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 Table of Contents  
ORIGINAL RESEARCH
Year : 2017  |  Volume : 9  |  Issue : 4  |  Page : 174-179

A study on changes in image quality with dose reduction in digital panoramic radiographs


1 Department of Oral Medicine and Radiology, Ahmedabad Dental College and Hospital, Ahmedabad, Gujarat, India
2 Department of Dentistry, GMERS Medical College and Hospital, Patan, Gujarat, India
3 Department of Pedodontics and Preventive Dentistry, Ahmedabad Dental College and Hospital, Ahmedabad, Gujarat, India
4 Department of Conservative Dentistry and Endodontics, AMC Dental College and Hospital, Ahmedabad, Gujarat, India
5 Department of Dentistry, Satyam Multispeciality Dental Hospital, Vadodara, Gujarat, India

Date of Web Publication21-Aug-2017

Correspondence Address:
Mayank K Chaturvedi
D1/2 Staff Quarters, GMERS Medical College and Hospital, Dharpur, Patan - 384 265, Gujarat
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jioh.jioh_138_17

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  Abstract 

Introduction: Panoramic radiography is frequently used for dental diagnosis and treatment planning. While smallest radiation exposure also being harmful to patients, every attempt must be made to reduce it as much as possible. Aims: The aim of the study was to assess effects of dose reduction on image quality of panoramic radiographs. Materials and Methods: The sample of 75 patients was selected from the patients coming at the outpatient department of the institute. Two panoramic radiographs were taken for each patient. A total of 150 panoramic radiographs were taken which were evaluated by two blinded observers for image quality. Results: Statistically nonsignificant difference was found between the image qualities of radiographs of the same patient with recommended exposures and those with altered exposure. Conclusion: Dose reduction did not cause significant loss of image quality using digital panoramic radiography machine when the dose was reduced by 36% by decreasing exposure time only.

Keywords: Dose-area product, panoramic radiography, radiation dosage


How to cite this article:
Barot AA, Chaturvedi MK, Butala PB, Rao VV, Patel PS, Barot AA. A study on changes in image quality with dose reduction in digital panoramic radiographs. J Int Oral Health 2017;9:174-9

How to cite this URL:
Barot AA, Chaturvedi MK, Butala PB, Rao VV, Patel PS, Barot AA. A study on changes in image quality with dose reduction in digital panoramic radiographs. J Int Oral Health [serial online] 2017 [cited 2019 Aug 25];9:174-9. Available from: http://www.jioh.org/text.asp?2017/9/4/174/213495


  Introduction Top


Nowadays, radiography is an essential procedure in the diagnosis of dental problems.[1] Dental radiographs are taken periodically and more often than any other radiographs.[2],[3] Dental radiology represents about 25% of all radiological examinations carried out each year.[4],[5],[6] Paatero and Hudson et al. developed panoramic radiography for clinical use during the 1940s and 1950s.[7] Dental panoramic radiography or more commonly known as orthopantomography (OPG) is a technique whereby an image of the entire dentition may be obtained on a single film, without superimposition of structures superficial or deep to the teeth and jaws.[8]

OPG is a favourite radiographic method for overall assessment of caries, periodontal diseases, malocclusion, and some of the other common dental disorders.[9] Panoramic radiography also has the additional benefits of reduced radiation exposure compared with full-mouth intraoral radiographs, and the availability of modifications to standard intraoral techniques for pediatric and disabled patients as well as those with gag reflex sensitivity.[10]

Whatever reduction in dosage is done, radiation is still hazardous. Early X-ray experiments also led scientists to observe that the passage of X-rays through living tissue could cause changes.[11],[12],[13] Dr. C. Edmund Kells who took the first intraoral radiograph in a live person was the first person to himself suffer from the hazards and report that long exposures caused a mild skin irritation which was similar to sunburn although it vanished after a short time.[14] To reduce the risk of radiation damage to patients, practitioners should follow the as low as reasonably achievable (ALARA) principles. Even small doses might cause damage to tissues, and the current thought is there is no threshold dose below which radiation is totally and predictably safe. As an attempt to reduce radiation exposure to patients, this study was conducted to determine whether changes in dose reduction would have an impact on the image quality of panoramic radiographs.


  Materials and Methods Top


  • This prospective study was conducted in the Department of Oral Medicine and Radiology of the institute for a period of 2 years based on convenience sampling method. The ethical approval for the study was obtained from the Ethical Committee of the institute.


Source of data and selection of subjects

  • The sample of patients for the study was selected from the outpatient department of the institute who were advised panoramic radiographs for diagnostic purpose. The sample size consisted of 75 patients with age ranging from 18 years and above
  • All the participants were clinically examined to determine whether panoramic radiograph was necessary for diagnosis and/or treatment planning. Only those patients who were 18 years or above in age were included in the study. Participants who had occupational radiation exposure, recent extensive radiographic examination, or any other systemic history were excluded from the study.


Method

Two panoramic radiographs were taken for each patient with digital panoramic radiography machine (X Mind Pano D+, Soredex) along with Lead aprons, Plastic sleeves for bite block and images obtained on a computer with installed software (Dfw. 2.8 version by Soredex), displayed on liquid crystal display (LCD) monitor.

Procedure

The first radiograph of all 75 patients was taken at standard kilovoltage peak (kVp), milliampere (mA), and exposure time (seconds) settings as recommended by the manufacturer, i.e. 73 kVp 10 mA and 17.6 s. A second radiograph was taken immediately without changing patient's position but by reducing exposure time from 17.6 s to 11 s, keeping other parameters constant, i.e. 73 kVp 10 mA and 11 s. All images were obtained by one radiographer [Figure 1], [Figure 2], [Figure 3], [Figure 4].
Figure 1: Patient positioned (with lead apron) in the digital panoramic radiography machine

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Figure 2: Dose-area product values (at the bottom) for three different sets of exposure parameters (as shown in a, b and c)

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Figure 3: (a) Panoramic radiograph taken with exposure parameters 73 kVp, 10 mA, and 17.6 s. (b) Panoramic radiograph of the same patient taken with exposure parameters 73 kVp, 10 mA, and 11 s

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Figure 4: (a) Panoramic radiograph taken with exposure parameters 85 kVp, 10 mA, and 17.6 s. (b) Panoramic radiograph of the same patient taken with exposure parameters 85 kVp, 10 mA, and 11 s

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Recording the dose

Dose-area product (DAP) readings were recorded from the display of the digital panoramic radiography machine used in the study for each set of exposure parameters.

Analysis of radiographs

The images obtained were given to two blinded independent observers for evaluation on a 29-inch LCD monitor with resolution of 265 dpi (Dots Per Inch) in Joint Photographic Experts Group format using Microsoft picture and fax viewer for displaying the radiographic images. Before evaluating the images, the observers received verbal and written explanation of the nature of the study and were trained to interpret panoramic radiographs. Image quality was assessed by means of the visibility of 24 anatomical landmarks which are commonly found on panoramic radiographs. Scoring criteria were used with scores from 1 to 5 suggesting subjective image qualities from inadequate to excellent which were recorded in specially prepared observation sheets.

Radiograph scoring criteria

  • 1 = Inadequate for diagnosis
  • 2 = Barely adequately represented
  • 3 = Adequately represented
  • 4 = More than adequately represented
  • 5 = Excellent.


Statistical analysis

For statistical analysis, the structures were divided into three regions (11 landmarks of maxilla, 9 of mandible, and 4 other miscellaneous landmarks) and bilateral landmarks were divided into two sides (left and right). An overall image quality score based on the mean of all regions was obtained for each image. Statistical analysis was done with paired samples t-test using SPSS (Statistical Package for the Social Sciences) version 12 (SPSS Inc., Chicago, IL, USA) for Windows (© Microsoft Corporation).


  Anatomical Landmarks Top


Maxillary landmarks

  • Anterior nasal spine
  • Nasal septum
  • Inferior concha
  • Maxillary tuberosity
  • Maxillary sinus
  • Floor of maxillary sinus
  • Zygomatic arch
  • Articular eminence
  • Periapical lamina dura
  • Periodontal ligament space
  • Interdental bone.


Mandibular landmarks

  • Condylar process
  • Coronoid process
  • Inferior cortex
  • Mandibular canal
  • Mental foramen
  • External oblique ridge
  • Periapical lamina dura
  • Periodontal ligament space
  • Interdental bone
  • Styloid process
  • External auditory meatus
  • Disc space
  • Hyoid bone.



  Results Top


The study consisted of 75 patients divided into two groups for two different exposure parameter changes. Two panoramic radiographs were taken for each patient as per the method mentioned above. A total of 150 panoramic radiographs were taken which were evaluated by two blinded observers for image quality.

[Table 1] shows DAP readings displayed by the digital panoramic radiography machine. With exposure parameters as recommended by the manufacturer, i.e. tube potential of 73 kVp and exposure time 17.6 s; the DAP was found to be 99.1 mGy cm 2. When only the exposure time was reduced to 11 s, the DAP was found to be 62 mGy cm 2. With increase in tube potential to 85 kVp and subsequent decrease in exposure time to 11 s, DAP was found to be 82.1 mGy cm 2.
Table 1: Dose-area product readings displayed by the digital panoramic radiography machine

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[Table 2] shows the correlation of scores given by both observers to radiographs exposed with exposure time 17.6 s. Scores of maxilla, mandible, and overall (average) showed partial positive correlation with Pearson's r = 0.290 (P = 0.012), 0.110 (P = 0.346), and 0.174 (P = 0.135), respectively. The scores for other regions showed no correlation between the observers with value of 0.054 (P = 0.643).
Table 2: Correlation of scores given by both observers to radiographs exposed with exposure time 17.6 s

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[Table 3] shows a correlation of scores given by both observers to radiographs exposed with exposure time 11 s. Scores of maxilla, mandible, and overall (average) showed partial positive correlation with values of 0.512 (P < 0.0001), 0.303 (P = 0.008), and 0.264 (P = 0.022), respectively. The scores for other regions showed no correlation between the observers with a value of 0.072 (P = 0.537).
Table 3: Correlation of scores given by both observers to radiographs exposed with exposure time 11 s

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[Table 4] shows a comparison of scores given by both observers to radiographs exposed with exposure times 17.6 s and 11 s. For observer 1 and exposure time 11 s, the mean ± standard deviation (SD) scores for maxilla, mandible, other regions and average were found to be 2.96 ± 0.201, 3.02 ± 0.251, 2.57 ± 0.233, and 2.85 ± 0.181, respectively, whereas those for exposure time 17.6 s were found to be 2.95 ± 0.239, 3 ± 0.297, 2.56 ± 0.269, and 2.84 ± 0.227, respectively. This gave P = 0.680, 0.583, 0.836, and 0.608 for maxilla, mandible, other, and average scores, respectively. For observer 2 and exposure time 11 s, the mean ± SD scores for maxilla, mandible, other regions, and average were found to be 2.57 ± 0.396, 2.74 ± 0.309, 1.97 ± 0.425, and 2.43 ± 0.284, respectively, whereas those for exposure time 17.6 s were found to be 2.59 ± 0.441, 2.74 ± 0.394, 1.97 ± 0.478, and 2.43 ± 0.368, respectively. This gave P = 0.756, 0.919, 0.954, and 0.916 for maxilla, mandible, other, and average scores, respectively.
Table 4: Comparison of scores given by both observers to radiographs exposed with exposure times 17.6 seconds and 11 s

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  Discussion Top


This study consisted analysis of radiographs of 75 patients who were exposed twice. However, greater sample size could have been more advisable, which was not possible in this study under the mentioned time period. In addition to panoramic radiographs, effect of dose reduction could also be observed on other frequently advised extraoral radiographs such as cephalometric radiographs. However, cephalometric radiographs were not selected for this study as they are frequently advised in adolescents and young adults who are more sensitive to radiation exposure.

When radiographs were taken with exposure parameters as recommended by the manufacturer, i.e. 73 kVp, 10 mA, and 17.6 s, the scores suggesting image quality based on recognition of normal anatomical landmarks showed that there was partial correlation between both the observers for landmarks of maxilla, mandible, and average scores (that suggested the overall image quality for that particular radiograph) which was also the case with study conducted by Kaeppler et al. where moderate agreement was found between the observers used in the study.[15]

No correlation between scores of the observers was seen for regions that included the landmarks such as styloid process, external auditory meatus, temporomandibular joints disc space, and hyoid bone. These are the structures that are routinely not looked for in panoramic radiographs, so observers' expectations are due to be varied regarding their image quality. The results suggested that there was some difference in scores given by both the observers, but this was expected as it was the subjective image quality that was considered and observer variations were expected.

When results for effect of dose reduction on panoramic radiographic image quality were studied, it could be seen that statistically nonsignificant difference was found when decrease in exposure time was done (73 kVp, 10 mA and 11 s).

The possibility of achieving dose reduction in digital panoramic radiography, by reducing kVp settings without loss of diagnostic image quality was shown by Dula et al. and Kaeppler et al., although Gibjels et al. found a higher dose for the salivary glands at lower kVp.[16] Dula et al. reported that, in an experimental evaluation of CCD-based (Orthophos DS) system, a decrease of up to 43% exposure without loss of diagnostic quality. They did mention that although reducing kVp reduced the skin dose, a steeper attenuation curve would be obtained for lower kVp settings due to more X-ray absorption in deeper tissues.[17],[18],[19],[20],[21] Alkurt et al. achieved a dose reduction of 25% by reducing mA with a nonsignificant difference in subjective image quality.[22] A decrease in the standard exposure setting of up to 70% has been described for other digital panoramic systems.[23]

Another observation that could be made was that the mean scores for mandibular landmarks were consistently higher compared to maxilla and other regions. This again reinforces the fact that panoramic radiographs are most useful for study of mandibular region.

The DAP is relatively easy to measure and is a better indicator of risk. The DAP correlates well with the total energy imparted to a patient, which is related to the effective dose and therefore to the overall health risk. This study was carried out to measure DAP using a DAP meter, which is easy to use the tool and to calculate effective doses.[24] In 1995, review of doses from common radiographic and fluoroscopic X-ray examinations held on a National Patient Dose Database by NRPB indicated that there had been on an average 30% reduction in entrance surface dose and DAP measurements over the previous 10-year period. This was estimated to lead to a substantial fall in the collective dose, assuming the number of such examinations had remained constant.[25] Similarly, in this study; we achieved a DAP reduction of about 36% which could prove significant with regard to cumulative dose and also in accordance with the ALARA principle.[26],[27],[28] Williams and Montgomery in 2000 concluded that average DAP value of panoramic radiograph was 113 mGy cm [2],[26],[27] Thus, this study introduces a means of reduction of radiation exposure to the patients. However, further research is needed for analyzing greater reduction by means of variations in the mA or kVp of the panoramic radiograph, which was not possible in this study as the panoramic machine did not allow the same.


  Conclusion Top


Partial positive correlation was found between majority of scores given to the panoramic radiographs by both the observers. However, statistically nonsignificant difference was found between the image qualities of radiographs of the same patient with recommended exposures and those with altered exposure. Nonsignificant differences were found between the image qualities of anatomical landmarks on the left and right sides for all the panoramic radiographs. The scores for identification of anatomical landmarks of mandible were consistently higher than that of maxilla and other regions. According to the results of this study, dose reduction did not cause significant loss of image quality using digital panoramic radiography machine when the dose was reduced by 36%. Thus, dose can be reduced by 36% by decreasing exposure time only.

Farman et al. (1998) showed that dose reductions could be achieved by increasing the beam energy to 80 kVp due to improvement in the sensitivity of the rare earth screens a study similar to which we have carried out further involving changes in both kVp and exposure time.[29] Further research is required for whether kVp should be increased or not to decrease X-ray absorption in the deeper tissues.

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

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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