Isao Yanagawa

Neural Basis of the Retrieval of People's Names: Evidence from Brain-Damaged Patients and fMRI

The aim of this study was to identify the neuroanatomical basis of the retrieval of peoples names. Lesion data showed that patients with language-dominant temporal lobectomy had impairments in their ability to retrieve familiar and newly learned peoples names, whereas patients with language-nondominant temporal lobectomy had difficulty retrieving newly learned peoples names. Functional magnetic resonance imaging experiments revealed activations in the left temporal polar region during the retrieval of familiar and newly learned peoples names, and in the right superior temporal and bilateral prefrontal cortices during the retrieval of newly learned information from face cues. These data provide new evidence that the left anterior temporal region is crucial for the retrieval of peoples names irrespective of their familiarity and that the right superior temporal and bilateral prefrontal areas are crucial for the process of associating newly learned peoples faces and names.

Neural Basis of Temporal Context Memory: A Functional MRI Study

Temporal context information is crucial to understanding human episodic memory. Human lesion and neuroimaging data indicate that prefrontal regions are important for retrieving temporal context memory, although the exact nature of their involvement is still unclear. We employed functional magnetic resonance imaging (fMRI) to elucidate the neural basis of two kinds of temporal context memory: the temporal order of items between lists and within a list. On the day of the fMRI experiment, subjects memorized a list of 30 pictures in the morning and another list of 30 pictures in the afternoon. During the scanning session, the subjects performed three tasks. In a between-lists task, they were asked to judge the temporal order between two items that had been presented in different lists. In a within-list task, they were asked to judge the temporal order between two items that had been presented in a single list. We found bilateral prefrontal activities during these two temporal context memory tasks compared with a simple item-recognition task. Furthermore, in direct comparison between these two tasks, we found differential prefrontal activities. Thus, right prefrontal activity was associated with temporal order judgment of items between lists, whereas left prefrontal activity was related to temporal order judgment of items within a list. These results indicate that retrieval processes of two kinds of temporal context memory are supported by different, but overlapping, sets of cerebral regions. We speculate that this reflects different cognitive processes for retrieving temporal context memory between separate episodes and within a single episode.

Brain Activation during the Fist-Edge-Palm Test: A Functional MRI Study

The purpose of our study is to clarify, using functional MRI, brain regions activated during the fist-edge-palm task (FEP) compared to relatively simple hand motor tasks using either the right or the left hand in right-handed normal volunteers. The FEP was introduced to detect a disorder of voluntary movement, and it is believed to be closely related to contralateral frontal lobe damage. However, this assumption still remains controversial. Ten subjects participated in this study. Hand motor tasks were as follows: (1) the FEP, in which the subjects were requested to place their hand in three different positions sequentially: a fist resting horizontally, a palm resting vertically, and a palm resting horizontally; (2) a fist-palm task (FP), in which the subjects were asked to clench and unclench their fist alternately; and (3) a control task requiring the subjects to knock lightly with their clenched fist. The contralateral sensomotor and premotor areas were activated in the FP with the right hand and the contralateral sensorimotor, premotor, and supplementary motor areas (SMA) were activated in the FP with the left hand. In the FEP with either hand, bilateral premotor and left parietal areas and ipsilateral cerebellum were also activated as well as contralateral sensorimotor area and SMA. Our results suggest that successful performance of the FEP requires the participation of more brain areas than FP, which may explain why some patients without frontal lobe damage failed to perform the FEP.

Evaluating the performance of a MOSFET dosimeter at diagnostic X-ray energies for interventional radiology

For reducing the risk of skin injury during interventional radiology (IR) procedures, it has been suggested that physicians track patients’ exposure doses. The metal-oxide semiconductor field effect transistor (MOSFET) dosimeter is designed to measure patient exposure dose during radiotherapy applications at megavoltage photon energies. Our purpose in this study was to evaluate the feasibility of using a MOSFET dosimeter (OneDose system) to measure patients’ skin dose during exposure to diagnostic X-ray energies used in IR. The response of the OneDose system was almost constant at diagnostic X-ray energies, although the sensitivity was higher than that at megavoltage photon energies. We found that the angular dependence was minimal at diagnostic X-ray energies. The OneDose is almost invisible on X-ray images at diagnostic energies. Furthermore, the OneDose is easy to handle. The OneDose sensor performs well at diagnostic X-ray energies, although real-time measurements are not feasible. Thus, the OneDose system may prove useful in measuring patient exposure dose during IR.

Evaluation of large intracranial aneurysm with three-dimensional MRI

Objective The purpose of this study was to evaluate large intracranial aneurysms by contrast-enhanced 3D MRI. Materials and Methods Eleven patients, nine women and two men, were examined. The aneurysms involved the internal carotid artery in seven patients, the middle cerebral artery in one, the basilar artery in two, and the posterior cerebral artery in one. Contrast-enhanced 3D MR images were obtained using FLASH (fast low angle shot) on a 1.5 T system. We obtained axial images first, then sagittal and coronal images by multiplanar reconstruction. Those images were reviewed for comparison with conventional and MR angiography. Results We could easily evaluate the true aneurysmal size, the intraaneurysmal constitution (patent lumen and intraluminal thrombus), and the detailed relationship of the aneurysm to the surrounding vascular and neural structures. Except for the cavernous internal carotid artery, we could identify the aneurysmal neck by carefully observing axial, sagittal, and coronal images. In addition, the progression of intraaneurysmal thrombosis and the patency of the parent arterial lumen after the endovascular treatment were well appreciated. Conclusion We consider that 3D MRI appears to be useful for evaluation of the large intracranial aneurysm.

Comparison of dose at an interventional reference point between the displayed estimated value and measured value

Today, interventional radiology (IR) X-ray units are required for display of doses at an interventional reference point (IRP) for the operator (IR physician). The dose displayed at the IRP (the reference dose) of an X-ray unit has been reported to be helpful for characterizing patient exposure in real time. However, no detailed report has evaluated the accuracy of the reference doses displayed on X-ray equipment. Thus, in this study, we compared the displayed reference dose to the actual measured value in many IR X-ray systems. Although the displayed reference doses of many IR X-ray systems agreed with the measured actual values within approximately 15%, the doses of a few IR units were not close. Furthermore, some X-ray units made in Japan displayed reference doses quite different from the actual measured value, probably because the reference point of these units differs from the International Electrotechnical Commission standard. Thus, IR physicians should pay attention to the location of the IRP of the displayed reference dose in Japan. Furthermore, physicians should be aware of the accuracy of the displayed reference dose of the X-ray system that they use for IR. Thus, regular checks of the displayed reference dose of the X-ray system are important.

Comparison of the radiation dose in a cardiac IVR X-ray system

In this study, the entrance surface dose rates received by a phantom during cineangiography and fluoroscopy were compared. The X-ray conditions used in the measurements were those normally used in facilities performing percutaneous coronary intervention. Although, today, the entrance surface doses (cineangiography and fluoroscopy) of X-ray equipment used for cardiac interventional radiology (IVR) tends to be lower than they were previously, some equipment produces a high radiation dose. Therefore, the X-ray equipment used for cardiac IVR procedures must be maintained in good repair and must be carefully calibrated. In addition, periodic measurement of the radiation dose from the X-ray equipment used for both cineangiography and fluoroscopy for cardiac IVR is necessary. If the radiation dose of the X-ray system in use is too high, the IVR staff should determine the reason and make an effort to reduce it. Hence, the IVR staff must be adequately trained in radiation protection.

Is the MOSFET Dosimeter Feasible at Diagnostic X-Ray Energies for Interventional Radiology?

To reduce the risk of skin injury during interventional radiology (IVR) procedures, it has been suggested that physicians track patients’ dose. However, the patient’s skin dose is very rarely monitored because of the lack of a feasible method for use in IVR. The metal oxide semiconductor field effect transistor (MOSFET) dosimeter is designed to measure patient exposure dose during radiotherapy applications at megavoltage photon energies. Our purpose in this preliminary study was to evaluate the feasibility of using a MOSFET dosimeter to measure patients’ skin dose during exposure to diagnostic X-ray energies used in IVR.