More than 350 scientists specialized in earth and life sciences work in the research labs of the Natural History Museum. One of them is the Imaging and Analysis Centre, in which the specialist team prepares and analyses all sorts of samples, from biological tissues to geological and synthetic material. Mostly, analyses are conducted for the NHM scientists, but also for any scientific visitors or consultancy projects that make a request.
Among all the analysis techniques the Centre can provide (including chemical analysis and micro-analysis), there are several pieces of instrumentation for 2D and 3D imaging of samples in the Imaging and Tomography part of the lab.
Let’s focus on three of their techniques: the micro-computed tomography (CT), variable pressure scanning electron microscopy and confocal microscopy.
Micro-computed tomography (CT)
What is it?
Micro-CT uses X-rays to create 3D models of the internal and external features of specimens. As a non-invasive and non-destructive technique, Micro-CT is of great interest for scientists who work with collections materials that needs to be preserved because samples can be analysed in detail without being spoiled.
How does it work?
More than 3,000 X-ray projections are taken over a 360° rotation on the sample that needs to be scanned. Then, a greyscale 3D volume is created, where the grey level reflects the X-ray attenuation of the object.
Focus on Nikon Metrology HMX ST 225
The Nikon Metrology HMX ST 225, a versatile micro-CT scanner, can analyse samples from 0.5 to 20 cm in diameter with additional capacity for specimens up to 70cm in height. As every scan produces over 3000 X-ray images that are collected in 16-bit quality on a four-megapixel detector, this technique is known to provide a large amount of high-quality data (total scan size, including raw X-ray images up to 60 GB and can be exported in TIFF, BMP, PNG or JPEG format. STL, PLY and OBJ mesh files can also be produced from the scans for further analyses).
Variable pressure scanning electron microscopy
What is it?
Scanning electron microscope (SEM) is a type of microscope able to produce images by scanning a studied object with a focus beam of electrons.
How does it work?
Inside the sample, electrons interact with atoms and produce a wide range of various signals that contain information about its surface topography and composition. Some of those microscopes can observe a specimen in variable pressures, like high or low vacuum conditions, depending on the sample types and the necessity to preserve them.
Focus on FEI Quanta 650 FEG scanning electron microscope (SEM)
The FEI Quanta 650 FEG scanning electron microscope (SEM) is used for high-resolution imaging and semi-quantitative X-ray microanalysis of both conductive and non-conductive specimens at nanometre resolution.
At the Imaging and Analysis Centre, the most recent applications of this technique concerned large area elemental mapping of fossilised arthropods, high-resolution backscattered imaging of very fine scale mineral particles and nano-CT visualisation of forams.
Confocal microscopy
What is it?
Confocal microscopy is an optical imaging technique for increasing optical resolution and contrast of a micrograph by scanning the sample using a laser beam in order to build up the image one line at a time.
How does it work?
In fact, this technique remains in the alliance of two engines: a Nikon Eclipse upright microscope which is then coupled to a Nikon A1-Si confocal microscope. By applying different dye and laser combinations to the sample, this technique can simultaneously label different parts of the sample to differentiate specific features in 3D.
Focus on Nikon Eclipse upright microscope with A1-Si confocal microscope
After scanning the sample, the sequential image planes obtained can be built up into a stack of images. Confocal microscope software enables 3D montaging, allowing the examination of large areas at high resolution in 3D and extended focus images, up to 4k x 4k pixel TIFF images.
This technique is known to apply to a wide range of specimen types, which is very useful in regard to the high diversity of samples that the NHM scientists work with.
Want to know more about Imaging techniques and microscopes?
See more at: http://www.nhm.ac.uk/our-science/departments-and-staff/core-research-labs/imaging-and-analysis-centre.html
This article was written by Julie Boisard a Master’s student in the Museum’s “Systematics, Evolution, and Paleontology” specialization.
Muséum national d'histoire naturelle 