EXACT CT Scanner
TM
EXACT: The heart of an
FAA-certified Explosives
Detection Scanner
3-D Image
System Block Diagram
X-ray CT scanner
Helical Cone Beam Data
Image Reconstruction
1.5 GOp/s, 50 processors
Automatic Explosives Detection
4 processors
3D Image Display
Reconstruction Engine
Requirements
Control and Status
(RS232)
Dual-energy
Helical Conebeam data
Images (SCSI)
Nutating Slice
Image Reconstruction
450 3D bags /hr
6064 samples/view
1.5 GOp/s
 90 2D slices/s
1080 views/s
Reconstruction Algorithm
• Nutating Slice
Reconstruction
• Prerequisite:
cone beam data
corrected for
detector
imperfections
Nutating Slice Reconstruction
HELICAL CONE-BEAM
SKYpack* Computer
• Application-specific repackaging of
standard 6U VME product
– originally developed for DARPA SAST
program
• Dual use in commercial applications
– explosives detection
– medical CT image reconstruction
*SKY Computers, Chelmsford, MA
SKYpack Components
• 1 RISC processor for I/O control
• 12 RISC processors for compute
processing
–
Labeled AP0-11 in diagram
• 6 SHARC processors
• 6 ASIC processors
• Shared Bus: SKYchannel
SKYpack Partitioning
• High and low energy images
reconstructed on different SKYpacks
• Processes are data driven and
asynchronous
Processor
Memory
Data Entry Point
SKYburst
Platform 2
Platform 0
AP 0
AP 1
AP 8
AP 9
64 MB
AP 2
AP 10
AP 3
AP 11
Platform 1
64 MB
SKY-CT
AP 4
AP 5
SCSI
SHARCS 4 MB
64 MB
AP 6
ASICS
AP 7
4 MB
SKYchannel
Control
Processor
SKYpack
RS232
SKYpack Partitioning
RS232
Correction
Cone Fan
Fan Hybrid
AP 0
o/p
0
Hybrid
i/p
AP 8
i/o
0
i/p
AP 9
i/o
1
Input
Data
AP 7
o/p
21
Filtering
Parallel
SHARC 0
SHARC 5
SKYpack Partitioning cont’d
Image Formatting
And Transfer (SCSI)
Backprojection
ASIC 0
Untilt
L Video
Memory
i/p
ASIC 5
i/o
0
o/p
0
AP 11
AP 10
R Video
Memory
i/o
13
o/p
249
SKYpack Partitioning
• System processor distributes cone
beam data to AP 0-7
• AP 0 does RS232 communication and
controls other processors
• AP 0-7 correct and convert cone to
hybrid data
• Each cone view contributes to 22
slices, every 12th view a new slice is
created
SKYpack Partitioning
• AP 8-9 convert hybrid data to parallel
• SHARCs high pass filter parallel data
using FFT
• ASICs backproject filtered data into
tilted slices
• AP 10 untilts tilted slices into parallel
• AP 11 formats images and carries out
SCSI communication
Verification and Validation
• Offline, single process software was
implemented
• Simulations to verify offline software
• Intermediate results from offline
software matched with online
software
Automatic Detection
Subsystem
• Consists of four processors
• Does image analysis, archiving and
display
• Image data is propagated along two
paths that search for two classes of
explosives
• Each path uses detection and
discrimination algorithms
References
• “Nutating Slices CT Image
Reconstruction Apparatus and
Method” United States Patent: 5,802,134, September
1998
• “Parallel Processing Architecture for
Computed Tomography Scanning
System using Non-Parallel Slices”
United States Patent: 5,887,047, March 23, 1999
• “Computed Tomography Apparatus
and Method for Classifying Objects”
United States Patent: 6,317,508, November 13, 2001