Patent Description:
Many medical imaging systems, such as positron emission tomography/computed tomography (PET/CT) imaging systems, are cooled by a cooling media such as liquid, air or a combination of liquid and air. With respect to air cooled imaging systems, it is desirable that the ambient air temperature in a scan room at a customer site wherein the imaging system operates be within a required operating temperature range for proper operation of the imaging system. The room temperature range required for proper operation of the imaging system is frequently too narrow for the needs of the customer site. Some customer sites have a room temperature that is lower than the required lower temperature limit for proper operation of the imaging system whereas other sites have a room temperature that is above the required upper limit for proper operation of the imaging system. When the room temperature is outside of the operating temperature range of the imaging system, warning and error indications are generated by the imaging system which may cause the imaging system to undesirably shut down.

Referring to <FIG>, an exemplary conventional air cooling system <NUM> for cooling a component <NUM> of an imaging system is shown. The cooling system <NUM> includes inlet <NUM> and outlet <NUM> conduits and a fan <NUM> located in the inlet conduit <NUM>. The cooling system <NUM> also includes a controller <NUM> that regulates a fan speed of the fan <NUM> in response to scan room ambient and component temperatures detected by scan room <NUM> and component <NUM> temperature sensors, respectively. In use, cooling air at atmospheric pressure is drawn through an air filter <NUM> and into the inlet conduit <NUM> by the fan <NUM> and flows through a low pressure zone <NUM> located before the fan <NUM>. The air then flows over the component <NUM> and dissipates heat from the component <NUM> thus cooling the component <NUM> and warming the air. Warm air at a relatively high pressure then exits from the outlet conduit <NUM>.

The conventional method to cooling has been to drive air in an open loop by controlling fan speed which changes the air flow rate through the cooling system <NUM>. In this method, fan speed is reduced when the scan room is relatively cold and then increased as the scan room temperature rises. Further, internal imaging system temperatures change with room temperature. When fan speed decreases, the internal imaging system temperature increases and when fan speed increases, the internal imaging system temperatures decrease. The cooling system <NUM> is driven by the ambient air room temperature and the heat load generated by the imaging system which may result in the exposure of internal imaging system components to a wide range of temperatures. For example, the range of controlled temperatures is normally set at a relatively wide temperature range (<NUM>-<NUM>, or <NUM> for example) since this is a function of the ambient air temperature (<NUM>-<NUM>, for example) and the heat being dissipated in the imaging system. However, the cooling system <NUM> may not be able to maintain the temperature of the components being cooled in their operating or targeted range when the ambient air room temperature goes outside specified limits. Further, in components such as silicon photomultipliers (SiPM) detectors used in PET/CT imaging systems, a temperature compensation circuit having a detector compensation algorithm is utilized to correct for temperature variability in the detector. However, the targeted temperature range (i.e., the range of controlled temperatures) can vary by more than <NUM>, for example. With such a range, the detector compensation algorithm becomes more difficult to characterize.

<CIT> may be considered to disclose a method of cooling at least one component of an imaging system located in a scan room, comprising: providing inlet and outlet air passageways to enable air flow into and out of the component; providing a return air passageway to enable a portion of warm outlet air from the component to flow in the return air passageway to provide recirculated air to a mixing zone in the inlet air passageway; mixing air with the recirculated air in the mixing zone to form mixed air wherein the mixed air flows over the component to cool the component and wherein the mixed air absorbs heat that warms the mixed air to form the warm outlet air. The document also may be considered to disclose the corresponding system.

A cooling system for cooling at least one component of an imaging system located in a scan room is disclosed. The system includes inlet and outlet channels in air flow communication with the component and a return channel in air flow communication with the inlet and outlet channels, wherein a portion of warm outlet air from a component outlet flows in the return channel to provide warm recirculated air to a mixing zone in the inlet channel. The system also includes a fan located in the inlet channel that draws scan room air into the inlet channel wherein the room air is mixed with the warm recirculated air in the mixing zone to form mixed air that flows over the component to cool the component and wherein the mixed air absorbs heat that warms the mixed air to form the warm outlet air. Further the system includes a valve located in the return channel, wherein the valve restricts or allows additional warm recirculated air to flow through the return channel to the mixing zone to mix with the scan room air to maintain a desired control temperature for the cooling system.

Those skilled in the art may apply the respective features of the present invention jointly or severally in any combination or sub-combination.

The exemplary embodiments of the invention are further described in the following detailed description in conjunction with the accompanying drawings, in which:.

Although various embodiments that incorporate the teachings of the present disclosure have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings. The scope of the disclosure is not limited in its application to the exemplary embodiment details of construction and the arrangement of components set forth in the description or illustrated in the drawings. The disclosure encompasses other embodiments and of being practiced or of being carried out in various ways. Unless specified or limited otherwise, the terms "mounted," "connected," "supported," and "coupled" and variations thereof are used broadly and encompass direct and indirect mountings, connections, supports, and couplings.

Referring to <FIG>, a perspective view of an exemplary medical imaging system <NUM> in accordance with an aspect of the invention is shown. The invention may be used in conjunction with a positron emission tomography/computed tomography (PET/CT) imaging system <NUM> having a CT portion <NUM> and a PET portion <NUM> although it is understood that the invention may be used in other types of imaging systems. The CT portion <NUM> includes a recording unit, comprising an X-ray source <NUM> and an X-ray detector <NUM>. The recording unit rotates about a longitudinal axis <NUM> during the recording of a tomographic image, and the X-ray source <NUM> emits X-rays <NUM> during a spiral recording. While an image is being recorded a patient <NUM> lies on a moveable bed <NUM> located on a table base <NUM>. The bed <NUM> is designed to move the patient <NUM> along a recording direction through an opening or tunnel <NUM> of a gantry <NUM> of the imaging system <NUM>. The table base <NUM> includes a control unit <NUM> connected to a computer <NUM> to exchange data. The computer <NUM> includes a determination unit <NUM> in the form of a computer program that can be executed on the computer <NUM>. The computer <NUM> is connected to an output unit <NUM> and an input unit <NUM>. The output unit <NUM> is, for example, one (or more) liquid crystal display (LCD) or plasma screen(s). An output <NUM> on the output unit <NUM> comprises, for example, a graphical user interface for actuating the individual units of the imaging system <NUM> and the control unit <NUM>. The input unit <NUM> is for example a keyboard, mouse, touch screen or a microphone for speech input.

Referring to <FIG>, the PET portion <NUM> includes a plurality of PET detector rings <NUM> arranged about the longitudinal axis <NUM>. For purposes of illustration, exemplary first <NUM>, second <NUM>, third <NUM> and fourth <NUM> detector rings are shown. Each detector ring <NUM>, <NUM>, <NUM>, <NUM> includes a plurality of PET detectors <NUM> used to scan the patient <NUM> located in the tunnel <NUM>. During a known operation of the PET portion <NUM> of imaging system <NUM>, a patient <NUM> located in the tunnel <NUM> is injected with a radioisotope. The radioisotope undergoes positron emission decay and emits a positron that encounters and annihilates with an electron to produce a pair of gamma rays moving in approximately opposite directions. The gamma rays are detected by the PET detectors <NUM> and information from the gamma rays is used to generate PET images. The PET images are then used in conjunction with CT images generated by the CT portion <NUM> of imaging system <NUM> to provide images of the patient <NUM> or part of a patient's anatomy. Each PET detector <NUM> generates heat during operation of the PET portion <NUM>.

Referring to <FIG>, an embodiment of a feedback air cooling system <NUM> for cooling at least one component <NUM> of an imaging system <NUM> is shown. By way of example, the imaging system <NUM> may be the PET/CT imaging system <NUM> and the component <NUM> may be a PET detector <NUM> although it is understood that other types of imaging systems and associated components are within the scope of the invention. In accordance with an aspect of the invention, a cooling fluid such as air is used to cool the component although a liquid, or combination of liquid and air, may be used. For purposes of illustration, the invention will be described in connection with a PET/CT imaging system <NUM> that uses air as a cooling fluid.

The cooling system <NUM> includes inlet <NUM> and outlet <NUM> channels that are in air flow communication with the component <NUM> to be cooled and a return channel <NUM> that is in air flow communication with the outlet <NUM> and inlet <NUM> channels. The cooling system <NUM> also includes at least one variable speed fan <NUM> and at least one valve <NUM> that are each connected to a controller <NUM> by respective control lines <NUM>. In an embodiment, the fan <NUM> is located in the inlet channel <NUM> and the valve <NUM> is located in the return channel <NUM>. In other embodiments, the fan <NUM> and valve <NUM> may be located in other suitable positions in the cooling system <NUM> in addition to or instead of the inlet <NUM> and return <NUM> channels. The cooling system <NUM> further includes first <NUM>, second <NUM>, third <NUM> and fourth <NUM> temperature sensors located in the scan room, the inlet channel <NUM>, on the component <NUM> and in the return channel <NUM>, respectively, that provide temperature data to the controller via respective signal lines <NUM> connected between the first <NUM>, second <NUM>, third <NUM> and fourth <NUM> temperature sensors and the controller <NUM>. The valve <NUM> is an electronically actuated valve controlled by the controller <NUM> to partially open as desired. In an embodiment, the valve <NUM> may be an electronically actuated butterfly valve. The controller <NUM> also controls a fan speed of the fan <NUM> to provide a desired flow of mixed air <NUM> to the component <NUM>.

In operation, the fan <NUM> draws in scan room ambient air <NUM> at atmospheric pressure through a filter <NUM> located on an inlet end <NUM> of the inlet channel <NUM>. The room air <NUM> then flows through a low pressure zone <NUM> formed before the fan <NUM> and subsequently past the fan <NUM> and the component <NUM> to dissipate heat from the component <NUM>. This cools the component <NUM> and forms warm outlet air <NUM> that exits a component outlet <NUM> at high pressure <NUM>. When the valve <NUM> is partially opened, a portion of warm outlet air <NUM> from the component outlet <NUM> flows through the return channel <NUM> to provide warm recirculated air <NUM> to an air mixing zone <NUM> in the inlet channel <NUM>. In the mixing zone <NUM>, the warm recirculated air <NUM> is mixed with the room air <NUM> by the fan <NUM> to form mixed air <NUM> that subsequently flows past the component <NUM> to cool the component <NUM> and forms the warm outlet air <NUM>. A remaining portion of the warm outlet air <NUM> that does not flow into the return channel <NUM> (i.e., exhaust air <NUM>) exits an outlet end <NUM> of the outlet channel <NUM>.

The mixing of warm recirculated air <NUM> with room air <NUM> provides mixed air <NUM> that is warmer than the room air <NUM>. The second temperature sensor <NUM> is positioned in the inlet channel <NUM> after the mixing zone <NUM> to provide mixed air temperature data to the controller <NUM>. The controller <NUM> may vary a valve opening of the valve <NUM> to restrict or allow additional warm recirculated air <NUM> into the return channel <NUM> and subsequently the mixing zone <NUM> based on the detected mixed air temperature provided by the second temperature sensor <NUM> in order to maintain a desired target or control temperature. The controller <NUM> may also adjust a fan speed of the fan <NUM> in order to maintain the control temperature and/or provide a desired air flow rate. In accordance with an embodiment of the invention, this provides a range of control temperatures for the mixed air <NUM> that is sufficient for cooling the component <NUM> and narrower than in conventional cooling systems. In addition, a control temperature of the cooling system can be set at a higher temperature to enable higher air flow into the cooling system.

It has been found that when the air speed of scan room air flowing across PET detectors is low, an undesirable temperature gradient develops across the PET detectors in an axial direction substantially parallel to the longitudinal axis <NUM>. <FIG> is a schematic representation of a temperature gradient <NUM> in an axial direction <NUM> substantially parallel to the longitudinal axis <NUM> (<FIG>) for exemplary PET detectors <NUM>-<NUM> (referenced as Det. <NUM> - Det. <NUM>) in a PET portion <NUM> (<FIG>) having eight PET detector rings. Each PET detector <NUM>-<NUM> generates heat during operation of the PET portions <NUM>. An amount of heat Q is transferred from each PET detector <NUM>-<NUM> to cooling air (depicted by arrow <NUM>) flowing at a relatively low air flow rate in the axial direction <NUM>. When using a relatively low air flow rate, the temperature of PET detector <NUM> is much less than that of PET detector <NUM>, for example, thus forming a relatively large temperature difference between the first PET detector (PET detector <NUM>) and last PET detector (PET detector <NUM>).

<FIG> is a schematic representation of a temperature gradient <NUM> in the axial direction <NUM> when the cooling air <NUM> flows at a higher air flow rate. When this occurs, the amount of heat Q transferred from each PET detector <NUM>-<NUM> to cooling air <NUM> flowing at a higher air flow rate is greater than that transferred at the lower air flow rate. This results in the temperature of PET detector <NUM> (the first PET detector) being much closer to that of PET detector <NUM> (the last PET detector), for example. In accordance with an aspect of the invention, the temperature difference between the PET detector <NUM> and PET detector <NUM> in the axial series is minimized by keeping the mixed air temperature <NUM> in a narrow range and the air flow rate high.

The invention may be used in PET systems having a long axial field of view (FoV), for example, an axial FoV of more than approximately <NUM>, wherein a higher air flow across the PET detectors lowers the temperature gradient across the PET detectors in the axial direction <NUM>, as shown in <FIG>. Additionally, the invention may be used in PET systems having a relatively short axial FoV (for example, a FoV of less than approximately <NUM>). In particular, a PET system having a short axial FoV may not provide sufficient heat dissipation to satisfy a lower temperature boundary and a slowest fan speed. The current invention enables additional air flow (i.e., a higher flow rate) in a short axial FoV system when the ambient air room temperature is low by opening the valve <NUM> to mix additional warm outlet air <NUM> into the cooling system <NUM>. In accordance with an aspect of the invention, the range of the control temperatures can be set to a narrower range than conventional cooling systems. In an embodiment, the range of control temperatures is approximately <NUM>-<NUM>.

<FIG> is a schematic representation of temperature gradients for a PET portion <NUM> having a short axial FoV when using the conventional cooling system <NUM> (i.e., open loop system) under cold and warm ambient conditions. The PET portion <NUM> includes exemplary PET detectors <NUM>-<NUM> (referenced as Det. <NUM> - Det. <NUM>) having three PET detector rings that form a short axial FoV system. A temperature gradient <NUM> under cold ambient temperature conditions and a low air flow rate indicates that the amount of heat transferred Q from each PET detectors <NUM>-<NUM> is less than the amount of heat transferred Q under warm ambient temperature conditions and a high air flow rate as indicated by temperature gradient <NUM>.

<FIG> is a schematic representation of temperature gradients for a PET portion <NUM> having a short axial FoV when using the cooling system <NUM> of the invention (i.e., warm air feedback) under cold and warm ambient conditions. In particular, <FIG> shows that a temperature gradient <NUM> under cold ambient temperature conditions and a low air flow rate is substantially similar to a temperature gradient <NUM> under warm ambient temperature conditions and a high air flow rate.

In addition to the advantages described above, the invention enables the use of a simplified detector compensation algorithms for the SiPM detectors used in PET/CT imaging systems. Further, the invention avoids the use of inline heaters to warm inlet air flow which would increase cost and power usage and undesirably increase the carbon footprint of an imaging system.

Claim 1:
A cooling system (<NUM>) for cooling at least one component (<NUM>) of an imaging system (<NUM>) located in a scan room, comprising:
inlet (<NUM>) and outlet (<NUM>) channels in air flow communication with the component (<NUM>);
a return channel (<NUM>) in air flow communication with the inlet (<NUM>) and outlet (<NUM>) channels, wherein a portion of warm outlet air (<NUM>) from a component outlet (<NUM>) flows in the return channel (<NUM>) to provide warm recirculated air (<NUM>) to a mixing zone (<NUM>) in the inlet channel (<NUM>); and
a fan (<NUM>) located in the inlet channel (<NUM>), wherein the fan (<NUM>) draws scan room air (<NUM>) into the inlet channel (<NUM>) and wherein the scan room air (<NUM>) is mixed with the warm recirculated air (<NUM>) in the mixing zone (<NUM>) to form mixed air (<NUM>) wherein the mixed air (<NUM>) flows over the component (<NUM>) to cool the component (<NUM>) and wherein the mixed air (<NUM>) absorbs heat that warms the mixed air (<NUM>) to form the warm outlet air (<NUM>).