Interactive MR-guided biopsy in an open-configuration MR imaging system

Magnetic resonance imaging-guided renal biopsy shows high safety and diagnostic yield: a tertiary cancer center experience

OBJECTIVES

To evaluate the technical success and outcomes of renal biopsies performed under magnetic resonance imaging (MRI) using a closed-bore, 1.5-Tesla MRI unit.

MATERIALS AND METHODS

We retrospectively reviewed our institutional biopsy database and included 150 consecutive MRI-guided biopsies for renal masses between November 2007 and March 2020. We recorded age, sex, BMI, tumor characteristics, RENAL nephrometry score, MRI scan sequence, biopsy technique, complications, diagnostic yield, pathologic outcome, and follow-up imaging. Univariate logistic regression was used to assess the association between different parameters and the development of complications. McNemar's test was used to assess the association between paired diagnostic yield measurements for fine-needle aspiration and core samples.

RESULTS

A total of 150 biopsies for 150 lesions were performed in 150 patients. The median tumor size was 2.7 cm. The median BMI was 28.3. The lesions were solid, partially necrotic/cystic, and predominantly cystic in 137, eight, and five patients, respectively. Image guidance using fat saturation steady-state free precession sequence was recorded in 95% of the biopsy procedures. Samples were obtained using both fine-needle aspiration (FNA) and cores in 99 patients (66%), cores only in 40 (26%), and FNA only in three (2%). Tissue sampling was diagnostic in 144 (96%) lesions. No major complication developed following any of the biopsy procedures. The median follow-up imaging duration was 8 years and none of the patients developed biopsy-related long-term complication or tumor seeding.

CONCLUSIONS

MRI-guided renal biopsy is safe and effective, with high diagnostic yield and no major complications.

CLINICAL RELEVANCE STATEMENT

Image-guided renal biopsy is safe and effective, and should be included in the management algorithm of patients with renal masses. Core biopsy is recommended.

KEY POINTS

• MRI-guided biopsy is a safe and effective technique for sampling of renal lesions. • MRI-guided biopsy has high diagnostic yield with no major complications. • Percutaneous image-guided biopsy plays a key role in the management of patients with renal masses.

Integration and evaluation of a gradient-based needle navigation system for percutaneous MR-guided interventions

The purpose of the present study was to integrate an interactive gradient-based needle navigation system and to evaluate the feasibility and accuracy of the system for real-time MR guided needle puncture in a multi-ring phantom and in vivo in a porcine model. The gradient-based navigation system was implemented in a 1.5T MRI. An interactive multi-slice real-time sequence was modified to provide the excitation gradients used by two sets of three orthogonal pick-up coils integrated into a needle holder. Position and orientation of the needle holder were determined and the trajectory was superimposed on pre-acquired MR images. A gel phantom with embedded ring targets was used to evaluate accuracy using 3D distance from needle tip to target. Six punctures were performed in animals to evaluate feasibility, time, overall error (target to needle tip) and system error (needle tip to the guidance needle trajectory) in vivo. In the phantom experiments, the overall error was 6.2±2.9 mm (mean±SD) and 4.4±1.3 mm, respectively. In the porcine model, the setup time ranged from 176 to 204 seconds, the average needle insertion time was 96.3±40.5 seconds (min: 42 seconds; max: 154 seconds). The overall error and the system error was 8.8±7.8 mm (min: 0.8 mm; max: 20.0 mm) and 3.3±1.4 mm (min: 1.8 mm; max: 5.2 mm), respectively.

Magnetic resonance and ultrasound image-guided navigation system using a needle manipulator

PURPOSE

Image guidance is crucial for percutaneous tumor ablations, enabling accurate needle-like applicator placement into target tumors while avoiding tissues that are sensitive to injury and/or correcting needle deflection. Although ultrasound (US) is widely used for image guidance, magnetic resonance (MR) is preferable due to its superior soft tissue contrast. The objective of this study was to develop and evaluate an MR and US multi-modal image-guided navigation system with a needle manipulator to enable US-guided applicator placement during MR imaging (MRI)-guided percutaneous tumor ablation.

METHODS

The MRI-compatible needle manipulator with US probe was installed adjacent to a 3 Tesla MRI scanner patient table. Coordinate systems for the MR image, patient table, manipulator, and US probe were all registered using an optical tracking sensor. The patient was initially scanned in the MRI scanner bore for planning and then moved outside the bore for treatment. Needle insertion was guided by real-time US imaging fused with the reformatted static MR image to enhance soft tissue contrast. Feasibility, targeting accuracy, and MR compatibility of the system were evaluated using a bovine liver and agar phantoms.

RESULTS

Targeting error for 50 needle insertions was 1.6 ± 0.6 mm (mean ± standard deviation). The experiment confirmed that fused MR and US images provided real-time needle localization against static MR images with soft tissue contrast.

CONCLUSIONS

The proposed MR and US multi-modal image-guided navigation system using a needle manipulator enabled accurate needle insertion by taking advantage of static MR and real-time US images simultaneously. Real-time visualization helped determine needle depth, tissue monitoring surrounding the needle path, target organ shifts, and needle deviation from the path.

Heterogeneity Diffusion Imaging of gliomas: Initial experience and validation

Objectives

Primary brain tumors are composed of tumor cells, neural/glial tissues, edema, and vasculature tissue. Conventional MRI has a limited ability to evaluate heterogeneous tumor pathologies. We developed a novel diffusion MRI-based method—Heterogeneity Diffusion Imaging (HDI)—to simultaneously detect and characterize multiple tumor pathologies and capillary blood perfusion using a single diffusion MRI scan.

Methods

Seven adult patients with primary brain tumors underwent standard-of-care MRI protocols and HDI protocol before planned surgical resection and/or stereotactic biopsy. Twelve tumor sampling sites were identified using a neuronavigational system and recorded for imaging data quantification. Metrics from both protocols were compared between World Health Organization (WHO) II and III tumor groups. Cerebral blood volume (CBV) derived from dynamic susceptibility contrast (DSC) perfusion imaging was also compared with the HDI-derived perfusion fraction.

Results

The conventional apparent diffusion coefficient did not identify differences between WHO II and III tumor groups. HDI-derived slow hindered diffusion fraction was significantly elevated in the WHO III group as compared with the WHO II group. There was a non-significantly increasing trend of HDI-derived tumor cellularity fraction in the WHO III group, and both HDI-derived perfusion fraction and DSC-derived CBV were found to be significantly higher in the WHO III group. Both HDI-derived perfusion fraction and slow hindered diffusion fraction strongly correlated with DSC-derived CBV. Neither HDI-derived cellularity fraction nor HDI-derived fast hindered diffusion fraction correlated with DSC-derived CBV.

Conclusions

Conventional apparent diffusion coefficient, which measures averaged pathology properties of brain tumors, has compromised accuracy and specificity. HDI holds great promise to accurately separate and quantify the tumor cell fraction, the tumor cell packing density, edema, and capillary blood perfusion, thereby leading to an improved microenvironment characterization of primary brain tumors. Larger studies will further establish HDI’s clinical value and use for facilitating biopsy planning, treatment evaluation, and noninvasive tumor grading.

Creating a Clinical Interventional MRI Service

The expansive technological developments that occurred over the past decades have clearly moved the field of Interventional MRI beyond the arena of the "proof of concept" to a viable option for minimally invasive diagnosis and therapy. State-of-the-art MRI technology can currently be employed to identify an occult target pathology, confidently steer an interventional device into complex anatomy, accurately deliver a device, drug, or energy, and/or monitor the real time effect of a treatment. Implementing a full-scope interventional MRI service requires substantial physical and conceptual modifications of the traditional diagnostic MRI environment. As such, it is essential to recognize that interventional MRI does not only involve the actual MRI-guided interventional event but should rather be perceived as a whole foundation of technology, development, set-up, conceptual training, and an institutional culture that realizes the opportunities offered by and understands the challenges and limitations of MRI-guided interventions. At Emory University, we had the privilege to build a de novo interventional MRI suite and to subsequently operate a high volume clinical interventional MRI service. The Emory program was launched with the goal of establishing a destination site for a comprehensive clinical service of MRI-guided interventions. The experience gained and the lessons learned are shared with the readers in this article.

Intraoperative Image Guidance during Endoscopic Sinus Surgery

Endoscopic sinus surgery (ESS) is one of the most commonly performed procedures in otorhinolaryngology and is associated with a definite risk for both intraoperative and postoperative complications. Intraoperative image guidance is expected to have a major effect on procedures such as ESS by allowing the clinician to more efficiently remove pathology and by improving surgeon confidence and knowledge of anatomy, particularly in revision procedures or in patients with altered anatomy. As a consequence, complications during these pro-’ cedures will decrease and patient safety will increase. Several guidance modalities are available including computed tomography (CT), magnetic resonance imaging (MRI), and fluoroscopy. This article will describe current applications of each of these three techniques with respect to ESS while focusing on innovative techniques that use MRI and CT to provide intraoperative guidance with unmatched convenience, reliability, and utility.

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.

Hybrid MRI-Ultrasound acquisitions, and scannerless real-time imaging

PURPOSE

To combine MRI, ultrasound, and computer science methodologies toward generating MRI contrast at the high frame rates of ultrasound, inside and even outside the MRI bore.

METHODS

A small transducer, held onto the abdomen with an adhesive bandage, collected ultrasound signals during MRI. Based on these ultrasound signals and their correlations with MRI, a machine-learning algorithm created synthetic MR images at frame rates up to 100 per second. In one particular implementation, volunteers were taken out of the MRI bore with the ultrasound sensor still in place, and MR images were generated on the basis of ultrasound signal and learned correlations alone in a "scannerless" manner.

RESULTS

Hybrid ultrasound-MRI data were acquired in eight separate imaging sessions. Locations of liver features, in synthetic images, were compared with those from acquired images: The mean error was 1.0 pixel (2.1 mm), with best case 0.4 and worst case 4.1 pixels (in the presence of heavy coughing). For results from outside the bore, qualitative validation involved optically tracked ultrasound imaging with/without coughing.

CONCLUSION

The proposed setup can generate an accurate stream of high-speed MR images, up to 100 frames per second, inside or even outside the MR bore. Magn Reson Med 78:897-908, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Hybrid Utrasound and MRI Acquisitions for High-Speed Imaging of Respiratory Organ Motion

Magnetic Resonance (MR) imaging provides excellent image quality at a high cost and low frame rate. Ultrasound (US) provides poor image quality at a low cost and high frame rate. We propose an instance-based learning system to obtain the best of both worlds: high quality MR images at high frame rates from a low cost single-element US sensor. Concurrent US and MRI pairs are acquired during a relatively brief offine learning phase involving the US transducer and MR scanner. High frame rate, high quality MR imaging of respiratory organ motion is then predicted from US measurements, even after stopping MRI acquisition, using a probabilistic kernel regression framework. Experimental results show predicted MR images to be highly representative of actual MR images.

18F-FDG PET/CT-directed biopsy: does it offer incremental benefit?

PURPOSE

To study whether the metabolic information provided by a prior PET/computed tomography (CT) scan can add valuable information and an incremental benefit while performing image-guided biopsies.

METHODS

Fluorine-18 fluorodeoxyglucose (F-FDG) PET/CT findings of 112 patients were available before biopsy and were considered for analysis. Biopsies were performed using standard techniques only after the needle tip was confirmed to be in the portion of the lesion corresponding to the hypermetabolic area seen on PET. This was achieved by visual coregistration and also by software registration algorithms that registered the intraprocedural CT images with the preselected PET/CT data. Only those biopsies for which a definitive histopathological diagnosis could be made were considered 'diagnostic'. Cases in which PET/CT added an incremental value were divided into three categories.

RESULTS

A total of 112 patients (66 male and 46 female, age range 16-74 years) underwent a biopsy based on PET findings. The biopsy sites were as follows: lung, 54; lymph nodes, 27; bone, 12; and soft-tissue masses/deposits, 19. Out of the 112 biopsies, an incremental benefit was seen overall in 53 patients (47.3%): in 40.7% (22/54) of patients who underwent lung biopsies, 44.4% (12/27) of those who underwent lymph node biopsies, 66.6% (8/12) of those who underwent bone biopsies and 57.8% (11/19) of those who underwent soft-tissue biopsies. Out of the cases that showed an incremental benefit, the highest number (30) belonged to the category in which the biopsy sample was obtained from the focal hypermetabolic portion of the apparently larger morphological lesion seen on CT.

CONCLUSION

PET/CT data coregistered with intraprocedural CT images can guide needle placement in the viable portion of the lesion, thus increasing the chances of achieving a definitive diagnosis. This approach can offer a significant incremental benefit while performing image-guided biopsies.

Device localization and dynamic scan plane selection using a wireless magnetic resonance imaging detector array

PURPOSE

A prototype wireless guidance device using single sideband amplitude modulation (SSB) is presented for a 1.5T magnetic resonance imaging system.

METHODS

The device contained three fiducial markers each mounted to an independent receiver coil equipped with wireless SSB technology. Acquiring orthogonal projections of these markers determined the position and orientation of the device, which was used to define the scan plane for a subsequent image acquisition. Device localization and scan plane update required approximately 30 ms, so it could be interleaved with high temporal resolution imaging. Since the wireless device is used for localization and does not require full imaging capability, the design of the SSB wireless system was simplified by allowing an asynchronous clock between the transmitter and receiver.

RESULTS

When coupled to a high readout bandwidth, the error caused by the lack of a shared frequency reference was quantified to be less than one pixel (0.78 mm) in the projection acquisitions. Image guidance with the prototype was demonstrated with a phantom where a needle was successfully guided to a target and contrast was delivered.

CONCLUSION

The feasibility of active tracking with a wireless detector array is demonstrated. Wireless arrays could be incorporated into devices to assist in image-guided procedures.

How MRI compatible is "MRI compatible"? A systematic comparison of artifacts caused by biopsy needles at 3.0 and 1.5 T

PURPOSE

This study was designed to systematically investigate artifacts caused by interventional needles recommended for use in MRI, with focus on field strength, needle/mandrin type, orientation and sequence.

METHODS

Eight different MRI compatible needles were placed in porcine tissue and examined at 1.5 and 3.0 T with balanced-steady-state-free-precession (B-SSFP) and T1-weighted-spoiled-gradient-echo (T1-SPGR) sequences in different orientations to B0. Artifact diameters with regards to the primary, inner, and secondary, outer artifacts were assessed and statistically evaluated.

RESULTS

The types and degree of artifacts varied considerably, especially between different mandrin types even for the same needles. Orientation of the needle in the magnetic field was another main contributor to the artifact dimensions. Less important factors were the type of pulse sequence and field strength. Artifacts ranged from 0.7 mm (steel, 0°, B-SSFP, 3.0 T, inner) to 71.4 mm (nitinol, 90°, B-SSFP, 1.5 T, outer). Inner artifact diameters in B-SSFP were slightly larger (8.2 ± 5.7 mm) than those in T1-SPGR (7.6 ± 5.4 mm) and comparable between 1.5 and 3.0 T (e.g., 8.0 vs. 8.4 mm, B-SSFP).

CONCLUSIONS

Although all were sold as "MR compatible," the artifacts differed greatly between needle types, and even more so for different mandrins. The results suggest an empirical approach to the needle choice based on lesion type and approach angle.

Augmented reality visualization with use of image overlay technology for MR imaging-guided interventions: assessment of performance in cadaveric shoulder and hip arthrography at 1.5 T

PURPOSE

To prospectively assess overlay technology in providing accurate and efficient targeting for magnetic resonance (MR) imaging-guided shoulder and hip joint arthrography.

MATERIALS AND METHODS

A prototype augmented reality image overlay system was used in conjunction with a clinical 1.5-T MR imager. A total of 24 shoulder joint and 24 hip joint injections were planned in 12 human cadavers. Two operators (A and B) participated, each performing procedures on different cadavers using image overlay guidance. MR imaging was used to confirm needle positions, monitor injections, and perform MR arthrography. Accuracy was assessed according to the rate of needle adjustment, target error, and whether the injection was intraarticular. Efficiency was assessed according to arthrography procedural time. Operator differences were assessed with comparison of accuracy and procedure times between the operators. Mann-Whitney U test and Fisher exact test were used to assess group differences.

RESULTS

Forty-five arthrography procedures (23 shoulders, 22 hips) were performed. Three joints had prostheses and were excluded. Operator A performed 12 shoulder and 12 hip injections. Operator B performed 11 shoulder and 10 hip injections. Needle adjustment rate was 13% (six of 45; one for operator A and five for operator B). Target error was 3.1 mm±1.2 (standard deviation) (operator A, 2.9 mm±1.4; operator B, 3.5 mm±0.9). Intraarticular injection rate was 100% (45 of 45). The average arthrography time was 14 minutes (range, 6-27 minutes; 12 minutes [range, 6-25 minutes] for operator A and 16 minutes [range, 6-27 min] for operator B). Operator differences were not significant with regard to needle adjustment rate (P=.08), target error (P=.07), intraarticular injection rate (P>.99), and arthrography time (P=.22).

CONCLUSION

Image overlay technology provides accurate and efficient MR guidance for successful shoulder and hip arthrography in human cadavers.

Magnetic resonance-guided interventions of large and small joints

Magnetic resonance (MR)-guided interventions of large and small joints are feasible and safe procedures offering several advantages compared with standard guiding techniques. Nevertheless, MR-guided interventions are not routinely performed in daily practice apart from a few centers. Accurate injections are crucial for clinical outcome in diagnostic arthrography as well as therapeutic joint injections. In particular, palpatory joint puncture was shown to be inaccurate or uncertain in a substantial percentage of injections of the shoulder, the hip, and the knee. Magnetic resonance imaging offers respective merits of a cross-sectional technique with high soft-tissue contrast. Exact depiction of structures, which should be preserved, such as the labrum, should be aimed for. Areas with complex anatomy can be approached by adapting the right imaging plane(s) because of multiplanar capacity. Lack of ionizing radiation for patients is of growing interest particularly in young patients with repeated interventions. Magnetic resonance guidance alone allows an "all-in-one" MR arthrography combining precise targeting with high-field-strength imaging. Modern short-bore and open-bore high-field-strength systems offer a good comfort for patients as well as clinicians and enhance patient positioning options such as supine or prone position. Thus, a tailored approach such as a posterior technique for suspected anterior lesions in shoulder MR arthrography is possible.In this article, we describe the advantages and limitations of MR guidance in joint interventions with focus on shoulder and hip interventions. We review the requirements for needle material and MR sequences, discuss several different techniques developed to date, and present current results in clinical outcome.

Magnetic resonance imaging-guided biopsy of musculoskeletal lesions using open low-field systems

With the development of open-configuration magnetic resonance imaging (MRI) systems, magnetic resonance-compatible navigational tools, and fast pulse sequences, MRI-guided biopsy of musculoskeletal lesions has evolved into an effective and safe, minimally invasive technique. Magnetic resonance-guided percutaneous biopsy of musculoskeletal lesions is especially suited for lesions that are detectable only with MRI, lesions that require double-angulated needle paths, and for patients in which radiation exposure needs to be avoided. In this article, we review pertinent principles, techniques, and clinical applications of low-field MRI for biopsy procedures in the musculoskeletal system.

Magnetic resonance imaging-guided biopsy in the musculoskeletal system using a cylindrical 1.5-T magnetic resonance imaging unit

OBJECTIVES

The objective of this study was to report a single-center experience with magnetic resonance imaging (MRI)-guided biopsy in the musculoskeletal system using a closed-bore, cylindrical, high-magnetic-field (1.5-T) MRI unit.

METHODS

From May 2010 to July 2011, 100 consecutive MRI-guided biopsy sessions were undertaken for musculoskeletal lesions in 97 patients. Patient demographics, tumor characteristics, and biopsy techniques were recorded. Biopsy results, treatment outcomes, and follow-up imaging studies were reviewed.

RESULTS

Biopsy procedures were technically successful in 99 cases (99%). Despite a mean body mass index of 30 kg/m, all patients fit within the bore of the magnet. There were 69 soft-tissue and 31 bone tumors. Most patients had both tissue core (n = 93) and fine-needle aspiration (n = 84) biopsies. All lesions were adequately imaged, localized, and targeted using rapid balanced steady-state free precession imaging (89%), fast T1 (4%), or combination of the 2 techniques (7%). A prototype real-time imaging sequence was used in 29 cases (29%) to guide biopsy needle insertion. There were no major complications. Sensitivity, specificity, and overall accuracy were 97%, 100%, and 97.6%, respectively.

CONCLUSIONS

Magnetic resonance imaging-guided biopsy in a closed-bore, high-field-strength magnet is a safe, easy, and effective technique for evaluation of musculoskeletal lesions. Ideally, the MRI suite should be equipped with an in-room radiofrequency-shielded monitor and a communication system. However, surface coils with adequate opening to grant access to the biopsy site, MRI-compatible needles, and MRI-compatible patient monitoring devices are absolutely necessary to perform MRI-guided biopsies.

The treatment of primary and metastatic hepatic neoplasms using percutaneous cryotherapy

Cryotherapy has been used clinically in the treatment of metastatic liver malignancies since the 1980s. Rapid freezing to sub-zero temperatures promotes ice formation in the extracellular space and the exit of intracellular water. Cellular death is the result of dehydration, protein denaturation, and microcirculatory failure. Cryotherapy probes use nitrogen or argon gas as a coolant and the development of the ice ball can be monitored using ultrasound, computed tomography, or magnetic resonance imaging. Traditionally, cryotherapy has been performed during laparoscopy or laparotomy, using intraoperative ultrasound for image guidance. A decrease in cryoprobe size (from ~24 Fr to ~15 gauge) in conjunction with experience gained in open cryosurgical treatment has allowed the development of minimally invasive percutaneous approaches. In this review, we describe the use of cryotherapy for treatment of primary or secondary liver neoplasms using a percutaneous approach.

Imaging in interventional oncology

Medical imaging in interventional oncology is used differently than in diagnostic radiology and prioritizes different imaging features. Whereas diagnostic imaging prioritizes the highest-quality imaging, interventional imaging prioritizes real-time imaging with lower radiation dose in addition to high-quality imaging. In general, medical imaging plays five key roles in image-guided therapy, and interventional oncology, in particular. These roles are (a) preprocedure planning, (b) intraprocedural targeting, (c) intraprocedural monitoring, (d) intraprocedural control, and (e) postprocedure assessment. Although many of these roles are still relatively basic in interventional oncology, as research and development in medical imaging focuses on interventional needs, it is likely that the role of medical imaging in intervention will become even more integral and more widely applied. In this review, the current status of medical imaging for intervention in oncology will be described and directions for future development will be examined.

Real-Time Estimation of 3-D Needle Shape and Deflection for MRI-Guided Interventions

We describe a MRI-compatible biopsy needle instrumented with optical fiber Bragg gratings for measuring bending deflections of the needle as it is inserted into tissues. During procedures, such as diagnostic biopsies and localized treatments, it is useful to track any tool deviation from the planned trajectory to minimize positioning errors and procedural complications. The goal is to display tool deflections in real time, with greater bandwidth and accuracy than when viewing the tool in MR images. A standard 18 ga × 15 cm inner needle is prepared using a fixture, and 350-μm-deep grooves are created along its length. Optical fibers are embedded in the grooves. Two sets of sensors, located at different points along the needle, provide an estimate of the bent profile, as well as temperature compensation. Tests of the needle in a water bath showed that it produced no adverse imaging artifacts when used with the MR scanner.

Real-time magnetic resonance-guided microwave coagulation therapy for pelvic recurrence of rectal cancer: initial clinical experience using a 0.5 T open magnetic resonance system

PURPOSE

This study aims to evaluate consecutive cases of recurrent rectal cancer in the pelvic cavity treated with microwave coagulation therapy using real-time navigation by an open magnetic resonance system.

METHODS

Nine recurrent pelvic lesions in 8 patients after curative resection of rectal cancer were treated with real-time magnetic resonance-guided microwave coagulation therapy as a palliative local therapy to reduce tumor volume and/or local pain. Clinical and pathological data were collected retrospectively by reviewing medical records and clinical imaging results.

RESULTS

Seven patients received other treatments before real-time magnetic resonance-guided microwave coagulation. Six patients had distant synchronous metastases. Three patients underwent surgery under lumbar anesthesia. Microwave coagulation was performed percutaneously in 5 lesions and under laparotomy in 4 lesions. Although adverse events related to microwave coagulation (skin necrosis and nerve injury) were observed, no fatal complications occurred. Local re-recurrence was observed in 2 of 9 ablated lesions. Except for 1 patient who died of chronic renal failure, the remaining 7 patients died of cancer. Median overall survival after microwave coagulation for all patients was 10 months (range, 4-37 mo). Median overall survival after discovery of pelvic recurrence in all patients was 22 months (range, 9-42 mo).

CONCLUSIONS

The benefits of using an open magnetic resonance system in the pelvic cavity include the abilities to treat tumors that cannot be visualized by other modalities, to demonstrate internal architectural changes during treatment, to differentiate treated vs untreated areas, and to allow adjustments to the treatment plan during the procedure. Additional studies are required to clarify the efficacy of tumor coagulation for local control.

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.

Characterization and reduction of saturation banding in multiplanar coherent and incoherent steady-state imaging

Hypointense band artifacts occur at intersections of nonparallel imaging planes in rapidly acquired MR images; quantitative or numerical analysis of these bands and strategies to mitigate their appearance have largely gone unexplored. The magnetization evolution in the different regions of multiplanar images was simulated for three common rapid steady-state techniques (spoiled gradient echo, steady state free precession, balanced steady state free precession). Saturation banding was found to be highly dependent on the pulse sequence, acquisition time, and phase-encoding order. Encoding the center of k-space at the end of the acquisition of each slice (i.e., reverse centric phase encoding) is demonstrated to be a simple and robust method for significantly reducing the relative saturation in all imaging planes. View ordering and resolution dependence were confirmed in multiplanar abdominal images. The added importance of reducing the artifact in accelerated acquisition techniques (e.g., parallel imaging) is particularly notable in multiplanar balanced steady state free precession images in the brain.

Integrated MR-laparoscopy system with respiratory synchronization for minimally invasive liver surgery

PURPOSE

The laparoscope has been invaluable in minimally invasive surgery, but provides only a surface view of target tissue; therefore it is lacking internal tissue information. In combination with the laparoscope for visualizing the cross-sectional view of the tissue, MRI is superior to ultrasonography or X-ray CT, because of its high soft-tissue contrast, arbitrary slice orientation and lack of radiation properties. Thus, we propose an integrated MR-laparoscopy system with a respiratory-synchronized navigation.

METHODS

A transmit/receive RF coil for localized MR imaging with a 0.5 T open-MRI was mounted onto the tip of an MR-compatible laparoscope. The signal detection of the coil was examined with an excised porcine liver sample, an agar phantom and the abdominal wall of a healthy volunteer. A real-time navigation system to compensate for respiratory motion was developed, and examined with a healthy volunteer.

RESULTS

The SNRs of the local MR images were 112, 62, and 62 in the liver sample, phantom, and volunteer. The navigation system successfully displayed the scope view, scope location and orientation, and MR images with respiratory-synchronized real time operation.

CONCLUSIONS

The MR-imaging and synchronization function of the proposed system seemed to be helpful for laparoscopic surgery.

Image-guided tumor ablation: standardization of terminology and reporting criteria

The field of interventional oncology with use of image-guided tumor ablation requires standardization of terminology and reporting criteria to facilitate effective communication of ideas and appropriate comparison between treatments that use different technologies, such as chemical (ethanol or acetic acid) ablation, and thermal therapies, such as radiofrequency (RF), laser, microwave, ultrasound, and cryoablation. This document provides a framework that will hopefully facilitate the clearest communication between investigators and will provide the greatest flexibility in comparison between the many new, exciting, and emerging technologies. An appropriate vehicle for reporting the various aspects of image-guided ablation therapy, including classification of therapies and procedure terms, appropriate descriptors of imaging guidance, and terminology to define imaging and pathologic findings, are outlined. Methods for standardizing the reporting of follow-up findings and complications and other important aspects that require attention when reporting clinical results are addressed. It is the group's intention that adherence to the recommendations will facilitate achievement of the group's main objective: improved precision and communication in this field that lead to more accurate comparison of technologies and results and, ultimately, to improved patient outcomes. The intent of this standardization of terminology is to provide an appropriate vehicle for reporting the various aspects of image-guided ablation therapy.

Intraprocedural diffusion-weighted PROPELLER MRI to guide percutaneous biopsy needle placement within rabbit VX2 liver tumors

PURPOSE

To test the hypothesis that diffusion-weighted (DW)-PROPELLER (periodically rotated overlapping parallel lines with enhanced reconstruction) magnetic resonance imaging (MRI) can be used to guide biopsy needle placement during percutaneous interventional procedures to selectively target viable and necrotic tissues within VX2 rabbit liver tumors.

MATERIALS AND METHODS

Our institutional Animal Care and Use Committee approved all experiments. In six rabbits implanted with 15 VX2 liver tumors, baseline DW-PROPELLER images acquired prior to the interventional procedure were used for apparent diffusion coefficient (ADC) measurements. Next, intraprocedural DW-PROPELLER scans were performed with needle position iteratively adjusted to target viable, necrotic, or intermediate border tissue regions. DW-PROPELLER ADC measurements at the selected needle tip locations were compared with the percentage of tumor necrosis qualitatively assessed at histopathology.

RESULTS

DW-PROPELLER images demonstrated intratumoral tissue heterogeneity and clearly depicted the needle tip position within viable and necrotic tumor tissues. Mean ADC measurements within the region-of-interest encompassing the needle tip were highly correlated with histopathologic tumor necrotic tissue assessments.

CONCLUSION

DW-PROPELLER is an effective method to selectively position the biopsy needle tip within viable and necrotic tumor tissues. The DW-PROPELLER method may offer an important complementary tool for functional guidance during MR-guided percutaneous procedures.

Use of real‐time magnetic resonance image guidance in endoscopic sinus surgery

We evaluated the effectiveness of magnetic resonance image (MRI) guidance using an optical tracking system (MRI-guided therapy: MRT) in performing endoscopic sinus surgery (ESS). The profiles of the fourteen patients in the present study were as follows: eleven with mucocele in the paranasal sinus, one with recurrent chronic sinusitis, one with maxillary cancer, and one with Graves' ophthalmopathy. Preparation of the MRT system required an additional 54 min in cases involving general anesthesia, and an additional 17 min in cases involving local anesthesia, in comparison with corresponding control groups undergoing ESS in a traditional operating room. We developed nonmetal probes that were visualized in a real-time mode and assistive devices for the optical tracking system that were equipped to avoid obstruction caused by surgical instruments as well as by the hands of surgeons. Using these unique devices, anatomic landmarks were visualized using the present MRT system. The prognosis of patients was favorable, and in particular, no patients with sinus mucocele showed a recurrence of their lesions. We concluded that the MRT system used here for performing ESS was beneficial, especially in terms of the intranasal marsupialization of sinus mucoceles and for the verification of orbital contents.

Biopsy of renal masses: when and why

Percutaneous image-guided biopsy of renal masses is a safe and accurate procedure. Although once reserved for the diagnosis of unresectable renal cell carcinoma, metastases, lymphoma, and infection, today percutaneous image-guided biopsy has an expanded role. There is increasing awareness that a substantial proportion of small, solid renal masses are benign neoplasms. Although imaging can be used to diagnose most of them, some are incorrectly believed to represent renal cell carcinoma and unnecessary surgery may be performed. Based largely on advances in cytological techniques, percutaneous biopsy can be now be used to diagnose benign neoplasms and thus prevent them from being treated unnecessarily. Concurrent advances in percutaneous ablation have also promoted its use. As a result, there are 8 established indications for percutaneous biopsy, and reason to believe that the number of indications will expand further in the future.

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

Needle tip visualization is of high importance in magnetic resonance imaging (MRI) guided interventional procedures, for example for taking biopsies from suspicious lesions in the liver or kidney. The exact position of the needle tip is often obscured by image artifacts arising from the magnetic properties of the needle. The authors investigated two special biopsy needle tip designs using diamagnetic coatings. For common interventional MR sequences, the needle tip can be identified in the MR image by several equidistant dark spots arranged along a straight line. A dotted instead of a solid line allows for an improved control of the movement of the needle, not only if the needle is tilted toward the imaging plane, but also if the needle leaves an empty canal with signal extinction, which cannot be distinguished from the needle material itself. With the proposed design the position of the needle tip can be estimated with a precision of approximately 1 mm using conventional FLASH, FISP, and TSE sequences, as used for interventional MR. Furthermore, the size of the biopsy probe can be estimated from the artifact. In using needles with a properly designed tip coating, taking biopsies under MR control is beginning to be greatly simplified. The approach to design artifacts using diamagnetic material in combination with paramagnetic material paves the way toward new instruments and implants, suitably tailored to the needs of the interventional radiologist.

MR systems for MRI-guided interventions

The field of MR imaging has grown from diagnosis via morphologic imaging to more sophisticated diagnosis via both physiologic and morphologic imaging and finally to the guidance and control of interventions. A wide variety of interventional procedures from open brain surgeries to noninvasive focused ultrasound ablations have been guided with MR and the differences between diagnostic and interventional MR imaging systems have motivated the creation of a new field within MR. This review discusses the various systems that research groups and vendors have designed to meet the requirements of interventional MR and suggest possible solutions to those requirements that have not yet been met. The common requirements created by MR imaging guidance of interventional procedures are reviewed and different imaging system designs will be independently considered. The motivation and history of the different designs are discussed and the ability of the designs to satisfy the requirements is analyzed.

MR-guided biopsy: a review of current techniques and applications

Biopsy has become a cornerstone of modern medicine and most modern biopsies are performed percutaneously using image guidance, typically computed tomography or ultrasound. MR-guided biopsy offers many advantages over these more traditional modalities, and the recent development of interventional MR imaging techniques has made MR-guided percutaneous biopsies and aspirations a clinical reality. As the field of MR-guided procedures continues to expand and to attract more attention from radiologists, it is important to understand the concepts, techniques, applications, advantages, and limitations of MR-guided biopsy/percutaneous procedures. Radiologists should also recognize the need for their significant involvement in the technical aspects of MR-guided procedures, since several user-defined parameters can alter device visualization in the MR imaging environment and affect procedure safety. This article reviews the prerequisites, systems, and applications of MR-guided biopsy.