MR-Guided Freehand Biopsy of Liver Lesions With Fast Continuous Imaging Using a 1.0-T Open MRI Scanner: Experience in 50 Patients

Magnetic Resonance Imaging Guidance for Percutaneous Needle Intervention

Magnetic resonance imaging (MRI) is one of the guiding modalities used for percutaneous needle insertion during interventional procedures. MRI guidance has several advantages, including multiplanar imaging capability, superior soft tissue contrast resolution, and the absence of ionizing radiation. When performing MRI-guided procedures, it is important to understand the suitable MRI systems, instruments, and imaging sequences for intervention. Furthermore, needle artifact characteristics must be fully understood to ensure safe and accurate needle insertion. In this article, we present the fundamental knowledge as regards the use of MRI guidance for percutaneous needle insertion and review its usefulness in representative interventional procedures, such as biopsy and tumor ablation.

Clinical benefits of MRI-guided freehand biopsy of small focal liver lesions in comparison to CT guidance

OBJECTIVES

To compare clinical success, procedure time, and complication rates between MRI-guided and CT-guided real-time biopsies of small focal liver lesions (FLL) < 20 mm.

METHODS

A comparison of a prospectively collected MRI-guided cohort (n = 30) to a retrospectively collected CT-guided cohort (n = 147) was performed, in which patients underwent real-time biopsies of small FLL < 20 mm in a freehand technique. In both groups, clinical and periprocedural data, including clinical success, procedure time, and complication rates (classified according to CIRSE guidelines), were analyzed. Wilcoxon rank sum test, Pearson's chi-squared test, and Fisher's exact test were used for statistical analysis. Additionally, propensity score matching (PSM) was performed using the following criteria for direct matching: age, gender, presence of liver cirrhosis, liver lobe, lesion diameter, and skin-to-target distance.

RESULTS

The median FLL diameter in the MRI-guided cohort was significantly smaller compared to CT guidance (p < 0.001; 11.0 mm vs. 16.3 mm), while the skin-to-target distance was significantly longer (p < 0.001; 90.0 mm vs. 74.0 mm). MRI-guided procedures revealed significantly higher clinical success compared to CT guidance (p = 0.021; 97% vs. 79%) as well as lower complication rates (p = 0.047; 0% vs. 13%). Total procedure time was significantly longer in the MRI-guided cohort (p < 0.001; 38 min vs. 28 min). After PSM (n = 24/n = 38), MRI-guided procedures still revealed significantly higher clinical success compared to CT guidance (p = 0.039; 96% vs. 74%).

CONCLUSION

Despite the longer procedure time, freehand biopsy of small FLL < 20 mm under MR guidance can be considered superior to CT guidance because of its high clinical success and low complication rates.

CLINICAL RELEVANCE STATEMENT

Biopsy of small liver lesions is challenging due to the size and conspicuity of the lesions on native images. MRI offers higher soft tissue contrast, which translates into a higher success of obtaining enough tissue material with MRI compared to CT-guided biopsies.

KEY POINTS

• Image-guided biopsy of small focal liver lesions (FLL) is challenging due to inadequate visualization, leading to sampling errors and false-negative biopsies. • MRI-guided real-time biopsy of FLL < 20 mm revealed significantly higher clinical success (p = 0.021; 97% vs. 79%) and lower complication rates (p = 0.047; 0% vs. 13%) compared to CT guidance. • Although the procedure time is longer, MRI-guided biopsy can be considered superior for small FLL < 20 mm.

Artifact reduction of coaxial needles in magnetic resonance imaging-guided abdominal interventions at 1.5 T: a phantom study

Needle artifacts pose a major limitation for MRI-guided interventions, as they impact the visually perceived needle size and needle-to-target-distance. The objective of this agar liver phantom study was to establish an experimental basis to understand and reduce needle artifact formation during MRI-guided abdominal interventions. Using a vendor-specific prototype fluoroscopic T1-weighted gradient echo sequence with real-time multiplanar acquisition at 1.5 T, the influence of 6 parameters (flip angle, bandwidth, matrix, slice thickness, read-out direction, intervention angle relative to B₀) on artifact formation of 4 different coaxial MR-compatible coaxial needles (Nitinol, 16G–22G) was investigated. As one parameter was modified, the others remained constant. For each individual parameter variation, 2 independent and blinded readers rated artifact diameters at 2 predefined positions (15 mm distance from the perceived needle tip and at 50% of the needle length). Differences between the experimental subgroups were assessed by Bonferroni-corrected non-parametric tests. Correlations between continuous variables were expressed by the Bravais–Pearson coefficient and interrater reliability was quantified using the intraclass classification coefficient. Needle artifact size increased gradually with increasing flip angles (p = 0.002) as well as increasing intervention angles (p < 0.001). Artifact diameters differed significantly between the chosen matrix sizes (p = 0.002) while modifying bandwidth, readout direction, and slice thickness showed no significant differences. Interrater reliability was high (intraclass correlation coefficient 0.776–0.910). To minimize needle artifacts in MRI-guided abdominal interventions while maintaining optimal visibility of the coaxial needle, we suggest medium-range flip angles and low intervention angles relative to B₀.

Percutaneous needle biopsy under 1.2 Tesla open MRI guidance

PURPOSE

To evaluate the feasibility of percutaneous needle biopsy using a 1.2 Tesla open magnetic resonance imaging (MRI) system, which has the highest field strength among the currently available open MRI systems.

MATERIALS AND METHODS

This single-center prospective study included 10 patients. The primary endpoint was the feasibility of biopsy needle insertion into a target lesion under 1.2 Tesla open MRI guidance. The secondary endpoints included adverse events, device failures, and success of tissue specimen acquisition. Biopsy was performed for targets in various organs using an MRI-compatible coaxial needle system consisting of a 16G introducer needle and 18G semi-automatic biopsy needle. A newly developed body coil with a suitable design for intervention was used for intraprocedural imaging.

RESULTS

Biopsy procedures were performed for six musculoskeletal masses, two retroperitoneal masses, one renal mass, and one liver mass. The median diameter of the targets was 4.9 cm (range 2.1-22.8 cm). MRI-guided biopsy needle insertion was feasible in all 10 patients. In total, four grade 1 adverse events (as per Common Terminology Criteria for Adverse Events version 4.0) occurred in three patients. Adequate biopsy specimens for pathological diagnosis were successfully obtained from all 10 patients.

CONCLUSION

Percutaneous needle biopsy using a 1.2 Tesla open MRI system was feasible for relatively large targets, especially in the musculoskeletal region.

MRI-based fat quantification of the liver: Is it time for commercially available products?

PURPOSE

(1) To assess the clinical applicability of commercially available solutions for MR-based quantification of the hepatic fat fraction (HFF) and (2) to compare their results with clinically established in-phase/oppose-phase (IP/OP) imaging as proposed by Dixon.

METHODS

Twenty-eight patients underwent MRI examinations using multigradient-echo sequences including multi-peak modeling and T₂^∗ correction, IP/OP imaging and multi-echo spectroscopy with successive HFF evaluation. Histopathological examination yielded the fraction of adipose hepatocytes (fAH) and the presence of increased liver iron concentration (LIC). We correlated HFF with fAH, and assessed concordance correlations among the MR-based methods with the presence of increased LIC as a control parameter. We investigated the liver segmentation quality and overall workflow of the postprocessing solutions (Philips LiverHealth and Siemens LiverLab).

RESULTS

IP/OP imaging yielded a very strong correlation (r=0.88) with fAH when excluding three cases with increased LIC. Multigradient echo imaging and multiecho spectroscopy quantifications yielded similar correlations (r=0.87…0.93) as IP/OP imaging but were insensitive to increased LIC. Visceral fat, kidney tissue and major vessels were included regularly in the segmentation. Spectroscopic fat quantification was sensitive to the inclusion of visceral fat.

CONCLUSIONS

IP/OP imaging allows HFF quantification when ruling out hepatic siderosis, whereas dedicated multi-echo imaging sequences and spectroscopy show no bias for increased iron concentration. The segmentation quality and workflow of both postprocessing solutions need to be improved. Nevertheless, all solutions are able to bring MRI-based hepatic fat quantification into the clinical application. We therefore recommend commercial hepatic fat quantification tools for institutions specialised to abdominal imaging.

MRI-guided percutaneous needle biopsy with 1.2T open MRI: study protocol for a prospective feasibility study (SCIRO-1701)

There has been growing interest in magnetic resonance imaging (MRI)-guided interventional procedures such as percutaneous needle biopsy. Although open MRI is preferable for MRI-guided procedures in terms of patient accessibility, its inferior imaging capability due to lower field strength is a substantial limitation. In this situation, the high-field (1.2T) open MRI has recently become available. This novel MRI system is expected to provide excellent image quality as well as good patient accessibility, potentially contributing to safe and accurate device manipulation. This trial is designed to investigate the feasibility of MRI-guided percutaneous needle biopsy with this system. Patients with lesions needing percutaneous needle biopsy for pathological diagnosis are included. The enrollment of ten patients is intended. The primary endpoint of this study is the feasibility of biopsy needle insertion under real-time MR-fluoroscopy guidance based on the presence of the notch of the biopsy needle within the target lesion. The secondary endpoints are adverse events, device failures, and success of specimen acquisition. Once the feasibility of MRI-guided biopsy with 1.2T open MRI is validated by this study, it may potentially encourage widespread use of MRI-guidance for biopsy procedures. Furthermore, it may lead to development of the other MRI-guided interventional procedures using this MRI system.

Touchless scanner control to support MRI-guided interventions

PURPOSE

MRI-guided interventions allow minimally invasive, radiation-free treatment but rely on real-time image data and free slice positioning. Interventional interaction with the data and the MRI scanner is cumbersome due to the diagnostic focus of current systems, confined space and sterile conditions.

METHODS

We present a touchless, hand-gesture-based interaction concept to control functions of the MRI scanner typically used during MRI-guided interventions. The system consists of a hand gesture sensor customised for MRI compatibility and a specialised UI that was developed based on clinical needs. A user study with 10 radiologists was performed to compare the gesture interaction concept and its components to task delegation-the prevalent method in clinical practice.

RESULTS

Both methods performed comparably in terms of task duration and subjective workload. Subjective performance with gesture input was perceived as worse compared to task delegation, but was rated acceptable in terms of usability while task delegation was not.

CONCLUSION

This work contributes by (1) providing access to relevant functions on an MRI scanner during percutaneous interventions in a (2) suitable way for sterile human-computer interaction. The introduced concept removes indirect interaction with the scanner via an assistant, which leads to comparable subjective workload and task completion times while showing higher perceived usability.

MRI-Guided Cryoablation of Hepatic Dome Hepatocellular Carcinomas Using 1-T Open High-Field-Strength Scanner

OBJECTIVE. The objective of our study was to prospectively evaluate the feasibility, safety, and effectiveness of 1-T open MRI-guided percutaneous cryoablation of hepatic dome hepatocellular carcinomas (HCCs). SUBJECTS AND METHODS. Thirty-seven patients with 37 hepatic dome HCCs underwent MRI-guided percutaneous cryoablations. MR fluoroscopy with a freehand technique was applied in the procedure. All lesions ranged in size from 8 to 38 mm. Patients were followed for at least 12 months after cryoablation or until death. Survival period, local tumor control, and complications were recorded. RESULTS. MRI-guided percutaneous cryoablation procedures were successfully performed on all 37 lesions. The technical success rate was 100%. The median follow-up time was 21.0 months (range, 10-26 months). Two patients with local tumor progression at the 4th and 11th month after the procedure were treated with a supplementary cryoablation. One patient died of upper gastrointestinal hemorrhage at the 10th month after cryoablation. Local tumor progression and overall survival rates were 2.7% (1/37) and 100% (37/37) at 6 months and 5.4% (2/37) and 97.3% (36/37) at 1 year, respectively. Postoperative hydrothorax that required chest tube drainage occurred in two patients; no other severe complications occurred. CONCLUSION. Cryoablation of hepatic dome HCCs with 1-T open MRI guidance is a feasible, safe, and effective therapy method.

Comparison of Projective Augmented Reality Concepts to Support Medical Needle Insertion

Augmented reality (AR) is a promising tool to improve instrument navigation in needle-based interventions. Limited research has been conducted regarding suitable navigation visualizations. In this work, three navigation concepts based on existing approaches were compared in a user study using a projective AR setup. Each concept was implemented with three different scales for accuracy-to-color mapping and two methods of navigation indicator scaling. Participants were asked to perform simulated needle insertion tasks with each of the resulting 18 prototypes. Insertion angle and insertion depth accuracies were measured and analyzed, as well as task completion time and participants' subjectively perceived task difficulty. Results show a clear ranking of visualization concepts across variables. Less consistent results were obtained for the color and indicator scaling factors. Results suggest that logarithmic indicator scaling achieved better accuracy, but participants perceived it to be more difficult than linear scaling. With specific results for angle and depth accuracy, our study contributes to the future composition of improved navigation support and systems for precise needle insertion or similar applications.

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.

Feasibility, efficacy, and safety of percutaneous MR-guided ablation of small (≤12 mm) hepatic malignancies

BACKGROUND

Percutaneous tumor ablation is commonly performed using computed tomography (CT) or ultrasound (US) guidance, although reliable visualization of the target tumor may be challenging. MRI guidance provides more reliable visualization of target tumors and allows for real-time imaging and multiplanar capabilities, making it the modality of choice, in particular if lesions are small.

PURPOSE

To investigate the feasibility, technical success, and safety of percutaneous MR-guided ablation (RFA n = 27 / MWA n = 16) of small (≤12 mm) hepatic malignancies.

STUDY TYPE

Retrospective case study.

POPULATION

In all, 45 patients (age: 61.1 ± 11.8) with hepatic malignancies and a lesion diameter of ≤12 mm scheduled for percutaneous MR-guided tumor ablation based on a tumor board decision were included.

FIELD STRENGTH

A 1.5T MR system was used for planning, targeting, and monitoring.

ASSESSMENT

Feasibility assessment included the detection of the target tumor, tumor delineation during MR-fluoroscopy guided targeting, and the number of attempts needed for precise applicator placement. Technical success was defined as successful performance of the procedure including a safety margin of 5 mm. Safety evaluation was based on procedure-related complications.

STATISTICAL TEST

Frequency.

RESULTS

Tumor ablation (mean diameter 9.0 ± 2.1 mm) was successfully completed in 43/45 patients. Planning imaging was conducted without a contrast agent in 79% (n = 37). In 64% (n = 30), the target tumors were visible with MR-fluoroscopy. In six patients (13%), planning imaging revealed new, unexpected small lesions, which were either treated in the same session (n = 4) or changed therapy management (n = 2) due to diffuse tumor progress. Postprocedural imaging revealed a technical success of 100% (43/43), with no major complications. During follow-up, no local tumor progression was observed (mean follow-up 24.7 ± 14.0 months) although 28% (12) patients developed new hepatic lesions distant to the ablation zone. No major complications were observed.

DATA CONCLUSION

MR-guided ablation is a feasible approach for an effective and safe treatment of small hepatic malignancies.

LEVEL OF EVIDENCE

4 Technical Efficacy: Stage 4 J. Magn. Reson. Imaging 2019;49:374-381.

Real-time MR-guided brain biopsy using 1.0-T open MRI scanner

OBJECTIVES

To evaluate the safety, feasibility and diagnostic performance of real-time MR-guided brain biopsy using a 1.0-T open MRI scanner.

METHODS

Medical records of 86 consecutive participants who underwent brain biopsy under the guidance of a 1.0-T open MRI scanner with real-time and MR fluoroscopy techniques were evaluated retrospectively. All procedures were performed under local anaesthesia and intravenous conscious sedation. Diagnostic yield, diagnostic accuracy, complication rate and procedure duration were assessed. The lesions were divided into two groups according to maximum diameters: ≤ 1.5 cm (n = 16) and > 1.5 cm (n = 70). The two groups were compared using Fisher's exact test.

RESULTS

Diagnostic yield and diagnostic accuracy were 95.3% and 94.2%, respectively. The diagnostic yield of lesions ≤ 1.5 cm and > 1.5 cm were 93.8% and 95.7%, respectively. There was no significant difference in diagnostic yield between the two groups (p > 0.05). Mean procedure duration was 41 ± 5 min (range 33-49 min). All biopsy needles were placed with one pass. Complication rate was 3.5% (3/86). Minor complications included three cases of a small amount of haemorrhage. No serious complications were observed.

CONCLUSIONS

Real-time MR-guided brain biopsy using a 1.0-T open MRI scanner is a safe, feasible and accurate diagnostic technique for pathological diagnosis of brain lesions. The procedure duration is shortened and biopsy work flow is simplified. It could be considered as an alternative for brain biopsy.

KEY POINTS

• Real-time MRI-guided brain biopsy using a 1.0-T open MRI scanner is safe, feasible and accurate. • No serious complications occurred in real-time MRI-guided brain biopsy. • Procedure duration is shortened and biopsy work flow is simplified.

Techniques for Interventional MRI Guidance in Closed-Bore Systems

Efficient image guidance is the basis for minimally invasive interventions. In comparison with X-ray, computed tomography (CT), or ultrasound imaging, magnetic resonance imaging (MRI) provides the best soft tissue contrast without ionizing radiation and is therefore predestined for procedural control. But MRI is also characterized by spatial constraints, electromagnetic interactions, long imaging times, and resulting workflow issues. Although many technical requirements have been met over the years-most notably magnetic resonance (MR) compatibility of tools, interventional pulse sequences, and powerful processing hardware and software-there is still a large variety of stand-alone devices and systems for specific procedures only.Stereotactic guidance with the table outside the magnet is common and relies on proper registration of the guiding grids or manipulators to the MR images. Instrument tracking, often by optical sensing, can be added to provide the physicians with proper eye-hand coordination during their navigated approach. Only in very short wide-bore systems, needles can be advanced at the extended arm under near real-time imaging. In standard magnets, control and workflow may be improved by remote operation using robotic or manual driving elements.This work highlights a number of devices and techniques for different interventional settings with a focus on percutaneous, interstitial procedures in different organ regions. The goal is to identify technical and procedural elements that might be relevant for interventional guidance in a broader context, independent of the clinical application given here. Key challenges remain the seamless integration into the interventional workflow, safe clinical translation, and proper cost effectiveness.

In vitro artifact assessment of an MR-compatible, microwave antenna device for percutaneous tumor ablation with fluoroscopic MRI-sequences

OBJECTIVE

To evaluate artifact configuration and diameters of a magnetic resonance (MR) compatible microwave (MW) applicator using near-realtime MR-fluoroscopic sequences for percutaneous tumor ablation procedures.

MATERIAL AND METHODS

Two MW applicators (14 G and 16 G) were tested in an ex-vivo phantom at 1.5 T with two 3 D fluoroscopic sequences: T1-weighted spoiled Gradient Echo (GRE) and T1/T2-weighted Steady State Free Precession (SSFP) sequence. Applicator orientation to main magnetic field (B₀), slice orientation and phase encoding direction (PED) were systematically varied. The influence of these variables was assessed with ANOVA and post-hoc testing.

RESULTS

The artifact was homogenous along the whole length of both antennas with all tested parameters. The tip artifact diameter of the 16 G antenna measured 6.9 ± 1.0 mm, the shaft artifact diameter 8.6 ± 1.2 mm and the Tip Location Error (TLE) was 1.5 ± 1.2 mm.The tip artifact diameter of the 14 G antenna measured 7.7 ± 1.2 mm, the shaft artifact diameter 9.6 ± 1.5 mm and TLE was 1.6 ± 1.2 mm. Orientation to B₀ had no statistically significant influence on tip artifact diameters (16 G: p = .55; 14 G: p = .07) or TLE (16 G: p = .93; 14 G: p = .26). GRE sequences slightly overestimated the antenna length with TLE(16 G) = 2.6 ± 0.5 mm and TLE(14 G) = 2.7 ± 0.7 mm.

CONCLUSIONS

The MR-compatible MW applicator's artifact seems adequate with an acceptable TLE for safe applicator positioning during near-realtime fluoroscopic MR-guidance.

Tailored interactive sequences for continuous MR-image-guided freehand biopsies of different organs in an open system at 1.0 tesla (T) - Initial experience

OBJECTIVES

To assess the feasibility, image quality, and accuracy of freehand biopsies of liver, bone, muscle, vertebral disc, soft tissue, and other lesions using balanced steady-state free precession (SSFP, balanced fast field echo: bFFE), spoiled and nonspoiled gradient echo (FFE), and turbo spin echo (TSE) sequences for interactive continuous navigation in an open magnetic resonance imaging (MRI) system at 1.0 tesla (T).

METHODS

Twenty-six MR-guided biopsies (five liver, five bone, four muscle, four vertebral disc, one lung, one kidney, one suprarenal gland, and five soft or other tissue) were performed in 23 patients in a 1.0-T open magnetic resonance (MR) scanner (Panorama HFO, Philips Healthcare, Best, the Netherlands). A total of 42 samples were obtained. Depending on lesion size and location, 14-18-gauge MR-compatible biopsy sets with a length of 100 or 200 mm (Somatex Medical, Teltow, Germany), 14-18-gauge MR-compatible semiautomatic biopsy guns with a length of 100 or 150 mm (Invivo, Schwerin, Germany), or 11-gauge MR-compatible bone marrow biopsy needles with a length of 100 mm (Somatex Medical, Teltow, Germany) were employed.

RESULTS

All lesions were visible with continuous interactive imaging. Our initial results indicate that bFFE is particularly suitable for fast-moving organs (pulmonary, paracardial); moving organs are targeted better with T1-weighted (T1W) TSE, T1W FFE (liver) or T2-weighted (T2W) TSE (complicated cysts, adrenal glands), and static organs are successfully approached with proton density (PD) (spine) or T1W TSE (peripheral bones, musculoskeletal system). No adverse events related to the use of MRI were obtained. No complications occurred according to the Society of Interventional Radiology (SIR) clinical practice guidelines.

CONCLUSION

Applying tailored interactive dynamic imaging sequences for continuous navigation to liver, bone, muscle, vertebral disc, soft tissue, and other lesions can improve the feasibility, image quality, and interventional accuracy of freehand MR-guided biopsies and may hence reduce the risk of complications.

Auditory feedback to support image-guided medical needle placement

PURPOSE

During medical needle placement using image-guided navigation systems, the clinician must concentrate on a screen. To reduce the clinician's visual reliance on the screen, this work proposes an auditory feedback method as a stand-alone method or to support visual feedback for placing the navigated medical instrument, in this case a needle.

METHODS

An auditory synthesis model using pitch comparison and stereo panning parameter mapping was developed to augment or replace visual feedback for navigated needle placement. In contrast to existing approaches which augment but still require a visual display, this method allows view-free needle placement. An evaluation with 12 novice participants compared both auditory and combined audiovisual feedback against existing visual methods.

RESULTS

Using combined audiovisual display, participants show similar task completion times and report similar subjective workload and accuracy while viewing the screen less compared to using the conventional visual method. The auditory feedback leads to higher task completion times and subjective workload compared to both combined and visual feedback.

CONCLUSION

Audiovisual feedback shows promising results and establishes a basis for applying auditory feedback as a supplement to visual information to other navigated interventions, especially those for which viewing a patient is beneficial or necessary.

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.

MR-guided percutaneous biopsy of solitary pulmonary lesions using a 1.0-T open high-field MRI scanner with respiratory gating

OBJECTIVES

To prospectively evaluate the feasibility, safety and accuracy of MR-guided percutaneous biopsy of solitary pulmonary lesions using a 1.0-T open MR scanner with respiratory gating.

METHODS

Sixty-five patients with 65 solitary pulmonary lesions underwent MR-guided percutaneous coaxial cutting needle biopsy using a 1.0-T open MR scanner with respiratory gating. Lesions were divided into two groups according to maximum lesion diameters: ≤2.0 cm (n = 31) and >2.0 cm (n = 34). The final diagnosis was established in surgery and subsequent histology. Diagnostic accuracy, sensitivity and specificity were compared between the groups using Fisher's exact test.

RESULTS

Accuracy, sensitivity and specificity of MRI-guided percutaneous pulmonary biopsy in diagnosing malignancy were 96.9 %, 96.4 % and 100 %, respectively. Accuracy, sensitivity and specificity were 96.8 %, 96.3 % and 100 % for lesions 2.0 cm or smaller and 97.1 %, 96.4 % and 100 %, respectively, for lesions larger than 2.0 cm. There was no significant difference between the two groups (P > 0.05). Biopsy-induced complications encountered were pneumothorax in 12.3 % (8/65) and haemoptysis in 4.6 % (3/65). There were no serious complications.

CONCLUSIONS

MRI-guided percutaneous biopsy using a 1.0-T open MR scanner with respiratory gating is an accurate and safe diagnostic technique in evaluation of pulmonary lesions.

KEY POINTS

• MRI-guided percutaneous lung biopsy using a 1.0-T open MR scanner is feasibility. • 96.9 % differentiation accuracy of malignant and benign lung lesions is possible. • No serious complications occurred in MRI-guided lung biopsy.

Navigated MRI-guided liver biopsies in a closed-bore scanner: experience in 52 patients

OBJECTIVES

To evaluate clinical effectiveness and diagnostic efficiency of a navigation device for MR-guided biopsies of focal liver lesions in a closed-bore scanner.

METHODS

In 52 patients, 55 biopsies were performed. An add-on MR navigation system with optical instrument tracking was used for image guidance and biopsy device insertion outside the bore. Fast control imaging allowed visualization of the true needle position at any time. The biopsy workflow and procedure duration were recorded. Histological analysis and clinical course/outcome were used to calculate sensitivity, specificity and diagnostic accuracy.

RESULTS

Fifty-four of 55 liver biopsies were performed successfully with the system. No major and four minor complications occurred. Mean tumour size was 23 ± 14 mm and the skin-to-target length ranged from 22 to 177 mm. In 39 cases, access path was double oblique. Sensitivity, specificity and diagnostic accuracy were 88 %, 100 % and 92 %, respectively. The mean procedure time was 51 ± 12 min, whereas the puncture itself lasted 16 ± 6 min. On average, four control scans were taken.

CONCLUSIONS

Using this navigation device, biopsies of poorly visible and difficult accessible liver lesions could be performed safely and reliably in a closed-bore MRI scanner. The system can be easily implemented in clinical routine workflow.

KEY POINTS

• Targeted liver biopsies could be reliably performed in a closed-bore MRI. • The navigation system allows for image guidance outside of the scanner bore. • Assisted MRI-guided biopsies are helpful for focal lesions with a difficult access. • Successful integration of the method in clinical workflow was shown. • Subsequent system installation in an existing MRI environment is feasible.

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.

Wireless mobile technology to improve workflow and feasibility of MR-guided percutaneous interventions

PURPOSE

A wireless interactive display and control device combined with a platform-independent web-based user interface (UI) was developed to improve the workflow for interventional magnetic resonance imaging (iMRI).

METHODS

The iMRI-UI enables image acquisition of up to three independent slices using various pulse sequences with different contrast weighting. Pulse sequence, scan geometry and related parameters can be changed on the fly via the iMRI-UI using a tablet computer for improved lesion detection and interventional device targeting. The iMRI-UI was validated for core biopsies with a liver phantom ([Formula: see text] [Formula: see text] 40) and Thiel soft-embalmed human cadavers ([Formula: see text] [Formula: see text] 24) in a clinical 1.5T MRI scanner.

RESULTS

The iMRI-UI components and setup were tested and found conditionally MRI-safe to use according to current ASTM standards. Despite minor temporary touch screen interference at a close distance to the bore ([Formula: see text]20 cm), no other issues regarding quality or imaging artefacts were observed. The 3D root-mean-square distance error was [Formula: see text] (phantom)/[Formula: see text] mm (cadaver), and overall procedure times ranged between 12 and 22 (phantom)/20 and 55 min (cadaver).

CONCLUSION

The wireless iMRI-UI control setup enabled fast and accurate interventional biopsy needle placements along complex trajectories and improved the workflow for percutaneous interventions under MRI guidance in a preclinical trial.

Diagnostic accuracy of MRI-guided percutaneous transthoracic needle biopsy of solitary pulmonary nodules

OBJECTIVE

The purpose of our study was to evaluate the diagnostic accuracy of MRI-guided percutaneous transthoracic needle biopsy (PTNB) of solitary pulmonary nodules (SPNs).

METHODS

Retrospective review of 69 patients who underwent MR-guided PTNB of SPNs was performed. Each case was reviewed for complications. The final diagnosis was established by surgical pathology of the nodule or clinical and imaging follow-up. Pneumothorax rate and diagnostic accuracy were compared between two groups according to nodule diameter (≤2 vs. >2 cm) using χ (2) chest and Fisher's exact test, respectively.

RESULTS

The success rate of single puncture was 95.6 %. Twelve (17.4 %) patients had pneumothorax, with 1 (1.4 %) requiring chest tube insertion. Mild hemoptysis occurred in 7 (7.2 %) patients. All of the sample material was sufficient for histological diagnostic evaluation. Pathological analysis of biopsy specimens showed 46 malignant, 22 benign, and 1 nondiagnostic nodule. The final diagnoses were 49 malignant nodules and 20 benign nodules basing on postoperative histopathology and clinical follow-up data. One nondiagnostic sample was excluded from calculating diagnostic performance. A sensitivity, specificity, accuracy, positive predictive value, and negative predictive value in diagnosing SPNs were 95.8, 100, 97.0, 100, and 90.9 %, respectively. Pneumothorax rate, diagnostic sensitivity, and accuracy were not significantly different between the two groups (P > 0.05).

CONCLUSIONS

MRI-guided PTNB is safe, feasible, and high accurate diagnostic technique for pathologic diagnosis of pulmonary nodules.

[Percutaneous interventions in an open MR system: technical background and clinical indications]

The latest and therefore more efficient open magnetic resonance (MR) scanners with a field strength of 1 T allow freehand fluoroscopic interventions with excellent image quality. Specifically designed interactive software simplifies examination planning and performance. Guidance in two imaging planes allows fast and accurate device positioning and interventional procedures during free breathing. The diagnostic and therapeutic spectrum includes a wide variety of interstitial percutaneous interventions. The most important are periradicular therapy (PRT), intra-abdominal drainage and nephrostoma placement, biopsies, especially in the breasts and liver and focal ablation therapy of malignant hepatic or renal lesions. As the approach is fast and robotic devices are not needed the method is increasingly being carried out in the clinical routine. A drawback of MR-guided interventions is the limitation in verbal communication during image acquisition. Furthermore, the portfolio of MR compatible instruments needs to be extended.

MR-guided freehand biopsy of breast lesions in a 1.0-T open MR imager with a near-real-time interactive platform: preliminary experience

PURPOSE

To identify the most appropriate magnetic resonance (MR) sequence for breast biopsy with regard to lesion visibility and artifact size and to assess feasibility and safety of this approach in a clinical setting.

MATERIALS AND METHODS

MR-guided interventions were performed in an open 1.0-T MR imager between November 2009 and January 2011. The prospective clinical study was approved by the institutional review board. Written informed consent was obtained. Four different fast dynamic sequences (balanced steady-state free precession, T1-weighted turbo gradient-echo, T1-weighted turbo spin-echo [SE], and T2-weighted single-shot SE sequences) were evaluated for artifact size of biopsy needle and in vivo for lesion visibility. In vivo breast biopsies were performed with the freehand technique and without immobilization or a positioning device by using an interactive MR mode that allowed continuous imaging in two orthogonal planes for guidance.

RESULTS

On the basis of good lesion detection in combination with small artifact size, T1-weighted SE imaging was used for biopsy. A total of 75 biopsies were performed successfully in 69 patients (mean age, 53 years; age range, 35-78 years) (mean lesion size, 7.1 mm; range, 4-15 mm). The interactive MR platform enabled immediate localization and correction of intended needle trajectory. Average time for freehand biopsy was 12 minutes (range, 8-23 minutes). No major complications were recorded.

CONCLUSION

MR-guided freehand biopsy of breast lesions with the near-real-time interactive MR platform in an open 1.0-T MR imager is safe and feasible in a clinical setting. The method simplifies work flow and intervention performance.

Performing MR-guided biopsies in clinical routine: factors that influence accuracy and procedure time

OBJECTIVE

To assess the accuracy, the duration and factors that influence the duration of MRI-guided liver or soft-tissue biopsies.

METHODS

Nineteen liver biopsies and 19 soft-tissue biopsies performed using 1.5T-MRI guidance were retrospectively analysed. Diagnostic performance and complications were assessed. Intervention time was subdivided into preparation period, puncture period and control period. Correlation between procedure time and target size, skin-to-target-distance, used sequences and interventionalists' experience were analysed.

RESULTS

Overall sensitivity, specificity and accuracy were 0.86, 1.0 and 0.92, respectively. Two minor complications occurred. Overall median procedure time was 103.5 min. Liver biopsies lasted longer than soft-tissue biopsies (mean([soft-tissue]): 73.0 min, mean([liver]): 134.1 min, P < 0.001). The most time consuming part was the preparation period in both, soft-tissue and liver biopsies corresponding to 59.6% and 47.4% of the total intervention time, respectively. Total procedure time in liver biopsies (P = 0.027) and puncture period in liver and soft-tissue biopsies (P ([liver]) = 0.048, P ([soft-tissue]) = 0.005) was significantly prolonged for longer skin-to-target-distances. Lower numbers of image acquisitions (P ([liver]) = 0.0007, P ([soft-tissue]) = 0.0012) and interventionalists' experience reduces the procedure duration significantly (P < 0.05), besides all false-negative results appeared during the first five biopsies of each individual radiologist.

CONCLUSION

The interventionalists' experience, skin-to-target-distances and number of image acquisition influence the procedure time significantly.

KEY POINTS

•Appropriate training and supervision is essential for inexperienced interventionalists. •Two perpendicular image orientations should confirm the correct biopsy needle position. •Communication between interventionalist and technician is essential for a fluent biopsy procedure. •To shorten intervention time appropriate previous imaging is essential.

Navigation concepts for magnetic resonance imaging-guided musculoskeletal interventions

Image-guided musculoskeletal (MSK) interventions are a widely used alternative to open surgical procedures for various pathological findings in different body regions. They traditionally involve one of the established x-ray imaging techniques (radiography, fluoroscopy, computed tomography) or ultrasound scanning. Over the last decades, magnetic resonance imaging (MRI) has evolved into one of the most powerful diagnostic tools for nearly the whole body and has therefore been increasingly considered for interventional guidance as well.The strength of MRI for MSK applications is a combination of well-known general advantages, such as multiplanar and functional imaging capabilities, wide choice of tissue contrasts, and absence of ionizing radiation, as well as a number of MSK-specific factors, for example, the excellent depiction of soft-tissue tumors, nonosteolytic bone changes, and bone marrow lesions. On the downside, the magnetic resonance-compatible equipment needed, restricted space in the magnet, longer imaging times, and the more complex workflow have so far limited the number of MSK procedures under MRI guidance.Navigation solutions are generally a natural extension of any interventional imaging system, in particular, because powerful hardware and software for image processing have become routinely available. They help to identify proper access paths, provide accurate feedback on the instrument positions, facilitate the workflow in an MRI environment, and ultimately contribute to procedural safety and success.The purposes of this work were to describe some basic concepts and devices for MRI guidance of MSK procedures and to discuss technical and clinical achievements and challenges for some selected implementations.

Simulation and experimental validation of resonant electric markers used for medical device tracking in magnetic resonance imaging

Magnetic resonance imaging (MRI), which was traditionally used for patient diagnosis, has gained in importance in minimally invasive interventions in the recent past. Hence, there is an increasing demand for medical devices compatible with the MR environment. One of the challenges is to visualize the medical devices, e.g. catheters, within the MR image. Several methods exist to cope with this task.