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Stephan E Maier

Publications and source records attributed to Stephan E Maier.

At least 19 recordsLinked to original sources
PubMed2006

Complementary aspects of diffusion imaging and fMRI; I: structure and function.

Studying the intersection of brain structure and function is an important aspect of modern neuroscience. The development of magnetic resonance imaging (MRI) over the last 25 years has provided new and powerful tools for the study of brain structure and function. Two tools in particular, diffusion imaging and functional MRI (fMRI), are playing increasingly important roles in elucidating the complementary aspects of brain structure and function. In this work, we review basic technical features of diffusion imaging and fMRI for studying the integrity of white matter structural components and for determining the location and extent of cortical activation in gray matter, respectively. We then review a growing body of literature in which the complementary aspects of diffusion imaging and fMRI, applied as separate examinations but analyzed in tandem, have been exploited to enhance our knowledge of brain structure and function.

Brain Diseases↗
PubMed2006

Biexponential characterization of prostate tissue water diffusion decay curves over an extended b-factor range.

Detailed measurements of water diffusion within the prostate over an extended b-factor range were performed to assess whether the standard assumption of monoexponential signal decay is appropriate in this organ. From nine men undergoing prostate MR staging examinations at 1.5 T, a single 10-mm-thick axial slice was scanned with a line scan diffusion imaging sequence in which 14 equally spaced b factors from 5 to 3,500 s/mm(2) were sampled along three orthogonal diffusion sensitization directions in 6 min. Due to the combination of long scan time and limited volume coverage associated with the multi-b-factor, multidirectional sampling, the slice was chosen online from the available T2-weighted axial images with the specific goal of enabling the sampling of presumed noncancerous regions of interest (ROIs) within the central gland (CG) and peripheral zone (PZ). Histology from prescan biopsy (n=9) and postsurgical resection (n=4) was subsequently employed to help confirm that the ROIs sampled were noncancerous. The CG ROIs were characterized from the T2-weighted images as primarily mixtures of glandular and stromal benign prostatic hyperplasia, which is prevalent in this population. The water signal decays with b factor from all ROIs were clearly non-monoexponential and better served with bi- vs. monoexponential fits, as tested using chi(2)-based F test analyses. Fits to biexponential decay functions yielded intersubject fast diffusion component fractions in the order of 0.73+/-0.08 for both CG and PZ ROIs, fast diffusion coefficients of 2.68+/-0.39 and 2.52+/-0.38 microm(2)/ms and slow diffusion coefficients of 0.44+/-0.16 and 0.23+/-0.16 um(2)/ms for CG and PZ ROIs, respectively. The difference between the slow diffusion coefficients within CG and PZ was statistically significant as assessed with a Mann-Whitney nonparametric test (P<.05). We conclude that a monoexponential model for water diffusion decay in prostate tissue is inadequate when a large range of b factors is sampled and that biexponential analyses are better suited for characterizing prostate diffusion decay curves.

Aged↗
PubMed2006

Collateral nerve fibers in human spinal cord: visualization with magnetic resonance diffusion tensor imaging.

Diffusion tensor magnetic resonance imaging provides structural information about nerve fiber tissue. The first eigenvector of the diffusion tensor is aligned with the nerve fibers, i.e., longitudinally in the spinal cord. The underlying hypothesis of this study is that the presence of collateral nerve fibers running orthogonal to the longitudinal fibers results in an orderly arrangement of the second eigenvectors. Magnetic resonance diffusion tensor scans were performed with line scan diffusion imaging on a clinical MR scanner. Axial sections were scanned in a human cervical spinal cord specimen at 625 microm resolution and the cervical spinal cord of four normal volunteers at 1250 microm resolution. The spinal cord specimen was fixed and stained for later light microscopy of the collateral fiber architecture at 0.53 microm resolution. Diffusion measured by MR was found to be anisotropic for both white and gray matter areas of the spinal cord specimen; the average fractional anisotropy (FA) was 0.63 +/- 0.09 (diffusion eigenvalues lambda1 0.38 +/- 0.05 micros/mm2, lambda2 0.14 +/- 0.03 micros/mm2, lambda3 0.10 +/- 0.03 micros/mm2) in white matter and 0.27 +/- 0.04 (lambda1 0.36 +/- 0.04 micros/mm2, lambda2 0.28 +/- 0.03 micros/mm2, lambda3 0.21 +/- 0.04 micros/mm2 in gray matter. The normal-volunteer FA values were similar, i.e., 0.66 +/- 0.04 (lambda1 1.66 +/- 0.14 micros/mm2, lambda2 0.55 +/- 0.02 micros/mm2, lambda3 0.40 +/- 0.01 micros/mm2) in white matter and 0.35 +/- 0.03 (lambda1 1.14 +/- 0.07 micros/mm2, lambda2 0.70 +/- 0.03 micros/mm2, lambda3 0.58 +/- 0.02 micros/mm2) in gray matter. The first eigenvector pointed, as expected, in the longitudinal direction. The second eigenvector directions exhibited a striking arrangement, consistent with the distribution of interconnecting collateral nerve fibers discerned on the histology section. This finding was confirmed for the specimen by quantitative pixel-wise comparison of second eigenvector directions and collateral fiber directions assessed on light microscopy image data. Diffusion tensor MRI can reveal non-invasively and in great detail the intricate fiber architecture of the human spinal cord.

Adult↗
PubMed2006

Fornix integrity and hippocampal volume in male schizophrenic patients.

BACKGROUND: The hippocampus has been shown to be abnormal in schizophrenia. The fornix is one of the main fiber tracts connecting the hippocampus with other brain regions. Few studies have evaluated the fornix in schizophrenia, however. A focus on fornix abnormalities and their association with hippocampal abnormalities might figure importantly in our understanding of the pathophysiology of schizophrenia. METHODS: Line-scan diffusion tensor imaging (DTI) was used to evaluate diffusion in the fornix in 24 male patients with chronic schizophrenia and 31 male control subjects. Maps of fractional anisotropy (FA) and mean diffusivity (D(m)), which are indices sensitive to white-matter integrity, were generated to quantify diffusion within the fornix. We used high spatial resolution magnetic resonance imaging (MRI) to measure hippocampal volume. RESULTS: FA and cross-sectional area of the fornix were significantly reduced in patients compared with control subjects. D(m) was significantly increased, whereas hippocampal volume was bilaterally reduced in patients. Reduced hippocampal volume was correlated with increased mean D(m) and reduced cross-sectional area of the fornix for patients. Patients also showed a significant correlation between reduced scores on neuropsychologic measures of declarative-episodic memory and reduced hippocampal volumes. CONCLUSIONS: These findings demonstrate a disruption in fornix integrity in patients with schizophrenia.

Adult↗
PubMed2006

Apparent diffusion coefficient in malignant lymphoma and carcinoma involving cavernous sinus evaluated by line scan diffusion-weighted imaging.

PURPOSE: To evaluate the apparent diffusion coefficient (ADC) of malignant lymphomas and carcinomas involving cavernous sinus by line scan diffusion-weighted imaging (LSDWI) and to determine the usefulness of this method for differentiating between the two tumors. MATERIALS AND METHODS: Four patients with malignant lymphomas and six patients with carcinomas were prospectively studied. LSDWI images were obtained with two different b values of 5 seconds/mm(2) and 1000 seconds/mm(2) in the coronal plane. The ADC values of the two types of tumors were calculated and compared. RESULTS: LSDWI provided diagnostic images with minimum susceptibility artifacts and enabled measurement of the ADC. The ADC value (mean +/- SD) was 0.51 +/- 0.06 x 10(-3) mm(2)/second in malignant lymphomas and 0.99 +/- 0.08 x 10(-3) mm(2)/second in carcinomas. A significant difference in ADC values was found between the two (P < 0.01). CONCLUSION: Malignant lymphomas showed significantly lower ADC value than carcinomas. ADC provides additional useful information about differentiation between these tumors.

Adult↗
PubMed2005

Convection-enhanced drug delivery: increased efficacy and magnetic resonance image monitoring.

Convection-enhanced drug delivery (CED) is a novel approach to directly deliver drugs into brain tissue and brain tumors. It is based on delivering a continuous infusion of drugs via intracranial catheters, enabling convective distribution of high drug concentrations over large volumes of the target tissue while avoiding systemic toxicity. Efficient formation of convection depends on various physical and physiologic variables. Previous convection-based clinical trials showed significant diversity in the extent of convection among patients and drugs. Monitoring convection has proven to be an essential, yet difficult task. The current study describes the application of magnetic resonance imaging for immediate assessment of convection efficiency and early assessment of cytotoxic tissue response in a rat brain model. Immediate assessment of infusate distribution was obtained by mixing Gd-diethylenetriaminepentaacetic acid in the infusate prior to infusion. Early assessment of cytotoxic tissue response was obtained by subsequent diffusion-weighted magnetic resonance imaging. In addition, the latter imaging methodologies were used to establish the correlation between CED extent and infusate's viscosity. It was found that low-viscosity infusates tend to backflow along the catheter track, whereas high-viscosity infusates tend to form efficient convection. These results suggest that CED formation and extent may be significantly improved by increasing the infusate's viscosities, thus increasing treatment effects.

Animals↗
PubMed2005

Fronto-temporal disconnectivity in schizotypal personality disorder: a diffusion tensor imaging study.

BACKGROUND: Using diffusion tensor imaging (DTI), we previously reported abnormalities in two critical white matter tracts in schizophrenia, the uncinate fasciculus (UF) and the cingulum bundle (CB), both related to fronto-temporal connectivity. Here, we investigate these two bundles in unmedicated subjects with schizotypal personality disorder (SPD). METHODS: Fifteen male SPD subjects and 15 male control subjects were scanned with line-scan DTI. Fractional anisotropy (FA) and mean diffusivity (D(m)) were used to quantify water diffusion, and cross-sectional area was defined with a directional threshold method. Exploratory correlation analyses were evaluated with Spearman's rho, followed by post hoc hierarchical regression analyses. RESULTS: We found bilaterally reduced FA in the UF of SPD subjects. For CB, there was no significant group difference for FA or D(m) measures. Additionally, in SPD, reduced FA in the right UF was correlated with clinical symptoms, including ideas of reference, suspiciousness, restricted affect, and social anxiety. In contrast, left UF area was correlated with measures of cognitive function, including general intelligence, verbal and visual memory, and executive performance. CONCLUSIONS: These findings in SPD suggest altered fronto-temporal connectivity through the UF, similar to findings in schizophrenia, and intact neocortical-limbic connectivity through the CB, in marked contrast with what has been reported in schizophrenia.

Adolescent↗
PubMed2005

Apparent diffusion coefficient and fractional anisotropy in spinal cord: age and cervical spondylosis-related changes.

PURPOSE: To present the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) change with age in the normal spinal cord and in cervical spondylosis. MATERIALS AND METHODS: A total of 11 normal volunteers and 79 cervical spondylosis patients entered this study. Line scan diffusion tensor images were obtained in a 1.5-Tesla whole-body scanner using a phased-array spine coil. The ADC and FA values were measured on a sagittal section. Spearman correlation of ADC/FA vs. age for normal spinal cord was calculated. RESULTS: The mean ADC of the normal spinal cord was 0.81 +/- 0.03 microm(2)/msec at the relatively wide C2-C3 level and 0.75 +/- 0.06 microm(2)/msec at the more narrow C4-C7 level. The FA at the corresponding level was 0.70 +/- 0.05 and 0.66 +/- 0.03, respectively. With age, ADC showed positive correlation (Spearman, r = 0.242) and FA exhibited negative correlation (Spearman, r = -0.244). A total of 54% of all spondylosis cases showed elevated ADC (P < 0.001) and decreased FA (P < 0.001) at the stenotic spinal canal level compared with the normal spinal cord. The average ADC and FA of high-signal lesions on T2-weighted images (seven patients) were 1.28 +/- 0.33 microm(2)/msec and 0.46 +/- 0.12, respectively. CONCLUSION: ADC increases and FA decreases with age in the normal spinal cord. Elevated ADC and reduced FA were measured in the spinal cord of spondylosis cases with clinical symptoms of myelopathy.

Adult↗
PubMed2005

High-resolution anatomic, diffusion tensor, and magnetization transfer magnetic resonance imaging of the optic chiasm at 3T.

PURPOSE: To evaluate techniques for anatomical and physiological imaging of the intracranial optic nerve (ON), optic chiasm (OC), and optic tract (OT) at 3T with the aim of visualizing axonal damage in multiple sclerosis (MS). MATERIALS AND METHODS: Imaging was performed on a 3T scanner employing a custom-designed head coil that consisted of a coil array with four coils (30 x 30 cm(2)). Oblique fast spin echo (FSE) images, magnetization transfer (MT)-enhanced 3D gradient-echo (GRE) time-of-flight (TOF) images, and line scan diffusion images (LSDI) were obtained. Full diffusion tensor (DT) analysis was performed, and apparent diffusion coefficient (ADC), fractional anisotropy (FA), and fiber direction maps were obtained. RESULTS: FSE anatomic images were obtained with an in-plane resolution of 0.39 x 0.52 mm(2). The in-plane resolution of the MT and LSDI images was 0.78 x 0.78 mm(2). The OC, intracranial ON, and OT can be seen on these images. The dominant fiber orientations in the OC, ON, and OT, as derived from the DT images, are displayed. CONCLUSION: This study shows that by using 3T and a custom-designed, four-channel head coil, it is possible to acquire high-resolution anatomical and physiological images of the OC, ON, and OT. The pilot results presented here pave the way for imaging the anterior visual pathway in patients with MS.

Adult↗
PubMed2005

Biexponential parameterization of diffusion and T2 relaxation decay curves in a rat muscle edema model: decay curve components and water compartments.

Quantitative T2 relaxation and diffusion imaging studies of a rat muscle edema model were performed in order to determine the effects of intra- and extracellular water compartmentation on the respective decay curves. The right hind paw of rats was injected with a carrageenan solution to generate edematous muscle. A Carr-Purcell-Meiboom-Gill (CPMG) imaging sequence was used to acquire T2 relaxation decay curves from both paws. A line scan diffusion imaging (LSDI) sequence was then used to acquire diffusion decay curves from the same paws over a wide b-factor range. Measurements were made from both edematous muscle (EM) and control muscle (CM). The EM and CM T2 relaxation decay curves were best fit with biexponential functions. The fraction of the fast T2 component dropped dramatically from approximately 0.95 in CM to 0.45 in EM, consistent with a water compartmentation model in which the fast and slow T2 components reflect intra- and extracellular water, respectively. Both CM and EM diffusion decay curves required biexponential fitting functions, and the diffusion coefficients of the fast and slow components were substantially larger in EM than CM. The fraction of the fast diffusion component, however, was not radically altered between CM and EM conditions (0.84 versus 0.89 for CM versus EM). Assuming a model in which intra- and extracellular water compartments are responsible for the fast and slow T2-decay components and for the slow and fast diffusion decay components, respectively, leads to fractional sizes of the diffusion components that are not supported by experiment. We conclude that intra- and extracellular water compartmentation is a reasonable interpretation for the two T2-decay components in both CM and EM but that other factors, such as restricted diffusion and/or alternate forms of water compartmentation like surface versus volume water, most probably have profound influences on the precise shapes of the diffusion decay curves, a complete understanding of which will require significant theoretical work.

Animals↗
PubMed2005

Magnetization transfer studies of the fast and slow tissue water diffusion components in the human brain.

Magnetization transfer (MT) properties of the fast and slow diffusion components recently observed in the human brain were assessed experimentally. One set of experiments, performed at 1.5 T in healthy volunteers, was designed to determine whether the amplitudes of fast and slow diffusion components, differentiated on the basis of biexponential fits to signal decays over a wide range of b-factors, demonstrated a different or similar magnetization transfer ratio (MTR). Another set of experiments, performed at 3 T in healthy volunteers, was designed to determine whether MTRs differed when measured from high signal-to-noise images acquired with b-factor weightings of 350 vs 3500 s/mm2. The 3 T studies included measurements of MTR as a function of off-resonance frequency for the MT pulse at both low and high b-factors. The primary conclusion drawn from all the studies is that there appears to be no significant difference between the magnetization transfer properties of the fast and slow tissue water diffusion components. The conclusions do not lend support to a direct interpretation of the 'components' of the biexponential diffusion decay in terms of the 'compartments' associated with intra- and extracellular water.

Adult↗
PubMed2005

On the strong field dependence and nonlinear response to gadolinium contrast agent of proton transverse relaxation rates in dairy cream.

Dairy cream, as a suspension of lipid droplets in water, is a potentially useful magnetic resonance imaging (MRI) phantom material and an interesting material for studying fundamental relaxation mechanisms. Here we report a strong increase in the transverse relaxation rates with field strength for both the water and lipid protons in dairy cream. Also, studies at 4.7 T reveal a nonlinear response of transverse relaxation rates with increasing concentration of a common gadolinium (Gd)-based contrast agent, including an initial decrease of water relaxation rates as measured with Hahn spin echoes at the lower Gd concentrations. The results are treated within the framework of a model in which the magnetic susceptibility difference between the lipid droplets and the aqueous phase plays the prominent role for transverse relaxation. Second-order polynomial fits of the water proton transverse relaxation rate dependence on field strength and on Gd concentration at 4.7 T provided experimental parameters from which model parameters are extracted and compared with expectations available from the literature.

Contrast Media↗
PubMed2005

In vivo visualization of white matter fiber tracts of preterm- and term-infant brains with diffusion tensor magnetic resonance imaging.

OBJECTIVE: The goal of this study was to test the feasibility of visualizing a 3-dimensional structure of cerebral white matter fiber tracts in preterm infants, postconceptional age (PCA) 28 weeks to term, by using volumetric diffusion tensor magnetic resonance imaging (DTI) data. MATERIALS AND METHOD: We combined tractography algorithms and visualization methods, currently available for adult DTI data, to trace the pixelated principal direction of a diffusion tensor originating from regions-of-interest with high fractional anisotropy. Consequently, white matter fiber bundles from the genu and the splenium of corpus callosum, the corticospinal tracts, the inferior fronto-occipital fasciculi, and optic radiations were visualized. RESULTS: Our results suggest that major white matter tracts of preterm infant brains, with PCAs ranging from 28 weeks to term (40 weeks old), can be successfully visualized despite the small brain volume and low anisotropy. CONCLUSION: The feasibility of fiber tractography in preterm neonates with DTI may add a new dimension in detection and characterization of white matter injuries of preterm infants.

Algorithms↗
PubMed2005

Diffusion tensor imaging of the spinal cord.

The spinal cord is an important part of the nervous system and provides the connection of the brain with the periphery. It consists not only of a large number of longitudinal fibers, but also contains collateral fibers and a central gray matter structure, which are part of autonomous circuits. Magnetic resonance diffusion tensor imaging can reveal this complex fiber architecture in great detail. This report summarizes the normal findings for ADC, diffusion anisotropy, and diffusion eigenvector directions in the spinal cord. Sagittal and axial diffusion-weighted images of the spinal cord were obtained with line scan diffusion imaging (LSDI) in adults, children, infants, and a spinal cord specimen.

Adolescent↗
PubMed2005

Usefulness of the apparent diffusion coefficient in line scan diffusion-weighted imaging for distinguishing between squamous cell carcinomas and malignant lymphomas of the head and neck.

BACKGROUND AND PURPOSE: Squamous cell carcinoma (SCC) and lymphoma are common malignant tumors of the head and neck. The purpose of this study was to determine whether the apparent diffusion coefficient (ADC) in line scan diffusion-weighted imaging (LSDWI) is useful for distinguishing between SCC and lymphoma of the head and neck. METHODS: LSDWI was prospectively performed in 39 patients with SCC and in 14 patients with lymphoma. Images were obtained with a diffusion-weighted factor (b factor) of 5 and 1000 s/mm(2), and ADC maps were generated. ADC values were measured for the two types of tumor. RESULTS: Mean ADC values were 0.96 +/- 0.11 x 10(-3) mm(2)/s for SCC and 0.65 +/- 0.09 x 10(-3) mm(2)/s for lymphoma; the difference was significant (P < .001). All but one of the patients with lymphoma had ADC values lower than the lowest ADC (0.76 x 10(-3) mm(2)/s) in patients with SCC. When an ADC of 0.76 x 10(-3) mm(2)/s was used to distinguish between SCC and lymphoma, accuracy was 98% (52 of 53 lesions). CONCLUSION: ADC values appear to be useful for distinguishing between SCC and lymphoma in the head and neck.

Adolescent↗
PubMed2004

High-b-value diffusion-weighted MR imaging for pretreatment prediction and early monitoring of tumor response to therapy in mice.

PURPOSE: To evaluate the use of diffusion-weighted magnetic resonance (MR) imaging with standard and high b values for pretreatment prediction and early detection of tumor response to various antineoplastic therapies in an animal model. MATERIALS AND METHODS: Mice bearing C26 colon carcinoma tumors were treated with doxorubicin (n = 25) and with aminolevulinic acid-based photodynamic therapy (n = 23). Fourteen mice served as controls. Conventional T2-weighted fast spin-echo and diffusion-weighted MR images were acquired once before therapy and at 6, 24, and 48 hours after treatment. Pretreatment and early (1-2 days) posttreatment water diffusion parameters were calculated and compared with later changes in tumor volumes measured on conventional MR images by using the Pearson correlation test. RESULTS: In chemotherapy-treated tumors, a significant correlation (P <.002, r = 0.6) was observed between diffusion parameters that reflected tumor viability, measured prior to treatment, and changes in tumor volumes after therapy. This correlation implies that tumors with high pretreatment viability will respond better to chemotherapy than more necrotic tumors. In tumors treated with photodynamic therapy, no such correlation was found. Changes observed in water diffusion 1-2 days after treatment significantly correlated with later tumor growth rate for both therapies (P <.002, r = 0.54 for photodynamic therapy; P <.0003, r = 0.61 for chemotherapy). CONCLUSION: High-b-value diffusion-weighted MR imaging has potential use for the early detection of response to therapy and for predicting treatment outcome prior to initiation of chemotherapy.

Animals↗
PubMed2004

Pathways that make voices: white matter changes in auditory hallucinations.

BACKGROUND: The origin of auditory hallucinations, which are one of the core symptoms of schizophrenia, is still a matter of debate. It has been hypothesized that alterations in connectivity between frontal and parietotemporal speech-related areas might contribute to the pathogenesis of auditory hallucinations. These networks are assumed to become dysfunctional during the generation and monitoring of inner speech. Magnetic resonance diffusion tensor imaging is a relatively new in vivo method to investigate the directionality of cortical white matter tracts. OBJECTIVE: To investigate, using diffusion tensor imaging, whether previously described abnormal activation patterns observed during auditory hallucinations relate to changes in structural interconnections between the frontal and parietotemporal speech-related areas. METHODS: A 1.5 T magnetic resonance scanner was used to acquire twelve 5-mm slices covering the Sylvian fissure. Fractional anisotropy was assessed in 13 patients prone to auditory hallucinations, in 13 patients without auditory hallucinations, and in 13 healthy control subjects. Structural magnetic resonance imaging was conducted in the same session. Based on an analysis of variance, areas with significantly different fractional anisotropy values between groups were selected for a confirmatory region of interest analysis. Additionally, descriptive voxel-based t tests between the groups were computed. RESULTS: In patients with hallucinations, we found significantly higher white matter directionality in the lateral parts of the temporoparietal section of the arcuate fasciculus and in parts of the anterior corpus callosum compared with control subjects and patients without hallucinations. Comparing patients with hallucinations with patients without hallucinations, we found significant differences most pronounced in the left hemispheric fiber tracts, including the cingulate bundle. CONCLUSION: Our findings suggest that during inner speech, the alterations of white matter fiber tracts in patients with frequent hallucinations lead to abnormal coactivation in regions related to the acoustical processing of external stimuli. This abnormal activation may account for the patients' inability to distinguish self-generated thoughts from external stimulation.

Adult↗