Contrasting Imaging Techniques for Sleep Disordered Breathing:
As a result of our recent editorial board meeting it was decided that the topic of Contrasting Imaging Techniques for Sleep Disordered Breathing is one that the readership was demanding. We decided to have our contributing editor Bradley Eli, DMD, MS do the review. The format is a dialogue and will introduce Dr Eli’s practice as an introduction and a form of disclosure.
Dr. Eli is a graduate of Temple University School of Dentistry. He received a post graduate Masters Degree in Oral Biology and a certificate in orofacial pain at UCLA. He is on the medical staff of Scripps Memorial, Scripps Mercy, Scripps Encinitas, TriCity Hospital, Palmerado Hospital, and UCSD Hospital he also holds a faculty position at UCSD School of Medicine. He is licensed by the American Board of Orofacial Pain, and is a member of numerous professional societies including the the American Board of Orofacial Pain, the American Academy of Orofacial Pain, and the American Academy of Dental Sleep Medicine.
SleepScholar: What is Sleep Treatment Partners?
Dr. Eli: Sleep Treatment Partners is a professional specialty practice separate from my pain practice and is set up for the diagnosis, treatment and education relative to sleep disorders. I realized the patient populations were mutually exclusive. When I graduated from the post doctoral program at UCLA in 1992, I identified that there were significant limitations in the existing field of sleep therapy regarding treatment options. I set out to establish a multi modality practice here in San Diego for that reason.
SleepScholar: How long have you been practicing sleep dentistry and what drew you into the practice?
Dr. Eli: When I entered the field in San Diego I was one of few like kind practitioners in the field of orofacial pain/sleep disordered breathing. In fact, I remain one of three practitioners with this credential in the south counties area of California. I very quickly realized the treatment of Pain and Sleep are inseparable in the patient population.
SleepScholar: What do you see as the crossover point between your sleep practice and your chronic pain practice?
Dr. Eli: Many treatments for pain involve medications which are sedating or have effect on sleep quality. In the early 1990’s, I presented on this topic at the American Academy of Pain Medicine in Denver, Colorado. The talk was called “Pain and Sleep”. Not a very dynamic name, however, I developed the material I drew on for the talk from my experiences on staff at Loma Linda, UCSD and Scripps. The medication given to most pain patents have a significant depressive effect on breathing. Our failure to provide any education to pain fellowship students to identify risk factors was missing. As a result, I founded Sleep Treatment Partners.
SleepScholar: What is your vision of airway imaging in treating Obstructive Sleep Apnea?
The industry has confirmed and no data has yet disputed the success of compliant CPAP therapy. Imaging of the airway is merely an interesting curiosity as everyone agrees that it is not done in real time on a sleeping patient. Therefore, it can never rise to the diagnostic level of PSG or HST. Required imaging to provide intraoral airway dilation or the assessment of nasal airway is just an added pool of data, useful when direct visualization or traditional imaging of the teeth and jaws is inadequate. Clearly, the addition of volumetric CT has had a significant effect on diagnostic testing. Our medical colleagues and patients expect to be advised as to possible success with oral airway dilation. This is a standard of medical and dental practice. We are required to advise the patient of the risks, benefits, and alternatives of their treatment. The assessment of airway diameter and the airway’s reaction to mandibular advancement is a critical piece of this process.
SleepScholar: Could you outline possible Imaging modalities for dental imaging of the airway?
systematically alter the alignment of this magnetization. This causes the nuclei to produce a rotating magnetic field detectable by the scanner—and this information is recorded to construct an image of the scanned area of the body.:36 Strong magnetic field gradients cause nuclei at different locations to rotate at different speeds. 3-D spatial information can be obtained by providing gradients in each direction.
MRI provides good contrast between the different soft tissues of the body, which make it especially useful in imaging the brain, muscles, the heart, and cancers compared with other medical imaging techniques such as computed tomography (CT) or X-rays. Unlike CT scans or traditional X-rays, MRI uses no ionizing radiation.
X-ray computed tomography (CT) is a medical imaging method employing tomography created by computer processing. Digital geometry processing is used to generate a three-dimensional image of the inside of an object from a large series of two-dimensional X-ray images taken around a single axis of rotation.
CT produces a volume of data that can be manipulated, through a process known as “windowing”, in order to demonstrate various bodily structures based on their ability to block the X-ray beam. Although historically the images generated were in the axial or transverse plane, orthogonal to the long axis of the body, modern scanners allow this volume of data to be reformatted in various planes or even as volumetric (3D) representations of structures.
When previously ordering typical CT predetermined “study” volumes were frustrating to and associated with unnecessarily high radiation exposure. Often 5 scans are required to achieve the same clinical yield as a single CBCT scan. CT scans are often read by a radiologist who does not have a background in sleep or dentistry. The report will often cite “clear of pathology” without taking into account the reason for the order. This is frustrating for the patient and the therapist. And therefore has limited value.
Cone beam computed tomography (commonly referred to by the acronym CBCT) is a medical imaging technique that has become increasingly important in treatment planning and diagnosis in implant dentistry, among other things. Perhaps because of the increased access to such technology, CBCT scanners are now finding many uses in dentistry, such as in the fields of endodontics and orthodontics, as well.
During a CBCT scan, the scanner rotates around the patient’s head, obtaining up to nearly 600 distinct images. The scanning software collects the data and reconstructs it, producing what is termed a digital volume composed of three dimensional voxels of anatomical data that can then be manipulated and visualized with specialized software.
CBCT is a fast and clinically rich imaging system. Software makes volume calculation easy and the landmarks resemble those taught in anatomy class.
CBCT tongue base axial view
Pharyngometer/ Rhinometer – measure a patients pharyngeal airway size and stability from the Oral Pharyngeal Junction to the Glottis. The Pharyngometer graphically displays the relationship between the cross-sectional area of the airway and distance down the airway in centimeters. Studies have shown a clear relationship between the existence of OSA and a narrow, collapsible, airway. The Pharyngometer accomplishes these measurements using acoustic reflection technology, similar to a ships sonar. Sound waves are projected down the airway and reflected back out in such a way that the Pharyngometer software can analyze and quantify changes in the airways cross-sectional area. The test is minimally invasive, free of radiation and takes 2-5 minutes to complete.
Rhinometer- allows for quick and easy measurements of nasal patency. The device gathers information using acoustic reflection. Sound waves are sent up the nasal passageway and they are reflected back out in such a way that the Eccovision® Acoustic Rhinometer can accurately map out the topography of the nasal airway. This allows us to clearly identify the location and severity of any obstruction in the airway. The test is completely non-invasive and takes 30 seconds to complete.
When first introduced to dental sleep market Pharyngometry/Rhinometry was the only technology to attempt to identify patients as inappropriate for treatment. The most damaging missteps in early dental sleep medicine was the placement of an OAD in a patient that was contra indicated due to physiologic non response. This had significant impact on early medical referral patterns. It continues to be the primary reason for non-referral for OAT.
Pharyngogram indicating anatomical Landmarks
An Orthopantomogram (OPG), also known as an “orthopantogram” or “panorex”, is a panoramic scanning dental X-ray of the upper and lower jaw. It shows a two-dimensional view of a half-circle from ear to earDental panoramic radiography equipment consists of a horizontal rotating arm which holds an X-ray source and a moving film mechanism (carrying a film) arranged at opposed extremities. The patient’s skull sits between the X-ray generator and the film. The X-ray source is collimated toward the film, to give a beam shaped as a vertical blade having a width of 4-7mm[ when arriving on the film, after crossing the patient’s skull. Also the height of that beam covers the mandibles and the maxilla regions. The arm moves and its movement may be described as a rotation around an instant center which shifts on a dedicatedtrajectory.
Cephalometric analysis is used in dentistry, and especially in orthodontics, to gauge the size and spacial relationships of the teeth, jaws, and cranium. This analysis informs treatment planning, quantifies changes during treatment, and provides data for clinical research.
SleepScholar: Based on the modalities available could you summarize the dental airway imaging requirement for Sleep Disordered breathing?
Dr. Eli: The field of Dental sleep medicine is constantly evolving with improved understanding on multiple levels. As is often the case, the value of technology is fleeting and is constantly under pressure to improve.
In 1995, the AASM published a stance on oral appliance treatment as a viable option. This challenged the dental sleep community to respond. Unlike positive pressure devices that rely on continuous positive air pressure to offset collapse of the airway, oral appliance treatment and tongue retaining devices provided anatomic change to effect a positive impact on the airway collapse. This mechanism of action is distinctly different and therefore creates a much greater level of variability in patient selection.
When a patient has been identified as being a candidate for oral device treatment, we are expected to provide our sleep physician colleagues and our patients with an informed treatment decision. Because of the anchoring and action of oral devices affecting the teeth, jaw and airway, imaging and assessment of these structures is needed. This is coupled with clinical examination of the intraoral structures, which must be provided by a trained caregiver familiar with “normal”.
Radiographic examination of the teeth was historically completed by “PA” x-rays. These show two to three teeth per film, and a “full mouth series” requires 14 or more shots. The temporomandibular joint is not seen in this series, therefore, a shot of the joint was recommended by the providers familiar with the mechanism of action of mandibular advancement devices. Needing a diagnostic image of the teeth and jaw joint, the panorex was a logical step in the screening process. Less time and greater field of view was the result of the panorex (aka PAN). Also, seen on the “PAN” was the nose and sinuses. This “added” benefit was available and therefore added to the image review. If gross abnormality is observed, ENT consult should be requested. The PAN, however, is severely limited by its two dimensions.
Pharyngometry as an indirect imaging technique as related to sleep medicine was first discussed in the 1990s. Under the continuing thread of “airway assessment” this tool was rapidly embraced by some in the field as a method to attempt to identify a reduced airway size and to provide the elusive treat / not treat point with intraoral appliance therapy. All of the individuals using this technique did so in the hope that this information would provide us with the data to assist in a pretreatment success or failure assessment. The sensitivity and specificity of this device failed, due to its use on awake, seated patients. The data provided by this imaging modality has little to no use for the user or the patient. This reality is a painful reminder of the limited value of technology and the speed of obsolescence, our offices have multiple pharyngometers/rhinometers that we no longer use.
With the need to image the teeth and TM Joint a dental necessity, and cone beam volumetric computerized tomography giving these two structures in a single image. It is obviously the single most valuable image currently available. It shows the entire airway, dentition and joint, fully accessible and transferable to any and all other providers. We no longer use any other imaging tool as all the information needed for our treatment and assessments of risk factors is available in a single session. Furthermore additional information including that needed by our surgical colleagues is also available utilizing CBCT.
The value of Dental experts in the field of sleep disorders is largely that of expanded treatment options and providing an informed treatment plan for patients with Sleep Disordered Breathing. CPAP failure is not the best reason for treatment with oral appliance therapy or tongue retaining device therapy.
As outlined clearly in the AASM 2005 position paper, due to compliance rates and acceptance many patients should be provided the option, of an oral appliance, as their initial therapy. Despite this position little change in sleep physician referral patterns has been seen. However this is an area that dentistry may provide the most education and value for in the future of the field and patients.
Our responsibility is to provide the field with reasonable expectations of treatment success based on valid, reliable data gathering. It is unreasonable to provide diagnostic testing that does not expand understanding of disease, or identify patients appropriate for treatment.
Failure to be vigilant on this path severely restricts both our current access to patients, and will irreversibly damage our standing in the medical community for the foreseeable future.
As a matter of disclosure Dr. Eli uses an outside imaging service for all diagnostic testing. He owns many pharyngometers purchased in 2001 these devices are no longer in use. Dr Eli has practices in Encinitas CA, Highland CA, Laguna Hills CA and Indio CA he can be reached at firstname.lastname@example.org his website is DrBradEli.com