This image that will be used for the cover of a bimonthly newsletter going to orthodontist, was done by converting sections of grayscale tones into line halftones.

Although an excellent filter by Andromeda (their Series 3 Screen Filter) can do these kinds of line conversions, I like the way Photoshop does it. With Photoshop, you can make your own custom line art.

For example, you could convert a section of gray tone into a line halftone using the Halftone Settings of 20 lines per inch, an angle of 90 degrees, and using the "line" pattern. Now, you could overlap that set of halftone lines with another line conversion made from the same section of gray tone, but using different Halftone Settings, maybe 38.22 degrees for the angle, 16 line per inch and "line" for the pattern (I always use line for the pattern).

There are just a hand full of steps involved in this process (most can be recorded as an action and saved), so follow the steps and see how it's done.