Sufferers of obstructive sleep apnea (OSA) can be evaluated with ultrasound images of the tongue captured as the patient, awake, performs a simple breathing exercise.
Taiwanese researchers demonstrated the usefulness of the procedure for planning treatment strategies, publishing their findings online Sept. 20 in Ultrasound in Medicine & Biology.
The researchers, from National Cheng Kung University in Tainan and Fu-Jen Catholic University in New Taipei City, designed their study to develop and verify a dedicated tracking algorithm for monitoring movements in the base of the tongue in patients with OSA.
They call their algorithm the modified optical flow-based method and explain how they tested its accuracy and demonstrated its use with ultrasound image sequences.
The team enrolled 21 patients with OSA and nine control volunteers. Each participant performed the Müller [breath] maneuver (MM), in the process “simulating the contour changes of the tongue base with a negative pharyngeal airway pressure” as experienced in sleep apnea, the authors explain.
The researchers obtained the ultrasound image sequences during a 10-second transition from normal breathing to the maneuver. These were measured using the team’s modified optical flow-based method.
They verified the performance of their method by gathering phantom and synthetic data, and they evaluated the efficacy of the algorithm by calculating the estimated displacement error.
The percentage changes in the tongue area were 2.2 percent in the controls and 1.3 percent in the OSA patients.
“All results indicated that the modified optical flow-based method exhibited higher accuracy” than another method used for comparison, the normalized cross-correlation method, the authors report.
“We found that quantitative assessment of tongue motion by ultrasound imaging is suitable for evaluating pharyngeal airway behavior in OSA patients with minimal invasiveness and easy accessibility,” they write. “We confirm the present method as an alternative objective clinical modality for simple and tolerable evaluation of the potential patterns and severity of upper-airway obstruction in patients with OSA while they are awake.”