Biomedical subjects

R Kikinis

Publications and source records attributed to R Kikinis.

161 records · Page 9Linked to original sources

PubMedDate not supplied

Monitoring and visualization techniques for MR-guided laser ablations in an open MR system.

Our purpose was to develop temperature-sensitive MR sequences and image-processing techniques to assess their potential of monitoring interstitial laser therapy (ILT) in brain tumors (n = 3) and liver tumors (n = 7). ILT lasted 2 to 26 minutes, whereas images from T1-weighted fast-spin-echo (FSE) or spoiled gradient-recalled (SPGR) sequences were acquired within 5 to 13 seconds. Pixel subtraction and visualization of T1-weighted images or optical flow computation was done within less than 110 msec. Alternating phase-mapping of real and imaginary components of SPGR sequences was performed within 220 msec. Pixel subtraction of T1-weighted images identified thermal changes in liver and brain tumors but could not evaluate the temperature values as chemical shift-based imaging, which was, however, more affected by susceptibility effects and motion. Optical flow computation displayed the predicted course of thermal changes and revealed that the rate of heat deposition can be anisotropic, which may be related to heterogeneous tumor structure and/or vascularization.

Brain Neoplasms↗

PubMedDate not supplied

MRI monitoring of laser ablation using optical flow.

The optical flow method is used for visualizing and quantifying the dynamics of tissue changes observed by MRI during thermal ablations. An approach was implemented for parallel two-dimensional optical flow calculations including the replacement of spurious velocities. Velocity magnitude results were found to be accurate in low-noise cases in tests using series of synthetic images. Optical flow results are presented from thermal ablation experiments utilizing a homogeneous polyacrylamide gel phantom and heterogeneous rabbit liver tissue in vivo, exhibiting heating and cooling with the accompanying quantitative characterization of the dilation and contraction of the thermally affected region. Results demonstrate that optical flow is capable of noninvasive real-time monitoring and control of interstitial laser therapy (ILT).

Acrylic Resins↗

PubMedDate not supplied

The auditory N2 component in schizophrenia: relationship to MRI temporal lobe gray matter and to other ERP abnormalities.

The N2 component of the auditory event-related potential (ERP) indexes cognitive processes involved in the categorization of deviant stimuli. Although N2 amplitude and latency abnormalities have been reported in schizophrenia, their relationship to MRI structural changes, clinical status, and P3 abnormalities has not been defined. We therefore studied the auditory N2 and P3 components elicited by an oddball paradigm in 15 right-handed male subjects with schizophrenia and 14 control subjects who had quantitative MRI measures of temporal lobe gray-matter structures. To provide a methodological comparison, we measured the auditory N2 from both the target ERP (N2t) and the target-minus-frequent ERP difference (N2d) waveforms. Both N2t and N2d amplitude were bilaterally reduced in schizophrenics, with N2d showing a more pronounced reduction. Within the schizophrenic group, N2 amplitude reduction was associated with reduction in gray-matter volume of the left superior temporal gyrus (STG) and of medial temporal lobe structures bilaterally, and clinically, with greater chronicity. P3 amplitude, in contrast, correlated only with left posterior STG volume, and was more prominently associated with delusions and thought disorder. These findings suggest that the N2 and P3 components, though occurring sequentially in the ERP, tap separable anatomic and behavioral abnormalities in schizophrenia.

Adult↗

PubMedDate not supplied

Aortic flow velocity patterns in chronic aortic regurgitation: implications for Doppler echocardiography.

Aortic regurgitation is associated with retrograde diastolic flow in the aorta. Echocardiographic quantitative analysis of the magnitude of the flow reversal is believed to provide an estimate of severity of regurgitant disease despite variations in flow profiles. The purpose of this study was to evaluate the uniformity of flow patterns in the aorta of patients with aortic regurgitation and to investigate the relationship between these profiles and the echocardiographic estimates of flow reversal. Seventeen patients with chronic aortic regurgitation underwent cine-phase magnetic resonance imaging in an axial section through the ascending and descending aorta. The regurgitant fraction in the ascending aorta 4 cm above the aortic valve and the descending aorta were calculated from the velocity maps. These results were compared with data from nine individual sample volumes in the ascending and descending aorta. The magnetic resonance ascending aortic regurgitant fraction was compared with Doppler echocardiographic descending aortic flow velocity patterns. The descending aortic regurgitant fraction correlated only weakly with the ascending aortic regurgitant fraction (descending aortic regurgitant fraction = 0.62% ascending aortic regurgitant fraction + 0.04%; r = 0.75; p < 0.001). Regurgitant proportions in all sample volumes in the descending aorta, but not in the ascending aorta, were significantly related to the ascending aortic regurgitant fraction. The best descending aortic Doppler echocardiographic parameter for predicting ascending aortic regurgitant fraction was the end-diastolic velocity (end-diastolic velocity = 32.2 cm/sec. ascending aortic regurgitant fraction + 1.4 cm/sec; r = 0.94; p < 0.001). Pulsedwave Doppler sampling of descending aortic flow reflects severity of aortic regurgitant disease, in part the result of more uniform blood-velocity profiles in the descending aorta compared with the ascending aorta. The Doppler end-diastolic velocity in the descending aorta is a useful parameter of severity of aortic regurgitation.

Aorta↗

PubMedDate not supplied

Computer-based imaging and interventional MRI: applications for neurosurgery.

Advances in computer technology and the development of open MRI systems definitely enhanced intraoperative image-guidance in neurosurgery. Based upon the integration of previously acquired and processed 3D information and the corresponding anatomy of the patient, this requires computerized image-processing methods (segmentation, registration, and display) and fast image integration techniques. Open MR systems equipped with instrument tracking systems, provide an interactive environment in which biopsies and minimally invasive interventions or open surgeries can be performed. Enhanced by the integration of multimodal imaging these techniques significantly improve the available treatment options and can change the prognosis for patients with surgically treatable diseases.

Biopsy↗

PubMedDate not supplied

Developmental stages of human brain: an MR study.

The differentiation of the telencephalon (TC) gyri and the myelination of TC and diencephalon were analyzed quantitatively in 50 children, 32-240 weeks' postconceptional age (PCA). For this purpose, a four-stage grading system was developed by correlating magnetic resonance images from age-matched postmortem brains with subsequently prepared myelin-stained macroslices. Gyration and myelination progressed in a occipito-rostral direction. Stages 3 and 4 myelination were recognized earlier on T1-weighted images [spin echo (SE) 500/30] than on T2-weighted images (SE 3,000/120). However, long repetition time/echo time sequences yielded better contrast and allowed finer differentiation between myelinated and nonmyelinated structures. At term, the posterior limb of the internal capsule was generally myelinated (stage 2), whereas in 50% of the children, myelin appeared in the TC between 55 and 65 weeks' PCA, e.g., between 3 and 6 months postnatally. The morphological differentiation of the brain surface preceded the biochemical maturation (myelination) by an average of 12 months. Applying such a grading system to a larger population will help establish normal standards for brain maturation and a "brain age" scale during the first 4 years of life.

Brain↗

PubMedDate not supplied

MR imaging of brain maturation in normal and developmentally handicapped children.

White matter myelination was assessed in the frontal, temporal, and occipital lobes and in the internal capsule in 91 neurodevelopmentally handicapped infants on T2-weighted images (spin echo 3,000/120 ms) and compared with myelination scores from 53 normal control subjects. Clinical diagnosis was birth asphyxia (34), seizures with delays of various causes (33), congenital infections (15), and intracerebral hemorrhages (9). Myelination in the total group of patients was generally delayed. However, we found distinct differences in myelin deposition between groups. Myelination of handicapped children with seizures or with intrauterine infections was retarded most severely at all ages. Children with intracerebral hemorrhages were almost never significantly different from normals in any part of the brain, whereas children with birth asphyxia had myelination scores in between. We conclude that magnetic resonance staging of developmental processes, such as myelination, in the infants' brain helps to recognize delays at an early age.

Asphyxia Neonatorum↗

PubMedDate not supplied

Three-dimensional segmentation of MR images of the head using probability and connectivity.

We describe a three-dimensional (3D) segmentation method that comprises (a) user interactive identification of tissue classes; (b) calculation of a probability distribution for each tissue; (c) creation of a feature map of the most probable tissues; (d) 3D segmentation of the magnetic resonance (MR) data; (e) smoothing of the segmented data; (f) extraction of surfaces of interest with connectivity; (g) generation of surfaces; and (h) rendering of multiple surfaces to plan surgery. Patients with normal head anatomy and with abnormalities such as multiple sclerosis lesions and brain tumors were scanned with a 1.5 T MR system using a two echo contiguous (interleaved), multislice pulse sequence that provides both proton density and T2-weighted contrast. After the user identified the tissues, the 3D data were automatically segmented into background, facial tissue, brain matter, CSF, and lesions. Surfaces of the face, brain, lateral ventricles, tumors, and multiple sclerosis lesions are displayed using color coding and gradient shading. Color improves the visualization of segmented tissues, while gradient shading enhances the perception of depth. Manipulation of the 3D model on a workstation aids surgical planning. Sulci and gyri stand out, thus aiding functional mapping of the brain surface.

Algorithms↗

PubMedDate not supplied

3D surface rendered MR images of the brain and its vasculature.

Both time-of-flight and phase contrast magnetic resonance angiography images are combined with stationary tissue images to provide data depicting two contrast relationships yielding intrinsic discrimination of brain matter and flowing blood. A computer analysis is based on nearest neighbor segmentation and the connection between anatomical structures to partition the images into different tissue categories: from which, high resolution brain parenchymal and vascular surfaces are constructed and rendered in juxtaposition, aiding in surgical planning.

Algorithms↗

PubMedDate not supplied

Semiautomated ROI analysis in dynamic MR studies. Part I: Image analysis tools for automatic correction of organ displacements.

The most important problem in the analysis of time sequences is the compensation for artifactual motion. Owing to motion, medical images of the abdominal region do not represent organs with fixed configuration. Analysis of organ function with dynamic contrast medium studies using regions of interest (ROIs) is thus not readily accomplished. Images of the organ of interest need to be registered and corrected prior to a detailed local analysis. We have developed an image analysis scheme that allows the automatic detection of the organ contours, the extraction of the motion parameters per frame, and the registration of images. The complete procedure requires only minimal user interaction and results in a readjusted image sequence, where organs of interest remain fixed. Both a visual analysis of the dynamic behavior of functional properties and a quantitative statistical analysis of signal intensity versus time within local ROIs are considerably facilitated using the corrected series.

Algorithms↗

PubMedDate not supplied

Computer-assisted quantification of periaxial bone rotation from X-ray CT.

PURPOSE: Numerous orthopedic disorders involve periaxial rotation of long bones. We have developed and evaluated a computer-assisted method that segments a bone from X-ray CT, graphically unwraps the bone around its long axis into a surface plot (signature landscape), and measures periaxial rotation as the translation shift of the landscape. Bones in known rotations and partially segmented surfaces were used, respectively, to test accuracy and problematic situations in bone segmentation. METHOD: CT images of three chicken femora at known rotations were analyzed to determine their relative periaxial rotations, which were compared with the known rotations. RESULTS: The regression slope between measured and expected periaxial rotations was 1.005 +/- 0.003, with a maximum discrepancy of 2 degrees for same-bone and 3 degrees for interbone comparisons. Rasterization artifacts and the use of partial surfaces (with < 40% surface omission) resulted in a < 3 and < 1 degree error, respectively. CONCLUSION: The current method provides accurate and objective periaxial rotation measurements of a long bone.

Animals↗

PubMedDate not supplied

Local maximum intensity projection (LMIP): a new rendering method for vascular visualization.

PURPOSE: The purpose of our study was to demonstrate a new visualization method (local maximum intensity projection; LMIP) that can clearly depict densitometric as well as geometric information in vascular visualization from 3D data such as obtained from MR and CT angiography. METHOD: LMIP is an extended version of maximum intensity projection (MIP). However, LMIP differs from MIP in that the latter method selects the maximum value along an optical ray, whereas LMIP selects the first local maximum value encountered that is larger than a preselected threshold value along an optical ray from a viewpoint in the viewing direction. RESULTS AND CONCLUSION: Examples are presented in which LMIP is used to visualize renal vessels from CT angiography data and cerebral vessels in the vicinity of an aneurysm from phase-contrast MR angiography data. We demonstrate that LMIP can clearly depict geometric information, as shaded surface display does, and densitometric information, as is done by volume rendering, in a straightforward and objective manner.

Angiography↗

PubMedDate not supplied

Three-dimensional optical flow method for measurement of volumetric brain deformation from intraoperative MR images.

A three-dimensional optical flow method to measure volumetric brain deformation from sequential intraoperative MR images and preliminary clinical results from five cases are reported. Intraoperative MR images were scanned before and after dura opening, twice during tumor resection, and immediately after dura closure. The maximum cortical surface shift measured was 11 mm and subsurface shift was 4 mm. The computed deformation field was most satisfactory when the skin was segmented and removed from the images before the optical flow computation.

Adult↗

PubMedDate not supplied

Temporal lobe abnormalities in a patient with schizophrenia who has word-finding difficulty: use of high-resolution magnetic resonance imaging and auditory P300 event-related potentials.

Postmortem, magnetic resonance, and event-related potential studies suggest the presence of temporal lobe abnormalities in schizophrenia. Analyses using convergent measurements of brain structure and function, however, have rarely been done in the same patients. We recently developed a protocol using high-spatial-resolution magnetic resonance scans, auditory P300 event-related potentials, and thought disorder scales to examine temporal lobe structure and function in the same patients. We report a case of schizophrenia that showed left-lateralized volume reduction in the superior temporal gyrus, hippocampus, and parahippocampal gyrus (also on right), with associated P300 amplitude reduction and thought disorder marked by word-finding difficulties and perseverations.

Anomia↗

PubMedDate not supplied

Development of the acetabulum in patients with slipped capital femoral epiphysis: a three-dimensional analysis based on computed tomography.

Orientation and shape of the acetabulum were determined by the use of three-dimensional reconstruction of computed tomography (CT) data sets in 22 patients with a total of 30 slipped capital femoral epiphyses. We developed an interactive three-dimensional software program to measure the anteversion and inclination of the acetabulum without projectional and pelvis-tilting errors. Furthermore, we determined the height, width, depth, volume, and surface of the acetabulum as parameters describing the acetabular shape. Comparison of the affected side with the contralateral unaffected hip showed no significant differences for acetabular orientation and shape. The relationship between the degree of the slip and the acetabular orientation was calculated. No correlation was found. Based on the results of this study, we conclude that the slipping of the capital femoral epiphysis has no influence on acetabular development.

Acetabulum↗

PubMedDate not supplied

Three-dimensional analysis of the proximal femur in patients with slipped capital femoral epiphysis based on computed tomography.

A three-dimensional (3D) analysis based on computed tomography was performed to study the 3D geometry of the proximal femur in cases of slipped capital femoral epiphysis (SCFE). For this purpose, new interactive software was developed to analyze hip joint geometry using 3D models without pelvis tilting and projected errors. Twenty-two patients, 8 girls and 14 boys, with a total of 30 slipped capital femoral epiphyses, were reviewed. In the affected hips, we observed a reduced femoral anteversion of 7.0 degrees (vs. 12.7 degrees) and a reduced femoral shaft neck angle of 134.2 degrees (vs. 141.0 degrees). In response to these results, we suggest that an SCFE is associated with reduced femoral anteversion and a reduced femoral shaft neck angle.

Adolescent↗

PubMedDate not supplied

Variations in levator ani volume and geometry in women: the application of MR based 3D reconstruction in evaluating pelvic floor dysfunction.

OBJECTIVE: We report on the comparative 3-dimensional (3D) living female pelvic floor geometry in five women, comparing the volume, morphology, and integrity of the levator sling, and pelvic anatomic relationships among study subjects. METHODS: Five women of varying ages, parity, continence, and prolapse status were studied. Two-dimensional (2D) imaging of the pelvic floor organs was performed on each subject in the supine position. Manual segmentation techniques and solid modeling software was used to build 3D models of each patient's pelvic floor structures, which could then be viewed and measured on the computer screen. We measured levator muscle volume, posterior urethro-vesical angle, distance from the urethra to pubo-coccygeal line, and the levator plate angle. The integrity of pubo-coccygeal attachments was also recorded. RESULTS: Levator muscle volume ranged from 68 ml in the nulliparous female, to 26 ml in the grand multipara with severe prolapse and mild genuine stress incontinence (GSI). The second lowest volume (30 ml) was in the multipara with GSI. Volumes in the parous subjects without stress urinary incontinence or pelvic organ prolapse were 36 and 39 ml. Pubo-coccygeal attachments were found to be torn in the 2 symptomatic subjects, and were intact in all 3 asymptomatic subjects. CONCLUSION: MR based 3D modeling is feasible and can be used in a research setting to evaluate complex anatomic relationships which may accompany pelvic floor dysfunction. The technique can also be used to evaluate levator muscle morphology and volume, as well as pelvic floor support integrity and its possible role in GSI and prolapse. We are currently conducting a larger study to validate our technique, and to better define the relationship between pelvic floor geometry and pelvic floor dysfunction.

Adult↗