A 58-year-old woman presents to the emergency department with acute onset dyspnea and pleuritic chest pain. She returned from a 12-hour flight 3 days ago. Vital signs: BP 128/82 mmHg, HR 112 bpm, RR 24/min, SpO₂ 92% on room air. D-dimer is elevated at 2.8 µg/mL. CT pulmonary angiography (CTPA) is performed. Which of the following CT findings would be most specific for acute pulmonary embolism?