Abstract
OBJECTIVE. The objective of our study was to assess the effects of compressing
source thin-section abdominal CT images on final transverse
average-intensity-projection (AIP) images.
MATERIALS AND METHODS. At reversible, 4:1, 6:1, 8:1, 10:1, and 15:1 Joint
Photographic Experts Group (JPEG) 2000 compressions, we compared the artifacts
in 20 matching compressed thin sections (0.67 mm), compressed thick sections (5
mm), and AIP images (5 mm) reformatted from the compressed thin sections. The
artifacts were quantitatively measured with peak signal-to-noise ratio (PSNR)
and a perceptual quality metric (High Dynamic Range Visual Difference Predictor
[HDR-VDP]). By comparing the compressed and original images, three radiologists
independently graded the artifacts as 0 (none, indistinguishable), 1 (barely
perceptible), 2 (subtle), or 3 (significant). Friedman tests and exact tests
for paired proportions were used.
RESULTS. At irreversible compressions, the artifacts tended to increase in the
order of AIP, thick-section, and thin-section images in terms of PSNR (p <
0.0001), HDR-VDP (p < 0.0001), and the readers' grading (p < 0.01 at 6:1 or
higher compressions). At 6:1 and 8:1, distinguishable pairs (grades 1-3) tended
to increase in the order of AIP, thick-section, and thin-section images.
Visually lossless threshold for the compression varied between images but
decreased in the order of AIP, thick-section, and thin-section images (p <
0.0001).
CONCLUSION. Compression artifacts in thin sections are significantly attenuated
in AIP images. On the premise that thin sections are typically reviewed using
an AIP technique, it is justifiable to compress them to a compression level
currently accepted for thick sections.
