Imlook4d (http://www.dicom-port.com) is a free Matlab based graphical user interface (GUI) tool useful for static, dynamic and gated PET studies. It supports reading and writing DICOM, Nifti, Analyze, ECAT. The DICOM reader is orders of magnitude faster than the Matlab imaging toolbox. Imlook4d requires no additional Matlab toolboxes.
The main benefit with imlook4d is that it is easily extendable with scripts, accessing exported variables such as the image matrix (4D) and a region-of-interest (ROI) matrix. Scripts are available via a menu in the imlook4d GUI, and can be used to manipulate the image-matrix and ROI data. There is also a menu option to export and import these variables to the Matlab workspace for interactive manipulation, useful for one-off fixes or for script development. There are presently about 30 scripts in categories such as ROI, Matrix, Header info etc. There is also direct export to ImageJ  and import back from ImageJ, thus giving access to all tools available within ImageJ.
Imlook4d has a built in volume-of-interest editor, with a brush tool for quick interactive ROI delineation, and via scripts, different ways of thresholding ROIs from parts of the image. Time activity data is saved to a tab-delimited text file.
The principal-component (PC) based Hotelling filter is an integrated part of the program, which allows for interactive noise reduction without loss of quantitation . A typical work flow for a dynamic data set is to turn on the filter for ROI delineation, and then there is the choice of turning it off for export of time-activity data. Also the PC images can be used to draw ROIs on, which under some circumstances gives enhanced contrast.
Calculation of parametric pharmacokinetic modelling images can be performed interactively, calculated slice by slice as the user scrolls through the volume. Reference models for Patlak, Logan and Averaged Simple Flow Model  applied on 15O-water are implemented, and it is relatively easy to implement other kinetic models. Similarly, scripts have been developed for regional Patlak and Logan models on ROI data.
 Rasband, WS, ImageJ, U. S. National Institutes of Health, Bethesda, Maryland, USA, http://imagej.nih.gov/ij/, 1997-2014
 Axelsson J, Sörensen J, The 2D Hotelling filter - a quantitative noise-reducing principal-component filter for dynamic PET data, with applications in patient dose reduction. BMC Med Phys. 2013 Apr 10;13:1. doi: 10.1186/1756-6649-13-1.
 Yoshida, K, Mullani, N and Gould KL, Coronary Flow and Flow Reserve by PET Simplified for Clinical Applications Using Rubidium-82 or Nitrogen-13-Ammonia, J Nucl Med 1996; 37:1701-1712
Figure 1. The imlook4d GUI with the user SCRIPTS menu selected. The group of ROI scripts was further selected. In the underlying image, a rough ROI is created.