Volume slicing
Prerequisites
Before starting this lesson, you should be familiar with:
Learning Objectives
After completing this lesson, learners should be able to:
Create slice views of volumetric image data
Master different ways of dealing with anisotropic voxels
Motivation
Volumetric data is intrinsically difficult to visualise, especially on a 2D computer monitor. Various volume rendering techniques, including VR, exist, however for quantitative image inspection, where it is critical to access the gray value of individual voxels, extracting one 2-D slice of a volume is the method of choice. Thus, such volume slicing is implemented in almost all image analysis software packages. A conceptual challenge is that microscopes often produce anisotropic data, where the voxel spacing along the z-axis is typically larger than in the x and y axes. Thus, creating a slice, e.g., in the zy plane needs to be done with special care.
Concept map
Figure
Activities
Create slice views of a 3D image
- Open a 3D image, e.g.,
- Create slice views of the 3D volume in XY, XZ, and YZ planes
- Appreciate and deal with anisotropic voxels sizes
- Optionally also create slice views at non-orthogonal planes
Show activity for:
ImageJ GUI
- Open a 3D image
- Use
Image > Properties
to check for anisotropic voxel sizes- Use
Image > Stacks > Orthogonal views
to view the data in XY, XZ and YZ planes- Understand how the anisotropy is dealt with
- Use
Image > Stacks > Reslice
to resample the data, exploring the below options for dealing with anisotropy
Output spacing
[ ] avoid interpolation
, if this is checked,Output spacing
is ignored- Use the line tool to draw a line ROI and again use
Image > Stacks > Reslice
to resample along this line- Slice the data at arbitrary angles using
Plugins > BigDataViewer > Open Current Image]
Shift-X/Y/Z
: slice along x,y,z.Left button drag
: slice along arbitray planeI
: toggle interpolation
ImageJ Macro
Python Napari
Assessment
Fill in the blanks
- A set of 2D ____ placed on top of each other form a 3D ____.
- An ____ voxel size can cause the image to appear ____ when viewing it at an angle.
- Rendering anisotropic voxels can be done in various ways, such as ____, ____, or ____.
Solution
- 2D slices placed on top of each other from a 3D stack.
- An anisotropic voxel size can cause the image to appear deformed when viewing at a certain angle.
- One can render anisotropic voxels, by (i) isotropic resampling, (ii) just showing them as a square anyway, (iii) showing them as a rectangle.
True or False
- Isotropic image data has voxels of equal XYZ dimensions.
- Slicing is the process of sectioning the data, that has more than two dimensions, along defined axes and dimensions.
- Reslicing is a term used to indicate repeated slicing.
Solution
- True
- True
- False - Typically, the term reslicing refers to resampling volumetric data from a different direction, such that the resulting image stack is a rotated version of the original stack.
Explanations
The word ‘slice’ is often used in different ways. The different ‘layers’ in the z-dimension are referred to as z-slices. Slicing (or subsetting) image data means that part of the image data is selected and ‘sliced out’ to form a new image. This can include selecting one or more dimensions, or just part of a dimension, for example selecting slice 6-12 of the Z-dimension. You can also rotate the data in one of the spatial dimensions and resample the data set to see that data from a different angle, which is sometimes referred to as ‘reslicing’.
Follow-up material
Recommended follow-up modules:
Learn more: