OPTIMAL IMAGE-RESOLUTION FOR DIGITAL STORAGE OF RADIOTHERAPY-PLANNINGIMAGES

Purpose: To evaluate the quality of digitized radiation-planning image s 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 qual ities of these five images (72, 48, 36, 24, and 18 dpi) were evaluated and given scores (4 = excellent; 3 = good; 2 = fair; and I = poor) by three radiation oncologists. An image data compression algorithm by t he Joint Photographic Experts Group (JPEG) (not reversible and some in formation will be lost) was also evaluated. Results: The scores of dig itized images with 72, 48, 36, 23, 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, respectiv ely. The quality of 36-dpi images were definitely worse compared to 72 -dpi images, but were good enough as planning films. Digitized plannin g images with 72- and 36-dpi resolution requires about 800 and 200 KBy tes, respectively. The JPEG compression algorithm produces little degr adation 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. (C) 1998 Els evier Science Inc.