2 new machines for in vivo imaging

June 28th 2018

The Center for Microscopy and Molecular Imaging (CMMI) has two new tools: with optoacoustic imaging and a 1-Tesla MRI machine, researchers can easily image mice and study many different pathologies.

Multi-spectral optoacoustic tomography (MSOT) is a recent technology, yet it relies on a principle that was discovered in the late 19th century: light produces sound. Lionel Larbanoix, head of the non-ionising in vivo imaging department at CMMI, explains: ‘When exposed to light, molecules experience a slight expansion, as the energy they absorb from light is converted into heat. This very brief thermal expansion produces an acoustic wave (ultrasound) that a machine can detect. A software program then reconstructs an image.’

What can we see using MSOT?

Three types of molecules present in mammals are especially good at absorbing light: haemoglobin, oxygenated haemoglobin (oxyhaemoglobin), and melanin. Absorption depends on the light’s wavelength, which means that by subjecting tissue to different wavelengths, an MSOT machine can determine in what quantities these molecules are present.
In addition, exogenous chromophores(1) can be injected into the patient before the imaging process, serving as trackers that will target and latch onto specific biomarkers.
‘MSOT lets us see blood vessels, tumours, or highly vascular organs: liver, kidney, spleen, etc.,’ adds Lionel Larbanoix. ‘It can also let us visualise melanin, which is very useful to observe melanomas and detect their metastases in the lymphatic system. As the machine can “see” up to 4 centimetres under the skin, it can produce images of a mouse's entire body.’

The benefits of the new MRI machine

The other new MRI machine, which uses a 1-Tesla magnet(2), can also produce images of a mouse's entire body. The CMMI already had a 9.4 Tesla MRI machine, so why the investment in a smaller machine? There are several reasons for this:
  • for routine or general applications: the 1-Tesla MRI machine is very well suited for morphological studies;
  • the 1-Tesla MRI machine is less costly;
  • the 1-Tesla MRI machine is similar to those used for clinical applications (1.5 to 3 teslas), which makes it attractive for human/animal translational studies. The shades of grey in the images are similar, and therefore easier to compare;
  • Contrast agents are more visible under 1 tesla than 9 teslas. As a result, the new machine is better suited to molecular MRI (which can target e.g. biomarkers) and to dynamic MRI, as well as to evaluate certain physiological functions.

(1) A chromophore is a molecule that absorbs light.
(2) Teslas are a unit used to measure the strength of magnetic fields.