Case Report/Clinical Techniques
Evaluation of Chronic Periapical Lesions by Digital
Subtraction Radiography by Using Adobe Photoshop CS: A
Technical Report
Fabiola B. Carvalho, DDS, MSc,* Marcelo Gonçalves, DDS, MSc, PhD,† and
Mário Tanomaru-Filho, DDS, MSc, PhD*
Abstract
The purpose of this study was to describe a new
technique by using Adobe Photoshop CS (San Jose, CA)
image-analysis software to evaluate the radiographic
changes of chronic periapical lesions after root canal
treatment by digital subtraction radiography. Thirteen
upper anterior human teeth with pulp necrosis and
radiographic image of chronic periapical lesion were
endodontically treated and radiographed 0, 2, 4, and 6
months after root canal treatment by using a film
holder. The radiographic films were automatically developed and digitized. The radiographic images taken
0, 2, 4, and 6 months after root canal therapy were
submitted to digital subtraction in pairs (0 and 2
months, 2 and 4 months, and 4 and 6 months) choosing
“image,” “calculation,” “subtract,” and “new document” tools from Adobe Photoshop CS image-analysis
software toolbar. The resulting images showed areas of
periapical healing in all cases. According to this methodology, the healing or expansion of periapical lesions
can be evaluated by means of digital subtraction radiography by using Adobe Photoshop CS software. (J
Endod 2007;33:493– 497)
Key Words
Digital subtraction, periapical lesion, radiograph
From the *Department of Restorative Dentistry, Araraquara Dental School, São Paulo State University, UNESP,
Araraquara, SP, Brazil; and †Department of Radiology, Araraquara Dental School, São Paulo State University, UNESP,
Araraquara, SP, Brazil.
Address requests for reprints to Dr. Mário Tanomaru Filho,
Rua Humaitá, 1680, Caixa Postal 331, Centro, 14801-903
Araraquara, SP, Brazil. E-mail address: tanomaru@uol.com.br
0099-2399/$0 - see front matter
Copyright © 2007 by the American Association of
Endodontists.
doi:10.1016/j.joen.2006.12.015
JOE — Volume 33, Number 4, April 2007
C
hronic periapical lesions associated with root-filled teeth are usually monitored by
conventional periapical radiography (1, 2). However, the suggested radiographic
criteria, including lesion persistence and increase of periapical lesion size, are qualitative and subjective (3). Several methods have been described to measure periapical
radiolucencies, including measurement of the diameter, distance between root surface
and radiolucency outlines, use of a specific classification, and determination of the area
by means of tracing (4).
Digital radiographic techniques and computed analysis methods allow measuring
of the periapical lesion area and provide a correlation among the images obtained at
different follow-up periods (3).
Digital subtraction radiography with specific software is considered as a valuable tool
for evaluation of periapical lesions because they are capable of detecting extremely small
bone alterations. It increases the accuracy for assessment of bone gain or loss during or after
root canal treatment (5). In addition, this technique almost duplicates the sensibility in
detecting lesions in comparison to conventional radiographic interpretation (6).
The importance of digital subtraction radiography as an evaluation tool of the
healing process of periapical lesions has been shown in follow-up studies with endodontically treated teeth (7–10). The results of those studies show that image subtraction is a good tool to be used in reliable diagnoses of minimal changes of periapical
tissues during short-time intervals. However, the technology involved in digital subtraction radiography together with the need of additional equipment (specific software like
X-PoseIt [XP, Torben Jorgensen, Lystrup, Denmark] and the EMAGO [Oral Diagnostic
Systems, Amsterdam, The Netherlands]) and computer support make this technique
complicated for use in daily practice (5).
Nonspecific image-analysis software can represent an alternative for the digital
subtraction radiographic technique in the evaluation of healing or increase of periapical
lesions. Adobe Photoshop CS image-analysis software allows digital subtraction of two
superposed images (11).
The aim of this study was to describe a new technique performed by using Adobe
Photoshop CS image-analysis software to evaluate the radiographic changes of chronic
periapical lesions after root canal treatment by digital subtraction radiography.
Materials and Methods
Thirteen upper anterior human teeth with pulp necrosis, asymptomatic, in normal
masticatory function, and a radiographic image of chronic periapical lesion larger than
5 mm in diameter measured in its largest long axis were selected for this study. Patient
written informed consent was obtained after the nature of the procedures and possible
discomforts and risks had been fully explained.
In each specific case, the root canal was prepared according to the crown-down
technique by using manual instrumentation and irrigation with 2.5% sodium hypochlorite. After biomechanical preparation, a calcium hydroxide-based paste (Calen PMCC;
SS White, Rio de Janeiro, Brazil) was placed as root canal dressing for at least 15 days.
Final obturation was done by lateral condensation of gutta-percha points and Sealapex
root canal sealer (SybronEndo/SDS, Glendora, CA).
Radiographs were taken 0, 2, 4, and 6 months after root canal filling by using Rinn XCP
film holder (Rinn Corp, Elgin, IL) stabilized with spherical rubber silicone impression
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Figure 1. Rinn XCP device for intraoral radiographs. (a) Mounted film holder: blue for upper and lower anterior regions, yellow for upper and lower posterior
regions, and red for bitewing radiographs. (b) Mounted film holder showing radiographic film and bite block stabilized with impression material.
material (Optosil Comfort, Heraeus Kulzer, Germany) to standardize image
geometry (Fig. 1). All radiographs were taken by using periapical film (Insight; Eastman Kodak Company, Rochester, NY) with GE 1000 X-ray device
(General Electric, Milwaukee, WI) at 90 kVp, 10 mA, and 0.12-second
exposure time
The exposed films were automatically developed in an automatic
film processor (Dent-X 9000; Dent-X Co, Elmsford, NY) by using 5
minutes of dry-to-dry time and digitized by using a desk scanner (SnapScan 1236s Flatbed Scanner; Agfa-Gevaert NV, Mortsel, Belgium) using
2400 dpi acquire resolution. The resulting images were stored in JPEG
format at low-compression level.
Radiographs taken 0, 2, 4, and 6 months after root canal treatment
were submitted to digital subtraction in pairs by using Adobe Photoshop
CS image-analysis software. The radiograph obtained after 2 months of
follow-up was subtracted from that taken immediately after root canal
therapy. In a sequence, the radiograph obtained after 4 months of
follow-up was subtracted from that taken after 2 months, and the
6-month follow-up radiograph was subsequently subtracted from the
previous one. Before digital subtraction, both radiographs were moved
in horizontal, vertical, or rotational directions applying software tools to
reduce geometric distortion. To remove bright and contrast variations,
both images were enhanced based on the mean of pixel intensity shown
Figure 2. Selection of a sequence of superposed radiographic images showing the “Subtract” and “New Document” commands of the “Calculation” tool, selected from
the “Image” submenu of the main menu of Adobe Photoshop CS image-analysis software.
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Figure 3. (a) Radiographic image obtained after root canal treatment. (b) Two months of follow-up. (c) Result of the digital subtraction.
in histogram scale. Then, these images were superposed and subtracted. First, “Image” option was selected on the main menu of Adobe
Photoshop CS image-analysis software. Next, in the “Image” submenu,
the “Calculation” tool was selected by a left click. A toolbar box was
opened; the following commands were chosen: “source 1” (later radiographic image), “source 2” (earlier radiographic image), “blending” (subtract) and “result” (new document) (Fig. 2). The images
resulting from digital subtraction were enhanced with brightness and
contrast tools to facilitate the observation of new bone tissue areas.
JOE — Volume 33, Number 4, April 2007
Results
The observation of the radiographic images resulting from digital
subtraction performed by using Adobe Photoshop CS image-analysis
software showed periapical healing areas in all studied cases. Only three
cases showed expansion of the radiolucent area between 2- and
4-month controls.
Regions that presented the same pixel intensity in both radiographic images were shown with grayscale on the digital subtraction
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Figure 4. (a) Two months of follow-up. (b) Four months of follow-up. (c) Result of the digital subtraction.
image. Regions that represent areas of new bone tissue exhibited a
radiopaque appearance, whereas regions with bone tissue resorption
were radiolucent (Figs. 3–5). A smooth anatomic image in black background was observed on digital subtraction images.
Discussion
Digital subtraction radiography has been shown to improve the
detection of periapical lesions compared with conventional radiographs (6), and its diagnostic accuracy has been shown (12, 13).
In vitro studies have shown that digital subtraction can increase the
detection of periapical bone lesions, particularly those confined to cancellous bone (12–14). Razmus (15) reported better findings in initial
diagnosis of caries and detection of bone changes in cases of periodontal disease and periapical lesions by using digital methods and radiographic subtraction. The results of the present study also showed that
digital subtraction was a reliable method to detect the healing of periapical lesions after root canal treatment, showing periapical bone
changes in small time intervals emphasizing the initial period of 2
months after completion of root canal therapy.
The success of digital subtraction radiography depends directly on
the reproducibility of the radiographic image, which is associated to
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contrast, brightness, and geometric distortion. Density standardization
can be obtained by careful repetition of technical incidence factors by
using the same brand of radiographic film and maintaining a strict
control of technical conditions (7, 16). In this study, all radiographs
were taken with the same X-ray equipment and using F-speed films that
reduce the exposure time by 20% when the films are automatically
processed with no detriment to diagnostic efficacy (17). However,
Radel et al. (18) used digitized F-speed films and showed lower accuracy than digital systems in endodontic measurement.
According to Van der Stelt (19) and Mikrogeorgis et al. (10), the
use of the parallel technique for radiographic acquisition is recommended in order to obtain images with good quality and a high degree
of reproducibility. Duckworth et al. (20) and Yoshioka et al. (9) used a
film holder associated with a custom-made bite block to provide geometric standardization of the radiographs used in digital subtraction.
The present study used the Rinn XCP film holding device stabilized with
a spherical rubber silicone impression material.
Adobe Photoshop CS image-analysis software is an excellent program for image editing that has different tools and produces good results in digital image manipulation (21). In the finding related by Sargent et al. (11), after conversion into grayscale and alignment of the
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Conclusions
The radiographic changes of chronic periapical lesions can be
evaluated by means of digital subtraction radiography by using Adobe
Photoshop CS image-analysis software. The use of nonspecific software
for digital subtraction can represent an important tool in follow-up
evaluations both in research and in clinical practice.
References
Figure 5. (a) Two months of follow-up. (b) Four months of follow-up. (c)
Result of the digital subtraction showing an area of radiolucency.
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of the “calculation” tool. In the present study, the same procedure was
performed maintaining a standardized radiographic technique because
this software is not specific for digital subtraction and has no specific
tools to correct any variation of image alignment.
Despite its limitations for this application, Adobe Photoshop CS
image-analysis software has shown a great potential for use in dentistry,
more specifically in endodontics and radiology.
JOE — Volume 33, Number 4, April 2007
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