I will do this for the engine example.
If you have slices:
dataimg = Import["ExampleData/CTengine.tiff"]
![enter image description here](http://community.wolfram.com//c/portal/getImageAttachment?filename=ScreenShot2016-04-08at13.10.30.png&userId=48754)
You combine them using Image3D (it does not really depend on the image dimensions of the individual images.
Image3D[dataimg]
![enter image description here](http://community.wolfram.com//c/portal/getImageAttachment?filename=ScreenShot2016-04-08at13.12.05.png&userId=48754)
You can change the box ratios by:
Image3D[dataimg, BoxRatios -> {1, 1, 2}]
![enter image description here](http://community.wolfram.com//c/portal/getImageAttachment?filename=ScreenShot2016-04-08at13.16.40.png&userId=48754)
You can also use
ImageResize[Image3D[dataimg], {300, 300, 150}]
to resize the image.
You will see that this is the same principle for the knee. If you use
Image3DSlices[ExampleData[{"TestImage3D", "MRknee"}]]
you will see the individual slices of the knee. Image3D reconstructs a 3D image from that.
![enter image description here](http://community.wolfram.com//c/portal/getImageAttachment?filename=ScreenShot2016-04-08at13.18.29.png&userId=48754)
Cheers,
Marco