Test object for image quality in conventional and spectral computed tomography.

Abstract

The invention relates to a test object (1) for simulating an object in a medical imaging device, comprising the following stack, according to a height of the test object taken on a longitudinal axis XX: - a first (11) solid made of a first material; - a second (21) solid made of the second material; the first material being different from the second material; the first solid (11) and the second solid (21) each comprising several housings (12, 22) extending over a part of the height of each solid (11, 21) and open on free faces of each of the first and second solids (11, 21). Figure for the abstract: Fig. 1

Description

Title of the invention: Test object for image quality in conventional and spectral computed tomography. Technical field

[0001] The invention relates to an imaging test object for evaluating the quality of computed tomographic images. In particular, it relates to the analysis of spectral images, either in dual-energy in combination with dual-energy scanners or in multi-energy in combination with photon counting scanners. STATE OF THE ART

[0002] Spectral images generated by dual energy computed tomography (DECT) and multi-energy scanners from photon counting scanners offer multiple advantages for various clinical applications, such as correction of metallic artifacts, increased attenuation of tissues enhanced by contrast products, injection-free image simulation, functional and quantitative analysis of tissues as well as the use of new contrast agents implementing different tissue spectral characteristics.

[0003] In this context, radiologists can use several types of spectral images: (1) non-material-specific maps, such as single-energy virtual images (MVI), Z-effective images and electron density images; (2) material-specific maps, such as iodine density, water images; (3) virtual images without contrast product based on a decomposition of tissues into 2 bases of iodine / water type for example and (4) K-edge images based on a decomposition into 3 materials exclusively accessible in multi-energy imaging.

[0004] These images are obtained by redistributing the ratio of the photoelectric effect and the Compton scattering in each voxel. They are calculated (in the projection domain or in the image domain) from the spectra of low and high energy photons, which can both be obtained during acquisition or detection depending on the scanner technology (dual-energy or photon counting) used.

[0005] Significant technological differences exist between these platforms and require their impact on spectral performance to be assessed.

[0006] In addition, the appearance of new photon counting scanners will make it possible to generate images that are no longer dual-energy but multi-energy and new contrast agents will be used clinically.

[0007] The test objects usually used for acquisitions in conventional scanners are not suitable for studying all the metrics useful for the evaluation of dif different spectral images. Indeed, they allow the evaluation of classic metrics (signal, noise, etc.) and advanced / innovative ones (Noise Power Spectrum (NPS), task-based transfer function (TTF) and detectability index) in clinical conditions close to those found for acquisitions in conventional scanners.

[0008] However, they are not suitable for spectral images because they are not composed of inserts with densities close to the contrast products used in clinical practice. Other test objects called "Dual-energy" or "Multi-energy" have these types of inserts but are not suitable for calculating these new advanced / innovative metrics. These characteristics constitute significant limitations to the translation of the results from the test object to humans.

[0009] There is thus a need to have a standardized test object to evaluate the performance of spectral images in combination of adapted metrics (classic and advanced / innovative). Statement of the invention

[0010] The invention proposes a test object for evaluating the performance of different images.

[0011] For this purpose, the invention proposes a test object for simulating an object in a medical imaging device, comprising the following stack, according to a height of the test object taken on a longitudinal axis XX:

[0012] - a first solid made of a first material;

[0013] - a second solid made of the second material;

[0014] - the first material being different from the second material;

[0015] - the first solid and the second solid each comprising several housings extending over a portion of the height of each solid and open on free faces of each of the first and second solids.

[0016] The invention is advantageously supplemented by the following characteristics, taken alone or in any of their technically possible combinations:

[0017] - it comprises several caps configured to tightly close each housing, each housing being adapted to receive a liquid.

[0018] - the first material of the first solid is PMMA and the second material of the second solid is extruded polystone.

[0019] - the first solid and the second solid are made up of several plates su perposed, the housings extending over part of the plates at the ends so as to leave solid central plates.

[0020] - each solid comprises three plates of 4 cm each or one plate of 8 cm and a 4 cm plate, the housings extending over two 4 cm plates or over one 8 cm plate, 75 mm long.

[0021] - it comprises five housings of 28.5 mm diameter, with a central housing being located at the center of each of the first and second solids and four housings positioned around the central housing, the centers of the peripheral housings being located 75 mm from the center of the central housing and 60 mm from the edge of the test object.

[0022] - each cap is adapted to tightly close each housing at by means of peripheral screws and an O-ring, for example a nylon seal.

[0023] - the test object is cylindrical in shape, 270 mm in diameter and 240 mm long, the first and second solids each being cylinders 270 mm in diameter and 120 mm long.

[0024] The test object according to the invention makes it possible to measure all of the metrics (classic & advanced / innovative presented above) useful for the evaluation of the different spectral images in varied clinical conditions.

[0025] The housings provided allow the introduction of inserts comprising different known concentrations (calcium and iodine in particular) or the direct injection of a contrast product with the desired concentration.

[0026] The test object according to the invention is thus modular and applies to various imaging modalities. PRESENTATION OF FIGURES

[0027] Other characteristics, aims and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0028] [Fig.l] illustrates an overview of the test object according to one embodiment of the invention;

[0029] [Fig.2] illustrates a side view of the test object according to one embodiment of the invention;

[0030] [Fig.3] illustrates a sectional view of the test object according to one embodiment of the invention.

[0031] Throughout the figures, similar elements bear identical references. DETAILED DESCRIPTION

[0032] The test object 1 illustrated in [Fig.l] is in the form of a cylinder composed of a first solid 11 made of a first material and a second solid 21 made of the second material. The test object extends from a first end 2 to a second end 3 in a longitudinal direction XX. The diameter of the test object is 270 mm and has a total length of 240 mm.

[0033] The first material is preferably different from the second material, in particular in terms of density and therefore contrast.

[0034] For example, the first material is PMMA and the second material is extruded polystone. These two materials make it possible to simulate peritoneal fat in the abdomen and abdominal tissues (liver, splenic, kidney) enhanced with iodine.

[0035] Of course, other materials can be used to simulate other tissues such as skeletal muscle or bone.

[0036] Advantageously, the test object 1 is composed of several cylindrical plates 11a, 11b, 11c, 21a, 21b, 21c superimposed on each other.

[0037] The use of several plates 11a, 11b, 11c, 21a, 21b, 21c makes it easier to manufacture the test object 1.

[0038] For reasons of homogeneity of the structure, each solid 11, 21 is made up of the same number of plates 11a, 11b, 11c, 21a, 21b, 22c.

[0039] For example, each solid 11 or 21 comprises three plates 11a, 11b, 11c or 21a, 21b, 21c. A different number of plates can of course be provided for each solid.

[0040] However, several plates of a solid can be replaced by a single plate of the same longitudinal dimension as that formed by the assembly of two plates.

[0041] Advantageously, each solid 11, 21 comprises several housings 12, 22, which are in the form of blind holes (comprising a bottom) formed in the height of each solid 11, 21. These housings 12, 22 extend over a portion of the height of each solid so that a central portion 4, 11c, 21a of the test object 1 is free of holes. As illustrated in [Fig.3], for each solid 11, 21 two plates out of three are crossed by the housings.

[0042] Each solid 11,21 comprises five housings 12,22 positioned at the center of the test object and at the four cardinal positions.

[0043] The four housings around the central housing have a center that is 75 mm from the center of the central housing and 60 mm from the edge of the test object.

[0044] The housings 12, 22 can be closed in a sealed manner by means of plugs 13, 23. For this purpose, a PMMA plug provided with several (for example four) peripheral screws and a Nylon O-ring is provided for each housing 12, 22.

[0045] Indeed, these housings 12, 22 are suitable for containing all types of liquids including in particular several types of contrast products of composition (for example based on atoms with high atomic number such as iodine, gadolinium, gold, bismuth, ytterbium, tantalum, hafnium, holmium), density and concentration chosen by the operator. In addition, in the absence of stoppers, these housings 12, 22 can contain different types of solid inserts of diameters adapted to the diameters thereof. Such inserts can be directly machined inside or inserted inter interchangeable. In addition, the inserts may not completely fill the corresponding slot in depth.

[0046] Advantageously, each plate 11a, 11b, 11c, 21a, 21b, 21c has a thickness: 4 cm thick. However, the plates 11a, 11b, 21b, 21c crossed by the housings can be grouped two by two into a single 8 cm plate.

[0047] Also, advantageously, each housing is cylindrical and has an internal diameter of 28.5 mm on each side and 75 mm in depth. The sections of the first and second solids 11, 21 which comprise housings into which the contrast agents and biological solutions (blood, water, serum) are injected make it possible to analyze different parameters such as the precision of the UH, the spatial resolution (in particular the task-based transfer function), the precision of the concentration of the atoms of a specific contrast agent (atoms with a high atomic number such as iodine, gadolinium, gold, bismuth, ytterbium, tantalum, hafnium, holmium).

[0048] The central section 4, 1 le, 21a which is homogeneous and not crossed by housings makes it possible to evaluate the amplitude, the homogeneity and the frequency distribution of the noise in the image in two different environments in particular via the use of the Noise Power Spectrum.

Claims

Claims

1. Test object (1) for simulating an object in a medical imaging device, comprising the following stack, according to a height of the test object taken on a longitudinal axis XX: - a first (11) solid made of a first material; - a second (21) solid made of the second material; the first material being different from the second material; the first solid (11) and the second solid (21) each comprising several housings (12, 22) extending over a part of the height of each solid (11, 21) and open on free faces of each of the first and second solids (11, 21).

2. Test object according to claim 1, comprising several stoppers (13, 23) configured to seal each housing (12, 22), each housing being adapted to receive a liquid.

3. Test object according to one of the preceding claims, wherein the first material of the first solid (11) is PMMA and the second material of the second solid (21) is extruded polystone.

4. Test object according to one of the preceding claims, in which the first solid (11) and the second solid (21) are made up of several superimposed plates (11a, 11b, 11c, 21a, 21b, 21c), the housings (12, 22) extending over a part of the plates (11a, 11b, 21b, 21c) at the ends so as to leave solid central plates (11c, 21a).

5. Test object according to claim 4, wherein each solid comprises three plates of 4 cm each, the housings extending over two plates (11a, 11b, 21b, 21c) over a length of 75 mm.

6. A test object according to any preceding claim, comprising five housings (12, 22) of 28.5 mm diameter, with a central housing being located at the center of each of the first and second solids (11, 21) and four housings positioned around the central housing, the centers of the peripheral housings being located 75 mm from the center of the central housing and 60 mm from the edge of the test object.

7. Test object according to one of claims 2 to 6, in which each cap (13, 23) is adapted to seal each housing (12, 22) by means of peripheral screws and an O-ring, for example a nylon seal.

8. Test object according to one of the preceding claims, of cy- lindic 270 mm in diameter and 240 mm long, the first and second solids each being cylinders 270 mm in diameter and 120 mm long.

Images