Diffusion MR technique shows promise for pediatric lung assessment

Hyperpolarized helium-3 diffusion MR can detect alveolar changes due to lung disease in children and provide quantitative data on airflow to the peripheral lobes, according to research presented at the RSNA meeting.

Improvements in therapeutic management have increased life expectancies for children with lung diseases, particularly those with cystic fibrosis. That benefit has prompted researchers to investigate various MRI techniques that allow lifelong scanning with no radiation exposure.

In one of the first studies of its kind, Dr. Talissa Altes and colleagues from the University of Virginia in Charlottesville sought to determine whether hyperpolarized helium-3 (HHe) diffusion MR can detect the expected alveolar enlargement that occurs with normal lung growth during childhood.

The researchers examined 29 normal children whose ages ranged from four to 30 years (only nine were older than 18). They used a FLASH-based pulse sequence during a breath-hold following inhalation of a mixture of HHe and nitrogen gas. The team calculated the apparent diffusion coefficient on a pixel-by-pixel basis and determined the mean ADC for each subject. They also determined lung volumes from the HHe scans.

All subjects successfully cooperated for the exam. The mean ADC increased with subject age (pp

In another study, Jim Wild, Ph.D., and colleagues from the University of Sheffield found that dynamic HHe can provide quantitative measurement of localized airway obstruction in the early stages of cystic fibrosis. The quantitative data were obtained by using the slope of the signal rise as a measure of airflow to the peripheral lung.

Researchers evaluated the signal kinetics of eight pediatric patients in six regions of interest, three in each lung. They compared these with spirometric pulmonary function tests.

In all patients, a pattern of low flow rate in the upper lobes was observed, which corresponds with the known preferential distribution of cystic fibrosis in the upper lobes, Wild said. The study also demonstrated that children can cooperate well with HHe diffusion MR.

Dr. Pedro Augusto Daltro and colleagues at Instituto Fernandes Figueira in Brazil compared the accuracy of MRI to detect the main pulmonary aspects of cystic fibrosis with CT.

Researchers found MRI ably depicted bronchiectasis, mucus plugging, bronchial wall thickening, consolidation, air-fluid level, and infiltration compared with the HRCT. A 3D lung perfusion imaging technique showed perfusion defects in parenchyma with severe changes and homogeneous perfusion in normal parenchyma.

MRI offers several advantages, including avoidance of radiation exposure and the ability to gather morphological and functional information in a single exam. The quality is not quite the same as HRCT, Daltro said, and MRI is more expensive and requires long breath-holds.

Given the longer life spans of children with lung diseases made possible by improvements in therapeutic management, however, MRI is an able tool for this patient population, he said.

For more online information, visit Diagnostic Imaging's RSNA Webcast.