8-bit Depth Research Articles

Integrating handheld PCs into a PACS network with commercially available components.

A palm computer with a 160 x 160-pixel display and 16-bit color depth can display useable images if the viewing software supports a larger image file size and zooming functions. Flash memory modules are now available. Storage of large image files is no longer a problem.

Optimal image resolution for digital storage of radiotherapy-planning images

Purpose: To evaluate the quality of digitized radiation-planning images at different resolution and to determine the optimal resolution for digital storage. Methods and Materials: Twenty-five planning films were scanned and digitized using a film scanner at a resolution of 72 dots per inch (dpi) with 8-bit depth. The resolution of scanned images was reduced to 48, 36, 24, and 18 dpi using computer software. Image qualities of these five images (72, 48, 36, 24, and 18 dpi) were evaluated and given scores (4 = excellent; 3 = good; 2 = fair; and 1 = poor) by three radiation oncologists. An image data compression algorithm by the Joint Photographic Experts Group (JPEG) (not reversible and some information will be lost) was also evaluated. Results: The scores of digitized images with 72, 48, 36, 24, and 17 dpi resolution were 3.8 ± 0.3, 3.5 ± 0.3, 3.3 ± 0.5, 2.7 ± 0.5, and 1.6 ± 0.3, respectively. The quality of 36-dpi images were definitely worse compared to 72-dpi images, but were good enough as planning films. Digitized planning images with 72- and 36-dpi resolution requires about 800 and 200 KBytes, respectively. The JPEG compression algorithm produces little degradation in 36-dpi images at compression ratios of 5:1. Conclusion: The quality of digitized images with 36-dpi resolution was good enough as radiation-planning images and required 200 KBytes/image.

Sensor noise in direct digital imaging (the RadioVisioGraphy, Sens-a-Ray, and Visualix/Vixa systems) evaluated by subtraction radiography

The aim of this study was to evaluate sensor noise with the use of the subtraction method in radiographs captured with three direct digital intraoral systems. Ten radiographs were taken of the lower left molar region of a phantom head at each of three exposure times: 0.20 seconds, 0.46 seconds, and 0.60 seconds with the use of the RadioVisioGraphy (Trophy Radiologie, Vincennes, France), Sens-a-Ray (Regam Medical Systems, AB, Sundsvall, Sweden), and Visualix (Gendex, Philips Medical Systems, Inc., Monza, Italy) systems. Neither the x-ray tube nor the phantom were moved between exposures, and the three sensors were identically positioned. The images were stored in the tagged image file format provided by the systems in 8-bit depth and imported by a subtraction program. Subtractions were performed between identical images taken with the three systems. The standard deviation for the distribution of the shades of grey in the subtraction image histogram served as an expression for image noise. Pairedt tests evaluated differences between the standard deviations of the subtraction images from the three systems. The standard deviation increased with increasing exposure time for all three systems (p < 0.00001). The standard deviation for the images performed with Visualix were 6.47, 10.34, and 11.16 at exposure times 0.20, 0.46, and 0.60, respectively. For the RadioVisioGraphy, these values were 1.61, 2.03, and 2.18, and for Sens-a-Ray 2.90, 3.98, and 3.96, respectively. The differences between the systems were highly statistically significant (p < 0.0001). Subjectively judged, the density of images taken with the Visualix system at 0.20 seconds was comparable to images taken with the RadioVisioGraphy system at 0.46 seconds and with the Sens-a-Ray at 0.60 seconds. The fastest system thus provided the most noisy images.

Computer-assisted, operator-interactive technique for calculating pulmonary arterial taper.

We have developed a computer-assisted, operator-interactive technique which performs fast, precise computations of pulmonary artery taper. Individual 35-mm cineframes from balloon-occlusion pulmonary arteriograms are digitized into a 640 X 480 matrix in 8-bit depth and loaded into a VAX 11/780 computer for analysis. After operator identification of the arterial segment, an automated process of caliber analysis is initiated. By fitting a cubic spline function to the densitometric profiles extracted from the arterial segment, serial arterial cross-sectional diameters are calculated from the mathematically-derived points along the fitted curves. Spurious profiles, caused by sectioning at bifurcations, can be overridden by an operator-interactive subroutine. Taper is derived from the slope of the least-squares fit of vessel caliber with respect to its distance along the arterial segment. Results obtained by calculations from the computer-assisted caliber measurements were compared with those obtained by hand-tracing the same vessel segments. Correlation between computer-traced inflection points and hand-traced taper was very significant (r = .96, n = 13, P less than 0.001).