0:00

So mammography in the US is very tightly regulated.

0:05

In fact, among all the imaging modalities,

0:08

mammography is one modality which is highly regulated,

0:13

checked on a routine basis, where the teamwork is very much essential,

0:17

and so forth.

0:18

1994, there is the act called Mammography Quality

0:22

Standard Act. MQSA Act was passed in

0:26

1994. From then onward, it made any

0:30

clinic using mammography as for a screening test

0:34

has to be certified prior to using on a patient.

0:39

The certification is a lengthy process and also requires

0:42

very stringent rules on the who reads the mammography films.

0:47

The radiologists have to have a special training, special experience,

0:50

and the continuous education is also strict.

0:54

And also it requires qualified medical physicist to

0:57

evaluate the system on an annual basis to make sure all the

1:01

physics parameters are in line. And the third one

1:05

is the technologist. All radiographers cannot be a

1:09

mammography tech. The mammography tech has an higher bar of

1:13

additional training requirement and continuous education.

1:17

So the MQSA Act kind of introduced the team model

1:21

in imaging, and this mammography, and the reason is like the

1:25

quality of the mammogram image, especially for screening

1:29

mammogram, is very critical if it has to

1:32

diagnose breast cancer in an early stage.

1:35

The reason is that the screening mammography has shown to

1:39

reduce breast cancer mortality by anywhere from 18% to

1:43

30%. And then this particular publication is from back in

1:47

1993 when the digital mammography was not

1:51

even there. Even with the film screen system, the screening

1:54

mammography is highly considered a

1:58

life-saving imaging process.

2:01

The decline in the rate of breast cancer death in the past few years

2:05

may be due in part of the widespread use of screen film

2:09

mammography. With that understanding of mammography, how it is

2:13

regulated in the US, and how tightly the quality control

2:17

is monitored, inspected on an annual basis, this same

2:21

model is now migrating into the CT,

2:25

MRI, or PET,

2:27

and that has become more as a part of the

2:30

accreditation of a modality in CT or MRI,

2:34

where the accreditation by the American College of Radiology

2:38

requires a specialized requirement for whoever

2:42

is doing the CT image reading, radiologist, and the medical

2:46

physicist, and the requirement for the technologist also all tied up.

2:50

And we see that the same model is moving to all the imaging modality.

2:54

So why is screening mammography so important?

2:58

Let's look at the breast anatomy and breast cancer incidence site.

3:02

If we look in here, you are imaging a muscle or a

3:06

soft tissue. There's no bone involved.

3:09

That itself will allow a different type

3:13

of X-rays for imaging.

3:16

In the beginning, I mentioned the type of X-ray imaging, such

3:19

as Bremsstrahlung radiation and characteristic X-rays.

3:24

And in mammography, we are utilizing the characteristic

3:27

X-rays to improve the spatial resolution.

3:31

So if we look in here, on the right-hand side is a

3:35

caricature showing the area of incidence of breast

3:39

cancer incidence sites on the breast, and there is a large amount of

3:42

breast cancer incidence at almost closer to the chest wall.

3:47

Because of that, there is a challenge how the breast is positioned

3:51

for taking an image. And that also has lot of these

3:55

challenges and

3:57

issues with respect to imaging is very important.

4:01

So what happened is like the mammography physics, in order to

4:05

understand mammography physics, we also have to understand how the X-ray

4:09

interact at a lower energy range.

4:12

There is what we see here is like small attenuation

4:16

differences exist between cancer and the cancerous tissue.

4:19

So if we look in here, this is the attenuation coefficient,

4:23

the X-ray stopping mechanism of different tissue,

4:27

mapped and the energy of the X-rays are used for imaging

4:31

purpose. If we use a regular radiography system, which is

4:35

done around 50 to 100 keV, the difference

4:39

between the glandular or the carcinoma tissues is very

4:43

difficult to differentiate.

4:45

Because of that, if you go down at the lower energy ranges here,

4:49

you see the difference, and that difference is exploited

4:53

by imaging mammography at a lower energy.

4:57

So the subject contrast between the normal and malignant

5:01

tissues in the breast is higher at lower energy, this

5:05

contrast. So you can see here, this is the energy and this is the

5:09

percentage contrast of ductal carcinoma.

5:12

As you can see here, at the higher energy, that contrast with respect

5:16

to the background, it becomes smaller and smaller.

5:20

At the lower energy between 15 and 25 keV, you

5:23

see a dramatic difference, almost greater difference at the lower

5:27

energy.

5:29

And the other thing is like you also need very high resolution

5:33

with low dose and low contrast detection is

5:37

required. And all those things creates a

5:40

challenge for designing a mammography tube and the physics

5:44

behind it. So

5:46

the mammography is done on an X-ray equipment

5:50

dedicated specially and optimized for breast cancer

5:54

incidence.