PARAMETERS

TECHNICAL FIELD This disclosure relates to a method and system for automating radiation dose parameters for computed tomography imaging systems.

BACKGROUND ART

Medical X-ray computed tomography system (CT) imaging results in a high radiation dose to patients. It is important that radiation dose to patients be reduced to a minimum whilst maintaining an image quality that allows for patient diagnosis. CT image quality is radiation dose dependent. A higher image quality generally means a higher radiation dose to patients. The radiation dose to patients can only be reduced while the image quality is still acceptable for patient diagnosis. In practical CT imaging, both the image quality and dose to patients are dependent on a number of image acquisition parameters such as peak voltage, kVp, and exposure (mAs, or milliampere x second). In general, the thicker the patient body, the less photons reach the photon detector (attenuation). The quantity of photons received by the photon detector impact image noise (an index for image quality). High numbers of photons received by the photon detector generate high quality images (i.e. low noise) whilst low numbers of photons received by the photon detector generate low quality images (i.e. high noise).

In prior art imaging devices, the exposure (photon flux) is increased or decreased during the CT scan in order to maintain the same noise level (i.e. the number of photons received by the detector is kept constant by varying exposure). Thus, prior art methods propose an automatic control of exposure in order to keep a constant noise level to reduce dose. l It is to be understood that, if any prior art is referred to herein, such reference does not constitute an admission that the prior art forms a part of the common general knowledge in the art, in Australia or any other country.

SUMMARY

Disclosed herein is a method for automating the calculation of radiation dose parameters for an imaging device (e.g. a CT scanner), the radiation dose parameters for application to a patient by the imaging device to generate an image of the patient. The method may comprise the steps of identifying a first section of a region of the patient for imaging, determining a first absorption parameter for the first section of the patient region, setting a first dose parameter for the imaging device in dependence on the first absorption parameter and setting a second dose parameter for the imaging device in dependence on the first absorption parameter, identifying a second section of the patient region for imaging, determining a second absorption parameter for the second section of the patient region; and calculating the second dose parameter in dependence on the second absorption parameter. Advantageously, this method allows for at least one dose parameter to be automated in dependence on the determined absorption parameters to reduce (e.g. optimise) the radiation dose to the patient. In at least one embodiment, determining the first and second absorption parameters comprises measuring a first depth of the first patient section and measuring a second depth of the second patient section. This allows for a change in depth (Ad) to be calculated (e.g. the difference between the first and second depths) then used to calculate the second dose parameter. In at least one embodiment, the method further comprises transmitting (e.g. sending via a network) the set first and second dose parameters and the calculated second dose parameter to a radiation emitter for use in generating an image of the patient. For example, the set and calculated parameters may be held on a system memory and then transmitted to a controller that forms part of the radiation emitter.

Also disclosed herein is a method for generating an image of a patient. The method may comprise determining the first and second dose parameters and measuring the first and second depths of the patient region in accordance with the steps detailed above. The method may also comprise retrieving the set first and second dose parameters; applying radiation using the radiation emitter to the first section of the patient region to generate an image of the first section of the patient region, the applied radiation having the set first dose parameter and set second dose parameter; retrieving the set first dose parameter and calculated second dose parameter; and applying radiation using the radiation emitter to the second section of the patient region to generate an image of the second section of the patient region, the applied radiation having the set first dose parameter and calculated second dose parameter. Advantageously, this allows for the radiation dose applied to the patient to be reduced.

In at least one embodiment, the method further comprises moving the radiation emitter between a first position, whereby the emitter is configured to apply radiation to the first section of the patient region, and a second position, whereby the emitter is configured to apply radiation to the second section of the patient region. The movement of the radiation emitter may be around and/or along the patient (e.g. the radiation emitter may take a helical path around and along the patient in order to generate the image). For example, the X-ray tube may translate along and around the patient when a multiple slice detector CT scanner having less than 16 slices is utilised to generate the image. This is because the detectors' coverage may be less than the intended imaging region. When a CT scanners having 64-320 slice detectors is utilised to generate the image, the translation of the X-ray tube along the patient may not be needed as the detector may cover the intended imaging region (e.g. the heart). In at least one embodiment, the method further comprises identifying a plurality of depths for a plurality of sections of the patient region, each of the plurality of sections being disposed between the first and second sections of the patient region. The plurality patient sections may be around and/or along the patient. In at least one embodiment, calculating the second dose parameter comprises calculating a plurality of second dose parameters in dependence on the plurality of section depths identified for the patient region.

In at least one embodiment, the method further comprises calculating the first dose parameter in dependence on the first depth of the first section of the patient region and re -calculating the first dose parameter in dependence on the second depth of the second section of the patient region. Advantageously, this allows for both the first and second dose parameters to be variable and thus optimised to further reduce the radiation dose applied to the patient.

In at least one embodiment, applying the radiation may comprise applying radiation having the calculated first dose parameter and the calculated second dose parameter to the first section of the patient region when the radiation emitter is in the first position.

In at least one embodiment, applying the radiation may further comprise applying radiation having the re-calculated first dose parameter and the calculated second dose parameter to the second section of the patient region when the radiation emitter is in the second position.

In at least one embodiment, re-calculating the first dose parameter comprises calculating a plurality of first dose parameters in dependence on the plurality of section depths identified for the patient region. In at least one embodiment, the radiation emitter is in the form of an x-radiation tube.

In at least one embodiment, the radiation is in the form of x-radiation (i.e. X-rays). In at least one embodiment, the first dose parameter of the x-radiation is in the form of kVp. In this form, the second dose parameter of the x-radiation is mAs.

In at least one embodiment, the first dose parameter of the x-radiation is in the form of mAs. In this form, the second dose parameter of the x-radiation is kVp. In at least one embodiment, the method further comprises running a scout scan on the patient region to determine the first and second absorption parameters.

In at least one embodiment, calculating the second dose parameter is performed only in dependence on the determined absorption parameters of the patient region (e.g. noise is not dynamically taken into account when calculating and setting the dose parameters).

Also disclosed herein is a system for automating radiation dose parameters implemented using computer processing and memory resources. The system may comprise a memory configured to store absorption data relating to an absorption characteristic of a patient, a radiation dose selection engine (e.g. a processor) configured to retrieve the absorption data from the memory and calculate a first dose parameter in dependence on the absorption data; and a radiation emitter configured to receive instructions from the radiation dose selection engine and apply radiation to the patient.

In at least one embodiment, the system may further comprise a driver configured to move the radiation emitter to thereby apply radiation to a plurality of sections of the patient, and wherein the radiation dose selection engine is configured to calculate the first dose parameter in dependence on absorption data for each section of the patient.

In at least one embodiment, the system may further comprise at least one user interface configured to receive user data relating to a second first radiation dose parameter retrieved from the user. In at least one embodiment, the system may further comprise a radiation detector configured to receive radiation applied by the radiation emitter and generate image generation data corresponding to the radiation received.

In at least one embodiment, the system may further comprise a data interpretation engine configured to receive the image generation data and generate a CT image, the at least one user interface further configured to receive the CT image generated by the data interpretation engine and display the CT image.

In at least one embodiment, the system may further comprise a dose optimisation engine configured to calculate the second dose parameter in dependence on the absorption data.

In at least one embodiment, the system may further comprise a radiation controller configured to receive instructions from the dose optimisation engine and the radiation dose selection engine and output instructions to the radiation emitter.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will now be described by way of example only, with reference to the accompanying drawings in which

Fig. 1 shows a cross-sectional view through a CT imaging system; Fig. 2 shows a method of automating radiation dose parameters;

Fig. 3 shows a cross-section view through a patient region;

Fig. 4 shows another method of automating radiation dose parameters; and

Fig. 5 shows a cross-sectional view through a CT imaging system and a radiation dose optimisation system. DETAILED DESCRIPTION

In the following detailed description, reference is made to accompanying drawings which form a part of the detailed description. The illustrative embodiments described in the detailed description, depicted in the drawings and defined in the claims, are not intended to be limiting. Other embodiments may be utilised and other changes may be made without departing from the spirit or scope of the subject matter presented. It will be readily understood that the aspects of the present disclosure, as generally described herein and illustrated in the drawings can be arranged, substituted, combined, separated and designed in a wide variety of different configurations, all of which are contemplated in this disclosure.

Fig. 1 shows a computed tomography system 1 having a radiation emitter, in the form of X-ray tube 3, which emits an X-ray beam 5. The X-ray beam 5 is emitted through a beam diaphragm 7 and towards a patient 9. The system includes a radiation detector 1 1 that receives the X-rays 9 that are not absorbed by the patient 9. The radiation detector 1 1 generates electrical signals corresponding to the attenuated X-rays received. The X-ray tube 3 and the radiation detector 1 1 are mounted on a rotatable gantry 13 that is rotated about the patient 9 by a drive 15. The X-ray beam 9 is therefore caused to rotate around the patient 9, so that a series of projections captured by the detector 1 1, respectively obtained at different projection angles, are generated. Each projection has a dataset of electrical signals to thereby form projection datasets. These datasets are supplied from the radiation detector 11, for each projection, to a data interpretation system. Software held on system memory then generates a CT image of the patient from the projection data. This will be further detailed with respect to Fig. 5. The image can then be displayed on a monitor 17.

The computing device includes a user interface that allows for a user to set dosing variables (e.g. peak voltage, kVp, and/or exposure, mAs). The system includes a controller that receives as output (e.g. instructions such as a user defined kVp) from the computing device and then outputs instructions to the X-ray tube 3. Again, this will be further detailed with respect to Fig. 5.

In prior art imaging devices, the exposure (photon flux) is increased or decreased during the CT scan in order to maintain the same noise level (i.e. the number of photons received by the radiation detector 1 1 is kept constant by alternating the patient's exposure). Thus, prior art methods propose an automatic control of exposure in order to keep a constant noise level.

Peak voltage (kVp) is an important scan parameter and has significant impact on both image quality and radiation dose. It is desirable to have an automatic kVp control for the CT imaging. The dependence of noise on kVp is non-linear, making automatic control difficult between the two variables. Furthermore, CT image quality is a complicated parameter which is clinical task dependent and involves the human observer (i.e. person that reviews the images produced in order to perform a diagnosis). Importantly, noise, otherwise termed 'noise index', is not an accurate image quality index.

Disclosed herein is a method for automating radiation dose parameters for an imaging device. In the detailed embodiments, the radiation is in the form of x- radiation ('X-rays') and the dose parameters are in the form of peak voltage (kVp) and exposure (mAs). Fig. 2 shows a block diagram detailing the high level method steps. Initially, an absorption parameter, in the form of depth (e.g. patient thickness), of a region of a patient is determined 19.

Typically, the depth (e.g. the thickness of a body part of a patient in a plane that is perpendicular to an axis extending between the head and toes of the patient) is determined by performing a scout scan. As will be evident to the skilled addressee, the thicker the patient, the higher the radiation dose required to produce an image of similar quality relative to a thinner patient. A scout scan is a low dose (i.e. low kVp and low mAs) CT scan that is used to detect the depth and/or attenuation of the subject patient, or region of the patient. Typically, the scout scan is only performed on the region of the patient that requires imaging (e.g. the section of the human body where the kidney is positioned if the kidney requires imaging). Further, the thickness of the patient region varies around and along the region. This can also be determined using a scout scan. The resultant absorption parameters can then be saved digitally to as a lookup table held on a system memory. As will also be evident to the skilled addressee, there are alternative methods to determine the absorption parameter of the patient. For example, the body mass index provides an indication of the thickness of a patient's body parts.

After determining the variation in depth across and/or around the patient region, a first dose parameter, in the form of kVp, and a second dose parameter, in the form of mAs, is set 21 in dependence on a determined first absorption parameter of the patient region (e.g. the depth at the starting point of the scan). This embodiment of the disclosure will be referred to as automatic exposure control. The selection of the initial kVp & mAs can be dependent on the human observer index (e.g. previous studies for patient regions that have successfully produced an acceptable image quality). For example, 120 kVp is a typical peak voltage & 240 mAs set for a patient of a certain thickness to generate an image of the patient's abdomen. In one form, a system memory holds a database (e.g. in the form of a look up table) that includes a plurality of values for body thickness and/or changes in body thickness (Ad) for the region of the patient that requires imaging (e.g. the kidney) and optionally also the initial kVp and mAs to be initially set by the system. The initial kVp and mAs set points may be recommended by the manufacturers of the CT scanner as pre-determined values for a specific anatomical region and clinical indication, based on clinical feedback. These values may change as the technology evolves such as the new iterative image reconstruction algorithms. The initial kVp and mAs set points may be automatically set (i.e. by the software) or may be set by the operator.

After setting the kVp and mAs as a starting point for the scan, mAs, is set 23 in dependence on the determined absorption parameter of the patient region (e.g. the Ad between the first and second sections of the patient region). This is performed by applying a relationship between the absorption parameter of the patient region and mAs that allows for the dose to be minimised whilst maintaining an acceptable image quality. The Applicant has determined a functional relationship between image quality and radiation dose. To establish the relationship, the human observer factor is taken into account. Thus, experimentally determined relationships between image quality and radiation dose are taken into account (e.g. experimental data that details the dose applied to a patient that resulted in an image that was sufficient for diagnosis). There are many factors that are taken into account when a large quantity of experimentally collected data is processed. For example, the skill of the analyser (i.e. the human observer performing the diagnosis) varies significantly. Experienced human observers may not require a relatively high quality image in order or perform a diagnosis relative to an inexperienced human observer. By analysing this data, the Applicant has derived an equation for the automatic controls of exposure and/or peak voltage in medical X-ray CT imaging. When kVp is set as a constant for the first dose parameter, the optimum mAs can be calculated using the equation: -

^■ mAs

This equation states that for every 1cm increase of the patient thickness (d), the exposure mAs needs to be increased by 3.8% to produce an image of acceptable quality. If the patient thickness is reduced by 1 cm, the exposure mAs can be reduced by 3.8% to reduce the dose of radiation applied to the patient and produce an image of acceptable quality. The system may include a software application processed by a processor that dynamically relates patient thickness to mAs and calculates optimal mAs required. After calculating mAs, radiation having the set kVp and the calculated mAs may be applied to the patient to generate an image. The constant may range depending on the scanner and manufacturer. This value can be determined once a specific scanner is defined. In another embodiment, the first dose parameter may be in the form of mAs. This embodiment of the disclosure will be referred to as automatic kVp control. Similar to kVp, mAs may be set 21 in dependence on the determined absorption parameter of the patient region. The initial selection of mAs & kVp can be dependent on the human observer index. After setting the mAs & kVp, the second dose parameter, in the form of kVp, is calculated 23 in dependence on the determined absorption parameter of the patient region (e.g. the Ad between the first and second sections of the patient region). Again, this is performed by applying a relationship between the absorption parameter of the patient region and kVp that allows for the dose to be minimised whilst maintaining an acceptable image quality. Similar to automatic exposure control, the Applicant has determined a functional relationship between image quality and radiation dose. To establish the function, the human observer factor is taken into account. When mAs is set as a constant for the first dose parameter, the optimum kVp can be calculated using the equation: -

This equation states that for every 1cm increase of the patient thickness (d), the kVp needs to be increased by 1.53% to produce an image of acceptable quality. If the patient thickness is reduced by 1 cm, the kVp can be reduced by 1.53% to reduce the dose of radiation applied to the patient and produce an image of acceptable quality. Again, the system may include a software application processed by a processor that dynamically relates the patient thickness to kVp and calculates optimal kVp required. After calculating kVp, radiation having the set mAs and the calculated kVp may be applied to the patient to generate an image. The constant may range depending on the scanner and manufacturer. This value can be determined once a specific scanner is defined.

The step of determining the patent thickness will now be described in further detail with reference to Fig. 3. Fig. 3 shows a cross-sectional view through the patient 9. Determining the absorption parameter (e.g. patent thickness) of the region of the patient comprises determining a first depth (dl in Fig. 3) of a first section 27 (i.e. at a position on the patient's body) of the patient region 9 and a second depth (d2 in Fig. 2) of a second section 29 of the patient region 9. As will be evident to the skilled addressee, any number of positions can be measured along the subject region of the patient's body.

The step of calculating the second dose parameter will now be described in further detail with reference to the embodiment whereby exposure is automatically controlled. Again, a similar calculation could also be performed for automatic kVp control. A first mAs can be calculated in dependence on the determined first depth (dl) and a second mAs can be calculated in dependence on the determined second depth (d2). As shown in Fig. 1, the imaging device, in the form of a CT scanner, includes a radiation emitter in the form of an X-ray tube. To produce an image, the radiation emitter is able to be moved between a first position, whereby the emitter is configured to apply radiation to the first section 27 of the patient region 9, and a second position, whereby the emitter is configured to apply radiation to the second section 29 of the patient regions. As such, the applied radiation can be varied during the scan to minimise dose where possible. For the cross section shown in Fig. 3, the radiation applied to the first body section 27 will be less than the radiation applied to the second body section 29 as d2 is less than dl . Where automatic mAs control methodology is applied, the mAs of the radiation emitted by the X-ray tube to the second body potion 29 will be less than the mAs of the radiation emitted by the X-ray tube to the first body potion 27. Similarly, where automatic kVp control methodology is applied, the kVp of the radiation emitted by the X-ray tube to the second body potion 29 will be less than the kVp of the radiation emitted by the X-ray tube to the first body potion 27. As shown by arrow 35 in Fig. 2, the second dose parameter can be continually calculated applied during the scan. Alternatively, a software application may pre- calculate the second dose parameter in dependence on the varying thickness of the patient region in order for the system to dynamically change the second dosing parameter during the scan.

Fig. 4 shows another embodiment of the method for automating radiation dose parameters for an imaging device. Indicia have been kept constant for functional blocks (19, 21, 23, 25) that are equivalent to those described with reference to Fig. 2. In this embodiment, the method further comprises iterative ly calculating 37 the first dose parameter (kVp) to further optimise the reduction in radiation dose. This embodiment will be referred to as automatic kVp and mAs control. Again, the optimised kVp can be calculated in dependence on patient thickness. When both kVp and mAs are allowed to vary (i.e. not set as constants), the optimum mAs & kVp can be calculated using the equation:-

The optimised kVp and mAs can be calculated for each position along the patient's scan region. Following optimisation of the kVp and mAs to reduce radiation dose, X-rays having the calculated dosing parameters is applied to the patient region. The constant may range from 2.38 to 2.79 depending on the scanner and manufacturer. This value can be determined once a specific scanner is defined.

Also disclosed herein is a radiation dose optimisation system implemented using computer processing and memory resources. Indicia have been kept constant for components that are equivalent to those described with reference to Fig. 1. The system includes at least one user interface, in the form of a display 17 that is configured to receive user data (e.g. an input from a user) relating to a second radiation dose parameter (e.g. kVp) retrieved from the user. In another form, the second radiation dose parameter may be generated by a computing device (i.e. not set by a user). As previously detailed, the absorption data (e.g. depth values for a plurality of sections of a region of the patient) may be determined by performing a scout scan. In this form, the system a memory 40 that is configured to store the absorption data (e.g. in the form of a look up table) that is determined by performing the scout scan. The system also includes a radiation dose selection engine 39 that is configured to retrieve absorption data from the memory and then calculate a first dose parameter (e.g. mAs) in dependence on the retrieved absorption data.

The radiation dose optimisation system also includes a radiation emitter, in the form of X-ray tube 3, configured to receive instructions from the radiation dose selection engine 39 and apply radiation 5 to the patient 9. The system further comprises a radiation detector 1 1 configured to receive radiation applied by the radiation emitter and generate image generation data (e.g. electrical signals) corresponding to the radiation received.

As previously detailed, the radiation emitter 3 is configured to move to thereby apply radiation to a plurality of section (i.e. across a region having varying thickness) of the patient 9. The radiation dose selection engine 39 is configured to calculate (e.g. before or during the scan) the first dose parameter in dependence on absorption data for each section of the patient 9.

A data interpretation engine 41 is configured to receive the image generation data and generate a CT image. The user interface 17 is able to receive the CT image generated by the data interpretation engine and display the CT image (e.g. for diagnostic purposes). In one embodiment, the user interface 17 that is configured to receive input data relating to the second dose parameter may be different to the user interface that displays the image (e.g. separate computing devices connected over a network). The system also includes a dose optimisation engine 43 configured to the first dose parameter in dependence on the absorption data and a radiation controller 45 configured to receive instructions from the dose optimisation engine 43 and the radiation dose selection engine 39 and output instructions to the X-ray tube 3. Example

The following example details the steps that may be performed to generate an image of a patient's heart.

Step 1 : Insert the patient into CT scanner. Step 2: Position the X-ray emitter such that it is positioned adjacent the patient's abdomen (e.g. the patient region to be scanned).

Step 3: Perform a scout scan of the patient's abdomen to establish and record the depth of a plurality of sections around the abdomen [e.g. the depth of section can vary from LAT (lateral position)= deff + 3.8 cm to AP(anterioposterior position) = deff - 4.5cm where deff = 32cm for an averaged adult (16cm for averaged children)] .

Step 4: Calculate Ad between each section and save Ad to the system memory.

Step 5 : Review a look up table (physical or digital) to retrieve initial parameters kVp (eg. .120 kVp) and mAs (240 mAs). Step 6: Select between automatic exposure control, automatic power control and automatic exposure and power control. In this example, automatic power (kVp) control is selected and mAs is therefore set to be constant (i.e. 240 mAs).

Step 7: Calculate kVp for each section of the patient's abdomen in dependence on Ad using the automatic power control equation for the specified scanner. Step 8: Apply radiation having differing kVp and constant mAs to the patient's abdomen to generate the image of the heart.

Variations and modifications may be made to the parts previously described without departing from the spirit or ambit of the disclosure.

In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.