SIRF-Exercises

This material is intended for practical demonstrations using SIRF on PET and MR Image Reconstruction.

This repository contains exercises to get you going with SIRF. Please check the INSTALL.md first. There is also some basic information on CIL functionality to show similarities with SIRF.

Authors:

• Kris Thielemans (this document and PET exercises)
• Christoph Kolbitsch (MR exercises)
• Johannes Mayer (MR exercises)
• David Atkinson (MR exercises)
• Evgueni Ovtchinnikov (PET and MR exercises)
• Edoardo Pasca (overall check and clean-up)
• Richard Brown (PET and registration exercises)
• Daniel Deidda and Palak Wadhwa (HKEM exercise)
• Ashley Gillman (overall check and clean-up)

This software is distributed under an open source license, see LICENSE.txt for details.

Gentle request

If you are attending the course, please read this before the course. A brief summary of the steps to get started is in our documentation for participants.

Introduction

The SIRF documentation can be found here. The current version of these exercises needs SIRF v3.0.0

We are using Python for the exercises. Python is an open-source interactive language, a bit like MATLAB. We provide Python scripts for the exercises, so you should be fine. Nevertheless, it would be best to read a Python tutorial first, see the Appendices.

We use Jupyter notebooks. If you have never used Jupyter notebooks, you could read the official documentation. A useful introduction to the notebook interface can be found here.

The rest of this document contains some information to get started.

Getting started

Some exercises use data that you will need. Check the installation instructions.

The MR exercises will need you to start a Gadgetron server. If you have installed SIRF properly, you should be able to type in a terminal

gadgetron

You can kill it at the end by going back to the terminal and pressing Ctrl-C.

Starting the jupyter server

To start with the exercises, you need to start the jupyter server. Depending on how/where you run these exercises, this will be in different ways:

On the VM using the web browser of your host system (recommended)

In the VM terminal, type

  jupyter notebook

You will get a message that ends Or copy and paste one of these URLs: http://(vagrant or 127.0.0.1):8888/?token=axxxxcf837a4ab78aa13275dc893af9b91143225c226xxxx

On your laptop/desktop, open a web-browser and use the full address from the message (including the token=... part). You will need to edit the (vagrant or 127.0.0.1) to 127.0.0.1. Alternatively, use the address http://localhost:8888 and then when requested, copy and paste the token value, which in this example would be axxxxcf837a4ab78aa13275dc893af9b91143225c226xxxx.

On the VM using a web browser in the VM

You will need to install a web browser on the VM such as Firefox.

   sudo apt install firefox

Now do

   jupyter notebook --browser firefox

which should start your web-browser automatically.

You have installed SIRF and the exercises yourself

You have a jupyter server (as you followed the installation instructions so just use

   cd /wherever/you/installed/it/SIRF-Exercises
   jupyter notebook

Using the notebooks

The initial web-page that you will see looks like a file browser (the Jupyter Notebook dashboard). Click on notebooks, and drill down until you find a file with the extension .ipynb that looks of interest, and click on that. This should open a new tab in your web browser with the notebook open, all ready to run.

You will normally work by executing each cell bit by bit, and then editing it to do some more work. Useful shortcuts:

• LEFT-CTRL + <RETURN> executes the current cell.
• SHIFT + <RETURN> executes the current cell and advances the cursor to the next cell.
• TAB tries to complete the word/command you have just typed.

Jupyter notebooks (normally) run iPython, see the section below for some useful commands.

Check the jupyter doc on closing a notebook. (Note: it is not just closing the browser tab).

Warning: Due to a limitation in SIRF (and ISMRMRD) you cannot have 2 Python sessions simultaneously accessing the same MR HDF5 file. You have to use “File->Close and halt” after you’ve finished with a notebook (or just “Kernel->Shutdown”).

Appendices

File extensions

• .dat: Siemens raw MR data file
• .h5: HDF5 file with MR data or images
• .hv: Interfile header for an image (volume)
• .ahv: (ignore) old-style Interfile header for an image
• .v: raw data of an image (in floats)
• .hs: Interfile header for PET acquisition data (sinograms)
• .s: raw data of PET acquisition data (in floats)
• .py: Python file
• .ipynb: jupyter notebook
• .par: STIR parameter files.
• .md: text file with documentation (in Markdown format)

A note on keyboard short-cuts inside a VirtualBox VM

On Windows and Linux, VirtualBox sets the "host-key" by default to Right-CTRL on Windows/Linux, so unless you change this, you have to use Left-CTRL to "send" the CTRL-keystroke to the Virtual Machine. So, below we will always type Left-CTRL.

Linux Terminal

If you have never used a Linux/Unix terminal before, have a look at a tutorial.

You can use UPARROW to go to previous commands, and use copy-paste shortcuts Left-CTRL-SHIFT-C and Left-CTRL-SHIFT-V.

Python

Here is some suggested material on Python (ordered from easy to quite time-consuming).

• The official Python tutorial. Just read Section 1, 3, a bit of 4 and a tiny bit of 6. https://docs.python.org/2/tutorial/

• Examples for matplotlib, the python module that allows you to make plots almost like in MATLAB https://github.com/patvarilly/dihub-python-for-data-scientists-2015/blob/master/notebooks/02_Matplotlib.ipynb

• You could read bits and pieces of Python the Hard Way http://learnpythonthehardway.org/book/index.html

• Google has an online class on Python for those who know some programming. This goes quite in depth and covers 2 days. https://developers.google.com/edu/python/?csw=1

One thing which might surprise you that in Python indentation is important. You would write for instance

for z in range(0,image.shape[0]):
   plt.figure()
   plt.imshow(image[z,:,:])
# now do something else

We use matplotlib, a python module that allows you to make plots almost like in MATLAB. Check here for some examples.

iPython

The jupyter notebooks will normally be running iPython, although this depends a bit on your configuration. iPython is Python with a few extensions to make the experience a bit friendlier.

Here are some useful iPython "magic" commands that you can use in the iPython console on the right (but not in the scripts). Most of these are identical to what you would use in the terminal. (Note: these commands do not work in a Python console.)

• change how figures appear

  • separate figures

  %matplotlib
  

  • inline with other output

  %matplotlib inline
  

  • inline in the notebook but with extra options for the figures (required for animations)

   %matplotlib notebook
  

• change to a new directory

    cd some_dir/another_subdir

• change back 2 levels up

    cd ../..

• print current working directory

    pwd

• list files in current directory

    ls *.hs

• Running system commands from the iPython prompt can be done via an exclamation mark

    !FBP2D FBP.par

• Get rid of everything in memory

    %reset