Characterization of the cadmium telluride photon-counting sensor as applies to its use in the QRMaster-P panoramic machine

Abstract

This study was undertaken to perform in vitro investigations of several potential important clinical applications of a new Cadmium Telluride Photon Counting (CdTe PC) sensor fitted to a newly designed panoramic machine. The study was divided into three parts and each of the three clinical applications was highly relevant to the current clinical practice of dentistry. More importantly, these functions were either not clinically possible with the use of existing panoramic machines or when standard panoramic devices were employed, clinically inaccurate data was obtained from the images. The aims of the three projects were as follows: Project 1. To investigate whether bone mineral density (quality) could be determined more accurately using the QR Master-P test machine than by one representative standard panoramic device and one representative hybrid pan cone beam computed tomography (CBCT) scanner in the standard pan mode; Project 2. To determine whether different restorative materials could be separated from each other and identified using the QR Master-P test device as compared to one standard panoramic machine and one hybrid pan-CBCT device in the standard pan mode and Project 3. To determine whether angular measurements could be made accurately using the QR Master-P test system as compared to a standard panoramic machine.

Methodology

The first project involved the use of a fiduciary hydroxyapatite object consisting of several known levels of hydroxyapatite mineral concentration and placed in an anatomical phantom with the upper jaw removed to make room for the placement of the fiduciary hydroxyapatite object in right side up and upside down configurations and in various locations on the occlusal plane of the mandible. The anatomical phantom was carefully positioned in a standard pan machine and a hybrid pan-CBCT device in standard pan mode and also in the new QR Master-P test pan scanner fitted with the CdTe PC sensor. The second project involved use of a standardized test block containing a variety of restorative (tooth filling) materials which was placed within a specially designed custom manufactured anatomical phantom. The test device and phantom were carefully positioned in a standard pan machine, in a hybrid pan-CBCT device in standard pan mode and in the new QR Master-P scanner fitted with the CdTe PC sensor. The third project involved the use of another phantom containing a 1 mm Wire grid meshwork within the central plane of the mandible and maxilla of the phantom. The phantom was carefully positioned in one standard pan machine and in the QR Master-P test device. The resultant image of the wire meshwork within the jaws allowed for the assessment of the accuracy of measured 45 and 90 degree angles.

Results

In project 1, it was found that the CdTe PC-fitted machine could more consistently separate each of the hydroxyapatite concentrations in all of the positioning configurations and locations including places where the effects of beam hardening would affect the image. However in its present form the QR Master-P test device is not appropriate for use in accurately determining bone quality. In project 2, the QR Master-P test machine fitted with the CdTe PC sensor did not distinguish well between all of the restorative materials; however it was superior to the other machines for the distinction of several of the dental filling compounds. In project 3 the test angles as measured from the wire grid within the Katsumata phantom proved to deviate from the known 45 and 90 degree values and each of the three individual measurements of each angle varied to some degree. Though the test machine performed better than the standard device, some measurement inaccuracy was present and the measurements were only slightly better in the test machine.

Discussion

The findings from Project 1 indicated that because the new sensor and software can separate the image energy data into three different bins, and using the dual energy equation which is possible in the QR Master-P device, the atomic or "Z" number and the electron density of the components of the unknown material can be separated and determined which in tum can identify the specific substances. This could be achieved with a simple low dose panoramic scan without the need for fiduciary standardization objects as are presently recommended or for higher dose medical computed tomography measurements or a medical dual x-ray absorptiometry (DXA) scan (unavailable in dental offices) which were considered the gold standards. In Project 2, the further development of the capability to apply the dual energy equation to accurately assess bone mineral quality which is not possible currently with a simple pan image is now recognized to be possible with the QR Master P system. Secondly when no previous history is available, this feature can be used to identify the contents of unknown restorative materials for the identification of the individual components. This information could be further applied to helping persons to overcome the debilitating oral effects of allergic reactions to these materials. In Project 3, it was found that more accurate angular measurements can be obtained by developing and applying a known software 3D surface mapping to produce 3D vector-based absolute angular measurements. Because of the QR Master-P machine's unique design and software capabilities, such a modification is entirely possible and could improve the treatment outcomes of millions of patients currently receiving less than accurate orthodontic diagnostic measurements and resulting less than ideal treatments which in the long term may in some cases be responsible for the breakdown and failure to achieve an esthetically pleasing, stable and functional dentition.

Conclusions

With respect to all three projects, it was concluded the QR Master-P test device did perform better in varying degrees to both of the standard pan machines. It was further postulated that based on the sensor's reported design and lower dose potential, these improved data could be obtained with as much as 3-5 times less radiation. This latter feature alone would in and of itself further endorse the preferential clinical use of the QR Master-P system at this time. Furthermore, these results indicate the methodologies as developed for this study can be used to test future outcomes including but not limited to: more sophisticated analyses to determine bone quality, accurate analysis and identification of unknown materials in patients' teeth and mouths; to obtain more accurate angular measurements which not only apply to orthodontic treatments, but also to implant placement next to adjacent teeth and abutment alignment for the design prosthetic devices. A hybrid pan-cone beam computed tomography version of the QR Master-P system which is currently under development may also prove to have similar capabilities.