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Now let's examine the image quality in mammography, which is very important.

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One of the ways we evaluate image quality in mammography system,

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as a physicist, we use a mammography phantom.

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This is a phantom almost every mammography center in the US,

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which are legally allowed to do screening mammogram, has this

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one because the technologist had to take an image every

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day to make sure the structure in the phantom are

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visible on the image.

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If not, by regulation, they cannot use

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that particular system for screening mammogram on that particular time

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until it is repaired. So this is one of the

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very recognizable phantom in imaging in mammography.

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This particular phantom is about four and a half centimeters thick to mimic

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an average breast size, and it has structure as

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the following. It has fibers of the same length of

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decreasing size.

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It has a bunch of specked groups, again, of a decreasing

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size. And that has a masses. So it's kind of mimicking the

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structure commonly seen in mammography in breast area.

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On top of it, it also has a disc to measure the contrast of the system and so

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forth.

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So the way it works by regulation is for a center

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to be accredited by the FDA for doing screening

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mammography, they need to submit the phantom images

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to the center, such as the American College of Radiology, which accredits the

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system. These images are sent to the reviewer, such as

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myself, for a phantom reviewer, a physics reviewer, who

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we are given strict instruction how to score the phantom.

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For example, here, if I start counting the number of

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fibers, I can start on the left-hand side, the more

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easily visible dark thick one, and the score will,

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in this case, is up to three and a half because the fourth fiber is

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broken. Even though I see the fifth fiber, I'm supposed to

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stop at this and score only three and a half.

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And the same thing for the speck. Here in this case, I can see the

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three full speck and only three minor speck in the fourth

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group, so I can call this as three and a half speck group.

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Similarly for the masses, now we can see here three and a

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half, so the greater three-fourth of the round parameter should be

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visible. That's why we can only score it at three and a half.

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So if this is a score, a system fails because the minimum

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required scoring is you should be able to see four

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fibers,

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three specks group, and three masses.

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Anything below that, the particular site will fail, and

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they cannot do mammography until the site passes.