WO2005071438A1 - Event positioning achieved via a lookup table - Google Patents

Event positioning achieved via a lookup table Download PDF

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Publication number
WO2005071438A1
WO2005071438A1 PCT/IB2005/050059 IB2005050059W WO2005071438A1 WO 2005071438 A1 WO2005071438 A1 WO 2005071438A1 IB 2005050059 W IB2005050059 W IB 2005050059W WO 2005071438 A1 WO2005071438 A1 WO 2005071438A1
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WIPO (PCT)
Prior art keywords
fraction
max
f2
sensors
f6
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PCT/IB2005/050059
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French (fr)
Inventor
Thomas L. Laurence
Steven E. Cooke
Michael J. Geagan
Donald R. Wellnitz
Steven R. Martin
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Koninklijke Philips Electronics, N.V.
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Priority to US60/536,756 priority
Application filed by Koninklijke Philips Electronics, N.V. filed Critical Koninklijke Philips Electronics, N.V.
Publication of WO2005071438A1 publication Critical patent/WO2005071438A1/en

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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01TMEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16Measuring radiation intensity
    • G01T1/161Applications in the field of nuclear medicine, e.g. in vivo counting
    • G01T1/164Scintigraphy
    • G01T1/1641Static instruments for imaging the distribution of radioactivity in one or two dimensions using one or several scintillating elements; Radio-isotope cameras
    • G01T1/1642Static instruments for imaging the distribution of radioactivity in one or two dimensions using one or several scintillating elements; Radio-isotope cameras using a scintillation crystal and position sensing photodetector arrays, e.g. ANGER cameras
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01TMEASUREMENT OF NUCLEAR OR X-RADIATION
    • G01T1/00Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
    • G01T1/16Measuring radiation intensity
    • G01T1/1603Measuring radiation intensity with a combination of at least two different types of detector
    • AHUMAN NECESSITIES
    • A61MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61BDIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B6/00Apparatus for radiation diagnosis, e.g. combined with radiation therapy equipment
    • A61B6/02Devices for diagnosis sequentially in different planes; Stereoscopic radiation diagnosis
    • A61B6/03Computerised tomographs
    • A61B6/037Emission tomography

Abstract

A diagnostic imaging system (10) comprises a matrix of sensors (22) situated to view an event. Each sensor (22) is connected to an analog-to-digital converters (24) for converting output analog values of associated sensors (22) to digital numbers. A sensor (50) in the matrix which, in response to the event, has a highest output value relative to the other sensors (22) is identified. Outer sensors (52) that are closest neighbors to the high sensor (50) are identified. The outputs of the outer sensors (52) are compressed by a use of various non-linear square-root functions to reduce a number of bits of the respective outputs. The outputs of sensors carrying the most information are compressed the least, while those carrying the least information are compressed the most. An address of each event is generated and stored in a lookup table (44). The lookup table (44) is used to perform real-time positioning iterative algorithms off-line.

Description

EVENT POSITIONING ACHIEVED VIA A LOOKUP TABLE

DESCRIPTION The present invention relates to the diagnostic imaging systems and methods. It finds particular application in conjunction with the Positron Emission Tomography (PET) and Single Photon Emission Tomography (SPECT) systems and will be described with particular reference thereto. It will be appreciated that the invention is also applicable to other like applications and diagnostic imaging modes. Nuclear imaging employs a source of radioactivity to image the anatomy of a patient. Typically, a radiopharmaceutical is injected into the patient. Radiopharmaceutical compounds contain a radioisotope that undergoes gamma-ray decay at a predictable rate and characteristic energy. A radiation detector is placed adjacent to the patient to monitor and record emitted radiation. Often, the detector is rotated or indexed around the patient to monitor the emitted radiation from a plurality of directions. Based on information such as detected position and energy, the radiopharmaceutical distribution in the body is determined and an image of the distribution is reconstructed to study the circulatory system, radiopharmaceutical uptake in selected organs or tissue, and the like. In a traditional scintillation detector, the detector has a scintillator made up of a large scintillation crystal or matrix of smaller scintillation crystals. In either case, the scintillator is viewed by a matrix of sensors. A commonly employed sensor is a photomultiplier tube ("PMT"). A collimator which includes a grid- or honeycomb- like array of radiation absorbent material may be located between the scintillator and the subject being examined to limit the angle of acceptance of radiation which impinges on the scintillator. Each radiation event impinging on the scintillator generates a corresponding flash of light (scintillation) that is seen by the PMTs. In a hexagonal close packed array of PMTs, the event is primarily seen by the closest PMT and the six PMTs that surround it. An individual PMT's proximity to the flash's origin affects the degree to which the light is seen by that PMT. Each PMT that sees an event generates a corresponding electrical pulse. The respective amplitudes of the electrical pulses are generally proportional to the distance of each PMT from the flash. Based on the outputs from the PMTs, the gamma camera maps radiation events, i.e., it determines the energy and position of radiation rays impinging the scintillator. Typically, the event position is determined using a conventional Anger method for event positioning, which sums and weights signals output by PMTs after the occurrence of an event. The Anger method for event positioning is based on a simple first moment calculation. The energy is typically measured as the sum of all the PMT signals, and the position is typically measured as the "center of mass" or centroid of all the PMT signals. However, the current real-time positioning algorithms are not as accurate as known iterative methods. Yet, the iterative methods are computationally intensive to support real-time image generation and processing. There is a need for the method and apparatus that would permit to use the iterative techniques to determine a more accurate position of the event. The present invention provides a new and improved imaging apparatus and method which overcomes the above-referenced problems and others.

In accordance with one aspect of the present invention, a diagnostic imaging system is disclosed. A matrix of sensors is situated to view an event, the sensors having respective outputs that are responsive to the event. Each of the sensors is connected to an individual analog-to-digital converter for converting output analog values of associated sensors to digital numbers. A means identifies a high sensor in the matrix which, in response to the event, has a highest output value relative to the other sensors. A means identifies a number of outer sensors in the matrix that are closest neighbors to the high sensor. A means compresses outputs of the outer sensors to reduce a number of bits of the respective outputs. A lookup table is addressed by the compressed outputs to retrieve a corresponding event location. In accordance with another aspect of the present invention, a method of diagnostic imaging is disclosed. Radiation is detected with a matrix of sensors of gamma cameras, which sensors are situated to view an event and having respective outputs that are responsive to the event. Output analog values of associated sensors are converted to digital numbers with analog-to-digital converters, each of the sensors being connected to an individual analog-to-digital converter. A high sensor in the matrix is identified, which high sensor, in response to the event, has a highest output value relative to the other sensors. A number of outer sensors in the matrix that are closest neighbors to the high sensor is identified. Outputs of the outer sensors are compressed to reduce a number of bits of the respective outputs. A lookup table is addressed by the compressed outputs to retrieve a corresponding event location. One advantage of the present invention resides in more accurate estimate of the event position through the use of iterative algorithms. Another advantage resides in performing event discrimination / elimination for events that cannot be properly positioned. Still further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.

The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. FIGURE 1 is a diagrammatic illustration of a diagnostic imaging system; FIGURE 2 is a diagrammatic illustration of a portion of a diagnostic imaging system; FIGURE 3 is a portion of a software program in accordance with the present invention; FIGURE 4 is a diagrammatic illustration of one encoding scheme in accordance with the present invention; FIGURE 5 is a diagrammatic illustration of a 4-tube cluster employing horizontal symmetry; FIGURE 6 is a diagrammatic illustration of another encoding scheme in accordance with the present invention; FIGURE 7 is a diagrammatic illustration of a 7-fube cluster, in which an event occurred close to the outer tubes; FIGURE 8 is a diagrammatic illustration of another encoding scheme in accordance with the present invention; and FIGURE 9 is a diagrammatic illustration of a 7-tube cluster in which an event occurred close to the center of the high tube.

With reference to FIGURE 1, a PET scanner 10 includes a plurality of detectors heads or gamma cameras or detectors 12 facing and, preferably, mounted for movement around a subject 14 (preferably containing a radionuclide distribution) located in an examination region 16. Each of the detectors 12 includes a scintillator 20 that converts a radiation event (e.g., a ray of radiation from the radionuclide distribution that impinges on the scintillator 20) into a flash of light or scintillation. A matrix of sensors such as photomultiplier tubes (PMT) 22 is situated to view or receive the light flashes from the scintillator 20. In the preferred embodiment, the matrix of sensors 22 is a close hexagonal packed arrangement of PMTs. However, other sensors and packing arrangements are also contemplated. Generally, the radiation produces gamma quanta that arise in the disintegration of radio isotopes. The disintegration quanta strike the scintillator 20, which preferably includes doped sodium iodide (Nal), causing a scintillation. Light from the scintillation is distributed over a number of the sensors 22. The amount of light from a particular scintillation that a given sensor 22 sees or receives tends to progressively diminish with the sensor's distance from the event. Each of the sensors 22 generates a respective output signal, e.g., an analog electrical pulse, in response to a received light flash, the output signal being proportional to that of the received light flash. Preferably, each of the sensors 22 is electrically connected to an analog-to-digital (A/D) converter 24 that converts the respective analog outputs to digital signals. The information is conveyed to a processor 28 which measures or otherwise determines the location (x, y) and/or energy (z) of respective scintillation events that occur relative to each detector head. For a given event, the output value of each sensor 22 is optionally determined by: integration of the sensor's output signal response to the event (i.e., finding the area or some portion thereof under a curve plotting amplitude or intensity vs. time for the output pulse of the sensor 22); the peak amplitude of the sensor's output signal response to the event; or, some other measure that is proportional or suitably related to the observed amount of light, hence the energy of the event. The location of an event on the scintillator 20 is resolved and/or determined in a two dimensional (2D) Cartesian coordinate system with nominally termed x and y coordinates. However, other coordinate systems are contemplated. With continuing reference to FIGURE 1, the scanner 10 is selectively operable as desired in either a SPECT mode or a PET mode. In the SPECT mode, the cameras 12 have collimators attached thereto (not shown) which limit acceptance of radiation to particular directions, i.e., along known rays. Thus, the determined location on the scintillator 20 at which radiation is detected and the angular position of the camera 12 define the ray along which each radiation event occurred. These ray trajectories and camera angular positions (e.g., obtained from an angular position resolver 30) are conveyed to a reconstruction processor 32 which backprojects or otherwise reconstructs the rays into a volumetric image representation which is stored in an image memory 34. In the PET mode, the collimators are removed. Thus, the location of a single scintillation event does not define a ray. However, the radionuclides used in PET scanning undergo an annihilation event in which two photons of radiation are emitted simultaneously in diametrically opposed directions, i.e., 180 degrees apart. A coincidence detector 36 detects when scintillations on two cameras 12 occur simultaneously. The locations of the two simultaneous scintillations define the end points of a ray through the annihilation event. A ray or trajectory calculator 38 calculates the corresponding ray through the subject 14 from each pair of simultaneously received scintillation events. The ray trajectories from the ray calculator 38 are conveyed to the reconstruction processor 32 for reconstruction into a volumetric image representation. The resultant image representation is stored in the volumetric image memory 34. In both SPECT and PET modes, a video processor 40 processes and/or formats the image representation data for display on a monitor 42. With continuing reference to FIGURE 1 and further reference to FIGURE 2, the processor 28 includes a lookup table 44 which is generated to perform real-time event positioning using iterative algorithms. Typically, prior to imaging, the PMTs 22 are calibrated by one of known isotopes. The location of the center of the high tube 50, like all PMTs, is known precisely from a priori information, e.g., physical measurement. The calibration information for each tube 22 is stored in the lookup table 44. The lookup table 44 is used to identify a location of an event relative to the center of the high tube. More specifically, the processor 28 includes a PMT value determining means 46 which determines initial values of the PMTs 22. A highest output determining means or algorithm 48 identifies a high tube 50 having the highest output value relative to all the other PMTs 22, and a number of closest neighboring tubes or outer tubes 52 adjacent the high tube 50, e.g. a PMT subset or a PMT cluster 54 as seen in FIGURE 5. Preferably, the maximum number of closest neighboring tubes 52 is six, defining a 7-PMT hexagonal, close-packed cluster, with the center sensor being the one having the highest output value. However, the cluster 54 may include a different number of tubes, e.g. three, or five. A fractions determining means 56 divides outputs of the tubes 50, 52 of the cluster 54 by the value of the high tube 50, accordingly eliminating one of the variables, e.g. the value of the high tube 50. The operation results in three to six 10 bit fractions F1-F6 depending on the number of the outer tubes 52 in the cluster 54. A fractions order determining means 58 identifies a descending order of the fractions F1-F6 of the tubes 52, e.g. the highest fraction Fl, the second highest fraction F2, and lower fractions F3-F6. The fractions FIFO are stored in a PMT values memory 60. The fractions F1-F6 identify the location of the event relative to the high tube center and could be used to address the lookup table 44. Typically, each analog-to-digital converter 24 outputs a 10 bit intensity value. As a result, without the compression, the lookup table 44 would have 1021 memory addresses. A compression means 70 dynamically applies a compression algorithm to reduce the number of bits for addressing the lookup table 44, e.g. the 10 bit fractions Fl- F6 are compressed to the space available in the lookup table 44 based on various criteria as discussed in a greater detail below. Specifically, a dynamic compression is preferably applied, which compresses low fractions to a greater degree than high fractions. Moreover, symmetry is used to eliminate the need to encode the event spatial location(s) of the next highest tube(s) relative to the highest tube 50. Of course, it is contemplated that the compression step might be omitted when the creation of the larger, e.g. 1021 lookup table, becomes feasible. With continuing reference to FIGURE 2, an encoding selection means 72 dynamically selects an encoding scheme for each event based upon the number of address bits available for the lookup table 44, the number of tubes 50, 52 in the cluster 54, the magnitude of the highest fraction Fl, and other criteria. The tubes 52 carrying the most information are compressed the least, while those carrying the least information are compressed the most. Preferably, a non-linear compression (e.g., a weighted square-root function) of the tube fractions F1-F6 is used to reduce the number of bits required for encoding each fraction. To minimize quantization errors, different non-linear compression algorithms are utilized based on the tube fraction ranges. Preferably, an address bit is used to indicate when biasing of a signal has been performed (e.g., a fixed value may be subtracted from the highest fraction) to reduce the dynamic range that the values must be compressed to minimize quantization errors. With continuing reference to FIGURE 2, an address generating means 74 generates an address of an event. The resulting event address accesses the lookup table 44 to retrieve the event location relative to the highest tube center. A position determining means 80 retrieves the 16 bit address that contains the event's x, y position and breaks it into distinct 8 bit x- and y- values. The x, y position of the center of the high tube location is adjusted with the lookup table output by a position adjusting means 82 to derive the event's final position. In the embodiment of FIGURE 5, the high tube 50 is disposed within a 4- tube cluster 54, i.e. the high tube 50 has three neighboring or outer tubes 52. A horizontal symmetry along a horizontal axis is used to reduce the number of cases by a factor of 2. The 4-tube cluster 54 is interpreted as if the outer tubes 52 are positioned on the top of the detector. Preferably, a flag is set to indicate that the highest fraction Fl always exists in the top quadrant. With reference again to FIGURE 2, a flipping means 84 flips the event location from the lookup about an axis of symmetry in accordance with the quadrant in which the highest fraction Fl is located. For example, the sign of the x-location adjustment is selected based on the location of the highest fraction Fl relative to the y-axis and the sign of the y-correction is adjusted based on location relative to the x-axis. In the illustrated four cluster example, the position determining means 80 performs the lookup at the encoded address and retrieves x, y position relative to the center of the high tube 50. If a flip is not performed, the position adjusting means 82 calculates the final x, y position as equal to the high tube 50 center location plus the relative x, y position. If a flip is performed, the position adjusting means 82 calculates the final x, y position as equal to the high tube 50 center location minus the relative x, y position. Of course, it is contemplated that a vertical symmetry is used as appropriate. With reference to FIGURES 2 and 3 and further reference to FIGURE 4, in step 90, the encoding scheme selecting means 72 dynamically selects the encoding scheme 6 to create the lookup table 44. Preferably, three address bits, e.g. bits 25-27, are used to indicate how the tube fractions F1-F3 have been encoded and compressed. In the encoding scheme 6, each fraction Fl, F2, F3 is converted to 8 bits (256 codes) using the square-root function (A):

(A) Fcomp = (int) ( sqrt( k * F ) + 0.5 ), where Fcomp is the weighted square root compression applied to the corresponding tube fraction F1-F6;

Λ is a constant scalar used to compress the tube fraction, k = (Codemax)2 / Fmax;

Codemax is the maximum code for each fraction F1-F6 that is equal 2bl,s - 1 = 255,

Emax is the maximum value for each fraction F1-F6 = 1023; k = (Codemax)2 / Fmax = 2552 / 1023 = 63.56304985.

The decoding or uncompression of each fraction F1-F6 encoded with the encoding scheme 6 is achieved by using the function:

(A) ' Funcomp = ((int) ((double) (Fcomp)2 / k + 0.5)

In the embodiment of FIGURE 7, the high tube 50 is disposed within a 7- tube cluster 54, i.e. the high tube 50 has six neighboring or outer tubes 52. Similar to the embodiment of FIGURE 5, the horizontal symmetry is used such that only three-highest fractions positions are needed. The flipping means 84 flips the tube signals if the highest- fraction Fl is one of the bottom tubes. With reference again to FIGURE 3, in step 92 the encoding scheme selecting means 72 selects encoding scheme 0, 1, or 2 when the cluster 54 has seven tubes and the highest fraction Fl is more than 255, e.g. the event occurs away from the high tube 50 center, approaching one or more of the neighboring tubes 52 which indicates a PMT double point d or triple point t. In step 94, the encoding scheme selecting means 72 discards the event when it is determined that the highest fraction Fl and the second highest F2 are not adjacent each other. In step 96, the encoding scheme selecting means 72 discards the event when it is determined that one of the lower fractions F3-F6 is greater than 255, which indicates that the event is contaminated. With reference to FIGURE 6, bits 25-27 are used to indicate how the tube fractions have been encoded and compressed. The encoding ID is set using the tube diagram of FIGURE 7 that indicates the position of the tube having the highest fraction Fl .

While most information is contained in the highest and second highest fractions Fl, F2, another address bit, e.g. bit 24, is preferably used to indicate the directional relationship

(clockwise or counter-clockwise) of the second highest fraction F2 to highest fraction Fl.

This allows more address bits to be allocated for the highest and second highest fractions Fl, F2 than for the lower fractions F3-F6. Preferably, bit 24 is ordinarily set to CCW, e.g. the second highest fraction F2 is counter-clockwise with respect to the highest fraction Fl.

Bit 24 is cleared if the second highest fraction F2 is clockwise with respect to the highest fraction Fl. With continuing reference to FIGURE 6, bits 17-22 are designated for the highest fraction Fl. A compression is performed by subtracting 255 (OxFF) from the highest fraction Fl and converting the result to 6 bits using the square-root function (B)

(input range is 0 to 768 [0x300]):

(B) Flcomp = (int) (sqrt ( k * (F 1 - 255) ) + 0.5 ), where Flcomp is the weighted square root compression applied to the corresponding tube fraction Fl ;

Λ is a constant scalar used to compress the tube fraction, k = (Codemax)2 / Flma ; Codemax is the maximum code for the fraction Fl that is equal to 2blts - 1 = 63; Flmax is the maximum value for the fraction Fl that is equal 768; k = 63 2 / 768 = 5.16796875.

The decoding or uncompression of fraction Fl encoded with the encoding function (B) is achieved by using the function:

(B)' Fluncomp = ((int) ((double) (Flcomp)2 / k + 0.5) + 255

With continuing reference to FIGURE 6, bits 12-16 are designated for the second highest fraction F2. The encoding scheme selecting means 72 selects the encoding scheme based on the value of the second highest fraction F2. If the second highest fraction F2 is greater than 200 (0xC8), the compression is performed by subtracting 201 (0xC9) from the value of the second highest fraction F2 and compressing the resultant value to 5 bits (32 codes) using the square-root function (C) (input range is 0 to 822 [0x336]). Bit 23 is set to 1 to indicate that the subtraction has been performed.

(C) F2comp = (int) ( sqrt( k * (F2 - 201) ) + 0.5 ),

where F2comp is the weighted square root compression applied to the second highest fraction F2; ft is a constant scalar used to compress the tube fraction, k = (Codemax)2 / F2max;

CodemttX is the maximum code for the fraction F2 that is equal to 2blts - 1 = 31;

F2max is the maximum value for the fraction F2 that is equal 822; ft = 312 / 822 = 1.169099757.

The decoding or uncompression of fraction F2 encoded with the encoding function (C) is achieved by using the function:

(C) ' F2uπcomp = ((int) ((double) (F2comp)2 / k + 0.5)) + 201 If the value of the second highest fraction F2 is equal to or less than 200 (0xC8), the compression is performed by compressing the second highest fraction value to 5-bits (32-codes) using the square-root function D (input range 0 to 200 [0xC8]) and clearing bit 23:

(D) F2comp = (int) ( sqrt( k * F ) + 0.5 ),

where F2comp is the weighted square root compression applied to the tube fraction F2; ft is a constant scalar used to compress the tube fraction, k = (Codemax)2 / F2max; Codemax is the maximum code for the fraction F2 that is equal to 2blts - 1 = 31, F2max is the maximum value for the fraction F2 that is equal 200; ft = 312 / 200 = 4.805. The decoding or uncompression of fraction F2 encoded with the encoding function (D) is achieved by using the function:

(D) ' F2uncomp = ((int) ((double) (Fcomp)2 / k + 0.5))

With continuing reference to FIGURE 6, bits 0-11 are designated for the lower fractions F3-F6, e.g. 3rd through 6th fractions. The lower fractions F3-F6 are converted each to 3 bits (8 codes) using the square-root function E. It is assumed that a maximum value of fraction F3-F6 is equal to 255 (OxFF):

(E) Fcomp = (int) ( sqrt( k * F ) + 0.5 ),

where Fcomp is the weighted square root compression applied to the corresponding tube fraction F3-F6; ft is a constant scalar used to compress the tube fraction, k = (Codemax)2 / Fmax; Codemax is the maximum code for the lower fractions F3-F6 that is equal to 2blts - 1 = 7; Fmax is the maximum value for the lower fractions F3-F6 that is equal 255; ft = 72 / 255 = 0.192156863.

The decoding or uncompression of fractions F3-F6 encoded with the encoding function (E) is achieved by using the function:

(E)' Fuπcomp = ((int) ((double) (Fcomp)2 / k + 0.5))

With reference again to FIGURE 3 and further reference to FIGURES 9-10, in step 98, the encoding scheme selecting means 72 selects encoding scheme 3 when the cluster 54 has seven tubes 50, 52 and the highest fraction Fl is more than 200 and is equal to or less than 255. Fractions F1-F6 are converted each to 4 bits (16 codes) using the square-root function G. It is assumed that a maximum fraction Fl is equal to 255 (OxFF):

(G) Fcomp = (int) ( sqrt( k * F ) + 0.5), where Fcomp is the weighted square root compression applied to the corresponding tube fraction F1-F6; ft is a constant scalar used to compress the tube fraction, k = (Codemax)2 / Fmax;

Codemax is the maximum code for each of the fractions F1-F6 that is equal to 2b,ts - 1 = 15;

Fmaxis the maximum value for the each fraction F1-F6 that is equal 255; ft = 152 / 255 = 0.882352941.

The decoding or uncompression of fractions F1-F6 encoded with the encoding function (G) is achieved by using the function:

(G) ' Funcomp = ((int) ((double) (Fcomp)2 / k + 0.5))

With continuing reference to FIGURES 4, and 9-10, in step 100, the encoding scheme selecting means 72 selects encoding scheme 4 when the cluster 54 has seven tubes 50, 52 and the highest fraction Fl is more than 160 and is equal to or less than 200, e.g. the event occurred near the center of the high tube 50. Fractions F1-F6 are converted to 4 bits (16 codes) using the square-root function H. It is assumed that a maximum fraction Fl is equal to 200 (0xC8):

(H) Fcomp = (int) ( sqrt( k * F ) + 0.5 ),

where Fcomp is the weighted square root compression applied to the corresponding tube fraction F1-F6; ft is a constant scalar used to compress the tube fraction, k = (Codemax)2 / Fmax; Codemax is the maximum code for each fraction F1-F6 that is equal to 2b,,s - l = 15,

Fmax is the maximum value for each fraction F1-F6 that is equal 200; ft = 152 / 200 = 1.125.

The decoding or uncompression of fractions F1-F6 encoded with the encoding function (H) is achieved by using the function:

(H) ' Funcomp = ((int) ((double) (Fcomp)2 / k + 0.5)) With continuing reference to FIGURES 4, 9 and 10, in step 102, the encoding scheme selecting means 72 selects encoding scheme 5 when the cluster 54 has seven tubes 50, 52 and the highest fraction Fl is equal to or less than 160. Fractions F1-F6 are converted each to 4 bits (16 codes) using the square-root function J. It is assumed that a maximum value of fractions F1-F6 be equal to 160 (OxAO):

(J) Fcomp = (int) ( sqrt( k * F ) + 0.5 ),

where FCOmP is the weighted square root compression applied to the corresponding tube fraction F1-F6; ft is a constant scalar used to compress the tube fraction, k = (Codemax)2 / Fmax;

Codemax is the maximum code for each fraction F1-F6 that is equal to 2blts - 1 = 15;

Fmax is the maximum value for each fraction F1-F6 that is equal 160; ft = (15)2 / 160 = 1.40625.

The decoding or uncompression of fraction F1-F6 encoded with the encoding function (J) is achieved by using the function:

(J) ' Funcomp = ((int) ((double) (Fcomp)2 / k + 0.5))

The invention has been described with reference to the preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

CLAIMS Having thus described the preferred embodiments, the invention is now claimed to be:
1. A diagnostic imaging system (10) comprising: a matrix of sensors (22) situated to view an event, the sensors (22) having respective outputs that are responsive to the event; analog-to-digital converters (24), each of the sensors (22) being connected to an individual analog-to-digital converter (24) for converting output analog values of associated sensors (22) to digital numbers; a means (48) for identifying a high sensor (50) in the matrix which, in response to the event, has a highest output value relative to the other sensors (22); a means (56) for identifying a number of outer sensors (52) in the matrix that are closest neighbors to the high sensor (50); a means (70) for compressing outputs of the outer sensors (52) to reduce a number of bits of the respective outputs; and a lookup table (44) which is addressed by the compressed outputs to retrieve a corresponding event location.
2. The system as set forth in claim 1, wherein the retrieved event location is relative to a center of the high sensor (50) and further including: a position adjusting means (82) for combining the event location with a location of the high sensor center.
3. The system as set forth in claim 1, wherein the sensors (22) are photomultiplier tubes (PMTs).
4. The system as set forth in claim 1, wherein the compression means (70) includes: an encoding scheme selecting means (72) for dynamically allocating a number of bits for each sensor output based upon probable range of outputs.
5. The system as set forth in claim 1, further including: a fractions determining means (56) for determining fractions (F1-F6) of the outer sensors (52) by dividing associated outputs by the highest output value; and a fractions order determining means (58) which determines a descending order of fractions (F1-F6) of the sensors (52) from a highest fraction (Fl) to a lowest fraction in descending order.
6. The system as set forth in claim 5, wherein symmetry is used along one of horizontal and vertical axis and further including: a flipping means (84) for flipping the event location about the axis of symmetry in accordance with a quadrant in which the highest fraction (Fl) is located.
7. The system as set forth in claim 5, wherein the compression means (70) includes: an encoding scheme selecting means (72) for dynamically selecting an encoding scheme (0-6) based on at least one of: a number of bits available in the lookup table (44); a number of the sensors (50, 52); or a value of the highest fraction (Fl).
8. The system as set forth in claim 7, wherein the compression scheme selecting means (72) sets at least one bit indicating which compression scheme is used.
9. The system as set forth in claim 7, wherein the high sensor (50) and outer sensors (52) define a 7-PMT cluster (54).
10. The system as set forth in claim 9, wherein the encoding scheme selecting means (72) discards the event when one of: the highest fraction (Fl) and the second highest fraction (F2) are not adjacent each other, or the value of one of lower fractions (F3-F6) is more than a first preselected value (VI).
11. The system as set forth in claim 9, wherein the value of the highest fraction (Fl) is more than a first preselected value (VI) and is compressed to a six bit fraction (Flcomp) by using a square-root function (B) Fl comp = (int) ( sqrt( k * (F - VI) ) + 0.5 ),
where Flcomp is a weighted square root compression applied to the highest fraction (Fl); k = (Codemax)2 / Flmax;
Codemax is a maximum selected code for the highest fraction (Fl);
Flmax is a maximum selected value for the highest fraction (Fl).
12. The system as set forth in claim 11, wherein the value of the second highest fraction (F2) is more than a second preselected value (V2) and is compressed to a five bit fraction (F2com) by using a square-root function (C)
F2comp = (int) ( sqrt( k * (F2 - (V2+1)) ) + 0.5 ), where F2comp is a weighted square root compression applied to the second highest fraction
(F2); k = (Codemax)2 / F2max;
Codemax is a maximum selected code for the second highest fraction (F2);
F2max is a maximum selected value for the second highest fraction (F2).
13. The system as set forth in claim 11, wherein the value of the second highest fraction (F2) is equal to or less than a second preselected value (V2) and is compressed to a five bit fraction (F2com) by using a square-root function (D)
F2comp = (int) ( sqrt( k * F2 ) + 0.5 ), where F2comp is a weighted square root compression applied to the second highest fraction (F2); k = (Codemax)2 / F2max;
Codemaχ is a maximum selected code for the second highest fraction (F2); F2max is a maximum selected value for the second highest fraction (F2).
14. The system as set forth in claim 11, wherein the values of the lower fractions (F3-F6) are compressed each to a three bit fraction (Fcom) by using a square-root function (E)
Fcomp = (int) ( sqrt( k * F ) + 0.5 ),
where Fcomp is the weighted square root compression applied to the corresponding lower fraction (F3-F6); k = (Codemax)2 / Fmax;
Codemax is a maximum selected code for the corresponding lower fraction (F3-F6);
Fmax is a maximum selected value for the corresponding lower fraction (F3-F6).
15. The system as set forth in claim 11, wherein the compression means (70) sets at least one bit to indicate a directional relationship of the second highest fraction (F2) to the highest fraction (Fl).
16. The system as set forth in claim 9, wherein the value of the highest fraction (Fl) is equal to or less than a first preselected value (VI) and more than a second preselected value (V2) and the values of the fractions (F1-F6) are compressed each to a four bit fraction (Fcom) by using a square-root function (G)
Fcomp = (int) ( sqrt( k * F ) + 0.5), where Fcomp is a weighted square root compression applied to the corresponding fraction (F1-F6); k = (Codemax)2 / Fmax;
Codemax is a maximum selected code for the corresponding fraction (F1-F6); Fmax is a maximum selected value for the corresponding fraction (F1-F6).
17. The system as set forth in claim 9, wherein the value of the highest fraction (Fl) is equal to or less than a second preselected value (V2) and more than a third preselected value (V3) and the values of the fractions (F1-F6) are compressed each to a four bit fraction (Fcom) by using a square-root function (H) Fcomp = (int) ( sqrt( k * F ) + 0.5 ), where FCOmp is a weighted square root compression applied to the corresponding tube fraction (F1-F6); k = (Codemax)2 / Fmax;
Codemax is a maximum selected code for the corresponding fraction (F1-F6);
Fmax is a maximum selected value for the corresponding fraction (F1-F6).
18. The system as set forth in claim 9, wherein the value of the highest fraction (Fl) is equal to or less than a third preselected value (V3) and the values of the fractions (F1-F6) are compressed each to a four bit fraction (Fcom) by using a square-root function (J)
Fcomp = (int) ( sqrt( k * F ) + 0.5 ),
where FCOmp is a weighted square root compression applied to the corresponding tube fraction (F1-F6);
K — CO emax) ' ^max)
Codemax is a maximum selected code for the corresponding fraction (F1-F6); Fmax is a maximum selected value for the corresponding fraction (F1-F6).
19. The system as set forth in claim 8, wherein the high sensor (50) and outer sensors (52) define a 4-PMT cluster (54).
20. The system as set forth in claim 19, wherein the values of the fractions (F1-F3) are compressed each to an eight bit fraction (Fcom) by using a square-root function (A)
Fcomp = (int) ( sqrt( k * F ) + 0.5 ),
where FCOmp is a weighted square root compression applied to the corresponding tube fraction (F1-F3); k = (Codemax)2 / Fmax;
Codemax is a maximum selected code for the corresponding fraction (F1-F3);
Fmax is a maximum selected value for the corresponding fraction (F1-F3).
21. A method of diagnostic imaging comprising: detecting radiation with a matrix of sensors (22) of gamma cameras (12), which sensors (22) are situated to view an event and having respective outputs that are responsive to the event; converting output analog values of associated sensors (22) to digital numbers with analog-to-digital converters (24), each of the sensors being connected to an individual analog-to-digital converter; identifying a high sensor (50) in the matrix which, in response to the event, has a highest output value relative to the other sensors (22); identifying a number of outer sensors (52) in the matrix that are closest neighbors to the high sensor (50); compressing outputs of the outer sensors (52) to reduce a number of bits of the respective outputs; and addressing a lookup table (44) by the compressed outputs to retrieve a corresponding event location.
PCT/IB2005/050059 2004-01-15 2005-01-05 Event positioning achieved via a lookup table WO2005071438A1 (en)

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Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007019708A1 (en) * 2005-08-18 2007-02-22 Societe De Commercialisation Des Produits De La Recherche Appliquee - Socpra Digital identification and vector quantization methods and systems for detector crystal recognition in radiation detection machines
US9904394B2 (en) 2013-03-13 2018-02-27 Immerson Corporation Method and devices for displaying graphical user interfaces based on user contact

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP5641930B2 (en) * 2007-05-16 2014-12-17 コーニンクレッカ フィリップス エヌ ヴェ Diagnostic imaging system, time stamp calculation method, processor for executing the method, and computer-readable medium programmed with the method
JP5664880B2 (en) * 2010-06-10 2015-02-04 株式会社島津製作所 Two-dimensional position map calibration method
CN104337531B (en) * 2013-07-25 2016-12-28 苏州瑞派宁科技有限公司 Method and system are met at heat input for digital PET system
JP2017532569A (en) * 2014-10-27 2017-11-02 コーニンクレッカ フィリップス エヌ ヴェKoninklijke Philips N.V. PET detector timing calibration
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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4956796A (en) * 1986-06-20 1990-09-11 The University Of Michigan Multiple sensor position locating system
US6049584A (en) * 1997-08-01 2000-04-11 Sirona Dental Systems Gmbh & Co. Kg X-ray diagnostic apparatus for producing panorama slice exposure of body parts of a patient
EP1104889A2 (en) * 1994-10-03 2001-06-06 Adac Laboratories Gamma camera system
US6326624B1 (en) * 1996-11-08 2001-12-04 Commissariat A L'energie Atomique Device and method for determining the assumed position of a phenomenon relative to a set of photodetectors, and application to gamma-cameras

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE69528949D1 (en) * 1994-10-03 2003-01-09 Koninkl Philips Electronics Nv Improved gamma camera system

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4956796A (en) * 1986-06-20 1990-09-11 The University Of Michigan Multiple sensor position locating system
EP1104889A2 (en) * 1994-10-03 2001-06-06 Adac Laboratories Gamma camera system
US6326624B1 (en) * 1996-11-08 2001-12-04 Commissariat A L'energie Atomique Device and method for determining the assumed position of a phenomenon relative to a set of photodetectors, and application to gamma-cameras
US6049584A (en) * 1997-08-01 2000-04-11 Sirona Dental Systems Gmbh & Co. Kg X-ray diagnostic apparatus for producing panorama slice exposure of body parts of a patient

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2007019708A1 (en) * 2005-08-18 2007-02-22 Societe De Commercialisation Des Produits De La Recherche Appliquee - Socpra Digital identification and vector quantization methods and systems for detector crystal recognition in radiation detection machines
US7791029B2 (en) 2005-08-18 2010-09-07 Societe De Commercialisation Des Produits De La Recherche Appliquee- Socpra Sciences Sante Et Humaines, S.E.C. Digital identification and vector quantization methods and systems for detector crystal recognition in radiation detection machines
US9904394B2 (en) 2013-03-13 2018-02-27 Immerson Corporation Method and devices for displaying graphical user interfaces based on user contact

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