System and method for predictive thermal output control of a medical device

A system and method for controlling thermal output of a medical device is disclosed. A thermal controller receives operational parameters for an impending use of a medical device and predicts a thermal output of the medical device from the operational parameters. The thermal controller compares the predicted thermal output to a desired limit on thermal output and, if the predicted thermal output exceeds the desired limit on thermal output, dynamically controls power consumption by the medical device to maintain an actual thermal output substantially at or below the desired limit on thermal output during use of the medical device.

BACKGROUND OF THE INVENTION

The present invention relates generally to medical devices and, more particularly, to a system and method for predictively controlling thermal output of a magnetic resonance (MR) imaging device.

When utilizing these signals to produce images, magnetic field gradients (Gx, Gy, and Gz) are employed. That is, active electric coils are used to drive the spatial gradients into the static magnetic B0field. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received NMR signals are digitized and processed to reconstruct the image using one of many well known reconstruction techniques.

Some imaging processes demand higher amplitude gradient fields, faster field transitions, and greater duty cycles to improve image resolution, contrast, and scan time. These processes, often referred to as enhanced imaging processes, typically require more power than non-enhanced processes and result in higher thermal dissipation within the MR imaging device. As such, for a given enhanced imaging process, the resulting thermal output of the MR imaging device may exceed desirable limits and, thus, it may not be possible to acquire data using the given process. Or, in some systems, a given scan may be interrupted as a result of an undesirable thermal dissipation.

That is, some MR imaging devices have a bore temperature monitoring system (BTMS) to monitor the temperature inside the bore. Specifically, the BTMS halts operation of the MR imaging device if a temperature in the bore has surpassed a desired level or limit. As such, the BTMS dynamically interrupts the scan to allow the temperature in and around the MR imaging device and, specifically, the bore, to decrease to the desirable level.

Relying solely on a BTMS to regulate the imaging process has some drawbacks. For example, a BTMS is a reactionary tool that only halts a given scan after bore temperature exceeds a given threshold. Furthermore, periodically halting operation of the MR imaging device to allow the bore temperature to drop injects undesirable delays into scheduled imaging processes and, as a result, increases scan time and negatively affects throughput. Accordingly, systems have been developed to avoid repeated engagement of the BTMS by setting a constant limit on a basic operating parameter of the MR imaging device, for example, coil current. That is, some MR imaging devices include software to limit temperatures by holding the root-mean-square (RMS) current levels used to generate the gradient fields to a predefined value.

Accordingly, these systems preclude prescription of enhanced imaging processes that would cause temperature levels to rise above desirable limits. However, by fixing the peak power supplied to a coil, these systems ignore the temporal response of the specific MR imaging device. That is, these systems, which employ hard limits, rely on assumptions concerning the use profile and boundary conditions of the MR imaging device and do not consider the actual thermal output of the MR device for a particular imaging process. Further, the assumptions concerning the use profile and boundary conditions of the MR imaging device are generally conservative so as to ensure that the MR imaging device is not driven to produce excessive temperatures.

As such, these predefined hard thresholds often limit the MR imaging device from performing many processes that the MR imaging device is otherwise capable of executing without producing excessive temperatures. That is, the MR imaging device is often conservatively controlled to not execute a given scan notwithstanding that the resulting thermal output would still remain below thermal limits. Specifically, because these predefined hard limits are based on quantities such as gradient current or power, they do not consider the actual temperatures in and around the MR imaging device, the frequency of the desired imaging process, the axes selection included in the desired imaging process, or the specific coils employed during the desired imaging process. Accordingly, the predefined limits, such as current limits, often restrict an operator from utilizing enhanced, or more aggressive, scanning procedures even through the associated temperatures would remain within acceptable limits. As a result, the diagnostic capability of the MR imaging is unnecessarily restricted.

It would therefore be desirable to have a system and method capable of dynamically controlling thermal output of a medical device. In particular, it would be desirable to have a system and method capable of predicting a thermal output of a medical device based on particulars of an impending use of the device and dynamically controlling the medical device substantially consistent with the particulars while maintaining the thermal output of the medical device within a desired temperature range. It would also be desirable to have a method and system to control power to coils of an MR device during execution of an enhanced imaging process without driving a bore temperature to a level in excess of a given value.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides a system and method for predictively controlling thermal output of a medical device. The thermal output of the medical device is predicted based on desired operational parameters. Power consumption of the medical device during use thereof is dynamically controlled to maintain an actual thermal output of the medical device within desired thermal limits. The invention is particularly advantageous for enhanced uses of the medical device where greater power consumption is typically experienced. The present invention also advantageously reduces power consumption of the device to permit implementation of enhanced protocols.

In accordance with one aspect of the invention, a thermal controller is disclosed that is configured to receive operational parameters for an impending use of a medical device and predict a thermal output of the medical device from the operational parameters. The thermal controller is further configured to compare the predicted thermal output to a desired limit on thermal output and, if the predicted thermal output exceeds the desired limit on thermal output, dynamically control power consumption by the medical device to maintain an actual thermal output substantially at or below the desired limit on thermal output during use of the medical device.

In accordance with another aspect, the invention includes a computer readable storage medium having a computer program stored thereon and representing a set of instructions that when executed by a computer of a medical imaging device, causes the computer to receive desired operational constraints for a scan to be performed with the medical imaging device from a user-input. The instructions further cause the computer to determine a potential thermal output of at least one heat-generating component of the medical imaging device from the desired operating constraints and a power to be delivered to the at least one heat-generating component during the scan. The computer is also caused to determine if the potential thermal output will cause an actual thermal output to surpass a desired limit on thermal output during the scan and, if the potential thermal output will cause the actual thermal output to surpass the desired limit on thermal output during the scan, adjust the power to be delivered to the at least one heat-generating component during the scan to substantially maintain the actual thermal output at or below the desired limit on thermal output when performing the scan according to the desired operating constraints.

According to another aspect of the invention, an MR imaging apparatus is disclosed that includes a plurality of gradient coils positioned about a bore of a magnet to impress a polarizing magnetic field, and an RF transceiver system and an RF switch controlled by a pulse module to transmit RF signals to an RF coil assembly to acquire MR images. The MR imaging apparatus also includes an operator console configured to receive operational characteristics of a desired imaging process and a computer. The computer is programmed to receive the operational characteristics of an impending MR scan from the operator console, determine a power delivery level to execute the impending MR scan according to the operational characteristics, and predict a thermal output to the bore of the magnet from the operational characteristics of the determined power delivery level. The computer is also programmed to predict a thermal output to the bore of the magnet to determine a predicted bore temperature, compare the predicted bore temperature to a desired limit threshold temperature, and, if the predicted bore temperature exceeds the desired threshold bore temperature, adjust the determined power delivery level to lower the predicted bore temperature.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring toFIG. 1, the major components of an MR imaging system10incorporating the present invention are shown. The operation of the system is controlled from an operator console or user input12which includes a keyboard or other input device13, a control panel14, and a display screen16. The input device13can include a mouse, joystick, keyboard, track ball, touch activated screen, light wand, voice control, or any similar or equivalent input device, and may be used for interactive geometry prescription. The console12communicates through a link18with a separate computer system20that enables an operator to control the production and display of images on the display screen16. The computer system20includes a number of modules which communicate with each other through a backplane20a. These include an image processor module22, a CPU module24and a memory module26, known in the art as a frame buffer for storing image data arrays. The computer system20is linked to disk storage28and tape drive30for storage of image data and programs, and communicates with a separate system control32through a high speed serial link34.

The system control32includes a set of modules connected together by a backplane32a. These include a CPU module36and a pulse generator module38which connects to the operator console12through a serial link40. It is through link40that the system control32receives commands from the operator to indicate the scan sequence and parameters thereof that is to be performed. The pulse generator module38operates the system components to carry out the desired scan sequence having the desired parameter to produce data that indicates the timing, strength and shape of the RF pulses produced, and the timing and length of the data acquisition window. The pulse generator module38connects to a set of gradient amplifiers42, to indicate the timing and shape of the gradient pulses that are produced during the scan. The pulse generator module38can also receive patient data from a physiological acquisition controller44that receives signals from a number of different sensors connected to the patient, such as ECG signals from electrodes attached to the patient. Additionally, the pulse generator module38connects to a scan room interface circuit46which receives signals from various sensors associated with the condition of the patient and the magnet system. It is also through the scan room interface circuit46that a patient positioning system48receives commands to move the patient to the desired position for the scan.

The gradient waveforms produced by the pulse generator module38are applied to the gradient amplifier system42having Gx, Gy, and Gzamplifiers. Each gradient amplifier excites a corresponding physical gradient coil in a gradient coil assembly generally designated50to produce the magnetic field gradients used for spatially encoding acquired signals. The gradient coil assembly50forms part of a magnet assembly52that surrounds a bore53and which may include a superconducting magnet54and/or a whole-body RF coil56. It is contemplated that magnet assembly52may include a cryostat and a cryocooler to cool the superconducting magnet54. While such cryocooler systems cool the superconducting magnet54, the gradient coil assembly50does generate heat that increases the temperature of the bore53. Therefore, one or more temperature sensors57are disposed in or about the gradient coil assembly50and are configured to communicate feedback indicating temperatures in or about the gradient coil assembly50that, as will be described, are used to control the temperature in the bore53.

A transceiver module58in the system control32produces pulses which are amplified by an RF amplifier60and coupled to the RF coil or antenna56by a transmit/receive switch62. Additionally, the MRI system may include an RF shield or RF shielding configured about the bore53to shield against extraneous RF signals. The resulting signals emitted by the excited nuclei in the patient may be sensed by the same RF coil56and coupled through the transmit/receive switch62to a preamplifier64. The amplified MR signals are demodulated, filtered, and digitized in the receiver section of the transceiver58. The transmit/receive switch62is controlled by a signal from the pulse generator module38to electrically connect the RF amplifier60to the coil56during the transmit mode and to connect the preamplifier64to the coil56during the receive mode. The transmit/receive switch62can also enable a separate RF coil (for example, a surface coil) to be used in either the transmit or receive mode. Additionally, as will be described, one or more temperature sensors65are disposed in or about the RF coil56and associated components and are configured to communicate feedback indicating temperatures in or about the RF coil56and associated components.

The MR signals picked up by the RF coil56are digitized by the transceiver module58and transferred to a memory module66in the system control32. A scan is complete when an array of raw k-space data has been acquired in the memory module66. This raw k-space data is rearranged into separate k-space data arrays for each image to be reconstructed, and each of these is input to an array processor68which operates to Fourier transform the data into an array of image data. This image data is conveyed through the serial link34to the computer system20where it is stored in memory, such as disk storage28. In response to commands received from the operator console12, this image data may be archived in long term storage, such as on the tape drive30, or it may be further processed by the image processor22and conveyed to the operator console12and presented on the display16.

As will be described in detail with respect toFIG. 2, the MR system10includes a thermal controller or thermal control system70. The thermal control system70includes a thermal controller72and, optionally, a bore temperature monitoring system (BTMS)74. The thermal control system70is configured to receive temperature feedback from the temperature sensors57,65, interpret the feedback, and communicate thermal control instructions to the system control32. As will be described, the thermal control system70and, more particularly, the thermal controller72, is configured to predict a thermal output of the MR system10and, more particularly, a temperature in the bore53, based on desired operational parameters input by a user via the operator console12or otherwise determined. Utilizing this predicted thermal output, the thermal control system70, and more particularly, the thermal controller72, is configured to dynamically control operational power of an impending scan while conforming to the operational parameters in order to maintain a desirable thermal output of the MR system10to, in turn, maintain a desirable temperature range within the bore53.

Referring now toFIG. 2, a flow chart setting forth the steps of a process80for controlling the thermal output of an MR imaging system is shown. The process80starts82upon receiving desired imaging process characteristics84. It is contemplated that the desired imaging process characteristics or constraints84include properties selected by an operator, such as those entered via operator console12ofFIG. 1, or properties derived from operator selections. For example, the imaging process characteristics84may include the type of imaging process desired (i.e. 2D, 3D, fast spin echo, and the like), slice selection image resolution, repetition time (TR), image axis (axial, coronal, sagittal, or oblique), gradient coils to be activated to encode a field-of-view (FOV) and/or weight and size of the subject to be imaged.

From the desired imaging process characteristics, command gradient fields86, (Gx, Gy, and Gz, typically measured in Gauss/cm) are determined. Accordingly, unlike traditional thermal limiting systems that employ a predetermined hard limit, the process80preferably adjusts the command gradient fields86to maintain system outputs, for example, bore temperature, specific absorption rate (SAR), and the like, within desirable limits without changing the process characteristics input by the user or otherwise determined.

The process80determines resistance and gain values specific to the particular components of the imaging device88. Specifically, the gain values (typically measured in Amps per G/cm) are preloaded for each coil set (Gx, Gy, and Gz) and the electrical resistances (R) are preloaded as a set of curves (ΔR vs. frequency) stored in memory and representing the effective resistance of each physical conductor. For example, the preloaded set of curves may include ΔR vs. frequency data for the gradient coils (Gx, Gy, and Gzfor inner & outer coils), any RF shielding, and the RF coil. It is contemplated that these ΔR vs. frequency curves may be acquired from impedance sweep data acquired during each stage of device or component assembly. More particularly, transient gradient fields are multiplied by appropriate gain values to quantify transient current levels in each coil. The resulting waveforms can be transformed to the frequency domain with a Fast Fourier transfer (FFT) to quantify the RMS current levels in each coil for each time period when each coil is energized. Additionally, the ΔR vs. frequency curves provide the effective resistance for each Fourier component of current magnitude and thus, as will be described, allow the prediction of total heat load in each conductor whenever a gradient coil is energized.

Accordingly, the desired power levels90attributable to the desired imaging process characteristics84and command gradient fields86when applied to the specific resistances and gains of the components of the imaging device88can be determined. As will be described, each component of the imaging device, as represented by their respective resistances and gains, forms a heat load when the desired power levels90are applied thereto. Furthermore, as will be described, the specific heat output from each heat-generating component, i.e. heat load, can be accurately predicted using a plurality of transfer functions92.

Specifically, power applied to a heat-generating component contributes to an actual temperature rise in the component. As such, a corresponding transfer function that is predefined with values that are particular to the component and heat source can be used to predict thermal characteristics of the component when power is applied thereto. In a preferred embodiment, a unique transfer function is defined for each heat-generating component. As such, temperature rises can be determined uniquely for each heat-generating component. Accordingly, in a preferred embodiment, a plurality of transfer functions92are used to predict temperature rises across multiple locations.

For example, one transfer function may convert the heat load from the inner Gzcoil to a temperature rise in the upper area of a gradient coil assembly at a location designated as Z=0. Therefore, this specific transfer function may be used to predict the actual temperature rise of the gradient coil assembly at the Z=0 location over multiple scan protocols. Similarly, a transfer function may be defined and used to predictably determine the thermal output of any heat-generating component at any position without requiring the transfer function to be tailored to a specific scan protocol.

According to one embodiment, the plurality of transfer functions92includes transfer functions94,96having values designed to correspond to conductors that reside within the gradient coil assembly50ofFIG. 1and/or any RF shield. Additionally, the plurality of transfer functions92includes transfer functions98,100having values designed to correspond to all conductors in the patient bore, for example, the RF coil56ofFIG. 1.

As the location where temperature information is needed is dependent upon the operating temperature profile of the particular MR scanner model, it is contemplated that the plurality of transfer functions92may be tailored to include values specific to a particular model or device. Additionally, as will be described, it is contemplated that the system may be designed to dynamically adjust the transfer functions to adapt generalized transfer functions to device-specific transfer functions over time.

With respect to the individual transfer functions94-100, it is contemplated that the transfer functions may be linear first order transfer functions that are mathematical representations modeling the temporal response of the heating of solid objects. That is, each transfer function utilizes a single heat load (q, typically measured in Watts) to generate a single value that is the change in temperature (ΔT, usually measured in degrees Celsius) resulting from q. Thus, any defined heat load q, which will generally vary in time, may be used to predict the resulting temperature change ΔT, which also varies in time. This mathematical relationship may be reduced to require two properties of the object to be quantified as values. Specifically, a value “A” represents the value that ΔT changes after prolonged exposure to a constant heat load of unit value and a value “τ” that represents the time constant which defines how quickly ΔT changes to variations in q. Additionally, a value “s” represents a mathematical transformation of the temporal characteristics of the heat load q. According, the linear first order transfer function can be represented as follows:

The above-described linear first order transfer function transforms one input, q, to one output, ΔT. However, this transfer function is just one of many mathematical formats that can be used to predict the thermal response of a component or location in response to a particular desired operation. Accordingly, it is contemplated that other forms of transfer functions may be equivalently utilized, such as the differential equation form of Eqn. 1 shown as follows:

m⁢⁢c⁢ⅆTⅆt=q-Δ⁢⁢TR;Eqn.⁢2
where “m” is the object mass, “c” is the specific heat of object, “dT/dt” is the temporal rate of change of the object temperature, “q” is the heat load into the object, “ΔT” is the difference between the object temperature and the temperature of its surroundings, and “R” quantifies the sensitivity of heat transfer between the object and its surroundings. As such, Eqn. 1 and Eqn. 2 relate as follows:
A=R  Eqn. 3; and
τ=mcR  Eqn. 4.

Referring again toFIG. 2, for any specific location, the net temperature rise is the sum of the outputs from the corresponding transfer functions92for all heat loads. Therefore, a sum102of the outputs of the transfer functions specific to the gradient coils and RF shield94,96yields ΔTgrad104. Similarly, a sum106of the outputs of the transfer functions specific to the bore98,100yields ΔTbore108. Therefore, the net temperature change at any location, for example, the gradient coil locality and the bore locality, is the sum of the outputs from the transfer functions representing those localities. As such, ΔTgrad104represents direct heating from currents in the gradient coils and ΔTbore108represents direct heating from currents in the RF antenna when a gradient coil is energized plus heat transfer with the gradient coil due to temperature differences therewith. Additionally, it is noted that ΔTgrad does not necessarily include that same heat transfer with the RF antenna because, while those levels can drive temperatures of the patient bore, the heat transfer is typically insignificant to net heating of the much larger gradient coil. While, for exemplary purposes, net temperature rises for only the gradient coil locality and the bore locality are determined, it is contemplated that net temperature rises for virtually any locality may be readily included.

The net temperature rise for the gradient coil locality, ΔTgrad104, is then summed110with appropriate boundary condition data112received from temperature sensors disposed about the locality, such as temperature sensors57,67ofFIG. 1. Specifically, one or more temperature sensors are included to report the boundary conditions for the gradient coil and/or coolant inlet (liquid and gas). This boundary condition data112is combined with the ΔTgrad prediction104to predict temperature values for the gradient coil locality. Therefore, the result of the summation110is the predicted temperature of the gradient coil locality, Tgrad114.

Similarly, the net temperature rise for the bore conductor locality, ΔTbore108, can be summed116with appropriate boundary condition data118received from temperature sensors disposed about the locality, such as temperature sensors57,65ofFIG. 1. Specifically, one or more temperature sensors are included to report the boundary condition for the bore, which may include ambient air temperature and, should a bore blower system (not shown) be included, air velocity. This boundary condition data118is combined with the ΔTbore108predictions to predict temperature values in the bore. Therefore, the result of the summation116is the predicted temperature of the bore conductor locality, Tbore120.

In accordance with one embodiment, to increase the accuracy of the determination of Tbore120, a differential feedback loop122is employed. Accordingly, Tgrad114and Tbore120are subtracted124and this difference is applied to another transfer function for the Tgrad/Tbore difference126. The output of the differential feedback loop is then included in the summation106to determine ΔTbore108.

Once Tbore120is determined, a check is made to determine if Tbore is within an acceptable temperature range128. If Tbore120is not within the acceptable range130, the desired power level132is automatically adjusted. Specifically, if the bore temperature, Tbore120, is predicted to rise above desired threshold or limit on temperature levels during the commanded scan, then the gradient waveforms are automatically adjusted to lower the power levels132while remaining consistent with the originally prescribed parameters or characteristics of the desired imaging process84. Additionally, it is contemplated that a user prompt may, optionally, be included to notify the operator134that the bore temperature120would exceed acceptable levels during the prescribed scan at the initially determined power levels and, as such, the power levels are should be or have been adjusted132. While not only effective in advising the user that data is to be acquired at reduced power levels, providing the aforementioned prompt may also be used to assist the user in prescribing future scans or planning each workday's patient schedule. Moreover, the prompt gives the user the opportunity to halt the scan at the reduced power levels if the highest possible power levels are critical. As such, the user can allow the measured temperatures to fall before scanning.

Once the power levels are adjusted132, the process80reiterates to recheck the predicted bore temperature with the adjusted power132. Therefore, the process80continues until the predicted Tbore120is within the acceptable range136. Once the predicted Tbore120is within the acceptable range136, imaging is performed, if necessary, at a reduced power, according to the desired imaging process characteristics138and process80ends at140.

The above-described process reduces errors associated with systems that limit the RMS level of composite gradient current regardless of any actual temperatures, frequency content, or axes selection. Accordingly, the process reduces the probability of carrying out a scan with resulting temperatures in excess of desirable limits. Additionally, the removal of artificial current limits facilitates more aggressive or enhanced scanning as long as previous imaging processes and present boundary conditions have not raised the bore temperature above an acceptable temperature. Therefore, the above-described process provides improved control of gradient power, maintains temperatures within a desired range, and increases overall scanner performance and efficiency.

Referring now toFIG. 3, a graph is shown qualitatively illustrating the difference between the thermal output of traditional hard limited current-based temperature controlling system142and the thermal output of an exemplary system that operates according to the above-described process144. While similar increases in performance and efficiency will be experienced during conventional scanning operations, to better highlight the advantages of the present invention,FIG. 3compares the thermal output of both systems142,144during enhanced imaging procedures.

Specifically,FIG. 3shows a thermal output of a traditional thermal control system employing hard limited RMS current thresholds to control temperature142over a time period. Additionally,FIG. 3shows a thermal output of a system employing the above-described thermal control technique144of the present invention over time. In system142, halts due to the thermal output surpassing the acceptable temperature range146occur repeatedly148,150as the duration of scanner use is increased. That is, when system142begins scanning, the system is at a relatively cool temperature152. However, as scanning procedures continue, the temperature increases154. While the system is permitted to cool during period156, if sufficient cooling does not occur, the temperature increases are compounded until the thermal output surpasses148,150the maximum desirable temperature threshold158. In this case, once the maximum desirable temperature threshold158is surpassed148, the BTMS engages and requires the system to discontinue use until the system cools to a minimum acceptable cool temperature160. As such, a prescribed scan may be interrupted due to the BTMS enforcing an unscheduled shutdown of the MR system142to allow for MR system cooling161.

To compound this problem, even though MR system142cools toward the minimum acceptable cool temperature160, the subsequently prescribed scan may still cause thermal output to exceed150the maximum desirable temperature threshold158and the BTMS again engages and forces the MR system142to discontinue use until it has cooled to the minimum acceptable cool temperature160. That is, it may be required that the MR system undergo a full cooling to the minimum temperature160before the scan is completed or a subsequent scan is permitted. Thus, a great lag in scan time is enforced for repeated enhanced scans.

In contrast, system144is configured to control thermal output according to the present invention. As such, repetitive enhanced scanning processes will be permitted without exceeding the maximum desirable temperature threshold158. That is, system144allows for significant increases in thermal output over conventional systems142as shown by its tolerance162for increased thermal output associated with high power consumption of repetitive enhanced imaging processes. Additionally, though the temperature about system144may approach the maximum acceptable temperature threshold158, by dynamically adjusting the power applied to the gradient coils to allow adequate cool-down, the temperature does not surpass the maximum desirable temperature threshold158. According, the BTMS is not engaged and thermal shut-downs are avoided while scans having increased speed and resolution are repetitively achieved. As such, the probability of a bore temperature in excess of a maximum desirable temperature threshold158is reduced. While adjusting power applied to the gradient coils may have an impact on contrast or resolution, the time-consuming delays and halts are avoided.

In accordance with a preferred embodiment of the invention, a BTMS is used for additional protection against excess bore temperatures. Therefore, the accuracy of predicted bore temperatures and adjusted power levels may be checked against the data acquired and the operation of the BTMS since, over significant periods of time, sequential use of the transfer functions may cause an accumulation of prediction error. However, it is recognized that the present invention advantageously reduces the frequency when the BTMS is activated.

Additionally, by including the BTMS, information from the BTMS may be utilized to adjust the preloaded values for A and τ, of Eqns. 1, 3, and 4, as scan experience is accumulated for a particular system. Those adjustments can be used to incrementally and dynamically decrease the differences between measured and predicted temperatures and, thus, substantially improve the accuracy of the preloaded values for a particular scanner compared to the preloaded values which must represent the statistical extremes of any scanner in the installed base.

However, it is also contemplated that the above-described thermal control technique may be utilized with systems that do not include a BTMS. In this case, the above-described thermal control technique not only controls thermal output but also provides thermal protection.

In summary, the present invention includes a control system configured to set dynamic limits on the power injected into the gradient coils. That dynamic limit will be determined for each commanded prescription as a function of the initial thermal and boundary conditions. This is accomplished through use of a thermal predictor module which provides a computational algorithm to model a series of coupled first order dynamic subsystems designed to simulate the actual thermal characteristics of the localities/components within the medical device. Therefore, the present invention uses thermal boundary and initial condition data with a prediction algorithm to dynamically set limits on the electrical power supplied to the gradient coils. This temporally predictive technique generally allows much higher power levels than those which employ a fixed limit on gradient current. Additionally, whenever energetic scanner use has caused high temperatures, the present invention automatically adjusts the input power so as to avoid an over-limit condition and its resulting sudden halt to scanning processes.

Therefore, the present invention includes a thermal controller that is configured to receive operational parameters for an impending use of a medical device and predict a thermal output of the medical device from the operational parameters. The thermal controller is further configured to compare the predicted thermal output to a desired limit on thermal output and, if the predicted thermal output exceeds the desired limit on thermal output, dynamically control power consumption by the medical device to maintain an actual thermal output substantially at or below the desired limit on thermal output during use of the medical device.

A computer readable storage medium having a computer program stored thereon and representing a set of instructions that when executed by a computer of a medical imaging device causes the computer to receive desired operational constraints for a scan to be performed with the medical imaging device from a user-input. The instructions further cause the computer to determine a potential thermal output of at least one heat-generating component of the medical imaging device from the desired operating constraints and a power to be delivered to the at least one heat-generating component during the scan. The computer is also caused to determine if the potential thermal output will cause an actual thermal output to surpass a desired limit on thermal output during the scan and, if the potential thermal output will cause the actual thermal output to surpass the desired limit on thermal output during the scan, adjust the power to be delivered to the at least one heat-generating component during the scan to substantially maintain the actual thermal output at or below the desired limit on thermal output when performing the scan according to the desired operating constraints.

An alternate embodiment of the present invention includes an MR imaging apparatus having a plurality of gradient coils positioned about a bore of a magnet to impress a polarizing magnetic field, and an RF transceiver system and an RF switch controlled by a pulse module to transmit RF signals to an RF coil assembly to acquire MR images. The MR imaging apparatus also includes an operator console configured to receive operational characteristics of a desired imaging process and a computer. The computer is programmed to receive the operational characteristics of an impending MR scan from the operator console, determine a power delivery level to execute the impending MR scan according to the operational characteristics, and predict a thermal output to the bore of the magnet from the operational characteristics and the determined power delivery level. The computer is also programmed to predict a thermal output to the bore of the magnet to determine a predicted bore temperature, compare the predicted bore temperature to a desired threshold bore temperature, and, if the predicted bore temperature exceeds the desired threshold bore temperature, adjust the determined power delivery level to lower the predicted bore temperature.