Techniques for Respiratory Motion-Resolved Magnetic Resonance Imaging of the Chest in Children with Spinal or Chest Deformities: A Comprehensive Overview

Abstract

Quantification of the severity of chest wall deformation in children with spinal deformities is essential for understanding the effects on trunk appearance and cardiopulmonary function. Magnetic resonance imaging (MRI) is particularly valuable for this purpose, as it does not employ ionizing radiation and can provide three-dimensional (3D) imaging of thoracic anatomy. Acquiring sufficient quality images of the chest wall, lungs and airways at key stages of the respiratory cycle, such as end-inspiratory or expiratory phase, is crucial for accurately assessing chest wall deformation and pulmonary function and mechanics. Regarding image quality, low proton density and short relaxation times of the lung tissues result in poor quality images, and long acquisition times result in blurring caused by respiratory and cardiac motion. This overview summarizes strategies developed to address the inherent challenges of visualization of lung tissue and respiratory motion in MRI acquisition of the chest of pediatric patients with spinal deformities. An overview of the main methods for motion-resolved image acquisition and measurement of chest wall motion and thoracic volumes is presented and discussed. It is concluded that despite the development of multiple techniques and diverse strategies for obtaining high-quality, motion-resolved chest MRI, further validation of these methods is required before their implementation in clinics for routine evaluation of chest deformation in pediatric spinal deformity patients.

Keywords: MRI; motion; respiration; scoliosis; thoracic deformity.

Figure 1

Navigator echo. (a) A thin field of view (green area) is excited over the diaphragm dome. (b) The respiratory waveform is reconstructed. This image does not represent a real navigator echo acquisition but is intended solely to illustrate the concept.

Figure 2

Main distances and diameters measured in dynamic MRI studies [8,21,26,28]. These are typically measured on full-inspiration and full-expiration images to estimate the chest and diaphragm motion by calculating the difference between both measurements. Abbreviations: DH = diaphragmatic height, AP = anteroposterior diameter, TR = transverse diameter.

Figure 3

Reconstruction of images at different respiratory phases. Images corresponding to different respiratory phases can be reconstructed by selecting different threshold values on the DC signal respiratory waveform. The red dotted lines delimit the thresholds between the three breathing phases. The white dotted line provides a visual aid to compare the diaphragm position among the three respiratory phases. This figure does not depict a real DC signal waveform or reconstruction but is intended solely to illustrate the concept.