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Temporal Resolution Improvement in Single Source and Dual ... fileTemporal Resolution Improvement in...
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Temporal Resolution Improvement in Single Source and Dual Source CT Clemens Maaß and Marc Kachelrieß Institute of Medical Physics, University of Erlangen-Nürnberg, Germany Purpose: Recently a new method called TRI- PICCS (Temporal Resolution Improved Prior Image Constrained Compressed Sensing) was proposed to improve the temporal resolution of a single source (SS) cardiac CT scan [1] (figures 1+2). This method aims at doubling the temporal resolution and at maintaining homogeneous temporal resolution independently of the location and the motion direction of a vessel. The aims of our study are two-fold. First we independently evaluate TRI-PICCS regarding the reported improvements and then we extend the algorithm to dual source CT and evaluate the results there as well. TRI-PICCS is compared with a standard short scan recon- struction regarding two properties: The temporal resolution (TR) and the dependency of the TR on the motion direction of a vessel (=reproducibility). Both properties are evaluated as a function of the position within the field of measurement (FOM). Methods: Simulations are used in order to ensure known and well-defined vessel motion. The scanner geometry and the rotation time chosen (280 ms) correspond to a state-of-the-art dual-source spiral cone- Results: Figure 7 shows the results of the anatomy preservation study. It can be observed that the temporal resolution of the inserts can be improved, however, the anatomy is also affected especially using the iTRI-CS method. The findings are the same for single source and dual source geometry. Figure 10 shows the results of the temporal resolution assessment. The visualized FOV is slightly larger than a 20 cm diameter circle. The single source TRI-PICCS and iTRI-CS results show significantly less temporal resolution than the standard dual source short scan. However, compared to a short scan of the same geometry, these compressed sensing based reconstruc- tions deliver slightly improved temporal resolution. The reproducibility of the single source method is low while the dual source methods show a high reproducibility for all methods. Conclusion: TRI-PICCS in single source CT shows less temporal resolution than standard reconstructions of dual source data. Depending on the location and motion direction TRI-PICCS may slightly im- prove the temporal resolution. In single source geometry the reproducibility is Figure 1: The recently published TRI-PICCS algorithm proposes to double the temporal resolution of a single source scanner. Figure 3: A border case of TRI-PICCS, not using a prior image during reconstruction (but only for initiali- zation) is investigated as well. Figure 2: In order to improve the temporal resolution the TRI-PICCS algorithm aims to reconstruct from a limited number of views. Figure 4: The straight-forward extension of the single source TRI-PICCS ideas on the dual source case are also investigated. Send correspondence requests to: Clemens Maaß Institute of Medical Physics (IMP), University of Erlangen–Nürnberg Henkestr. 91, 91052 Erlangen, Germany [email protected] state-of-the-art dual-source spiral cone- beam CT scanner (Somatom Definition Flash, Siemens Healthcare, Forchheim, Germany). In a first study we simulate sixteen calcifications at different locations that move either radially or azimuthally all using the same motion profile (figure 5). These simulated rawdata are added to the rawdata obtained by forward projecting a static cardiac CT volume. This allows us to assess the anatomy preservation during the reconstructions. For this study two motion profiles according to figure 6 are used. The first profile moves the calcifications with constant velocity while the second profile has a short rest interval where no motion is present. In a second study we use the same reconstruction parameters to assess the temporal resolution and the reproducibility (figures 8+9). Thereby we vary the motion direction and the position of the vessel in the FOM. As a result we are able to provide maps of the temporal resolution and its motion direction dependency as a function of the position in the FOM. To quantify the temporal resolution we vary the length of the rest interval and the shortest rest interval that still allows to reconstruct the correct CT-value at the vessel position is taken as temporal resolution of a given algorithm at a given FOM- position. This poster is available for download at www.imp.uni-erlangen.de. source geometry the reproducibility is thereby reduced. The additionally inves- tigated iTRI-CS algorithm shows, that using the prior image for initialization only and dropping it for the subsequent iterative reconstruction process can further improve the temporal resolution at the cost of anatomy preservation. Acknowledgment: This work was supported by the Staedtler-Stiftung under grant DS/eh 27/09. Parts of the reconstruction soft- ware, in particular the high speed for- ward and backprojectors and the projec- tion simulator, were provided by Ray- ConStruct GmbH, Nürnberg, Germany. SCCT 2010 Figure 5: In a first study the preservation of the anatomy is investigated by mounting moving vessels in a static patient background. Figure 6: Two different kinds of motion are used. A continuous motion of the vessel and a motion pattern where the vessel rests for a given time interval. Figure 7: Results of the anatomy preservation study using continuous (left) and resting (right) motion. The anatomy is partially lost with CS methods. Figure 8: In a second study the resting motion pattern is used to assess the temporal resolution by evaluation of the blurring of a moving vessel. [1] GH. Chen, J. Tang, and J. Hsieh, Temporal resolution improvement using PICCS in MDCT cardiac imaging, Med. Phys. 36(6), 2009. [2] S. Achenbach, D. Ropers, J. Holle, G. Muschiol, W. G. Daniel, and W. Moshage, In-plane coronary arterial motion velocity: Measurement with electron-beam CT, Radiology 216(2), pp. 457-463, 2000. Figure 9: The motion direction dependency of the temporal resolution (=reproducibility) is quantified as variation of the TR over different motion directions. Figure 10: The results of the temporal resolution assessment show highest TR for dual source geometries. CS methods improve the TR only slightly.
Transcript of Temporal Resolution Improvement in Single Source and Dual ... fileTemporal Resolution Improvement in...
Temporal Resolution Improvement in Single Source and Dual Source CT
Clemens Maaß and Marc KachelrießInstitute of Medical Physics, University of Erlangen-Nürnberg, Germany
Purpose:Recently a new method called TRI-PICCS (Temporal Resolution ImprovedPrior Image Constrained CompressedSensing) was proposed to improve thetemporal resolution of a single source(SS) cardiac CT scan [1] (figures 1+2).This method aims at doubling thetemporal resolution and at maintaininghomogeneous temporal resolutionindependently of the location and themotion direction of a vessel. The aimsof our study are two-fold. First weindependently evaluate TRI-PICCSregarding the reported improvementsand then we extend the algorithm todual source CT and evaluate the resultsthere as well. TRI-PICCS is comparedwith a standard short scan recon-struction regarding two properties: Thetemporal resolution (TR) and thedependency of the TR on the motiondirection of a vessel (=reproducibility).Both properties are evaluated as afunction of the position within the field ofmeasurement (FOM).
Methods:Simulations are used in order to ensureknown and well-defined vessel motion.The scanner geometry and the rotationtime chosen (280 ms) correspond to astate-of-the-art dual-source spiral cone-
Results:Figure 7 shows the results of theanatomy preservation study. It can beobserved that the temporal resolution ofthe inserts can be improved, however,the anatomy is also affected especiallyusing the iTRI-CS method. The findingsare the same for single source and dualsource geometry.Figure 10 shows the results of thetemporal resolution assessment. Thevisualized FOV is slightly larger than a20 cm diameter circle. The single sourceTRI-PICCS and iTRI-CS results showsignificantly less temporal resolutionthan the standard dual source shortscan. However, compared to a shortscan of the same geometry, thesecompressed sensing based reconstruc-tions deliver slightly improved temporalresolution. The reproducibility of thesingle source method is low while thedual source methods show a highreproducibility for all methods.
Conclusion:TRI-PICCS in single source CT showsless temporal resolution than standardreconstructions of dual source data.Depending on the location and motiondirection TRI-PICCS may slightly im-prove the temporal resolution. In singlesource geometry the reproducibility is
Figure 1: The recently published TRI-PICCSalgorithm proposes to double the temporal resolutionof a single source scanner.
Figure 3: A border case of TRI-PICCS, not using aprior image during reconstruction (but only for initiali-zation) is investigated as well.
Figure 2: In order to improve the temporal resolutionthe TRI-PICCS algorithm aims to reconstruct from alimited number of views.
Figure 4: The straight-forward extension of the singlesource TRI-PICCS ideas on the dual source case arealso investigated.
Send correspondence requests to:
Clemens MaaßInstitute of Medical Physics (IMP), University of Erlangen–Nürnberg
Henkestr. 91, 91052 Erlangen, [email protected]
state-of-the-art dual-source spiral cone-beam CT scanner (Somatom DefinitionFlash, Siemens Healthcare, Forchheim,Germany).In a first study we simulate sixteencalcifications at different locations thatmove either radially or azimuthally allusing the same motion profile (figure 5).These simulated rawdata are added tothe rawdata obtained by forwardprojecting a static cardiac CT volume.This allows us to assess the anatomypreservation during the reconstructions.For this study two motion profilesaccording to figure 6 are used. The firstprofile moves the calcifications withconstant velocity while the secondprofile has a short rest interval whereno motion is present.In a second study we use the samereconstruction parameters to assessthe temporal resolution and thereproducibility (figures 8+9). Therebywe vary the motion direction and theposition of the vessel in the FOM. As aresult we are able to provide maps ofthe temporal resolution and its motiondirection dependency as a function ofthe position in the FOM. To quantify thetemporal resolution we vary the lengthof the rest interval and the shortest restinterval that still allows to reconstructthe correct CT-value at the vesselposition is taken as temporal resolutionof a given algorithm at a given FOM-position.
This poster is available for download atwww.imp.uni-erlangen.de.
source geometry the reproducibility isthereby reduced. The additionally inves-tigated iTRI-CS algorithm shows, thatusing the prior image for initializationonly and dropping it for the subsequentiterative reconstruction process canfurther improve the temporal resolutionat the cost of anatomy preservation.
Acknowledgment:This work was supported by theStaedtler-Stiftung under grant DS/eh27/09. Parts of the reconstruction soft-ware, in particular the high speed for-ward and backprojectors and the projec-tion simulator, were provided by Ray-ConStruct GmbH, Nürnberg, Germany.
SCCT 2010
Figure 5: In a first study the preservation of theanatomy is investigated by mounting moving vesselsin a static patient background.
Figure 6: Two different kinds of motion are used. Acontinuous motion of the vessel and a motion patternwhere the vessel rests for a given time interval.
Figure 7: Results of the anatomy preservation studyusing continuous (left) and resting (right) motion. Theanatomy is partially lost with CS methods.
Figure 8: In a second study the resting motion patternis used to assess the temporal resolution byevaluation of the blurring of a moving vessel.
[1] GH. Chen, J. Tang, and J. Hsieh, Temporal resolutionimprovement using PICCS in MDCT cardiac imaging, Med.Phys. 36(6), 2009.
[2] S. Achenbach, D. Ropers, J. Holle, G. Muschiol, W. G.Daniel, and W. Moshage, In-plane coronary arterial motionvelocity: Measurement with electron-beam CT, Radiology216(2), pp. 457-463, 2000.
Figure 9: The motion direction dependency of thetemporal resolution (=reproducibility) is quantified asvariation of the TR over different motion directions.
Figure 10: The results of the temporal resolutionassessment show highest TR for dual sourcegeometries. CS methods improve the TR only slightly.
