Optimal contrast enhancement liquid for dynamic MRI of swallowing.

Several dynamic magnetic resonance imaging (MRI) techniques to observe swallowing and their parameters have been reported. Although these studies used several contrast enhancement liquids, no studies were conducted to investigate the most suitable liquids. The purpose of this study was to identify the optimal contrast enhancement liquid for dynamic MRI of swallowing. MRI was performed using a new sequence consisting of true fast imaging with steady-state precession, generalised auto-calibrating partially parallel acquisition and a keyhole imaging technique. Seven liquids were studied, including pure distilled water, distilled water with thickener at 10, 20 and 30 mg mL(-1) concentrations and oral MRI contrast medium at 1, 2 or 3 mg mL(-1) . Distilled water showed the highest signal intensity. There were statistically significant differences among the following contrast media: distilled water with thickener at 20 mg mL(-1) and the oral MRI contrast medium at 2 mg mL(-1) and 1 mg mL(-1) . It can be concluded that the optimal liquid for dynamic MRI of swallowing is a water-based substance that allows variations in viscosity.

An approach for three-dimensional visualization using high-resolution MRI of the temporomandibular joint.

OBJECTIVES: To visualize the temporomandibular joint (TMJ) and the surrounding tissues in detail utilizing high-resolution MR images for the diagnosis of soft- and hard-tissue abnormalities. Clinically routine MR slices are processed by tissue segmentation and three-dimensional (3D) reconstruction and viewed with visualization software. MATERIALS AND METHODS: A 1.5 T MRI system was used. The double-echo procedure for taking oblique sagittal images was applied to obtain both proton density-weighted (PDW) and T2 weighted (T2W) images simultaneously, with separate examinations in both open and closed mouth positions. Diagnosis of the abnormality in the placement and morphology of articular discs and the joint effusion status is usually performed using multiple MRI slices. Clinically routine continuous MR slices were processed by segmentation, reconstruction and visualization algorithms, and the mandibular condyle, fossa, articular disc and other intra-articular tissues were visualized on the 3D and two-dimensional (2D)-3D fusion images. RESULTS: In a clinical case, the anterior disc displacement without reduction, with mouth open and closed, was clearly depicted in the 3D images. Also 2D-3D superposed images with changeable tissue transparency successfully depicted the stereoscopic TMJ morphology in three dimensions. DISCUSSION AND CONCLUSION: High-resolution PDW- and T2W MR images could be processed by tissue segmentation and 3D-reconstruction procedures, and the resultant images showed the anatomical details in an easily recognizable way. By the simultaneous visualization of both bony surfaces and soft tissues, disc displacement and deformity can be recognized in a 3D context. The additional superposition of the 3D visualization with the original 2D MR slices allows for a combination with conventional diagnostics.

Two cases of schwannoma with marked cystic changes.

We report two cases of schwannoma displaying marked cystic changes; one in the temporalis muscle and one in the submandibular space. The first patient, a 44-year-old male, presented after complaining of a swelling rapidly increasing in size in the left temporal region. Computed tomography (CT) indicated a low-density area surrounded by soft tissue. Magnetic resonance imaging (MRI) revealed signal hypointensity on T1 weighted imaging and strong signal hyperintensity on T2 weighted imaging. The extirpated tumour specimen measured 58 mm x 58 mm x 30 mm. Histopathological examination identified schwannoma, comprising spindle cell proliferation in a palisading pattern with obvious cystic changes. The second case involved a 46-year-old female who presented with swelling of the right submandibular region. Panoramic radiography and lateral oblique mandible projection, which were used together with conventional sialography of the submandibular gland, revealed the so-called "ball in hand" appearance of the submandibular gland, and contrast-enhanced CT identified a lesion of 30 mm diameter with a well-defined annular margin and homogeneous low-density near the tumour centre. Benign pleomorphic adenoma was suspected, but histopathological examination identified schwannoma, predominantly comprising Antoni B type tissue.

Three-dimensional volumetric visualization of arteriovenous malformation of the maxilla.

The appearance of an arteriovenous malformation is described from images derived from spiral CT and reconstructed in three dimensions using computer graphics. The existence and shape of a vascular malformation is demonstrated using a vascular protocol. This three-dimensional CT technique is an important adjunct to diagnosis using CT, MRI and conventional radiography.

Digital imaging modalities for dental practice.

The introduction of the computed tomograph in the 1970s revolutionized medical diagnosis by initiating the transition from analogue to digital imaging. During this period, more specialized equipment for image processing was developed, such as cathode-ray tubes for image display, special sensors for image acquisition, and storage devices for image archiving. Digital imaging systems designed exclusively for use in dentistry were developed in the latter half of the 1980s. Some are now being clinically applied under conditions of close scrutiny to determine diagnostic accuracy, image quality, and radiation exposure to patients. This article reviews the enabling technologies of digital systems used in dentistry, and focuses upon intraoral digital imaging systems, concepts for digital image acquisition, and variations in radiation dose and their effects on diagnostic accuracy of caries detection.

Sensitometric properties of Agfa Dentus OrthoLux, Agfa Dentus ST8G, and Kodak Ektavision panoramic radiographic film.

OBJECTIVES: The purpose of this study was to compare the sensitometric properties of and visualization of anatomical structures with Agfa OrthoLux green-sensitive panoramic radiographic film, Agfa ST8G green sensitive panoramic radiographic film, and Kodak Ektavision green-sensitive panoramic radiographic film used in combination with an Agfa Ortho Regular 400 imaging screen, Kodak Ektavision imaging screen, and Kodak Lanex Regular imaging screen. METHODS: The density response and resolution of panoramic radiographic film/intensifying screen combinations was evaluated by means of Hunter and Driffield curves, modulation transfer functions, and noise-equivalent number of quanta. Image clarity of selected anatomical structures was rated independently by 6 oral and maxillofacial radiologists. RESULTS: The ISO speed for the Agfa OrthoLux panoramic radiographic film combinations was the fastest, and the ISO speed for the Kodak Ektavision green-sensitive panoramic radiographic film combinations was the slowest. The average gradient for the Agfa ST8G systems was relatively steep in comparison with those for the other film/screen combinations. The modulation transfer functions for the Kodak Ektavision film were higher than those for the other films, irrespective of the screen combination used, and those for Agfa OrthoLux film were slightly higher than those for Agfa ST8G film. The noise-equivalent number of quanta for the Agfa ST8G film/screen combinations was lower than those for the other film/screen combinations. The noise-equivalent number of quanta for the Kodak Ektavision film/screen combinations was well within the high-frequency range, whereas Agfa OrthoLux combined with either the Kodak Ektavision imaging screen or the Kodak Lanex Regular imaging screen produced a noise-equivalent number of quanta similar to those of the Kodak Ektavision film/screen combinations in the low-frequency range. Agfa OrthoLux was perceived to provide clearer images of the selected anatomical details than Agfa ST8G, and the Agfa OrthoLux/Agfa Ortho Regular 400 combination was not significantly different from the Kodak Ektavision/Kodak Lanex Regular combination in terms of perceived image quality. CONCLUSION: Agfa OrthoLux is an improvement over Agfa ST8G in film speed, spatial resolution, granularity, and perceived diagnostic image quality. The Agfa OrthoLux/Agfa Ortho Regular 400 combination did not exceed the Kodak Ektavision film/Kodak Ektavision imaging screen combination in resolution, granularity, or perceived image quality.

Computed tomography of emphysema following tooth extraction.

Subcutaneous and tissue space emphysema following surgical extraction of mandibular third molars is a rare and serious complication of dental surgery. Recognition of mediastinal emphysema following surgical extraction is difficult because there are no absolute clinical symptoms and signs. We present two cases of emphysema following extraction of a lower third molar and discuss the contribution of CT to the early recognition of the presence and spatial migration of air and to clinical management.

Suitability of the general-purpose graphic printer as an image output device for digital dental x-ray images.

OBJECTIVES: The purpose of this study was to evaluate the suitability of the general-purpose graphic printer as an image output device for digital dental x-ray images. METHODS: The image quality as obtained by a thermal printer and by a dye sublimation printer was investigated. A grid pattern image was used to check parallelism and verticality of lines in each hard copy. A step-wedge image was printed with each printer, and the optical density, gradient, and root mean square granularity were compared. Depiction ability was also compared by using test images, including small signals. RESULTS: All of the lines were parallel and vertical on hard copies of both printers. The dye sublimation printer showed better results on optical density, gradient, root mean square granularity, and depiction ability. CONCLUSION: The dye sublimation printer produces images of the depiction ability comparable to the cathode ray tube display and seems suitable as an image output device for digital dental x-ray images.

Contrast-enhanced conventional CT in patients after surgery for malignant tumors: evaluation of the optimal method of the administration of the contrast medium.

Patients after ablative surgery for malignant tumors require computed tomography (CT) examination of a wide area on the head and neck to follow-up for recurrence and lymph metastasis. The aim of this study was to determine a more effective method for the infusion of the contrast medium into post-operative patients undergoing conventional CT, based on the relationship between the method of administering the contrast medium and the contrast-enhancing effect in the internal jugular vein. First eleven images were selected from the existing contrast-enhanced and plain CT images in a manner such that the CT values of the internal jugular vein were distributed evenly in a range of 50-180. Seven experienced observers evaluated the contrast-enhancing effect of each image set at a window value of 40 and window widths of 120, 200, and 280. Secondly, the CT values of the right internal jugular vein were measured in a total of 10 CT images from the thyroid to maxillary sinus level from each of 60 post-operative patients. The injection needles and contrast-enhancing techniques used in the 60 patients were drip infusion using an 18G injection needle in 20, drip infusion using a 21G injection needle with bolus intravenous injection immediately before scanning in 20, and drip infusion using a 23G injection needle with bolus intravenous injection immediately before scanning in 20. A CT value of 100 or above, preferably 120 or above, in the internal jugular vein was needed for the contrast-enhancing effect of a CT image to be judged as clinically significant. Our results found that, when a conventional CT was used in patients after surgery for malignant tumors, drip infusion using a 21G or 23G injection needle should be combined with bolus injections immediately before the beginning of scanning, and at the glottis or submandibular gland level during the scanning. A sufficient contrast-enhancing effect can also be obtained by drip infusion using an 18G injection needle without bolus injection.

Assessing the image quality of a CCD-based digital intraoral radiography system: application of perceptibility curve test.

The perceptibility curve test is a method for evaluating the psychophysical properties of radiographic systems. The concept of the perceptibility curve is based on the minimum perceptible exposure differences that are recorded by a particular imaging system. The perceptibility curve test was applied to a Charge-Coupled Device (CCD)-based digital intraoral radiography system in this study. A test object was made of a square aluminum block, 28 mm in both height and length and 10 mm in thickness. The test object had ten contrast details in the form of round holes with diameters of 1.5 mm. The depths of the holes ranged from 0.05 mm to 0.5 mm in steps of 0.05 +/- 0.01 mm. An X-ray unit was used that operated in the range of 60 to 90 kVp. Test radiographs were shown to observers in random order. Six observers were asked to rate them regarding the number of spots representing holes that they could perceive. The smallest perceptible difference in gray level on the computer monitor, a 15-inch cathode-ray tube (CRT), was then found. The minimum difference in gray level between a perceptible detail and the background was determined. Dose response functions were employed to determine exposures corresponding to these gray levels. For each case, delta logE as a function of the number of object details was calculated. Finally the reciprocal of all values of (delta logE)min were calculated. The number of details which the observers perceived decreased linearly with decreasing delta logE values. The maximum number of details that observers perceived was eight or nine. The perceptibility curves showed that their peaks shifted slightly with a change of the kVp but that their shapes were similar at different kVp settings.

Dependency of dose response of five charge-coupled device-based digital intra-oral radiographic systems on tube voltage.

OBJECTIVE: To compare the dependency of dose response of five CCD-based digital intra-oral radiographic systems on tube voltage. METHODS: Characteristic curves for Sens-A-Ray (old and new generations; Regam Medical Systems, Sundsvall, Sweden), Computed Dental Radiography (Schick Technologies, Long Island City, NY, USA), CompuRay (Yoshida, Tokyo, Japan), and VIXA (Dentsply/Gendex, Des Plaines, IL, USA) were generated between 60 and 90 kVp at intervals of 10 kVp and corrected by subtraction of dark current. Their sensitivities were compared. RESULTS: The sensitivity of the old generation Sens-A-Ray decreased with increase in tube voltage whereas in the other systems it increased. CONCLUSION: In the newer systems using a rare earth intensifying screen as a scintillator, the sensitivity increases with increase in tube voltage, thus reducing the radiation dose to the patient.

A sensitometric comparison of Kodak Ektavision and Fuji Super HR-S panoramic radiographic films.

OBJECTIVES: The purpose of this study was to compare the combination of Ektavision film and Ektavision intensifying screen with the combination Super HR-S panoramic radiographic film and HR-4 intensifying screen with respect to sensitometric properties and the visualization of anatomic structures. METHODS: The density response and resolution of both panoramic radiographic film/intensifying screen combinations were evaluated through use of the generated characteristic curves and the modulation transfer function. The diagnostic clarity was evaluated by five oral and maxillofacial radiologists who used a rating scale to evaluate the image clarity of selected anatomic structures. RESULTS: The film speed and radiographic contrast, respectively, were 1.3 and 1.2 times higher for Ektavision than for Super HR-S. The image resolution with Ektavision was similar to that with Super HR-S. Ektavision was perceived to provide clearer images of the selected anatomic details than did Super HR-S. CONCLUSION: With respect to the clarity of anatomic structures, Ektavision film, with its higher speed and higher contrast, proved superior to Super HR-S film.

Sensitometric effects of varying the intensifying screens used with Agfa Dentus ST8G and RP6 panoramic radiographic films.

OBJECTIVES: To compare the sensitometric effects and information yield of varying the intensifying screens used with both Dentus ST8G and RP6 Agfa Gevaert, Dormagen, Germany panoramic radiographic films. MATERIAL AND METHODS: Four screen-film combinations were employed for each of the two film types. The screens used were blue fluorescing PX-III (Kasei Optonix, Tokyo, Japan) and Special (Siemens AG, Bensheim, Germany), as well as green fluorescing Lanex Regular (Eastman Kodak, Rochester, NY, USA) and Trimax T16 (3M, Mineapolis, Minnesota, USA). The density response for each screen-film combination was evaluated using the characteristic curves generated. Information yield, as determined by the radiographic detection of defects in an aluminium test object, was evaluated by nine observers. RESULTS: The characteristic curves for ST8G were different when green and blue fluorescing screens were used; however, those for RP6 varied little irrespective of the choice of intensifying screens. Observers were able to perceive defects at significantly lower radiation exposures for ST8G combined with green fluorescing screens compared with blue emitting screens. RP6 with all screen combinations provided similar image detail perceptibility at comparable exposures with ST8G with green-fluorescing screens. CONCLUSIONS: RP6 is suitable for use with either the spectrally matched blue emitting screens or green-emitting screens. ST8G radiographic film should always be matched to rare earth screens.

Evaluation of XD/A Plus and ST8G films for cephalometric radiography with Grenex G8 and BH-III screens.

OBJECTIVES: Sensitometric properties, clinical image quality, and patient dose requirements are important considerations when selecting film for cephalometrics. Two recently released films, XD/A Plus and ST 8G green sensitive films, were studied. METHODS: The films were each combined with Grenex G8 (Fuji Medical) green-fluorescing matched and BH-III (Kasei Optonix) blue-fluorescing mismatched intensifying screens. The density response and resolution for each screen-film combination were evaluated by use of the characteristic curve and modulation transfer function. The kilovoltage settings providing clinically acceptable images were assessed individually by 12 observers. Clinically acceptable images for each combination were also compared, and the skin entrance doses in the temporomandibular joint region were determined. RESULTS: The average contrast at the most effective density range was found to be slightly higher for the BH-III group than for the G8 group. The modulation transfer function for the BH-III group was inferior to that for the G8 screens. There were no significant differences in diagnostically acceptable image quality among the four combinations; nevertheless the BH-III screen group required two to three times more exposure than the G8 screen group. CONCLUSIONS: XD/A Plus and ST8G films provide acceptable image detail for cephalometrics. To minimize the patient dose they should be used with green-emitting screens.

Perceptibility of defects in an aluminum test object: a comparison of the RVG-S and first generation VIXA systems with and without added niobium filtration.

OBJECTIVE: To compare the first generation VIXA (Gendex, Milan, Italy) and the RVG-S (Trophy Radiologie, Vincennes, France) for detection of defects in an aluminium test object at various exposures both with and without added niobium filtration. METHODS: Images of a 7 mm aluminium test object with defects ranging from 0.1 to 1.5 mm with standardized projection geometry. Seven dentists acted as observers. Perceptibility curves were developed for both sensors under the various filtration conditions and exposures. RESULTS: At optimum exposures both the VIXA and the RVG-S permitted the same number of defects to be observed. The optimum exposures were similar for the two systems, but the dynamic range was greater for the RVG-S. Addition of niobium filtration did not appreciably alter the radiation dose required to perceive a given number of defects using either system. CONCLUSIONS: The two systems performed equally at optimum exposure when the dose is approximately the same irrespective of the presence or absence of niobium filtration. Beyond the optimal level, the RVG-S outperformed the VIXA system.

A dual sensitivity screen system for TMJ image enhancement in cephalometric radiography: sensitometric evaluation.

OBJECTIVES: An in vitro evaluation of the image quality of the TMJ OrthoCeph Slimline Cassette System (TOSCS). METHODS: The density response, resolution and clarity of the system were evaluated by use of the characteristic curve, modulation transfer function and root mean square quantum mottle. Relative sharpness was evaluated qualitatively by five observers. RESULTS: Increased density with Trimax 12 gave almost the same contrast as that with Trimax 8 in the diagnostic range, whereas MTF and RMS for Trimax 12 were inferior. CONCLUSIONS: The dual-sensitivity screen system should lead to improved radiographic contrast of the TMJ region in cephalometric radiography. The reduction in sharpness is probably clinically insignificant.

Objective and subjective assessments of Kodak Ektaspeed plus new dental X-ray film: a comparison with other conventional X-ray films.

A new dental X-ray film called EKTASPEED Plus has been released by the Eastman Kodak Company. Its sensitometric properties, inclusive of modulation transfer function (MTF) and Wiener spectrum (WS) and the visibility of radiographic details, were compared with those of other conventional dental X-ray films, EKTASPEED EP-22 (Eastman Kodak Co.) and Ultra-Speed DF-57 (Eastman Kodak Co.). The base plus fog density of EKTASPEED Plus was between those for EKTASPEED and Ultra-Speed. Relative speed of EKTASPEED Plus was slightly faster than EKTASPEED, and about two times faster than that of Ultra-Speed. The contrast of EKTASPEED plus was close to that of Ultra-Speed. Only minor differences existed between the film types studied when the sharpness and the granularity were compared. The MTF and WS also revealed no substantial differences between the films. Perceptibility testing showed minor differences between the three films, with EKTASPEED Plus consistently revealing more defects at lower exposures irrespective of whether a Burger's phantom or aluminum test block was used.

Observer performance in the assessment of contract enhanced CT: effects of contrast medium and grey scale window on detection of defects in a simulated peripheral rim border.

The image contrast of X-ray CT systems depends on the properties of the imaging system, the number of grey scales used in the digital sampling process, and the addition or otherwise of a contrast medium. The effect of contrast medium is often emphasized in the peripheral rim of pathologic masses. In this study, a special hexagonal test object made of acrylic phosphate and a cylindrical container were employed. When the contrast medium IOPAMIRON 300 was used to fill the space between the test object and its cylindrical container, a contrast-enhanced peripheral rim with or without signal of defect was observed. Visual perceptibility was examined from the signals resulting from varying contrast by use of contrast medium and adjusting the grey scale by image processing. Threshold contrast influenced by window width was recorded in each image contrast, different ranges of window width was recorded in each instance using statistical analyses. While window width was inversely proportional to image contrast, different ranges of window width and image contrast provided better visual perceptibility for each concentration of the contrast medium. The range of window width for obtaining the best visual perceptibility was determined for a contrast-enhanced image.

Comparing the sensitometric properties of dental X-ray films.

This article describes a study that compared the sensitometric properties and information yields of four dental X-ray films: Eastman Kodak Ultra-Speed DF-57 and Ektaspeed EP-21, Flow DV-58 and Agfa Gevaert Dentus M2 Comfort. Dentus M2 Comfort gave the greatest contrast, a speed between the conventional D- and E-speed film groups and an exposure latitude wider than Ultra-Speed but less than DV-58. A significant difference in detail was found with low exposures, Dentus M2 Comfort and Ektaspeed outperforming the other two film types.

Quantitative assessment of image quality using niobium filtration for cephalometric radiography.

The effect of added niobium filtration on image quality in cephalometric radiography was quantitatively evaluated using the Modulation Transfer Function (MTF). A conventional full-wave cephalometric X-ray generator (Quint Sectograph) and a constant potential, high frequency X-ray generator (Orthophos CD) were compared with respect to the effects on the MTF of the added filtration. There was a slight reduction in image quality with both machines when adding niobium filtration.