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Patent Application Titled "Methods and Systems for Increasing the Sensitivity of Simultaneous Multi-Isotope Positron Emission Tomography" Published...

January 27, 2014

Patent Application Titled "Methods and Systems for Increasing the Sensitivity of Simultaneous Multi-Isotope Positron Emission Tomography" Published Online

By a News Reporter-Staff News Editor at Clinical Trials Week -- According to news reporting originating from Washington, D.C., by NewsRx journalists, a patent application by the inventors Olcott, Peter D. (Stanford, CA); Levin, Craig S. (Palo Alto, CA), filed on March 30, 2012, was made available online on January 16, 2014 (see also Patents).

No assignee for this patent application has been made.

Reporters obtained the following quote from the background information supplied by the inventors: "In PET imaging, a positron emitting isotope is disposed within an object being imaged. Typically, the positron emitting isotope is included in a chemical tracer, which is thereby labeled with the isotope. Positrons emitted by the isotope rapidly encounter an electron within the object and annihilate, thereby creating a pair of oppositely directed 511 keV gamma ray photons. Coincidence detection of the 511 keV photons is employed in an imaging detector array to provide spatially resolved imaging of the annihilation events (i.e., the PET image).

"Positron emitting isotopes can be roughly divided into so-called 'clean' emitters and 'dirty' emitters depending on whether or not positron emission is accompanied by other kinds of radioactive emission. For clean emitters, there is relatively little non-positron emission (e.g., 10% or less), while dirty positron emitters can have greater non-positron emission (e.g., more than 10%). Since the non-positron radiation emitted by dirty positron emitters can cause undesirable background noise in a PET system, clean positron emitters are preferred in conventional PET systems. Some attention has been paid to correcting PET imaging results for the presence of background noise from dirty positron emitters, e.g., as considered in U.S. Pat. No. 7,777,189 and in US 2008/0283758.

"Some attention has also been paid to exploiting dirty emitters to provide more information from a PET system than can be obtained using conventional clean positron emitters. An example of this approach is described in an article by Andreyev et al. ('Feasibility study of dual-isotope PET', IEEE Nuclear Science Symposium 1020 Conference Record pp 2108-2111). In this work, two isotopes are used simultaneously in PET, where the first isotope is a clean positron emitter, and the second isotope is a dirty positron emitter that provides a prompt gamma ray in addition to a positron. Signals from the two isotopes are distinguished by determining whether a detected event is a 2-photon event (attributed to the clean emitter) or a 3-photon event (attributed to the dirty emitter)."

In addition to obtaining background information on this patent application, NewsRx editors also obtained the inventors' summary information for this patent application: "We have found that satisfactory imaging of 3-photon events (also referred to as triple-coincidence events) can be very difficult in a conventional PET system. The basic reason for this is low detection efficiency. For conventional PET, the detection rate for the 2 annihilation photons is typically about 1-3%. The detection rate for a prompt gamma in a PET system also tends to be quite low, and these two low efficiencies would be multiplied to obtain the detection efficiency of 3-photon events. Low efficiency leads to poor statistics (i.e., reduced signal/noise), which in turn degrades the ability to detect, visualize or quantify the spatial extent and concentration of triple coincidence emitters.

"The present work relates to PET systems having configurations for improved detection of 3-photon events, thereby alleviating the above-described problem of low sensitivity, and enabling improved dual isotope PET with clean and dirty emitters simultaneously imaged.

"One or more prompt gamma detectors is placed in proximity to the rest of the PET system. The PET system processor is capable of distinguishing between 2-photon events and 3-photon events according to signals provided by the imaging detector array of the PET system (which is responsive to 511 keV photons) and by the prompt gamma detectors (which are responsive to prompt gamma photons, but are not responsive to 511 keV annihilation photons). The prompt gamma detectors need not provide spatial resolution, so large single-element and/or single-channel detectors can be used for the prompt gammas to provide improved prompt gamma detection efficiency without greatly adding to system cost. Note that a naive approach of extending the size/coverage of the PET imaging array to improve detection efficiency for prompt gammas would be much more costly than the present approach.

"The present approach provides various significant advantages. By increasing the sensitivity of 3-photon event detection, simultaneous PET imaging of 2-photon and 3-photon emitters can be enabled. This advantageously reduces total imaging time compared to performing two imaging runs in sequence. If two runs are performed in sequence, it would be necessary to wait for the first tracer to clear before starting the second imaging run, so the time savings can be highly significant. Furthermore, such PET imaging may provide rich biochemical information by performing multi-tracer imaging simultaneously with full temporal and spatial registration.


"FIGS. 1a-c show a first embodiment of the invention.

"FIGS. 2a-b show a second embodiment of the invention.

"FIGS. 3a-b show a third embodiment of the invention.

"FIGS. 4a-b show a fourth embodiment of the invention.

"FIG. 5a shows an experimental configuration relating to principles of the invention.

"FIG. 5b shows results from the experiment of FIG. 5a.

"FIG. 6 shows a simplified nuclear energy level diagram for the transition from I-124 to Te-124."

For more information, see this patent application: Olcott, Peter D.; Levin, Craig S. Methods and Systems for Increasing the Sensitivity of Simultaneous Multi-Isotope Positron Emission Tomography. Filed March 30, 2012 and posted January 16, 2014. Patent URL:

Keywords for this news article include: Patents, Clinical Trials and Studies.

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Source: Clinical Trials Week

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