Technique and Significance, Looking at Cell Migration
What is Time-Lapse Microscopy (TLM)?
Time-lapse microscopy may be described as a type
of time-lapse photography in microscopy. Here, the film frames are captured at
a lower frequency than the frequency used to play the sequence which makes time
appear to be moving faster and lapsing when the sequence is played at normal
speed. Therefore, this technique is a manipulation of time where real life
events that may have taken minutes or hours get to be observed to completion
within a matter of seconds.
Time-lapse microscopy was first reported in 1909
where Jean Comandon, a French student, successfully captured image sequences by using an
enormous cinema film camera coupled to a much smaller dark field microscope.
Using his technique, Comandon was able to create a time-lapse video of syphilis
producing sinochaetes. In the following half of the 20th Century, compact
16-milimeter cameras were used for capturing image sequences. Here, the cameras
were used on microscopes equipped with phase contrast illumination while the
time interval between successive image captures were controlled by bulky
auxiliary intervalometers given that electronic shutters were not available.
While these techniques represented some breakthrough in microscopy, they
heavily relied on film cameras that were subject to a number of challenges.
For instance, films had to be taken out for commercial processing, which means
that it took days and even weeks to get results. In addition to being costly,
the technique was also subject to a number of processing variations, which means
that there were chances of the results being inconsistent.
In the 1970s, video tube cameras and frame
grabber computer cards were integrated with microscopes, which significantly
reduced uncertainties of exposure settings associated with film cameras. In
addition to reduced costs, this new technique also allowed for image sequences
to be viewed during acquisition with the result of extended time-lapse
experiments being available immediately.
Today, digital still cameras are being
used to record individual image frames rather than using a video recorder.
These cameras allow for a number of advantages including lower overall cost
and recording individual frames as well as precise software control over
Time-Lapse Imaging Technique
Essentially, time-lapse microscopy can be
conducted using any microscope system that can accommodate a digital imaging
camera with time lapse capabilities. Here, the time intervals between image
capture can simply be preset on the camera being used or integrated camera
microscope software. Time interval between image capture simply refers to the
regular interval between each individual capture. For instance, one may set for
an image scene to be captured once each second.
The duration of these intervals
is very important in that it ultimately determines the temporal resolution with
the resulting video sequence showing the cells or organism in motion. For very
rapid events, imaging often requires that cameras have high temporal
resolution, which allows for capturing detail and high sensitivity in order to
capture enough signals within a short period of time.
Time-Lapse Microscopy & Cell Migration
Cell migration is a dynamic process that is
central to the development and maintenance of multicellular organisms. It is particularly
important for such events as embryonic development, tissue repair, functioning
of the immune system as well as tumor invasion among others. Therefore, cell
migration generally refers to the translation of cells from a given location to
another. For this reason, it is essential that the specimen is kept alive
during time-lapse microscopy.
Depending on the specimen (cells) under
investigation, it is important that a suitable environment is created to allow
the cells to remain viable during the acquisition of the images. This therefore
involves controlling the temperature, humidity, light as well as providing the
appropriate media among other factors.
It is now possible for scientists to track the movement of cells, study cell motility or conduct chemotaxis experiments among other applications. Here, labels and stains are not used given that they are invasive and can either change the behaviour of the cell or kill it.
Breast Cancer Cell Time-Lapse
To observe the migratory behaviour of cells,
living cells of interest have to be placed in the appropriate culture media
(different cells require different media) and then placed under the microscope.
Here, the images of given regions of interest are then taken at the set regular
intervals over a given period of time (minutes, hours or even a day). Here, the
position of given individual cells have to be marked in consecutive images,
which allows for easy tracking or following the positional changes of the cells
over a period of time.
The tracking procedure simply involves the
"point and click" systems. This involves pointing the cursor at the
cell and clicking on it to follow its movements. However, this method has been
shown to result in errors that may affect the integrity of the results
obtained. For this reason, new methods are in development to help avoid such
errors. A good example of this is the multi-target tracking technology that is
also used in military radar tracking techniques.
Using this method, it becomes
easier to develop a full automated cell identification and tracking system for
screening the video sequences of the unstained living cells. Whereas manual
tracking of cells has been shown to be time consuming and ineffective at times,
recent advances in automated cell tracking in time lapse microscopy have made it
easier to track specific cells even in large populations of cells for
quantitative, systematic and high-throughput measures of cells behaviour.
Significance of Time-Lapse Microscopy
Time-lapse microscopy presents significant
advantages in observing and studying cell migration. One of the biggest
advantages is that it is a
high-throughput and noninvasive tool for studying cells. As such, it has proved
particularly beneficial when studying or identifying stem cells and embryo and
their development. Through this technique, stains are not required, which means
that the cells are basically observed in their natural state.
Time-lapse microscopy can be said to be one of the methods that extends live
cell imaging from a single observation in time to observation of cellular
dynamics over a long period of time.
This makes this technique a cornerstone technology for the assessment of
cells given that it allows for users to observe the dynamic events in a large
number of cells and the single-cell level.
Johannes Huth, Malte Buchholz, Johann M Kraus,
Martin Schmucker, Götz von Wichert, Denis Krndija, Thomas Seufferlein, Thomas M
Gress and Hans A Kestler (2010) Significantly improved precision of cell
migration analysis in time-lapse video microscopy through use of a fully
automated tracking system.
Kevin E. Loewke and Renee A. Reijo Pera (2010)
The Role of Time-Lapse Microscopy in Stem Cell Research and Therapy.
Konda, R. (2014). Automated cell tracking in
time-lapse microscopy images. PhD thesis, Department of Electrical and
Electronic Engineering, The University of Melbourne.
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