PACS What is PACS Picture Archiving and Communications

PACS

What is PACS ? Picture Archiving and Communications System (actually more than name implies) n PACS provides the ability to electronically (ie, computer and network technology) to: n – Input images from (digital) modalities – Distribute images to PCs and workstations – Read on computer display (diagnostic & clinical) – Store (both long and short term) images – Transmit (to other areas or off-site)

Reasons for PACS n More Efficient Workflow: – RTs spend up to 50% of time “handling” film – Reader cannot effectively interpret exams on film consisting of hundreds of images (eg, MSCT) n Faster Medical Care Delivery: – Images available to reader at exam completion – Clinical consults possible via remote access n Potential Cost Savings: – Eliminate lost film – Improved productivity – Eliminate lost film preventing lost revenue

PACS COMPONENTS Network (to acquire/distribute/transmit) n Servers (to maintain/control database) n Storage (secondary storage devices) n – Short term (current studies) – Long term (archives) n Workstations (reading and clinical review) In many cases, specials requirements for PACS push the limits of technology

PACS Basics: “Size” of Studies Useful Facts and Terms to Know: 1 K x 1 K = 1 M (eg, 2 K x 1. 5 K = 3 M) n 1 K x 1 M = 1 G (Gig), etc n Digital images consist of a “matrix” of “pixels” n Each pixel contains a binary number representing the gray level of the pixel n One or two bytes/pixel n – One: (US, NM) – Two (CT, MR, DR)

PACS Basics: “Size” of Studies n Example 1: 4 -View Digital Radiography Exam: – 2 K x 2. 5 K matrix: 2 K x 2. 5 K = 5 Mega. Pixels (MP) – 5 MP x 2 bytes/pixel = 10 Megabytes (MB)/Image – 4 images/exam x 10 MB/image = 40 MB/Exam n Example 2: Average CT Exam (300 images): – 512 x 512 matrix: 0. 5 K x 0. 5 K = 0. 25 Mega. Pixels – 0. 25 MP x 2 bytes/pixel = 0. 5 Megabytes/image – 300 images/exam x 0. 5 MB/image = 150 MB/exam n Example 3: Large CT Exam (1200 images): – 0. 5 Megabytes/image (same as above) – 1200 images/exam x 0. 5 MB/image = 600 MB/exam

PACS Components: Network n “Communications” part of PACS: – Acquire/ distribute/transmit images – Entirely “standards” based n Network Hardware: – Ethernet (most common) using 10 - or 100 -Base T – Gigabit (1000 Base-T) & Fiber channel “backbones” n Protocols and Software: – Network protocol: TCP/IP (the Internet Standard) – Image Formats: DICOM 3 (this is key)

PACS Components: Network Issues n Average CT Exam (150 MB) on 100 -Base T – 100 Base-T: maximum 100 Mbits/sec (60 average) – 150 Mbytes x 8 bits/byte = 1200 Mbits – 1200 Mbits/60 Mbits/second = 20 seconds n Large CT Exam (600 MB) on 100 -Base T – 100 Base-T: maximum 100 Mbits/sec (60 average) – 600 Mbytes x 8 bits/byte = 4800 Mbits – 4800 Mbits/60 Mbits/second = 80 seconds (seems like forever if you’re sitting and waiting)

PACS COMPONENTS n Network (to acquire/distribute/transmit) n Servers: maintain/control database (database is the exam directory: patient demographics, what exams performed and when, where the images are stored, etc): – Must maintains database for 5 or more years – Size and speed requirements depend on facility – May have multiple servers to share duties – May have “mirrored” servers for high availability

PACS COMPONENTS Network (to acquire/distribute/transmit) n Servers (to maintain/control database) n Storage (using secondary storage devices) n – Short term (current studies): – Long term (archives)

PACS Components: Storage n Short Term Storage: – For current studies (and relevant prior studies) – Need fast retrieval: when reader selects exam to read, server must deliver it within seconds – Most Common: RAID – Typically need 3 -4 weeks of short term storage – Prefer to have ~ 1 year (rapid access to priors) – Actual amount is cost/performance trade-off

PACS Components: Storage n Long Term Storage: For “archived”studies – Speed not as critical (usually exams pre-fetched) – Must have copies at two sites (JCAHO, HIPAA) – Need to archive at least 5 years (CT state law) – Type of archive basically cost/speed tradeoff n Archive Technologies: – Hard disk based: fastest, most expensive – DVD: intermediate speed, moderate cost – Tape (DLT, LTO, etc): cheap but slow (reliable? ? ) – Offsite archiving (Service Provider)

PACS Storage Issues: Data Volume n Volume of Radiology Data (HH): – CT: 40, 000 exams x 150 MB/exam = 6 Terabytes – Radiography: 75, 000 x 40 MB/exam = 3 Terabytes – All others: 1 Terabyte TOTAL: 10 TB/years n Archive Requirements: – 5 years x 10 TB/year = 50 Terabytes Note: 50 TB = 51, 200 Gigabytes !! 50 TB = 52, 428, 800 Megabytes !!

PACS COMPONENTS n Network n Servers n Storage n Workstations –reading/clin view –usually high end PC –Diag: 2 -4 monitors –Often 3 rd monitor (for color/text)

PACS Components: Workstations n Diagnostic Workstation: (for radiologists) n Diagnostic Quality Displays (expensive) – Very High Resolution: • 2 K x 1. 5 K for radiography (1280 x 1024 max-avg PC) • 2 K x 2. 5 K common (required for digital mammo) – Very High Brightness: to display graylevels • 10 bits/pixel (1024 graylevels displayed • 700 cd/m 2 (70 -120 for normal CT monitor)