Abstract:
To improve the scanning effect, a scanning method is provided, which comprises the steps of performing at least one of an nCT scan and a CTA scan on an object so as to obtain a set of images; detecting characteristics of a region of interest based on the set of images; and performing a CTP scan on the region of interest by adopting the characteristics to obtain a CTP image. By deriving the characteristics of the region of interest, e.g. a lesion or an area covering the lesion, before performing the CTP scan, and by adapting the subsequent CTP scan based on the characteristics of the region of interest, the drawback introduced by a limited scan area of the CTP scanner is mitigated, or even overcome.

Description:
FIELD OF THE INVENTION 
     The present invention relates to a scanning method and system, particularly a CT (Computed Tomography) scanning system. 
     BACKGROUND OF THE INVENTION 
     Thrombolysis is a very effective therapy for stroke patients. Instead of limiting thrombolysis within three hours after the onset of a stroke symptom, it is observed that, based on the patient&#39;s individual status, the time window of applying thrombolysis can be extended to 6 or 9 hours. This observation underscores the shift from the old concept of “Time is Brain” to the new concept of “Physiology is Brain”. 
     In current practice, the following protocols are widely used in the case of multi-protocol CT imaging.  FIG. 1  shows the steps of a multi-protocol CT scan. First, in step S 110 , an nCT (native CT) is performed to check whether a hemorrhagic stroke exists; if this hemorrhagic stroke does not exist, a CTP (CT perfusion) scan is performed in step S 120  to determine the physiological parameters. Then, in step S 125 , a saline flash is optionally performed to clean the vascular system so as to prevent the influence of a previously applied contrast agent. In step S 130 , a CTA (CT angiography) can be performed to determine the status of the vessels and detect the clot that causes the ischemic stroke. It is possible to change the sequence between CTP and CTA after performing nCT. In current practice, the operation of CTP is the same, no matter whether it is performed before or after CTA. 
     However, CTP has the drawback that it is limited to a small portion of the brain. Currently, only two or four slices of the head are acquired at a standardized position that covers the territory of the MCA (mid cerebral artery). Although most ischemic stroke lesions (about 75%) can be found in the MAC territory, about 25% of the ischemic strokes are missed from the outset. 
     To extend CTP to the whole brain, a method named “Neuron Perfused Blood Volume Imaging” is proposed. This method extends the spatial coverage by reducing the number of time points to exactly two, which reduce the imaging resolution. The method is still in its testing phase. Another drawback of this method is its low image resolution. 
     SUMMARY OF THE INVENTION 
     It is an object, according to one embodiment of the present invention, to improve the method and system of CT scanning. 
     In a first aspect, according to one embodiment of the present invention, a method of scanning an object comprises the steps of: performing at least one of an nCT scan and a CTA scan on an object so as to obtain a set of images; detecting characteristics of a region of interest based on the set of images; and performing a CTP scan on the region of interest by adopting the characteristics to obtain a CTP image. 
     A region of interest, such as a lesion or an area comprising the lesion, is detected by applying the detection step to the set of images, e.g. an nCT image and/or a CTA image. Use of characteristics of this region of interest in the subsequent CTP scan as input parameter(s) provides the advantage that the CTP scan is performed in an appropriate field of view, i.e. in the region covering the lesion. More specifically, the relevant parts of the object, e.g. the brain, will be imaged. It is an advantage to mitigate or even overcome the influence of limited scan coverage of the CTP scan on the multi-protocol CT scan, and/or improve the scan accuracy to detect the potential clots, especially those outside the MCA territory. Furthermore, there is another advantage over the method of “Neuron Perfused Blood Volume Imaging” in that there is no need for a whole-brain CTP scanner, which saves costs and does not suffer from a low image resolution. 
     Optionally, when the set of images comprises at least one nCT image and one CTA image, which means that an nCT scan and a CTA scan are performed, a registration on the nCT image and the CTA image is performed during the detection step so as to obtain a spatial correlation, which can be further used to detect the region of interest, e.g. the lesion. 
     In other embodiments, automatic image-processing methods without user interaction are also provided, including applying grey value and pattern-based processing on the nCT image, and/or applying vessel tree extraction and analysis on the CTA image, so as to detect the region of interest. This provides the advantage that the image is processed without the need of user interaction to which current image-processing algorithms and methods are applicable. 
     In other embodiments, the physician&#39;s experience can be incorporated in the detection of the region of interest by presenting part or whole of the set of images, e.g. the nCT image and/or the CTA image, through a user interface and receiving input information through the user interface or another interface. The input information may indicate the possible location of the lesion, based on the physician&#39;s visual analysis. Advantageously, the input information can be obtained on the basis of combination and comparison of the nCT image and the CTA image. 
     In other embodiments, the computer-based image-processing and manual input can be combined. This method, referred to as semi-automatic image-processing, is advantageous because it does not only take the experience of physicians into account, but also advanced image-processing technologies. 
     In a second aspect, according to one embodiment of the invention, a scanning system comprises: a processor configured to detect characteristics of a region of interest comprised in a scan object, based on at least one of an nCT image and a CTA image; and a scanner configured to perform a CTP scan on the region of interest. 
     Use of this scanning system has the advantage that the region of interest, e.g. a lesion or an area covering the lesion, is located and that the characteristic or characteristics of the region of interest are utilized to locate the CTP scan area. Furthermore, while keeping the current high image resolution, there is no need to update the CTP scanner to a whole-brain CTP scanner. 
     In one embodiment, the characteristic or characteristics of the region of interest comprise at least one of location, quantity, size and extension of the region of interest. 
     Optionally, according to one embodiment, the scanner is further configured to perform an nCT scan and a CTA scan. In this situation, the scanner can be referred to as multi-protocol CT scanner. 
     According to one embodiment, the processor comprises a registration unit configured to register the nCT image and the CTA image so as to establish a spatial correlation between the CTA image and the nCT image. The spatial correlation is useful in improving the detection of the region of interest, i.e. the lesion. 
     Optionally, an nCT scanner and a CTA scanner are incorporated in this scanning system. It is also possible to only utilize nCT images and CTA images obtained from other scan systems. 
     To facilitate intervention by physicians, the lesion-based system optionally provides a user interface configured to present the nCT image and the CTA image and to receive input information indicating the suspected area in which the lesion is possibly located. The physician&#39;s experience is taken into consideration during detection of the lesion. 
     To overcome the influence introduced by a patient&#39;s movement during scanning, a motion correction processor is optionally incorporated in the scanning system in one embodiment of the present invention. The motion correction processor is configured to perform motion correction on the CTP image so as to mitigate movement of the patient during a CTP scan. In the system having an nCT scanner and a CTA scanner, the motion correction processor is further configured to perform motion correction on the nCT image and the CTA image. 
     A drawback of the current CTP scanner is its limited scan coverage. In current practice, the CTP scan is performed on the same area, i.e. the MCA territory, irrespective of the sequence of a CTP scan and a CTA scan. This may introduce the loss of some potential clots, which are located outside the MCA. The basic idea of the invention is that, before performing the CTP scan, the characteristics of the region of interest are detected, and the detected information is used as the scan parameter so as to help the CTP scanner to scan the interested area which might comprise a lesion, instead of merely scan the MCA territory. The influence of a limited scan area of the CTP scanner on the multi-protocol CT scanning method can thus be mitigated, or even overcome. 
     These and other aspects, features and/or advantages of the invention are apparent from and will be elucidated with reference to the embodiments described hereinafter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flowchart of a known multi-protocol CT scan; 
         FIG. 2  is a flowchart, according to one embodiment of the present invention, of a lesion-based scan method; 
         FIG. 3  is the flowchart of an image-processing method based on the combination of nCT and CTA images, according to one embodiment of the present invention; 
         FIG. 4  is a block diagram of a scanning system according to one embodiment of the present invention. 
     
    
    
     In these drawings, identical or similar reference numerals denote the same or similar functions/apparatuses. 
     DESCRIPTION OF EMBODIMENTS 
     According to one embodiment,  FIG. 2  shows a method of first detecting a region of interest (e.g. a lesion/stroke area, such as a clot) and subsequently performing a CTP scan on the detected region of interest. In the method  200 , nCT is performed first, in step S 210 , so as to judge whether the current stroke is a hemorrhagic stroke, which requires a different therapy. If there is no hemorrhagic stroke, a CTA scan is performed in step S 220  so as to generate a CTA image, which may be a 3D image including vessel trees. Step S 220  may be optional if the output of S 210 , i.e. the nCT image, is enough to ascertain the location/size/extension of a lesion. In step S 230 , detection is performed to detect the lesion, based on at least one of the nCT image and CTA image. As a result, the output of S 230  should include at least one characteristic of the region of interest, e.g. location, size, extension, quantity, or any other parameter that can be used to represent a lesion. In step S 240 , the characteristic of the region of interest is used as a scan parameter to help the CTP scanner to scan the region of interest, which may cover the lesion. 
     In one preferred embodiment, it is advantageous to use the combination of nCT image and CTA image to detect the region of interest. Since the nCT image and the CTA image can provide different information, the combination may provide more extensive and accurate information about the lesion. To this end, in one embodiment, a registration is performed on the nCT image and the CTA image so as to establish a spatial correlation. The registration can adopt any currently available registration method, such as rigid registration techniques and mutual information-based registration techniques. The spatial correlation is useful in improving the accuracy when detecting the region of interest. 
       FIG. 3  is a detailed flowchart of an embodiment of an image-processing method using the registration technique. In the method  300 , the nCT image and the CTA image are registered so as to establish a spatial correlation between these two images in step S 310 . In step S 320 , the size, location and/or extension of the lesion can be detected. Different methods can be used in this step. For example, in automatic methods, grey value and pattern-based approaches can be applied to the nCT image and, if necessary, vessel tree extraction and analysis approaches can be applied to the CTA image. Other methods applicable to segment the combination of nCT and CTA images can also be used. 
     Alternatively, the physician&#39;s experience is taken into account. It is advantageous to present the nCT image and/or the CTA image to the physician through a user interface. The physician can use his expertise and/or other methods/apparatuses to judge the location and/or size of the lesion. It is also practical for the physician to only indicate a special area in which he thinks the lesion may be located. The physician&#39;s opinion can be received through the user interface or another user interface, and may be used as a scan parameter for the CTP scanner to perform a subsequent CTP scan. 
     It is also practical to combine the physician&#39;s experience and the advantages of image-processing methods. For example, the physician can indicate the suspected area and use the image-processing method to pay more attention to the indicated area. In other embodiments, the image-processing method may present some suspected areas, and the physician can select one or more areas based on his experience. The selected areas can be used as input parameters for CTP scanning. 
     It is also practical to perform a lesion detection based on user input, e.g. a region growth starting from a user-defined seed point. To this end, the size and/or extension of the lesion is calculated in step S 330 . The extension is useful because the affected brain tissue may include some irrecoverably damaged tissue, affected but still recoverable tissue, and unaffected tissue. Physicians can specify a territory around the lesion manually. Alternatively, a specific area including the lesion detection based on automatic methods can be selected as a scan area. It is also practical to combine the physician&#39;s input and image-process algorithms. It is advantageous to enable the physician to correct the selected scan area. 
       FIG. 4  shows a scanning system for performing the lesion-based scanning method proposed above. The scanning system  400  comprises a processor  410  and a CTP scanner  420 . The processor  410  is configured to detect characteristics of a region of interest of a scan object, based on at least one of an nCT image and a CTA image. The CTP scanner  420  is configured to perform a CTP scan on the region of interest by adopting the characteristics of this region of interest. 
     Optionally, the processor  410  may include a registration unit  412  for registering the nCT image and the CTA image so as to obtain a spatial correlation. 
     In one embodiment, the processor can have the capability to perform grey value and pattern-based methods on the nCT image, and/or vessel tree extraction and analysis on the CTA image. 
     The lesion-based scan system may further incorporate an nCT scanner  430  and/or a CTA scanner  440 . The nCT scanner  430  performs an nCT scan on the scan object so as to generate an nCT image, and the CTA scanner  440  performs a CTA scan on the scan object so as to generate a CTA image. The nCT image and the CTA image can also be output from other scan systems and are re-usable in the lesion-based scanning system  400 . 
     To facilitate intervention by physicians, the system  400  further includes a user interface  450 . The user interface  450  has the basic function of receiving input information from the physician/operator, indicating at least one of location, size and extension of the suspected lesion. The user interface  450  can also be configured to present at least one of the nCT image and the CTA image to the physician/operator. 
     In practice, a patient always moves during scanning. The lesion-based scanning system  400  may further comprise a motion correction processor  460  which is configured to perform motion correction on the CTP image so as to mitigate movement of the patient during a CTP scan. For the system including nCT scanner  430  and CTA scanner  440 , the motion correction processor  460  may be further configured to correct the patient&#39;s movement during the nCT/CTA scan. 
     This embodiment has the advantage of helping the CTP scanner in scanning a suspected area instead of the central brain. Moreover, there is no need to extend the CTP scan to the whole brain, which may be expensive and provides a low image resolution. 
     The embodiment of  FIG. 4  shows three CT scanners, including one nCT scanner  430 , one CTA scanner  440 , and one CTP scanner  420 . Alternatively, one multi-protocol scanner can perform the functions of nCT scanning, CTA scanning and CTP scanning, and can be incorporated in a single CT scanner, referred to as multi-protocol scanner. 
     The invention can be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention or some of its features can be implemented as computer software. The elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units. As such, the invention may be implemented in a single unit, or may be physically and functionally distributed between different units and processors. 
     Although the present invention has been described with reference to the specified embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. In the claims, use of the verb “comprise” and its conjugations does not exclude the presence of other elements or steps. Although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. Furthermore, reference signs in the claims shall not be construed as limiting the scope.