Assessment of image quality in dental radiography, part 1: Phantom validity

doi:10.1016/S1079-2104(99)70304-5

Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology, and Endodontology

Volume 87, Issue 1, January 1999, Pages 115-122

https://doi.org/10.1016/S1079-2104(99)70304-5 Get rights and content

Abstract

Objective. The purpose of this study was to describe and validate an image-quality phantom to be used in dental radiography for comparison of film and digitally acquired images. Study Design. An aluminum block of 12 steps, with 7 holes in each step, was covered by acrylic blocks. This phantom was radiographed with Kodak Ultra-speed and Ektaspeed Plus films at 70, 65, and 60 kVp with the whole exposure range available. All together, 50 dental films were randomly sequenced and presented to 7 observers. The average number of perceptible holes from all steps was plotted against exposure for each tube voltage and film type, generating a modified perceptibility curve. The tentative optimum exposure level was determined from perceptibility curves in each experimental condition and compared with that determined by means of the standard aluminum stepwedge and the preset time of the x-ray machine. The density range of this phantom at the optimum exposure was compared with that of clinical dental radiographs. Validity of the phantom was evaluated according to the optimum exposure level from the modified perceptibility curves and the overall density range. Finally, the average maximum numbers of perceptible holes at the tentative optimum exposure level were compared for each tube voltage and film type. The statistical test used was a 2-way factorial analysis of variance. Results. The exposure at the perceptibility curve peak approximated that obtained by means of the standard aluminum stepwedge and the time preset by the manufacturer. The overall density range at the perceptibility curve peak covered the clinical density range for each tube voltage and film type. There were no statistically significant differences between film types or among tube voltages. Conclusions. The x-ray attenuation range for this phantom seemed to approximate clinical conditions. In addition, differences in image quality could be quantitatively evaluated by means of the number of the holes seen in the phantom. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1999;87:115-22)

Section snippets

Phantom for dental radiography

Fig 1 shows an overview of the phantom.

. Phantom for dental radiography. A, Lateral view shows aluminum block placed in acrylic box. B, Overview shows aluminum step block with holes of increasing depths.

An aluminum block of 12 steps, with 7 holes drilled in each step, was covered by acrylic blocks. The thickness interval of each step was 1 mm. The depth of the 7 holes in each step sequentially increased from 0.05 to 0.35 mm. The thicknesses of the front and back acrylic plates were 10 and 2 mm,

RESULTS

Fig 3 shows the changes of the modified PCs depending on the varying confidence levels in the Ultra-speed film radiographed at 70 kVp.

. Changes of modified PCs depending on varying confidence levels in Ultra-speed film radiographed at 70kVp. Vertical lines show SD. Maximum number of holes is 12 × 7 = 84. Curves were fitted by third-order polynomial functions through use of a least squares approximation. Confidence level 1: y = 8.19 + 1.29x – 0.0148x ² + 0.0000552x ³; r = 0.99. Confidence level 2:

DISCUSSION

PCs have been used by a number of authors to compare the detectability of radiographic systems.14, 15, 16, 17, 18 PC testing is relatively easy to perform, and reproducible quantitative results can be obtained. Data obtained from such tests provide useful information about the contrast properties of each system.¹⁸ The main disadvantage is that these are laboratory tests; the results do not predict clinical diagnostic outcomes. One reason for this seems to be the even thickness of the simple

Acknowledgements

We thank our colleagues in the Department of Oral and Maxillofacial Radiology, who served as observers.

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There was no significant difference in perceptibility detection between the Lenovo M92z desktop, iPad 3, and iPad mini. However, on average, all 3 were significantly better than the Lenovo Z580 laptop (P values ≤.015). No significant difference in the mean absolute error was noted for working length measurements among the 4 viewing devices (P = .3509).
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As described above a test object used to construct PCs is usually a homogeneous block. An aluminum step phantom with small holes may be used to simulate the clinical radiation contrast range (Fig. 4) [16]. Using this phantom, differences in image quality could be quantitatively evaluated according to the number of visible holes in the radiographs [17].
The radiological diagnostic process is composed of the three major phases, psychophysical, psychological and nosological. An apparent improvement in image quality in the psychophysical phase does not necessarily imply an increased diagnostic performance. This may be true for the general diagnostic processes, but may not for the caries diagnosis, because psychophysical phase is of most significance in such special and relatively simplified task. In this article the processes to correlate perception to approximal caries diagnosis are reviewed using the Perceptibility Curve (PC) tests and Receiver Operating Characteristic (ROC) curve tests. The PC test was developed to represent the psychophysical property of the radiographic imaging system. Since physical properties are shown to be closely correlated with psychophysical properties, it is possible to theoretically calculate psychophysical properties of the radiographic systems from their physical properties. In a similar manner, observers' low contrast detectability in the psychophysical phase can be predicted from some physical parameters of the radiographic system. observers' low contrast detectability is also correlated with the diagnostic performance obtained from ROC curve in the task of approximal caries diagnosis. Thus, considerably high correlation between psychophysical properties and diagnostic accuracy indicates close relationship between perception and approximal caries diagnosis. It implies that an improvement in the physical image quality leads to increased diagnostic performance to some extent in the approximal caries diagnosis.
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While there are a number of studies dealing with the comparison of film and digital radiographs with respect to marginal bone level,20 periapical lesions,21 or caries diagnoses,22 there is a dearth of objective ROC-based in vitro perceptibility studies according to literature review. An aluminum step wedge as test phantom was used in the present study, following the phantom design of the well-known “perceptibility curve test” for intraoral radiographic systems.3-8 A major disadvantage of the design was the imbalance between images showing dark spots (18 images) and those showing no spots (5 images), resulting in a prevalence ratio of 0.78/0.22.
To compare experimentally the image quality of charged-coupled device (CCD)-based digital, flatbed scanner digitized, and dental film radiographs.
High-contrast standardized radiographs of an aluminum step wedge containing boreholes were obtained on dental radiographic film (F) and a CCD receptor (D). Digitization (S) was done with a flatbed scanner. Each radiograph was separated into 23 single images, 18 of which showed a dark spot. Thirty observers indicated their confidence on the visibility of the spots for a receiver operating characteristic (ROC) analysis.
Mean Az values (area beneath the ROC curves) differed significantly (P < .05), being highest for D (Az = 0.76), followed by F (Az = 0.71) and S (Az = 0.60). Mean sensitivity of S (0.45) was significantly (P = .000) lower than for D (0.66) and F (0.67).
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Contrast perception in digitized panoramic radiographs compared with their film-based origin
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Objectives. We sought to compare the visual image quality of film-based and digitized panoramic radiographs through use of a hole-containing test wedge. Study Design. An aluminum wedge containing 100 cells, of which 90 were given shallow holes, was exposed in the film-based Orthophos CD panoramic unit. Two radiographs subjectively exhibiting optimum contrast were selected. Films were digitized with a charge-coupled device flatbed scanner at 300 dpi. Films and digitized images were rated cellwise by 2 similar groups of 50 observers each with respect to spot perception. Results. The mean sensitivity was 0.26 ± 0.09 for film and 0.20 ± 0.07 for digitized images (P =.000), with a pronounced decline in the latter in regions of high background density. The average specificity was 0.93 ± 0.07 for film versus 0.92 ± 0.08 for digitized images (P = 0.213). Conclusion. Film yielded a significantly higher sensitivity, but this absolute difference was actually small compared with that of the digitized images. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2002;94:388-94)
Comparison between PAI and quantitative digital radiographic assessment of apical healing after endodontic treatment
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The change from one film type to the other was not expected to affect either observer performance or densitometric analysis. Both film types have been found to have similar contrast and sensitometric properties over the useful range of densities,23,24 with no significant difference found between them.25 Both film types have also been shown to have similar ability to detect root resorption.26
Objective: The purpose of this study was to compare both subjective (Periapical Index, PAI) and objective (densitometric) radiographic evaluation of healing after endodontic treatment for apical periodontitis. Study Design: Standardized radiographs of 103 teeth taken at baseline (immediately after endodontic treatment) and at 1, 4, 12, 26, and 52 weeks were evaluated. Consensus PAI scores obtained from 7 calibrated observers served as “true scores.” Densitometric estimates of periapical status were obtained from digitized radiographs as the ratio of mean gray value of an area of radiolucency (AR) to an adjacent and similar-sized normal (N) area (AR/N). The selected regions of interest on baseline images were automatically superimposed on postoperative images. All estimates of change were measured with respect to baseline. The subtraction estimate was expressed as AR_S-N_S. Linear regression was used to analyze longitudinal changes against baseline and to assess the relationship of PAI and AR/N and of change in PAI with respect to baseline and AR_S-N_S. Results: Five hundred fifty-six PAI scores were generated, with 547 AR/N values and 444 subtraction estimates. PAI, AR/N, and AR_S-N_S demonstrated statistical significance for change (P ≤.05) starting at 12 weeks. PAI was significantly correlated with AR/N (P <.0001), as was CHPAI with AR_S-N_S (P <.024). Conclusion: The PAI and 2 densitometric estimates (AR/N and AR_S-N_S) detected healing of apical periodontitis at 12 weeks after treatment. No difference could be observed among the methods.(Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001;92:108-15)

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^☆: Reprint requests:Kazunori Yoshiura, DDS, PhD,Maidashi 3-1-1,Higashi-ku,Fukuoka 812-8582,Japan

^☆☆: This work was supported in part through a Grant-in-Aid for Scientific Research (C) from the Japanese Ministry of Education, Science and Culture.

^★: Department of Oral and Maxillofacial Radiology, Faculty of Dentistry.

^★★: 1079-2104/99/$8.00 + 0 7/16/94509

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Assessment of image quality in dental radiography, part 1: Phantom validity☆,☆☆,★,★★

Abstract

Section snippets

Phantom for dental radiography

RESULTS

DISCUSSION

Acknowledgements

Oral Surg Oral Med Oral Pathol

Oral Surg Oral Med Oral Pathol Oral Radiol Endod

Oral Surg Oral Med Oral Pathol Oral Radiol Endod

Oral Surg Oral Med Oral Pathol

Oral Surg Oral Med Oral Pathol

Oral Surg Oral Med Oral Pathol

Oral Surg Oral Med Oral Pathol

Oral Surg Oral Med Oral Pathol Oral Radiol Endod

Oral Surg Oral Med Oral Pathol

Oral Surg Oral Med Oral Pathol

Oral Surg Oral Med Oral Pathol Oral Radiol Endod

Oral Surg Oral Med Oral Pathol Oral Radiol Endod

Computed dental radiography: evaluation of a new charge-coupled device-based intraoral radiographic system

Quintessence International

The imaging performance of a storage phosphor system for dental radiography

Br J Radiol

Digital radiology in dental diagnosis: a critical view

Dentomaxillofacial Radiology

In vitro comparison of D- and E-speed film radiography, RVG, and Visualix digital radiography for the detection of enamel approximal and dentinal occlusal caries lesions

Caries Res

RVG-S, VIXA, and Ektaspeed film in detection of proximal enamel defects under orthodontic bands

Angle Orthod