PET Images Adjustable Window Level in MPR

[Michael-Andersen]

I noticed using the OHIF Viewer that PET images in 2DMPR mode can't have their window level changed (using the WWWC tool) like CT images can. After some investigation I found that because the range of window width and window center is much smaller with PET then CT the rounding that takes place effectively makes changes impossible.

publicAPI.windowLevelFromMouse = pos => {  
const range = model.volumeActor  
  .getMapper()  
  .getInputData()  
  .getPointData()  
  .getScalars()  
  .getRange();  
const imageDynamicRange = range[1] - range[0];  
const multiplier =  
  Math.round(imageDynamicRange / 1024) * publicAPI.getLevelScale();  
const dx = Math.round((pos[0] - model.wlStartPos[0]) * multiplier);  
const dy = Math.round((pos[1] - model.wlStartPos[1]) * multiplier);  
let windowWidth = model.levels.windowWidth + dx;  
let windowCenter = model.levels.windowCenter - dy; 

from vtkInteractorStyleMPRWindowLevel.js

For PET the multiplier gets rounded to 0 and leaves dx and dy as 0 as well. For reasonable changes to take place in the levels in PET we want dx and dy values between -1 and 1. If I remove all three Math.round calls then I can adjust the window level for both PET and CT with no issues.

If others agree that the rounding here is unnecessary I'd be happy to make a PR to address this. I'm open to other solutions to this issue as well.