# Patent

## Title
System and method for three-dimensional airway reconstruction, assessment and analysis

## Abstract

This invention relates to a system and method for three-dimensional airway reconstruction, assessment and analysis. Specifically, the invention relates to a system and method for acquiring one- and two-dimensional data regarding a cavity, such as an esophagus or an airway, and manipulating that data to reconstruct a three-dimensional geometrical object representing that cavity. Suitable data collection methods include, but are not limited to, non-ionizing, non-invasive protocols including acoustic reflectometry, such as that performed by a DOS®- or Windows®-based pharyngometer or rhinometer. The resulting three-dimensional geometric object of the subject cavity can be used to diagnose cavity morphology/obstruction, aid in management and treatment of the obstruction, evaluate efficacy of management and treatment of the obstruction and also provide information for use in outcome analysis and forensic and medico-legal evaluation of diagnosis and treatment of cavity obstruction/stenosis.

## Background
BACKGROUND OF THE INVENTION
The invention relates to a system and method for three-dimensional airway reconstruction, assessment and analysis. Specifically, the invention relates to a system and method for acquiring one- and two-dimensional data regarding a cavity, such as an esophagus or an airway, and manipulating that data to reconstruct a three-dimensional geometrical object representing that cavity. Suitable data collection methods include, but are not limited to, non-ionizing, non-invasive protocols including acoustic reflectometry, such as that performed by a DOS®- or Windows®-based pharyngometer or rhinometer. The resulting three-dimensional geometric object of the subject cavity can be used for diagnostics assessments, such as cavity constriction/obstruction, and therefore aid in the management and treatment of the constriction/obstruction, evaluate the efficacy of management and treatment of the constriction/obstruction and also provide information for use in outcome analysis, as well as forensic and medico-legal evaluations of diagnosis and treatment of cavity constriction/obstruction.
1. Field of the Invention
Obstruction/constriction of certain body cavities, such as airway passages, can create serious health problems. For example, sleep apnea is a debilitating and life-threatening condition that affects people worldwide. Sleep apnea occurs when tissues in the upper airway block the breathing passages. Obstructive sleep apnea is the most common type of sleep apnea. Normally, the muscles in the upper part of the throat allow air to flow into the lungs. When a person with obstructive sleep apnea falls asleep, these muscles are not able to keep the air passage open all the time. When the airway closes, breathing stops, oxygen levels fall and sleep is disrupted in order to open the airway. The disruption of sleep usually lasts only a few seconds. These brief arousals disrupt continuous sleep and prevent obstructive sleep apnea sufferers from reaching the deep stages of slumber, such as rapid eye movement (REM) sleep, which the body needs in order to rest and replenish its strength. Once breathing is restored, obstructive sleep apnea sufferers fall asleep only to repeat the cycle throughout the night.
Sleep apnea is suffered by adults and children alike. Sleep apnea can cause the sufferer to be sleepy throughout the day and is associated with cardiovascular disorders, including hypertension, coronary artery disease, heart failure, cardiac arrhythmia, stroke and metabolic abnormalities. Sleep apnea can be treated today by both surgical and non-surgical approaches. For example, by use of Continuous Positive Airflow Pressure (“CPAP”), the sufferer wears a mask that supplies a steady stream of air during sleep, where the airflow keeps the nasal passages open sufficiently to prevent airway collapse and apnea. Weight loss, change of sleep habits, behavior modification and wearing of oral appliances during sleep can also promote normal sleep.
In addition, people suffer from airway obstructions or constriction/narrowing (stenosis) due to congenital conditions and/or accidents.
In each case, evaluation of a cavity such as an airway is a valuable tool in analyzing a problem, and then developing a management and/or treatment plan for the sufferer of the problem. Also, evaluation of a cavity such as an airway is useful in providing information on outcome analysis for management and/or treatment plans for both care providers and insurance providers. Additionally, evaluation of the cavity has forensic and medico-legal uses.
2. Description of Related Art
Methods for acquiring data regarding the anatomy of body cavities and organs are known. For example, techniques such as radiographs (x-rays), including lateral cephalographs; CT scans, including cone-beam tomography, and nuclear MRI are often used to image body organs and cavities for evaluation and diagnostic purposes. These techniques have limited uses, however. Radiographs, including cephalographs, and CT scans expose the patient to potentially harmful ionizing radiation requiring appropriate precautions. Also, certain patient groups such as pregnant women might be excluded from such protocols. Also, certain techniques such as CT scans and nuclear MRI require post-processing of data to isolate certain cavities, such as the airway, because all tissues, including skin, muscle, bone, etc., are imaged simultaneously. Other techniques, such as cone-beam tomography, generate huge file sizes, which may exceed the resources available at a typical care-provider's office. Additionally, these techniques tend to be expensive, time-consuming and often require specially trained personnel.
Acoustic reflectometry is a non-invasive, non-ionizing protocol that produces a “one-dimensional” curve of the distance into the airway versus a two-dimensional cross-sectional area map of the upper airway. For example, U.S. Pat. No. 5,316,002, issued to Jackson et al. entitled “Nasopharyngealometric Apparatus and Method,” the disclosure of which is incorporated by reference, discloses an apparatus and method for: determining the profile of the nasopharyngeal cavity by introducing acoustic signals into the nasal cavities of a subject; detecting the acoustic signals and acoustic reflections; generating electrical signals proportional to the amplitude of the acoustic signals and acoustic reflections; determining the length of the nasal septum separating the nasal cavities, and computing the value of the area-distance function of the nasopharyngeal cavity from the electrical signals and the length of the nasal septum. U.S. Pat. No. 5,823,965, issued to Rasmussen entitled “Device for Reflectometric Examination and Measurement of Cavities,” the disclosure of which is incorporated by reference, also discloses an apparatus and method for reflectometric examination and measurement of human and animal cavities such as air and food passages. U.S. Pat. Nos. 5,746,699 and 5,666,960, both issued to Fredberg et al. and both entitled “Acoustic Imaging”, the disclosures of which are incorporated by reference, disclose an apparatus for providing an output signal characteristic of the morphology of the respiratory tract. A transducer launches acoustical energy toward the opening of the tract, producing an incident wave and a reflected wave to form a transient wave-field representative of the morphology of the tract. In each of these disclosures, the result is a “two-dimensional” measurement of the cross-sectional area of the measured cavity as a function of a “one-dimensional” distance into the cavity.
Practitioners have used acoustical reflectometry to assess preoperative and postoperative nasal septal surgery; see LARRY SHEMEN, M.D., F.R.C.S., F.A.C.S. and RICHARD HAMBURG, M.D., F.A.C.S., “PREOPERATIVE AND POSTOPERATIVE NASAL SEPTAL SURGERY ASSESSMENT WITH ACOUSTIC RHINOMETRY,” presented at the Annual Meeting of the American Academy of Otolaryngology-Head and Neck Surgery, Washington, D.C., September 29-Oct. 2, 1996, p. 338. The authors reported that the acoustic rhinometer allows objective measurement of nasal cavity volume, which is crucial in the diagnosis of nasal dysfunction. Such objective measurement allows for planning of appropriate treatment and evaluation of results after medical or surgical treatment. The authors also noted that objective documentation of nasal obstruction before and after surgery is being demanded by third-party payers, and allows for comparison of alternative procedures.
Other practitioners have noted that acoustic reflectometry can detect within seconds, and without the use of capnography, characteristic, distinctive and specific area-length profiles for both endotracheal and esophageal intubation. See DAVID T. RAPHEAL, M.D., Ph.D., “ACOUSTIC REFLECTOMETRY PROFILES OF ENDOTRACHEAL AND ESOPHAGEAL INTUBATION,” Anesthesiology. 92(5): 1293-1299, May 2000.
Certain practitioners have reported on the size and pressure/area relationship of the pharynx as important factors in the pathogenesis of obstructive sleep apnea. See BRIGADIER GENERAL IBRAHIM KAMAL, M.D., “NORMAL STANDARD CURVE FOR ACOUSTIC PHARYNGOMETRY,” available from the ENT Department, Police Authority Hospital, 26 Makram Oubaid Street, Nasr City, Egypt. Dr. Kamal reported that assessment of the upper airway for possible site(s) of obstruction/constriction is one of the keys to successful management of the condition, and that acoustic pharyngometry has the potential for localizing such sites. Dr. Kamal further reported that the acoustic pharyngometry technique is easy, rapid and cost-effective.
Acoustic reflectometry has also been used in connection with detection of conditions of the middle ear. For example, U.S. Pat. Nos. 5,868,682 and 5,699,809, both issued to Combs et al. and both entitled “Device and Process for Generating and Measuring the Shape of an Acoustic Reflectance Curve of an Ear”, the disclosures of which are incorporated by reference, disclose a device and process for analysis of acoustic reflectance of components of an ear. The results can assist in diagnosis of an ear pathology such as abnormal pressure, presence of fluid in the middle ear or conductive hearing loss.
SUMMARY OF THE INVENTION
The invention relates to a system and method for three-dimensional airway reconstruction, assessment and analysis. The inventive system and method can be performed using data input captured, stored and exported using a DOS® or Windows®-based pharyngometer or rhinometer. A three-dimensional geometric object of the airway can be generated from the data input, in contrast to the “one-dimensional” curve of the cross-sectional area of the measured airway as a function of distance into the airway that is output from a pharyngometer or rhinometer. This computer-generated three-dimensional object can be presented graphically, and allows care providers to make assessments and comparisons for diagnostic or treatment purposes. The resulting three-dimensional geometric object can also be used for objective documentation of nasal obstruction before and after surgery as demanded by third-party payers, or can be used for forensic or medico-legal purposes.
The inventive system and method is fast, easy to use, does not require specialized training for the operator and can run on personal computers and laptops as may be found in a care provider's office. In addition, acoustic reflectometry is a non-ionizing, non-invasive protocol that can safely be used without the precautions, disadvantages and post-processing of previously known imaging methods, such as radiographs, including cephalographs, CT scans, including cone-beam tomography and MRI scans.
The resulting geometric object of the airway can be superimposed on a two-dimensional digital radiograph or digital photograph. This functionality permits the user to visualize a more anatomically-correct three-dimensional airway, and may provide the user with further information on site-specific airway obstruction/constriction e.g., before and after treatment, with or without an oral appliance etc.
It is therefore an object of the invention to provide a system and method to create a reconstructed three-dimensional geometric object representing a cavity, such as an airway, using one- and two-dimensional input data, such as cross-sectional area of an airway measured as a function of distance from the opening of the airway cavity.
It is another object of the invention to provide a system and method to create a reconstructed three-dimensional geometric object representing a cavity, such as an airway, using one- and two-dimensional input data including cross-sectional area of an airway measured as a function of distance from the opening of the airway cavity using non-ionizing, non-invasive protocols, such as acoustic reflectometry.
It is another object of the invention to provide a system and method to create a reconstructed three-dimensional geometric object representing a cavity, such as an airway, using one- and two-dimensional input data including cross-sectional area of an airway measured as a function of distance from the opening of the airway cavity using acoustic reflectometry.
It is yet another object of the invention to provide a system and method to create a reconstructed three-dimensional geometric object representing a cavity, such as an airway, using one- and two-dimensional input data including cross-sectional area of an airway measured as a function of distance from the opening of the airway cavity using acoustic reflectometry techniques including a PharyngometerTM or rhinometer.
It is yet another object of the invention to superimpose a reconstructed three-dimensional geometric object representing a cavity, such as an airway, created using one- and two-dimensional input data including cross-sectional area of an airway as measured as a function of distance from the opening of the airway cavity onto a two dimensional digital radiograph or digital photograph of that cavity.
It is yet another object of the invention to provide a process and system for digital manipulation of a reconstructed three-dimensional geometric object representing a cavity, such as an airway, created using one- and two-dimensional input data including cross-sectional area of an airway as measured as a function of distance from the opening of the airway cavity.
It is yet another object of the invention to provide a system and method for analyzing cavity characteristics, such as length, area and volume to identify and quantify airway obstructions/constrictions/narrowing (stenosis), using a reconstructed three-dimensional geometric object representing a cavity, such as an airway, created using one- and two-dimensional input data including cross-sectional area of an airway measured as a function of distance from the opening of the airway cavity.
It is yet another object of the invention to provide a system and method for assessing/evaluating treatment methods/protocols to manage and/or alleviate cavity dysfunction, such as airway obstructions, using a reconstructed three-dimensional geometric object representing a cavity, such as an airway, created using one- and two-dimensional input data including cross-sectional area of an airway measured as a function of distance from the opening of the airway cavity.
It is yet another object of the invention to provide a system and method for assessing/evaluating the efficacy of treatments of and/or management of cavity obstructions, such as airway obstructions, using a reconstructed three-dimensional geometric object representing a cavity, such as an airway, created using one- and two-dimensional input data including cross-sectional area of an airway measured as a function of distance from the opening of the airway cavity.
The system and method of the invention include a programmable processor for receiving one- and two-dimensional data representing cross-sectional area and distance of a cavity, such as an airway, measured from the opening of the cavity; calculating a plurality of circles, which represent the cross-sectional area of the cavity at known distances from the starting point (the opening of the cavity) and from each other (adjacent circular cross-sectional areas) from the input data; forming a triangular mesh from the plurality of circles that represent the cross-sectional area of the cavity; and creating output data including a three-dimensional geometric object comprising the triangular mesh representative of the cavity enclosed by a rendered surface, along with other data representing length, area and volume parameters of the cavity. The three-dimensional geometric object can be manipulated to evaluate and compare the management and/or treatment of any conditions of the cavity, such as obstruction of an airway. Further, different three-dimensional geometric objects can be compared to evaluate pre- and post-treatment efficacy due to management and/or treatment of the cavity, such as an obstruction of an airway. Additionally, the three-dimensional geometric object can be superimposed on a digital radiograph or digital photograph of the cavity to permit the user to visualize a more anatomically-correct three-dimensional airway, and provide the user with further information on site-specific airway obstruction/constriction.
Further, different three-dimensional geometric objects can be manipulated to compute an averaged or mean cavity, such as an average airway. Furthermore, these averaged or mean objects can be compared for diagnostic or treatment planning purposes.
Yet further, groups of different three-dimensional geometric objects can be represented and plotted in statistical space, so that a new, three-dimensional geometric object can be compared to evaluate the chances of that new object being in the same group or a different group with respect to the three-dimensional geometric objects plotted.
These and other features of various embodiments will become readily apparent to those skilled in the art upon review of the detailed description that follows.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph depicting a one-dimensional curve obtainable from an acoustic reflectometry device, such as a PharyngometerTM or rhinometer, and showing the cross-sectional area of a measured airway as a function of distance from the opening of the airway.
FIG. 2 is a table showing typical output data of an acoustic reflectometry device, such as a PharyngometerTM or rhinometer.
FIG. 3 is a schematic diagram of the system of the invention.
FIG. 4 is a graphic depicting a three-dimensional geometric object of a cavity, such as an airway, created using output data such as that shown in FIG. 2.
FIG. 5 is a flowchart depicting the steps performed in one embodiment of the method of the invention.
FIG. 6 is a depiction of a reconstructed three-dimensional geometric object of an airway superimposed on a digital radiograph of the corresponding patient, according to one embodiment of the invention.



DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
For the purposes of promoting an understanding of the embodiments described herein, reference will be made to preferred embodiments and specific language will be used to describe the same. The terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention. As used throughout this disclosure, the singular forms “a,” “an,” and “the” include plural reference unless the context clearly dictates otherwise. Thus, for example, a reference to “a composition” includes a plurality of such compositions, as well as a single composition, and a reference to “a geometric object” is a reference to one or more geometric objects and equivalents thereof known to those skilled in the art, and so forth.
Acoustic reflectometry provides one- and two-dimensional information on a cavity. For example, the Eccovision Acoustic Pharyngometer® and/or Eccovision Acoustic Rhinometer® manufactured by Hood Laboratories, located in Pembroke, Massachusetts and distributed by Sleep Group Solutions LLC of Miami, Florida, are non-invasive, non-ionizing protocols that can determine the dimensions of the oral airway past the epiglottis or the nasal cavity. Details on the operation of the Eccovision Acoustic Pharyngometer® and/or Eccovision Acoustic Rhinometerg® are available from Hood Laboratories, and are hereby incorporated by reference. The output of the Eccovision Acoustic Pharyngometer® and/or Eccovision Acoustic Rhinometer® is a one-dimensional graph/curve providing information on the cross-sectional area of the oral airway past the epiglottis or nasal cavity as a function of the distance into the oral airway past the epiglottis or nasal cavity. FIG. 1 depicts a typical output for a Eccovision Acoustic PharyngometerTM and an Eccovision Acoustic RhinometerTM.
The system and method of the invention processes the data acquired from the Eccovision Acoustic Pharyngometer® and/or Eccovision Acoustic Rhinometer® to create a three-dimensional geometric object depicting the oral airway past the epiglottis or the nasal cavity. The output of the Eccovision Acoustic Pharyngometer® and/or Eccovision Acoustic Rhinometer® are files containing a sequence of distances (d0, d1, . . . , dn−1) and the corresponding cross-sectional areas (A0, A1, . . . An−1) of the oral or nasal airway past the epiglottis or nasal cavity, respectively. A table depicting the typical file content from the Eccovision Acoustic Pharyngometer® and/or Eccovision Acoustic Rhinometer® is included in FIG. 2. A graph of these data provides a curve similar to that shown in FIG. 1.
The system 300 of the invention is depicted in FIG. 3, and includes a processor 310 programmed to process data acquired from an Eccovision Acoustic Pharyngometer® and/or Eccovision Acoustic Rhinometer® from a cavity to be measured. Typically, data measured by the Eccovision Acoustic Pharyngometer® and/or Eccovision Acoustic Rhinometer® are captured, stored and saved in proprietary format, and then exported to the system of the invention 300 over link 320. The acquired data are then stored as simple ASCII or text files 330i in a storage unit 340. The stored files 330i are processed by the processor 310 according to programmed algorithms that encode a method for three-dimensional airway reconstruction, assessment and analysis. Alternatively, the acquired data can be processed directly by the processor 310 to provide a reconstructed three-dimensional airway or cavity. The system 300 can be installed on a personal computer or laptop.
The processor 310 checks the acquired data for format, including errors during data capture and consistency and modifies the data if necessary prior to storage in files 330i in the data storage area 340. Alternatively, the acquired data can be checked for format prior to processing, if the acquired data are to be processed prior to storage in files 330i in data storage area 340. For example, measurements associated with the acoustic reflectometer tube are discarded, as well as null pairs and repeated distances. Details on the operation of the Pharyngometer and Rhinometer are available and on how the data are initially processed are available from Hood Laboratories, and are hereby incorporated by reference. The data storage area 340 that is used to store the data that is acquired from the Eccovision Acoustic Pharyngometer® and/or Eccovision Acoustic Rhinometer® can include any storage now known or later developed, and can include a 3.5′′floppy disk, ZIP disk, CD, USB-drive or mini hard-drive.
The processor 310 upon command retrieves a stored file 330i, and then processes the acquired data stored in file 330i according to the method of the invention to create output data 350i that can be graphed to form a three-dimensional geometric object representative of the cavity, along with other data representative of length, area and volume parameters of the cavity. FIG. 4 depicts typical graphical outputs of three-dimensional geometrical objects of a cavity created using one- and two-dimensional data acquired from an acoustic reflectometer, such as the Eccovision Acoustic Pharyngometer® and/or Eccovision Acoustic Rhinometer®. Alternatively, output data 350i can be obtained by directly processing and graphing acquired data from the acoustic reflectometer, without first storing the acquired data in a file 330i in data storage area 340. The output data 350i can be stored in the data storage area 340 or exported if required or desired.
The processor 310 is further programmed to retrieve and compare output data 350i to other data, including standardized data or data relating to the same cavity but taken at different points in time, such as pre-treatment and post-treatment. Such comparison may be useful for diagnostic and treatment planning purposes, measuring efficacy of management and/or treatment of conditions of the cavity, such as obstructions/narrowing of the airway, for example to compare effectiveness of pre- and post-management and treatment of the cavity. The processor 310 can be further programmed to manipulate the stored output data 350i to evaluate management and/or treatment of any conditions of the cavity, such as obstruction/narrowing of an airway. Additionally, the processor 310 can be programmed to superimpose the stored output data 350i on a digital radiograph or digital photograph of the cavity to permit a user to visualize a more anatomically-correct 3-D airway, and provide the user with further information on site-specific airway obstruction/constriction, as seen in FIG. 6. A display unit 360 can be placed in communication with the processor 310 or with any system to which output data 350i may be exported that can graphically display the output data 350i as well as the manipulations of the output data 350i, using standard personal computer monitors and similar visual display units. Additionally, the output data 350i can be exported or printed on various media using standard personal computer printers and peripherals. Alternatively, output data 350i can be compared to other images, be displayed on display unit 360 , or manipulated without first storing the output data 350i in data storage area 340.
As known to those skilled in the art, the Eccovision Acoustic Pharyngometer® and/or Eccovision Acoustic Rhinometer® are operable using standard DOS® and Windows® operating systems installed on personal computers. The processors of those computer systems can easily perform the processing steps to manipulate the acquired data to provide the geometric objects depicting the cavity according to the invention, and the output data files 350i are of a size that computer systems found in typical care-provider offices can easily store a plurality of such files.
A flow scheme of the method of the invention is depicted in FIG. 5. At 500, data are measured using an acoustic reflectometer, such as an Eccovision Acoustic Pharyngometer® and/or Eccovision Acoustic Rhinometer®, from a cavity. The Eccovision Acoustic Pharyngometer®and/or Eccovision Acoustic Rhinometer® can be operated at standard operating conditions, as described in literature available from Hood Laboratories and as known to those skilled in the art. The measured data are acquired by the processor 310 of the system of the invention at 510. At 520, the acquired data are checked by the processor 310 for format, including errors during data capture and consistency, and stored in files 330i in the storage unit 340 if the files are acceptable according to predetermined protocols and standards. The stored files 330i are retrieved by the processor 310 at 530, and the data stored in the stored files 330i are processed at 540 according to the method of the invention to create output data 350i that can be graphed to form a three-dimensional geometric object representative of the cavity, along with other data representative of length, area and volume parameters of the cavity. FIG. 4 depicts typical graphical outputs of three-dimensional geometrical objects of a cavity created using one- and two-dimensional data acquired from an acoustic reflectometer, such as Eccovision Acoustic Pharyngometer® and/or Eccovision Acoustic Rhinometer®. In another embodiment, acquired data is processed by processor 310 at 540 directly prior to storage in files 330i. The output data 350i can be stored at 540 in the data storage area 340 or exported if required or desired.
At 550, the processor 310 may retrieve and compare output data 350i from a plurality of stored files 330i for diagnostic and treatment planning purposes, measuring efficacy of management and/or treatment of conditions of the cavity, such as obstructions/narrowing of the airway, for example to compare effectiveness of pre- and post-management and treatment of the cavity. At 560, the processor 310 can further manipulate the stored output data 350i to evaluate management and/or treatment of any conditions of the cavity, such as obstruction/narrowing of an airway. At 570, the processor 330 can superimpose the stored output data 350i on a digital radiograph or digital photograph of the cavity to permit a user to visualize a more anatomically-correct three-dimensional airway, and provide the user with further information on site-specific airway obstruction/constriction. At 580, the output data 350i can be graphically displayed on display unit 360 as well as the manipulations of the output data 350i. At 590, the output data 350i can be exported or printed on various media using standard personal computer printers and peripherals. Any of steps 550 through 590 can be performed individually or in combination with any other step, or may be performed in any order desired by the user of the system and method of the invention. In one embodiment, output data 350i are not stored in data storage area 340 as shown in 550 and then retrieved prior to comparison, manipulation and/or superimposition, but rather output data 350i can be used for comparison, manipulation and/or superimposition purposes and applications substantially directly after processing of the acquired data by processor 310.
The method of the invention uses programmed algorithms that encode a method for three-dimensional airway reconstruction, assessment and analysis. The method begins using data acquired from an acoustic reflectometer, which data comprise n data points, including distance and corresponding cross-sectional area as shown in FIG. 2. A plurality of circles, each having a plurality of nodes, are generated from the acquired data as follows.
Each circle represents the corresponding cross-sectional area at a known distance as recorded and captured using an acoustic reflectometer, such as an Eccovision Acoustic Pharyngometer® and/or Eccovision Acoustic Rhinometer®. The number of nodes and the number of circles are calculated when n two-dimensional points are acquired and a net three-dimensional surface is obtained having nl times nr nodes, where nl can be equal or not to n.
Each node represents homologous points on each circle. In one embodiment, the number of nodes per circle nr equals 40, but this can be changed according to the requirements of the user in order to increase or decrease resolution of the three-dimensional object that is generated. For example, a featureless (smooth) three-dimensional object indicates that default settings should be increased, while excessive resolution can result in a correspondingly large file size and default values may be decreased, if desired or if necessary. Those of ordinary skill in the art will be able to select other values of nr to provide desired results to provide a desired three-dimensional object and file size.
The number of circles, or nl, is then calculated by the formula:

nl=nr(dmax/2πrave)

where dmax and rave are calculated from the acquired data and comprise the maximum distance d from the origin of the cross-sectional area of a measured cavity area having radius r[i], and rave comprises the average radius of the cross-sectional areas of the measured cavity area. When processing the acquired data, new radii can be interpolated according to the requirements of the user. Typically, nr will equal or exceed at least 3 and nl will equal or exceed at least 2, but there is no limit on the upper value limit of nr and nl. However, the value for nl is related to the data input from the acoustic reflectometer.

nl times nr nodes are then generated using the following formulae:

x[i][k]=D[i];

y[i][k]=R[i]*cos(cita(k)); and

z[i][k]=R[i]*sin(cita(k)),

where D[i] is the distance of the cross-sectional area from the origin, cita(k) moves step by step from 0 to 180 degrees (nr steps), and i goes from 0 to (nl−1). The nodes obtained are then morphed, or bent, starting from three parameters: dPC1, dPC2 and dAngle. This process provides a more anatomically correct airway, since the default data input from the acoustic reflectometer provides a “straight tube.” These parameters are selected according to the patient's anatomical features. For example, the data input from the acoustic reflectometer starts at the teeth or nostril. The user of the system and method of the invention can decide where to bend the “straight tube” by examining the corresponding patient's lateral cephalograph or by other measurements or techniques, knowing that certain features of the “straight tube” (for example, its narrowest part) are to be superimposed on the epiglottis of the corresponding patient's lateral cephalograph. During superimposition, the user has enough elements to morph the airway according to the corresponding patient's radiograph. dPC1 represents the site where bending will begin, dPC2 represents the site where bending will end and dAngle represents the angle at which the “straight tube” will be bent between these two sites.

The number of rotations performed in the morphing step are calculated as follows:

nl(dPC2−dPC1)/100=#rotations,

where the first [nl*(dPC1/100)] circles are not transformed. For example, where nl=100, dPC1=30%, dPC2=70% and dAngle=45°, 40 rotations would be executed, and the first 30 circles are not transformed. The resulting rotation is then distributed evenly per circle over the site to be bent such that bending is implemented by rotation of the circles located between dPC1 and dPC2. In this example, the following rotations are carried out:


















Circles simultaneously



Rotation Number
Rotation angle
rotated









1
45°/40 = 1.125°
31, 32, 33, 34, 35 . . . 99



2
45°/40 = 1.125°
32, 33, 34, 35 . . . 99



3
45°/40 = 1.125°
33, 34, 35 . . . 99



.
.
.



.
.
.



.
.
.



40 
45°/40 = 1.125°
70 . . . 99










In performing the rotations, in the first rotation the first circle as well as all of the following circles are rotated simultaneously. In the second rotation, the second circle as well as all of the following circles are rotated simultaneously, but the first circle (or, in the case of the third and later rotations, all circles before them) remain unchanged.

The plurality of nodes following the morphing step describes the three-dimensional form, or geometric object, of the cavity. The generated circles comprising the generated nodes are connected to form a triangular mesh, as shown in FIG. 4. The triangles are generated by standard triangulation routines known to those of ordinary skill in the art.
Once the triangles are generated from the acquired data and connected to create the final form as seen in FIG. 4, the final form can be bent or morphed, using a spline interpolation. The final form can be bent or morphed in the three planes of space to any angle between 0-360°. This process involves comparing homologous triangular finite elements as calculated from the acquired data using finite element analysis. FIG. 4 depicts a reconstructed three-dimensional object representing a portion of an airway, having eighty (80) nodes.
Finite element analysis consists of a computer model of a material or design that is stressed and analyzed for specific results. Finite element analysis can be used to modify an existing structure to analyze the structure under a new condition, and can be used to determine design modifications to meet the new condition. Finite element analysis uses a complex system of points called nodes which make a grid called a mesh, which mesh is programmed to contain the material and structural properties which define how the structure will react to certain loading conditions. Nodes are assigned at a certain density throughout the material depending on the anticipated stress levels of a particular area. Regions which will receive large amounts of stress usually have a higher node density than those which experience little or no stress.
In this case, the nodes are homologous landmarks evenly distributed throughout the form. The mesh acts like a spider web in that from each node, there extends a mesh element to each of the adjacent nodes. From these data, area factor, deformation factor and principal axes are calculated which are useful for detecting changes in size (e.g. length, area or volume), changes in shape (e.g. a sphere (soccer ball) changing into an ellipsoid (football) of the same volume), and the directionality in which those changes occurred (e.g. in the vertical, horizontal or transverse axes). The parameters to be taken into account during transformation of the final form include circumference diameter D; circumference area Ac; ellipse major axis S1; ellipse minor axis S2; ellipse area Ae; unit vector along S1 axis e1; and unit vector along S2 axis e2. From these values, the following factors can be calculated that are used to describe mathematically how the triangle was transformed:
















Area factor
fA = Ae/Ac



Deformation factor
fD = S1/S2



Principal axis direction
e1










Those of ordinary skill in the art of finite element analysis can calculate these parameters without undue experimentation.

The ability to transform the final form aids in evaluating management and/or treatment methods of conditions of the cavity. For example, management and/or treatment of sleep apnea may be aided by transforming the final form to determine the parameters of certain treatments, such as oral appliances or the settings for CPAP.
The final form as represented by the output data 350i which is created by connecting the triangular mesh can be stored in the data storage unit 340. The output data 350i includes data regarding lengths, areas and volumes of the cavity. The final form can also be displayed on a display unit 360, using surface rendering. While on the display unit 360, the final form output data 350i can be superimposed on other three-dimensional data or on two-dimensional digital radiographs or digital photographs of the cavity. FIG. 6 depicts the superimposition of a final form of a reconstructed three-dimensional object representing an airway onto a digital radiograph of the corresponding patient's airway. This functionality permits the user to visualize a more anatomically-correct three-dimensional airway, and may provide the user with further information on site-specific airway obstruction/constriction e.g., before and after treatment, with or without an oral appliance, etc.
Stored forms can be compared to other stored forms, as well. For example, using finite-element analysis, a stored form of a normal subject can be compared with the stored form of a patient with sleep apnea, having the same number of nodes. Using a pseudocolor-coded scale, the user can evaluate the degree of severity of the condition, using finite-element analysis to localize and quantify the changes. As well, an average form can be computed for a population. For example, the average airway of adult males can be compared with the average airway of adult females. Similarly, the average airway of boys can be compared with the average airway of girls, etc.
The output data 350i is useful for many purposes, including but not limited to analysis of airway obstructions/constrictions and analysis of management/treatment options; determination of efficacy of treatment of airway obstructions by comparison of pre- and port-treatment output data; objective measurement of efficacy of treatment for use by third parties, such as insurance carriers; and forensic and medicolegal applications.
It is possible to extend the inventive system and method to three-dimensional elements as well. Triangles are replaced by pyramids (tetrahedrons) with four landmarks as vertices. The circumference inside the triangle becomes a sphere inside the pyramid, which is transformed into an ellipsoid. Area factor is replaced by Volume factor, and two deformation factors and three parameters are required to define ellipsoid orientation. In this context, only Volume factor is considered for pyramids.
Frequently, three-dimensional forms are described by the enveloping surface, which is mathematically simulated by a mesh composed of a large number of triangular elements that are transformed simultaneously with the transformation. Area and deformation factors can also be obtained for these triangular elements.
Although the system and method was described in terms of data measured by an acoustic reflectometer of an airway cavity, the system and method is also suitable for other types of data and other cavity measurements where three-dimensional reconstruction and analysis would be desirable such as tracheal stenosis, either analog or digital. Other suitable modifications and adaptations of the variety of conditions and parameters normally encountered in therapy are within the spirit and scope of the invention.

## Claims

1. A system comprising:
a processor configured to receive
cross-sectional data representative of cross-sectional areas of a cavity of an object being measured by an acoustic reflectometer at a plurality of distances from an origin point of the cavity, and
feature data representative of at least a portion of the anatomical features of the object; and

a storage unit configured to store a plurality of data files, the data files comprising the received cross-sectional data,
wherein the processor is programmed to create a three-dimensional graphical representation of the cavity by calculating a plurality of nodes based on the cross-sectional data, forming a plurality of circles based on the calculated nodes, rotating the plurality of circles in accordance with the feature data, and connecting the nodes following rotation of the plurality of circles to form a triangular mesh, and
the storage unit is configured to store the three-dimensional graphical representation.

2. The system of claim 1, further comprising a display unit to display the three-dimensional representation of the cavity.

3. The system of claim 1, wherein the object comprises a mammal.

4. The system of claim 3, wherein the object comprises a human being.

5. The system of claim 1, wherein the cavity comprises an airway.

6. The system of claim 1, wherein the acoustic reflectometer comprises one of a pharyngometer or a rhinometer.

7. The system of claim 1, wherein the processor is further programmed to manipulate the three-dimensional representation of the cavity to analyze the effect of a new condition of the cavity.

8. The system of claim 7, wherein the processor is further programmed to measure changes in size, changes in shape, and the directionality of changes to the cavity under a new condition.

9. The system of claim 1, wherein the processor is programmed to superimpose the three-dimensional representation of the cavity on a digital radiograph or digital photograph of the cavity.