Clinical effectiveness of MRA for suspected pulmonary embolism

The most common symptoms of pulmonary embolism (PE), which is associated with significant morbidity and mortality. are nonspecific and include chest pain, shortness of breath, and loss of consciousness.

Computed tomography angiography (CTA) is the current gold standard for diagnosing PE. Pulmonary contrast magnetic resonance angiography (MRA) is an alternative examination that does not expose a patient to ionizing radiation. In a study published in Emergency Radiology, radiologists and emergency physicians at the University of Wisconsin in Madison found similar outcomes in patients imaged with CTA and MRA.

The use of pulmonary MRA is increasing, but widespread implementation has yet to occur.¹ A multidisciplinary team of physicians at the University of Wisconsin attributed this to multiple factors. CTA is a highly accurate, rapid, and available imaging exam for patients seen in emergency departments. MRA is more costly, has a longer turnaround time, and may be less available to emergency patients.

Because a CTA exposes a patient to a high radiation dose, clinicians need to be better educated about the risks of cumulative radiation exposure, especially to younger patients, according to radiologist Donald G. Benson, MD, and colleagues in the British Journal of Radiology. Only 5% to 10% of patients presenting with symptoms of PE and undergoing CTA are subsequently diagnosed with PE, and up to 19 patients are unnecessarily exposed to radiation, according to radiologists at Brigham and Women’s Hospital in Boston.²

In addition to avoiding radiation exposure, especially beneficial for women under age 35 to minimize the risk of breast cancer, patients with renal insufficiency avoid the risk of contrast-induced nephropathy. MRA is also beneficial for patients with allergies to iodinated contrast.

The optimal patient for a MRA has a low-to-intermediate suspicion for PE based on clinical decision rules, according to presenting radiologists at a recent International Workshop for Pulmonary Functional Imaging (IWPFI).³ Clinical decision rules include the Wells score, the PE Rule-Out Criteria (PERC), the Revised Geneva score, and/or the Simplified Revised Geneva score and a D-dimer test.

Dr. Benson and colleagues recommend that radiology departments establish a rapid clinical protocol for rapid turnaround of reporting of MRA exams. They recommend protocols that have a short table time with sequences that can be obtained in a single breath-hold for a total exam time of under 10 minutes, and describe one in detail in their article.

The Wisconsin physicians do not question the diagnostic efficacy of CTA, but they feel its diagnostic advantages should be weighed against MRA in terms of clinical effectiveness. To evaluate the utility of both CTA and MRA in guiding treatment decisions that affect patient outcomes, they conducted a pragmatic, real-world retrospective study to measure the 6-month patient outcomes following MRA and to compare these with an age- and sex-matched cohort of patients evaluated during the same five-year time frame.

Led by Michael D. Repplinger, MD, PhD, the authors identified 592 patients who underwent MRA for the evaluation of PE and randomly selected a matched cohort of 581 patients who had a CTA. For each group, they identified patients who had major venous thromboembolism events, major bleeding, or death during the six months following the initial MRA or CTA scan. The major adverse PE-related event rate (MAPE) was 5.4% in the MRA group and 13.6% in the CTA control group. The lower rate was attributed in part to a younger population in the MRA group who may have had fewer comorbidities and been healthier.

“The University of Wisconsin has offered pulmonary MRA as a clinical service for a decade,” Dr. Repplinger told Applied Radiology. “This retrospective study offers further evidence of its clinical effectiveness and safety. We now need to study what has led to the success of our program compared with others and how to best disseminate our methods.”

The authors reported that the technical success rate of 93% was “likely due to a combination of maturing scanner technology, including improved phased array coils, advanced 2D versus 1D parallel imaging algorithms, use of diluted contrast, and triphasic acquisitions.”

They stated that the results of their study “support the need for a prospective, multicenter, randomized clinical effectiveness trial of MRA versus CTA for primary evaluation of PE using clinical outcomes (MAPE) instead of imaging-focused outcomes.”

REFERENCES

1. Benson DG, Schiebler ML, Repplinger MD, et al. Contrast-enhanced pulmonary MRA for the primary diagnosis of pulmonary embolism: current state of the art and future directions. Br J Radiol. 2017 90(1074):20160901.
2. Raja AS, Ip IK, Prevedello LM, et al. Effect of computerized clinical decision support on the use and yield of CT pulmonary angiography in the emergency department. Radiology. 2012 262(2):468-74.
3. Tsuchiya N, van Beek EJ, Ohno Y, et al. Magnetic resonance angiography for the primary diagnosis of pulmonary embolism: A review from the international workshop for pulmonary functional imaging. World J Radiol. 2018 10(6):52-64.
4. Repplinger MD, Nagle SK, Harringa JB, et al. Clinical outcomes after magnetic resonance angiography (MRA) versus computed tomographic angiography (CTA) for pulmonary embolism evaluation. Emerg Radiol. Published online May 10, 2018. doi: 10.1007/s10140-018-1609-8.