Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B5/00—Measuring for diagnostic purposes; Identification of persons
  • A61B5/103—Detecting, measuring or recording devices for testing the shape, pattern, colour, size or movement of the body or parts thereof, for diagnostic purposes
  • A61B5/107—Measuring physical dimensions, e.g. size of the entire body or parts thereof
  • A61B5/1075—Measuring physical dimensions, e.g. size of the entire body or parts thereof for measuring dimensions by non-invasive methods, e.g. for determining thickness of tissue layer
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
  • A61B6/50—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment specially adapted for specific body parts; specially adapted for specific clinical applications
  • A61B6/501—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment specially adapted for specific body parts; specially adapted for specific clinical applications for diagnosis of the head, e.g. neuroimaging or craniography
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T7/00—Image analysis
  • G06T7/60—Analysis of geometric attributes
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T2207/00—Indexing scheme for image analysis or image enhancement
  • G06T2207/10—Image acquisition modality
  • G06T2207/10072—Tomographic images
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T2207/00—Indexing scheme for image analysis or image enhancement
  • G06T2207/10—Image acquisition modality
  • G06T2207/10116—X-ray image
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T2207/00—Indexing scheme for image analysis or image enhancement
  • G06T2207/30—Subject of image; Context of image processing
  • G06T2207/30004—Biomedical image processing
  • G06T2207/30008—Bone
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T2207/00—Indexing scheme for image analysis or image enhancement
  • G06T2207/30—Subject of image; Context of image processing
  • G06T2207/30004—Biomedical image processing
  • G06T2207/30016—Brain
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
  • G06T2207/00—Indexing scheme for image analysis or image enhancement
  • G06T2207/30—Subject of image; Context of image processing
  • G06T2207/30196—Human being; Person

Definitions

• This invention generally relates to diagnostic/prognostic analyses. More specifically, the invention provides a method for providing individualized normative values for 3D cephalometry. In a preferred embodiment of the method of the invention, normative values for 3D measurements on and off the midsagittal plane are obtained, said method being based on previously available 2D cephalometric norms. The invention also includes applying this method to other existing cephalometric longitudinal growth studies, to obtain control groups that can be derived without exposing new untreated subjects to radiation.
• a headfilm is a 2-dimensional (2D) shadow of a 3-dimensional (3D) structure, produced by a non-parallel beam that results in a distorted and enlarged image (more so in some regions than in others) (Baumrind, S., Frantz, RC, 1971).
• Contemporary imaging technologies such as magnetic resonance imaging (MRI) and computed tomography (CT) have permitted 3D assessment of the craniofacial complex with a greater degree of accuracy and reproducibility than available previously (Adams, GL et al., 2004; Disler, DG et al., 1994; Hilgers, ML et al., 2005).
• the applicability of both technologies in a routine orthodontic environment is limited by their high equipment costs, by the MRI's long acquisition time (50 minutes for a full head scan), and by the CT's high radiation levels (-2,000 ⁇ Sv) (Swennen GR, Schutyser, F, 2006).
• 3D assessment can be conducted in all three planes of space, on images with life-size magnification, and without distortion or overlapping structures. Furthermore, head position during exam acquisition is not critical for 3D assessment; the spatial relationship among the various points is not changed in any way by variations in head orientation (Ludlow, JB et al., 2007). These features provide ease of landmark identification and precise superimposition of serial images, which are critical for research purposes (Cevidanes, LH et al., 2007).
• Hilgers et al. in 2005 made measurements directly in skulls of mandibular dimensions using a digital caliper and secondary MPR images obtained in a conical beam tomography, (iCAT: axial with 0.4 mm thick), and compared with measurements taken in teleradiographs conventional (lateral, frontal).
• the present invention provides normative values for any 3-dimensional analysis adapted from the 2D analysis to which normative values can be obtained for a particular individual using a method that translates the measurements taken from a lateral head film to those taken from a CBCT in human subjects. To our knowledge, this is the first time an attempt has been made to produce normal values for measurements made on 3D examinations using previously-known norms from 2D evaluations.
• Document WO 2007/100823 describes a cone beam CT imaging system that incorporates the phase contrast in-line method, in which the phase coefficient rather than only the attenuation coefficient is used to reconstruct the image.
• the terms in the interference formula can be approximately expressed as a line integral that is the requirement for all CBCT algorithms. So, the CBCT reconstruction algorithms, such as the FDK algorithm, can be applied for the in-line holographic projections.
• Document WO 06000063 describes a method for performing a cephalometric or anthropometric analysis comprising the steps of : - acquiring a 3D scan of a person's head using a 3D medical image modality, - generating a 3D surface model using data from the 3D scan, - generating from the 3D scan at least one 2D cephalogram geometrically linked to the 3D surface model, - indicating anatomical landmarks on the at least one 2D cephalogram and/or on the 3D surface model, - performing the analysis using the anatomical landmarks.
• the method of the invention provides the obtainment of 3D images from 2D images, by forming a right triangle.
• the invention provides, between others, a method for deriving individualized normative values for 3D cephalometry.
• Said right triangle provides the correction of distortions/magnifications of 2D images when applying the following criteria:
• Hypotenuse represents the 3D measurement of the length of a known parameter, so as a method for obtaining "mean values” for 3D measurements taken from known mean values of 2D measurements using basic trigonometry is applied;
• the Projection Side represents the projection of the 3D measurement on the plane where C lies.
• the Projection Side (PS) is equal to the measurement from a lateral cephalogram measurements (LC), reduced by the known magnification;
• the invention provides a method for providing individualized normative values for 3D measurements on and off the midsagittal plane, based on previously available 2D cephalometric norms.
• the invention also includes applying this method to other existing cephalometric longitudinal growth studies, to derive control groups and without exposing new untreated subjects to radiation. These control groups can then be used to assess the net effect of a given treatment.
• the method comprises the following steps:
• H represents the 3D measurement of either the mandibular length (Co-Gn) or the midfacial length (Co- point A);
• Condylion to Midsagittal Plane Side represents distance between Condylion and the midsagittal plane
• the Projection Side represents the projection of the 3D measurement on the midsagittal plane.
• the Projection Side (PS) is equal to the measurement from a lateral cephalogram (LC) 1 reduced by the known magnification;
• measurements on the midsagittal plane are obtained simply by reducing the magnification since the cosine of zero is equal to one.
• the hypotenuse is obtained when both the Projected Side and the Condylion to Midsagittal Plane distance are known, using the Pythagorean Theorem. If the Condylion to Midsagittal Plane distance is not known, the hypotenuse is obtained easily by dividing the Projected Side by the cosine of the angle "X" between the hypotenuse and the Projected Side.
• the method of invention was assessed in a sample comprised of 13 adult subjects with ideal occlusions and well-balanced faces who have had conventional lateral head radiographs and 3D scan of their heads using a CBCT scanner. All the exams were coded in order to de-identify all subjects prior to the beginning. Data Acquisition
• Two-dimensional Acquisition The conventional 2-D lateral cephalograms were taken with the Frankfort Horizontal plane (FHP) parallel to the floor; the subject's head position was determined by a cephalostat. The magnification for the radiographs produced by that particular machine (Orthoceph OC100, lnstrumentarium Corp., Finland; 77 kVp; 12 mAs) was 10%.
• radiographs then were traced on acetate paper and checked for accuracy of anatomical outline and landmark location.
• Three measurements (midfacial length, mandibular length, LAFH) then were obtained directly from the tracing with a digital caliper.
• Three-dimensional Acquisition The same subjects were positioned in the CBCT machine (iCAT, Imaging Sciences International, Hatfield, PA. 120 kVp, 18.66 mAs) with the aid of guiding lights, with the FHP parallel to the floor and the midsagittal plane passing through Glabella. A head strap rather than the chin rest was used to stabilize the patients head during the examination to prevent distortion of the soft tissue profile and changes in mandibular position.
• the CBCT machine was set for a 20-second acquisition time with a 9 inch field of view to minimize radiation exposure (slices were reconstructed with 0.4 mm increments and 0.1 mm interval).
• the raw data from the CBCT scan were reconstructed, coded and converted into a Dicom3 file format using the native iCAT software.
• the Dicom3 files then were imported to software (Mimics 8.13, Materialize Co., Leuven, Belgium) for assessment.
• the points were marked using the 2D multi-planar reconstruction (MPR) images (axial, sagittal and coronal slices) according to their descriptions. It is important that the points satisfy all of the description requirements in all three planes of space at the same time.
• MPR multi-planar reconstruction
• a method for providing the translation of the measurements taken from lateral radiographs to those taken from CBCT scans This translation is enabled by using two of the points chosen for the analysis of Condylion Right and Condylion Left (CoR and CoL) which are located at the central focus of the X-ray beam, where the effects of magnification are negligible; the other points are located at the midsagittal plane where the magnification is determined.
• the magnification however, varies depending on the plane where a given structure lies (Broadbent, BH, 1931 , Ahlqvist, J et al., 1986). Based on these premises, a right triangle can be drawn with sides described as follows:
• the Hypotenuse (H) represents the 3D measurement of either the mandibular length (Co-Gn) or the midfacial length (Co- point A).
• the Condylion to Midsagittal Plane Side represents distance between Condylion and the midsagittal plane.
• the Projection Side represents the projection of the 3D measurement on the midsagittal plane.
• the Projection Side is equal to the measurement from a lateral cephalogram (LC), reduced by the magnification.
• the Magnification Group measurements from the cephalogram reduced by the magnification.
• the Method Group the measurements from the cephalogram corrected for magnification and distortion using the method.
• the CBCT Group measurements directly from the CBCT scan.
• the intraobserver variability is 0.5 millimeters for the cephalometric measurements and 0.2 mm for the CBCT measurements according to Dahlberg's formula: V ⁇ D 2 /2N.
• the mean values of the four groups tested for the three measurements are compared using a Repeated Measures Analysis of Variance (R-ANOVA). Post-hoc comparisons of means are carried out using the Bonferroni correction for multiple comparisons.
• the power analysis determined that there is 99% power to detect a difference greater than 0.5 millimeter within the four groups of repeated measures, for each one of the three measurements, with a sample of 13 subjects.
• the 3D analysis presented in this invention is used as a diagnostic tool that further enriches the information gathered from 3D imaging examinations due to the availability of normal values for its measurements.
• the knowledge accumulated during decades of assessing craniofacial growth and diagnosing orthodontic patients must be borne in mind to avoid unnecessary mistakes with this new methodology.
• the method of the invention is used to translate existing 2D cephalomethc norms on and off the midsagittal plane into 3D Norms, so they are compared to the 3D measurements that are made more accurately and individually for the right and left sides of the maxilla and mandible.
• the mean difference between mandibular length measured on a conventional radiograph and the same measurement on a CBCT is relatively small (1.2 mm); however, this difference still is statistically and clinically significant. This relatively small mean difference is due to the magnification increase that partially compensates the reduction that occurs when the mandible is projected on a 2D film.

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