Biomedical subjects

R Kikinis

Publications and source records attributed to R Kikinis.

At least 145 records · Page 8Linked to original sources

PubMed1994

Video registration virtual reality for nonlinkage stereotactic surgery.

We have combined three-dimensional (3D) computer-reconstructed neuroimages with a novel video registration technique for virtual reality-based, image-guided surgery of the brain and spine. This technique allows the surgeon to localize cerebral and spinal lesions by superimposing a 3D-reconstructed MR or CT scan on a live video image of the patient. Once the patient's scan has been segmented into the relevant components (e.g., tumor, edema, ventricles, arteries, brain and skin), the surgeon studies the 3D anatomy to determine the optimal surgical approach. The proposed intraoperative surgeon's perspective is displayed in the operating room at the time of surgery using a portable workstation. The patient is then brought to the operating room and positioned according to the planned approach. A video camera is trained on the patient from the proposed intraoperative surgeon's perspective. A video mixer merges the images from the video camera and the 3D computer reconstruction. This video mixer can vary the output intensity of the two input images between 100% of either and 50% of both. This visually superimposes the two images, not unlike a photographic double exposure. The patient's position and the 3D reconstruction are then adjusted until the images on the video mixer's output monitor are identical in terms of scale, position and rotation. This superimposition is facilitated by aligning various surface landmarks such as the external auditory canal, lateral canthus, and nasion. In some cases, such as with spinal tumors, capsules placed on the skin prior to scanning serve as fiducials.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗

PubMed1994

Dynamic nature of the aortic regurgitant orifice area during diastole in patients with chronic aortic regurgitation.

BACKGROUND: The effective aortic regurgitant orifice area varies with aortic pressure in animal models of acute aortic regurgitation. The purpose of this study was to determine whether the aortic regurgitant orifice area changes during diastole in patients with chronic aortic regurgitation. METHODS AND RESULTS: Two-dimensional and Doppler echocardiography were performed immediately before and after magnetic resonance velocity mapping using a cine phase contrast sequence in 17 patients with chronic aortic regurgitation. ECG-gated continuous-wave Doppler velocity time integrals and magnetic resonance flow rates were measured 16 times per cardiac cycle. The mean aortic regurgitant orifice area (centimeters squared) was calculated by the continuity equation. The regurgitant orifice area was also determined for each diastolic acquisition interval. Changes in the regurgitant orifice area during diastole were modeled using an asymptotic exponential decay model to determine the static and dynamic components of the orifice. The regurgitant orifice area increased directly with regurgitant fraction (y[cm2] = 0.0072[cm2/%]*x[%]-0.0409[cm2]; r = .86, P < .0001). In 15 of 17 (88%) patients, the regurgitant orifice area decreased during diastole. The dynamic component of the regurgitant orifice area decreased with increasing regurgitant fraction (y[%] = -0.98x[%]+96.9[%]; r = -.90, P < .0001). There were no significant differences in heart rate, systolic or diastolic blood pressures, or continuous-wave Doppler velocity time integrals measured before or after the magnetic resonance examination. CONCLUSIONS: The effective regurgitant orifice area decreases during diastole in patients with chronic aortic regurgitation. This phenomenon should be considered when evaluating aortic regurgitant severity.

Aortic Valve↗

PubMed1994

Longitudinal MRI in multiple sclerosis: correlation between disability and lesion burden.

We followed 18 multiple sclerosis patients clinically and with repeated brain MRIs with and without gadolinium for over 1 year. Clinical evaluations included scoring on the Kurtzke Expanded Disability Status Scale (EDSS) and the Ambulation Index (AI) scale. There was a significant correlation between the change in EDSS or AI and the change in number of lesions on MRI and between cumulative number of lesions on MRI and cumulative change in EDSS or AI. Our findings support the validity of MRI as a measure of clinical activity and potentially as an objective quantitative outcome measure for assessing response to therapy.

Adult↗

PubMed1993

Auditory P300 abnormalities and left posterior superior temporal gyrus volume reduction in schizophrenia.

Abnormalities in the auditory P300 event-related potential are one of the most robust findings in schizophrenia. To investigate the brain source(s) of this major functional abnormality, we combined P300 recordings with the use of a new generation of magnetic resonance imaging (MRI) technology to examine specific temporal lobe gray matter regions of interest in schizophrenics and normal controls. In schizophrenics, gray matter volume reductions in the left posterior superior temporal gyrus (STG), which includes Heschl's gyrus and the planum temporale, were highly and specifically associated with both P300 amplitude reduction and left < right topographic asymmetry. In contrast, left hippocampus and parahippocampal gyrus gray matter volume reductions, although present in schizophrenics, were not associated with any P300 abnormalities. There were also no statistically significant correlations between P300 amplitude at any of the central or left-sided electrode sites or any of the MRI-defined volumes of gray matter regions of interest in the right temporal lobe, superior frontal gyrus, or cingulate gyrus; additional work will thus be required to determine the role of these regions, if any, in P300 generation, along with the role of other brain areas not examined in the present study. These initial data appear most compatible with a model that postulates a major role for bilateral STG sources in P300 generation: The strongly asymmetric STG volume reduction (left < < right STG volume) found in many schizophrenic subjects produces asymmetric P300 amplitudes (left < < right) at lateral electrode sites, where the influence of the abnormal region is most easily detected.

Adult↗

PubMed1993

Neuropsychological correlates of MRI temporal lobe abnormalities in schizophrenia.

OBJECTIVE: The authors evaluated the neuropsychological correlates of temporal lobe abnormalities in schizophrenic patients. METHOD: Fifteen schizophrenic patients underwent assessment of memory, by the Wechsler Memory Scale--Revised, and abstraction/categorization, by the similarities subtest of the Wechsler Adult Intelligence Scale--Revised and the Wisconsin Card Sorting Test. Neuropsychological tests of motor and constructional functions were used as control tasks. The patients also underwent magnetic resonance imaging (MRI) studies in which new neuroimaging techniques were used to derive measurements of volume and three-dimensional surface renderings of temporal lobe structures. RESULTS: Spearman rank-order correlations indicated significant associations between poor scores on tests of verbal memory, abstraction, and categorization and reduced volume in temporal lobe structures, including the parahippocampal gyrus and posterior superior temporal gyrus (left and right). By contrast, performance on tests of visual memory and on control tasks was not correlated with MRI temporal lobe abnormalities. CONCLUSIONS: These findings suggest a significant but modest relation between reduced volume in specific temporal lobe regions and neuropsychological deficits in abstraction, categorization, and verbal memory, all of which may reflect a dysfunctional semantic system in schizophrenia.

Adult↗

PubMed1993

Computer-assisted three-dimensional planning in craniofacial surgery.

Three-dimensional surface reconstruction from computed tomographic (CT) data has been used to plan craniofacial operations. Cephalometric and anthropometric databases were integrated with three-dimensional CT reconstructions to quantitate the skeletal deformity and to assist in the design of the surgical procedure. Interactive techniques were developed to simulate osteotomies and skeletal movements in three dimensions on the computer-generated surface images. The ocular globes were referenced to position the orbital segments; i.e., the osteotomized segments were transposed into normal anatomic relationship with respect to the eyes. The measurements from the computer graphic simulation were used intraoperatively to establish the correct position of the skeletal segments.

Adolescent↗

PubMed1992

Abnormalities of the left temporal lobe and thought disorder in schizophrenia. A quantitative magnetic resonance imaging study.

BACKGROUND: Data from postmortem, CT, and magnetic resonance imaging (MRI) studies indicate that patients with schizophrenia may have anatomical abnormalities of the left temporal lobe, but it is unclear whether these abnormalities are related to the thought disorder characteristic of schizophrenia. METHODS: We used new MRI neuroimaging techniques to derive (without knowledge of the diagnosis) volume measurements and three-dimensional reconstructions of temporal-lobe structures in vivo in 15 right-handed men with chronic schizophrenia and 15 matched controls. RESULTS: As compared with the controls, the patients had significant reductions in the volume of gray matter in the left anterior hippocampus-amygdala (by 19 percent [95 percent confidence interval, 3 to 36 percent]), the left parahippocampal gyrus (by 13 percent [95 percent confidence interval, 3 to 23 percent], vs. 8 percent on the right), and the left superior temporal gyrus (by 15 percent [95 percent confidence interval, 5 to 25 percent]). The volume of the left posterior superior temporal gyrus correlated with the score on the thought-disorder index in the 13 patients evaluated (r = -0.81, P = 0.001). None of these regional volume decreases was accompanied by a decrease in the volume of the overall brain or temporal lobe. The volume of gray matter in a control region (the superior frontal gyrus) was essentially the same in the patients and controls. CONCLUSIONS: Schizophrenia involves localized reductions in the gray matter of the left temporal lobe. The degree of thought disorder is related to the size of the reduction in volume of the left posterior superior temporal gyrus.

Adult↗

PubMed1992

Comparative analysis of computed tomographic and magnetic resonance imaging scans in Alzheimer patients and controls.

Ten patients with Alzheimer's disease underwent computed tomography and magnetic resonance imaging at the same point in time. The mean Mini-Mental State examination score of the patients was 23, indicating that they were mildly impaired. Ten age-equivalent controls also obtained computed tomographic and magnetic resonance imaging scans. A semiautomated computer program analyzed nine comparable regions of interest on each set of scans. When regions of interest from both types of scans were combined in the same discriminant function analysis, the first two variables selected were from the magnetic resonance imaging data set, and they significantly differentiated 95% of the patients and controls.

Aged↗

PubMed1992

Common carotid artery bifurcation: evaluation with spiral CT. Work in progress.

To determine the utility of spiral computed tomography (CT) in evaluation of carotid artery stenosis, spiral CT images of 20 patients were compared with images obtained with conventional angiography (20 patients), ultrasound (US) (15 patients), and magnetic resonance (MR) angiography (six patients). The category of stenosis was determined for each internal carotid artery on the basis of the percentage of narrowing: mild = less than 30%, moderate = 30%-69%, and severe = 70%-99%. Occlusions were also noted. The degree of carotid stenosis determined with spiral CT correlated with that determined with conventional angiography in 92% of cases, with that determined with US in 97% of cases, and with that determined with MR angiography in 100% of cases. Calcifications and large ulcers were also well delineated. Spiral CT provided an accurate anatomic depiction of the carotid bifurcation, which could be helpful in preoperative evaluation. The major disadvantage of the technique was the need to postprocess data to remove veins, calcifications, and bone structures from the images.

Adult↗

PubMed1991

Application of automated MRI volumetric measurement techniques to the ventricular system in schizophrenics and normal controls.

As an initial approach to computer-automated segmentation of cerebral spinal fluid (CSF) vs. brain parenchyma in MR scans, and the transformation of these data sets into volumetric information and 3D display, we examined the ventricular system in a sample of ten chronic schizophrenics with primarily positive symptoms and 12 normal subjects. While no significant differences were noted between groups on volumetric measures of ventricular brain ratio or lateral ventricle size, normals showed a pattern of left greater than right lateral ventricular volume asymmetry not present in the schizophrenics. Within the schizophrenic group, departure from the normal left greater than right pattern was highly correlated with thought disorder.

Adult↗

PubMed1989

Magnetic resonance imaging of the brain in congenital cytomegalovirus infection.

Ten children (age 2 months to 8 years) with a congenital cytomegalovirus (CMV) infection were studied by magnetic resonance imaging (MRI) using a 2.35 Tesla magnet. CMV infection was confirmed by serological investigations and virus culture in the neonatal period. Nine children had severe mental retardation and cerebral palsy, 1 patient suffered from microcephaly, ataxia and deafness. The cranial MRI examination showed the following abnormalities (N): dilated lateral ventricles (10) and subarachnoid space (8), oligo/pachygyria (8), delayed/pathological myelination (7), paraventricular cysts (6), intracerebral calcification (1). This lack of sensitivity for calcification is explainable by the basic principles of MRI. The paraventricular cystic lesions were adjacent to the occipital horns of the lateral ventricles and separated only by a thin membrane. This finding might represent a "new sign" for congenital CMV infection in MRI examinations, being characteristic but nevertheless nonspecific, like calcification in CT.

Brain↗

PubMed1989

Larynx: MR imaging at 2.35 T.

To study the consequences of an improvement in spatial resolution, the authors compared magnetic resonance (MR) images of nine laryngeal specimens with whole-organ histologic slides of the same specimens. Five of the specimens were obtained during laryngectomies performed on patients with high-stage tumors of the larynx. Four specimens were from patients with no known disease. The MR images were obtained on a 2.35-T system with a closely fitting probe head. A conventional spin-echo sequence was used, with T1- and T2-weighted settings. The in-plane resolution obtained was about 0.3 mm. The T2-weighted images generally showed better contrast and allowed identification of the perichondrium. The resolutions used were not much greater than those clinically available. The findings suggest that there will be important advances in clinical MR imaging of the larynx in the near future.

Aged↗

PubMed1988

[Magnetic resonance in pediatric research and clinical practice. II. Studies on the development and pathology of the brain in neonates, infants and young children].

We are investigating metabolism and morphological differentiation of the developing brain in neonates and children under non-invasive conditions combining MR imaging (MRI) with spectroscopy (MRS) on a high-field/small-bore (2.35 Tesla/40 cm) system. By the end of 1987, 116 neonates, infants and young children with various perinatal problems, congenital abnormalities and different neurological diseases have been examined with MRI. In addition, MRS studies were subsequently performed on 46 of these children using the same instrument and within the same session. The small, sometimes very sick and instable patients require careful monitoring and elaborate technical devices in the high magnetic field. We are presenting solutions for methodological and technical developments and adaptations, concepts for sedation and measurement protocols in various age groups and first results of the combined use of MRI and MRS to investigate the brain in neonates and infants.

Brain↗

PubMed1987

Normal and hydronephrotic kidney: evaluation of renal function with contrast-enhanced MR imaging.

Four healthy volunteers and six patients with hydronephrosis underwent magnetic resonance (MR) imaging after the injection of gadolinium-diethylenetriaminepenta-aceticacid for the assessment of renal function. Coronal angulated 10-second images were obtained during suspended respiration (inspiratory apnea) and showed excellent anatomic detail. In healthy volunteers, the renal cortex showed an increase in signal intensity after Gd-DTPA injection, and the renal medulla showed a precipitous decrease in intensity approximately 1 minute after injection, followed by a gradual increase in intensity. The renal pelvis showed a gradual decrease in intensity after several minutes, with occasional signal-void areas in adjacent structures. In patients with hydronephrosis, the decrease in intensity in the medulla and pelvis was not observed; instead, an increase in intensity occurred. The physiologic function of glomerular filtration and in vitro results of serial dilutions of Gd-DTPA suggest that the decrease in intensity is due to T2 and susceptibility effects occurring at high concentrations of Gd-DTPA.

Adult↗

PubMed1987

[Computerized tomography in the classification of hypopharyngeal and laryngeal cancers].

CT scans of 26 patients with laryngeal or hypopharyngeal carcinoma were compared with macrosections and histological slices obtained from laryngectomy specimens in order to assess the role of CT scanning in the staging of hypopharyngolaryngeal carcinoma. Of the 26 cases six could not be staged correctly without CT. Computed tomography proved particularly useful in staging medium sized carcinomas (T2/3) of the supraglottic and piriform sinus region.

Carcinoma, Squamous Cell↗

PubMed1987

[Computed tomography for the preoperative classification of oral cavity and oropharyngeal carcinomas].

CT scans of 40 patients with oral cavity or oropharyngeal carcinoma were compared with clinical tumour descriptions and operation and pathology reports in order to assess the role of CT scanning in the preoperative work-up and staging of oral and oropharyngeal carcinoma. Overall clinical staging was superior to radiological staging (73% vs 55% correct T stages). However, because of the additional information obtained from CT scans we would still recommend CT evaluation for most oral cavity and oropharyngeal carcinomas.

Carcinoma, Squamous Cell↗

PubMedDate not supplied

Routine quantitative analysis of brain and cerebrospinal fluid spaces with MR imaging.

A computerized system for processing spin-echo magnetic resonance (MR) imaging data was implemented to estimate whole brain (gray and white matter) and cerebrospinal fluid volumes and to display three-dimensional surface reconstructions of specified tissue classes. The techniques were evaluated by assessing the radiometric variability of MR volume data and by comparing automated and manual procedures for measuring tissue volumes. Results showed (a) the homogeneity of the MR data and (b) that automated techniques were consistently superior to manual techniques. Both techniques, however, were affected by the complexity of the structure, with simpler structures (eg, the intracranial cavity) showing less variability and better spatial correlation of segmentation results between raters. Moreover, the automated techniques were completed for whole brain in a fraction of the time required to complete the equivalent segmentation manually. Additional evaluations included interrater reliability and an evaluation that included longitudinal measurement, in which one subject was imaged sequentially 24 times, with reliability computed from data collected by three raters over 1 year. Results showed good reliability for the automated segmentation procedures.

Body Fluid Compartments↗

PubMedDate not supplied

Rapid tip tracking with MRI by a limited projection reconstruction technique.

To rapidly track invasive devices within MRI systems, a novel approach using a limited projection reconstruction technique is presented. Our method exploits the difference between images reconstructed from a limited number of projections and serves to depict the tip of a needle during its advancement. This method was implemented on a standard MRI system with a radial fast-spin-echo sequence and examined in phantom studies. We demonstrated that the proposed method could track the tip every 300 msec and the tip depicted by the present technique was consistently displaced along the needle by a small distance (5 mm).

Feasibility Studies↗