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, GermanyClemens.maass@imp.uni-erlangen.de

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.