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Khader M Hasan

Publications and source records attributed to Khader M Hasan.

At least 19 recordsLinked to original sources
PubMed2006

Diffusion tensor imaging-based tissue segmentation: validation and application to the developing child and adolescent brain.

We present and validate a novel diffusion tensor imaging (DTI) approach for segmenting the human whole-brain into partitions representing grey matter (GM), white matter (WM) and cerebrospinal fluid (CSF). The approach utilizes the contrast among tissue types in the DTI anisotropy vs. diffusivity rotational invariant space. The DTI-based whole-brain GM and WM fractions (GMf and WMf) are contrasted with the fractions obtained from conventional magnetic resonance imaging (cMRI) tissue segmentation (or clustering) methods that utilized dual echo (proton density-weighted (PDw)), and spin-spin relaxation-weighted (T2w) contrast, in addition to spin-lattice relaxation weighted (T1w) contrasts acquired in the same imaging session and covering the same volume. In addition to good correspondence with cMRI estimates of brain volume, the DTI-based segmentation approach accurately depicts expected age vs. WM and GM volume-to-total intracranial brain volume percentage trends on the rapidly developing brains of a cohort of 29 children (6-18 years). This approach promises to extend DTI utility to both micro and macrostructural aspects of tissue organization.

Adolescent↗
PubMed2006

Demonstration of interstitial cerebral edema with diffusion tensor MR imaging in type C hepatic encephalopathy.

Brain water may increase in hepatic encephalopathy (HE). Diffusion tensor imaging was performed in patients with cirrhosis with or without HE to quantify the changes in brain water diffusivity and to correlate it with neuropsychological (NP) tests. Thirty-nine patients with cirrhosis, with minimal (MHE) or overt HE, were studied and compared to 18 controls. Mean diffusivity (MD) and fractional anisotropy (FA) were calculated in corpus callosum, internal capsule, deep gray matter nuclei, periventricular frontal, and occipital white matter regions in both cerebral hemispheres. The MD and FA values from different regions in different groups were compared using analysis of variance and Spearman's rank correlation test. In 10 patients with MHE, repeat studies were performed after 3 weeks of lactulose therapy to look for any change in MD, FA, and NP scores. Significantly increased MD was found with insignificant changes in FA in various regions of brain in patients with MHE or HE compared with controls, indicating an increase in interstitial water in the brain parenchyma without any microstructural changes. A significant correlation was found between MD values from corpus callosum, internal capsule, and NP test scores. After therapy, MD values decreased significantly and there was a corresponding improvement in NP test scores. Further analysis showed that MD values were different for different grades of minimal or overt HE. In conclusion, the increase in MD with no concomitant changes in FA in cirrhosis with minimal or early HE indicates the presence of reversible interstitial brain edema.

Adolescent↗
PubMed2006

Focal Wallerian degeneration of the corpus callosum in large middle cerebral artery stroke: serial diffusion tensor imaging.

PURPOSE: To detect lesion-related focal Wallerian degeneration (WD) changes in different segments of the corpus callosum (CC) in patients with large middle cerebral arterial (MCA) territory stroke using diffusion tensor imaging (DTI). MATERIALS AND METHODS: Eight patients underwent DTI scans at three different time points: six to eight weeks, 10-12 weeks, and beyond six months of stroke onset. Eight healthy age-matched controls were also scanned using the same protocol at three different time points. Region-of-interest (ROI) analysis was performed on seven segments of the CC to determine the fractional anisotropy (FA), mean diffusivity (MD), and corresponding callosal cross-sectional areas. RESULTS: On repeated-measures analysis of variance (ANOVA), a significant reduction in the FA values was observed from the first to the third study compared to controls, reflecting temporal degeneration in the rostrum, genu, rostral body, anterior midbody, and splenium of the CC. However, a significant temporal elevation in MD values was observed in only the rostral body and anterior midbody of the CC. This was associated with a significant region-specific reduction in the cross-sectional areas at time points beyond six months, and appears to be consistent with the loss of callosal structural components due to interruption of the cortico-callosal fibers secondary to WD. CONCLUSION: These results indicate that cortico-callosal topographical changes exhibit a significant temporal decline in observed FA values that is suggestive of cortico-callosal WD in patients with large MCA territory stroke.

Adult↗
PubMed2006

Measurement of DTI metrics in hemorrhagic brain lesions: possible implication in MRI interpretation.

PURPOSE: To understand the biological basis of possible mechanisms responsible for increased fractional anisotropy (FA) in different stages of hemorrhage and hemorrhagic brain lesions. MATERIALS AND METHODS: A total of 19 patients with cerebral hemorrhage (CH), five patients with hemorrhagic infarct (HI), and nine patients with hemorrhagic brain tumor (HBT) were prospectively evaluated with diffusion tensor imaging (DTI) and the FA and mean diffusivity (MD) was quantified. Ex vivo DTI of blood clot and histology of the blood clot and HBT were performed to interpret the temporal changes in the DTI metrics. RESULTS: High FA (>0.20) with low MD in the acute and early subacute stage and low FA (<0.20) with increased MD in the late subacute and chronic stage of CH and HI were observed. HBT showed high FA with low MD at all stages. In CH and HI, a significant reduction in FA (P < 0.001) with increased MD (P < 0.001) was seen in the late subacute and chronic stages compared to the acute and early subacute stages, normal white matter (NWM), and HBT. In HBT, there was no significant statistical difference in the FA values between different stages. Histology of HBT and ex vivo blood clot showed structural organization of intact red blood cells (RBCs) with fibrin mesh where the FA values were high compared to normal tissue region that is devoid of blood. CONCLUSION: Intact RBCs entangled within fibrin mesh appear to be responsible for high FA in hemorrhagic brain lesions.

Adolescent↗
PubMed2006

In vivo serial diffusion tensor imaging of experimental spinal cord injury.

In vivo longitudinal diffusion tensor imaging (DTI) of rodent spinal cord injury (SCI) was carried out over a period of eight weeks post-injury. A balanced, rotationally invariant, alternating gradient polarity icosahedral diffusion encoding scheme was used for an unbiased estimation of the DTI metrics. The fractional anisotropy (FA), diffusivities along (longitudinal), and perpendicular (transverse) to the fiber tracts, were estimated for the ventral, dorsal, and lateral white matter. In all the three regions, the DTI metrics were observed to be significantly different in injured cords relative to the uninjured controls close to the epicenter of the injury. However, these differences gradually disappeared away from the epicenter. The spatio-temporal changes in the DTI metrics showed a recovery pattern that is region specific. Although the temporal trends in the tissue recovery in rostral and caudal sections seem to be similar, overall the DTI metrics were observed to be closer to the normal tissue values in the caudal relative to the rostral sections (rostral-caudal asymmetry).

Animals↗
PubMed2006

Retrospective measurement of the diffusion tensor eigenvalues from diffusion anisotropy and mean diffusivity in DTI.

A simple theoretical framework to compute the eigenvalues of a cylindrically symmetric prolate diffusion tensor (D) from one of the rotationally-invariant diffusion anisotropy indices and average diffusivity is presented and validated. Cylindrical or axial symmetry assumes a prolate ellipsoid shape (lambdaparallel=lambda1>lambdaperpendicular=(lambda2+lambda3)/2; lambda2=lambda3). A prolate ellipsoid with such symmetry is largely satisfied in a number of white matter (WM) structures, such as the spinal cord, corpus callosum, internal capsule, and corticospinal tract. The theoretical model presented is validated using in vivo DTI measurements of rat spinal cord and human brain, where eigenvalues were calculated from both the set of diffusion coefficients and a tensor analysis. This method was used to retrospectively analyze literature data that reported tensor-derived average diffusivity, anisotropy, and eigenvalues, and similar eigenvalue measurements were obtained. The method provides a means to retrospectively reanalyze literature data that do not report eigenvalues. Other potential applications of this method are also discussed.

Adult↗
PubMed2005

Diffusion tensor imaging of the developing human cerebrum.

Diffusion tensor imaging (DTI) was performed on 15 fresh spontaneously or therapeutically aborted normal fetuses and five term infants at different gestational ages. Regional cortical fractional anisotropy (FA) values were observed to increase with gestational age (GA) from 15 to 28 weeks, followed by a decrease through 36 weeks. The early increase in the cortical FA value, which has never been reported before, is consistent with neuronal migration from the germinal matrix. A statistically significant inverse correlation between GA and the FA values in the germinal matrix was observed (r = -0.81, P = 0.004). In addition, there was a significant difference in the FA values in the right and left frontal cortices (P = 0.007, sign test), suggesting cortical lateralization during the early stage of development. Our studies suggest that the DTI-estimated anisotropy could be useful in following neuronal migration, cortical maturation, and associated changes in the germinal matrix during early brain development.

Anisotropy↗
PubMed2005

Diffusion tensor fractional anisotropy of the normal-appearing seven segments of the corpus callosum in healthy adults and relapsing-remitting multiple sclerosis patients.

PURPOSE: To investigate the utility of whole-brain diffusion tensor imaging (DTI) in elucidating the pathogenesis of multiple sclerosis (MS) using the normal-appearing white matter (NAWM) of the corpus callosum (CC) as a marker of occult disease activity. MATERIALS AND METHODS: A high signal-to-noise ratio (SNR) and optimized entire brain DTI data were acquired in 26 clinically-definite relapsing and remitting multiple sclerosis (RRMS) patients and 32 age-matched healthy adult controls. The fractional anisotropy (FA) values of seven functionally distinct regions in the normal-appearing CC were compared between patients and controls. RESULTS: This study indicates that 1) there was a gender-independent FA heterogeneity of the functionally specialized CC segments in normal volunteers; 2) FA in the MS group was significantly decreased in the anterior (P=0.0039) and posterior (P=0.0018) midbody subdivisions of the CC, possibly due to a reduction of small-caliber axons; and 3) the FA of the genu of the CC was relatively intact in the MS patients compared to the healthy age-matched controls (P=0.644), while the splenium showed an insignificant trend of reduced FA values (P=0.248). The decrease in FA in any of the CC subdivisions did not correlate with disease duration (DD) or the expanded disability status scale (EDSS) score. CONCLUSION: The preliminary results are consistent with published histopathology and clinical studies on MS, but not with some published DTI reports. This study provides insights into the pathogenesis of MS, and the role played by compromised axonal integrity in this disease.

Adult↗
PubMed2005

Diffusion tensor imaging of in vivo and excised rat spinal cord at 7 T with an icosahedral encoding scheme.

Regional values of fractional anisotropy (FA) and mean diffusivity (D(av)) of in vivo and excised rat spinal cords were measured using an iscosahedral encoding scheme that is based on 21 uniformly distributed and alternating gradient directions with an echo planar imaging (EPI) readout. Based on the water phantom studies, this scheme was shown to provide unbiased estimation of FA. The stability of the scanner during the acquisition of diffusion tensor imaging (DTI) data was evaluated. Repeated measurements of the FA values demonstrated excellent reproducibility, as assessed by the Bland-Altman analysis. These studies demonstrated a reduced anisotropy in excised samples relative to in vivo cords. Diffusion in the spinal cord gray matter was shown to be anisotropic. The FA value in the dorsal white matter (WM) was found to be higher relative to the ventral WM. Results from these studies should provide the necessary baseline data for serial in vivo DTI of injured spinal cord.

Animals↗
PubMed2005

Reduced anterior corpus callosum white matter integrity is related to increased impulsivity and reduced discriminability in cocaine-dependent subjects: diffusion tensor imaging.

Brain imaging studies find evidence of prefrontal cortical dysfunction in cocaine-dependent subjects. Similarly, cocaine-dependent subjects have problems with behaviors related to executive function and impulsivity. Since prefrontal cortical axonal tracts cross between hemispheres in the corpus callosum, it is possible that white matter integrity in the corpus callosum could also be diminished in cocaine-dependent subjects. The purpose of this study was to compare corpus callosum white matter integrity as measured by the fractional anisotropy (FA) on diffusion tensor imaging (DTI) between 18 cocaine-dependent subjects and 18 healthy controls. The Barratt Impulsiveness Scale (BIS-11) and a continuous performance test: the Immediate and Delayed Memory Task (IMT/DMT) were also collected. Results of the DTI showed significantly reduced FA in the genu and rostral body of the anterior corpus callosum in cocaine-dependent subjects compared to controls. Cocaine-dependent subjects also had significantly higher BIS-11 scores, greater impulsive (commission) errors, and reduced ability to discriminate target from catch stimuli (discriminability) on the IMT/DMT. Within cocaine dependent subjects there was a significant negative correlation between FA in the anterior corpus callosum and behavioral laboratory measured impulsivity, and there was a positive correlation between FA and discriminability. The finding that reduced integrity of anterior corpus callosum white matter in cocaine users is related to impaired impulse control and reduced ability to discriminate between target and catch stimuli is consistent with prior theories regarding frontal cortical involvement in impaired inhibitory control in cocaine-dependent subjects.

Adult↗
PubMed2005

Diffusion tensor imaging in late posttraumatic epilepsy.

PURPOSE: The main objective of this study was to use diffusion tensor imaging (DTI) to search and quantify the extent of abnormality beyond the obvious lesions seen on the T2 and fluid-attenuation inversion recovery (FLAIR) magnetic resonance images in patients with chronic traumatic brain injury (TBI) with and without epilepsy. METHODS: DTI was performed on 23 chronic TBI patients (with late posttraumatic epilepsy, n=14; without epilepsy, n=9) and 11 age-matched controls. The ratios of fractional anisotropy (FA) and mean diffusivity (MD) between the regions of interest beyond the T2/FLAIR-visualized abnormality and the corresponding contralateral normal-appearing region were calculated. FA and MD ratios were compared for relative changes in these parameters among the TBI subjects with and without epilepsy and controls. Tissue volumes exhibiting abnormalities on DTI also were measured in these patients. RESULTS: The mean regional FA ratio was significantly lower, whereas the mean regional MD value was higher in patients with TBI compared with controls. The mean regional FA ratio was significantly lower in TBI patients with epilepsy (0.57+/-0.059) than in those without epilepsy (0.68+/-0.039). Although the regional MD ratio was higher in TBI patients with epilepsy (1.15+/-0.140) relative to those without epilepsy (1.09+/-0.141), the difference did not reach statistical significance. The tissue volume with low FA value also was found to be higher in TBI patients with epilepsy than without. CONCLUSIONS: Severity of injury as predicted by the DTI-derived increased volume of microstructure damage is associated with delayed posttraumatic epilepsy in TBI patients. These findings could be valuable in predicting epileptogenesis in patients with chronic TBI.

Adolescent↗
PubMed2005

High fractional anisotropy in brain abscesses versus other cystic intracranial lesions.

BACKGROUND AND PURPOSE: It is known that intracranial mass lesions are relatively isotropic on diffusion-weighted imaging. The purpose of this study is to report an unusually high fractional anisotropy (FA) and mean diffusivity (D(av)) in the cavity of the brain abscess compared with other cystic lesions. METHODS: We performed diffusion tensor imaging (DTI) in 12 patients with cystic intracranial lesions (pyogenic abscess, n = 5; cysticercus cysts, n = 2; and low-grade astrocytoma, n = 5). Mean FA, D(av) from the lesion core, perifocal edema, and corresponding contralateral normal-appearing regions were measured and compared for relative changes in these parameters. In the abscess cases, we placed regions of interest on areas with FA >0.2 and FA <0.2 to get FA and D(av) values. RESULTS: There were two patterns of FA values in the abscess cavity in all five patients. Part of the abscess showed mean FA = 0.440 +/- 0.135, with D(av) = (0.993 +/- 0.185) x 10(-3) mm(2)/s, whereas other parts had FA = 0.131 +/- 0.039 with D(av) = (0.824 +/- 0.183) x 10(-3) mm(2)/s. The cystic tumors and neurocysticercosis showed very high D(av) = (2.806 +/- 0.25, 2.654 +/- 0.35)x 10(-3) mm(2)/s, with low FA = (0.108 +/- 0.037, 0.08 +/- 0.01), respectively. CONCLUSION: Brain abscess cavity shows regions of increased FA values with restricted mean diffusivity compared with other cystic intracranial lesions. This information may prevent misinterpretation of the DTI information as white matter fiber bundle abnormalities associated with mass lesions.

Adolescent↗
PubMed2004

Diffusion tensor eigenvector directional color imaging patterns in the evaluation of cerebral white matter tracts altered by tumor.

PURPOSE: To categorize the varied appearances of tumor-altered white matter (WM) tracts on diffusion tensor eigenvector directional color maps. MATERIALS AND METHODS: Diffusion tensor imaging (DTI) was obtained preoperatively in 13 patients with brain tumors ranging from benign to high-grade malignant, including primary and metastatic lesions, and maps of apparent diffusion coefficient (ADC), fractional anisotropy (FA), and major eigenvector direction were generated. Regions of interest (ROIs) were drawn within identifiable WM tracts affected by tumor, avoiding grossly cystic and necrotic regions, known fiber crossings, and gray matter. Patterns of WM tract alteration were categorized on the basis of qualitative analysis of directional color maps and correlation analysis of ADC and FA. RESULTS: Four basic patterns of WM alteration were identified: 1) normal or nearly normal FA and ADC, with abnormal tract location or tensor directions attributable to bulk mass displacement, 2) moderately decreased FA and increased ADC with normal tract locations and tensor directions, 3) moderately decreased FA and increased ADC with abnormal tensor directions, and 4) near isotropy. FA and ADC were inversely correlated for Patterns 1-3 but did not discriminate edema from infiltrating tumor. However, in the absence of mass displacement, infiltrating tumor was found to produce tensor directional changes that were not observed with vasogenic edema, suggesting the possibility of discrimination on the basis of directional statistics. CONCLUSION: Tumor alteration of WM tracts tends to produce one of four patterns on FA and directional color maps. Clinical application of these patterns must await further study.

Adult↗
PubMed2004

Does fractional anisotropy have better noise immunity characteristics than relative anisotropy in diffusion tensor MRI? An analytical approach.

Fractional anisotropy (FA) and relative anisotropy (RA) are the two most commonly used scalar measures of anisotropy in diffusion tensor (DT) MRI. While a few published studies have shown that FA has superior noise immunity relative to RA, no theoretical basis has been proposed to explain this behavior. In the current study, the diffusion tensor invariants were used to derive a simple analytical expression that directly relates RA and FA. An analysis based on that analytical expression demonstrated that the FA images have a higher signal-to-noise ratio (SNR) than RA for any value of tensor anisotropy RA or FA > 0. This theoretical behavior was verified using both Monte Carlo simulations and bootstrap analysis of DT-MRI data acquired in a spherical water phantom and normal human subjects.

Anisotropy↗
PubMed2003

White matter tractography using diffusion tensor deflection.

Diffusion tensor MRI provides unique directional diffusion information that can be used to estimate the patterns of white matter connectivity in the human brain. In this study, the behavior of an algorithm for white matter tractography is examined. The algorithm, called TEND, uses the entire diffusion tensor to deflect the estimated fiber trajectory. Simulations and imaging experiments on in vivo human brains were performed to investigate the behavior of the tractography algorithm. The simulations show that the deflection term is less sensitive than the major eigenvector to image noise. In the human brain imaging experiments, estimated tracts were generated in corpus callosum, corticospinal tract, internal capsule, corona radiata, superior longitudinal fasciculus, inferior longitudinal fasciculus, fronto-occipital fasciculus, and uncinate fasciculus. This approach is promising for mapping the organizational patterns of white matter in the human brain as well as mapping the relationship between major fiber trajectories and the location and extent of brain lesions.

Algorithms↗
PubMed2003

Computation of the fractional anisotropy and mean diffusivity maps without tensor decoding and diagonalization: Theoretical analysis and validation.

Diffusion tensor MRI (DT-MRI) is a promising modality for in vivo mapping of the organization of deep tissues. The most commonly used DT-MRI invariant maps are the mean diffusivity, mu(D), relative anisotropy (RA), and fractional anisotropy (FA). Because of the computational burden, anisotropy maps are generally computed offline. The availability of a simple procedure to compute RA, FA, and mu(D) online would make DT-MRI more useful in clinical applications that require immediate feedback. In this study, analytical expressions that relate the commonly used tensor anisotropy measures obtained from the decoded and diagonalized DT with those obtained from the first and second moments of the measured diffusion-weighted (DW) data are derived. Specifically, it is shown that for the principal icosahedron encoding scheme, RA is related to the mean and standard deviation (SD) of the DW measurements that can be computed online. Since FA is commonly used as an anisotropy measure, an analytical expression relating RA and FA was derived from the tensor invariants. These results were validated using both Monte Carlo simulations and high-resolution, normal whole-brain DT-MRI measurements acquired with different b-factors, encoding schemes, and signal-to-noise ratio (SNR) levels. The bias introduced by the rotationally variant encoding schemes into the diffusion measures is also investigated.

Algorithms↗
PubMed2002

Diffusion-tensor imaging of white matter tracts in patients with cerebral neoplasm.

OBJECT: Preserving vital cerebral function while maximizing tumor resection is a principal goal in surgical neurooncology. Although functional magnetic resonance imaging has been useful in the localization of eloquent cerebral cortex, this method does not provide information about the white matter tracts that may be involved in invasive, intrinsic brain tumors. Recently, diffusion-tensor (DT) imaging techniques have been used to map white matter tracts in the normal brain. The aim of this study was to demonstrate the role of DT imaging in preoperative mapping of white matter tracts in relation to cerebral neoplasms. METHODS: Nine patients with brain malignancies (one pilocytic astrocytoma, five oligodendrogliomas, one low-grade oligoastrocytoma, one Grade 4 astrocytoma, and one metastatic adenocarcinoma) underwent DT imaging examinations prior to tumor excision. Anatomical information about white matter tract location, orientation, and projections was obtained in every patient. Depending on the tumor type and location, evidence of white matter tract edema (two patients), infiltration (two patients), displacement (five patients), and disruption (two patients) could be assessed with the aid of DT imaging in each case. CONCLUSIONS: Diffusion-tensor imaging allowed for visualization of white matter tracts and was found to be beneficial in the surgical planning for patients with intrinsic brain tumors. The authors' experience with DT imaging indicates that anatomically intact fibers may be present in abnormal-appearing areas of the brain. Whether resection of these involved fibers results in subtle postoperative neurological deficits requires further systematic study.

Adenocarcinoma↗