mrstats: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/lib/mrtrix/bin/mrstats - from package: mrtrix

You may install the required package with command apt-get install {package}
Error in other languages:
mrstats: bevel nie gevind nie
mrstats: comandă negăsită
mrstats: comando não encontrado
mrstats: commande introuvable
mrstats: command not found
mrstats: käsku ei ole
mrstats: không tìm thấy lệnh
mrstats: komanda nerasta
mrstats: Kommando nicht gefunden.
mrstats: kommandot finns inte
mrstats: komut yok
mrstats: nie znaleziono polecenia
mrstats: níor aimsíodh an t-ordú
mrstats: no se encontró la orden
mrstats: no s'ha trobat l'ordre
mrstats: opdracht niet gevonden
mrstats: parancs nem található
mrstats: perintah tidak ditemukan
mrstats: príkaz nenájdený
mrstats: příkaz nenalezen
mrstats: команда не найдена
mrstats: командата не е открита
mrstats: 命令找不到
mrstats: コマンドが見つかりません