Thoracic MRI: An alternative to chest CT for HIV-positive children

Thoracic magnetic resonance imaging (MRI) may be a viable alternative to chest computed tomography (CT) for HIV-positive children presenting with pulmonary symptoms. The diagnostic accuracy of 3T lung MRI is nearly comparable to chest CT for detecting nodules greater than 4 mm, effusion, and lymphadenopathy, according to a study from India published in the September 13, 2019, online edition of Pediatric Radiology.¹

Avoiding the radiation of CT is advantageous for HIV-positive children, who are at high risk for recurrent pulmonary diseases and permanent lung changes because they may require many more imaging exams and incur much higher cumulative radiation exposure than their non-HIV-positive peers.

Researchers at the Post Graduate Institute of Medical Education and Research in Chandigarh conducted a prospective study to evaluate 3T thoracic MRI against chest CT. Twenty-five HIV-positive children, aged 5 to 15 years, with pulmonary symptoms underwent both chest CT and  3T thoracic MRI exams within 72 hours following an abnormal chest X-ray suspicious for  pulmonary tuberculosis, pneumonia, interstitial lung disease, and empyema. Two patients were asymptomatic, but their chest radiographs suggested pulmonary involvement.

Principal investigator Kushaljit Singh Sodhi, MD, PhD, said he and his colleagues developed a rapid,3T thoracic MRI protocol to avoid the need for sedation while obtaining maximum information in the shortest possible scan time. Sequences included a T2-weighted (T2W)  turbo spin-echo sequence, steady-state free precession gradient echo sequence, T2W turbo spin-echo MiltiVane XD sequence, and T1-weighted modified Dixon sequences. Scan time averaged 6 minutes, and patients spent 20 to 30 minutes in the MRI suite. Exam time could be further decreased if limited sequences in indexed cases were selected.

Two pediatric radiologists without access to the patients’ clinical records independently reviewed the MRI and CT scans. Summarizing their comparison with chest CT, the researchers found that thoracic MRI diagnosed:

• All 18 children with lymphadenopathy,
• All 3 children with pleural effusion,
• All 5 children with pulmonary nodules greater than 4 mm,
• 7 of 20 children with pulmonary nodules smaller than 4 mm,
• 15 of 16 children with consolidation/collapse,
• 9 of 12 children with bronchiectasis; and,
• 6 of 8 children with ground-glass opacities.

“Thoracic MRI should be used conditionally as it showed high sensitivity and specificity, mainly for consolidation, nodules (>4 mm), effusion, and lymphadenopathy in HIV-positive children,” Dr. Sodhi told Applied Radiology. “Nodules less than 4 mm were not well detected on MRI in our study, with a sensitivity of only 35%.”

“We have shown in previous research work that evaluation of septal thickening, ground-glass opacity, small nodules, and cysts is limited with 3T lung MRI,” he added.² “So, in cases with interstitial lung disease, MRI may not pick up all the findings expected to be seen on CT. And in cases where small nodules are expected radiological findings, such as in lung metastasis or in centrilobular nodules, lung MRI may not be actually beneficial. Hence, lung MRI should be used judiciously in a given clinical setting and not across the board for all purposes.”

Dr. Sodhi was encouraged with the study findings and the MRI protocols used to acquire diagnostic quality images. “The MRI protocol used in our study may be used in children across all age groups. It has the potential of changing our diagnostic algorithms and saving these children from unnecessary radiation as we can perform fast … MRI scans in these children instead of performing a CT scan,” he said. “When a protocol we developed and validated for thoracic imaging with 1.5T MRI scanner, the scan takes only two minutes.”³

“Finally, in cases where baseline CT has already been done, MRI can be used as a radiation free modality to look for the resolution or progression of the disease in follow-up imaging,” he said.

REFERENCES

1. Rana P, Sodhi KS, Bhatia A, et al. Diagnostic accuracy of 3-T lung magnetic resonance imaging in human immunodeficiency virus-positive children. Pediat Radiol. Published online September 13, 2019. doi: 10.1007/s00247-019-04523-0.
2. Sodhi KS, Sharma M, Lee EY, et al. Diagnostic utility of 3T Lung MRI in children with interstitial lung disease: A prospective pilot study. Acad Radiol. 2018;25(3):380-386.
3. Sodhi KS, Khandelwal N, Saxena AK, et a. Rapid lung MRI in children with pulmonary infections: Time to change our diagnostic algorithms. J Magn Reson Imaging. 2016;43(5):1196-1206.