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EP2080015A1 - Procédé d'étalonnage pour tomographie à deux ou plusieurs spectres - Google Patents

Procédé d'étalonnage pour tomographie à deux ou plusieurs spectres

Info

Publication number
EP2080015A1
EP2080015A1 EP07818508A EP07818508A EP2080015A1 EP 2080015 A1 EP2080015 A1 EP 2080015A1 EP 07818508 A EP07818508 A EP 07818508A EP 07818508 A EP07818508 A EP 07818508A EP 2080015 A1 EP2080015 A1 EP 2080015A1
Authority
EP
European Patent Office
Prior art keywords
calibration
spectra
phantom
decomposition
coefficients
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP07818508A
Other languages
German (de)
English (en)
Inventor
Marc Kachelriess
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
CT Imaging GmbH
Original Assignee
VAMP VERFAHREN und APP DER MED
VAMP Verfahren und Apparate der Medizinischen Physik GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by VAMP VERFAHREN und APP DER MED, VAMP Verfahren und Apparate der Medizinischen Physik GmbH filed Critical VAMP VERFAHREN und APP DER MED
Publication of EP2080015A1 publication Critical patent/EP2080015A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
    • A61B6/48—Diagnostic techniques
    • A61B6/482—Diagnostic techniques involving multiple energy imaging
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
    • A61B6/02—Arrangements for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
    • A61B6/03—Computed tomography [CT]
    • A61B6/032—Transmission computed tomography [CT]
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
    • A61B6/58—Testing, adjusting or calibrating thereof
    • A61B6/582—Calibration
    • A61B6/583—Calibration using calibration phantoms
    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T11/00—2D [Two Dimensional] image generation
    • G06T11/003—Reconstruction from projections, e.g. tomography
    • G06T11/008—Specific post-processing after tomographic reconstruction, e.g. voxelisation, metal artifact correction
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00—Apparatus or devices for radiation diagnosis; Apparatus or devices for radiation diagnosis combined with radiation therapy equipment
    • A61B6/40—Arrangements for generating radiation specially adapted for radiation diagnosis
    • A61B6/405—Source units specially adapted to modify characteristics of the beam during the data acquisition process
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2223/00—Investigating materials by wave or particle radiation
    • G01N2223/30—Accessories, mechanical or electrical features
    • G01N2223/303—Accessories, mechanical or electrical features calibrating, standardising
    • G—PHYSICS
    • G06—COMPUTING OR CALCULATING; COUNTING
    • G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
    • G06T2211/00—Image generation
    • G06T2211/40—Computed tomography
    • G06T2211/408—Dual energy

Definitions

  • the invention relates to a method for calibrating computer tomographs in two- or multi-spectral tomography.
  • X-ray computer tomography provides information about the density or attenuation coefficient distribution of an object. Due to the fact that it is measured with polychromatic spectra, this information is a kind of average over all energy values.
  • Dual or multi-spectral tomography measures the object with two or more different spectra (in the diagnostic energy range below 1 MeV, two scans with two different spectra are sufficient for the base material decomposition and in the following description the representations are reduced to two-spectral methods without restriction of generality) and so on create a base function decomposition of the attenuation coefficient distribution. Material-specific images are provided in this way. This basic function decomposition can be made from analytical assumptions about the spectra and the material weakening or from empirical measurements.
  • the linear attenuation coefficient can be considered as a decomposition of spatial and energy dependence
  • the spatial functions f t may represent the density distribution of material 1 and material 2 and the energy functions ⁇ , whose energy dependence may be in the form of the mass attenuation coefficient.
  • decomposition is the location function as a mass fraction (for example, in% of the base material /) of a material to understand. Frequently, the physical underlying cross sections for the photo and Compton effect are used as energy function so that the reconstructed images / ( directly show the cross section distribution.
  • the index L represents the integration line (ray). Since the corrections discussed below are independent of L, this index is not explicitly noted for the sake of simplicity.
  • the spectrum itself is called a normalized function W j (E) with
  • This energy weighting includes not only the X-ray spectrum but also the detector sensitivity and may also include other effects ("Detected Spectrum").
  • Thicknesses various combinations of materials 1 and 2) and interpolated by analytical calculation of the "monochromatic weakenings", see A.J. Coleman and M. Sinclair, A Beam-Hardening Correction Using Dual-Energy Computed Tomography, Physics in Medicine and
  • Accuracies in the micrometer range can be achieved.
  • such empirical methods often use only a limited beam range (eg, the central beam) and then achieve relatively high calibration errors. After all, those on pure
  • Measurements based on scattering measurements do not detect and compensate for measurement errors based on scattered radiation.
  • calibration methods are also described in some cases in which an object of known shape and composition (often a cylindrical phantom) is scanned and the theoretical attenuation profile is adapted to the measured one by a nonlinear fit method.
  • the Positioning accuracy can be a problem in this case, because the profile functions to be apprehended, for example, can not respond to accidental tilting or rotation of the phantom.
  • scattering effects and the non-linearities of the polychromatic attenuation measurement will distort the fit.
  • An object of the present invention is to obviate the aforementioned errors and to provide a simple calibration method that directly incorporates the material decomposition equations calculated.
  • a calibration phantom consisting of homogeneous regions of both base materials (one base material per spectrum) and possibly also of foreign materials is scanned (CT scan).
  • CT scan a calibration phantom consisting of homogeneous regions of both base materials (one base material per spectrum) and possibly also of foreign materials is scanned (CT scan).
  • the raw data is transformed and reconstructed by suitable basic functions. It is only in the image space that the images thus reconstructed are combined to form an object by means of a linear combination, in such a way that the two homogeneous regions are also homogeneous in the image.
  • the coefficients of the linear combination thus determined are then the decomposition coefficients to be used for later measurements.
  • An essential idea of the invention is not to perform the calibration in the raw data space (attenuation space). Instead, images are first created. The calibration (determination the coefficients) then takes place with the generated image data in the spatial domain. An exact knowledge of the dimensions and the position of the phantom is therefore no longer necessary.
  • the phantom consists of at least two materials. Essential to the invention is that the measurements are carried out with at least two voltages. In the case described above, there is a "dual energy" calibration, in other words a mapping from R 2 to R 2 (two voltages, two materials) Two template images (one for each image) are used.
  • a calibration phantom is scanned.
  • the phantom should have at least one homogeneous (ie easily segmentable) area per base material. The phantom is allowed too
  • the templates for material 1 and material 2 are then given by 1 if r in material 1 0 if r in material 2 or air? if r in undef. Ranges 1 if r in material 2 0 if r in material 1 or air if r in undef. areas
  • a weighting image is additionally generated. Its pixel values reflect the security about the pixel content of the associated CT image of the calibration phantom:
  • edges of the respective associated template image may be weighted away by the weighting image
  • the method described can also be combined with analytical methods. Often the case arises that the correction function depends on additional parameters such as the location of the detector pixel which is about to be corrected. Thus, a host of calibration functions is to be determined.
  • the mentioned location dependency can have many causes:
  • the rays emanating from an X-ray tube will have a slightly different spectrum depending on the angle of emission.
  • a hybrid method is advantageous: an analytical precorrection and first material decomposition followed by the image-based calibration method described above.
  • the invention is not limited to two-spectra tomography. A generalization to any higher dimensions (maps from R N to R N ) is possible. Moreover, the invention is not limited to any particular type of computed tomography.
  • Density e.g., teflon, bone
  • FIGS. 6-9 second images of the calibration phantom (second CT
  • Density e.g., water
  • black outside means air. Inside the phantom means one dark color is a low density material (eg water); a bright color means a high density material (eg Teflon, bone). It can be seen that the two inner materials are not homogeneous. It gets lighter towards the edge (see “Water”, but also applies to “Bones”).
  • a low density material eg water
  • a bright color means a high density material (eg Teflon, bone).
  • the standard reconstruction (FIG. 1) is used for segmentation and for determining the weighting and template images. From this, the material decomposition images are reconstructed.
  • the weighted difference images (FIGS. 5, 9) show only minimal deviations from the template and impressively demonstrate the mode of operation of the method.
  • CT images are taken, once with 8OkV, once with 14OkV tube voltage.
  • Dual-energy CT is a modality that takes one and the same object with two different X-ray spectra. Normally, the data is generated by two different voltages, but other methods such as different pre-filtering, post-filtering or layered detectors are also used.
  • DECT is used for energy or material selective reconstruction, with the reduction of
  • Jet hardening artifacts is another useful effect, cf. R. Alvarez and A. Macovski, "Energy-selective reconstructions in x-ray CT,” Phys. Med. Biol. , vol. 21, no. 5, pp. 733-744, 1976; R. Alvarez and E. Seppi, "A Comparison of noise and dose in conventional and energy selective computed tomography," IEEE Transactions on Nuclear Science, vol. NS-26, no. 2, pp. 2853-2856, Apr. 1979; A. Coleman and M. Sinclair, "A beam-hardening correction using dual-energy computed tomography," Phys. Med. Biol. , vol. 30, no. 11, pp.
  • the two-spectra CT is based on the assumption that the attenuation coefficient ⁇ (F, E), which depends on the location F and the photon energy E, can be decomposed as follows:
  • SR denotes the operator of the 2D radon transformation or the operator of the 3D x-ray transformation.
  • Empirical Dual Energy Calibration proposed here presents a novel empirical calibration algorithm. Unlike other methods, EDEC requires neither knowledge of the spectrum nor the attenuation coefficients. The geometry, size and position of the calibration phantom are not needed. EDEC is based on similar principles as the Empirical Cupping Correction (ECC; see K. Sourbelle, M. Kachelr understand, and WA Calender, "Empirical Water Precorrection for Cone-Beam Computed Tomography", IEEE Medical Imaging Conference Record, pp. 431-145) 1871-1875, Oct. 2005, M. Kachelr understand, K. Sourbelle, and W.208, "Empirical cupping correction: A first order raw data precorrection for cone-beam computed tomography," Med. Phys., Vol. no. 5, pp. 1269-1274, May 2006).
  • ECC Empirical Cupping Correction
  • the total number of basis functions is (K + 1) (L + 1).
  • the total number of coefficients in each coefficient vector C 1 is thus 25 for each material, increasing the total number of unknown coefficients to 50.
  • the task of EDEC is to determine these coefficients C 1 . It should be noted that EDEC is not limited to polynomials, other basic functions may also be chosen.
  • the decomposition according to material 2 is completely analogous.
  • the weighting function w (r) is used to eliminate unwanted structures of the calibration phantom that occurs in the optimization process.
  • the calibration phantom contains homogeneous regions with sufficient quantities of material 1 and 2 and ensures that all meaningful combinations of path lengths in material 1 and 2 are detected. To obtain the basic images, these raw data are transferred to the (K + 1) (L + 1) basis functions and reconstructed. A standard reconstruction of the calibration phantom serves as the basis for determining t (r) and w (r), which are determined by thresholding.
  • the material template / (F) represents the a priori knowledge of the regions containing material 1 and those that certainly do not contain material 1 (ie material 2 or air): 1 for re material 1
  • the material template need not be defined, since these regions are suppressed by the weighting.
  • the image of the material template is set equal to one wherever the content of the voxel r is unique. This is true in regions of material 1 or 2 and in air.
  • w (r) is set equal to zero.
  • the weight and material template images are shown in binary and in black and white.
  • EDEC was also used to calibrate measured data from a clinical two-spectrum CT scanner and a micro CT scanner. The experiments with real data confirmed the results of the simulations.
  • image-based empirical two-spectra calibration is a simple, effective, and accurate method for calibrating two-spectrum CT.

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  • Health & Medical Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Medical Informatics (AREA)
  • Physics & Mathematics (AREA)
  • Radiology & Medical Imaging (AREA)
  • Surgery (AREA)
  • Nuclear Medicine, Radiotherapy & Molecular Imaging (AREA)
  • Optics & Photonics (AREA)
  • Pathology (AREA)
  • Biophysics (AREA)
  • Biomedical Technology (AREA)
  • Heart & Thoracic Surgery (AREA)
  • Molecular Biology (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Animal Behavior & Ethology (AREA)
  • General Health & Medical Sciences (AREA)
  • Public Health (AREA)
  • Veterinary Medicine (AREA)
  • Theoretical Computer Science (AREA)
  • Pulmonology (AREA)
  • General Physics & Mathematics (AREA)
  • Apparatus For Radiation Diagnosis (AREA)

Abstract

L'invention concerne un procédé d'étalonnage de tomographies assisté par ordinateur, utilisé en tomographie à deux ou plusieurs spectres. Le procédé est caractérisé par un calcul direct des équations de décomposition de matière Pi = Di(qj ) avec i = 1, ..., I, i désignant le nombre des matériaux et j = 1,..., J, j désignant le nombre des spectres. La fonction de décomposition Di, qui est une combinaison linéaire de fonctions de base Bn, peut être présentée de la façon suivante : (formule) et les coefficients Cin de décomposition de matière dans l'espace d'image sont définis au moyen d'une combinaison linéaire des images reconstruites.
EP07818508A 2006-10-18 2007-09-27 Procédé d'étalonnage pour tomographie à deux ou plusieurs spectres Withdrawn EP2080015A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102006049664A DE102006049664A1 (de) 2006-10-18 2006-10-18 Kalibriermethode für Zwei- oder Mehrspektrentomographie
PCT/EP2007/008425 WO2008046498A1 (fr) 2006-10-18 2007-09-27 procédé d'étalonnage pour tomographie à deux ou plusieurs spectres

Publications (1)

Publication Number Publication Date
EP2080015A1 true EP2080015A1 (fr) 2009-07-22

Family

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EP07818508A Withdrawn EP2080015A1 (fr) 2006-10-18 2007-09-27 Procédé d'étalonnage pour tomographie à deux ou plusieurs spectres

Country Status (3)

Country Link
EP (1) EP2080015A1 (fr)
DE (1) DE102006049664A1 (fr)
WO (1) WO2008046498A1 (fr)

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102009053664A1 (de) 2009-11-17 2011-05-19 Ziehm Imaging Gmbh Verfahren zur empirischen Bestimmung einer Korrekturfunktion zur Korrektur von Strahlungsaufhärtungs- und Streustrahleneffekten in der Projektionsradiografie und in der Computertomografie
DE102010040041B3 (de) 2010-08-31 2012-01-26 Siemens Aktiengesellschaft Verfahren zur Korrektur von durch zeitliche Veränderungen von Schwächungswerten auftretenden Artefakten
WO2012176088A1 (fr) 2011-06-21 2012-12-27 Koninklijke Philips Electronics N.V. Appareil d'imagerie
JP2018532468A (ja) 2015-09-23 2018-11-08 コーニンクレッカ フィリップス エヌ ヴェＫｏｎｉｎｋｌｉｊｋｅ Ｐｈｉｌｉｐｓ Ｎ．Ｖ． スペクトル撮像ファントム及び方法
EP3552547B1 (fr) * 2018-04-13 2022-12-07 Siemens Healthcare GmbH Procédé de fourniture d'informations de conversion à un ensemble de données d'image, dispositif à rayons x, programme informatique et support de données lisible électroniquement

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6173034B1 (en) * 1999-01-25 2001-01-09 Advanced Optical Technologies, Inc. Method for improved breast x-ray imaging

Non-Patent Citations (4)

* Cited by examiner, † Cited by third party
Title
GLEASON S. ET AL: "Reconstruction of Multi-Energy X-Ray Computed Tomography Images of Laboratory Mice", IEEE TRANSACTIONS ON NUCLEAR SCIENCE, vol. 46, no. 4, 1 August 1999 (1999-08-01), pages 1081 - 1086, XP011088472
MARC KACHELRIEB ET AL: "Empirical Dual Energy Calibration (EDEC) for Cone-Beam Computed Tomography", NUCLEAR SCIENCE SYMPOSIUM CONFERENCE RECORD, 2006. IEEE,, 1 October 2006 (2006-10-01), pages 2456 - 2550, XP031083875
STENNER P. ET AL: "Empirical dual energy calibration (EDEC) for cone-beam computed tomography", MEDICAL PHYSICS, vol. 34, no. 9, 1 September 2007 (2007-09-01), pages 3630 - 2405, XP002462936
STENNER P.: "Empirical dual energy calibration (EDEC) for cone-beam computed tomography", MEDICAL PHYSICS, vol. 34, no. 9, 1 September 2007 (2007-09-01), pages 3630 - 3641, XP002462936

Also Published As

Publication number Publication date
WO2008046498A1 (fr) 2008-04-24
DE102006049664A1 (de) 2008-05-08

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