What Size PACS Do I Need?

Posted by Les Trachtman on Feb 26, 2018 11:45:00 AM

The PACS Sizing Calculator.jpeg

We are often asked this question by providers who are considering replacing their PACS.  They want to replace it with a PACS that is big enough to serve their needs but not one that is expensive beyond their means. Here's how to calculate the PACS size you really need....

So how big should your PACS be?

We have found that there are some simple metrics you can use to determine the right size of your new PACS as long as you consider these three questions:

  1. What are the predominant modalities that your practice uses? Are most of the studies you store high resolution CTs or MRIs? Are they time duration ultrasounds? Or are they more radiographs?

  2. Do you have legacy data that you want to move from your existing PACS to this new PACS?

  3. What is the monthly or annual number of studies that you expect to generate? Is that number growing?

We estimate that most PACS should last about five years.  Some may last longer, but the hard drives that comprise the storage used in your PACS can’t usually be counted on to last much longer than that.  We always recommend that you configure your PACS with a RAID array, which will enable you to replace drives when they fail.  Assuming you are diligent, in most RAID arrays, if a single drive fails, it can be replaced without any worry about data integrity.

The formula

The way to calculate the size of your PACS then is a relatively easy equation.

Take the number of studies you expect to generate each year, multiply that number by 100 Megabytes if you answered Question 1 (from earlier) with half or more of your studies being x-rays, otherwise multiply that number by 200 Megabytes.  Then multiply that number by 5 for the expected life of the hardware device.  Add in the legacy storage that you currently have and then divide that resulting number by .75.  We use the .75 divisor to accommodate the redundancy required by most RAID systems.

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Here's an example

Dr. Doe's practice generates about three quarters of its studies from MRIs and CTs.  They typically create 35 studies per day.  The legacy studies at the practice occupy about 3.2 Terabytes of existing storage.

To calculate the size of the new PACS that Dr. Doe should consider, we created the following calculation:

((35 studies/day x 250 days per year X 200 Megabytes/study average X 5) + 3.2 Terabytes))/ .75


8,750,000 Megabytes + 3.2 Terabytes / .75


11.95 Terabytes / .75


16 Terabytes

 1 Terabyte = 1,000,000 Megabytes when making this calculation

Since most come with at least 4 drives, smaller PACS typically come in sizes that are divisible by 4.  So, when calculating the size you need, round up to the nearest number of Terabytes divisible by 4.  If the PACS size you need is greater than 18 Terabytes, you should round up to the nearest 6 since you will likely have a 6 or more drive PACS.

Using this formula will be a great rule of thumb in how large a PACS you should consider.  Of course, we always suggest you should consult with a professional before buying a PACS to ensure that every consideration of your specific practice is taken into consideration. However, we feel strongly that everyone should have the knowledge to better their existing infrastructure. 

Final thought

Having the wrong size PACS can negatively affect your pratice. You don't want to be caught without sufficent stores for your images, and you most certainly don't want to be overpaying for your solution. Having the right knowledge can significantly behoove your unique situation. That's what we are here for. Interested in figuring out once and for all what size PACS you really need? Click here, and fill out the form. We'll do all the calculations for you...for free. No strings attached. 

PACS sizing calculator

Topics: PACS size

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