Peter van Ooijen, MSc, PhD, University Medical Center Groningen, University of Groninge; Alain R. Viddeleer, MD; Floris Meijer, MD; Matthis Oudkerk, MD, PhD

With the more widespread introduction of PACS about a decade ago, a lot of institutions would perform long term storage on trusted archival systems using tape. However, this was disputed by others who set off to use more novel techniques, such as long term storage on CD-R. For this storage, it was guaranteed that the CD-Rs would last for many years, provided optimal storage conditions are met. In this study we wanted to get an indication of current performance, based on our old CD-R archive.

Although we already migrated to DVD storage years ago, an old CD-R archive ranging from 1992 to 1999 was still available in boxes. This old archive consisted of 600 CD-Rs, containing about 600 Megabyte of lossless compressed data per CD-R. All CDs were stated to be dedicated for archival purposes by the vendor (InfoGuardTM protection writable CD from Eastman Kodak Company, Rochester). The official position of Kodak on the lifetime is a guaranteed lifetime for InfoGuard protection system CDs of over 100 years.

For testing the CD-Rs, a high quality DVD-writer (Plextor 716A, firmware revision 1.11, Plextor Ltd., Milpitas, CA, USA) was used.

Of these CD-Rs a random sample of 25 CD-Rs was taken to be diagnosed using a dedicated, freeware, software tool (CD Tester, Profiler 3D, www.profiler3d.de) THAT tests the readability of the CD by opening all data, checking all binary data, displaying any failures, and if possible, determining the cause of the failure.

Another random sample of 25 CD-Rs was physically analyzed by determining the low level C1 and C2 error count, as well as unrecoverable errors, by using the Plextools Professional LE v3.13 analysis software with a constant read speed of 8 times.

To serve as a benchmark, other old CDs, without special protective coating, were deliberately scratched and exposed to sunlight in order to determine the correct performance of the CD tester software. In addition, the proper functioning of these tools was evaluated by reading other old CD-Rs with known problems.

Finally, all CD-Rs were scanned for DICOM files. A selection was uncompressed and transferred to a harddrive location using dedicated software tools.

Using test CDs, it was shown that minor scratching or damage on non-data parts did not cause any problems. With significant damage hampering the readability of the CD, either the CD-ROM drive failed to read the CD altogether or the CD tester software prompted with one or multiple errors on the CD. In addition, old, white label, CDs that were 5 years old already presented with reading errors when using CD Tester software.

A random sample of 25 actual archive CDs were tested using CD Tester software, with an average of 3,608 files per disk. Search speed was reported to be 3393 kilo Byte (KB) per second on average. Mean amount of data stored on the CDs was 564.17 MB, with a total of 89,997 DICOM files and 9.6 Gigabyte. Of those 25 CDs, none reported failures during the technical scanning.

The random sample of 25 archive CDs that was analyzed had an average age of 9.5 years. These CDs showed a remarkably low mean C1 error count (4807±2137) and a mean C2 error count of 24,8. These C2 errors were present on six of the 25 CDs, while the remaining CDs did not contain any C2 errors. No relation was found between CD age and the number of errors. All errors (C1 and C2) could be corrected by the DVD drive’s error correction algorithms.

However, using the DICOM scanning tool on all 600 CD-Rs, 9 contained severe read errors and could not be read, while DICOM data could be extracted from the remaining CD-Rs without any problems. Visual examination of the damaged CD-Rs revealed that the majority of the problems were caused by corrosion of the reflective layer, with scratches playing only a minor role. This corrosion mainly occurred at the inner ring of the CD-R, suggesting a defective sealing of the reflective layer, often close to text written on the CD with a special CD marker.

This study shows that in current (10-15 years) PACS installations, problems with the CD archives can occur, even when all data are stored on guaranteed media. White label tests showed that CDs can be damaged after 4-5 years. The main conclusion is that storage on portable media such as CD is not as safe as suggested by the manufacturer. Using CD marker pens may speed up the deterioration, but a direct relation between the writing location and the offset of the defects was not found.

Claims of vendors about the lifetime of storage media are very high. However, one bad CD could cause serious problems in medical care. Our study shows that in current (10-15 years) PACS installations, problems already exist with the CD archives, even when all data is stored on guaranteed media. White label tests showed that these CDs can be damaged after 4-5 years. The main conclusion has to be that storage on portable media, such as CD, is not as safe as suggested by the manufacturer. Even when using more expensive, guaranteed media, after 10 years several discs became unreadable. Using CD marker pens may speed up this process.