Please refer to the published article for general information
acquisition. Here you can find details on some topics that are only
described in the article.
Please find technical details in the published article.
As can be seen from the picture, the motorized stage holds 8 slides.
workstation controlling the microscope and acquisition is the right
one, while the
left computer processes the image data. The digital camera is
fiber-optics to the workstation. The scanning and the processing
communicate through a standard 100 Mbit ethernet connection.
The computer that controls the motorized microscope is a
standard 2 GHz Microsoft Windows workstation. The processing
a 2.6 GHz Microsoft Windows workstation.
Pixel size and resolution limit:
A pixel size of 0.26 um corresponds to more
than 90 000 dpi. Even this is however not the highest possible
resolution. With our microscope settings the laws of optics
postulate that the
maximum resolution with a NA (Numerical Aperture) of 1.3 is < 0.10
would provide even more details in the virtual slides, but would
also result in
a more than four-fold increase in scanned image data amount. As
in the published article, the 0.26 um resolution was considered
by most pathologists.
As discussed in the article, slide scanning with
a 10x or 20x objective would have resulted in much fewer image tiles
autofocusing operations during image capture, but the
resulting image quality
was disappointing. The main reason for this is that with a 10x or
the area of the view field is much larger, resulting in bad
autofocusing due to
always present height variations in the slides. Also, the subjective
quality when scanning with the oil-40x objective was clearly
superior. We intend
to publish test series of the same slide scanned with different
The depth of field: For most histological specimens the depth
of field of the
light microscope is much smaller than the thickness of the specimen.
microscope this limitation can be overcome by continually adjusting
by moving the zone of sharpness up and down the optical axis and
getting a mental image of a structure’s three-dimensional shape. The
field depends on the objective lens’s numerical aperture, in that a
objective such as the one used to scan the virtual slides on this
a narrow depth of field. Capturing image data with an objective with
numerical aperture would increase the depth of field. The numerical
can also be lowered by simply closing down the condenser iris
But as the depth of field increases, there is a corresponding loss
in the captured image. The theoretical resolving power as a function
of a lens’
numerical aperture can be calulated as
R = λ / ( 2 N.A.)
where R is the resolving power in µm, λ is in µm, and N.A. is the
There are, however other ways to extend the depth of field in a
except for using a smaller numerical aperture. A functional solution
is to aquire
and use multiple focal planes in the same virtual slide, or
digitally merge them.