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Objectives: To compare the gamma distribution (GD), intravoxel incoherent motion (IVIM), and monoexponential (ME) models in terms of their goodness-of-fit, correlations among the parameters, and the effectiveness in the differential diagnosis of various orofacial lesions. Methods: A total of 85 patients underwent turbo spin-echo diffusion-weighted imaging with six b-values. The goodness-of-fit of three models was assessed using Akaike Information Criterion. We analysed the correlations and compared the effectiveness in the differential diagnosis among the parameters of GD model (κ, shape parameter; θ, scale parameter; fractions of diffusion: ƒ1, cellular component; ƒ2, extracellular diffusion; ƒ3, perfusion component), IVIM model (D, true diffusion coefficient; D*, pseudodiffusion coefficient; f, perfusion fraction), and ME model (apparent diffusion coefficient, ADC). Results: The GD and IVIM models showed a better goodness-of-fit than the ME model (p < 0.05). ƒ1 had strong negative correlations with D and ADC (ρ = –0.901 and –0.937, respectively), while ƒ3 had a moderate positive correlation with f (ρ = 0.661). Malignant entity presented significantly higher ƒ1 and lower D and ADC than benign entity (p < 0.0001). Malignant lymphoma had significantly higher ƒ1 in comparison to squamous cell carcinoma (p = 0.0007) and granulation (p = 0.0075). The trend in ƒ1 was opposite to the trend in D. Malignant lymphoma had significant lower ƒ3 than squamous cell carcinoma (p = 0.005) or granulation (p = 0.0075). Conclusions: The strong correlations were found between the GD- and IVIM-derived parameters. Furthermore, the GD model’s parameters were useful for characterising the pathological structure in orofacial lesions.

This study conducted a receiver operating characteristic (ROC) analysis by applying improved cluster signal-to-noise (CSN) analysis to digital intraoral radiographs and develop an observer-free method of analyzing image quality related to the observer performance in the detection task.Two aluminum step phantoms with a thickness interval of 1.0 mm were used for this study. One phantom had holes of increasing depth (from 0.05 to 0.35 mm) and the other had no holes. Phantom images were obtained under various exposure dose and image capture modes using a dental X-ray unit, a photostimulable phosphor imaging plate, and scanner system. These phantom images were analyzed using the FindFoci plugin in ImageJ software. Subsequently, true positive rates (TPRs) and false positive rates (FPRs) were calculated by analyzing phantom images with and without holes. We constructed ROC curves by plotting the TPRs against the FPRs and calculated the area under the ROC curve (AUC). Using the same phantom images with holes, eight observers assessed the number of detectable holes. Correlations between observer detection performance and AUC values were evaluated.AUC values increased as the exposure dose increased and showed different tendencies depending on the image capture mode. The AUC values showed a high correlation with observer detection performance (r = 0.76).AUC values obtained from CSN analysis reflect image quality and replace the observer detection performance test of image quality.

Objective: To determine whether the γ distribution (GD) model of diffusion MRI is useful in the evaluation of the isocitrate dehydrogenase (IDH) mutation status of glioblastomas. Methods: 12 patients with IDH-mutant glioblastomas and 54 patients with IDH-wildtype glioblastomas were imaged with diffusion-weighted imaging using 13 b-values from 0 to 1000 s/mm2. The shape parameter (κ) and scale parameter (θ) were obtained with the GD model. Fractions of three different areas under the probability density function curve (f1, f2, f3) were defined as follows: f1, diffusion coefficient (D) < 1.0×10−3 mm2/s; f2, D > 1.0×10−3 and −3 mm2/s; f3, D > 3.0 × 10−3 mm2/s. The GD model-derived parameters measured in gadolinium-enhancing lesions were compared between the IDH-mutant and IDH-wildtype groups. Receiver operating curve analyses were performed to assess the parameters' diagnostic performances. Results: The IDH-mutant group’s f1 (0.474 ± 0.143) was significantly larger than the IDH-wildtype group’s (0.347 ± 0.122, p = 0.0024). The IDH-mutant group’s f2 (0.417 ± 0.131) was significantly smaller than the IDH-wildtype group’s (0.504 ± 0.126, p = 0.036). The IDH-mutant group’s f3 (0.109 ± 0.060) was significantly smaller than the IDH-wildtype group’s (0.149 ± 0.063, p = 0.0466). The f1 showed the best diagnostic performance among the GD model-derived parameters with the area under the curve value of 0.753. Conclusion: The GD model could well describe the pathological features of IDH-mutant and IDH-wildtype glioblastomas, and was useful in the differentiation of these tumors. Advances in knowledge: Diffusion MRI based on the γ distribution model could well describe the pathological features of IDH-mutant and IDH-wildtype glioblastomas, and its use enabled the significant differentiation of these tumors. The γ distribution model may contribute to the non-invasive identification of the IDH mutation status based on histological viewpoint.

AIM To compare the goodness of fit and correlations between diffusion kurtosis imaging (DKI) and a mono-exponential (ME) model, to compare the corrected apparent diffusion coefficient (Dapp) and apparent kurtosis (Kapp) of the DKI model, and the apparent diffusion coefficient (ADC) of the ME model among the various orofacial lesions, and to evaluate the diagnostic performances between the two models. MATERIALS AND METHODS A total of 100 orofacial lesions underwent echo-planar diffusion magnetic resonance imaging (MRI) with four b-values. The goodness of fit was evaluated using Akaike information criterion. The correlations of the diffusion-derived parameters were evaluated. The diagnostic performance was analysed by receiver operating characteristics (ROC). RESULTS The DKI model showed a significantly better goodness of fit than the ME model (p CONCLUSION The DKI model had better goodness of fit than the ME model. Furthermore, the Dapp and Kapp were also characteristic for each pathological category; however, the DKI model did not yield a significantly higher diagnostic performance than the ME model, which might be related to the high correlation among the diffusion-derived parameters and wide variation among categories.

Objectives: This study evaluated the correlation among the diffusion-derived parameters obtained by monoexponential (ME), intravoxel incoherent motion (IVIM) and γ distribution (GD) models and compared these parameters among representative orofacial tumours. Methods: Ninety-two patients who underwent 1.5 T MRI including diffusion-weighted imaging were included. The shape parameter (κ), scale parameter (θ), ratio of the intracellular diffusion (ƒ1), extracellular diffusion (ƒ2) and perfusion (ƒ3) were obtained by the GD model; the true diffusion coefficient (D) and perfusion fraction (f) were obtained by the IVIM model; and the apparent diffusion coefficient (ADC) was obtained by the ME model. Results: ƒ1 had a strongly negative correlation with the ADC (ρ = −0.993) and D (ρ = −0.926). A strong positive correlation between f and ƒ3 (ρ = 0.709) was found. Malignant lymphoma (ML) had the highest ƒ1, followed by squamous cell carcinoma (SCC), malignant salivary gland tumours, pleomorphic adenoma (Pleo) and angioma. Both the IVIM and GD models suggested the highest perfusion in angioma and the lowest perfusion in ML. The GD model demonstrated a high extracellular component in Pleo and revealed that the T4a+T4b SCC group had a lower ƒ2 than the T2+T3 SCC group, and poor to moderately differentiated SCC had a higher ƒ1 than highly differentiated SCC. Conclusions: Given the correlation among the diffusion-derived parameters, the GD model might be a good alternative to the IVIM model. Furthermore, the GD model’s parameters were useful for characterizing the pathological structure.

The preoperative imaging-based differentiation of primary central nervous system lymphomas (PCNSLs) and glioblastomas (GBs) is of high importance since the therapeutic strategies differ substantially between these tumors. In this study, we investigate whether the gamma distribution (GD) model is useful in this differentiation of PNCSLs and GBs. Twenty-seven patients with PCNSLs and 57 patients with GBs were imaged with diffusion-weighted imaging using 13 b-values ranging from 0 to 1000 sec/mm2. The shape parameter (κ) and scale parameter (θ) were obtained with the GD model. Fractions of three different areas under the probability density function curve (f1, f2, f3) were defined as follows: f1, diffusion coefficient (D) −3 mm2/sec; f2, D >1.0×10−3 and −3 mm2/sec; f3, D >3.0 × 10−3 mm2/sec. The GD model-derived parameters were compared between PCNSLs and GBs. Receiver operating characteristic (ROC) curve analyses were performed to assess diagnostic performance. The correlations with intravoxel incoherent motion (IVIM)-derived parameters were evaluated. The PCNSL group's κ (2.26 ± 1.00) was significantly smaller than the GB group's (3.62 ± 2.01, p = 0.0004). The PCNSL group's f1 (0.542 ± 0.107) was significantly larger than the GB group's (0.348 ± 0.132, p

The purpose of this study was to clarify the effects of exposure parameters and image-processing methods when using CBCT to detect clear and unclear mandibular canals (MCs).24 dry half mandibles were divided into 2 groups with clear and unclear MCs based on a previous CBCT study. Mandibles were scanned using a CBCT system with varying exposure parameters (tube voltages 60 kV, 70 kV and 90 kV; and tube currents 2 mA, 5 mA, 10 mA and 15 mA) to obtain a total of 144 scans. The images were processed with different slice thicknesses using ImageJ software (National Institutes of Health, Bethesda, MD). Five radiologists evaluated the cross-sectional images of the first molar region to detect the MCs. The diagnostic accuracy of varying exposure parameters and image-processing conditions was compared with the area under the curve (Az) in receiver-operating characteristic analysis.The Az values for clear MCs were higher than those for unclear MCs (p 0.0001). With increasing exposure voltages and currents, Az values increased, but no significant differences were found with high voltages and currents in clear MCs (p = 1.0000 and p = 0.9340). The Az values of serial images were higher than those of overlaid images (p 0.0001), and those for thicker slices were higher than those for thinner slices (p 0.0001).Our findings indicate that detection of unclear MCs requires either higher exposure parameters or processing of the images with thicker slices. To detect clear MCs, lower exposure parameters can be used.

The primary taste cortex is located in the insula. However, exactly where in the insula the human primary taste cortex is located remains a controversial issue. Human neuroimaging studies have shown prominent variation concerning the location of taste-responsive activation within the insula. A standard protocol for gustatory testing in neuroimaging studies has not been developed, which might underlie such variations. In order to localize the primary taste cortex in an fMRI experiment, we used a taste delivery system to suppress non-taste stimuli and psychological effects. Then, we compared brain response to taste solution during a passive tasting task condition and a taste quality identification task condition to verify whether this cognitive task affected the location of taste-responsive activation within the insula. To examine which part of insula is the primary taste area, we performed dynamic causal modeling (DCM) to verify the neural network of the taste coding-related region and random-effects Bayesian model selection (BMS) at the family level to reveal the optimal input region. Passive tasting resulted in activation of the right middle insula (MI), and the most favorable model selected by DCM analysis showed that taste effect directly influenced the MI. Additionally, BMS results at the family level suggested that the taste inputs entered into the MI. Taken together, our results suggest that the human primary taste cortex is located in the MI.

There are no credible data to support the notion that individual taste qualities have dedicated pathways leading from the tongue to the end of the pathway in the brain. Moreover, the insular cortex is activated not only by taste but also by non-taste information from oral stimuli. These responses are invariably excitatory, and it is difficult to determine whether they are sensory, motor, or proprioceptive in origin. Furthermore, umami is a more unfamiliar and complex taste than other basic tastes. Considering these issues, it may be effective to minimize somatosensory stimuli, oral movement, and psychological effects in a neuroimaging study to elicit cerebral activity by pure umami on the human tongue. For this purpose, we developed an original taste delivery system for functional magnetic resonance imaging (fMRI) studies for umami. Then, we compared the results produced by two authorized models, namely, the block design model and event-related design model, to decide the appropriate model for detecting activation by umami. Activation by the umami taste was well localized in the insular cortex using our new system and block design model analysis. The peaks of the activated areas in the middle insular cortex by umami were very close to another prototypical taste quality (salty). Although we have to carefully interpret the perceiving intensities and brain activations by taste from different sessions, this study design might be effective for detecting the accession area in the cortex of pure umami taste on the tongue.

OBJECTIVES: To compare the results of a new quantitative image quality evaluation method that requires no observers with the results of receiver operating characteristic (ROC) analysis in detecting the mandibular canal (MC) in cone beam CT (CBCT) images. METHODS: A Teflon (polytetrafluoroethylene) plate phantom with holes of different depths was scanned with two CBCT systems. One CBCT system was equipped with an image intensifier (Experiment 1), and the other was equipped with a flat panel detector (Experiment 2). Holes that were above the threshold gray value (ΔG), calculated using just-noticeable difference (JND), were extracted. The number of extracted holes was used as the index of the image quality, and was compared with the Az values calculated by ROC analysis to detect the MC. RESULTS: The number of extracted holes reflected the influence of different scanning conditions, and showed a strong correlation with the Az values calculated by ROC analysis. Indices of the number of extracted holes corresponding to high Az values for detecting the MC were obtained in both experiments. CONCLUSIONS: Our image quality evaluation method applying JND to images of a standardized phantom is a quantitative method that could be useful for evaluating the detectability of the MC in CBCT images.

Introduction Traditional cephalometric radiographs can analyze facial soft-tissues 2 dimensionally. Because they cannot provide information about the nose, lips, cheeks, and mouth, another method is needed to analyze these soft tissues. We introduce a new method for analyzing the 3-dimensional (3D) shape and size of facial soft-tissue morphology. Methods A 3D average face model was constructed based on 3D computed tomography images of Japanese male and female adult volunteers who had well-balanced faces and normal occlusions. To test the feasibility of evaluating the quantitative effects of surgery, preoperative and postoperative 3D computed tomography images of facial soft tissues of 1 man and 1 woman were superimposed on the average faces. Results This quantitative assessment provided a comprehensive evaluation of the characteristics that separate size and shape. It was possible to view the superimposed images from any desired angle on a personal computer. Conclusions This method provides easy-to-understand information for patients and appears to be useful for clinical diagnosis and pretreatment and posttreatment soft-tissue morphologic evaluations of patients with jaw deformities.

We propose a method for evaluating the reliability of a coordinate system based on maxillofacial skeletal landmarks and use it to assess two coordinate systems. Scatter plots and 95% confidence ellipses of an objective landmark were defined as an index for demonstrating the stability of the coordinate system. A head phantom was positioned horizontally in reference to the Frankfurt horizontal and occlusal planes and subsequently scanned once in each position using cone-beam computed tomography. On the three-dimensional images created with a volume-rendering procedure, six dentists twice set two different coordinate systems: coordinate system 1 was defined by the nasion, sella, and basion, and coordinate system 2 was based on the left orbitale, bilateral porions, and basion. The menton was assigned as an objective landmark. The scatter plot and 95% ellipse of the menton indicated the high-level reliability of coordinate system 2. The patterns with the two coordinate systems were similar between data obtained in different head positions. The method presented here may be effective for evaluating the reliability (reproducibility) of coordinate systems based on skeletal landmarks.

A sequence for T 1 relaxation time measurements that allows a high-resolution image to be obtained within a short acquisition time is described. Its application to the orofacial region is investigated. The sequence is based on the Look–Locker (LL) method and employs a magnetization-preparation pulse prior to data acquisition, with either a turbo-field echo (TFE) or turbo-field echo echo-planar imaging (TFEPI) sequence. We applied the multiple LL sequence by synchronizing the data acquisition with the virtual electrocardiogram. T 1 results from the LL sequence were compared with those from the inversion recovery (IR) sequence. In an in vitro study, we evaluated the T 1 maps of contrast medium at different concentrations. In an in vivo study, we evaluated the T 1 maps in seven volunteers. In the in vitro study, the correlation between the T 1 values obtained from the LL sequence and those from the IR sequence was high, with an R 2 of more than 0.99. For T 1 values between 200 and 1,500 ms, the difference between the two methods was less than 7%. In the in vivo study, a high correlation was observed between the T 1 values from the IR sequence and those from the LL sequence. The scan duration for the LL sequence was less than 3 min. Our method, based on the LL sequence, was found to be clinically useful for producing a T 1 map.

fMRI indicated that the primary taste cortex is activated not only by taste but also by non-taste information from oral stimuli. Head movements caused by swallowing are very critical problem in fMRI and inherent difficulties to modulate taste stimuli in the mouth exist to elucidate functional segregation of human brain. We developed a novel automated taste stimulus delivery system for fMRI studies to segregate the pure taste area in the primary taste cortex in humans. As a novel intra-oral device, an elliptic cylinder was attached to an individual mouthpiece and then subject placed the tongue tip in it. Using a computer-controlled extra-oral device, the solutions ran through the intra-oral device in constant conditions. Three adult volunteers participated in the experimental session, alternately consisting of 30 pairs of taste stimuli (0.5 mol/l sucrose solution) and control (water) blocks. The typical findings of the three subjects revealed activation only in the primary taste cortex (P

Objective The purpose of this study was to investigate in vitro the accuracy of three-dimensional (3D) magnetic resonance imaging (MRI) to measure the mandible. Study design The optimal MRI sequence for 3D mandible from the data of 2 volunteers was determined to be 3D vibe. MRI and computed tomography (CT) scans of tube, mandible, and hemimandible phantoms were obtained. MRI with 3D vibe and standard parameters used in clinical practice for 3D reconstructions of jawbones on CT were used. Pearson’s correlation coefficient, standard deviation (SD), and accuracy in measurement on reconstructed 3D MRI and CT were compared to direct osteometric measurement of the phantoms. Results The correlation coefficient between MRI and direct osteometry was high, with r = 0.85 to 0.99 (P < .001). The difference ranged from –1.5 to 0.7 mm (–8.9%-11.1%) on smaller distances, which is important for orthognathic surgery. The accuracy of MRI was similar to that of CT. Conclusion 3D vibe MRI provided adequate dimensional accuracy and image quality during in vitro examination of the mandible.

Size measurements of jaw muscles reflect their force capabilities and correlate with facial morphology. Using MRI, we examined the size and orientation of jaw muscles in patients with mandibular laterognathism in comparison with a control group. We hypothesized that the muscles of the deviated side would be smaller than those of the non-deviated side, and that the muscles of both sides would be smaller than in controls. In patients, a comparison of deviated and non-deviated sides showed, in orientation, differences for masseter and medial pterygoid muscles, but, in size, differences only for the masseter muscle. Nevertheless, muscle sizes in patients were much smaller than in controls. Lateral displacement of the mandible can explain the orientation differences, but not the smaller muscle size, in patients. It is possible that the laterodeviation initiates an adaptive process in the entire jaw system, resulting in extensive atrophy of the jaw muscles.

Muscle cross-sectional area (CSA) is used as a measure for maximum muscle force. This CSA is commonly determined at one location within the muscle and for one jaw position. The purpose of this study was to establish a method to standardize the analysis of the CSA of the masticatory muscles in vivo, and to compare the CSAs along their entire length for two different jaw positions (opened and closed). The CSAs in the planes perpendicular to the long axes of the masseter, medial, and lateral pterygoid muscles were measured in ten normal young adult subjects by magnetic resonance imaging. Our results showed large differences among the muscles and a non-uniform change in CSA after jaw-opening. The method enables the CSA measurement to be standardized in vivo, and allows for a correct comparison of CSAs in different skull morphologies.

Objective To evaluate quantitatively the long-term changes in alveolar bone around toothimplant connections using a digital subtraction technique.

Most jaw muscles are complex, multipennate with multiple components. The morphologic heterogeneity of masticatory muscles reflects their functions. We hypothesized that the volume of masticatory muscles changes between jaw closing and opening, and that there is a difference in the volume change among the muscles. Magnetic resonance images of the entire head were obtained in ten normal young adult subjects before and after maximum jaw opening. The volume changes of the masseter, medial, and lateral pterygoid muscles were measured. Only slight changes were seen in the masseter and medial pterygoid muscles. The lateral pterygoid muscle, however, significantly decreased its volume during jaw opening. The results provide normative values of muscle volume in living subjects, and suggest that the volume changes differ among jaw muscles.

A medical application subgroup of The SPring-8 Users Society drew up a plan of a building design for a Biomedical Imaging Center (BMIC) in cooperation with RIKEN. 1 From our experiences of more than 15 years in this field we have found that various energies of monochromatic X-rays, strong photon densities, as well as large exposure fields are necessary, and will thus implement them in the BMIC. We therefore proposed the installation of an undulator and a wiggler. The BMIC is located 200 m from the light source to obtain a 20 cm-wide exposure field supposing that the wiggler device is installed at the light source. White X-rays from the undulator irradiate a target element generating fluorescent, semi-monochromatic, and widely spread X-rays. Monochromatic X-rays, K α , may be specifically extracted by cutting off the K β component. A monochromatic undulator beamline is now being constructed. The last light source should be the wiggler to cover a wide range of medical applications.

Objectives. The purpose of this study was to develop a new diagnostic method that has the merits of both sialography and sonography. Study design. Saline solution and various contrast media (Urografin 76%; 100%, 90%, and 67% Lipiodol Ultra-Fluide; 5% and 1% barium sulfate; and Levovist) were injected into thin tubes at a rate of approximately 0.001 to 0.1 mL/s. The relationship between the Doppler signal intensity and the kind, concentration, and velocity of the fluid was analyzed. Results. Levovist, 90% and 67% Lipiodol Ultra-Fluide, and the barium sulfate solutions produced Doppler signals. The mixture of Lipiodol Ultra-Fluide and saline solution produced high signals at any concentration, in contrast with the barium sulfate solutions. Signals could be observed at any speed, from the speed of normal sialography down to 0.001 mL/s, and there was a proportional relationship between signal intensity and velocity for all fluids producing signals. Conclusion. The fact that we could obtain high signals with several fluids indicates potential clinical diagnostic usefulness of sialographic sonography. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2001;91:719-27)

Recently, computer imaging technology has developed very high-quality image and fast processing time. X-rays have been used for many purposes such as medical diagnosis and analyzing the structure of industrial materials. However, as X-rays are hazardous to the human body, it is desirable to reduce its exposed dose to a minimum. For this purpose, it is necessary to use a semiconductor radiation detector with a high efficiency for X-rays. We have developed photon-counting CdTe array detector system for medical and industrial use. The bone densitometer for Dual Energy X-ray Absorptometry (DEXA) has been developed to make diagnosis of osteoporosis, and it is developed to analyze a material element for industrial use. Recently, we have developed a monochromatic X-ray CT using a 256 ch CdTe array detector. We found that the array detector systems are very useful for medical and industrial applications.

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)

Objective. The purpose of this study was to compare 2 film systems and several digital intraoral systems with regard to visual image quality through use of a test phantom developed for this purpose. Study Design. The detectors used for digital imaging were as follows: Computed Dental Radiography (CDR), Digora, Dixel, and Sens-A-Ray without scintillator layer. Two types of digital images were prepared for the observer performance test: one with original gray scales and another with contrast enhancement. Images with and without enhancement from the 4 systems were displayed to 7 observers. The change in the average number of perceptible holes was plotted against exposure, and modified perceptibility curves were created and compared with curves for the film systems. The exposure level at which the maximum number of holes was perceived was defined to be optimum. The optimum exposure levels were determined for each digital system and compared with that of the film systems. At the optimum exposure, the average maximum numbers of perceptible holes in each digital system with and without contrast enhancement were compared with the maximum numbers for the film systems. The minimum exposure levels were determined to be those at which the number of perceptible holes exceeded the number for film, and the possibility of exposure reduction was evaluated. Results. All digital systems except the Digora system showed lower optimum exposures than E-speed film. In all digital images without enhancement, however, the maximum number of perceptible holes was significantly lower than that for the film systems at that exposure. With contrast enhancement, all digital systems except the Sens-A-Ray system showed visibility superior to that of the film systems. With the CDR, Digora, and Dixel systems, exposures could be further reduced by a considerable amount, with greater retention of information than was associated with film. Conclusions. Our results strongly suggest that digital systems, if properly used, can exceed film systems in the detection of small mass changes. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1999;87:123-9)

To develop a new quantitative method for the visual discrimination of image texture.Two kinds of image phantoms were prepared, one for evaluating the effects of change in size and gray values of individual pixels (primitives) on perceived coarseness and the other for evaluating changes in groups of pixels (clusters) on perceived heterogeneity. The phantom images were displayed on a CRT and presented to 11 observers who assessed heterogeneity and coarseness on a 10-point scale between -5 and +5. On the basis of the observers' results, a new texture analysis method termed two-dimensional gray-scale clustering analysis was developed and applied to measure quantitatively the texture of the phantoms. The results obtained were then compared with those of the visual evaluation.The size of the primitives and the clusters greatly affected the visual evaluation of heterogeneity and coarseness. Changes in the gray value had only a slight effect. The intra-observer variation for heterogeneity was significantly larger than that for coarseness. Two-dimensional gray-scale clustering analysis could differentiate heterogeneity from coarseness. A high correlation was obtained between the visual evaluation and the quantitative data.Quantitative two-dimensional gray-scale clustering analysis appears to be a useful means of texture analysis.

It remains unclear how the cerebral cortex of humans perceives taste temporally, and whether or not such objective data about the brain show a correlation with the current widely used conventional methods of taste-intensity sensory evaluation. The aim of this study was to investigate the difference in the time-intensity profile between salty and sweet tastes in the human brain. The time-intensity profiles of functional MRI (fMRI) data of the human taste cortex were analyzed using finite impulse response analysis for a direct interpretation in terms of the peristimulus time signal. Also, time-intensity sensory evaluations for tastes were performed under the same condition as fMRI to confirm the reliability of the temporal profile in the fMRI data. The time-intensity profile for the brain activations due to a salty taste changed more rapidly than those due to a sweet taste in the human brain cortex and was also similar to the time-intensity sensory evaluation, confirming the reliability of the temporal profile of the fMRI data. In conclusion, the time-intensity profile using finite impulse response analysis for fMRI data showed that there was a temporal difference in the neural responses between salty and sweet tastes over a given period of time. This indicates that there might be taste-specific temporal profiles of activations in the human brain.

To assess the three-dimensional (3D) position of the temporomandibular joint (TMJ) in the cranial base structure, the 3D morphology of the TMJ, and the fossa-condyle interspaces in subjects with normal occlusion and patients with mandibular asymmetries using 3D computed tomography (CT) images. We hypothesized that the fossa-condyle interspaces and the shape or size of the TMJ would correlate with mandibular asymmetry.Twenty women with mandibular asymmetry and nine control subjects were recruited. The TMJ position, linear distances, angles, surface areas, and the fossa-condyle relationship were assessed with 3D CT images of the TMJ.The fossa surface area was larger on the contralateral side, although no significant difference was observed in the linear or angular measurements of the fossa. The condylar neck height and condylar angle on the contralateral side were larger than those on the deviated side, and the frontal neck angle on the deviated side was larger than that on the contralateral side and of the control. No significant difference was observed in the condylar area. The fossa-condyle interspaces in the posterolateral section of the TMJ were smaller on the deviated side.The condyle in the patients with mandibular asymmetry was rotated posterolaterally within the fossa on the deviated side. Patients with mandibular asymmetry showed larger fossas and longer condylar processes on the contralateral side and narrower fossa-condyle interspaces on the deviated side, especially in the posterolateral section of the TMJ.

The purpose of this study was to compare a dental cone beam computed tomography (dental CBCT) and a multi-detector row CT (MDCT) using effective doses and physical image quality. A dental mode (D-mode) and an implant mode (I-mode) were employed for calculating effective doses. Field of view (FOV) size of the MDCT was 150 mm. Three types of images were obtained using 3 different reconstruction functions: FC1 (for abdomen images), FC30 (for internal ear and bone images) and FC81 (for high resolution images). Effective doses obtained with the D-mode and with the I-mode were about 20% and 50% of those obtained with the MDCT, respectively. Resolution properties obtained with the D-mode and I-mode were superior to that of the MDCT in a high frequency range. Noise properties of the D-mode and the I-mode were better than those with FC81. It was found that the dental CBCT has better potential as compared with MDCT in both dental and implant modes.

The method of obtaining the primary x-ray spectrum by the Compton scattering correction has been practically established for relatively high x-ray tube voltages. However, for mammography, the tube voltages are less than 30 to 35 kV and there exists an intense characteristic x-ray peak at 17.5 keV from the molybdenum target. The influence of Rayleigh scattering can not be neglected in this mammography energy range. Accurate data of Rayleigh and Compton cross sections for the scatterer material are required for obtaining the primary x-ray spectrum by correcting the scattered x-ray spectrum of mammography. The purpose of this study is to investigate the Rayleigh and Compton scattering cross sections for PMMA scatterer material in the mammography energy range theoretically and experimentally. Fluorescent x-rays of 15 to 25 keV were generated by exciting four metal targets including molybdenum by synchrotron radiation. The produced fluorescent x-rays were incident on a sphere of PMMA (polymethyl methacrylate), and scattered x-rays at 90, 120, 150, and 165 degrees, respectively, were measured with a CdTe detector. The scattered fluorescent x-ray spectrum was separated into the Rayleigh and Compton scattering peaks by using a curve fitting technique with two Gaussian functions. We compared the measured cross section data to those obtained from theoretical values. In addition, we calculated the scattered fluorescent x-ray spectra using the Monte Carlo simulation and compared them to the measured spectra. As a result, the ratio of the Rayleigh to the total scattering ratio agreed to theoretical value within 10%. The shapes of the scattered spectra calculated by Monte Carlo simulation agreed fairly well with those of measured spectra.

The measurement of bone mineral content is important for diagnosis of demineralization diseases such as osteoporosis. A reliable method of obtaining bone mineral images using a digital magnification mammography system has been developed. The full-field digital phase contrast mammography (PCM) system, which has a molybdenum target of 0.1mm focal spot size, was used with 1.75 x magnification. We have performed several phantom experiments using aluminum step wedges (0.2 mm - 6.0 mm in thickness) and a bone mineral standard phantom composed of calcium carbonate and polyurethane (CaCO 3 concentration: 26.7 - 939.0 mg/cm 3 ) within a water or Lucite phantom. X-ray spectra on the exposure field are measured using a CdTe detector for evaluation of heel effect. From the equations of x-ray attenuation and the thickness of the subjects, quantitative images of both components were obtained. The quantitative images of the two components were obtained for different tube voltages of 24 kV to 39 kV. The relative accuracy was less than 2.5% for the entire aluminum thickness of 0.5 to 6.0 mm at 5 cm water thickness. Accuracy of bone mineral thickness was within 3.5% for 5cm water phantom. The magnified quantitative images of a hand phantom significantly increased the visibility of fine structures of bones. The digital magnification mammography system is useful not only for measurement of bone mineral content, but also high-resolution quantitative imaging of trabecular structure.

Introduction Traditionally, cephalograms have been used to evaluate a patient's maxillofacial skeleton and facial soft-tissue morphology. However, magnification and distortion of the cephalograms make detailed morphologic analysis difficult in patients with complex deformities. The purpose of this article was to introduce a new method for visualizing deformation and deviation of the maxillofacial skeleton and facial soft tissues. Methods Standard 3-dimensional Japanese head models were sized to match the sella-to-nasion distance obtained from 2 patients' (1 man, 1 woman) maxillofacial skeletal images. Then, the scaled standard model was superimposed on each patient's 3-dimensional computed tomography image. Results This system provided clear shape information independent of size and facilitated the visualization of shape variations in maxillofacial skeletal and facial soft-tissue morphology. Conclusions This method will be useful for 3-dimensional morphologic analysis of patients with jaw deformities.

The detection of microcalcifications is very important for early detection of breast cancer. The smallest visible size of microcalcification is said to be about 0.15 to 0.2 mm in diameter. If the microcalcification content is measured quantitatively, it may provide additional information for diagnosis. Clinical mammography x-ray equipment is not suitable for quantitative imaging as the energy spectrum is composed of characteristic radiation and bremsstrahlung, which causes a beam hardening effect.

Many researchers have attempted to clarify the complex relationships between stomatognathic function and craniofacial morphology. Most studies investigated the trajectories of incisal or condylar points and measured temporomandibular morphology projected onto 2-dimensional radiographic films. Although these methods provided valuable information, their diagnostic capabilities were limited. We introduce a new 4-dimensional (4D) analysis of stomatognathic function that combines the 3-dimensional (3D) computed tomography of the cranium and mandible, dental surface imaging with a noncontact 3D laser scanner, and mandibular movement data recorded with a 6 degrees of freedom jaw-movement analyzer. This method performs dynamic and precise simulations that can analyze and display condyle to fossa distances and occlusal contacts during mandibular function. These comprehensive relationships can be analyzed and displayed not only at intercuspal position, but also at any mandibular position during functional movements. We believe that our 4D analyzing system will be useful for diagnosing temporomandibular disorders of patients with jaw deformities and other malocclusions.

Introduction: Traditionally, lateral and frontal cephalograms are used with facial photographs to evaluate a patient's maxillofacial skeletal and facial soft-tissue morphology. However, the enlargement and distortion of 2-dimensional radiography made it difficult to accurately conceptualize the patient's anatomy. The purpose of this article was to introduce a new method for comparing 3-dimensional (3D) standard values of the maxillofacial skeletal and facial soft-tissue morphology before and after orthognathic surgery. Methods: Normative 3D standard values of the maxillofacial skeletal and facial soft-tissue morphology were calculated from normal women. The pre- and postoperative morphology of one woman who underwent orthognathic surgery was compared with the normative data. Results: This 3D analysis has clinical value to evaluate patients before and after surgical treatment. Conclusions: This quantitative assessment of 3D maxillofacial morphology can evaluate the area and degree of displacement and rotation of the facial skeleton and facial soft tissues. This method is sufficiently useful for routine clinical applications.

To correlate diagnostic accuracy for proximal caries with perceptibility of low contrast image details using regression analysis. The other purpose was to determine the attenuation range required for proximal caries diagnosis.The results of the two types of observer performance tests described above were retrieved from previous studies. Recording media included in those studies were the Compuray and the Dixel, direct digital radiographic systems, and Ektaspeed Plus film. The average numbers of perceptibility of image details from five observers were calculated for each step and for every combination of contiguous steps of the aluminium test phantom from the perceptibility test. The average diagnostic accuracy for proximal caries from the same five observers was correlated with the total number of perceptible details from the phantom using regression analysis. Finally, attenuation range required for proximal caries diagnosis was calculated from the attenuation range of the phantom where the maximum correlation coefficient was obtained.Maximum correlation (r=0.68) was obtained at the combination of five contiguous steps of the aluminium test phantom. Attenuation range required for proximal caries diagnosis corresponded to the 2 mm to 6 mm thickness of aluminium with acrylic block of 12 mm thickness.There is a correlation between perceptibility of low contrast image details and diagnostic accuracy for proximal caries. There may be a possibility to simplify observer performance tests for proximal caries diagnosis by using the standardized phantom simulating its attenuation range.

The first purpose of this study was to quantify the sonographic images of the salivary gland to differentiate the Sjogren syndrome (SS) group from the non-SS group. We included 132 patients in this study who had been referred to our department because of a suspicion of SS. A total of 91 patients fulfilled the criteria for SS, whereas the remaining 41 patients did not. We placed the regions-of-interest within the lesion. The first purpose was to evaluate which indices obtained by the texture analyses were useful for differentiating the SS group from the non-SS group. The second purpose was to evaluate the relationship between the indices and the degree of severity in the SS group. Out of the several indices evaluated, Hurst coefficients, obtained by fractal analysis, of SS group were found to be significantly lower than those of the non-SS group. Moreover, the Hurst coefficient was associated with the degree of destruction of the parotid gland as assessed by sialography. The Hurst coefficient of a globular stage and an advanced stage were both significantly lower than that of a normal pattern, whereas the Hurst coefficient of a punctate stage was almost similar to that of the normal stage. The Hurst coefficient showed a very weak correlation with the results of either the gum test or serologic tests. (E-mail: chikui@rad.dent.kyushu-u.ac.jp )

Purpose: Three-dimensional (3D) computer models of the human craniofacial structure have been constructed with computed tomography (CT). However, the high cost of CT and the radiation exposure are drawbacks to this method. Attempts to create a 3D reconstruction from lateral and frontal cephalograms have failed because of problems with magnification, distortion, and limitations of landmark identification, among others. We introduce a new method that creates a standard head model for a patient from anatomic measurement points extracted from x-ray images, facial stereo photographs, and dental casts. Material: To obtain precise 3D coordinates from cephalograms, several equations were introduced to compensate for radiographic image magnification and distortion. Results: By comparing the constructed model and 3D-CT images, this method proved to be accurate. Conclusions: It is possible to produce a 3D head model on a personal computer and to view it from any desired angle; this will provide easy-to-understand information for patients and establish a diagnostic or therapeutic method for communication with other health care providers.

The purpose of this study was to quantify the sonographic images of salivary gland tumors. The study population consisted of 21 pleomorphic adenomas, seven Warthin's tumors and 15 malignant tumors. We selected the region-of-interest within the lesion. We made a contour map and evaluated the complexity of the contour lines using the 2-D box-counting (BC) method. We also evaluated the 2-D distribution of the pixel values by the 3-D BC method and the fractional brownian movement (F BM) model. The fractal dimension by the 2-D BC method of pleomorphic adenoma was significantly larger than that of malignant tumors. The FD by the 3-D BC method of pleomorphic adenoma was significantly larger than both that of Warthin's tumors and that of malignant tumors. The Hurst index obtained by the F BM model of pleomorphic adenoma was significantly lower than that of the malignant tumor.

The aim of this study was to assess the changes in the power Doppler sonographic findings in patients with oral cancer undergoing chemotherapy and radiotherapy. We performed US examinations on 187 cervical lymph nodes (71 metastatic and 116 reactive nodes) excised from 52 patients before and after preoperative therapy. On Power Doppler images, we calculated the vascular index (VI) and evaluated the vascular pattern. We also assessed the diagnostic power using receiver operating characteristic (ROC) curve analysis. Irradiation caused an increase of the VI and better visualization of the vessels within the lymph node in the reactive nodes; however, in the metastatic nodes, the VI was not significantly different between that before and after irradiation. When the reader observed the images before irradiation, the area under an ROC curve (Az values) observed by B-mode sonography were closely similar to those obtained by B-mode plus power Doppler sonography. With both images before and after irradiation, the Az value obtained by B-mode plus power Doppler sonography was higher than that by B-mode sonography alone. After irradiation, the enhanced Doppler signals contributed to a better visualization of the vessels and a better detection of any vascular abnormalities.

A fluorescent x‐ray source for medical imaging, such as K‐edge subtraction angiography and monochromatic x‐ray CT, has been developed. Using a 6.5 GeV accumulation ring in Tsukuba, fluorescent x rays, which range from about 30 to 70 keV are generated by irradiating several target materials. Measurements have been made of output intensities and energy spectra for different target angles and extraction angles. The intensities of fluorescent x rays at a 30 mA beam current are on the order of 1–3×106 photons/mm2/s at 30 cm from the local spot where the incident beam is collimated to 1 mm2. A phantom which contains three different contrast media (iodine, barium, gadolinium) was used for the K‐edge energy subtraction, and element selective CT images were obtained.

Monochromatic X-ray CT has several advantages over conventional CT, which utilizes bremsstrahlung white X-rays from an X-ray tube. Although various types of monochromatic X-ray CT systems using synchrotron radiation have been developed using a parallel X-ray beam for imaging of small samples with a high spatial resolution, imaging of large objects such as the human body have not been developed yet. The authors have developed a fan-beam monochromatic X-ray CT system for the large objects. The CT system consists of a fluorescent X-ray source, a rotating table, a CdTe array detector and a personal computer. The fluorescent X-ray source has several advantages such as wide beam size, wide energy range and rapid energy switching and no higher order harmonics. The 256-channel CdTe array detector was used in the photon counting mode. The size of the detector element was 1.98 mm(h)/spl times/1.98 mm(w)/spl times/0.5 mm(t) and the length of total sensitive area was 512 mm. The authors made phantom experiments using fluorescent X-rays ranging from 42 to 59 keV, CT images of relatively large phantoms such as head phantoms and test phantoms commonly used for conventional CT were obtained. Measured CT numbers were compared with linear attenuation coefficients, and they showed a good linearity over a wide range of contrast media concentrations. Monochromatic X-ray CT images of a head phantom containing gadolinium contrast medium were obtained at the energies just above and below the gadolinium K-edge. A gadolinium image was also obtained by K-edge subtraction.

Though the intraoral radiography is most frequently and widely used in clinical dentistry, this method is very special comparing with other extraoral radiography for jaw bones. The radiographer must consider a lot of factors, such as, the anatomical form of maxilla or mandible unique to each patient, direction and size of the tooth, the position of the film, and the position and angle of the cone-head. It is not easy to master this technique because of these factors associated with this technique. Computer-assisted training system may be useful to learn the effects of these factors on the radiograph. The purpose of this study was to develop a computer simulation system for intraoral radiography by a projection from point focus using the three dimensional data of the head with CT scanner.

We have developed a photon-counting 256ch CdTe line detector system for a monochromatic x-ray CT system using fluorescent x-rays generated by synchrotron radiation. The size of each detector element is 1.98 mm(w) X 1.98 mm(h) X 0.5 mm(t). Each element has two discriminators (an upper and a lower discriminator) and two 16-bit counters (an upper and a lower counter). Each discriminator rejects pulses having a pulse height lower than the chosen voltage limits. All pulses in between the upper and lower voltage limits were obtained by subtracting the upper counter value from the lower counter value. By changing the voltage limits, we can obtain an incident x-ray energy spectrum. Several energy spectra for the fluorescent x-ray and standard (gamma) -ray sources were measured by using this detector. The detector showed a sufficient energy resolution, and has been found to be suitable as a detector of monochromatic x-ray CT.

We, a user group for medical applications of the SPring-8, have proposed the introduction of white X-rays from insertion devices to BMIC (BioMedical Imaging Center) for clinical uses so that enough photon fluxes to a subject is guaranteed. The photon flux, depending on various monochromatizing methods, was compared at the surface of the subject 200 m from a light source.

Monochromatic x-ray CT has several advantages over conventional CT, which utilizes bremsstrahlung white x-rays from an x-ray tube. Although various types of monochromatic x-ray CT systems using synchrotron radiation have been developed using a parallel x-ray beam for imaging of small samples with a high spatial resolution, imaging of large objects such as the human body have not been developed yet. We have developed a fan-beam monochromatic x-ray CT using fluorescent x-rays generated by irradiating metal targets by synchrotron radiation. A CdTe linear array detector of 512 mm sensitive width was used in the photon counting mode. We made phantom experiments using fluorescent x-rays ranging from 32 to 75 keV. Monochromatic x-ray CT images of a cylindrical lucite phantom filled with several contrast media have been obtained. Measured CT numbers are compared with linear attenuation coefficients, and they showed a good linearity over a wide range of contrast media concentrations.