Yo Taniguchi

Three-Dimensional Tracking Method of Tissue Motion with Biplane Images

For real-time three-dimensional tissue motion detection using biplane ultrasound images, we investigated the efficiency of a correlation method in which each region of interest (ROI) is divided into sub-regions so small that the deformation in each subregion can be ignored when estimating its motion in and perpendicular to the image planes. The allowed range of displacement perpendicular to the image planes in sensitively estimating tissue motion by cross-correlation was analyzed. In vitro results with a phantom revealed that the velocity component in the image plane could be detected when the perpendicular displacement between two consecutive frames was as small as 0.4 mm. Moreover it was also revealed that the subregion size must be larger than the speckle size. We also performed in vivo experiments on human liver and found that the tissue motion induced by systole was detectable by our cross-correlation method. The obtained results demonstrated the potential usefulness of the proposed method in medical applications, such as an image guide for minimally invasive therapy.

Quantitative Susceptibility Mapping Using the Multiple Dipole-Inversion Combination with k-space Segmentation Method

Quantitative susceptibility mapping (QSM) is a new magnetic resonance imaging (MRI) technique for noninvasively estimating the magnetic susceptibility of biological tissue. Several methods for QSM have been proposed. One of these methods can estimate susceptibility with high accuracy in tissues whose contrast is consistent between magnitude images and susceptibility maps, such as deep gray-matter nuclei. However, the susceptibility of small veins is underestimated and not well depicted by using the above approach, because the contrast of small veins is inconsistent between a magnitude image and a susceptibility map. In order to improve the estimation accuracy and visibility of small veins without streaking artifacts, a method with multiple dipole-inversion combination with k-space segmentation (MUDICK) has been proposed. In the proposed method, k-space was divided into three domains (low-frequency, magic-angle, and high-frequency). The k-space data in low-frequency and magic-angle domains were obtained by L1-norm regularization using structural information of a pre-estimated susceptibility map. The k-space data in high-frequency domain were obtained from the pre-estimated susceptibility map in order to preserve small-vein contrasts. Using numerical simulation and human brain study at 3 Tesla, streaking artifacts and small-vein susceptibility were compared between MUDICK and conventional methods (MEDI and TKD). The numerical simulation and human brain study showed that MUDICK and MEDI had no severe streaking artifacts and MUDICK showed higher contrast and accuracy of susceptibility in small-veins compared to MEDI. These results suggest that MUDICK can improve the accuracy and visibility of susceptibility in small-veins without severe streaking artifacts.

A high-speed MRI simulator using the transition matrix method and periodicity of magnetization

An MRI simulator is a tool for understanding MR phenomena and developing new pulse sequences, which determine picture quality and information included in MR signals. Conventional simulators calculate the Bloch equations approximately to reduce the computation time. This paper presents a technique for solving the equations exactly at high speed and for creating images. The processing time is made practical by using the transition matrix method and the periodicity of the magnetization.