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EP-4498919-B1 - CONTRAST AGENT ATTENUATION GRADIENT

EP4498919B1EP 4498919 B1EP4498919 B1EP 4498919B1EP-4498919-B1

Inventors

  • SCHMITT, HOLGER
  • LANGZAM, Eran
  • GRASS, MICHAEL
  • HAASE, CHRISTIAN
  • NICKISCH, Hannes

Dates

Publication Date
20260506
Application Date
20230320

Claims (12)

  1. A computer-implemented method of calculating a value of a contrast agent transluminal attenuation gradient (110) for a lumen (120) in a vasculature, the method comprising: receiving (S110) spectral computed tomography, CT, data (130 1 , 130 2 ) representing a distribution of an injected contrast agent along the lumen (120), the spectral CT data defining X-ray attenuation at a plurality of energy intervals (ΔE 1..m ); analyzing (S120) the spectral CT data to isolate from the spectral CT data, contrast agent attenuation data (140) representing the distribution of the contrast agent along the lumen (120); calculating, from the contrast agent attenuation data (140), an average value of the contrast agent attenuation across the lumen (120), at a plurality of positions (P a , P 1..4 , P d ) along the lumen; and calculating (S130) a value of a gradient (110) of the contrast agent along one or more portions (P a - P d ) of the lumen using the average values of the contrast agent attenuation across the lumen, to provide the value of the contrast agent transluminal attenuation gradient (110).
  2. The computer-implemented method according to claim 1, further comprising identifying a centerline (150) of the lumen (120); and wherein the calculating (S130) an average value of the contrast agent attenuation across the lumen (120), at a plurality of positions (P a , P 1..4 , P d ) along the lumen; is performed at the plurality of positions (P a , P 1..4 , P d ) along the centerline of the lumen.
  3. The computer-implemented method according to any one of claims 1 - 2, wherein the analyzing (S120) the spectral CT data, further comprises: analyzing the spectral CT data (130 1 , 130 2 ) to isolate from the spectral CT data, artifact attenuation data representing attenuation arising from one or more artifacts; and weighting the isolated contrast agent attenuation data such that an impact of the artifacts on the isolated contrast agent attenuation data (140) is reduced.
  4. The computer-implemented method according to claim 3, wherein the one or more spectral CT data energy intervals (ΔE 1..m ) comprises a relatively lower energy interval (ΔE 1 ) and a relatively higher energy interval (ΔE 2 ); and wherein the contrast agent attenuation data (140) is isolated from the spectral CT data (130 1 , 130 2 ) by subtracting the spectral CT data corresponding to the relatively higher energy interval (ΔE 2 ) from the spectral CT data corresponding to the relatively lower energy interval (ΔE 1 ); and wherein the artifact attenuation data (140) is provided by the spectral CT data corresponding to the relatively higher energy interval (ΔE 2 ).
  5. The computer-implemented method according to any one of claims 1 - 4, wherein the contrast agent attenuation data comprises (140) projection data, or wherein the contrast agent attenuation data (140) comprises reconstructed image data; and wherein the calculating (S130) a value of a gradient (110) of the contrast agent along one or more portions (P a - P d ) of the lumen, is performed in the projection domain, or in the image domain, respectively.
  6. The computer-implemented method according to any one of claims 1 - 5, wherein the method further comprises: receiving spectral CT data representing a flow of the injected contrast agent in the lumen (120); analyzing the spectral CT data representing the flow of the injected contrast agent in the lumen to isolate from said data, contrast agent attenuation flow data (160) representing the flow of the injected contrast agent in the lumen (120); and wherein the method further comprises: triggering a generation of the spectral CT data (130 1 , 130 2 ) representing the distribution of the injected contrast agent along the lumen (120), if the injected contrast agent in the lumen represented in the contrast agent attenuation flow data satisfies a predetermined threshold condition.
  7. The computer-implemented method according to claim 6, wherein the triggering a generation of the spectral CT data (130 1 , 130 2 ) representing the distribution of the injected contrast agent along the lumen (120), comprises initiating the generation of the spectral CT data (130 1 , 130 2 ) representing the distribution of the injected contrast agent along the lumen (120), if an intensity of the injected contrast agent represented in the contrast agent attenuation flow data (160) exceeds a predetermined threshold value at a predetermined position in the lumen (120).
  8. The computer-implemented method according to claim 7, wherein the received spectral CT data representing the flow of the injected contrast agent in the lumen (120) comprises projection data that is generated during a rotation of an X-ray source detector arrangement (270, 230) around the lumen (120), and wherein the method further comprises: reconstructing the projection data into an image slice; and wherein the initiating the generation of the spectral CT data (130 1 , 130 2 ), comprises analyzing an image intensity within a region of interest (170) in the reconstructed image slice, and initiating the generation of the spectral CT data (130 1 , 130 2 ) representing the distribution of the injected contrast agent along the lumen (120), if the image intensity within the region of interest exceeds the predetermined threshold value.
  9. The computer-implemented method according to any one of claims 7-8, further comprising determining a temporal profile of the intensity of the injected contrast agent within the region of interest (170); and normalizing the calculated value of the gradient of the contrast agent along the one or more portions (P a - P d ) of the lumen, based on an intensity of the injected contrast agent in the temporal profile.
  10. The computer-implemented method according to any previous claim, wherein the method further comprises: receiving spectral CT data representing a planar image (180) including the lumen (120) and one or more anatomical landmarks, the anatomical landmarks including one or more bone landmarks and one or more tissue landmarks; analyzing the spectral CT data representing the planar image (180), and isolating from said data, tissue data representing the lumen and the one or more tissue landmarks; and outputting a planar planning image (190) representing the tissue data.
  11. The computer-implemented method according to claim 10 when dependent on claim 8 or claim 9, wherein the method further comprises: identifying the at least one region of interest in the planar planning image (190); and wherein the identifying the at least one region of interest is performed automatically, or in response to user input received from a user input device.
  12. The computer-implemented method according to any previous claim, wherein the method further comprises: determining a value of a blood flow parameter for the lumen, using the calculated value of the gradient (110) of the contrast agent along the one or more portions (P a - P d ) of the lumen (120).

Description

TECHNICAL FIELD The present disclosure relates to calculating a value of a contrast agent attenuation gradient for a lumen in a vasculature. A computer-implemented method, a computer program product, and a system, are disclosed. BACKGROUND Various clinical investigations involve performing an assessment of blood flow in the vasculature. For example, investigations for coronary artery diseases "CAD" often perform an assessment of blood flow. In this regard, various blood flow parameters have been investigated, including the Fractional Flow Reserve "FFR", the instantaneous wave-free ratio "iFR", the Coronary Flow Reserve "CFR", the Thrombolysis in Myocardial Infarction "TIMI" flow grade, the Index of Microvascular Resistance "IMR", and the Hyperemic Microvascular Resistance index "HMR". Such blood flow parameters have historically been measured using invasive devices such as a pressure-wire. However, more recently, angiographic measurements have been used. By way of an example, the Fractional Flow Reserve "FFR" is often determined in order to assess the impact of a stenosis on delivery of oxygen to the heart muscle in a CAD assessment. The FFR is defined by the ratio Pd/Pa, wherein Pd represents a distal pressure at a distal position with respect to the stenosis, and Pa represents a proximal pressure with respect to the stenosis. Historically, values for these pressures have been determined by positioning an invasive device, such as a pressure wire, at the respective positions in the vasculature. However, more recently, angiographic techniques for determining the FFR have been developed. According to fluid flow theory, pressure changes are linked to changes in fluid velocity. In the example of the FFR, angiographic images of an injected contrast agent may be analyzed in order to determine the blood flow velocity. The FFR may then be calculated by using a haemodynamic model to estimate pressure values in the lumen from the blood flow velocity. Thus, the FFR, as well as other blood flow parameters may be determined angiographically. A challenge with such angiographic techniques for assessing blood flow in a vasculature is the need to provide an accurate angiographic model that represents the lumen under investigation. An alternative angiographic technique, and which does not necessitate such a haemodynamic model, is based on a measurement of the attenuation gradient of an injected contrast agent, the attenuation gradient being measured along the lumen. In this regard, a document by Wong, D. T. L, et al., "Transluminal Attenuation Gradient in Coronary Computed Tomography Angiography Is a Novel Noninvasive Approach to the Identification of Functionally Significant Coronary Artery Stenosis: A Comparison With Fractional Flow Reserve", JACC Vol. 61, No. 12, 2013, pates 1271 - 1279, reports on a technique that has recently received increased clinical interest. The technique disclosed in the aforementioned document uses a single static cardiac CT image as input. The coronary arteries are segmented in this three-dimensional image, and the gradient of the Hounsfield Unit contrast agent attenuation "transluminal attenuation gradient" is determined at multiple positions along the centerlines of the coronary arteries. The magnitude of the gradient has been found to correlate with stenoses, i.e. narrowings, in the arterial lumen. The document concludes that angiographic measurements of the attenuation gradient along a lumen provide an acceptable prediction of invasive FFR measurements, and may provide a non-invasive technique for detecting functionally significant coronary stenoses. A document US 2014/0243662 A1 describes a method for non-invasively determining the functional severity of arterial stenosis in a selected portion of an arterial network. The method includes gathering patient-specific data related to concentration of a contrast agent within an arterial network using a coronary computed tomography angiography scan. The data can be gathered under rest or stress conditions. Estimation of a loss coefficient can be used to eliminate the need for data gathered under stress. The data is used to calculate a transluminal attenuation gradient. The data may be corrected for imaging artifacts at any stage of the analysis. Transluminal attenuation flow encoding is used to determine an estimate of flow velocity. Once velocity is determined, pressure gradient, coronary flow reserve, and/or fractional flow reserve can be determined through a variety of methods. These estimates can be used to estimate functional severity of stenosis. However, there remains room to improve the accuracy of angiographic measurements of the contrast agent attenuation gradient in a lumen, and to thereby provide more accurate measurements of blood flow parameters for the lumen, such as for example the FFR. SUMMARY According to one aspect of the present disclosure, a computer-implemented method of calculating a value of a contrast agent transluminal at