NRRDToDicom: 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/NRRDToDicom - from package: pixelmed-apps

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

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