Mikio Suga

Measurement of in vivo local shear modulus using MR elastography multiple-phase patchwork offsets

Magnetic resonance elastography (MRE) is a method that can visualize the propagating and standing shear waves in an object being measured. The quantitative value of a shear modulus can be calculated by estimating the local shear wavelength. Low-frequency mechanical motion must be used for soft, tissue-like objects because a propagating shear wave rapidly attenuates at a higher frequency. Moreover, a propagating shear wave is distorted by reflections from the boundaries of objects. However, the distortions are minimal around the wave front of the propagating shear wave. Therefore, we can avoid the effect of reflection on a region of interest (ROI) by adjusting the duration of mechanical vibrations. Thus, the ROI is often shorter than the propagating shear wavelength. In the MRE sequence, a motion-sensitizing gradient (MSG) is synchronized with mechanical cyclic motion. MRE images with multiple initial phase offsets can be generated with increasing delays between the MSG and mechanical vibrations. This paper proposes a method for measuring the local shear wavelength using MRE multiple initial phase patchwork offsets that can be used when the size of the object being measured is shorter than the local wavelength. To confirm the reliability of the proposed method, computer simulations, a simulated tissue study and in vitro and in vivo studies were performed.

Keyhole method for high-speed human cardiac cine MR imaging.

Although electrocardiographic (ECG)‐gated magnetic resonance (MR) imaging is widely used for cardiac imaging, it has several disadvantages, such as long imaging time, respiratory artifacts, and motion artifacts induced by arrhythmia. An MR image can be acquired within about 0.3 seconds by using a fast gradient‐echo imaging method. When this method is continuously applied, only two to three images can be obtained during a single cardiac cycle. The goal of this study is to obtain cine MR images in a single cardiac cycle using fast gradient‐echo imaging combined with the “keyhole” method. The optimal conditions for the keyhole method for cardiac cine imaging were obtained by computer simulation based on a simplified cardiac model. When the read‐out direction was set parallel to the cardiac short axis, left ventricular motion was almost correctly reproduced by the keyhole method with acquisition time reduced to one‐fourth. J. Magn. Reson. Imaging 1999;10:778–783.

Development of a magnetic resonance elastic microscope system

Magnetic resonance elastography (MRE) is a method that can visualize the propagating acoustic strain waves in elastic materials under mechanical excitation. The local quantitative values of shear modulus are derived from the acquired data. The MRE could improve early detection of pathology because it is known that malignant tumors tend to be much harder than normal tissues and most benign tumors. In order to observe tissues such as the early stage of tumors in mouse embryo, spatial resolution of the MRE image is not enough because of hardware limitation of the conventional MRI system. We developed the elasticity measurement system using the MR microscope which spatial resolution is about 200 mm. The external vibration system and MR pulse sequences are developed for an MR elastic microscope. Experiments were performed with homogeneous and heterogeneous agarose gel phantoms. These results suggest the developed MR elastic microscope system makes it possible to generate image that depict distribution of stiffness.

A measurement system for the behavior of children with developmental disorder using an omnidirectional camera

In the evaluation of children with developmental disorder, such as autism and learning disabilities (LD), an interview and behavior observation by a doctor or a clinical psychologist, as well as the hearing or behavior checklist completed by the parent or classroom teacher, are employed. Those, however, cannot be quantitative, and it is difficult to analyze in detail the long-term observation or effectiveness of education or therapy. From such a viewpoint, it is desired to establish a method that can measure the behavior of the child on a more objective and quantitative basis. As a means of behavior measurement, the child may carry a transmitter or a marker, but a child with a developmental disorder often rejects an instrument that directly touches the body, which makes the application difficult. A wide-angle camera may be employed, but its use is not simple, such as the need for calibration at the site of installation. In this study, a noncontact behavior measurement system is constructed, in which an omnidirectional camera with a hyperbolic mirror is used to determine the spatial position of the child in an objective and quantitative way. Using the constructed system, the behavior of the child with a developmental disorder is examined, and characteristic patterns are observed. It is concluded that the result of such a measurement can be a useful index in the evaluation of the observation of the course of the child with a developmental disorder, as well as in the evaluation of the effectiveness of education or therapy.

Integration and immersive presentation of various head information

This paper describes the measurement of various head images and the presentation of integrated images on an immersive projection system (IPS). We handled optical and magnetic methods to obtain the information about face, head, brain and blood vessels. The system enables one to observe the inside of a head interactively using a joystick, which gives the impression of travelling in a human head freely. It is thought that the integrated images are available not only for diagnosis but also treatment of brains in the future by robot surgical operation with a manipulator or a micro-machining device.