PRIORITY STATEMENT

The present application hereby claims priority under 35 U.S.C. § 119 to European patent application number EP 19198986.2 filed Sep. 23, 2019, the entire contents of which are hereby incorporated herein by reference.

FIELD

Embodiments of the invention generally relate to a method, an apparatus, a computed tomography system and a computer program for producing a spectral computed tomography X-ray image data set.

BACKGROUND

Computed tomography (CT) is an imaging method which is primarily used for medical diagnostics. In CT, a radiation source, for example an X-ray source, and an X-ray detector cooperating therewith rotate about an object under examination, in particular a patient, to record spatially three-dimensional image data. During the rotational movement, “measured projection data” are in each case recorded within an angular sector. The measured projection data are a projection or plurality of projections containing information about the attenuation of the radiation by the object under examination from various projection angles. Based upon this measured projection data, also known as raw data sets, it is possible to reconstruct a two-dimensional cross-sectional image or a three-dimensional volume image of the object under examination, for example by way of “filtered backprojection” or by way of an iterative reconstruction method.

The measurement data also contains spectral information, since absorption in the object under examination is dependent on the energy of the X-rays, i.e. the energy of the X-ray photons, which pass through the object under examination. This spectral information may be indicative of the composition of the object under examination and make it possible to differentiate between different materials in the object under examination. However, it cannot conventionally be accessed via a conventional CT device with an energy-integrating X-ray detector.

One possible way of gaining access to the spectral information involves recording measured projection data with X-rays which have at least two mutually differing energy spectra, for example one energy spectrum with a low energy level and one with a higher energy level and jointly processing the resultant measurement data via a spectral data processing technique. It is known in this case to use “dual source” CT devices which have two angularly offset X-ray sources, each with an opposing X-ray detector, and wherein the two X-ray sources emit two energy spectra which differ from one another.

It is also known to use X-ray tubes with a “split filter”, i.e. having a prefilter which is divided for example along the axis of rotation of the CT device, wherein two mutually differing energy spectra are emitted in different spatial regions and different regions of an X-ray detector are accordingly illuminated with different energy spectra. Another possibility which may be mentioned is “kV switching”, wherein an X-ray source is used which is configured alternately to emit X-rays with two different energy spectra in rapid temporal succession by alternately switching in rapid temporal succession between two tube voltages.

In addition to using X-rays with at least two mutually differing energy spectra, spectral CT examinations can also be enabled by using energy-resolving X-ray detectors. A photon-counting, direct-converting X-ray detector may, for example, be used. Such X-ray detectors are capable of converting incident X-rays or photons into electrical pulses via a suitable converter material. CdTe, CZT, HgI2, GaAs, or the like, may for example be used as the converter material. The electrical pulses are assessed by evaluation electronics, for example an integrated circuit (application specific integrated circuit (ASIC). In counting X-ray detectors, incident X-rays are then measured by counting the electrical pulses which are triggered by absorption of X-ray photons in the converter material. The height or also the length of a produced electrical pulse is generally proportional to the energy of the absorbed X-ray photon. In this manner, spectral information can be extracted by comparing the height or length of the electrical pulse with an energy threshold. If, for example, two energy thresholds are supplied for comparison, measurement signals may be generated or output which are resolved into two energy ranges which are defined by the two energy thresholds. Dual layer X-ray detectors which can enable access to spectral information are furthermore known.

SUMMARY

The inventors have discovered that in spectral CT examinations, one essential criterion for spectral raw data or image processing algorithm quality (e.g. for calculating base material images, for calculating pseudo-monoenergy images, or for classifying materials in the CT image) is the spectral separation of the at least two spectrally differing raw data sets or measurement data sets which are used for the spectral data processing technique. The inventors have discovered that it would be ideal to work with spectral input data sets which differ completely with regard to X-ray energy range, but this was not achievable with known methods.

At least one embodiment of the invention provides an improved method for producing a spectral CT image data set, wherein improved spectral separation of the measurement signals is enabled.

Further advantageous and in part per se inventive embodiments and developments of the invention are described in the claims and the following description.

The inventive solution of embodiments of the invention are described below with regard both to the method and to the apparatus. Features, advantages or alternative embodiments mentioned in this connection are likewise also transferable to the other claimed subjects and vice versa. In other words, the substantive claims (e.g. directed to an apparatus) may also be developed with the features which are described or claimed in connection with a method. The corresponding functional features of the method are here formed by corresponding substantive modules.

At least one embodiment of the invention relates to a method for producing a spectral computed tomography image data set (CT image data set) via a detection unit having at least one photon-counting X-ray detector and an X-ray source unit comprising adapting, emitting, detecting, producing and outputting.

The X-ray source unit of at least one embodiment is configured according to at least one embodiment of the invention to emit X-rays having a first energy spectrum and having a second energy spectrum which differs from the first. The X-ray source unit comprises at least one X-ray source for this purpose. The X-ray source may, for example, be configured as an X-ray tube. The X-ray source unit may, however, also comprise more than one X-ray source. In the case of a dual-source CT device, the X-ray source unit comprises for example two angularly offset X-ray sources which are arranged rotatably about a common axis of rotation around the object under examination in order to record measurement signals within different angular sectors.

At least one embodiment of the invention moreover relates to an apparatus for producing a spectral CT image data set. The apparatus according to at least one embodiment of the invention comprises:

an X-ray source unit configured to emit X-rays having a first energy spectrum and X-rays having a second energy spectrum which differs from the first,

a detection unit having at least one photon-counting X-ray detector and configured to generate X-ray measurement signals based upon detected X-rays, which measurement signals are resolved at least into a first adaptable energy range and a second adaptable energy range,

an adaptation unit configured to adapt the first energy range and the second energy range as a function of the first energy spectrum and the second energy spectrum, wherein in each case at least one limiting energy of a respective energy range is adapted,

an image processing unit configured to produce the spectral CT image data set by way of a spectral image processing technique based upon the generated measurement signals, wherein at least one first generated measurement signal is included in the production as a function of the first energy range and the first energy spectrum and a second generated measurement signal as a function of the second energy range and the second energy spectrum, and

an interface for outputting the spectral CT image data set.

At least on embodiment of the invention is directed to a method for producing a spectral computed tomography image data set via a detection unit including at least one photon-counting X-ray detector and configured to convert detected X-rays into measurement signals, resolved at least into a first adaptable energy range and a second adaptable energy range, and configured to emit, via an X-ray source unit, X-rays having a first energy spectrum and having a second energy spectrum which differs from the first energy spectrum, the method comprising:adapting the first adaptable energy range and the second adaptable energy range as a function of the first energy spectrum and the second energy spectrum, respectively, via an adaptation unit, wherein at least one respective limiting energy, of each of a respective one of the first adaptable energy range and the second adaptable energy range, is adapted during the adapting;emitting X-rays having the first energy spectrum and emitting X-rays having the second energy spectrum, via the X-ray source unit;detecting the X-rays emitted having the first energy spectrum and detecting the X-rays emitted having the second energy spectrum, via the detection unit, wherein at least one first measurement signal is generated as a function of the first adaptable energy range and the first energy spectrum and wherein at least one second measurement signal is generated as a function of the second adaptable energy range and the second energy spectrum;producing the spectral computed tomography image data set at least based upon the first measurement signals generated and the second measurement signals generated, with assistance of a spectral image processing technique, via an image processing unit; andoutputting the spectral computed tomography image data set via an interface.

At least one embodiment is directed to an apparatus for producing a spectral computed tomography image data set comprising:an X-ray source unit configured to emit X-rays having a first energy spectrum and configured to emit X-rays having a second energy spectrum, different from the first energy spectrum;a detection unit including at least one photon-counting X-ray detector and configured to generate measurement signals based upon detected X-rays, the measurement signals being resolved at least into a first adaptable energy range and a second adaptable energy range;an adaptation unit, configured to respectively adapt the first adaptable energy range and the second adaptable energy range as a function of the first energy spectrum and the second energy spectrum, wherein at least one limiting energy, of at least one of the first adaptable energy range and the second adaptable energy range, is generated;an image processing unit configured to produce the spectral computed tomography image data set using a spectral image processing technique based upon the measurement signals generated, wherein at least one first generated measurement signal is included in production of the spectral computed tomography image data set as a function of the first adaptable energy range and the first energy spectrum and a second generated measurement signal is included in production of the spectral computed tomography image data set as a function of the second adaptable energy range and the second energy spectrum,an interface to output the spectral computed tomography image data set produced.

At least one embodiment is directed to an apparatus for producing a spectral computed tomography image data set comprising:an X-ray source configured to emit X-rays having a first energy spectrum and configured to emit X-rays having a second energy spectrum, different from the first energy spectrum;a detector including at least one photon-counting X-ray detector and configured to generate measurement signals based upon detected X-rays, the measurement signals being resolved at least into a first adaptable energy range and a second adaptable energy range;at least one processor, configured toadapt the first adaptable energy range and the second adaptable energy range as a function of the first energy spectrum and the second energy spectrum, respectively, wherein at least one limiting energy, of at least one of the first adaptable energy range and the second adaptable energy range, is generated, andproduce the spectral computed tomography image data set using a spectral image processing technique based upon the measurement signals generated, wherein at least one first generated measurement signal is included in production of the spectral computed tomography image data set as a function of the first adaptable energy range and the first energy spectrum and a second generated measurement signal is included in production of the spectral computed tomography image data set as a function of the second adaptable energy range and the second energy spectrum; andan interface to output the spectral computed tomography image data set produced.

At least one embodiment is directed to a computed tomography system comprising the apparatus of an embodiment.

