Optimal image resolution for digital storage of radiotherapy-planning images.
OBJECTIVE
To evaluate the quality of digitized radiation-planning images at different resolution and to determine the optimal resolution for digital storage.


METHODS
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.


CONCLUSIONS
The quality of digitized images with 36-dpi resolution was good enough as radiation-planning images and required 200 KBytes/image.
Baba
Y
Y
Department of Radiology, Kumamoto University School of Medicine, Japan.
Furusawa
M
M
Murakami
R
R
Baba
T
T
Yokoyama
T
T
Nishimura
R
R
Takahashi
M
M
D006801:Humans; D011856:Radiographic Image Enhancement; D011873:Radiology Information Systems