Impact of various imaging modalities on PACS archiving and storage

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Impact of various imaging modalities on PACS
archiving and storage

• Eugene Mah, M.Sc.
• Jay Crawford, MHA
• Medical University of South Carolina

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PACS Archive Analysis

• 11 years worth of archived studies were analyzed
• Monthly data obtained for 7 modalities
• Storage requirements computed based on estimated
  image file sizes
• Did not consider compression by the archive

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Modalities Examined
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Image File Sizes
File sizes based on 2 bytes/pixel except for US
which are screen captures (1 byte/pixel)
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PACS Archive Analysis

• Looked for changes in storage requirements due to
• additional modalities
• additional equipment
• changes in technology
• protocol changes
• increased volume

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Data collected from DB query

• Number of studies per month
• Total images per month
• Average images/study per month
• Maximum images in a study
• Minimum images in a study

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Computed statistics

• GB per month
• For CT and MR
• Number of studies per month per scanner
• Number of images per month per scanner
• GB per month per scanner

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Archiving strategy at MUSC

• Archive everything
• Better data integrity
• Validated against the RIS
• Full data set archived
• Can retrospectively reconstruct any study without
  date limits
• More storage consumption
• Increased archival costs
• Increased transmission and retrieval times

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Notable time points

• CT scanners
• Upgraded from single to dual/quad slice scanners
  in 2000/2001.
• Dual/quad slice replaced with 16 slice in 2003.
• Replaced 1 16 slice with 64 slice, added CT-Sim,
  1 64 slice in 2004/2005.
• 1 16 slice replaced with dual source scanner in
  2006.

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Notable time points

• Converted to all digital mammography in 2005 (4
  units)
• 3T MRI magnet (4) added in 2002
• Open MRI magnet (5) added in 2005
• PET added in 2001. Upgraded to PET/CT-16 in 2006

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Studies Per Month
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Studies Per Month
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Images Per Month
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Images Per Month
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Storage Requirements
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Storage Requirements
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Storage Requirements
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Studies Per GB
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Images Per GB
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Case Study CR

• Relatively stable
• Majority of growth tends to come from additional
  service locations
• Large images, low volume
• Generally used to dictate PACS requirements

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CR Studies/Month
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CR Total images/month
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CR Average Images/Study
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CR GB Per Month
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Case Study CT

• CT contributes most in terms of of images
• Small images but high volume
• Majority of archive storage is now used for CT
  images
• Increased use of 3D reconstructions and
  multi-planar reformats means studies containing
  10 000 images are now routine

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CT Studies/Month
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CT Studies/scanner
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CT Total images/month
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CT Average Images/Study
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CT Max images/study
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CT Average GB/Scanner
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Case Study Technology changes in CT

• One physical CT scanner location analyzed from
  1998 to 2006
• Outpatient setting
• Location changed from single slice to 16 slice to
  dual-source scanner during this time period

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Studies/month
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Total images/month
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Images/study/month
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Case Study MRI

• Few changes in technology aside from additional
  scanners
• Acquisition protocols tend to be relatively
  static
• Changes in storage requirements mostly due to
  increases in volume

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MRI Studies/Month
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MRI Studies/Scanner
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MRI Total Images/Month
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MRI Average Images/Study
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MRI Max images/study
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MRI Average GB/Scanner
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Case Study PET/CT

• Started with dedicated PET scanner shared with
  neighbouring hospital in 2001
• Upgraded to non-shared PET/CT-16 in 2006
• Current PET/CT workload is 6-7 patients/day

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Case Study PET/CT

• Data sent to PACS
• CT (3.75 mm slice thickness)
• Non-attenuation corrected PET
• Attenuation corrected PET
• Screen captures of axial, coronal, sagittal fused
  slices

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PET/CT Studies Per Month
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PET/CT Images Per Month
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PET/CT Average Images Per Study
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PET/CT GB Per Month
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Data Retention

• Using the GB/Month data, we can calculate how
  many months of online storage a given size of
  disk array can hold
• Can also calculate how large the disk array must
  be to maintain N months of data online

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Study Retention
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24 Month Retention
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Storage Considerations
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Changing storage requirements

• Changes significantly with widespread
  implementation of MDCT
• In the early days of PACS, CR dominated storage
  requirements
• Major contributors to PACS storage requirements
  are CR, CT, MR, MG
• Make up about 98 of storage requirements at MUSC

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Changing storage requirements

• Digital mammography has a large effect on storage
  requirements
• Low volume but very large images
• Dynamic multi-frame data looked at briefly
• Not a major contributor to storage
• Currently 10 of total
• US is the biggest contributor

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Growth Patterns

• MDCT
• Exponential growth in CT images during early
  phase as new protocols are developed and
  implemented and scanner capabilities are explored
• Growth rate expected to level off as capacity is
  reached and scan protocols established

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Predicting Storage Requirements

• Obtain monthly data on storage history ( images
  each month for CR, CT, MR, MG) for the past year
• Estimate total storage per month based on image
  file sizes
• Examine data for trends
• Apply a realistic model (linear, polynomial,
  power, exponential) to forecast future growth

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Future Needs

• CR, CT, MR, MG are the Big 4
• Planning for future PACS archiving or archive
  expansion needs to consider current storage
  trends
• MDCT and digital mammography places large demands
  on storage and must be considered