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At least 469 records · Page 26Linked to original sources
PubMed2004

White matter hemisphere asymmetries in healthy subjects and in schizophrenia: a diffusion tensor MRI study.

Hemisphere asymmetry was explored in normal healthy subjects and in patients with schizophrenia using a novel voxel-based tensor analysis applied to fractional anisotropy (FA) of the diffusion tensor. Our voxel-based approach, which requires precise spatial normalization to remove the misalignment of fiber tracts, includes generating a symmetrical group average template of the diffusion tensor by applying nonlinear elastic warping of the demons algorithm. We then normalized all 32 diffusion tensor MRIs from healthy subjects and 23 from schizophrenic subjects to the symmetrical average template. For each brain, six channels of tensor component images and one T2-weighted image were used for registration to match tensor orientation and shape between images. A statistical evaluation of white matter asymmetry was then conducted on the normalized FA images and their flipped images. In controls, we found left-higher-than-right anisotropic asymmetry in the anterior part of the corpus callosum, cingulum bundle, the optic radiation, and the superior cerebellar peduncle, and right-higher-than-left anisotropic asymmetry in the anterior limb of the internal capsule and the anterior limb's prefrontal regions, in the uncinate fasciculus, and in the superior longitudinal fasciculus. In patients, the asymmetry was lower, although still present, in the cingulum bundle and the anterior corpus callosum, and not found in the anterior limb of the internal capsule, the uncinate fasciculus, and the superior cerebellar peduncle compared to healthy subjects. These findings of anisotropic asymmetry pattern differences between healthy controls and patients with schizophrenia are likely related to neurodevelopmental abnormalities in schizophrenia.

Adult↗
PubMedDate not supplied

Near-infrared frequency-domain optical spectroscopy and magnetic resonance imaging: a combined approach to studying cerebral maturation in neonatal rabbits.

The neonatal rabbit brain shows prolonged postnatal development both structurally and physiologically. We use noninvasive near-IR frequency-domain optical spectroscopy (NIRS) and magnetic resonance imaging (MRI) to follow early developmental changes in cerebral oxygenation and anatomy, respectively. Four groups of animals are measured: NIRS in normals, MRI in normals, and both NIRS and MRI with hypoxia-ischemia (HI) (diffusion MRI staging). NIRS and/or MRI are performed from P3 (postnatal day=P) up to P76. NIRS is performed on awake animals with a frequency-domain tissue photometer. Absolute values of oxyhemoglobin concentration ([HbO2]), deoxyhemoglobin concentration ([HbR]), total hemoglobin concentration (HbT), and hemoglobin saturation (StO2) are calculated. The brains of all animals appeared to be maturing as shown in the diffusion tensor MRI. Mean optical coefficients (reduced scattering) remained unchanged in all animals throughout. StO2 increased in all animals (40% at P9 to 65% at P43) and there are no differences between normal, HI controls, and HI brains. The measured increase in StO2 is in agreement with the reported increase in blood flow during the first 2 months of life in rabbits. HbT, which reflects blood volume, peaked at postnatal day P17, as expected since the capillary density increases up to P17 when the microvasculature matures.

Animals↗
PubMed2003

Water diffusion measurements in perfused human hippocampal slices undergoing tonicity changes.

Diffusion MRI has the potential to probe the compartmental origins of MR signals acquired from human nervous tissue. However, current experiments in human subjects require long diffusion times, which may confound data interpretation due to the effects of compartmental exchange. To investigate human nervous tissue at shorter diffusion times, and to determine the relevance of previous diffusion studies in rat hippocampal slices, water diffusion in 20 perfused human hippocampal slices was measured using a wide-bore 17.6-T magnet equipped with 1000-mT/m gradients. These slices were procured from five patients undergoing temporal lobectomy for epilepsy. Tissue viability was confirmed with electrophysiological measurements. Diffusion-weighted water signal attenuation in the slices was well-described by a biexponential function (R(2) > 0.99). The mean diffusion parameters for slices before osmotic perturbation were 0.686 +/- 0.082 for the fraction of fast diffusing water (F(fast)), 1.22 +/- 0.22 x 10(-3) mm(2)/s for the fast apparent diffusion coefficient (ADC), and 0.06 +/- 0.02 x 10(-3) mm(2)/s for the slow ADC. Slice perturbations with 20% hypotonic and 20% hypertonic artificial cerebrospinal fluid led to changes in F(fast) of -8.2% and +10.1%, respectively (ANOVA, P < 0.001). These data agree with previous diffusion studies of rat brain slices and human brain in vivo, and should aid the development of working models of water diffusion in nervous tissue, and thus increase the clinical utility of diffusion MRI.

Analysis of Variance↗
PubMed2004

Diffusion-weighted MRI of soft tissue tumours.

The purpose of this study was to evaluate the clinical utility of a multi-shot spin-echo echo-planar (SE-EPI) diffusion-weighted sequence in the diagnostic work-up of soft tissue tumours. There were 29 patients, 16 with a benign lesion and 13 with a sarcoma. Four of the sarcomas were examined both before and after radiation therapy. Diffusion-weighted imaging was performed with a multi-shot SE-EPI sequence. The b values were 0 and 600 s/mm(2). Phase navigation and pulse trigging were applied. The apparent diffusion constant (ADC) value of a large region of interest (ROI) representing the lesion was measured and compared to diagnosis and treatment. The ADC values of the benign lesions (mean 1.8 x 10(-3) mm(2)/s) overlapped with non-treated sarcomas (mean 1.7 x 10(-3) mm(2)/s). The ADC value increased in all radiated sarcomas. A multi-shot SE-EPI diffusion imaging sequence of less than 2-min duration is technically feasible in soft tissue tumours of the extremities and the trunk. The ADC values of benign soft tissue tumours and sarcomas overlapped and could not be used to differentiate between the bulk of benign and malignant tumours. However, the increase in ADC values of soft tissue sarcomas after radiotherapy warrants further studies of diffusion imaging for evaluating therapy response.

Adult↗
PubMed2004

Combined MR spectroscopic imaging and diffusion tensor MRI visualizes corticospinal tract degeneration in amyotrophic lateral sclerosis.

Motor neuron damage and cortical spinal tract (CST) degeneration are pathological features of amyotrophic lateral sclerosis (ALS). We combined whole-brain diffusion tensor imaging (DTI) and three-dimensional magnetic resonance spectroscopic imaging (MRSI) to study the CST at different locations. Eight ALS patients were compared with normal controls. Fractional anisotropy (FA) and mean diffusivity (MD), and the ratio of N-acetyl-aspartate (NAA) to creatine (Cr) were measured at various locations in the CST, including the subcortical white matter (SWM), centrum semiovale (CS), periventricular white matter (PV), posterior limb of the internal capsule (PIC) and cerebral peduncle (CP). Patients showed significantly lower FA than controls in the CST, including the SWM, CS, PV and PIC. Although there was a trend towards elevated MD in ALS patients, this did not reach statistical significance. NAA/Cr ratios were also decreased in ALS patients compared with normal controls, with significant differences in the SWM and PV but not in PIC. Combined whole-brain DTI and MRSI can detect axonal degeneration in ALS. Measurements of FA obtained in the SWM, CS, PV and PIC, and NAA/Cr ratios in the SWM and PV yield the most robust results.

Adult↗
PubMed2005

Cytotoxic edema is responsible for raised intracranial pressure in fulminant hepatic failure: in vivo demonstration using diffusion-weighted MRI in human subjects.

It is not clear whether cerebral edema in fulminant hepatic failure is predominantly vasogenic or cytotoxic, though cytotoxic edema due to astrocyte swelling is more likely. Diffusion-weighted magnetic resonance imaging can differentiate vasogenic from cytotoxic edema. We performed diffusion-weighted imaging in patients with fulminant hepatic failure to clarify the issue by measuring apparent diffusion coefficient, which quantifies movement of water molecule across cell membrane. Seven patients with fulminant hepatic failure underwent conventional and diffusion-weighted magnetic resonance imaging. Apparent diffusion coefficient was measured in four cortical areas and 12 deep white and gray matter regions in both cerebral hemispheres. Thirteen healthy subjects served as controls. The apparent diffusion coefficient values in patients and controls were compared using Wilcoxon signed rank test. Two patients who survived underwent repeat imaging using same protocol. Patients with FHF had significantly lower apparent diffusion coefficient in all cortical and deep white and gray matter regions of interest compared to controls (p < 0.001), suggesting cytotoxic cell swelling. In two survivors with repeat imaging, one showed complete resolution while the changes persisted in the other, suggesting ischemic injury. Cerebral edema in fulminant hepatic failure is predominantly due to cytotoxic edema.

Adolescent↗
PubMed2007

Serial diffusion-weighted MRI in hemorrhagic shock and encephalopathy syndrome.

This report presents a case of hemorrhagic shock and encephalopathy syndrome. In the acute stage, brain magnetic resonance imaging demonstrated symmetrical hyperintensity on diffusion-weighted images and hypointensity on the apparent diffusion coefficient maps in the subcortical white matter. Whereas the abnormal diffusion-weighted imaging signals of the white matter resolved in the subacute stage, the adjacent gray matter became hyperintense on diffusion-weighted images and hypointense on apparent diffusion coefficient maps. The evolution of diffusion-weighted imaging signals is thus considered to be one of the early findings in hemorrhagic shock and encephalopathy syndrome.

Brain↗
PubMed2006

Natural history of Canavan disease revealed by proton magnetic resonance spectroscopy (1H-MRS) and diffusion-weighted MRI.

Canavan disease is a childhood leukodystrophy caused by mutations in the gene for human aspartoacylase ( ASPA), which leads to an abnormal accumulation of the substrate molecule N-acetyl-aspartate (NAA) in the brain. This study was designed to model the natural history of Canavan disease using MRI and proton magnetic resonance spectroscopy ( (1)H-MRS). NAA and various indices of brain structure (morphology, quantitative T1, fractional anisotropy, apparent diffusion coefficient) were measured in white and gray matter regions during the progression of Canavan disease. A mixed-effects statistical model was used to fit all outcome measures. Longitudinal data from 28 Canavan patients were directly compared in each brain region with reference data obtained from normal, age-matched pediatric subjects. The resultant model can be used to non-invasively monitor the natural history of Canavan disease or related leukodystrophies in future studies involving drug, gene therapy, or stem cell treatments.

Age Factors↗
PubMed2006

Single breath-hold diffusion-weighted MRI of the liver with parallel imaging: initial experience.

AIM: To evaluate prospectively the improvement in the signal:noise ratio (SNR), with the use of parallel technique in single breath-hold diffusion-weighted imaging (DWI) of the liver and its affect on apparent diffusion coefficient (ADC) measurements. MATERIALS AND METHODS: This study was approved by our institutional review board. Written informed consent was obtained from all participants. Fifteen patients underwent single breath-hold DWI of the liver with and without parallel imaging technique. SNR and ADC values were measured over a lesion-free right hepatic lobe by two radiologists in both series. When a focal hepatic lesion was present the contrast:noise ratio (CNR) and ADC were also measured. Paired Student's t-tests were used for statistical analysis. RESULTS: Mean SNR values of the liver were 20.82+/-7.54 and 15.83+/-5.95 for DWI with and without parallel imaging, respectively. SNR values measured in DWI using parallel imaging were found to be significantly higher (p<0.01). Mean ADC of the liver were 1.61+/-0.45 x 10(-3)mm(2)/s and 1.56+/-0.28 x 10(-3)mm(2)/s for DWI with and without parallel imaging, respectively. No significant difference was found between the two sequences for hepatic ADC measurement (p>0.05). Overall lesion CNR was found to be higher in DWI with parallel imaging. CONCLUSION: Parallel imaging is useful in improving SNR of single breath-hold DWI of the liver without compromising ADC measurements.

Adult↗
PubMed2004

A comparative evaluation of a RARE-based single-shot pulse sequence for diffusion-weighted MRI of musculoskeletal soft-tissue tumors.

The purpose of this study was to evaluate the feasibility of a centric-reordered modified rapid acquisition with relaxation enhancement (mRARE) sequence for single-shot diffusion-weighted magnetic resonance imaging (DWI) of soft-tissue tumors in the musculoskeletal system. In the evaluation of this sequence, DWI was performed in a liquid phantom, in excised human tumor samples embedded in bovine muscle, and in nine patients suffering from different types of soft-tissue tumors. The measurements were compared to DWI using a spin-echo sequence and a single-shot echo planar imaging (EPI) sequence. The phantom measurements in water and dimethyl sulfoxide showed a difference of less than 5% when comparing the apparent diffusion coefficients (ADCs) determined by the mRARE sequence and the two other techniques. Comparing mRARE and EPI, the differences in the ADCs were about 10% in the excised tumor tissue and, typically, about 15% in vivo. ADCs between 0.8 x 10(-3) mm2/s and 1.4 x 10(-3) mm2/s, depending on the tumor type, were found in solid tumor tissue; in cystic tumor areas, ADCs greater than 2.0 x 10(-3) mm2/s were determined with the mRARE and the EPI sequences. Diffusion-weighted images of the mRARE sequence were less distorted than those acquired with the single-shot EPI sequence, and provided more anatomic information, since the muscle and fat signals were considerably higher.

Aged↗
PubMed2000

Concurrent MRI and diffuse optical tomography of breast after indocyanine green enhancement.

We present quantitative optical images of human breast in vivo. The images were obtained by using near-infrared diffuse optical tomography (DOT) after the administration of indocyanine green (ICG) for contrast enhancement. The optical examination was performed concurrently with a magnetic resonance imaging (MRI) exam on patients scheduled for excisional biopsy or surgery so that accurate image coregistration and histopathological information of the suspicious lesions was available. The ICG-enhanced optical images coregistered accurately with Gadolinium-enhanced magnetic resonance images validating the ability of DOT to image breast tissue. In contrast to simple transillumination, we found that DOT provides for localization and quantification of exogenous tissue chromophore concentrations. Additionally our use of ICG, an albumin bound absorbing dye in plasma, demonstrates the potential to differentiate disease based on the quantified enhancement of suspicious lesions.

Aged↗
PubMed1997

MRI diffusion-weighted spectroscopy of reversible and irreversible ischemic injury following closed head injury.

The objective of this study was to detect the threshold between reversible and irreversible secondary insult of hypoxia and hypotension following closed head injury as measured by MRI. Adult Sprague rats were separated into 3 groups: I: Sham (n = 6), II: Trauma and hypoxia coupled with mild hypotension of 40-50 mmHg (n = 6), III: Trauma and hypoxia coupled with severe hypotension of 30-40 mmHg (n = 6). The measurement of brain water content (BWC) was based on T1, whereas the differentiation between reversible and irreversible secondary insult on the measurement apparent diffusion coefficient (ADC). The ADCs in both trauma and secondary insult groups decreased rapidly from a control level of 0.68 +/- 0.5 x 10(-3) to significantly different minimum levels of 0.52 +/- 0.5 x 10(-3) in Group II and 0.42 +/- 0.5 x 10(-3) mm2/second in Group III at 30 minutes. In Group II rats there was a complete recovery in ADC as well as in their clinical conditions, whereas ADC in Group III rats remained at the minimum level and the animals were brain dead. The BWC was also significantly different at four hours post injury (Group II: 80.3 +/- 0.7%, Group III: 81.8 +/- 0.8%). The data lead the authors to suggest that the threshold between reversible and irreversible posttraumatic secondary insult is very narrow, and the measurement of ADC can provide information that will enable the clinician to identify critical threshold beyond which recovery is not possible.

Animals↗