Change data probe to view MIP HU


Hi, I’m looking at very small features on CTA scans and there are 2 things I’d like data probe to do but it doesn’t and I’m not sure how to modify it to get the behaviour I want.

  1. When I am in one of the slice viewers, e.g. the red one, and scroll up and down with the mouse wheel or the arrows in a fixed point, data probe does not update the HU nor the position. I have to move the mouse in the viewer for data probe to update. Is there a way to make it update even when the mouse position has not changed but the slice has?

  2. I am visualizing MIP in the slice views with this code, however when I move the mouse around one of the slice viewer, the scalar value that I see in data probe in the left bottom corner is still the HU of the single slice, not the one of the MIP. Is there a way to change this behaviour? (I have attached an example in case it’s not clear: in the screenshot I am looking at a 5 mm MIP. The mouse arrow is not captured but I was pointing at the red slice exactly on the intersection of the yellow and green axes. I’d like data probe to show me the HU of the MIP view, so something around 300, but it shows me the HU of the single slice which is 7)


Thank you for any help,


(James Butler) #2

Hi Marta,

Sorry for not getting a response sooner!

Regarding 1) what you are describing is behavior that is like the same as issue 3262 in Slicer’s issue tracker. I have added a note to that issue specifying with your experience as a way to increase its likelihood of it getting fixed in the future.

Regarding 2) I’m not exactly sure what is going on there. I would point you to using the SimpleFilters module which makes it easy to generate projections and use other volume filters. You would set the output volume to be a new volume, and DataProbe should provide you updated results when you move your mouse position over this output volume.

(Andras Lasso) #3

Since thick slice feature is not exposed on the GUI, we most likely not update the data probe’s behavior for now. However, you can print pixel value of the resliced image by copy-pasting this code snippet into the Python interactor:

def onMouseMoved(observer,eventid):  
  xyz = [0,0,0]
  pixelValue = reslice.GetOutput().GetScalarComponentAsDouble(int(xyz[0]),int(xyz[1]), int(xyz[2]), 0)
  print("{0} -> {1}".format(xyz, pixelValue))

sliceNode = slicer.mrmlScene.GetNodeByID('vtkMRMLSliceNodeRed')
appLogic =
sliceLogic = appLogic.GetSliceLogic(sliceNode)
sliceLayerLogic = sliceLogic.GetBackgroundLayer()
reslice = sliceLayerLogic.GetReslice()

crosshairNode.AddObserver(slicer.vtkMRMLCrosshairNode.CursorPositionModifiedEvent, onMouseMoved)

Why do you need the MIP value?

(James Butler) #4

@mag To provide you with an update, the issue described in 1) I can now confirm is solved thanks to a fix by @lassoan. You can download and install today’s nightly build and it will have that fix.


That’s awesome, thanks so much!


I am extending an existing study and need to determine the location of maximum contrast enhancement in some vascular segments. The way the previous research fellow did it was to look at 5 mm MIP to find the maximum HU on the axial view, then refine the location by scrolling up and down single slices, so I am trying to follow the exact same steps even if with a different software. Once I have the point of interest I create a small spherical segment and get the average HU at that position.