Biomedical subjects

R Kikinis

Publications and source records attributed to R Kikinis.

At least 55 records · Page 3Linked to original sources

PubMed2001

MR imaging-guided prostate biopsy with surgical navigation software: device validation and feasibility.

Magnetic resonance (MR) imaging--guided prostate biopsy in a 0.5-T open imager is described, validated in phantom studies, and performed in two patients. The needles are guided by using fast gradient-recalled echo and T2-weighted fast spin-echo images. Surgical navigation software provided T2-weighted images critical to targeting the peripheral zone and the tumor. MR imaging can be used to guide prostate biopsy.

Biopsy, Needle↗

PubMed2001

A functional magnetic resonance imaging study of auditory mismatch in schizophrenia.

OBJECTIVE: Previous research has noted functional and structural temporal lobe abnormalities in schizophrenia that relate to symptoms such as auditory hallucinations and thought disorder. The goal of the study was to determine whether the functional abnormalities are present in schizophrenia at early stages of auditory processing. METHOD: Functional magnetic resonance imaging activity was examined during the presentation of the mismatch stimuli, which are deviant tones embedded in a series of standard tones. The mismatch stimuli are used to elicit the mismatch negativity, an early auditory event-related potential. Ten patients with schizophrenia and 10 comparison subjects were presented the mismatch stimuli condition and a control condition in which only one tone was presented repeatedly. RESULTS: The superior temporal gyrus showed the most prevalent and consistent activation. The superior temporal gyrus showed less activation in the schizophrenic subjects than in the comparison subjects only during the mismatch stimuli condition. CONCLUSIONS: This result is consistent with those of mismatch negativity event-related potential studies and suggests that early auditory processing is abnormal in chronic schizophrenia.

Acoustic Stimulation↗

PubMed2001

Impaired cerebral cortical gray matter growth after treatment with dexamethasone for neonatal chronic lung disease.

OBJECTIVE: The specific aim of this study was to quantify at term the influence of postnatal systemic dexamethasone treatment for neonatal chronic lung disease on subsequent brain growth and development in premature infants without evidence of severe intraventricular hemorrhage or white matter injury. METHODS: Eighteen premature (23 to 31 weeks) infants, 7 treated with dexamethasone and 11 not treated, were studied at term, ie, 38 to 41 postconceptional weeks, by an advanced quantitative volumetric 3-dimensional magnetic resonance imaging (MRI) technique to quantify cerebral tissue volumes. Fourteen healthy term infants also were studied for comparison. A sequence of image processing algorithms was used to segment each of the MRI slices into the following separate tissue classes: cerebral cortical gray matter, basal ganglia/thalami, unmyelinated white matter, myelinated white matter, and cerebrospinal fluid, all classified based on magnetic resonance signal intensity and anatomic location. A final summing of voxels for each tissue class was performed to compute absolute volumes in milliliters. RESULTS: Cerebral cortical gray matter volume in premature infants treated with dexamethasone was reduced 35% when compared with gray matter volume in premature infants not treated with dexamethasone (mean +/- standard deviation, 130.3 +/- 54.0 vs 200.6 +/- 35.1 mL, respectively). Subcortical gray matter volumes (basal ganglia and thalami) and myelinated and unmyelinated white matter volumes were not significantly different among the treated and untreated groups. However, premature infants treated with dexamethasone exhibited a reduction (30%) in total cerebral tissue volume compared with total cerebral tissue volume in both the premature infants not treated with dexamethasone and the control term infants (312.7 +/- 43.7 vs 448.2 +/- 50.2 and 471.6 +/- 36.4 mL respectively). This latter finding relates primarily to the decrease in cerebral cortical gray matter volume. CONCLUSIONS: The data suggest an impairment in brain growth, principally affecting cerebral cortical gray matter, secondary to systemic dexamethasone therapy. Although the premature infants who received dexamethasone were smaller with more severe respiratory disease, these findings are consistent with growing evidence of a potential deleterious effect of dexamethasone on neonatal brain and subsequent neurodevelopmental outcome. This apparent deleterious effect should be taken into consideration by clinicians when weighing the potential risks and benefits of this therapy for low birth weight infants with neonatal chronic lung disease.

Case-Control Studies↗

PubMed2001

Microstructural brain development after perinatal cerebral white matter injury assessed by diffusion tensor magnetic resonance imaging.

OBJECTIVE: Brain injury in premature infants is characterized predominantly by perinatally acquired lesions in the cerebral white matter (WM). The impact of such injury on the subsequent development of cerebral WM is not clear. This study uses diffusion tensor magnetic resonance imaging (MRI) to evaluate the effects of cerebral WM injury on subsequent microstructural brain development in different WM areas of the brain. METHODS: Twenty premature infants (gestational age: 29.1 +/- 1.9 weeks) were studied by conventional MRI within the first 3 weeks of life and again at term, with the addition at the latter time of diffusion tensor MRI. Ten of the preterm infants had cerebral WM injury identified by the early MRI and were matched with 10 premature infants of similar gestational age and neonatal course but with normal neonatal MRI scans. Diffusion tensor MRI at term was acquired in coronal and axial planes and used to determine the apparent diffusion coefficient, a measure of overall restriction to water diffusion, and the relative anisotropy (RA), a measure of preferred directionality of diffusion, in central WM, anterior frontal WM, occipital WM, temporal WM, and the posterior limb of the internal capsule. Diffusion vector maps were generated from the diffusion tensor analysis to define the microstructural architecture of the cerebral WM regions. RESULTS: At term, the diffusion tensor MRI revealed no difference in apparent diffusion coefficient among preterm infants with or without perinatal WM lesions. By contrast, RA, the measure of preferred directionality of diffusion and thereby dependent on development of axonal fibers and oligodendroglia, was 25% lower in central WM, the principal site of the original WM injury. However, RA was unaffected in relatively uninjured WM areas, such as temporal, anterior frontal, and occipital regions. Notably, RA values in the internal capsule, which contains fibers that descend from the injured cerebral WM, were 20% lower in the infants with WM injury versus those without. Diffusion vector maps showed striking alterations in the size, orientation, and organization of fiber tracts in central WM and in those descending to the internal capsule. CONCLUSIONS: Perinatal cerebral WM injury seems to have major deleterious effects on subsequent development of fiber tracts both in the cerebral WM and more distally. The ultimate impact of brain injury in the newborn should be considered as a function not only of tissue destruction, but also of impaired subsequent brain development.

Humans↗

PubMed2001

Neuronavigation in interventional MR imaging. Frameless stereotaxy.

The main thrust of diagnostic MR imaging is to discern normal and pathologic patient morphology and function. Intraprocedural imaging, however, serves a different goal: to furnish the surgeon or interventionalist with updates on intraoperative changes and how they may modify preintervention data. Although researchers have not established whether MR image-guided therapy can improve clinical outcomes and reduce complication rates definitively, the intraoperative and preoperative data generated will improve the ability of every neurosurgeon to navigate in the surgical field more accurately.

Brain Neoplasms↗

PubMed2000

Serial magnetic resonance imaging in multiple sclerosis: correlation with attacks, disability, and disease stage.

Serial MRI and clinical testing was performed on 45 well-defined untreated multiple sclerosis patients in different categories of disease (relapsing-remitting, progressive, stable). Up to 24 MRIs were scheduled over a 1-year period for each patient. Clinical evaluation was performed monthly and at times of attacks using the Expanded Disability Status Scale (EDSS) and the Ambulation Index (AI). MRI scans were performed both with and without gadolinium enhancement. MRI lesion volume was determined by computerized analysis and gadolinium-enhancing lesions were counted by radiologists. We observed an increase in lesion volume over 1 year in all patient groups except those classified clinically as stable. In relapsing-remitting patients there were correlations between increases in the number of gadolinium enhancing lesions and increases in EDSS and the occurrence of attacks. In chronic progressive patients, increases in lesion volume were correlated with both increases in EDSS and AI. These results demonstrate a linkage between MRI and clinical disease that depends both on the stage of MS and the MRI measures used and support the use of MRI as a surrogate marker of clinical disability in the study of multiple sclerosis.

Adult↗

PubMed2000

Changes in activated T cells in the blood correlate with disease activity in multiple sclerosis.

OBJECTIVE: To determine whether changes in activation markers on peripheral blood T cells correlate with disease activity in patients with multiple sclerosis. DESIGN: In a prospective longitudinal study during 1 year, we analyzed the change in percentage of activated T lymphocytes in the peripheral blood of 40 patients with multiple sclerosis in relation to clinical findings and changes on brain magnetic resonance imaging (MRI) scans. The patients underwent repeated imaging of the brain (mean number of MRIs for each patient, 22) at the time blood samples were obtained as well as at monthly neurological examinations, and at the time of scoring on the Kurtzke Expanded Disability Status Scale (EDSS) and ambulation index scale. RESULTS: A change in the percentage of cells expressing the activation markers interleukin 2 receptor (CD25), class II major histocompatibility complex (MHC) (I3) or surface dipeptidyl peptidase (CD26) correlated significantly with a change in lesion volume or a change in number of gadolinium-enhancing lesions as detected on MRI. Changes in CD25( +) cells and in CD4(+) cells expressing class II MHC also correlated with changes in disability as measured by EDSS in patients with relapsing-remitting disease, and changes in CD4(+)CD25(+) cells correlated with the occurrence of attacks in patients with relapsing-remitting disease. These correlations are dependent on measurement of changes between time points sampled at 1- or 2-week intervals. CONCLUSION: There is a linkage between peripheral T-lymphocyte activation as measured by cell surface markers and disease activity in patients with multiple sclerosis. Arch Neurol. 2000;57:1183-1189

Adult↗

PubMed2000

Planum temporale and Heschl gyrus volume reduction in schizophrenia: a magnetic resonance imaging study of first-episode patients.

BACKGROUND: Magnetic resonance imaging studies in schizophrenia have revealed abnormalities in temporal lobe structures, including the superior temporal gyrus. More specifically, abnormalities have been reported in the posterior superior temporal gyrus, which includes the Heschl gyrus and planum temporale, the latter being an important substrate for language. However, the specificity of the Heschl gyrus and planum temporale structural abnormalities to schizophrenia vs affective psychosis, and the possible confounding roles of chronic morbidity and neuroleptic treatment, remain unclear. METHODS: Magnetic resonance images were acquired using a 1.5-T magnet from 20 first-episode (at first hospitalization) patients with schizophrenia (mean age, 27.3 years), 24 first-episode patients with manic psychosis (mean age, 23.6 years), and 22 controls (mean age, 24.5 years). There was no significant difference in age for the 3 groups. All brain images were uniformly aligned and then reformatted and resampled to yield isotropic voxels. RESULTS: Gray matter volume of the left planum temporale differed among the 3 groups. The patients with schizophrenia had significantly smaller left planum temporale volume than controls (20.0%) and patients with mania (20.0%). Heschl gyrus gray matter volume (left and right) was also reduced in patients with schizophrenia compared with controls (13.1%) and patients with bipolar mania (16.8%). CONCLUSIONS: Compared with controls and patients with bipolar manic psychosis, patients with first-episode schizophrenia showed left planum temporale gray matter volume reduction and bilateral Heschl gyrus gray matter volume reduction. These findings are similar to those reported in patients with chronic schizophrenia and suggest that such abnormalities are present at first episode and are specific to schizophrenia.

Adolescent↗

PubMed2000

An image processing strategy for the quantification and visualization of exercise-induced muscle MRI signal enhancement.

Exercise increases the skeletal muscle water signal in T2-weighted images. Potential medical applications of MR studies of exercise-induced muscle signal intensity changes are the assessment of myopathies, sport training regimens, and physical therapy approaches following surgeries. We developed an automated image processing technique that provides volumetric analysis and visualization of exercise-related T2-weighted image intensity changes. The image processing was applied to the segmentation and quantification of activated muscle volumes. Qualitative assessment of muscle activation is demonstrated with three-dimensional surface rendering. Quantitative determination of active muscle volume, signal intensity, and change over time is demonstrated. Visualization of the activated muscles allows functional anatomical assessment of exercise, which in turn allows detection of muscle utilization.

Exercise↗

PubMed2000

[Computer-assisted planning of corrective osteotomies in cases of epiphysiolysis capitis femoris].

Slipped capital femoral epiphysis (SCFE) leads to an unphysiologic function in adolescent hips. Evaluation of the slippage as well planning of corrective osteotomies is a major three-dimensional (3D) problem. Therefore, the current clinical evaluation, which is based on biplanar plain radiographs, cannot be satisfying. More is needed than simply measuring the femoral geometry to evaluate the impact of a slippage onto the physiologic hip function. We have developed a computer-based system for planning and evaluation of reorienting osteotomies in severe cases of SCFE. In our system, CT-based 3D computer models of the hip are used to simulate the range of motion within physiologic cartilage-to-cartilage contact. This helps to visualize and quantify the early impingement due to the slippage. In addition, 3D techniques allow to simulate and plan the corrective osteotomy in an intuitive way on the computer screen. Using the same range of motion system mentioned above, the projected result can be evaluated quantitatively and compared to other approaches. The motion simulation is based on the surface geometry of the joint partners rather than on a predefined, fixed rotation center. The presented system allows a much more intuitive and appropriate system for indicating and planning corrective osteotomies than conventional methods.

Adolescent↗

PubMed2000

3D-shaded surface rendering of gadolinium-enhanced MR angiography in congenital heart disease.

BACKGROUND: Gadolinium-enhanced three-dimensional (3D) MR angiography is a useful imaging technique for patients with congenital heart disease. OBJECTIVE: This study sought to determine the added value of creating 3D shaded surface displays compared to standard maximal intensity projection (MIP) and multiplanar reformatting (MPR) techniques when analyzing 3D MR angiography data. MATERIALS AND METHODS: Seventeen patients (range, 3 months to 51 years old) with a variety of congenital cardiovascular defects underwent gadolinium-enhanced 3D MR angiography of the thorax. Color-coded 3D shaded surface models were rendered from the image data using manual segmentation and computer-based algorithms. Models could be rotated, translocated, or zoomed interactively by the viewer. Information available from the 3D models was compared to analysis based on viewing standard MIP/ MPR displays. RESULTS: Median postprocessing time for the 3D models was 6 h (range, 3-25 h) compared to approximately 20 min for MIP/MPR viewing. No additional diagnostic information was gained from 3D model analysis. All major findings with MIP/MPR postprocessing were also apparent on the 3D models. Qualitatively, the 3D models were more easily interpreted and enabled adjacent vessels to be distinguished more readily. CONCLUSION: Routine use of 3D shaded surface reconstructions for visualization of contrast enhanced MR angiography in congenital heart disease cannot be recommended. 3D surface rendering may be more useful for presenting complex anatomy to an audience unfamiliar with congenital heart disease and as an educational tool.

Adolescent↗

PubMed2000

Volume assessment of the normal female cervix with MR imaging: comparison of the segmentation technique and two geometric formula.

RATIONALE AND OBJECTIVES: The purpose of this study was to determine the volume of the normal female cervix and to determine the geometric formula that yields the best estimate. MATERIALS AND METHODS: Magnetic resonance images of the pelvis in 30 young women were reviewed retrospectively. The volume of the cervix was estimated by using the formulas for an ellipse and a cylinder. Manual labeling and segmentation of the cervix were also performed, and the volume was calculated on the basis of the number and size of the voxels. Comparison of these methods was then performed by using a two-tailed Student t test. RESULTS: No statistically significant difference was found (P = .7) between the volume calculated with the segmentation technique (25.3 mL) and that estimated with the formula for a cylinder (24.8 mL). A statistically significant difference (P < .05) was found between the volume calculated with the segmentation technique and that estimated with the formula for an ellipse (16.4 mL). CONCLUSION: The normal volume of the cervix in this population of young women was approximately 25 mL. The volume of the cervix should be estimated with the formula for a cylinder.

Adult↗

PubMed2000

Adaptive, template moderated, spatially varying statistical classification.

A novel image segmentation algorithm was developed to allow the automatic segmentation of both normal and abnormal anatomy from medical images. The new algorithm is a form of spatially varying statistical classification, in which an explicit anatomical template is used to moderate the segmentation obtained by statistical classification. The algorithm consists of an iterated sequence of spatially varying classification and nonlinear registration, which forms an adaptive, template moderated (ATM), spatially varying statistical classification (SVC). Classification methods and nonlinear registration methods are often complementary, both in the tasks where they succeed and in the tasks where they fail. By integrating these approaches the new algorithm avoids many of the disadvantages of each approach alone while exploiting the combination. The ATM SVC algorithm was applied to several segmentation problems, involving different image contrast mechanisms and different locations in the body. Segmentation and validation experiments were carried out for problems involving the quantification of normal anatomy (MRI of brains of neonates) and pathology of various types (MRI of patients with multiple sclerosis, MRI of patients with brain tumors, MRI of patients with damaged knee cartilage). In each case, the ATM SVC algorithm provided a better segmentation than statistical classification or elastic matching alone.

Algorithms↗

PubMed2000

Affine adaptive filtering of CT data.

A novel method for resampling and enhancing image data using multidimensional adaptive filters is presented. The underlying issue that this paper addresses is segmentation of image structures that are close in size to the voxel geometry. Adaptive filtering is used to reduce both the effects of partial volume averaging by resampling the data to a lattice with higher sample density and to reduce the image noise level. Resampling is achieved by constructing filter sets that have subpixel offsets relative to the original sampling lattice. The filters are also frequency corrected for ansisotropic voxel dimensions. The shift and the voxel dimensions are described by an affine transform and provides a model for tuning the filter frequency functions. The method has been evaluated on CT data where the voxels are in general non cubic. The in-plane resolution in CT image volumes is often higher by a factor of 3-10 than the through-plane resolution. The method clearly shows an improvement over conventional resampling techniques such as cubic spline interpolation and sinc interpolation.

Humans↗

PubMed2000

Fast re-rendering of volume and surface graphics by depth, color, and opacity buffering.

A method for quickly re-rendering volume data consisting of several distinct materials and intermixed with moving geometry is presented. The technique works by storing depth, color and opacity information, to a given approximation, which facilitates accelerated rendering of fixed views at moderate storage overhead without re-scanning the entire volume. Storage information in the ray direction (what we have called super-r depth buffering), allows rapid transparency and color changes of materials, position changes of sub-objects, dealing explicitly with regions of overlap, and the intermixing or separately rendered geometry. The rendering quality can be traded-off against the relative storage cost and we present an empirical analysis of output error together with typical figures for its storage complexity. The method has been applied to the visualization of medical image data for surgical planning and guidance, and presented results include typical clinical data. We discuss the implications of our method for haptic (or tactile) rendering systems, such as for surgical simulation, and present preliminary results of rendering polygonal objects in the volume rendered scene.

Algorithms↗

PubMed2000

Virtual CT cystoscopy: color mapping of bladder wall thickness.

RATIONALE AND OBJECTIVES: To improve the conspicuity of bladder tumors in a virtual environment, we developed an algorithm for color mapping the thickness of the bladder wall. The purpose of this study was to demonstrate the feasibility of this algorithm as a component of virtual CT cystoscopy. METHODS: Five subjects with a history of superficial transitional-cell carcinoma of the bladder underwent helical CT scanning after insufflation of the bladder with air. Source images were transformed into three-dimensional models, and the thickness of the bladder wall was demarcated by using a new computer algorithm and a fixed color scale. Results were compared with those obtained by conventional cystoscopy. RESULTS: Three tumors, one site of benign wall thickening, and normal wall thickness were correctly identified by using axial source images and virtual cystoscopy with color mapping. CONCLUSIONS: Color mapping of bladder wall thickness is feasible and demonstrates both normal and thickened urothelium. Its value in identification of small or sessile tumors will require further trials.

Aged↗

PubMed2000

Nondistorting flattening maps and the 3-D visualization of colon CT images.

In this paper, we consider a novel three-dimensional (3-D) visualization technique based on surface flattening for virtual colonoscopy. Such visualization methods could be important in virtual colonoscopy because they have the potential for noninvasively determining the presence of polyps and other pathologies. Further, we demonstrate a method that presents a surface scan of the entire colon as a cine, and affords the viewer the opportunity to examine each point on the surface without distortion. We use certain angle-preserving mappings from differential geometry to derive an explicit method for flattening surfaces obtained from 3-D colon computed tomography (CT) imagery. Indeed, we describe a general method based on a discretization of the Laplace-Beltrami operator for flattening a surface into the plane in a conformal manner. From a triangulated surface representation of the colon, we indicate how the procedure may be implemented using a finite element technique, which takes into account special boundary conditions. We also provide simple formulas that may be used in a real-time cine to correct for distortion.

Algorithms↗

PubMed2000

Disruption of attention to novel events after frontal lobe injury in humans.

OBJECTIVE: To investigate whether frontal lobe damage in humans disrupts the natural tendency to preferentially attend to novel visual events in the environment. METHODS: Nine patients with chronic infarctions in the dorsolateral prefrontal cortex (DLPFC) and 23 matched normal controls participated in a study in which subjects viewed repetitive background stimuli, infrequent target stimuli, and novel visual stimuli (for example, fragmented or "impossible" objects). Subjects controlled viewing duration by a button press that led to the onset of the next stimulus. They also responded to targets by pressing a foot pedal. The amount of time spent looking at the different kinds of stimuli, and the target detection accuracy and speed served as dependent variables. RESULTS: Overall, normal controls spent significantly more time than frontal lobe patients looking at novel stimuli. Analysis of responses across blocks showed that initially frontal lobe patients behaved like normal controls by directing more attention to novel than background stimuli. However, they quickly began to distribute their viewing time evenly between novel and background stimuli, a pattern that was strikingly different from normal controls. By contrast, there were no differences between frontal lobe patients and normal controls for viewing duration devoted to background and target stimuli, target detection accuracy, or reaction time to targets. Frontal lobe patients did not differ from normal controls in terms of age, education, estimated IQ, or mood, but were more apathetic as measured by self report and informants' judgments. Attenuated responses to novel stimuli significantly correlated with degree of apathy. CONCLUSIONS: This study demonstrates that DLPFC injury selectively impairs the natural tendency to seek stimulation from novel and unusual stimuli. These data provide the first quantitative behavioural demonstration that the human frontal lobes play a critical part in directing and sustaining attention to novel events. The impairment of novelty seeking behaviour may contribute to the characteristic apathy found in patients with frontal lobe injury.

Aged↗