Subtraction radiography and morphometric analysis in periodontics

“A Simple Method to Assess Bone Fill through Digital Subtraction Technique and Morphometric Analysis”- Guest lecture as a part of Dr NTRUHS Zonal CDE programme at Army College of Dental Sciences, Hyderabad, India on 18/1/2014.

1. Dr R Viswa Chandra MDS;DNB Associate Professor Department of Periodontics SVS Institute of Dental Sciences Mahabubnagar AP A SIMPLE METHOD TO ASSESS BONE FILL THROUGH DIGITAL SUBTRACTION TECHNIQUE AND MORPHOMETRIC ANALYSIS

2. INTRODUCTION One of the important endpoints of regenerative periodontal therapy is new bone formation. However, the identification and quantification of new bone formation within the treated area remains a great challenge to periodontists in general.

3. C onventional radiography has its own drawbacks when used to assess bone fill after periodontal therapy Conventional radiographs produce a 2-dimensional representation of the 3-dimensional bone defect. 2. Errors in the assessment of bone gain may occur because of image quality, angular distortions or the use of non-standardized images.

4. Digital subtraction radiography (DSR) facilitates qualitative and quantitative visualization of even minor density changes (<5%) in bone by enhancing the changed osseous components in the image. The use of appropriate software in DSR is paramount as it relies on comparing the pixel values of two images of the same region taken at different time intervals and then by subtracting the first image from the second.

5. The cost and complexity of the software * and the additional training required have been cited as barriers to the adoption of DSR in a dental office. The ability to optimize an image and extract measurement functions is the foundation for a myriad of software, commercial and open source, medical and non-medical, expensive and free. *van der Stelt PF. Better imaging: the advantages of digital radiography. J Am Dent Assoc 2008; 139 Suppl: 7S-13S.

6. Only small differences in diagnostic accuracy are found in subtraction images from low and high-cost equipment * thus aiding the practitioner in adopting a more open approach to utilize software supporting DSR. Möystad A, Svanaes DB, Larheim TA. Personal computer equipment for dental digital subtraction radiography vs. industrial computer equipment and conventional radiography. Scand J Dent Res 1992; 100(2):117-22.

7. Apart from identifying sites with bone fill, the quantitative analysis of sites with bone fill is of particular challenge. Fixott-Everett Grid Predefined lines Percentage Bone Fill

8. Even in radiographs obtained by digital radiography, the choice of bone graft and the bone defect morphology may impact the quantitative assessment of bone fill. Radiographically, combined, two and three-wall defects are difficult to distinguish due to superimposition of the external cortical bone and tooth whereas one-wall infrabony defect is the most easily distinguishable. * *Gomes-Filho IS, Sacramento VA, de Castro MS et al. Radiographic features of periodontal bone defects: evaluation of digitized images. Dentomaxillofacial Radiology 2007; 36:256-262.

9. Radiolucent bone grafts show an increase in density that correlates with de novo bone fill. * This increase in density is sometimes imperceptible when a radioopaque bone graft is used leading to inaccurate assessment of bone fill even in digitized radiographs. ** *Williams AL, Gornet MF, Burkus JK. CT evaluation of lumbar interbody fusion: current concepts. AJNR Am J Neuroradiol 2005; 26(8):2057-66. **Sciadini MF, Johnson KD. Evaluation of recombinant human bone morphogenetic protein-2 as a bone-graft substitute in a canine segmental defect model. J Orthop Res 2000; 18(2):289-302.

10. In these situations, the enhanced sensitivity of image subtraction holds enormous potential in assessing and quantifying bone fill to the practicing periodontist. Specific image analysis software are available; yet for a variety of reasons, there are few applicable methods and consequently scant literature on using non-specific image analysis software to assess and quantify post-periodontal surgery bone-fill.

11. This presentation describes the method of digital subtraction radiography (DSR) and morphometric area analysis (MA) in assessing bone fill following regenerative periodontal therapy by using two image processing software.

12. RADIOGRAPH STANDARDIZATION After the imaging plate was placed in the film holder for paralleling technique (XCP Kits for Digital Sensors®, BlueDent, Chennai, India) , addition silicon impression material was added around the biting surface and allowed to set. This arrangement ensured standardized alignment of the aiming device and the holder ensuring correct positioning of the collimator in subsequent radiographs.

13. Digital Subtraction Technique (DSR) The radiographs obtained at 12/24 weeks should be subtracted from the radiograph taken at the baseline.

14. To reduce brightness and contrast variations, both images were adjusted based on the levels and the curves in the software. Before digital subtraction, both radiographs were moved in appropriate directions as needed to reduce geometric distortion. DSR was performed by using Adobe Photoshop® 6.0

15. These images can then be superimposed and subtracted by selecting the image>calculation>exclusion> new channel tools.

16. The excluded interdental layer can be outlined by using the polygonal lasso tool and saved as a separate joint photographic expert group (JPEG) document at low compression

17. Morphometric Area Analysis (MA) ImageJ is a public domain Java image processing program.

18. The layer has to be converted into a grayscale image, and the measurement scale set to account for any magnification/reduction of the radiograph because of RVG

19. The area of the layer can be calculated (in mm 2 ) by initially enclosing the entire area with the rectangular selection tool and then by using Analyze>Analyze Particles tool

20. DISCUSSION Two recent studies on bone-fill following periodontal therapy have used Adobe Photoshop® software primarily for density estimation * and bone fill estimation. ** While this software can be used for volumetric analysis * , the procedure is more complicated in underexposed radiographs. *Jenabian N et al. Clinical and radiographic evaluation of Bio-Gen with biocollagen compared with Bio-Gen with connective tissue in the treatment of class II furcation defects: a randomized clinical trial. J Appl Oral Sci 2013; 21(5):422-9. **Guimarães Mdo C et al. Digital subtraction radiographic analysis of the combination of bioabsorbable membrane and bovine morphogenetic protein pool in human periodontal infrabony defects. J Appl Oral Sci 2010; 18(4):379-84.

21. Interestingly, several recent studies * have utilized ImageJ for volumetric analysis of bone fill after periodontal regenerative procedures. However, the analysis was done by measuring linear distances on pre-determined landmarks and using relavent formulae to determine the percentage bone fill or the net volume. ImageJ supports automated area measurement of a complex object obviating the need for measurements and formulae. The tool is easy to use and is not susceptible to noise in the outline of bone fill *Sowmya NK et al. Clinical evaluation of regenerative potential of type I collagen membrane along with xenogenic bone graft in the treatment of periodontal intrabony defects. J Indian Soc Periodontol. 2010; 14(1):23-9.

22. DSR vs Conventional Radiography Recent studies* have indicated that conventional radiographic interpretation is more subjective and may underestimate bone fill when compared with subtraction radiography. Combined and two-wall defects present with a cortico-cancellous bone loss and DSR evaluates change by subtracting images in a buccolingual direction making it more accurate . * Gomes-Filho IS, Sacramento VA, de Castro MS, da Costa NP, da Cruz SS, Trindade SC, de Freitas COT, de Santana Passos J. Radiographic features of periodontal bone defects: evaluation of digitized images. Dentomaxillofacial Radiology 2007; 36:256-262.

23. LIMITATIONS The software, while exhibiting good sensitivity to bone fill are not specific for digital subtraction and can be affected by the competency of the evaluator especially during the demarcation of the excluded bone fill slice.   Still 2D measurement of a 3D slice; accuracy of current radiographic methods of determining architecture of osseous defects and bone fill are still subject to debate. * * Mohan R, Singh A, Gundappa M. Three-dimensional imaging in periodontal diagnosis - Utilization of cone beam computed tomography. J Indian Soc Periodontol 2011; 15(1):11-7.

24. “It's supposed to be automatic, but actually you have to push this button. ” ― John Brunner

25. THANK YOU