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Pratik Mukherjee

Publications and source records attributed to Pratik Mukherjee.

At least 19 recordsLinked to original sources
PubMed2006

Pyramidal tract maturation after brain injury in newborns with heart disease.

OBJECTIVE: Our objective was to quantify white matter tract development in term newborns with congenital heart disease, a population at high risk for perioperative brain injury, using magnetic resonance imaging diffusion tensor tractography (DTT). METHODS: Twenty-five newborns with congenital heart disease were imaged before and after surgery, with a median of 2 weeks between serial magnetic resonance imaging examinations. DTT was performed to segment bilateral pyramidal tracts using semiautomated fiber tracking software, and manual region of interest measurements were taken for comparison. RESULTS: Significant maturational rates of increasing fractional anisotropy (median, 4.4% per week) and decreasing mean diffusivity (D(av)) (median, -2.0% per week) in the pyramidal tract were measured in infants without brain injury. Fractional anisotropy maturation rates were highest in newborns with normal scans, intermediate (median, 2.4% per week) in those with postoperative injury, and lowest (median, 0.9% per week) in those with preoperative injury, indicating a significant trend across brain injury groups (p = 0.015). D(av) maturation rates did not differ across injury groups (p = 0.15). Manual region of interest measures showed greater variability in serial measurements, and no significant differences were identified between injury groups, suggesting that DTT may provide more sensitive measures. INTERPRETATION: DTT is feasible in term newborns and may help to characterize abnormal white matter tract development following acquired brain injury.

Brain Injuries↗
PubMed2006

Q-ball reconstruction of multimodal fiber orientations using the spherical harmonic basis.

Diffusion tensor imaging (DTI) accurately delineates white matter pathways when the Gaussian model of diffusion is valid. However, DTI yields erroneous results when diffusion takes on a more complex distribution, as is the case in the brain when fiber tracts cross. High angular resolution diffusion imaging (HARDI) overcomes this limitation of DTI by more fully characterizing the angular dependence of intravoxel diffusion. Among the various HARDI methods that have been proposed, QBI offers advantages such as linearity, model independence, and relatively easy implementation. In this work, reconstruction of the q-ball orientation distribution function (ODF) is reformulated in terms of spherical harmonic basis functions, yielding an analytic solution with useful properties of a frequency domain representation. The harmonic basis is parsimonious for typical b-values, which enables the ODF to be synthesized from a relatively small number of noisy measurements and thus brings the technique closer to clinical feasibility from the standpoint of total imaging time. The proposed method is assessed using Monte Carlo computer simulations and compared with conventional q-ball reconstruction using spherical RBFs. In vivo results from 3T whole-brain HARDI of adult volunteers are also provided to verify the underlying mathematical theory.

Adult↗
PubMed2006

Diffusion tensor imaging and tractography of human brain development.

Over the past decade, diffusion tensor imaging (DTI) has offered researchers and clinicians a new noninvasive window into the developing human brain, from preterm infants through adolescents and young adults. DTI improves on conventional MR imaging, such as T1-weighted and T2-weighted sequences, through its sensitivity to many microstructural features of neural organization. This has enabled visualization of the early cerebral laminar architecture in premature infants, of developing white matter before myelination, and of the microarchitecture of the cerebral cortex during preterm maturation. DTI provides reproducible quantitative measures, such as mean diffusivity and fractional anisotropy, that reflect the underlying tissue properties of gray matter and white matter and may therefore become useful as developmental milestones for the improved assessment of abnormal brain maturation. Furthermore, three-dimensional fiber tractography based on DTI can reveal the developing axonal connectivity of the human brain as well as aberrant connectivity in structural brain malformations. In this article, applications of DTI and fiber tractography to the study of human brain development are reviewed. The new insights into brain maturation afforded by DTI promise to improve the diagnostic evaluation of an array of congenital, metabolic, and neurodevelopmental disorders.

Adolescent↗
PubMed2005

Quantitative diffusion tensor MRI fiber tractography of sensorimotor white matter development in premature infants.

Diffusion tensor MRI (DTI) fiber tracking is the first non-invasive and in vivo technique for the delineation and quantitation of specific white matter pathways. In this study, quantitative fiber tracking was used to assess the structural development of the motor tract and somatosensory radiation in premature human newborns. These pathways are unmyelinated in the youngest premature infants and begin to myelinate during late preterm maturation. Previous studies have only been able to delineate parts of these pathways that could be manually outlined in 2D based on anatomical landmarks. Furthermore, these previous studies could not separate motor and sensory regions. A high-sensitivity neonatal head coil was employed in conjunction with an MR-compatible incubator to perform high-resolution imaging of the premature infant brain. The motor and somatosensory tracts were successfully delineated with 3D DTI fiber tracking in 37 exams of preterm newborns between 28 and 43 weeks gestational age. Both streamline deterministic and probabilistic methods were employed to perform quantitative fiber tractography. Tract-specific measurements of diffusion parameters including fractional anisotropy, directionally averaged diffusivity, and eigenvalues were obtained from the motor and sensory pathways. Using both deterministic and probabilistic fiber tracking, all tract-specific diffusion parameters were found to be significantly correlated with age and the motor tracts were found to have higher anisotropy and lower diffusivity than the sensory pathway. By segmenting the 3D fiber tracks by slice, measurements from different axial levels of the brain were found to vary with region and age. In summary, deterministic and probabilistic DTI fiber tracking methods were used to quantify the developmental changes of motor and somatosensory pathways in premature infants.

Adult↗
PubMed2005

Tractography-based quantitation of diffusion tensor imaging parameters in white matter tracts of preterm newborns.

PURPOSE: To evaluate the feasibility of performing diffusion tensor tractography (DTT) to map and quantify the pyramidal white matter tracts of premature newborns. MATERIALS AND METHODS: Fourteen diffusion tensor MRI (DTI) examinations of nine premature newborns were evaluated. DTT was performed to segment bilateral pyramidal tracts, using a fiber-tracking algorithm originating in the cerebral peduncle (CP) and filtering through the posterior limb of the internal capsule (PLIC) and precentral gyrus (PCG). Voxels containing the resulting tracts were then used for quantitation of DTI parameters along the tract. The DTT-based tract measurements were compared with standard manually placed region-of-interest (ROI) measurements at four locations along the pyramidal tract, and the reproducibility of each technique was evaluated. RESULTS: DTT demonstrated improved reproducibility over manual ROI measurement for pyramidal tract quantitation and was less subject to intra-operator variability (P < 0.0001, Fisher test for equal variance). In general, the anatomic locations and measurements obtained with the two techniques were in good agreement, although some systematic differences were identified in the PLIC and CP. CONCLUSION: Fiber DTT is feasible in premature newborns, provides more reproducible tract measurements than manual ROI methods, and allows quantitation along the entire tract for more detailed DTI assessment of white matter maturation.

Diffusion Magnetic Resonance Imaging↗
PubMed2005

Early brain injury in premature newborns detected with magnetic resonance imaging is associated with adverse early neurodevelopmental outcome.

OBJECTIVE: To determine the neurodevelopmental outcome of prematurely born newborns with magnetic resonance imaging (MRI) abnormalities. STUDY DESIGN: A total of 89 prematurely born newborns (median age 28 weeks postgestation) were studied with MRI when stable for transport to MRI (median age, 32 weeks postgestation); 50 newborns were studied again near term age (median age, 37 weeks). Neurodevelopmental outcome was determined at 18 months adjusted age (median) using the Mental Development Index (Bayley Scales Infant Development II) and a standardized neurologic exam. RESULTS: Of 86 neonatal survivors, outcome was normal in 51 (59%), borderline in 22 (26%), and abnormal in 13 (15%). Moderate/severe MRI abnormalities were common on the first (37%) and second (32%) scans. Abnormal outcome was associated with increasing severity of white matter injury, ventriculomegaly, and intraventricular hemorrhage on MRI, as well as moderate/severe abnormalities on the first (relative risk [RR] = 5.6; P = .002) and second MRI studies (RR = 5.3; P = .03). Neuromotor abnormalities on neurologic examination near term age (RR = 6.5; P = .04) and postnatal infection (RR = 4.0; P = .01) also increased the risk for abnormal neurodevelopmental outcome. CONCLUSIONS: In premature newborns, brain abnormalities are common on MRI early in life and are associated with adverse neurodevelopmental outcome.

Brain Injuries↗
PubMed2005

Comparing microstructural and macrostructural development of the cerebral cortex in premature newborns: diffusion tensor imaging versus cortical gyration.

This study assessed microstructural development in four regions of the human cerebral cortex during preterm maturation using diffusion tensor imaging (DTI), compared to the macrostructural development of cortical gyration evaluated using three-dimensional volumetric T1-weighted MR imaging. Thirty-seven premature infants of estimated gestational age (EGA) ranging from 25 to 38 weeks were prospectively enrolled and imaged in an MR-compatible neonatal incubator with a high-sensitivity neonatal head coil. Cortical gyration was measured quantitatively as the ratio of gyral height to width on the volumetric MR images in four regions bilaterally (superior frontal, superior occipital, precentral, and postcentral gyri). Mean diffusivity (D(av)), fractional anisotropy (FA-the fraction of D(av) that is anisotropic), and the three DTI eigenvalues (components of diffusivity radial and tangential to the pial surface of cortex) were measured in the same cortical regions. Cortical gyration scores, FA, and radial diffusivity were all significantly correlated with EGA (P < 0.0001). However, in multivariate analysis, no significant relationship (P > 0.05) was found between DTI parameters and cortical gyration beyond their common association with estimated gestational age. Pre- and postcentral gyri had significantly lower anisotropy than the superior occipital and superior frontal gyri (P < 0.05), indicating that DTI is sensitive to regional heterogeneity in cortical development. Maturational changes in the DTI eigenvalues of cortical gray matter were found to differ from those that have previously been described in developing white matter, with a significant age-related decline in the radial diffusivity (P < 0.0001) but not in the tangential diffusivities (P > 0.05).

Algorithms↗
PubMed2005

Diffusion tensor imaging and fiber tractography in acute stroke.

Diffusion tensor imaging (DTI) permits the quantitative evaluation of white matter pathology using measures of diffusion anisotropy. Fiber tractography based on DTI can reveal the three-dimensional white matter connectivity of the human brain. DTI fiber tractography is used to localize stroke lesions in relation to functionally important pathways and to assess wallerian degeneration, which may allow more accurate prognosis of long-term recovery or disability. DTI also improves the evaluation of hypoxic-ischemic injury to the developing brain of newborns and infants. DTI and fiber tractography may prove useful in elucidating alterations in brain connectivity resulting from neuroplasticity after stroke.

Anisotropy↗
PubMed2005

Diffusion tensor imaging with three-dimensional fiber tractography of traumatic axonal shearing injury: an imaging correlate for the posterior callosal "disconnection" syndrome: case report.

OBJECTIVE: To demonstrate that magnetic resonance diffusion tensor imaging (DTI) with three-dimensional (3-D) fiber tractography can visualize traumatic axonal shearing injury that results in posterior callosal disconnection syndrome. METHODS: A 22-year-old man underwent serial magnetic resonance imaging 3 days and 12 weeks after blunt head injury. The magnetic resonance images included whole-brain DTI acquired with a single-shot spin echo echoplanar sequence. 3-D DTI fiber tractography of the splenium of the corpus callosum was performed. Quantitative DTI parameters, including apparent diffusion coefficient and fractional anisotropy, from the site of splenial injury were compared with those of a normal adult male volunteer. RESULTS: Conventional magnetic resonance images revealed findings of diffuse axonal injury, including a lesion at the midline of the splenium of the corpus callosum. DTI performed 3 days posttrauma revealed that the splenial lesion had reduced apparent diffusion coefficient and fractional anisotropy, reflecting a large decrease in the magnitude of diffusion parallel to the white matter fibers, which had partially recovered as revealed by follow-up DTI 12 weeks postinjury. 3-D tractography revealed an interruption of the white matter fibers in the posteroinferior aspect of the splenium that correlated with the patient's left hemialexia, a functional deficit caused by disconnection of the right visual cortex from the language centers of the dominant left hemisphere. CONCLUSION: DTI with 3-D fiber tractography can visualize acute axonal shearing injury, which may have prognostic value for the cognitive and neurological sequelae of traumatic brain injury.

Adult↗
PubMed2004

Hand somatosensory cortex activity following selective dorsal rhizotomy: report of three cases with fMRI.

INTRODUCTION: Selective dorsal rhizotomy (SDR) is an effective treatment for lower extremity spasticity in cerebral palsy. Cortical organization in sensory cortex may be abnormal in cerebral palsy, and deafferentation is known to lead to cortical reorganization in many situations. METHODS: We used functional magnetic resonance imaging (fMRI) of hand sensory stimulation to determine if the partial deafferentation of the lower extremity sensory system, associated with SDR, led to any alterations in the cortical somatosensory representation for the upper limbs. Three patients with spastic diplegia were studied with blood oxygen level-dependent (BOLD)-fMRI before and after SDR. fMRI during tactile stimulation of the digits of the right hand was used to map hand somatosensory cortex. Comparison of the cortical maps devoted to the hand before and after SDR assessed for cortical reorganization following partial deafferentation of the lower extremity. RESULTS: In the one patient with upper extremity involvement, the hand sensory representation was markedly enhanced following SDR. In the other two patients, a normal pattern, but with diminished activity, was seen compared with preoperative findings. SDR for lower limb spastic diplegia does not lead to extensive reorganization of cortex dedicated to the representation of the upper limb. An essentially normal pattern of activation was seen both before and after SDR. CONCLUSION: The relief of attention demands associated with spasticity may explain the modulation in intensity seen after SDR in the patients who exhibited no upper extremity involvement despite lower limb spasticity.

Adolescent↗
PubMed2004

Single-shot fast spin-echo diffusion tensor imaging of the brain and spine with head and phased array coils at 1.5 T and 3.0 T.

In this study, we investigated the use of a single-shot fast spin-echo-based sequence to perform diffusion tensor imaging (DTI) with improved anatomic fidelity through the entire brain and the cervical spine. Traditionally, diffusion tensor images have been acquired by single-shot echo-planar imaging (EPI) methods in which large distortions result from magnetic susceptibility effects, especially near air-tissue interfaces. These distortions can be problematic, especially in anterior and inferior portions of the brain, and they also can severely limit applications in the spine. At higher magnetic fields these magnetic susceptibility artifacts are increased. The single-shot fast spin-echo (SSFSE) method used in this study utilizes radiofrequency rephasing in the transverse plane and thus provides diffusion images with negligible distortion even at 3 Tesla. In addition, the SSFSE sequence does not require multiple fast-receivers, which are not available on many magnetic resonance (MR) systems. Phased array coils were used to increase the signal-to-noise ratio of the images, offering a major inherent advantage in diffusion tensor imaging of the spine and brain. The mean diffusion measurements obtained with the SSFSE acquisition were not statistically different (p > 0.05) from EPI-based acquisitions. Compared to routine T(2)-weighted MR images, the DTI-EPI sequence showed up to 20% in elongation of the brain in the anterior-posterior direction on a sagittal image due to magnetic susceptibility distortions, whereas in the DTI-SSFSE, the image distortions were negligible. The diffusion tensor SSFSE method was also able to assess diffusion abnormalities in a brain stem hemorrhage, unaffected by the spatial distortions that limited conventional EPI acquisition.

Adult↗
PubMed2004

Subcortical pathways serving cortical language sites: initial experience with diffusion tensor imaging fiber tracking combined with intraoperative language mapping.

The combination of mapping functional cortical neurons by intraoperative cortical stimulation and axonal architecture by diffusion tensor MRI fiber tracking can be used to delineate the pathways between functional regions. In this study the authors investigated the feasibility of combining these techniques to yield connectivity associated with motor speech and naming. Diffusion tensor MRI fiber tracking provides maps of axonal bundles and was combined with intraoperative mapping of eloquent cortex for a patient undergoing brain tumor surgery. Tracks from eight stimulated sites in the inferior frontal cortex including mouth motor, speech arrest, and anomia were generated from the diffusion tensor MRI data. The regions connected by the fiber tracking were compared to foci from previous functional imaging reports on language tasks. Connections were found between speech arrest, mouth motor, and anomia sites and the SMA proper and cerebral peduncle. The speech arrest and a mouth motor site were also seen to connect to the putamen via the external capsule. This is the first demonstration of delineation of subcortical pathways using diffusion tensor MRI fiber tracking with intraoperative cortical stimulation. The combined techniques may provide improved preservation of eloquent regions during neurological surgery, and may provide access to direct connectivity information between functional regions of the brain.

Adult↗
PubMed2004

Early laminar organization of the human cerebrum demonstrated with diffusion tensor imaging in extremely premature infants.

Diffusion tensor imaging (DTI) was used to delineate early laminar organization of the cerebrum in two extremely premature infants imaged postnatally at estimated ages of 25 and 27 menstrual weeks. The diffusivity and anisotropy of the cortical plate, subplate zone, intermediate zone, subventricular and periventricular zones, and germinal matrix are examined. Automated segmentation of diffusion tensor images to reveal the laminar architecture of the developing human cerebrum is also demonstrated.

Aging↗
PubMed2004

Diffusion tensor imaging: serial quantitation of white matter tract maturity in premature newborns.

Magnetic resonance diffusion tensor imaging (DTI) enables the discrimination of white matter pathways before myelination is evident histologically or on conventional MRI. In this investigation, 14 premature neonates with no evidence of white matter abnormalities by conventional MRI were studied with DTI. A custom MR-compatible incubator with a novel high sensitivity neonatal head coil and improved acquisition and processing techniques were employed to increase image quality and spatial resolution. The technical improvements enabled tract-specific quantitative characterization of maturing white matter, including several association tracts and subcortical projection tracts not previously investigated in neonates by MR. Significant differences were identified between white matter pathways, with earlier maturing commissural tracts of the corpus callosum, and deep projection tracts of the cerebral peduncle and internal capsule exhibiting lower mean diffusivity (Dav) and higher fractional anisotropy (FA) than later maturing subcortical projection and association pathways. Maturational changes in white matter tracts included reductions in Dav and increases in FA with age due primarily to decreases in the two minor diffusion eigenvalues (lambda2 and lambda3). This work contributes to the understanding of normal white matter development in the preterm neonatal brain, an important step toward the use of DTI for the improved evaluation and treatment of white matter injury of prematurity.

Anisotropy↗
PubMed2004

Diffusion-tensor imaging-guided tracking of fibers of the pyramidal tract combined with intraoperative cortical stimulation mapping in patients with gliomas.

OBJECT: The goal of this study was to use diffusion-tensor (DT) magnetic resonance (MR) imaging to track fibers combined with cortical stimulation mapping to delineate descending motor pathways. Subcortical localization of motor pathways in relation to a glioma may provide critical information to guide tumor resection and prevent surgical morbidity. METHODS: Eleven adult patients harboring gliomas underwent MR imaging 1 day prior to image-guided intraoperative cortical motor mapping and tumor resection. Screens depicting 27 cortical motor sites on a surgical navigation system were saved to launch DT imaging of fiber tracks of descending motor pathways. The position and organization of motor tracts were visualized by fiber tracking. Tracks from 16 motor stimulation sites followed descending pathways from the precentral gyrus, through the corona radiata and internal capsule, and into the cerebral peduncle. These tracks were also observed on DT images to diverge along crossing white matter bundles (four patients) and to terminate or deviate in regions of peritumoral vasogenic edema (five patients). CONCLUSIONS: The use of precise intraoperative cortical mapping information and DT images of fiber tracks can reveal the course of motor pathways beneath the cortex. The subcortical fiber tracks generated are consistent with the known anatomical course and somatotopic organization of the motor tract in relation to its cortical origins. Tracking fibers by using DT imaging in combination with functional localization has the potential to reduce surgical morbidity by revealing subcortical connections of the functional cortex.

Adult↗
PubMed2003

Measurement of cerebral blood flow in chronic carotid occlusive disease: comparison of dynamic susceptibility contrast perfusion MR imaging with positron emission tomography.

BACKGROUND AND PURPOSE: Our purpose was to evaluate the accuracy of cerebral blood flow (CBF) measurements obtained by using dynamic susceptibility contrast-enhanced MR imaging, including the influence of arterial input function (AIF) selection, compared with those obtained by using [(15)O]-H(2)O positron emission tomography (PET) for patients with chronic carotid occlusion. METHODS: MR images and PET scans were obtained of seven patients with unilateral carotid occlusion and were co-registered for region of interest analysis. PET CBF maps were generated by using the autoradiographic method. MR imaging CBF maps were calculated by deconvolution of the susceptibility time curve with a proximal middle cerebral artery AIF and were converted to absolute flow rates either by assuming a constant contralateral white matter CBF value of 22 mL/100 mL/min or by using individually determined PET white matter CBF values. RESULTS: Although CBF values measured by PET and MR imaging were positively correlated for every patient, the slopes and y intercepts of the regression lines varied widely among patients. The correlation was better when individual white matter CBF values measured by PET were used to scale the white matter CBF values measured by MR imaging (r = 0.84, P <.0001) than when constant contralateral CBF values were assumed (r = 0.54, P <.0001). The choice of AIF ipsilateral or contralateral to the occluded carotid artery made no statistically significant difference (P >.05) to the correlation coefficient, slope, or y intercept of the MR imaging versus PET CBF regressions for six of the seven patients. CONCLUSION: Although linearly correlated with CBF values measured by PET, dynamic susceptibility contrast-enhanced MR imaging was not accurate for measuring absolute CBF values. AIF selection relative to the side of carotid occlusion did not significantly affect calculated MR imaging CBF values for six of the seven patients.

Aged↗