Imaging description

Although CT pulmonary angiography (CTPA) is regarded by many as the reference standard for the diagnosis of pulmonary embolism in the acute setting, several studies have reported a high rate of non-diagnostic examinations due to poor image quality. In the PIOPED II study, which utilized 4-, 8-, and 16-channel CT scanners, nearly 10% of patients had an inconclusive scan. This was within the 6–11% range reported in other studies [1, 2]. The most common causes for an indeterminate CTPA are motion artifact and poor contrast enhancement [3]. Breathing artifact can be the cause of both, but rapid advances in CT technology have resulted in shorter scan times, reducing the frequency of these artifacts [4].

Despite optimal contrast timing, some patients still demonstrate suboptimal pulmonary arterial opacification, which can be either generalized or localized [5]. It is believed that this artifact is due to suspended deep inspiration with a Valsalva maneuver, which causes unopacified blood from the inferior vena cava to pass preferentially into the right heart and pulmonary arteries [5]. In patients with a patent foramen ovale the Valsalva maneuver may cause blood to pass preferentially from the right to the left heart [6]. This phenomenon has been termed “transient contrast bolus interruption.”