nifti_stats: command not found

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/bin/nifti_stats - from package: nifti-bin

You may install the required package with command apt-get install {package}

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