Progressive topological disorganization of brain network in focal epilepsy.

OBJECTIVE: Increasing evidence has suggested that epilepsy is a network disease. Graph theory is a mathematical tool that allows for the analysis and quantification of the brain network. We aimed to evaluate the influences of duration of epilepsy on the topological organization of brain network in focal epilepsy patients with normal MRI using the graph theoretical analysis based on diffusion tenor imaging. METHODS: We prospectively enrolled 66 patients with focal epilepsy (18/66 patients were newly diagnosed) and 84 healthy subjects. All of the patients with epilepsy had normal MRI on visual inspection. All of the subjects underwent diffusion tensor imaging that was analyzed using graph theory to obtain network measures. RESULTS: The measures of characteristic path length and small-worldness in the patients with focal epilepsy were significantly decreased, even after multiple corrections (P < .01). Moreover, the measures including mean clustering coefficient and global efficiency in the patients with epilepsy had strong tendency to decrease compared to those in healthy subjects (P = .0153 and P = .0138, respectively). When comparing the measures among the patients with newly diagnosed/chronic epilepsy and healthy subjects using ANOVA, the characteristic path length (P = .006), small-worldness (P = .032), and global efficiency (P = .004) were significantly different. In addition, the duration of epilepsy was negatively correlated with global efficiency (r = -.249, P = .0454). CONCLUSIONS: We newly found a progressive topological disorganization of the brain network in focal epilepsy. In addition, we demonstrated disrupted topological organization in focal epilepsy, shifting toward a more random state.

Effective connectivity in temporal lobe epilepsy with hippocampal sclerosis.

OBJECTIVE: We hypothesized that temporal lobe epilepsy (TLE) patients with and without hippocampal sclerosis (HS) showed differences in their limbic networks. This study aimed to evaluate the role of the thalamus in TLE patients with HS. MATERIALS AND METHODS: Twenty-nine TLE patients with HS and 30 controls were enrolled in this study. In addition, we included eight TLE patients without HS as a disease control group. Using whole-brain T1-weighted MRIs, we analyzed the volumes of the limbic structures, including the hippocampus, thalamus, and total cortex, with FreeSurfer 5.1. We also investigated the effective connectivity among these structures using SPSS Amos 21 based on these volumetric measures. Moreover, we quantified correlations between epilepsy duration and the volumes of these structures. RESULTS: There was a statistically significant effective connectivity from the hippocampus to the thalamus in TLE patients with HS. Moreover, the volumes of the left and right thalamus were negatively correlated with epilepsy duration (r=-.42, P=.0315 and r=-.52, P=.0062, respectively). However, neither TLE patients without HS nor normal controls had a significant effective connectivity from the hippocampus to the thalamus. CONCLUSIONS: The limbic networks of TLE patients with and without HS could be different, and the thalamus might play a critical role in TLE patients with HS.

Brain morphology in juvenile myoclonic epilepsy and absence seizures.

OBJECTIVE: We evaluated the differences in brain morphology among patients with juvenile myoclonic epilepsy according to the occurrence of absence seizures. MATERIALS AND METHODS: Twenty-one juvenile myoclonic epilepsy patients with (n = 6) and without (n = 15) absence seizures were enrolled. We analyzed whole-brain T1-weighted magnetic resonance imaging using FreeSurfer 5.1. Measures of cortical morphology, such as thickness, surface area, volume, and curvature, and the volumes of subcortical structures, the cerebellum, and cerebrum, were compared between the groups. Moreover, we quantified correlations between clinical variables and each measures of abnormal brain morphology. RESULTS: Compared to normal controls, patients without absence seizures demonstrated thinning of the cortical thickness in the right hemisphere, including the post-central, lingual, orbitofrontal, and lateral occipital cortex. Compared to normal controls, patients with absence seizures had more widespread thinning of the cortical thickness, including the right post-central, lingual, orbitofrontal, and lateral occipital cortexes as well as the right inferior temporal cortex. Additionally, the volume of cerebellar white matter in patients without absence seizures was significantly smaller than that in normal controls. Patients with absence seizures had a much smaller cerebellar white matter volume than normal controls or patients without absence seizures. Moreover, there was significantly positive correlation between the age of seizure onset and the volume of cerebellar white matter in patients with juvenile myoclonic epilepsy. CONCLUSIONS: We demonstrated that there were significant brain morphology differences in patients with juvenile myoclonic epilepsy according to the presence of absence seizures. These findings support the hypothesis that juvenile myoclonic epilepsy may be a heterogeneous syndrome.

Chemical-shift imaging with large magnetic field inhomogeneity.

A new echo-time-encoded chemical-shift imaging technique applicable to dual-peak spectroscopic imaging with large magnetic field inhomogeneity is proposed and studied. The basic concept and its applications to modest field homogeneity (approximately 3.0 ppm) as well as to relatively large field inhomogeneity (approximately 10.5 ppm) are discussed. Actual pulse sequences are given and some experimental results on human volunteers obtained with a 2.0-T KAIS NMR system are also presented.

NMR angiography of coronary vessels with 2-D planar image scanning.

On the basis of the principles of the time-of-flight method and the 3-D angiogram obtained by the 2-D planar image scanning technique using 90 degrees RF pulses with short repetition time, we have obtained a coronary angiogram around the heart including the coronary arteries and veins. The cine NMR imaging technique is also incorporated in synchronizing ECG R waves to reduce the motion artifact and at the same time to induce the saturation effect on the static samples. Images of the large bulk blood flow corresponding to the heart chamber and descending aorta are further removed by postprocessing. The final 3-D angiogram is then formed by stacking the 2-D images and contrast is further enhanced by the maximum ray tracing algorithm.

Extraction of cardiac and respiratory motion cycles by use of projection data and its applications to NMR imaging.

A technique of extracting cardiac and respiratory motion cycles by use of projection data is proposed and studied. These extracted cardiac and respiratory motion cycles are applied to the cine imaging of heart and motion artifact reduction in abdominal imaging instead of the conventional ECG gating devices. The basic concepts and their applications are discussed. Experimental results on human volunteers obtained with the KAIS 2.0-T whole-body NMR imaging system together with the pulse sequences used for the experiments are presented.

Further improvement of high-speed NMR flow-velocity measurement using a differential phase-encoding technique.

An NMR imaging technique applicable to high-velocity flow imaging is described. By subtraction of two phase images obtained by varying the flow-encoding gradient, it is possible to extract much larger ranges of velocity components. This differential phase-encoding technique is tested by experiments in a phantom as well as a human volunteer.

Some results of high-flow-velocity NMR imaging using selection gradient.

A simple and new flow velocity measurement technique using conventional spin-echo sequence is proposed and its applications to a preclinical result are presented. This technique utilizes the phase velocity encoding effect due to 180 degrees rf and its corresponding selection gradient. This phase encoding and its phase velocity relations have been obtained by numerical solution of the Bloch equation. A flow velocity measurement obtained with a volunteer using this proposed technique indicates close agreement with other previously measured values.

In vitro MR imaging of the resected stomach with a 4.7-T superconducting magnet.

PURPOSE: To study the effects of formalin fixation, signal intensity characteristics of the stomach-wall layers, and findings suggestive of cancerous invasion to the stomach wall in vitro with magnetic resonance (MR) imaging in humans. MATERIALS AND METHODS: MR images of nine specimens of stomach cancer and 29 normal specimens were obtained at 4.7 T; 26 of the normal specimens were fixed in 10% formalin for 2 hours to 187 days before imaging. The field gradient was 10 G/cm; the spatial resolution, 0.1 mm. RESULTS: The mucosal, submucosal, and proper-muscle layers were clearly identifiable. The submucosa of the fresh specimens had the lowest signal intensity of all specimens on both T1- and T2-weighted images (P < .01). No statistical correlation existed between signal intensity and duration of fixation. Tumor invasion was detected in seven of eight specimens with mucosal invasion, all eight specimens with submucosal invasion, and three of six specimens with muscle invasion. CONCLUSION: In vitro MR imaging enabled differentiation of all three layers of the stomach wall, detection of the cancer, and measurement of the depth of invasion.

Proton magnetic resonance spectroscopy (1H-MRS) findings for the brain in patients with liver cirrhosis reflect the hepatic functional reserve.

OBJECTIVE: Proton magnetic resonance spectroscopy (1H-MRS) has been used to assess the metabolic changes in the brain in patients with liver cirrhosis. Decreased myo-inositol and increased glutamine levels were noted to be the most sensitive spectroscopic markers for cirrhotic patients with hepatic encephalopathy (HE). The purpose of this study was to assess how the abnormalities seen on the 1H-MRS of the brain in patients with liver cirrhosis are related to clinical and laboratory parameters. METHODS: In a prospective study, localized 1H-MRS was performed in the basal ganglia and parietal white matter regions in liver cirrhosis patients with (n = 48) and without (n = 52) HE and chronic hepatitis (CH) (n = 15), and in normal controls (n = 20). RESULTS: Among cirrhotic patients, the myo-inositol levels were significantly lower (p < 0.01) and the glutamine levels were higher (p < 0.05) for patients with HE than for those without HE. The myo-inositol and glutamine levels, respectively, were inversely (r = -0.50; p < 0.001) and linearly (r = 0.50; p < 0.001) related to the Child-Pugh score. However, by subgroup analysis of Child-Pugh class C patients, there were no significant differences in the myo-inositol and glutamine levels between cirrhotic patients with (n = 40) and without HE (n = 24). A follow-up study of eight cirrhotic patients with HE showed no significant differences in the myo-inositol and glutamine levels after clinical improvement of HE. CONCLUSIONS: The abnormalities seen on the 1H-MRS of the brain of patients with liver cirrhosis are not likely to reflect the severity of HE or acute alteration in the level of consciousness. Rather, we believe they represent the chronic metabolic derangement of the brain associated with hepatic functional reserve.

Occlusive and reperfused myocardial infarction: detection by using MR imaging with gadolinium polylysine enhancement.

PURPOSE: To assess the capability of gadolinium polylysine-enhanced cardiac magnetic resonance (MR) imaging in depicting normal and ischemic myocardium during occlusion and reperfusion of the left anterior descending artery. MATERIALS AND METHODS: Contrast-enhanced MR images were obtained in 18 cats during 90 minutes each of occlusion and reperfusion. The change in signal intensity (SI) was compared among normal myocardium and central and peripheral ischemic zones. Results were compared with those of 2,3,5-triphenyltetrazolium chloride staining. RESULTS: During occlusion, the ischemic zone lacked enhancement while normal myocardium had gradual enhancement. During reperfusion, the ischemic zone had strong enhancement. In cats with large infarction, the central and peripheral ischemic zones had intermediate and high SI, respectively; in cats with focal or no infarction, the entire ischemic zone had high SI. CONCLUSION: Occlusive and reperfused myocardial infarction can be detected at gadolinium polylysine-enhanced MR imaging by means of differential SI changes in normal myocardium and central and peripheral ischemic zones.

Novel application of breath-hold turbo spin-echo T2 MRI for detection of acute myocardial infarction.

To assess the clinical utility of the breath-hold turbo spin-echo T2-weighted MRI in patients with acute myocardial infarction, the results of MRI were compared with those of electrocardiography, coronary angiography, and thallium-201 single photon emission tomography (SPECT) in 23 patients and 5 healthy volunteers. To compare MRI and thallium-SPECT, the left ventricle was divided into five segments, and the presence of myocardial infarction was determined in each segment. MRI demonstrated an abnormally bright signal in 49 of 140 segments (five segments each from 23 patients and 5 volunteers); thallium-SPECT showed a fixed perfusion defect in 52 segments, for an 85% diagnostic concordance rate. The size of the myocardial infarction measured on MRI corresponded well to that measured on thallium-SPECT (r = .70, P < .01). Breath-hold turbo spin-echo T2 MRI can be used for detection of acute myocardial infarction in conjunction with thallium-SPECT, especially when accurate localization of lesion, increased spatial resolution, and anatomic landmarks are needed.