|Year : 2018 | Volume
| Issue : 1 | Page : 4-9
Application of cone beam computed tomography gray scale values in the diagnosis of cysts and tumors
Aarfa Nasim, Ravi Prakash Sasankoti Mohan, K Nagaraju, Sangeeta S Malik, Sumit Goel, Swati Gupta
Department of Oral Medicine and Radiology, Subharti Dental College, Meerut, Uttar Pradesh, India
|Date of Submission||18-Jan-2018|
|Date of Acceptance||17-Feb-2018|
|Date of Web Publication||23-Apr-2018|
Dr. Ravi Prakash Sasankoti Mohan
Department of Oral Medicine and Radiology, Subharti Dental College, Meerut, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background: Studies have unveiled that in CBCT the degree of x-ray attenuation is shown by gray scale (voxel value) that is used in determining the pathologic lesion. Gray value is to assess the density or quality of bone and the density varies depending on radiation attenuation. CBCT gray values are considered approximate values and its measurement allows differentiation of soft tissue and fluid with that of hard tissue. Aim and Objective: We aimed to evaluate the application of CBCT gray scale value of cysts and tumors to assess the difference of bony changes and to determine the significance in diagnosing the contents of the lesions. Materials and Methods: The study was conducted in the department of Oral Medicine and Radiology. Patient clinically diagnosed either with cysts or tumors over a period of 18 months were included in the study. The gray scale reading was taken and radiological diagnosis was made which was further compared with the histopathological report of cysts and tumors. Results: CBCT gray scale value was found to be effective and superior to conventional radiographic tool and more useful in diagnosing the nature of cysts and tumors pre-operatively. Conclusion: CBCT gray value can be considered as a major tool in diagnosis of cyst and tumor and other soft or hard tissue lesion without any microscopic evaluation. CBCT gray scale measurement is superior to conventional intraoral radiographic methods for diagnosing the nature of lytic lesion of jaw.
Keywords: Cone beam CT, conventional, cysts, gray scale, lytic lesion, tumors
|How to cite this article:|
Nasim A, Sasankoti Mohan RP, Nagaraju K, Malik SS, Goel S, Gupta S. Application of cone beam computed tomography gray scale values in the diagnosis of cysts and tumors. J Indian Acad Oral Med Radiol 2018;30:4-9
|How to cite this URL:|
Nasim A, Sasankoti Mohan RP, Nagaraju K, Malik SS, Goel S, Gupta S. Application of cone beam computed tomography gray scale values in the diagnosis of cysts and tumors. J Indian Acad Oral Med Radiol [serial online] 2018 [cited 2018 Jul 20];30:4-9. Available from: http://www.jiaomr.in/text.asp?2018/30/1/4/230893
| Introduction|| |
In the last three decades, dental radiography has been quintessential in the diagnosis of orofacial pathologies and subsequent treatment planning was employed in routine dental practice. Traditionally, the diagnosis of any type of pathology was based on clinical, radiological, and histopathological examination. Conventional radiography has limitation as they do not allow differentiation between cyst and tumors. However, diagnosis of orofacial pathology is difficult with the two-dimensional (2D) images obtained alone from conventional radiograph. The major drawback of conventional radiograph has resulted in an increased application of cone beam computed tomography (CBCT). Ever since the breakthrough in 1982, several CBCT systems have been developed with three-dimensional (3D) modalities. It is becoming the better alternative against conventional radiograph in the branch of dentistry. The recent CBCT systems with reduced radiation exposure, high-contrast images, which are almost equal to bone window computed tomography (CT) resulted in an increase in the indications for CBCT application in the evaluation of the orofacial structures. CBCT scans have shown to aid in bone density assessment, complex diagnostic and treatment planning, surgical assessment of pathology, and many more. CBCT has been reported with disadvantage such as high levels of radiation scatter and artifacts in measuring bone density. A large number of studies had shown a linear relationship between Hounsfield unit (HU) in CT scan and gray scale in CBCT that can be used for estimation of bone density.
The ability of CBCT to display differences in attenuation is related to the ability of the detector to detect subtle contrast differences. This parameter is called the bit depth of the system and determines the number of shades of gray available to display the attenuation. CBCT unit uses detector capable of recording gray scale difference of 12 bit or higher. A 12-bit detector provides 212 or 4096 shades to display contrast. A 16-bit detector provides 216 or 65,536 shades of gray. Although higher bit-depth images in CBCT imaging are possible, this added information comes at the expense of increased computational time and substantially larger file size. If 12-bit detector is used to define scales, 4096 shades are available to display contrast.
The use of CBCT as a delineating imaging modality for cysts, benign, and malignant tumors is reported in very few studies. This study is an effort in evaluating the application of CBCT gray scale value in diagnosing cyst and tumors and implementing the use preoperatively to avoid surgical complication.
Aims and objective
The purpose of this study is to determine the application of CBCT gray scale value of cysts and tumors, and to determine whether gray scale values help in diagnosing it. The objective is to assess the difference of bony changes between cysts or tumors by following radiological diagnostic criteria. The clinical diagnosis, conventional radiograph, and CBCT features are taken into consideration with histopathological report to determine the significance of gray scale values in diagnosis of cysts or tumors.
| Patients and Methods|| |
The present study was conducted in the department of Oral Medicine and Radiology over a period of 18 months with approval of protocol from institutional ethical committee. The study group comprised of 60 patients clinically diagnosed either having cystic lesion or tumors. All procedures followed were in accordance with the ethical standards of the responsible committee. Informed consent was obtained from all patients before any of the procedure has started. The patient consent was also taken for the radiological investigation with both 2D (conventional or digital) and 3D (CBCT) imaging.
The study was selected based on following criteria:
- Patients whose conventional radiograph showed lytic lesion suspected as cysts or tumors (benign odontogenic or nonodontogenic) involving the jaw
- Lytic lesion seen in radiograph as radiolucent or mixed lesion as to differentiate with the gray levels of various lesion.
- Pregnant females
- Patient with maxillofacial trauma
- Cysts and tumors with radiopaque material that could easily be differentiated without the help of gray scale.
The 2D images were obtained were periapical radiograph and panoramic radiograph taken by Gnatus Dental X-ray unit at [70 kVp, 8 mA, 0.7 s, 2.5 mm Al/eqiv filtration, 60 mm beam diameter, and focal spot- to-skin distance of 200 mm] and VATECH PAX-400C Digital X-ray system [110V-230V, 50/60Hz with 2.0 KvA radiation dose of 9-24 μSv] and for 3D imaging Cone-Beam CT scanner [Sirona GALILEOS comfort CBCT scanner (Sirona Dental System GmbH, D 64625 Bensheim, Germany) with the effective radiation dose of 68–1073 μSv]. The radiological interpretation of jaws lesion was based on the four radiological criteria such as location, periphery and shape, internal structure, and effect on surrounding structure. After the radiological diagnosis was made gray scale measurements were taken. The measurements were done on tangential section. The evaluation was done with the help of a reference point. For analysis of the gray values, the epicenter of the lesion was evaluated. The two intersecting lines were made at 90-degree angle which was considered as the epicenter of the lesion where they meet. In terms of mixed lesion, the epicenter was taken from the point where there are no bony trabeculae. The steps of measurement of gray scale value are shown in [Figure 1]. The mean gray value was taken of cystic or benign lesion after which the radiological diagnosis was given that was further compared with the final diagnosis [Figure 2].
|Figure 1: Measurement includes two intersecting lines drawn that are at 90 degree angulation considered as reference point in the center of lesion|
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|Figure 2: (a) extraoral photograph showing swelling on left side of maxilla,(b) intraoral photograph showing expansion of buccal cortical plate,(c) OPG reveals radiolucent lesion in left maxilla suggestive of lytic lesion,(d)CBCT image of tangential section with gray scale measurement and,(e) histological report confirming the diagnosis of cyst after surgical excision|
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Statistical analysis of the data was performed by using Statistical Package for Social Sciences (SPSS 17.0) (SPSS Inc., Chicago, Illinois, USA) and inferences were drawn. P < 0.001 was considered to be highly significant.
| Results|| |
In the comparative study done on both cysts and tumors a total of 60 patients were included. The age at the time of diagnosis ranged from 8 years to 80 years. Total numbers of cases for cyst was 34 and tumor was 26. The detailed distribution of the patients' age are mentioned in [Table 1]. The mean age for cysts in 34 cases was 28.4 with standard deviation of ±4.5 and in tumor with 26 cases was 33.19 with standard deviation of ±7.3. The study group with cyst 25 (73.5%) were male and 9 (26.5%) were female; male to female ratio was 1.2:1 whereas in tumor cases the ratio was 3.2:1 in which 14 (53.8%) were male and 12 (46.2%) were female.
Provisional diagnosis includes various clinical symptoms to diagnose it as cyst and tumors such as pain, swelling, facial asymmetry, and consistency. Patient diagnosed with pain in cyst was 20 (58.8%) and in tumor was 12 (46.2%), and swelling was more significantly found in tumor with 21 (80.8%) than in cyst 12 (35.3%). In cyst 4 (11.8%) patients and in tumor 17 (65.4%) patients were having facial asymmetry. Intraoral examination includes mainly vestibular obliteration, expansion, pus discharge, displacement, mobility, and missing of teeth that were eminent in both cyst and tumor [Figure 3]a and [Figure 3]b. Expansions were commonly seen in cases of tumor than cyst which was categorized into buccal, lingual, buccal, and lingual expansion. Eight (30.8%) patients of tumor were diagnosed with both buccal and lingual expansion and 4 (11.8%) patients of cyst were having buccal expansion.
|Figure 3: (a and b) Clinical manifestation of recorded in cysts and tumor|
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The detailed distribution of the lesion according to location in cysts and tumors radiographically are mentioned in [Table 2]. The greater predilection of lesion among the recorded case of cyst were anterior maxilla with 12 (35.3%). In tumor, posterior right mandible with 14 (53.8%) cases was the most common site. The study includes those cases of cysts and tumors whose internal structure was radiolucent and mixed. The density of the lesion was judged as radiolucent in 33 (97.1%) cases of cyst and 10 (38.5%) cases of tumor. In cases of mixed lesion 16 (61.5%) tumor cases and 1 (2.9%) cyst case were mostly seen and are stated in [Figure 4]. The borders of the lesion associated with well-defined boundaries in cyst were 10 (29.4%) cases and in tumor 3 (11.5%) cases. The poorly or ill-defined boundaries were significantly found in 23 (67.6%) cases of cyst and 22 (84.6%) cases of tumor. The borders with interrupted margins were seen in 1 (2.9%) case of cyst and 1 (3.8%) case of tumor as stated in [Figure 5]. Lesion caused root resorption in 7 (20.6%) cyst and 7 (26.9%) tumor. The association of impacted tooth with a lesion was seen in 4 (11.8%) cyst cases and 2 (7.7%) tumor cases. Displacement of wall of maxillary sinus was found in 7 (20.6%) of cyst and 3 (11.5%) of tumor. Displacement of involved teeth and expansion of cortical plate was significantly found in 4 (15.4%) and 2 (7.7%) of tumor cases. Displacement of inferior alveolar canal were reported in 4 cases with 2(5.9%) of cysts and 2(7.7%) of tumor.
|Figure 4: Internal structure of 60 cases of cyst and tumor having radiolucent and mixed lesion|
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The bone density was calculated by gray scale measurement from epicenter of both cyst and tumor as tabularized in [Table 3]. In calculated gray scale of cyst, the mean value with standard deviation of 8 cases of dentigerous cyst was 1302 ± 144.6, whereas 5 cases of odontogenic keratocyst showed 1258 ± 1.4. There were 16 cases of radicular cyst in which 7 were infected and showed mean value 1336.7 ± 7.5 which was of higher density. Tumor gray scale value was recorded in which least gray scale value was seen in adenomatoid odontogenic tumor, odontogenic ghost cell tumor, and myxoma. The higher gray scale density ranging 1384–1936 was seen in lateral periodontal cyst, residual cyst, acanthomatous ameloblastoma, cementoblastoma and multiple myeloma. The average mean value of cyst was 1292.2 ± 6.4 and tumor was 1469 ± 70.4. The P value that was calculated by Chi-square test was <0.001 which showed highly significant result. The bone density was also compared with the normal anatomical structure of maxillofacial region to draw the inference between normal and pathological structure. The result showed that minimum gray scale value is seen in radiolucent area like maxillary sinus and highest in radiopaque region like enamel [Table 4].
|Table 3: Calculated gray scale mean of reported cases of cysts and tumors|
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|Table 4: Mean gray scale value of anatomical landmark of maxillofacial region|
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| Discussion|| |
Many lesions occur in head and neck with the diagnosis of cysts or tumors. These lesions could be odontogenic and nonodontogenic. Among odontogenic lesions without mineralization such as ameloblastoma, dentigerous cyst, and odontogenic keratocyst can all appear as well-defined, unilocular, well-corticated lucent lesion that are often associated with crown of impacted or unerupted tooth. Among cystic lesion periapical cyst appears as a unilocular lucent lesion in the periapical region. Odontogenic lesion with mineralization includes complex odontoma which contains multiple masses of dental tissue and compound odontome that contain multiple tooth-like structures. Other odontogenic lesion such as odontogenic myxoma shows osseous changes of varying size with expansile nature and ill-defined borders. Nonodontogenic lesions that mimic odontogenic lesion include benign fibro-osseous lesion (fibrous dysplasia, ossifying fibroma, cemento-osseous dysplasia), central giant cell granuloma., These lesions are difficult to differentiate clinically and radiographically and so microscopic tissue evaluation is required to confirm the diagnosis. Before the advent of 3D imaging radiographical diagnosis was limited with 2D images. As the advanced imaging was introduced it revolutionized the medical and dental imaging by making it possible to diagnose the lytic lesion preoperatively. CT imaging was a major breakthrough in the branch of radiology in diagnosing the lesions. The radiation attenuation in CT imaging of different tissue was calculated by HU thus making it easier to define what a given finding may represent. HU measures the radiodensity and quantitative scale. Typical values of different elements and tissue ranges from -1000 to 3000 (air versus bone) which makes it possible to evaluate as either benign or malignant. Radiolucent lesion containing water or having attenuation corresponding to blood range from −1000 to +40 and radiopaque lesion having cancellous or dense bone may have attenuation ranging from +700 to 1000. CBCT introduced for dental use has many advantages such as high-resolution acquisition and, compared with conventional CT, lower radiation doses with smaller and less-expensive equipment. Manufacture of CBCT scanners provides viewer software that allows the user to open the CBCT dataset and to study the case. Conventionally, this software has the tools necessary for basic analyses such as multi-planar, dimension measurement, radiographic density calculation, and the calculation of the mean value of voxel gray values. CBCT gray values are considered approximate values and thus cannot be that expressed as HU as in case of conventional CT scan., Digital imaging, with pixel intensity (PI), holds the possibility of qualitative and quantitative analyses of bone density and architecture. PI analysis is considered as a simple method that provide objective measures of radiographic density of alveolar bone. Its means measurement of blackness or whiteness in a 8-bit digital image on a scale from zero (totally black) to 255 (totally white). The number and size of the pixels, together with the number of shades of gray available in radiograph, decided the amount of information in an image. Most studies have reported that the gray values obtained by CBCT are higher than the HU values obtained by conventional CT of the same region., Mishra et al. reported in his study that CBCT may be more convenient and suitable than multislice computed tomography for the evaluation of bony lesions of the jaws caused by cysts and tumors. Reeves et al. concluded in the study that the gray scale levels taken from CBCT scan can be used to derive HU in clinical environment. This capability along with the decreased patient radiation exposure, ease of access, greater resolution than medical CT, and affordability should solidify CBCT as the imaging modality of choice in orofacial pathology. According to their study, correlation coefficient of gray scale is 0.99 which is the standard for measuring bone density result could be altered due to soft tissue effect. Shrout et al. digitized radiographic image using 256 gray scales and computed a cumulative percent histogram. He concluded in his study that granulomas had a narrower range and lower gray scale value than cyst. Simon et al. in his study carried on 17 large periapical lesion concluded that CBCT scan gray value can measure and differentially diagnose a solid from a fluid-filled lesion or cavity. Camps J et al. also used a gray level correction method to assess treatment results. Many studies have used CBCT gray values for the differential diagnosis and follow-up of bony lesions.,,,
In present study, there is strong correlation of gray scale value that is seen in cases of cysts and tumors which can be attributed to the bone density level and therefore considered as a major diagnostic tool in branch of dentistry. It is suggested that further studies should be carried out with other CBCT scanner that can be used for clinical application of other orofacial pathology.
| Conclusion|| |
We conclude from this study that CBCT gray value can be considered as a major tool in diagnosis of cyst and tumor and other soft or hard tissue lesion without any microscopic evaluation. CBCT gray scale measurement is superior to conventional intraoral radiographic methods for diagnosing the nature of lytic lesion of jaw.
Declaration of patient consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]
[Table 1], [Table 2], [Table 3], [Table 4]