Volume Rendering of Human Hand Anatomy

TL;DR

The paper addresses visualizing complex hand anatomy from MRI by introducing per-tissue transfer-function design for volume rendering. It proposes two TF families, interior-emphasized and fat-emphasized, and uses ray-mesh intersection-based material assignment to avoid staircase artifacts and preserve context. Evaluations on five hand-motion sequences show improved visualization over standard surface and volume rendering, with practical rendering times and modest memory use. The approach enables tunable emphasis of internal anatomy or subcutaneous fat, aiding interpretation and potential FEM debugging.

Abstract

We study the design of transfer functions for volumetric rendering of magnetic resonance imaging (MRI) datasets of human hands. Human hands are anatomically complex, containing various organs within a limited space, which presents challenges for volumetric rendering. We focus on hand musculoskeletal organs because they are volumetrically the largest inside the hand, and most important for the hand's main function, namely manipulation of objects. While volumetric rendering is a mature field, the choice of the transfer function for the different organs is arguably just as important as the choice of the specific volume rendering algorithm; we demonstrate that it significantly influences the clarity and interpretability of the resulting images. We assume that the hand MRI scans have already been segmented into the different organs (bones, muscles, tendons, ligaments, subcutaneous fat, etc.). Our method uses the hand MRI volume data, and the geometry of its inner organs and their known segmentation, to produce high-quality volume rendering images of the hand, and permits fine control over the appearance of each tissue. We contribute two families of transfer functions to emphasize different hand tissues of interest, while preserving the visual context of the hand. We also discuss and reduce artifacts present in standard volume ray-casting of human hands. We evaluate our volumetric rendering on five challenging hand motion sequences. Our experimental results demonstrate that our method improves hand anatomy visualization, compared to standard surface and volume rendering techniques.

Figures (17)

• Figure 1: The classification of transfer functions. © 2022 John Wiley and Sons. Reproduced, with permission, from Ljung et al. Ljung:2016:START-TF.
• Figure 2: Examples of volume rendering from related work. Reprinted with permission.
• Figure 3: Ray-casting. For each pixel, one ray is fired through the volume. The ray is sampled at discrete positions to evaluate the volume-rendering integral.
• Figure 4: Left: Bones and joints of the human hand (Source: Wikimedia Commons). Middle: Muscles of the human hand (Image downloaded from https://commons.wikimedia.org/wiki/File:1121_Intrinsic_Muscles_of_the_Hand.jpg by OpenStax under license CC-BY-4.0). Right: Tendons of the human hand ((C) 2022 Elsevier. Image adapted, with permission, from https://3d4medical.com).
• Figure 5: MRI slices (a) and corresponding mesh geometry (b-f) in the neutral pose.