Initially planned to be in Barcelona, due to COVID-19, the International Conference on Acoustics, Speech and Signal Processing ICASSP 2020, the world’s largest and most comprehensive technical conference focused on signal processing and its applications, took place from May 4-8 in a completely virtual environment. It had over 8000 participants which made this year’s event the largest ever ICASSP conference over the past 45 years.

Members of the  CIBM SP EPFL Mathermatical Imaging Section, Prof. Michael Unser and  Dr. Pol del Aguila Pla, presented a three part tutorial (~3 hours) on Biomedical Image Reconstruction :

  • Part I: Imaging as an inverse problem and classical image reconstruction
  • Part II: Sparsity-based image reconstruction
  • Part III: The (deep) learning (r)evolution

See video of the complete tutorial or download the  ICASSP 2020 Biomedical Image Reconstruction Tutorial slides 

About the tutorial

Biomedical imaging plays a key role in medicine and biology. Its range of applications and its impact in research and medical practice have increased steadily during the past 4 decades. Part of the astonishing improvements in image quality and resolution is due to the use of increasingly sophisticated signal-processing techniques. This, in itself, would justify the tutorial. Nonetheless, the field is now transitioning towards the deep-learning era, where disruptive improvements and lack of theoretical background go hand-in-hand. To harness the power of these new techniques without suffering from their pitfalls, a structured understanding of the field is fundamental.

We start the tutorial by presenting the building blocks of an image-reconstruction problem, from the underlying image that lives in function spaces to its observed discrete measurements. Most importantly, we detail the small collection of forward and sampling operators that allow one to model most biomedical imaging problems, including magnetic resonance imaging, bright-field microscopy, structured-illumination microscopy, x-ray computed tomography, and optical diffraction tomography. This leads up to our exposition of 1st-generation methods (e.g., filtered back-projection, Tikhonov regularization), the regimes in which they are most attractive, and how to implement them efficiently.

We then transition to 2nd-generation methods (non-quadratic regularization, sparsity, and compressive sensing) and show how advanced signal processing allows image reconstruction with smaller acquisition times, less invasive procedures, and lower radioactive and irradiation dosage. We expose the foundations of these methods (results in compressed-sensing recovery, representer theorems, infinite-divisible distributions) and the most useful algorithms in imaging (proximal operators, projected gradient descent, alternate-direction method of multipliers), again exemplifying their efficient implementation.

Finally, we present the state of the art in 3rd-generation methods (deep-learning reconstruction of images), categorizing them using the building-block terminology introduced throughout the tutorial. In this manner, we emphasize the links to 1st- and 2nd-generation methods in order to provide intuition and guidelines to devise and understand novel 3rd-generation methods. Furthermore, we state the benefits of each proposal and give cautionary examples of the dangers of overreliance on training data.

About the speakers

Michael Unser is a Professor leading the Biomedical Imaging Group at the Ecole Polytechnique Federale de Lausanne and Head of the CIBM SP EPFL Mathematical Imaging Section.

Pol del Aguila Pla is a Research Staff Scientist at the CIBM SP EPFL Mathematical Imaging Section and a postdoctoral fellow at the Biomedical Imaging Group, EPFL.



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