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W E Reddick

Publications and source records attributed to W E Reddick.

12 recordsLinked to original sources
PubMed1997

Establishing norms for age-related changes in proton T1 of human brain tissue in vivo.

The goal of this study was to determine the expected normal range of variation in spin-lattice relaxation time (T1) of brain tissue in vivo, as a function of age. A previously validated precise and accurate inversion recovery method was used to map T1 transversely, at the level of the basal ganglia, in a study population of 115 healthy subjects (ages 4 to 72; 57 male and 58 female). Least-squares regression analysis shows that T1 varied as a function of age in pulvinar nucleus (R2 = 56%), anterior thalamus (R2 = 51%), caudate (R2 = 50%), frontal white matter (R2 = 47%), optic radiation (R2 = 39%), putamen (R2 = 36%), genu (R2 = 22%), occipital white matter (R2 = 20%) (all p < 0.0001), and cortical gray matter (R2 = 53%) (p < 0.001). There were no significant differences in T1 between men and women. T1 declines throughout adolescence and early adulthood, to achieve a minimum value in the fourth to sixth decade of life, then T1 begins to increase. Quantitative magnetic resonance imaging provides evidence that brain tissue continues to change throughout the lifespan among healthy subjects with no neurologic deficits. Age-related changes follow a strikingly different schedule in different brain tissues; white matter tracts tend to reach a minimum T1 value, and to increase again, sooner than do gray matter tracts. Such normative data may prove useful for the early detection of brain pathology in patients.

Adolescent↗
PubMed1997

Automated segmentation and classification of multispectral magnetic resonance images of brain using artificial neural networks.

We present a fully automated process for segmentation and classification of multispectral magnetic resonance (MR) images. This hybrid neural network method uses a Kohonen self-organizing neural network for segmentation and a multilayer backpropagation neural network for classification. To separate different tissue types, this process uses the standard T1-, T2-, and PD-weighted MR images acquired in clinical examinations. Volumetric measurements of brain structures, relative to intracranial volume, were calculated for an index transverse section in 14 normal subjects (median age 25 years; seven male, seven female). This index slice was at the level of the basal ganglia, included both genu and splenium of the corpus callosum, and generally, showed the putamen and lateral ventricle. An intraclass correlation of this automated segmentation and classification of tissues with the accepted standard of radiologist identification for the index slice in the 14 volunteers demonstrated coefficients (ri) of 0.91, 0.95, and 0.98 for white matter, gray matter, and ventricular cerebrospinal fluid (CSF), respectively. An analysis of variance for estimates of brain parenchyma volumes in five volunteers imaged five times each demonstrated high intrasubject reproducibility with a significance of at least p < 0.05 for white matter, gray matter, and white/gray partial volumes. The population variation, across 14 volunteers, demonstrated little deviation from the averages for gray and white matter, while partial volume classes exhibited a slightly higher degree of variability. This fully automated technique produces reliable and reproducible MR image segmentation and classification while eliminating intra- and interobserver variability.

Adult↗
PubMed1997

Age-related changes in the pediatric brain: quantitative MR evidence of maturational changes during adolescence.

PURPOSE: To determine whether a quantitative MR imaging method to map spin-lattice relaxation time (T1) can be used to characterize maturational changes in the normal human brain. METHODS: An inversion-recovery technique was used to map T1 transversely at the level of the basal ganglia in a study population of 19 healthy children (4 to 10 years old) and 31 healthy adolescents (10 to 20 years old), and in a normative population of 20 healthy adults (20 to 30 years old). RESULTS: Nonparametric analysis of variance showed that T1 decreases with age in the genu, frontal white matter, caudate, putamen, anterior thalamus, pulvinar nucleus, optic radiation, cortical gray matter (all P < .0001), and occipital white matter. There was a significant reduction in T1 between childhood (mean age, 7.1 +/- 1.4) and adolescence (mean age, 13.5 +/- 2.6) in all brain structures, but there was also a significant reduction in T1 between adolescence (mean age, 13.5 +/- 2.6) and adulthood (mean age, 26.5 +/- 3.4) in all brain structures except occipital white matter. Regression shows that T1 declines to within the range (mean +/- 2 SD) of young adult T1 values by about 2 years in the occipital white matter, by about 4 years in the genu, by 11 years in the cortical gray matter, by 11 years in the frontal white matter, and by 13 years in the thalamus. CONCLUSION: Brain structures mature at strikingly different rates, yet the ratio of gray matter T1 to white matter T1 does not change significantly with age. Thus, conventional MR imaging methods based on inherent contrast are insensitive to these changes. Age-related changes tend to reach completion sooner in white matter than in gray matter tracts. Such normative data are essential for studies of specific pediatric disorders and may be useful for assessing brain maturation in cases of developmental delay.

Adolescent↗
PubMed1996

Clinical value of proton magnetic resonance spectroscopy for differentiating recurrent or residual brain tumor from delayed cerebral necrosis.

PURPOSE: Delayed cerebral necrosis (DN) is a significant risk for brain tumor patients treated with high-dose irradiation. Although differentiating DN from tumor progression is an important clinical question, the distinction cannot be made reliably by conventional imaging techniques. We undertook a pilot study to assess the ability of proton magnetic resonance spectroscopy (1H MRS) to differentiate prospectively between DN or recurrent/residual tumor in a series of children treated for primary brain tumors with high-dose irradiation. METHODS AND MATERIALS: Twelve children (ages 3-16 years), who had clinical and MR imaging (MRI) changes that suggested a diagnosis of either DN or progressive/recurrent brain tumor, underwent localized 1H MRS prior to planned biopsy, resection, or other confirmatory histological procedure. Prospective 1H MRS interpretations were based on comparison of spectral peak patterns and quantitative peak area values from normalized spectra: a marked depression of the intracellular metabolite peaks from choline, creatine, and N-acetyl compounds was hypothesized to indicate DN, and median-to-high choline with easily visible creatine metabolite peaks was labeled progressive/recurrent tumor. Subsequent histological studies identified the brain lesion as DN or recurrent/residual tumor. RESULTS: The patient series included five cases of DN and seven recurrent/residual tumor cases, based on histology. The MRS criteria prospectively identified five out of seven patients with active tumor, and four out of five patients with histologically proven DN correctly. Discriminant analysis suggested that the primary diagnostic information for differentiating DN from tumor lay in the normalized MRS peak areas for choline and creatine compounds. CONCLUSIONS: Magnetic resonance spectroscopy shows promising sensitivity and selectivity for differentiating DN from recurrent/progressive brain tumor. A novel diagnostic index based on peak areas for choline and creatine compounds may provide a simple discriminant for differentiating DN from recurrent or residual primary brain tumors.

Adolescent↗
PubMed1995

Liver volume as a determinant of drug clearance in children and adolescents.

Many drugs eliminated by the liver exhibit age-related differences in systemic clearance, necessitating different dosage requirements in children and adults. However, the physiological basis for these age-related changes is not well defined, including the importance of liver size in determining systemic clearance. Therefore, magnetic resonance imaging was used to determine liver volume in pediatric and adolescent patients, in whom systemic clearance of three model substrates [lorazepam (0.03 mg/kg), antipyrine (10 mg/kg), and indocyanine green (ICG; 0.5 mg/kg)] was also determined. In 16 children (ages 3.3-18.8 years; 8 boys), liver volume ranged from 469 to 1640 ml (median 937), and was significantly related to age, body weight, and body surface area (BSA). Younger children had larger liver normalized to body weight (ml/kg), but there was no difference when liver volume was normalized to BSA (ml/m2). Unnormalized lorazepam and ICG clearances (ml/min) were significantly related to absolute liver volume (r2 = 50.2% and 31.4%, respectively), whereas unnormalized antipyrine clearance was not. Lorazepam, ICG, and antipyrine clearance normalized to BSA did not exhibit age-related changes, nor did lorazepam or ICG clearance normalized to body weight decreased significantly with increasing age (r2 = 36.9%, p=0.012), as did antipyrine clearance relative to liver volume. Thus, age-related changes in drug clearance and the importance of liver volume may differ based on the principal hepatic mechanisms involved in drug elimination.

Adolescent↗
PubMedDate not supplied

Automated pixel-by-pixel mapping of dynamic contrast-enhanced MR images for evaluation of osteosarcoma response to chemotherapy: preliminary results.

An automated technique for pixel-by-pixel computer mapping of tumor necrosis was developed to improve the accuracy and applicability of dynamic contrast agent-enhanced magnetic resonance (MR) imaging in assessing the response of osteosarcoma to preoperative chemotherapy. The technique was evaluated in nine osteosarcoma patients who underwent MR imaging at diagnosis (n = 7) and after preoperative chemotherapy (n = 9). Sequential FLASH (fast low-angle shot) images of the tumor were obtained in one plane every 15 seconds before and for 3 minutes after gadopentetate dimeglumine injection. A region of interest was selected that included the entire tumor area. Slopes representing percent increase in signal intensity over baseline values per minute were calculated automatically for each pixel and displayed as gray-scale maps of the tumor. Matching histologic maps of each tumor were obtained. Visual region-by-region comparison of the pixel and histologic maps showed a high degree of correlation and the ability of the MR imaging technique to help identify small foci of residual viable tumor.

Adolescent↗
PubMedDate not supplied

Discrete signal processing of dynamic contrast-enhanced MR imaging: statistical validation and preliminary clinical application.

A high-resolution image-based method was developed to analyze dynamic contrast agent-enhanced magnetic resonance images quantitatively. This method determines the initial rate of contrast agent accumulation, the delayed rate of accumulation, and the maximum enhancement in each pixel. These three parameters allow characterization of the dynamic signal features. Simulated noisy test sets of dynamic enhancement curves have shown this method to yield a fast and accurate characterization of the dynamic signal. Clinical examples of both qualitative image parameter maps and quantitative statistical analysis of the parameter distributions demonstrated the quality and potential of the technique. The technique is designed to yield imaging and quantitative information on contrast agent accumulation that can be useful in detecting residual tumor and evaluating response to therapy, while requiring less than 7 minutes of imaging time and 5 minutes of processing time per study.

Adult↗
PubMedDate not supplied

Precise and accurate measurement of proton T1 in human brain in vivo: validation and preliminary clinical application.

Precise and accurate inversion-recovery (PAIR) magnetic resonance (MR) measurements of T1 were obtained in eight brain regions and cerebrospinal fluid of 26 healthy volunteers. Accuracy of the technique was assessed by measuring T1 in small fluid volumes with the PAIR technique and with two independent spectroscopic techniques. The mean difference between T1 measured with PAIR and with the two spectroscopic techniques was 3.1% +/- 1.3. The precision (reproducibility) of measurements with the PAIR technique was excellent. The coefficient of variation (CV) across 16 measurements in a head phantom was 2.0%, compared with a CV of 2.7% across 45 separate measurements in a single subject. The within-subject CV was 1.8% +/- 0.6 in white matter and 1.4% +/- 1.0 in basal ganglia. The between-subject CV in 26 healthy volunteers was 3.6% +/- 0.6 in white matter and 4.1% +/- 1.9 in basal ganglia. Comparison between a patient with an active recurrent brain tumor and an age-matched patient with an inactive brain tumor showed that T1 was significantly elevated throughout the brain of the active-tumor patient, especially in white matter tracts, even though no tumor or edema was detected in the white matter on standard MR images. Comparisons between five brain tumor patients and four healthy volunteers of similar age showed that T1 was significantly and substantially elevated throughout the white matter tracts and in the caudate nucleus, putamen, and thalamus. These results are consistent with the hypothesis that white matter tracts are selectively vulnerable to edema and that T1 increases in white matter are a sensitive indicator of patient status or tumor aggressiveness.

Adolescent↗
PubMedDate not supplied

Dynamic contrast-enhanced MR imaging evaluation of osteosarcoma response to neoadjuvant chemotherapy.

Assessment of osteosarcoma response to neoadjuvant chemotherapy has prognostic implications, but conventional imaging techniques have been unable to provide an accurate quantitative measure of tumor response. We developed an analysis of dynamic contrast-enhanced MR imaging (DEMRI) to render an image of dynamic vector magnitudes (DVM) and to summarize the result in a quantitative parameter, mean DVM for the lesion (mu DVM). We compared the mu DVM from the examination before surgery with histologic results from an en bloc resection of the tumor in 19 cases. The final mu DVM value provided an accurate (89.5%) measure of tumor necrosis in osteosarcoma. Further, we analyzed the findings in 17 patients with osteosarcoma who completed three DEMRI examinations during the course of therapy. Tumors with higher mu DVM values at presentation had greater decreases in the parameter over the course of therapy. These results are consistent with the distribution of DVM values in these lesions serving as an indicator of tumor perfusion and a possible surrogate variable for drug delivery.

Adolescent↗
PubMedDate not supplied

Quantitative MR imaging of children with sickle cell disease: striking T1 elevation in the thalamus.

Nineteen patients with sickle cell disease (SCD) were examined with conventional MR imaging (cMRI), including T1- and T2-weighted sequences and MR angiography (MRA). qMRI mapping of T1 was also done using a precise and accurate inversion-recovery (PAIR) technique optimized and validated previously. In addition, 21 healthy African-American control subjects had the qMRI examination. Nonparametric Kruskal-Wallis analysis of variance of control subjects, of SCD patients without stroke, and of SCD patients with stroke showed that T1 increased with disease severity in the thalamus, frontal white matter, genu, and occipital white matter. T1 was significantly longer in SCD patients without stroke (n = 13) than in control subjects (n = 21) in the thalamus and frontal white matter. In addition, T1 values were significantly longer in SCD patients with stroke than in patients without stroke in the genu and frontal white matter. Abnormality of the thalamus was identified by qMRI in a substantial fraction of patients read as normal by both cMRI and MRA, suggesting that it may be possible to use T1 elevation to identify a subset of patients with SCD who are at elevated risk for stroke.

Adolescent↗
PubMedDate not supplied

Statistical error mapping for reliable quantitative T1 imaging.

We developed a statistically based error image for rapid appreciation of unreliable regions in quantitative water proton T1 images. The chi-squared error and co-efficient of variation of the fitted parameter were used to estimate uncertainties in the goodness-of-fit to mono-exponential T1 relaxation and the reliability of the calculated T1, respectively, for each pixel. Errors exceeding a statistical threshold based on a .1 acceptance criterion were displayed as a color-coded overlay on the T1 image. Error maps of quantitative T1 images from 31 healthy volunteers showed a characteristic error structure; few pixels within the parenchyma had excessive errors. Clinical cases with stroke and sickle cell disease showed deviations from the normal pattern in the spatial distribution and magnitude of chi-squared errors. Disease states may deviate from mono-exponential T1 relaxation more than normal brain does. The color-coded error map is a valuable tool for investigators using quantitative MR imaging to determine tissue relaxation parameters.

Adult↗