Utility of a diffusion kurtosis model in the differential diagnosis of orofacial tumours.

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<0.0001). The Kapp had a strongly negative correlation with the Dapp (ρ=-0.749) and ADC (ρ=-0.938). A strongly positive correlation existed between the Dapp and ADC (ρ=0.906). All parameters differed significantly between benign tumours and malignant tumours (p<0.05). In differentiating benign tumours from the malignant tumours, the AUC of Dapp (0.871) was larger than that of ADC (0.805); however, a significant difference was not found (p=0.102). 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.

Size and orientation of masticatory muscles in patients with mandibular laterognathism.

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.

Correlation between diagnostic accuracy and perceptibility.

OBJECTIVES: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

In vivo cross-sectional area of human jaw muscles varies with section location and jaw position.

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.

Volume changes in human masticatory muscles between jaw closing and opening.

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.

Integration of a picture archiving and communication system with videocapture and computed radiography in a dental hospital.

A method for the integration of a picture archiving and communication system (PACS) at Kyushu University Dental Hospital with radiological information (RIS) and hospital information (HIS) systems is described. CT, US and DSA from different manufacturers were integrated by videocapture and then subsequently integrated with computed radiography (CR) by means of DICOM. The approximate amount of data stored each month on optical discs is 2 GB. The system does not incorporate intra-oral radiography.

Possibility of sialographic sonography: a Doppler phantom study.

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.

Sonographic analysis of rat submandibular glands in experimentally-induced sialadenitis.

OBJECTIVES: To correlate the sonographic features of experimentally-induced obstructive sialadenitis in rat submandibular glands with the histopathological changes. MATERIALS AND METHODS: Changes in sonograms of ligated and non-ligated rat submandibular glands were compared with the wet weight and histopathology. Sonograms were obtained at 1, 2, 3, 4, 5, 7 and 21 days after duct ligation at 13 and 14 MHz for B-mode and for power Doppler mode respectively. Changes in gland size, echo intensity, distribution of internal echoes and vascularity were evaluated both qualitatively and quantitatively. RESULTS: Changes in size of the ligated glands were very similar to changes in wet weight. The ligated glands showed lower echo intensity than the non-ligated glands. The ligated glands showed higher echo intensity in the central portion at 4-7 days after duct ligation which resulted in heterogeneity of the glands. Vascularity of the ligated glands increased in the acute phase, and then decreased to the level of the non-ligated glands. CONCLUSIONS: The three phases in the changes in ligated glands identifiable histopathologically can be differentiated by B-mode sonography. Power Doppler can differentiate the acute phase. Sonography therefore appears useful for the diagnosis of the degree of gland damage.

Magnetic resonance imaging of experimentally-induced sialadenitis in rat submandibular glands.

OBJECTIVES: To correlate the features of magnetic resonance (MR) images of experimentally induced obstructive sialadenitis in rat submandibular glands with the histopathological changes. METHODS: Changes in MR images of ligated and non-ligated rat submandibular glands were compared with the histopathological changes and wet weight ratios. Spin echo T1 weighted images (SE T1WI), fast spin echo T2 weighted images (FSE T2WI), and gradient echo T2 weighted images (GE T2WI) were obtained at 1, 2, 3, 4, 5, 7 and 21 days after duct ligation with a 0.3 T MR imaging system. RESULTS: There was a significant difference (P<0.05) between the signal intensity ratios of both ligated and non-ligated glands on each day, except at 21 days on GE T2WI. On SE T1WI, small interval changes of signal intensity ratios were observed on both glands, whereas there were large interval changes at 1 - 2 days, 4 - 7 days and 21 days after duct ligation with FSE T2WI. These three periods correlated highly with three phases of histopathological changes, swelling of acinar cells at 1 - 2 days, atrophy of acinar cells and increase of duct-like structures at 3 - 7 days, and proliferation of connective tissue at 21 days, and the changes in wet weight ratios. A similar tendency was observed on GE T2WI to FSE T2WI. CONCLUSIONS: As FSE T2WI showed large changes in signal intensity that correlated highly with histopathological three phases, it is recommended as the MR sequence of choice for diagnosing the degree of damage in obstructive sialadenitis.

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

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 step-wedge 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.

Assessment of image quality in dental radiography, part 2: optimum exposure conditions for detection of small mass changes in 6 intraoral radiography systems.

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.

Two-dimensional gray-scale clustering for texture analysis.

OBJECTIVES: To develop a new quantitative method for the visual discrimination of image texture. METHODS: 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. RESULTS: 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. CONCLUSION: Quantitative two-dimensional gray-scale clustering analysis appears to be a useful means of texture analysis.

Ultrasonographic texture characterization of salivary and neck masses using two-dimensional gray-scale clustering.

OBJECTIVES: To evaluate the clinical usefulness of texture analysis in ultrasonography (US) of head and neck masses. METHODS: Sixty-one cases with salivary or neck masses were examined by US with a linear 7.5MHz array. Images were digitized and quantitatively evaluated by two-dimensional gray-scale clustering using two texture indices, M and SD, as measures of coarseness and homogeneity respectively. RESULTS: Coarseness of Warthin's tumors was significantly higher than that of the other salivary tumors. Malignant lymphomas had finer texture values than other lymph node lesions. CONCLUSIONS: Quantitative texture analysis appears to be a useful complement in diagnostic US.