In-silico study of accuracy and precision of left-ventricular strain quantification from 3D tagged MRI

Cardiac Magnetic Resonance Imaging (MRI) allows quantifying myocardial tissue deformation and strain based on the tagging principle. In this work, we investigate accuracy and precision of strain quantification from synthetic 3D tagged MRI using equilibrated warping. To this end, synthetic biomechanical left-ventricular tagged MRI data with varying tag distance, spatial resolution and signal-to-noise ratio (SNR) were generated and processed to quantify errors in radial, circumferential and longitudinal strains relative to ground truth. Results reveal that radial strain is more sensitive to image resolution and noise than the other strain components. The study also shows robustness of quantifying circumferential and longitudinal strain in the presence of geometrical inconsistencies of 3D tagged data. In conclusion, our study points to the need for higher-resolution 3D tagged MRI than currently available in practice in order to achieve sufficient accuracy of radial strain quantification.

Pharyngeal enlargement via tongue advancement differs with mandibular advancement therapy response and improves treatment prediction

Introduction Mandibular advancement splint (MAS) treatment outcome prediction for obstructive sleep apnoea (OSA) is currently unreliable. Lower baseline AHI has been associated with better MAS response but is a poor predictor on its own. Imaging markers may enhance prediction. We investigate how the upper airway enlarges via posterior tongue advancement, using tagged MRI during mandibular advancement, as a potential predictor of MAS treatment response. Methods 101 untreated OSA participants (AHI 10–102 events/hr) underwent an MRI scan wearing a MAS. Mid-sagittal tagged MRI images were collected to quantify tongue movement during passive jaw advancement. Upper airway cross-sectional areas were measured with the mandible in a neutral position and advanced to 70% of the maximum protrusion. Treatment outcome was determined after a minimum of 9 weeks of therapy. Results 71 participants completed the study: 33 were responders (AHI<5 or AHI≤10 events/hr with >50% AHI reduction), 11 were partial responders (>50% AHI reduction but AHI>10 events/hr), and 27 non-responders (AHI reduction<50% and AHI≥10 events/hr). Responders had the greatest naso- and oropharyngeal tongue advancement (0.40±0.08 and 0.47±0.13mm, respectively) and oropharynx enlargement (6.41±2.12%) per millimetre of mandibular advancement. The inclusion of these imaging markers along with baseline AHI in a multivariate model classified more patients in the right MAS response group (69.2%) than a model based only on baseline AHI (50.0%) when the mandible was advanced by at least 4 mm. Conclusions Tongue advancement and upper airway enlargement with mandibular advancement in conjunction with baseline AHI improves MAS treatment response categorisation to a satisfactory level.