niftitodicom: 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/niftitodicom - from package: vtk-dicom-tools

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

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