dcm_mask_image: 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/dcm_mask_image - from package: ctn

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

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