Acute pulmonary embolism to the subsegmental level: diagnostic accuracy of three MRI techniques compared with 16-MDCT

The purpose of this study was to assess the individual and combined usefulness of MRI techniques in cases of acute pulmonary embolism and to compare the usefulness of these techniques with that of 16-MDCT.

Sixty-two patients with symptoms indicating acute pulmonary embolism underwent an MRI protocol that progressed from real-time MRI through MR perfusion imaging to MR angiography. The results were compared with those of 16-MDCT, which was the reference standard. Thoracic incidental diagnoses other than pulmonary embolism also were sought with CT and MRI.

Pulmonary embolism was diagnosed with CT in 19 patients for totals of 90 lobar, 245 segmental, and 434 subsegmental arteries. On a per-patient basis, the sensitivities of real-time MRI, MR angiography, MR perfusion imaging, and the combined protocol were 85%, 77%, 100%, and 100%, respectively. The specificities were 98%, 100%, 91%, and 93%. The kappa values in a comparison of the MR techniques with CT were 0.89, 0.87, 0.86, and 0.9. On a per-embolus basis, the sensitivities of real-time MRI, MR angiography, and MR perfusion imaging for lobar pulmonary embolism were 79%, 62%, and 100%. The sensitivities for segmental pulmonary embolism were 86%, 83%, and 97%, respectively. MR perfusion imaging had a sensitivity of 93% for subsegmental pulmonary embolism. Eight of nine incidental findings revealed on CT were also subsequently diagnosed with real-time MRI. MRI failed to reveal a case of emphysema. Mean MRI examination time was 9 minutes 56 seconds.

The combined MR protocol is both reliable and sensitive in comparison with 16-MDCT in the diagnosis of pulmonary embolism. MR perfusion imaging is sensitive for the detection of pulmonary embolism, whereas real-time MR and MR angiography are specific.