Biomedical subjects

J H Burdette

Publications and source records attributed to J H Burdette.

10 recordsLinked to original sources

PubMed2000

Enterobacter sakazakii brain abscess in the neonate: the importance of neuroradiologic imaging.

BACKGROUND: Enterobacter sakazakii is a rare but important cause of life-threatening neonatal sepsis and meningitis complicated by the development of brain abscess. OBJECTIVE: Given the neurotropic qualities of this organism, early diagnosis and treatment are crucial as a poor prognosis follows brain abscess formation. MATERIALS AND METHODS: Cross-sectional imaging (CT and MRI) play an important role in the diagnostic work-up. CONCLUSION: A biopsy-proven case of E. sakazakii brain abscess, which was diagnosed on MR images, is presented, and the importance of prompt radiologic imaging of the central nervous system in the work-up of patients with this life-threatening disease is discussed.

Biopsy↗

PubMed2000

False cerebral activation on BOLD functional MR images: study of low-amplitude motion weakly correlated to stimulus.

BACKGROUND AND PURPOSE: Movements of the participant during blood oxygen level-dependent (BOLD) functional MR imaging cerebral activation studies are known to produce occasionally regions of false activation, especially when these movements are relatively large (>3 mm) and highly correlated with the stimulus. We investigated whether minimal (<1 mm), weakly correlated movements in a controlled functional MR imaging model could produce false activation artifacts that could potentially mimic regions of true activation in size, location, and statistical significance. METHODS: A life-size brain phantom was constructed by embedding vials of a dilute carboxylic acid solution within a gadolinium-doped gelatin mold. Imaging was performed at 1.5 T using a 2D spiral sequence (3,000/5 [TR/TE]; flip angle, 88 degrees; matrix, 64 x 64; field of view, 24 cm; section thickness, 5 mm). Controlled, in-plane, submillimeter movements of the phantom were generated using a pneumatic system and were made to correlate with a hypothetical "boxcar" stimulus over the range 0.31 < r < 0.96. Regions of false activation were sought using standard statistical methods (SPM96) that excluded phantom edges and accounted for spatial extent (regions tested at P < .05, corrected for multiple comparisons). A similar experiment was performed on a resting volunteer. RESULTS: The pneumatic system provided motion control with average in-plane displacements and rotations of 0.74 mm and 0.47 degrees, respectively, in the 18 data sets analyzed. No areas of false activation in the phantom were identified for poorly correlated motions (r < 0.52). Above this level, false activations occurred with increasing frequency, scaling in size and number with the degree of motion correlation. For motions with r > 0.67, areas of false activation were seen in every experiment. For a statistical threshold of P = .001, the median number of falsely activated regions was 3.5, with a mean size of 71.7 voxels (approximately 5 cc). Areas of possibly false activation of average size 72.5 voxels resulting from passive motion of the resting human participant were observed in two of four experiments. CONCLUSION: Participant movements of 1 mm or less that are only modestly correlated with a blocked stimulus paradigm can produce appreciable false activation artifacts on BOLD functional MR imaging studies, even when strict image realignment methods are used to prevent them.

Artifacts↗

PubMed1999

Acute cerebral infarction: quantification of spin-density and T2 shine-through phenomena on diffusion-weighted MR images.

PURPOSE: To quantify the relative contributions of spin density and T2 effects ("shine through") on diffusion-weighted (DW) magnetic resonance (MR) images of acute and subacute cerebral infarction. MATERIALS AND METHODS: In 30 patients, 1.5-T imaging was performed within the first 7 days after onset of cerebral infarction. Estimates of T2, spin density, and apparent diffusion coefficient (ADC) in the region of stroke and contralateral normal brain were computed by means of standard regression techniques after quadruple-echo conventional MR imaging and single-shot echo-planar DW imaging with a maximum b value of 1,000 sec/mm2. Expected signal intensity (S) enhancement ratios resulting from independent changes in T2, spin density, and ADC were then calculated for the DW sequence. RESULTS: The overall SI of cerebral infarction on DW images was significantly higher than that of normal brain throughout the 1st week after stroke (mean relative SI enhancement ratio, 2.29; P < .001). During the first 2 days after stroke, decreased ADC within the stroke region made the dominant contribution to increased SI on DW images. By day 3, increased T2 values in the stroke region became equally important, and, from days 3-7, the contribution to SI from T2 effects became dominant. A slight increase of spin density in the stroke region made a relatively small and constant contribution to DW SI over the 1st week. CONCLUSION: The increased SI of subacute cerebral infarction on DW images reflects not only a shortening of ADC but a prolongation of T2 and spin-density values.

Acute Disease↗

PubMed1999

A comparison of fast spin-echo, fluid-attenuated inversion-recovery, and diffusion-weighted MR imaging in the first 10 days after cerebral infarction.

BACKGROUND AND PURPOSE: Echo-planar diffusion-weighted and fluid-attenuated inversion-recovery (FLAIR) imaging have both proved valuable for detecting acute ischemic infarcts, but little is known about the value of diffusion-weighted imaging beyond the acute infarct period. Furthermore, no direct comparison of the techniques has been published. We compared the diagnostic utility of diffusion-weighted, FLAIR, and T2-weighted fast spin-echo (FSE) imaging for detecting cerebral infarctions up to 10 days old. METHODS: FSE, FLAIR, and diffusion-weighted MR sequences were obtained prospectively over a 6-month period in 212 patients with suspected cerebral infarctions. Seventy patients with nonhemorrhagic ischemic infarcts less than 10 days old whose symptoms lasted longer than 48 hours were identified. The three sequences were compared for detectability and conspicuity of abnormalities that correlated with the neurologic deficit. RESULTS: Seventy-two symptomatic infarcts were found in the 70 patients. Diffusion-weighted imaging detected 70 (97%), FLAIR, 69 (96%), and FSE, 64 (89%) of the 72 lesions. Only the difference between diffusion-weighted and FSE imaging approached statistical significance. There was no difference in the number of lesions detected in the patients imaged 48 hours or more after infarction. Lesion conspicuity on diffusion-weighted images was judged superior to that on FSE and FLAIR images in 55 (77%) and 47 (67%) of the cases, respectively. FLAIR images were judged superior to FSE in 34 (48%) of the cases. CONCLUSION: Diffusion-weighted images showed more infarcts than FLAIR and FSE images, and FLAIR images showed more than FSE images, but the differences were not statistically significant. Lesion conspicuity, however, was consistently better on diffusion-weighted images than on either FLAIR or FSE images throughout the 10-day period. Acquisition of diffusion-weighted images in the late acute and subacute periods after ischemic cerebral infarction appears to be beneficial.

Acute Disease↗

PubMed1998

Cerebral infarction: time course of signal intensity changes on diffusion-weighted MR images.

OBJECTIVE: The objective of this study was to determine the time course of signal intensity changes on diffusion-weighted MR images after cerebral infarction. MATERIALS AND METHODS: Echoplanar diffusion-weighted MR images were obtained at 1.5 T in 212 patients referred for suspected cerebral infarction over a 6-month period. Of those patients, 85 met strict criteria for inclusion in this study: final clinical diagnosis of stroke, reliable timing of clinical ictus by history, and neurologic symptoms persisting longer than 48 hr after onset. Using adjacent or contralateral normal brain for comparison, diffusion-weighted images were visually analyzed retrospectively to evaluate for abnormalities in signal intensity. Because three patients were scanned on two occasions and five patients had two anatomically separable infarctions, 93 reliably dated brain lesions were analyzed. RESULTS: Diffusion-weighted images showed abnormal findings in 13 (100%) of 13 lesions less than 1 day old, 46 (96%) of 48 lesions 1-4 days old, 16 (94%) of 17 lesions 5-9 days old, three (60%) of five lesions 10-14 days old, and zero (0%) of 10 lesions more than 14 days old. CONCLUSION: Abnormal signal intensity was present on all diffusion-weighted MR studies obtained in patients within 24 hr of acute cerebral infarction and in up to 94% of patients scanned during the first 2 weeks after ictus. The percentage of abnormal diffusion studies declined with time, and no signal intensity abnormality was seen in stroke patients scanned more than 2 weeks after symptom onset.

Aged↗

PubMed1996

Alzheimer disease: improved visual interpretation of PET images by using three-dimensional stereotaxic surface projections.

PURPOSE: To compare the diagnostic usefulness of three-dimensional (3D) stereotaxic surface projection (SSP) with that of standard transaxial display in brain positron emission tomography (PET) in Alzheimer disease (AD). MATERIALS AND METHODS: Standard transaxial section display and 3D-SSP PET image sets obtained after administration of 2-deoxy-2-[fluorine-18]fluoro-D-glucose in 39 patients with probable AD (aged 53-82 years; 15 men, 24 women) and 40 subjects without AD (aged 21-78 years; 14 men, 26 women) were randomly interpreted. Receiver operating characteristic (ROC) analysis was performed. RESULTS: Diagnostic performance was superior with 3D SSP (Az[section]=0.94,Az[3D SSP]=0.99[Az=area under the ROC curve];P=.043). With 3D SSP, diagnosis of AD was equally good in beginners and experts. The sensitivity and specificity in questionable or mild dementia were 94% and 99% with 3D SSP and 79% and 88% with standard transaxial display. CONCLUSION: Accuracy of detecting AD was improved in PET with 3D SSP.

Aged↗

PubMed1985

The influence of ascorbic acid on the occurrence of tibial dyschondroplasia in young broiler chickens.

Two distinctly different basal diets were used to test the influence of supplementary ascorbic acid on the occurrence of tibial dyschondroplasia. Addition of either .1 or .25% ascorbic acid to these diets did not alter the occurrence of tibial dyschondroplasia in 25-day-old broiler chickens. However, supplementary ascorbic acid did increase the amounts of ascorbic acid present in blood plasma. Also, individual differences in circulating ascorbic acid were not associated with this disease. Furthermore, two strains of chickens selected for high or low incidence of tibial dyschondroplasia had similar amounts of this vitamin in blood plasma. In contrast to the results reported for the Willow Ptarmigan, ascorbic acid does not appear to be involved in the development of tibial dyschondroplasia in the young broiler chicken.

Animals↗

PubMed1981

Effect of fasting on hormones and metabolites in plasma of fast-growing, lean and slow-growing obese pigs.

Plasma concentrations of glucose, free fatty acids (FFA), insulin and growth hormone (GH) were determined immediately after food removal and then hourly for 24 hours. Blood was sampled from six lean and six obese pigs at 10 weeks of age via indwelling catheters. Plasma glucose decreased but was similar in both pig strains shortly after feed removal; at the end of the 24-hr fast, plasma glucose was higher (P less than .01) in lean pigs. Plasma FFA concentrations were similar in lean and obese pigs and increased five-fold within 24 hr of fasting. Plasma insulin was higher (P less than .05) in obese pigs than in lean pigs immediately after food removal only (21.4 +/- 3.0 vs 9.8 +/- 2.4 microU/ml). Pattern of GH secretion over 24 hr was episodic; average plasma GH was lower in obese pigs than in lean pigs (2.8 +/- .7 vs 9.4 +/- 1.9 ng/ml). In summary, FFA mobilization was similar in lean and obese pigs, GH concentrations were lower in plasma of obese pigs and relative differences in plasma glucose and insulin between pig strains were influenced by time after feed removal.

Animals↗

PubMedDate not supplied

Calculation of apparent diffusion coefficients (ADCs) in brain using two-point and six-point methods.

We evaluated the relative accuracy of calculating apparent diffusion coefficients (ADCs) of intracranial tissues using a two-point versus a six-point regression technique. Echo planar diffusion-weighted MRI was performed at 1.5 T in three standard locations and in pathologic regions in 10 subjects using gradient strengths corresponding to b values of 1, 100, 200, 500, 800, and 1,000 s/mm2. Estimation of ADCs was made using two methods: a nonlinear regression model using measurements from the full set of b values (six-point technique) and linear estimation using b values of 1 and 1,000 only (two-point technique). A high correlation between the two methods was noted (R2 = 0.999), and the mean percentage difference was 0.84%. These results suggest there is little error in estimating brain ADCs using a two-point technique.

Adult↗

PubMedDate not supplied

High b-value diffusion-weighted MRI of normal brain.

PURPOSE: As MR scanner hardware has improved, allowing for increased gradient strengths, we are able to generate higher b values for diffusion-weighted (DW) imaging. Our purpose was to evaluate the appearance of the normal brain on DW MR images as the diffusion gradient strength ("b value") is increased from 1,000 to 3,000 s/mm2. METHOD: Three sets of echo planar images were acquired at 1.5 T in 25 normal subjects (mean age 61 years) using progressively increasing strengths of a diffusion-sensitizing gradient (corresponding to b values of 0, 1,000, and 3,000 s/mm2). All other imaging parameters remained constant. Qualitative assessments of trace images were performed by two neuroradiologists, supplemented by quantitative measures of MR signal and noise in eight different anatomic regions. RESULTS: As gradient strength increased from b = 1,000 to 3,000, both gray and white matter structures diminished in signal as expected based on their relative diffusion coefficients [calculated average apparent diffusion coefficient (ADC) values: gray matter = 8.5 x 10(-4) mm2/s, white matter = 7.5 x 10(-4) mm2/s]. The signal-to-noise ratios for the b = 1,000 images were approximately 2.2 times higher than for the b = 3,000 images (p < 0.0001). As the strength of the diffusion-sensitizing gradient increased, white matter became progressively hyperintense to gray matter. Relative to the thalamus, for example, the average MR signal intensity of white matter structures increased by an average of 27.5%, with the densely packed white matter tracts (e.g., middle cerebellar peduncle, tegmentum, and internal capsule) increasing the most. CONCLUSION: Brain DW images obtained at b = 3,000 appear significantly different from those obtained at b = 1,000, reflecting expected loss of signal from all areas of brain in proportion to their ADC values. Consequently, when all other imaging parameters are held constant, b = 3,000 DW images appear significantly noisier than b = 1,000 images, and white matter tracts are significantly more hyperintense than gray matter structures.

Adult↗