Magnetic resonance diffusion tensor imaging for characterizing diffuse and focal white matter abnormalities in multiple sclerosis.

High-resolution diffusion tensor imaging (DTI) was performed in 14 patients with clinically definite multiple sclerosis (MS) and the trace of the diffusion tensor () and the fractional anisotropy (FA) were determined in normal appearing white matter (NAWM) and in different types of focal MS lesions. A small but significant increase of the in NAWM compared to control white matter ((840 +/- 85) x 10(-6) mm(2)/sec vs. (812 +/- 59) x 10(-6) mm(2)/sec; P < 0.01) was found. In addition, there was a significant decrease in the FA of normal-appearing regions containing well-defined white matter tracts, such as the genu of the internal capsule. In non-acute lesions, the of T(1)-hypointense areas was significantly higher than that of T(1)-isointense lesions ((1198 +/- 248) x 10(-6) mm(2)/sec vs. (1006 +/- 142) x 10(-6) mm(2)/sec; P < 0. 001), and there was a corresponding inverse relation of FA. Diffusion characteristics of active lesions with different enhancement patterns were also significantly different. DTI with a phase navigated interleaved echo planar imaging technique may be used to detect abnormalities of isotropic and anisotropic diffusion in the NAWM and selected fiber tracts of patients with MS throughout the entire brain, and it demonstrates substantial differences between various types of focal lesions.     

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.     

Demyelinating plaques in relapsing-remitting and secondary-progressive multiple sclerosis: assessment with diffusion MR imaging

BACKGROUND AND PURPOSE: Conventional MR imaging does not provide specific information that can be reliably associated with the pathologic substrate and clinical status of patients with multiple sclerosis (MS). Our goals were 1) to determine whether the orientationally averaged water diffusion coefficient () can be used to distinguish between plaques of different severity in these patients and 2) to assess possible correlations between values and disease duration, Expanded Disability Status Scale (EDSS) score, and signal intensity on T1-weighted MR images. METHODS: Twenty patients (10 with relapsing-remitting MS and 10 with secondary-progressive MS) and 11 healthy volunteers underwent a combined conventional and diffusion-weighted MR study of the brain. , a parameter that is proportional to the trace of the diffusion tensor, was computed by averaging the apparent diffusion coefficients measured in the x, y, and z directions. measurements were obtained for selected areas of white matter plaques. Differences in among the three groups were tested using analysis of variance. RESULTS: was significantly higher (1.445 +/- 0.129 x 10(-3) mm2/s) in secondary-progressive lesions than in relapsing-remitting lesions (0.951 +/- 0.08), and both values were higher than in normal white matter (0.732 +/- 0.02). There was a significant negative correlation between and the degree of hypointensity on T1-weighted images, and a positive correlation between and both EDSS score and disease duration. CONCLUSION: Our findings suggest that is useful for distinguishing MS lesions of different severities, which are associated with different degrees of clinical disability.     

Single breath-hold diffusion-weighted imaging of the abdomen

PURPOSE: To generate high quality diffusion-weighted images (DWI) and corresponding isotropic ADC maps of the abdomen with full organ (kidneys) coverage in a single breath-hold. MATERIALS AND METHODS: DWI was performed in 12 healthy subjects with an asymmetric, spin-echo, single-shot EPI readout on a system with high performance gradients (40 mT/minute). The isotropic diffusion coefficient was measured from maps and SNR was determined for both diffusion-weighted and reference images in the liver, spleen, pancreas, and kidneys. In six patients, single-axis diffusion encoding along three orthogonal axes (12 NEX) was employed to assess anisotropic diffusion in kidneys. RESULTS: This technique yielded images of quality and resolution which compares favorably to that of prior work. SNR ranged from 27.0 in liver to 44.1 in kidneys for the diffusion-weighted images, and from 19.6 in liver to 39.0 in kidneys in reference images. ADCs obtained in the renal medulla, renal cortex, liver, spleen, and pancreas were (2091 +/- 55) x 10(-6), (2580 +/- 53) x 10(-6), (1697 +/- 52) x 10(-6), (1047 +/- 82) x 10(-6), and (2605 +/- 168) x 10(-6) mm(2)/second, respectively (mean +/- SE). Apparent diffusion coefficient (ADC) in the renal medulla and cortex were significantly different by paired t-test (P = 4.22 x 10(-10)). Renal medulla and cortex yielded anisotropy indices (AI) of 0.129 and 0.067, respectively. CONCLUSIONS: 1) Single-shot SE EPI DWI in the abdomen with this technique provides high quality images and maps with full organ coverage in a single breath-hold; 2) ADCs obtained in the renal medulla and cortex are significantly different; and 3) diffusion within the renal medulla is moderately anisotropic.     

Effects of dexamethasone on cerebral perfusion and water diffusion in patients with high-grade glioma

BACKGROUND AND PURPOSE: The mechanisms by which the glucocorticoid dexamethasone produces its therapeutic action in patients with intracranial tumors still remain unclear. The purpose of this study was to investigate whether dexamethasone affects cerebral perfusion and water molecule diffusion by using quantitative dynamic susceptibility contrast perfusion MR imaging (DSC-MR imaging) and diffusion tensor MR imaging (DT-MR imaging). METHODS: Ten consecutive patients with glioblastoma multiforme underwent DSC-MR imaging and DT-MR imaging before and 48-72 hours after dexamethasone treatment (16 mg/day). Cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), and water mean diffusivity () were measured for enhancing tumor, nonenhancing peritumoral edematous brain, and normal-appearing contralateral white matter before and after steroid therapy. The percentage change in CBF, CBV, MTT, and for the 3 tissue types was calculated for each patient, a mean value obtained for the population, and the statistical significance determined by using a paired-samples Student t test. RESULTS: After dexamethasone treatment, there was no significant change in tumor CBF, CBV, or MTT. Edematous brain CBV and MTT were also unchanged. There was, however, an increase in edematous brain CBF (11.6%; P = .05). was reduced in both enhancing tumor (-5.8%; P = .001) and edematous brain (-6.0%; P < .001). There was no significant change in CBF, CBV, MTT, or for normal-appearing contralateral white matter after treatment. CONCLUSION: These data suggest that dexamethasone does not significantly affect tumor blood flow but may, by reducing peritumoral water content and local tissue pressure, subtly increase perfusion in the edematous brain.     

Diffusion MRI findings in Wilson's disease.

Six patients having Wilson's disease were studied with diffusion MRI in order to characterize cerebral lesions. Diffusion MRI was obtained using the spin-echo, echo-planar sequence with a gradient strength of 30 mT/m. The trace protocol was used in the axial imaging plane. Heavily diffusion-weighted (b=1000s/mm(2)) images, and the ADC (apparent diffusion coefficient) values from automatically generated ADC maps were studied. The ADC values of the normal brain parenchyma were available in 17 age-matched cases for comparison (ADC values, 0.85+/-0.11 x 10(-3)mm(2)/s). In Wilson's disease two distinct diffusion MRI patterns were observed by quantitative evaluations of the ADC maps; cytotoxic edema-like (ADC values, 0.52+/-0.03 x 10(-3)mm(2)/s), and vasogenic edema-like (ADC values, 1.42+/-0.17 x 10(-3)mm(2)/s) patterns. Diffusion imaging appears to be a promising sequence to evaluate the changes in the brain tissue in Wilson's disease at least by revealing two different patterns.     

The role of diffusion-weighted imaging and the apparent diffusion coefficient (ADC) values for breast tumors.

OBJECTIVE: We wanted to evaluate the role of diffusion-weighted imaging (DWI) and the apparent diffusion coefficient (ADC) for detecting breast tumors, as compared with the T1- and T2-weighted images. MATERIALS AND METHODS: Forty-one female patients underwent breast MRI, and this included the T1-, T2-, DWI and dynamic contrast-enhanced images. Sixty-five enhancing lesions were detected on the dynamic contrast-enhanced images and we used this as a reference image for detecting tumor. Fifty-six breast lesions were detected on DWI and the histological diagnoses were as follows: 43 invasive ductal carcinomas, one mucinous carcinoma, one mixed infiltrative and mucinous carcinoma, seven ductal carcinomas in situ (DCIS), and four benign tumors. First, we compared the detectability of breast lesions on DWI with that of the T1- and T2-weighted images. We then compared the ADCs of the malignant and benign breast lesions to the ADCs of the normal fibroglandular tissue. RESULTS: Fifty-six lesions were detected via DWI (detectability of 86.2%). The detectabilities of breast lesions on the T1- and T2-weighted imaging were 61.5% (40/65) and 75.4% (49/65), respectively. The mean ADCs of the invasive ductal carcinoma (0.89+/-0.18 x 10(-3)mm(2)/second) and DCIS (1.17+/-0.18 x 10(-3)mm(2)/ second) are significantly lower than those of the benign lesions (1.41+/-0.56 x 10(-3)mm(2)/second) and the normal fibroglandular tissue (1.51+/-0.29 x 10(-3)mm(2)/ second). CONCLUSION: DWI has a high sensitivity for detecting breast tumors, and especially for detecting malignant breast tumors. DWI was an effective imaging technique for detecting breast lesions, as compared to using the T1- and T2-weighted images.     

Evaluation of diffusion-weighted imaging for the differential diagnosis of poorly contrast-enhanced and T2-prolonged bone masses: Initial experience

PURPOSE: To determine whether quantitative diffusion-weighted imaging (DWI) is useful for characterizing poorly contrast-enhanced and T2-prolonged bone masses. MATERIALS AND METHODS: We studied 20 bone masses that showed high signal intensity on T2-weighted images and poor enhancement on contrast-enhanced T1-weighted images. These included eight solitary bone cysts, five fibrous dysplasias, and seven chondrosarcomas. To analyze diffusion changes we calculated the apparent diffusion coefficient (ADC) for each lesion. RESULTS: The ADC values of the two types of benign lesions and chondrosarcomas were not significantly different. However, the mean ADC value of solitary bone cysts (mean +/-SD, 2.57 +/- 0.13 x 10(-3) mm(2)/second) was significantly higher than that of fibrous dysplasias and chondrosarcomas (2.0 +/- 0.21 x 10(-3) mm(2)/second and 2.29 +/- 0.14 x 10(-3) mm(2)/second, respectively, P < 0.05). None of the lesions with ADC values lower than 2.0 x 10(-3) mm(2)/second were chondrosarcomas. CONCLUSION: Although there was some overlapping in the ADC values of chondrosarcomas, solitary bone cyst, and fibrous dysplasia, quantitative DWI may aid in the differential diagnosis of poorly contrast-enhanced and T2-prolonged bone masses.     

Apparent diffusion coefficient: a quantitative parameter for in vivo tumor characterization

PURPOSE: The purpose of the this study was to evaluate the potential of diffusion weighted imaging (DWI) to distinguish different tissue compartments in early, intermediate and advanced tumor stages. MATERIALS AND METHODS: Twenty-two male mice were induced with squamous cell tumor (SCCVII) and scanned with a clinical 1.5 T scanner. T1-SE, T2-FSE, diffusion weighted Line-Scan-MRI and contrast enhanced T1-SE were obtained from mice with early (tumor volume 10-100 mm(3)), intermediate (200-600 mm(3)), advanced tumors (600-1000 mm(3)) and tumor necrosis (>1500 mm(3)). The apparent diffusion coefficient (ADC) of different tumor compartments was calculated offline with a pixel-by-pixel method. The animals were sacrificed immediately after scanning and histopathologic correlation was performed. RESULTS: In early stages of tumor development, tumors appeared homogeneous on diffusion weighted images with an ADC of 0.64+/-0.06 x 10(-3) mm(2)/s. With tumor progression the ADC in the rim areas of tumor increased significantly (intermediate stage: 0.70+/-0.11 x 10(-3) mm(2)/s; advanced stage: 0.88+/-0.11 x 10(-3) mm(2)/s; tumor necrosis 1.03+/-0.06 x 10(-3) mm(2)/s), whereas the ADC in viable tumor remained constant. Histologically the areas with an increased ADC correlated well with areas of necrosis (reduced cell density). CONCLUSION: The ADC is a non-invasive technique to monitor changes in the biological structure of tumor tissue during tumor progression. Thus, DWI is a potential diagnostic tool for in-vivo tissue characterization.     

Diffusion tensor imaging in cases of adrenoleukodystrophy: preliminary experience as a marker for early demyelination?

BACKGROUND AND PURPOSE: Diffusion tensor imaging measures the proton diffusivity and preferential orientation of the diffusion tensor. X-linked adrenoleukodystrophy is a demyelinating disease for which therapy depends on the onset and extension of demyelination. We investigated the ability of diffusion tensor imaging to detect changes in the demyelinated lesions and in the normal appearing white matter. METHODS: Diffusion tensor imaging of three related boys with X-linked adrenoleukodystrophy and seven age-matched control participants was performed. Isotropic diffusion (D') and fractional anisotropy (FA) values were determined in 18 regions of interest in the white matter of both hemispheres. RESULTS: In all the demyelinated white matter areas, a pattern with increased D' and loss of FA was found. For example, mean D' was 1.772 x 10(-3)mm(2)/s in patient 2 with blindness and extensive demyelination of the occipital white matter and was 0.693 x 10(-3)mm(2)/s in control participants (P =.01). In the same region, mean FA was 0.103 (0.464 in control participants, P <.0001). Significant alterations of D' and FA were also observed in normal appearing white matter. For example, mean D' was 0.802 x 10(-3)mm(2)/s in the parietal white matter of patient 1 with no visible alterations on T2-weighted images (0.715 x 10(-3) mm(2)/s in control patients, P =.03), whereas mean FA was 0.320 (0.400 in control participants, P =.003). CONCLUSION: Elevated D' and loss of FA revealed by diffusion tensor imaging are consistent with severe demyelination in patients with X-linked adrenoleukodystrophy. Significant alterations of D' and FA in normal appearing white matter may indicate early demyelination in areas that are not yet visibly altered on conventional MR images. Further evaluation in a larger series of patients and long-term study are needed.     

Tuberous sclerosis: diffusion MRI findings in the brain

Diffusion MRI has mainly been used for detection of acute ischemia, and for distinction of cytotoxic and vasogenic edema. We applied diffusion MRI in patients with tuberous sclerosis in order to evaluate diffusion imaging characteristics of parenchymal changes. Five children with known tuberous sclerosis were included in this study. The MRI examinations were performed on a 1.5-T MR unit. Diffusion MRI was obtained using the echo-planar imaging sequence. Apparent diffusion coefficient (ADC) values from the abnormal brain parenchyma were calculated directly from automatically generated ADC maps. Seven normal children were available for comparison. In this control group the mean ADC value of the normal white matter was 0.84 +/- 0.12 x 10(-3) mm(2)/s. In tuberous sclerosis patients the mean ADC value of the white matter hamartomas ( n=20) was apparently high (1.52 +/- 0.24 x 10(-3) mm(2)/s) compared with that of normal white matter. The ADC value of calcified hamartomas was "zero". The ADC value within a giant cell tumor was 0.89 x 10(-3) mm(2)/s, similar to that of normal cerebral white matter. The ADC maps were superior to b=1000 s/mm(2) (true diffusion) images with respect to lesion evaluation, and they provided mathematical information on tissue integrity. With respect to detection of the exact numbers and sizes of the parenchymal hamartomas fluid-attenuated inversion recovery images were superior to ADC maps. It is believed that diffusion MRI can be useful in evaluation of various parenchymal changes associated with tuberous sclerosis. Further studies on tuberous sclerosis, and on various brain lesions, would provide increasing data on this relatively new MRI sequence.     

Line scan diffusion imaging of the spine

BACKGROUND AND PURPOSE: Recent findings suggest that diffusion-weighted imaging might be an important adjunct to the diagnostic workup of disease processes in the spine, but physiological motion and the challenging magnetic environment make it difficult to perform reliable quantitative diffusion measurements. Multi-section line scan diffusion imaging of the spine was implemented and evaluated to provide quantitative diffusion measurements of vertebral bodies and intervertebral disks. METHODS: Line scan diffusion imaging of 12 healthy study participants and three patients with benign vertebral compression fractures was performed to assess the potential of line scan diffusion imaging of the spinal column. In a subgroup of six participants, multiple b-value (5-3005 s/mm(2)) images were obtained to test for multi-exponential signal decay. RESULTS: All images were diagnostic and of high quality. Mean diffusion values were (230 +/- 83) x 10(-6) mm(2)/s in the vertebral bodies, (1645 +/- 213) x 10(-6) mm(2)/s in the nuclei pulposi, (837 +/- 318) x 10(-6) mm(2)/s in the annuli fibrosi and ranged from 1019 x 10(-6) mm(2)/s to 1972 x 10(-6) mm(2)/s in benign compression fractures. The mean relative intra-participant variation of mean diffusivity among different vertebral segments (T10-L5) was 2.97%, whereas the relative difference in mean diffusivity among participants was 7.41% (P <.0001). The estimated measurement precision was <2%. A bi-exponential diffusion attenuation was found only in vertebral bodies. CONCLUSION: Line scan diffusion imaging is a robust and reliable method for imaging the spinal column. It does not suffer as strongly from susceptibility artifacts as does echo-planar imaging and is less susceptible to patient motion than are other multi-shot techniques. The different contributions from the water and fat fractions need to be considered in diffusion-weighted imaging of the vertebral bodies.     

Apparent diffusion coefficient in pancreatic cancer: characterization and histopathological correlations

PURPOSE: To clarify the components primarily responsible for diffusion abnormalities in pancreatic cancerous tissue. MATERIALS AND METHODS: Subjects comprised 10 patients with surgically confirmed pancreatic cancer. Diffusion-weighted (DW) echo-planar imaging (b value = 0, 500 s/mm(2)) was employed to calculate the apparent diffusion coefficient (ADC). ADC values of cancer and noncancerous tissue were calculated. Furthermore, ADC values of the cancer were compared with histopathological results. RESULTS: The mean (+/-standard deviation) ADC value was significantly lower for tumor (1.27 +/- 0.52 x 10(-3) mm(2)/s) than for noncancerous tissue (1.90 +/- 0.41 x 10(-3) mm(2)/s, P < 0.05). Histopathological examination showed similar proportions of fibrotic area, cellular component, necrosis, and mucin in each case. Regarding the density of fibrosis in cancer, three cases were classified in the loose fibrosis group and the remaining seven cases were classified in the dense fibrosis group. The mean ADC value was significantly higher in the loose fibrosis group (1.88 +/- 0.39 x 10(-3) mm(2)/s) than in the dense fibrosis group (1.01 +/- 0.29 x 10(-3) mm(2)/s, P < 0.05). In quantitative analysis, ADC correlated well with the proportion of collagenous fibers (r = -0.87, P < 0.05). CONCLUSION: Collagenous fibers may be responsible for diffusion abnormalities in pancreatic cancer.     

Diffusion magnetic resonance imaging of solid vestibular schwannomas

Six patients with solid vestibular schwannomas were studied by diffusion magnetic resonance imaging to assess if this modality adds new information for these tumors, because there is no previous report in the relevant literature. The sizes of the tumors ranged from 2.2 to 4.7 cm with respect to their largest diameters. They were isointense to the normal brain parenchyma on b = 1,000 s/mm2 images. The apparent diffusion coefficient (ADC) values in the tumors were high (range: 1.14-1.72 x 10(-3) mm2/s, mean = 1.42 +/- 0.17 x 10(-3) mm2/s) compared with normal brain parenchyma ADC values (mean = 0.80 +/- 0.11 x 10(-3) mm2/s). High ADC values of solid vestibular schwannomas were in conformity with increased diffusion rates, indicating the presence of increased amounts of extracellular water (a relatively loose tissue) in the tumor matrix.     

Water diffusion compartmentation at high b values in ischemic human brain

BACKGROUND AND PURPOSE: We studied the evolution of brain water compartments during the early stage of ischemic stroke. METHODS: Diffusion-weighted imaging was performed at 1.5 T in 10 volunteers and 14 patients with stroke. We used a single-shot echo-planar technique with 11 b values of 0-5000 s/mm(2). Regions of interest were selected in the white matter (WM) and striatum of the volunteers and in the ischemic core of the patients. Measurements were fitted on the basis of a biexponential decay with the b factor as follows: S(b) = S(0)[(f(slow) x exp(-b x ADC(slow)) + (f(fast) x exp(-b x ADC(fast))] where S(b) is the signal intensity in the presence of a diffusion gradient, S(0) is the signal intensity without diffusion sensitization, ADC(slow) and ADC(fast) are the respective apparent diffusion coefficients (ADCs) of slow diffusing compartments (SDCs) and fast diffusing compartments (FDCs), and f(slow) and f(fast) the respective contributions to the signal intensity of SDC and FDC. RESULTS: In healthy subjects, FDC represents 74.3 +/- 3.1% of brain water, with ADC(fast) = (124.6 +/- 12.0) x 10(-5) mm(2)/s and ADC(slow) = (15.5 +/- 3.9) x 10(-5) mm(2)/s. In stroke, decreased FDC (49.1% +/- 10.9%; P = 1.05 x10(-5)) and increased ADC(slow) ([22.4 +/- 8.1] x 10(-5) mm(2)/s; P = 8.07 x 10(-3)) were observed, but ADC(fast) was not significantly changed ([135.6 +/- 25.7] x 10 (-5) mm(2)/s; P =.151). CONCLUSION: The restricted diffusion observed in the early stroke is mainly related to a redistribution of water from the FDC to the SDC.     

Diffusion MRI: apparent diffusion coefficient (ADC) values in the normal brain and a classification of brain disorders based on ADC values.

Diffusion-weighted imaging, dependent on motion of water molecules, provides information regarding tissue integrity. Apparent diffusion coefficient (ADC) values in the normal brain parenchyma, and those in a variety of lesions were studied by echo-planar diffusion MRI in 310 cases. Brain disorders were classified based on their ADC values, taking the ADC values of the normal brain white matter as the principal category. In the normal white matter ADC ranges were 0.60-1.05x10(-3)mm(2)/s, and the mean ADC value was 0.84+/-0.11x10(-3)mm(2)/s. It was possible to distribute brain disorders, as well as artefacts on diffusion MRI to five major categories: category 1, ADC similar to normal white matter; category 2, ADC lower than normal white matter; category 3, ADC higher than normal white matter; category 4, ADC similar to CSF; and category 5, markedly low or high ADC. Further studies can provide addition of different lesions as well as refinements of these categories.     

Diffusion-weighted magnetic resonance imaging in radiation-induced cerebral necrosis. Apparent diffusion coefficient in lesion components

OBJECTIVE: The objective of this retrospective study was to investigate the diffusivity of different components of radiation-induced cerebral necrosis with the hypothesis that the diffusivity of the various components is elevated to different degrees. METHODS: Twenty-two patients (18 men, 4 women, aged 34-72 years) with radiation injury to the temporal lobes after radiation therapy (RT) for nasopharyngeal carcinoma with diagnosis confirmed on serial magnetic resonance imaging (MRI) were studied with coronal T2-weighted, diffusion-weighted, and gadolinium-enhanced MRI. Using three diffusion directions for diffusion-weighted MRI, the apparent diffusion coefficients (ADCs) of the enhanced component, the cystic or liquefied component, and the edema component were measured. RESULTS: ADCs of all components of RT-induced cerebral necrosis (154 +/- 21.6 x 10(-5) mm2/s for contrast-enhanced component; 188 +/- 47.4 x 10(-5) mm2/s for cystic/liquefied component; 177 +/- 35.4 x 10(-5) mm2/s for edema component) were all significantly higher (P<0.00001) than ADC of the normal frontal lobe white matter (82 +/- 12.4 x 10(-5) mm2/s). The ADC of the enhanced component was significantly lower than that of the cystic/liquefied component (P=0.0096) and the edema component (P=0.003). A significantly lower ADC was shown in the enhanced component in temporal lobes showing both short-term morphologic deterioration (P=0.024) and occurrence of deterioration on long-term follow-up (P=0.04) compared with the temporal lobes that showed improvement or stable morphology. CONCLUSIONS: ADCs of the contrast-enhanced component, cystic/liquefied component, and edema in RT-induced cerebral necrosis was significantly higher than in normal brain parenchyma. There is association between a lower ADC in the contrast-enhanced component and morphologic deterioration.     

Biological correlates of diffusivity in brain abscess.

Restricted diffusion in brain abscess is assumed to be due to a combination of inflammatory cells, necrotic debris, viscosity, and macromolecules present in the pus. We performed diffusion-weighted imaging (DWI) on 41 patients with proven brain abscesses (36 pyogenic and five tuberculous), and correlated the apparent diffusion coefficient (ADC) from the abscess cavity with viable cell density, viscosity, and extracellular-protein content quantified from the pus. On the basis of the correlation between cell density and ADC in animal tumor models and human tumors in the literature, we assumed that the restricted ADC represents the cellular portion in the abscess cavity. We calculated restricted and unrestricted lesion volumes, and modeled cell density over the restricted area with viable cell density per mm(3) obtained from the pus. The mean restricted ADC in the cavity (0.65 +/- 0.01 x 10(-3) mm(2)/s) correlated inversely with restricted cell density in both the pyogenic (r = -0.90, P = <0.05) and tuberculous (0.60 +/- 0.04 x 10(-3) mm(2)/s, r = -0.94, P = <0.05) abscesses. We conclude that viable cell density is the main biological parameter responsible for restricted diffusion in brain abscess, and it is not influenced by the etiological agents responsible for its causation.     

Diffusion MRI in neurofibromatosis type 1: ADC evaluations of the optic pathways, and a comparison with normal individuals.

In a control group of 12 normal children (ages ranging from 9 months to 3 years; mean=1.6 years) the mean apparent diffusion coefficient (ADC) value of the normal white matter, obtained from automatically generated ADC maps, was 0.84 +/- 0.14 x 10(-3)mm(2)/s. A patient with neurofibromatosis type 1 with bilateral optic gliomas, and extensive optic pathway involvement was evaluated by diffusion MRI. Multiple measurements of ADC values throughout the involved optic radiations revealed a higher mean value: 1.16 +/- 0.06 x 10(-3)mm(2)/s than that of the normal white matter, suggesting relatively high molecular motion in these regions, probably representing myelin vacuolization. ADC evaluation of a thalamic hamartoma revealed a lower value (=1.06 x 10(-3)mm(2)/s) than this. The mean ADC value obtained from multiple measurements of the enlarged optic chiasm, and intraorbital portions of the nerve was similar (=0.81+/- 0.09 x 10(-3)mm(2)/s) to that of the normal cerebral white matter of the control cases. It appears that diffusion imaging can be useful in evaluation of optic pathway involvement in NF1, and might contribute to differentiating optic gliomas from hamartomas, and myelin vacuolization, however, further studies will be required for assessing the role of diffusion imaging in such lesions.     

Diffusion-weighted MR imaging in normal human brains in various age groups

BACKGROUND AND PURPOSE: Few studies have concerned the absolute apparent diffusion coefficient (ADC) values in the normal human brain and the effect of aging on diffusion. Therefore, our purpose was to determine whether the average ADC (ADC(av)) values in the various regions of the brain differ with age, sex, or hemisphere and to establish reference values of the absolute ADC(av) for further studies. METHODS: Subjects (40 men and 40 women) were chosen from a healthy population; age groups were 20-34, 35-49, and 50-64 years and 65 years or older (n = 20 each). All subjects were examined with MR imaging, including conventional and diffusion-weighted imaging in three orthogonal directions with two b values (0 and 1000 s/mm(2)) at 1.5 T. Bilateral ADC(av) values were determined in 36 regions of interest encompassing the entire brain. RESULTS: ADC(av) values were highest in the cortical gray matter ([0.89 +/- 0.04] x 10(-3) mm(2)/s; range, 0.78-1.09 x 10(-3)), lower in the deep gray matter ([0.75 +/- 0.03] x 10(-3) mm(2)/s; range, 0.64-0.83 x 10(-3)), and lowest in the white matter ([0.70 +/- 0.03] x 10(-3) mm(2)/s; range, 0.62-0.79 x 10(-3)). The ADC(av) values did not significantly change with aging, except for an increase in the lateral ventricles. No difference was observed between women and men or between the hemispheres. CONCLUSION: The data reported herein are representative, and the ADC(av) values can be used for reference in future studies and in clinical settings.