command line usage?

I didn't find any tshark executable on my Mac

If you installed Wireshark from a dmg downloaded from Wireshark.org, try re-installing it, and don't un-check the install option for the command-line tools. That should put a tshark command in /usr/local/bin.

If you installed Wireshark from somewhere else, check with whatever source provided Wireshark to see how to get the command-line tools installed.

if my dicom server is listening on port 11112 Woud filtering on dicom (within wireshark) work or does dicom filtering assume port 104?

DICOM filtering assumes that Wireshark/TShark/whatever dissected the packet as DICOM.

DICOM dissection assumes port 104 by default; that's why I said "You might have to use -o dicom.tcp.port:NNNN if the DICOM traffic is on port NNNN rather than the default port, 104."

So, if the DICOM server is listening on port 11112, you'd need to do

tshark -o dicom.tcp.port:11112 -Y dicom -V -r {your file}

in TShark, and would need to change the DICOM preference "DICOM ports" to include port 11112 in Wireshark.

So if I want dicom on both port 104 and port 11112 then I specify both separated by a comma in the prefrenced?

P.S. I had different columns selected in wireshark, like Source Port and Destination Port. I assume those columns that I want to include in my text export can be specified on the tshark command line as well?

What if I don't want the TCP/IP portion of the text output but just the DICOM message?

O.k. @Guy Harris was 28 seconds faster ;-)

I didn't find any tshark executable on my Mac

See the answer to this question

http://ask.wireshark.org/questions/30819/how-to-setup-and-run-tshark-on-os-x-1092