Percutaneous punctures with MR imaging guidance: comparison between MR imaging-enhanced fluoroscopic guidance and real-time MR Imaging guidance

Fully Integrated Laser Guidance for CT-Based Punctures: A Study in Phantoms and Patients

PURPOSE

To test the hypothesis of equal or even superior applicability and accuracy of a fully integrated, laser-based computed tomography (CT) navigation system compared with conventional CT guidance for percutaneous interventions.

MATERIALS AND METHODS

CT-guided punctures were first performed in phantoms. Four radiologists with different experience levels (2 residents (L.B., C.D.) and 2 board-certified radiologists (B.M., K.R.) performed 48 punctures using both conventional image-guided and laser-guided approaches. Subsequently, 12 punctures were performed in patients during a clinical pilot trial. Phantom targets required an in-plane or a single-/double-angulated, out-of-plane approach. Planning and intervention time, control scan number, radiation exposure, and accuracy of needle placement (measured by deviation of the needle tip to the designated target) were assessed for each guidance technique and compared (Mann-Whitney U test and t test). Patient interventions were additionally analyzed for applicability in a clinical setting.

RESULTS

The application of laser guidance software in the phantom study and in 12 human patients in a clinical setting was both technically and clinically feasible in all cases. The mean planning time (P = .009), intervention time (P = .005), control scan number (P < .001), and radiation exposure (P = .013) significantly decreased for laser-navigated punctures compared with those for conventional CT guidance and especially in punctures with out-of-plane-trajectories. The accuracy significantly increased for laser-guided interventions compared with that for conventional CT (P < .001).

CONCLUSIONS

Interventional radiologists with differing levels of experience performed faster and more accurate punctures for out-of-plane trajectories in the phantom models, using a new, fully integrated, laser-guided CT software and demonstrated excellent clinical and technical success in initial clinical experiments.

Practical setting and potential applications of interventions guided by PET/MRI

Multimodality imaging has emerged from a vision thirty years ago to routine clinical use today. Positron emission tomography (PET)/magnetic resonance imaging (MRI) is still relatively new in this arena and particularly suitable for clinical research and technical development. PET/MRI-guidance for interventions opens up opportunities for novel treatments but at the same time demands certain technical and organizational requirements to be fulfilled. In this work, we aimed to demonstrate a practical setting and potential application of PET/MRI guidance of interventional procedures. The superior quantitative physiologic information of PET, the various unique imaging characteristics of MRI, and the reduced radiation exposure are the most relevant advantages of this technique. As a noninvasive interventional tool, focused ultrasound (FUS) ablation of tumor cells would benefit from PET/MRI for diagnostics, treatment planning and intervention. Yet, technical limitations might impeed preclinical research, given that PET/MRI sites are per se not designed as interventional suites. Nonetheless, several approaches have been offered in the past years to upgrade MRI suites for interventional purposes. Taking advantage of state of the art and easy-to-use technology it is possible to create a supporting infrastructure that is suitable for broad preclinical adaption. Several aspects are to be addressed, including remote control of the imaging system, display of the imaging results, communication technology, and implementation of additional devices such as a FUS platform and an MR-compatible robotic system for positioning of the FUS equipment. Feasibility could be demostrated with an examplary experimental setup for interventional PET/MRI. Most PET/MRI sites could allow for interventions with just a few add-ons and modifications, such as comunication, in room image display and sytems control. By unlocking this feature, and driving preclinical research in interventional PET/MRI, translation of the protocol and methodology into clinical settings seems feasible.

Percutaneous MR-guided interventions using an optical Moiré Phase tracking system: Initial results

The aim of this study was the development and evaluation of a real-time guidance support using optical Moiré Phase Tracking (MPT) for magnetic resonance (MR) guided percutaneous interventions. A gradient echo sequence, capable of real-time position updates by the MPT system, was modified to enable needle guidance based on four rigidly attached MPT markers at the back of a needle. Two perpendicular imaging planes were automatically aligned along the calibrated needle and centered at its tip. For user guidance, additional information about the needle trajectory and the tip to target distance were added as image overlay. Both, images and guiding information were displayed on the in-room monitor to facilitate MR guided interventions. The guidance support was evaluated by four experienced interventional radiologists and four novices targeting rubber O-rings embedded in a custom-made phantom on a 3T wide-bore MRI system (80 punctures). The skin to target time, user error, system error and total error were analyzed. The mean skin to target time was 146s±68s with no statistically significant difference between experts and novices. A low mean user error (0.91mm±0.43mm), system error (0.53mm±0.27mm) and total error (0.99mm±0.47mm) was reached in all directions. No statistically significant difference in user error, system error and total error could be found between experts and novices. The presented tracking and image guidance system combined with the user interface offers continuous and interactive control of the imaging plane while puncturing in the magnet enabling accurate real-time feedback for both, experienced and non-experienced users.

Concepts for augmented reality visualisation to support needle guidance inside the MRI

During MRI-guided interventions, navigation support is often separated from the operating field on displays, which impedes the interpretation of positions and orientations of instruments inside the patient's body as well as hand–eye coordination. To overcome these issues projector-based augmented reality can be used to support needle guidance inside the MRI bore directly in the operating field. The authors present two visualisation concepts for needle navigation aids which were compared in an accuracy and usability study with eight participants, four of whom were experienced radiologists. The results show that both concepts are equally accurate (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$2.0 \pm 0.6$\end{document}2.0±0.6 and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$1.7 \pm 0.5\, {\rm mm}$\end{document}1.7±0.5mm), useful and easy to use, with clear visual feedback about the state and success of the needle puncture. For easier clinical applicability, a dynamic projection on moving surfaces and organ movement tracking are needed. For now, tests with patients with respiratory arrest are feasible.

MR Coagulation: A Novel Minimally Invasive Approach to Aneurysm Repair

PURPOSE

To demonstrate a proof of concept of magnetic resonance (MR) coagulation, in which MR imaging scanner-induced radiofrequency (RF) heating at the end of an intracatheter long wire heats and coagulates a protein solution to effect a vascular repair by embolization.

MATERIALS AND METHODS

MR coagulation was simulated by finite-element modeling of electromagnetic fields and specific absorption rate (SAR) in a phantom. A glass phantom consisting of a spherical cavity joined to the side of a tube was incorporated into a flow system to simulate an aneurysm and flowing blood with velocities of 0-1.7 mL/s. A double-lumen catheter containing the wire and fiberoptic temperature sensor in 1 lumen was passed through the flow system into the aneurysm, and 9 cm³ of protein solution was injected into the aneurysm through the second lumen. The distal end of the wire was laid on the patient table as an antenna to couple RF from the body coil or was connected to a separate tuned RF pickup coil. A high RF duty-cycle turbo spin-echo pulse sequence excited the wire such that RF energy deposited at the tip of the wire coagulated the protein solution, embolizing the aneurysm.

RESULTS

The protein coagulation temperature of 60°C was reached in the aneurysm in ∼12 seconds, yielding a coagulated mass that largely filled the aneurysm. The heating rate was controlled by adjusting pulse-sequence parameters.

CONCLUSIONS

MR coagulation has the potential to embolize vascular defects by coagulating a protein solution delivered by catheter using MR imaging scanner-induced RF heating of an intracatheter wire.

Feasibility and efficacy of primary tractography during percutaneous catheter drainage

BACKGROUND

The indication of percutaneous catheter drainage (PCD) has expanded with the development of guiding modalities. Since serious complications still occur, efforts and new techniques have been continuously searched for safer PCD.

PURPOSE

To evaluate the feasibility and efficacy of primary tractography for establishing a safe needle pathway during PCD.

MATERIAL AND METHODS

A total of 42 patients (20 men, 22 women; mean age, 50.7 years) who underwent primary tractography during PCD were prospectively enrolled between April 2009 and August 2013. The locations of fluid collection included sub-phrenic (n = 8), between bowel loops (n = 21), pelvic cavity (n = 8), within solid organ (n = 2), and others (n = 3). The interposed anatomic structures were analyzed on the basis of primary tractography findings. Complications related to PCD or primary tractography were evaluated.

RESULTS

Interposition of any significant anatomic structure was confirmed in 10 of 42 patients (23.8%). The entrapped anatomic structures were the omental vessel (n = 4), bowel (n = 2), pleura (n = 2), bile duct (n = 2), and a branch of the left inferior epigastric artery (n = 1). In one patient, both the pleura and bile duct were interposed simultaneously. The technical and clinical success rates of PCD were 97.6% and 97.6%, respectively. No complications related to PCD or primary tractography occurred during the follow-up period.

CONCLUSION

Primary tractography is a simple and feasible method to evaluate the entrapment of normal anatomic structure during PCD. This method may aid in preventing possible serious PCD-related complications, such as bleeding and fistula.

Targeting Accuracy, Procedure Times and User Experience of 240 Experimental MRI Biopsies Guided by a Clinical Add-On Navigation System

OBJECTIVES

MRI is of great clinical utility for the guidance of special diagnostic and therapeutic interventions. The majority of such procedures are performed iteratively ("in-and-out") in standard, closed-bore MRI systems with control imaging inside the bore and needle adjustments outside the bore. The fundamental limitations of such an approach have led to the development of various assistance techniques, from simple guidance tools to advanced navigation systems. The purpose of this work was to thoroughly assess the targeting accuracy, workflow and usability of a clinical add-on navigation solution on 240 simulated biopsies by different medical operators.

METHODS

Navigation relied on a virtual 3D MRI scene with real-time overlay of the optically tracked biopsy needle. Smart reference markers on a freely adjustable arm ensured proper registration. Twenty-four operators - attending (AR) and resident radiologists (RR) as well as medical students (MS) - performed well-controlled biopsies of 10 embedded model targets (mean diameter: 8.5 mm, insertion depths: 17-76 mm). Targeting accuracy, procedure times and 13 Likert scores on system performance were determined (strong agreement: 5.0).

RESULTS

Differences in diagnostic success rates (AR: 93%, RR: 88%, MS: 81%) were not significant. In contrast, between-group differences in biopsy times (AR: 4:15, RR: 4:40, MS: 5:06 min:sec) differed significantly (p<0.01). Mean overall rating was 4.2. The average operator would use the system again (4.8) and stated that the outcome justifies the extra effort (4.4). Lowest agreement was reported for the robustness against external perturbations (2.8).

CONCLUSIONS

The described combination of optical tracking technology with an automatic MRI registration appears to be sufficiently accurate for instrument guidance in a standard (closed-bore) MRI environment. High targeting accuracy and usability was demonstrated on a relatively large number of procedures and operators. Between groups with different expertise there were significant differences in experimental procedure times but not in the number of successful biopsies.

In vitro evaluation of a novel fiducial marker for computed tomography and magnetic resonance imaging of soft tissues in small animals

OBJECTIVE

To construct and optimize a fiducial marker suitable for both CT and MRI.

SAMPLE

Fiducial markers containing serial dilutions of iopamidol mixed with water.

PROCEDURES

IV tubing sets were infused with serial dilutions (0% to 100%; increments of 10%) of iopamidol. Tubing ends were sealed; additional seals were added to create an equilateral triangle. A reference point was created by placing a crimp in 1 side. Markers were fixed to a gelatin soft tissue-attenuating phantom and evaluated by use of CT and MRI. For CT, simple linear regression analysis was used to assess the relationship between the percentage of marker contrast medium and quantitative variables, including marker attenuation, attenuation changes in the phantom, and beam-hardening artifact length. A subjective grading scheme for artifact creation on CT images and marker visibility on MRI images was used. Measurements were obtained by investigators who were unaware of the contents of each marker.

RESULTS

Percentage of contrast medium in each marker was strongly correlated with marker attenuation (r(2) = 0.96), artifact length (r(2) = 0.765), and mean attenuation changes within the phantom (r(2) = 0.826) for CT. Subjective CT scores indicated that concentrations of contrast medium > 50% resulted in excessive artifacts. Markers with concentrations of iopamidol > 50% had poor subjective MRI visibility scores. No artifacts were seen on MRI.

CONCLUSIONS AND CLINICAL RELEVANCE

A marker containing a 10% solution of iodinated contrast medium mixed with water provided ideal contrast for both CT and MRI.

Radiation exposure of abdominal cone beam computed tomography

PURPOSE

To evaluate patients radiation exposure of abdominal C-arm cone beam computed tomography (CBCT).

METHODS

This prospective study was approved by the institutional review board; written, informed consent was waived. Radiation exposure of abdominal CBCT was evaluated in 40 patients who underwent CBCT during endovascular interventions. Dose area product (DAP) of CBCT was documented and effective dose (ED) was estimated based on organ doses using dedicated Monte Carlo simulation software with consideration of X-ray field location and patients' individual body weight and height. Weight-dependent ED per DAP conversion factors were calculated. CBCT radiation dose was compared to radiation dose of procedural fluoroscopy. CBCT dose-related risk for cancer was assessed.

RESULTS

Mean ED of abdominal CBCT was 4.3 mSv (95 % confidence interval [CI] 3.9; 4.8 mSv, range 1.1-7.4 mSv). ED was significantly higher in the upper than in the lower abdomen (p = 0.003) and increased with patients' weight (r = 0.55, slope = 0.045 mSv/kg, p < 0.001). Radiation exposure of CBCT corresponded to the radiation exposure of on average 7.2 fluoroscopy minutes (95 % CI 5.5; 8.8 min) in the same region of interest. Lifetime risk of exposure related cancer death was 0.033 % or less depending on age and weight.

CONCLUSIONS

Mean ED of abdominal CBCT was 4.3 mSv depending on X-ray field location and body weight.

Using C-arm x-ray imaging to guide local reporter probe delivery for tracking stem cell engraftment

Poor cell survival and difficulties with visualization of cell delivery are major problems with current cell transplantation methods. To protect cells from early destruction, microencapsulation methods have been developed. The addition of a contrast agent to the microcapsule also could enable tracking by MR, ultrasound, and X-ray imaging. However, determining the cell viability within the microcapsule still remains an issue. Reporter gene imaging provides a way to determine cell viability, but delivery of the reporter probe by systemic injection may be hindered in ischemic diseases. In the present study, mesenchymal stem cells (MSCs) were transfected with triple fusion reporter gene containing red fluorescent protein, truncated thymidine kinase (SPECT/PET reporter) and firefly luciferase (bioluminescence reporter). Transfected cells were microencapsulated in either unlabeled or perfluorooctylbromide (PFOB) impregnated alginate. The addition of PFOB provided radiopacity to enable visualization of the microcapsules by X-ray imaging. Before intramuscular transplantation in rabbit thigh muscle, the microcapsules were incubated with D-luciferin, and bioluminescence imaging (BLI) was performed immediately. Twenty-four and forty-eight hours post transplantation, c-arm CT was used to target the luciferin to the X-ray-visible microcapsules for BLI cell viability assessment, rather than systemic reporter probe injections. Not only was the bioluminescent signal emission from the PFOB-encapsulated MSCs confirmed as compared to non-encapsulated, naked MSCs, but over 90% of injection sites of PFOB-encapsulated MSCs were visible on c-arm CT. The latter aided in successful targeting of the reporter probe to injection sites using conventional X-ray imaging to determine cell viability at 1-2 days post transplantation. Blind luciferin injections to the approximate location of unlabeled microcapsules resulted in successful BLI signal detection in only 18% of injections. In conclusion, reporter gene probes can be more precisely targeted using c-arm CT for in vivo transplant viability assessment, thereby avoiding large and costly systemic injections of a reporter probe.