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 various features.
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.
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.
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.
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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