Добавил:
Sekretar
kiopkiopkiop18@yandex.ru
t.me/Prokururor I Вовсе не секретарь, но почту проверяю
Опубликованный материал нарушает ваши авторские права? Сообщите нам.
Вуз:
Предмет:
Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_4421_Библиотеки_им_академика_М_И_Перельмана.pdf
Cone-Beam CT Use forAirway Imaging
87
8
8.2 Accuracy andReliability ofMeasuring
theAirway Using CBCT
Validation of CBCT technology to measure the airway has been evaluated in several studies [3, 7–11].
Accuracy and reliability of airway volume digital
measurements of CBCT compared with the manual
measurements of an airway model was investigated by
constructing an acrylic airway model attaching it to a
human dry skull in the natural position of the airway
passage [7]. The total and internal airway volumes, as
well as the most constricted airway area, were measured manually on the model and on the CBCTs taken
after the model was attached to the skull. Results suggested that the CBCT digital measurements of the
airway volume and the most constricted area of the
airway are reliable and accurate [7]. Another article
evaluated the accuracy of measurements made on
CBCT images compared with the gold standard which
is measurements made on a coordinate measuring
machine [8]. The authors found that the coordinate
correlation coefcient was virtually identical between
the 3-3D CBCT images and the coordinate measuring
machine measurements [8]. Evaluation of upper airway using airway phantoms report high accuracy and
reliability of CBCTs in measuring airway [9]. Amirlak
etal. used a manual segmentation program to test the
reliability and accuracy of CBCT images in measuring
volumes, of articial defects, subsequently lled with
polyvinyl siloxane (PVS). They used a water displacement technique for comparing the CBCT volumes
with actual volumes and found that the manually segmented volumes were highly accurate compared to the
water displacement technique which is considered as
the gold standard [10]. Tsolakis etal. investigated the
difference between CBCT and the acoustic reection
(AR) imaging technique in calculating airway volumes
and areas. Subjects with prescribed CBCT images as
part of their records were also asked to have AR performed. A total of 59 subjects had their upper airway
measured from CBCT images, acoustic rhinometry,
and acoustic pharyngometry. It was found that CBCT
is an accurate method for measuring anterior nasal
volume, nasal minimal cross-sectional area, pharyngeal volume, and pharyngeal minimal cross-sectional
area [11]. Commercially available digital imaging and
communications in medicine (DICOM) viewers for
measuring upper airway volumes were compared to
show that manual segmentation was more accurate
than semiautomatic segmentation, but all of them
showed high correlations, suggesting the existence
of a systematic error in the derivation of the airway
volume[3].
8.3 Evaluation ofUpper Airway Using CBCT
This section provides a step-by-step guide for the airway
analysis.
(a) Orientation
In order to create different views in a standardized way
and to obtain consistent measurements using CBCT
images, image orientation should be the rst step within
the software. A simple way to orient the volume can be
done by adjusting the midsagittal plane on the skeletal
midline of the face, then adjusting the axial plane on top
of the Frankfort horizontal plane, and the coronal plane
so it passes through the level of the furcation point of
the right maxillary rst molar (. Fig. 8.2) [12]. The
Case Western Reserve University (CWRU) orientation
method is a more complex one and uses ve biologically
relevant anatomic structures and one plane [13].
(b) Segmentation
Upper airway segmentation can be performed accurately either manually which is more time consuming
or semiautomatically which is signicantly faster. In the
semiautomatic approach, the software automatically differentiates the air and the surrounding soft tissues by
using the differences in density values of these structures
because the air space is of a greater negative Hounseld
unit than the more dense surrounding soft tissue. A
new tool in commercial software products allows us to
visualize the different densities in different tissues in
the craniofacial complex with the aid of the Hounseld
Unit Color Mapping, which helps distinguish between
different biological structures according to their radiolucency measurements. A graph displays the colors as
they fall on the Hounseld Scale as a reference, while the
image on the screen is colored accordingly (.
Fig.8.3).
Automatic segmentation also allows the airway to be
measured along a curved path, instead of simply along
horizontal slices and an airway color coded by constriction is presented. Another method to measure the airway by setting boundaries to the region of interest based
on specic anatomical landmarks. Although it is mainly
automatic, adjusting the airway sensitivity scale and
placing seeds in the regions of interest to allow accurate
segmentation is required in some commercial software
products. .
Figures8.4, 8.5, and 8.6 show the different
methods to measure the upper airway.
Segmentation of Different Regions of Interest. The
below regions of interest are areas commonly studied
with suggested anatomic limits for proper reliability.
There may be slight variations found in different studies,
and slight variations with the true anatomic denition
of such region.
88
J. M. Palomo et al.
8
. Fig. 8.2 Volume orientation can be done by adjusting the mid-
sagittal plane on the skeletal midline of the face, then adjusting the
axial plane on top of the Frankfort horizontal plane, and the coronal
plane, so it passes through the level of the furcation point of the
right maxillary rst molar
. Fig. 8.3 Three-dimensional reconstructed images in different
planes of space showing different densities in different tissues in the
craniofacial complex with the aid of the Hounseld Unit Color
Mapping tool, which helps you to distinguish between different bio-
logical structures according to their radiolucency measurements. A
graph displays the colors as they fall on the Hounseld Scale as a
reference, while the image on the screen is colored in accordingly
Cone-Beam CT Use forAirway Imaging
89
8
. Fig. 8.4 Setting boundaries to the region of interest based on specic anatomical landmarks. Although it is mainly automatic, adjusting
the airway sensitivity scale and placing seeds in the regions of interest to allow accurate segmentation is required
1. Nasal Passage: The volume is dened as being the
pharyngeal volume located between the palatal plane
and a parallel plane passing through the last axial
sented in an automatic setting with volume measurement or can be enabled through features in different
software packages (. Fig.8.12).
slice before the nasal septum fused with the posterior
pharyngeal wall. Once boundaries are outlined in the
sagittal plane, additional boundaries outlining the
8.4 CBCT and OSA
respective airway are made in the axial and coronal
planes (. Figs.8.7 and 8.8).
2. Oropharynx Volume: The volume is dened as the
pharyngeal volume located between a plane passing
through the palatal plane (PNS-ANS) and a parallel
plane passing through the most antero- inferior point
of the second cervical vertebrae (.
Fig.8.9).
3. Hypopharynx Volume: The volume is dened as the
pharyngeal volume located between the inferior limit
of the oropharynx volume and a parallel plane passing through the most antero-superior point of the
hyoid bone (. Fig.8.10).
4. Retro-palatal Volume: From the level of posterior
nasal spine to the lower edge of the soft palate
(. Fig.8.11a).
5. Retro-glossal Volume: From the lower edge of the
soft palate to the hyoid bone (. Fig.8.11b).
6. The minimum axial area, also known as the area of
maximum constriction (mm
2
), can be determined for
the whole airway volume or just in specic region of
interest. Maximum constriction area can be pre-
OSA is a common disorder characterized by collapse
of the upper airway during sleep resulting in hypoxemia and arousal [14]. CBCT can be employed to assess
the location of obstruction in OSA patients. One study
compared the upper airway structure in OSA patients
and control subjects using CBCT images [15]. It was
shown that OSA subjects presented lower total airway
volume, smaller anterior-posterior dimension of the
minimum cross-section segment, and smaller minimum
cross-section area. Also, the OSA group showed ellipticshaped airway, while the non-OSA group showed round
or square airway [15]. Another study compared CBCT
scan measurements between patients with OSA and
snorers to develop a prediction model for OSA based
on CBCT imaging and the Berlin questionnaire. It was
found out that the upper airway dimension was signicantly smaller in the OSA patients [16]. Recent study
evaluated the upper airway dimensions of OSA and
control subjects using CBCT.Results showed that OSA
subjects had a signicantly smaller average airway area,
90
J. M. Palomo et al.
8
. Figs. 8.5 and 8.6 Automatic segmentation of the airway measured along a curved path, instead of simply along horizontal slices and an
airway color coded by constriction is presented
Cone-Beam CT Use forAirway Imaging
91
8
. Fig. 8.5 and 8.6 (continued)
92
J. M. Palomo et al.
8
. Fig. 8.7 Nasal passage volume is dened as being the pharyngeal volume located between the palatal plane and a parallel plane passing
through the last axial slice before the nasal septum fused with the posterior pharyngeal wall
average airway volume, total airway volume, and mean
8.5.1 CPAP
airway width. OSA subjects had a signicantly larger
airway length measurement [17].
The hyoid bone which is a predictor of airway obstruc-
tion plays an important role in the airway patency. Links
between hyoid position and airway resistance have been
demonstrated in the literature [18–20]. The increased distance of the hyoid bone to mandibular plane has shown
to be correlated to OSA in the literature; more than
15mm is considered abnormal and associated with OSA
[21]. One study demonstrated the correlation of upper
airway resistance with the posterior airway space and the
vertical/horizontal position of the hyoid bone. A more
downward position of the hyoid bone was demonstrated
in OSA subjects compared to normal subjects [22].
CPAP is the most effective method to manage OSA.It
improves subjective and objective measures of sleepiness [24].The most signicant effect is enlargement of
the airway by dimensional changes of the lateral pharyngeal walls. Our study in the 1980s showed that CPAP
acts as a pneumatic splint and passively open the upper
airway to prevent obstructive apnea [14]. A recent study
evaluated OSA patients by taking CBCT scans during
application of positive and negative pressures to the
respiratory system while awake and seated [25].The rst
scan was taken during a cycle of resting breathing. Two
other images were obtained when pressure was applied
using a full facemask also in the seated posture during
wakefulness. The mask was connected to a positive/negative pressure source. One scan was taken while breath-
8.5 Evaluation ofOSA Treatment
Approaches Using CBCT
ing on a mask pressure of +10cm H2O and the other
scan was taken while the patient breathed against a mask
pressure of– 2cm H2O (. Figs.8.13 and 8.14). Positive
Continuous positive air pressure (CPAP) is the standard, rst-line therapy for treating OSA; however, the
general effectiveness of initial CPAP therapy is dependent on patient acceptance and adherence to treatment
[23]. Other options include oral appliances, nerve stimulation, and surgical procedures to anatomically improve
airway function.
pressure application of +10cm H2O showed signicant
airway volume increase in all regions (36%). The hypopharynx volume increased the most with 50%, followed
by oropharynx with 23%, and the nasopharynx with
17.7%. The minimal cross-section area changed from
100.57±38.74mm2 to 130.64±64.01mm2.There was
no signicant change of the tongue length when using
Cone-Beam CT Use forAirway Imaging
93
8
. Fig. 8.8 Nasal passage volume segmentation and outcome
positive pressure. Superimposition on the cranial base
showed no change in the hyoid bone position vertically
or horizontally. Negative pressure showed a signicantly
airway volume decrease in all regions (−28%). The volume of the upper airway was nearly collapsed with the
negative pressure. The oropharynx decreased the most,
with −31%, followed by the hypopharynx with 30%,
and the nasopharynx with 19.0%. The average minimal
cross-section area changed from 100.57±38.74mm2 to
52.00±23.01mm2 with no change in hyoid bone posi-
tion and tongue length. It was concluded that increases
and decreases in intraluminal pressure alter the airway
geometry but do so without changing hyoid position.
8.5.2 Oral Appliances
An oral appliance is tted to the upper and lower teeth
and is designed to work by xing and/or anterior positioning the mandible, preventing the collapse of the
94
J. M. Palomo et al.
8
. Fig. 8.9 Oropharynx volume is dened as the pharyngeal volume located between a plane passing through the palatal plane (PNS-ANS)
and a parallel plane passing through the most antero- inferior point of the second cervical vertebrae
tongue and/or increasing the posterior oropharyngeal
airway space, therefore reducing the collapse of the upper
airway during sleep [26]. Oral appliances can be rstline therapy but are more commonly used for patients
who are not compliant with CPAP and diagnosed with
mild and moderate OSA; and oral appliance also treats
simple snoring. Recently, the American Academy of
Sleep Medicine recommended the oral appliances as a
rst line of therapy in patients with mild- to- moderate
OSA.In a randomized clinical trial, the treatment outcome of oral appliances and CPAP therapy of OSA
shown that the upper airway was increased mainly by
increasing the volume of the velopharynx [29].
. Figure8.15 shows airway volume changes for one
patient with and without oral appliance.
Dental side effects associated with oral appliances
and CPAP were assessed in a randomized clinical trial to
show that there is a small dental change with oral appliances but signicant if compared with CPAP.Different
studies showed decrease in overbite and overjet, proclination of lower incisors, retroclination of upper incisors
[30–35].
patients was reported to show that oral appliance should
be considered as an alternative to CPAP in patients with
mild-to-moderate OSA.While patients with severe OSA,
8.5.3 Maxillomandibular Advancement
CPAP should remain the rst line of treatment [26].The
most commonly used oral appliances are the mandibular advancement devices which reposition the mandible,
tongue, and hyoid bone anteriorly to increase dimensions
of the upper airway [27, 28]. The upper airway structures
were evaluated in patients with OSA by using MRI scans
of upper airway with and without oral appliances. It was
Maxillomandibular advancement (MMA) surgery is a
well-established treatment of obstructive OSA [36]. The
rationale for MMA is to increase the anteroposterior
and the lateral dimensions at multilevels of the upper
airway [37], and reduce upper airway collapsibility
with the superior and anterior movement of the hyoid
Cone-Beam CT Use forAirway Imaging
95
8
. Fig. 8.10 Hypopharynx volume is dened as the pharyngeal volume located between the inferior limit of the oropharynx volume and a
parallel plane passing through the most antero-superior point of the hyoid bone
bone [38]. In systematic review of data regarding MMA
advancement for OSA treatment, it was shown that
MMA advancement is the most successful surgical therapy for OSA [39]. Schendel etal. evaluated 10 patients
with moderate or severe OSA who underwent MMA
surgery by preoperative and postoperative cone beam
computed tomography scans and polysomnograms. The
volume of the UAS increased signicantly by 237% as a
result of the MMA.The retropalatal volume increased
more than retroglossal volume, 361% to 165% [21].
Linear and volumetric morphological changes of upper
airway after MMA for OSA patients were assessed using
CBCT. It was shown that MMA increased the airway
total volume, minimal cross-sectional area, anteroposterior and lateral dimensions, airway index, airway length,
posterior airway space morphology, Apnea–hypopnea
index (AHI), and Epworth sleepiness score [36]. CBCT
images are recommended for three-dimensional airway
and soft tissue evaluation in treatment of obstructive
sleep apnea syndrome (. Fig.8.16) [40].
8.6 Upper Airway Stimulation
A relatively novel and cutting edge treatment is upper
airway electrical stimulation (UAS) therapy using a
fully implanted system. The Inspire implant (Inspire
Medical Systems, Inc., Maple Grove, MN and FDA
approved in April 2014) is offered for the treatment of
moderate-to- severe obstructive sleep apnea who cannot
use CPAP therapy, and is known to decrease the severity and symptoms of OSA in selected patients [41–44].
The therapeutic approach, as initially described, is to
deliver stimulation to the hypoglossal nerve, synchronized with breathing efforts [45]. The patient can turn
the therapy on before bedtime, and off in the morning
96
J. M. Palomo et al.
8
. Fig. 8.11 a Retropalatal volume: From the level of posterior nasal spine to the lower edge of the soft palate. b Retroglossal volume: From
the lower edge of the soft palate to the hyoid bone
. Fig. 8.12 The minimum axial area, also known as the area of maximum constriction (mm2), which can be determined for the whole air-
way volume or just in specic region of interest
using a remote control. When the device is activated, it
senses the person’s breathing patterns, delivering mild
stimulation in order to keep the airway open, acting in a
similar way than a pacemaker. The level of stimulation
can be custom to each patient depending on patient’s
unique BMI and AHI.The UAS system is implanted
on the right-hand side of the patient while under general anesthesia, through three surgical incisions. The
median time for implantation has been reported to
average 140minutes, with most patients spending the
night at the hospital [43]. A recent study evaluated
seven patients who had previously undergone surgical implantation for UAS therapy at the University
Hospitals Case Medical Center (Cleveland, OH); all
were regularly using therapy. Each had been deemed a
candidate on the basis of (a) CPAP intolerance, (b) an