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PubMed1997

Evolution of anisotropic diffusion in the developing rat corpus callosum.

Diffusion anisotropy was investigated in the developing rat brain [postnatal day (P)6-29] with the use of ion-selective microelectrodes to measure the three-dimensional distribution of tetramethylammonium (TMA+) iontophoresed into the extracellular space (ECS). The diffusion parameters, ECS volume fraction alpha (alpha = ECS volume/total tissue volume), tortuosity lambda (lambda2 = apparent diffusion coefficient/free diffusion coefficient), and nonspecific TMA+ uptake (k'), were studied in cortical gray matter (layer V) and corpus callosum (CC) of anesthetized rats. ECS volume fraction in cortex and CC was about twice as large in the newborn rat as in adults. In this study, more detailed analysis revealed that alpha in CC gradually decreased from P4, when alpha ranged between 0.42 and 0.45, and reached a final value of 0.26 +/- 0.01 (SE, n = 12 measurements, 6 animals) at about P21. Diffusion in the ECS of CC was isotropic until about P12, i.e., there was no significant difference in the tortuosity factor, lambda, between the three perpendicular axes. From P13 to P17 anisotropy greatly increased as a result of preferential diffusion along the myelinated axons (X-axis). At P21-23 the tortuosity values were lambda(x) = 1.46 +/- 0.03, lambda(y) = 1.70 +/- 0.01, and lambda(z) = 1.72 +/- 0.02 (n = 12), and there were no further changes up to the last postnatal day studied, P29. In contrast to the myelinated CC, cortical gray matter remained isotropic up to P29, with a tortuosity of 1.54 +/- 0.02 (n = 12). The results suggest that diffusion anisotropy in the rat CC is related to myelination; it reaches a maximum at P17, when myelination is well advanced. In myelinated pathways, preferential diffusion of ions and transmitters occurs along the axons. These results are relevant to volume transmission and the interpretation of diffusion-weighted magnetic resonance imaging.

Animals↗

PubMed2002

Water diffusion in the rabbit lens in vivo.

PURPOSE: To examine water diffusion in the crystalline lens and sugar cataracts in the rabbits in vivo. MATERIALS AND METHODS: Water self-diffusion in the lens cortices of alloxan-diabetic and galactosemic rabbits was examined with magnetic resonance imaging (MRI). The animals were positioned in a 4.7-tesla animal system in conjunction with a 1-inch surface coil for the eye. Diffusion-weighted MRI was conducted using a pulsed-gradient spin-echo sequence with a gradient strength of 0-6 Gs/cm in the primary and secondary coordinates. Other MRI parameters included TR (repetition time)/TE (echo time) = 2,000/10 ms, a field of view of 4 cm, and a 256 x 128 matrix. RESULTS: There appeared an increase in water relaxation resulting in an increase of % (equatorial cortex depth)/(lens long axis) from 18 in the lenses of normal rabbits to 30.4 and 39.9 in the lenses of galactosemic and diabetic rabbits, respectively. In addition, water diffusion changed in the lens of the diabetic rabbit with an increasing intracellular fluidity along the long axis of the cortical fibers, for example, the diffusion coefficient changed from a normal of 0.48 to 0.96 x 10(-5) cm2 s-1 in the lens of the diabetic rabbit. These results showed altered water mobility due to subcellular disturbances occurring before any apparent lens opacities. Further, there also was an increase in the water diffusivity in the aqueous humor from a normal of 1.77 to 2.67 x 10(-5) cm2 s-1 in the galactosemic rabbit eye suggesting an increase in either free water proportion or thermal convection. CONCLUSIONS: Resistance to water self-diffusion appeared to relate to lens fiber orientation and intracellular protein order. Diffusion imaging therefore can be used to examine water self-diffusion to detect early osmotic alteration of lens fibers.

Animals↗

PubMed2006

Measuring brain stem and cerebellar damage in parkinsonian syndromes using diffusion tensor MRI.

OBJECTIVE: To use diffusion tensor MRI to quantify and compare degeneration of the pons and cerebellar peduncles in multiple system atrophy (MSA), progressive supranuclear palsy (PSP), and Parkinson disease (PD) and to relate changes in diffusion measures to clinical features and localized atrophy. METHODS: We used a region-of-interest approach to measure changes in fractional anisotropy and mean diffusivity in the middle cerebellar peduncles, decussation of the superior cerebellar peduncles, and pons in 17 patients with MSA, 17 with PSP, 12 with PD, and 12 healthy volunteers. We also evaluated atrophy of the cerebellar peduncles and pons on T2-weighted magnetic resonance images in patients with MSA and PSP. RESULTS: In MSA, fractional anisotropy was markedly reduced in the middle cerebellar peduncles, and mean diffusivity increased both here and in the pons compared with other groups, whereas in PSP, mean diffusivity was strikingly increased in the decussation of superior cerebellar peduncles. Cerebellar ataxia was related to mean diffusivity in the middle cerebellar peduncles (r = 0.71, p = 0.001) and pons (r = 0.60, p = 0.01) in MSA. Diffusion measures were related to localized atrophy in both MSA and PSP. CONCLUSIONS: Diffusion tensor MRI can be used to quantify neurodegenerative processes in different brain stem and cerebellar structures in multiple system atrophy and progressive supranuclear palsy during life, and may have diagnostic value. Larger studies of early, undifferentiated parkinsonian syndromes are indicated to provide estimates of the relative diagnostic value of diffusion measures, atrophy measures, and visual assessment of scans.

Aged↗

PubMed2002

Metabolite diffusion in giant muscle fibers of the spiny lobster Panulirus argus.

The time- and orientation-dependence of metabolite diffusion in giant muscle fibers of the lobster Panulirus argus was examined using (31)P- and (1)H-pulsed-field gradient nuclear magnetic resonance. The (31)P resonance for arginine phosphate and the (1)H resonances for betaine, arginine/arginine phosphate and -CH(2)/-CH groups were suitable for measurement of the apparent diffusion coefficient, D. Diffusion was measured axially, D(//), and radially, D( perpendicular ), in fibers over diffusion times of 20 to 300 ms. Diffusion was strongly anisotropic, and D(//) was higher than D( perpendicular ) at all times. Radial diffusion decreased with time until a steady-state value was reached at a diffusion time of approximately 100 ms. Changes in D( perpendicular ) occurred over a time scale that was consistent with previous measurements from fish and mammalian muscle, indicating that diffusion is hindered by the same types of barriers in these diverse muscle types. The time dependence indicated that the sarcoplasmic reticulum is the principal intracellular structure that inhibits mobility in an orientation-dependent manner in skeletal muscle. The abdominal muscles in P. argus are used for anaerobic, burst contractions during an escape maneuver. The fact that these muscle fibers have diameters that may exceed hundreds of microns in diameter, and nearly all of the mitochondria are localized near the sarcolemmal membrane, suggests that barriers that hinder radial diffusion of ATP equivalents may ultimately limit the rate of post-contractile recovery.

Abdominal Muscles↗

PubMed2005

Glioblastoma multiforme with atypical diffusion-weighted MR findings.

The aim of this study is to review the diffusion-weighted MRI findings of glioblastomas, to investigate those with atypical characteristics and to emphasise the reasons responsible for the atypical features on diffusion-weighted MR images. 48 cases of histologically proven glioblastomas were included in this study. In addition to conventional sequences of routine tumour protocol, diffusion-weighted MRI with spin-echo echo-planar sequence was performed. The cystic-necrotic components of the lesions, according to the conventional sequences, were determined on the diffusion-weighted MR images and were classified as typical or atypical. The presence of high signal intensity was accepted as an atypical feature while low signal intensity was accepted as typical. The apparent diffusion coefficient (ADC) values of the cystic components were calculated. The statistical significance of the typical and atypical glioblastomas was evaluated with the students t-test. In six of the cases apparent high signal intensity in diffusion weighted MR images was interpreted. In three cases the high signal intensity occupied all of the cystic component and in the other three most of the cystic component. The ADC values of the lesions varied between 0.86 x 10(-3) mm(2) s(-1) and 1.39 x 10(-3) mm(2) s(-1) (mean value 1.06+/-0.17 x 10(-3) mm(2) s(-1)). In 42 of the lesions the cystic-necrotic component demonstrated low signal intensity and the ADC values varied between 1.56 x 10(-3) mm(2) s(-1) and 3.32 x 10(-3) mm(2) s(-1) (mean value 2.36+/-0.46 x 10(-3) mm(2) s(-1)). The difference between ADC values of atypical and typical lesions was statistically significant (p<0.001). The vast majority of glioblastomas do not exhibit restricted diffusion in diffusion-weighted MRI, but some of them display homogeneous or heterogeneous high signal intensity and decrease of ADC values. Diffusion-weighted MRI alone is not helpful in the differentiation of malignant tumours from abscesses with low ADC values and similar conventional MRI findings.

Adult↗

PubMed2006

Continuous photobleaching in vesicles and living cells: a measure of diffusion and compartmentation.

We present a comprehensive and analytical treatment of continuous photobleaching in a compartment, under single photon excitation. In the very short time regime (t<0.1 ms), the diffusion does not play any role. After a transition (or short time regime), one enters in the long time regime (t>0.1-5 s), for which the diffusion and the photobleaching balance each other. In this long time regime, the diffusion is either fast (i.e., the photobleaching probability of a molecule diffusing through the laser beam is low) so that the photobleaching rate is independent of the diffusion constant and dependent only of the laser power, or the diffusion is slow (i.e., the photobleaching probability is high) and the photobleaching rate is mainly dependent on the diffusion constant. We illustrate our theory by using giant unilamellar vesicles ranging from approximately 10 to 100 microm in diameter, loaded with molecules of various diffusion constants (from 20 to 300 microm2/s) and various photobleaching cross sections, illuminated under laser powers between 3 and 100 microW. We also demonstrated that information about compartmentation can be obtained by this method in living cells expressing enhanced green fluorescent proteins or that were loaded with small FITC-dextrans. Our quantitative approach shows that molecules freely diffusing in a cellular compartment do experience a continuous photobleaching. We provide a generic theoretical framework that should be taken into account when studying, under confocal microscopy, molecular interactions, permeability, etc.

Biophysics↗

PubMed2007

Anisotropy and temperature dependence of myoglobin translational diffusion in myocardium: implication for oxygen transport and cellular architecture.

Pulsed field gradient NMR methods have determined the temperature-dependent diffusion of myoglobin (Mb) in perfused rat myocardium. Mb diffuses with an averaged translational diffusion coefficient (DMb) of 4.24-8.37x10(-7)cm2/s from 22 degrees C to 40 degrees C and shows no orientation preference over a root mean-square displacement of 2.5-3.5 microm. The DMb agrees with the value predicted by rotational diffusion measurements. Based on the DMb, the equipoise diffusion PO2, the PO2 in which Mb-facilitated and free O2 diffusion contribute equally to the O2 flux, varies from 2.72 to 0.15 in myocardium and from 7.27 to 4.24 mmHg in skeletal muscle. Given the basal PO2 of approximately 10 mmHg, the Mb contribution to O2 transport appears insignificant in myocardium. In skeletal muscle, Mb-facilitated diffusion begins to contribute significantly only when the PO2 approaches the P50. In marine mammals, the high Mb concentration confers a predominant role for Mb in intracellular O2 transport under all physiological conditions. The Q10 of the DMb ranges from 1.3 to 1.6. The Mb diffusion data indicate that the postulated gel network in the cell must have a minimum percolation cutoff size exceeding 17.5 A and does not impose tortuosity within the diffusion root mean-square displacement. Moreover, the similar Q10 for the DMb of solution versus cell Mb suggests that any temperature-dependent alteration of the postulated cell matrix does not significantly affect protein mobility.

Animals↗

PubMed1996

Diffusion of water in rat sciatic nerve measured by 1H pulsed field gradient NMR: compartmentation and anisotropy.

Diffusion of water was measured in rat sciatic nerve at 22.5 +/- 0.5 degrees C using the spinecho pulsed-field gradient sequence. Three effective diffusion coefficients (ca. 1.1, 0.23, and 0.02 x 10(-9) m2/s) were obtained at a diffusion time of 10 ms in fresh nerve and they showed minimal orientation dependency. The extracellular water signal was quenched by 10 mM MnCl2, and 10% of the water signal remained. Two diffusion coefficients of water were now observed at a diffusion time of 10 ms. The faster coefficient (65% of the remaining signal) was 0.8 x 10(9) m2/s when the axis of the nerve fiber was set parallel to the gradient (D0), and was 0.3 x 10(9) m2/s when the axis of the nerve fiber was set perpendicular to the gradient (D90). The values of D90 and D0 decreased when the diffusion time was increased from 3 ms to 50 ms. A cylinder diameter of 5.4 microns was obtained on the assumption of restricted diffusion in a cylindrical geometry. This agrees with the average inner diameter of axons in the rat sciatic nerve. The slower diffusion component (0.02 x 10(-9) m2/s, 35% of the remaining signal) did not show orientation or diffusion time dependency, and may be attributed to the intracellular water of the Schwann cell body.

Animals↗

PubMed1999

MR line scan diffusion imaging of the brain in children.

BACKGROUND AND PURPOSE: MR imaging of the self-diffusion of water has become increasingly popular for the early detection of cerebral infarction in adults. The purpose of this study was to evaluate MR line scan diffusion imaging (LSDI) of the brain in children. METHODS: LSDI was performed in four volunteers and 12 patients by using an effective TR/TE of 2736/89.4 and a maximum b value of 450 to 600 s/mm2 applied in the x, y, and z directions. In the volunteers, single-shot echo planar imaging of diffusion (EPID) was also performed. The patients (10 boys and two girls) ranged in age from 2 days to 16 years (average age, 6.6 years). Diagnoses included acute cerebral infarction, seizure disorder, posttraumatic confusion syndrome, complicated migraine, residual astrocytoma, encephalitis, hypoxia without cerebral infarction, cerebral contusion, and conversion disorder. In all patients, routine spin-echo images were also acquired. Trace images and apparent diffusion coefficient maps were produced for each location scanned with LSDI. RESULTS: In the volunteers, LSDI showed less chemical-shift and magnetic-susceptibility artifact and less geometric distortion than did EPID. LSDI was of diagnostic quality in all studies. Diffusion abnormalities were present in five patients. Restricted diffusion was present in the lesions of the three patients with acute cerebral infarction. Mildly increased diffusion was present in the lesions of encephalitis and residual cerebellar astrocytoma. No diffusion abnormalities were seen in the remaining seven children. CONCLUSION: LSDI is feasible in children, provides high-quality diffusion images with less chemical-shift and magnetic-susceptibility artifact and less geometric distortion than does EPID, and complements the routine MR examination.

Acute Disease↗

PubMed1984

Diffusion of new technologies: rational and irrational.

The diffusion of medical technology, the process by which new clinical procedures and devices come into use in the health care system, is an historical topic, as old as medicine itself. Hospitals, physicians, manufacturers, third-party payers, and patients all are factors in the demand for, and adoption and diffusion of, new medical technologies. The federal government also plays a role both in furthering technology diffusion through federally financed health programs and in attempting to control diffusion by stimulating state certificate of need and other regulatory programs. The history of the CT scanner's diffusion illustrates the problems that can result from the lack of a coherent strategy to control the diffusion of major medical technologies. Some of these same problems are now appearing in the diffusion of magnetic resonance imaging (MRI) devices. In the current health care environment, prospective payment and the continuing period of remarkable technological innovation are major influences on technology diffusion and on initiatives for technology assessment. The diffusion of technology can be made more rational by instituting a formal process to identify technologies (both old and new) that require assessment, by financial support for assessment efforts, by selective reimbursement for clinical trials, and by regionalization of costly procedures.

Certificate of Need↗

PubMed2001

Computing diffusion rates in T2-dark hematomas and areas of low T2 signal.

BACKGROUND AND PURPOSE: It has been suggested that restricted diffusion is present within hematomas with intact red cell membranes; however, computing apparent diffusion coefficient (ADC) values in areas of low T2 signal can be problematic. Our purpose was to show the pitfalls of measuring diffusion within hematomas with intracellular blood products and to present a framework based on the properties of expected values for computing ADC values from regions with signal intensities close to that of the background noise (ie, T2-dark hematomas). METHODS: Twelve patients with intracranial hematomas who had undergone diffusion imaging were retrospectively identified during a 2-year period (four intracellular oxyhemoglobin, seven intracellular deoxyhemoglobin, one intracellular methemoglobin). Regions of interest were drawn on the hematomas, the contralateral white matter, and over the background. ADC values were computed using a variety of methods: 1) using expected values incorporating the variance of the background, 2) computing the mean of the regions of interest before taking the natural log, 3) masking negative values, and 4) masking the background at 0.5% increments from 0.5 to 5.5% and including the masked voxels (an intrinsically flawed method). Two-tailed Student's t test was performed between the white matter and the hematoma ADC values. RESULTS: There was no statistically significant difference between the hematomas and the white matter for methods 1 through 3 (P = .14, P = .23, and P = .83, respectively). Only method 4 revealed a statistically significant difference, beginning at 0.5% masking (P = .04) and becoming progressively more significant with increased masking (P = 4.14 x 10(-7) at 5.5% masking). The effect of masking was limited to the T2-dark hematomas. CONCLUSION: There is no restriction of diffusion for in vivo hematomas with intracellular blood products. The T2 blackout effect for T2-dark hematomas on diffusion-weighted images should not be interpreted as fast diffusion. The method of expected values can be used to obtain measurements for regions with signal intensities near the background noise. Using literature values for RBC self-diffusion, we computed lower limits of diffusion for hematomas with intracellular blood products to be 0.3 x 10(-3) mm2/s.

Cerebral Hemorrhage↗

PubMed2001

Arterial hyperintensity on fast fluid-attenuated inversion recovery images: a subtle finding for hyperacute stroke undetected by diffusion-weighted MR imaging.

BACKGROUND AND PURPOSE: Diffusion-weighted MR imaging is generally acknowledged to be more sensitive in detecting acute stroke than is conventional MR imaging. Our purpose in the present study was to evaluate the utility of fast fluid-attenuated inversion recovery (FLAIR) MR imaging compared with that of diffusion-weighted MR imaging for the diagnosis of hyperacute stroke. METHODS: We reviewed patient records and cerebral MR images from all patients in a 13-month period from whom diffusion-weighted and fast-FLAIR imaging were obtained within 6 hours after symptom onset (n = 11). Special attention was paid to the presence or absence of arterial hyperintensity on FLAIR images and abnormally high-signal regions on diffusion-weighted images in the affected vascular territories. RESULTS: Arterial hyperintensity was found in eight of 11 patients, all of whom had embolic or thrombotic infarctions with middle cerebral arterial (MCA) distribution. Arterial hyperintensity was negative in the remaining three patients; the vascular territories were the posterior circulation region in two of these patients and the MCA region in one, and the types of infarction in these same patients were lacunar in two and embolic in one. Regions with high-signal diffusion abnormalities relevant to the patients' symptoms were found in 10 of 11 patients. One patient showed no diffusion abnormalities but the presence of arterial hyperintensity in the affected MCA territory on the initial MR examination, and manifested embolic infarction along with arterial hyperintensity on the initial FLAIR image. CONCLUSION: Although diffusion-weighted MR imaging is highly sensitive to stroke, diffusion-weighted MR imaging alone may not rule out a possible infarction. Arterial hyperintensity on FLAIR images can precede diffusion abnormalities and may provide a clue to the early detection of impending infarction.

Aged↗

PubMed2001

Diffusion-weighted MR imaging after angioplasty or angioplasty plus stenting of arteries supplying the brain.

BACKGROUND AND PURPOSE: There has been concern regarding the safety of revascularization procedures of vessels supplying the brain vessels because of the risk of cerebral embolization during the procedure. We have observed a high incidence of hyperintense lesions on diffusion-weighted MR images of the brain after stenting at the carotid bifurcation. The hypothesis of this study is that diffusion-weighted MR imaging of the brain can reveal new diffusion abnormalities after angioplasty or angioplasty plus stenting of arteries supplying the brain, other than at the carotid bifurcation. Therefore, we prospectively obtained diffusion-weighted MR images of the brain before and after such revascularization procedures. METHODS: Thirty-seven revascularization procedures were performed in 32 patients. Eleven interventions were performed at the distal internal carotid artery, two at the external carotid artery, two at the common carotid artery, five at the innominate artery, five at the vertebral artery, and 12 at the proximal subclavian artery. Diffusion-weighted MR imaging of the brain was performed before and 24 hours after the procedures. RESULTS: After eight (22%) of 37 procedures, new hyperintensities were visible on the diffusion-weighted MR images. With six of these eight procedures, the hyperintensities occurred in the vascular territory supplied by the treated vessel. In total, 35 new cerebral lesions could be seen, 33 (94%) of which occurred in the vascular territory supplied by the treated vessel. None of the patients in whom new diffusion abnormalities were found had new neurologic symptoms or deficits. No new lesions could be seen after procedures at the subclavian artery. CONCLUSION: Revascularization procedures of arteries supplying the brain were associated with new lesions on the diffusion-weighted MR images of the brain after 22% of the procedures, provided that MR imaging could be performed, indicating the occurrence of cerebral microemboli during such procedures. Diffusion-weighted MR imaging of the brain can be used as a tool to assess the impact of modifications of procedural technique and/or the use of cerebral protection devices on the occurrence of such lesions.

Adult↗

PubMed2002

Diffuse large B-cell lymphoma and its variants.

According to the World Health Organization classification of neoplastic diseases of the hematopoietic and lymphoid tissues, diffuse large B-cell lymphoma comprises about 40% of adult cases of non-Hodgkin s lymphoma. It consists of the following morphological variants: 1) centroblastic (with or without multilobulated nuclei); 2) immunoblastic (>90% of immunoblasts); 3) T cell/histiocytes rich; and 4) anaplastic. Rare morphological variants plasmablastic type, mediastinal (thymic) diffuse large B-cell lymphoma, intravascular, and primary effusion B-cell lymphoma are considered distinct variants of diffuse large B-cell lymphoma due to their unique topographic presentation and clinical behavior, as well as immunophenotypic and genetic characteristics. T-cell/histiocyte-rich B-cell lymphoma is morphologically characterized by up to 25% of large neoplastic B cells and 75-90% of reactive, non-neoplastic T cells. Mediastinal (thymic) diffuse large B-cell lymphoma is considered a subtype of diffuse large B-cell lymphoma arising in the mediastinum, with distinctive morphological, immunohistochemical, genotypic, and clinical features. Mediastinal diffuse large B-cell lymphoma is an aggressive disease with poor outcome, which probably originates from thymic B cells at the terminal stage of differentiation. During the 1997-2001 period, 720 patients were diagnosed with non-Hodgkin s lymphoma in our institution. Out of 101 (14%) patients with diffuse large B-cell lymphoma, 17 had T-cell-rich B-cell lymphoma and their median survival was less than 20 months, with no difference regarding sex, bone marrow involvement, CD30 positivity, or histiocytic component of the tumor. Twenty out of 101 patients had mediastinal B-cell lymphoma and their median survival was 21 months, with sex or degree of necrosis of the involved lymph node having no impact on survival. We studied the frequency of bcl-2 gene rearrangement in fusion with immunoglobulin receptor gene of t(14;18) and found no such event among 20 of our patients with mediastinal diffuse large B-cell lymphoma. Despite extensive efforts and constant progress in our understanding of non-Hodgkin s lymphoma pathogenesis, the diffuse large B-cell lymphoma group remains heterogeneous entity awaiting further pathological and clinical stratification.

Adult↗

PubMed2003

Increased diffusion in the brain of professional boxers: a preclinical sign of traumatic brain injury?

BACKGROUND AND PURPOSE: Professional boxing is associated with chronic, repetitive head blows that may cause brain injuries. Diffusion-weighted imaging is sensitive to microscopic changes and may be a useful tool to quantify the microstructural integrity of the brain. In this study, we sought to quantify microscopic alterations associated with chronic traumatic brain injury in professional boxers. METHODS: MR and diffusion-weighted imaging were performed in 24 boxers and in 14 age- and sex-matched control subjects with no history of head trauma. Using distribution analysis, the average diffusion constant of the entire brain (BD(av)) and diffusion distribution width (sigma) were calculated for each subject; findings in professional boxers were compared with those of control subjects. In the boxer group, correlations between diffusion changes and boxing history and diffusion changes and MR imaging findings were assessed. RESULTS: The measured diffusion values in the boxer group were significantly higher than those measured in the control group (BD(av), P <.0001; sigma, P <.01). In the boxer group, a robust correlation was found between increased BD(av) and frequency of hospitalization for boxing injuries (r = 0.654, P <.05). The most common MR finding in the boxer group was volume loss inappropriate to age followed by cavum septum pellucidum, subcortical white matter disease, and periventricular white matter disease. CONCLUSION: Boxers had higher diffusion constants than those in control subjects. Our data suggest that microstructural damage of the brain associated with chronic traumatic brain injury may elevate whole-brain diffusion. This global elevation can exist even when routine MR findings are normal.

Adult↗

PubMed2003

Delayed encephalopathy of acute carbon monoxide intoxication: diffusivity of cerebral white matter lesions.

BACKGROUND AND PURPOSE: Carbon monoxide intoxication has delayed effects on the cerebral white matter characterized by bilateral, confluent lesions that reflect diffuse demyelination. To increase our understanding of this process, we assessed the diffusion characteristics of these lesions. METHODS: Five consecutive patients with delayed encephalopathy of CO intoxication were examined with diffusion MR imaging. Diffusion-weighted images (DWIs) were obtained 25-95 days after their exposure to CO and during a relapse of neuropsychiatric symptoms, which occurred after an initial recovery. Imaging was performed at 1.5 T by using a spin-echo echo-planar sequence with diffusion gradients of 0, 500, and 1000 s/mm(2). DWIs and apparent diffusion coefficient (ADC) maps were visually evaluated, and mean ADCs were calculated from the periventricular white matter and the centrum semiovale, where confluent hyperintensity was seen on T2-weighted images. Findings were compared with those of normal-looking white matter. RESULTS: In all five patients, both T2-weighted images and DWIs showed the white matter lesions as bilateral, diffuse, confluent areas of hyperintensity in the periventricular white matter and centrum semiovale. On ADC maps, these lesions were isointense, with focal areas of hypointensity (n = 4) or diffuse hypointensity (n = 1). Mean ADC values of the white matter lesions were significantly lower than those of normal-looking white matter, regardless of their isointensity or hypointensity on ADC maps (P <.05). CONCLUSION: Bilateral, confluent, white matter lesions in patients with delayed encephalopathy of CO intoxication show decreased diffusivity.

Aged↗

PubMed2006

Evaluation of parenchymal changes at the operation site with early postoperative brain diffusion-weighted magnetic resonance imaging.

PURPOSE: To evaluate diffusion changes in the brain parenchyma at the operation site during the first 24 hours following surgery. MATERIALS AND METHODS: The study group consisted of 52 patients, 39 who had tumor resection surgery and 13 who had epilepsy surgery. Early postoperative magnetic resonance imaging (MRI) included diffusion-weighted imaging (DWI) and routine contrast-enhanced cranial MRI, together with T2* weighted images on a 3T system. DWI findings and the presence of hemorrhage in the brain parenchyma were evaluated. Correlation between the findings, the primary lesion leading to surgery, and operation site were evaluated. RESULTS: Diffusion restriction in the parenchyma surrounding the resection cavity was seen in 17 tumor patients (32.7%, n=52) and in 8 epilepsy patients (15.4%, n=52). DWI showed increased diffusion in 7 patients and no abnormality in 4 patients. Twenty patients showed restricted diffusion pattern related to hemorrhage (38.5%, n=52). CONCLUSION: Restricted diffusion was the most common abnormality observed in the early postoperative DWI of brain parenchyma at the operation site after surgery, which suggested tissue injury caused by surgery. Yet, hemorrhaging in the operation bed can constitute another cause of a reduced apparent diffusion coefficient (ADC) value. Increased diffusion and normal diffusion can also be observed, though rarely.

Adolescent↗

PubMed1991

Molecular diffusion nuclear magnetic resonance imaging.

This review summarizes the work performed during the last 40 years in the field of diffusion measurement by nuclear magnetic resonance (NMR), with emphasis on biomedical diffusion imaging. Measuring molecular displacements in biological tissues in vivo has an enormous potential, but remains technically challenging. After a review of the nature of the diffusion process, the basic principles of diffusion measurements with NMR are introduced, followed by a presentation of various diffusion imaging methods. The paper covers many previously resolved theoretical and technical issues and new problems that are more specific to clinical diffusion imaging, such as the calculation of diffusion effects in the presence of multiple magnetic field gradient pulses, the elimination of motion artifacts, and the meaning of anisotropic or restricted diffusion in relation to tissue microdynamics and microstructure. The concept of diffusion imaging is then extended to blood microcirculation imaging. Finally, the current and potential clinical applications of these techniques are described.

Animals↗