A 33-years-old woman presents to accident and emergency with severe right flank plain. The pain staed 3 hours ago and is not constant, occasionally moving towards her right iliac fossa. The patient also feels nauseous and has a low-grade fever. The most appropriate investigation is:
Abdominal x-ray Magnetic resonance imaging (MRI) scan Intravenous urography Abdominal ultrasound (US) scan