Impact of various Impact of various imaging modalities on imaging modalities on PACS archiving and PACS archiving and storagestorage

Eugene Mah, M.Sc.Eugene Mah, M.Sc.

Jay Crawford, MHAJay Crawford, MHA

Medical University of South Medical University of South CarolinaCarolina

PACS Archive AnalysisPACS Archive Analysis

11 years worth of archived studies 11 years worth of archived studies were analyzedwere analyzed

Monthly data obtained for 7 Monthly data obtained for 7 modalitiesmodalities

Storage requirements computed Storage requirements computed based on estimated image file sizesbased on estimated image file sizes

Did not consider compression by Did not consider compression by the archivethe archive

Modalities ExaminedModalities Examined

CTCT Computed TomographyComputed Tomography

MRMR Magnetic Resonance ImagingMagnetic Resonance Imaging

CRCR Computed RadiographyComputed Radiography

NMNM Nuclear MedicineNuclear Medicine

MGMG Digital MammographyDigital Mammography

PTPT PET/PET CTPET/PET CT

USUS UltrasoundUltrasound

Image File SizesImage File Sizes

ModalityModality Matrix SizeMatrix Size File Size File Size (MB)(MB)

CTCT 51251222 0.50.5

MRMR 51251222 0.50.5

CRCR 2048x24942048x2494 1010

NMNM 25625622 0.1280.128

MGMG 4096x33284096x3328 26.626.6

PTPT 12812822 0.0320.032

USUS 640x480640x480 0.30.3File sizes based on 2 bytes/pixel except for US which are screen captures (1 byte/pixel)

PACS Archive AnalysisPACS Archive Analysis

Looked for changes in storage Looked for changes in storage requirements due torequirements due to– additional modalitiesadditional modalities– additional equipmentadditional equipment– changes in technologychanges in technology– protocol changesprotocol changes– increased volumeincreased volume

Data collected from DB Data collected from DB queryquery Number of studies per monthNumber of studies per month Total images per monthTotal images per month Average images/study per monthAverage images/study per month Maximum images in a studyMaximum images in a study Minimum images in a studyMinimum images in a study

Computed statisticsComputed statistics

GB per monthGB per month For CT and MR:For CT and MR:

– Number of studies per month per Number of studies per month per scannerscanner

– Number of images per month per Number of images per month per scannerscanner

– GB per month per scannerGB per month per scanner

Archiving strategy at Archiving strategy at MUSCMUSC Archive everythingArchive everything Better data integrityBetter data integrity

– Validated against the Validated against the RIS RIS

– Full data set archivedFull data set archived– Can retrospectively Can retrospectively

reconstruct any study reconstruct any study without date limitswithout date limits

More storage More storage consumptionconsumption– Increased archival Increased archival

costscosts– Increased Increased

transmission and transmission and retrieval timesretrieval times

PACS Workflow Manager

Recon WorkstationReading Area 2

Recon WorkstationReading Area 1

Thin Client Server

DIC

OM CT Studies

AutoRouted

Query/Retrieve

Thin Clients

20 Tb Disk Storage

2 Tb Disk Storage

Th

in S

lice

s

Full Data Set Storage

CT

Query/R

etrieve

Qu

ery

/Re

trie

ve

Notable time pointsNotable time points

CT scannersCT scanners– Upgraded from single to dual/quad Upgraded from single to dual/quad

slice scanners in 2000/2001.slice scanners in 2000/2001.– Dual/quad slice replaced with 16 slice Dual/quad slice replaced with 16 slice

in 2003.in 2003.– Replaced 1 16 slice with 64 slice, Replaced 1 16 slice with 64 slice,

added CT-Sim, 1 64 slice in added CT-Sim, 1 64 slice in 2004/2005.2004/2005.

– 1 16 slice replaced with dual source 1 16 slice replaced with dual source scanner in 2006.scanner in 2006.

Notable time pointsNotable time points

Converted to all digital Converted to all digital mammography in 2005 (4 units)mammography in 2005 (4 units)

3T MRI magnet (#4) added in 3T MRI magnet (#4) added in 20022002

Open MRI magnet (#5) added in Open MRI magnet (#5) added in 20052005

PET added in 2001. Upgraded to PET added in 2001. Upgraded to PET/CT-16 in 2006PET/CT-16 in 2006

Studies Per MonthStudies Per Month

Images Per MonthImages Per Month

Storage RequirementsStorage Requirements

Storage RequirementsStorage Requirements

Studies Per GBStudies Per GB

Images Per GBImages Per GB

Case Study: CRCase Study: CR

Relatively stableRelatively stable Majority of growth tends to come Majority of growth tends to come

from additional service locationsfrom additional service locations Large images, low volumeLarge images, low volume Generally used to dictate PACS Generally used to dictate PACS

requirementsrequirements

CR: Studies/MonthCR: Studies/Month

CR: Total CR: Total images/monthimages/month

CR: GB Per MonthCR: GB Per Month

Case Study: CTCase Study: CT

CT contributes most in terms of # of CT contributes most in terms of # of imagesimages

Small images but high volumeSmall images but high volume Majority of archive storage is now used Majority of archive storage is now used

for CT imagesfor CT images Increased use of 3D reconstructions Increased use of 3D reconstructions

and multi-planar reformats means and multi-planar reformats means studies containing 10 000 images are studies containing 10 000 images are now routinenow routine

CT: Studies/MonthCT: Studies/Month

CT: Studies/scannerCT: Studies/scanner

CT: Total CT: Total images/monthimages/month

CT: Average CT: Average Images/StudyImages/Study

CT: Max images/studyCT: Max images/study

CT: Average CT: Average GB/ScannerGB/Scanner

Case Study: Case Study: Technology changes in Technology changes in CTCT One physical CT scanner location One physical CT scanner location

analyzed from 1998 to 2006analyzed from 1998 to 2006 Outpatient settingOutpatient setting Location changed from single Location changed from single

slice to 16 slice to dual-source slice to 16 slice to dual-source scanner during this time periodscanner during this time period

Studies/monthStudies/month

Total images/monthTotal images/month

Images/study/monthImages/study/month

Case Study: MRICase Study: MRI

Few changes in technology aside Few changes in technology aside from additional scannersfrom additional scanners

Acquisition protocols tend to be Acquisition protocols tend to be relatively staticrelatively static

Changes in storage requirements Changes in storage requirements mostly due to increases in volumemostly due to increases in volume

MRI: Studies/MonthMRI: Studies/Month

MRI: Studies/ScannerMRI: Studies/Scanner

MRI: Total MRI: Total Images/MonthImages/Month

MRI: Average MRI: Average Images/StudyImages/Study

MRI: Max images/studyMRI: Max images/study

MRI: Average MRI: Average GB/ScannerGB/Scanner

Case Study: PET/CT Case Study: PET/CT

Started with dedicated PET Started with dedicated PET scanner shared with neighbouring scanner shared with neighbouring hospital in 2001hospital in 2001

Upgraded to non-shared PET/CT-Upgraded to non-shared PET/CT-16 in 200616 in 2006

Current PET/CT workload is 6-7 Current PET/CT workload is 6-7 patients/daypatients/day

Case Study: PET/CTCase Study: PET/CT

Data sent to PACSData sent to PACS– CT (3.75 mm slice thickness)CT (3.75 mm slice thickness)– Non-attenuation corrected PETNon-attenuation corrected PET– Attenuation corrected PETAttenuation corrected PET– Screen captures of axial, coronal, Screen captures of axial, coronal,

sagittal fused slicessagittal fused slices

PET/CT: Studies Per PET/CT: Studies Per MonthMonth

PET/CT: Images Per PET/CT: Images Per MonthMonth

PET/CT: Average PET/CT: Average Images Per StudyImages Per Study

PET/CT: GB Per MonthPET/CT: GB Per Month

Data RetentionData Retention

Using the GB/Month data, we can Using the GB/Month data, we can calculate how many months of calculate how many months of online storage a given size of disk online storage a given size of disk array can holdarray can hold

Can also calculate how large the Can also calculate how large the disk array must be to maintain N disk array must be to maintain N months of data onlinemonths of data online

Study RetentionStudy Retention

24 Month Retention24 Month Retention

Storage Storage ConsiderationsConsiderations

Changing storage Changing storage requirementsrequirements Changes significantly with Changes significantly with

widespread implementation of widespread implementation of MDCTMDCT

In the early days of PACS, CR In the early days of PACS, CR dominated storage requirementsdominated storage requirements

Major contributors to PACS storage Major contributors to PACS storage requirements are CR, CT, MR, MGrequirements are CR, CT, MR, MG– Make up about 98% of storage Make up about 98% of storage

requirements at MUSCrequirements at MUSC

Changing storage Changing storage requirementsrequirements Digital mammography has a large Digital mammography has a large

effect on storage requirementseffect on storage requirements– Low volume but very large imagesLow volume but very large images

Dynamic multi-frame data looked Dynamic multi-frame data looked at brieflyat briefly– Not a major contributor to storageNot a major contributor to storage– Currently ~10% of totalCurrently ~10% of total– US is the biggest contributorUS is the biggest contributor

Growth PatternsGrowth Patterns

MDCTMDCT– Exponential growth in CT images Exponential growth in CT images

during early phase as new protocols during early phase as new protocols are developed and implemented and are developed and implemented and scanner capabilities are exploredscanner capabilities are explored

– Growth rate expected to level off as Growth rate expected to level off as capacity is reached and scan capacity is reached and scan protocols establishedprotocols established

Predicting Storage Predicting Storage RequirementsRequirements Obtain monthly data on storage Obtain monthly data on storage

history (# images each month for CR, history (# images each month for CR, CT, MR, MG) for the past yearCT, MR, MG) for the past year

Estimate total storage per month Estimate total storage per month based on image file sizesbased on image file sizes

Examine data for trendsExamine data for trends Apply a realistic model (linear, Apply a realistic model (linear,

polynomial, power, exponential) to polynomial, power, exponential) to forecast future growthforecast future growth

Future NeedsFuture Needs

CR, CT, MR, MG are the Big 4CR, CT, MR, MG are the Big 4 Planning for future PACS archiving Planning for future PACS archiving

or archive expansion needs to or archive expansion needs to consider current storage trendsconsider current storage trends

MDCT and digital mammography MDCT and digital mammography places large demands on storage places large demands on storage and must be consideredand must be considered