 Now I'm going to talk about part three of mechanisms for obtaining and optimizing mammography and I'm going to start with the use of a grid. So in the last talk, when I ended with digital breast tomosynthesis I said we don't use grids for digital breast tomosynthesis, but we do for 2D mammography. Grids are used for two purposes. Their main purpose is to maximize image quality and they do this by doing two things, reducing scatter, thus improving contrast. Scatter increases with breast thickness and increased peak voltage. So the thicker the breast the more necessary it is to use a grid to decrease scatter because there will be more of it. Mammography usually uses moving grids and the typical grid ratio is four to one or five to one. So what's the downside of grids? It sounds great. We're decreasing scatter, we're improving contrast. The problem is it does increase dose to the patient and it can increase dose to the patient by three times. So there is a downside but the upside is better image quality which leads to better detection of breast cancers. So radiation dose. So right using a grid increases the dose of radiation, what's the problem with that? Well, as we know, radiation is a carcinogen and so we want to optimize the dose to minimize radiation exposure to patients. However, there are no known cases of mammography induced breast cancers, even with older higher dose mammography. Now that mammography has been optimized, we're using tomosynthesis, we're using CV, we're using all these new techniques, grids, you know, all this stuff. It has actually decreased compared to previous. However, we do know patients who get mantle radiation, in other words therapeutic irradiation for Hodgkin's lymphoma. We have seen associated radiation induced breast cancer. So we do know radiation can induce breast cancer. We have just never seen it at the doses of mammography. However, it's hard to really separate out what breast cancers are due to mammography and not due to many confounding factors. So how do we talk about breast dose? Well, we talk about breast dose from mammography in mean glandular dose or MGD. And that is the measure of dose and mammography. And it can be estimated from the measured entrance skin exposure x-ray beam peak voltage and half value layer. Mean glandular dose is dependent on breast composition. So if you have a fattier breast, your mean glandular dose is going to be different than someone in extremely dense breast. The mean glandular dose is however based when they give a measurement on a breast that is 50% glandular tissue and 50% adipose tissue for dose symmetry. Using a grid doubles the mean glandular dose. But as we talked about before, it improves image quality and contrast. The ACR recommends that the mean glandular dose for a 4.2 centimeter thick breast be less than 3mG. And that's for either a film screen with a grid or a digital full field with a grid. So we want it to be less than 3mG per the ACR. So let's talk about the radiation risk. Well, it's important to remember that all the epidemiological studies we know about radiation induced cancers were based on single large dose radiation events. They were not based on small doses of radiation over time, which is what mammography does. Mammography would be many small radiation doses over time. So 3mG every year for 40 years, right? They instead are based on atomic bomb survivor data. So one massive radiation dose at one point in time. So it's really hard to fully extrapolate, you know, that just because a large one time dose of radiation can cause breast cancer, can we extrapolate that to multiple small radiation doses over many years causing breast cancer. And all of our data on radiation risk for women undergoing mammography is based on this high exposure data. So we really don't know. The important thing to remember is most radiation induced breast cancers are resulting from a mean glandular dose of 1 to 20 gray at one time. And there is little to no data on exposures under 0.5 grade. It's important to remember, right? 3mG is the exposure from a mammogram. So the likelihood of there being any significant risk from mammography is low. There's a conservative risk that I think is really great to give people an idea of the benefits versus the risk is a mammography. So a very, very conservative risk would be there may be a risk of radiation induced breast cancer in one in 10,000 people undergoing mammography. And that's conservative. It's probably way smaller than that. But we do know a woman's risk of getting a fatal breast cancer is 1 in 200 to 250. So clearly you have a much greater risk of getting a fatal breast cancer than getting cancer from a mammogram. The other great ways to compare radiation dose from a mammogram for patients is it's the same amount of radiation dose as flying from Boston to LA. So a mammogram, no one thinks at all about flying across country and radiation, and it's the same as a mammogram, yet people will worry about a mammogram. And also normal background radiation a year is around 3mG. So just living without even getting a mammogram, you're getting about the same radiation as a mammogram. So I think it's really important to put it in perspective for patients or referring clinicians who are concerned about radiation risk. And that is it for mechanisms for obtaining and optimizing mammography.