Kazuhiro Takeo

Three-dimensional probabilistic anatomical cranio-cerebral correlation via the international 10–20 system oriented for transcranial functional brain mapping

The recent advent of multichannel near-infrared spectroscopy (NIRS) has expanded its technical potential for human brain mapping. However, NIRS measurement has a technical drawback in that it measures cortical activities from the head surface without anatomical information of the object to be measured. This problem is also found in transcranial magnetic stimulation (TMS) that transcranially activates or inactivates the cortical surface. To overcome this drawback, we examined cranio-cerebral correlation using magnetic resonance imaging (MRI) via the guidance of the international 10-20 system for electrode placement, which had originally been developed for electroencephalography. We projected the 10-20 standard cranial positions over the cerebral cortical surface. After examining the cranio-cerebral correspondence for 17 healthy adults, we normalized the 10-20 cortical projection points of the subjects to the standard Montreal Neurological Institute (MNI) and Talairach stereotactic coordinates and obtained their probabilistic distributions. We also expressed the anatomical structures for the 10-20 cortical projection points probabilistically. Next, we examined the distance between the cortical surface and the head surface along the scalp and created a cortical surface depth map. We found that the locations of 10-20 cortical projection points in the standard MNI or Talairach space could be estimated with an average standard deviation of 8 mm. This study provided an initial step toward establishing a three-dimensional probabilistic anatomical platform that enables intra- and intermodal comparisons of NIRS and TMS brain imaging data.

Multimodal assessment of cortical activation during apple peeling by NIRS and fMRI

An intriguing application of neuroimaging is directly measuring actual human brain activities during daily living. To this end, we investigated cortical activation patterns during apple peeling. We first conducted a pilot study to assess the activation pattern of the whole lateral cortical surface during apple peeling by multichannel near-infrared spectroscopy (NIRS) and detected substantial activation in the prefrontal region in addition to expected activations extending over the motor, premotor and supplementary motor areas. We next examined cortical activation during mock apple peeling by simultaneous measurement using multichannel NIRS and functional magnetic resonance imaging (fMRI) in four subjects. We detected activations extending over the motor, premotor and supplementary motor areas, but not in the prefrontal cortex. Thus, we finally focused on the prefrontal cortex and examined its activation during apple peeling in 12 subjects using a multichannel NIRS. We subsequently found that regional concentrations of oxygenated hemoglobin significantly increased in the measured region, which encompassed portions of the dorsolateral, ventrolateral and frontopolar areas of the prefrontal cortex. The current study demonstrated that apple peeling as practiced in daily life recruited the prefrontal cortex but that such activation might not be detected for less laborious mock apple peeling that can be performed in an fMRI environment. We suggest the importance of cortical study of an everyday task as it is but not as a simplified form; we also suggest the validity of NIRS for this purpose. Studies on everyday tasks may serve as stepping stone toward understanding human activities in terms of cortical activations.

Morphofunctional organization in three patients with unilateral polymicrogyria: Combined use of diffusion tensor imaging and functional magnetic resonance imaging

We examined the fiber organization of the brain in three patients with unilateral polymicrogyria (PMG) using diffusion tensor imaging (DTI) in combination with functional magnetic resonance imaging (fMRI). DTI revealed altered fiber tract architecture in patients with PMG. Long projection fibers, such as the corticospinal tract, were reduced the most, whereas long association fibers were less affected. The diminution of the fiber tracts was relevant to the loss of functionality of the PMG-affected cortex. Our preliminary study suggests that the combination of DTI and fMRI reinforces the clinical assessment of functionality in PMG.

FASCINATE: a pulse sequence for simultaneous acquisition of T2-weighted and fluid-attenuated images.

A pulse sequence that enables simultaneous acquisition of T2‐weighted and fluid‐attenuated images is presented. This sequence is referred to as FASCINATE (Fluid‐Attenuated Scan Combined with Interleaved Non‐ATtEnuation). In this new technique, the inversion pulse of conventional fast fluid‐attenuated inversion recovery (FLAIR) is replaced with a fast spin echo (FSE) acquisition that has an additional 180(y)–90(x) pulse train for driven inversion. By using appropriate scan parameters, the first part of the sequence provides T2‐weighted images and the second part provides fluid‐attenuated images, thus allowing simultaneous acquisition in a single scan time comparable to that of fast FLAIR. FASCINATE was compared with conventional scanning techniques using a normal volunteer and a patient. A signal simulation was also conducted. In the human study, both T2‐weighted and fluid‐attenuated images from FASCINATE showed the same image quality as conventional images, suggesting the potential for this technique to replace the combination of fast FLAIR and T2‐weighted FSE for scan time reduction. Magn Reson Med 51:205–211, 2004.

Magnetization Transfer Contrast and Its Application to Magnetic Resonance Angiography

Magnetization transfer contrast (MTC) has been noted as an important technique for improving image quality of magnetic resonance (MR) angiography. In this chapter, the authors have reviewed the mechanisms of MTC, in particular focusing on the distribution of water in biological tissues. From this study, it was determined that the effect of MTC depends on the difference in water content of the tissues, and also on the differences of composition of the macromolecules contained in each tissue, according to the distribution of free and bound water. In clinical experience of magnetic resonance angiography (MRA) applied to the brain, use of MTC was demonstrated not only to make the outline of cerebral blood vessels much more evident but also to permit visualizing smaller vessels that could not be seen before its application. We are convinced that utilization of MTC can substantially enhance the quality of time-of-flight (TOF) MR angiography of the brain and contribute to its wider clinical uses, even in the instance of medical checkup of asymptomatic intracranial lesions.