Apparatus and method of determining optimal energy window for optimal positron emission tomography

An apparatus and method for determining an optimal energy window for optimal positron emission tomography (PET) is disclosed. An optimal energy window determining apparatus may include a data corrector configured to correct data measured from an image quality phantom, an image quality measurer configured to measure an image quality for the corrected data, and an optimal energy window determiner configured to determine the optimal energy window based on the measured image quality. The data corrector may correct the measured data based on a difference between sensitivities measured using different radiopharmaceuticals in at least one energy window.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Korean Patent Application No. 10-2013-0163677, filed on Dec. 26, 2013, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND

1. Field of the Invention

The present invention relates to a technology for determining an optimal energy window to determine settings for optimal positron emission tomography (PET).

2. Description of the Related Art

Positron emission tomography (PET) refers to one of nuclear medicine test technologies for injecting, into a human body, radiopharmaceuticals emitting positrons and reconfiguring, using an exclusive scanner, a shape of the injected radiopharmaceuticals used in the human body.

In general, such PET has been adopted to diagnose various types of cancers and also has been known as an efficient test to perform a differential diagnosis on a cancer, clinical staging, an evaluation of recurrence, and a determination as to the treatment effect. In addition, a receptor image or a metabolic image used for evaluating heart disease, brain disease, and brain functions may be acquired using the PET.

Positrons may be emitted from radioactive isotopes, such as, C-11, N-13, O-15, and F-18, as a kind of radiation. The radioactive isotopes correspond to principal constituent components of a biomaterial and thus, radiopharmaceuticals, that is, a tracer for applying a predetermined change in physiological, chemical, and functional views may be produced using the radioactive isotopes.

SUMMARY

An embodiment provides an apparatus for determining an optimal energy window in positron emission tomography (PET), the apparatus including a data corrector configured to correct data measured from an image quality phantom, an image quality measurer configured to measure an image quality for the corrected data, and an optimal energy window determiner configured to determine the optimal energy window based on the measured image quality. The data corrector may correct the measured data based on a difference between sensitivities measured using different radiopharmaceuticals in at least one energy window.

The data corrector may correct the measured data by calculating a ratio of a first sensitivity to a difference value between the first sensitivity measured using a first radiopharmaceutical and a second sensitivity measured using a second radiopharmaceutical.

The data corrector may correct the measured data by subtracting, from the measured data, a value in which the calculated ratio is applied to a scatter component corresponding to the measured data.

The image quality measurer may measure at least one of non-uniformity (NU) information, recovery coefficient (RC) information, and a spill over ratio (SOR) from the corrected data.

The optimal energy window determiner may calculate a figure of merit (FOM) based on the measured image quality, and may determine the optimal energy window based on the calculated FOM.

The optimal energy window determiner may calculate the FOM based on NU information, RC information, and an SOR measured from the corrected data by the image quality measurer.

Another embodiment provides a method of determining an optimal energy window in PET, the method including correcting, by a data corrector, data measured from an image quality phantom, measuring, by an image quality measurer, an image quality for the corrected data, and determining, by an optimal energy window determiner, the optimal energy window based on the measured image quality. The correcting of the measured data may include correcting the measured data based on a difference between sensitivities measured using different radiopharmaceuticals in at least one energy window.

The correcting of the measured data may include calculating a difference value between a first sensitivity measured using a first radiopharmaceutical and a second sensitivity measured using a second radiopharmaceutical, calculating a ratio of the first sensitivity to the calculated difference value, and correcting the measured data based on the calculated ratio.

The correcting of the measured data based on the calculated ratio may include correcting the measured data by subtracting, from the measured data, a value in which the calculated ratio is applied to a scatter component corresponding to the measured data.

The measuring of the image quality may include measuring at least one of NU information, RC information, and an SOR from the corrected data.

The determining of the optimal energy window determiner may include calculating a FOM based on the measured image quality, and determining the optimal energy window based on the calculated FOM.

The determining of the optimal energy window determiner may include calculating the FOM based on NU information, RC information, and an SOR measured from the corrected data.

DETAILED DESCRIPTION

When it is determined detailed description related to a related known function or configuration they may make the purpose of the present invention unnecessarily ambiguous in describing the present invention, the detailed description will be omitted here. Also, terminologies used herein are defined to appropriately describe the exemplary embodiments of the present invention and thus, may be changed depending on a user, the intent of an operator, or a custom. Accordingly, the terminologies must be defined based on the following overall description of this specification.

FIG. 1is a block diagram illustrating an optimal energy window determining apparatus100according to an embodiment.

The optimal energy window determining apparatus100may determine an optimal energy window for positron emission tomography (PET) through a data correction including a single gamma photon correction.

To this end, the optimal energy window determining apparatus100may include a data corrector110, an image quality measurer120, and an optimal energy window determiner130.

Specifically, the data corrector110may correct data measured from an image quality phantom.

High-energy gamma photons may degrade an image quality. Single gamma photons that may be classified into the high-energy gamma photons may act as a background noise factor in reconfigured PET. Thus, the single gamma photons need to be corrected to enhance the image quality.

Data measured from the image quality phantom may include single gamma photons. Thus, the data corrector110may correct the measured data by correcting the single gamma photons.

The data corrector110may correct the measured data based on a difference between sensitivities measured using different radiopharmaceuticals in at least one energy window.

Specifically, to correct the measured data, the data corrector110may calculate a difference value between a first sensitivity measured using a first radiopharmaceutical and a second sensitivity measured using a second radiopharmaceutical. The data corrector110may calculate a ratio of the first sensitivity to the calculated difference value, and may correct the measured data based on the calculated ratio.

The calculated ratio may be defined as a single gamma photon fraction (SGF).

Radioactive isotopes such as C-11, N-13, O-15, F-18, and I-124 may be used as radiopharmaceuticals. An embodiment of correcting measured data using radiopharmaceuticals of F-18 and I-124 is described herein. However, it is only an example and thus, various radiopharmaceuticals may be used in addition to the radiopharmaceuticals of F-18 and I-124.

The data corrector110may use I-124 as the first radiopharmaceutical and may use F-18 as the second radiopharmaceutical.

More specifically, the data corrector110may calculate an SGF according to Equation 1.

In Equation 1,124I sensitivity denotes the first sensitivity measured from the image quality phantom using the radiopharmaceutical of I-124, and18F sensitivity denotes the second sensitivity measured from the image quality phantom using the radiopharmaceutical of F-18.

The SGF is further described with reference toFIG. 2.

FIG. 2is a table200describing an SGF according to an embodiment.

The table200ofFIG. 2shows sensitivities measured in energy windows of 350 to 550, 350 to 600, 350 to 650, 350 to 750, 390 to 550, and 400 to 590 keV, which are different energy bands, and SGFs according thereto.

For example, SGFs may be calculated as expressed by Equation 2 by applying sensitivities measured in the energy band of 350 to 750 keV of the table200. For reference, in the present embodiment, a first sensitivity is “9.83” measured using the radiopharmaceutical of I-124 in the energy band of 350 to 750 keV and a second sensitivity is “6.81” measured using the radiopharmaceutical of F-18 in the energy band of 350 to 750 keV.

Referring again toFIG. 2, the image quality measurer120may measure an image quality for the corrected data. Specifically, the image quality measurer120may measure at least one of non-uniformity (NU) information, recovery coefficient (RC) information, and a spill over ratio (SOR) from the corrected data.

The optimal energy window determiner130may determine the optimal energy window based on the measured image quality. For example, the optimal energy window determiner130may calculate a figure of merit (FOM) based on the NU information, the RC information, and the SOR measured from the corrected data, and may determine the optimal energy window based on the calculated FOM.

More specifically, the optimal energy window determiner130may calculate the FOM according to Equation 3.

In Equation 3, NU denotes NU information measured from the corrected data and sensitivity denotes sensitivity information. Also, SORairdenotes RC information measured from the air and SORwaterdenotes RC information measured from the water, among a plurality of sets of RC information. In addition, RC1to RC5denote different sets of RC information measured from different energy windows, respectively.

For example, the optimal energy window determiner130may determine, as an optimal energy window band, an energy window band corresponding to a FOM having the smallest size among FOMs calculated in different energy windows.

FIG. 3is a diagram describing an image quality phantom310according to an embodiment.

The image quality phantom310may use F-18 and I-124 of 100 μCi as a source. Also, a scan time of I-124 may be set as 80 minutes, and a scan time of F-18 may be set as 20 minutes. Accordingly, the image quality phantom may obtain data in different energy windows, for example, 350 to 550, 350 to 600, 350 to 650, 350 to 750, 390 to 550, and 400 to 590 keV.

Also, an energy window-by-energy window SOR may be measured using materials, such as the water and the air, on one side320of the image quality phantom310. Energy window-by-energy window RC information may be measured using holes having different apertures on another side330of the image quality phantom310.

FIGS. 4A,4B, and4C are graphs410,420, and430describing an embodiment of performing a single gamma photon correction on data measured from an image quality phantom according to an embodiment.

The graph410ofFIG. 4Ashows a shape in which data measured from the image quality phantom is attenuated, and the graph420ofFIG. 4Bshows a shape in which the measured data is distorted due to attenuation and scattering. The graph430ofFIG. 4Cshows a single gamma photon formed based on the shape in which the measured data is attenuated and distorted.

Single gamma photons may act as a background noise factor in reconfigured PET. Accordingly, such single gamma photons need to be corrected to enhance the image quality.

FIG. 5illustrates an embodiment of correcting the single gamma photon ofFIG. 4.

A data corrector according to an embodiment may correct the measured data by subtracting, from the measured data, a value in which the calculated ratio, that is, an SGF is applied to a scatter component corresponding to the measured data. A process of correcting the measured data by subtracting, from the measured data, the value in which the SGF is applied may be interpreted as a single gamma photon correction.

For example, to correct the single gamma photon, the data corrector may perform a correction by applying the calculated SGF to a measured sinogram510. The measured sinogram510may be interpreted as information that is reconfigured from data measured from the image quality phantom.

To this end, the data corrector may calculate a corrected sinogram530with respect to the measured sinogram510according to Equation 4.
Corrected sonogram=measured sinogram−scatter component*background scale factor (=1−SGF)  [Equation 4]

For example, if SGF “0.31” calculated in the energy band of 350 to 750 keV is used, “1−0.31=0.69” may be applied to “scatter component” as “background scale factor” and a result of the applying may be subtracted from “measured sinogram”. That is, if “scatter component*0.69” is subtracted from “measured sinogram”, a result of the subtracting may be “corrected sinogram” in the energy window of 350 to 750 keV.

FIG. 6is a graph600describing NU information measured by an image quality measurer according to an embodiment.

The graph600shows NU information measured using I-124 and F-18 in energy windows of 350 to 550, 350 to 600, 350 to 650, 350 to 750, 390 to 550, and 400 to 590 keV, which are different energy bands.

The graph600shows NU information measured using I-124 and NU information measured using F-18. Here, the NU information measured using I-124 may be interpreted as information in which a single gamma photon correction is applied using an SGF. Also, the NU information measured using F-18 may be interpreted as information in which only a scatter correction is applied.

As shown in the graph600, NU information between about 6.3% and about 7.3% may be measured.

FIG. 7is a graph700describing RC information measured by an image quality measurer according to an embodiment.

The image quality measurer according to an embodiment may measure different sets of RC information based on a diameter of an image quality phantom rod for each energy window. RC information may increase according to an increase in the diameter of the image quality phantom rod. However, a difference in RC information according to a difference in an energy window may be insignificant.

FIGS. 8A and 8Bare graphs810and820describing an SOR measured by an image quality measurer according to an embodiment.

An SOR may be measured due to a material difference for rods disposed on the same side of an image quality phantom. The graph810shows an SOR with respect to the air for each energy window, and the graph820shows an SOR with respect to the water for each energy window. Also, each SOR may be measured from data of I-124 in which a single gamma correction is applied and data of F-18 in which a scatter correction is applied.

FIG. 9is a graph900showing a decrease ratio of an SOR after a single gamma photon correction is applied.

A difference in an SOR may occur due to a single gamma photon correction.

Referring to the graph900, an SOR after the single gamma photon correction is appeared was largest in the energy window of 350 to 750 keV and no significant difference in an SOR was found in remaining energy windows.

FIG. 10is a table1000showing a FOM calculated for each energy window.

A box1010indicated by a dotted line represents FOMs in the energy window of, for example, 350 to 750 keV among energy windows.

Referring to the box1010, an attenuation corrected (AC) FOM was calculated as “86.98” and an attenuation corrected and scatter corrected (AC&SC) FOM was calculated as “70.65” in the energy window of 350 to 750 keV. A single gamma photon corrected FOM in which an SGF is further applied to an attenuation correction and a scatter correction was calculated as “64.64”, which is lowest among a total of FOMs in the table1000.

Accordingly, the energy window of 350 to 750 keV may be determined as the optimal energy window.

For reference, an FOM in an energy window may be calculated according to Equation 3, which is described above with reference toFIG. 1.

FIG. 11is a flowchart illustrating an optimal energy window determining method according to an embodiment.

In operation1101, the optimal energy window determining method may correct data measured from an image quality phantom. Specifically, the optimal energy window determining method may correct the data measured from the image quality phantom using a data corrector.

For example, the optimal energy window determining method may correct the measured data based on a difference between sensitivities measured using different radiopharmaceuticals in at least one energy window.

More specifically, the optimal energy window determining method may calculate a difference value between a first sensitivity measured using a first radiopharmaceutical and a second sensitivity measured using a second radiopharmaceutical. The optimal energy window determining method may calculate a ratio of the first sensitivity to the calculated difference value, and may correct the measured data based on the calculated ratio. As an example, the optimal energy window determining method may correct the measured data by subtracting, from the measured data, a value in which the calculated ratio is applied to a scatter component corresponding to the measured data.

In operation1102, the optimal energy window determining method may measure an image quality for the corrected data. For example, the optimal energy window determining method may measure at least one of NU information, RC information, and an SOR from the corrected data.

In operation1103, the optimal energy window determining method may determine an optimal energy window based on the measured image quality. The optimal energy window determining method may determine the optimal energy window based on the measured image quality using an optimal energy window determiner.

Specifically, the optimal energy window determining method may calculate a FOM based on NU information, RC information, and an SOR measured from the corrected data, and may determine the optimal energy window based on the calculated FOM.