Needle biopsy of anatomically unfavorable liver lesions with an electromagnetic navigation assist device in a computed tomography environment

Accuracy of a CT-Ultrasound Fusion Imaging Guidance System Used for Hepatic Percutaneous Procedures

PURPOSE

To evaluate the accuracy of a fusion imaging guidance system using ultrasound (US) and computerized tomography (CT) as a real-time imaging modality for the positioning of a 22-gauge needle in the liver.

MATERIALS AND METHODS

The spatial coordinates of 23 spinal needles placed at the border of hepatic tumors before radiofrequency thermal ablation were determined in 23 patients. Needles were inserted up to the border of the tumor with the use of CT-US fusion imaging. A control CT scan was carried out to compare real (x, y, z) and virtual (x', y', z') coordinates of the tip of the needle (D for distal) and of a point on the needle located 3 cm proximally to the tip (P for proximal).

RESULTS

The mean Euclidian distances were 8.5 ± 4.7 mm and 10.5 ± 5.3 mm for D and P, respectively. The absolute value of mean differences of the 3 coordinates (|x' - x|, |y' - y|, and |z' - z|) were 4.06 ± 0.9, 4.21 ± 0.84, and 4.89 ± 0.89 mm for D and 3.96 ± 0.60, 4.41 ± 0.86, and 7.66 ± 1.27 mm for P. X = |x' - x| and Y = |y' - y| coordinates were <7 mm with a probability close to 1. Z = |z' - z| coordinate was not considered to be larger nor smaller than 7 mm (probability >7 mm close to 50%).

CONCLUSIONS

Positioning errors with the use of US-CT fusion imaging used in this study are not negligible for the insertion of a 22-gauge needle in the liver. Physicians must be aware of such possible errors to adapt the treatment when used for thermal ablation.

In vivo comparison of two navigation systems for abdominal percutaneous needle intervention

PURPOSE

To compare the accuracy of a Kinect-Optical navigation system with an electromagnetic (EM) navigation system for percutaneous liver needle intervention.

MATERIALS AND METHODS

Five beagles with nine artificial tumors were used for validation. The Veran IG4 EM navigation system and a custom-made Kinect-Optical navigation system were used. Needle insertions into each tumor were conducted with these two guidance methods. The target positioning error (TPE) and the time cost of the puncture procedures were evaluated.

RESULTS

A total of 18 needle insertions were performed to evaluate the navigation accuracy of the two guidance approaches. The targeting error was 6.78 ± 3.22 mm and 8.72 ± 3.5 mm for the Kinect-Optical navigation system and the EM navigation system, respectively. There is no statistically significant difference in the TPE between the Kinect-Optical navigation system and the EM navigation system (p = 0.229). The processing time with the Kinect-Optical system (10 min) is similar to that of the Veran IG4 system (12 min).

CONCLUSIONS

The accuracy of the Kinect-Optical navigation system is comparable to that of the EM navigation system.

CT-guided liver biopsy with electromagnetic tracking: results from a single-center prospective randomized controlled trial

OBJECTIVE

The purpose of this study is to evaluate the effectiveness of electromagnetic tracking in assisting CT-guided liver biopsies.

MATERIALS AND METHODS

This was a single-center prospective randomized controlled trial comparing nonfluoroscopic CT-guided liver biopsy using an advance-and-scan technique with and without electromagnetic tracking. Fifty patients with a liver lesion referred for biopsy (women, 52%; mean age, 59.7 years; mean lesion size, 3.6 cm) were enrolled in the study and were randomly assigned to either arm. The primary and secondary objectives were to assess and quantify differences in the number of intraprocedural scans, cumulative effective radiation dose, number of needle manipulations, and procedure time from skin-stick to the target lesion with and without assistance.

RESULTS

Electromagnetic tracking significantly decreased the number of scans, effective radiation dose, number of manipulations per procedure, and time from skin-stick to the target lesion. The ratio of the number of scans (electromagnetic tracking to control) was 0.55 (95% CI, 0.42-0.73; p<0.0001). The mean difference in effective radiation dose (electromagnetic tracking-control) was -4.7 mSv (95% CI, -7.01 to -2.44 mSv; p=0.0001), and the median difference was -5.1 mSv (95% CI, -7.01 to -3.56 mSv; p<0.0001). The ratio of the number of manipulations (electromagnetic tracking to control) was 0.36 (95% CI, 0.24-0.54; p<0.0001). The mean difference for the time from skin-stick to the target lesion was -247.6 seconds (95% CI, -394.34 to -100.83 seconds; p=0.0014) and the median difference was -253.0 seconds (95% CI, -325.00 to -124.00 seconds; p=0.0001).

CONCLUSION

Electromagnetic tracking assistance has the potential to decrease the number of intraprocedural CT scans and needle manipulations and to reduce patient radiation dose during CT-guided liver biopsy.

Comparison of freehand-navigated and aiming device-navigated targeting of liver lesions

BACKGROUND

Accurate needle placement is crucial for the success of percutaneous radiological needle interventions. We compared three guiding methods using an optical-based navigation system: freehand, using a stereotactic aiming device and active depth control, and using a stereotactic aiming device and passive depth control.

METHODS

For each method, 25 punctures were performed on a non-rigid phantom. Five 1 mm metal screws were used as targets. Time requirements were recorded, and target positioning errors (TPE) were measured on control scans as the distance between needle tip and target.

RESULTS

Time requirements were reduced using the aiming device and passive depth control. The Euclidian TPE was similar for each method (4.6 ± 1.2-4.9 ± 1.7 mm). However, the lateral component was significantly lower when an aiming device was used (2.3 ± 1.3-2.8 ± 1.6 mm with an aiming device vs 4.2 ± 2.0 mm without).

DISCUSSION

Using an aiming device may increase the lateral accuracy of navigated needle insertion.

Electromagnetic tracking navigation to guide radiofrequency ablation of a lung tumor

Radiofrequency ablation (RFA) may be an option for patients with lung tumors who have unresectable disease and are not suitable for available palliative modalities. RFA electrode positioning may take several attempts, necessitating multiple imaging acquisitions or continuous use of computed tomography. Electromagnetic tracking uses miniature sensors integrated with RFA equipment to guide tools in real time, while referencing to preprocedure imaging. This technology was demonstrated successfully during a lung tumor ablation, and this was more accurate at targeting the tumor compared with traditional freehand needle insertion. It is possible, although speculative and anecdotal, that more accuracy could prevent unnecessary repositioning punctures and decrease radiation exposure. Electromagnetic tracking has theoretical potential to benefit minimally invasive interventions.

Electromagnetic tracking in the clinical environment

When choosing an electromagnetic tracking system (EMTS) for image-guided procedures several factors must be taken into consideration. Among others these include the system's refresh rate, the number of sensors that need to be tracked, the size of the navigated region, the system interaction with the environment, whether the sensors can be embedded into the tools and provide the desired transformation data, and tracking accuracy and robustness. To date, the only factors that have been studied extensively are the accuracy and the susceptibility of EMTSs to distortions caused by ferromagnetic materials. In this paper the authors shift the focus from analysis of system accuracy and stability to the broader set of factors influencing the utility of EMTS in the clinical environment. The authors provide an analysis based on all of the factors specified above, as assessed in three clinical environments. They evaluate two commercial tracking systems, the Aurora system from Northern Digital Inc., and the 3D Guidance system with three different field generators from Ascension Technology Corp. The authors show that these systems are applicable to specific procedures and specific environments, but that currently, no single system configuration provides a comprehensive solution across procedures and environments.

Electromagnetic tracking for CT-guided spine interventions: phantom, ex-vivo and in-vivo results

An electromagnetic-based tracking and navigation system was evaluated for interventional radiology. The electromagnetic tracking system (CAPPA IRAD EMT, CASinnovations, Erlangen, Germany) was used for real-time monitoring of punctures of the lumbar facet joints and intervertebral disks in a spine phantom, three pig cadavers and three anaesthesized pigs. Therefore, pre-interventional computed tomography (CT) datasets were transferred to the navigation system and puncture trajectories were planned. A coaxial needle was advanced along the trajectories while the position of the needle tip was monitored in real time. After puncture tracts were marked with pieces of wire another CT examination was performed and distances between wires and anatomical targets were measured. Performing punctures of the facet joints mean needle positioning errors were 0.4 +/- 0.8 mm in the spine phantom, 2.8 +/- 2.1 mm ex vivo and 3.0 +/- 2.0 mm in vivo with mean length of the puncture tract of 54.0 +/- 10.4 mm (phantom), 51.6 +/- 12.6 mm (ex vivo) and 50.9 +/- 17.6 mm (in vivo). At first attempt, intervertebral discs were successfully punctured in 15/15 in the phantom study, in 12/15 in the ex-vivo study and 14/15 in the in-vivo study, respectively. Immobilization of the patient and optimal positioning of the field generator are essential to achieve a high accuracy of needle placement in a clinical CT setting.

Non-rigid registration of pre-procedural MR images with intra-procedural unenhanced CT images for improved targeting of tumors during liver radiofrequency ablations

In the United States, unenhanced CT is currently the most common imaging modality used to guide percutaneous biopsy and tumor ablation. The majority of liver tumors such as hepatocellular carcinomas are visible on contrast-enhanced CT or MRI obtained prior to the procedure. Yet, these tumors may not be visible or may have poor margin conspicuity on unenhanced CT images acquired during the procedure. Non-rigid registration has been used to align images accurately, even in the presence of organ motion. However, to date, it has not been used clinically for radiofrequency ablation (RFA), since it requires significant computational infrastructure and often these methods are not sufficient robust. We have already introduced a novel finite element based method (FEM) that is demonstrated to achieve good accuracy and robustness for the problem of brain shift in neurosurgery. In this current study, we adapt it to fuse pre-procedural MRI with intra-procedural CT of liver. We also compare its performance with conventional rigid registration and two non-rigid registration methods: b-spline and demons on 13 retrospective datasets from patients that underwent RFA at our institution. FEM non-rigid registration technique was significantly better than rigid (p < 10-5), non-rigid b-spline (p < 10-4) and demons (p < 10-4) registration techniques. The results of our study indicate that this novel technology may be used to optimize placement of RF applicator during CT-guided ablations.