Abstract: Devices and methods are disclosed which relate to the calibration and quality assurance of motion tracking enabled radiation therapy machines. A phantom, capable of mimicking human breathing through inflation and deflation of the lungs, houses an independently moving target (tumor) that detects the amount of radiation received from the radiation therapy machine. This amount can be compared with a desired amount to determine if adjustment or repositioning is necessary. The servo-mechanism(s) of the motion tracking enabled radiation therapy machine(s) are adjusted in comparison of detected versus programmed motion of the respiring phantom having incorporated independently moving target that incorporated radiation dose detector(s). In the invention, motion tracking and irradiation mechanisms of the radiation therapy machine are adjusted to calibrate with reference to performance specifications of the radiation therapy machine.

Abstract: A method of extrapolating a bidimensional grey-level image using a radiography device.

Abstract: A method for evaluating the spatial resolution of a volumetric medical imaging system comprises imaging an image phantom including a sphere surrounded by a uniform medium. The image phantom is imaged and the resulting volumetric data set is used to generate an edge response function in three dimensions. Differentiating the edge response function produces a plane spread function. The method simultaneously measures the spatial resolution in all directions, providing a bulk measurement resolution. Alternatively, the edge response function may be assembled in a manner so as to independently measure the axial and trans-axial resolution of the volumetric imaging system.

Abstract: A helical scanning operation is performed while a bed is moved, so that data by one-time rotation is collected while positional relationships between a detecting system and a phantom relatively are changed. Further, data obtained by scanning an air region and data obtained by scanning a water region are discriminated on the basis of positional information obtained by positioning scanning or the difference between the air and the water in X-ray absorptance, and correction data is created on the basis of the discrimination.

Abstract: A technique is provided for geometrical analysis and calibration of a volumetric imaging system. The technique includes computing a projection error between estimated locations of a set of markers of a phantom based on a estimated imaging geometry and observed locations of the respective markers for at least one projection image, decomposing the computed projection error into one or more error components corresponding to respective geometric parameters of the imaging geometry, and updating at least one parameter of the estimated imaging geometry based on the one or more error components.

Abstract: The provision of calibration information for a given high energy-based scanner having a plurality of detectors can comprise forming (103) detector-level calibration information for that scanner. This can comprise calculating (201) a theoretical trajectory as pertains to relative movement as between the plurality of detectors and a calibration object as a function of known geometry parameters for this particular scanner and then causing (202) relative movement as between this plurality of detectors and a calibration object to develop a corresponding observed trajectory for the calibration object. These teachings then provide for determining (203), for each of at least some of the plurality of detectors, a value that corresponds to a difference between the theoretical trajectory and the observed trajectory to thereby provide the detector-level calibration information.

Abstract: The present invention comprises a top plate 31 for placing a cylindrical phantom 100, an X-ray tube 22 that generates X-rays, an X-ray detector 23 that detects X-rays transmitted through the phantom 100 placed on a top plate 31, a supporting body drive part 25 that rotates the X-ray tube 22 and X-ray detector 23, a tomographic image data generating part 60 that generates tomographic image data on the phantom 100 based on a results of detecting X-rays by the X-ray detector 23, a calculation processing part 80 that calculates displacement of the cylinder axis J of the phantom 100 relative to the center of rotation (center of scan) by the supporting body drive part 25, based on the tomographic image data, and the angle of gradient of the cylinder axis J relative to the normal direction (direction of slice) of the rotation plane of said rotation, and a monitor 5 that displays the calculated results.

Abstract: The invention relates to a method for speeding up the scattered radiation correction in a computed tomography system with a radiation source and a detector constructed in large-area format with a number of rows of detectors, by which an object is scanned from numerous projection angles, uses the measured values for the attenuation of the radiation in generating projection data which is postprocessed for the purpose of reconstructing tomographic views, in doing which a beam hardening correction is applied directly to the projection data, whereby according to the invention the scattered radiation correction is also applied directly to the projection data.

Abstract: A phantom for quality monitoring of a medical system, in particular a medical therapy system, or particle therapy system, is described. The phantom has a fixation device for coupling the phantom to a positioning device. In an aspect, a method for quality monitoring in a medical system, in particular a medical therapy system or particle therapy system is described, in which such a phantom is coupled via a fixation device to a positioning device and, with the aid of the positioning device, is brought to a predefined position. In another aspect, a particle therapy system has a treatment chamber, with a positioning device to which a phantom can be coupled so that the phantom can be brought to a predefined spatial position using the positioning device.

Abstract: A system, method, and computer readable medium for facilitating the assessment of performance quality of an imaging system having a sensor subsystem. An imaging mode of operation of the imaging system is selected and at least one current set of digital image data of an imaging phantom device is acquired with the imaging system via the sensor subsystem. The currently acquired set of digital phantom image data is automatically compared to at least one previously acquired set of digital phantom image data representing a standard image of quality corresponding to the selected imaging mode of operation and the imaging phantom device to automatically determine if at least one sensor parameter of the sensor subsystem has changed.

Abstract: An adjustable phantom (36) includes a base (202), an actuator (204) and a phantom (210). The phantom includes first (210a) and second portions (210b), each having a different value of a physical characteristic measured by a scanner (10). The phantom (210) is movable with respect to the base (202). In one embodiment, the phantom is well suited to simulating the arrival of contrast agent in a contrast enhanced imaging examination.

Abstract: Provided is a phantom device having an internal organ simulating phantom. The phantom device comprises: a phantom receiving radiation emitted from a radiation emitting unit and comprising therein a simulant that simulates an internal organ; a lifting unit installed under the phantom to support the phantom and moving the phantom relative to the radiation emitting unit, the lifting unit comprising: a worm shaft axially rotated by an external torque and having a worm formed on an outer circumferential surface thereof, a cylindrical worm wheel having gear grooves formed on an outer circumferential surface thereof to engage with the worm and a female screw formed on an inner circumferential surface thereof, and rotated by the axial rotation of the worm shaft; and a driven screw engaging with the female screw of the worm wheel, and moved up and down by the rotation of the worm wheel to move up and down the phantom; and a horizontal moving unit interlocking with the lifting unit and horizontally moving the phantom.

Abstract: There is described a method for correction of truncation artifacts in reconstructed tomographic images in a reconstruction method for tomographic images with truncated projection image data in the reconstructed tomographic images, in which divergent radiation is emitted from a radiographic source, an object to be examined is x-rayed with the divergent radiation in different projection directions, the radiation penetrating through the object to be examined is detected by a detector as projection images, with the data of the signal being arranged in a number of projection data rows and projection images detected by the detector being expanded line-by-line through extrapolation of the projection data rows.

Abstract: The invention relates to a method for correcting truncation artifacts in reconstructing computer tomography recordings. The projection images of the computer tomography recordings are extended by extrapolation. An equivalent body is determined which in the peripheral region of the projection image attenuates the radiation emanating from a radiation source of the computer tomography according to the object to be examined, and the attenuation is determined outside the projection image for extrapolated image points. A smoothing of the signal of a projection data line is effected with a digital polynomial filter to reduce the noise portion of the signal. The truncated portion of the projection data line is computed from the smoothed signal of the projection data line by an extrapolation method.

Abstract: A phantom for use in measuring characteristics of a digital radiography imaging system has at least one substrate having a patterned foil layer. The pattern in the foil layer being defined by a plurality of apertures within which the substrate is exposed.

Abstract: The invention relates to a method and an apparatus for correcting truncation artifacts in a tomographic process of an object under medical examination. To prevent truncation artifacts in a tomographic process, it is proposed to extrapolate truncated projection images by projecting an equivalent body disposed at the location of the object under examination onto an extended detector surface according to the beam geometry.

Abstract: The object of the invention is a process for determining the mechanical resistance of a bone from a digitized two dimensional image, obtained by imaging, characterized in that there is carried out a correlation between the bone mineral density determined from this two dimensional image by any means suitable to this type of image, and a structural parameter obtained from the same two dimensional image.

Abstract: In an X-ray computerized tomography scanner, a correction phantom embedding an X-ray absorbing object is put on or around a non-vertical rotary axis between an X-ray source and a two-dimensional X-ray detector, and two dimensional imaging data of the phantom is acquired. Then a locus of the X-ray absorbing material is determined in the two-dimensional imaging data, and based on the locus an ideal locus is obtained in the direction of the rotary axis. Next, a difference between the calculated position of the ideal locus and a measured position is determined in the direction of the rotary axis. The difference is used to correct deviation in the direction of the rotary axis.

Abstract: Devices and methods are disclosed which relate to the calibration and quality assurance of motion tracking enabled radiation therapy machines. A phantom, capable of mimicking human breathing through inflation and deflation of the lungs, houses an independently moving target (tumor) that detects the amount of radiation received from the radiation therapy machine. This amount can be compared with a desired amount to determine if adjustment or repositioning is necessary. The servo-mechanism(s) of the motion tracking enabled radiation therapy machine(s) are adjusted in comparison of detected versus programmed motion of the respiring phantom having incorporated independently moving target that incorporated radiation dose detector(s). In the invention, motion tracking and irradiation mechanisms of the radiation therapy machine are adjusted to calibrate with reference to performance specifications of the radiation therapy machine.

Abstract: An X-ray measuring instrument in which an object under examination is irradiated with X-rays, measurement data on the object is detected, a filter for adjusting the amount of transmitted X-rays is disposed between an X-ray source and the object, the relative position of the X-ray source to the object is varied, and the acquired measurement data is computed. The measurement data is subjected to logarithm transform to acquire projection data, and the amount of absorbed X-rays of the filter corresponding to the acquired projection data is determined. The thickness of the filter is computed by using a predetermined transform formula for the acquired amount of absorbed X-rays. A correction coefficient corresponding to the projection data acquired from the computed thickness of the filter is determined, and the projection data is multiplied by the determined correction coefficient. The projection data multiplied by the correction coefficient is restructure-computed to obtain a three-dimensional image.

Abstract: A phantom assembly includes a plurality of cylindrical shaped phantoms connectable to each other and/or a plurality of column-shaped phantoms connectable to each other with fitting portions. An x-ray radiation measuring device for measuring an x-ray radiation from an x-ray CT device is inserted in a through-hole of the phantom.

Abstract: Processes for producing a microCT image for virtual histology using x-ray microscopic computed tomography are described along with processes for rapid and inexpensive high-throughput methods of high resolution imaging for screening an ex vivo embryo for phenotype using computed tomography imaging. Staining of particular components of specimens with one or more staining agents is described which contributes to high quality image generation and identification of anatomical structures as well as localization of molecular targets. Inventive animal and specimen holders are detailed which allow for reduced post-imaging processing of generated images. In particular, animal and specimen holders are provided which include a highly transparent bed or liner which separates the animal or specimen from a less transparent structure.

Abstract: An X-ray CT apparatus comprising a storage device which stores therein a first table where fat contents are respectively associated with the values of the ratios of CT numbers, a CT number measurement unit which irradiates an object with X-rays under a plurality of different irradiation conditions, and which obtains actually-measured CT numbers for the respective irradiation conditions, and a fat content extraction unit which calculates the ratio of the actually-measured CT numbers for the respective irradiation conditions, and which extracts the fat content corresponding to the ratio of the actually-measured CT numbers, by referring to the first table.

Abstract: The method is analytical, involves a single irradiation of the object at a plurality of incidences in order to obtain a first three-dimensional image of the total radiation received by the detector, but a double irradiation of a set of calibration phantoms, such as planar plates, in order to obtain their images of the total radiation and the scattered radiation. The three-dimensional image serves only to precisely evaluate, for each projection of the radiation through the object, the equivalent length of the material of the phantoms in order to obtain a similar scattered radiation. In a known manner, a ratio of scattered radiation layers is then calculated for the object and the phantoms according to the total radiation that they have received, and the scattered radiation of the object is obtained by the radiation scattered by the phantoms, which have been measured, and the ratio.

Abstract: A method for evaluating the spatial resolution of a volumetric medical imaging system comprises imaging an image phantom including a sphere surrounded by a uniform medium. The image phantom is imaged and the resulting volumetric data set is used to generate an edge response function in three dimensions. Differentiating the edge response function produces a plane spread function. The method simultaneously measures the spatial resolution in all directions, providing a bulk measurement resolution. Alternatively, the edge response function may be assembled in a manner so as to independently measure the axial and trans-axial resolution of the volumetric imaging system.

Abstract: The present invention relates to calibration devices and to methods of using these devices.

Abstract: A deformable phantom apparatus for simulating motion of a patient's anatomy in 3D during breathing, the apparatus comprising a chamber fillable with a first fluid, a deformable member comprising tissue equivalent material of the anatomy being simulated, the deformable member being positionable within the chamber in the first fluid and having an open end in fluid communication with a second fluid outside the chamber in use; and a mechanism for causing the second fluid to flow through the open end to deform the deformable member between a normal state and a deformed state to simulate motion during breathing.

Abstract: A phantom and associated method for calibrating registration in a multi-modal medical diagnostic imaging system are presented. The phantom features a plurality of emission point sources arranged in multiple parallel planes along the length of the phantom, with enough planes to allow mode registration to be calibrated over the length of an entire full-body scan. According to the method, calibration scans are performed at each of several scan positions along the length of the phantom, with at least two planes of emission point sources covered by the scan at each position.

Abstract: A multimodality imaging phantom is disclosed which is useful for calibrating devices for imaging vascular conduits. The phantom is compatible with X-ray, ultrasound and magnetic resonance imaging techniques. It allows testing, calibration, and inter-modality comparative study of imaging devices, in static or dynamic flow conditions. It also provides a geometric reference for evaluation of accuracy of imaging devices. The tissue-mimicking material is preferably an agar-based solidified gel. A vessel of known desired geometry runs throughout the gel and is connected to an inlet and outlet at its extremities for generating a flow circulation in the vessel. Said phantom also contains fiducial markers detectable in the above-mentioned modalities. The markers are preferably made of glass and are embedded in a layer of agar gel containing a fat component.

Abstract: Disclosed is a method for pictorially representing and determining tissue densities of a body region, especially in the mouth/jaw/face region (1), of a patient. According to said method, a set of three-dimensional image data representing the body region as well as calibration data that is provided as three-dimensional image data and represents a calibration phantom (5, 8, 15) having a previously known density are photographed by generating an image while the tissue densities are derived from a comparison of the calibration data with the image data. The image data and the calibration data are photographed in the framework of the same shot and in an upright position of the patient, particularly during sitting or standing. The calibration phantom (5, 8, 15) is held in the immediate vicinity of the body region (1) that is to be photographed during the shot by means of a fixture (4, 10, 14) which is fixed independently of the patient's body and in a defined relation to the imaging device.

Abstract: Methods and devices for improving the machine-to-machine and temporal (e.g., inter and intra-machine) and database consistency of coronary calcium scoring by applying a filtering algorithm that sharpens and/or smoothes the image so as to return a filtered image having a spatial resolution of a certain reference value.

Abstract: The invention relates to a phantom for the quality control of a radiotherapy treatment virtual simulation system which comprises a medical imaging device, characterized in that it comprises: a support casing (1), a core (4) which is arranged in the support casing (1) and which is constituted by a plurality of elements (5, 6, 7, 8, 11, 12, 14, 15, 16, 17) of different shapes, dimensions and densities, the densities simulating the densities of various organs and media of the human body, two of these elements (11, 12) being constituted by two truncated pyramids of different densities which are fitted one inside the other, at least one of them not being completely symmetrical relative to the longitudinal axis thereof, balls (9, 10, 13) of a non-radiotransparent material arranged in the core (4), at least two removable lateral faces (18, 21) which face each other and which comprise metal wires which define geometric figures.

Abstract: A method for determining a correction for beam hardening in CT images includes obtaining air scans at a plurality of kVp's, determining detection efficiencies for detector elements of the CT imaging apparatus, and estimating projection values through a combination of at least two different materials of different thicknesses. The method further includes determining a transfer function that translates the estimated projection values into ideal projection values for at least two of the different materials and storing the transfer function as the beam hardening correction for images of the CT imaging apparatus.

Abstract: The invention relates to a method and an apparatus for correcting truncation artifacts in a tomographic process of an object under medical examination. To prevent truncation artifacts in a tomographic process, it is proposed to extrapolate truncated projection images by projecting an equivalent body disposed at the location of the object under examinations onto an extended detector surface according to the beam geometry.

Abstract: A method for normalizing a calibration of a computed tomographic (CT) imaging apparatus having a plurality of detector rows includes utilizing a prestored, predetermined inversion matrix and CT numbers obtained from images of a phantom to determine normalized calibration vectors for each row of a plurality of detector rows, and storing the determined normalized calibration vectors for each row of the plurality of detector rows in a memory for use in subsequent image reconstructions.

Abstract: A hybrid calibration method uses a calibration phantom (exterior reference) scanned simultaneously with the patient, and one or more known tissues of the subject (interior reference) to create a hybrid calibration reference that improves the measurement of tissue densities throughout the body. In addition, the calibration method is used to quantitatively define boundaries of tissue and organs for more accurate measurements of lengths, areas and volumes. Another aspect of the invention uses the calibrated images to quantitatively preset absolute window/levels for filming and image display, which provides standardized viewing for diagnostic purposes.

Abstract: The invention is based, in part, on the discovery that by combining certain components one can generate a tissue-like phantom that mimics any desired tissue, is simple and inexpensive to prepare, and is stable over many weeks or months. In addition, new multi-modal imaging objects (e.g., beads) can be inserted into the phantoms to mimic tissue pathologies, such as cancer, or merely to serve as calibration standards. These objects can be imaged using one, two, or more (e.g., four) different imaging modalities (e.g., x-ray computed tomography (CT), positron emission tomography (PET), single photon emission computed tomography (SPECT), and near-infrared (NIR) fluorescence) simultaneously.

Abstract: Certain embodiments relate to a method for calibrating an imaging system having an array of detector elements arranged with respect to a reference position and having an energy source moving in a pattern to irradiate the array of detector elements. The method includes initiating estimated detector positions for the array of detector elements and an estimated motion pattern for the energy source defined with respect to a reference position. The method also includes scanning a phantom having pins located at positions in the phantom. The method further includes calculating estimated pin positions, with respect to the reference position, based on at least one of the estimated detector positions and motion pattern and modifying at least one of the estimated detector positions and pin positions based on at least two of the estimated detector positions, motion pattern and pin positions.

Abstract: An adaptive CT data acquisition system and technique is presented whereby radiation emitted for CT data acquisition is dynamically controlled to limit exposure to those detectors of a CT detector assembly that may be particularly susceptible to saturation during a given data acquisition. The data acquisition technique recognizes that for a given subject size and position that pre-subject filtering and collimating of a radiation beam may be insufficient to completely prevent detector saturation. Therefore, the present invention includes implementation of a number of CT data correction techniques for correcting otherwise unusable data of a saturated CT detector. These data correction techniques include a nearest neighbor correction, off-centered phantom correction, off-centered synthetic data correction, scout data correction, planar radiogram correction, and a number of others.

Abstract: The present invention comprises a top plate 31 for placing a cylindrical phantom 100, an X-ray tube 22 that generates X-rays, an X-ray detector 23 that detects X-rays transmitted through the phantom 100 placed on a top plate 31, a supporting body drive part 25 that rotates the X-ray tube 22 and X-ray detector 23, a tomographic image data generating part 60 that generates tomographic image data on the phantom 100 based on a results of detecting X-rays by the X-ray detector 23, a calculation processing part 80 that calculates displacement of the cylinder axis J of the phantom 100 relative to the center of rotation (center of scan) by the supporting body drive part 25, based on the tomographic image data, and the angle of gradient of the cylinder axis J relative to the normal direction (direction of slice) of the rotation plane of said rotation, and a monitor 5 that displays the calculated results.

Abstract: The present system and method for simulating particles and waves is useful for calculations involving nuclear and full spectrum radiation transport, quantum particle transport, plasma transport and charged particle transport. The invention provides a mechanism for creating accurate invariants for embedding in general three-dimensional problems and describes means by which a series of simple single collision interaction finite elements can be extended to formulate a complex multi-collision finite element.

Abstract: Projection images of a calibration phantom are picked up and stored. Three-dimensional position information on an X-ray tube and an area detector is obtained from the projection images and three-dimensional arrangement information on markers inside the calibration phantom. Three-dimensional position information is obtained for all projection images, and stored in a three-dimensional position information storage unit. Projection images of an object under examination are picked up by following the same tracks and the same sequence as when radiographing the calibration phantom. Radiographic data of the projection images is read. A reconstructing calculation is carried out for the object based on the three-dimensional position information on the X-ray tube and area detector relative to the calibration phantom, to create slice images or three-dimensional volume data of a selected site of the object.

Abstract: An object of the present invention is to calculate a more accurate beam-hardening correction coefficient. A phantom having an oblong section or a phantom having an annular (sector) section and a uniform thickness is positioned in an X-ray CT system, and scanned from plural directions in order to acquire a plurality of views. The results of the scan are used to calculate a correction coefficient that is used to correct projection information to be acquired from a subject.

Abstract: The invention relates to a method for x-ray examination of an object where two categories of materials are taken into consideration, comprising: the use of broad spectrum x-rays; measurements of the x-rays by bands of the spectrum; expressions ({circumflex over (M)}) of thicknesses or masses of the two categories of materials passed through by the x-rays, the expressions ({circumflex over (M)}) being functions of at least two of the measurements (mesk) and coefficients (A); and applying a selection criterion from among the expressions ({circumflex over (M)}) to deduce from this an expression (final {circumflex over (M)}) considered true; characterized in that the selection criterion comprises a combination (f) of the expressions with weighting factors (a), and a calculation of the weighting factors such that the combination has minimal variation according to variations of the measurements.

Abstract: An X-ray computed tomographic (CT) system includes: a beam-hardening correction block that corrects first projection information in terms of the beam-hardening effect so as to produce second projection information; a first fitting block that fits a first function to the second projection information so as to produce third projection information; a second fitting block that fits a second function to the third projection information values that are provided as functions having as independent variables the second projection information values sampled in relation to all the views and each of the channels of an X-ray detector; and a correction coefficient modification block that modifies a second correction coefficient, which is calculated using a second phantom larger in dimensions than a first phantom, using a first correction coefficient calculated using the first phantom.

Abstract: A method for calibrating a computed tomographic imaging apparatus having a gantry, a radiation source operable at a plurality of kVp's, and a detector array having a plurality of detector elements includes using a system detection function to estimate signals of each detector element that would have been detected through air and through a given thickness of water to determine estimated datasets. The estimated datasets are used to determine data pair sets each comprising a normalized water projection value and an ideal projection value for each detector element. The method further includes determining and storing a representation of a mapping function of the normalized water projections values to the ideal projection values in a memory of the computed tomographic imaging apparatus as a spectral calibration of the computed tomographic imaging apparatus.

Abstract: In the field of medical imaging minimizing the number of acquisitions required to calibrate a radiological device. Calibration of the radiological imaging device is provided by moving the device with respect to a calibration object and performing a series of acquisitions, each acquisition being associated to a calibration position of the device. Based on the acquisitions performed, determining the projection parameters associated to each calibration position of the device. For an additional position that has not been taken by the device during the acquisition, determining the projection parameter values associated to this additional position according to the parameters associated to the calibration positions.

Abstract: Phantoms and discrete spatial and frequency methods for quantitatively measuring the alignment of radiographic imaging systems are described. One embodiment comprises phantoms for use in mechanically aligning radiographic imaging systems. These phantoms comprise: a radio-opaque material capable of holding a well-defined edge that allows quantitative image resolution measurements to be obtained thereof; wherein once the quantitative image resolution measurements are obtained, the spatial frequency response of the radiographic imaging system at a given focal plane can be calculated therefrom, thereby defining the mechanical alignment, resolution, and resolution uniformity of the radiographic imaging system. Systems and methods for mechanically aligning radiographic imaging systems, and methods for obtaining a quantitative measurement of the mechanical alignment, resolution and resolution uniformity of radiographic imaging systems, are also disclosed.

Abstract: A radiographic apparatus has a radiation source that emits radiation two-dimensionally, a two-dimensional radiation detector disposed so as to detect radiation emitted from the radiation source, a rotation unit driven so that a subject is relatively rotated with respect to said radiation source and said radiation detector, a detachable water phantom, disposed on the rotation unit, having a size that covers a portion of a detection area of the radiation detector from radiation emitted from the radiation source, the portion extending in the direction perpendicular to the rotation axis for the entire range of the detection area and in the direction of the rotation axis for a part of the range of the detection area, and a calibration unit that performs water calibration of data obtained by radiography of the subject, using data obtained by radiography of the water phantom across the entire detection area while moving a position of the water phantom along the axis rotation of the rotation unit.

Abstract: A method is for determining correction coefficients or parameters, in particular channel correction coefficients and/or spacing coefficients, for detector channels for a computed tomograph. In the method, a scan is carried out in order to obtain a sinogram of a phantom (11) which is formed with a smooth cross-sectional profile and is inserted into the computed tomograph in such a way that two or more different attenuation values are detected in a full scan of virtually all the detector channels (3). Attenuation profiles that are obtained from the sinogram are subjected to high-pass filtering for each projection of the scan, in order to obtain discrepancies of an ideal profile which is predetermined by the phantom (11). A model function is matched to the discrepancies that are obtained for each of the detector channels (3) as a function of the detected attenuation values, from which the coefficients or parameters are obtained.