Cine MR imaging provides the 3D isotropic resolution necessary to obtain very high spatial and temporal imaging of the entire upper airway and surrounding soft tissue, allowing for high-quality computerized reconstruction of the entire airway, according to researcher Mark Wagshul, Ph.D., who introduced the technique at RSNA 2011 and presented his most recent findings at RSNA 2012.
“Cine MR imaging offers complete coverage of the entire upper airway with isotropic resolution, allowing image reformatting in any plane you desire,” said Dr. Wagshul, an associate professor at the Gruss Magnetic Resonance Research Center at the Albert Einstein College of Medicine, New York. “Also, the entire airway is collected under identical respiratory conditions. Finally, the technique provides retrospective gating which can be used to limit imaging to specific physiological conditions such as normal tidal breathing versus an apneic event.”
OSAS affects 3 to 7 percent of the adult population, more than half of whom are overweight. Other risk factors for OSAS include a narrowed airway, family history, being older (OSAS occurs significantly more in those over 60), and use of alcohol, sedatives or tranquilizers. Untreated, OSAS can lead to heart attacks, strokes, impotence, irregular heartbeat, high blood pressure and heart disease and can cause daytime sleepiness resulting in accidents, work-related problems and interpersonal problems, among other issues.
OSAS is also present in 2 to 4 percent of children, but the incidence increases by as much as 50 percent for obese children. “It’s becoming especially important given the increasing prevalence of obesity in children in the U.S.,” Dr. Wagshul said. “Obstructive sleep apnea syndrome is associated with fatigue and poor school performance.”
Very detailed computational models of the airway and surrounding tissues can be created using the dynamic information available, providing the physicians with information about flow, pressure and airway motion unique to OSAS patients. The technology will also allow simulation of surgical procedures, allowing physicians to see the impact a procedure such as tonsil removal would have on airway flow.
“This is critical for allowing surgeons to practice a more focused and physiology-based approach to resection with better outcomes,” Dr. Wagshul said.
In their latest study, Dr. Wagshul and colleagues examined 20 females between 13 and 18 years old who being were evaluated for polycystic ovary syndrome (PCOS), a disorder affecting 5 to 10 percent of girls and women of reproductive age which leads to obesity and has been associated with OSAS. OSAS is 30 times more prevalent in females with PCOS than in the general population, Dr. Wagshul said.
Researchers detected three patients with severe OSAS and four with mild OSAS and imaged the computerized models of the girls’ upper airways while they were awake. Images of the severe cases revealed the upper portions of the airway constricting during one part of the breathing cycle and at the same time expanding lower down in the airway. Cases of mild OSAS revealed more synchronous motion of the entire airway.
“In the more severe patients, we can see an abrupt change in the timing of the airway motion going from the velopharynx into the oropharynx, precisely at the site of restriction in the severe cases,” Dr. Wagshul said. “Other studies in the group have shown that such motion may be due to activation of the muscles surrounding the airway, likely compensation for change in airflow due to the airway constriction.
Dr. Wagshul continues to examine data from the study.
Although the standard diagnostic test for OSAS is a polysomnogram, Brazilian researchers contend that multislice craniofacial CT imaging can aid ENT physicians and maxillofacial surgeons in detecting soft tissue and skeletal factors that can alter the mechanical properties of the upper airway and its tendency to collapse during sleep.
A number of anatomical features can predispose a person to OSAS, many of them potentially treated with surgery, said Natalia Sabaneeff, M.D., a radiologist at Centro De Diagnostico Por Imagem in Rio de Janeiro who presented, “3D CT Cephalometric Analysis and Sleep Apnea: How Can We Help the Otorhinolaryngologist?” at RSNA 2012.
“Retrognathia and maxillary deficiency, low positioned hyoid bone, enlarged soft palate and tongue and tonsillar hypertrophy are some of the conditions that can increase the incidence of sleep disorders,” Dr. Sabaneeff said. “MDCT and cephalometric analysis can help diagnose anatomical causes of sleep apnea, affecting the management of such patients.”
Cephalometric analysis—the study of dental and skeletal relationships in the head—can be performed by radiograph, CT and even MR imaging, Dr. Sabaneeff said. “However, MDCT is the best single imaging method to study patients with sleep apnea,” she added. “It provides great spatial resolution in a short acquisition time and allows tridimensional reconstructions for studying skeletal abnormalities and soft tissue/airway analysis.”
MDCT can further aid ENT physicians by providing information to determine a course of treatment potentially more helpful than continuous positive airway pressure (CPAP), the standard OSAS treatment. This is especially true when patients using oral appliances such as tongue-retaining devices present with anatomic factors that could result in OSAS. In addition, MDCT can help physicians decide whether to perform surgical treatments such as nasal surgery, uvulopalatopharyngoplasty, genioglossus advancement, adenotonsillectomy and maxillomandibular advancement.
“In order to decide the best treatment option, it is essential to perform cephalometric studies in those patients,” Dr. Sabaneeff said. q
Hear Mark Wagshul, Ph.D., an associate professor at the Gruss Magnetic Resonance Research Center at the Albert Einstein College of Medicine, New York, discuss:
To access an abstract of the research, “Novel Retrospective, Respiratory-Gating Method Enables 3D, High Resolution, Dynamic Imaging of the Upper Airway During Tidal Breathing,” by Dr. Wagshul and colleagues, go to www.ncbi.nlm.nih.gov/pubmed/23401041.
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