Ultrasound Physics with Sononerds Unit 16

[@marcioborges1146]

Hi! Awesome videos! Will you be talking about Doppler in soon?

[@Sononerds]

Hemodynamics and then Doppler :) probably not for a couple weeks though

[@marcioborges1146]

@@Sononerds thank you so much! Your lectures are helping me a lot! They are outstanding! I’m studying w the green book..

[@kaylam8651]

In Edelman it says that fewer shades of gray degrade contrast resolution? but in this video you say it is improved with less shades of gray, I'm confused

[@Sononerds]

I read through my Dr. Edelman material and can't find that statement. Could you point me in the right direction? In general, contrast resolution is the ability to differentiate one shade of gray from another. And in this chapter, I try to approach it from a "detectability" standpoint. In ultrasound, the detectability of a lesion is going to be better with a low dynamic range, when reflectors are very similar because it increases contrast.

[@kaylam8651]

​@@Sononerds table 15.3, maybe im confusing contrast in general with contrast resolution

[@Sononerds]

@@kaylam8651 Oh thank you! I only looked through Chapter 16. I think this chart and dynamic range are talking about slightly different concepts. Chart 15.3 is exactly what you said. A machine with 8 bits per pixel has the capability to display more grays than a 2-bit/pixel machine, thus it has better contrast resolution. If we take that 8-bit/pixel machine and image a liver with lesions in it that are very similar in echogenicity to liver tissue, it will be hard to see unless we reduce the dynamic range. Reducing the dynamic range will improve the detectability because the image has more contrast in it.

[@user-yy4pi3bw3u]

Does changing the dynamic range change the number of shades of grays or just change the values of the echoes that displayed in each shade of gray?

[@Sononerds]

A little bit of both. Dynamic range is going to change the number of grays used to display most of the reflectors coming back so that their values can be better appreciated.

[@user-yy4pi3bw3u]

Thanks for your reply.