A 52-year-old woman with a history of type 2 diabetes and chronic kidney disease (eGFR 35 mL/min/1.73 m²) is being evaluated for asymptomatic coronary artery disease (CAD). She has no chest pain but has multiple risk factors. Which investigation is most appropriate to assess the extent and severity of atherosclerotic plaque burden and guide further management without exposing her to iodinated contrast?