Biomedical subjects

S R Williams

Publications and source records attributed to S R Williams.

At least 37 records · Page 2Linked to original sources

PubMed2000

Apparent diffusion coefficient and MR relaxation during osmotic manipulation in isolated turtle cerebellum.

The apparent diffusion coefficient (ADC) and relaxation times of water were measured by magnetic resonance imaging (MRI) in the isolated turtle cerebellum during osmotic cell volume manipulation. The aim was to study effects of cell volume changes, a factor in ischemia and spreading depression, in isolation from considerations of blood flow and metabolism. Cerebella were superfused at 12-14 degrees C with solutions ranging from 50-200% normal osmolarity. Hypotonic solutions, which are known to cause cell swelling, led to reductions of ADC and increases of T(2), while hypertonic solutions had the opposite effect. This supports the concept that ADC varies with the extracellular space fraction and, combined with published data on extracellular ion diffusion, is consistent with fast or slow exchange models with effective diffusion coefficients that are approximately 1.7 times lower in intracellular than in extracellular space. Spin-spin relaxation can be affected by osmotic disturbance, though such changes are not seen in all pathologies that cause cell swelling.

Animals↗

PubMed2000

Acute changes in MRI diffusion, perfusion, T(1), and T(2) in a rat model of oligemia produced by partial occlusion of the middle cerebral artery.

Oligemic regions, in which the cerebral blood flow is reduced without impaired energy metabolism, have the potential to evolve toward infarction and remain a target for therapy. The aim of this study was to investigate this oligemic region using various MRI parameters in a rat model of focal oligemia. This model has been designed specifically for remote-controlled occlusion from outside an MRI scanner. Wistar rats underwent remote partial MCAO using an undersize 0.2 mm nylon monofilament with a bullet-shaped tip. Cerebral blood flow (CBF(ASL)), using an arterial spin labeling technique, the apparent diffusion coefficient of water (ADC), and the relaxation times T(1) and T(2) were acquired using an 8.5 T vertical magnet. Following occlusion there was a decrease in CBF(ASL) to 35 +/- 5% of baseline throughout the middle cerebral artery territory. During the entire period of the study there were no observed changes in the ADC. On occlusion, T(2) rapidly decreased in both cortex and basal ganglia and then normalized to the preocclusion values. T(1) values rapidly increased (within approximately 7 min) on occlusion. In conclusion, this study demonstrates the feasibility of partially occluding the middle cerebral artery to produce a large area of oligemia within the MRI scanner. In this region of oligemic flow we detect a rapid increase in T(1) and decrease in T(2). These changes occur before the onset of vasogenic edema. We attribute the acute change in T(2) to increased amounts of deoxyhemoglobin; the mechanisms underlying the change in T(1) require further investigation.

Animals↗

PubMed2000

Burst excitation for quantitative diffusion imaging with multiple b-values.

A quantitative imaging sequence has been developed to exploit the intrinsic sensitivity of Burst NMR data to molecular diffusion. In the scan time of a single spin echo experiment, it is possible to acquire many images of the same slice, with a different T(2) and diffusion weighting. Under favorable conditions, it is possible to obtain both the diffusion coefficient and T(2) from the same experiment; or, by correcting for T(2) relaxation using a control image, more precise diffusion coefficients may be measured. The quantitative values in rat brain are in agreement with those from conventional experiments. The major gains of this method are the potentially reduced scan time, the higher number of acquired images corresponding to different diffusion weightings, the reduced sensitivity to inter-scan motion artifact and to local variations in magnetic susceptibility, and an automatic co-registration between T(2) and diffusion images. Problems with the sequence include a lower signal-to-noise ratio than is achievable with diffusion-weighted spin-echo imaging, the limitation of measuring only in-plane components of diffusion and, at present, single-slice acquisition.

Animals↗

PubMed2000

Prospective evaluation of mild to moderate pediatric acetaminophen exposures.

STUDY OBJECTIVE: To determine whether pediatric patients with acute, mild to moderate acetaminophen exposures, treated with home monitoring alone, develop systemic signs of hepatic injury. METHODS: A prospective, observational study of calls to a regional poison center over a 25-month period was performed. Patients were eligible for the study if they were younger than 7 years and had an acute maximum possible acetaminophen exposure of up to 200 mg/kg. Exclusion criteria included previous decontamination measures, possibility of ingestion of an extended-release preparation, health or medication issues that could increase susceptibility to hepatotoxicity, current symptoms of hepatotoxicity, and indeterminable ingestions. Study protocol included reviewing the signs and symptoms of early and late acetaminophen toxicity, a 4- to 6-hour follow-up call, and a 72-hour follow-up call. Outcome measures were defined as a verbal report by the patient's parent or guardian of the presence or absence of signs or symptoms of hepatotoxicity. RESULTS: A total of 1,039 patients were enrolled in the study, including 519 girls and 520 boys, with exposures ranging from 20 to 200 mg/kg. Eighteen patients were lost to follow-up; data were incomplete for 2 patients. At 72-hour follow-up, the remaining 1,019 patients were all doing well, without signs or symptoms of hepatotoxicity. CONCLUSION: On the basis of these data, pediatric patients with acute acetaminophen exposures of up to 200 mg/kg, treated with home monitoring alone, do not develop signs or symptoms of hepatic injury.

Acetaminophen↗

PubMed2000

Anterior electroencephalographic asymmetry changes in elderly women in response to a pleasant and an unpleasant odor.

Greater left than right frontal EEG activation has been associated with increased positive and/or decreased negative affect, whereas greater right than left frontal activation has been associated with the opposite pattern. Substantial research has documented the trait properties of asymmetry, as well as responses to pleasant and unpleasant stimuli. The present study examined changes in anterior alpha asymmetries in response to pleasant (vanilla), unpleasant (valerian), and neutral (water) odors. As predicted, vanilla produced relative left frontal activation compared to valerian and water. Frontal asymmetry did not differ in response to valerian compared to water. The results are consistent with the hypothesis that the left frontal region of the brain is involved in positive/approach-related emotion, and extend previous results into the olfactory realm.

Affect↗

PubMed2000

Gene expression analysis by massively parallel signature sequencing (MPSS) on microbead arrays.

We describe a novel sequencing approach that combines non-gel-based signature sequencing with in vitro cloning of millions of templates on separate 5 microm diameter microbeads. After constructing a microbead library of DNA templates by in vitro cloning, we assembled a planar array of a million template-containing microbeads in a flow cell at a density greater than 3x10(6) microbeads/cm2. Sequences of the free ends of the cloned templates on each microbead were then simultaneously analyzed using a fluorescence-based signature sequencing method that does not require DNA fragment separation. Signature sequences of 16-20 bases were obtained by repeated cycles of enzymatic cleavage with a type IIs restriction endonuclease, adaptor ligation, and sequence interrogation by encoded hybridization probes. The approach was validated by sequencing over 269,000 signatures from two cDNA libraries constructed from a fully sequenced strain of Saccharomyces cerevisiae, and by measuring gene expression levels in the human cell line THP-1. The approach provides an unprecedented depth of analysis permitting application of powerful statistical techniques for discovery of functional relationships among genes, whether known or unknown beforehand, or whether expressed at high or very low levels.

Cell Line↗

PubMed2000

Intestinal metabolism after ischemia-reperfusion.

PURPOSE: This study explores the effects of ischemia-reperfusion on various metabolic aspects of the small intestine. METHODS: Intestinal ischemia-reperfusion was obtained by clamping and unclamping the superior mesenteric artery in adult rats. Four groups of animals were studied: (A) sham operation for 150 minutes, (B) 90-minute intestinal ischemia, (C) 150-minute intestinal ischemia, and (D) 90-minute intestinal ischemia followed by 60-minute reperfusion. Body temperature was maintained at normothermia (36.5 to 37.5 degrees C). Concentrations of intestinal glucose, succinate, lactate, amino acids, phosphocholine (PC), glycerophosphocholine (GPC), choline, and phosphoenergetics were measured using magnetic resonance spectroscopy of freeze-clamped small intestine extracts. RESULTS: Intestinal ischemia (groups B and C) alone caused a significant drop in glucose and phosphoenergetics but caused an increase in amino acids, succinate, and lactate. Ischemia and ischemia-reperfusion decreased PC and GPC but increased choline. After intestinal reperfusion (group D), no recovery of phosphoenergetics was observed, but there was partial recovery of glucose, succinate, lactate, and amino acids. CONCLUSIONS: There is no recovery of phosphoenergetics after 90 minutes of intestinal ischemia followed by 60 minutes of reperfusion. Partial recovery of glucose, succinate, lactate, and amino acids may reflect equilibration of these metabolites between damaged cells and extracellular fluid.

Amino Acids↗

PubMed2000

Falsely elevated digoxin level of 45.9 ng/mL due to interference from human antimouse antibody.

CASE REPORT: We report the case of a 77-year-old man who was admitted to the intensive care unit with a serum digoxin level of 45.9 ng/mL. The patient was hemodynamically stable throughout his hospital course and did not require antidigoxin antibody fragments. The elevated digoxin level was determined by subsequent testing to be falsely elevated by interference from human antimouse antibodies in his serum. A repeat digoxin measurement using an assay not affected by human antimouse antibodies indicated a level of 1.3 ng/mL. Newer digoxin assays are not affected by human antimouse antibody interference, but clinicians should be aware of possible human antimouse antibody interference with older digoxin assays and in other tests utilizing mouse monoclonal antibody reagents.

Aged↗

PubMed2000

Elevated plasma cholecystokinin at high altitude: metabolic implications for the anorexia of acute mountain sickness.

The aims of the present study were to measure the satiety neuropeptide cholecystokinin (CCK) in humans at terrestrial high altitude to investigate its possible role in the pathophysiology of anorexia, cachexia, and acute mountain sickness (AMS). Nineteen male mountaineers aged 38 +/- 12 years participated in a 20 +/- 5 day trek to Mt. Kanchenjunga basecamp (BC) located at 5,100 m, where they remained for 7 +/- 5 days. Subjects were examined at rest and during a maximal exercise test at sea-level before/after the expedition (SL1/SL2) and during the BC sojourn. There was a mild increase in Lake Louise AMS score from 1.1 +/- 1.2 points at SL1 to 2.3 +/- 2.3 points by the end of the first day at BC (P < 0.05). A marked increase in resting plasma CCK was observed on the morning of the second day at BC relative to sea-level control values (62.9 +/- 42.2 pmol/L(-1) vs. SL1: 4.3 +/- 8.3 pmol/L(-1), P < 0.05 vs. SL2: 26.5 +/- 25.2 pmol/L(-1), P < 0.05). Maximal exercise increased CCK by 78.5 +/- 24.8 pmol/L(-1), (P < 0.05 vs. resting value) during the SL1 test and increased the plasma concentration of non-esterified fatty acids and glycerol at BC (P < 0.05 vs. SL1/SL2). The CCK response was not different in five subjects who presented with anorexia on Day 2 compared with those with a normal appetite. While there was no relationship between the increase in CCK and AMS score at BC, a more pronounced increase in resting CCK was observed in subjects with AMS (> or =3 points at the end of Day 1 at BC) compared with those without (+98.9 +/- 1.4 pmol/L(-1) vs. +67.6 +/- 37.2 pmol/L(-1), P < 0.05). Caloric intake remained remarkably low during the stay at BC (8.9 +/- 1.4 MJ.d(-1)) despite a progressive decrease in total body mass (-4.5 +/- 2.1 kg after 31 +/- 13 h at BC, P < 0.05 vs. SL1/SL2), which appeared to be due to a selective loss of torso adipose tissue. These findings suggest that the satiogenic effects of CCK may have contributed to the observed caloric deficit and subsequent cachexia at high altitude despite adequate availability of palatable foods. The metabolic implications of elevated CCK in AMS remain to be elucidated.

Adult↗

PubMed2000

The relationship between the apparent diffusion coefficient measured by magnetic resonance imaging, anoxic depolarization, and glutamate efflux during experimental cerebral ischemia.

A reduction in the apparent diffusion coefficient (ADC) of water measured by magnetic resonance imaging (MRI) has been shown to occur early after cerebrovascular occlusion. This change may be a useful indicator of brain tissue adversely affected by inadequate blood supply. The objective of this study was to test the hypothesis that loss of membrane ion homeostasis and depolarization can occur simultaneously with the drop in ADC. Also investigated was whether elevation of extracellular glutamate ([GLU]e) would occur before ADC changes. High-speed MRI of the trace of the diffusion tensor (15-second time resolution) was combined with simultaneous recording of the extracellular direct current (DC) potential and on-line [GLU]e from the striatum of the anesthetized rat. After a control period, data were acquired during remote middle cerebral artery occlusion for 60 minutes, followed by 30 minutes of reperfusion, and cardiac arrest-induced global ischemia. After either focal or global ischemia, the ADC was reduced by 10 to 25% before anoxic depolarization occurred. After either insult, the time for half the maximum change in ADC was significantly shorter than the corresponding DC potential parameter (P < 0.05). The [GLU]e remained at low levels during the entire period of varying ADC and DC potential and did not peak until much later after either ischemic insult. This study demonstrates that ADC changes can occur before membrane depolarization and that high [GLU]e has no involvement in the early rapid ADC decrease.

Animals↗

PubMed2000

Hypercarbia and mild hypothermia, only when not combined, improve postischemic bioenergetic recovery in neonatal rat brain slices.

In the immature brain, postischemic metabolism may be influenced beneficially by the effect of inducing hypercarbia or hypothermia. With use of 31P nuclear magnetic resonance spectroscopy, intracellular pH (pHi) and cellular energy metabolites in ex vivo neonatal rat cerebral cortex were measured before, during, and after substrate and oxygen deprivation in in vitro ischemia. Early postischemic hypothermia (fall in temperature -3.2 +/- 1.0 degrees C) delayed the normalization of pHi after ischemia by inducing an acid shift in pHi (P < 0.01). Postischemic hypercarbia (Krebs-Henseleit bicarbonate buffer equilibrated with 10% carbon dioxide in oxygen) and hypothermia induced separate, but potentially additive, reversible decreases in pHi, each of approximately -0.16 pH unit (P < 0.05). When these postischemic perturbations were applied in isolation, there was significant improvement of approximately 20% in the recovery of beta-ATP (P < 0.05). In combination, however, hypercarbia and hypothermia worsened recovery in ATP by approximately 20% (P < 0.05). In control tissue, which had not been exposed to ischemia, ATP content was also significantly reduced by co-administration of the two treatments (P < 0.05), an effect that persisted even after discontinuing the perturbing conditions. Therefore, in this vascular-independent neonatal preparation, early postischemic modulation of metabolism by hypercarbia or hypothermia appears to confer improved bioenergetic recovery, but only if they are not administered together.

Adenosine Triphosphate↗

PubMed2000

Site independence of EPSP time course is mediated by dendritic I(h) in neocortical pyramidal neurons.

Neocortical layer 5 pyramidal neurons possess long apical dendrites that receive a significant portion of the neurons excitatory synaptic input. Passive neuronal models indicate that the time course of excitatory postsynaptic potentials (EPSPs) generated in the apical dendrite will be prolonged as they propagate toward the soma. EPSP propagation may, however, be influenced by the recruitment of dendritic voltage-activated channels. Here we investigate the properties and distribution of I(h) channels in the axon, soma, and apical dendrites of neocortical layer 5 pyramidal neurons, and their effect on EPSP time course. We find a linear increase (9 pA/100 microm) in the density of dendritic I(h) channels with distance from soma. This nonuniform distribution of I(h) channels generates site independence of EPSP time course, such that the half-width at the soma of distally generated EPSPs (up to 435 microm from soma) was similar to somatically generated EPSPs. As a corollary, a normalization of temporal summation of EPSPs was observed. The site independence of somatic EPSP time course was found to collapse after pharmacological blockade of I(h) channels, revealing pronounced temporal summation of distally generated EPSPs, which could be further enhanced by TTX-sensitive sodium channels. These data indicate that an increasing density of apical dendritic I(h) channels mitigates the influence of cable filtering on somatic EPSP time course and temporal summation in neocortical layer 5 pyramidal neurons.

Animals↗

PubMed2000

Time course and magnitude of movement-related gating of tactile detection in humans. II. Effects of stimulus intensity.

This study examined the effect of systematically varying stimulus intensity on the time course and magnitude of movement-related gating of tactile detection and scaling in 17 human subjects trained to perform a rapid abduction of the right index finger (D2) in response to a visual cue. Electrical stimulation was delivered to D2 at five different intensities. At the lowest intensity, approximately 90% of stimuli were detected at rest (1 x P(90)); four multiples of this intensity were also tested (1.25, 1.5, 1.75, and 2. 0 x P(90)). At all intensities of stimulation, detection of stimuli applied to the moving digit was diminished significantly and in a time-dependent manner, with peak decreases occurring within +/-12 ms of the onset of electromyographic activity in the first dorsal interosseous (25-45 ms before movement onset). Reductions in the proportion of stimuli detected were greatest at the lowest stimulus intensity and progressively smaller at higher intensities. No shift in the timing of the decreases in performance was seen with increasing intensity. Once the weakest intensity at which most stimuli were perceived during movement had been established (2 x P(90)), magnitude estimation experiments were performed using two stimulus intensities, 2 x P(90) (5 subjects) and 3 x P(90) (3 subjects). Significant movement-related decreases in estimated stimulus magnitude were observed at both intensities, the time course of which was similar to the time course of reductions in detection performance. As stimulus intensity increased, the magnitude of the movement-related decrease in scaling diminished. A model of detection performance that accurately described the effect of stimulus intensity and timing on movement-related reductions in detection was created. This model was then combined with a previous model that described the effects of stimulus localization and timing to predict detection performance at a given stimulation site, intensity, and time during movement. Movement-related gating of tactile perception represents the end result of movement-related effects on the transmission and subsequent processing of the stimulus. The combined model clearly defines many of the requirements that proposed physiological mechanisms of movement-related gating will have to fulfill.

Adolescent↗

PubMed1999

Mechanisms and consequences of action potential burst firing in rat neocortical pyramidal neurons.

1. Electrophysiological recordings and pharmacological manipulations were used to investigate the mechanisms underlying the generation of action potential burst firing and its postsynaptic consequences in visually identified rat layer 5 pyramidal neurons in vitro. 2. Based upon repetitive firing properties and subthreshold membrane characteristics, layer 5 pyramidal neurons were separated into three classes: regular firing and weak and strong intrinsically burst firing. 3. High frequency (330 +/- 10 Hz) action potential burst firing was abolished or greatly weakened by the removal of Ca2+ (n = 5) from, or by the addition of the Ca2+ channel antagonist Ni2+ (250-500 microm; n = 8) to, the perfusion medium. 4. The blockade of apical dendritic sodium channels by the local dendritic application of TTX (100 nM; n = 5) abolished or greatly weakened action potential burst firing, as did the local apical dendritic application of Ni2+ (1 mM; n = 5). 5. Apical dendritic depolarisation resulted in low frequency (157 +/- 26 Hz; n = 6) action potential burst firing in regular firing neurons, as classified by somatic current injection. The intensity of action potential burst discharges in intrinsically burst firing neurons was facilitated by dendritic depolarisation (n = 11). 6. Action potential amplitude decreased throughout a burst when recorded somatically, suggesting that later action potentials may fail to propagate axonally. Axonal recordings demonstrated that each action potential in a burst is axonally initiated and that no decrement in action potential amplitude is apparent in the axon > 30 microm from the soma. 7. Paired recordings (n = 16) from synaptically coupled neurons indicated that each action potential in a burst could cause transmitter release. EPSPs or EPSCs evoked by a presynaptic burst of action potentials showed use-dependent synaptic depression. 8. A postsynaptic, TTX-sensitive voltage-dependent amplification process ensured that later EPSPs in a burst were amplified when generated from membrane potentials positive to -60 mV, providing a postsynaptic mechanism that counteracts use-dependent depression at synapses between layer 5 pyramidal neurons.

Action Potentials↗

PubMed1999

All thalamocortical neurones possess a T-type Ca2+ 'window' current that enables the expression of bistability-mediated activities.

1. The existence of a non-negligible steady-state ('window') component of the low threshold, T-type Ca2+current (IT) and an appropriately large ratio of IT to ILeak conductance (i.e. gT/gLeak) have been shown to underlie a novel form of intrinsic bistability that is present in about 15 % of thalamocortical (TC) neurones. 2. In the present experiments, the dynamic clamp technique was used to introduce into mammalian TC neurones in vitro either an artificial, i.e. computer-generated, IT in order to enhance endogenous IT, or an artificial inward ILeak to decrease endogenous ILeak. Using this method, we were able to investigate directly whether the majority of TC neurones appear non-bistable because their intrinsic ionic membrane properties are essentially different (i.e. presence of a negligible IT 'window' component), or simply because they possess a gT or gLeak conductance that is insufficiently large or small, respectively. 3. The validity of the dynamic clamp arrangement and the accuracy of artificial IT were confirmed by (i) recreating the low threshold calcium potential (LTCP) with artificial IT following its block by Ni2+ (0.5-1 mM), and (ii) blocking endogenous LTCPs with an artificial outward IT. 4. Augmentation of endogenous IT by an artificial analog or introduction of an artificial inward ILeak transformed all non-bistable TC neurones to bistable cells that expressed the full array of bistability-mediated behaviours, i.e. input signal amplification, slow oscillatory activity and membrane potential bistability. 5. These results demonstrate the existence of a non-negligible IT 'window' component in all TC neurones and suggest that rather than being a novel group of neurones, bistable cells are merely representative of an interesting region of dynamical modes in the (gT, gLeak) parameter space that may be expressed under certain physiological or pathological conditions by all TC neurones and other types of excitable cells that possess an IT 'window' component with similar biophysical properties.

Animals↗

PubMed1999

Examination of the metabolic status of rat air pouch inflammatory exudate by high field proton NMR spectroscopy.

High field proton (1H) NMR spectroscopy was employed to investigate the metabolic status of rat air pouch inflammatory exudates obtained subsequent to the induction of inflammation with carrageenan, and the 1H NMR profiles of these fluids were compared and contrasted with those of inflammatory human synovial fluid, rat plasma and human serum. The characteristic biochemical features obtained from 1H NMR analysis of these exudates consisted of (1) substantially elevated levels of lactate (11.40+/-1.46x10-3 mol dm-3 for samples collected at a time point of 24 h post induction) with little or no NMR-detectable glucose, data consistent with a hypoxic environment and consequent anaerobic metabolism in the inflamed air pouch, and (2) high levels of the ketone body 3-d-hydroxybutyrate, providing evidence for an increased utilization of fats for energy by lymphocytes, the predominant leucocytes present in this environment. These phenomena represent a pathological extreme of the abnormal metabolic status of inflammatory human synovial fluids.

Air↗

PubMed1999

Recurrent and persistent coagulopathy following pit viper envenomation.

BACKGROUND: Coagulation abnormalities following crotaline (pit viper) snakebite have traditionally been considered short-lived, but laboratory studies have rarely been reported beyond the first few days of treatment for envenomation. During the course of an antivenom clinical trial, we observed coagulation defects as late as 2 weeks following envenomation. OBJECTIVES: To document and characterize the recurrence or persistence of coagulopathy among patients envenomed by pit vipers and treated with a Fab antivenom. METHODS: Patients with moderate pit viper envenomation were enrolled in a multicenter, prospective clinical trial. A Fab-based antivenom preparation, antivenom polyvalent crotalid (ovine) Fab, was administered in all cases. Platelet count, fibrinogen level, presence of fibrin split products, prothrombin time, and partial thromboplastin time were determined before treatment and at standard intervals during the following 2 weeks. RESULTS: Of 38 patients completing the study, 20 (53%) had recurrent, persistent, or late coagulopathy 2 to 14 days after envenomation. Thrombocytopenia occurred in patients with prior thrombocytopenia; hypofibrinogenemia occurred only in those with prior hypofibrinogenemia or positive fibrin split products. No patient experienced significant spontaneous bleeding. One patient with coagulopathy developed minor bleeding following minor surgery 12 days after envenomation. CONCLUSIONS: Prolonged or recurrent coagulopathy may occur after envenomation by North American pit vipers. Patients treated with Fab-based antivenom may benefit from periodic rather than single-bolus dosing. Patients with coagulopathy should undergo close monitoring during the first 2 weeks after snakebite.

Adolescent↗

PubMed1999

Rapid T2* mapping using interleaved echo planar imaging.

Magnetic resonance imaging methods that are sensitive to T2* are widely used in the study of blood oxygenation changes, most notably in functional studies of the brain. In these studies the signal intensity change in T2*-weighted imaging is related to the coupling of cerebral blood flow and metabolism. Rapid measurement of T2* itself would offer a valuable method to quantify blood oxygenation changes indirectly and monitor their time course. An interleaved echoplanar imaging (EPI) sequence is presented here that allows maps of T2* to be generated in a few seconds. The sequence benefits from reduced geometric distortion and an improved point spread function compared with single-shot EPI. A comparison among a set of T2*-weighted interleaved EPI images, single-shot EPI, and conventional gradient-echo and spin-echo methods is made using a compartmentalized doped water phantom. The interleaved sequence yields accurate T2* values when compared with reference measurements made using the slower gradient-echo technique. Data acquired from the rat brain at 2.35 T prior to and during an anoxic challenge show, with high temporal resolution, the reduction in T2* associated with increased levels of deoxyhemoglobin.

Animals↗