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The stimulus-preceding negativity (SPN) is an event-related potential that reflects emotional and perceptual anticipation. The SPN is characterized by a right hemisphere preponderance in amplitude, and previous studies suggest that activity in the insular cortex might contribute to the amplitude of the SPN. Although the insula might contribute to the SPN's occurrence, the exact role of the insula in the pattern of SPN right hemisphere dominance remains unclear. In the present study, we manipulated task difficulty and brain activation was measured using event-related fMRI, to examine the relationship between insula functioning and the right hemisphere preponderance of the SPN. Twenty-three participants performed a time estimation task, in which they had to press a button when they thought a predetermined time had elapsed. Three seconds after pressing the button, a feedback stimulus was presented, informing subjects as to whether their response was correct, too early, or too late. There were four experimental conditions: easy, moderate, difficult, and no feedback. The fMRI results showed significantly increased activation in the bilateral insular cortex during the pre-feedback anticipation phase, in which the subjects prepare to pay attention to the occurrence of feedback stimuli. In addition, in the Difficult-Easy and Difficult-Moderate contrasts, significantly increased activations of the right anterior insula were demonstrated, suggesting the possibility that this area does underlie the SPN right hemisphere preponderance. Because the right anterior insula is related to awareness of viscerosensory information, the SPN right hemisphere preponderance might itself be related to the awareness of interoceptive information that precedes feedback stimuli.

Aiming at real-time 3-D visualization of organ motion to navigate surgical procedures in MRI-guided surgery, a new 4-D MR imaging technique called "Adaptive 4-D Scan" has been proposed. The technique is designed to acquire a time series of volumetric 3-D images (4-D image) of cyclically moving organ, even in a low-field open-configuration MR scanner. A pre-operative 4-D image is acquired with respiratory phase parameter, which is monitored by using navigator-echo-based real-time tracking of the liver and diaphragm. During operation, the respiratory phase is again monitored in real-time, and a 3-D image, reflecting the current state of the target organ, is extracted from the pre-operative 4-D image and provided to physicians as a pseudo real-time 3-D image. We implemented Adaptive 4-D Scan into a 0.5 Tesla open-configuration clinical MRI system for intervention. Phantom and volunteer studies were performed to assess feasibility of this technique, in terms of image quality, imaging time and position accuracy of the imaged subject. A 4-D image (matrix: 256 x 128 x 10 x 8) of cyclically moving phantom was acquired in 719 s, and RMS position error between the imaged subject and the real subject was 2.3 mm, where the range of motion was 50 mm. 4-D image of the moving liver was also successfully acquired under near clinical condition. In conclusion, the study shows that the proposed method is feasible and has capability to provide real-time dynamic 3-D atlas for surgical navigation.

MRI (magnetic resonance imaging) with 129Xe has gained much attention as a diagnostic methodology because of its affinity for lipids and possible polarization. The quantitative estimation of net detectability and stability of hyperpolarized 129Xe in the dissolved phase in vivo is valuable to the development of clinical applications. The goal of this study was to develop a stable hyperpolarized 129Xe experimental 3T system to statistically analyze the dissolved-phase 129Xe signal in the rat lungs. The polarization of 129Xe with buffer gases at the optical pumping cell was measured under adiabatic fast passage against the temperature of an oven and laser absorption at the cell. The gases were insufflated into the lungs of Sprague-Dawley rats (n = 15, 400-550 g) through an endotracheal tube under spontaneous respiration. Frequency-selective spectroscopy was performed for the gas phase and dissolved phase. We analyzed the 129Xe signal in the dissolved phase to measure the chemical shift, T2*, delay and its ratio in a rat lungs on 3T. The polarizer was able to produce polarized gas (1.1+/-0.47%, 120 cm3) hundreds of times with the laser absorption ratio (25%) kept constant at the cell. The optimal buffer gas ratio of 25-50% rendered the maximum signal in the dissolved phase. Two dominant peaks of 211.8+/-0.9 and 201.1+/-0.6 ppm were observed with a delay of 0.4+/-0.9 and 0.9+/-1.0 s from the gas phase spectra. The ratios of their average signal to that of the gas phase were 5.6+/-5.2% and 4.4+/-4.7%, respectively. The T2* of the air space in the lungs was 2.5+/-0.5 ms, which was 3.8 times shorter than that in a syringe. We developed a hyperpolarized 129Xe experimental system using a 3T MRI scanner that yields sufficient volume and polarization and quantitatively analyzed the dissolved-phase 129Xe signal in the rat lungs.

Abstract: We used functional magnetic resonance imaging to investigate brain activity related to motivational function of informative feedback stimuli in a time estimation task. In that task, subjects pressed a button as a response 3s after a cue stimulus; a visual feedback stimulus was presented 2s after the response. In a true feedback condition, subjects received true information (informative feedback) about their time-estimation performance. In the false feedback condition, the same visual signs were used, but they were presented randomly. Therefore, they were not related to actual performance. In the 20 subjects examined, higher hemodynamic responses were identified in the insular cortex, the thalamus, and the striatum by comparing the true feedback condition to the false feedback condition. The time estimation performance and subjective score on motivation were also markedly higher in the true feedback condition. The anterior insular cortex and striatal regions are known to be involved in motivational and reward processing. Therefore, the hemodynamic responses observed in this study suggest that the motivational function of the feedback information is a crucial factor for behavioral learning; it is considered that the informative feedback might serve as an implicit reward for humans. [Copyright &y& Elsevier]

The advantage of magnetic resonance imaging (MRI)-guided surgery, in which MR images taken during surgery are used to guide the surgery, has been recognized recently. However, there is a problem, due to long imaging time of MRI, that it is difficult to capture the respiratory organ motion. It is often a constraint that the patient must hold his or her breath, especially in the treatment of the abdominal region. Consequently, this paper proposes a method of eliminating this constraint in MRI-guided surgery by real-time monitoring of the movement of the organ involved in the surgery by means of the signal derived from MRI. Specifically, the navigator echo is extracted in imaging during surgery. The movement of the organ involved in surgery is detected on the basis of the change in the calculated projection profile, and the results are presented to the surgeon. In this study, the procedure is built into a 1.5-T clinical MRI system. The feasibility of the proposed system was examined under clinical conditions by evaluating its accuracy and delay in a phantom experiment, and also in an in vivo experiment on the liver of a volunteer. The results are reported in this paper. © 2005 Wiley Periodicals, Inc. Syst Comp Jpn, 37(1): 83–92, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/scj.20186 [ABSTRACT FROM AUTHOR]

Xenon is a promising candidate for an exogenous MRI tracer because of its affinity for lipids and possible polarization. The estimation of net detectability of dissolved phase xenon in vivo is important for a development of diagnostic applications. The purposes of this study were to develop a hyperpolarized 129Xe experiment system on 3-T and to measure dissolved phase signal in a rat lung. The 129Xe gas was polarized using the optical pumping technique, was manually insufflated to male Sprague–Dawley rat under spontaneous respiration anesthetized by intraperitoneal injection of urethane (1 mg/g), and was measured in a rat lung by frequency selective spectroscopy. A full fractional optimum experiment of two-factor (flip angle, TR) and three-level (30°, 60°, 90°, 600, 1000, 1400 ms) was designed for SNR. A flip angle (∼60°) with 1 s TR made maximum signal in dissolved phase dynamic spectroscopy. Two dominant peaks of 212 for RBC and 201 ppm for tissue were observed, and their average signal ratio to that of gas was 5.6% and 4.4%, respectively. We have developed a hyperpolarized 129Xe experiment system, which could yield enough amount and polarization for dynamic analysis in a rat lung using the 3-T MRI system. [Copyright &y& Elsevier]