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PubMed2000

Detectability and detection rate of acute cerebral hemisphere infarcts on CT and diffusion-weighted MRI.

Our purpose was to compare the detectability and detection rate of acute ischaemic cerebral hemisphere infarcts on CT and diffusion-weighted MRI (DWI). We investigated 32 consecutive patients with acute hemisphere stroke with unenhanced CT and DWI within 6 h of stroke onset. The interval between CT and DWI ranged from 15 to 180 min (mean 60 min). Infarct detectability on CT and DWI was determined by comparing the initial CT, DWI and later reference images in a consensus reading of five independent examiners. The "true" detection rate was assessed by analysing all single readings. Two patients had intracerebral haematomas on DWI and CT and were excluded. There were 27 patients with ischaemic infarcts; all were visible on DWI and proven by follow-up. DWI was negative in three patients without a final diagnosis of infarct (100% sensitivity, 100% specificity, chi2 = 30, P < 0.0001). Ischaemic infarcts were visible on 15 and not seen on 12 CT studies (55 % sensitivity, 100% specificity, chi2 = 1.48, P = 0.224). With regard to the single readings (30 examinations x 5 examiners = 150 readings), 63 CT readings were true positive and 72 false negative (sensitivity 47 %, specificity 86%, chi2 = 2.88, P = 0.089). Of the DWI readings 128 were true positive and 7 false negative (sensitivity 95%, specificity 87 %, chi2 = 70.67, P < 0.0001). Interobserver agreement was substantial for CT (chi = 0.72, 95 % confidence interval, 0.6-0.84) and DWI (chi = 0.82, 95 % confidence interval, 0.46-1). Taken together, detectability and detection rate of acute (< 6 h) hemisphere infarcts are significantly higher with DWI than with CT.

Brain↗
PubMedDate not supplied

Diffusion-weighted MRI: detection of cerebral ischemia before and after carotid thromboendarterectomy.

PURPOSE: Conventional postoperative evaluation of patients following carotid thromboendarterectomy (TEA) consists of a clinical neurologic examination to assess neurologic deficits, color duplex ultrasound to document the surgically reestablished patency of the carotid artery, and CT for exclusion of postoperative ischemic infarctions. Recent studies prove that diffusion-weighted MRI is more sensitive in the detection of fresh insults than conventional MRI and CT. The objective of the study was to ascertain the incidence of clinically asymptomatic peri-and postoperative ischemic infarctions visualized at MRI. METHOD: We included 52 patients in the study. Fifty-one patients (31 men, 20 women; average age 68 years) underwent cranial MR examination including a diffusion-weighted sequence at 24 h prior to carotid TEA and again 24 h following the procedure. One patient did not agree to participate. RESULTS: In 29 of 51 patients (56%), neither the pre-nor the postoperative MR scans showed any diffusion abnormalities. In 16 patients (31%), however, preoperative MRI detected fresh ischemic insults. In nine patients (17.6%), the size of the insult resulted in surgery being postponed for 4 weeks. In six patients (11.8%), postoperative MRI returned findings of fresh disturbances of diffusion suggestive of ischemia that were not visualized on preoperative scans. Discrete neurologic deficits were observed in only two (3.9%) of these patients. Deficits were transient and disappeared within 72 h. CONCLUSION: Our findings underscore MRI's capacity for visualizing perioperative ischemic events. Moreover, MRI provides evidence of clinically asymptomatic embolisms that occur perioperatively.

Acute Disease↗
PubMed2004

Diffusion-weighted MRI in the evaluation of renal lesions: preliminary results.

The purpose of this study was to evaluate the capability and the reliability of diffusion-weighted MRI in the evaluation of normal kidney and different renal lesions. 39 patients (10 normal volunteers and 29 patients with known renal lesions) underwent MRI of the kidneys by using a 1.5 T superconducting magnet. Axial fat suppressed turbo spin echo (TSE) T(2) and coronal fast field echo (FFE) T(1) or TSE T(1) weighted images were acquired for each patient. Diffusion-weighted (DW) images were obtained in the axial plane during breath-hold (17 s) with a spin-echo echo planar imaging (SE EPI) single shot sequence (repetition time (TR)=2883 ms, echo time (TE)=61 ms, flip angle=90 degrees ), with b value of 500 s mm(-2). 16 slices were produced with slice thickness of 7 mm and interslice gap of 1 mm. An apparent diffusion coefficient (ADC) map was obtained at each slice position. The ADC was measured in an approximately 1 cm region of interest (ROI) within the normal renal parenchyma, the detected renal lesions and the collecting system if dilated. ADC values in normal renal parenchyma ranged from 1.72 x 10(-3) mm(2) s(-1) to 2.65 x 10(-3) mm(2) s(-1), while ADC values in simple cysts (n=13) were higher (2.87 x 10(-3) mm(2) s(-1) to 4.00 x 10(-3) mm(2) s(-1)). In hydronephrotic kidneys (n=6) the ADC values of renal pelvis ranged from 3.39 x 10(-3) mm(2) s(-1) to 4.00 x 10(-3) mm(2) s(-1). In cases of pyonephrosis (n=3) ADC values of the renal pelvis were found to be lower than those of renal pelvis of hydronephrotic kidneys (0.77 x 10(-3) mm(2) s(-1) to 1.07 x 10(-3) mm(2) s(-1)). Solid benign and malignant renal tumours (n=7) showed ADC values ranging between 1.28 x 10(-3) mm(2) s(-1) and 1.83 x 10(-3) mm(2) s(-1). In conclusion diffusion-weighted MR imaging of the kidney seems to be a reliable way to differentiate normal renal parenchyma and different renal diseases. Clinical experience with this method is still preliminary and further studies are required.

Adult↗
PubMed2003

Diffusion tensor MRI and fiber tractography of cerebellar atrophy in phenytoin users.

PURPOSE: The usefulness of diffusion tensor magnetic resonance imaging (DT-MRI) is still in debate, and the development of clinically feasible scan protocol is encouraged. The purpose of this study was to investigate the afferent fiber system to the cerebellum in patients with phenytoin (PHT)-induced cerebellar atrophy in comparison with cerebellar atrophy of other etiologies by using DT-MRI. METHODS: Thirteen patients (M/F ratio, 7:6; mean age, 42.5 years) and age-matched normal controls (n = 8) participated in this study. The patient group consisted of epilepsy patients who had received PHT therapy (n = 9) and clinically diagnosed as having olivopontocerebellar atrophy (OPCA; n = 4). DT-MRI was performed by using diffusion weighting of b = 600 s/mm2, and fractional anisotropy (FA) and color-coded vector maps were generated. FA of the middle cerebellar peduncle (MCP), the cerebellum, and transverse pontine fibers (TPF) was measured and compared between PHT and OPCA patients. RESULTS: Normal subjects showed FA values of 0.81 +/- 0.07 in MCP, 0.69 +/- 0.04 in TPF, and PHT users showed FA values of 0.84 +/- 0.09 in MCP, 0.72 +/- 0.08 in TPF, and 0.21 +/- 0.04 in cerebellum. OPCA patients showed FA values of 0.39 +/- 0.11 in MCP, 0.46 +/- 0.12 in TPF, and 0.22 +/- 0.07 in cerebellum. PHT users showed a statistically significant reduction of FA only in cerebellum, whereas OPCA demonstrated significant decrease of FA in MCP, TPF, and cerebellum (one-way analysis of variance, p < 0.01). Three-dimensional reconstruction of fiber tracts demonstrated decreased volume and altered fiber integrity within the peduncles and transverse pontine fibers in the OPCA group, whereas fiber course patterns in PHT users were similar to those in controls. CONCLUSIONS: PHT users showed normal orientation and anisotropy of MCP and TPF, whereas OPCA demonstrated impaired values, suggesting that PHT directly affects the cerebellum. DT-MRI can demonstrate detailed fiber configurations in degenerative diseases of brainstem and cerebellum and provides insight into the pathomechanisms of cerebellar atrophy.

Adult↗
PubMedDate not supplied

Diffusion-weighted MRI of the cervical cord in acute spinal cord injury with type II odontoid fracture.

The authors present a case of acute spinal cord injury demonstrated by diffusion-weighted MRI (DWI) of the cervical cord. DWI taken 2 hours after injury showed intramedullary hyperintensity with a decrease of the apparent diffusion coefficient (ADC) value at C1-C2 vertebral levels. On T -weighted images obtained 1 month after injury, the lesion was hyperintense, indicating the existence of myelomalacia. DWI of the cervical cord provided satisfactory images and was a useful method for detecting and visualizing of the affected cord in the super-early stage.(2)

Cervical Vertebrae↗
PubMed2001

Normal-appearing white matter in ischemic leukoaraiosis: a diffusion tensor MRI study.

Ischemic leukoaraiosis is a consistent concomitant of vascular dementia. Conventional MRI provides little information about underlying white matter tract disruption and correlates poorly with cognitive dysfunction. Diffusion tensor MRI may provide better markers of tract integrity. Changes in the normal-appearing white matter were demonstrated in 30 patients with ischemic leukoaraiosis compared with 17 age-matched control subjects. These changes correlated with executive dysfunction assessed by the Wisconsin Card Sorting Test.

Aged↗
PubMedDate not supplied

Detection of acute cytotoxic changes in progressive neuronal degeneration of childhood with liver disease (Alpers-Huttenlocher syndrome) using diffusion-weighted MRI and MR spectroscopy.

Alpers-Huttenlocher syndrome (AHS) is a rare mitochondrial disorder of childhood onset that is characterized by progressive encephalopathy and hepatopathy. MRI studies are rare and have not added substantial information to the pathogenesis of the encephalopathy. Diffusion-weighted MRI (DWI) and MR spectroscopy (MRS) were used in a patient with AHS during acute clinical deterioration and after improvement. DWI detected signal hyperintensity in several brain areas not restricted to any vascular territory. MRS revealed an unequivocal lactate peak and a reduced N-acetyl-aspartate-creatinine (NAA/Crea) ratio. DWI signal hyperintensity was correlated with neurologic symptoms and decreased after clinical improvement. Potentially reversible neuronal cytotoxic edema resulting from acute impairment of mitochondrial function is strongly suggested to be an important pathogenetic mechanism in AHS encephalopathy.

Aspartic Acid↗
PubMed2004

The effect of gradient sampling schemes on measures derived from diffusion tensor MRI: a Monte Carlo study.

There are conflicting opinions in the literature as to whether it is more beneficial to use a large number of gradient sampling orientations in diffusion tensor MRI (DT-MRI) experiments than to use a smaller number of carefully chosen orientations. In this study, Monte Carlo simulations were used to study the effect of using different gradient sampling schemes on estimates of tensor-derived quantities assuming a b-value of 1000 smm(-2). The study focused in particular on the effect that the number of unique gradient orientations has on uncertainty in estimates of tensor-orientation, and on estimates of the trace and anisotropy of the diffusion tensor. The results challenge the recently proposed notion that a set of six icosahedrally-arranged orientations is optimal for DT-MRI. It is shown that at least 20 unique sampling orientations are necessary for a robust estimation of anisotropy, whereas at least 30 unique sampling orientations are required for a robust estimation of tensor-orientation and mean diffusivity. Finally, the performance of sampling schemes that use low numbers of sampling orientations, but make efficient use of available gradient power, are compared to less efficient schemes with larger numbers of sampling orientations, and the relevant scenarios in which each type of scheme should be used are discussed.

Algorithms↗
PubMed2001

Line scan diffusion tensor MRI of the cervical spinal cord in preterm infants.

Line scan diffusion tensor magenetic resonance imaging (DT-MRI) of the cervical spinal cord was demonstrated in vivo for unsedated preterm (gestational age 24-30 weeks at birth), very low birthweight (birthweight 620-1300 g) infants at postmenstrual ages from 29-40 weeks. Scalar invariant measures of diffusion [apparent diffusion coefficient (ADC) and relative anisotropy (RA)] determined from a cervical cord region of interest in each case are reported, characterizing the maturational status of the normal third trimester and newborn spinal cord. Mean ADC of 11 infants was 1.2 +/- 0.1 microm(2)/msec and the mean RA was 24.3 +/- 4.9%. Normal infant cord neural fiber tract morphology was visualized using a mapping of the predominant diffusion tensor eigenvector. Potential clinical applications of line scan DT-MRI of the spinal cord of preterm and term newborns for assessment of spinal cord injury are discussed. J. Magn. Reson. Imaging 2001;13:949-953.

Adult↗
PubMed2006

Diffusion-weighted MRI predicts prognosis in severe hypoglycemic encephalopathy.

A 20-year-old woman presented unconscious due to hypoglycemia after a self-administered insulin injection. Diffusion-weighted MRI (DWI), performed 5 days after admission, demonstrated heterogeneous high-intensity signal areas in both the cortex and subcortex but sparing the motor and sensory centers. On the 11th day after admission, she began making incomprehensible verbal sounds, eye opening spontaneously and moving her extremities with pyramidal tract signs. Three months later, she had aphasia, agnosia and apraxia but a normal gait without pyramidal tract signs or ataxia. DWI is thus considered useful to predict the functional outcome of patients with severe hypoglycemia.

Adult↗
PubMed2004

Short-term accrual of gray matter pathology in patients with progressive multiple sclerosis: an in vivo study using diffusion tensor MRI.

The mechanisms underlying the progressive course of multiple sclerosis (MS) are not fully understood yet. Since diffusion tensor (DT) MRI can provide quantitative estimates of both MRI-visible and MRI-occult brain damage related to MS, the present study investigated the value of DT MRI-derived measures for the assessment of the short-term accumulation of white and gray matter (GM) pathology in patients with primary progressive (PP) and secondary progressive (SP) MS. Fifty-four patients with PPMS and 22 with SPMS were studied at baseline and after a mean follow-up of 15 months. Dual-echo, T1-weighted, and DT MRI scans of the brain were acquired on both occasions. Total lesion volumes (TLV) and percentage brain volume changes (PBVC) were computed. Mean diffusivity (MD) and fractional anisotropy (FA) maps of the normal-appearing white (NAWM) and gray matter (NAGM) were produced, and histogram analysis was performed. In both patient groups, a significant increase of average lesion MD (P = 0.01) and of average NAGM MD (P = 0.007) was found at follow-up. No significant differences between PPMS and SPMS patient groups were found for the on-study changes of any MRI-derived measure. No significant correlations were found between the percentage changes of DT MRI-derived measures and those of TLV and PBVC. No significant changes of DT MRI-derived measures were observed in age-matched healthy controls over the same study period. Over a 1-year period of follow-up, DT MRI can detect tissue changes beyond the resolution of conventional MRI in the NAGM of patients with progressive MS. The accumulation of DT MRI-detectable gray matter damage does not seem to merely depend upon the concomitant increase of T2-visible lesion load and the reduction of brain volume. These observations suggest that progressive NAGM damage might yet be an additional factor leading to the accumulation of disability in progressive MS.

Adult↗
PubMed2002

Independent component analysis applied to diffusion tensor MRI.

The accuracy of the outcome in a diffusion tensor imaging (DTI) experiment depends on the acquisition scheme as well as the postprocessing methods used. In the present study, the DTI results acquired after applying different combinations of diffusion-weighted (DW) gradient orientations were initially compared. Then, spatially independent component analysis (ICA) was applied to the T(2) and DW images. In all cases a single component was detected that was similar to the map of the trace of the diffusion tensor, but contained a reduced amount of noise. Furthermore, when no correction for eddy current artifacts was used in the image acquisition scheme, the effects of eddy currents were separated by ICA into independent components. After these components were removed, conventional estimation of the diffusion tensor was performed on the modified data. No artifact was contained in the final rotationally invariant scalar quantities that describe the intrinsic diffusion properties. Additionally, independent components that mapped major white matter fiber tracts in the human brain were identified. Finally, the noise included in the original T(2) and DW images was also separated by ICA into independent components. These components were subsequently removed and a reduction of noise in the final DTI results was achieved.

Adult↗
PubMed2003

Measurement of fractional anisotropy using diffusion tensor MRI in supratentorial astrocytic tumors.

In vivo, water diffusion displays directionality due to presence of complex microstructural barriers in tissue. The extent of directionality of water diffusion can be expressed as a fractional anisotropy (FA) value, using diffusion tensor MR imaging (DTI). The aim of this study was to determine whether FA values indicate microstructures in astrocytic tumors. We performed DTI in 31 patients with astrocytic tumor, and measured the FA values of tumor and normal brain regions prior to CT-guided stereotactic biopsy. After biopsy, FA values were compared to assess the cellularity and vascularity of tumor tissue. Although mean FA values trended to differ among histological types, all mean tumor FA values were lower than those of normal brain regions. Positive correlation was observed between FA values and both cellularity (r = 0.65, p < 0.05) and vascularity (r = 0.45, p < 0.05). We had hypothesized that the FA value of an astrocytic tumor would be determined by a balance between factors increasing the directionality of water diffusion, such as high cellularity and/or vascularity, and factors decreasing the directionality of water diffusion, such as fiber destruction. However, our results suggest that the FA values of glioblastoma, anaplastic astrocytoma, diffuse astrocytoma and pilocytic astrocytoma are largely affected by cellularity and/or vascularity, whereas that of gliomatosis cerebri are largely affected by the preservation of nerve fibers. Measurement of FA value using DTI will allow prediction of histological characteristics such as cellularity, vascularity and/or fiber structure in astrocytic tumors.

Adult↗
PubMed2003

Diffusion-weighted MRI of the cervical spinal cord using a single-shot fast spin-echo technique: findings in normal subjects and in myelomalacia.

We have implemented a new diffusion-weighted MRI (DWI) sequence based on the single-shot fast spin-echo technique. We hypothesised that this would add information to conventional MRI for diagnosis of lesions of the cervical spinal cord. DWI was performed using a technique in which echo collection after the application of motion-probing gradients was done in the same manner as in the single-shot fast spin-echo technique. We first imaged six healthy volunteers to demonstrate the cervical spinal cord using the sequence. Then we applied the sequence to 12 patients with cervical myelomalacia due to chronic cord compression. The spinal cord was well seen in all subjects without the distortion associated with echo-planar DWI. In the patients, lesions appeared as areas of low- or isointense signal on DWI. Calculated apparent diffusion coefficients of the lesions (3.30+/-0.38x10(-3) mm(2)/s) were significantly higher than those of normal volunteers (2.26+/-0.08x10(-3) mm(2)/s). Increased diffusion in areas of cervical myelomalacia, suggesting irreversible damage, can be detected using this technique.

Adult↗
PubMed2000

[Usefulness of diffusion-weighted MRI in the diagnosis of transient ischemic attacks].

Diffusion-weighted imaging(DWI) has been demonstrated to be valuable for assessment of ischemic stroke patients. The aim of this study is to evaluate clinical usefulness of DWI in the diagnosis of transient ischemic attack(TIA). Nineteen patients with symptoms of TIA were studied. DWI was taken with 1.5 Tesla MRI system using spin echo EPI sequence. Seven patients revealed areas of hyperintensity (brightness) on DWI and of hypointensity on apparent diffusion coefficient(ADC) maps relative to normal brain. As the duration of TIA symptom elongated, the percentage of patients with DWI abnormalities became higher. DWI enabled to detect areas of hyperintense lesion in all three patients as early as 3 hours after the onset, while conventional T2 weighted imaging showed in one. All the DWI abnormalities were irreversible in spite of the complete recovery from TIA. DWI is an useful technique for the detection of responsible lesions in TIA. However, TIA cannot be ruled out even if DWI does not demonstrate any abnormal signals.

Aged↗
PubMed1994

[Unilateral external ophthalmoplegia caused by ipsilateral oculomotor nuclear lesion: analysis with diffusion weighted MRI].

A 49-year-old man who had been suffering from poorly controlled diabetes mellitus for 20 years was admitted to our hospital with the chief complaints of diplopia and right ptosis. The onset of his symptoms was sudden. On admission, he had right palpebral ptosis, upward and left lateral gaze paresis of the right eye. Hess screen chart examination revealed paresis of the right superior rectus, inferior oblique and medial rectus muscles. T2 weighted magnetic resonance imaging (MRI) revealed high intensity area in the medial part of the right midbrain tegmentum where the oculomotor nucleus located, and diffusion weighted MRI demonstrated high intensity area which corresponded to the oculomotor fascicles of the midbrain. The latter represented Wallerian degeneration of the fascicles. The diagnosis of small infarction of the right oculomotor nucleus presenting ipsilateral external ophthalmoplegia was made. The superior rectus muscle is innervated by the neurons in the contralateral oculomotor nucleus, and the other external ocular muscles innervated by the third cranial nerve are conducted by the neurons in the ipsilateral oculomotor nucleus; therefore, unilateral oculomotor nuclear lesion generally causes ipsilateral ophthalmoplegia plus contralateral superior rectus palsy. Our case presented here shows that there may be such a case with oculomotor nuclear disturbance which masquerades with oculomotor fascicular or infranuclear disturbance; therefore, it is important to include these lesions in differential diagnosis.

Cerebral Infarction↗
PubMed2006

[Diffusion weighted MRI of spine tumors].

PURPOSE: To evaluate the contribution of diffusion weighted MR imaging in malignant spine pathology. Materials and methods. Between February 2004 and January 2005, 49 patients (43 to 86 years old) were included. Three groups were made: osteoporotic collapses (n = 13), malignant collapses (n = 15) and malignant spine lesions (n = 21). The MRI (Symphony 1.5T) allowed SENSE imaging. After conventional MRI examination (T1, T2 fat sat, T1 with Gadolinium), all patients underwent diffusion weighted imaging (Spin Echo) with variable b values: 0, 250, 500, 750 and 1000. The diffusion sequence lasted 2 min 29 s. The Apparent Diffusion Coefficient (ADC) was calculated automatically. The analysis was qualitative (signal study b = 1,000 mm2/s) and quantitative (ADC measurement). RESULTS: The image quality was good except for some cervical examinations. Qualitative analysis did not show a difference between benign and malignant lesions. Quantitative results are: malignant spine lesion (mean ADC = 0.826 10-3 s/mm2), malignant spinal collapses (mean ADC = 0.912 10-3 s/mm2) and benign spinal collapses (mean ADC = 1.497 10-3 s/mm2). There was overlapping results between benign and malignant lesion. The statistical study showed a significant difference (t test with p < 1/10 000). For an ADC threshold value of 1.089 (malignant lesion ADC < 1.089), ROC curve showed a specificity = 80% and a sensitivity = 83.3%. CONCLUSION: Performing diffusion weighted imaging of the spine is easy with new MR technology. The ADC measurement of spine lesion provides important additional information, but does not serve as a substitute for the routine MRI sequences. In the future, it could become an important point in this difficult diagnosis.

Adult↗