Estimation of phase signal change in neuronal current MRI for evoke response of tactile detection with realistic somatosensory laminar network model

Magnetic field generated by neuronal activity could alter magnetic resonance imaging (MRI) signals but detection of such signal is under debate. Previous researches proposed that magnitude signal change is below current detectable level, but phase signal change (PSC) may be measurable with current MRI systems. Optimal imaging parameters like echo time, voxel size and external field direction, could increase the probability of detection of this small signal change. We simulate a voxel of cortical column to determine effect of such parameters on PSC signal. We extended a laminar network model for somatosensory cortex to find neuronal current in each segment of pyramidal neurons (PN). 60,000 PNs of simulated network were positioned randomly in a voxel. Biot–savart law applied to calculate neuronal magnetic field and additional phase. The procedure repeated for eleven neuronal arrangements in the voxel. PSC signal variation with the echo time and voxel size was assessed. The simulated results show that PSC signal increases with echo time, especially 100/80 ms after stimulus for gradient echo/spin echo sequence. It can be up to 0.1 mrad for echo time = 175 ms and voxel size = 1.48 × 1.48 × 2.18 mm³. With echo time less than 25 ms after stimulus, it was just acquired effects of physiological noise on PSC signal. The absolute value of the signal increased with decrease of voxel size, but its components had complex variation. External field orthogonal to local surface of cortex maximizes the signal. Expected PSC signal for tactile detection in the somatosensory cortex increase with echo time and have no oscillation.     

Head trauma

Computed tomography is currently the modality of choice in imaging acutely traumatized patients. This is based upon CT's documented ability to detect surgically significant lesions. Furthermore, the use of MRI is limited by a lack of bone detail, the degradation of MR images in frequently uncooperative patients, and a limited supply of nonferromagnetic monitoring equipments. CT and MRI are largely equivalent in their ability to diagnose epidural hematoma, but CT is readily available and quick. MRI provides information in addition to that obtained by CT in many instances, such as subacute and chronic subdural hematomas, contusions, and intracerebral hematomas.     

Hemodynamic and neurohumoral effects of ketanserin, a 5-HT2 receptor antagonist in patients with congestive heart failure

Ketanserin, a recently developed 5-HT2 receptor antagonist, competitively and selectively blocks the vasoconstrictor activity of 5-hydroxytryptamine (serotonin). We explored a possible contribution of serotonin to augmented vascular tone in patients with severe heart failure, using intravenous and oral formulations of ketanserin. When administered intravenously (10 mg bolus, 4 mg/hr infusion for +/- 40 min) to 10 patients with congestive heart failure (NYHA III or IV) secondary to congestive cardiomyopathy (n = 8) or ischemic heart disease (n = 2), the drug produced a significant increase in cardiac output (rest 24%, p less than 0.001; exercise 19%, p less than 0.01) which was accompanied by a fall in systemic arterial pressure (rest 7%, p less than 0.001; exercise 10%, p less than 0.05) and pulmonary wedge (rest 17%, p less than 0.05; exercise 23%, p less than 0.001) pressure. Calculated systemic vascular resistance (SVR, rest 27%, p less than 0.001; exercise 23%, p less than 0.05) decreased significantly. No significant hemodynamic changes were observed when 40 mg of ketanserin was administered orally to the same group of patients. Plasma catecholamines (norepinephrine, NEP:epinephrine, EP:dopamine) were measured before and after ketanserin at rest and during exercise. Baseline NEP levels were markedly elevated at rest and during exercise in all patients (rest: 878 +/- 381 ng/mL, exercise: 1453 +/- 697 ng/mL). Baseline EP levels were within normal limits. Ketanserin did not produce any change in catecholamine concentration.(ABSTRACT TRUNCATED AT 250 WORDS)     

MR imaging of neurocysticercosis

Magnetic resonance (MR) was performed in 50 patients with neurocysticercosis. Comparison was made with other neuroradiological imaging modalities including CT, myelography, CT ventriculography, and CT myelocisternography. Eighteen patients were found to have intraventricular cysts. In several patients, these were multiple and 22 intraventricular cysts were discovered. Although 4 of the 22 ventricular cysts were missed by MR, T1-weighted images can play a significant role in the early detection of intraventricular cysticercosis cysts, showing the cyst wall (9 of 22), a high intensity mural nodule (6 of 22), and increased signal intensity of the cyst fluid (5 of 22). Cisternal cysts (14 cysts in 10 patients) could be identified; they appear similar to intraventricular cysts, but mural nodules are infrequently seen (1 of 14). Twenty-nine patients had 69 parenchymal cysts. An attempt was made to assess the viability of these parenchymal lesions by matching the CT and MR findings with the Escobar pathologic staging system. Neuroimaging findings seemed compatible with early parenchymal lesions in the vesicular stage in 11 instances. Findings in cases with later stage cysts tend to support the concept that a dying larva provokes pronounced inflammatory reaction in the adjacent brain. Computed tomography remains the superior modality for depicting parenchymal calcifications within dead larvae. A case of a spinal cysticercosis cyst demonstrated with MR (in a patient with extensive intracranial cisternal cysts and a fourth ventricular cyst) is described.     

Distinct effects of surgical denervation on hepatic perfusion, bowel ischemia, and oxidative stress in brain dead and living donor porcine models.

The liver function and perfusion following brain death is mainly influenced by the sympathetic nerves and hormones. We examined the specific influence of surgical liver denervation on systemic and hepatic perfusion parameters, bowel ischemia and oxidative stress in hemodynamically stable BD and control (living donor [LD]) pigs. Brain death was induced in 8 pigs via saline infusion into the balloon of an epidural Tieman-catheter (1 mL/15 minutes) and compared to the control group (n = 6) over 4 hours. At 2 hours postoperatively, complete liver denervation was initiated. We analyzed systemic cardiocirculatory parameters (mean arterial pressure, aortic flow, bowel ischemia (endotoxin, and endotoxin-neutralizing capacity) and oxidative stress (total glutathione in erythrocytes [tGSH(E)]) and compared them to local/hepatic perfusion parameters (hepatic artery and portal venous flow, liver blood flow index, and microperfusion), local bowel ischemia (intramucosal pH [pHi] of stomach [pHi(S)]/colon[pHi(C)]), and liver oxidative stress (glutathione [rGSH(L), GSSG(L)]). Following brain death, the parameters including mean arterial pressure, aortic flow, pHi, endotoxin, and tGSH(E) showed no significant changes at 2 hours. Portal venous flow and microperfusion were decreased significantly and hepatic arterial buffer response was ineffective. Hepatic oxidative stress was increased in BD animals (decrease rGSH(L), increase GSSG(L)). Surgical denervation/manipulation increased portal venous flow significantly, hepatic arterial buffer response became effective, and stomach pHi decreased (BD and LD groups). Hepatic oxidative stress was reduced in the BD group (increase rGSH(L)/GSSG(L); P < 0.001) while it was increased in the LD group (decrease rGSH(L)/GSSG(L); P < 0.001). In conclusion, denervation reduces hepatic oxidative stress in BD only in contrast to the LD. The reciprocal effect of denervation depends on the state of neural activation and postulates a potential benefit of surgical denervation before organ harvesting in brain death.     

The comparative evaluation of uterine and cervical mucosa cytology with endometrial histopathology in cows

Reproductive tract abnormalities especially in the uterus and ovaries of cows often results in infertility. The object of this study was to determine the relationship between the cytology of uterine and cervical mucosa and endometrial histopathology in normal and endometritic cows. In this study, the genital tracts of 131 slaughtered cows were collected. According to macroscopic appearances and histopathological evaluation, reproductive tracts were divided into normal and abnormal. Cytological samples were obtained from the discharges of cervical mucosa and uterine fluid that were collected by wet cotton swab and gentle aspiration. Differential cellular counts were carried on Giemsa stained smears of the mucosa. Comparison of cell densities of normal cows with endometritic cows showed significant differences (P<0.05) in the macrophage presence both by swab (0.00±0.00) and aspiration (0.16±0.55) methods. Comparison of cell densities in different grades of endometritis showed a significant difference (P<0.05) in the neutrophil percentage in cervical mucosa between the swabbing and aspiration methods. In this study, there were no significant differences in cell densities between the two collection methods in cows affected with either acute or chronic endometritis. However, there was significant difference in the neutrophil density in aspirated cervical mucosa compared to the swab collection in cows affected with subacute endometritis. Cytological methods can be useful for the diagnosis of clinical and subclinical endometritis of cows.