David Lee

YNIMG Journal 2024 Journal Article

Multicompartment imaging of the brain using a comprehensive MR imaging protocol

• James Lo
• Kevin Du
• David Lee
• Chun Zeng
• Jiyo S. Athertya
• Melissa Lou Silva
• Reese Flechner
• Graeme M. Bydder

In this study, we describe a comprehensive 3D magnetic resonance imaging (MRI) protocol designed to assess major tissue and fluid components in the brain. The protocol comprises four different sequences: 1) magnetization transfer prepared Cones (MT-Cones) for two-pool MT modeling to quantify macromolecular content; 2) short-TR adiabatic inversion-recovery prepared Cones (STAIR-Cones) for myelin water imaging; 3) proton-density weighted Cones (PDw-Cones) for total water imaging; and 4) highly T2 weighted Cones (T2w-Cones) for free water imaging. By integrating these techniques, we successfully mapped key brain components—namely macromolecules, myelin water, intra/extracellular water, and free water—in ten healthy volunteers and five patients with multiple sclerosis (MS) using a 3T clinical scanner. Brain macromolecular proton fraction (MMPF), myelin water proton fraction (MWPF), intra/extracellular water proton fraction (IEWPF), and free water proton fraction (FWPF) values were generated in white matter (WM), grey matter (GM), and MS lesions. Excellent repeatability of the protocol was demonstrated with high intra-class correlation coefficient (ICC) values. In MS patients, the MMPF and MWPF values of the lesions and normal-appearing WM (NAWM) were significantly lower than those in normal WM (NWM) in healthy volunteers. Moreover, we observed significantly higher FWPF values in MS lesions compared to those in NWM and NAWM regions. This study demonstrates the capability of our technique to volumetrically map major brain components. The technique may have particular value in providing a comprehensive assessment of neuroinflammatory and neurodegenerative diseases of the brain.

IROS Conference 2021 Conference Paper

Extended Tactile Perception: Vibration Sensing through Tools and Grasped Objects

• Tasbolat Taunyazov
• Luar Shui Song
• Eugene Lim
• Hian-Hian See
• David Lee
• Benjamin C. K. Tee
• Harold Soh

Humans display the remarkable ability to sense the world through tools and other held objects. For example, we are able to pinpoint impact locations on a held rod and tell apart different textures using a rigid probe. In this work, we consider how we can enable robots to have a similar capacity, i. e. , to embody tools and extend perception using standard grasped objects. We propose that vibro-tactile sensing using dynamic tactile sensors on the robot fingers, along with machine learning models, enables robots to decipher contact information that is transmitted as vibrations along rigid objects. This paper reports on extensive experiments using the BioTac micro-vibration sensor and a new event dynamic sensor, the NUSkin, capable of multi-taxel sensing at 4 kHz. We demonstrate that fine localization on a held rod is possible using our approach (with errors less than 1 cm on a 20 cm rod). Next, we show that vibro-tactile perception can lead to reasonable grasp stability prediction during object handover, and accurate food identification using a standard fork. We find that multi-taxel vibro-tactile sensing at a sufficiently high sampling rate (above 2 kHz) led to the best performance across the various tasks and objects. Taken together, our results provide both evidence and guidelines for using vibro-tactile perception to extend tactile perception, which we believe will lead to enhanced competency with tools and better physical human-robot interaction.

TCS Journal 2001 Journal Article

Approximate evaluations of characteristic polynomials of Boolean functions

• David Lee
• Henryk Woźniakowski

AAAI Conference 1994 Short Paper

Quantitative Evaluation of the Exploration Strategies of a Mobile Robot

• David Lee

How should a mobile robot explore its environment in order to build a high-quality world model as efficiently as possible? We address this question through experimentation with a sonar-equipped mobile robot. The robot is taken to be a delivery robot, such as could be used in an office, hospital or home. Its objective is to execute efficient collision-free paths between user-specified locations. A grid-based free-space map is generated for this purpose. This map is derived from a feature-based map, built using techniques similar to those of (Leonard and Durrant-Whyte 1992).