Abstract:
A brain imager includes a compact ring-like static PET imager mounted in a helmet-like structure. When attached to a patient&#39;s head, the helmet-like brain imager maintains the relative head-to-imager geometry fixed through the whole imaging procedure. The brain imaging helmet contains radiation sensors and minimal front-end electronics. A flexible mechanical suspension/harness system supports the weight of the helmet thereby allowing for patient to have limited movements of the head during imaging scans. The compact ring-like PET imager enables very high resolution imaging of neurological brain functions, cancer, and effects of trauma using a rather simple mobile scanner with limited space needs for use and storage.

Description:
The United States of America may have certain rights to this invention under Management and Operating contract No. DE-AC05-06OR23177 from the Department of Energy. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to PET imaging and more particularly to a compact and mobile high resolution PET imaging system for imaging the neurological brain functions of a patient. 
     BACKGROUND OF THE INVENTION 
     Brain diseases, such as Alzheimer&#39;s and Parkinson&#39;s, are becoming more prevalent in the aging population because of increased life span. As US and European populations continue to age, Alzheimer&#39;s disease will increase with the US expected to have 16 million cases by 2050. An estimated 1.5 million people in the US have Parkinson&#39;s, which affects 1% of Americans over 60 and includes about 100,000 new cases each year. 
     Although many new PET radiopharmaceuticals for brain function imaging are under development, imaging modalities for the brain such as PET+CT and MRI+PET are insufficient due to poor PET resolution and poor CT/MRI/fMRI specificity. Current clinical PET scanners have a resolution of 4-5 mm, which is insufficient in many brain imaging situations. In addition, current clinical PET scanners are large, expensive, not optimized for brain imaging, and usually are available only in a package with CT. The existing standard PET imagers are bulky devices that are placed in dedicated imaging rooms and require patient to be brought to the imager. Some patients cannot be transported to the imaging room, which could be in a far away part of the medical complex, particularly in situations when they need to be hooked to life-saving and monitoring machines or when quick diagnostic and staging decision is important. In many other situations it would be an advantage to have the brain imaging scanner in an outpatient location, for example in a neurological department. In the current state of the art, brain imagers are bulky and heavy devices and are not capable of providing dynamic high resolution 2D or 3D images. 
     What is needed therefore, is a compact and mobile dedicated brain imager capable of producing dynamic high resolution 2D or 3D images. The compact and mobile imager should be capable of being easily attached to a patient&#39;s head to enable high resolution imaging of the patient&#39;s brain. 
     SUMMARY OF THE INVENTION 
     The present invention is a brain imager that includes a compact ring-like static PET imager mounted in a helmet-like structure. When attached to a patient&#39;s head, the helmet-like brain imager maintains the relative head-to-imager geometry fixed through the whole imaging procedure. The brain imaging helmet contains radiation sensors and minimal front-end electronics. A flexible mechanical suspension/harness system supports the weight of the helmet thereby allowing for patient to have limited movements of the head during imaging scans. The compact ring-like PET imager enables very high resolution imaging of neurological brain functions, cancer, and effects of trauma using a rather simple mobile scanner with limited space needs for use and storage. 
     OBJECTS AND ADVANTAGES 
     Several advantages are achieved with the compact high resolution brain imager of the present invention, including:
         (1) The helmet-like brain imager maintains the relative head-to-imager geometry fixed through the whole imaging procedure thereby enhancing the accuracy of images.   (2) The brain imager provides high efficiency and high resolution in a compact application-specific device.   (3) The PET brain imager includes a high resolution of less than 2 mm.   (4) The higher spatial resolution of the proposed imager enables detection of smaller abnormalities and earlier detection and more accurate diagnosis of brain disease.   (5) As a result of being compact and mobile, the organ-specific imager can be moved to the patient, such as in the ER, ICU, hospital bed, or outpatient center, to provide in-situ imaging, especially when the patient cannot be moved to the PET imaging center   (6) The high-resolution and economical dedicated PET brain imager can have an important impact on early detection of brain disease and on therapy planning and monitoring.   (7) When used in combination with disease-specific biomarkers, the brain imager improves early diagnosis of the brain disease.   (8) The brain imager of the present invention can be adapted for use on other parts of the patient&#39;s body such as extremities, neck and thyroid, and the breast if reconfigured with a modified gantry.   (9) The brain imager includes a dedicated lightweight mobile gantry for stationary or optional translational/rotational scan.   (10) Real-time static tomographic imaging of an approximate 10 cm brain/head slice width and a field-of-view of less than 25 cm.   (11) Compact geometry allows close positioning while scanning the entire head.   (12) The brain imager provides 3D reconstructed resolution of less than 2.5 mm FWHM in the entire field-of-view (1.5-1.7 mm in center).   (13) Capable of fast continuous dynamic scans for high-quality complete angular sampling.       

     These and other objects and advantages of the present invention will be better understood by reading the following description along with reference to the drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a conceptual view from above the patient&#39;s head of a brain imaging system according to the present invention including a ring of detector modules arranged around the patient&#39;s head. 
         FIG. 2  is a sectional view of a PET imager detector module constructed using a modular approach according to the present invention. 
         FIG. 3  is a sectional view of a PET imager detector module constructed using a modular approach according to the present invention. 
         FIG. 4  depicts a basic initial 12.5 mm silicon PMT imaging module constructed of an array of sixteen 3 mm×3 mm readout pixels or pads arranged in a 4×4 array. 
         FIG. 5  depicts an array of 2×2 of the basic four-side buttable modules of  FIG. 5  butted together to form an approximately one inch square photodetector. 
         FIG. 6  depicts the concept for a plug-in replacement module that can be implemented by arranging 16 (in array of 4×4) basic imaging modules. 
         FIG. 7  is a conceptual view from above the patient&#39;s head of a single head/neck imager ring with 12 individual detector modules. 
         FIG. 8  is an exploded perspective view of a helmet brain imager according to the present invention. 
         FIG. 9  is a side view of a ring PET brain imager  80  suspended from a mobile gantry and placed around the head of a patient that is exercising on a treadmill. 
     
    
    
     INDEX TO REFERENCE NUMERALS IN DRAWINGS 
     
         
         
           
               20  brain imaging system, first embodiment 
               22  ring 
               24  photodetector module 
               26  patient 
               30  photodetector module, first embodiment 
               31  position sensitive photomultiplier tube (PSPMT) 
               32  readout electronics 
               33  scintillator array 
               34  window 
               35  reflective strip 
               36  dead region 
               37  outer shell or shield 
               40  photodetector module, second embodiment 
               43  Burle MCP PMT 
               44  optical spreader window 
               45  scintillation array 
               46  window 
               47  reflective strip 
               50  photodetector module, third and preferred embodiment 
               52  silicon PMT (SiPM) basic imaging module 
               54  basic silicon unit or pad 
               55  readout channel comprised of four pads 
               56  readout channel comprised of sixteen pads 
               57  one inch square silicon photodetector 
               58  dead region 
               60  brain imaging system, second embodiment 
               62  imager ring 
               64  photodetector module 
               66  scintillation array 
               68  photodetector 
               70  helmet imager 
               72  imaging ring 
               74  detector module 
               76  inner shell or liner 
               78  outer shell 
               79  hook 
               80  ring PET brain imager 
               81  mobile gantry 
               82  head 
               83  patient 
               84  treadmill 
               85  mechanical mount 
               86  suspension 
               87  counterweight 
           
         
       
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to  FIG. 1  there is shown a compact and mobile brain imaging system  20  according to the present invention including a ring  22  with a set of photodetector modules  24  viewing the brain of a patient  26 . A plurality of the photodetector modules  24  are formed into a ring  22  composed of 12-30 closely spaced and individually read imaging modules  24 . The ring of imaging modules  24  provide enough surface coverage and angular views for high resolution 2D/3D PET image slice reconstruction of the brain. 
     A compact and mobile high resolution PET imager  20  according to the present invention would include a tomographic slice reconstruction of between 5 and 15 cm, and a 3D reconstruction resolution (over narrow slice involved) of between 1.5 and 2.0 mm. The compact ring imager  20  is preferably mounted in a suspended lightweight helmet with a 20 to 25 cm inner diameter opening for the head and neck. To limit detector volume and weight (including also less shielding), only minimal readout electronics are placed in the ring enclosure. Data acquisition (DAQ) electronics are located in a mobile cabinet (not shown), with small cross-section robust cable connection between the detector ring modules  24  and the DAQ module. The data acquisition and processing system is capable of recording data with at least 200 kHz trigger rate in a list mode, to enable prompt limited data analysis, and fast data replay and image reconstruction during the same scan session. 
     Several imaging technologies can be implemented in the brain imaging device of the present invention. The brain imager will preferably include a scintillator as a sensor/energy converter of 511 keV annihilation gamma rays, while various photodetectors serve as detectors of the scintillation light produced by the absorbed 511 keV gamma rays in the scintillator gamma sensor. The scintillator sensor part is preferably made of pixellated or plate crystal scintillator materials such as LSO, LYSO, GSO, BGO, LaBr3, NaI(Tl), CsI(Tl), CsI(Na), and other. The photodetector part is preferably a standard or multi-element photomultiplier, position sensitive, flat panel or microchannel plate based photomultiplier, avalanche photodiode arrays or large size avalanche photodiodes with resistive etc readout, and different variants of the silicon photomultiplier. 
     Referring to  FIG. 2  there is shown a first embodiment of a PET photodetector module  30  for constructing the compact brain imager of the present invention. The photodetector module  30  is based on compact, 1″ or 2″ in size, position sensitive photomultipliers (PSPMTs)  31  from Hamamatsu Corporation of Bridgewater, N.J. or Burle Industries of Lancaster, Pa. The photomultipliers  31  are coupled to an array  33  of 2×2×10 mm LYSO scintillator pixels. In the present invention, a modular approach is used in constructing the PET photodetector module  30 . The detector module  30  includes an array of compact H8500 or H9500 flat panel PMTs  31  using high-rate resistive readout electronics  32 . The position sensitive flat panel PMTs  31  are placed in a tight array and coupled to the scintillator array  33  through a window  34  and an optical light guide. The flat panel Hamamatsu H8500 or H9500 PMTs are each approximately 5 cm×5 cm in size, to obtain coverage of about 20 cm per detector module  30 . Reflective strips  35  are placed in the dead regions  36  between the flat panel PMTs  31  to improve scintillation light collection from the approximately 2 cm wide dead regions  36  between the PMTs  31 . An outer shell  37  is placed around the detector  30  for protection. The compact H8500 or H9500 flat panel PMTs, 1″ or 2″ in size, are available from Hamamatsu Corporation of Bridgewater, N.J. 
     Referring to  FIG. 3  there is shown a second embodiment of a compact brain PET detector module  40  based on an array of 16 (4×4) Burle 85001-501 MCP (microchannel plates) PMTs  43  available from Burle Industries of Lancaster, Pa. The 85001-501 PMTs  43  are coupled through optical spreader window  44  to a scintillation array  45  encapsulated behind a window  46 . Reflective strips  47  are placed in the dead regions between the MCP PMTs to improve scintillation light collection from ˜2 cm wide dead regions between these MCP PMTs. The shielding is omitted in this figure. 
     Referring to  FIGS. 4-6 , a third and preferred embodiment of the PET detector head is produced using silicon photomultipliers (SiPMTs) in lieu of the position sensitive PMTs. The third embodiment of the photodetector module  50  is the preferred construction for the brain imager of the present invention as the SiPMTs provide a more compact and lighter weight imager. Typically SiPMT modules come in smaller size units of approximately 3 mm×3 mm to 5 mm×5 mm area and 1.5 mm in thickness. When combined with onboard electronics, the thickness of the SiPMT plus onboard electronics is less than 1 cm. Arrays of SiPMTs are needed to cover the desired active field of view.  FIGS. 4-6  show an example of how to achieve a silicon PMT based photodetector  50  ( FIG. 6 ) of approximately 5 cm×5 cm active field of view using nominal 12.5 mm silicon PMT basic imaging modules  52  ( FIG. 4 ) each composed of sixteen 3 mm basic silicon PMT units  54 . As shown in  FIG. 4 , the basic initial imaging module  52  can have an array of sixteen 3 mm×3 mm readout pixels or pads  54  arranged in a 4×4 array. The 3 mm pads or units  54  can be either read separately with four pads  54  connected to one readout channel  55  or coarsely  56  with all 16 pads  54  connected to one readout channel  56 , as shown schematically at center and bottom of  FIG. 4 , respectively. As shown in  FIG. 5 , an array of 2×2 of these basic four-sides buttable modules (8×8=64 of 3 mm pads) forms an approximately 1″ square photodetector  57  equivalent for example to a commercially available Hamamatsu R8520-C12 PSPMT. The basic imaging modules  52  will be four-side buttable with an estimated 1 mm dead space at the edges. As shown in  FIG. 6 , the photodetector modules are preferably arranged in major imaging modules  50  composed of 4×4 basic modules  52 , with coverage and readout needs equivalent to the H8500 or H9500 flat panel PMT discussed hereinabove. The major imaging module  50  can be used as a plug-in replacement module for the H8500/H9500 flat panel PMT with an approximate 5 cm×5 cm active surface. The dead regions  58  between the basic modules will be about 1-2 mm wide, which will enable adequate scintillation signal sampling for uniform energy and spatial response. Silicon PMTs are available from several manufacturers including SensL USA of Mountain View, Calif. and Radiation Monitoring Devices, Inc. of Watertown, Mass. 
     With reference to  FIG. 7  there is shown a second embodiment of a brain imaging system  60  according to the present invention. The brain imager  60  includes a single head/neck imager ring  62  with 12 individual detector modules  64  as viewed from above the patient&#39;s head. To cover the active FOV of such a brain imager, the brain imager would be provided with a plurality of rings. In such a case, assuming an approximate 2″×2″ size of each imager module, the imager would be provided with 1-3 rings, depending on the exact function of the imager and method of obtaining tomographic (3-dimensional) images in a static situation (no rotating parts). If information is desired on a specific region of the brain, a one-ring version of the imager can be positioned to image that region of the patient&#39;s brain or neck. c 
     Each high rate capable detector module  64  is a separate entity with separate parallel readout and separate data acquisition channels to maximize overall rate capability. Each scintillation array  66  is coupled via proper optical light guide to a selected individual photodetector device  68 . 
     With reference to  FIG. 8 , there is shown a helmet brain imager  70  according to the present invention. The helmet imager  70  includes a ring  72  of detector modules  74  attached to a rigid inner shell or liner  76 . The inner liner  76  is mounted inside an outer cover or shell  78 . The outer shell  78  includes an attached hook  79  for accommodating a harness or tether (not shown) for attaching to the outside suspension mechanism for supporting the weight of the imaging helmet  70 . Electronics and cabling are omitted from the drawing. 
     With reference to  FIG. 9 , there is shown an approximate 25 cm ring PET brain imager  80  suspended from a mobile gantry  81  around the head  82  of a patient  83  that is standing on a treadmill  84 .  FIG. 9  depicts a hypothetical imaging procedure to image a slice of the patient&#39;s brain to evaluate brain function and blood flow. The compact brain imager  80  of the present invention will be supported by a mechanical mount  85 , suspension  86 , and counterweight  87  to assure that the imager  80  is kept still relative to the patient&#39;s head  82  during the duration of the scan. The suspension  86  will support the weight of the imager  80  when placed on the patient&#39;s head  82  or neck. Although one support apparatus is shown in  FIG. 9 , other support schemes with the ring PET imager are possible, such as having the ring imager suspended from a rolling support on a spring or counterbalance to enable more flexible and comfortable placement of the imager. In any support arrangement, the helmet or ring brain imager ensures that small movements of the patient&#39;s body and head will be accommodated naturally with the imager helmet following the patient&#39;s movements. 
     At least four major categories of imager helmet support are possible, including: 1) attached to a fixture mounted in the ceiling of a room above a patient&#39;s chair, 2) attached to a fixture mounted above the patient&#39;s chair in the wall of the room on a rigid or articulate arm or bracket, 3) attached to a movable or rolling type support frame that can be moved along with the patient&#39;s chair, and 4) attached to an extension of an extended back support of the patient&#39;s chair itself, forming one compact mechanical unit. 
     Preferably, the weight of the helmet imager will be well-balanced by suspending it using a flexible support and will be attached to the patients head through straps or similar comfortable means. The critical aspect of the helmet imager of the present invention is to assure that the patient can move his or her body and head during the scan and the imager will follow all the head movements. At the required level of resolution of about 1-2 mm, any movements of the patient&#39;s head relative to the imager ring or rings would produce blurriness of the image and obstruct desired details of the image. 
     Monitoring of the position of patient&#39;s head or other organs is a serious consideration in cases of high resolution imaging when imaging modality requires a prolonged (longer than seconds) imaging procedure. Complicated means to monitor, such as optical sensors or magnetic sensors, and to correct in software for the organ movements, are implemented in many clinical imaging procedures. The helmet imager of the present invention and its secure attachment to the patient&#39;s head provides a significant advantage in that the complicated movement monitoring methods required in prior art imagers will be reduced to minimum. 
     The compact and mobile helmet imager of the present invention will provide high resolution and high-performance molecular imaging which, when used in combination with new biomarkers such as Pittsburgh Compound B (PiB) for detection of Alzheimer&#39;s, is expected to greatly improve early diagnosis of brain diseases. The detection and diagnoses of other diseases such as Parkinson&#39;s and Pick&#39;s disease will also be improved. 
     Although the description above contains many specific descriptions, materials, and dimensions, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Thus the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.