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Results for “Image Enhancement”

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At least 19 recordsLinked to original sources
PubMed1992

Limitations of image enhancement for the visually impaired.

Image enhancement as an aid for the visually impaired may improve visibility of TV programs and provide portable visual aid. This paper describes the current techniques for image enhancement and their underlying models. The limitations of the various techniques and of potential methods of implementation are high-lighted. Initial work in this area was based on a linear model. The finite dynamic range available in the video display and contamination of the enhanced image by high spatial frequency noise limited the model's usefulness. I propose a method to address some limitations of the original model that considers the nonlinear response of the visual system and requires enhancement of subthreshold spatial information only. This modification may increase the dynamic range available by decreasing the range previously used by the linear models to enhance visible details. However, for the modified technique to be most effective, the enhancement has to be continuously tuned, based on the patient's visual loss and the spatial frequency content of the displayed images. The implications of these limitations for the potential implementation in TV are discussed. Implementation of an image-enhancing visual aid in a head-mounted, binocular, full-field, virtual vision device may cause substantial difficulties. Patient adaptation may be difficult due to head movement and interaction of the vestibular system response with the head-mounted display. An alternate, bioptic design is proposed in which the display is positioned above or below the line of sight to be examined intermittently, possibly in a freeze-frame mode. Such implementation is also likely to be less expensive, enabling more users access to the device.

Audiovisual Aids↗
PubMed1991

MR differentiation of hepatic haemangioma and hepatocellular carcinoma: value of delayed-phase Gd-DTPA enhanced images.

The efficacy of three different approaches (precontrast and delayed-phase postcontrast T1-weighted (T1-W) images, measurement of T2 value, and dynamic FLASH imaging) for differentiation between hepatic haemangiomas and hepatocellular carcinomas, was compared. Most haemangiomas (89%) showed iso- or hypointensity on precontrast T1-W images and hyperintensity on delayed-phase postcontrast T1-W images. By using both pre/postcontrast T1-W images and T2 measurement, 30 out of 32 lesions (94%) were correctly differentiated. The dynamic FLASH imaging did not significantly improve the overall accuracy although it played a critical role in a few problematic cases. It is concluded that the combination of pre/postcontrast T1-W images is a promising approach for differentiation of small hepatic tumours, and plays a complementary role with T2 measurement.

Adult↗
PubMed1992

Spleen: dynamic enhancement patterns on gradient-echo MR images enhanced with gadopentetate dimeglumine.

To examine the pattern of immediate enhancement with gadopentetate dimeglumine on dynamic magnetic resonance (MR) images of the spleen, this study was divided into two parts: In the first part, the authors retrospectively reviewed the dynamic MR images obtained with a fast low-angle shot (FLASH) sequence in the abdomen immediately after injection of gadopentetate dimeglumine in 137 patients. In the second part, dynamic gadolinium-enhanced FLASH images were prospectively compared with contrast material-enhanced computed tomographic (CT) scans in 17 patients with focal splenic lesions discovered on CT scans. In the first part, 108 patients (79%) had an arciform pattern of contrast enhancement; 22 patients (16%), a uniform pattern of high signal intensity; and seven patients (5%), a uniform pattern of low signal intensity. Most patients had arciform enhancement of the spleen; uniform enhancement occurred in some patients with underlying malignant or inflammatory disease. In the second part, all focal lesions seen on CT scans were seen on dynamic MR images (75 lesions), significantly more than were seen on FLASH images (15 lesions) (P < .001).

Adolescent↗
PubMed1992

[Low flip angle spin-echo MR imaging to obtain better Gd-DTPA enhanced imaging with ECG gating].

ECG-gated spin-echo imaging (ECG-SE) can reduce physiological motion artifacts. However, ECG-SE does not provide strong T1-weighted images because repetition time (TR) depends on heart rate (HR). We investigated the usefulness of low flip angle spin-echo imaging (LFSE) in obtaining more T1-dependent contrast with ECG gating. in computer simulation, the predicted image contrast and signal-to-noise ratio (SNR) obtained for each flip angle (0-180 degrees) and each TR (300 msec-1200 msec) were compared with those obtained by conventional T1-weighted spin-echo imaging (CSE: TR = 500 msec, TE = 20 msec). In clinical evaluation, tissue contrast [contrast index (CI): (SI of lesion-SI of muscle)2*100/SI of muscle] obtained by CSE and LFSE were compared in 17 patients. At a TR of 1,000 msec, T1-dependent contrast increased with decreasing flip angle and that at 38 degrees was identical to that with T1-weighted spin-echo. SNR increased with the flip angle until 100 degrees, and that at 53 degrees was identical to that with T1-weighted spin-echo. CI on LFSE (74.0 +/- 52.0) was significantly higher than CI on CSE (40.9 +/- 35.9). ECG-gated LFSE imaging provides better T1-dependent contrast than conventional ECG-SE. This method was especially useful for Gd-DTPA enhanced MR imaging.

Contrast Media↗
PubMed1992

Image enhancement filters significantly improve reading performance for low vision observers.

As people age, so do their photoreceptors; many photoreceptors in central vision stop functioning when a person reaches their late sixties or early seventies. Low vision observers with losses in central vision, those with age-related maculopathies, were studied. Low vision observers no longer see high spatial frequencies, being unable to resolve fine edge detail. We developed image enhancement filters to compensate for the low vision observer's losses in contrast sensitivity to intermediate and high spatial frequencies. The filters work by boosting the amplitude of the less visible intermediate spatial frequencies. The lower spatial frequencies. These image enhancement filters not only reduce the magnification needed for reading by up to 70%, but they also increase the observer's reading speed by 2-4 times. A summary of this research is presented.

Adult↗
PubMed1991

Similar features in Z bands of both skeletal and cardiac muscle revealed by image enhancement.

We have shown previously that the small square (ss) and basket weave (bw) states of the Z band lattice in cardiac and skeletal muscle are related to the contractile state of the muscle. We have used two-dimensional image processing techniques on digitized electron micrographs to enhance the structural features of each projected lattice form in cardiac and skeletal muscle. Four different processing techniques were employed to assess the effect of enhancement artifacts on the resulting Z band images. We observed only slight differences between enhanced images of a particular Z band form produced by the four different techniques. Every enhanced image showed an approximate four-fold symmetry independent of muscle type or Z band lattice form. Each enhanced image showed four cross-connecting Z-filaments which appeared to connect each axial filament to the four nearest axial filaments. In bw images from both cardiac and skeletal muscle, axial filaments had a greater apparent diameter and a greater interaxial filament spacing than in the ss images. In both muscle types, the cross-connecting Z-filaments appeared to overlap half-way between axial filaments in the ss images while the bw images showed no such overlap. These structural features are consistent with a dynamic Z band lattice that participates in muscle contraction.

Algorithms↗
PubMed1978

Digital image enhancement of cephalograms.

Quantification of cephalometric X-rays requires the use of hand tracings of the structures to delineate points, lines, and angles. The structures, especially soft tissue, are often obscure and are therefore approximated. Recent biomedical application of image enhancement by digital computer promises a method whereby landmarks in the cranium are more clearly defined. Development of this technique will enable a more extensive and accurate utilization of cephalometric radiographs for diagnostic and research purposes.

Cephalometry↗
PubMed1979

Image enhancement by digital-analog filtration. I. Technical description of device.

A device for general (10 x 10 pixels) image filtration of 24 cm x 30 cm roentgenograms in the image domain (10(6) pixels) is described. It combines analog and digital techniques and records the processed image on film in the same scale as the original. Results from preliminary tests of the equipment are reported and it is concluded that it yields images with increased perceptibility of large-scale objects of low photographic contrast in the presence of disturbing structures of high spatial frequency and comparably high photographic contrast.

Bone and Bones↗
PubMed1991

Craniospinal magnetic resonance imaging enhanced with Gd-DTPA in von Hippel-Lindau disease.

The case presented illustrates the utility of enhancement with gadolinium diethylenetriaminepenta-acetic acid in magnetic resonance imaging (MRI) of the brain and the spinal cord in a patient with von Hippel-Lindau disease. The patient had numerous lesions in the brain stem and the cervical and the thoracic spinal cord, most of which were not demonstrated or were only poorly demonstrated with noncontrast MRI. Contrast-enhanced MRI should be performed in two sessions with a separate dose of contrast agent for each. Regular follow-up examinations should be conducted in the same manner.

Adult↗
PubMed1979

Image enhancement by digital-analog filtration. II. Tests of filters.

The function of a device for frequency filtration of roentgenograms with digital filters has been tested with the use of different filters. The image was altered in the expected way, which means that the device is suitable for investigating the possibilities of different filters to improve the diagnostic ability. The results of the tests indicate that improvement should be achieved by low-pass filtration.

Femur↗