Patent Description:
Diagnostic medical imaging apparatuses include, by way of non-limiting example computed tomography (CT), two-dimensional digital radiography (DR), positron emission tomography (PET), magnetic resonance imaging (MRI), PET/CT, and PET/MRI modalities. Many of these imaging apparatuses or systems include a toroidal-shaped gantry structure through which is inserted a patient table. The gantry includes one or more electromagnetic radiation detectors, which emit electrons in response to incident photons of electromagnetic radiation. In some modalities, the incident photons are transmitted X-rays or ionized radiation emissions at the higher end of the electromagnetic frequency range, while in other modalities the incident photons are within the radio frequency range. The output electrons of the detector are processed by detector electronics to generate detector output signals, which are subsequently processed by the imaging apparatus to generate patient images. Exemplary electromagnetic radiation detectors include photomultiplier tubes (PMTs) and silicon photomultipliers (SiPMs). Detector electronic packages are often housed with the detectors within the gantry structure. In order to generate usable patient image information during a patient scan, the detectors and detector electronic packages are maintained within relatively narrow temperature fluctuation and operational temperature bandwidths. Exceeding the desired temperature fluctuations and operational temperature bandwidths may result in inaccurate detector readings and/or excessive noise generation components in the readings, leading to a poorer quality set of patient images.

During and between patient scans, gantries and other components of imaging systems generate cyclic, fluctuating heat. In order to maintain detectors and detector electronics within desired temperature bandwidths, heat generated within the gantry structure is transferred out of the gantry. Known gantry cooling systems for medical imaging apparatuses typically transfer heat from the gantry into the ambient air of the imaging room, resulting in spikes of increased room temperature during and after a patient scan. Such gantry cooling systems are known e.g. from <CIT>. The increasing imaging room temperature is uncomfortable for patients and medical technicians in the room, often requiring use of air conditioning systems to cool the room. Sporadically increasing ambient room temperature through sequentially scheduled patient scans over the course of the day also raises internal gantry temperature - potentially raising the internal gantry temperature above the desired detector operating temperature bandwidth.

Exemplary embodiments described herein transfer imaging apparatus generated heat, including gantry heat, to solid material heatsinks, by circulating fluid in coolant lines passing through the gantry and the heatsink. The solid material heatsinks have relatively large, steady-state heat capacitance, capable of absorbing cycles of transient heat generated during one or more patient imaging scans. In some embodiments, the heatsinks are coupled to the medical imaging apparatus, or are located remote the apparatus, in building structure within or outside of the imaging room that houses the imaging apparatus. In some embodiments, the heatsinks are incorporated directly within the building structure, or in ground. Heatsinks integral with the building structural floor, walls, ceiling of the imaging room save floor space in the imaging room. Transferring gantry or other apparatus generated heat to thermal mass of a solid material heatsink, by circulating coolant fluid within the fluid coolant lines, reduces waste heat that would otherwise raise ambient temperature of the imaging room during any individual patent scan. In some embodiments, the only energy required to transfer gantry heat to the solid heat sink is for operation of a low pressure, coolant circulating pump. In some embodiments, the gantry waste heat is recycled to reduce total energy use of the building structure housing the medical imaging apparatus. For example, in some embodiments, heat retained within the heatsink is utilized for steady-state, passive heating of the imaging room. In other embodiments, heat retained within the heatsink is subsequently used by building environmental control systems (e.g., HVAC systems) and/or domestic hot water heating systems.

Exemplary embodiments feature a cooling system for a gantry of a diagnostic medical imaging apparatus that is oriented in an imaging room of a building structure. Diagnostic medical imaging apparatuses include, by way of non-limiting example computed tomography (CT), two-dimensional digital radiography (DR), positron emission tomography (PET), magnetic resonance imaging (MRI), PET/CT, and PET/MRI modalities. The imaging apparatuses or systems respectively include a gantry structure, having therein one or more electromagnetic radiation detectors and a first coolant passage for absorption of heat generated within the gantry. The gantry includes one or more electromagnetic radiation detectors, which emit electrons in response to incident photons of electromagnetic radiation. In some modalities, the incident photons are transmitted X-rays or ionized radiation emissions at the higher end of the electromagnetic frequency range, while in other modalities the incident photons are within the radio frequency range. A solid material heatsink, having enough thermal mass to receive and absorb all heat generated within the gantry, is oriented external the gantry. The heatsink defines a second coolant passage. A coolant fluid conduit couples the first and second coolant passages in at least one closed fluid loop. A coolant fluid circulates within the at least one closed fluid loop of the coolant fluid conduit, for transferring heat generated within the gantry from the first coolant passage to the second coolant passage defined within the heat sink. The second coolant passage transfers the gantry heat from the coolant fluid to the heatsink by thermal conduction.

Other exemplary embodiments feature a method for cooling a gantry of a diagnostic medical imaging apparatus, by orienting a medical imaging apparatus in an imaging room of building structure. The medical imaging apparatus has a gantry, which includes therein at least one electromagnetic radiation detector and a first coolant passage for absorption of heat generated within the gantry. A solid material heatsink is oriented external the gantry. The heatsink has enough thermal mass to receive and absorb all heat generated within the gantry. The heatsink defines a second coolant passage. The first and second coolant passages are coupled in at least one closed fluid loop, with a coolant fluid conduit. Coolant fluid is circulated within the coolant fluid conduit, for transferring heat generated within the gantry from the first coolant passage to the second coolant passage defined within the heatsink. The second coolant passage transfers the gantry heat from the coolant fluid to the heatsink by thermal conduction.

The respective features of the exemplary embodiments that are described herein are applied jointly or severally in any combination or sub-combination.

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

The figures are not drawn to scale.

Exemplary embodiments are utilized in a gantry cooling system of a diagnostic medical imaging apparatus, which transfers gantry heat and other apparatus generated heat to a solid material heatsink, via a circulating-fluid coolant conduit. The solid material heatsink has enough thermal mass to receive and absorb all heat generated within the gantry. In some exemplary embodiments, the heatsink is a slab of concrete, with embedded coolant conduit loops, located in the ground or within the building structure housing the apparatus. In other exemplary embodiments, the heat sink is a structural building panel, with embedded coolant conduit loops, used to form walls, floors, and/or ceilings of an imaging room that houses the medical imaging apparatus. Advantageously, in some embodiments, gantry heat transferred to and retained within the heatsink is released into the building structure's ambient air by convection, for energy-efficient passive heating, or as a regenerative heat source for the building's HVAC environmental control system and/or domestic hot water heating system. Some embodiments of the heatsink are retrofitted to existing types of gantry cooling systems, including those in the field already incorporating air-fluid or fluid-fluid heat exchangers. Other embodiments of the heatsink are incorporated into revised designs of gantry cooling systems, in newly manufactured medical imaging apparatuses. Some embodiments of the solid material heatsink are coupled directly to the medical imaging apparatus.

Exemplary cooling system embodiments described herein reduce detector and/or detector electronics package temperature fluctuations to less than <NUM> degree Celsius (<NUM>) within a single patient imaging scan and temperature variation bandwidth among a plurality of sequential patient scans within six degrees Celsius (<NUM>), to generate usable patient image information. In other embodiments, the cooling systems reduce detector and/or detector electronics package temperature fluctuations to less than one-half degree Celsius (<NUM>) within a single patient imaging scan and temperature variation bandwidth among a plurality of sequential patient scans within two degrees Celsius (<NUM>).

<FIG> shows a building structure <NUM>, including an imaging room <NUM> with a floor <NUM>, walls <NUM> and a ceiling <NUM>; typically constructed of concrete or other dense material for structural support and electromagnetic isolation within the room. A medical imaging apparatus <NUM>, such as a PET scanner, includes a gantry <NUM> with a toroidal central bore circumscribing a patient table <NUM>. The gantry <NUM> houses one or more electromagnetic radiation detectors <NUM> and one or more electronics packages <NUM>, with only one of each shown for illustrative purposes. Heat Q is generated within the gantry <NUM> during scanner operation, which will otherwise raise internal temperature of the imaging apparatus, as well as the ambient temperature of the imaging room <NUM>. A gantry cooling system <NUM> transfers the heat Q from the gantry <NUM> to a heatsink <NUM>, comprising a solid thermal mass, via a coolant fluid conduit <NUM>. The coolant fluid conduit <NUM> is a fluid loop, comprising a first coolant passage <NUM>, shown as a coolant pipe for illustrative purposes, in the gantry <NUM> and a second coolant fluid passage <NUM>, shown as a serpentine coolant pipe loop for illustrative purposes, embedded in the heatsink <NUM>. Either of the types of first <NUM> or second <NUM> coolant passages are selectively constructed to exchange heat with fluid coolant, including by way of nonlimiting example any one or more of finned or non-finned heat plates, tubing, fluid-fluid heat exchangers, air-fluid heat exchangers, embedded cooling passages within components, condensers, and evaporators. While the embodiment of <FIG> has a single continuous coolant fluid conduit <NUM>, other embodiments comprise plural fluid conduits, including parallel or series cooling loop and/or subloops in fluid communication with the coolant fluid conduit.

A variable-speed circulating pump <NUM> circulates coolant fluid within the coolant fluid conduit <NUM>. A thermal controller <NUM> selectively varies flow rate of the circulating pump <NUM> at least partially based on temperature T, sensed by a temperature sensor <NUM> in the gantry <NUM>. In some embodiments, the thermal controller <NUM> is in a feedback loop with the temperature sensor <NUM>, to maintain gantry operational temperature within a defined bandwidth during imaging apparatus <NUM> operation over plural patient imaging scans and to maintain a defined temperature fluctuation parameters within any individual imaging scan. In some embodiments, there is no thermal controller or temperature sensor: the circulating pump is a non-variable speed pump or alternatively, a variable-speed pump operated at a designated flow rate. In some embodiments, there is no circulating pump; coolant fluid circulates only by thermal convection. In embodiments where the coolant fluid conduit comprises multiple subloops and/or branches, circulating pumps are selectively incorporated in one or more of them: with or without a thermal controller and/or a temperature sensor.

In <FIG>, the variable-speed circulating pump <NUM> circulates coolant fluid within the coolant fluid conduit <NUM>, which transfers heat Q generated within the gantry <NUM> from the coolant pipe of the first coolant passage <NUM> to the serpentine coolant pipe loop of the second coolant passage <NUM>, defined within the heatsink <NUM>. The solid material forming the heatsink is concrete, which also forms the floor <NUM> of the imaging room <NUM>.

When building a new imaging room <NUM>, the serpentine coolant pipe loop or any other desired fluid conduit pattern of the second coolant passage <NUM> is easily embedded into a newly poured concrete floor slab <NUM>, or walls <NUM> or ceiling <NUM>. Concrete is often utilized in new imaging room <NUM> construction for its excellent electromagnetic energy isolation properties. Concrete has a relatively high thermal capacitance, Cp of approximately <NUM> kilo- Joules/Kg-°C. As will be described in modeling below, a heatsink comprising a concrete floor slab, roughly approximating the floor space of a typical imaging room has sufficient thermal mass to absorb all gantry heat generated during a typical eight hour work shift, while only warming the floor less than thirteen degrees Celsius. The concrete floor slab radiates heat back to the imaging room relatively slowly, which advantageously allows patients and imaging staff to walk comfortably on a warm floor during work shifts, and helps maintain the imaging room at a more comfortable ambient temperature between work shifts.

Referring to <FIG>, modular panels <NUM>, (e.g., concrete, metal, or other solid building material), comprise the heatsink <NUM>. The modular panels <NUM> provide a useful alternative to poured-in-place, heatsinks, when a new or remodeled imaging room is constructed with prefabricated panels. A serpentine coolant pipe loop comprises the second coolant fluid passage <NUM>, which is embedded or otherwise coupled to the modular panel <NUM>, to form the heatsink <NUM>. The modular panels <NUM> are used to form imaging room ceilings, walls, and/or floors. In some embodiments, one or more modular panels <NUM> are laid over an existing building floor or affixed to existing walls or ceiling. One or more modular panels <NUM> are coupled to the coolant fluid conduit <NUM> and the first coolant passage <NUM> of the gantry, in a continuous loop or a plurality of branched loops, to complete the cooling system <NUM>. In some embodiments, the modular panel <NUM> is coupled directly to the medical imaging apparatus, rather than being integrated or otherwise coupled to the imaging room's building structure or other portion of the building.

, the gantry cooling system <NUM> waste heat generated within the gantry <NUM> and stored within the heatsink <NUM> heats the building structure's environmental control system and/or domestic hot water system. Specifically, the coolant fluid conduit <NUM> transfers gantry heat absorbed by the first coolant passage <NUM> to the second coolant passage <NUM> of the heatsink <NUM>. Heat Q within the heatsink <NUM> flows to the building's HVAC system <NUM> via an HVAC coolant loop <NUM> and flows to the building's domestic hot water system through the hot-water heat exchanger <NUM> via a hot-water feed loop <NUM>. Heated domestic water feeds through hot water line <NUM>, for example to a faucet or tap <NUM>.

The gantry cooling system <NUM> of <FIG> interposes a fluid-fluid heat exchanger <NUM> in the coolant fluid conduit <NUM>, between the first coolant passage <NUM> of the gantry <NUM> and the second coolant passage <NUM> of the heatsink <NUM>. In some embodiments, the heat exchanger <NUM> is oriented in the gantry <NUM>. In other embodiments, the heat exchanger <NUM> is oriented elsewhere in the medical imaging apparatus or in a remote location inside or outside of the imaging room. A first coolant conduit subloop <NUM> transfers heat from the gantry <NUM> to the heat exchanger <NUM>. The gantry heat in turn is transferred in a second coolant conduit subloop <NUM> to the heatsink <NUM>. Advantageously, the embodiment of <FIG> facilitates retrofitting of the heatsink <NUM> to an existing design fluid-fluid gantry cooling system in an existing imaging system design - whether for an existing apparatus or for a newly manufactured apparatus.

The gantry cooling system <NUM> of <FIG> utilizes an air-fluid heat exchanger <NUM> in the gantry <NUM>. Cooling air is circulated within the gantry <NUM>, passing over the coolant-filled tubes in the heat exchanger <NUM> that form the first coolant passage <NUM>. Coolant fluid in the coolant fluid conduit <NUM> circulates between the air-fluid heat exchanger <NUM> and the second coolant passage <NUM> of the heatsink <NUM>. Advantageously the embodiment of <FIG> facilitates retrofitting of the heatsink <NUM> to an existing design air-fluid gantry cooling system in an existing imaging system design - whether for an existing apparatus or for a newly manufactured apparatus.

The gantry cooling systems of <FIG> utilize known liquid and mixed phase liquid/gaseous coolant fluids, including by way of non-limiting example: glycol, water, water-glycol, oil, and ammonia. The cooling systems <NUM> described herein utilize any known type of coolant fluid used in medical imaging apparatuses.

The cooling system embodiment of <FIG> incorporates a mixed-phase (i.e., liquid and gas mixture) coolant. Exemplary ammonia or chlorofluorocarbon coolant media are circulated within a coolant fluid conduit <NUM> between an evaporator <NUM> in the gantry <NUM> and a condenser <NUM> formed in the heatsink <NUM>. Liquid coolant is compressed in a compressor or pump <NUM> into expansion valve <NUM>, exiting as a gaseous coolant, which absorbs heat in the evaporator <NUM>. The gaseous coolant re-condenses to liquid form in the condenser <NUM>, transferring the gantry heat to the heatsink <NUM>. The evaporator <NUM> and condenser <NUM> are shown schematically for illustrative purposes.

In <FIG>, the coolant fluid conduit <NUM> of the cooling system <NUM> incorporates a first coolant passage <NUM> for general gantry <NUM> cooling, and a branch or subloop comprising coolant passage <NUM> and a cooling pipe <NUM> of the first coolant passage, respectively for direct cooling and thermal isolation of the detector <NUM> and the electronics package <NUM> from the general ambient temperature within the gantry. For illustrative purposes, the gantry structure <NUM> is shown schematically in dashed lines. In this embodiment, the coolant passage <NUM> is integrated into the structure of the detector <NUM>. The serpentine profile cooling pipe <NUM> abuts or otherwise is in direct thermal communication with one or more exterior surfaces of the electronics package <NUM>. The coolant fluid branch <NUM> and <NUM> and the first coolant passage <NUM> off the coolant fluid conduit <NUM> are joined in a shared fluid manifold <NUM>. In some embodiments, the fluid manifold includes coolant flow restrictors for varying coolant flow rates among the branches (not shown). In some embodiments comprising multiple parallel or branched cooling subloops of the first coolant passage <NUM> within the cooling system <NUM>, each subloop can vary heat transfer rates, during initial design or by field adjustment, to draw heat out of the gantry <NUM> to the second coolant passages <NUM> of the heatsink <NUM> and/or to isolate thermal zones within the gantry from higher temperature regions within the gantry. For example, an electromagnetic radiation source (not shown) within a gantry generates heat during operation. In some embodiments that source will have a dedicated, isolated first coolant passage subloop, filled with a coolant (e.g., oil), having a higher vaporizing temperature than other coolants in the cooling system, with its own dedicated fluid-fluid heat exchanger in thermal communication with the fluid coolant conduit. In some embodiments, other subloops of first coolant passages function as thermal isolators, such as the branch or subloop coolant passage <NUM> and the cooling pipe <NUM> of <FIG> that isolates the detector <NUM> and the electronics package <NUM> from higher temperature zones in the gantry <NUM>.

In the embodiment of <FIG>, the cooling system <NUM> incorporates a thermal controller <NUM>. In some embodiments, the thermal controller comprises digital electronic controller platform architecture and implementation by software modules executed by a computer processor. Exemplary embodiments of the thermal controller <NUM> are implemented in various forms of hardware, software, firmware, special purpose processors, or a combination thereof. Preferably, aspects of the embodiments are implemented in software as a program tangibly embodied on a program storage device. The program is uploaded to, and executed by, a machine comprising any suitable architecture. Preferably, the machine is implemented on a computer platform having hardware such as one or more central processing units (CPU), a random-access memory (RAM), and input/output (I/O) interface(s). The computer platform also includes an operating system and microinstruction code. The various coolant temperature sensing and fluid circulation processes and functions described herein are either part of the microinstruction code or part of the program (or combination thereof) which is executed via the operating system. In addition, various other peripheral devices may be connected to the computer/controller platform, such as the temperature sensor <NUM>.

Solid material heatsinks, such as the heatsink <NUM> embodiments described herein, utilize relatively large thermal mass to absorb heat generated within the gantry, or other components of a medical imaging apparatus during patient imaging procedures scheduled throughout a day. Imaging apparatus heat generation tends to be sporadic in nature, with heating spikes occurring during individual patient scans, followed by non-heat generating quiescent periods. In known gantry cooling systems that release gantry heat into the imaging room, ambient air temperature of the room spikes proportionally during a patient scanning procedure. In the cooling system embodiments described herein, thermal mass of the heatsink is selected, based on anticipated heat generation cycles of the medical imaging apparatus, including its gantry, during a designated time interval, and ability of the heatsink to release the retained heat slowly enough not to raise ambient temperature of the scanning room and/or the scanning detectors and/or the electronic packages of the medical imaging apparatus beyond permissible limits. For example, a heatsink embedded within a concrete floor of an imaging room can be sized to absorb transient heating cycles of a gantry of a medical imaging apparatus and release that absorbed transient heat back into the ambient air of imaging room at a rate that is not uncomfortable to patients or medical personnel occupying the room.

Using the following example, a heatsink formed within a concrete slab of a medical imaging room's floor absorbs all heat energy (E) generated by a PET scanner injecting a continuous <NUM>-kilowatt sustained waste heat load (Q) throughout total time (t) of an eight-hour shift of scheduled patient scans. The total generated heat energy (E) that can be absorbed by the concrete is approximately <NUM> kilojoules. It is unlikely that any PET scanner would be in continuous use for an eight-hour period, as there are inherent delays preparing individual patients for periodically scheduled scans. It is also overly pessimistic to assume that the concrete floor absorbs and retains <NUM>% of the PET scanner's waste heat (Q) over the entire eight-hour period. Thus, the following estimation of the concrete heatsink' s temperature rise is a worst-case assumption for modeling purposes. Assuming that the concrete slab is <NUM> thick, with a surface area of approximately <NUM><NUM>, the total volume (v) of concrete is approximately <NUM><NUM>. With an approximate concrete density (p) of <NUM>/m<NUM>, the total mass (M) of the concrete slab is approximately <NUM>. Heat capacitance of concrete (Cp) is approximately <NUM> kJ/kg-°C. Using the following formula, increase in temperature of the concrete (ΔT), i.e., final temperature (Tf) after slab heating minus initial slab temperature (Ti), will be:<MAT>.

The concrete's temperature rise (ΔT) is approximately <NUM> after absorbing the <NUM>-kJ heat energy load of the PET scanner, with the explicit assumption that the concrete heatsink retains all the heat load over the entire eight-hour shift. Assuming that prior to initiating the imaging scans at the beginning of the scanning shift the concrete floor's temperature was <NUM> (matching desired ambient temperature of the imaging room maintained by the building's HVAC system) and that the floor released no heat to its surroundings, floor temperature will rise <NUM> by the end of the scheduled eight hour shift, to an environmentally acceptable <NUM>. The absorbed heat is released back into the scanning room, until the heated floor surface again matches the room's <NUM> ambient temperature achieved again.

The same general heat transfer objectives are achievable with other suitably sized solid material heatsinks - whether embedded within building structural components or the ground or formed as stand-alone components in the imaging room or coupled directly to the medical imaging apparatus. By way of another exemplary embodiment, an imaging scanner apparatus incorporates the solid material heatsink within a mass of a seismic plate or electromagnetic shield that is coupled to the apparatus.

In many embodiments, operational energy needed to cool the gantry with a solid material heatsink described herein is reduced compared to known gantry cooling systems that dump gantry heat directly into the ambient air of the imaging room, which often require use of combinations of relatively noisy powered compressors, chillers and forced air fan ducts. Some cooling system embodiments described herein rely on thermal convection to circulate coolant fluid between the gantry and the heatsink. Others rely on relatively low energy consumption fluid circulating pumps to circulate coolant fluid relatively quietly.

The cooling system embodiments, including the solid material heatsinks described herein, offer a broad range of potential individual benefits, including: low maintenance and operating energy consumption, simple construction, low noise, as well as narrower bandwidths of temperature fluctuation during individual imaging scans and narrower bandwidths of temperature range over a plurality of sequential imaging scans. The heatsink embodiments described herein are easily incorporated into other imaging apparatus components (e.g., seismic plates or radiation shields) and in the floor, walls and/or ceilings of the imaging room structure and the surrounding building structure.

Claim 1:
A cooling system (<NUM>) for a gantry (<NUM>) of a diagnostic medical imaging apparatus (<NUM>), comprising:
a medical imaging apparatus (<NUM>) oriented in an imaging room (<NUM>) of a building structure (<NUM>);
a gantry (<NUM>) of the medical imaging apparatus, having therein at least one electromagnetic radiation detector (<NUM>) and a first coolant passage (<NUM>) for absorption of heat (Q) generated within the gantry;
a solid material heatsink (<NUM>), oriented externally to the gantry, the heatsink defining a second coolant passage (<NUM>);
a coolant fluid conduit (<NUM>) coupling the first and second coolant passages in at least one closed fluid loop; and
coolant fluid circulating within the at least one closed fluid loop of the coolant fluid conduit, for transferring heat generated within the gantry from the first coolant passage to the second coolant passage defined within the heat sink, the second coolant passage transferring the gantry heat from the coolant fluid to the heatsink by thermal conduction, characterised in that
the solid material heatsink has enough thermal mass to receive and absorb all heat generated within the gantry during patient imaging procedures.