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H Rusinek

Publications and source records attributed to H Rusinek.

51 records · Page 3Linked to original sources
PubMed1989

Interactive graphic editor for analysis and enhancement of medical images.

We have developed an interactive graphic editor to define subregions within a volume of medical images arranged in serial sections. The editing methods include tracing and automatic growing of connected components defined by the gray level range. The editor performs a statistical analysis of the signal contained in each subvolume and is used in studies of magnetic resonance (MR) signal in medical images. The graphic editor is also used for creating 3D views from MR images based on the new volume-rendering algorithm. The editor transforms the volume of images by remapping their gray levels and by multiplanar cuts. The ability to suppress regions having the same signal intensity as the region of interest is important in generating an unobstructed view of the anatomical structures.

Brain↗
PubMed1989

Volumetric rendering of MR images.

The authors developed new techniques for three-dimensional display of magnetic resonance (MR) images that preserve soft-tissue definition, are fully automatic, and work with routinely used section thicknesses. MR images are segmented, selectively enhanced, and displayed by means of a volumetric rendering algorithm. These techniques were used to illustrate normal anatomy of the brain, knee, and liver. Three-dimensional rendering of balanced spin-echo images shows the ventricles and extracerebral veins and of T1-weighted images, the sulci and gyri. The large hepatic and portal vessels can be seen with these enhancement techniques. Three-dimensional views of the knee reveal articular surfaces of the tibia and clearly depict menisci and posterior and anterior cruciate ligaments. These techniques make it possible to image multiple soft tissues simultaneously while preserving the detail contained in the original images. Three-dimensional presentation of complex, overlapping anatomic regions is helpful in surgical planning and should lead to improved diagnosis.

Algorithms↗
PubMed1989

Cerebral cortical and white matter reactivity to carbon dioxide.

We measured cerebrovascular reactivity to carbon dioxide in the cerebral cortex and the subcortical white matter of 12 healthy adult volunteers (four young subjects aged 21-24, four middle-aged subjects aged 34-40, and four elderly subjects aged 62-85 years). Blood flow was computed from the concentration history of xenon-133 in the volume of interest measured with an ultrapure germanium detector array. End-tidal PaCO2 ranged from 35.4 to 42.6 mm Hg. The mean +/- SD baseline blood flows in the cerebral cortex were 60 +/- 7, 51 +/- 9, and 33 +/- 4 ml/100 cm3/min in the young, the middle-aged, and the elderly subjects, respectively; the corresponding subcortical white matter baseline blood flows were 21 +/- 1, 22 +/- 3, and 16 +/- 5 ml/100 cm3/min. Mean +/- SD cerebrovascular reactivities to carbon dioxide in the cerebral cortex were 2.03 +/- 0.58, 1.36 +/- 0.41, and 0.72 +/- 0.19 ml/100 cm3/min/mm Hg PaCO2 for the young, the middle-aged, and the elderly subjects, respectively; the corresponding reactivities in the subcortical white matter were 0.69 +/- 0.11, 0.59 +/- 0.17, and 0.36 +/- 0.41 ml/100 cm3/min/mm Hg PaCO2. Blood flow and cerebrovascular reactivity in the cerebral cortex of the young subjects were significantly higher than those for white matter and significantly higher than those in the elderly subjects (p less than 0.001). Age vs. blood flow (for the cortex) and age vs. cerebrovascular reactivity (for both cortical gray and subcortical white matter) also showed significant linear correlation (p less than 0.05). However, the age-related changes in white matter blood flow and cerebrovascular reactivity were slow, and the differences among the age groups were not statistically significant.

Adult↗
PubMed1986

Multicompartmental analysis of tracer clearance and its application to cerebral blood flow measurement.

A new algorithm for computing cerebral blood flow is shown to overcome compartmental slippage and unstability problems associated with the conventional bicompartmental analysis. The tracer clearance curve is decomposed into a nonnegative linear combination of predetermined flow components. A weighted average of flows above (below) a fixed threshold yields the gray (white) matter flow. The accuracy and the stability of the new algorithm are analyzed by Monte-Carlo simulations, determining the effect of factors such as random error in tracer concentration, gray-white flow difference, tissue content of gray matter, and end-fit time. While the new algorithm requires 50-100% more CPU time and memory space than the bicompartmental method, its accuracy and stability is superior, especially as the conditions of the measurement deteriorate. The results suggest that more than twofold error reduction in measuring the blood flow in pathological brain tissue is possible.

Aged↗
PubMed1980

An ultrapure germanium detector array for quantitating three-dimensional distribution of a radionuclide: a study of phantoms.

A new stationary 200-element ultrapure germanium (HPGe) array has been tested for accuracy and sensitivity in quantitating the distributed concentration of single-gamma-emitting radionuclides in phantoms approximating the size of the human brain. The phantoms consisted of 42 blocks of 39.1 cm3 average volume. Fourteen different permutations were studied. The concentrations in the blocks varied from 0i to 4.64 muCi/cm3. This first-generation instrument makes it possible to reconstruct the distributed concentration with a mean relative error of 8.3% at 200,000 counts per sample (1,000 counts/detector), and has sensitivities of 6,200 and 12,000 cps, respectively, for 1 muCi/cm3 of Xe-133 and Tc-99. The reconstruction algorithm is based on the conjugate gradient method of solving the set of linear equations that account for geometric, attenuation, and scatter factors. The results have implications for measuring the distribution of the partition coefficients, blood flow, blood volume, and concentration of tracers emitting single gamma photons in 42 anatomic subvolumes (30 cm3 average) of the entire brain simultaneously.

Cadmium↗
PubMedDate not supplied

Design of gradient coils for permanent magnets.

Designing gradient coils for permanent magnets requires modeling the interaction between the currents and the ferromagnetic material. We have developed and tested an iterative design approach based on the boundary element method. The power dissipated by the gradient coil is treated as a constraint of the minimization problem. The technique is illustrated on a magnet with a rectangular prismatic cavity and two ferromagnetic plates adjacent to the coil. The procedure improved the linearity of the field from 10.5% to 3.4% and reduced the power dissipation to 63% of the power of the unoptimized coil. The optimized distribution of currents has been transformed to variable locations of coil windings without loss of gradient uniformity. The new approach significantly reduces computation time and memory storage and yields practical designs of gradient coils for permanent magnets.

Electricity↗
PubMedDate not supplied

Segmentation analysis in functional MRI: activation sensitivity and gray-matter specificity of RARE and FLASH.

Brain activation is accompanied by local decreases in vascular deoxyhemoglobin. Theoretically, gradient-echo and spin-echo sequences show similar sensitivity to capillary deoxyhemoglobin, but spin-echo sequences should be less sensitive to venous deoxyhemoglobin. This is an important distinction in the context of cortical localization. We report herein a direct experimental comparison of a gradient-echo sequence (fast low-angle shot [FLASH]) with a spin-echo sequence (rapid acquisition with relaxation enhancement [RARE]) for functional MRI (fMRI) in seven subjects undergoing visual stimulation. A Student t test analysis was used to locate areas of significant activation, and then computerized image segmentation was performed to determine the type of activated tissue. Contrary to previous reports, both sequences proved equally sensitive to overall activation. RARE activation, however, was more specific for gray matter, as suggested by prior theoretical models.

Adult↗
PubMedDate not supplied

Hippocampal formation glucose metabolism and volume losses in MCI and AD.

We used MRI volume sampling with coregistered and atrophy corrected FDG-PET scans to test three hypotheses: 1) hippocampal formation measures are superior to temporal neocortical measures in the discrimination of normal (NL) and mild cognitive impairment (MCI); 2) neocortical measures are most useful in the separation of Alzheimer disease (AD) from NL or MCI; 3) measures of PET glucose metabolism (MRglu) have greater diagnostic sensitivity than MRI volume. Three groups of age, education, and gender matched NL, MCI, and AD subjects were studied. The results supported the hypotheses: 1) entorhinal cortex MRglu and hippocampal volume were most accurate in classifying NL and MCI; 2) both imaging modalities identified the temporal neocortex as best separating MCI and AD, whereas widespread changes accurately classified NL and AD; 3) In most between group comparisons regional MRglu measures were diagnostically superior to volume measures. These cross-sectional data show that in MCI hippocampal formation changes exist without significant neocortical changes. Neocortical changes best characterize AD. In both MCI and AD, metabolism reductions exceed volume losses.

Aged↗
PubMedDate not supplied

Frequency of hippocampal formation atrophy in normal aging and Alzheimer's disease.

We used CT and MR to examine the frequency of occurrence of hippocampal formation atrophy (HA) in a research clinic population of 130 normal elderly, 72 nondemented patients with very mild memory and cognitive impairments (MCI), 73 mild Alzheimer's disease (AD) patients, and 130 patients with moderate to severe AD. HA was found in 29% of the normal elderly group and its frequency of occurrence was strongly related to increasing age. For normal elderly 60-75 years of age, 15% had HA: the proportion rose to 48% in subjects 76-90 years of age. Among the three groups of impaired patients, the frequencies of HA ranged from 78% in the MCI patients to 96% in the advanced AD group. Unlike the normal elderly group, the percentages were not related to age. In both the normal elderly group and MCI group disproportionately more males than females had HA. After controlling for learning and the effects of generalized brain changes as reflected in ventricular size, only in the normal group was HA associated with reduced delayed verbal recall performance. Follow-up examinations for 15 individuals with baseline HA. 4 who at entry were MCI and 11 probable AD, yielded clinical and neuropathologic diagnoses of AD in all cases. The results of the present study indicate that hippocampal formation atrophy is associated with memory and cognitive impairments. Further longitudinal and neuropathologic work is required to validate the relationship between hippocampal formation atrophy and AD.

Aged↗
PubMedDate not supplied

Specific hippocampal volume reductions in individuals at risk for Alzheimer's disease.

Our goal was to ascertain the involvement of the temporal lobe in the preclinical (not yet diagnosable) stages of dementia of the Alzheimer's type (DAT) by using MRI-derived volumes. We assessed anatomical subdivisions of the temporal lobe on three groups of carefully screened age- and education-matched elderly individuals: 27 normal elderly (NL), 22 individuals with minimal cognitive impairment (MCI), who did not fulfill DAT criteria but were regarded at high risk for future DAT, and 27 DAT individuals. We found hippocampal volume reductions of 14% for the MCI and 22% for the DAT group compared to the NL group. Utilizing regression analyses and after accounting for gender head size-age, generalized atrophy (CSF), and other temporal lobe subvolumes, the hippocampal volume separated NL from MCI individuals, correctly classifying 74%. For NL and MCI groups combined the hippocampal volume was the only temporal lobe subvolume related to delayed recall memory performance. When contrasting MCI and DAT individuals, the fusiform gyrus volume uniquely improved the ability of the hippocampal volume to separate MCI from DAT individuals from 74 to 80%. Our cross-sectional data suggest that, within the temporal lobe, specific hippocampal volume reductions separated the group at risk for DAT from the normal group. By the time impairments are sufficient to allow a diagnosis of DAT to be made, in addition to the medial temporal lobe volume reductions, the lateral temporal lobe is also showing volume reductions, most saliently involving the fusiform gyrus.

Aged↗
PubMedDate not supplied

Atrophy of the medial occipitotemporal, inferior, and middle temporal gyri in non-demented elderly predict decline to Alzheimer's disease.

Our goal was to ascertain, among normal elderly and individuals with mild cognitive impairment, which temporal lobe neocortical regions predicted decline to dementia of the Alzheimer's type (DAT). Individuals received an MRI at baseline and a clinical and cognitive evaluation at baseline and follow-up. By using the baseline MRI we assessed the anatomical subdivisions of the temporal lobe: anteromedial temporal lobe (hippocampus and parahippocampal gyrus), medial occipitotemporal (fusiform) gyrus, middle and inferior temporal gyri, and superior temporal gyrus. We studied two groups of carefully screened age- and education-matched elderly individuals: 26 normal elderly (NL) and 20 individuals with mild cognitive impairment (MCI). Fourteen individuals (12 from the MCI group and two from the NL group) declined to DAT within the 3.2-year follow-up interval. We used logistic regression analyses to ascertain whether the baseline brain volumes were useful predictors of decline to DAT at follow-up after accounting for age, gender, individual differences in brain size, and other variables known to predict DAT. After accounting for age, gender, and head size, adding the volume of the anteromedial temporal lobe (the aggregate of hippocampus and parahippocampal gyrus) and an index of global atrophy raised the accuracy of overall classification to 80.4%. However, the ability to detect those individuals who declined (sensitivity) was low at 57%. When baseline medial occipitotemporal and the combined middle and inferior temporal gyri were added to the logistic model, the overall classification accuracy reached 95.6% and, most importantly, the sensitivity rose to 92.8%. These data indicate that the medial occipitotemporal and the combined middle and inferior temporal gyri may be the first temporal lobe neocortical sites affected in AD; atrophy in these areas may herald the presence of future AD among nondemented individuals. No other clinical baseline variables examined predicted decline with sensitivities above 71%. The apolipoprotein APOE epsilon4 genotype was not associated with decline.

Age Factors↗
PubMedDate not supplied

Long term study of random noise and signal uniformity in spin-echo brain imaging.

Random noise and MR signal uniformity were analyzed for a period of 9 months using two head coils on a 1.5 T commercial imager. Signal response from a cylindrical phantom filled with a 0.1 mmol/L CuSO4 solution was incorporated in a correction scheme and the effect of correction on uniformity and accuracy of tissue volume determination was measured. There was little change in random noise (CV < 5%) and image uniformity (CV < 15%) over the time of the study. The uniformity in a 130 cm2 region was 4% for a double saddle coil and 5.3% for a mirror coil. After correction, uniformity was improved to 1.1% for the double saddle coil and 1.2% for the mirror coil. In a 40 cm2 central region the uniformity was approximately three times better than in the 130 cm2 region. A second phantom, mimicking the relaxation times of CSF and the brain, consisted of saline encapsulated in vials of volume ranging from 35.6 ml to 249.6 ml and placed in a 0.1 mmol/L solution of MnCl2. Uniformity correction reduced the average error in volume measurement from 8.6% to 6.1%.

Adult↗
PubMedDate not supplied

Cerebral distribution of 133-Xe and blood flow measured with high purity germanium.

Distribution of cerebral blood flow was measured with an array of 200 ultra-pure germanium radiation detectors and 133-Xe by inhalation. The array "sees" the head as a composite of different subvolumes and enables measurement of the concentration history of tracer every 1-10 sec in each subvolume simultaneously. Subvolume mean flows, (fm), and partition coefficients, lambda m, are derived by compartmental analysis of tissue concentration washout curves. Errors from "cross talk," scalp radiation, "look through," and assumed partition coefficients are eliminated. Average fm adjusted for 40 mm Hg PACO2 in 14 cortical subvolumes (7 right, 7 left) of four normal 21-24 year old controls ranged from 50 to 60 ml/100 cc tissue/min, and lambda m ranged from 0.97 to 1.14. Average fm and lambda m in white matter was 24 ml/100 cc/min and 1.42 - 1.14 respectively. During CO2 inhalation, right and left hemispheric fm increased 6.4% and 5.7%/mm Hg respectively, whereas white matter fm increased 2.2% and 3.4% mm Hg respectively. There was no systematic difference between front and back or dominant vs non-dominant sides. Three 73-84 year old controls had reduced fm and CO2 reactivity in all subvolumes, lambda m was in the same range as in younger controls. Two patients with intracranial cerebrovascular disease showed excellent localization of ischemic subvolumes. One patient with asymptomatic unilateral 98% stenosis of the internal carotid artery had a similar distribution of blood flow in both hemispheres.

Adult↗
PubMedDate not supplied

Hippocampal formation size in normal human aging: a correlate of delayed secondary memory performance.

Although mild progressive memory impairment is commonly associated with normal human aging, it is unclear whether this phenomenon can be explained by specific structural brain changes. In a research sample of 54 medically healthy and cognitively normal elderly persons (ages 55-87, x = 69.0 +/- 7.9), magnetic resonance imaging (MRI) was used to derive head-size-adjusted measurements of the hippocampal formation (HF) (dentate gyrus, hippocampus proper, alveus, fimbria, subiculum), the superior temporal gyrus (STG), and the subarachnoid cerebrospinal fluid (CSF) (to estimate generalized cerebral atrophy). Subjects were administered tests of primary memory (digit span) and tests of secondary memory with immediate and delayed recall components (paragraph, paired associate, list recall; facial recognition). Separate composite scores for the immediate and delayed components were created by combining, with equal weighting, the subtests of each category. The WAIS vocabulary subtest was used as a control measure for language and intelligence. A highly significant correlation (P < 0.001), independent of age, gender, and generalized cerebral atrophy was found between HF size and delayed memory performance. No significant correlations were found between HF size and primary or immediate memory performance. STG size was not significantly correlated with any of the composite memory variables. These results suggest that HF atrophy may play an important independent role in contributing to the memory loss experienced by many aging adults.

Aged↗