From pixel to image analysis.

Over the past 50 years, computer technology has evolved enormously. This has made it possible to carry out radiography in a completely new way, allowing to process X-ray images in an advanced manner and to extract the information from the image data. This article gives an overview of some of the most important developments in dental radiology. These include capturing the images, analysing and interpreting the image information and using the images for 3D reconstruction.

[Panoramic radiographs in dental diagnostics]. / Panoramische röntgenopnamen in de tandheelkundige diagnostiek.

Panoramic radiographs are frequently used in dental practice in addition to bitewing radiographs and periapical radiographs. The way a panoramic photograph is created is different from that of a projection image, such as bitewing and periapical radiographs. As a result, the sharpness of detail is much less, and overlap of structures occurs in different areas of the image. Consequently the diagnostic utility is limited to the recognition of anomalies for which small details play a lesser role. The advantage of a panoramic radiograph is that structures over a large area are shown in their relative location. Because of the lower resolution and the higher dose of radiation to the patient compared with a series of intraoral images, the panoramic radiograph is not indicated during a periodic check-up. If clinical inspection indicates a need for it and as a supplement to an intraoral radiograph, a panoramic radiograph can, however, be appropriate in cases of abnormalities that extend over a larger area, such as tumours and developmental disorders.

[Cone beam computed tomography: is more also better?]. / Conebeamcomputertomografie: is meer ook beter?

Cone beam computed tomography (CBCT) is a radiographic technique that has now been available in dentistry for about 20 years. The ability to display three-dimensional structures is of importance for many defects in the maxillofacial area. A disadvantage, however, is that the dose of a CBCT-study is higher than the dose of more conventional imaging techniques. This should be taken into account when prescribing a CBCT-examination. Because a CBCT-image usually displays a larger area than that of conventional radiography, there is the possibility that abnormalities may be shown that are outside the direct field of experience of the dentist. For all these reasons, the user of a CBCT-device needs to have additional knowledge.

[Oral and maxillofacial radiology: laws and regulations]. / Tandheelkundige radiologie: wet- en regelgeving.

Since the discovery of X-rays, medical imaging has been one of its most important applications. In the course of years, understanding of the potentially harmful effects of radiation on tissue has substantially increased as a result of experience and scientific studies. This has led to the International Commission on Radiological Protection (ICRP), the organisation that is now regarded as the most authoritative in the field of information on radiation and radiation protection. In most countries the law governing radiation is based on the 3 principles of the ICRP: justification, ALARA and dosage limits. For the Dutch situation, these are the Nuclear Energy Act (Kernenergiewet) and the Radiation Protection Decree (Besluit stralingsbescherming). The Practice Guidelines on Radiology are available for the practical implementation of the regulations. By working according to the Practice Guidelines, the dentist satisfies the legal regulations, but, more importantly, he can apply X-ray diagnostics in a manner that is safe for him, the dental team, the patients and all other visitors of the practice.

Reducing an already low dental diagnostic X-ray dose: does it make sense? Comparison of three cost-utility analysis methods used to assess two dental dose-reduction measures.

OBJECTIVES: To find a method that is suitable for providing an objective assessment of the cost effectiveness of a dose-reducing measure used for diagnostic dental X-ray exposures. METHODS: Three cost-utility analysis (CUA) methods were evaluated by comparing their assessments of two dose-reduction measures, a rectangular collimator and the combination of two devices that reduce the radiation dose received during orthodontic lateral cephalography. The following CUA methods were used: (1) the alpha value (AV), a monetary valuation of dose reduction used in the nuclear industry; (2) the value of a statistical life for valuation of the reduction in stochastic adverse effects; and (3) the time-for-time method, based on the postulate that risk reduction is effective when the number of years of life gained is more than the years that an average worker must work to earn the costs of the risk-reducing measure. The CUA methods were used to determine the minimum number of uses that was required for the dose-reducing device to be cost effective. The methods were assessed for coherence (are comparable results achieved for comparable countries?) and adaptability (can the method be adjusted for age and gender of specific patient groups?). RESULTS: The performance of the time-for-time method was superior to the other methods. Both types of dose-reduction devices tested were assessed as cost effective after a realistic number of uses with all three methods except low AVs. CONCLUSIONS: CUA for the methods of X-ray dose reduction can be performed to determine if investment in low dose reduction is cost effective. The time-for-time method proved to be a coherent and versatile method for performing CUA.

Dose reduction in orthodontic lateral cephalography: dosimetric evaluation of a novel cephalographic thyroid protector (CTP) and anatomical cranial collimation (ACC).

OBJECTIVES: To test the dose-reducing capabilities of a novel thyroid protection device and a recently introduced cranial collimator to be used in orthodontic lateral cephalography. METHODS: Cephalographic thyroid protector (CTP) was designed to shield the thyroid while leaving the cervical vertebrae depicted. Using a RANDO(®) head phantom (The Phantom Laboratory, Salem, NY) equipped with dosemeters and a Proline XC (Planmeca, Helsinki, Finland) cephalograph, lateral cephalograms were taken, and the effective dose (ED) was calculated for four protocols: (1) without shielding; (2) with CTP; (3) with CTP and anatomical cranial collimator (ACC); and (4) with a thyroid collar (TC). RESULTS: The ED for the respective protocols was (1) 8.51; (2) 5.39; (3) 3.50; and (4) 4.97 µSv. The organ dose for the thyroid was reduced from 30.17 to 4.50 µSv in Protocols 2 and 3 and to 3.33 µSv in Protocol 4. CONCLUSIONS: The use of just the CTP (Protocol 2) resulted in a 36.8% reduction of the ED of a lateral cephalogram. This was comparable to the classical TC (Protocol 4). A 58.8% reduction of the ED was obtained when combining CTP and ACC (Protocol 3). The dose to the radiosensitive thyroid gland was reduced by 85% in Protocols 2 and 3 and by 89% in Protocol 4.

Assessment of Random Error in Phantom Dosimetry with the Use of Error Simulation in Statistical Software.

OBJECTIVE: To investigate if software simulation is practical for quantifying random error (RE) in phantom dosimetry. MATERIALS AND METHODS: We applied software error simulation to an existing dosimetry study. The specifications and the measurement values of this study were brought into the software (R version 3.0.2) together with the algorithm of the calculation of the effective dose (E). Four sources of RE were specified: (1) the calibration factor; (2) the background radiation correction; (3) the read-out process of the dosimeters; and (4) the fluctuation of the X-ray generator. RESULTS: The amount of RE introduced by these sources was calculated on the basis of the experimental values and the mathematical rules of error propagation. The software repeated the calculations of E multiple times (n = 10,000) while attributing the applicable RE to the experimental values. A distribution of E emerged as a confidence interval around an expected value. CONCLUSIONS: Credible confidence intervals around E in phantom dose studies can be calculated by using software modelling of the experiment. With credible confidence intervals, the statistical significance of differences between protocols can be substantiated or rejected. This modelling software can also be used for a power analysis when planning phantom dose experiments.

Validation of anatomically shaped cranial collimation (ACC) in orthodontic lateral cephalography.

The use of an anatomically shaped cranial collimator (ACC) to reduce patient dose in orthodontic lateral cephalography was investigated in this study. The aim was to evaluate the potential interference of the ACC on landmark identification for orthodontic cephalometry. Consecutive orthodontic patients underwent a total of 100 cephalograms using an ACC mounted on a Veraviewepocs(®) 3D X550 (J. Morita Co., Kyoto, Japan) X-ray unit. 10 observers were asked whether the identification of 5 landmarks close to the collimated area was hindered or rendered impossible by the presence of the collimator. Of the 500 landmarks that were judged by the 10 observers, 496 (99.2%) were reported to lack hindrance. In three landmarks, a minority of the observers reported hindrance. In 1 landmark, 8 of the 10 observers reported hindrance by the collimator. In no instance did the observers state that the identification of landmarks was impossible as a result of the collimation. Application of the ACC on the cephalostat of the X-ray unit is a viable way of reducing patient dose, as it only marginally interferes with the diagnostic yield of the exposure. The need to retake images when the ACC is applied was found to be extremely low.

Anatomically shaped cranial collimation (ACC) for lateral cephalometric radiography: a technical report.

Lateral cephalograms in orthodontic practice display an area cranial of the base of the skull that is not required for diagnostic evaluation. Attempts have been made to reduce the radiation dose to the patient using collimators combining the shielding of the areas above the base of the skull and below the mandible. These so-called "wedge-shaped" collimators have not become standard equipment in orthodontic offices, possibly because these collimators were not designed for today's combination panoramic-cephalometric imaging systems. It also may be that the anatomical variability of the area below the mandible makes this area unsuitable for standardized collimation. In addition, a wedge-shaped collimator shields the cervical vertebrae; therefore, assessment of skeletal maturation, which is based on the stage of development of the cervical vertebrae, cannot be performed. In this report, we describe our investigations into constructing a collimator to be attached to the cephalostat and shield the cranial area of the skull, while allowing the visualization of diagnostically relevant structures and markedly reducing the size of the irradiated area. The shape of the area shielded by this "anatomically shaped cranial collimator" (ACC) was based on mean measurements of cephalometric landmarks of 100 orthodontic patients. It appeared that this collimator reduced the area of irradiation by almost one-third without interfering with the imaging system or affecting the quality of the image. Further research is needed to validate the clinical efficacy of the collimator.

Prediction of osteoporosis with dental radiographs and age.

OBJECTIVES: In this study age and the trabecular pattern present on dental radiographs were used to predict the presence of osteoporosis. The objective was to evaluate the contribution of the trabecular pattern to the prediction. METHODS: In this project, 671 women between 45 and 71 years of age were recruited. Medical history was obtained and dental radiographs were made. Bone mineral density (BMD) was measured at three sites to assess the presence of osteoporosis according to the World Health Organization criteria. The radiographs were subjected to image analysis methods yielding measurements of the trabecular pattern. Thereafter, discriminant analysis was used to predict the presence of osteoporosis by means of the trabecular pattern and age. Sensitivity and specificity of age and the trabecular pattern were compared. Also, it was checked whether the inclusion of the trabecular pattern improved the sensitivity and specificity that were obtained when only age was used as the predictor. RESULTS: The sensitivity and specificity of the trabecular pattern present on dental radiographs were almost equal to those of age. However, combining age with the trabecular pattern increased the sensitivity from 0.71 to 0.75 and the specificity from 0.72 to 0.78; the latter increase was statistically significant. CONCLUSIONS: The trabecular pattern predicts the presence of osteoporosis just as well as age does. When combining the trabecular pattern with age, the sensitivity and specificity increased. Only the latter increase was statistically significant.

[Radiodiagnostics: between looking and observing]. / Röntgendiagnostiek: tussen kijken en waarnemen.

The quality of radiodiagnostics is crucial because of its important role in general diagnostics and the subsequent treatment planning. Nowadays, digital radiology is providing many new opportunities, such as optimization of contrast and brightness of the radiographic image. Nevertheless, it is a fact that not every abnormality is discovered and recognized, in spite of the technological advancements. The perceptive abilities of the observer is in many circumstances the limiting factor. The question is how crucial an incorrect observation of the presence or absence of an abnormality on the radiograph is and what the clinician can do to minimize the chance of mistakes as much as possible. The decision to make a radiograph and the choice of imaging technique are essential. An oral health care provider can take advise with several guidelines, indicating what is currently considered good practice by the profession.

Selecting regions of interest on intraoral radiographs for the prediction of bone mineral density.

OBJECTIVES: A previous study showed that the trabecular pattern on dental radiographs correlates with femoral and spinal bone mineral density (BMD). The objective of this study was to determine if the correlation is affected by the size and location of the region of interest (ROI). METHODS: In a European research project on osteoporosis, BMD was measured at the left hip and the lumbar spine of 525 women. From all subjects, intraoral radiographs were made of the premolar region in the upper and lower jaws. Two ROIs were indicated manually on each scanned image. The smallest region involved only trabecular bone and the largest also included parts of the neighbouring teeth. The ROIs were subjected to automatic image analysis, yielding 26 measurements per ROI. Stepwise linear regression was used to predict femoral and spinal BMD. RESULTS: Inner and outer regions predicted BMD equally well. The radiographs of lower and upper jaw also predicted BMD equally well. Combining inner and outer regions did not improve the prediction of femoral and spinal BMD, but combining lower and upper jaws did. CONCLUSIONS: This study shows that it is possible to include parts of neighbouring teeth in the ROI used to assess the trabecular pattern and predict BMD. This simplifies the process of selecting the ROIs because no efforts have to be made to exclude neighbouring teeth. Combining ROIs of lower and upper jaws significantly improves the prediction of BMD.

Detection of in vitro proximal caries in storage phosphor plate radiographs scanned with different resolutions.

OBJECTIVES: To investigate the effect of the scanning resolution of storage phosphor plate (SPP) radiographs on the detection of proximal caries lesions. METHODS: 10 dentists evaluated 72 proximal surfaces of premolars with respect to caries from SPP radiographs scanned with theoretical spatial resolutions of: (1) the Digora FMX at 7.8 lp mm(-1); (2) the Digora Optime at both 7.8 lp mm(-1) and 12.5 lp mm(-1); and (3) the Dürr VistaScan at 10 lp mm(-1) and 20 lp mm(-1), respectively. The lesions were validated by histological examination. Receiver operating characteristic (ROC) analysis was employed. RESULTS: The A(z) value for the radiographs scanned with the Dürr VistaScan at 10 lp mm(-1) is significantly lower than those for the other series of radiographs (P = 0.000). CONCLUSIONS: For SPP radiographs, an increased theoretical spatial resolution per se is not related to an improved detection of proximal caries.

Spatial orientation in bone samples and Young's modulus.

Bone mass is the most important determinant of the mechanical strength of bones, and spatial structure is the second. In general, the spatial structure and mechanical properties of bones such as the breaking strength are direction dependent. The mean intercept length (MIL) and line frequency deviation (LFD) are two methods for quantifying directional aspects of the spatial structure of bone. Young's modulus is commonly used to describe the stiffness of bone, which is also a direction-dependent mechanical property. The aim of this article is to investigate the relation between MIL and LFD on one hand and Young's modulus on the other. From 11 human mandibular condyles, 44 samples were taken and scanned with high-resolution computer tomography equipment (micro-CT). For each sample the MIL and LFD were determined in 72602 directions distributed evenly in 3D space. In the same directions Young's modulus was determined by means of the stiffness tensor that had been determined for each sample by finite element analysis. To investigate the relation between the MIL and LFD on one hand and Young's modulus on the other, multiple regression was used. On average the MIL accounted for 69% of the variance in Young's modulus in the 44 samples and the LFD accounted for 72%. The average percentage of variance accounted for increased to 80% when the MIL was combined with the LFD to predict Young's modulus. Obviously MIL and LFD to some extent are complementary with respect to predicting Young's modulus. It is known that directional plots of the MIL tend to be ellipses or ellipsoids. It is speculated that ellipsoids are not always sufficient to describe Young's modulus of a bone sample and that the LFD partly compensates for this.

Preliminary images from an adaptive imaging system.

I-ImaS (Intelligent Imaging Sensors) is a European project aiming to produce real-time adaptive X-ray imaging systems using Monolithic Active Pixel Sensors (MAPS) to create images with maximum diagnostic information within given dose constraints. Initial systems concentrate on mammography and cephalography. In our system, the exposure in each image region is optimised and the beam intensity is a function of tissue thickness and attenuation, and also of local physical and statistical parameters in the image. Using a linear array of detectors, the system will perform on-line analysis of the image during the scan, followed by optimisation of the X-ray intensity to obtain the maximum diagnostic information from the region of interest while minimising exposure of diagnostically less important regions. This paper presents preliminary images obtained with a small area CMOS detector developed for this application. Wedge systems were used to modulate the beam intensity during breast and dental imaging using suitable X-ray spectra. The sensitive imaging area of the sensor is 512 x 32 pixels 32 x 32 microm(2) in size. The sensors' X-ray sensitivity was increased by coupling to a structured CsI(Tl) scintillator. In order to develop the I-ImaS prototype, the on-line data analysis and data acquisition control are based on custom-developed electronics using multiple FPGAs. Images of both breast tissues and jaw samples were acquired and different exposure optimisation algorithms applied. Results are very promising since the average dose has been reduced to around 60% of the dose delivered by conventional imaging systems without decrease in the visibility of details.

Osteoporosis and the general dental practitioner: reliability of some digital dental radiological measures.

OBJECTIVES: Dental radiographs are relatively inexpensive and are regularly made of a large fraction of the adult population; therefore, they represent an enormous potential as a screening tool for osteoporosis. Monitoring the population by means of dual X-ray absorptiometry (DXA), which is currently the most accepted method for diagnosing osteoporosis, involves enormous costs and facilities. In previous studies, it was shown that the radiographic trabecular pattern shows correlations with the bone mineral density (BMD) as measured by DXA. The objective of this study was to assess the reproducibility of the quantitative analysis of the trabecular pattern on dental radiographs. METHODS: Six regions of interest were selected manually on three digital radiographic images of 20 women. This process was performed 10 times resulting in 1200 image samples. For each image sample 26 parameters were measured. The reliability of the parameters was evaluated by means of Cronbach's alpha. RESULTS: Of the values of Cronbach's alpha 83% is at least 0.9 and 99% is at least 0.8. CONCLUSIONS: The measurements of the parameters used in this study are very reproducible. Therefore, the manual selection of the regions of interest does not introduce large amounts of noise. The imaging parameters potentially offer an accurate tool for the prediction of BMD values.

Detection of proximal caries with high-resolution and standard resolution digital radiographic systems.

AIMS: The aim of this study was to: (1) compare the diagnostic accuracy of the high-resolution and standard resolution settings of four digital imaging systems for caries diagnosis and (2) compare the effect on the diagnostic accuracy of reducing the high-resolution image sizes to the standard resolution dimensions, and vice versa. MATERIALS AND METHODS: 90 extracted human premolars were mounted in groups of 5 in plaster blocks, containing 4 test teeth and 1 non-test tooth. Two blocks at a time were placed in a jig to simulate a bitewing radiograph. Radiographs were taken using four digital systems (Planmeca Dixi 2; Gendex Visualix HDI; Dürr Vistascan; Digora Optime), each at two resolution settings. Next, the teeth were sectioned and a total of 65 surfaces were incorporated in the study. Additionally, the bicubic interpolation method was applied to reduce the high-resolution original images and to enlarge the standard resolution images. The original, reduced and enlarged images were randomly shown to five observers in two random sessions. The observers were asked to assess caries depth on a 4-point scale. The observers' scores were compared with the results from a histological examination. Data were analysed using the statistical theory for multivariate discrete data. Cohen's kappa was used to determine the agreement with the gold standard. RESULTS: None of the comparisons between the spatial resolution settings, or the comparisons between increased or reduced image size and the original image sizes, showed significant differences in the probability of caries detection (chi2=26.59, df=26, P approximately 0.50). The four digital systems used in this study differ significantly in the probability of caries detection (chi2=41.55, df=24, P<0.02). Compared with the gold standard, the Gendex Visualix HDI CCD sensor has the highest measure of agreement (kappa=0.31). CONCLUSION: Caries diagnosis does not improve when using high-resolution settings compared with the standard settings. The use of bicubic convolution interpolation for zooming has no detectable effect on caries diagnosis and therefore is recommended to use when enlarging or reducing radiographs. The probability of caries detection, however, was different for the sensor systems of the different manufacturers.

Detection of proximal caries in vitro using standard and task-specific enhanced images from a storage phosphor plate system.

Eight dentists evaluated 72 proximal surfaces of premolars with respect to all caries lesions and to lesions into dentine in digital images from a storage phosphor plate system. The images were processed in four different ways: (1) the default algorithm of the standard imaging system (DF); (2) an algorithm correcting for attenuation and visual response (AV), and two proprietary caries-specific enhancement algorithms (3) K1, and (4) K2, respectively. The lesions were validated by histological examination. There were no significant differences in the areas under the receiver operating characteristic curves between differently processed radiographs for the categories of all caries lesions and caries into dentine.