NFL Commissioner Roger Goodell said here Sunday he remains hopeful that the league and the players’ union will resolve their differences on blood testing for human growth hormone during the upcoming offseason, so that the testing program could be put into effect next season.

“I hope so,” Goodell said, speaking to reporters at M&T Bank Stadium prior to the Ravens-Texans playoff game. “There’s certainly enough time. We had a meeting just on Friday between the two parties to try to address those issues. We understand the issues they’ve raised. We’ve answered those questions…. All of the scientists agree that this test is valid. So we think we have a valid test. It’s been proven on a global basis. We hope to get it implemented as quickly as possible.”

The two sides agreed in their 10-year labor deal to have players blood-tested for HGH and targeted the beginning of the current season to begin the testing. But they did not agree to details of the program in time for testing to take place during the regular season.

Players and union officials have said they first want to have a population study conducted to determine what should constitute a positive test for athletes the size of NFL players.

“I’m open to getting it done in a credible way,” Goodell said. “That’s my only requirement is that whatever the outcome is, it has to be a credible program.”

Goodell also said he thinks the league’s latest changes to its procedures for dealing with players’ concussions are working well. Those changes include having independent observers at games to help identify players who might have suffered concussions, and allowing teams’ medical staffs to watch video replays on the sideline for issues related to possible head injuries suffered by players.

“I think they’re significant improvements because we have more eyes on the field and we can detect when that injury is occurring and make sure that the doctors are performing the proper evaluation, and take those decisions out of the players’ hands,” Goodell said. “In addition, I think the video is just another helpful tool for them in making those determinations. So there are two very positive steps just in the last few weeks.”

Earlier, Goodell said during a question-and-answer session with Ravens fans that there was a reduction in concussions this season but the sport’s leaders will continue to study the issue and seek further improvements.

“We have not finished yet,” Goodell said.

Goodell told the fans that the rule changes affecting kickoffs this season made the sport safer, even while many players and coaches complained about the increase in touchbacks resulting from moving the kickoff closer to the opposite end zone.

“It reduced the injuries very significantly,” Goodell said. “It made the play safer. We’ll continue to evaluate that and see if there’s a better balance. But it achieved its purpose.”

Goodell said the league is contemplating making approximately 10 of its game officials full-time employees. Those officials, in addition to working games, would aid the weekly process of evaluating the calls made in games, Goodell said. Currently officials are part-time employees.

“If we do this what I call semi-part-time thing, I think it could add to our consistency,” Goodell said.

The league will study the possibility of closing the loophole that allowed assistant coach Josh McDaniels to join the New England Patriots’ coaching staff during the postseason, Goodell said. But Goodell said the feedback he has received so far indicates that other teams “don’t think it’s a big issue.”

Goodell reiterated that the league could increase the number of games that it plays overseas in future seasons, and left open the possibility of a franchise eventually being based overseas.