Overview of Automated Image Registration

What is included in the AIR package
What is not included in the AIR package
What is needed to use the AIR package
Where to find more information about the algorithms used

The Automated Image Registration (AIR) package is primarily designed to solve several different registration problems that arise in tomographic data sets:

intrasubject, intramodality registration (e.g., PET to PET or MRI to MRI)
intrasubject, intermodality registration (e.g., PET to MRI)
intersubject registration (e.g. subject to subject or subject to atlas template)

Intrasubject registration of brain images uses a rigid-body model. Intermodality registration has been validated for some (MRI-PET), but not all modalities. Intersubject registration can be performed using any of a variety of linear models to register different subjects to one another or to an atlas template (for example, an averaged brain in "Talairach space"). These less restrictive linear models may also be useful for intrasubject registration of organs that are more deformable than brain or for tracking intrasubject developmental changes over time.

In addition to 3D models, AIR 2.0 also includes homologous 2D deformation models that may be useful in selected circumstances (e.g., single slice fMRI data, pure 2D images, etc.).

Once the registration parameters are known, the AIR package allows the data to be resampled to generate a final image using any of the following interpolation models:

nearest neighbor
trilinear
windowed sinc
mixed linear/windowed sinc
unwindowed sinc

What is included

The AIR package includes automated routines for aligning and reslicing tomographic image data. In addition, a number of utility routines and error checking routines are provided. The routines are invoked as standard UNIX commands and (with one exception) neither expect nor allow user interaction once the command has been issued. In addition, a series of C subroutines which comprise the AIR library are provided. The AIR library can be used to easily incorporate automated image registration into site specific programs adapted to your particular needs.

AIR 2.0 also includes graphical user interfaces for two of the most frequently used programs. These interfaces are written in Tcl/Tk.

The AIR package is distributed only as source code.

What is not included

The AIR package does not provide any graphics or image display capabilities. No file format converters are provided.

What is needed to use the AIR package

UNIX workstation
C compiler
16+ megabytes of RAM
image file format converters
Tcl/Tk (optional)

This package was originally developed on Sun SPARCstations with 16 Mbytes of RAM using the C compiler previously provided by Sun as part of the standard system software. The default image file format is compatible with the ANALYZE format developed at the Mayo Clinic. If you currently use 8 bits/pixel or 16 bits/pixel ANALYZE file format on a Sun SPARCstation equipped with the standard C compiler, have at least 16 Mbytes of RAM, and are familiar with the UNIX operating system, you should be able to install and use the AIR package without additional assistance, even if you know nothing about C programming. However, if any of these conditions is not met, it is likely that you will need the assistance of a C programmer who is familiar with the UNIX operating system.

Tcl/Tk is required to use the graphical user interface (GUI), but all of the functionality of the AIR package can be accessed without the GUI.

Where to find more information about the algorithms used

The information provided here is intended to supplement the information provided in the original publications describing the automated registration methods.