4. For Randomization to CTPA or VQ imaging: Pre-imaging CIN risk ≥25% (CINRisk Score ≥2 points) • A lower-risk subset of 100 patients (CINRisk Score <2) will be enrolled and followed. These patients will complete the CTPA as ordered by their provider (not randomized). Data from this lower-risk subset, along with high-risk patients randomized to CTPA will be used will be used to validate the CINRisk Score, alone and in combination with NGAL and eGFRCYS (Study Aims 1 and 3).