An integrated visualization system for surgical planning and guidance using image fusion and an open MR

Advanced computer assistance for magnetic resonance-guided microwave thermocoagulation of liver tumors

RATIONALE AND OBJECTIVES

The purpose of this study was to utilize computer assistance effectively for both easy and accurate magnetic resonance (MR) image-guided microwave thermocoagulation therapy of liver tumors.

MATERIALS AND METHODS

An open configuration MR scanner and a microwave coagulator at 2.45 GHz were used. Navigation software, a 3D Slicer, was customized to combine fluoroscopic MR images and preoperative MR images for the navigation. New functions to display MR temperature maps with simple parameter setting, and to record and display the coagulated areas by multiple microwave ablations in the 3-dimensional space (footprinting), were also introduced into the software. The VGA signal of the computer display was directly transferred to the surgeon's monitor.

RESULTS

The customized software could be used for both accurate image navigation and convenient and easy temperature monitoring. Because repeated punctures and ablations are usually required in this procedure, the footprinting function made targeting of the tumors both easy and accurate and was quite effective in achieving the necessary and sufficient treatment. Furthermore, clear display on the surgeon's monitor, which was obtained by direct transfer of the VGA signal, enabled precise image navigation.

CONCLUSION

The newly developed computer assistance was quite useful and helpful for this MR-guided procedure.

Segmentation and visualization of nasopharyngeal carcinoma using MRI

In this study, a semi-automatic system was developed for nasopharyngeal carcinoma (NPC) tumor segmentation, volume measurement and visualization using magnetic resonance imaging (MRI). Some novel algorithms for tumor segmentation from MRI and inter-slice interpolation were integrated in this medical diagnosis system. This system was applied to 10 MR image data sets of NPC patients and satisfactory results were achieved. This system can be used as a clinical image analysis tool for doctors or radiologists to obtain tumor location from MRI, tumor volume estimation, and 3D information.

Display of fused images: methods, interpretation, and diagnostic improvements

The use of integrated visualization for medical images aims at assisting clinicians in the difficult task of mentally translating and integrating medical image data from multiple sources into a three-dimensional (3D) representation of the patient. This interpretation of the enormous amount and complexity of contemporary, multiparameter, and multimodal image data demands efficient methods for integrated presentation. This article reviews methods for fused display with the main focus on integration of functional with anatomical images. First, an overview of integrated two-dimensional (2D) and 3D medical image display techniques is presented, and topics related to the interpretation of the integrated images are discussed. Then we address the key issue for clinical acceptance, ie, whether these novel visualization techniques lead to diagnostic improvements. Methods for fused display appear to be powerful tools to assist the clinician in the retrieval of relevant information from multivariate medical image data. Evaluation of the different methods for fused display indicates that the diagnostic process improves, notably as concerns the anatomical localization (typically of functional processes), the registration procedure, enhancement of signal, and efficiency of information presentation (which increases speed of interpretation and comprehension). Consequently, fused display improves communication with referring specialists, increases confidence in the observations, and facilitates the intra- and intersubject comparison of a large part of the data from the different sources, thereby simplifying the extraction of additional, valuable information. In most diagnostic tasks the clinician is served best by providing several (interactive and flexible) 2D and 3D methods for fused display for a thorough assessment of the wealth of image information from multiple sources.

Surgical navigation in the open MRI

The introduction of MRI into neurosurgery has opened multiple avenues, but also introduced new challenges. The open-configuration intraoperative MRI installed at the Brigham and Women's Hospital in 1996 has been used for more than 500 open craniotomies and beyond 100 biopsies. Furthermore the versatile applicability, employing the same principles, is evident by its frequent use in other areas of the body. However, while intraoperative scanning in the SignaSP yielded unprecedented imaging during neurosurgical procedures their usage for navigation proved bulky and unhandy. To be fully integrated into the procedure, acquisition and display of intraoperative data have to be dynamic and primarily driven by the surgeon performing the procedure. To use the benefits of computer-assisted navigation systems together with immediate availability of intraoperative imaging we developed a software package. This "3D Slicer" has been used routinely for biopsies and open craniotomies. The system is stable and reliable. Pre- and intraoperative data can be visualized to plan and perform surgery, as well as to accommodate for intraoperative deformations, "brain shift", by providing online data acquisition.

Future perspectives in intraoperative imaging

Of all the advances in imaging science in the past twenty years, none has had a greater impact than Magnetic Resonance Imaging. Since its introduction as a diagnostic tool in the mid-1980's, MRI has evolved into the premier neuroimaging modality, and with the addition of higher field magnets, we are able to achieve spatial resolution of such superb quality that even the most exquisite details of the brain anatomy can be visualized. With the implementation of intraoperative, neurosurgical MRI, we can not only monitor brain shifts and deformations; we can achieve intraoperative navigation using intraoperative image updates. In the future, intraoperative MRI can be used not only to localize, target, and resect brain tumors and other lesions but also to fully comprehend the surrounding cortical and white matter functional anatomy. In addition to the inclusion of new imaging methods such as diffusion tensor imaging, new therapeutic methods will be applied. Especially encouraging are the promising results in MRI-guided Focused Ultrasound Surgery, in which the non-invasive thermal ablation of tumors is monitored and controlled by MRI. With the clinical introduction of these advances, intraoperative MRI is changing the face of Neurosurgery today.

De novo cerebellar medulloblastoma in a 26-year recurrence-free case of temporal glioblastoma multiforme

The authors describe a patient who survived 26 years after resection of a right temporal glioblastoma multiforme (GBM) without signs of tumor recurrence. Preoperative emergency angiography demonstrated a hypovascular mass localized in the right temporal lobe with right-to-left shift of the vascular structures. At surgery, the tumor had cystic and solid components localized in the lateral occipitotemporal gyrus, reaching the posterolateral wall of the inferior horn of the right lateral ventricle and extending to the trigone and posterior horn. The initial pathological diagnosis of a GBM was reviewed and confirmed throughout the follow-up period. Twenty-six years after surgery and subsequent radiosurgery, the patient underwent resection of a medulloblastoma localized in the right cerebellum as well as stereotactic biopsy sampling of tissue at the original GBM site. Neither radiological nor histological evidence of recurrence of the GBM could be documented. The intraoperative, histological, and radiological findings are described.

Three-dimensional magnetic resonance imaging assessment of levator ani morphologic features in different grades of prolapse

OBJECTIVE

The study was undertaken to identify the morphologic changes in the levator ani in different grades of prolapse by using reconstructed three-dimensional models of magnetic resonance images (MRI) and to subclassify prolapse into different categories on the basis of their levator ani morphologic characteristics.

STUDY DESIGN

Sixty-one women were studied, 8 women in stage I, 15 women in stage II, 22 women in stage III, 7 women in stage IV prolapse, and 9 asymptomatic volunteers with stage 0 prolapse. Axial, sagittal, and coronal T2-weighted pelvic magnetic resonance scans were obtained with the patient in the supine position. The three-dimensional models were reconstructed from the source images by using manual segmentation and surface modeling. The morphologic characteristics of the puborectalis were assessed on these reconstructed models by measuring (1). the levator symphysis gap, (2). the width of the levator hiatus, and (3). the length of the levator hiatus. To assess the iliococcygeus, we measured (1). the maximum width of the iliococcygeus, (2). the direction of its fibers that was assessed by measuring the iliococcygeal angle, and (3) the levator plate angle. Nine nulliparous asymptomatic women were studied as controls.

RESULTS

Alterations in levator ani morphologic features are not dependent on the grade of the prolapse, and not all women with pelvic floor prolapse have abnormal morphologic features. In healthy control subjects, the iliococcygeal width measured less than 40 mm and the iliococcygeal angle measured less than 20 degrees. On the basis of the MRI findings, four patterns of changes in the levator ani have been identified. Both the levator symphysis gap and the levator hiatus, which is dependent on the puborectalis function, widen with increasing grade of prolapse.

CONCLUSION

It is possible to subclassify prolapse on the basis of morphologic changes in the levator ani by using MRI. This may be a very useful predictor as to which patients have recurrent prolapse develop after surgery.

Reconstruction and web distribution of measurable arterial models

In this paper a novel framework for the segmentation, 3D reconstruction and web distribution of vessel structures specifically tailored to the assessment of abdominal aortic aneurysms for endovascular surgery planning is presented. Deformable models are used for segmentation, while VRML97 and ECMA scripting are used to obtain models that are not only viewable from any VRML97 enabled browser, but that also allow users to perform, directly from standard web browsers, guided measurements of geometrical parameters, relevant to surgical planning.

New assistive devices for MR-guided microwave thermocoagulation of liver tumors

RATIONALE AND OBJECTIVES

The purpose of this study was to develop and test new assistive devices to aid in the performance of safe, easy, and accurate microwave thermocoagulation therapy guided by magnetic resonance (MR) imaging.

MATERIALS AND METHODS

An open-configuration MR imager with an optical tracking system for image plane control and a microwave coagulator operating at 2.45 GHz were used. Liver tumors were percutaneously punctured under the guidance of MR images and ablated. Handpiece adapters were then prepared for the optical tracking system. An MR-compatible endoscopic system also was used. Navigation software was installed and customized. These devices were combined to provide near-real-time MR image-guided navigation during thermocoagulation therapy for liver tumors.

RESULTS

The handpiece adapters improved the flexibility of approaches for percutaneous puncture of tumors. The MR-compatible endoscope was used as a thoracoscope, and tumors just below the diaphragm were safely and easily punctured through the diaphragm. The customized navigation software displayed near-real-time MR images together with two reformatted images (on the same plane and on a perpendicular plane) from the registered high-resolution three-dimensional data, enabling accurate MR imaging navigation.

CONCLUSION

These new assistive devices made it easier to perform safe, easy, and accurate MR-guided thermocoagulation therapy of liver tumors.

Incorporating Non-rigid Registration into Expectation Maximization Algorithm to Segment MR Images

The paper introduces an algorithm which allows the automatic segmentation of multi channel magnetic resonance images. We extended the Expectation Maximization-Mean Field Approximation Segmenter, to include Local Prior Probability Maps. Thereby our algorithm estimates the bias field in the image while simultaneously assigning voxels to different tissue classes under prior probability maps. The probability maps were aligned to the subject using nonrigid registration. This allowed the parcellation of cortical sub-structures including the superior temporal gyrus. To our knowledge this is the first description of an algorithm capable of automatic cortical parcellation incorporating strong noise reduction and image intensity correction.

Feasibility of MR imaging-guided breast lumpectomy for malignant tumors in a 0.5-T open-configuration MR imaging system

RATIONALE AND OBJECTIVES

The authors performed this study to develop the technology for and evaluate the utility of a 0.5-T vertical open-configuration magnetic resonance (MR) imaging system for imaging-guided breast lumpectomy of malignant tumors.

MATERIALS AND METHODS

Twenty women with breast cancer underwent MR imaging-guided lumpectomy in a 0.5-T vertical open-configuration MR system. During lumpectomy, pre- and postresection images were acquired with and without contrast material. Images were used both for tumor localization and to monitor resection. If residual enhancement was observed, additional resection was performed in an effort to secure negative pathologic margins.

RESULTS

The procedure evolved over time with technology innovations and improvements. Specifically, instruments were acquired that were compatible with MR imaging breast procedures, the echo time with the Dixon technique was modified to optimize image quality, contrast material injection was timed for maximum lesion enhancement, breath-hold image acquisition was instituted, and the biopsy cavity was filled with saline and the incision closed before image acquisition.

CONCLUSION

All breast lesions were identified despite limited spatial resolution and fat-suppression techniques. The evolved techniques facilitated intraoperative margin evaluation and prompted additional surgical margin resection in five patients, sparing four from an additional surgical procedure. Intraoperative MR imaging has the potential to improve the complete pathologic excision of invasive breast cancer.

SMART-PET: multimodality white matter imaging and display without loss of quantitative information

PURPOSE

To improve analysis of cerebral white matter (WM) in fluoro-deoxy-glucose positron emission tomography (PET) images.

MATERIALS AND METHODS

A multimodality analysis technique (segmented MRI and registered Talairach-transformed PET [SMART-PET]) was used for quantitative assessment of WM metabolism. Data processing included Talairach transformation of three-dimensional magnetic resonance imaging (MRI) and subsequent automated segmentation and coregistration to normalized PET images. Color model transformations were used for combined display: the hue saturation value color model was regarded as a three-dimensional data matrix, integrating quantitative voxel data of both modalities. The technique was applied in normal subjects and in patients suffering from different WM diseases. Regional analysis was performed to classify metabolic impairment on a five-point scale.

RESULTS

Using SMART-PET, a considerable gain in image contrast for WM was achieved in all cases. In the normal subjects, WM metabolism was shown to be homogeneously unimpaired. Sum scores of regional analysis revealed metabolic WM changes in all patients. Extent of WM hypometabolism exceeded the extent of the lesions as delineated by MRI signal changes.

CONCLUSION

The potential of the method for further elucidation of the role of WM diseases in brain dysfunction in patients is discussed.

Linear measurements in 2-dimensional pelvic floor imaging: the impact of slice tilt angles on measurement reproducibility

OBJECTIVE

Magnetic resonance imaging techniques have improved the study of female pelvic dysfunction. However, disagreements between magnetic resonance measurements and their derived 3-dimensional reconstructions were noted. We tested the hypothesis that these discrepancies stemmed from variations in magnetic resonance acquisition angle.

STUDY DESIGN

Images from the pelvis of the Visible Human Female (a thinly sliced cadaveric image data set) were obtained. Slices in the axial plane were rotated around pivot points in the pelvis to yield a set of similar-appearing para-axial images. A parameter that described the maximum anterior-posterior dimension of the levator hiatus was defined. This levator hiatus parameter was measured on all of the rotated images and compared with an expected value that was calculated from trigonometry. The levator hiatus was also measured on a group of similar-appearing slices rotated slightly around a defined point.

RESULTS

In 1 group of slices, expected levator hiatus variation was 1.5 to 6.1%, whereas measured variation was 4% to 15%. Among the similar-appearing rotated slices, 4.8% to 16.0% variations were seen in the levator hiatus.

CONCLUSION

Identical measurements made on radiologic images can vary widely. Slice acquisition must be standardized to avoid errors in data comparison.