Analytics API- Get MCF data = Blank Results

Question

I am trying to retrieve MCF data from an analytics account. So far I am able to get GA Data successfully, but when I try MCF I get blank data.

Am I reading the data correctly, or is MCF data in a different format?

$results= $analytics->data_mcf->get('ga:'.$profileId,'yesterday','today','mcf:assistedConversions');

if (count($results->getRows()) > 0) {
    $rows = $results->getRows();
    $sessions = $rows[0][0];

   printf(" Analytics Name: $PropertyName  AnalyticsID:$PropertyId \n");
   printf(" ->Sessions: $sessions\n");