Wave propogation research applied to the diagnosis and monitoring of patients
Cancers are complex and evolving multi-scale systems, characterised by profound spatial and temporal heterogeneity. In this context, imaging plays an essential role in the description of tumours and in the monitoring of their evolution.
This program, in partnership with the Higher School of Industrial Physics and Chemistry (ESPCI - Langevin Institute), proposes the use of recent innovations in physics applied to imaging. Several approaches are being developed:
- Improve existing ultrasound imaging by adding new parameters such as elastography and ultrafast vascular imaging
- Develop optical imaging methods for the analysis of tissue samples
- Develop new diagnostic imaging methods coupling optics and ultrasound
Review and characterise biological tissues in a non-invasive way
A) Elastography 2D / 3D : a "palpation imaging"
Project coordinated by Drs Mickaël Tanter (Inserm / ESPCI), Jean-Luc Gennisson (ESPCI) and Delphine Sebbag-Sfez (IC), Anne Tardivon (IC) and Anne Vincent-Salomon (IC)
Elastography is to apply a mechanical or vibratory force to tissue in order to understand its rigidity. The majority of malignant tumours are much more rigid than the healthy tissue and deforms less in response to compression. Through this technique, it is possible to make an ultrasound "palpation" of lesions even when they are located deep in an organ.
The original method of ultrasound elastography developed by the teams of the Langevin Institute uses shear waves associated with ultra-fast imaging allowing direct quantification of tissue hardness. An early collaboration between physicists and radiologists enabled clinical validation of this imaging method in 3 dimensions. It also enabled the demonstration of its added value for breast cancer diagnosis.
The current project focuses on the clinical validation of an exploration of tumours by elastography in 3 dimensions during treatment with chemotherapy, compared to histological response. Changes in the tumour elasticity could indeed be an early non-invasive biomarker of response to treatment. In parallel, a clinical evaluation of the development of ultra-fast vascular imaging will be performed. This new imaging technique gives vascular information with 50 times the sensitivity compared to conventional ultrasound.
B) Acousto-optical imaging : characterisation of tissue with submillimetre resolution
Project coordinated by Drs François Ramaz (ESPCI), Jean-Luc Gennisson (ESPCI), Jean-Baptiste Landereau, Vincent Servois (IC) and Pascale Mariani (IC)
The speckle effect (laser speckle) is the set of rapidly fluctuating small spots that appear in the instant texture of an image and give it a grainy appearance. They are due to either broadcasting waves of a spatially coherent light beam (originated from a laser for example) by a target having irregularities on the scale of the wavelength, or the spread of a coherent beam in an atmosphere characterized by random refractive index variations.
The acoustic wave locally shakes the tissue and creates a change in the speckle. Progress has been made recently on the detection of this effect. Achieving the recording of these changes would save the optical variations in depth.
The current objective of the project is to develop a clinical diagnostic tool, based on the coupling of the two methods - optical and acoustic – and allowing tissue in-depth analysis. This tool will then be tested on a model of liver metastases from uveal melanoma.
C) Optical imaging: full field optical tomography (FF-OCT)
Project coordinated by Prof Claude Boccara (ESPCI) and Drs Eugenie Dalimier (LLTech), Brigitte Sigal (IC), Anne-Thérèse Nadan (IC), Jean-Marc Guinebretière (IC), and Vincent Servois (IC)
Optical imaging is used in various fields of cancer: tumour imaging in small animals, pathological and clinical imaging in humans (e.g. deep imaging of the skin or mucous membranes), imaging of transparent tissues such as eye or endoscopic procedures (e.g. cystoscopy and bronchoscopy).
In the near future, we expect that optical imaging will play a major role in the analysis or preoperative or percutaneous biopsies. But diagnostic failures from percutaneous image-guided biopsies still persist today. The main problems are the anatomical location of the tumour, its size and its characteristics (abundance of fibrosis or tumour necrosis).
Histological evaluation in real time of tissue fragments obtained by percutaneous image guided procedures is not common practice. It would require the presence of a pathologist in the medical imaging services which is hardly conceivable. Today, the development of personalised treatment induced a significant increase in the number of percutaneous biopsies at tumour lesions reworked by previous treatments. The development of alternative and rapid methods before conventional pathological examination without distorting the biopsy sample is becoming a necessity.
The optical coherence tomography (Optical Coherence Tomography: OCT) by interferometric selection ballistic photons, appears as an original imaging technique for the analysis of biological tissues. Full field OCT (FFOCT) takes directly "in front" images using megapixel cameras and an immersion microscope. Available in the configuration of the apparatus developed by the LLTech company, the interferometer is moved to change the focal plane at different depths beneath the surface of the sample thereby to produce 3D tomographic images. The high resolution of about 1 micron, provides very similar macroscopic pathology images.
The objective of this project is to evaluate the diagnostic value of OCT for extemporaneous analysis of tissue samples obtained during percutaneous samples (micro and macro biopsies) by comparison to conventional histological data.