Radiologists and other fans look at storage

In the spirit of the book "Baseball for Brain Surgeons and Other Fans," by Tim McCarver, Dr. David Channin gave a SCAR University pitch Saturday morning titled "Storage for Radiologists and Other Fans."

First, Channin said radiologists don't need to worry about underlying technologies when shopping for storage because those change rapidly.

"You don't need to know how to forge iron to use a hammer. You only need to know what your requirements are for that storage," he said.

PACS databases contain much more than just images. There are DICOM Structured Reporting objects and Key Image Notes objects, among other DICOM objects.

It helps to know how many images you make, and the average number of them is going up.

"In 1999, we were generating 100 CT slices per study. Now, the slices per study has doubled," said Channin, director of imaging informatics at Northwestern University Medical Center.

Storage requirements go up as CT slices go up.

Next, you have to know who's looking at the images, what Channin calls the "eyeball curiosity factor." In one week at Northwestern Memorial Hospital, Channin recorded over 24,000 viewing episodes, 90% of which were satisfied from PACS's short-term storage.

"The fact that there are more images available to look at means that more images will be viewed," he said.

A 90% short-term satifaction rate means that the system found it necessary to fetch a study from the long-term archive only 10% of the time.

"That also means the phone never rings with some oncologist unhappy that he can't get a prior study fast enough," Channin said.

With image volume increasing so rapidly, it is necessary to add about 20% of storage per year to maintain the 90% short-term satisfaction rate.

Channin noted several things to remember when shopping for storage:
? PACS is not really a PACS, it's an image manager, an actor in IHE terminology.
? Any DICOM object less than x days old shall be delivered to another actor in less than y seconds.
? Anything older than x days shall be delivered in no less than z seconds.
? Any access to the PACS archive database must go through the PACS database schema.

"The reason for schema access is that the archive is dumb," Channin said.

If you store Ms. Smith's study and Ms. Smith marries and becomes Mrs. Jones, only the database knows that. The archive doesn't know it.

"The database schema access is your prenuptial agreement if you want to get divorced," Channin said.