How can I install the dicom gem using rvm on ubuntu 11?

I have rvm installed, and the default set to 1.9.2. Whenever I try to get the dicom gem, I get these error messages:

$ rvmsudo gem install dicom
ERROR:  Loading command: install (LoadError)
    no such file to load -- zlib
ERROR:  While executing gem ... (NameError)
    uninitialized constant Gem::Commands::InstallCommand

These errors happen after I run the instructions here, ie:

$ rvmsudo rvm remove ruby-1.9.2
$ rvmsudo rvm pkg install zlib
$ rvmsudo rvm install ruby-1.9.2
$ rvmsudo --default use 1.9.2

These errors also happen after removing all 开发者_开发知识库sudo apt-get installed ruby versions (ie, I ran sudo apt-get remove ruby*), and uses the most recent rvm (1.8 as of this question)

RVM instructions tell that you have to install ruby this way

rvm install 1.9.2 --with-zlib-dir=$rvm_path/usr

after installing zlib package