Patent Description:
Non-invasive imaging technologies allow images of the internal structures or features of a patient or a subject to be obtained without performing an invasive procedure on the patient or the subject. In particular, such non-invasive imaging technologies rely on various physical principles, such as the differential transmission of X-rays through the target volume or the reflection of acoustic waves, to acquire data and to construct images or otherwise represent the observed internal features of the patient or the subject.

For example, in computed tomography (CT) and other X-ray based imaging technologies, X-ray radiation is directed toward a subject, typically a patient in a medical diagnostic application, a package or baggage in a security screening application, or a fabricated component in an industrial quality control or inspection application. A portion of the radiation impacts a detector where the image data is collected. In digital X-ray systems, a detector generates digital signals representative of the amount or intensity of radiation impacting discrete pixel regions of the detector surface. The signals may then be processed to generate an image that may be displayed for review. In the images produced by such systems, it may be possible to identify and examine the internal structures and organs within a patient's body, objects within a package or container, or defects (e.g., cracks) within a fabricated component. In volumetric imaging systems (such as computed tomography (CT), tomosynthesis, or C-arm angiography systems) a detector array, including a series of detector elements, produces similar signals through various positions as one or both of the source and detector are displaced around the imaged volume, allowing data to be acquired over a limited or complete angular range.

In certain instances, during an X-ray exposure where a subject is being imaged but relatively little attenuation is present (e.g., due to the size, positioning, or structure of the imaged subject, such as at a skin line or tissue boundary) there is a possibility that portions of the detector array in this region of insufficient attenuation will be saturated, while other areas where more attenuation is present are not. That is, the accumulated charge at a given pixel or set of pixels may reach a limit, such that additional exposure does not result in a corresponding increase in measured charge at the pixel. Saturation leads to the loss of information and is characteristic of a detector having insufficient dynamic range to accommodate the X-ray exposure levels, in this instance a failure to accommodate the highest levels of radiation observed at imaged regions of interest, such as near the tissue edge or skin line. Therefore, there is a need for an improved X-ray imaging system and method.

<CIT> describes a method, apparatus, system, and computer program product for automatically determining exposure time for an intraoral image. The method includes acquiring a low dose pilot projection image of an object to be imaged, performing a sanity check to ensure that a usable exposure is attainable, estimating a remaining exposure time required for an additional projection image, taking the additional projection image and adding the two images together to generate a final image wherein the dose delivered to the x-ray detector is influenced by patient specific dental anatomy.

In accordance with an embodiment of the present technique a medical imaging system is provided. The medical imaging system includes an X-ray source for transmitting X-rays through a subject and a detector to receive the X-ray energy of the X-rays after having passed through the subject. The medical imaging system further includes a processing system programmed to generate a pre-shot image of the subject using low energy X-ray intensity from the X-ray source and to determine a plurality of acquisition parameters for a main scan of the subject based on the pre-shot image. The processing system is also configured to determine a saturation time of the detector for the corresponding acquisition parameters based on detector calibration data and to determine a number of time frames required to reach the targeted dose based on the saturation time. Further, the processing system is programmed to apply an X-ray dosage level of the subject using the X-ray source based on the number of time frames and to generate the image of the subject based on the detected X-ray energy at the X-ray detector for the applied X-ray dosage level.

In accordance with another embodiment of the system, a method for imaging a subject is provided. The method includes providing an X-ray source for transmitting X-rays through a subject and providing a detector operative to receive the X-ray energy of the X-rays after having passed through the subject. The method further includes generating a pre-shot image of a subject using low energy X-ray intensity from the X-ray source and determining a plurality of acquisition parameters for a main scan of the subj ect based on the pre-shot image. The method also includes determining a saturation time of the detector for the corresponding acquisition parameters based on detector calibration data and determining a number of time frames required to reach the targeted dose based on the saturation time. Finally, the method includes applying an X-ray dosage level of the subject using the X-ray source based on the number of time frames and generating the image of the subject based on the detected X-ray energy at the X-ray detector for the applied X-ray dosage level.

When introducing elements of various embodiments of the present embodiments, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. Furthermore, any numerical examples in the following discussion are intended to be non-limiting, and thus additional numerical values, ranges, and percentages are within the scope of the disclosed embodiments. Furthermore, the terms "circuit" and "circuitry" and "controller" may include either a single component or a plurality of components, which are either active and/or passive and are connected or otherwise coupled together to provide the described function.

The present approaches relate to automatic exposure control (AEC) used in an X-ray imaging system. Based on a low exposure image (also referred to as pre-shot image), the AEC computes the acquisition parameters for the main acquisition that are needed to reach the required image quality. For example, in an embodiment, the pre-shot may be a low resolution two-dimensional ("2D") image acquired via a lower X-ray dose compared to subsequent X-ray dose that is used for obtaining images of the patient and used to make a medical diagnosis. The pre-shot image is also used to predict X-ray time for the main acquisition. Based on the acquisition parameters, predicted X-ray time and an X-ray detector saturation model, an additional parameter which is a number of time frames required to reach the targeted X-ray dose without saturating the detector is determined. The addition of the acquired time frames gives the resulting unsaturated image of the subject. As used herein, a subject is a human (or patient), an animal, or a phantom.

With the preceding in mind, an example of an X-ray based imaging system <NUM> suitable for acquiring X-ray attenuation data for image reconstruction as discussed herein is provided in <FIG>. In certain implementations the imaging system <NUM> operates so as to improve the dynamic range of the detector panel <NUM>. For example, the detector <NUM> may be fabricated using complementary metal-oxide semiconductor (CMOS) materials and techniques so as to incorporate active pixels on the detector array. Such active pixels, as used herein, include amplification circuitry (e.g., an amplifier) within the respective pixel circuits themselves (as opposed to downstream and separate from the detector array) and are suitable for non-destructive readout during an imaging session. As used herein, such a non-destructive readout allows the charge at a given pixel to be inferred (i.e., read) by measuring a voltage present at the pixel at a given time. Thus, this inferred charge is determined without resetting, destroying, or otherwise losing the charge at the pixel (i.e., the pixel charge is not reset to zero). Though CMOS-based detectors are discussed in certain examples herein, it should be appreciated that the present approaches may be more generally applied to any detector capable of non-destructive readout operations, regardless of whether the fabrication of the detector utilizes CMOS components or other. Further in certain implementations the CMOS-based detector <NUM> is fabricated using crystalline silicon (c-Si) or amorphous silicon (a-Si).

In the embodiment illustrated in <FIG>, imaging system <NUM> includes a source of X-ray radiation <NUM> along with the detector <NUM>. The X-ray source <NUM> may be an X-ray tube, a distributed X-ray source (such as a solid-state or thermionic X-ray source) or any other source of X-ray radiation suitable for the acquisition of medical or other images. The X-rays <NUM> generated by the source <NUM> pass into a region in which a patient <NUM> (or an object or other subject to be imaged), is positioned during a procedure.

In the depicted example, a portion of the X-ray radiation <NUM> passes through or around the patient <NUM> (or other subject of interest) and impacts a detector array, represented generally as the detector <NUM>. As discussed herein, detector elements (i.e., pixels) of the detector <NUM> produce electrical signals that represent the intensity of the incident X-rays <NUM>. These signals are acquired and processed, as discussed herein, to reconstruct images of the features within the patient <NUM> or imaged object of interest.

In accordance with present embodiments, one or both of the source <NUM> or detector <NUM> may be moved (e.g., rotated and/or linearly translated) relative to the patient or imaged object along or about one or more axes during an examination procedure during which projection data is acquired. For example, the source <NUM> and/or detector <NUM> may move about one or more axes of rotation so as to facilitate acquisition of projection data at a variety of different radial views with respect to the imaged volume. Such imager motion may be supplemented by motion of the underlying patient support (e.g., table) to achieve complex imaging trajectories with respect to the relative position and motion between the imager and patient over time. In one embodiment, the translation and rotation of the imager components may be determined or coordinated in accordance with a specified protocol.

The movement of the imager components may be initiated and/or controlled by one or more linear/rotational subsystems <NUM>. The linear/rotational subsystems <NUM>, as discussed in further detail below, may include support structures, motors, gears, bearings, and the like, that enable the rotational and/or translational movement of the imager components. In one embodiment, the linear/rotational subsystems <NUM> may include a structural apparatus (e.g., a C-arm apparatus having rotational movement about at least two axes, a gantry, and so forth) supporting the source and detector <NUM>, <NUM>.

Other systems and subsystems may be present to support operation of the imaging components when in use. By way of example, a suitable system <NUM> may include a system controller <NUM> to coordinate and control the imaging components. Such a system controller may include one or more of an X-ray controller <NUM> for controlling operation of source <NUM>, a motor controller <NUM> for controlling motion of movable subsystems, and a data acquisition system (DAS) <NUM> for handling signal readout of the detector <NUM>. In practice, the system controller <NUM> may incorporate one or more processing devices that include or communicate with tangible, non-transitory, machine readable media collectively storing instructions executable by the one or more processors to perform the operations described herein.

As illustrated, the X-ray controller <NUM>, the motor controller <NUM>, and the data acquisition systems <NUM> may share one or more processing components <NUM> that are each specifically configured to cooperate with one or more memory devices <NUM> storing instructions that, when executed by the processing components <NUM>, perform the image acquisition and reconstruction techniques described herein. Further, the processing components <NUM> and the memory components <NUM> may coordinate in order to perform the various image reconstruction processes. The system controller <NUM> and the various circuitry that it includes, as well as the processing and memory components <NUM>, <NUM>, may be accessed or otherwise controlled by an operator via an operator workstation <NUM>. The operator workstation <NUM> may be communicatively coupled to a printer <NUM> for printing images, patient data, and the like. The operator workstation <NUM> may also be in communication with a display <NUM> that enables the operator to view various parameters in real time, to view images produced by the acquired data, and the like. The operator workstation <NUM> may also, in certain embodiments, be communicatively coupled to a picture archiving and communication system (PACS) <NUM>, which may allow images to be shared with other facilities, for example, a remote client <NUM>.

As discussed herein, the imaging system <NUM>, which may include a detector <NUM> may be used in imaging processes that address various dynamic range issues that arise in certain imaging contexts. For example, in certain circumstances one or more pixels of the detector <NUM> may become saturated during an exposure event. Turning to <FIG> an example of such a saturation event is provided in the context of a mammography scan. In this example, a single time frame acquisition (i.e., a scan in which a single read event of the detector <NUM> is performed) is depicted.

As shown schematically in <FIG>, a breast <NUM> to be imaged is compressed between a compression plate <NUM> and the detector <NUM> such that a portion <NUM> of the breast <NUM> is at a uniform thickness. A portion of <NUM> the breast <NUM>, however, is compressed to a thinner, typically non-uniform, thickness due to the amount of tissue present. A third imaging region <NUM> is devoid of intervening breast tissue and is exposed to unattenuated X-rays during a scan.

In the depicted example three pixels <NUM> are shown schematically such that each pixel <NUM> corresponds to a respective region <NUM>, <NUM>, or <NUM> having different X-ray exposure characteristics. For example, pixel 90c, underlying the thick breast tissue region <NUM> receives the most attenuated X-rays and is unlikely to saturate over the exposure time (x-axis), as shown by charge accumulation line <NUM> and saturation threshold <NUM> of <FIG>. Conversely, pixel 90a is positioned outside the boundary of the breast tissue <NUM> and is fully exposed to the unattenuated X-ray radiation. As a result, the pixel 90a saturates much earlier than do those pixels underneath tissue. Lastly, pixel 90b is schematically illustrated as being positioned in the vicinity of the skin line (i.e., at the tissue boundary), such that the radiation incident on the pixel 90b is partially attenuated compared to that incident on pixel 90c. That is, the X-rays incident on pixel 90b pass through some portion of tissue, and so are not unattenuated, but, as shown by charge accumulation line <NUM> of <FIG>, in the scan interval associated with a single time frame read (indicated as readout <NUM>, shown by dotted), the pixel 90b becomes saturated before the scan in completed and the pixel 90b is readout. As a result, valuable information is lost at the boundary of the imaged tissue (i.e., the skin line). This limitation with respect to the dynamic range of the detector <NUM> (i.e., saturation at tissue regions of interest) can result in artifacts at the skin line, such as discontinuities <NUM> and/or other roughness at the edges of the tissue image, as seen in <FIG>.

One approach to address saturation issues for regions where the tissue is of non-uniform thickness and where attenuation is less than what is seen for thicker tissue regions being imaged is described with reference to <FIG> and <FIG>. In this approach multiple destructive (i.e., charge depleting) readout operations are performed over the course of a single scan exposure. This is graphically illustrated in <FIG>, where an exposure event <NUM> occurs over a time t. Over the course of the exposure <NUM>, multiple destructive readout operations <NUM> (also referred to as multiple time frames) are performed, with readout events generally timed so as to avoid saturation of pixels in those areas of the detector panel underlying tissue regions where uniform thickness cannot be achieved (e.g., near the tissue boundary within the image and so forth). Each readout operation <NUM> or time frame generates attenuation data that can be reconstructed into a separate image <NUM>. Some or all of the multiple images <NUM> can be combined or summed to generate a final image <NUM> with reduced skin line artifacts. Alternatively, as shown in <FIG>, some or all of the multiple images may be used in an estimation process <NUM> in which various image parameters (e.g., the skin line boundary, electronic noise, signal-to-noise, optimized pixel intensity) are estimated and used to generate a final or diagnostic image. For example, in one implementation, the skin line boundary (dotted line <NUM>) may be estimated and the final image may include pixels populated with intensity data up to the boundary so as to minimize data loss at the boundary region.

Turning to <FIG>, a graphical representation of pixel charge accumulation for such a multi-frame embodiment is shown which is similar to the graphical representation of <FIG> and which is based on the pixel arrangement shown in <FIG>. In this example pixel 90c, underlying the thick breast tissue region <NUM> receives the most attenuated X-rays and does not saturate between readout events132, as shown by charge accumulation lines <NUM> and sensor saturation threshold <NUM>. Pixel 90a is positioned outside the boundary of the breast tissue <NUM> and is fully exposed to the unattenuated X-ray radiation. As a result, the pixel 90a saturates much earlier than do those pixels underneath tissue, even in this multi-frame scenario. Pixel 90b is schematically illustrated as being positioned in the vicinity of the skin line (i.e., at the tissue boundary), such that the radiation incident on the pixel 90b is partially attenuated compared to that incident on pixel 90c. As shown by charge accumulation lines <NUM> of <FIG>, in the scan intervals associated with multiple readout events <NUM>, the pixel 90b approaches saturation but, even if saturation is reached, does not spend substantial time in the elapsed state before being readout and the charge cleared. As a result, attenuation information is generally not lost at the boundary of the imaged tissue (i.e., the skin line) or in the regions where the tissue thickness is less than the uniformly compressed regions.

As will be appreciated, the depicted example is idealized and, in practice, the charge accumulation lines <NUM> may reflect that the readout events occur prior to the pixel 90b reaching saturation threshold <NUM> or, alternatively, some minimal amount of time may be spent in a saturated state before readout for these pixels 90b. However, due to general retention of attenuation data at the skin line, the summing or estimation processes employed to construct final image <NUM> from the multiple images <NUM> may reflect a generally expanded or extended dynamic range for the detector <NUM>.

In accordance with an embodiment of the present technique, an automatic exposure control (AEC) algorithm is used to generate relevant acquisition parameters needed for main scan of the patient. It should be noted that the main scan event here refers to the image acquisition of the patient based on which the patient disorder diagnosis is determined. The AEC algorithm controls the X-ray exposure per image and helps avoid saturation of the detector <NUM> and may be implemented in X-ray controller <NUM> of <FIG>. In general, the preferred embodiment of the AEC algorithm utilizes a pre-shot image from detector <NUM>. The pre-shot image is obtained from a small dose of X-rays occurring before the main X-ray exposure that results in an image of a patient. A plurality of acquisition parameters is then determined from the pre-shot image. The plurality of acquisition parameters includes X-ray tube current, X-ray tube voltage, targeted X-ray dose etc. An additional parameter- saturation time of the detector is determined using a calibration method. Based on the plurality of acquisition parameters and the saturation time of the detector, a number of time frames or scan events required to reach the targeted dose without saturating the detector are determined.

<FIG> shows a flow chart <NUM> of a method for imaging a subject in accordance with an embodiment of the present technique. The method includes acquiring a pre-shot image of the subject in step <NUM>. As explained earlier, the pre-shot image is obtained from a small dose of X-rays before the main X-ray exposure of the subject that results in an image of the subject obtained for diagnosis. At step <NUM>, the method includes determining a plurality of acquisition parameters based on the pre-shot image. The plurality of acquisition parameters includes X-ray tube current, X-ray tube voltage, and targeted X-ray dose of the detector among others.

In one embodiment, determining the acquisition parameter may be based on configuration settings determined while taking the pre-shot image such as one of an anode material of the X-ray source, a peak kilovoltage ("kVp") of the X-ray source, a milliamperes ("mA") per pulse of the X-ray source, i.e., the integral of a current flowing through a ray tube/generator of the source during a pulse which may be in milliampere-seconds ("mAs"). As will be understood, in embodiments, the acquisition parameters may be derived from the configuration settings via one or more models, e.g., a look up table containing values for anode material, filter selection, kVp, mAs per pulse and/or time.

In step, <NUM>, a saturation time for the detector corresponding to the plurality of acquisition parameters is determined based on detector calibration data. It should be noted that the detector calibration data obtained by pre-calibrated the detector in advance of the main scan of the subject. In general, there are at a plurality of settings in the X-ray system - X-ray tube voltage (kV), X-ray tube anode material (track), and material used for X-ray beam filtration (filter), X-ray source current (mA), targeted X-ray dosage (mAs). To calibrate the detector, the naked detector <NUM> (i.e., without the subject to be scanned) is illuminated by the X-ray source <NUM> in every possible configuration setting of X-ray system <NUM>. For each of these configuration settings and a corresponding X-ray tube current, the time at which the detector saturates is determined. In one embodiment the saturation time may be determined by dividing the saturation scan total exposure by the saturation scan tube current. Thus, saturation times for various configuration settings of the X-ray system <NUM> are stored in a look up table and at the time of the main scan of the subject, the look up table provides the saturation time corresponding to the plurality of acquisition parameters.

Based on the plurality of acquisition parameters and the saturation time, a number of time frames or scan events required to reach the targeted dose without saturating the detector are determined in step <NUM>. At step <NUM>, the method includes applying an X-ray dosage level of the subject based on the number of time frames. The X-ray dosage level is applied by X-ray source <NUM> based on the X-ray controller commands which provides the number of time frames. Finally, at step <NUM>, the image of the subject is generated based on the detected X-ray energy for the applied X-ray dosage level.

<FIG> shows a schematic diagram <NUM> of a portion of imaging system <NUM> of <FIG>. In one embodiment, the portion <NUM> is part of the X-ray controller <NUM> of <FIG>. X-ray controller <NUM> includes a calibration module <NUM> and an AEC acquisition module <NUM>. As used herein, the term "module" refers to software, hardware, or firmware, or any combination of these, or any system, process, or functionality that performs or facilitates the processes described herein.

In general, as discussed earlier, there are at least three settings in the X-ray system - X-ray tube voltage (kV), X-ray tube anode material (track), and material used for X-ray beam filtration (filter) which are varied to apply the X-ray dosage of the subject according to the thickness and density (e.g., breast thickness and density). In one embodiment, the calibration module <NUM> illuminates the naked detector <NUM> (i.e., without the subject to be scanned) by the X-ray source <NUM> in every possible configuration of these three settings. In another embodiment, instead of illuminating the naked detector in every possible configuration, only a few configuration points are considered and an interpolation from only those points of measure is considered. The AEC spectrum <NUM> of all these configuration points is provided to calibration module <NUM> as an input.

Calibration module <NUM> determines a saturation time <NUM> of the detector <NUM> for each of the configuration settings (kV, track, filter). In one embodiment, to determines the saturation time <NUM>, calibration module <NUM> first measures the saturation scan total exposure (mAs) <NUM> which is the X-ray exposure at which the detector saturates for the given configuration setting. Thereafter, the calibration module <NUM> measures the saturation scan tube current (mA) <NUM> that was applied and then based on the tube current mA and the saturation scan total exposure the saturation time <NUM> is determined. In one embodiment the saturation time <NUM> may be determined by dividing saturation scan total exposure by the saturation scan tube current (i.e., mAs/mA). Thus, saturation times for various configuration settings of the X-ray system <NUM> are stored in a look up table by the calibration module <NUM>.

The AEC module <NUM> first acquires a pre-shot or pre-exposure image <NUM> which is used to measure the attenuation property of the subject. In certain embodiments, the attenuation property is polymethyl methacrylate-equivalent thickness at densest location of the subject. The pre-shot image is generated based on low energy X-ray intensity exposure of the subject from the X-ray source. It should be noted here that the low energy X-ray intensity here refers to the X-ray intensity which has a lower value compared to the X-ray intensity used for main scan of the subject. As will be appreciated by those skilled in the art, based on the low exposure scan results, it is possible to determine how much X-ray radiation is being attenuated (i.e., attenuation properties) by the subject. Once the attenuation properties are determined then based on the attenuation properties of the subject, the spectrum values <NUM>, tube current <NUM> and total exposure <NUM> for the main scan can be determined. Spectrum values <NUM> includes configuration settings (kV, track, filter) for the main scan. AEC module <NUM> then provides the configuration settings <NUM> to the calibration module <NUM>, which determines saturation time <NUM> from the look up table corresponding to the configuration settings <NUM>.

Further, main scan total exposure (mAs) <NUM> and main scan tube current (mA) <NUM> are also determined from the attenuation properties of the subject. In one embodiment, based on the main scan tube current <NUM> and the main scan total exposure <NUM>, main scan X-ray time <NUM> is determined. For example, the main scan X-ray time <NUM> may be determined by dividing main scan total exposure <NUM> value by the main scan tube current <NUM> value. AEC module <NUM> further determines a time frame <NUM> by subtracting a buffer time <NUM> from the saturation time <NUM> corresponding to the same configuration as that of main scan configuration. The buffer time <NUM> is used to provide some extra time margin to integrate the whole signal from the main x-ray acquisition. Finally, a number of time frames <NUM> required for main scan acquisition are determined based on time frame <NUM> and X-ray time <NUM>. In one embodiment, the number of time frames <NUM> may be determined by dividing X-ray time <NUM> by time frame <NUM>. The plurality of time frames as determined by the number <NUM> are then used to apply X-ray dosage level of the subject using the X-ray source <NUM> for acquiring the main scan and to generate the image of the subject for disorder diagnosis.

<FIG> shows a schematic diagram <NUM> of an example time frame calculation system of <FIG>. As can be seen from schematic <NUM>, based on pre-shot image <NUM>, AEC acquisition module <NUM> determines the main scan tube current <NUM> to be <NUM> mA and main scan total exposure <NUM> to be <NUM> mAs. Further, based on the main scan tube current <NUM> and the main scan total exposure <NUM>, the X-ray time <NUM> is determined to be (<NUM> mAs/<NUM> mA=) <NUM> second. Moreover, based on pre-shot image <NUM>, main scan configuration settings <NUM> are determined to be X-ray tube voltage = 34kV, filter=Silver and track =Rhodium. These main scan configuration settings <NUM> are provided to calibration module <NUM> which determines that for given X-ray tube current <NUM> (<NUM> mA), the detector X-ray saturation exposure <NUM> occurs at <NUM> mAs. Thus, based on X-ray tube current <NUM> and X-ray saturation exposure <NUM>, the saturation time <NUM> is determined to be <NUM> seconds.

In the schematic diagram <NUM>, the buffer time is set as <NUM> seconds. Accordingly, AEC acquisition module <NUM> determines a time frame <NUM> equal to (<NUM>-<NUM>=) <NUM> seconds. Finally, a total number of time frames <NUM> are determined by dividing X-ray time <NUM> (<NUM> seconds) by the time frame <NUM> (<NUM> seconds) which is equal to <NUM> time frames. These <NUM> time frames are then applied to the X-ray source <NUM> to generate the image of the subject for diagnosis.

Claim 1:
A medical imaging system (<NUM>) comprising:
an X-ray source (<NUM>) operative to transmit X-rays (<NUM>) through a subject (<NUM>);
a detector (<NUM>) operative to receive the X-ray energy of the X-rays after having passed through the subject; and
a processing system (<NUM>) programmed to:
generate (<NUM>) a pre-shot image of the subject using low energy X-ray intensity from the X-ray source;
determine (<NUM>) a plurality of acquisition parameters for a main scan of the subject based on the pre-shot image;
determine (<NUM>) a saturation time of the detector corresponding to the plurality of acquisition parameters based on detector calibration data, wherein the detector calibration data is predetermined in advance of the main scan and wherein the processing system is programmed to determine the detector calibration data by illuminating the detector without the subject in a plurality of configuration settings of the medical imaging system and recording the saturation time for each of the plurality of configuration settings in a look up table;
determine (<NUM>) a number of time frames required to reach a targeted dose based on the saturation time;
apply (<NUM>) an X-ray dosage level of the subject using the X-ray source based on the number of time frames; and
generate (<NUM>) an image of the subject based on the detected X-ray energy at the X-ray detector for the applied X-ray dosage level.