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PubMed2003

Diffusion-weighted MRI of cerebral toxoplasma abscess.

OBJECTIVE: This retrospective study reports the diffusion-weighted MRI appearance of Toxoplasma abscesses, rim-enhancing cerebral masses resulting from toxoplasmosis infection. In all patients, the signal intensity of the abscess core on diffusion-weighted MRI was equal to or less than that of normal, unaffected cerebral white matter and the measured apparent diffusion coefficient was greater than that of unaffected white matter. Histopathology revealed necrotic tissue in the center of these abscesses but no purulent fluid. CONCLUSION: Unlike pyogenic abscesses, the core tissue of rim-enhancing Toxoplasma abscesses shows no restriction of water diffusion.

Adult↗

PubMed2006

An objective method for regularization of fiber orientation distributions derived from diffusion-weighted MRI.

Spherical deconvolution is an elegant method by which the orientation of crossing fibers in the brain can be estimated from a diffusion-weighted MRI measurement. However, higher resolution of fiber directions comes at the cost of higher susceptibility to noise. In this study, we describe the use of linear regularization of the fiber orientation distribution function by Damped Singular Value Decomposition. Furthermore, the degree of regularization is optimized on a voxel-by-voxel basis with no user interaction using Generalized Cross Validation. We find, by simulations, that regularization can improve the reliability of fiber orientation determination when the signal-to-noise ratio is low. Simulations and in vivo measurements indicate that spurious peaks of the fiber orientation distribution function in regions with low anisotropy largely disappear when regularization is introduced. The methods examined are fast enough to be used on a routine basis with diffusion MRI data sets and may improve estimation of water diffusion properties in heterogeneous white matter and boost reliability of fiber tracking through regions of brain with complex fiber geometry.

Brain↗

PubMed2004

Parallel imaging and diffusion tensor imaging for diffusion-weighted MRI of the liver: preliminary experience in healthy volunteers.

OBJECTIVE: Our aim was to determine whether parallel imaging and diffusion tensor imaging affect the measurement of apparent diffusion coefficient (ADC) during diffusion-weighted MRI of the liver in healthy volunteers. SUBJECTS AND METHODS: We performed breath-hold single-shot echo-planar diffusion-weighted MRI of the liver in 10 healthy volunteers using conventional diffusion, conventional diffusion with parallel imaging, and diffusion tensor with parallel imaging sequences. TE values for the three sequences were 83, 74, and 63, respectively. Liver signal intensity was measured on all sequences and normalized to the SD of the measurement. Hepatic ADC was calculated by acquiring all sequences with b values of 0 and 500 sec/mm(2). RESULTS: The normalized liver signal intensity was higher on diffusion tensor with parallel imaging and conventional diffusion with parallel imaging than on conventional diffusion without parallel imaging for a b value of 500 sec/mm(2) (13.0 and 10.1 vs 9.1, respectively; p < 0.03) and for a b value of 0 sec/mm(2) (9.0 and 7.6 vs 6.9, respectively; without reaching a significant difference, p = 0.12). Hepatic ADC was not significantly different between sequences (p = 0.16). CONCLUSION: Higher signal intensity can be obtained when using parallel imaging and diffusion tensor imaging during diffusion-weighted MRI of the liver without compromising hepatic ADC measurement.

Adult↗

PubMed2000

Combined SPECT and diffusion-weighted MRI as a predictor of infarct growth in acute ischemic stroke.

UNLABELLED: In acute ischemic stroke, the infarcted core is surrounded by a zone of tissue that has decreased perfusion. Some of this tissue may be salvaged by prompt, effective treatment. Diffusion-weighted MRI is sensitive in detecting the infarcted tissue, whereas SPECT also detects the hypoperfused tissue around the infarcted core. We studied the potential of combined diffusion-weighted MRI and SPECT to predict infarct growth and clinical outcome in patients not receiving thrombolytic treatment. METHODS: Sixteen patients with acute stroke were examined consecutively with diffusion-weighted MRI and 99mTc-ethyl cysteinate dimer (99mTc-ECD) SPECT within 24 h of the onset of symptoms. Follow-up diffusion-weighted MRI was performed on the second day and after 1 wk. The volumes of infarcted and hypoperfused brain tissue were measured from diffusion-weighted MRI and SPECT, respectively. The volume difference between the hypoperfused and infarcted tissue on the first day was compared with the possible increase in infarct volume during the follow-up. Each patient's neurologic status was assessed with the National Institutes of Health Stroke Scale (NIHSS). RESULTS: The volume of infarcted tissue increased from 48 +/- 54 cm3 (mean +/- SD) on the first day to 88 +/- 93 cm3 on the second day (P = 0.001) and to 110 +/- 121 cm3 at 1 wk (P = 0.001). The volume of hypoperfused tissue on the first day was significantly greater than the infarct volume (102 +/- 135 cm3; P = 0.001). The volume difference between the hypoperfused and infarcted tissue on the first day correlated significantly with the infarct growth between the first day and 1 wk (r = 0.71; P < 0.01). Between the first day and 1 wk, the increase of the infarct volume correlated significantly with the change in the NIHSS (r = 0.54; P < 0.05). CONCLUSION: A large hypoperfusion zone around the infarct core in the acute phase of ischemic stroke predicts the infarct growth during the first week, and this correlates significantly with the change in the neurologic status of the patient. Combined diffusion-weighted MRI and SPECT performed within 24 h after the onset of symptoms can be useful in the evaluation of acute stroke to predict infarct growth.

Acute Disease↗

PubMed1999

Diffusion-weighted MRI in sporadic Creutzfeldt-Jakob disease.

Diffusion-weighted MRI (DWI) was used in three patients with autopsy-proven sporadic Creutzfeldt-Jakob disease (CJD) to provide a rapid noninvasive way to make this sometimes confusing diagnosis. DWI prompted the diagnosis of CJD at an early stage and appears to be particularly useful for monitoring the progression of the disease. We suggest that patients with suspected CJD and no abnormalities on T2- and proton density-weighted images may have cortical involvement on DWI.

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PubMed1999

Normal diffusion-weighted MRI during stroke-like deficits.

BACKGROUND: Diffusion-weighted MRI (DWI) represents a major advance in the early diagnosis of acute ischemic stroke. When abnormal in patients with stroke-like deficit, DWI usually establishes the presence and location of ischemic brain injury. However, this is not always the case. OBJECTIVE: To investigate patients with stroke-like deficits occurring without DWI abnormalities in brain regions clinically suspected to be responsible. METHODS: We identified 27 of 782 consecutive patients scanned when stroke-like neurologic deficits were still present and who had normal DWI in the brain region(s) clinically implicated. Based on all the clinical and radiologic data, we attempted to arrive at a pathophysiologic diagnosis in each. RESULTS: Best final diagnosis was a stroke mimic in 37% and a cerebral ischemic event in 63%. Stroke mimics (10 patients) included migraine, seizures, functional disorder, transient global amnesia, and brain tumor. The remaining patients were considered to have had cerebral ischemic events: lacunar syndrome (7 patients; 3 with infarcts demonstrated subsequently) and hemispheric cortical syndrome (10 patients; 5 with TIA, 2 with prolonged reversible deficits, 3 with infarction on follow-up imaging). In each of the latter three patients, the regions destined to infarct showed decreased perfusion on the initial hemodynamically weighted MRI (HWI). CONCLUSIONS: Normal DWI in patients with stroke-like deficits should stimulate a search for nonischemic cause of symptoms. However, more than one-half of such patients have an ischemic cause as the best clinical diagnosis. Small brainstem lacunar infarctions may escape detection. Concomitant HWI can identify some patients with brain ischemia that is symptomatic but not yet to the stage of causing DWI abnormality.

Aged↗

PubMed2000

Hemodynamic effect of iodinated high-viscosity contrast medium in the rat kidney: a diffusion-weighted MRI feasibility study.

RATIONALE AND OBJECTIVES: To assess the abilities of dynamic diffusion-weighted MRI to demonstrate the effects in vivo of a high-viscosity iodinated contrast agent on medullary and cortical blood flow in the rat kidney. METHODS: Dynamic diffusion-weighted, echoplanar MR images obtained from five b-value single-shot acquisitions and their isotropic apparent diffusion coefficient maps were obtained from nine rats anesthetized by pentobarbital sedation, before and after intravenous injection of a high-viscosity, dimeric iso-osmolar iodinated contrast medium (iodixanol), and compared with those obtained from four control rats that received saline. RESULTS: The mean baseline apparent diffusion coefficient values were 1.64 +/- 0.05 x 10(-3) mm2/s for the cortex and 1.75 +/- 0.06 x 10(-3) mm2/s for the medulla. In the iodixanol group, a significant decrease in renal diffusion was observed at 12 minutes and lasted at least until 24 minutes. The decrease in diffusion occurred earlier for the cortex and lasted less than for the medulla. There was no significant modification in diffusion over time in the control group. CONCLUSIONS: This preliminary experience in rats shows that dynamic diffusion-weighted MRI can be used to study noninvasively the in vivo renal hemodynamic response after injection of iodinated contrast.

Animals↗

PubMedDate not supplied

The earliest manifestation of focal encephalitis on diffusion-weighted MRI.

We report the case of an adult patient with a focus of meningioencephalitis in whom the earliest magnetic resonance imaging (MRI) manifestation was hyperintense signal on diffusion-weighted (DW) sequence only. To our knowledge, this is the first adult encephalitis case to be reported with the MRI diffusion-weighted pulse sequence being the only positive MRI finding. A brief review of the pertinent literature is included.

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PubMed2005

Clinically silent choroid plexus cyst: evaluation by diffusion-weighted MRI.

We retrospectively reviewed diffusion-weighted magnetic resonance images of 57 patients with a choroid plexus cyst diagnosed by contrast-enhanced T1-weighted imaging. All the cysts appeared to represent incidental findings. Thirty-eight of 57 patients had bilateral cysts and 19 had unilateral ones. On diffusion-weighted images, 78 of 95 cysts showed homogeneously high signal intensity, 12 showed focal high signal areas, and 5 had no portion with a high signal. The apparent diffusion coefficient of the high signal areas in the cysts was (1.46+/-0.14) x10(-3) mm(2)/s, intermediate between the apparent diffusion coefficients of cerebrospinal fluid and cerebral white matter, (3.15+/-0.67) x10(-3) and (0.79+/-0.22) x10(-3) mm(2)/s, respectively. Pathological correlation was available in one case, showing high signal intensity areas in the glomera of the choroid plexuses in the lateral ventricles on diffusion-weighted images corresponding to gelatinous cysts with highly proteinaceous content.

Adult↗

PubMed1993

[Study of diffusion weighted magnetic resonance imaging in Wilson's disease].

We analyzed diffusion weighted magnetic resonance images (diffusion MRI) of the basal ganglia, which were obtained from four patients with Wilson's disease, and compared them with the images from ten age-matched normal individuals. In all patients, T2-MRI of the basal ganglia disclosed low or iso-signals, but diffusion MRI revealed abnormal high signals in some areas of the basal ganglia in each case. Pathological changes except for copper and/or iron deposits are difficult to estimate by T2-MRI because the low signal on T2-MRI emphatically reflects the deposits, while the abnormal high signal on diffusion MRI is thought to reflect parenchymal lesions such as cell loss, demyelination and/or increase of the extracellular fluid. From our results, we confirmed that diffusion MRI was very useful for estimating parenchymal lesions with metal deposits.

Adult↗

PubMed1999

Diffusion tensor MRI assesses corticospinal tract damage in ALS.

BACKGROUND: A number of neurophysiologic and neuroimaging techniques have been evaluated in the research setting to assess upper motor neuron (UMN) damage in ALS. Changes in tissue structure in the CNS modify the diffusional behavior of water molecules, which can be detected by diffusion tensor MRI. OBJECTIVES: To explore the hypothesis that degeneration of the motor fibers in ALS would be reflected by changes in the diffusion characteristics of the white matter fibers in the posterior limb of the internal capsule and that these changes could be detected by diffusion tensor MRI. METHODS: We studied 22 patients with El Escorial definite, probable, or possible ALS-11 with limb onset (mean age 54.5 +/- 10.7 years) and 11 with bulbar onset (mean age 49.6 +/- 11.7 years)-and compared them with 20 healthy, age-matched controls (mean age 46.0 +/- 12.6 years). We assessed central motor conduction time (CMCT), threshold to stimulation, and silent period using transcranial magnetic stimulation. Diffusion tensor MRI was performed using a 1.5-T GE Signa system (Milwaukee, WI) fitted with Advanced NMR hardware and software capable of producing echo planar MR images. Data were acquired from seven coronal slices centered to include the posterior limb of the internal capsule. Maps of the mean diffusivity, fractional anisotropy, and T2-weighted signal intensity were generated. RESULTS: There were no differences between the subject groups on measures of CMCT, threshold to stimulation, and silent period. However, the CMCT correlated with clinical measures of UMN involvement. We found a significant increase in the mean diffusivity and reduction in fractional anisotropy along the corticospinal tracts between the three subject groups, most marked in the bulbar-onset group. The fractional anisotropy correlated with measures of disease severity and UMN involvement, whereas the mean diffusivity correlated with disease duration. CONCLUSION: The results support the use of diffusion tensor MRI in detecting pathology of the corticospinal tracts in ALS.

Adult↗

PubMed2006

Visualizing neuronal structures in the human brain via diffusion tensor MRI.

Acquisition, analysis, and visualization of diffusion tensor magnetic resonance imaging (DT-MRI) is still an evolving technology. This article reviews the fundamentals of the data acquisition process and the pipeline leading to visual results that are interpretable by physicians in their clinical practice. The limitations of common approaches for visualizing the retrieved data are discussed and a new statistical method is presented to assess the reliability of the acquired tensor field. A novel visualization method is proposed which is discussed in light of neurophysiological considerations of the perception of colored patterns. It is argued that this method is more accurate for medical data while providing a nearly optimal visual stimulus. The method is evaluated on a patient study with a brain tumor.

Adult↗

PubMed2005

Meningoencephalitis caused by Streptococcus pneumoniae: a diagnostic and therapeutic challenge. Diagnosis with diffusion-weighted MRI leading to treatment with corticosteroids.

Streptococcus pneumoniae is a common cause of bacterial meningitis but only rarely causes other infections such as brain abscess, encephalitis, encephalomyelitis or meningoencephalitis. We report on three adult patients with meningoencephalitis caused by S. pneumoniae. In all three, CT and MRI revealed widespread brain lesions, suggesting extensive parenchymal injury. Diffusion-weighted MRI showed lesions with restricted diffusion, reflecting local areas of ischaemia with cytotoxic oedema secondary to an immunologically mediated necrotising vasculitis and thrombosis. High levels of markers of neuronal, glial and myelin damage were found in the cerebrospinal fluid. According to the literature, brain parenchyma lesions in adults with pneumococcal meningoencephalitis are often associated with death or severe neurological deficit. Our patients were treated with pulse doses of glucocorticoids: this resulted in dramatic clinical improvement and an excellent final neurological recovery.

Adult↗

PubMed2005

Quantification of cervical cord pathology in primary progressive MS using diffusion tensor MRI.

OBJECTIVE: To investigate the extent and severity of cervical cord damage using diffusion tensor MRI (DT-MRI) and histogram analysis in patients with primary progressive MS (PPMS). METHODS: Diffusion-weighted sensitivity-encoded (SENSE) echoplanar images of the cervical cord and brain dual-echo and diffusion-weighted scans were acquired from 24 patients with PPMS and 13 healthy controls. Cord and brain mean diffusivity and fractional anisotropy histograms were produced. An analysis of variance model, adjusting for cord volume, was used to compare cord DT-MRI parameters from controls and patients. RESULTS: Compared to healthy controls, PPMS patients had reduced cervical cord cross-sectional area and average cord fractional anisotropy (p = 0.007), and increased cord mean diffusivity (p = 0.024). No correlations were found between DT-MRI metrics of the cord and quantities obtained from conventional and DT-MRI of the brain. CONCLUSIONS: DT-MRI of the cervical cord can quantify the extent of diffuse cord pathology in patients with PPMS. Such cord diffusivity changes in patients with PPMS are likely to reflect irreversible axonal injury and reactive gliosis and seem to be independent of brain damage.

Adult↗

PubMed2000

Late resolution of diffusion-weighted MRI changes in a patient with prolonged reversible ischemic neurological deficit after thrombolytic therapy.

BACKGROUND: Reduced apparent diffusion coefficients (ADCs) correlate with cerebral ischemia. The combination of ADC with techniques to measure cerebral perfusion may help to assess the effect of treatment. CASE DESCRIPTION: The authors describe a patient who experienced an acute stroke with hemianopia, consequently treated with intravenous recombinant tissue plasminogen activator. Positron emission tomographic imaging and MRI, including diffusion-weighted MRI, were performed during and shortly after treatment with recombinant tissue plasminogen activator and 34 to 35 hours later. Cerebral perfusion of the left occipital region was reduced to 74%. Diffusion-weighted MRI detected a territory of restricted water movement in the corresponding area. Further magnetic resonance sequences did not show any pathologies. In follow-up, positron emission tomography demonstrated reperfusion. The volume of diffusion and ADC abnormalities detected by MRI decreased markedly. A few hours later, the patient recovered completely. A third MRI examination 10 days later showed normal findings. CONCLUSIONS: In a patient with prolonged reversible ischemic neurological deficit, resolution of early diffusion changes corresponded to cerebral reperfusion and to the recovery of clinical symptoms.

Acute Disease↗

PubMed2006

Applications of diffusion-weighted MRI in thoracic spinal cord injury without radiographic abnormality.

Diffusion-weighted MRI (DWI) has been proposed as a method to evaluate the integrity of white matter tracts in the spinal cord. The integrity of the spinal cord reflects the exact stage of traumatic injury. The purpose of this study was to evaluate the diagnostic value of DWI in SCIWORA in the thoracic spine. A total of five patients with thoracic SCIWORA underwent MRI and DWI within 48 h of injury. DWIs were obtained with a single-shot fast spin-echo (SSFSE) sequence; TI- and T2-weighted images were obtained with spin echo. Consistency among the clinical presentation, outcome, MRI and DWI was analysed. There was complete injury in one patient and partial in four patients. Four patients showed hypointense T1-weighted signal and hyperintense T2-weighted signal, and one patient had no changes on MRI. All patients showed hyperintense signal on DWI. Two patients made good recoveries (ASIA grades D and E), one had a moderate recovery (ASIA grade C), and two showed minimal or no improvement (ASIA grade A or B) in neurological function. Patients with no cord changes on MRI showed abnormal signals on DWI. It is likely that in the future DWI may provide important information complimentary to conventional MRI and allow a better prognostic evaluation of recovery from SCIWORA.

Adult↗

PubMed2004

Acute basilar artery occlusion: diffusion-perfusion MRI characterization of tissue salvage in patients receiving intra-arterial stroke therapies.

BACKGROUND AND PURPOSE: Diffusion-perfusion MRI in patients with anterior circulation occlusions has demonstrated salvage of threatened tissue after thrombolytic therapy. Similar studies have not been reported with posterior circulation occlusions. METHODS: Patients with acute basilar artery occlusion treated with intra-arterial thrombolytics were studied with multimodal MRI before treatment, several hours after treatment, and at day 7. RESULTS: Ten patients were studied (9 men, 1 woman). Mean age was 70 years, and median pretreatment National Institutes of Health Stroke Scale (NIHSS) score was 14. In 6 patients imaged before treatment and at day 7, mean pretreatment diffusion-weighted imaging (DWI) lesion volume was 11 cm(3), and day 7, lesion volume was 2.6 cm(3). Significant mismatch was visualized in all 5 patients with pretreatment perfusion-diffusion imaging (mean, 73%; range, 49% to 99%). Late imaging obtained in 4 of these 5 patients demonstrated that mean posttreatment DWI lesion volume (21 cm(3)) was less than the mean initial perfusion lesion volume (62 cm(3)). Although there was no direct correlation between pretreatment DWI volume and initial NIHSS (r=-0.113), there was good correlation between pretreatment perfusion-weighted imaging volume and initial NIHSS (r=0.72). CONCLUSIONS: In this first report of diffusion-perfusion MRI in patients with acute basilar artery occlusions treated with intra-arterial thrombolysis, significant mismatch was visualized on pretreatment studies, suggesting that large volumes of salvageable tissue were present. Final infarct volumes were smaller than pretreatment perfusion volumes, suggesting that substantial volumes of tissue were salvaged by thrombolytic reperfusion.

Acute Disease↗

PubMed2000

Comparison of diffusion-weighted MRI and CT in acute stroke.

OBJECTIVE: To compare diffusion-weighted MRI (DWI) and CT with respect to accuracy of localizing acute cerebral infarction; sensitivity, specificity, and interrater reliability for identifying more than one-third middle cerebral artery (MCA) territory involvement; and correlation of acute lesion volume with final infarct volume. METHOD: Nineteen consecutive stroke patients underwent CT and DWI within 7 hours of stroke onset and a follow-up DWI examination 36 hours after symptom onset, which served as the "gold standard" for lesion location and extent of MCA involvement. Each scan was evaluated for acute ischemic lesions by two experienced observers. After 30 days, T2-weighted MRI was obtained for assessment of the final infarct volume. RESULTS: The acute CT and DWI scans were obtained on average 2.6 and 5.1 hours after symptom onset. On DWI the acute lesion was identified correctly in all instances and on CT it was identified correctly in 42 to 63% of patients. Sensitivity for detection of more than 33% MCA involvement was better for DWI (57 to 86%) than for CT (14 to 43%), whereas specificity was excellent for both. Interrater reliability was moderately good for both (kappa, 0.6 for DWI; 0.5 for CT). A positive correlation (r = 0.79; p = 0.001) existed between lesion volume on acute DWI and final infarct volume, whereas no correlation was found between CT volume and final infarct volume. CONCLUSION: When compared with CT, DWI was more accurate for identifying acute infarction and more sensitive for detection of more than 33% MCA involvement. In addition, lesion volume on acute DWI, but not on acute CT, correlated strongly with final infarct volume. Additional studies are required to demonstrate whether these advantages of DWI are clinically relevant in the management of patients with acute stroke.

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