How to create visualisation on medical data?
If you have good working knowledge in Python than you are good for it. D3.js actually has a Python comparable called Bokeh. You question implies a lot of ramifications and does explain fully what you are trying to achieve so let's go by parts.

Some 2D Scientific Plotting Python Libraries:


Matplotlib
ggplot
Bokeh
Chaco
pyQtGraph (This one has some interesting features in volume slicing if it suits you)


Some UI development Python libraries:


PyQt5
PyQt4 (there are significant changes to PyQt5, thus the suggestion)
PySide (also a Qt port)
wxPython


Some Python numerical libraries:


Pandas
Numpy
Scipy
Scikit-learn (You can do some serious data analysis with this)


Using combinations of the above you can build some very powerful software solutions. Any of the UI libraries suggested has spreadsheet widgets. There are libraries to read csv and excel, among others (JSON, HDF5, etc.).

The data problem can be resolved by either building your own randomized data or by using resources on the net like this or this.