U.S. patent application number 15/206692 was filed with the patent office on 2017-05-11 for radiopharmaceutical czt sensor and apparatus.
This patent application is currently assigned to CARDINAL HEALTH 414, LLC. The applicant listed for this patent is CARDINAL HEALTH 414, LLC. Invention is credited to Chad Edward Bouton, Mehmet Husnu.
Application Number | 20170131412 15/206692 |
Document ID | / |
Family ID | 47518412 |
Filed Date | 2017-05-11 |
United States Patent
Application |
20170131412 |
Kind Code |
A1 |
Husnu; Mehmet ; et
al. |
May 11, 2017 |
RADIOPHARMACEUTICAL CZT SENSOR AND APPARATUS
Abstract
A gamma ray detector includes a gamma ray detecting rod
elongated along a longitudinal axis, wherein gamma ray detection is
enhanced along the longitudinal axis, and a gamma ray shield
encapsulating the rod, the shield having an aperture at an end of
the detecting rod along the longitudinal axis to admit gamma rays
substantially parallel to the longitudinal axis of the elongated
detecting rod, wherein gamma ray detection is enhanced along the
longitudinal axis and aperture to substantially collimate the
sensitivity of the gamma ray detector along the combined aperture
and longitudinal axis of the detecting rod.
Inventors: |
Husnu; Mehmet; (Phoenix,
AZ) ; Bouton; Chad Edward; (Darien, CT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CARDINAL HEALTH 414, LLC |
Dublin |
OH |
US |
|
|
Assignee: |
CARDINAL HEALTH 414, LLC
Dublin
OH
|
Family ID: |
47518412 |
Appl. No.: |
15/206692 |
Filed: |
July 11, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13550282 |
Jul 16, 2012 |
9417332 |
|
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15206692 |
|
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61508402 |
Jul 15, 2011 |
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61508294 |
Jul 15, 2011 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01T 1/161 20130101;
G01T 1/24 20130101; H01L 31/0296 20130101; G01T 1/2928 20130101;
H01L 31/0203 20130101; H01L 31/02966 20130101; G01T 1/167 20130101;
H01L 31/085 20130101; G01T 1/249 20130101; G01T 1/241 20130101;
G01T 1/1648 20130101 |
International
Class: |
G01T 1/161 20060101
G01T001/161; G01T 1/29 20060101 G01T001/29; H01L 31/0296 20060101
H01L031/0296; H01L 31/08 20060101 H01L031/08; H01L 31/0203 20060101
H01L031/0203; G01T 1/24 20060101 G01T001/24; G01T 1/167 20060101
G01T001/167 |
Claims
1-17. (canceled)
18. A radioactivity detecting device comprising: a gamma ray
detector comprising a solid state material, the gamma ray detector
elongated along a longitudinal axis; and a shield encapsulating the
gamma ray detector, the shield having an aperture adjacent a
longitudinal end of the gamma ray detector, wherein the gamma ray
detector is configured to detect gamma rays which pass through the
aperture in a direction substantially parallel to the longitudinal
axis.
19. The radioactivity detecting device of claim 18, wherein a
length of the gamma ray detector is measured along the longitudinal
axis.
20. The radioactivity detecting device of claim 19, wherein
detection of the gamma rays is enhanced along the length of the
gamma ray detector, and wherein a sensitivity of the gamma ray
detector is collimated by the aperture and the length of the gamma
ray detector.
21. The radioactivity detecting device of claim 19, wherein a
thickness of the gamma ray detector is measured transverse to the
longitudinal axis, and wherein the length is greater than the
thickness.
22. The radioactivity detecting device of claim 18, wherein the
solid state material comprises cadmium zinc telluride (CZT).
23. An apparatus for detecting radioactivity of a sample in a
container of known dimensions, the apparatus comprising: a first
gamma ray detector arranged below a lower surface of the container
with respect to gravity; and a second gamma ray detector arranged
above an upper surface of the container with respect to gravity,
opposite the first gamma ray detector; wherein each of the first
gamma ray detector and the second gamma ray detector detect a
radioactivity from the sample in the container; and wherein a ratio
of the radioactivity detected by the second gamma ray detector to
the radioactivity detected by the first gamma ray detector
correlates to a fill level of the sample in the container.
24. The apparatus of claim 23, wherein the first gamma ray detector
and the second gamma ray detector comprise cadmium zinc telluride
(CZT).
25. The apparatus of claim 23, wherein: each of the first gamma ray
detector and the second gamma ray detector is elongated along a
longitudinal axis; each of the first gamma ray detector and the
second gamma ray detector is enclosed in a shield having an
aperture adjacent a longitudinal end of the respective gamma ray
detector; and wherein the first gamma ray detector and the second
gamma ray detector are configured to detect gamma rays which pass
through the respective aperture in a direction substantially
parallel to the longitudinal axis.
26. The apparatus of claim 23, wherein a logarithm of the ratio of
the radioactivity detected by the second gamma ray detector to the
radioactivity detected by the first gamma ray detector is
substantially linear in proportion to a fill level of the sample
present in the container.
27. The apparatus of claim 23, wherein each of the first gamma ray
detector and the second gamma ray detector have enhanced
sensitivity along their respective longitudinal axes.
28. The apparatus of claim 23, wherein the container is a
cylinder.
29. A method of detecting radioactivity of a sample present in a
container, comprising: providing a container and a gamma ray
detector; determining a constant volume of a sample to add to the
container; adding the constant volume of the sample to the
container; observing the constant volume of the sample using the
gamma ray detector to measure a radioactivity of the sample present
in the container; and determining a concentration of a radionuclide
in the sample based on the constant volume of the sample observed
by the gamma ray detector and the radioactivity detected by the
gamma ray detector.
30. The method of claim 29, wherein the gamma ray detector
comprises cadmium zinc telluride (CZT).
31. An apparatus for detecting radioactivity of a sample in a
container of known dimensions, the apparatus comprising: a
container having a known volume of a sample; and a gamma ray
detector that detects a radioactivity from the sample in the
container; wherein the concentration of a radionuclide in the
sample correlates to the radioactivity detected by the gamma ray
detector.
32. The apparatus of claim 31, wherein: the gamma ray detector is
elongated along a longitudinal axis and is enclosed in a shield
having an aperture adjacent a longitudinal end of the gamma ray
detector; and wherein the gamma ray detector is configured to
detect gamma rays which pass through the aperture in a direction
substantially parallel to the longitudinal axis.
33. The apparatus of claim 31, wherein the gamma ray detector has
enhanced sensitivity along the longitudinal axes.
34. The apparatus of claim 31, wherein the container is a
cylinder.
35. The apparatus of claim 31, wherein the gamma ray detector
comprises cadmium zinc telluride (CZT).
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
patent application Ser. No. 13/550,282 entitled
"RADIOPHARMACEUTICAL CZT SENSOR AND APPARATUS" filed on Jul. 16,
2012; which claims priority to U.S. Provisional Patent Application
No. 61/508,402 entitled "RADIOPHARMACEUTICAL CZT SENSOR AND
APPARATUS" filed on Jul. 15, 2011; and U.S. Provisional Patent
Application No. 61/508,294 entitled "SYSTEMS, METHODS, AND DEVICES
FOR PRODUCING, MANUFACTURING, AND CONTROL OF
RADIOPHARMACEUTICALS-FULL" filed on Jul. 15, 2011. The entirety of
each of U.S. Provisional Application Nos. 61/508,402 and 61/508,294
are incorporated by reference herein.
BACKGROUND
[0002] I. Field
[0003] Aspects of the present invention relate generally to gamma
ray sensors, and more particularly to methods and devices for
detecting radioisotope concentration, activity and volume using
gamma ray detection with cadmium zinc telluride (CZT) solid state
detectors.
[0004] II. Background
[0005] Diagnostic techniques in nuclear medicine generally use
radioactive tracers which emit gamma rays from within the body.
These tracers are generally short-lived isotopes linked to chemical
compounds which permit specific physiological processes to be
studied. These compounds, which incorporate radionuclides, are
known as radiopharmaceuticals, and can be given by injection,
inhalation or orally. One type of diagnostic technique includes
detecting single photons by a gamma-ray sensitive camera which can
view organs from many different angles. The camera builds an image
from the points from which radiation is emitted, and the image is
electronically enhanced and viewed by a physician on a monitor for
indications of abnormal conditions.
[0006] A more recent development is Positron Emission Tomography
(PET), which is a more precise and sophisticated technique using
isotopes produced in a cyclotron, where protons are introduced into
the nucleus resulting in a deficiency of neutrons (i.e., becoming
proton rich).
[0007] The nucleus of a radioisotope usually becomes stable by
emitting an alpha and/or beta particle (or a positron). These
particles may be accompanied by the emission of energy in the form
of electromagnetic radiation known as gamma rays. This process is
known as radioactive decay.
[0008] A positron-emitting radionuclide is introduced into the body
of a patient, usually by injection, and accumulates in the target
tissue. As the radionuclide decays, a positron is emitted, and the
emitted positron combines with a nearby electron in the target
tissue, resulting in the simultaneous emission of two identifiable
gamma rays in opposite directions, each having an energy of 511
keV. These gamma rays are conventionally detected by a PET camera,
and provide a very precise indication of their origin. PET's most
important clinical role is typically in oncology, with fluorine-18
(F-18) as the tracer, since F-18 has proven to be the most accurate
non-invasive method of detecting and evaluating most cancers.
Fluorine-18 (F-18) is one of several positron emitters (including
also, Carbon-11, Nitrogen-13, and Oxygen-15) that are produced in a
cyclotron and are used in PET for studying brain physiology and
pathology, in particular for localizing epileptic focus, and in
dementia, psychiatry and neuropharmacology studies. These positron
emitters also have a significant role in cardiology. F-18 in FDG
(fluorodeoxyglucose) has become very important in detection of
cancers and the monitoring of progress in cancer treatment, using
PET. A radioactive product such as F-18 in FDG is a specific
example of a radiopharmaceutical.
[0009] F-18 has a half-life of approximately 110 minutes, which is
beneficial in that it does not pose a long-term environmental
and/or health hazard. For example, after 24 hours, the
radioactivity level is approximately 0.01% of the product when
freshly produced in a cyclotron. However, transport time from the
production source to clinical use should be minimized to retain a
maximum potency for accurate diagnostic value.
[0010] Whereas PET cameras are effective in imaging uptake of F-18
present in administered FDG, PET cameras are generally too large
and ineffective in production settings where characterization of
the source product, and not physiological response, is the goal.
There is a need, therefore, for a method and apparatus to timely
calibrate the radioactivity of a sample at the production source
and time of production or packaging for delivery so that the level
of radioactivity is predictably known at the time of use.
SUMMARY
[0011] The following presents a simplified summary of one or more
aspects of a method and apparatus for detecting radioisotope
concentration, activity and sample volume.
[0012] In one example aspect of the invention, a gamma ray detector
may include a gamma ray detecting rod elongated in one direction to
a specified length, and a gamma ray shield encapsulating the rod,
the shield having an opening opposite an end of the elongated rod
to admit gamma rays substantially parallel to the long axis of the
elongated rod, wherein the long axis of the rod and the opening are
directed toward a volume of gamma ray emitting material observable
by the detector on the basis of the length of the elongated rod and
the opening in the gamma ray shield.
[0013] In another example aspect of the disclosure, an apparatus
for detecting a volume concentration and activity of a radionuclide
content in a container includes a container of known dimensions for
receiving the radionuclide. A first gamma ray detector is arranged
below the container with respect to gravity and directed toward the
container. A second gamma ray detector is arranged above the
container with respect to gravity and opposite the first gamma ray
detector, and directed toward the container. Detection circuitry
and a processor are coupled to the first and second gamma ray
detectors, wherein the processor is configured to measure radiation
intensity received at the first and second gamma ray detectors and
determine a level of content of radionuclide in the container on
the basis of the radiation detected by the first and second gamma
ray detectors.
[0014] To the accomplishment of the foregoing and related ends, the
one or more example aspects comprise the features hereinafter fully
described and particularly pointed out in the claims. The following
description and the annexed drawings set forth in detail certain
illustrative aspects of the one or more aspects. These aspects are
indicative, however, of but a few of the various ways in which the
principles of various aspects may be employed and the described
aspects are intended to include all such aspects and their
equivalents.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] These and other sample aspects of the invention will be
described in the detailed description that follow, and in the
accompanying drawings, wherein:
[0016] FIG. 1 is a conceptual illustration of a gamma ray
collimated detector in accordance with various aspects of the
invention;
[0017] FIG. 2 is a conceptual side illustration of the detector of
FIG. 1, in accordance with various aspects of the invention;
[0018] FIG. 3 is a conceptual circuit diagram for measuring gamma
rays with the detector of FIGS. 1 and 2, in accordance with various
aspects of the invention;
[0019] FIG. 4 is a conceptual illustration of an apparatus for
measuring concentration, activity and content volume of a
radiopharmaceutical using the detector and circuitry of FIGS. 1-3
in accordance with various aspects of the invention;
[0020] FIG. 5 presents a conceptual processing system for measuring
the content volume of the radiopharmaceutical in the apparatus of
FIG. 4, in accordance with various aspects of the invention;
[0021] FIG. 6 presents a flowchart of the functions of components
of a flexible programmable gate array (FPGA) of the processing
system of FIG. 5, in accordance with various aspects of the
invention;
[0022] FIG. 7 is a plot of gamma ray activity in counts per second
(cps) of a top detector and a bottom detector of the apparatus in
FIG. 3 as a container between the two detectors is filled, in
accordance with various aspects of the invention;
[0023] FIG. 8 is a logarithmic plot of the ratio of counts in the
top detector to the bottom detector as a function of fill level in
the container of the apparatus of FIG. 3, in accordance with
various aspects of the invention;
[0024] FIG. 9 presents an exemplary system diagram of various
hardware components and other features, for use in networking the
apparatus for measuring concentration, activity and content volume,
in accordance with various aspects of the invention; and
[0025] FIG. 10 is a block diagram of various exemplary system
components for providing communications with and between various
components of the apparatus for measuring concentration, activity
and content volume, in accordance with various aspects of the
invention.
[0026] In accordance with common practice, some of the drawings may
be simplified for clarity. Thus, the drawings may not depict all of
the components of a given apparatus (e.g., device) or method.
Finally, like reference numerals may be used to denote like
features throughout the specification and figures.
DETAILED DESCRIPTION
[0027] Various aspects of methods and apparatus are described more
fully hereinafter with reference to the accompanying drawings.
These methods and devices may, however, be embodied in many
different forms and should not be construed as limited to any
specific structure or function presented throughout this
disclosure. Rather, these aspects are provided so that this
disclosure will be thorough and complete, and will fully convey the
scope of these methods and apparatus to those skilled in the art.
Based on the descriptions herein teachings herein one skilled in
the art should appreciate that that the scope of the disclosure is
intended to cover any aspect of the methods and apparatus disclosed
herein, whether implemented independently of or combined with any
other aspect of the disclosure. For example, an apparatus may be
implemented or a method may be practiced using any number of the
aspects set forth herein. In addition, the scope of the disclosure
is intended to cover such an apparatus or method which is practiced
using other structure, functionality, or structure and
functionality in addition to or other than the various aspects of
the disclosure set forth herein. It should be understood that any
aspect of the disclosure herein may be embodied by one or more
elements of a claim.
[0028] In a radiopharmaceutical production facility, a cyclotron
may be used to prepare a bolus of a material containing a
radioisotope of interest which is delivered to a synthesis system.
The radioisotope may emit one or more kinds of radiation, including
electrons, positrons, gamma rays/x-rays, protons, neutrons, alpha
particles, and other possible nuclear ejecta. In one example, a
radioisotope, when added to other materials to be administered to a
subject, may emit a positron, which then annihilates with an
electron, for example, in human tissue, to produce gamma rays.
[0029] Aspects of the current invention describe a gamma ray
detector and methods of measuring the activity, concentration, and
volume of a liquid radionuclide as it fills or is drained from a
container. In the production of radiopharmaceuticals, the
radionuclide may be introduced into a molecular vehicle by chemical
synthesis to produce the radiopharmaceutical. Various dosage,
concentration, activity and volume requirements for differing
medical applications may generally result in splitting, dilution
and redistribution of the radioisotope for the production of the
various radiopharmaceuticals, wherein a sensor monitors the various
production processes.
[0030] FIG. 1 shows a schematic illustration of a gamma ray
collimated detector 100. According to various aspects, the sensor
100 may include a cadmium zinc telluride (CdZnTe, or CZT) element
110. However, other solid state materials such as, e.g., other
solid state materials, currently available or yet to be discovered
may be used. CZT is a direct bandgap semiconductor and can operate
in a direct-conversion (e.g., photoconductive) mode at room
temperature, unlike some other materials (particularly germanium)
which may require cooling, in some cases, to liquid nitrogen
temperature. Advantages of CZT over germanium or other detectors
include a high sensitivity for x-rays and gamma-rays that is due to
the high atomic numbers and masses of Cd and Te relative to atomic
numbers and masses of other detector materials currently in use,
and better energy resolution than scintillator detectors. A gamma
ray (photon) traversing a CZT element 110 liberates electron-hole
pairs in its path. In operation and according to various aspects, a
bias voltage applied across electrodes 115 (not shown in FIG. 1)
and 116 on the surface of the element 110 (both shown in a side
view in FIG. 2) causes charge to be swept to the electrodes 115,
116 on the surface of the CZT (electrons toward an anode, holes
toward a cathode). According to various aspects, wires 125 and 126
may connect electrodes 115 and 116, respectively, to a source of
the applied voltage.
[0031] According to various aspects, the sensor 100 can function
accurately as a spectroscopic gamma energy sensor, particularly
when the element 110 is CZT. However, geometric aspects may be
considered. In conventional use of CZT as a gamma ray detector, the
CZT element 110 may be a thin platelet, sometimes arranged in
multiples to form arrays for imaging, generally perpendicularly to
the source of gamma ray emission. Therefore, gamma rays of
differing energies all traverse a detector element of substantially
the same thickness. While absorption of the gamma ray may generally
be less than 100% efficient, higher energy gamma rays may liberate
more electron-hole pairs than lower energy gamma rays, producing a
pulse of greater height. The spectrum and intensity of gamma ray
energies may thus be spectroscopically determined by counting the
number of pulses generated corresponding to different pulse
heights.
[0032] According to various aspects, because higher energy photons
may travel a greater distance in the CZT rod 110 before complete
absorption, it is advantageous for the CZT rod 110 to be greater in
length in a direction longitudinally (i.e., a long axis)
intersecting a known source volume of radionuclide being measured.
Gamma rays incident on the CZT rod off or transverse to the long
axis may not be fully absorbed, and thus, the CZT rod may not be as
sensitive a detector of such gamma rays as a result. Thus,
according to various aspects, elongating the CZT rod in one
direction introduces a degree of collimation and directional
sensitivity along the extended direction.
[0033] According to various aspects, the absorption coefficient for
511 keV gamma ray absorption in CZT is .mu.=0.0153 cm.sup.2/gm. The
absorption probability as a function of .mu., density .rho. (=5.78
gm/cm.sup.3) and penetration distance h is p(.mu.,
h)=1-e.sup.-.mu.ph.
[0034] Therefore, the ratio of absorption in a 10 mm length of CZT
to a 1 mm length is
P ( .mu. , 10 mm ) P ( .mu. , 1 mm ) .about. 9.613 .
##EQU00001##
That is, the directional sensitivity for gamma ray detection of CZT
at 511 keV along the 10 mm length of the detector is nearly 10
times greater than in the 1 mm thick transverse direction.
[0035] Referring to FIGS. 1 and 2, according to various aspects,
the sensor may be a CZT rod 110 as described above, encased in a
shielded case 105 (e.g., tungsten) with an aperture 120 open and
directed toward a vial or other container containing a
radiopharmaceutical sample to expose to the CZT rod 110 along the
long dimension of the rod 110, while shielding the CZT rod 110 from
gamma rays incident laterally to the long dimension of the rod 110,
e.g., from directions other than along the longitudinal dimension.
According to various aspects, the combination of shielding,
aperture and extended length of the CZT detector in the direction
of gamma ray emission from a portion of the radiopharmaceutical
sample provides a substantial directional "virtual" collimation of
the CZT detector's sensitivity to gamma rays incident from a volume
of the radiopharmaceutical that is defined by the collimation and
the size (e.g., diameter) of the radiopharmaceutical container and
the collimation of the acceptance aperture 120 of the detector 100.
According to various aspects, on the basis that the volume of the
radiopharmaceutical that is "observable," or detectable, by the
sensor 100 is constant from measurement to measurement, the
concentration and activity of the radionuclide can be determined,
after calibration.
[0036] FIG. 3 shows a conceptual circuit diagram for measuring
gamma rays with the detector 100. According to various aspects, a
charge amplifier 130 coupled to the electrodes 115 and 116
amplifies the charge. According to various aspects, a pulse
generator 140 converts the sensed charge to a pulse, where the
pulse height is proportional to the energy of the gamma ray. A
counting circuit 150 may determine the number of pulses as a
function of energy.
[0037] FIG. 4 is a conceptual illustration of an apparatus 400 for
measuring concentration, activity and content volume in a container
415 containing a radionuclide such as F-18 in solution, or a
radiopharmaceutical such as F-18 in FDG, using the detector 100 and
circuitry of FIGS. 1-3. According to various aspects, the container
415 may have known dimensions, and therefore is known to be able to
hold a specified maximum volume of the radionuclide in a liquid
form. In operation, according to various aspects, a first detector
100-b may be located opposite a bottom face 425-b of the container
415. Similarly, according to various aspects, a second detector
100-t may be located opposite a top face 425-t of the container,
and is similarly configured to detect gamma radiation from the
container 415. According to various aspects, the two detectors
100-b, 100-t may be similar or substantially the same. According to
various aspects, the two detectors may be identical. Both of the
detectors 100-t and 100-b is coupled to a differential measurement
processing system 450, shown in greater detail in FIG. 5.
[0038] FIG. 5 is a block diagram describing the differential
processing system 450 coupled to the two detectors, 100-t, 100-b,
according to various aspects. The processing system 450 may include
a high voltage supply 452 to provide the bias voltage that operates
each of the detectors 100-t, 100-b. Charge output from the
detectors 100-t and 100-b are separately input (optionally) to
signal conditioning circuitry 452 if noise filtering or DC offset
correction, or other artifact removal is warranted. Alternatively,
the signals from the detectors 100-t, 100-b may be directly input
to a dual channel analog-to-digital converter (ADC) 456 for
processing in digital format by a customized chip, such as a
flexible programmable gate array (FPGA) 458. The function of the
FPGA 458 will be discussed further below. Output of the FPGA 458
includes at least computed values for the activity sensed by each
of the detectors 100-t, 100-b and the volume of radionuclide in
liquid accumulated in the container 415. The output of the FPGA 458
may be communicated to a computing platform, such as a personal
computer (PC) 460, or other computing controller for purposes of
controlling such processes as filling or emptying the container 415
and identifying parameters associated with the pharmaceutical
content for documentation (e.g., date, activity, volume content,
labeling, etc.).
[0039] The processing system 450 may be distributed across a
network to facilitate, for example, efficient use of computing
resources to serve a plurality of detectors 100 and containers 415.
The division of the processing system 450 across the network may be
selected at any of several points. For example, one or more access
nodes (not shown) and network links (not shown) may be placed
between the dual channel analog-to-digital converter (ADC) 456 and
the FPGA 458, in which case the FPGA 458 and the computing platform
PC 460 may be remotely located across the network. Alternatively,
the access nodes and network links may be located between the FPGA
458 and the PC 460. It should be understood that other network
linking arrangements between the detectors 100 and computing and
control resources may be configured. The PC 460 may also be a
network configured computing resource, which may also be
distributed across one or more networks. For example, the computing
resource PC 460 may include a server, memory, and other
accessories, also located remotely from each other across the one
or more networks to provide the operational control of the
plurality of detectors 100 coupled to respective containers
415.
[0040] FIG. 6 is a flowchart 600 describing the functions of
components of the FPGA 458. Digitized data from each channel (i.e.,
top and bottom) of the ADC 456 is input to respective counters for
pulse counting (process block 602). In conjunction with a clocking
signal from a timing source (not shown) the pulse counts per unit
of time (e.g., seconds) are converted to respective count rates
(process block 604).
[0041] The count rates are then linearized (in process block 606
for each respective detector 100-t, 100-b). The linearization
process may include statistical or calibration-based correction,
for example, when the count rate becomes so high that pulses may
overlap, an effect referred to as "pile up."
[0042] The measured count rate, as counted by the detector and
associated electronics, may become lower than the true count rate
at high count rates. This is caused by effects in the bias
circuitry, crystal, and the electronics. In the bias circuitry and
crystal, a high photon flux can cause a shift in the spectral
response (as a decreased photopeak to background ratio) which can
cause undercounting. Also, the pulse width (governed by the crystal
and preamplifier characteristics) along with the pulse counting
electronics can have an impact on linearity. At high count rates,
pulses can pile up and double or triple pulses may be combined and
counted as one instead of two or three separate pulses
respectively. This is exacerbated when the pulse width is increased
or the counting electronics is too slow to count fast pulse rates
(long retrigger times, etc.).
[0043] To linearize the count rate, a nonlinearity calibration is
performed, along with implementing a look-up table or nonlinearity
correction equation. To perform calibration, a high activity sample
(e.g., having a maximum expected activity) is placed in front of
each sensor and allowed to decay. Data is then collected over
several half-lives until the count rate is low (i.e., in the linear
range where no pulse pile up occurs). Curve fitting is then
performed (e.g., polynomial, Lambert-W, etc.) to describe the
relationship between true count rate and the measured count rate.
Once established, the curve for each sensor (detector and
electronics) can be used in a look-up table or equation-based
correction to linearize measurements made.
[0044] Accordingly, a correction may be applied on a calibration
basis to correct for an undercounting of pulses due to pulse
overlap. If a background count has been detected (such as, for
example, before the container is filled), a command may be issued
for each detector rate to read the background rate (in process
blocks 608-t, 608-b, whether from a look-up table, a previous
reading from the detectors prior to filling the container, etc.).
The background rates are subtracted (in process blocks 610-t and
610-b) from the respective linearized count rates.
[0045] The ratio of the resulting "adjusted" counting rates is
computed (in process block 612) and the logarithm of the ratio is
computed (in process block 613) which, as it happens is
approximately linear in proportion to the fill level of the
container 415. In one embodiment, the log ratio measurement may be
referred to a lookup table to compute the fill volume of the
container (as in process block 614). The fill volume depends on a
known value of the shape, cross-section and height of the container
415. The adjusted count rate for each detector is compared with the
computed volume to determine the lookup activity (in process blocks
616-t and 616-b) for each respective detector 100-t, 100-b. The
outputs to the PC 460 include the top activity level, bottom
activity level, and container volume.
[0046] FIG. 7 is a plot of gamma ray activity in counts per second
(cps) of the top detector 425-t and the bottom detector 425-b of
the apparatus in FIG. 3 as a container between the two detectors is
filled, according to various aspects. Because the two detectors
425-t and 425-b may be placed opposite each other, they both
interrogate substantially a same volume element. When the container
430 is nearly empty, both detectors register substantially zero
counts, apart from background counts, however the ratio
asymptotically approaches zero, and the logarithmic ratio becomes
large negative. When the container 430 is full, both detectors
425-t, 425-b interrogate substantially the same volume, and
therefore register equal counts. Therefore, the ratio between the
counts of both detectors 425-t and 425-b is equal to one, and the
logarithmic value of the ratio is thus 0. According to various
aspects, FIG. 8 is a logarithmic plot of the ratio of counts of the
top detector 425-t to the counts of the bottom detector 425-b as a
function of fill level in the container 430 of the apparatus 400.
For intermediate levels of fill, the log ratio is approximately
linear, and the linearized logarithmic measure of the count ratio
may be used to determine the fill volume of the entire container,
because it may be assumed that the dimensions and shape of the
container 430 is defined (e.g., a cylinder of known constant
cross-section area and height). With the fill volume and activity
thus determined, the concentration of the radionuclide can be
determined.
[0047] According to various aspects, FIG. 9 presents an exemplary
system diagram of various hardware components and other features,
for use in networking the apparatus for measuring concentration,
activity and content volume, in accordance with an aspect of the
present invention. Computer system 900 may include a communications
interface 924. Communications interface 924 allows software and
data to be transferred between computer system 900 and external
devices. Examples of communications interface 924 may include a
modem, a network interface (such as an Ethernet card), a
communications port, a Personal Computer Memory Card International
Association (PCMCIA) slot and card, etc. Software and data
transferred via communications interface 924 are in the form of
signals 928, which may be electronic, electromagnetic, optical or
other signals capable of being received by communications interface
924. These signals 928 are provided to communications interface 924
via a communications path (e.g., channel) 926. This path 926
carries signals 928 and may be implemented using wire or cable,
fiber optics, a telephone line, a cellular link, a radio frequency
(RF) link and/or other communications channels. In this document,
the terms "computer program medium" and "computer usable medium"
are used to refer generally to media such as a removable storage
drive 980, a hard disk installed in hard disk drive 970, and
signals 928. These computer program products provide software to
the computer system 900. The invention is directed to such computer
program products.
[0048] Computer programs (also referred to as computer control
logic) are stored in main memory 908 and/or secondary memory 910.
Computer programs may also be received via communications interface
924. Such computer programs, when executed, enable the computer
system 900 to perform the features of the present invention, as
discussed herein. In particular, the computer programs, when
executed, enable the processor 910 to perform the features of the
present invention. Accordingly, such computer programs represent
controllers of the computer system 900.
[0049] In an aspect where the invention is implemented using
software, the software may be stored in a computer program product
and loaded into computer system 900 using removable storage drive
914, hard drive 912, or communications interface 920. The control
logic (software), when executed by the processor 904, causes the
processor 904 to perform the functions of the invention as
described herein. In another aspect, the invention is implemented
primarily in hardware using, for example, hardware components, such
as application specific integrated circuits (ASICs). Implementation
of the hardware state machine so as to perform the functions
described herein will be apparent to persons skilled in the
relevant art(s).
[0050] In yet another aspect, the invention is implemented using a
combination of both hardware and software.
[0051] FIG. 10 is a block diagram of various exemplary system
components for providing communications with and between various
components of the apparatus for measuring concentration, activity
and content volume, in accordance with an aspect of the present
invention. FIG. 10 shows a communication system 1000 usable in
accordance with the present invention. The communication system
1000 includes one or more accessors 1060, 1062 (also referred to
interchangeably herein as one or more "users") and one or more
terminals 1042, 1066. In one aspect, data for use in accordance
with the present invention is, for example, input and/or accessed
by accessors 1060, 1064 via terminals 1042, 1066, such as personal
computers (PCs), minicomputers, mainframe computers,
microcomputers, telephonic devices, or wireless devices, such as
personal digital assistants ("PDAs") or a hand-held wireless
devices coupled to a server 1043, such as a PC, minicomputer,
mainframe computer, microcomputer, or other device having a
processor and a repository for data and/or connection to a
repository for data, via, for example, a network 1044, such as the
Internet or an intranet, and couplings 1045, 1046, 1064. The
couplings 1045, 1046, 1064 include, for example, wired, wireless,
or fiber optic links. In another aspect, the method and system of
the present invention operate in a stand-alone environment, such as
on a single terminal.
[0052] The previous description is provided to enable any person
skilled in the art to fully understand the full scope of the
disclosure. Modifications to the various configurations disclosed
herein will be readily apparent to those skilled in the art. Thus,
the claims are not intended to be limited to the various aspects of
the disclosure described herein, but is to be accorded the full
scope consistent with the language of claims, wherein reference to
an element in the singular is not intended to mean "one and only
one" unless specifically so stated, but rather "one or more."
Unless specifically stated otherwise, the term "some" refers to one
or more. A claim that recites at least one of a combination of
elements (e.g., "at least one of A, B, or C") refers to one or more
of the recited elements (e.g., A, or B, or C, or any combination
thereof). All structural and functional equivalents to the elements
of the various aspects described throughout this disclosure that
are known or later come to be known to those of ordinary skill in
the art are expressly incorporated herein by reference and are
intended to be encompassed by the claims. Moreover, nothing
disclosed herein is intended to be dedicated to the public
regardless of whether such disclosure is explicitly recited in the
claims. No claim element is to be construed under the provisions of
35 U.S.C. .sctn.112, sixth paragraph, unless the element is
expressly recited using the phrase "means for" or, in the case of a
method claim, the element is recited using the phrase "step
for."
[0053] While aspects of this invention have been described in
conjunction with the example features outlined above, various
alternatives, modifications, variations, improvements, and/or
substantial equivalents, whether known or that are or may be
presently unforeseen, may become apparent to those having at least
ordinary skill in the art. Accordingly, the example aspects of the
invention, as set forth above, are intended to be illustrative, not
limiting. Various changes may be made without departing from the
spirit and thereof. Therefore, aspects of the invention are
intended to embrace all known or later-developed alternatives,
modifications, variations, improvements, and/or substantial
equivalents.
* * * * *