Annotations on Selected MR
Images of the Embryo
Experts annotated MR images to record chick embryo
development for the benefit to all classrooms. Below
are thirteen annotated MR images documenting key
changes in the chick embryo development process. To
facilitate understanding of this development process,
all the images shown here are side views of the
However, before proceeding forward, a clarification
is in order. Although this was a 21-day project
(April 10 to May 1, 1996), images were acquired by
classrooms for thirteen days only due to breaks, such
as weekends and late start date. This created some
confusion in the numbering of the incubation days.
So, for sake of clarity, please consider the
Incubation Day 0 as the first day of image
acquisition, and Incubation Day 16 as the last day of
image acquisition. So, there were thirteen image
acquisition days. In future, we will avoid such
confusion! After all, the embryo keeps developing
even on weekends!
Incubation Day 0. In the early stages of
incubation, it is difficult to see the embryo through
MR images. However, there is identifiable yolk,
albumen, and latebra in the image. Yolk is the yellow
of the egg that serves as a primary source of food for
the growing embryo. Albumen is the white of the egg.
Latebra is an area of white yolk located in the center
of the yolk. Notice a thin strand of the latebra,
which extends from the center to the surface of the
Notice also the image or instrumental artifact (like
dirt on a camera lens). You will find artifacts in many
different images. The air sac is the space between
shell membranes. The air space can be seen when the egg
is candled. Check out the candled image of an egg in Day 4 of Today's News section.
Incubation Day 1. This image of 24 hour
embryo is not very different from the previous
image. However, notice the difference in image
contrast between the two images. Contrast is the
difference in brightness between different areas of
the image which enables one to see things. The MRI
system can be adjusted to change the contrast (like
changing the color of light to illuminate an object),
such as T1 or T2. T1 contrast enhances fats, while T2
contrast tends to enhance the brightness of liquids
such as water. Day 0 image is an example of T1
contrast, while Day 1 image is an example of T2
Incubation Day 2. At this stage the amnion
begins to surrounds the developing embryo. The image
identifies what probably could be the embryo. Amnion
is the transparent sac filled with colorless fluid
that protects the developing embryo, but it is not
clearly visible in this image.
Incubation Day 3. Now the embryo seems to be
growing in size.
Incubation Day 4. The yolk seems to have now
flattened more than in the previous image. The white
area above yolk has greatly increased in size. The
chick is using the yolk as a food source.
Incubation Day 7. This image shows many
features of the chick, such as the eyes which are very
large at this stage. The beak begins formation.
Allantois is the sac that is connected to the embryo's
abdomen, and it stores excretions.
Incubation Day 8. The chick is moving a lot,
and so it is difficult to get clear images.
Incubation Day 9. In this image, blood
vessels are visible. These are used by the chick to
get oxygen. The yolk continues to deform, becoming
flatter and smaller.
Incubation Day 10. The chick is moving, but
one can see some structures of the embryo clearly
(such as the eyes). The amnion is generally "stirred
up" by the chick's motion.
Incubation Day 11. The chick is moving even
more than in previous images. It is difficult to get
very clear pictures as the chick will not hold still
long enough. Notice the image shows "motion artifact"
due to the chick's movement. This means that if one
would repeatedly request the same image over and over,
the image would look different each time. The bright
spots in the amnion are caused by "sloshing" of the
fluid as the chick moves.
Incubation Day 14. The chicken is growing a
lot. It now is as long as the egg is wide. Since it is
still moving, the image is blurred. The egg
structures are changing too.
Incubation Day 15. The chick seems to be more
or less in the same position, as in the previous day
image. Perhaps, it is now too cramped in the egg for
it to turn around.
Incubation Day 16. The chick continues to
grow, and is getting close to hatching. In this image
you can see a spot between and below the eyes. This is
probably an air passage, either the mouth or a nasal
or sinus passage. It is dark because there is no
longer any fluid in it; the chick is breathing air
from the air sac!
As the side view images may not always reveal all
chick structures, please check out Today's News
section for additional images.
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