Magnetic Resonance Imaging Evaluation of Pulmonary Vascular Malformations: Conclusion
The MRI detection and localization of PVM also allows preprocedural planning for selective pulmonary angiography, though pulmonary angiography still remains the gold standard for depicting the number of lesions and the vascular supply of those lesions, especially in those patients who will have therapeutic embolization or surgical resection. Moreover, the spatial resolution and anatomic resolution of pulmonary angiography is superior to MRI at this time.
The first MRI studies demonstrating PVM utilized nongated and later gated spin-echo sequences and showed either flow void or mixed gray signal. The presence of thrombus or slowly flowing blood may create gray signal within the lesion and thus lead to a nonspecific diagnosis. Later work confirmed these observations but added GRE sequences with the increased inherent sensitivity to flowing blood; the GRE sequences showed the pulmonary AVM with increased conspicuity regardless of size. Dins-more et al noted pulsatility of the signal intensity within the pulmonary AVM on cine sequences which may provide a distinguishing feature between slow blood flow and thrombus. Canadian Family Pharmacy
As is shown in Figure 3, GRE cine MRI sequences do have limitations with respect to specificity. As reported by Glover and Pelc, the MRI appearance of flowing blood is dependent on the velocity of flowing blood with respect to the imaging plane and the MRI parameters. Intravoxel phase dispersion secondary to complex flow appears as regions of decreased signal intensity on GRE images and can cause interpretive errors of AVM with relatively rapid flow. Mucus, atelectasis, and various stages of thrombus may appear bright on GRE images (Fig 2), which might lead to a false-positive diagnosis of PVM. On the other hand, surgical clips, various stages of hemorrhage, or calcifications may yield signal intensity loss secondary to inhomogeneous magnetic fields. Magnetic susceptibility changes at air-water interfaces may also falsely decrease the size of the lesion.