Biomedical subjects

J H Duyn

Publications and source records attributed to J H Duyn.

At least 19 recordsLinked to original sources

PubMed2001

High-sensitivity single-shot perfusion-weighted fMRI.

A method is presented for measurement of perfusion changes during brain activation using a single-shot pulsed spin labeling technique. By employing a double-inversion labeling strategy, stationary tissue (background) signal was suppressed while minimally affecting perfusion sensitivity. This allowed omission of the otherwise required reference scan, resulting in twofold-improved temporal resolution. The method was applied to visual and motor cortex activation studies in humans, and compared to standard FAIR-type perfusion labeling techniques. Experiments performed at 1.5T and 3.0T indicate a close to 90% suppression of background signal, at a cost of an 11% and 9%, respectively, reduction in perfusion signal. Combined with the twofold increase in signal averaging, and a reduction in background signal fluctuations, this resulted in a 64% (1.5T, N = 3) and a 128% (3T, N = 4) overall improvement in sensitivity for the detection of activation-related perfusion changes. Magn Reson Med 46:88-94, 2001. Published 2001 Wiley-Liss, Inc.

Brain↗

PubMed2001

Simultaneous BOLD/perfusion measurement using dual-echo FAIR and UNFAIR: sequence comparison at 1.5T and 3.0T.

Functional MRI (fMRI) studies designed for simultaneously measuring Blood Oxygenation Level Dependent (BOLD) and Cerebral Blood Flow (CBF) signal often employ the standard Flow Alternating Inversion Recovery (FAIR) technique. However, some sensitivity is lost in the BOLD data due to inherent T1 relaxation. We sought to minimize the preceding problem by employing a modified UN-inverted FAIR (UNFAIR) technique, which (in theory) should provide identical CBF signal as FAIR with minimal degradation of the BOLD signal. UNFAIR BOLD maps acquired from human subjects (n = 8) showed significantly higher mean z-score of approximately 17% (p < 0.001), and number of activated voxels at 1.5T. On the other hand, the corresponding FAIR perfusion maps were superior to the UNFAIR perfusion maps as reflected in a higher mean z-score of approximately 8% (p = 0.013), and number of activated voxels. The reduction in UNFAIR sensitivity for perfusion is attributed to increased motion sensitivity related to its higher background signal, and, T2 related losses from the use of an extra inversion pulse. Data acquired at 3.0T demonstrating similar trends are also presented.

Brain↗

PubMed2000

A protocol for assessing subtraction errors of arterial spin-tagging perfusion techniques in human brain.

A protocol for assessing signal contributions from static tissue (subtraction errors) in perfusion images acquired with arterial spin-labeling (ASL) techniques in human brain is proposed. The method exploits the reduction of blood T(1) caused by the clinically available paramagnetic contrast agent, gadopentetate dimeglumine (Gd-DTPA). The protocol is demonstrated clinically with multislice FAIR images acquired before, during, and after Gd-DTPA administration using a range of selective inversion widths. Perfusion images acquired postcontrast for selective inversion widths large enough (threshold) to avoid interaction with the imaging slice had signal intensities reduced to noise level, as opposed to subtraction errors manifested on images acquired using inversion widths below the threshold. The need for these experiments to be performed in vivo is further illustrated by comparison with phantom results. The protocol allows a one-time calibration of relevant ASL parameters (e.g., selective inversion widths) in vivo, which may otherwise cause subtraction errors. Magn Reson Med 43:896-900, 2000. Published 2000 Wiley-Liss, Inc.

Artifacts↗

PubMed2000

High-speed interlaced spin-echo magnetic resonance imaging.

A new method is introduced for increasing the efficiency in multislice single spin-echo MRI. The method interlaces the excitation and measurement of different slices, resulting in an effective use of the echo delay time between RF excitation and reception. Under certain conditions, the method allows for scan time reduction compared to standard single spin-echo MRI, in particular for long echo times. The technique is demonstrated in examples of brain scans, indicating that a substantial increase is scan speed can be achieved without loss in image signal-to-noise ratio or contrast. Potential applications include perfusion imaging using T(2)-contrast agents, as well as BOLD-based functional imaging. Magn Reson Med 43:905-908, 2000. Published 2000 Wiley-Liss, Inc.

Brain↗

PubMed2000

Proton MR spectroscopic imaging without water suppression.

To improve reproducibility in proton magnetic resonance (MR) spectroscopic imaging in human brain, simultaneous acquisition of the internal water reference and metabolite signals was evaluated. Measurements in healthy volunteers showed that the increase in dynamic range from signal oversampling was sufficient to avoid digitization errors. In addition, use of singular value decomposition techniques and finite impulse response filters proved effective in separating water and metabolite signals and providing estimates of the metabolite concentrations.

Adult↗

PubMed2000

Proton magnetic resonance spectroscopic imaging in children with recurrent primary brain tumors.

PURPOSE: Proton magnetic resonance spectroscopic imaging ((1)H-MRSI) is a noninvasive technique for spatial characterization of biochemical markers in tissues. We measured the relative tumor concentrations of these biochemical markers in children with recurrent brain tumors and evaluated their potential prognostic significance. PATIENTS AND METHODS: (1)H-MRSI was performed on 27 children with recurrent primary brain tumors referred to our institution for investigational drug trials. Diagnoses included high-grade glioma (n = 10), brainstem glioma (n = 7), medulloblastoma/peripheral neuroectodermal tumor (n = 6), ependymoma (n = 3), and pineal germinoma (n = 1). (1)H-MRSI was performed on 1. 5-T magnetic resonance imagers before treatment. The concentrations of choline (Cho) and N-acetyl-aspartate (NAA) in the tumor and normal brain were quantified using a multislice multivoxel method, and the maximum Cho:NAA ratio was determined for each patient's tumor. RESULTS: The maximum Cho:NAA ratio ranged from 1.1 to 13.2 (median, 4.5); the Cho:NAA ratio in areas of normal-appearing brain tissue was less than 1.0. The maximum Cho:NAA ratio for each histologic subtype varied considerably; approximately equal numbers of patients within each tumor type had maximum Cho:NAA ratios above and below the median. Patients with a maximum Cho:NAA ratio greater than 4.5 had a median survival of 22 weeks, and all 13 patients died by 63 weeks. Patients with a Cho:NAA ratio less than or equal to 4.5 had a projected survival of more than 50% at 63 weeks. The difference was statistically significant (P =.0067, log-rank test). CONCLUSION: The maximum tumor Cho:NAA ratio seems to be predictive of outcome in children with recurrent primary brain tumors and should be evaluated as a prognostic indicator in newly diagnosed childhood brain tumors.

Adolescent↗

PubMed1999

Optimization of fast acquisition methods for whole-brain relative cerebral blood volume (rCBV) mapping with susceptibility contrast agents.

Fast gradient-echo magnetic resonance scan techniques with spiral and rectilinear (echoplanar) k-space trajectories were optimized to perform bolus-tracking studies of human brain. Cerebral hemodynamics were studied with full brain coverage, a spatial resolution of 4 mm, and a temporal resolution of 2 seconds. The sensitivity of the techniques to detect image signal-intensity changes during the first pass of the contrast agent was studied at a range of TEs using dedicated experiments. For single-shot versions of spiral scanning and echoplanar imaging techniques with a 0.1-mmol/kg injection of gadolinium diethylenetriamine pentaacetic acid using a mechanical injector at 10 mL/sec under 1.5 T, the maximum sensitivity was obtained at TEs between 35 and 45 msec. At TEs less than 35 msec, signal-intensity artifacts were observed in the images. Analysis of the point-spread function revealed that susceptibility changes induced by the contrast agent can result in signal shifts to neighboring voxels. These artifacts are attributed to susceptibility-related signal changes during the acquisition window.

Artifacts↗

PubMed1999

Multislice perfusion imaging in human brain using the C-FOCI inversion pulse: comparison with hyperbolic secant.

Perfusion studies based on pulsed arterial spin labeling have primarily applied hyperbolic secant (HS) pulses for spin inversion. To optimize perfusion sensitivity, it is highly desirable to implement the HS pulse with the same slice width as the width of the imaging pulse. Unfortunately, this approach causes interactions between the slice profiles and manifests as residual signal from static tissue in the resultant perfusion image. This problem is currently overcome by increasing the selective HS width relative to the imaging slice width. However, this solution increases the time for the labeled blood to reach the imaging slice (transit time), causing loss of perfusion sensitivity as a result of T(1) relaxation effects. In this study, we demonstrate that the preceding problems can be largely overcome by use of the C-shaped frequency offset corrected inversion (FOCI) pulse [Ordidge et al., Magn Reson Med 1996;36:562]. The implementation of this pulse for multislice perfusion imaging on the cerebrum is presented, showing substantial improvement in slice definition in vivo compared with the HS pulse. The sharper FOCI profile is shown to reduce the physical gap (or "safety margin") between the inversion and imaging slabs, resulting in a significant increase in perfusion signal without residual contamination from static tissue. The mean +/- SE (n = 6) gray matter perfusion-weighted signal (DeltaM/M(o)) without the application of vascular signal suppression gradients were 1.19 +/- 0. 10% (HS-flow-sensitive alternating inversion recovery [FAIR]), and 1. 51 +/- 0.11% for the FOCI-FAIR sequence. The corresponding values with vascular signal suppression were 0.64 +/- 0.14%, and 0.91 +/- 0. 08% using the HS- and FOCI-FAIR sequences, respectively. Compared with the HS-based data, the FOCI-FAIR results correspond to an average increase in perfusion signal of up to between 26%-30%. Magn Reson Med 42:1098-1105, 1999.

Brain↗

PubMed1999

Comparison of 3D BOLD functional MRI with spiral acquisition at 1.5 and 4.0 T.

In order to investigate the merit of high field strength for BOLD-contrast-based functional magnetic resonance imaging (fMRI) studies, multishot gradient-echo fMRI experiments during motor cortex activation were performed on 1.5- and 4.0-T scanners with equivalent hardware, on the same volunteers. In these studies, artifactual vascular enhancement related to inflow effects was minimized, and large brain areas were covered by using a 3D scan technique. Temporal signal stability was optimized by using spiral readout gradients. The sensitivity for detection of activated regions was assessed by measuring the number of "activated voxels" and their average t score in predefined regions of interest. When comparing fMRI experiments with the same total scan time, performed on six subjects, and with acquisition parameters optimized for each field strength separately, the 4.0-T scanner proved to give superior results, with a 70% greater number of activated voxels and a 20% higher average t score for the activated voxels.

Humans↗

PubMed1999

Investigation of low frequency drift in fMRI signal.

Low frequency drift (0.0-0.015 Hz) has often been reported in time series fMRI data. This drift has often been attributed to physiological noise or subject motion, but no studies have been done to test this assumption. Time series T*2-weighted volumes were acquired on two clinical 1.5 T MRI systems using spiral and EPI readout gradients from cadavers, a normal volunteer, and nonhomogeneous and homogeneous phantoms. The data were tested for significant differences (P = 0.001) from Gaussian noise in the frequency range 0.0-0.015 Hz. The percentage of voxels that were significant in data from the cadaver, normal volunteer, nonhomogeneous and homogeneous phantoms were 13.7-49.0%, 22.1-61.9%, 46.4-68.0%, and 1.10%, respectively. Low frequency drift was more pronounced in regions with high spatial intensity gradients. Significant drifting was present in data acquired from cadavers and nonhomogeneous phantoms and all pulse sequences tested, implying that scanner instabilities and not motion or physiological noise may be the major cause of the drift.

Adult↗

PubMed1999

Technical solution for an interactive functional MR imaging examination: application to a physiologic interview and the study of cerebral physiology.

Studies with functional magnetic resonance (MR) imaging produce large unprocessed raw data sets in minutes. The analysis usually requires transferring of the data to an off-line workstation, and this process frequently occurs after the subject has left the MR unit. The authors describe a hardware configuration and processing software that captures whole-brain raw data files as they are being produced from the MR unit. It then performs the reconstruction, registration, and statistical analysis, and displays the results in seconds after completion of the MR image acquisition.

Brain↗

PubMed1998

A comparison of fast MR scan techniques for cerebral activation studies at 1.5 tesla.

To evaluate the sensitivity of fast, gradient-echo MR scan techniques in their ability to detect blood oxygenation level dependent (BOLD) signal changes in task activation studies, three dedicated fast scan techniques, each with whole-brain coverage, were compared during a 3-min finger tapping paradigm on nine normal volunteers on a clinical 1.5 T scanner. Multislice (2D) single-shot spiral, 3D spiral, and multislice (2D) single-shot EPI scan techniques were done with similar temporal and spatial resolutions on each of the volunteers in random order. After image registration and statistical analysis, the sensitivity to detect activation was evaluated for the techniques by calculating t scores and number of activated voxels in predetermined regions of interest, including the contralateral primary sensorimotor cortex, the premotor region, the parietal region, the supplementary motor area, and the ipsilateral cerebellum. Baseline images acquired with the three techniques were qualitatively comparable and had a similar effective spatial resolution of around 5 x 5 x 5 mm3, as determined from autocorrelation analysis. The anatomical coverage was somewhat reduced (4 less slices per volume) with EPI at the identical temporal resolution of 1.76 s for all techniques. The use of multislice 2D spiral scan for motor cortex fMRI experiments provided for a superior overall temporal stability, and an increased sensitivity compared with multislice 2D EPI, and 3D spiral scan. The difference in sensitivity between multislice 2D spiral and EPI scans was small, in particular in the case of a ramp-sampled version of EPI. The difference in performance is attributed mainly to the difference in scan-to-scan stability.

Brain↗

PubMed1998

Multislice imaging of quantitative cerebral perfusion with pulsed arterial spin labeling.

A method is presented for multislice measurements of quantitative cerebral perfusion based on magnetic labeling of arterial spins. The method combines a pulsed arterial inversion, known as the FAIR (Flow-sensitive Alternating Inversion Recovery) experiment, with a fast spiral scan image acquisition. The short duration (22 ms) of the spiral data collection allows simultaneous measurement of up to 10 slices per labeling period, thus dramatically increasing efficiency compared to current single slice acquisition protocols. Investigation of labeling efficiency, suppression of unwanted signals from stationary as well as intraarterial spins, and the FAIR signal change as a function of inversion delay are presented. The assessment of quantitative cerebral blood flow (CBF) with the new technique is demonstrated and shown to require measurement of arterial transit time as well as suppression of intraarterial spin signals. CBF values measured on normal volunteers are consistent with results obtained from H2O15 positron emission tomography (PET) studies and other radioactive tracer approaches. In addition, the new method allows detection of activation-related perfusion changes in a finger-tapping experiment, with locations of activation corresponding well to those observed with blood oxygen level dependent (BOLD) fMRI.

Artifacts↗

PubMed1998

Simple correction method for k-space trajectory deviations in MRI.

A method is presented to correct for the imperfections of spatial encoding gradients in MRI. The approach is simple and fast, can be performed with standard scanner hardware, and does not require separate measurements with reference phantoms. The new method, using the MR signal to accurately measure the k-space trajectory of the imaging sequence, allows for correction of gradient hardware imperfections and eddy-current effects. Initial measurements are presented which demonstrate the efficacy of the method to correct images acquired with spiral and EPI scan techniques.

Algorithms↗

PubMed1998

Reproducibility of proton magnetic resonance spectroscopic imaging in patients with schizophrenia.

Using proton magnetic resonance spectroscopic imaging (1H-MRSI) we found in a previous study a specific pattern of neuronal pathology in patients with schizophrenia as determined by relative loss of signal from N-acetyl-containing compounds (NAA). The purpose of the present study was to assess the reproducibility of the results of 1H-MRSI both in patients with schizophrenia and in normal controls. We studied twice 10 patients and 10 controls on 2 days separated by, on average, 3 months. Reproducibility was assessed with several statistical procedures including ANOVA, coefficients of variation (CVs) and intra-class correlation coefficients (ICC). Patients showed significant reductions of NAA/creatine-phosphocreatine (CRE) and NAA/choline-containing compounds (CHO) selectively in the hippocampal region (HIPPO) and in the dorsolateral prefrontal cortex (DLPFC) on both experimental days. A repeated measures ANOVA showed no effect of time on metabolite ratios in all subjects. CVs were fairly low (especially for NAA/CRE and CHO/CRE) and did not differ significantly between patients and controls. The ICCs of the ROIs reached statistical significance only in a few instances. The present multislice 1H-MRSI study shows that: (1) patients with schizophrenia, when compared as a group to normal controls, show a consistent 1H-MRSI pattern of group differences, i.e., bilateral reductions of NAA/CRE and NAA/CHO in HIPPO and DLPFC; (2)1H-MRSI data in both patients and controls do not show significant changes over this 90-day period; however, absolute metabolite ratios in individuals show low predictability over this time interval; (3) 1H-MRSI data show relatively low variability (as measured by the CVs) both in patients and normal controls, especially for NAA/CRE and CHO/CRE.

Acetylation↗

PubMed1998

Common pattern of cortical pathology in childhood-onset and adult-onset schizophrenia as identified by proton magnetic resonance spectroscopic imaging.

OBJECTIVE: Multislice proton magnetic resonance spectroscopic imaging (1H-MRSI) permits simultaneous acquisition and mapping of signal intensities of N-acetyl-containing compounds (mainly N-acetylaspartate, NAA), choline-containing compounds (CHO), and creatine plus phosphocreatine (CRE) from multiple whole-brain slices consisting of small single-volume elements. Previous 1H-MRSI studies of adult patients with schizophrenia showed small NAA relative signals in the hippocampal area and in the dorsolateral prefrontal cortex in comparison with healthy subjects. As part of a program to address the pathophysiological continuity between childhood-onset and adult-onset schizophrenia, the authors performed 1H-MRSI of patients with childhood-onset schizophrenia to specifically test whether the hippocampal area and dorsolateral prefrontal cortex show the same abnormalities as seen in adult-onset schizophrenia. METHOD: A 1.5-T nuclear magnetic resonance machine was used to test 14 patients (mean age, 16.4 years) and 14 comparison subjects. Ratios of areas under the metabolite peaks of the proton spectra were determined (i.e., NAA/CRE, NAA/CHO, CHO/CRE) for multiple cortical and subcortical regions. RESULTS: The patients showed significantly lower NAA/CRE ratios bilaterally in the hippocampal area and the dorsolateral prefrontal cortex than the comparison subjects. There were no significant differences in CHO/CRE or in NAA ratios in any other area sampled. CONCLUSIONS: The present study shows that patients with childhood-onset schizophrenia have smaller than normal regional NAA relative signals, suggesting neuronal damage or malfunction in the hippocampal area and dorsolateral prefrontal cortex. These differences were similar in magnitude to those found in patients with adult-onset schizophrenia. The present data extend other evidence of a biological continuum between childhood- and adult-onset schizophrenia.

Adolescent↗

PubMed1998

Age-related vasodilatory response to acetazolamide challenge in healthy adults: a dynamic contrast-enhanced MR study.

PURPOSE: We examined age-related changes in baseline regional cerebral blood volume (rCBV) and response to acetazolamide stimulation by using dynamic contrast-enhanced MR imaging. METHODS: Thirty healthy volunteers ranging widely in age (23 to 82 years) were examined before and after intravenous injection of acetazolamide with dynamic susceptibility contrast-enhanced MR imaging. rCBV values were normalized for intersubject and intrasubject comparison by estimating an arterial input function directly from the imaging data. Preacetazolamide baseline rCBV and the percentage volume change index (PVCI) of the postacetazolamide to preacetazolamide state were calculated and examined as a function of age. RESULTS: Older adults (>50 years) had lower baseline rCBV per unit tissue than did younger adults (<50 years), but higher rCBV after acetazolamide stimulation. Baseline rCBV tended to decrease with age in the medial frontal and frontoparietal gray matter regions. Response to acetazolamide stimulation, measured by PVCI, showed a significant age-related increase in gray matter, approximately 0.5% per year. CONCLUSION: rCBV can be significantly increased after acetazolamide stimulation in the healthy aged. These results support the notion that age-related decreases in rCBV measured at rest reflect reduced regional metabolic requirements rather than reduced capacity for regional substrate delivery. These data serve as a normative baseline for comparison studies of rCBV vascular reserve in aging persons with various cerebrovascular disorders.

Acetazolamide↗

PubMed1998

Serial whole-brain magnetization transfer imaging in patients with relapsing-remitting multiple sclerosis at baseline and during treatment with interferon beta-1b.

BACKGROUND AND PURPOSE: To determine whether occult disease fluctuates with macroscopic lesions during the natural history of multiple sclerosis (MS) and whether therapeutic interventions affect occult disease, we performed serial monthly magnetization transfer (MT) imaging in patients with relapsing-remitting MS in a crossover trial with interferon beta-lb. METHODS: Serial whole-brain magnetization transfer ratios (MTRs) in eight patients with relapsing-remitting MS and in four control subjects were plotted as normalized histograms, and MTR parameters were compared with contrast-enhancing lesions and bulk white matter lesion load. RESULTS: In patients with relapsing-remitting MS, the histographic peak of 0.25+/-0.01 and the histographic mean of 0.21+/-0.01 were statistically lower than corresponding values in control subjects, in whom the histographic peak was 0.27+/-0.01 and the histographic mean was 0.23+/-0.01. When histograms (with MTRs ranging from 0.0 to 0.5) were analyzed by quartiles (quartile 1 to quartile 4) based on histographic area, voxels with low MTRs in quartile 1 (0 to 0.12) increased during the baseline period and corresponded to bulk white matter lesion load. Interferon beta-lb reduced enhancing lesions by 91% and mean bulk white matter lesion load by 15%, but had no effect on MTR in this patient cohort. CONCLUSION: Occult disease in normal-appearing white matter of patients with relapsing-remitting MS measured by MTR parallels the waxing and waning pattern of enhancing lesions and bulk white matter lesion load during the baseline period. MTR is not altered by interferon beta-lb, which raises the possibility of ongoing disease in normal-appearing white matter (not detected by conventional MR sequences).

Adjuvants, Immunologic↗