-guided BD puncture was successful in all cases. Planning and BD puncture times were 1:36 ± 2.13 (0:16-11:07) min. and 3:58 ± 2:35 (1:11-9:32) min. Positioning adjustments of the PN was necessary in two patients. Repeated capsular puncture was not necessary in any case. All biliary interventions were completed successfully without major complications.

CONCLUSION

A hybrid approach which employs MRI-guided BD puncture for subsequent fluoroscopy-guided biliary intervention is feasible in clinical routine and yields high technical success in patients with non-dilated BD and/or unfavorable conditions for US-guided puncture. Excellent visualization of BD and PN in near-real-time interventional MRI allows successful cannulation of the BD.

MRI-guided percutaneous transhepatic cholangiodrainage: feasibility study in a porcine model

BACKGROUND AND STUDY AIMS

MRI-guided procedures combine high-quality imaging with lack of radiation. Percutaneous transhepatic cholangiodrainage under real-time MRI guidance (MRI-PTCD) seems promising, allowing targeted puncture and avoiding multiple blind passes and use of contrast, which are associated with standard PTCD's heaviest complications.

PATIENTS AND METHODS

Aim of this study was to investigate the feasibility of MRI-PTCD in three outbred piglets. Obstructive cholestasis was induced by common bile duct ligation. Two days later, MRI-PTCD was performed (open MRI, 1.0 Tesla) with prototype MRI-compatible accessories. Visualization was achieved with a balanced steady-state free precession real-time sequence (bSSFP: 0.75 frames/s, TR/TE [ms]: 7.2/3.6; flip angle: 45°; 200 × 200 matrix size; resolution: 1.3 × 1.3 mm(2), slice thickness: 7 mm). Cannulation of the bile ducts was followed by placement of Yamakawa drainages.

RESULTS

Twelve punctures were performed (four per animal, 10/12 successful); in 2/10 the bile ducts could not be cannulated. Animal survival was 100% and no significant complications occurred.

CONCLUSIONS

Initial data show that MRI-PTCD can be successfully performed. This may lead to establishment of a new optimized PTCD technique compared to the standard approach under fluoroscopy.

Percutaneous transhepatic cholangiodrainage under real-time MRI guidance: initial experience in an animal model

AIMS

To assess percutaneous transhepatic cholangiodrainage (PTCD) under real-time MRI-guidance and compare it to procedures performed under fluoroscopy.

METHODS

We developed an in vitro model for MRI-guided and conventional PTCD, using an animal organ set including liver and bile ducts placed in an MRI-compatible box and tested it in a 1.0-Tesla open MRI-scanner. Prototype 18G needles and guide wires, standard guide wires, dilatation bougies, and drainages were used (MRI-compatible). MRI-visualization was by means of a bFFE real-time sequence using a surface coil (Flex-L). Outcome measurements were success rates and time needed for bile duct puncture using real-time MRI-guidance versus conventional radiologic methods in the model. Cannulation and drainage placement were also analysed.

RESULTS

Fifty MRI-guided experiments were performed, leading to rapid (mean: 43s, range: 15-72s) and successful puncture and cannulation in 96% of procedures. Median drainage placement time was 321.5s (range: 241-411s). In 35 control experiments under fluoroscopy, puncture success was 69%, whereas times were significantly longer (mean 273s, range 45-631s).

CONCLUSIONS

Initial in vitro experience shows that PTCD can be successfully and rapidly performed under real-time MRI-guidance and demonstrates improved performance compared to the conventional radiologic approach.

MR-guided intravascular interventions: techniques and applications

Magnetic resonance imaging (MRI) offers several advantages over other imaging modalities that make it an attractive imaging tool for diagnostic and therapeutic procedures. This tremendous potential of MRI has provided the rationale for increased attention toward MR-guided endovascular interventions. MR guidance has been used recently to navigate endovascular catheters and deliver stents, vena cava filters, embolization materials, and septum closure devices. However, its potential goes beyond just copying existing procedures toward the development of new minimally invasive techniques that cannot be performed with conventional guiding techniques. Because of technical limitations and safety issues associated with some of the currently available devices, a limited number of clinical studies have been performed so far. The overall success for this developing field requires considerable interdisciplinary research within both the interventional and the MR community. Only through a combined effort can this complex technology find its way into clinical practice. This review discusses the hardware and software improvements that have helped to advance endovascular interventions under MR imaging guidance from a pure research tool to become a clinical reality. In addition, technical and safety issues specific to endovascular MR image guidance will be described and practical applications will be shown that take advantage of the benefits of MR for endovascular interventions.

MR-guided endovascular interventions: device visualization, tracking, navigation, clinical applications, and safety aspects

Reliable visualization and tracking are essential for guiding endovascular devices within blood vessels. The most commonly used methods are susceptibility artifact-based tracking that relies on the artifact created within the image by the device and microcoil- or antenna-based tracking that uses the high signal generated by small MR endovascular receive coils when the transmit coil emits a nonselective radiofrequency pulse. To date, the use of endovascular MR guidance techniques has primarily been confined to animal experiments. There are only a few reports on MR-guided endovascular applications in patients. Therefore, access to the patient within the scanner, dedicated devices, and safety issues remain major challenges. To face these challenges, attention from all radiologists, especially interventional radiologists, is required to make MR-guided endovascular procedures a clinical reality.