Transcript Computed Radiology

PACS
What is PACS ?
Picture Archiving and Communications
System (actually more than name implies)
 PACS provides the ability to electronically
(ie, computer and network technology) to:

–
–
–
–
–
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

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)

Faster Medical Care Delivery:
– Images available to reader at exam completion
– Clinical consults possible via remote access

Potential Cost Savings:
– Eliminate lost film
– Improved productivity
– Eliminate lost film preventing lost revenue
PACS COMPONENTS
Network (to acquire/distribute/transmit)
 Servers (to maintain/control database)
 Storage (secondary storage devices)

– Short term (current studies)
– Long term (archives)

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, 2K x 1.5 K = 3 M)
1 K x 1 M = 1 G (Gig), etc
Digital images consist of a “matrix” of “pixels”
Each pixel contains a binary number representing
the gray level of the pixel
One or two bytes/pixel
– One: (US, NM)
– Two (CT, MR, DR)
PACS Basics: “Size” of Studies
 Example
1: 4-View Digital Radiography Exam:
– 2K x 2.5K matrix: 2K x 2.5K = 5 MegaPixels (MP)
– 5 MP x 2 bytes/pixel = 10 Megabytes (MB)/Image
– 4 images/exam x 10 MB/image = 40 MB/Exam
 Example
2: Average CT Exam (300 images):
– 512 x 512 matrix: 0.5K x 0.5K = 0.25 MegaPixels
– 0.25 MP x 2 bytes/pixel = 0.5 Megabytes/image
– 300 images/exam x 0.5 MB/image = 150 MB/exam
 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

“Communications” part of PACS:
– Acquire/ distribute/transmit images
– Entirely “standards” based

Network Hardware:
– Ethernet (most common) using 10- or 100-Base T
– Gigabit (1000Base-T) & Fiber channel “backbones”

Protocols and Software:
– Network protocol: TCP/IP (the Internet Standard)
– Image Formats: DICOM 3 (this is key)
PACS Components: Network Issues

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

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
Network (to acquire/distribute/transmit)
 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)
 Servers (to maintain/control database)
 Storage (using secondary storage devices)

– Short term (current studies):
– Long term (archives)
PACS Components: Storage

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

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
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

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
 Archive
Requirements:
– 5 years x 10 TB/year = 50 Terabytes
Note: 50 TB = 51,200 Gigabytes !!
50 TB = 52,428,800 Megabytes !!
PACS COMPONENTS
Network
 Servers
 Storage
 Workstations

–reading/clin view
–usually high end PC
–Diag: 2-4 monitors
–Often 3rd monitor
(for color/text)
PACS Components: Workstations

Diagnostic Workstation: (for radiologists)

Diagnostic Quality Displays (expensive)
– Very High Resolution:
• 2K x 1.5K for radiography (1280x1024 max-avg PC)
• 2K x 2.5K common (required for digital mammo)
– Very High Brightness: to display graylevels
• 10 bits/pixel (1024 graylevels displayed
• 700 cd/m2 (70-120 for normal CT monitor)