D
E F I N I T I O N S
The
definitions of different parameters of the comet are dependent on the software
one is using:
For
Komet^{TM} software
the definitions are as follows
A typical comet showing analysis cell with head, tail and Background ROIs
(ROIs - regions of interest)
Tail Length:
Tail Length is the distance of DNA migration from the body of the nuclear core
and it is used to evaluate the extent of DNa
damage.
Tail Length = Tail Extent
(Tail from Center) Tail
Extent + Head Extent/2
Olive Tail
Moment: Tail moment is defined as the product of the tail length and
the fraction of total DNA in the tail. Tail moment incorporates a measure of
both the smallest detectable size of migrating DNA (reflected in the comet tail
length) and the number of relaxed / broken pieces (represented by the intensity
of DNA in the tail).
Olive Tail Moment=(Tail.mean - Head.mean) X Tail%DNA/100.
Extent Tail Moment=Tail Length X Tail%DNA/100.
Head
% DNA = (Head.OptInten /(Head.OptInten + Tail.OptInten)) X 100.
Tail
% DNA = 100 - Head%DNA.
For
Vis Comet^{TM} software
the definitions are as follows:
1
Comet extent
2
Comet total intensity
3
Comet total area
4
Tail extent
5
Tail extent moment
6
Tail (Olive) moment
7
Tail integrated intensity (Singh)
8
Tail integrated intensity ratio (Singh)
9
Tail area (Singh)
10 Tail
break Number (Singh)
1)
Comet Extent
The extent is the distance from the leading edge to the trailing edge and
defined as follows.
2)
Comet total intensity
Sums all pixel intensities from the grayscale image when there is a
corresponding pixel in the binary mask image. The resulting value is normalized
by the maximum intensity value that can be represented in the data buffer.
Example:
When working with 8-bit images, the maximum intensity value can be 255. Working
with 12-bit images, the maximum intensity can be 4095. In case of an 8-bit
image, the total intensity would be:
3)
Comet total area
The number of pixels in
the binary comet image (including pixels that belong to fragments) is counted.
The area is returned in calibrated units.
5)
Tail extent moment
It is defined as
follows:
L= length of the tail or body
DNA = DNA of tail or body given as a percentage
6)
Olive Moment
It
is defined as follows:
CG = center of gravity of the tail or body
weighted by gray values
CG_{H} = center of gravity of the head weighted by gray values
DNA = tail or body DNA
7)
Integrated intensity
The
integrated intensity is a feature, that incorporates different geometric
parameters. Due to the fact, that damaged cells change their length and breadth,
exactly these two geometric parameters are used for the calculation.
The
algorithm starts from the beginning of the tail and examines each vertical scan
line until the end of the tail is reached. Each vertical scan line is processed
from top to bottom and only those pixels are considered that are identified as
signal pixels.
From
each vertical scan line the product of breadth, position and total intensity is
accumulated.
The
integrated intensity is calculated as
follows:
I_{p} is the product of breadth, position and total intensity of one
column
8.) Tail
Intensity Ratio:
The integrated
intensity ratio is calculated as follows:
where
I_{T} = sum of all intensity values
The figure below demonstrates the
mechanism for the calculation.
9)Tail Area:
The number of pixels in the binary tail region of image (including pixels that
belong to fragments) is counted. The area is returned in calibrated units.
10)
Tail Breaks Number:
All objects (or sometimes called blobs or fragments) in the tail area (red overlay area) are counted. This number minus 1 is number of
DNA breaks.
Courtesy:
Dr. N.P. Singh |