Magnetic Resonance-Guided Large-Core Breast Biopsy Inside a 1.5-T Magnetic Resonance Scanner Using an Automatic System

Phantom-based assessment of motion and needle targeting accuracy of robotic devices for magnetic resonance imaging-guided needle biopsy

BACKGROUND

The current study proposes simple methods for assessing the performance of robotic devices intended for Magnetic Resonance Imaging (MRI)-guided needle biopsy.

METHODS

In-house made agar-based breast phantoms containing biopsy targets served as the main tool in the evaluation process of an MRI compatible positioning device comprising a needle navigator. The motion accuracy of mechanical stages was assessed by calliper measurements. Laboratory evaluation of needle targeting included a repeatability phantom test and a laser-based method. The accuracy and repeatability of needle targeting was also assessed by MRI.

RESULTS

The maximum error of linear motion for steps up to 10 mm was 0.1 mm. Needle navigation relative to the phantom and alignment with the various biopsy targets were performed successfully in both the laboratory and MRI settings. The proposed biopsy phantoms offered tissue-like signal in MRI and good haptic feedback during needle insertion.

CONCLUSIONS

The proposed methods could be valuable in the process of validating the accuracy of MRI-guided biopsy robotic devices in both laboratory and real environments.

Robotics in MRI-Guided Interventions

Robots have been found to be a useful tool in magnetic resonance imaging (MRI)-guided intervention. The utility of robots in MRI-guided therapy ranges from aid for precision targeting to high-dexterity surgical tools to improve or even enable new MRI-guided therapy options. The objective of this article is to review the technical aspects of robotics in MRI-guided interventions, highlight the role of MRI robots in prostate interventions, and finally discuss the future contribution of emerging robotics technology useful in MRI-guided intervention.

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.

Enabling Technology for MRI-Guided Intervention

The use of magnetic resonance imaging (MRI) for image-guided intervention poses both great opportunity and challenges. Although MRI is distinguished by its excellent contrast resolution and lack of ionizing radiation, it was not till the 1990s that technologic innovations allowed for adoption of MRI as a guidance modality for intervention. With advances in magnet, protocol, coil, biopsy needle, and ablation probe design, MRI has emerged as a viable, and increasingly, preferable alternative to other image guidance modalities. With the development of targeting software, augmented reality, robotic assist devices, and MR thermometry, the future of MRI-guided interventions remains promising.

Integrated navigation and control software system for MRI-guided robotic prostate interventions

A software system to provide intuitive navigation for MRI-guided robotic transperineal prostate therapy is presented. In the system, the robot control unit, the MRI scanner, and the open-source navigation software are connected together via Ethernet to exchange commands, coordinates, and images using an open network communication protocol, OpenIGTLink. The system has six states called "workphases" that provide the necessary synchronization of all components during each stage of the clinical workflow, and the user interface guides the operator linearly through these workphases. On top of this framework, the software provides the following features for needle guidance: interactive target planning; 3D image visualization with current needle position; treatment monitoring through real-time MR images of needle trajectories in the prostate. These features are supported by calibration of robot and image coordinates by fiducial-based registration. Performance tests show that the registration error of the system was 2.6mm within the prostate volume. Registered real-time 2D images were displayed 1.97 s after the image location is specified.

MRI-compatible manipulator with remote-center-of-motion control

PURPOSE

To develop and assess a needle-guiding manipulator for MRI-guided therapy that allows a physician to freely select the needle insertion path while maintaining remote center of motion (RCM) at the tumor site.

MATERIALS AND METHODS

The manipulator consists of a three-degrees-of-freedom (DOF) base stage and passive needle holder with unconstrained two-DOF rotation. The synergistic control keeps the Virtual RCM at the preplanned target using encoder outputs from the needle holder as input to motorize the base stage.

RESULTS

The manipulator assists in searching for an optimal needle insertion path which is a complex and time-consuming task in MRI-guided ablation therapy for liver tumors. The assessment study showed that accuracy of keeping the virtual RCM to predefined position is 3.0 mm. In a phantom test, the physicians found the needle insertion path faster with than without the manipulator (number of physicians = 3, P = 0.001). However, the alignment time with the virtual RCM was not shorter when imaging time for planning were considered.

CONCLUSION

The study indicated that the robot holds promise as a tool for accurately and interactively selecting the optimal needle insertion path in liver ablation therapy guided by open-configuration MRI.

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.

Classification of small contrast enhancing breast lesions in dynamic magnetic resonance imaging using a combination of morphological criteria and dynamic analysis based on unsupervised vector-quantization

PURPOSE

To evaluate the diagnostic value of breast magnetic resonance imaging (MRI) in small focal lesions using dynamic analysis based on unsupervised vector quantization in combination with a score for morphologic criteria.

MATERIALS AND METHODS

We examined 85 mammographically indetermintate lesions (BIRADS 3-4; 47 malignant, mean lesion size 1.2 cm; 38 benign, mean lesion size 1.1 cm). MRI was performed with a dynamic T1-weighted gradient echo sequence (1 precontrast and 5 postcontrast series). Lesions with an initial contrast enhancement >/=50% were selected with semiautomatic segmentation. For conventional dynamic analysis, we calculated the mean initial signal increase and postinitial course of all voxels included in a lesion. Secondly, all voxels within the lesions were assigned to 4 clusters using minimal-free-energy vector quantization. Dynamic and morphologic criteria were summarized in a diagnostic score and evaluated by receiver operating characteristic analysis.

RESULTS

In the present collection of small lesions, morphologic criteria [area under the curve (AUC) = 0.610] were inferior to dynamic criteria in the detection of breast cancer. Dynamic analysis with vector quantization (AUC = 0.760) presented slightly better results compared with standard dynamic analysis (AUC = 0.693). There was no benefit for combined morphologic and dynamic analysis.

CONCLUSION

In small MR-mammographic lesions, dynamic analysis with vector quantization alone tends to result in a higher diagnostic accuracy compared with combined morphologic and dynamic analysis.

Magnetic resonance-compatible robotic and mechatronics systems for image-guided interventions and rehabilitation: a review study

The continuous technological progress of magnetic resonance imaging (MRI), as well as its widespread clinical use as a highly sensitive tool in diagnostics and advanced brain research, has brought a high demand for the development of magnetic resonance (MR)-compatible robotic/mechatronic systems. Revolutionary robots guided by real-time three-dimensional (3-D)-MRI allow reliable and precise minimally invasive interventions with relatively short recovery times. Dedicated robotic interfaces used in conjunction with fMRI allow neuroscientists to investigate the brain mechanisms of manipulation and motor learning, as well as to improve rehabilitation therapies. This paper gives an overview of the motivation, advantages, technical challenges, and existing prototypes for MR-compatible robotic/mechatronic devices.

Magnetic resonance mammography has limited ability to estimate pathological complete remission after primary chemotherapy or radiofrequency ablation therapy

Recently, primary systemic chemotherapy has been used not only for locally advanced breast cancers but also for operable cases for which adjuvant chemotherapy is necessary. Moreover, various kinds of ablation therapies have been tried to treat early breast cancer non-surgically, such as radiofrequency ablation (RFA), interstitial laser surgery, cryosurgery and focused ultrasound surgery (FUS). If pathological complete remission (pCR) can be correctly assessed by magnetic resonance mammography (MRM) or ultrasonography (US), a non surgical approach can be used for treatment. MRM is now widely used to assess the effect of chemotherapy in the neoadjuvant setting. However, the ability of MRM to estimate pCR is not yet sufficient to allow a non-surgical approach to breast cancer. Conversely, ultrasonography (US) might over-diagnose fibrous change as residual invasive cancer. If both MRM and US reveal no abnormal finding, there might be no residual cancer on pathological examination. However, such circumstances are encountered in only 2-3% of cases given the neoadjuvant treatment. Other cases, such as US showing residual disease in spite of pCR on MRM, have some potential for false positivity. Therefore, US-guided needle biopsy, especially vacuum-assisted breast biopsy, might be suitable to judge whether true pCR was achieved in the targeted lesion.

MRI-Guided percutaneous biopsy of breast lesions: materials, techniques, success rates, and management in patients with suspected radiologic-pathologic mismatch

MR imaging of the breast allows the detection of suspicious breast lesions that are occult at mammography and ultrasound. For the histologic verification of such lesions, percutaneous MR imaging-guided biopsy techniques can now be offered as an alternative to open breast biopsy. This review focuses on the currently available devices and techniques for MR imaging-guided percutaneous breast biopsy and reports their achievable diagnostic accuracy. Technical success rates and strategies for patient management are also outlined. In addition, new developments in MR imaging-guided minimally invasive therapeutic interventions are discussed, as well as the potential for research opportunities and directions.

Evaluation of the Stereotactic 8G Vacuum-Assisted Breast Biopsy in the Histologic Evaluation of Suspicious Mammography Findings (BI-RADS IV)

PURPOSE

The purpose of this study was to evaluate the potential of the new 8G stereotactic vacuum-assisted breast biopsy (ST-driver, Mammotome; Ethicon Endosurgery) in the histologic evaluation of BI-RADS IV microcalcifications.

MATERIALS AND METHODS

Fifty-eight patients with 61 mammographic BI-RADS IV microcalcifications underwent stereotactic vacuum-assisted breast biopsy (SVAB). The new 8G system was mounted on the ST driver, which was formerly used only with the hand-held version under sonographic guidance. The evaluation criteria for each biopsy were minimally invasive and operative histologies, the time needed for biopsy, the amount of bleeding, number of rotations and specimen, the degree of resection, and the complications.

RESULTS

Fifty-eight of 61 biopsies were technically successful because > or = 50% were resected (29 x 100%, 8 x 90%, 5 x 80%, 6 x 70%, 3 x 50%, 3 x 0%). In 7 cases with representative biopsies of segmental suspicious microcalcifications, the degree of resection could not be exactly measured. All but 2 biopsies were performed without clinically relevant complications and after gaining enough specimens (Ø 12.6 specimen, 1.85 rotations). Those 2 patients showed evidence of severe bleeding into the breast tissue and operative revision had to be performed (3.5%). The size of intramammary hematoma was measurable in 27 biopsies and showed a range from 0.5 to 5 cm (Ø 2.7 cm). The average external bleeding was still low with 16 mL (5-80 mL). In 3 of 61 lesions, it was not possible to gain representative tissue as a result of displacement of the lesion after introducing or shooting the needle. The average time needed for all biopsies was 28.2 minutes for all but 5 very complicated biopsies, which took 16.1 minutes. The histologic findings with further operative workup were: 10 ductal carcinomas in situ (DCIS), 4 atypical ductal hyperplasias, 1 atypical lobular hyperplasias (ALH), 3 lobular carcinomas in situ (LCIS), and 6 invasive ductal carcinomas. In 7 of 12 of the initial DCIS histologies, the operative histology was also DCIS, whereas in 4 of 12, no residual malignant tumor was found. In 1 of 12 patients with an initial DCIS histology, operative histology revealed invasive ductal cancer (8.3%). The cases with lobular lesions (ALH, LCIS) did not show any evidence for residual tissue in the operative workup. Most frequent benign histologies were mastopathy (13), ductal hyperplasia (9), fibroadenoma (8), and sclerosing adenosis (5). The control examinations (maximum 1 year) did not show any signs for a false-negative biopsy.

CONCLUSION

The 11-G SVAB has proven to be a perfect adjunct to the existing breast biopsy methods. The new 8G SVAB speeds up the method when used for the same size of lesions and enables the user to representatively biopsy lesions up to 3 cm in diameter. The method is still minimally invasive; however, the amount of hematomas as well as clinically relevant complications is increased.