Image quality degradation by light scattering in display devices.
(17/3327)
Veiling glare and ambient light reflection can significantly degrade the quality of an image on a display device. Veiling glare is primarily associated with the diffuse spread of image signal caused by multiple light scattering in the emissive structure of the device. The glare ratio associated with a test image with a 1-cm-diameter black spot is reported as 555 for film, 89 for a monochrome monitor, and 25 for a color monitor. Diffuse light reflection results from ambient light entering the display surface and returning at random emission angles. The diffuse reflection coefficient (luminance/illuminance, 1/sr) is reported as 0.026 for film, 0.058 for a monochrome monitor, and 0.025 for a color monitor with an antireflective surface coating. Both processes increase the luminance in black regions and cause contrast reduction. Specular reflections interfere with detail in the displayed scene. The specular reflection coefficient (luminance/luminance) is reported as 0.011 for film, 0.041 for a monochrome monitor, and 0.021 for a color monitor with an antireflective coating. (+info)
Optimization of a contrast-detail-based method for electronic image display quality evaluation.
(18/3327)
The authors previously reported a general technique based on contrast-detail methods to provide an overall quantitative evaluation of electronic image display quality. The figure-of-merit reflecting overall display quality is called maximum threshold contrast or MTC. In this work we have optimized the MTC technique through improvements in both the test images and the figure-of-merit computation. The test images were altered to match the average luminance with that observed for clinical computed radiographic images. The figure-of-merit calculation was altered to allow for contrast-detail data with slopes not equal to -1. Preliminary experiments also were conducted to demonstrate the response of the MTC measurements to increased noise in the displayed image. MTC measurements were obtained from five observers using the improved test images displayed with maximum monitor luminance settings of 30-, 50-, and 70-ft-Lamberts. Similar measurements were obtained from two observers using test images altered by the addition of a low level of image noise. The noise-free MTC and MTC difference measurements exhibited standard deviations of 0.77 and 1.55, respectively. This indicates good measurement precision, comparable or superior to that observed using the earlier MTC technique. No statistically significant image quality differences versus maximum monitor luminance were seen. The noise-added MTC measurements were greater than the noise-free values by an average of 4.08 pixel values, and this difference was statistically significant. This response is qualitatively correct, and is judged to indicate good sensitivity of the MTC measurement to increased noise levels. (+info)
Quantitation of iodine-123-beta-CIT dopamine receptor uptake in a phantom model.
(19/3327)
OBJECTIVE: The purpose of this study was to determine the effects of technical factors such as collimation and filtration on the measurement of 123I-beta-CIT uptake in the striatum. METHODS: All SPECT studies were performed using a brain phantom containing striata within a bone- and tissue-equivalent skull. The effects of collimator resolution and septal penetration were assessed from 99mTc and 123I studies containing variable activities in the striata and background regions. Optimum attenuation coefficients (mu) were determined from studies containing uniform activity in the brain. RESULTS: For 99mTc, mu was 0.095 cm-1 and 0.07 cm-1 for parallel-hole and fanbeam collimators, respectively. For 123I, these values dropped to 0.09 cm-1 and 0.00 cm-1 (zero) for medium-energy and fanbeam collimators, respectively. Striatal uptake was significantly underestimated, particularly for medium-energy and general-purpose collimators. With 99mTc, fanbeam collimation gave a 50% increase in the measured striatal uptake, compared to medium-energy collimation. However, with 123I, this gain was eliminated by septal penetration and scatter. Increasing transaxial slice thickness, ROI size and decreasing filter cutoff frequency all degraded apparent striatal uptake. CONCLUSION: Partial volume effects, combined with the averaging effects of increasing slice thickness and ROI size, are the most significant factors affecting measurement of striatal uptake of 123I-beta-CIT. The increased resolution of low-energy high-resolution collimators, compared to a medium-energy collimator, is offset by the increased septal penetration and scatter. (+info)
Tagged MR imaging of intracranial aneurysm models.
(20/3327)
We used tagged MR imaging to investigate the flow in two lateral and two terminal saccular intracranial aneurysm models of different neck sizes. Imaging was performed with a 1.5-T superconducting MR system using 2D fast spatial modulation of magnetization (SPAMM) sequences with an intersegmental delay of 25 milliseconds. The flow in the saccular aneurysm models varied with the shape and size of the neck: flow was faster in wider-necked aneurysms than in those with narrower necks. (+info)
High-resolution MR cisternography of the cerebellopontine angle: 2D versus 3D fast spin-echo sequences.
(21/3327)
BACKGROUND AND PURPOSE: The clinical usefulness of MR cisternography of the cerebellopontine angle, applying 2D or 3D fast spin-echo sequences, has been reported recently. Our purpose was to investigate the cause of signal loss in CSF in the prepontine or cerebellopontine angle cistern on 2D FSE MR images and to compare the cisternographic effects of 2D and 3D FSE sequences. METHODS: Preliminary experiments were performed in four volunteers to assess the causes of signal loss. Initially, using a 2D cardiac-gated cine phase-contrast method with a velocity encoding value of 6 cm/s, we measured the velocity and flow pattern of CSF. Comparisons were made to assess the effects of intravoxel dephasing, amplitude of the section-selecting gradient, echo time (TE), and section thickness. Four healthy subjects and 13 patients with ear symptoms were examined, and multisection 3-mm-thick 2D images and 30-mm-slab, 1-mm-section 3D images were compared qualitatively and quantitatively. Then, 3D MR cisternography was performed in 400 patients with ear symptoms, and qualitative evaluation was performed. RESULTS: In volunteers, the average peak velocity of CSF was 1.2 cm/s. With TE = 250, CSF may move an average of 3 mm, and can be washed out of a 3-mm-thick 2D section volume. The CSF signal relative to that of a water phantom decreased gradually as TE increased on single-section 3-mm-thick 2D images. The CSF signal relative to that of the water phantom increased gradually as section thickness increased. No significant differences were noted in intravoxel dephasing and amplitude of the section-selecting gradient. The contrast-to-noise ratio (CNR) between CSF and the cerebellar peduncle, and the visibility of the cranial nerves and vertebrobasilar artery were significantly improved on 3D images in 17 subjects. In images from 400 patients, no significant signal loss in the cistern was observed using 3D FSE. CONCLUSION: CSF signal loss in thin-section 2D MR cisternography is mainly attributable to the wash-out phenomenon. 3D acquisition can reduce this phenomenon and provide thinner sections. The scan time for 3D acquisition is not excessive when a long echo train length and half-Fourier imaging are used. MR cisternography should be performed using a 3D acquisition. (+info)
Power Doppler ultrasound scan imaging of the level of red blood cell aggregation: an in vitro study.
(22/3327)
PURPOSE: The purpose of this study was to evaluate the effect of the shear rate on red blood cell (RBC) aggregation with power Doppler ultrasound scanning (PDU), pulsed-wave Doppler scanning, and color Doppler flow imaging. METHODS: Equine and porcine blood were circulated with a steady flow in a phantom with a diameter of 9.52 mm. The color Doppler flow imaging mode was used to estimate the velocity profile and the shear rate across the tube. A transfer function that related the Doppler scan power, measured in gray level with the PDU method, to the power, measured in decibels with the pulsed-wave Doppler scan technique, was used to estimate the echogenicity of blood and the level of aggregation. RESULTS: For the four experiments reported, the power peaked at low shear rates probably because of increased RBC collisions and aggregation and then decreased thereafter because of disaggregation. The largest power variations were measured at shear rates of less than 40 seconds -1. At flow rates that varied between 75 and 500 mL/min, the echogenicity was low near the wall of the tube, increased toward the middle, and decreased at the tube center. The Doppler scan power was uniform across the tube at flow rates of 750 and 1000 mL/min. CONCLUSION: PDU is reliable to quantify the echogenicity of blood and the level of RBC aggregation. In comparison with other methods proposed to measure RBC aggregation, ultrasound scanning is applicable in vivo and may help to improve our basic understanding of the relationship between the hemodynamic of the circulation and RBC aggregation in human vessels. (+info)
Quantitative and clinical analysis of SPECT image registration for epilepsy studies.
(23/3327)
This study reports quantitative measurements of the accuracy of two popular voxel-based registration algorithms--Woods' automated image registration algorithm and mutual information correlation--and compares these with conventional surface matching (SM) registration. METHODS: The registration algorithms were compared (15 different matches each) for (a) three-dimensional brain phantom images, (b) an ictal SPECT image from a patient with partial epilepsy matched to itself after modification to simulate changes in the cerebral blood flow pattern and (c) ictal/interictal SPECT images from 15 patients with partial epilepsy. Blinded visual ranking and localization of the subtraction images derived from the patient images were also performed. RESULTS: Both voxel-based registration methods were more accurate than SM registration (P < 0.0005). Automated image registration algorithm was more accurate than mutual information correlation for the computer-simulated ictal/interictal images and the patient ictal/interictal studies (P < 0.05). The subtraction SPECTs from SM were poorer in visual ranking more often than the voxel-based methods (P < 0.05). CONCLUSION: Voxel intensity-based registration algorithms provide significant improvement in ictal/interictal SPECT registration accuracy and result in a clinically detectable improvement in the subtraction SPECT images. (+info)
A radionuclide therapy treatment planning and dose estimation system.
(24/3327)
An object-oriented software system is described for estimating internal emitter absorbed doses using a set of computer modules operating within a personal computer environment. The system is called the Radionuclide Treatment Planning and Absorbed Dose Estimation System (RTDS). It is intended for radioimmunotherapy applications, although other forms of internal emitter therapy may also be considered. METHODS: Four software modules interact through a database backend. Clinical, demographic and image data are directly entered into the database. Modules include those devoted to clinical imaging (nuclear, CT and MR), activity determination, organ compartmental modeling and absorbed dose estimation. RESULTS: Both standard phantom (Medical Internal Radiation Dose [MIRD]) and patient-specific absorbed doses are estimated. All modules interact with the database backend so that changes in one process do not influence other operations. Results of the modular operations are written to the database as computations are completed. Dose-volume histograms are an intrinsic part of the output for patient-specific absorbed dose estimates. A sample dose estimate for a potential 90Y monoclonal antibody is described. CONCLUSION: A four-module software system has been implemented to estimate MIRD phantom and patient-specific absorbed doses. Computations of the doses and their statistical distribution for a pure beta emitter such as 90Y take approximately 1 min on a 300 MHz personal computer. (+info)