dicomhead: 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/dicomhead - from package: dicomnifti

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

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