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CIVM research

Xiaolian Guo - 2012 international visiting PhD student (supervised by Cristian Badea (with Samuel M. Johnston, G. Allan Johnson, Cristian T. Badea)

Comparision of sampling strategies for dual-energy micro-CT

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(Information extracted from a poster presented at SPIE Medical Imaging 2012: Physics of Medical Imaging, and included in Proceedings SPIE 8313: 83133, 2012.) Although (now Dr.) Guo returned to her home country and graduated from Tsinghua University in China, her work is still contributing to the success of our micro-CT imaging.

SUMMARY

  • In the clinic, dual energy CT provides better separation / classification of material composites vs. standard CT.
  • But for preclinical imaging, dual energy micro-CT is less common, and no commercial micro-CT system exists that can implement all these sampling strategies (single-source sequential; simultaneous dual-source; single source with kVp switching), and a new proposed sampling strategy that combines dual source and kVp switching).
  • We implemented and compared these various small animal dual source micro-CT imaging imaging strategies on equipment at the Center for In Vivo Microscopy that can handle all these techniques.
SAMPLING PROTOCOLS FOR DUAL-ENERGY MICRO-CT

 

(a) Single source sequential: Available on standard micro-CT systems. Doubles scanning time and is prone to misregistration errors.

 

(b) Dual source simultaneous: 2 tubes firing simultaneously at 2 different kVps. Scanning time equals that of a single scan. Requires geo-metric calibration procedure that will put the 2 reconstructed sets in the same reference system [2]

 

(c) Single source with kVp switching: Requires software control of the EMD generator during scanning. Achieved via a serial port communication with a LabVIEW sampling script. Response time was about 1.6 seconds.

 

(d) Dual source with kVp switching: Combines the previous strategies. Low and high kVps alternate for each source in sequential views. With our system, sampling time was close to that of single source with kVp switching. Interleaving projections from the two imaging chains creates better registration between the two energy sets.


   
 
This figure shows micro-CT axial slices from an animal study. Two regions containing calcium (bone) and iodine-enhanced blood at the two energies were imaged, and methods were compared. The kVp switching scan produced the cleanest decomposed images.

 

Reconstructions of the different scans with filtered backprojection at 40 kVp and 80 kVp and the decomposed iodine (I) and calcium-bone (Ca) images.

(1) Single source sequential

(2) Dual source simultaneous

(3) Single source with kVp switching

(4) Dual source with kVp switching

(White arrows indicate errors in decomposition resulting from imperfect registration of the two 40 and 80 kVp sets.)

 


CONCLUSIONS:

  • Each protocol has tradeoffs in complexity, time, and image quality.
  • Dual source is fastest, but involves more hardware that must be synchronized and calibrated, and the imperfections in the geometric calibration may lead to artifacts in the decomposed images.
  • The voltage-switching scan produces images free of motion or misregistration artifacts, but takes more than conventional scan time and requires using a software-controlled generator.
  • The novel combined dual source and kVp switching has the potential to reduce sampling time and provide better decomposition performance.
REFERENCES: Although Two new publications now in press demonstrate the dual energy technique, and this work also contributed to another publication:

R Bhavane, C Badea, KB Ghaghada, D Clark, D Vela, Anoosha Moturu, Ananth Annapragada, GA Johnson, JT Willerson, A Annapragada, Dual-energy computed tomography imaging of atherosclerotic plaques in a mouse model using a liposomal-iodine nanoparticle contrast agent, Circulation, in press 2013.

Darin P. Clark, Ketan Ghaghada, Everett J. Moding, David G. Kirsch, Cristian T. Badea, In vivo characterization of tumor vasculature using iodine and gold nanoparticles and dual energy micro-CT, Physics in Medicine and Biology, in press 2013.

CT Badea, X Guo, D Clark, SM Johnston, C Marshall, C Piantadosi. Lung imaging in rodents using dual energy micro-CT. Proceedings of SPIE 8317, 83171I, 2012

 

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