CROSS-REFERENCE TO RELATED APPLICATIONS

N/A

BACKGROUND

The present disclosure relates to systems and methods to produce images or maps of a subject using computed tomography data. More particularly, the present disclosure provides systems and methods for producing images and/or maps of a subject with reduced noise levels/increased contrast to noise ratios.

In computed tomography (CT) systems, an x-ray source projects a beam that is collimated to lie within an X-Y plane of a Cartesian coordinate system, termed the “imaging plane.” The x-ray beam passes through the object being imaged, such as a medical patient, and impinges upon an array of radiation detectors. The intensity of the radiation received by each detector element is dependent upon the attenuation of the x-ray beam by the object and each detector element produces a separate electrical signal that relates to the attenuation of the beam. The linear attenuation coefficient is the parameter that describes how the intensity of the x-rays changes when passing through an object.

To achieve this process, a source and detector array are rotated on a gantry within the imaging plane and around the object so that the projection angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements from the detector array at a given angle is referred to as a “view” and a “scan” of the object. These views are collected to form a set of views made at different angular orientations during one or several revolutions of the x-ray source and detector. In a two dimensional (2D) scan, data are processed to construct an image that corresponds to a 2D slice taken through the object. The prevailing method for reconstructing an image from 2D data is referred to in the art as the filtered backprojection (FBP) technique. This process converts the attenuation measurements from a scan into integers called “CT numbers” or “Hounsfield units”, which are used to control the brightness of a corresponding pixel on a display.

CT imaging has become the gold standard driving clinical care in a wide variety of clinical applications. As just one example, cerebral CT perfusion (CTP) imaging is widely used to diagnose acute ischemic stroke and identify patients who are most likely to benefit from endovascular reperfusion therapy, because parametric CTP maps can assist physicians to identify the existence of hypoperfused but salvageable tissue upon reperfusion, and to differentiate this tissue from irreversibly damaged tissue (ischemic core) for which reperfusion is futile or even lethal. CTP is usually performed together with a non-contrast head CT (NCCT) for ruling out intracranial hemorrhage and a CT angiography (CTA) for estimating the location of thrombus. This CT imaging package of CTP imaging and NCCT imaging is carried out in less than 10 minutes in the same imaging suite and bed position, which is highly efficient compared with other imaging protocols, such as a combination of CT and magnetic resonance imaging (MRI) imaging studies. Even for post stroke treatment follow-up or imaging work-ups of chronic stroke and other neurological diseases, a CTP study is often prescribed together with NCCT imaging to provide more comprehensive and mutually complementary diagnostic information.

Despite the clinical utility, the current CTP imaging technology still faces a major challenge reflected by poor contrast-to-noise ratio (CNR) of parametric CTP maps. This low CNR can hinder reliable or consistent stroke diagnosis for individual patients. For example, one clinical study (Gonzalez, “Current State of Acute Stroke Imaging,” Stroke 44, 3260-3264, 2013.) found that the CNR of an ischemic core in CTP maps could be smaller than “1”, while the same core identified in diffusion weighted MRI images demonstrated a CNR of more than “8”. Observations such as this motivated researchers to conclude that “the inherently poor CNR of CTP derived images is the fundamental flaw in the technique.” Morelli N, Rota E, Michieletti E, Guidetti D. The “Vexata Quaestio” on lacunar stroke: the role of CT perfusion imaging. AJNR Am J Neuroradiol. 2017; 38(2):E11-2.

Thus, there is a continuing need for new and improved imaging techniques that provide clinicians with robust and consistent information for clinical use, particularly, in critical care situations, such as head or brain imaging, including situations involving stroke.

SUMMARY

The present disclosure overcomes the aforementioned drawbacks by providing systems and methods for improving CT perfusion studies by reducing the noise in baseline image(s) by utilizing non-contrast CT image data to create the baseline image(s). For example, a non-contrast CT image volume data and CT perfusion data can be combined or “fused” to generate baseline image(s), such that the baseline image(s) have a higher CNR than delivered by the CT perfusion data, which substantially improves overall CNR of parametric maps generated from the CT perfusion data. For example, thee improved CNR is substantially greater than increased dose applied to the CT perfusion data could yield and/or without subjecting the patient to further dose because the non-contrast CT data is available. That is, the present disclosure recognizes that the noise of a Cerebral Blood Volume (CBV) map is strongly influenced by the noise level of the baseline CT image for both deconvolution and non-deconvolution-based CTP techniques. With this realization, the present disclosure provides systems and methods for improving CT perfusion studies by reducing the noise in baseline images.

In accordance with one aspect of the disclosure, a medical imaging system is provided that includes an x-ray source configured to deliver x-rays to an imaging patient. The medical imaging system also includes a detector array configured to receive the x-rays after passing the imaging patient and a controller configured to rotate the x-ray source and the detector array about the imaging patient as the x-ray source delivers the x-rays to the imaging patient and the detector array receives the x-rays. The system further includes a computer system configured to control operation of the x-ray source and the detector array to perform a non-contrast computed tomography (NCCT) imaging acquisition to acquire NCCT data. The computer system is further configured to control operation of the x-ray source and the detector array to perform a computed tomography perfusion (CTP) imaging acquisition to acquire CTP data, create a baseline image using the NCCT data, and generate a parametric map using the CTP data and the baseline image.

In accordance with another aspect of the disclosure, a method is provided for generating a parametric map of a subject's brain. The method includes receiving non-contrast computed tomography (NCCT) imaging data and receiving computed tomography perfusion (CTP) data. The method further includes creating a baseline image using the NCCT data and generating a parametric map using the CTP data and the baseline image

In accordance with one other aspect of the disclosure, a computer system is provided that is configured to generate a parametric map of a subject's brain. The computer system includes a memory storing or having access to store non-contrast computed tomography (NCCT) imaging data acquired from the subject and computed tomography perfusion (CTP) data acquired from the subject. The computer system also includes a processor having access to the memory and configured to create a baseline image using the NCCT data and generate a parametric map using the CTP data and the baseline image.

The foregoing and other aspects and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention, however, and reference is made therefore to the claims and herein for interpreting the scope of the invention.

