Assessment of Tissue Viability in Hyperacute Infarction with Using the Diffusion- and Perfusion-weighted Images

PURPOSE: The presence of a perfusion-diffusion mismatch is a useful indicator for predicting the progression of acute cerebral infarction. However, not all the area of the perfusion-diffusion mismatch progresses to infarction and a large proportion survives with hypoperfusion. The purpose of this study was to assess 1) whether tissue viability can be predicted using quantitative perfusion values and 2) whether there is correlation between the perfusion value and the time that elapsed after the onset of symptoms. MATERIALS AND METHODS: Twenty-two patients with acute infarction in the middle cerebral artery territory within 12 hours after symptom onset were included in this study. We excluded those patients in whom thrombolysis was attempted or the lesion volume was less than 5 mL. Patients without perfusion-diffusion mismatch on the mean transit time (MTT) map were also excluded. We categorized the ischemic lesions into 3 areas: 1) the initial infarction, 2) the area that progressed to infarction, and 3) the hypoperfused but surviving area, based on the initial and follow up diffusion-weighted images and initial mean transit time (MTT) map. We obtained the relative cerebral blood volume (rCBV), the cerebral blood flow (rCBF) and the MTT in each area by comparing to the contralateral normal area. Statistical analysis was performed using one-way ANOVA to test whether there was a difference in perfusion values between each area. The threshold value was calculated between areas 2 and 3 using the receiver operating characteristics curve. We analyzed the correlation between the perfusion values of each area and the time that elapsed after the inset of symptoms. RESULTS: The perfusion values among each region were significantly different on the rCBV, rCBF and MTT maps. Between regions 2 and 3, the rCBV and rCBF maps showed a significant difference (Bonferroni post hoc analysis), but in case of rCBV, the mean perfusion values in each region approached to the normal level and it was difficult to differentiate between the two regions on the rCBV map. The rCBF in the regions 1, 2 and 3 was 0.40, 0.64, and 0.84, respectively. The difference of the threshold values of the rCBF between regions 2 and 3 was 0.75. There was no significant correlation between the time that elapsed after symptom onset and the perfusion values of each region on the rCBV, rCBF and MTT map. CONCLUSION: The perfusion values between the area of the initial infarction, the area that progressed to infarction and the hypoperfused but surviving area showed significant differences. The rCBF was the most useful parameter in differentiating between areas that progressed to infarction and the surviving areas. Quantitative measurement of the perfusion values may have a role in selecting the candidates for thrombolysis after they have suffered hyperacute stroke.

Cortical Involvement of Marchiafava-Bignami Disease: A Case Report

Marchiafava-Bignami disease is a rare complication of chronic alcoholism and this malady typically manifests as callosal lesion. I report here on one patient with Marchiafava-Bignami disease (MBD) who has symmetric restricted diffusion in both lateral-frontal cortices, in addition to the callosal lesion.

Assessment of Tissue Viability Using Diffusion- and Perfusion-Weighted MRI in Hyperacute Stroke

OBJECTIVE: The aim of this study was to investigate the relationship between the diffusion and perfusion parameters in hyperacute infarction, and we wanted to determine the viability threshold for the ischemic penumbra using diffusion- and perfusion-weighted imaging (DWI and PWI, respectively). MATERIALS AND METHODS: Both DWI and PWI were performed within six hours from the onset of symptoms for 12 patients who had suffered from acute stroke. Three regions of interest (ROIs) were identified: ROI 1 was the initial lesion on DWI; ROI 2 was the DWI/PWI mismatch area (the penumbra) that progressed onward to the infarct; and ROI 3 was the mismatch area that recovered to normal on the follow-up scans. The ratios of apparent diffusion coefficient (ADC), the relative cerebral blood volume (rCBV), and the time to peak (TTP) were calculated as the lesions' ROIs divided by the contralateral mirror ROIs, and these values were then correlated with each other. The viability threshold was determined by using the receiver operating characteristic (ROC) curves. RESULTS: For all three ROIs, the ADC ratios had significant linear correlation with the TTP ratios (p < 0.001), but not with the rCBV ratios (p = 0.280). There was no significant difference for the ADC and rCBV ratios within the ROIs. The mean TTP ratio/TTP delay between the penumbras' two ROIs showed a significant statistical difference (p < 0.001). The cutoff value between ROI 2 and ROI 3, as the viability threshold, was a TTP ratio of 1.29 (with a sensitivity and specificity of 86% and 73%, respectively) and a TTP delay of 7.8 sec (with a sensitivity and specificity of 84% and 72%, respectively). CONCLUSION: Determining the viability thresholds for the TTP ratio/delay on the PWI may be helpful for selecting those patients who would benefit from the various therapeutic interventions that can be used during the acute phase of ischemic stroke.

Brain Diffusion Tensor MR Imaging

The development of MR imaging techniques during the past decade has enabled researchers to use MR imaging as a noninvasive tool for evaluating structural and physiologic states in biologic tissues by measuring the diffusion process of water molecules. More recently, diffusion tensor MR imaging (DTI) technique based on the dependency of molecular diffusion on the orientation of white matter fiber tracts has been used to analyze the trajectory, shape, fiber structure, location, topology and connectivity of neuronal fiber pathways in living humans. Numerous efforts have been made by MR physicists, brain scientists, and medical doctors to advance MR techniques and computer-based algorithms which result in more accurate quantification of diffusion tensor and the generation of white matter fiber tract maps and to determine the pathophysiology of brain disease by DTI and useful clinical applications of DTI. In this article, we describe the tensor theory used to characterize molecular diffusion in white matter and a process of measuring tensor elements using diffusion-sensitive MR images to fiber mapping. We then provide review of current literature and some clinical examples that have been published and are on-going.

Acute Necrotizing Encephalopathy: Diffusion MR Imaging and Localized Proton MR Spectroscopic Findings in Two Infants

In this report, we describe the findings of diffusion MR imaging and proton MR spectroscopy in two infants with acute necrotizing encephalopathy in which there was characteristic symmetrical involvement of the thalami. Diffusion MR images of the lesions showed that the observed apparent diffusion coefficient (ADC) decrease was more prominent in the first patient, who had more severe brain damage and a poorer clinical outcome, than in the second. Proton MR spectroscopy detected an increase in the glutamate/glutamine complex and mobile lipids in the first case but only a small increase of lactate in the second. Diffusion MR imaging and proton MR spectroscopy may provide useful information not only for diagnosis but also for estimating the severity and clinical outcome of acute necrotizing encephalopathy.

Acute Cerebral Infarction in a Rabbit Model: Perfusion and Diffusion MR Imaging

PURPOSE: The present study was undertaken to evaluate the usefulness of cerebral diffusion (DWI) and perfusion MR imaging (PWI) in rabbit models with hyperacute cerebral ischemic infarction. MATERIALS AND METHODS: Experimental cerebral infarction were induced by direct injection of mixture of Histoacryl glue, lipiodol, and tungsten powder into the internal cerebral artery of 6 New-Zealand white rabbits, and they underwent conventional T1 and T2 weighted MR imaging, DWI, and PWI within 1 hour after the occlusion of internal cerebral artery. The PWI scan for each rabbit was obtained at the level of lateral ventricle and 1cm cranial to the basal ganglia. By postprocessing using special imaging software, perfusion images including cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) maps were obtained. The detection of infarcted lesion were evaluated on both perfusion maps and DWI. MTT difference time were measured in the perfusion defect lesion and symmetric contralateral normal cerebral hemisphere. RESULTS: In all rabbits, there was no abnormal signal intensity on T2WI. But on DWI, abnormal high signal intensity, suggesting cerebral infarction, were detected in all rabbits. PWI (rCBV, CBF, and MTT map) also showed perfusion defect in all rabbits. In four rabbits, the calculated square of perfusion defect in MTT map is larger than that of CBF map and in two rabbits, the calculated size of perfusion defect in MTT map and CBF map is same. Any rabbits do not show larger perfusion defect on CBF map than MTT map. In comparison between CBF map and DWI, 3 rabbits show larger square of lesion on CBF map than on DWI. The others shows same square of lesion on both technique. The size of lesion shown in 6 MTT map were larger than DWI. In three cases, the size of lesion shown in CBF map is equal to DWI. But these were smaller than MTT map. The calculated square of lesion in CBF map, equal to that of DWI and smaller than MTT map was three. And in one case, the calculated square of perfusion defect in MTT map was largest, and that of DWI was smallest. CONCLUSION: DWI and PWI may be useful in diagnosing hyperacute cerebral ischemic infarction and in evaluating the cerebral hemodynamics in the rabbits.

Diffusion Weighted MR Image of Intracranial Hemorrhage

PURPOSE: To determine changes in the signal intensity of intracerebral hemorrhagic lesions according to the time interval, between the onset of symptoms and MR imaging in the T1-weighted (T1W1), T2-weighted (T2W1) and diffusion-weighted modes. MATERIALS AND METHODS: Thirty-four patients with hemorrhagic stroke who underwent DWI and conventional MRI were involved in this study. Hemorrhagic phase was determined according to the time interval between the onset of symptoms and MR scanning, and was as follows: acute (3 days or less): eight patients); early subacute (7 days or less): ten patients; late subacute (4 weeks or less): seven patients; early chronic (3 months or less) : four patients); and late chronic (more than 3 months): five patients. Using a 1.5T MR imager and the single-shot echo-planar imaging technique, T1-weighted, fast spin-echo T2-weighted, and diffusion-weighted were obtained. In all cases qualitative signal intensity (SI) at the center of a lesion was recorded, and the ratio between this and normal brain parenchyma was calculated. RESULTS: SI at the center of a lesion was found to be iso or high/high/high (T1WI/T2WI/DWI) in five of eight acute-phase cases (interval of 24 hours or less) and low/low/low in the remaining three (interval of 72 hours or less). Other signal intensities were as follows: early subacute phase: high/low/low (all ten cases); late subacute phase: high/high/high (all seven cases); early chronic phase: high/high/high (all four cases); late chronic phase: low/high/low (all five cases). Mean SIRs were as follows: in the five acute-phase cases in which SI was iso or high: 1.42+/-0.78 / 2.58+/-0.84 / 1.35+/-0.08 (T1WI / T2WI / DWI); in the remaining three acute-phase cases: 0.94 +/-0.18 / 0.63+/-0.16 / 0.27+/-0.10; in the early subacute phase, 1.35+/-0.01 / 0.97+/-0.21 / 0.86+/-0.22 in early subacute phase, 1.58+/-0.04 / 1.54+/-0.09 / 1.44+/-0.14; in the early chronic phase: 1.26+/-0.11 / 1.06+/-0.14 / 0.97+/-0.12; and in the late chronic phase: 0.65+/-2.23 / 1.51+/-0.12 / 0.23+/-0.18. CONCLUSION: The DWI findings of intracerebral hemorrhage reflect the findings of T2WI. When interpreting the DWI findings in patients with intracerebral hemorrhage, an understanding of the temporal evolution of this is very helpful.

Measurement of Fractional Anisotropy in Normal Cerebral White Matter and Brain Tumors with Diffusion Tensor Imaging

PURPOSE: The purpose of this study was to measure the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) of normal adult brain tissue and tumors, and to compare the differences. MATERIALS AND METHODS: Eight normal adults and ten patients in whom intracranial tumors had been diagnosed were included. Imaging was performed using a 1.5 T MR unit and a single-shot spin-echo EPI pulse sequence (TR/TE=4024/94 msec, 128 acquisition/256 reconstruction, 23 cm FOV, 5 mm thickness, 2 mm interslice gap, 4 NSA), six different direction gradients (x, y, z, xy, yz, xz), and 2 b-values (0, 1000). Isotropic ADC (D) was obtained from seven images per slice, and fractional anisotropy (FA) was calculated from the isotropic ADC and eigenvalues of three directions. A region of interest was drawn at frontal gray and white matter, periventricular white matter, the corpus callosum, internal capsule, caudate nucleus and center of the tumor mass, and for each region, fractional anisotropy readings were obtained. RESULTS: In normal adults, the findings were as follows: frontal gray matter: D=0.81+/-0.06, FA=0.32+/-0.03; frontal white matter: D=0.79+/-0.04, FA=0.56+/-0.09, periventricular white matter: D=0.77+/-0.02, FA=0.51 +/-0.04; corpus callosum: D=0.79+/-0.07, FA=0.82+/-0.07; internal capsule: D=0.73+/-0.04, FA=0.77+/-0.05; caudate nucleus: D=0.76+/-0.05, FA=0.35+/-0.05. High anisotropy was demonstrated in white matter, especially in the corpus callosum and internal capsule, and the degree of anisotropy was similar in gray and deep gray matter. For most brain tumors, isotropic ADC was similar to that of white matter, but fractional anisotropy was lower. A low-grade astrocytoma showed higher isotropic ADC and lower fractional anisotropy than normal white matter, and at the center of a meningioma, fractional anisotropy was high. CONCLUSION: For the classification of brain tumors and determination of the extent of disease, comparison between the apparent diffusion coefficient and fractional anisotropy is useful.

Diffusion-weighted MR Imaging after Intracranial Tumor Resection

PURPOSE: To evaluate the usefulness of diffusion-weighted imaging after intracranial surgery in patients with intracranial tumors. MATERIALS AND METHODS: Within ten days of intracranial surgery, diffusion-weighted MR images were obtained in 68 patients with intracranial tumors which included meningioma (n=31), glioma (n=21), neurogenic tumor(n=4), hemangiopericytoma (n=3), and in three cases involved metastasis. The signal intensity of the resected margin and adjacent parenchyma was visually assessed on diffusion-weighted images, and the signal intensities on seen T1-and T2-weighted images were also analyzed. In patients with newly developed hyperintense lesions in parenchyma adjacent to the resection sites seen on postoperative T2-weighted images, apparent diffusion coefficients (ADC) were calculated and analyzed on follow-up MR images. RESULTS: Immediate postoperative diffusion-weighted images showed various signal intensities at the resected margins visible on conventional and diffusion-weighted MR images. In 15 patients, newly developed hyperintense lesions adjacent to resected sites were seen on postoperative T2-weighted images. On diffusion-weighted images, nine of these lesions were hyperinteuse and and were shown by follow-up MR imaging to be subject to focal tissue loss and atrophy, and six were isointense but with no sign of tissue loss or atrophy. Among the 15 patients with postoperative lesions near the site of tumorectomy, diffusion-weighted imaging showed that the ADC values of hyperintense lesions were significantly lower than those of isointense lesions (independent sample t-test: p<0.05). CONCLUSION: In patients with intracranial tumors, immediate postoperative diffusion-weighted imaging is useful for differentiating between ischemic tissue damage and vasogenic edema.

Diffusion-Weighted MR Imaging of the Brain Tumors: The Clinical Usefulness

PURPOSE: To evaluate the clinical usefulness of diffusion weighted MR imaging(DWI) in the differential diagnosis of brain tumors. MATERIALS AND METHODS: DWI and conventional MR images of nineteen patients with brain tumors(10 metastatic tumors, 4 high grade gliomas , 4 low grade astrocytomas, one oligodendroglioma)were obtained on 1.5T unit. DWI was obtained using single shot spin echo planar imaging with b-value near 1000. We analyzed the signal intensities of lesions including solid portion, necrotic or cystic portion and peritumoral edema of brain tumors (classified five grades comparison with the signal intensities of brain parenchyma and CSF)and calculate the SIR(signal intensity ratio)of lesions to the contralateral normal brain parenchyma. We analyzed statistically the signal intensities and SIR of tumors using independence T test. RESULTS: In solid portions of tumors, all the metastatic tumors and high grade gliomas showed high signal intensities, but low grade astrocytomas and oligodendroglioma showed iso or slight high signal intensities to the normal brain parenchyma. The SIR of solid portion has positive correlation with malignant potential(metastatic tumors 1.52, high grade gliomas 1.38, low grade astrocytomas 1.16, oligodendroglioma 1.31)(p<0.05). In peritumoral edema where seen in 14 tumors, seven of 10 metastatic tumors and two of 4 high grade gliomas showed iso signal intensities, whereas edemas in other 5 brain tumors showed hyperintense to the normal brain parenchyma. The SIRs of peritumoral edemas in metastatic tumors(1.14) was lower than high grade gliomas(1.31),but statistically insignificant. The SIR of cystic or necrotic portion of brain tumors was 0.63. In non enhancing solid portions, three of six cases showed hyperintense to the adjacent peritumoral edema. CONCLUSION: On DWI, the signal intensities of solid portion has positive correlation with malignant potential, and perilesional edema of brain tumors appear various signal intensities owing to "T2 shine through effect" and the extensiveness of vasogenic edema. Another merit using DWI on the evaluation of brain tumors is to improved better delineation of tumor margins from the adjacent edemas, especially at the non enhancing solid portion of the tumors.