Biopsy needle tips with markers--MR compatible needles for high-precision needle tip positioning

Real-time probe tracking using EM-optical sensor for MRI-guided cryoablation

BACKGROUND

A method of real-time, accurate probe tracking at the entrance of the MRI bore is developed, which, fused with pre-procedural MR images, will enable clinicians to perform cryoablation efficiently in a large workspace with image guidance.

METHODS

Electromagnetic (EM) tracking coupled with optical tracking is used to track the probe. EM tracking is achieved with an MRI-safe EM sensor working under the scanner's magnetic field to compensate the line-of-sight issue of optical tracking. Unscented Kalman filter-based probe tracking is developed to smooth the EM sensor measurements when occlusion occurs and to improve the tracking accuracy by fusing the measurements of two sensors.

RESULTS

Experiments with a spine phantom show that the mean targeting errors using the EM sensor alone and using the proposed method are 2.21 mm and 1.80 mm, respectively.

CONCLUSION

The proposed method achieves more accurate probe tracking than using an EM sensor alone at the MRI scanner entrance.

Technical Note: MR-visualization of interventional devices using transient field alterations and balanced steady-state free precession imaging

PURPOSE

In interventional magnetic resonance imaging, instruments can be equipped with conducting wires for visualization by current application. The potential of sequence triggered application of transient direct currents in balanced steady-state free precession (bSSFP) imaging is demonstrated.

METHODS

A conductor and a modified catheter were examined in water phantoms and in an ex vivo porcine liver. The current was switched by a trigger pulse in the bSSFP sequence in an interval between radiofrequency pulse and signal acquisition. Magnitude and phase images were recorded. Regions with transient field alterations were evaluated by a postprocessing algorithm. A phase mask was computed and overlaid with the magnitude image.

RESULTS

Transient field alterations caused continuous phase shifts, which were separated by the postprocessing algorithm from phase jumps due to persistent field alterations. The overlaid images revealed the position of the conductor. The modified catheter generated visible phase offset in all orientations toward the static magnetic field and could be unambiguously localized in the ex vivo porcine liver.

CONCLUSIONS

The application of a sequence triggered, direct current in combination with phase imaging allows conspicuous localization of interventional devices with a bSSFP sequence.

MRI-guided vascular access with an active visualization needle

PURPOSE

To develop an approach to vascular access under magnetic resonance imaging (MRI), as a component of comprehensive MRI-guided cardiovascular catheterization and intervention.

MATERIALS AND METHODS

We attempted jugular vein access in healthy pigs as a model of "difficult" vascular access. Procedures were performed under real-time MRI guidance using reduced field of view imaging. We developed an "active" MRI antenna-needle having an open-lumen, distinct tip appearance and indicators of depth and trajectory in order to enhance MRI visibility during the procedure. We compared performance of the active needle against an unmodified commercial passively visualized needle, measured by procedure success among operators with different levels of experience.

RESULTS

MRI-guided central vein access was feasible using both the active needle and the unmodified passive needle. The active needle required less time (88 vs. 244 sec, P = 0.022) and fewer needle passes (4.5 vs. 9.1, P = 0.028), irrespective of operator experience.

CONCLUSION

MRI-guided access to central veins is feasible in our animal model. When image guidance is necessary for vascular access, performing this component under MRI will allow wholly MRI-guided catheterization procedures that do not require adjunctive imaging facilities such as x-ray or ultrasound. The active needle design showed enhanced visibility, as expected. These capabilities may permit more complex catheter-based cardiovascular interventional procedures enabled by enhanced image guidance.

On the feasibility of MRI-guided navigation to demarcate breast cancer for breast-conserving surgery

PURPOSE

The aim of this study was to investigate the feasibility of image-guided navigation approaches to demarcate breast cancer on the basis of preacquired magnetic resonance (MR) imaging in supine patient orientation.

METHODS

Strategies were examined to minimize the uncertainty in the instrument-tip position, based on the hypothesis that the release of instrument pressure returns the breast tissue to its predeformed state. For this purpose, four sources of uncertainty were taken into account: (1) U(ligaments): Uncertainty in the reproducibility of the internal mammary gland geometry during repeat patient setup in supine orientation; (2) U(r_breathing): Residual uncertainty in registration of the breast after compensation for breathing motion using an external marker; (3) U(reconstruction): Uncertainty in the reconstructed location of the tip of the needle using an optical image-navigation system (phantom experiments, n = 50); and (4) U(deformation): Uncertainty in displacement of breast tumors due to needle-induced tissue deformations (patients, n = 21). A Monte Carlo study was performed to establish the 95% confidence interval (CI) of the combined uncertainties. This region of uncertainty was subsequently visualized around the reconstructed needle tip as an additional navigational aid in the preacquired MR images. Validation of the system was performed in five healthy volunteers (localization of skin markers only) and in two patients. In the patients, the navigation system was used to monitor ultrasound-guided radioactive seed localization of breast cancer. Nearest distances between the needle tip and the tumor boundary in the ultrasound images were compared to those in the concurrently reconstructed MR images.

RESULTS

Both U(reconstruction) and U(deformation) were normally distributed with 0.1 +/- 1.2 mm (mean +/- 1 SD) and 0.1 +/- 0.8 mm, respectively. Taking prior estimates for U(ligaments) (0.0 +/- 1.5 mm) and U(r_breathing) (-0.1 +/- 0.6 mm) into account, the combined impact resulted in 3.9 mm uncertainty in the position of the needle tip (95% CI) after release of pressure. The volunteer study showed a targeting accuracy comparable to that in the phantom experiments: 2.9 +/- 1.3 versus 2.7 +/- 1.1 mm, respectively. In the patient feasibility study, the deviations were within the 3.9 mm CI.

CONCLUSIONS

Image-guided navigation to demarcate breast cancer on the basis of preacquired MR images in supine orientation appears feasible if patient breathing is tracked during the navigation procedure, positional uncertainty is visualized and pressure on the localization instrument is released prior to verification of its position.

Magnetic resonance-guided upper abdominal biopsies in a high-field wide-bore 3-T MRI system: feasibility, handling, and needle artefacts

OBJECTIVE

To investigate the feasibility and handling of abdominal MRI-guided biopsies in a 3-T MRI system.

METHODS

Over a 1-year period, 50 biopsies were obtained in 47 patients with tumours of the upper abdominal organs guided by 3-T MRI with a large-bore diameter of 70 cm. Lesions in liver (47), spleen (1) and kidney (2) were biopsied with a coaxial technique using a 16-G biopsy needle guided by a T1-weighted three-dimensional gradient recalled echo volumetric interpolated breath-hold examination (T1w-3D-GRE-VIBE) sequence. Sensitivity, specificity, accuracy, complication rate, interventional complexity, room/intervention time and needle artefacts were determined.

RESULTS

A sensitivity of 0.93, specificity of 1.0 and accuracy of 0.94 were observed. Three patients required a rebiopsy. There was a minor complications rate of 13.6%, and no major complications were observed. Histopathology revealed 38 malignant lesions, and 3-month follow-up confirmed 9 benign lesions. Mean lesion diameter was 3.4 ± 3.1 cm (50% being smaller than 2 cm). Mean needle tract length was 10.8 ± 3.3 cm. Median room time was 42.0 ± 19.8 min and intervention time 9.3 ± 8.1 min. Needle artefact size was about 9-fold greater for perpendicular access versus access parallel to the main magnetic field.

CONCLUSION

Biopsies of the upper abdomen can be performed with great technical success and easy handling because of the large-bore diameter. The MRI-guided biopsy needle had an acceptable susceptibility artefact at 3 T. However future research must aim to reduce the susceptibility effects of the biopsy systems.