Patent Application
20220273237
The present document relates to a method and system of quantifying lesion evolution of a portion of a body. Particularly, the present document relates to a method and system of quantifying, visualizing a lesion evolution of a portion of a body, based on magnetic resonance imaging techniques.
A lesion can be any damages or abnormal changes in a tissue of an organism, usually caused by a disease or trauma. Lesions can appear as a result of trauma or degenerative diseases. However, lesions can also indicate a region of a tumor. Lesions can exhibit different types of states, such as inflammation, edema, tissue destruction and necrosis. Lesions can occur anywhere in a body. Lesions may occur in humans, as well as other animals.
Lesions can be detected by different types of imaging techniques, including Magnetic Resonance Imaging (MRI).
A typical MRI scanner comprises a large, powerful magnet, and can send signals to, e.g., a body portion of a patient. The returning signals can be detected and converted into images of the body portion by a computing device. The images can be obtained in multiple planes (axial, sagittal, coronal, or oblique) without repositioning the patient.
The MRI techniques are generally based on relaxation properties of excited hydrogen nuclei (protons) of an object under test. When the object to be imaged is placed in a powerful, uniform magnetic field of the MRI scanner, the spins of the atomic nuclei of water in the object with non-integer spin numbers within the object all align either parallel or anti-parallel to the magnetic field. From an MR acquisition, several physical properties of the object under test can be determined. And an image can be reconstructed based on an acquired magnetic resonance sequence generated with the excitation.
Proton density (PD) refers to a concentration of protons in a tissue, wherein the protons are the hydrogen nuclei that resonate and give rise to the nuclear magnetic resonance signal. Since most visible tissue protons are resident in water, it is often seen as looking at a water content. The proton density PD of a tissue usually refers to the concentration of protons in the tissue, relative to that in the same volume of water at the same temperature.
The following time constants involved in the relaxation processes, which establish equilibrium following RF excitation, should be introduced in order to understand the MRI techniques. A nuclear magnetic resonance signal is affected by two simultaneous relaxation processes. The loss of coherence of the spin system attenuates the MRI signal with a time constant called a transverse relaxation time (T2). Concurrently, the magnetization vector slowly relaxes towards its equilibrium orientation that is parallel to the magnetic field by a time constant called longitudinal relaxation time (T1). A longitudinal relaxation rate R1 is the reciprocal of the longitudinal relaxation time T1 (R1=1/T1). A transverse relaxation rate R2 is the reciprocal of the transverse relaxation time T2 (R2=1/T2). The relaxation times T1 and T2 are typically measured in milliseconds (ms) or seconds (s). The corresponding relaxation rates R1 and R2 are therefore measured in units of ms−1 or s−1.
Normally, an acquired MRI sequence can result in images of the same anatomical section under different contrasts, such as T1-weighted, T2-weighted and PD-weighted images. The MRI techniques relies on differences in relaxation properties and proton density of the imaged tissue to display the different tissues with contrast, e.g., in different signal intensities or different colors, in the resulting MR images. The contrast in MR images originates from the fact that different tissues have, in general, different R1 and R2 relaxation rates, and different PD. For example, Warntjes, M. J. B. 1973, Dahlqvist, O. 1978, West, J., & Lundberg, P. 1958. (2008). Rapid magnetic resonance quantification on the brain: Optimization for clinical usage. Magnetic Resonance in Medicine, 60(2), 320-329 teaches that these physical properties, e.g., R1 and R2 relaxation rates and PD, can be acquired by performing a single MR acquisition, to provide quantitative values of the imaged portion.
Thus, using MRI technique, it is possible to generate various types of MR images, e.g., contrast weightings images which enhance and suppress different tissue types. By observing the MR contrast weighted images, e.g., the T1-weighted images, it is possible to get an idea of a status of an imaged portion.
However, even with the help of the MRI techniques, it is still difficult to accurately understand the status of a lesion describing how severe the tissue damage is, and/or how well the tissue recovers, as the grey scale MR images cannot provide too much details about the lesion evolution. Further, it is difficult to compare lesion statuses of different patients or patient groups, and/or of the same lesion over time in a quantitative way.
Thus, there is a need to provide a method and system to improve the quantifying, visualization and assessment of lesion evolution.
It is an object of the present disclosure, to provide a new method and system of quantifying lesion evolution of a portion, which eliminates or alleviates at least some of the disadvantages of the prior art.
The invention is defined by the appended independent claims. Embodiments are set forth in the appended dependent claims, and in the following description and drawings.
According to a first aspect, there is provided a method of quantifying lesion evolution, comprising: acquiring, by an MR scanning device, a first magnetic resonance, MR, sequence of a portion of a body comprising quantitative information of the portion; generating, by a processing circuit, a first MR image representing the portion, based on the first MR sequence, wherein each voxel of the first MR image represents a corresponding volume of the portion; and for a voxel of a first region of interest of the first MR image, determining a lesion evolution value indicating a status of lesion evolution, based on quantitative values of the voxel and a lesion evolution model; wherein the lesion evolution model comprises at least two sets of quantitative values comprising a first set of quantitative values representing the portion of an initial status of lesion evolution, and a second set of quantitative values representing the portion of a final status of lesion evolution; and wherein a lesion evolution value indicating a status of lesion evolution is associated to each of the at least two sets of quantitative values, wherein a first lesion evolution value indicating the initial status of lesion evolution is associated to the first set of quantitative values, and a second lesion evolution value indicating the final status of lesion evolution is associated to the second set of quantitative values.
Quantitative MRI (qMRI) is one division of the MRI techniques which measures absolute values, instead of measuring relative scales, of physical properties of a portion. The first MR sequence may be a quantitative MR sequence. By analyzing measured absolute values of certain physical properties of an imaged portion, it is possible to determine tissue composition of the imaged portion. Since the tissue composition normally changes along with the lesion evolution, e.g., due to inflammation and oedema, the tissue composition, and/or changes of the tissue composition, may be used to estimate and/or quantify lesion evolution of the imaged portion.
The tissue composition of the imaged portion may be estimated and/or quantified based on the measured absolute values of the physical properties. It may provide a fast and reliable tissue composition analysis of the imaged portion. The lesion evolution of the imaged portion may be estimated and/or quantified based on the determined tissue composition.
A lesion evolution value may indicate a status of lesion evolution, i.e. a severity of the lesion. For example, a low evolution value, such as 0, may resemble a healthy portion, a high evolution value, such as 100, may indicate tissue destructions and necrosis of the portion, and an evolution value in between, such as 1-99, may respectively indicate a unique status of lesion evolution between a healthy status to a necrosis status.
The method may provide a fast and reliable lesion evolution analysis of the imaged portion. It may facilitate monitoring of the lesion evolution or recovery over time. It may facilitate comparison of lesion evolution between portions of different objects, e.g., different patients. A quantified lesion evolution may be readily visualized.
Voxels are frequently used in the visualization and analysis of medical 3D images. A voxel is a volume element, used to represent a tiny 3D volume in an imaged portion. Here, each voxel of the MR image represents a corresponding tiny volume of the imaged portion. Thus, each voxel may have quantitative values, e.g., R1 and R2, representing physical properties of the corresponding tiny volume of the imaged portion.
A pixel is an element, used to represent a tiny 2D part in a 2D image. The 3D imaged portion may be sliced into a stack of slices each having a thickness. A voxel may be considered to correspond to a pixel for a given slice thickness. In other words, a voxel can be considered as a volumetric pixel for the given slice thickness. Thus, a 3D image may be converted into a series of 2D images. Consequently, the voxels may be converted into a series of pixels.
The step of acquiring the MR sequence and the step of generating the MR image may be one step instead of two. It is common that an MR scanner may perform an acquisition and result in one or more MR images representing a layer of the imaged portion.
The quantitative information may comprise information of at least two physical properties: a longitudinal relaxation rate R1, a transverse relaxation rate R2, and a Proton Density, PD.
Using a combination of at least two different physical properties, the tissue composition can be determined.
The physical properties R1 and/or R2 may be replaced by the physical properties longitudinal relaxation time T1 and transverse relaxation time T2, respectively.
The step of determining a lesion evolution value may comprise: among the at least two sets of quantitative values of the lesion evolution model, determining a set of quantitative values being closest to the quantitative values of the voxel, and determining the lesion evolution value of the voxel being equal to the lesion evolution value associated to the determined set of quantitative values.
The term “closest” may refer to one set of quantitative values being the same as another set of quantitative values.
Alternatively, the term “closest” may refer to one set of quantitative values having a least difference, i.e. a least deviation, from another set of quantitative values. There are many known mathematical methods for comparing two sets of values and determining a difference between them.
The method may comprise for at least one of the at least two sets of quantitative values, calculating the lesion evolution value to be associated, based on said set of quantitative values.
When said set of quantitative values comprises a value of the longitudinal relaxation rate and a value of the transverse relaxation rate, the method may further comprise calculating the lesion evolution value to be associated by
Lesion Evolution Value=norm(R1)*norm(R2),
wherein Lesion Evolution Value refers to the lesion evolution value to be associated to said set of quantitative values, R1 and R2 respectively refer to the values of the longitudinal relaxation rate and the transverse relaxation rate of said set of quantitative values, norm refers to a norm function.
The above equation is an example of how to determine the lesion evolution value based on the set of quantitative values.
The method may comprise scatter-plotting the at least two sets of quantitative values into at least two lesion evolution points, respectively, in a coordinate system, wherein the first and second set of quantitative values are scatter-plotted into a first lesion evolution point and a second lesion evolution point, respectively.
The coordinate system may be a Cartesian coordinate system. The coordinate system may be of different dimensions, such as two dimensions or three dimensions, depending on the number of values of each set of quantitative values. For example, if quantitative information comprises information of two physical properties: R1 and R2, then the coordinate system may be a two-dimensional coordinate system comprising an x-axis and a y-axis representing the values of R1 and R2, respectively.
The method may comprise generating a lesion evolution curve passing through the at least two lesion evolution points one by one in the coordinate system, following an order of lesion evolution from the initial status to the final status, wherein the lesion evolution curve starts from the first lesion evolution point, and ends at the second lesion evolution point, or following an order of lesion evolution from the final status to the initial status, wherein the lesion evolution curve starts from the second lesion evolution point, and ends at the first lesion evolution point.
The lesion evolution curve may be generated by connecting the lesion evolution points one by one in the coordinate system. The lesion evolution curve may be continuous or comprising at least two discontinuous portions.
The lesion evolution curve may comprise a straight portion.
The method may comprise generating a parametric representation describing a relationship of the at least two lesion evolution points in the coordinate system, based on the at least two sets of quantitative values.
The parametric representation may be a parametric equation defining a group of quantities as functions of independent parameters. Parametric equations are commonly used to express points making up a curve or surface of a coordinate. For example, the parametric representation may be a polynomial function describing a relationship of the at least two lesion evolution points in the coordinate system, based on the at least two sets of quantitative values.
The method may comprise creating a predetermined number of new lesion evolution points between the first and the second lesion evolution point in the coordinate system, based on the generated lesion evolution curve or the generated parametric representation, wherein each of the new lesion evolution points corresponds to a new set of quantitative values.
The new lesion evolution points may be generated by interpolation.
The method may comprise for each new set of values of quantitative information, associating a new lesion evolution value indicating a new status of lesion evolution.
For each new set of quantitative values, the associated new lesion evolution value may be determined based on the generated lesion evolution curve or the generated parametric representation, and the at least two sets of quantitative values and their associated lesion evolution values.
The lesion evolution value, the lesion evolution point, and the set of quantitative values may have a one-to-one corresponding relationship. That is, by knowing the quantitative values of a voxel representing a corresponding volume of a portion, the voxel's lesion evolution value for indicating the status of lesion evolution of the corresponding volume can be determined.
In other words, the lesion evolution points in the coordinate system may link the lesion evolution values of a voxel with the quantitative values of said voxel.
For a new lesion evolution point positioned between the first and second lesion evolution point, its associated new lesion evolution value may be determined by the position of the new lesion evolution point along the lesion evolution curve.
For example, if the new lesion evolution point is positioned in the middle point along the lesion evolution curve between the first and second lesion evolution point, its associated new lesion evolution value may be an average of the first and second lesion evolution value.
The method may comprise generating a new lesion evolution curve or refining an existing lesion evolution curve in the coordinate system, which passes through the at least two lesion evolution points and the generated new lesion evolution points one by one, following an order of lesion evolution from the initial status to the final status, wherein the generated new lesion evolution curve or the refined lesion evolution curve starts from the first lesion evolution point, and ends at the second lesion evolution point, or following an order of lesion evolution from the final status to the initial status, wherein the generated new lesion evolution curve or the refined lesion evolution curve starts from the second lesion evolution point, and ends at the first lesion evolution point.
For example, the first lesion evolution value is 0 and the second lesion evolution value is 4, and there are three newly created lesion evolution points sequentially positioned between the first and the second lesion evolution points based on the parametric representation. These three new lesion evolution points may be used to refine the already generated lesion evolution curve. The associated new lesion evolution values, e.g., 0.5, 2.5 and 3, for the three new set of values of quantitative information may be determined based on the parametric representation, and the first and the second lesion evolution value of the end points of the lesion evolution curve.
The new lesion evolution points and the at least two lesion evolution points may be evenly positioned along the generated new lesion evolution curve or the refined lesion evolution curve. The associated lesion evolution values of the at least two sets of quantitative values and of the new sets of quantitative values may form an arithmetic progression; wherein the arithmetic progression starts with the first lesion evolution value, and ends with the second lesion evolution value; and wherein a position of each lesion evolution value of the arithmetic progression corresponds to a position of its corresponding lesion evolution point along the generated new lesion evolution curve or the refined lesion evolution curve.
An arithmetic progression is a sequence of numbers, wherein a difference between any two consecutive numbers is constant.
For example, the first lesion evolution value is 0 and the second lesion evolution value is 100, and there are nine new lesion evolution points sequentially positioned between the first and the second lesion evolution points along the lesion evolution curve. Then, the newly created lesion evolution point positioned immediately adjacent to the first lesion evolution point may have a lesion evolution value “10”, its next lesion evolution point may have a lesion evolution value “20”, . . . , and the nineth new lesion evolution point positioned immediately adjacent to the second lesion evolution point may have a lesion evolution value “90”. In this example, the lesion evolution values of the lesion evolution points form an arithmetic progression (0, 10, 20, . . . , 90, 100), regardless of whether the new lesion evolution points are arranged evenly in between the first and second lesion evolution point.
The term “evenly” may refer to a fixed distance between any two adjacent lesion evolution points along the lesion evolution curve. As the previous example, if the nine new lesion evolution points are evenly and sequentially positioned between the first and the second lesion evolution points along the lesion evolution curve, the lesion evolution values of these nine lesion evolution points together with the first lesion evolution value 0 and the second lesion evolution value 100, may form an arithmetic progression having 11 numbers, starts with 0 and ends with 100. Consequently, the nine lesion evolution values of the nine new lesion evolution points are respectively 10, 20, . . . , 80 and 90. That is, the arithmetic progression is 0, 10, 20, . . . , 80, 90, 100.
The initial status may be a normal status and the final status may be an abnormal status. Alternatively, the initial status may be an abnormal status and the final status may be a normal status.
The normal status may refer to a healthy status of a portion. The abnormal status may refer to an unhealthy status, including but not limited to an inflammation status, an oedema status, or a necrosis status.
The lesion evolution model may cover an entire lesion evolution from a healthy status to a necrosis status, or from the necrosis status to the healthy status. Alternatively, the lesion evolution model may cover only a part of the entire lesion evolution.
The method may comprise visualizing lesion evolution of the portion.
The step of visualizing lesion evolution may comprise displaying, by a user interface, the determined lesion evolution value.
The method may comprise repeating the step of determining a lesion evolution value for each voxel of the first region of interest. That is, the status of lesion evolution of any volume corresponding to a voxel of the first region of interest may be determined.
The first region of interest may be a part of the first MR image or the entire first MR image.
An average lesion evolution value of the first region of interest may be determined. This average lesion evolution value may indicate an average status of lesion evolution of a portion corresponding to the first region of interest of the first MR image. Thus, the status of lesion evolution of the first region of interest may be represented by one value, which can simplify the representation of the lesion status. That is, the lesion status of the portion may be visualized by one or more numerical values instead of any images, e.g., the MR images with an overlay in
Even though the numerical representation of the lesion status of the portion may be considered simple, it is a powerful tool in many scenarios. For example, the numerical representation can be used to provide a fast comparison between different patient groups, and/or between a patient group and its healthy peers. Further, the numerical representations of a same patient may change over time and from scan to scan, which can be used to monitor the lesion status development and recovery process of a patient.
The average values calculated for one or more regions of the MR image may be displayed and/or output as a table, e.g., for recording and reporting.
The method may comprise for each determined lesion evolution value, calculating a volume size of a partial portion having the status of lesion evolution indicated by said determined lesion evolution value.
It is possible to determine an absolute volume size, e.g., in the unit of ml, of a partial portion of a tissue corresponding to the first region of interest of the MR image, having said determined status of lesion evolution.
Alternatively, the volume size may be a percentage value, indicating a percentage of the partial portion having said determined status of lesion evolution.
This may provide additional valuable information about the tissue corresponding to the first region of interest of the MR image, e.g., exactly how much tissue exhibits a status of necrosis within the tissue.
The method may comprise displaying a distribution of determined lesion evolution values for each voxel of the first region of interest. The distribution may in the form of histogram or a table of numbers.
The distribution of the lesion evolution values may provide a fast and straightforward view of the overall status of the tissue.
The distribution of the lesion evolution values can be used for monitoring the lesion evolution of one patient over time or comparing the lesion evolutions of different patients. It is advantageous as it is much easier to perform a comparison between two distributions than performing a comparison between two MR images.
The step of visualizing lesion evolution of the portion may comprise displaying the first MR image, wherein the voxels of the first region of interest are displayed differently, based on their respective lesion evolution value.
The voxels of the first region of interest may be displayed with different colors and/or different intensities based on their respective lesion evolution values.
For example, a voxel having a high lesion evolution value may be displayed in a high intensity and/or a bright color, and another voxel having a low lesion evolution value may be displayed in a low brightness and/or a dark color.
Colors and/or intensities may visualize the status of lesion evolution.
The term “intensity”, also known as “signal intensity”, in the field of MR may refer to a shade of grey of a tissue or of a voxel representing the tissue in an MR image. Generally, a high intensity means it would look “white/bright” in the MR image, an intermediate intensity means it would look “grey” in the MR image, and a low intensity means it would look “black” in the MR image.
The step of visualizing lesion evolution of the portion may comprise displaying the first MR image or a different MR image representing the portion as a background image; and displaying an overlay to the background image, wherein voxels of the overlay corresponding to the voxels of the first region of interest are displayed differently, based on the lesion evolution values of the voxels of the first region of interest.
The different MR image may be an MR image without any quantitative information. For example, the different MR image may be a T1-weighted (T1W) image.
By displaying the background image representing an anatomy of the imaged portion, a user may easily correlate a lesion evolution value to an original anatomy of the lesion portion, such that the assessment of the lesion can be facilitated.
The method may comprise displaying a color scale as a reference for visualizing a lesion evolution value for each displayed color of the voxels displayed differently; and/or displaying an intensity scale as a reference for visualizing a lesion evolution value for each displayed intensity of the voxels displayed differently.
The method may comprise acquiring a second MR sequence of the portion comprising quantitative information of the portion; generating a second MR image representing the portion, based on the second MR sequence, wherein the second MR image comprises a second region of interest corresponding to the first region of interest; for a voxel of the second region of interest, determining a second lesion evolution value, based on quantitative values of said voxel of the second region of interest and the lesion evolution model; and based on the determined second lesion evolution value, and the lesion evolution value of its corresponding voxel of the first region of interest, determining a change of status of lesion evolution of the portion during a first time when the first MR sequence of the portion being acquired to a second time when the second MR sequence of the portion being acquired.
This may be advantageous as it is possible to compare the lesion evolution of a same lesion over time for a patient. This may facilitate a better monitoring of the changes of lesions. This may be used for predicting further lesion changes, such as the tissue destruction progress.
The portion of the body may comprise a head.
According to a second aspect, there is provided a system for quantifying lesion evolution, comprising a processing circuit configured to: acquire a first magnetic resonance, MR, sequence of a portion of a body comprising quantitative information of the portion; generate a first MR image representing the portion, based on the first MR sequence, wherein each voxel of the first MR image represents a corresponding volume of the portion; and determine a lesion evolution value indicating a status of lesion evolution for a voxel of a first region of interest of the first MR image, based on quantitative values of the voxel and a lesion evolution model; wherein the lesion evolution model comprises at least two sets of quantitative values, comprising a first set of quantitative values representing the portion of an initial status of lesion evolution, and a second set of quantitative values representing the portion of a final status of lesion evolution; wherein a lesion evolution value indicating a status of lesion evolution is associated to each of the at least two sets of quantitative values, wherein a first lesion evolution value indicating the initial status of lesion evolution is associated to the first set of quantitative values, and a second lesion evolution value indicating the final status of lesion evolution is associated to the second set of quantitative values.
The system may further comprise a user interface configured to display information for visualizing lesion evolution of the portion.
The user interface may be configured to output information, such as texts, sounds, images, etc.
The user interface may be configured to receive input, e.g., a command, from a terminal or an input device via a wire or wirelessly. The user interface may be configured to receive input from a user.
According to a third aspect, there is provided a non-transitory computer readable recording medium having computer readable program code recorded thereon which when executed on a device having processing capability is configured to perform the method of the first aspect.
The present invention will now be described more fully with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown.
In connection with
The system 1 comprises a processing circuit 3. The processing circuit 3 is configured to carry out overall control of functions and operations of the system 1. The processing circuit 3 may include a processor, such as a central processing unit (CPU), microcontroller, or microprocessor. The system 1 may comprise a memory. The processing circuit 3 may be configured to execute program codes stored in the memory, in order to carry out functions and operations of the system 1.
The memory may be one or more of a buffer, a flash memory, a hard drive, a removable medium, a volatile memory, a non-volatile memory, a random access memory (RAM), or another suitable device. In a typical arrangement, the memory may include a non-volatile memory for long term data storage and a volatile memory that functions as system memory for the system 1. The memory may exchange data with the processing circuit 3 over a data bus. Accompanying control lines and an address bus between the memory and the processing circuit 3 also may be present.
Functions and operations of the system 1 may be embodied in the form of executable logic routines (e.g., lines of code, software programs, etc.) that are stored on a non-transitory computer readable medium (e.g., the memory) of the system 1 and are executed by the processing circuit 3. Furthermore, the functions and operations of the system 1 may be a stand-alone software application or form a part of a software application that carries out additional tasks related to the system 1. The described functions and operations may be considered a method that the corresponding device is configured to carry out. Also, while the described functions and operations may be implemented in software, such functionality may as well be carried out via dedicated hardware or firmware, or some combination of hardware, firmware and/or software.
The system 1 may comprise an MR scanning device 2. The MR scanning device 2 may be configured to acquire an MR sequence of a portion comprising a head. A plurality of slices may be generated based on the MR sequence of the portion, wherein each slice represents a layer of the portion.
The system 1 may comprise a user interface 4. The user interface 4 may be configured to output data and information, e.g., determined lesion evolution values, a first and second MR image. The user interface 4 may be configured to receive data and information, such as a command, from one or several input devices. The input device may be a computer mouse, a keyboard, a track ball, a touch screen, or any other input device. The user interface 4 may send the received data and information to the processing circuit 3 for further processing.
The method of quantifying lesion evolution comprises acquiring, by an MR scanning device 2, a first magnetic resonance, MR, sequence of a portion of a body comprising quantitative information of the portion; generating, by a processing circuit 3, a first MR image representing the portion, based on the first MR sequence, wherein each voxel of the first MR image represents a corresponding volume of the portion.
It is known that conventional imaging techniques, e.g., conventional MRI techniques, can generate images of a relative scale, such as contrast weighted images of a relative intensity scale. However, quantitative MRI (qMRI) techniques can measure absolute values of physical properties of observed tissues of the imaged portion. That is, a quantitative MRI acquisition may generate an MR sequence comprising quantitative information of the observed tissue. An MR image may be generated to represent the observed tissue, based on the MR sequence. The acquisition of the MR sequence and generation of the MR image may be two independent steps or combined as one step.
The application uses Multiple Sclerosis (MS) as the example for illustrating how the invention works. However, other diseases are analogously applicable.
Multiple Sclerosis (MS) is a well-known autoimmune disease and is characterized by focal areas of demyelination, inflammation, axonal loss and gliosis in neurological tissue. These changes of tissue occur dynamically, and not in any typical order.
Typically, the lesion will progress over time. Lesion evolution may represent the change of lesion tissue over time, e.g., from an initial status to a final status. The initial status and the final status may be defined differently, e.g., covering an entire lesion progress or a partial part of the entire lesion progress.
The lesion may progress or recover, e.g., by remyelination, to a healthy status. If no recovery occurs, the lesion may undergo necrosis, and an expansion of extracellular space may form, caused by tissue destruction which would cause extracellular free water to accumulate within the lesion tissue.
The changes of tissues may to some extent be observed in the contrast weighted MRI images generated by the conventional MRI techniques without quantitative information. For example, the MS lesion can be detected in a T2-weighted MR image by their hyperintense appearance. The MS lesions may shrink in size and become less hyperintense over time due to remyelination and decreasing edema. During active inflammation, most MS lesions appear hypointense in the T1-weighted image, but some may appear isointense. The hypointense appearance in this phase is a sign of inflammation, edema, demyelination and glial activation. Progressive repair processes including remyelination and resorption may change the tissue composition, causing the lesion to appear isointense again. However, some portion of the lesions may evolve to persistent black holes which is associated with permanent demyelination and severe axonal loss with irreversible tissue destruction and necrosis. The relevant information can be seen in e.g., Àlex Rovira, Cristina Auger, & Juli Alonso. (2013). Magnetic resonance monitoring of lesion evolution in multiple sclerosis. Therapeutic Advances in Neurological Disorders, 6, and Sahraian, M. A., Radue, E.-W., Haller, S., & Kappos, L. (2010). Black holes in multiple sclerosis: definition, evolution, and clinical correlations. Acta Neurologica Scandinavica, 122(1), 1-8.
In connection with
The T2FLAIR image is based on an MR sequence with an inversion recovery set to null fluids. When an MS lesion suffers from severe tissue destruction, it may generate a hypointense signal in the T2FLAIR image. This is caused by the increased water content, which is suppressed by the inversion pulse in the Fluid-attenuated inversion recovery (FLAIR) setting. In other words, when the imaged portion is the brain, the T2FLAIR image can highlight MS lesions by suppressing CSF effects on the image. Thus, in T2FLAIR images, such as
In the T1W images, such as
Three MS lesions of different lesion statuses are respectively marked as 1, 2 and 3 in
Both the T2FLAIR images and the T1W images generated by the conventional MRI techniques cannot give any sufficient information of an exact lesion status. In other words, it is not possible to fully understand the severeness of inflammation and destruction of a lesion tissue from the conventional contrast weightings.
In connection with
It is known that the qMRI techniques can measure absolute values of different physical properties of the imaged portion, e.g., the longitudinal relaxation rate R1, the transverse relaxation rate R2, and the proton density PD. The relaxation rates R1 and R2 are the respective inverse of the relaxation times T1 and T2, i.e. R1=1/T1 and R2=1/T2. The absolute values of physical properties measured by the qMRI techniques are independent of the MR scanning device's settings, and inhomogeneities of the magnetic field.
Different tissue types, such as white matter (WM), gray matter (GM) and cerebrospinal fluid (CSF) of the brain tissues, normally have different absolute values of physical properties, as seen in West, J. 1982, Warntjes, M. 1973, & Lundberg, P. 1958. (2012). Novel whole brain segmentation and volume estimation using quantitative MRI. European Radiology, 22(5), 998-1007. Table. 1 is an example of R1, R2 and PD values of WM, GM and CSF measured at 1.5 T.
Based on the measured absolute values of at least two physical properties, a tissue composition of the imaged tissue may be determined. For example, if the values of R1 and PD of one tissue are 1.7 s −1 and 67%, respectively, the imaged tissue is determined to be WM, based on Table 1.
Consequently, when inflammation, edema and tissue destruction happen, due to the increased water content, the R1 and R2 values of the tissue may decrease and the PD value of the tissue may increase. When the destruction is severe, an extracellular space may be widened and filled by water. Then the absolute values of R1, R2 and PD of the imaged tissue may be similar to that of the CSF in Table 1, due to the large amount of water.
An MR image representing a portion of a brain of a patient is respectively shown in the upper left corner and bottom right corner of
Each data point in the plot of
The data points represented the voxels of the healthy region of interest and the voxels of the lesion region of interest are displayed in the plot of
In the plot of
GM and CSF are marked in the plot of
In the plot of
When the MS lesion is formed, e.g., due to demyelination, inflammation and edema, changes of the composition of the healthy brain tissues may happen. Consequently, the imaged portion comprising MS lesions may present a different pattern, e.g., a R1-R2 pattern, different from the typical pattern of the healthy brain parenchyma. Such a different pattern can be called a migration pattern. The migration pattern visualizes the changes in the quantitative values that occur during the different stages of the lesion evolution. Comparing to the brighter data points, the darker data points form the migration patten of a reduced R1 and/or R2 values.
In the lesion region of interest, a faint hyperintense (bright) area representing the lesion tissue can be seen. Moving towards the center of the hyperintense area, the signal intensity is increased, and the R1 and R2 values of the voxels are further decreased. A necrotic core can be seen in the center of the lesion, which causes an influx of free water, resulting the quantitative values of the voxels very close to that of the CSF in Table 1.
Some of the brighter and darker data points overlap in the plot of
The quantitative information may comprise information of at least two of physical properties: a longitudinal relaxation rate R1, a transverse relaxation rate R2, and a Proton Density, PD. The physical properties R1, R2 can be replaced by T1, T2, respectively. That is, plotting R1 and R2 values as in
A combination of more than two physical properties may be used. For example, values of more than two physical properties may be plotted in a multiple-dimensional space. For example, if the quantitative information comprises information of R1, R2 and PD, a three-dimensional (3D) space (R1-R2-PD space) may be used to plot the R1, R2 and PD values.
The plot can be used for facilitating analysis of the imaged portion. However, the analysis can be performed merely based on quantitative information of the portion, without using any plots.
The method of quantifying lesion evolution comprises for a voxel of a first region of interest of the first MR image, determining a lesion evolution value indicating a status of lesion evolution, based on quantitative values of the voxel and a lesion evolution model. The lesion evolution model comprises at least two sets of quantitative values comprising a first set of quantitative values representing the portion of an initial status of lesion evolution, and a second set of quantitative values representing the portion of a final status of lesion evolution. The lesion evolution model may comprise additional sets of quantitative values representing the portion of intermediate statuses of lesion evolution, between the initial and final status of lesion evolution.
A more accurate estimation of lesion evolution status may be achieved by a large number of sets of quantitative values. For each set of quantitative values, there may be an evolution value indicating the status of lesion evolution associated to the set of quantitative values. A first lesion evolution value indicating the initial status of lesion evolution is associated to the first set of quantitative values, and a second lesion evolution value indicating the final status of lesion evolution is associated to the second set of quantitative values.
The lesion evolution value to be associated may be calculated based on said set of quantitative values.
For example, when a set of quantitative values comprises a value of the longitudinal relaxation rate R1 and a value of the transverse relaxation rate R2, the lesion evolution value to be associated may be calculated by these two values R1 and R2. One example is
Lesion Evolution Value=norm(R1)*norm(R2).
Lesion Evolution Value refers to the lesion evolution value to be associated to said set of quantitative values, and norm refers to a norm function.
The above equation is an example of how to determine the lesion evolution value based on the set of quantitative values. For example, the first lesion evolution value indicating the initial status of lesion evolution associated to the first set of quantitative values may be calculated, and/or the second lesion evolution value indicating the final status of lesion evolution associated to the second set of quantitative values may be calculated.
The lesion evolution values associated to other sets of quantitative values may be calculated by the same equation. Alternatively, they can be determined by known mathematical methods, based on the calculated lesion evolution value and the sets of quantitative values, such as interpolation.
In connection with
From
The lesion evolution model may match the tissue composition to a lesion evolution status. That is, based on the lesion evolution model and a set of quantitative values, it is possible to determine the lesion evolution status of the tissue having the quantitative values.
The R1 and R2 values of the upper point “WM” in
The lesion evolution model may comprise a plurality of sets of quantitative values. The lesion evolution value of a voxel of an MR image (representing an imaged tissue) may be determined by comparing its quantitative values (e.g., R1 and R2 values) with the plurality of sets of quantitative values of the lesion evolution model. A set of quantitative values of the lesion evolution model which is closest to the quantitative values of the voxel may be determined, and the lesion evolution value of the voxel may be determined to be equal to the lesion evolution value associated to the determined set of quantitative values.
For example, if the R1 and R2 values of a voxel corresponding to an imaged tissue are 1.5 s−1 and 12.9 s−1, respectively, which are closest to the first set of R1 and R2 values of WM (R1=1.6 s−1 and R2=12.8 s−1), the lesion evolution value of this tissue can be determined to be equal to the lesion evolution value associated to the determined first set of quantitative values. In other words, this tissue is considered to be a healthy tissue.
The term “closest” may be interpreted as a minimal deviation between two sets of data. There are various mathematical ways to calculate such deviation between two sets of data, each set comprising at least two elements.
The at least two sets of quantitative values of the lesion evolution model may be scatter-plotted as at least two lesion evolution points, respectively in a coordinate system, wherein the first and second set of quantitative values are scatter-plotted into a first lesion evolution point, e.g., the lesion evolution point “WM” and a second lesion evolution point, e.g., the lesion evolution point “CSF” in the R1-R2 space of
The method may comprise generating a lesion evolution curve passing through the at least two lesion evolution points one by one in the coordinate system, following an order of lesion evolution from the initial status to the final status, wherein the lesion evolution curve starts from the first lesion evolution point, e.g., the lesion evolution point “WM”, and ends at the second lesion evolution point, e.g., the lesion evolution point “CSF” in the R1-R2 space of
The lesion evolution curve may be generated based on the diamond-shaped points of
In
Alternatively, or in combination, a parametric representation describing a relationship of the at least two lesion evolution points in the coordinate system, based on the at least two sets of quantitative values, may be generated, with or without scatter-plotting the at least two sets of quantitative values.
The lesion evolution curve may be generated by connecting the at least two lesion evolution points one by one.
The lesion evolution curve may be a continuous line or may comprise a plurality of discontinuous portions. The lesion evolution curve may comprise a straight portion and/or a curved portion.
A portion of the lesion evolution curve between two lesion evolution points may be straight, e.g., a shortest straight line between the two lesion evolution points in the coordinate system.
The portion of the lesion evolution curve between two lesion evolution points may be curved. The exact shape of the curve may be defined by the parametric representation.
Following any one of the four examples of lesion evolution curves of
However, if the lesion recovers, it may travel along the lesion evolution curve in the opposite direction. The quantitative values of the physical properties, e.g., R1 and R2, of the tissue may travel from left to right following any of the examples of the lesion evolution curves.
The final status and the initial status may be determined based on different types of lesions. The initial to final status may cover an entire lesion process of health to necrosis, or a recover process. The initial to final status may cover only a part of the entire process.
The set of quantitative values and/or the combination of physical properties may be different for different types of lesions and/or different body portions. For example, for a brain tissue, it is known that it comprises mainly white matter, grey matter and water. However, a knee portion comprises mainly muscles, bones and cartilage. Naturally, the lesion evolution model for different diseases of different body portions may be very different.
It can be difficult to predict the exact pathological migration pattern, e.g., the diamond-shaped points in
Based on the generated lesion evolution curve, a predetermined number of new lesion evolution points may be generated between the first and the second lesion evolution point in the coordinate system. The new lesion evolution points may be points of the lesion evolution curve.
Based on the parametric representation, a predetermined number of new lesion evolution points may be generated between the first and the second lesion evolution point in the coordinate system. Each of the new lesion evolution points corresponds to a new set of quantitative values. The new sets of quantitative values may also fulfill the parametric representation.
For each tissue (a voxel of an MR image presenting the tissue), its lesion evolution value may be determined to be the lesion evolution value of the lesion evolution point having a shortest distance to the evolution point of the tissue. A large number of lesion evolution points may improve the accuracy of the method.
For each new set of quantitative values, a new lesion evolution value indicating a new status of lesion evolution may be associated. The associated new lesion evolution value may be determined based on the generated lesion evolution curve or the generated parametric representation, and the at least two sets of quantitative values and their associated lesion evolution values.
After the generation of the new lesion evolution points, a new lesion evolution curve may be generated in the coordinate system. The new lesion evolution curve may start from the first lesion evolution point, pass through the new lesion evolution points one by one, end at the second lesion evolution point, following an order of lesion evolution from the initial status to the final status. The new lesion evolution curve may start from the second lesion evolution point, pass through the new lesion evolution points one by one, end at the first lesion evolution point, following an order of lesion evolution from the final status to the initial status.
Alternatively, or in combination, after the generation of the new lesion evolution points, an existing lesion evolution curve in the coordinate system, e.g., any of the four examples of the lesion evolution curves of
The generated new lesion evolution points and the at least two lesion evolution points may be evenly positioned along the generated new lesion evolution curve or the refined lesion evolution curve.
The associated lesion evolution values of the at least two sets of quantitative values and of the new sets of quantitative values may form an arithmetic progression, starting with the first lesion evolution value and ending with the second lesion evolution value. A position of each lesion evolution value of the arithmetic progression corresponds to a position of its corresponding lesion evolution point along the generated new lesion evolution curve or the refined lesion evolution curve.
For example, the lesion evolution curve may comprise 101 points evenly distributed throughout the line, each being assigned with a lesion evolution value being an element of an arithmetic progression of 101 elements, which are 0, 1, 2, . . . , 98, 99 and 100. A lesion evolution value of 0 indicates a healthy status, a lesion evolution value of 50 indicates a status of a progressed lesion, and a lesion evolution value of 100 indicates a status of total tissue destruction.
Although the lesion evolution curves are used as examples, it is noted that the lesion evolution model may merely comprise sets of quantitative values. These set of quantitative values may be presented in the form of a table, a polynomial function, or a parametric curve for defining the relationship of the sets of quantitative values.
The method may comprise repeating the step of determining a lesion evolution value for each voxel of the first region of interest. Consequently, the lesion evolution value for each voxel of the first region of interest may be determined. The lesion evolution value for each voxel of the first MR image may be determined.
In connection with
The method may comprise segmenting a part of the imaged portion. The segmenting may result in a region of interest of the MR image representing the segmented part of the imaged portion. Segmenting or segmentation is a well-known method for analyzing the MR images.
The lesion evolution of the portion may be visualized, e.g., by displaying the determined lesion evolution value.
An overlay may be visualized. The voxels of the overlay corresponding to the voxels of the regions of interest may be displayed differently based on the different lesion evolution values of the voxels of the regions of interest.
An intensity scale may be displayed as a reference for correlating a lesion evolution value to an intensity of the voxels displayed differently.
By analyzing the overlay, it is possible to draw conclusions about the lesion evolution status of the lesions. Comparing with the T2FLAIR image of
Alternatively, or in combination, the voxels of the overlay corresponding to the voxels of the region of interest may be displayed in different colors based on the lesion evolution values of these voxels of the region of interest. A color scale may be displayed as a reference for correlating a lesion evolution value to a color of the voxels displayed differently. In the example of
Alternatively, using the overlay and the background image is not necessary. Visualizing lesion evolution of the portion may comprise displaying the voxels of the first region of interest of the first MR image differently, based on their respective lesion evolution value. In other words, it is possible to visualize the lesion evolution in the first MR image generated based on the first MR sequence, without any overlays.
The method may further comprise displaying a distribution of the determined lesion evolution value for each voxel of the first region of interest.
In the example of
From the histograms of
The example of
The Grades 1-3 of
The method may further comprise for each determined lesion evolution value, calculating a volume size of a partial portion having the status of lesion evolution indicated by said determined lesion evolution value.
The volume sizes may be in the form of percentage (%) indicating a percentage of the tissue of different lesion evolution stages.
Other information may be further derived based on the determined lesion evolution values, e.g., the distribution of the determined lesion evolution values.
The derived information may be presented as texts, e.g., in a table as
The method may comprise acquiring a second MR sequence of the portion comprising quantitative information of the portion; generating a second MR image representing the portion, based on the second MR sequence, wherein the second MR image comprises a second region of interest corresponding to the first region of interest. For a voxel of the second region of interest, a second lesion evolution value may be determined, based on quantitative values of said voxel of the second region of interest and the lesion evolution model. Based on the determined second lesion evolution value, and the lesion evolution value of its corresponding voxel of the first region of interest, a change of status of lesion evolution of the portion during a first time when the first MR sequence of the portion being acquired to a second time when the second MR sequence of the portion being acquired, may be determined.
The change of status of lesion evolution of the portion may be determined by comparing the determined lesion evolution values, or any of the generated overlays such as
In connection with
From
From
The MS lesions are isointense or hypointense (dark, i.e. low signal intensity compared to surrounding tissue) in the T1W image of
T2FLAIR image.
As shown in
Thus, the validity of the invention can be demonstrated by the examples of
The present invention can provide not only the information of the T1W and T2FLAIR images, but also a more detailed and quantified information of the lesion evolution. The detailed and quantified information of the lesion evolution approach may be presented in a variety of ways for different usages. A great advantage is that the invention is based on quantitative information, making it possible to study the lesion evolution changes over time for an individual patient. Such quantified lesion evolution may be used as an indicator, e.g., for screening for diseases, for predicting the tissue destructions, etc.
