Method, apparatus, and system of electric-signal detection by asynchronous demultiplexing

Some embodiments include methods, devices and systems of radiation detection by asynchronous demultiplexing. In some embodiments, an apparatus to read a plurality of electrical signals received from an electrode may include two or more electrical signal readers, wherein each of the signal readers is individually switchable between a coupled state in which an input of the signal reader is coupled to the electrode, and a decoupled state in which the input is decoupled from the electrode; and a controller to detect the plurality of electrical signals, to selectively switch the two or more signal readers to the coupled state to receive at least one sequence of two or more of the detected electrical signals, respectively, and to selectively activate the two or more signal readers to process the two or more detected electrical signals, respectively. Other embodiments are described and claimed.

FIELD

Some embodiments relate to electric signal detectors, and in particular to photon counting detectors in the field of medical imaging.

BACKGROUND

A semiconductor radiation detector may be used to detect photons for medical imaging systems. Photons of ionizing radiation, e.g., X-ray or gamma ray radiation, are absorbed by a semiconductor and generate measurable electric charge, which may be collected by anodes deposited on the semiconductor. The electric charge collected by the anodes may be read and converted into electric signals by readout circuits coupled to the anodes. The energy of the absorbed photon is measured according to the energy level of the electric signals, and the location of absorption of the photon corresponds to the location of the anodes collecting the electric charge. The energy level and location of the absorbed photons are used for image reconstruction.

Unfortunately, in some cases the radiation flux may be too high for the readout circuit to distinguish between individual photons. For example, when the measured radiation flux is relatively high and the area of the anode is relatively small. This may adversely affect the quality of the reconstructed image.

SUMMARY

Some embodiments provide a method, apparatus, and/or system of radiation detection by asynchronous demultiplexing.

Some embodiments enable a radiation detector to distinguish between individual photons for an anode that receives high flux levels.

Some demonstrative embodiments include a photon counting radiation detection system, which may include at least one radiation detector including an array of anodes to generate a plurality of electrical signals in response to absorbing photons of ionizing radiation; an array of electrical signal detectors to read the plurality of electrical signals; and a readout system to generate an output corresponding to the radiation based on an output of the array of electrical signal detectors. At least one of the electrical signal detectors may include two or more electrical signal readers, wherein each of the signal readers is individually switchable between a coupled state in which an input of the signal reader is coupled to the electrode, and a decoupled state in which the input is decoupled from the electrode; and a controller to detect the plurality of electrical signals, to selectively switch the two or more signal readers to the coupled state to receive at least one sequence of two or more of the detected electrical signals, respectively, and to selectively activate the two or more signal readers to process the two or more detected electrical signals, respectively.

In some demonstrative embodiments, the controller is to detect a signal to be read by a first signal reader of the two or more signal readers, which is at the coupled state; and, at the end of a predefined time period after detecting the signal, to switch the first signal reader from the coupled state to the decoupled state and to switch a second signal reader of the two or more signal readers from the decoupled state to the coupled state.

In some demonstrative embodiments, the controller is to deactivate the first signal reader at the end of a predefined time period after switching the first signal reader to the decoupled state.

In some demonstrative embodiments, the controller is to activate the second signal reader at the end of a predefined switching time period after coupling the second signal reader.

In some demonstrative embodiments, the two or more electrical signal readers may include n readers, and the controller may be capable of cyclically switching the n signal readers to the coupled state according to a predefined switching sequence, such that each of the n readers is to sequentially read a first electrical signal of the sequence of electrical signals and a second electrical signal of a consecutive sequence of the detected electrical signals.

In some demonstrative embodiments, a number of the two or more signal readers is equal to or greater than a ratio between a flux of the plurality of electrical signals received from the electrode and a reading time of each of the signal readers.

In some demonstrative embodiments, at least one signal reader of the signal readers may include a signal readout circuit including a charge-sensitive amplifier to be switchably coupled to the input via a switchable gate; and a shaper coupled to an output of the amplifier.

In some demonstrative embodiments, a number of the two or more signal readers may be equal to or greater than a ratio between a flux of the plurality of electrical signals received from the electrode and a time constant of the shaper.

In some demonstrative embodiments, the two or more signal readers are coupled to a common output.

In some demonstrative embodiments, the system may include a medical imaging system.

In some demonstrative embodiments, the radiation may include X-ray or Gamma radiation.

Some demonstrative embodiments include an apparatus to read a plurality of electrical signals received from an electrode. The apparatus may include two or more electrical signal readers, wherein each of the signal readers is individually switchable between a coupled state in which an input of the signal reader is coupled to the electrode, and a decoupled state in which the input is decoupled from the electrode; and a controller to detect the plurality of electrical signals, to selectively switch the two or more signal readers to the coupled state to receive at least one sequence of two or more of the detected electrical signals, respectively, and to selectively activate the two or more signal readers to process the two or more detected electrical signals, respectively.

In some demonstrative embodiments, the controller is to detect a signal to be read by a first signal reader of the two or more signal readers, which is at the coupled state; and, at the end of a predefined time period after detecting the signal, to switch the first signal reader from the coupled state to the decoupled state and to switch a second signal reader of the two or more signal readers from the decoupled state to the coupled state.

In some demonstrative embodiments, the controller is to deactivate the first signal reader at the end of a predefined time period after switching the first signal reader to the decoupled state.

In some demonstrative embodiments, the controller is to activate the second signal reader at the end of a predefined switching time period after switching the second signal reader to the coupled state.

In some demonstrative embodiments, the two or more electrical signal readers include n readers, and the controller is to cyclically switch the n signal readers to the coupled state according to a predefined switching sequence, such that each of the n readers is to sequentially read a first electrical signal of the sequence of electrical signals and a second electrical signal of a consecutive sequence of the detected electrical signals.

In some demonstrative embodiments, the first and second electrical signals are separated by n electrical signals.

In some demonstrative embodiments, a number of the two or more signal readers is equal to or greater than a ratio between a flux of the plurality of electrical signals received from the electrode and a reading time of each of the signal readers.

In some demonstrative embodiments, at least one signal reader of the signal readers may include a signal readout circuit including a charge-sensitive amplifier to be switchably coupled to the input via a switchable gate; and a shaper coupled to an output of the amplifier.

In some demonstrative embodiments, a number of the two or more signal readers is equal to or greater than a ratio between a flux of the plurality of electrical signals received from the electrode and a time constant of the shaper.

In some demonstrative embodiments, the signal reader may include a reset switch connected in parallel to the charge-sensitive amplifier, and wherein the controller is to switch the signal reader to the coupled state by closing the gate, and to activate the signal reader by opening the reset switch.

In some demonstrative embodiments, the two or more signal readers are coupled to a common output.

In some demonstrative embodiments, the apparatus may include a radiation detector including an array of anodes, wherein the electrode may include an anode of the array of anodes.

In some demonstrative embodiments, the radiation detector may include a radiation detector to detect an ionizing radiation selected from the group consisting of X-ray radiation and Gamma ray radiation.

In some demonstrative embodiments, the radiation detector may include a single photon counting semiconductor radiation detector.

In some demonstrative embodiments, the semiconductor radiation detector may include cadmium zinc telluride.

Some demonstrative embodiments include a method of reading a plurality of electrical signals received from an electrode of a radiation detector. The method may include detecting the plurality of electrical signal; and individually reading at least one sequence of two or more of the detected electrical signals by two or more electrical signal readers, respectively, by selectively switching the two or more electrical signal readers between a coupled state in which an input of the signal reader is coupled to the electrode and a decoupled state in which the input is decoupled from the electrode, and selectively activating the two or more signal readers to process the two or more detected signals, respectively.

In some demonstrative embodiments, the method may include detecting a signal to be read by a first signal reader of the two or more signal readers, which is at the coupled state; and, at the end of a predefined time period after detecting the signal, switching the first signal reader from the coupled state to the decoupled state and switching a second signal reader of the two or more signal readers from the decoupled state to the coupled state.

In some demonstrative embodiments, the method may include deactivating the first signal reader at the end of a predefined time period after switching the first signal reader to the decoupled state.

In some demonstrative embodiments, the method may include activating the second signal reader at the end of a predefined switching time period after switching the second signal reader to the coupled state.

In some demonstrative embodiments, the two or more electrical signal readers include n readers, and the selectively switching may include cyclically switching the n signal readers to the coupled state according to a predefined switching sequence, such that each of the n readers is to sequentially read a first electrical signal of the sequence of electrical signals and a second electrical signal of a consecutive sequence of the detected electrical signals.

In some demonstrative embodiments, the first and second electrical signals are separated by n electrical signals.

In some demonstrative embodiments, a number of the two or more signal readers is equal to or greater than a ratio between a flux of the plurality of electrical signals received from the electrode and a reading time of each of the signal readers.

In some demonstrative embodiments, the reading may include using a shaper, and wherein a number of the two or more signal readers is equal to or greater than a ratio between a flux of the plurality of electrical signals received from the electrode and a time constant of the shaper.

In some demonstrative embodiments, the electrode may include an anode of an array of anodes of a radiation detector.

In some demonstrative embodiments, the radiation detector may include a single photon counting semiconductor radiation detector.

In some demonstrative embodiments, the semiconductor radiation detector may include cadmium zinc telluride.

Some embodiments may provide other and/or additional benefits and/or advantages.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of some demonstrative embodiments. However, some embodiments may be practiced without these specific details. In other instances, well-known methods, procedures, components, units and/or circuits have not been described in detail so as not to obscure the discussion. It is intended that the embodiments and figures disclosed herein be considered illustrative rather than restrictive.

Portions of the discussion herein utilizing terms such as “processing,” “computing,” “calculating,” “determining,” or the like, refer to the action and/or processes of a computer or computing system, or similar electronic computing device, that manipulate and/or transform data represented as physical, such as electronic, quantities within the computing system's registers and/or memories into other data similarly represented as physical quantities within the computing system's memories, registers or other such information storage, transmission or display devices. In addition, the term “plurality” may be used herein to describe two or more items; for example, a plurality of items includes two or more items.

FIG. 1schematically illustrates, in cross-section, a semiconductor radiation detector99according to some demonstrative embodiments. Detector99includes a semiconducting sheet10having a plurality of electrodes12and14coupled thereto. Electrodes12include one or more cathodes12coupled to one side of sheet10; and a plurality of anodes14coupled to an opposite side of sheet10. In one non-limiting example, sheet10may be produced from cadmium-zinc-telluride (CdZnTe or “CZT”), or from any other suitable semiconductor material capable of detecting ionizing radiation, such as silicon and/or germanium.

In operation of detector99, photons of radiation are absorbed by sheet10to form electrons and holes. The electrons and holes drift to anodes14and cathodes12, respectively, generating measurable electrical signals on anodes14and cathodes12. A level of the electric signals may provide a measure of the energy of the absorbed photon, and/or the location of absorption of the photon may correspond to the location of the anodes generating the signal. The energy level and location of the absorbed photons may be used for image reconstruction. For example, detector99may be part of a pixilated detector, with an array of detector elements99arranged in a grid layout that corresponds to pixels of the reconstructed image. Accordingly, anodes14may also be referred to herein as pixels14.

If the measured radiation flux is high, for example, of the order of at least 108photons (events) per second per square-millimeter, then for an anode having an area of the order of 1 mm2, the radiation flux may be too high for a conventional readout circuit coupled to the anode to distinguish between individual photons.

Although embodiments are not limited in this respect, in the following description, unless otherwise stated, anodes14may be assumed by way of example to receive of the order of 108events per second. In other embodiments, radiation received by anodes14may include radiation of any other suitable flux, e.g., lower or higher than 108events per second.

In some embodiments, detector99may include an electric signal detector97coupled to anode14to detect ionizing radiation such as, high flux X-ray or gamma ray radiation, generating electrical signals at anode14, e.g., by single photon counting. Electrical signal detector97may be capable of distinguishing between individual photons of a high flux radiation, e.g., of an order of at least of 108events per second, which may be received by anode14, resulting in a reconstructed image at a relatively high level of reliability, e.g., as described herein.

In some demonstrative embodiments, electric signal detector97may include a plurality of electrical signal readers98, e.g., n electrical signal readers denoted98a. . .98n, coupled to a common output93. Each of readers98may be individually switchable between a first (“coupled”) state in which an input of the reader is coupled to anode14to receive a detected signal from anode14, and a second (“decoupled”) state in which the input of the reader is decoupled from anode14, e.g., as described below. Each of readers98may also be individually activated, for example, when the reader is at the coupled and/or decoupled states, to processes the received signal, e.g., as described below.

In some demonstrative embodiments, electric signal detector97may also include a switching controller95to detect the electrical signals generated by anode14, and to selectively switch signal readers98to the coupled state and/or to selectively activate signal readers98, thereby to read at least one sequence of two or more of the detected electrical signals by signal readers98, respectively, e.g., as described in detail below.

FIG. 2schematically illustrates an electric signal detector circuit30in accordance with some demonstrative embodiments. Although embodiments of the invention are not limited in this respect, in some demonstrative embodiments circuit30may perform the functionality of electric signal detector97(FIG. 1), to detect signals from anode14of radiation detector99(FIG. 1). In some embodiments, a pixilated radiation detector, such as detector99(FIG. 1), may have one or more detectors substantially similar to circuit30coupled to one or more respective anode14. Accordingly, anode14is also referred to herein as pixel j of the pixilated radiation detector99(FIG. 1).

Circuit30includes a signal detection circuit34and a plurality of n signal readout circuits32, wherein n is a positive integer equal to or greater than 2. In one non-limiting example, the value of n may be of the order of 10, although the value of n may be selected according to characteristics of each circuit32and according to an expected radiation flux, as is described in more detail below.

Although embodiments of the invention are not limited in this respect, in some demonstrative embodiments signal readout circuits32may perform the functionality of electric signal readers98(FIG. 1); and/or signal detection circuit34may perform the functionality of switching controller95(FIG. 1), e.g., as described below.

In some demonstrative embodiments, each circuit32is able to operate as a channel conveying an input signal from pixel j to a common output terminal50of circuit30. The individual circuits32are labeled as32a,32b, . . .32nand are also termed herein channel1, channel2, . . . channel n, respectively.

In some demonstrative embodiments, signal detection circuit34may controllably switch readout circuits32between first and second states of operation, e.g., as described in detail below.

In some demonstrative embodiments, one or more of readout circuits32, e.g., each of readout circuits32, may include a charge amplifier circuit36, a shaper44, a sample and hold circuit46, and an output stage48. One or more of charge amplifier circuits36, e.g., each of charge amplifier circuits36, may include a reset switch38and a charge amplifier element40. One or more of readout circuits32, e.g., each of readout circuits32, may also include a gate switch42to control whether the electrical input signal from pixel j is passed to the channel corresponding to readout circuit32. Elements of the individual readout circuits32a-32nare correspondingly labeled with respective letter designations.

In some demonstrative embodiments, one or more of readout circuits32, e.g., each of readout circuits32, may be switchable between a first (“coupled”) state, in which the readout circuit is coupled to receive the electrical input signal from pixel j; and a second (“decoupled”) state, in which the readout circuit is decoupled from the electrical input signal, e.g., as described in detail below. One or more of readout circuits32, e.g., each of readout circuits32, may also be selectively activated, e.g., when at the coupled and/or decoupled states, to process the received signal, e.g., as described in detail below.

In some demonstrative embodiments, circuit36may be coupled to receive a signal from pixel j, for example, when gate switch42between pixel j and the charge amplifier input is closed. Circuit36may be decoupled from pixel j, for example, when gate switch42between pixel j and the charge amplifier input is open.

The output of charge amplifier circuit36is passed via shaper44, sample and hold circuit46, and output stage48to output terminal50. Output stage48may be, for example, an analog-to-digital (A/D) converter, a multiple threshold comparator, or the like.

In some demonstrative embodiments, each of circuits32may be selectively activated to process the signal received from pixel j, e.g., by selectively opening reset switch38. For example, circuit32may be activate to process the received signal, when reset switch38is open, thereby allowing shaper44to receive the output of amplifier circuit36. Circuit32may be deactivated by closing reset switch38. For example, as shown inFIG. 2, circuit32ais in the coupled state, e.g., since gate42ais closed, whereas circuit32band circuit32nare in the decoupled state, since gates42band42nare open. In addition, as shown inFIG. 2, circuit32ais active, e.g., since reset switch38ais open, whereas circuits32band32nare inactive, e.g., since reset switches38band38nare closed.

In some demonstrative embodiments, a circuit of circuits32may be active when the circuit is in the coupled and/or decoupled states. For example, channel1may be activated, e.g., by opening reset switch38a, for example, after receiving a signal via closed gate42a, and may continue to be active as long as reset switch38ais open, e.g., even after channel1is decoupled by opening gate42a, as described below. According to this example, the capacitor of charge sensitive amplifier36may be charged, e.g., when gate42ais closed, and may provide an input signal to shaper44a, e.g., even after gate42ais opened. Accordingly, shaper44amay continue to process the electric signal received from pixel j even after channel1is decoupled from pixel j. Shaper44amay continue to process the received signal after the decoupling of channel1, e.g., until, reset switch38ais closed.

In some demonstrative embodiments, reset switch38amay be closed just before the arrival of another electric signal, e.g., of a successive sequence of signals, to be processed by channel1, e.g., as described below. Accordingly, shaper44amay continue to process the received signal, even when other channels are coupled to pixel j and/or process other signals received from pixel j. Therefore, shaper44amay be allowed to have relatively long processing time, which may result in an improved the Signal-to-Noise-Ratio (SNR).

In some demonstrative embodiments, shaper44may be the “slowest” element among the elements of circuit32, e.g., since shaper44may a long response time compared to other elements of readout circuit32, as described below. Accordingly, the rate in which the shaper44operates may be selected to be approximately the rate of flux received at pixel j, divided by the number n of electronic channels32, e.g., as described below. In one example, shaper44may operate at an appropriate rate, e.g., to handle approximately 1 events per second, to accommodate a relatively high flux rate of 108events per second at pixel j, e.g., if n is of the order of 10.

In some demonstrative embodiments, signal detection circuit34may selectively couple and/or activate readout circuits32, e.g., as described in detail below.

In some demonstrative embodiments, detection circuit34may include a charge amplifier52, a comparator54, a modulo n counter56, and a switching control58, e.g., including n switching controls58a-58n.

In accordance with some demonstrative embodiments, charge amplifier52may be configured to operate at the expected rate of radiation flux at anode14. For example, in the example described herein, charge amplifier52may be configured to operate at the relatively high rate of 108events per second. The output of amplifier52is transferred to comparator54, which acts as an event discriminator. By comparing the output of amplifier52with a preset threshold voltage level, denoted V_trh, comparator54may determine if an event has occurred at anode14. Comparator54may output a predefined signal, e.g., a “true” level, to counter56, for example, each time an event is detected by comparator54.

In some demonstrative embodiments, counter56may include a modulo n counter, which acts to cyclically switch channels1-n, i.e., signal readout circuits32a-32n, via switching control58. In some embodiments, counter56and switching control58may be configured such that at any given time only one channel of channels32is coupled to pixel14, and all other channels32are decoupled from that pixel. Counter56and switching control58may also selectively activate one or more of circuits32to process the signals received by the n channels, e.g., as described herein. In one example, two or more of the n channels may be active simultaneously to allow processing of the received signals during a time period longer than an average time between the electric signals received from pixel14, e.g., as described herein. For example,FIG. 2illustrates the situation when channel1is coupled and active, e.g., since gate42ais closed and reset switch38ais open; and channels2-nare decoupled and inactive, e.g., since gates42b-42nare open and reset switches38b-38nare closed.

FIG. 3schematically illustrates an input timeline301, a processing timeline302and an output timeline303illustrating the timing of pulses processed by an electric signal detector in accordance with some demonstrative embodiments. Although embodiments of the invention are not limited in this respect, in some demonstrative embodiments timelines301,303, and303may be implemented by an electric signal detector, e.g., circuit30(FIG. 2), coupled to a detector element of a pixilated radiation detector, e.g., detector99(FIG. 1).

Timeline301shows a series of pulses from pixel j being input to circuit30(FIG. 2) in two cycles,311and312. Each cycle includes a sequence of n pulses, with the time of a cycle varying according to the time of arrival of the pulses from pixel j. As shown inFIG. 3, the pulses are distributed between channels1-nby signal detection circuit34(FIG. 2) of circuit30(FIG. 2) associated with pixel j, which may act as a demultiplexer for the incoming pulses. For example, as described above, the pulses may be distributed to the n channels cyclically, such that the first pulse of input cycle311is sent to channel1, the n-th pulse of input cycle311is sent to channel n, and the first pulse of input cycle312, e.g., the n+1-th pulse, is again sent to channel1.

Each pulse may be processed within its respective channel, e.g., as described herein. For example, the processing time of a processing a pulse of cycle311by a channel may begin starts with the arrival the pulse into the channel, and may end just before the arrival at the channel of a next pulse from cycle312, e.g., in order to allow a relatively long processing time for shaper44(FIG. 2). During the processing of the pulse of cycle311at a channel, other channels may be selectively coupled/decoupled and/or activated to process other respective pulses of cycle311, e.g., as described herein. The output of each channel may be combined or multiplexed at output terminal50(FIG. 2) of circuit30(FIG. 2), giving an output that corresponds to the input received by the circuit.

As shown inFIG. 3, the cycles generated by circuit34(FIG. 2), e.g., cycles311and312, may span unequal time periods, for example, since the stepping from channel to channel may depend on signal detection circuit34(FIG. 2) detecting a pulse. However, as shown in processing timeline302, by demultiplexing the input from pixel j into n channels, the time between each pulse within a specific channel is increased, by a factor of approximately n, compared to the timing of pulses arriving at pixel j.

In some embodiments, the operation rate of shaper44(FIG. 2) may be determined by its peaking and/or shaping time, adjusted to improve SNR. The shaping time of shaper44(FIG. 2) is generally longer than the time between events generated at a given anode14(FIG. 2). The demultiplexing process described herein, which distributes events received at a given detector element, e.g., anode14(FIG. 2), into multiple channels32(FIG. 2), increases the time between each pulse within a specific channel32(FIG. 2). This allows shaper44(FIG. 2) to process the pulses in channel32(FIG. 2) at a rate that is slower than the incoming event rate produced at the given anode14(FIG. 2). The events processed in channels32(FIG. 2) are recombined at output50(FIG. 2) to generate an event rate that is similar to the event rate received from the given anode, as shown in output timeline303. Accordingly, circuit30(FIG. 2) is able to process the events received for each anode14(FIG. 2), even though the processing time for each event, e.g., mainly dictated by shaper44(FIG. 2), is longer than the time between the events received at the anode.

In some demonstrative embodiments, the timing of the incoming pulses may be generally governed by Poisson statistics. The actual increase in timing within each channel may also generally be a function of Poisson statistics.

In some demonstrative embodiments, the number of channels n may be determined so as to allow each channel32(FIG. 2) of circuit30(FIG. 2) sufficient time to process its corresponding pulses, using one or more of the considerations described above, e.g., including the radiation flux at pixel j and/or the statistical variation of the flux.

FIG. 4schematically illustrates a timing diagram of an electric signal detector in accordance with some demonstrative embodiments. Although embodiments of the invention are not limited in this respect, in some demonstrative embodiments, the timing diagram ofFIG. 4may be implemented by a switching controller, e.g., signal detection circuit34(FIG. 2), of a detector circuit, e.g., circuit30(FIG. 2), coupled to a detector element, e.g., anode14(FIG. 1), of a pixilated radiation detector, e.g., detector99(FIG. 1).

The diagram ofFIG. 4shows the states of gates1,2and n, e.g., gates42a,42band42n(FIG. 2), respectively, and reset switches1,2, and n, e.g., reset switches38a,38band38n(FIG. 2), respectively of channels1,2and n, respectively, to demultiplex n+1 pulses of a demultiplexing cycle including n pulses. The states of the gates and reset switches ofFIG. 4may be controlled, for example, by the outputs of switching control58(FIG. 2). The initial time of the diagram ofFIG. 4corresponds to the positions of gates1,2, and n, and reset switches1,2, and n, as illustrated inFIG. 2. Thus, in this example, initially channel1is coupled and active, and the other n−1 channels are decoupled and inactive.

As shown inFIG. 4, at a time T1, signal detection circuit34(FIG. 2) may detect a pulse, denoted “First Pulse”. Circuit34(FIG. 2) may use switching controls58(FIG. 2) to decouple channel1, e.g., by opening gate1, and to couple channel2, e.g., by closing gate2, for example, at the end of a predefined time period, denoted Δt, after the detection of the first pulse. The opening of gate1and the closing of gate2may be performed substantially. The detected first pulse may also be received by channel1via closed gate1, e.g., prior to the decoupling of channel1. As shown inFIG. 4, reset switch1is already open, when channel1is decoupled. The time period Δt between the detection of the first pulse and the decoupling of channel1may be set to be larger than a rise time of the electric signal in charge sensitive preamplifier40(FIG. 2), e.g., in order to allow the detection of the peak amplitude of the electric signal. Channel1may be deactivated by closing reset switch1a predefined delay time period, denoted Δt1after opening gate1. The time period Δt1may be set to be longer than a shaping/processing time of shaper44, e.g., to allow for shaper44a(FIG. 2) of channel1to complete processing the detected electric signal. Delay time period Δt1may be set to be shorter than a typical demultiplexing time of n pulses, such that reset switch1may be closed before a next pulse from a next demultiplexing cycle arrives at channel1.

In some demonstrative embodiments, signal detection circuit34(FIG. 2) may close gate2to couple channel2, at the end of the time period Δt; and may open reset switch2at the end of a predefined buffer time period Δt2following the time period Δt, thus making channel2active and ready for receiving the second pulse only at the end of time period Δt2. Maintaining reset switch2closed during the time period Δt2, while switching gate2into the closed state may prevent switching noise from being transferred through channel2. Channel2may continue to be active during the time period Δt1after the decoupling of channel2. The activation of channel2may end with the closing of reset switch2. At a time T2, circuit34(FIG. 2) may detect a second pulse, denoted “second pulse”, which is to be processed by channel2. At the end of the time period Δt after the detection of the second pulse, circuit34(FIG. 2) may open gate2to decouple channel2, and may close a gate3(not shown) to couple a channel3for receiving a third electronic signal. Upon detecting the second pulse, gate2may be already closed. Gate2may be switched to the open state at the end of the time period Δt after the detection of the second pulse. Reset switch2of channel2is switched to the open state at the end of the time period Δt2, e.g., analogously to the switching sequence described above with reference to channel1after detection of a pulse.

Similarly, an (n−1)thpulse is detected at a time Tn−1. At a time Δt after the (n−1)thpulse is detected, circuit34(FIG. 2) may open gate (n−1) (not shown) and close gate n. Circuit34(FIG. 2) may open reset switch n, e.g., at the end of the buffer time Δt2after closing the gate n, to prevent switching noise being transferred through channel n, thus making channel n active and ready for receiving the n-th pulse. Channel (n−1) continues to be active until the end of the time period Δt1after the opening of gate (n−1), which corresponds to a time period Δt+Δt1after the time Tn−1. Channel (n−1) continues to be active as long as the reset switch (n−1) is open, e.g., even when gate (n−1) is open, since the capacitor of charge sensitive amplifier40at the input of shaper44is still charged with the electric charge of the electric signal. At a time Tncircuit34(FIG. 2) may detect the nthpulse, which is to be processed by channel n. Upon detecting the nthpulse, circuit34(FIG. 2) may switch the gates and resets of channel n and channel1, after the time delays described above, for example, analogously to the switching sequence described above with relation to the channels1and2after detection of a pulse, e.g., as illustrated for the “First Pulse”.

It can be seen that the states of the gates and reset switches at times T1and Tn+1for channels1and2repeat themselves. For example, states of the gates and resets in every channel32(FIG. 2) may repeat themselves every n pulses, corresponding to one demultiplexing cycle of a sequence of n detected electrical signal received from anode14(FIG. 2).

FIG. 5schematically illustrates a system109in accordance with some demonstrative embodiments. In one non-limiting example, system109may include an imaging system, e.g., a medical imaging system.

System109including a plurality of electric signal detection circuits30coupled to a detector element of a pixilated radiation detector99(FIG. 1) Referring toFIG. 1, it is assumed that radiation detector99(FIG. 1) includes m anodes14, wherein m is a positive integer. Each j-th anode of the m anodes14may be coupled to a respective detection circuit30j, e.g., as described above with reference toFIG. 2), of m detection circuits30. Accordingly, as shown inFIG. 5, the m detection circuits30may provide m respective circuit outputs50a-50m, referred to inFIG. 5as “Output Pixel1”, . . . “Output Pixel m”, respectively.

The m outputs50a-50mare coupled to a suitable readout system100. In one non-limiting example, readout system100which may include or be generally similar to the readout system described in U.S. patent application Ser. No. 11/446,772, entitled “Digital Readout System”, filed Jun. 3, 2006, and Published Dec. 6, 2007 as US Application Publication US2007/0278387 (“the '772 application”) the entire disclosure of which is incorporated herein by reference.

In some demonstrative embodiments, there may be a relatively high probability to receive at readout system100events from different anodes14, e.g., substantially simultaneously, for example, since the m anodes14may generate events at a relatively high rate. Readout system100may have the capability to provide an address of the anodes14generating specific pulses, and energies of the pulses, arriving simultaneously at different anodes, e.g., as described in the '772 application.

In one example, readout system100may include an array of, e.g., similar, detector output units (not shown) corresponding to the array of anodes14and coupled to the m circuit outputs50, e.g., as described in the '772 application. As described in the '772 application, each detector output unit may have an amplifier (not shown) that is able to hold an indication of a charge (“the indication”), generated by the anode receiving a photon, e.g., until the indication is read from the amplifier onto a readout line of the unit. As further described in the '772 application, each detector output unit may output a request-to-read (request) signal when the amplifier has the indication, and may receive a select-to-read (select) signal and use it to cause the indication to be read from the amplifier. In one example, one readout amplifier may be connected to all the readout lines of the array of units.

To form an event-driven readout system having an extremely fast readout time, the array of output units may be coupled to a set of selectors, e.g., all substantially similar, which are connected together in the form of a tree. The tree is arranged in rows, each row having fewer selectors than a preceding row. A final row of the tree may include a single final selector. A request signal from an output unit having the charge indication (“the origin unit”) may be routed forward through the tree by the selectors to the final selector, and from the final selector to a processor. The processor may generate a select signal that is routed back, via the same selectors, to the origin unit. Upon receipt of the request signal, the processor may activate the readout amplifier, so that the charge indication on the origin unit may be read by the processor.

In addition to being configured to route the select signal along the same path as the request signal, the selectors may be configured to effectively queue request signals by acting as memory elements, to prioritize request signals so as to ensure that detector output units are read equitably, and/or to automatically register the address of the originating detector unit.

The description above assumed, by way of example, that each of the detector elements14receives on the order of 108events per second; and that each signal circuit32(FIG. 2) is capable of handling approximately 107events per second, e.g., as determined by the response time of the slowest element (shaper44). According to this example, setting n to be approximately equal to 10, i.e., having 10 channels, may allow circuit30(FIG. 2) to distinguish between individual events. In a more general example, for anodes that receive F events per second, wherein each signal circuit is capable of handling S events per second, then the number of channels n allowing circuit30(FIG. 2) to distinguish between individual events may be approximated, for example, as follows: