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 egg.

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!

Day 0 Image

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 yolk.

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.

Day 1 Image

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 contrast.

Day 2 Image

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.

Day 3 Image

Incubation Day 3. Now the embryo seems to be growing in size.

Day 4 Image

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.

Day 7 Image

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.

Day 8 Image

Incubation Day 8. The chick is moving a lot, and so it is difficult to get clear images.

Day 9 Image

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.

Day 10 Image

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.

Day 11 Image

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.

Day 14 Image

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.

Day 15 Image

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.

Day 16 Image

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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