Absolute bioluminescence imaging at the single-cell level with a light signal at the Attowatt level.

Bioluminescence imaging (BLI) demonstrates cellular events as a light signal at the single-cell level using a highly sensitive, cooled CCD camera. However, BLI signals are relative values and thus, images taken on different days or using different equipment cannot be compared directly. We established a reference LED light source that was characteristic of the total flux and light distribution and calibrated the BLI system as an absolute light signal. This calibrated BLI system revealed that the average light signal of beetle luciferase was at an attowatt level per sec at the single cell level.

Light-emitting-diode Lambertian light sources as low-radiant-flux standards applicable to quantitative luminescence-intensity imaging.

Planar-type Lambertian light-emitting diodes (LEDs) with a circular aperture of several tens of µm to a few mm in diameter were developed for use as radiant-flux standard light sources, which have been in strong demand for applications such as quantitative or absolute intensity measurements of weak luminescence from solid-state materials and devices. Via pulse-width modulation, time-averaged emission intensity of the LED devices was controlled linearly to cover a wide dynamic range of about nine orders of magnitude, from 10 µW down to 10 fW. The developed planar LED devices were applied as the radiant-flux standards to quantitative measurements and analyses of photoluminescence (PL) intensity and PL quantum efficiency of a GaAs quantum-well sample. The results demonstrated the utility and applicability of the LED standards in quantitative luminescence-intensity measurements in Lambertian-type low radiant-flux level sources.

Study of the visual evoked magnetic field with the m-sequence technique.

PURPOSE: Multifocally stimulated visual evoked magnetic field (VEF) examination with an m-sequence technique (multifocal VEF; mVEF) was studied, and the neural generators at peaks of mVEF were estimated in the visual cortex. METHODS: Visual field stimulation was generated by a multifocal testing system with use of the m-sequence technique. The stimulation pattern covered a central area extending from 0.6 degrees to 10 degrees in radius outward from the center of four visual-field quadrants. The stimulation pattern was projected onto a screen by a liquid crystal projector. VEFs of 14 healthy adults were recorded with a 160-channel, whole-head-type magnetoencephalography (MEG) system. The output signals of 16 selected MEG sensors covering the occipital region were recorded for each subject with the multifocal testing system, and the second-order responses were calculated. The analyzed response data files were transferred to the MEG system, a single equivalent current dipole (ECD) was estimated to locate the neural generator, and the localization was superimposed onto the corresponding brain magnetic resonance image of the subject. RESULTS: mVEFs showed three peak waves (N75m, P100m, N145m) in 75% of the subjects and two peak waves (N75m, N145m) in 25%. (N, P and m denote negative, positive, and magnetic fields, respectively.) Latencies of the first and the last peak were similar between the two kinds of peak waves. ECD examination showed more than 97% of goodness of fit at all peaks, and the relation between EDCs and the stimulated visual field coincided with a retinotopic organization that fit a cruciform model in all subjects. ECD depths from the occipital pole were similar to the depth expected from the human linear cortical magnification factor model in all subjects. Main neural generators of all mVEF components (N75m, P100m, N145m) were shown in the striate cortex (V1). CONCLUSIONS: Testing the VEF with an m-sequence technique showed stable responses to simultaneous stimulation of four visual-field quadrants. Consistency of correlation of the estimated ECD with the known cortical organization of the primary visual cortex confirmed the reliability of this examination. The three mVEF peaks were thought to derive mainly from V1 activity.

Detecting functional asymmetries through the dipole moment of magnetoencephalography.

To assess the accuracy of magnetoencephalography (MEG) as a tool for quantitative detection of neuronal activity, the dipole moment was estimated at N20m of somatosensory evoked fields (SEFs) produced by median nerve stimulation. Neurologically stable patients were examined twice within 2 weeks. Since the estimated moment values of the two examinations should be essentially the same, we assessed the margin of error for our measurement system. The results showed that a change of more than 5.2 nAm is statistically significant (p=0.05; n=91). The patients were classified as without or with functional asymmetries by measuring the conventional cerebral blood flow (CBF) with single photon emission CT (SPECT), and the dipole moment difference between hemispheres was measured. Hemispheric moment differences were statistically larger for the group with CBF laterality, indicating consistency between conventional CBF results and the moment measurements as a group. Moreover, MEG was able to detect more functional asymmetries than CBF study. The dipole moment provided a reliable quantitative index of cortical response to somatosensory stimulus, and the moment measurement thus holds promise as a clinical tool for direct quantification of cortical response.

Usefulness of somatosensory evoked magnetic field dipole measurements by magnetoencephalography for assessing spinal cord function.

OBJECT: Objective assessment of sensory function disorders is difficult. In the present study, the authors investigated the possibility of assessing cervical myelopathy-induced sensory disorders by using magnetoencephalography (MEG) to measure somatosensory evoked magnetic fields (SSEMFs). METHODS: In 12 patients with cervical myelopathy, SSEMFs were measured before and after surgery by using a 160-channel helmet-type MEG system to stimulate the median nerve, and the intensity and latency of N20m (first response occurring 20 msec after stimulation) were then determined. Additionally, the severity of the sensory disorder was assessed before and after surgery by obtaining sensory scores determined using the Neurosurgical Cervical Spine Scale. Furthermore, in 11 healthy individuals (control group), the intensity and latency of N20m were measured in the same fashion. Analysis of the results showed that the preoperative intensity of N20m in the 12 patients with cervical myelopathy was significantly lower than that demonstrated in the control patients (p < 0.005, Student t-test). In addition, of six patients in whom sensory scores improved postoperatively, there were significant increases in the intensity of N20m (p < 0.005, paired t-test). Furthermore, there was a significant correlation between sensory scores and dipole intensity (p < 0.001, Spearman correlation coefficient by rank test). CONCLUSIONS: Somatosensory evoked magnetic field measurements determined by MEG are useful in objectively and noninvasively assessing sensory disorders caused by cervical myelopathy.

Bioluminescence imaging of dual gene expression at the single-cell level.

Bioluminescence imaging reveals the long-term dynamics of individual gene expression in a single cell. However, methods for simultaneously imaging multiple gene expression patterns have been unknown to date. Here, we constructed a dual-path optical luminescence imaging system using a two-color reporter system and could simultaneously track two gene expression patterns for several days in a single cell.

Spatiotemporal characteristics of MEG and EEG entrainment with photic stimulation in schizophrenia.

We examined the periodic synchronous characteristic response to photic stimulation in schizophrenia using electroencephalography (EEG) and magnetoencephalography (MEG). We tested whether neural synchronization deficits were present in subjects with schizophrenia using photic stimulation to evaluate the frequency entrainment in 18 normal subjects and 19 schizophrenia patients. A conventional vertical-type 160-channel MEG (PQ1160C, Yokogawa Electric Corporation) was used. Photic stimulation was at frequencies from 8 to 10.5 Hz at intervals of 0.5 Hz. There were ten stimuli at each frequency, and each lasted 10 seconds. The power spectrum at each site was based on the international 10/20 derivation. The power spectrum in schizophrenia patients was smaller than that in normal subjects at each site. A gender difference was observed in normal subjects, but not in schizophrenia patients. MEG, like EEG, is an effective method for research on neuropathy of the psyche.

Interictal patterns of cerebral glucose metabolism, perfusion, and magnetic field in mesial temporal lobe epilepsy.

PURPOSE: To characterize the epileptogenic condition of patients with mesial temporal lobe epilepsy, the interictal patterns of glucose metabolism, perfusion, and magnetic field in the temporal lobe were evaluated by using [18F]fluorodeoxyglucose-positron emission tomography, [99mTc]-ethylcysteinate dimer-single photon emission computed tomography, and magnetoencephalography (MEG). METHODS: Twenty-one patients with mesial temporal lobe epilepsy related to hippocampal sclerosis were studied. The ictal-onset area was located by continuous video-EEG monitoring. Quantitative analysis of glucose metabolism and perfusion in the temporal lobe was performed, and the cerebral magnetic field was evaluated to measure the equivalent current dipole (MEG-ECD). RESULTS: Although hypometabolism and hypoperfusion in the temporal lobe were lateralized with the ictal-onset area in 16 (76.2%) and in 11 (52.4%) respectively, they were localized in diverse ways without any coupling. MEG-ECD was distributed in diverse ways unrelated to the ictal-onset area: ipsilateral medial temporal origin in five (23.8%), ipsilateral lateral temporal origin in two (9.5%), ipsilateral mixed (medial and lateral) temporal origin in six (28.6%), bilateral temporal origin in four (19.0%), and contralateral temporal origin in two (9.5%). CONCLUSIONS: MEG-ECD was distributed in varied ways with the disorder and uncoupling of glucose metabolism and perfusion in the temporal lobe. These results may help resolve the clinical controversy over the possibility that the cortical irritative area generating the interictal epileptic discharge is distinct from the ictal-onset area, and also may have some functional implications in identifying different brain compartments in the generation of metabolic signals.