Impact of various imaging modalities on PACS archiving and storage Eugene Mah, M.Sc. Jay Crawford, MHA Medical University of South Carolina

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

Modalities Examined CT Computed Tomography MR Magnetic Resonance Imaging CR Computed Radiography NM Nuclear Medicine MG Digital Mammography PT PET/PET CT USUltrasound

Image File Sizes Modality Matrix Size File Size (MB) CT MR 0.5 CR2048x NM MG4096x PT US640x File sizes based on 2 bytes/pixel except for US which are screen captures (1 byte/pixel)

PACS Archive Analysis Looked for changes in storage requirements due to Looked for changes in storage requirements due to –additional modalities –additional equipment –changes in technology –protocol changes –increased volume

Data collected from DB query Number of studies per month Number of studies per month Total images per month Total images per month Average images/study per month Average images/study per month Maximum images in a study Maximum images in a study Minimum images in a study Minimum images in a study

Computed statistics GB per month GB per month For CT and MR: For CT and MR: –Number of studies per month per scanner –Number of images per month per scanner –GB per month per scanner

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

Notable time points CT scanners CT scanners –Upgraded from single to dual/quad slice scanners in 2000/2001. –Dual/quad slice replaced with 16 slice in –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.

Notable time points Converted to all digital mammography in 2005 (4 units) Converted to all digital mammography in 2005 (4 units) 3T MRI magnet (#4) added in T MRI magnet (#4) added in 2002 Open MRI magnet (#5) added in 2005 Open MRI magnet (#5) added in 2005 PET added in Upgraded to PET/CT-16 in 2006 PET added in Upgraded to PET/CT-16 in 2006

Studies Per Month

Images Per Month

Storage Requirements

Studies Per GB

Images Per GB

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

CR: Studies/Month

CR: Total images/month

CR: Average Images/Study

CR: GB Per Month

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

CT: Studies/Month

CT: Studies/scanner

CT: Total images/month

CT: Average Images/Study

CT: Max images/study

CT: Average GB/Scanner

Case Study: Technology changes in CT One physical CT scanner location analyzed from 1998 to 2006 One physical CT scanner location analyzed from 1998 to 2006 Outpatient setting Outpatient setting Location changed from single slice to 16 slice to dual-source scanner during this time period Location changed from single slice to 16 slice to dual-source scanner during this time period

Studies/month

Total images/month

Images/study/month

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

MRI: Studies/Month

MRI: Studies/Scanner

MRI: Total Images/Month

MRI: Average Images/Study

MRI: Max images/study

MRI: Average GB/Scanner

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

Case Study: PET/CT Data sent to PACS 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

PET/CT: Studies Per Month

PET/CT: Images Per Month

PET/CT: Average Images Per Study

PET/CT: GB Per Month

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

Study Retention

24 Month Retention

Storage Considerations

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

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

Growth Patterns MDCT 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

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

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