Abstract:
A novel technique of quantifying nuclear medicine data is provided. The novel technique is characterized in that information acquired from nuclear medicine image data is normalized with bone mineral content (BMC) or bone mineral density (BMD). Some embodiments use, instead of the conventional SUV, the SUVbone that has been invented by the inventors of the present application such as the following: SUVbone={Amount of attenuation-corrected radioactivity in region of interest (kBq)÷Volume of region of interest (ml)}/{Administered radioactivity dose (kBq)÷Bone mineral content (g)} or SUVbone={Amount of attenuation-corrected radioactivity in region of interest (kBq)÷Volume of region of interest (ml)}/{Administered radioactivity dose (kBq)÷Bone mineral density (g/m 2 )}. BMC or BMD may be estimated from sex, age, height, or weight of a subject.

Description:
FIELD 
       [0001]    The present invention relates to processing of nuclear medicine image data. More particularly, the present invention relates to providing a novel technique for objectively evaluating results of nuclear medicine examinations. 
       BACKGROUND 
       [0002]    The principle of imaging technology based on nuclear medicine techniques, such as positron emission tomography (PET), single-photon emission computed tomography (SPECT), and scintigraphy, is to perform imaging by administering an agent (radiopharmaceutical) labeled with radioactive material into a subject&#39;s body and detecting radiation emitted from within the body. A tissue having an abnormality indicates different metabolism of the radiopharmaceutical from that in normal tissues. Thus, functional abnormality of tissue can be imaged by selectively using a radiopharmaceutical having desired metabolic characteristics. 
         [0003]    PET, SPECT, and other similar techniques provide primary images that are visualized values of radiation count values. In such images, sites having high-concentration of radiopharmaceutical are illuminated. In other words, the pixels corresponding to the sites have high pixel values. Radioactivity count values, however, are subject to various factors, and thus higher pixel values of specific pixels or in a region of interest do not always indicate abnormality in the corresponding tissue. Thus, efforts have been made to normalize each pixel value according to some rules so as to enable objective evaluation of pixel values. The most famous one of such normalizing values is the standardized uptake value (SUV). The SUV is obtained as follows: 
         [0000]      SUV={Amount of attenuation-corrected radioactivity in region of interest (kBq)÷Volume of region of interest (ml)}/{Administered radioactivity dose (MBq)÷Body weight of subject (kg)}  [Formula 1]
 
         [0004]    Thus, the SUV is a value obtained by normalizing the radioactivity concentration in a region of interest with the administered radioactivity dose per kg body weight. The SUV can be an indicator that reflects the uptake of radioactivity or a radiopharmaceutical. 
         [0005]    With regard to tissues working in a similar manner, the SUV has been expected to take similar values independent of different subjects. In other words, the SUV is expected to have such characteristics that it takes, for example, similar values for liver tissues having no abnormality regardless of different subjects, and, for example, similar values for lung tissues having no abnormality regardless of different subjects. If this is true, comparison is possible among a plurality of measurement results from different subjects, or from the same subject at different times. (In the technical field pertaining to the present application, converting a measured value to a comparable value is referred to as “quantification”.) A modified SUV has recently been used, which is obtained by using body weight excluding body fat (referred to as lean body weight) instead of using body weight as it is. 
       LIST OF PRIOR ART DOCUMENTS 
     Non Patent Literature 
       [0000]    
       
         Non Patent Literature 1: Yoshifumi Sugawara, Kenneth R. Zasadny et al., “Reevaluation of the Standardized Uptake Value for FDG: Variations with Body Weight and Methods for Correction”, November 1999 Radiology, 213, 521-525. 
       
     
       SUMMARY 
       [0007]    However, the inventors of the present application are skeptical about the use of the SUV when radiopharmaceuticals used are bone disease diagnostic agents. Bone disease diagnostic agents, which are radiopharmaceuticals used for detecting, for example, bone metastases of cancer, are distributed to bones. The SUV is a value normalized with body weight and is not a value normalized with information on bones. 
         [0008]    The inventors of the present application have performed an experiment on the following group of subjects to verify the validity of the SUV:
       Number of subjects: 15 (8 males and 7 females)   Age: 57 to 79 (67 on average)   Body weight: 39 to 69 kg (53.3 kg on average)       
 
         [0012]    The inventors of the present application performed PET measurement on the subjects by administering  18 F-NaF as a bone disease diagnostic agent, calculated SUVs by setting a region of interest to the lumbar vertebrae in the obtained image data, and plotted the results on a graph having the age on the abscissa axis. The administered radioactivity doses were 133.7 to 217.8 MBq, the average of which was 176.1 MBq. The results are indicated in  FIG. 1 . 
         [0013]    As the graph in  FIG. 1  clearly illustrates, age dependency is recognized from the results. For reference, fitting the results to a straight line establishes the following: 
         [0000]        y= 0.0557 x+ 1.813. 
         [0014]    Here, R 2 =0.3584 is established. Testing a null hypothesis with a level of 5%, which states that the slope of the regression line is not significant, resulted in P=0.018, and hence the significance of the slope is recognized. 
         [0015]    In other words, the experiment performed by the inventors of the present application has revealed that the SUV has age dependency with respect to the bone disease diagnostic agent. This suggests that the SUV may possibly be inappropriate as an indicator that reflects the uptake of bone disease diagnostic agents. If this is the case, an urgent task is to establish a novel technique of quantifying nuclear medicine data for bone disease diagnostic agents. 
         [0016]    The inventors of the present application have focused on bone mineral content (BMC) and bone mineral density (BMD) as indicators related to bones in which bone disease diagnostic agents are distributed. The inventors consider that the stability of quantitative assessment on bone disease diagnostic agents can be improved by using BMC or BMD for normalization of nuclear medicine images instead of using body weight, which has been used for the conventional SUV. 
         [0017]    On the basis of the consideration, the inventors of the present application provide the SUVbone defined by the following formula 3 or 4, instead of the conventional SUV, as an indicator reflecting the uptake of bone disease diagnostic agents, for example. 
         [0000]      SUVbone={Amount of attenuation-corrected radioactivity in region of interest (kBq)÷Volume of region of interest (ml)}/{Administered radioactivity dose (kBq)÷Bone mineral content (g)}  [Formula 2]
 
         [0000]      SUVbone={Amount of attenuation-corrected radioactivity in region of interest (kBq)÷Volume of region of interest (ml)}/{Administered radioactivity dose (kBq)÷Bone mineral density (g/m 2 )}  [Formula 3]
 
         [0018]    In formulas 2 and 3, the “region of interest” may be a region corresponding to one pixel, or a region including a plurality of pixels. 
         [0019]      FIG. 2  illustrates the data indicating an advantage of the SUVbone. 
         [0020]      FIG. 2A  illustrates a graph of the same experimental data as that of  FIG. 1 . The graph has been created by setting the same region of interest as that provided the results in  FIG. 1  (that is, setting the region of interest to the lumbar vertebra), calculating the SUVbones defined by formula 2, and plotting the results on the graph having the age on the abscissa axis. For comparison, the same conventional SUVs as that illustrated in  FIG. 1  are plotted on the graph. As is clear from the graph, the SUVbone is extremely low in age dependency, and indicates a substantially constant value regardless of age. For reference, fitting the SUVbones to a straight line establishes the following: 
         [0000]        y= 0.0009 x+ 0.1371. 
         [0021]    Here, R 2 =0.0854 is established. That is, effective age dependency is not recognized. In order to confirm its statistical significance, the null hypothesis that the slope of the regression line is not significant was tested with a level of 5%. This test resulted in P=0.29, and hence the slope of the regression line is not recognized statistically as well. 
         [0022]    This indicates that the invention of the present application that uses BMC to normalize nuclear medicine images is extremely advantageous in quantifying the uptake of the radiopharmaceuticals characterized by concentration in bones. 
         [0023]    The following describes the data indicating an advantage of the SUVbone defined by formula 3.  FIG. 2B  illustrates a graph of the same experimental data as that of  FIG. 1 . The graph has been created by setting the same region of interest as that provided the results in  FIG. 1  (that is, setting the region of interest to the lumbar vertebra), calculating the SUVbones defined by formula 3, and plotting the results on the graph having the age on the abscissa axis. In the same manner as  FIG. 2A , the same conventional SUVs as that illustrated in  FIG. 1  are plotted on the graph for comparison. As is clear from the graph, the SUVbone defined by formula 3 is extremely low in age dependency, and indicates a substantially constant value regardless of age. For reference, fitting the SUVbones to a straight line establishes the following: 
         [0000]        y= 0.0002 x+ 0.0918. 
         [0000]    Here, R 2 =0.0089 is established. That is, effective age dependency is not recognized. In order to confirm its statistical significance, the null hypothesis that the slope of the regression line is not significant was tested with a level of 5%. This test resulted in P=0.73, and hence the slope of the regression line is not recognized statistically as well. That is, the slope of the regression line is statistically zero, and the age dependency of the SUVbone has been proved to be not present statistically. 
         [0024]    These results indicate that the invention of the present application that uses BMD to normalize nuclear medicine images is extremely advantageous in quantifying the uptake of the radiopharmaceuticals characterized by concentration in bones. 
         [0025]    Thus, embodiments of the invention of the present application are generally characterized in that information acquired from nuclear medicine image data is normalized with bone mineral content (BMC) or bone mineral density (BMD). 
         [0026]    In some embodiments, BMC or BMD may be estimated from sex, age, height, or weight of a subject. 
         [0027]    An example of preferred embodiments of the invention of the present application is a system. The system includes: 
         [0028]    first means for loading nuclear medicine image data; 
         [0029]    second means for loading sex information on a subject of the nuclear medicine image data; 
         [0030]    third means for loading age information on the subject; 
         [0031]    fourth means for loading height information on the subject; 
         [0032]    fifth means for loading weight information on the subject; 
         [0033]    sixth means for loading information on a radioactivity dose administered to the subject; 
         [0034]    seventh means for acquiring certain information from the nuclear medicine image data; 
         [0035]    eighth means for calculating bone mineral content or bone mineral density based on at least one of the sex information acquired by the second means, the age information acquired by the third means, the height information acquired by the fourth means, or the weight information acquired by the fifth means; 
         [0036]    ninth means for normalizing the certain information acquired by the seventh means based on the administered radioactivity dose information acquired by the sixth means, and the bone mineral content or the bone mineral density acquired by the eighth means; and 
         [0037]    tenth means for outputting one or more normalized values acquired by the ninth means. 
         [0038]    An example of preferred embodiments of the invention of the present application is a computer program. The computer program includes a program instruction that causes, when executed by processing means of a system, the system to perform: 
         [0039]    loading nuclear medicine image data; 
         [0040]    loading sex information on a subject of the nuclear medicine image data; 
         [0041]    loading age information on the subject; 
         [0042]    loading height information on the subject; 
         [0043]    loading weight information on the subject; 
         [0044]    loading information on a radioactivity dose administered to the subject; 
         [0045]    acquiring certain information from the nuclear medicine image data; 
         [0046]    calculating bone mineral content or bone mineral density based on at least one of the sex information, the age information, the height information, or the weight information; 
         [0047]    normalizing the certain information based on the information on the administered radioactivity dose, and the bone mineral content or the bone mineral density; and 
         [0048]    outputting the normalized information. 
         [0049]    An example of preferred embodiments of the invention of the present application is a system. The system includes: 
         [0050]    first means for loading nuclear medicine image data; 
         [0051]    second means for loading information on a radioactivity dose administered to a subject of the nuclear medicine image data; 
         [0052]    third means for loading information on bone mineral content or bone mineral density of the subject; 
         [0053]    fourth means for acquiring certain information from the nuclear medicine image data; 
         [0054]    fifth means for normalizing the certain information acquired by the fourth means based on the administered radioactivity dose information acquired by the second means, and the bone mineral content or the bone mineral density acquired by the third means; and sixth means for outputting one or more normalized values acquired by the fifth means. 
         [0055]    An example of preferred embodiments of the invention of the present application is a computer program. The computer program includes a program instruction that causes, when executed by processing means of a system, the system to perform: 
         [0056]    loading nuclear medicine image data; 
         [0057]    loading information on a radioactivity dose administered to a subject of the nuclear medicine image data; 
         [0058]    loading information on bone mineral content or bone mineral density of the subject; 
         [0059]    acquiring certain information from the nuclear medicine image data; 
         [0060]    normalizing the certain information based on the information on the administered radioactivity dose, and the bone mineral content or the bone mineral density; and 
         [0061]    outputting the normalized information. 
         [0062]    Several preferred embodiments of the present invention are specified in the claims included in the attached claims. However, the embodiments specified in the claims do not necessarily include all the novel technical ideas disclosed in the present description and the drawings. The applicants claim to possess the right to have a patent granted on all the novel technical ideas disclosed in the present description and the drawings regardless of whether the novel technical ideas are claimed in the current claims. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0063]      FIG. 1  is a graph illustrating that the SUV has age dependency in diagnosis of bone metastases using a nuclear medicine technique. 
           [0064]      FIG. 2A  is a graph illustrating that the SUVbone (using BMC) developed by the inventors of the present application indicates no age dependency. 
           [0065]      FIG. 2B  is a graph illustrating that the SUVbone (using BMD) developed by the inventors of the present application indicates no age dependency. 
           [0066]      FIG. 3  is an explanatory diagram of a system configuration that can embody the present invention. 
           [0067]      FIG. 4  is an explanatory diagram of exemplary processing according to the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0068]      FIG. 3  is a diagram illustrating a main configuration of an apparatus or a system  100 , which is exemplary hardware capable of executing various processes disclosed in the present description. As illustrated in  FIG. 3 , the system  100  is similar to a general-purpose computer in terms of hardware, and may include a central processing unit (CPU)  102 , a main memory  104 , an auxiliary storage unit  106 , a display interface  107 , a peripheral device interface  108 , and a network interface  109 , for example. Similarly to a general-purpose computer, a high-speed random access memory (RAM) may be used as the main memory  104 , and an inexpensive, large-capacity hard disk or a solid state disk (SSD) may be used as the auxiliary storage unit  106 . To the system  100 , a display for displaying information may be connected through the display interface  107 . Also to the system  100 , a user interface such as a keyboard, a mouse, or a touch panel may be connected through the peripheral device interface  108 . The network interface  109  may be used to connect the system  100  to another computer or the Internet via a network. 
         [0069]    The auxiliary storage unit  106  may store therein, for example, an operating system (OS)  110  and an analysis program  120  for providing characteristic processes disclosed in the present description. The most basic functions of the system  100  are provided when the CPU  102  executes the OS  110 . 
         [0070]    In addition, novel processes disclosed in the present description are provided when the CPU  102  executes the analysis program  120 . A program instruction group constructing the analysis program  120  may be programmed in any of existing computer program languages such as C++ and JAVA (registered trademark). The program instruction group may be converted to an executable format by a preferred compiler and stored in the auxiliary storage unit  106 . 
         [0071]    The auxiliary storage unit  106  may store therein, for example, nuclear medicine image data  132  subject to an analysis by the analysis program  120 , measurement condition data  134  containing various measurement conditions of the nuclear medicine image data  132 , data  136  containing information calculated during processes, and data  138  containing results of the processes. 
         [0072]    Other than the components illustrated in  FIG. 3 , the system  100  may include the same units as those of a general computer system, such as a power source and a cooling unit. Various embodiments of a computer system employing various techniques have been known, such as distributed, redundant, or virtualized storage units, use of multiple CPUs, CPU virtualization, use of a processor suitable for a specific process such as digital signal processing (DSP), and implementation of a specific process as hardware to be used with a CPU. The matters disclosed in the present description may be implemented in any form of computer system. The form of computer system does not limit the scope of the present invention. The matters disclosed in the present description may generally be embodied as: (1) a computer program containing an instruction configured to cause, when executed by processing means, an apparatus or a system including the processing means to execute various processes described in the present description; (2) a method for operating the apparatus or the system, the method being performed when the processing means executes the computer program; and (3) the apparatus or the system including the computer program and the processing means configured to execute the computer program. 
         [0073]    Note that the pieces of data  132  to  138  are not stored in the auxiliary storage unit  106  in many cases at the time of manufacture, sales, and initial start-up of the system  100 . These pieces of data may be transferred from an external apparatus to the system  100  through the network interface  109 , for example. In some embodiments, the pieces of data  136  and  138  may be generated and stored when the CPU  102  executes the computer program  120  or other computer programs. In some embodiments of the computer program  120  or the OS  110 , the pieces of data  136  and  138  are stored only in the main memory  104  instead of being stored in the auxiliary storage unit  106 . In some cases, the data  134  is combined with the data  132 , so that the data  134  does not exist as an individual data file. Note that the scope of the present invention is not limited by the existence of the pieces of data  132  to  138 . 
         [0074]    The following describes the nuclear medicine image data  132  subject to an analysis in an example. The nuclear medicine image data  132  may be image data acquired by PET measurement for diagnosis of bone metastases or other purposes. For example, the nuclear medicine image data  132  may be image data generated on the basis of radiation count values acquired by administering  18 F-NaF as a radiopharmaceutical to a subject, and detecting radiation emitted from within the subject&#39;s body with a PET apparatus. In general, each pixel has a value corresponding to a radioactivity count value; that is, each pixel value indicates the intensity of radioactivity. Note that possible nuclear medicine image data subject to an analysis according to the present invention is not limited to PET images acquired using  18 F-NaF. Various nuclear medicine images (PET images, SPECT images, and scintigraphy images) acquired using other radiopharmaceuticals (e.g., Technetium ( 99m Tc) Hydroxymethylenediphosphonate Injection, Technetium ( 99m Tc) Methylenediphosphonate Injection) may be subject to an analysis according to the present invention. 
         [0075]    The measurement condition data  134  contains various conditions regarding PET measurement on the basis of which PET images contained in the nuclear medicine image data  132  have been created. The conditions contained in the measurement condition data  134  preferably include at least sex, age, height, and weight of a subject, and also the amount of administered radiopharmaceutical. In some cases, the content of the measurement condition data  134  is contained in the nuclear medicine image data  132 , so that the measurement condition data  134  does not exist as an individual data file. In some embodiments, at least one of the conditions contained in the measurement condition data  134  may be input by a user with a keyboard or other devices connected to the peripheral device interface  108 . In some embodiments, the measurement condition data  134  may be stored on the main memory  104  instead of the auxiliary storage unit  106 . 
         [0076]    The following describes characteristic processes in a preferred example with reference to  FIG. 4 . These processes may be performed by the system  100  when the CPU  102  executes the analysis program  120 . 
         [0077]    Step  200  indicates the start of processing. In step  202 , at least part of the nuclear medicine image data  132  is copied to the main memory  104  for preparation of an analysis process to be performed by the analysis program  120 . 
         [0078]    In step  204 , information on measurement conditions on the nuclear medicine image data  132 , such as an administered radioactivity dose, is acquired. In one example, this step is performed by loading the measurement condition data  134 . In another example, this step is performed by loading information on various conditions contained in the nuclear medicine image data  132 . In still another example, various conditions may be input with a keyboard or other devices connected through the peripheral device interface  108 . In this case, according to an instruction from the analysis program  120 , the CPU  102  may cause, through the display interface  107 , a display connected to the display interface  107  to display a message for prompting input of a measurement condition. In some embodiments, the information on measurement conditions acquired in step  204  may include information on a subject (sex, age, weight, height, or other attributes) of the nuclear medicine image data  132 . 
         [0079]    In step  206 , bone mineral content (BMC) or bone mineral density (BMD) is calculated. BMC or BMD can be estimated from sex, age, height, or weight of a subject. A prior research has been conducted specifically on Japanese people using databases (for example, European Journal of Clinical Nutrition (2001)  55 , pp. 462-470). According to this document, BMC and BMD can be estimated by the following formulas: 
         [0000]      Bone mineral content (Male: kg)=−1.81−0.0015×Age+1.89×Height+0.017×Weight
 
         [0000]      Bone mineral content (Female: kg)=−1.05−0.009×Age+1.57×Height+0.017×Weight
 
         [0000]      Bone mineral density (Male: g/m 2 )=0.934−0.00081×Age+0.003×Weight
 
         [0000]      Bone mineral density (Female: g/m 2 )=0.824−0.00368×Age+0.137×Height+0.0026×Weight
 
         [0080]    In these formulas, the unit of age is year, the unit of weight is kilogram (kg), and the unit of height is meter (m). 
         [0081]    In the present example, the analysis program  120  contains therein these formulas and is configured to control the CPU  102  to substitute, into these formulas, the information on the sex, age, height, and weight of a subject acquired in step  204  and to calculate the bone mineral content BMC and the bone mineral density BMD. In some embodiments, the calculated BMC and/or BMD may be stored, as the data  136  for example, on the auxiliary storage unit  106  or the main memory  104  for example. 
         [0082]    Step  208  indicates a phase at which certain information is obtained from the nuclear medicine image data  132 . In later steps, this information is normalized with the BMC or the BMD (step  210 ), and output as a map or a numeric value (step  214 ). The information acquired in step  208  may vary depending on embodiments. In one embodiment, the information is the pixel value of each pixel. In this case, the data has already been loaded in step  202 , and thus step  208  is unnecessary. In some embodiments, the information acquired in step  208  may be the radioactivity concentration of each pixel. In this case, in step  208 , each pixel value in the image data  132  may be multiplied by a certain factor, such as the reciprocal of the volume of the pixel, in order to convert the pixel value of each pixel to radioactivity concentration. 
         [0083]    In some embodiments, in step  208 , correction may be performed to correct the pixel value (count) of each pixel in the nuclear medicine image data  132 . This correction may correct the effect of absorption or scatter of radiation within the body, and the attenuation of radioactivity due to the decay of radionuclide. These corrections have generally been performed in nuclear medicine techniques, and thus the detail of the corrections is not described here. In some embodiments, the nuclear medicine image data  132  may have been subjected to such corrections. 
         [0084]    In some embodiments, in step  208 , calculation may be performed on the radioactivity count value of a region including a plurality of pixels, or the radioactivity concentration of a region including a plurality of pixels (that is, a value obtained by dividing the radioactivity dose in a region including a plurality of pixels by the volume of the region). These values may be subjected to the attenuation correction described above. 
         [0085]    In some embodiments, in step  208 , a plurality of pieces of information may be calculated. For example, two or more types of information (values) may be calculated out of the radioactivity count value of each pixel, the radioactivity concentration of each pixel, the radioactivity count value of a region including a plurality of pixels, and the radioactivity concentration of a region including a plurality of pixels. These value&#39;s may be subjected to the attenuation correction described above. 
         [0086]    In step  210 , the information acquired in step  208  is normalized. Specifically, the information (value) acquired in step  208  is subjected to division, that is, (Administered radioactivity dose BMC) or (Administered radioactivity dose BMD), where the administered radioactivity dose is the value acquired in step  204 , and the BMC or the BMD is the value acquired in step  206 . In some embodiments, the units of the administered radioactivity dose, the BMC, and the BMD may be changed as appropriate. 
         [0087]    When the information acquired in step  208  is attenuation-corrected radioactivity concentration for example, then a value obtained by the normalization process in step  210  is the SUVbone defined by formula 2 or 3. 
         [0088]    The value normalized in step  210  is output in step  214 . In some embodiments, an additional process may be performed before the output.  FIG. 4  illustrates such an optional process in step  212 . For example, when the information acquired in step  208  is the attenuation-corrected radioactivity concentration of each pixel, which is normalized in step  210  (that is, SUVbones are calculated in step  210 ), SUVbones in a region of interest including a plurality of pixels may be integrated in step  212 . 
         [0089]    In step  214 , the values calculated in step  210  and/or  212  are output. The output may include visualizing and displaying the values calculated in step  210  and/or  212 , and/or displaying the values as numeric values. Alternatively, the output may include storing the values as the data  138  on the auxiliary storage unit  106 . 
         [0090]    When the values calculated in step  210  are the normalized radioactivity concentration of respective pixels (that is, SUVbones of respective pixels), these values can be displayed as an image in a map view similarly to a tomogram. When the normalized attenuation-corrected radioactivity concentration of a region including a plurality of pixels is calculated in step  210  or  212 , it may be displayed as a value. In some embodiments, a map of normalized values of respective pixels and a normalized value of a region of interest may be displayed together. The display may be performed on, for example, a display connected to the display interface  107 . 
         [0091]    Step  220  indicates the end of the processing. 
         [0092]    Embodiments of the present invention have been described with reference to preferred examples; however, the description of these examples are not intended to limit the scope of the present invention, but intended to satisfy the requirements of the Patent Law and to contribute to the understanding of the present invention. The present invention can be embodied in various forms, and embodiments of the present invention include a number of variations other than the embodiments exemplified herein. The present invention is applicable to nuclear medicine images (PET images, SPECT images, and scintigraphy images) acquired using various radiopharmaceuticals other than the PET images acquired using  18 F-NaF described above. 
         [0093]    Individual features included in various examples that have been described in the description are not limited to usage with examples in which these features are explicitly explained to be included, but may be used in combination with other examples that have been described herein or various specific embodiments that have not been described. In particular, the processes presented in the flowchart do not necessarily need to be performed in the described order. According to the preference of an executor, the processes may be performed in a changed order or in parallel, as a plurality of blocks integrally implemented or in a manner divided to a plurality of sub-blocks, or in a loop as appropriate. In some embodiments, some of the blocks in the flowchart may be omitted. For example, step  212  may be unnecessary for some embodiments as described above. In other cases, BMC or BMD has already been calculated for some embodiments, and thus recalculation of the BMC or the BMD in step  206  may be unnecessary. The BMC and the BMD may be values separately measured by known methods. Quantification of BMC and BMD may be performed by various known methods (for example, the method described in “SHIKAHOUSHASEN (Dental Radiology), Volume 18 (1978) pp. 278 to 295”) other than generally known methods using bone mineral quantification devices. In this case, step  206  can be replaced with a loading process of BMC or BMD. These variations are all included in the scope of the present invention. The order of the description of the processes defined in the claims does not necessarily specify the mandatory order of the processes. For example, an embodiment specifying a different order of the processes and an embodiment that executes the processes in a loop are also included in the scope of the present invention according to the claims. It should be noted that the applicants claim to possess the right to have a patent granted on all the embodiments not deviating from the spirit of the present invention regardless of whether a patent is claimed in the current set of attached claims. 
       REFERENCE SIGNS LIST 
       [0000]    
       
           100  system 
           102  CPU 
           104  main memory 
           106  auxiliary storage unit 
           107  display interface 
           108  peripheral device interface 
           109  network interface 
           110  OS 
           120  analysis program