Day 9: Name That Artifact

An MRI's View

The 9-day chick is moving around a lot. We cannot get very clear pictures, because it won't hold still long enough! Because of the "motion artifacts" caused by all this movement, the same slice aquired over and over looks different each time. The bright spots seen mostly in the amnion, are caused by the "sloshing" of amniotic fluid as the chick moves. Frame 78 and 82 are actually the images of the same slice. Note the differences caused by the moving fluid.

In Frame 45 and 78, we clearly see the blood-filled membranes just inside the shell. These are the chorioallantoic membranes or "breathing membranes". The chick does not use its lungs until just before it hatches. Until then it must rely on the chorioallantoic membrane lining the eggshell to breath. The chorioallantoic membrane is made up of the chorion and the allantois which begin to fuse at about day 6. The chorion lines the inside surface of the porous eggshell where it can exchage oxygen and carbon dioxide freely. The blood vessels of the allantois pick up oxygen and take it to the embryo. They also bring waste products such as carbon dioxide and urine from the embryo to release into the chorioallantoic cavity. The movement of the blood flowing in the allantoic vessels causes the membranes to appear white on this MRI image. Blood vessels within the embryo's body can also be seen in this image as white spots.

The albumen continues to differentiate into two layers, one above and one below the yolk. This is particularly evident on frames 82 and 87, where the different imaging techniques make the two layers appear differently. The yolk continues to deform, becoming flatter and smaller.

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