Methods and apparatus for extended low contrast detectability for radiographic imaging systems

Abstract

Evaluating dose performance of a radiographic imaging system with respect to image quality using a phantom, a channelized hotelling observer module as a model observer, and a printer, a plaque, or an electronic display includes scanning and producing images for a plurality of sections of the phantom using the radiographic imaging system, wherein the plurality of sections represent a range of patient sizes and doses and wherein the sections of the phantom contain objects of measurable detectability. Also included is analyzing the images to determine detectability results for one or more of the contained objects within the images of the plurality of sections of the phantom, wherein the analyzing includes using a channelized hotelling observer (CHO) module as a model observer; and displaying, via the printer, the plaque, or the electronic display, a continuous detectability performance measurement function using the determined detectability results.

What is claimed is: 
     
         1 . A method for evaluating dose performance of a radiographic imaging system with respect to image quality using a phantom, a channelized hotelling observer module as a model observer, and a printer, a plaque, or an electronic display, said method comprising:
 scanning and producing images for a plurality of sections of the phantom using the radiographic imaging system, wherein the plurality of sections represent a range of patient sizes and doses and wherein the sections of the phantom contain objects of measurable detectability;   analyzing the images to determine detectability results for one or more of the contained objects within the images of the plurality of sections of the phantom, wherein said analyzing comprises using a channelized hotelling observer (CHO) module as a model observer; and   displaying, via the printer, the plaque, or the electronic display, a continuous detectability performance measurement function using the determined detectability results.   
     
     
         2 . A method in accordance with  claim 1  wherein said displaying further comprises displaying the detectability performance measurement function as a function of fluxindex to obtain a family of detectability performance functions. 
     
     
         3 . A method in accordance with  claim 2  wherein said radiographic imaging system is a first radiographic imaging system, and further comprising reproducing imaging performance of the first radiographic imaging system using a second radiographic imaging system, said reproducing comprising:
 translating the family of detectability measure values at a flux index of the first radiographic imaging system to a family of detectability functions of a second radiographic imaging system using the families of detectability performance functions of both the first radiographic imaging system and the second radiographic imaging system; and 
 providing an indication of settings needed to produce said imaging performance on the second radiographic imaging system using a family of fluxindex values of the second radiographic imaging system. 
 
     
     
         4 . A method in accordance with  claim 2  further comprising displaying the family of detectability performance functions as a function of mAs at a fixed D w . 
     
     
         5 . A method in accordance with  claim 2  further comprising displaying the detectability performance functions as a function of CTDIvol at a fixed D. 
     
     
         6 . A method in accordance with  claim 2  further comprising displaying the detectability performance functions as a function of D m , at a fixed mAs. 
     
     
         7 . A method in accordance with  claim 1  further comprising:
 determining a first scaling parameter using at least one contrast value of an image relative to a selected contrast reference; 
 determining a second scaling parameter using a diameter of an object in the phantom relative to a selected reference object diameter; 
 scaling the detectability results of a plurality of objects in the phantom using the first scaling parameter and the second scaling parameter; and 
 using the resulting scaled detectability results of the plurality of objects in the phantom to obtain a one-dimensional detectability performance function as a function of fluxindex. 
 
     
     
         8 . A method in accordance with  claim 7  wherein said radiographic imaging system is a first radiographic imaging system, said method further comprising:
 reproducing the performance of the first imaging system using a second imaging system and the one-dimensional performance function of the first imaging system, said reproducing including finding a detectability value on a detectability performance function of the second radiographic imaging system and an associated fluxindex to indicate settings of the second radiographic imaging system needed to reproduce said performance. 
 
     
     
         9 . A method in accordance with  claim 7  further comprising displaying the one-dimensional detectability performance function as a function of mAs at a fixed D w . 
     
     
         10 . A method in accordance with  claim 7  further comprising displaying the one-dimensional detectability performance function as a function of CTDIvol at a fixed D w . 
     
     
         11 . A method in accordance with  claim 7  further comprising displaying the one-dimensional detectability performance function as a function of D weq  at a fixed mAs. 
     
     
         12 . A phantom for use with radiographic imaging systems, said phantom comprising one or more sections, wherein each section further comprises a plurality of cross-sectional areas that include:
 (a) a region having objects to be detected by the radiographic imaging system;   (b) a background region with no objects; and   (c) regions having densities matching objects to be detected and that are sufficiently large so as to enable the measurement of effective contrasts of the objects to be detected.   
     
     
         13 . A phantom in accordance with  claim 12  wherein the sections comprise discrete cylinders. 
     
     
         14 . A phantom in accordance with  claim 12  wherein the plurality of cross-sectional areas each comprise a continuously changing conical shape. 
     
     
         15 . A phantom in accordance with  claim 12  wherein the objects comprise cylindrically shaped objects. 
     
     
         16 . A phantom in accordance with  claim 12  wherein the objects comprise objects having ellipsoidally shaped surfaces. 
     
     
         17 . A phantom in accordance with  claim 12  wherein the multiplicity of cross-sectional areas comprise anthropomorphic shapes. 
     
     
         18 . A phantom in accordance with  claim 17  wherein the anthropomorphic shapes include shapes that simulate lesion models. 
     
     
         19 . A phantom in accordance with  claim 18  having a background that simulates anatomic features. 
     
     
         20 . A phantom in accordance with  claim 12  wherein the plurality of cross-sectional areas include non-circular shapes. 
     
     
         21 . A method for setting a protocol for imaging a patient using a computerized radiographic imaging device, said method comprising:
 (a) imaging a phantom containing a plurality of objects using a plurality of flux settings within an operating range for at least one operating protocol of the computerized radiographic imaging device to obtain projection data;   (b) reconstructing the projection data into a plurality of reconstructed images of the phantom corresponding to the plurality of flux settings using the radiographic imaging apparatus;   (c) for each said flux setting, with the computerized radiographic imaging apparatus:
 (1) automatically calculating a detectability of the objects in a reconstructed image corresponding to the flux setting; 
 (2) selecting the automatically calculated detectable objects in accordance with a detectability criterion; 
 (3) determining a contrast measure for the selected said objects; and 
 (4) associating a contrast performance with the flux setting of the image in accordance with the determined contrast measures; and 
   (d) imaging the patient with the computerized radiometric imaging device using a radiation dose in accordance with the associated contrast performance and flux settings to produce an image of the patient having a desired image quality.   
     
     
         22 . A method in accordance with  claim 21  wherein said imaging the phantom containing the plurality of objects comprises imaging the phantom containing a plurality of objects of different sizes and further wherein said automatically calculating the detectability of the objects comprises calculating the detectability of the objects of different sizes. 
     
     
         23 . The method of  claim 22  wherein said selecting the automatically calculated detectable objects in accordance with the detectability criterion comprises selecting smallest objects of said automatically calculated detectable objects. 
     
     
         24 . The method of  claim 22  wherein said imaging the phantom containing the plurality of objects of different sizes comprises imaging the phantom containing the plurality of objects of different sizes selected to generate samples along a logarithmic contrast level axis. 
     
     
         25 . The method of  claim 21  wherein said imaging the patient with the computerized radiometric imaging system in accordance with the associated contrast performance and flux settings comprises imaging the patient with the computerized radiometric imaging system using a limited dose scan in accordance with the associated contrast performance and flux settings. 
     
     
         26 . The method of  claim 21  performed for a selected protocol on both a first computerized radiographic imaging apparatus and on a second computerized radiographic imaging apparatus, and further comprising, for a selected contrast performance of the selected protocol of the first computerized radiographic imaging system, imaging an object with the selected protocol with the second radiographic imaging system at a flux setting having a contrast performance in accordance with the selected contrast performance of the first computerized radiographic imaging system. 
     
     
         27 . The method of  claim 21  wherein said computerized radiographic imaging apparatus is an energy discriminating radiographic imaging apparatus and said imaging the phantom containing the plurality of objects further comprises imaging the phantom containing a plurality of objects of different energy sensitivity. 
     
     
         28 . The method of  claim 27  wherein said imaging the phantom containing the plurality of objects of different energy sensitivity further comprises imaging the phantom containing objects comprising calcium hydroxyapatite. 
     
     
         29 . The method of  claim 27  wherein said imaging the patient with the computerized radiometric imaging system comprises imaging the patient to produce at least two images at different kV settings. 
     
     
         30 . The method of  claim 27  wherein said imaging the patient with the computerized radiometric imaging system comprises imaging the patient to obtain a set of basis material images. 
     
     
         31 . The method of  claim 30  wherein said imaging the patient to obtain the set of basis material images comprises imaging the patient to produce a calcium image and a water image. 
     
     
         32 . The method of  claim 27  wherein said imaging the patient with the computerized radiometric imaging system comprises imaging the patient to obtain data for at least one member of the set consisting of basis material images and basis material projection data, and further comprising combining said basis material images, said basis material projection data, or both to produce a monochromatic image at a selected keV. 
     
     
         33 . The method of  claim 21  wherein said determining the contrast measure for the selected said objects further comprises automatically:
 (a) calibrating the reconstructed images of the phantom to obtain calibrated phantom images; 
 (b) defining a map of pixel locations within a geometric area of each selected said object using the calibrated phantom images; and 
 (c) using the map of pixel locations to measure an average contrast measure, wherein said determined contrast measure is said average contrast measure. 
 
     
     
         34 . The method of  claim 21  performed for a plurality of operating modes of the computerized radiographic imaging system, wherein the operating modes includes a change in at least one of an X-ray tube energy of the computerized radiographic imaging system, a source filter and collimator of the computerized radiographic imaging system, and a reconstruction mode of the computerized radiographic imaging system. 
     
     
         35 . The method of  claim 34  wherein the reconstruction mode includes a non-linear reconstruction mode. 
     
     
         36 . The method of  claim 21  further comprising calibrating the phantom to compensate for manufacturing tolerances of the phantom and spectral characteristics of the computerized radiographic imaging system. 
     
     
         37 . The method of  claim 21  wherein said selecting the automatically calculated detectable objects in accordance with the detectability criterion comprises selecting a smallest said object using a Contrast Determination Factor (CDF) or a variation thereof. 
     
     
         38 . The method of  claim 21  wherein said selecting the automatically calculated detectable objects in accordance with the detectability criterion comprises selecting a smallest said object using a Rose Criterion Derivation. 
     
     
         39 . The method of  claim 21  wherein said selecting the automatically calculated detectable objects in accordance with the detectability criterion comprises selecting a smallest said object using a Rose-Ideal detectability index. 
     
     
         40 . The method of  claim 21  wherein said selecting the automatically calculated detectable objects in accordance with a detectability criterion comprises selecting a smallest said object using a matched filter. 
     
     
         41 . The method of  claim 40  wherein said reconstructing the attenuation data into a plurality of reconstructed images comprises non-linearly reconstructing the attenuation data into a plurality of reconstructed images. 
     
     
         42 . The method of  claim 21  wherein the computerized radiographic imaging system is a CT scanner. 
     
     
         43 . The method of  claim 21  wherein the computerized radiographic imaging system is a digital radiography system. 
     
     
         44 . The method of  claim 21  wherein the computerized radiographic imaging system is a mammography system. 
     
     
         45 . The method of  claim 21  wherein the computerized radiographic imaging system is a nuclear medicine system. 
     
     
         46 . The method of  claim 21  wherein the computerized radiographic imaging system is a SPECT system. 
     
     
         47 . The method of  claim 21  wherein steps (a) and (b) and steps (c)(1) through (c)(4) are performed for a plurality of imaging protocols, and wherein said associating the contrast performance with the flux setting of the image in accordance with the determined contrast measures comprises associating the contrast performance, the flux setting, and the performed imaging protocol used to image the phantom, and wherein imaging the patient with the computerized radiometric imaging system comprises selecting a dose, contrast performance, and protocol in accordance with the associated contrast performances, flux settings, and imaging protocols. 
     
     
         48 . The method of  claim 47  wherein a parameter of said plurality of imaging protocols is slice thickness. 
     
     
         49 . The method of  claim 47  wherein a parameter of said plurality of imaging protocols is water equivalent diameter. 
     
     
         50 . The method of  claim 47  wherein a parameter of said plurality of imaging protocols is scan time. 
     
     
         51 . The method of  claim 47  wherein a parameter of said plurality of imaging protocols is tube current. 
     
     
         52 . A method of determining an extended low contrast detectability performance function as a relation between a flux index and a contrast index for an operating range for a core operating mode of a radiographic imaging system using actual reconstructed images, the method comprising the steps of:
 selecting a plurality of protocols distributed across said operating range of the radiographic imaging system;   imaging a phantom containing a plurality of objects over each of the protocols;   computing a detectability for each object in order to determine a relative flux and contrast index set of ordered pairs for each object;   determining a smallest detectable object size for each contrast set;   computing the contrast index for each protocol for each contrast set; and   utilizing the ordered pairs of flux index and contrast index to determine the extended low contrast detectability performance function for the radiographic imaging system.   
     
     
         53 . The method of  claim 52  further comprising tracking the extended low contrast detectability performance function over time. 
     
     
         54 . The method of  claim 52  wherein said radiographic imaging system is a first computerized radiographic imaging system having a first extended low contrast detectability performance function, and further comprising:
 (a) performing said method on a second computerized radiographic imaging system having a second extended low contrast detectability function; and, 
 (b) using said determined first extended low contrast detectability performance function and said determined second extended low contrast detectability function, determining, for a first clinical protocol on said first computerized radiographic imaging system, an equivalent second clinical protocol for at least said second computerized radiographic imaging system corresponding to said first clinical protocol. 
 
     
     
         55 . The method of  claim 52  wherein said radiographic imaging system is a computerized radiographic imaging system and said method further comprising adjusting a scanning protocol of the computerized radiographic imaging system to reduce a dosage to the patient while maintaining imaging quality. 
     
     
         56 . The method of  claim 52  wherein said radiographic imaging system is a first computerized radiographic imaging system having a first low contrast detectability performance function, and further comprising:
 (a) performing said method on a second computerized radiographic imaging system having a second extended low contrast detectability function; and, 
 (b) using said determined first extended low contrast detectability performance function and said determined second extended low contrast detectability function, identifying protocols on said first computerized radiographic imaging system that relate to protocols on said second computerized radiographic imaging system having equivalent determined extended low contrast detectability function values.