[MRI-assisted bile duct drainage: evaluation of passive catheter imaging in an animal model]

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.

Ability of MR cholangiography to reveal stent position and luminal diameter in patients with biliary endoprostheses: in vitro measurements and in vivo results in 30 patients

OBJECTIVE

Our goal was to evaluate the ability of MR cholangiography to show stent position and luminal diameter in patients with biliary endoprostheses.

MATERIALS AND METHODS

Susceptibility artifacts were evaluated in vitro in three different stent systems (cobalt alloy-based, nitinol-based, and polyethylene) using two breath-hold sequences (rapid acquisition with relaxation enhancement, half-Fourier acquisition single-shot turbo spin echo) on a 1.5-T MR imaging system. The size of the stent-related artifact was measured, and the relative stent lumen was calculated. In vivo stent position and patency were determined in 30 patients (10 cobalt alloy-based stents, five nitinol-based stents, and 15 polyethylene stents).

RESULTS

In vitro, the susceptibility artifact of the cobalt stent caused complete obliteration of the stent lumen. The relative stent lumens of the nitinol-based and polyethylene stents were 38-50% and 67-100%, respectively. In vivo, all stents were patent at the time of imaging. The position of the cobalt alloy-based stent could be determined in nine of 10 patients, but stent patency could not be evaluated. Stent position of nitinol stents could not be adequately evaluated in any of the five patients, and internal stent diameter could be visualized in only one patient. In nine of 15 patients, the fluid column within the implanted polyethylene stent was seen on MR cholangiography.

CONCLUSION

The internal stent lumen could be visualized in most patients with an indwelling polyethylene stent, but not in patients with cobalt alloy- or nitinol-based stents.

Visualization, tracking, and navigation of instruments for magnetic resonance imaging-guided endovascular procedures

Interventional procedures using magnetic resonance imaging (MRI) guidance have increased in interest during the last few years. Central to the success and safety of MRI-guided procedures is the accurate visualization of the interventional instruments relative to the surrounding anatomy. A variety of methodologies for visualizing and automatically tracking instruments, including needles, radiofrequency and laser ablation devices, endoscopes, catheters, and guidewires have been developed and introduced to help the interventionalist to safely guide the device toward the target region. This article describes and compares characteristics of the four most commonly used localization and tracking systems used for MRI-guided interventional procedures: those based on the susceptibility artifact of the device, those that intentionally create field inhomogeneity along the device, those that rely on an optical tracking system, and active tracking systems using micro receive coils.