According to a new study, using two MRI sequences along with a traditional MR angiography procedure enhances the diagnosis of pulmonary embolism. More details on the study are published online in the journal Radiology.
Pulmonary embolism is a life-threatening disorder that is usually detected using CT. The condition takes place when a blood clot, mainly from the leg, moves through blood vessels and reaches the lung. This clot then blocks the pulmonary artery or its main branches. Although CT angiography is main technique for detection of pulmonary embolism, the procedure includes delivering high doses of ionizing radiation in addition to iodinated contrast agent. This means higher risks for patients with allergic reactions and kidney problems.
Diego R. Martin, M.D., Ph.D., head of the Department of Radiology at the University of Arizona College of Medicine in Tucson, said "MRI is developing much faster than CT. The images we're getting are already significantly better than they were a year ago. There is no doubt that in the future we will be able to offer a non-radiation-based alternative to CT for the diagnosis of pulmonary embolism." MRI has been used for detection of pulmonary embolism among certain types of patients, such as pregnant women and patients with impaired kidney function. This is because such patients would be affected by the side effects of the usual CT angiography procedure.
In their study, the Prospective Investigation of Pulmonary Embolism Diagnosis III (PIOPED III), it was noted that some difficulties affected the quality of MR pulmonary angiography (MRPA). The research team said that MRPA would be useful if they were carried out at centers that routinely and correctly used this technique. In addition, the team said that MRPA should be considered only for patients who were not suitable candidates for CT angiography.
During their study, the team evaluated the effect of two additional MRI sequences on the accuracy of MRPA. Dr. Martin said that contrast-enhanced volumetric interpolated breath-hold examination (VIBE) and non-contrast true fast imaging with steady-state precession (true FISP) were used along with MRPA.
Using VIBE technique offers a gray scale that helps in differentiating between the clot/thrombus and the lung. Both usually look dark on MRPA. Dr. Martin added "Also, VIBE is not time sensitive. If the patient coughs, you can do it again. You don't have that option with MRPA." In regards to true FISP test, it does not need a contrast agent or a breath hold. This is an important feature especially for patients who are not able to hold their breath long enough during MRPA procedures.
Dr. Martin and his team compared the three MRI based techniques to CTA on 22 patients for detection of pulmonary embolism. Sensitivity for MRPA was 55%, 67% for true FISP, and 73% for VIBE. A combination of the 3 techniques resulted in 84% sensitivity. As for specificity, 100% was reported for all techniques except MRPA, as the technique provided false positive results.
Dr. Martin spoke about the study. He said "PIOPED III did not answer the question of whether or not MRI is a useful alternative to CT, because it didn't use all the tools available," He added that the findings indicate that a new redesigned PIOPED study is now required.