correct_dwi_distortion: 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/lib/cmtk/bin/correct_dwi_distortion - from package: cmtk

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

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