Non-magnetic external defibrillator

Abstract

A non-magnetic defibrillator is provided that can be operated next to or in the MRI scanner.

Description

NON-MAGNETIC EXTERNAL DEFIBRILLATORCROSS REFERENCE(S) TO RELATED APPLICATION(S)

[0001] This application claims priority to U.S. Provisional Application No. 63 / 735,034, filed December 17, 2024, and U.S. Provisional Application No. 63 / 897,201 , filed October 10, 2025, the entire contents of each being hereby incorporated by reference.TECHNICAL OVERVIEW

[0002] The technology described herein relates to defibrillators. More particularly, the technology described herein relates to non-magnetic defibrillators or those without magnetic elements.INTRODUCTION

[0003] There are millions of magnetic resonance imaging (MRI) scans done each year in the United States. In many instances anesthesia or sedation is used on the patients for scans. Anesthesia is performed for a variety of reasons including for patients with neurologic disorders, congenital heart disease, learning disorders, movement disorders, claustrophobia, those whose position is limited by pain, ventilated patients, and patients who can’t keep still or are having surgery with intraoperative MRI. This is especially true in pediatrics where as many as 28% of MRI scans are done with anesthesia, since the use of anesthesia has allowed the increased utilization of MRI, which is preferred over CT due to better diagnostic contrast and reduced radiation.

[0004] However, cardiac arrest from ventricular fibrillation can complicate anesthesia administration. Even with modern anesthetics and anesthesia equipment, cardiac arrest still can occur during anesthesia management, with mortality as high as 30%. This is especially a problem in pediatric scans, where most patients are treated under sedation or anesthesia, and where adverse eventrates for anesthesia and sedation are similar. Moreover, cardiac arrest can occur during MRI scans even without anesthesia.

[0005] The American Congress of Radiology Manual on MRI Safety set forth patient monitoring and availability of resuscitation equipment during anesthesia management. The manual specifies that when a patient has a medical emergency in the MRI scanner, that the patient should be removed from the scanner to a “designated safe location,” where a defibrillator is available, along with other resuscitation equipment.

[0006] In addition to anesthesia-based procedures, there are a number of MRI-guided interventions, such as MRI-guided biopsy, resection, and thermal ablation of head, spine, abdominal, and pelvic tumors, where there is an increased risk of needing defibrillation during the procedure. There are also MRI-guided interventions that are not currently being performed routinely, such as ablation of ventricular tachycardia, because of the very high risk of ventricular fibrillation, and the lack of the availability of immediate defibrillation.

[0007] In some instances, delays in defibrillation can occur due to removal of the patient from the MRI scanner, the placement of the patient onto a stretcher, and the relocation of the patient to a nearby environment (e.g., the “designated safe location”) that may have resuscitation equipment. It will be appreciated that a typical defibrillator cannot be near an MRI machine since the magnet of the MRI machine can draw a defibrillator into the bore of the scanner and / or cause the defibrillator to malfunction.

[0008] Defibrillation can be further delayed by uncertainty in diagnosing lifethreatening arrhythmias due to ECG artifacts caused by the MRI-fields. Since these types of events can occur infrequently, it gives operators little experience in promptly recognizing such events and taking appropriate action.

[0009] When a patient undergoes cardiac arrest or the like, each minute in delay to defibrillation can decrease the chances of survival of the patient. For example, each minute of delay may correlate to a 5-10% drop-in survival rate.

[0010] Accordingly, it will be appreciated that new and improved techniques, systems, and processes are continually sought after in these and other area(s) of technology. For example, techniques / that would allow defibrillation in an MRI scanner room (such as in proximity to the MRI machine) and / or in the bore of the MR scanner itself. Such techniques may decrease delays in having defibrillation performed and save lives.SUMMARY

[0011] In certain example embodiments, a defibrillator is provided that can be operated next to or in the MRI scanner. In some examples, this allows for defibrillation to be performed in the MRI scanner. In some examples, a defibrillator is provided, and the example defibrillator decreases the delay for when defibrillation can be performed. In some examples, by providing a defibrillator near and MRI scanner, procedures with a higher risk of arrhythmias can be performed (e.g., under MRI guidance).

[0012] An example defibrillator can be used next to an MRI scanner due to using non-magnetic and / or MRI compatible properties. In some examples, motion of the patient caused by defibrillation (e.g., a shock) is decreased (e.g., substantially) by a ramped High Frequency Alternating Current waveform that decreases (e.g., substantially) the accelerations caused by shock-induced skeletal muscle contraction. Accordingly, when defibrillation is applied to a patient, they may react and contact the walls of the bore of the scanner because of a “jump” caused by the shock. The defibrillation techniques may decrease delays for when defibrillation is applied during any or all anesthesia-based and / or (e.g., routine) MRI scans.

[0013] This Summary is provided to introduce a selection of concepts that are further described below in the Detailed Description. This Summary is intended neither to identify key features or essential features of the claimed subject matter, nor to be used to limit the scope of the claimed subject matter; rather, this Summary is intended to provide an overview of the subject matter described in this document. Accordingly, it will be appreciated that the above-described features are merely examples, and that other features, aspects, and advantages of the subject matter described herein will become apparent from the following Detailed Description, Figures, and Claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] These and other features and advantages will be better and more completely understood by referring to the following detailed description of example non-limiting illustrative embodiments in conjunction with the drawings of which:

[0015] Figure 1 shows is an illustrative example of a non-magnetic defibrillator provided in association with an MRI machine according to certain example embodiments;

[0016] Figure 2 is a system diagram that includes an example defibrillator that includes a tetanizing system according to certain example embodiments;

[0017] Figures 3-7 illustrate different (e.g., non-magnetic) components that may be used with an example defibrillator in accordance with certain example embodiments;

[0018] Figure 8 includes graphs of results from comparative defibrillation tests in accordance with certain examples;

[0019] Figure 9 illustrates a standard defibrillator modified with example embodiments, alone with successful defibrillation of ventricular fibrillation in an MRI scanner;

[0020] Figure 10 is a circuit diagram of a first circuit that may be used in connection with certain example embodiments; and

[0021] Figure 11 is a circuit diagram of a second circuit that may be used in connection with certain example embodiments;

[0022] Figure 12 is a block diagram of circuit components and functions of an example MRI Defibrillator that may be used in connection with certain example embodiments and Figure 13 is a circuit diagram of example circuits used for the MRI Defibrillator from Figure 12 according to certain example embodiments;

[0023] Figures 14, 15, and 17 are circuit diagrams describing sections A, B, and C of the circuit shown in Figure 13 according to certain example embodiments;

[0024] Figures 16 and 18 are circuit diagrams of another embodiment that uses one less transformer according to certain example embodiments; and

[0025] Figure 19 shows another example circuit according to certain example embodiments. .DETAILED DESCRIPTION

[0026] In the following description, for purposes of explanation and nonlimitation, specific details are set forth, such as particular nodes, functional entities, techniques, protocols, etc. in order to provide an understanding of the described technology. It will be apparent to one skilled in the art that other embodiments may be practiced apart from the specific details described below. In other instances, detailed descriptions of well-known methods, devices, techniques, etc. are omitted so as not to obscure the description with unnecessary detail.

[0027] Sections are used in this Detailed Description solely in order to orient the reader as to the general subject matter of each section; as will be seen below, the description of many features spans multiple sections, and headings should not be read as affecting the meaning of the description included in any section. Overview

[0028] There are over 30 million MRI scans performed each year in the United States. Anesthesia or sedation is used on patients for many of thesescans. Anesthesia is performed for a variety of reasons including for patients with neurologic disorders, congenital heart disease, learning disorders, movement disorders, claustrophobia, ventilated patients, those who can’t keep still, and those with intraoperative MRI. In addition, there has been a steady increase in the number of units providing anesthesia for MRI, as well as the number of interventions and operations performed within the MRI environment. Many MRI scans in pediatrics are performed with anesthesia, since the use of anesthesia has allowed the increased utilization of MRI, which is preferred over CT due (for example) increased diagnostic sensitivity and reduced radiation.

[0029] MRI-guided surgical intervention is a growing field. For example, MRI-guided biopsy, resection, and thermal ablation of head, spine, abdominal, and pelvic tumors can be performed. MRI-guided pediatric congenital interventions are also increasing. However, such procedures can have an increased risk of ventricular fibrillation over routine scans.

[0030] MRI-guided cardiac arrhythmia ablations with intra-procedure imaging are another possible type of operation and are being explored to reduce the currently large (e.g., 30-50%) rate of post-procedural arrhythmia recurrence.Using MRI can be advantageous as it provides information on both myocardial necrosis and edema post-ablation, separating between permanent and transient ablation lesions. The presence of transient lesions is a major reason for arrhythmia recurrence. Existing electrical tests for assessing the completeness of ablation may not be able to determine if lesions are permanent or not.

[0031] In some instances, in order to accomplish intra-procedure imaging, the entire procedure is done inside an MRI scanner. Some procedures can be more complex / problematic. For example, ventricular tachycardia ablation can require multiple defibrillations. Further the lack of an MRI conditional defibrillator may prevent such procedures from being performed.

[0032] Accordingly, the techniques discussed herein seek to address problems that arise from the challenges associated with performing defibrillation in the vicinity of an active MRI scanner. Conventional defibrillators, which often contain ferromagnetic components, are incompatible with the high magnetic fields generated by MRI machines. These fields can cause defibrillators to malfunction or even become dangerous projectiles, necessitating the removal of the patient from the MRI environment to a designated safe location for defibrillation. This relocation process introduces significant delays in administering life-saving defibrillation, particularly during cardiac arrest events, where each minute of delay substantially reduces survival rates. In some instances, the electromagnetic interference from MRI machines can corrupt signals (e.g., ECG signals), making the diagnosis (e.g., of arrhythmias) more challenging and less timely. These limitations can be magnified during MRI-guided interventions, which may be associated with a higher arrhythmia risk. Certain procedures (e.g., ventricular tachycardia ablation) may be prevented (or more difficult) from being performed under MRI guidance.

[0033] Techniques discussed herein propose a solution by introducing a non-magnetic, MRI-conditional defibrillator capable of operating safely and effectively within the MRI environment, including inside the bore of the scanner. The defibrillator utilizes non-magnetic components, such as specialized transformers, capacitors, and shielding, to maintain compatibility with the MRI’s magnetic field. By removing the need to relocate the patient, the solution discussed herein can decrease (e.g., significantly) delays in defibrillation and broadens the range of MRI-guided procedures, enhancing patient outcomes — specifically in more urgent health scenarios. Description Of Figure 1

[0034] In certain example embodiments, a non-magnetic defibrillator is provided that allows for operation next to or in an MRI machine. Figure 1 showsan MRI machine 100 with a patient 102. A non-magnetic defibrillator 104 is provided that allows for defibrillation in the MRI scanner. This can decrease delays in providing defibrillation. Moreover, providing such a non-magnetic defibrillator allows for performing procedures under MRI guidance - including those with potentially a higher risk of arrhythmias.

[0035] A non-magnetic defibrillator can obviate the need to move a patient out of the MRI scanner room for defibrillation. Providing a non-magnetic defibrillator can allow patients to be defibrillated inside the bore of the MRI scanner (e.g., where the rapid and violent skeletal muscle contraction caused by the shocks would be decreased, reduced, or even eliminated by the techniques described herein - thereby preventing the patient from hitting the scanner bore wall).

[0036] In certain example embodiments, a non-magnetic defibrillator is provided as being MRI-conditional. More specifically, an MRI-conditional defibrillator can be used in the MRI environment with specific conditions (e.g., in accordance with one or more conditions, such as being used only with scanners of a particular field strength (e.g.: 1 .5 or 3Tesla), having to use specific defibrillator electrode pads, and / or having to use specific defibrillator cables to connect the patient to the defibrillator generator)

[0037] In certain examples, a condition of use of an MRI-conditional defibrillator is that MRI field specific (1 .5 or 3 Tesla) resonant Radio Frequency (RF) traps are added along the cables connecting the generator to the defibrillation pads. Such a setup may (e.g., will) prevent inadvertent heating of the cables during even the most intense MR imaging sequences. In certain examples, the defibrillator pads, cable, and generator can be inside the scanner bore.Accordingly, the system (e.g., the defibrillator and / or associated components) may be rendered MRI-conditional by having all components, including the transformers, without any ferromagnetic materials, as well as having appropriate shielding andfiltering. RF emissions are decreased (e.g., eliminated) via RF filters. This can prevent noise produced by the defibrillator generator at the MRI’s operating frequency from reaching the scanner and interfering with the imaging, and also prevent RF generated by the MRI scanner from interfering with the operation of the defibrillator.

[0038] In certain example embodiments, a muscle conditioning waveform may be delivered just prior to the shock delivered by the defibrillator. The conditioning of the patient’s muscles can lead to a decrease in skeletal muscle contraction when shock energy from the defibrillator is delivered.

[0039] In some examples, the conditioning may be provided by delivering a preceding, ramped 1 -KHz waveform at a relatively small amplitude (e.g., from 0 to 50, or up to 140 volts), with a relatively longer duration (e.g., 0.5 seconds to 1 second). The delivery of this conditioning energy to the patient can cause the skeletal muscles to contract more (e.g., much more) slowly. At the same time, the cardiac muscle of the patient may be not affected (or at least not substantially affected).

[0040] After delivering the skeletal muscle conditioning energy, the defibrillator shock may be applied to the patient. The defibrillator shock may be at a relatively higher voltage (500-3000 volts), but with a relatively shorter duration (e.g., 5-15ms, or about 8ms). When this defibrillator shock is delivered, the chest muscles in the patient generate accelerations that are much less than those encountered during conventional defibrillation (e.g., without first delivering the conditioning energy to the patient). This accordingly can result in substantially reduced patient motion caused by the defibrillator shock. Accordingly, a patient is less likely to impact the sidewall of the MRI machine or lose registration with the pre-acquired landmarks.

[0041] Results of a comparative defibrillation tests are shown in Figure 8. A comparative test recorded acceleration of a limb and the abdomen usingacceleration sensors in connection with the application of defibrillation. Graph A in Figure 8 shows a biphasic only approach to defibrillation (e.g., that typically performed) and Graph B shows application of the rHFAC waveform prior to application of the biphasic pulse. The top trace in each graph is the voltage of the waveform that is delivered, while the bottom traces show acceleration (in gs) from the acceleration sensors placed on a limb and the abdomen. Results show that with a Biphasic pulse (e.g., 150J) alone (A) vs. the combined rHFAC (duration=0.5s, peak voltage=25 V) and Biphasic pulse (B), that the rHFAC waveform decreased peak limb acceleration by greater than 70% (e.g., from 10g to 2g).Description Of Figure 2

[0042] Figure 2 is a system diagram that includes an example defibrillator that includes a tetanizing system 201 according to certain example embodiments.

[0043] The system shown in Figure 2 includes a defibrillator (e.g., an example being a Zoll R Series) that is linked to an example tetanizing unit that is configured to deliver a ramped High Frequency Alternating Current (rHFAC) waveform. The unit generates the tetanizing pulses and applies them just prior to a biphasic defibrillator shock.

[0044] In certain example embodiments, an example MRI-Conditional external defibrillator system incorporates rHFAC. As an illustrative example, a Zoll R-series Defibrillator and a tetanizing unit (rHFAC) are used in combination with defibrillation pads.

[0045] The block diagram in Figure 2 includes an example MRI-Conditional External Defibrillator System 200. This includes components of the tetanizing system 201 , as well as MRI-conditional components 208.

[0046] The tetanizing system 201 includes a Defibrillator Component 202 (e.g., where V=500-3000V, 8ms Bi-phasic pulses and a Tetanizing unit 204 (a low voltage, such as 0-140 v) that operates (e.g., 1 KHz ramped signal with a durationof 0-1000ms) to generate defibrillation signal output 206 (e.g., that is provided inside the tetanizing unit chassis). Components of the MRI-conditional system 208 include: 1 ) an RF 9-Pole Low-Pass Filter 210 (e.g., -120dB at Larmor); and 2) MR-compatible High-Voltage Cables with Resonant RF-Traps 212. The defibrillation pads 214 may be disposable patches in certain example embodiments.

[0047] The rHFAC waveform is controlled by the tetanizing Unit 204, which triggers the defibrillator to deliver a shock (e.g., tetanizing+biphasic waveform) after delivering the rHFAC pulse (e.g., the tetanizing waveform). In some examples, the triggering of the defibrillator to deliver a shock occurs once a threshold is reached. The threshold may be up to, for example, 40 milliseconds after the rHFAC waveform has ended.Description Of Figures 3-7: Non-Maqnetic Components

[0048] Figures 3-7 illustrate different (e.g., non-magnetic) components that may be used with an example defibrillator in accordance with certain example embodiments.

[0049] An example MRI conditional defibrillator includes non-magnetic components so the defibrillator will not become a projectile and be drawn into the MRI scanner. Accordingly, in certain example embodiments, a display for the defibrillator may be non-magnetic. In some examples, a display may be a nonmagnetic liquid crystal display panels that are installed into non-magnetic stainless-steel cases. This is illustrated in Figure 3 with non-magnetic display 300 coupled to the MRI-conditional defibrillator 200..

[0050] Other non-magnetic components of the defibrillator include nonmagnetic shock capacitors 400 and / or non-magnetic, isolation transformers 402. These components are illustrated in Figure 4 and may not be affected by the 1 .5 T magnetic field of the MRI machine, since if they were ferromagnetic they would be drawn into the bore of the MRI scanner.

[0051] When a defibrillator includes electronics, the isolation of such electronics from leakage from the supplied AC power can be critical for patient safety. In some instances, this is accomplished with a ferromagnetic-core, isolation transformer. In certain example embodiments, an isolation system may be used by incorporating a clinical-grade-isolated, non-magnetic, transformer.

[0052] Figures 5A-5B illustrates aspects of example isolation circuity (e.g., Non-magnetic, patient-isolated power supplies) that may be used in connection with certain example embodiments. Figures 5A-5B show an example illustrative clinical grade isolation that is provided by the non-magnetic transformer ( T, 500), whose Primary is driven by the H-Bridge (Q1-Q4), and whose isolated Secondary is connected to the load, which is the rest of the circuitry of the defibrillator. An illustrative example 520 of an H-bridge with drivers and non-magnetic isolation transformer hardware (e.g., with a transformer, resistor load, and capacitor) is shown in Figure 5B. In some examples, voltages applied to the Primary of the isolation transformer are also applied with the same peak-to-peak voltage transferred to an isolated Secondary.

[0053] For electrical isolation, the AC line voltage is rectified to a direct current voltage (as shown in Figure 5A - Vdc) and applied to the H- bridge (as shown in Figure 5A - Q1 -Q4). This can produce a 500 kHz AC voltage which is transferred to the isolated Secondary. A 200-volt peak-to-peak AC voltage applied to the Primary can be transferred 1 :1 to the Secondary. Or can be transferred at a lower ratio with less voltage in other embodiments.

[0054] In some instances, a defibrillator can charge a capacitor to the desired energy and then discharge it for defibrillation. The high voltage to charge the capacitor is typically generated with a ferromagnetic-core transformer. However, in connection with the certain example embodiments herein, such a ferromagnetic transformer has been replaced with a non-magnetic transformer, of which an illustrative example is shown in Figures 6A-7.

[0055] Figures 6A and 7 illustrate an example high voltage circuit 600 according to certain example embodiments. Figure 6A is a photo of electronics showing the AC generating H bridge (602), non-magnetic transformer (610), series diode (604), non-magnetic, high voltage shock capacitor (606), and one or more magnets (608). The magnet is placed to show the non-magnetic properties of the transformer and capacitor, as shown by the magnet not sticking to the transformer nor the capacitor. Figure 7 shows the charging of the shock capacitor for a defibrillator. The upper trace (650) shows an input voltage (100 volts peak-to- peak on the primary of the transformer) while the lower trace (652) shows the voltage on the shock capacitor (which has been rectified by the diode). In some examples, the capacitor charges to 1200V in less than about 3 sec.

[0056] In some examples, such a non-magnetic transformer can charge a capacitor in a few seconds (e.g., less than 5 seconds). For example, applying 50- volt peak AC to a transformer (as shown in the upper part of Figure 7) charged the capacitor to 1200 Volts (e.g., 72 Joules) in less than about 3 sec (as shown in the lower part of Figure 7). In some examples, a charge to 360 Joules (e.g., maximum allowed) in 3 sec may use a peak AC input voltage of about 250 volts.Example Defibrillation Inside MRI Machine

[0057] In some examples, a typical defibrillator may be modified with components as shown in Figure 9. For example, a system may be modified by adding a low pass filter and a 4.0 m long high-voltage twisted-pair cable that had resonant RF traps (“Baluns”) placed at 0.30 m increments (as shown in “A” of Figure 9). These components were added to prevent RF interference from corrupting the MRI image and / or preventing heating of the cable caused by the MRI imaging pulses. Defibrillation pads may then be placed on the chest, and a powered defibrillator generator placed outside the scanner’s 30 Gauss line. This example implementation was performed on a swine inside an MIR scanner. The pigs were fibrillated by applying 20 V, 60Hz AC to the defibrillator pads (as shownin “B” and “C1 ” of figure 9). After ventricular fibrillation was detected, defibrillation was delivered, with successful restoration of sinus rhythm (as shown in “C2” of Figure 9).Description of Figure 10: Example Circuit

[0058] Figure 10 is a circuit diagram of a first circuit 900 that may be used in connection with certain example embodiments. The circuit shown in Figure 10 includes 4 different sections (or boards).

[0059] Section 1 includes a full wave rectifier (R1 ) that rectifies the power line voltage to 160V DC. This voltage is then converted through an H-Bridge (H1 ) to alternating current with a frequency of 300KHz. Note that this first block may be isolated from the rest of the circuit through the 200W transformer T1 , which has a 1 :1 winding for the main 300KHz signal that goes to Section 2 and a step-down winding to generate the 24V AC that goes to Section 3.

[0060] For section 2 the rectifier (R2) rectifies the input signal to 160 VDC that the H-Bridge(H2) converts to a 100KHz signal that is amplified by a 3x voltage multiplier (M1 ) to 400 VDC. Consequently, the H-Bridge (H3) converts the signal to 300KHz, and it will pass through the transformer (T2) followed by the diode and capacitor to obtain up to a 3200 VDC output that will be converted by the H-Bridge (H4) to the signal that will go to (e.g., be delivered) the patient.

[0061] For section 3 the 24V AC arriving from T 1 is transformed by a full wave rectifier (F2) to a 36 VDC that goes to an isolator, which is then used to power the electronics. The output of F2 also goes to the battery charger to charge the batteries that will supply the system when it is not connected to the wall AC power supply.

[0062] Section 3 also includes an H-bridge (H5) and a 7x voltage multiplier (M2) that will convert the energy from the battery to a 160 VDC signal that will be the input of the H-Bridge H2 when the system is working with the battery.

[0063] Section 4 is a controller board with all the connectors for Display, I / O, ECG Monitor / Sync, Pacing / Tetanizing, and Isolator (e.g., solid state relays) to transfer the signals coming out from section 2, as well as from Pacing / Tetanizing to the patient.

[0064] In the circuit shown in Figure 10, the voltage multipliers can be simple, well known, diode-capacitor multipliers. It will be appreciated that the parameters shown in the circuit are provided by way of example and may be varied over one or more ranges (e.g., + / - 5, 10, or 25 or more percent). Description Of Figure 11 : Example Circuit

[0065] Figure 11 is a circuit diagram of another circuit that may be used in connection with certain example embodiments. In some example embodiments, no voltage multipliers are used in the circuit. Instead, in certain examples, the circuit can use non-magnetic transformers for generating the high voltage for the shock that is delivered by the defibrillator. This can advantageously simplify the circuitry, make the circuitry more robust, and / or allow for easier integration of a battery for portable applications.

[0066] Section A includes components for connecting to main power (e.g., 95V-250VAC) for the defibrillator for powering the device.

[0067] Section B includes a nonmagnetic transformer that operates at a higher frequency (e.g., typically above 50kHZ) that serves to isolate the defibrillator circuitry from main power. Various power supply topologies can be used that can incorporate the nonmagnetic transformer to output the higher frequency but lower than mains voltage signal.

[0068] The higher frequency signal is rectified to produce a DC output, which may be around 28 Volts in some examples. The 28-volt signal is used to charge the non-magnetic battery. In some examples, the non-magnetic battery may be lead acid or lithium polymer, as well as supply power for the rest of the defibrillatorcircuity, including operating the microcontroller, capacitor charging circuity, ECG monitoring, and muscle conditional signal circuitry.

[0069] Non-magnetic DC-DC converters are uses to supply the 3.3V, 5V, and 15 V needed for the circuit components. A sensing resistor is present to measure the current flowing into the defibrillator circuitry so appropriate error messages can be generated and appropriate actions taken if over or under current conditions are noted. The microcontroller controls all functions, including applying appropriate switching signals to start charging, end charging, route the ECG signal to the display, generate the display graphics, route the muscle conditioning signals to the patient, determine the appropriate voltage level and charge to that level for delivering the desired energy shock, and respond to user inputs.

[0070] Two H bridges are used for transforming the 24-28 Volts of DC into a 200 Volt signal using one non-magnetic transformer and then converting the rectified 200 Volt signal into an alternating current signal for application to another non-magnetic transformer which is shown in section C.

[0071] In some examples, both of the H bridges can be combined into one H bridge circuit with the use of a single transformer. One advantage of the two- transformer topology is that the voltages needed for the muscle conditioning signal can be additionally generated by the lower voltage transformer and the higher voltage transformer can be turned off when the discharge capacitor reaches the desired voltage, allowing the lower voltage transformer to continue to supply voltage for the muscle conditioning signal.

[0072] For section C, the signal from the high voltage H bridge H2 is applied to the high voltage non-magnetic transformer which converts it into a signal (typically 2000-3500 volts peak) that is rectified by a diode and used to charge the shock capacitor to the desired voltage. Another H bridge (H3) is used to generate the shock, biphasic waveform.

[0073] Non-magnetic semiconductor switches are present to isolate the ECG and muscle conditioning circuitry from the shock signal during shock delivery, and then connect the muscle conditioning and ECG circuitry to the patient when a high voltage shock is not being delivered. The ECG circuity may be connected to the patient at all times — except when the muscle conditioning or shock signals are being delivered.

[0074] In certain example embodiments, a combination of voltage multipliers (e.g., as discussed in connection with Figure 10) and voltage transformers (e.g., as discussed in connection with Figure 11 ) can be used.Description of Figures 12-19: Additional Example Circuits

[0075] Figure 12 is a block diagram of circuit components of an example MRI defibrillator 1100 (e.g., an MRI conditional defibrillator) that may be used in connection with certain example embodiments. The aspects discussed in connection with Figures 12-19 may be used in combination with the other aspects discussed herein.

[0076] Figure 13 a circuit diagram of example circuits used for the MRI defibrillator from Figure 12 according to certain example embodiments. The example MRI defibrillator 1100 may be used to provide electrical stimulation to a patient 1 101 .

[0077] The defibrillator 1100 includes 3 sections, section A 1102, section B 1104, and section C 1106. The sections are electrically isolated from each other.

[0078] Section A 1102 includes a non-isolated mains supply and the nonisolated part of the 28-volt power supply. Figure 14 shows an illustrative example of circuitry that may be included within section A 1 102.

[0079] Section B 1104 includes the isolated part of the power supply, the battery, battery charger, power monitoring, microcontroller, part of the shock capacitor charging circuity, and separate, isolated power supplies for powering the ECG circuitry, the display with user inputs, and parts of the separate circuitry forisolating control and analog signals going to and from Section C 1106. Figures 13, 15, and 16 each provide different examples of circuitry that may be included as part of Section B (e.g., the isolated power supply, controller, display, charging) 1104 in certain examples.

[0080] Section C 1106 includes the rest of the shock capacitor charging circuitry, the H bridge for generating the shock waveform, the circuity for delivering HFAC, the ECG measuring circuity, isolated power supplies for powering the HFAC amplifier and the shock delivering H bridge, as well as parts of the isolators for the control and analog signals. Figures 13, 17, 18, and 19 each provide different examples of circuitry that may be included as part of Section C (e.g., the shock capacitor charging circuitry) 1106 in certain examples.1 ) Section A: Figure 14

[0081] Figure 14 is a circuit diagram of section A 1 102 from Figures 12 and 13 according to certain example embodiments. An LLC power supply is shown in Figure 14. However, other types of power supplies may be used (e.g., that are non-magnetic).

[0082] The LLC power supply is a resonant converter, where the input stage includes a full wave rectifier (1304) that converts the applied mains AC (1302) into DC which is filtered by a capacitor (1306). The capacitor filters the DC voltage from the rectifier (1304) resulting in a more stable DC voltage before it is provided to the switching stage.

[0083] The filtered DC is applied to an H-bridge (1310) which converts the applied DC into a high frequency AC waveform with a preferred frequency of around 60 kHz, although higher frequencies will allow the use of smaller transformers. Switching power to the H-bridge (1310) is applied by an H-bridge driver (1314) which is controlled by the LLC Controller (1308). The AC waveform from the H-bridge (1310) is applied to the primary of transformer T 1 (1320) through capacitor C1 p (1312).

[0084] A resonant circuit is formed by the series combination of capacitor C1 p (1312) and the leakage inductance of the transformer (Lr). The magnetizing inductance of the transformer (Lm) is the transformer’s shunt inductance.

[0085] Transformer T1 provides electrical isolation between the non-isolated Section A 1 102 and the isolated Section B 1104. T ransformer T 1 includes multiple secondaries for different outputs. One secondary (1320a) of transformer T1 is applied to a full wave rectifier followed by a filtering capacitor to supply 28 V power circuitry (e.g., a majority or most of the circuits) of the defibrillator. A second secondary (1320b) of T1 provides feedback to the LLC controller (1308) to stabilize the output. A third secondary (1320c) of T1 is applied to a separate full wave rectified to provide the 30V needed to charge the battery.2) Section B: Figure 15

[0086] The 28VDC from the full wave rectifier / filter capacitor is applied to an isolator circuit (1402) that passes the 28VDC to the rest of the defibrillator circuitry and blocks the battery voltage (1406) from being applied to the rest of the defibrillator circuity when AC mains power is applied. If AC mains power is not applied, as detected by the power module, under control of the microcontroller (1404), or automatically if an array of diodes is used, then battery power (1406) will be applied to the rest of the defibrillator circuitry.

[0087] A separate full wave rectifier / filter capacitor can supply 30VDC charging voltage to the Battery Charging Circuity which charges the battery. AC mains-derived or battery derived DC power passes through the Sensing Resistor (1408), where the voltage drop across it is measured by Current Sense (1410) under control of the Microcontroller (1404). For example, as current flows through the sensing resistor (1408), it may create a small voltage drop (e.g., in millivolts) proportional to the current (e.g., V = I x R). Current Sense 1410 can then magnify this small voltage to a workable signal. In some examples, this signal is then fed into the MCU (1404) via ADC (analog-to-digital converter) inputs. If excessivepower is being drawn by the defibrillator, or no power is being drawn, and error message is displayed on the display 1 110 and / or an alarm is sounded. Power Monitor 1412 may be used to confirm / determine if AC or DC power is being used and appropriately provide this status to the microcontroller 1404, which may then be output on display 1110 indicating which of AC or DC is being used.

[0088] DC power coming out of sensing resistor (1408) is applied to an isolated DC to DC converter 1420, preferably based on a Max256 integrated circuit to produce 3.3 volts of additionally isolated power to supply power to the ECG amplifier so that is can be active whenever the defibrillator is turned on. DC power is also applied to non-isolated linear regulators (1418) that provide 15V to the H1 -Bridge driver (1416); 5V to the Current Sense (1410), Power Monitor (1412), Charging Circuit 1402, and Isolator 1402; and 3.3V to the MCU 1404.

[0089] The Driver 1416 for the H1 -Bridge 1414 is controlled by the MCU 1404 via the CTRL line (1421 ), and switches H1 -Bridge to produce a square wave (e.g., at 128 kHz) from the supplied DC power. This 128 kHz power (which may be up to 300 Watts) is applied to the primary of non-magnetic, isolation transformer T2 (1424) through resonant capacitor C1 (1422). This frequency can be much higher which will allow smaller transformers to be used.

[0090] Transformer T2 has a voltage step up. The voltage step up may be, for example, between 5 and 20 times. For example, a voltage step up of 12 times may be used. The secondary (1426) of T2 (1424) is connected through resonant capacitor C2 (1428) to apply the output of T2 to the input of non-magnetic, isolation transformer T3 (1430). Transformer T3 (1430) also includes a voltage step up, which may be between 5-20 times. In some examples, the voltage step up that is used may be 10x. In some examples, the voltage step up provided by T3 is greater than that provided by T2 and in other examples the voltage step up provided by T3 is less than that provided by T2. In some examples, the voltage step up provided by T3 is the same as that provided by T2.

[0091] The microcontroller 1404 has digital outputs for controlling the isolator circuity (1402) for switching between mains-derived and battery power. The microcontroller 1404 has another digital output for switching the defibrillator shock generating H2-bridge via isolator Iso 1 (1432a). Another digital output is for switching the Solid-State Relays (SSRs) in Section C for applying HFAC via Iso 3 (1432c). An analog to digital input to the microcontroller via Iso 4 (1432d) is for measuring ECG when the defibrillator shock is not being applied. Another digital output is for opening, via Iso 3 (1432c) the High Voltage SSRs when the defibrillator shock is being applied to isolate the HFAC and ECG circuity from the high voltage defibrillator shock. The microcontroller 1404 also has analog to digital converters for measuring the voltage on the charging capacitor, as well as a digital to analog converter for generating the HFAC waveform. All of the signals from or to the microcontroller that affect circuity in Section C pass through appropriate isolators Iso 1 -4 (1432a-1432d).

[0092] The microcontroller (1404) also interfaces with the non-magnetic display (1110). Display 1110 may include a non-magnetic 316 stainless steel case, as well as the non-magnetic user input buttons for setting the defibrillator energy output, HFAC voltage and duration, as well as for initiating charging the shock capacitor C3 (in section C) and delivering the defibrillator shock.3) Section C: Figure 17

[0093] A secondary (1504) of T ransformer T3 (1430) charges shock capacitor C3 (1506) using current rectified by Diode D1 . A full wave rectifier can also be used. This rectified current is used to produce a relatively high DC voltage (e.g. up to 3200V). The shock waveform is generated by the H2 bridge (1507) under control of the H2 bridge driver (1508) using signals from the microcontroller (1404) that passes through Isolator lso-1 (1432a).

[0094] Additional secondaries of Transformer T2 (1424) drive Diodes D2, D3, and D4 through isolation capacitors C4, C6, C7, C9, and C10 to produce the+ / - 60 Volts that powers the HFAC amplifier (1510) to produce the HFAC waveform, as well as producing the Isolated 15 volts (15V ISO) needed to power the H2 Bridge Driver (1508).

[0095] The separate Isolated 5V supply (5V Iso) is needed to power the ECG amplifier (1512).

[0096] The Digital to Analog waveform needed to generate the HFAC waveform is output from the Microcontroller, passes through Isolator ISO-2 (1432b), and is applied to the HFAC amplifier (1510) .

[0097] Inputs to the ECG amplifier (1512) and output from the HFAC amplifier (1510) are switched onto the lines connected to the patient through solid state relays (SSRs) (1516) controlled by signals from the Microcontroller that pass-through Isolator lso-3 (1432c). Those signals also control the High Voltage SSRs (1514) that are switched off and isolate the ECG amplifier and HFAC circuitry from the shock waveform when a shock is being delivered. The High Voltage SSRs (1514) are switched on when a shock is not being delivered, which allows ECG signals from the patient to be passed to the ECG amplifier and also allows the HFAC waveform to be delivered to the patient just prior to delivery of the Shock Waveform. The ECG amplifier output is routed to an analog to digital converter in the Microcontroller via Isolator lso-4 (1432d).Technical Details of Example Non-Maqnetic Transformers

[0098] The following are examples of non-magnetic transformers that may be used in accordance with the transformers shown in the example circuits discussed herein including Figures 1 1 , 13, and 15.Alternative Section B: Figure 16

[0099] Figures 16 and 18 are circuit diagrams of another embodiment that uses fewer transformers. Specifically, an additional embodiment of Section B can eliminate transformer T3 (1430), which is shown in Figure 16. In this embodiment, the step-up that is accomplished by T2 and T3 may be performed by T2 (1450) alone. This embodiment shares many of the aspects discussed in connection with Figures 13 and 15. Accordingly, Driver 1416 for the H1 -Bridge 1414 is controlled by the MCU 1404 via the CTRL line (1421 ), and switches H1 -Bridge to produce a square wave. In this embodiment that square wave that is generated may be, for example, greater than 400 kHz from the supplied DC power. This greater than 400kHz power (which may be up to 300 Watts) is then applied to the primary of nonmagnetic, isolation transformer T2 (1450) through resonant capacitor C1 (1422).

[0100] Transformer T2 (1450) has a voltage step up. The voltage step up of T2 (1450) may be, for example, between 90 and 150 times. For example, a voltage step up of 120 times may be used for T2 (1450). A secondary (1452) of T2 (1450) is connected to resonant capacitor C2 (1454) to apply the output of T2 to diode D1 (which may be then be the same or similar to what is shown in Figures 13 or 17) to charge the Shock Capacitor in Section C (1506). In some examples resonant capacitor C2 (1454) is not used.

[0101] In some examples, MOSFETs such as STD85N10F7s are used for H1 -bridge 1414 to generate the greater than approximately 400 kHz waveform. In other examples GaN FETs such as EPC2204s are used to generate the greater than approximately 800 kHz waveforms to drive transformer T2 (1450).Alternative Section C: Figure 17

[0102] In this embodiment a secondary of Transformer T2 (1450) charges shock capacitor C3 (1506) through optional resonant capacitor C2 (1454) using current rectified by Diode D1 . A full wave rectifier can also be used. This rectified current is used to produce a relatively high DC voltage (e.g. up to 3200V). The shock waveform is generated by the H2 bridge (1507) under control of the H2 bridge driver (1508) using signals from the microcontroller (1404) that passes through Isolator lso-1 (1432a).

[0103] In some examples, the illustrative defibrillator operates through charging, delivery, and recovery phases. Referring to Figure 17, at the charging phase, T2 provides voltage step-up and patient isolation, C2 provides a resonant boost, and D1 rectifies the current for storage into C3. For charging: T2 receives AC drive signal from the primary side. The T2-C2 resonant tank oscillates at designed frequency. The voltage across tank rises due to Q multiplication and D1 conducts at positive peaks, charging C3. The C3 voltage builds up to 3200V DC.During this charging process the H2-Bridge remains off (e.g., as all IGBTs are non-conducting).

[0104] For stimulation, the H2 Bridge Driver receives a trigger command and the diagonal IGBT pairs switch on in sequence. 03 discharges through the patient via High Voltage IGBT bridge H2 and a Biphasic pulse is achieved by alternating which diagonal conducts. The Pulse width and timing may be controlled by driver electronics including the defibrillator.

[0105] After discharge, the defibrillator moves to a recovery mode when the H2-Bridge switches off. The resonant circuit recharges (as discussed above) C3 for next pulse when appropriately activated, and the ECG / Impedance block monitors response from the patient. Similar description may apply to the other circuitry embodiments discussed herein.Technical Details of Example Non-Maqnetic Transformer Used In A Single Transformer Capacitor Charging Circuit

[0106] The following is an example of non-magnetic transformer that may be used in accordance with the transformer T2 (1450 or 1804) shown in Figures 16 and / or 18.

[0107] This design may allow for 100x voltage step-up to be provided by transformer T2. Higher frequency use can allow for smaller transformers to be used in some examples. Equivalent sized Litz wire may improve efficiency by reducing power loss, especially with the larger diameter wires.Description of Figure 19: Shock Capacitor Charging Circuit with Non-maqnetic Transformer in Series with a Voltage Multiplier

[0108] Figure 19 shows another embodiment that includes a non-magnetic transformer (T2) 1804 (e.g., a non-magnetic isolation transformer) and a voltage multiplier 1802 that is provided in an example MRI defibrillator 1800. The example MRI defibrillator 1800 may be the same or similar to example MRI defibrillator 1100 discussed herein. The voltage multiplier 1802 may be provided as part of, for example, section C 1 106. Section B may be the same or similar to section B 1104 discussed in Figure 16 and section A may be the same or similar to section A discussed in connection with Figure 13.

[0109] This arrangement of MRI defibrillator 1800 allows for one (e.g., a single) transformer to be used in the circuitry. In comparison to the embodiment shown in Figure 13 for example, this allows for elimination of C2, T3, and D1 shown in Figure 13 (or Figure 17). The approach shown in Figure 19 thus advantageously allows for elimination of the high voltage insulation requirement of T3 as well as the high voltage rated diode D1 . The voltage multiplier may be implemented with diode capacitor voltage multipliers and / or may have a multiplication factor of between 2-20 times. For example, by using a Cockcroft- Walton multiplier. In use, the voltage multiplier 1802 may charge capacitor C3 using input to the multiplier from one secondary of T2(1804). During stimulationevents, the H2 bridge 1810 rapidly discharges C3 to apply the shock to the patient.

[0110] The following is an example of non-magnetic transformer that may be used in accordance with the transformer T2 (1804) shown in Figures 17 and 19.

[0111] In certain example embodiments, the voltage multiplier may be preferably at least 5 times, preferably between 8-15 times, and more preferably between 10-12 times. In certain examples, for a 300-volt input, the diodes and capacitors in the voltage multiplier 1802 may be rated above 300 volts (e.g., typically may be rated for twice that amount). However, this rating may be advantageously lower than the, for example, 3000 voltage rating needed for D1 and T2 from Figure 13. The voltage generated by H1 ma be typically a 500 kHz square wave with a peak amplitude of 24-28 volts. The square wave is applied toC1 and the primary of T2. The resonance between C1 and the leakage inductance of T2, along with the load of the voltage multiplier, then causes the secondary to have a voltage that starts at zero at the beginning of a C3 charge cycle, and increase to, for example, around 300 volts at the end of the charge cycle.

[0112] The circuit shown in Figure 19 may be similar to that shown in Figures 17 or 18. However, instead of the D1 diode C2 capacitor as shown in Figure 18, the circuit in Figure 19 may include the voltage multiplier. In certain example embodiments, as an illustrative example of transformer T2 in combination with the examples shown in Figure 19, if a voltage multiplier uses a 5-stage Cockcroft- Walton configuration and the primary of T2 is fed with approximately 24-28V AC, then the secondary of T2 1804 would produce roughly 250-320V AC peak, which when multiplied by 10 (five stages x 2) would yield about 3200V DC for the H2- Bridge rail.Defibrillation Examples

[0113] The techniques discussed herein allow for defibrillation to be performed inside the bore of an MRI scanner that is powered. The techniques discussed herein also allow for defibrillation to be performed just outside the bore of the MRI scanner. Such defibrillation may be performed using any of the circuits described herein.

[0114] In testing the techniques discussed herein, a swine was placed inside the bore of a 1 .5 T MRI system. The swine was instrumented with defibrillation pads and connected to cabling. A defibrillator cable (e.g., with balun(s) arranged to extend out to an example defibrillator. The defibrillator was placed adjacent to the MRI scanner (e.g., similar the illustrative view shown in Figure 1 ) which was powered and on. In the example, the swine was in VF and then defibrillation was performed. After defibrillation, the swine was observed with a sinus rhythm.

[0115] In another example, the techniques for non-magnetic defibrillators were also applied to a 3T MRI scanner. In that example, a swine was placed intoVF on the 3T MRI table outside of the scanner that was active. Resulting application of defibrillation to the swine using an example non-magnetic defibrillator provided restoration of sinus rhythm to the swine after defibrillation has been performed using an example non-magnetic defibrillator. As with the other examples, the non-magnetic defibrillator awas placed adjacent to the MRI scanner during operation thereof (e.g., inside the 400 Gauss line).

[0116]

[0117] In certain examples, a method of providing defibrillation to a patient in an MRI machine is provided an includes: delivering a ramped High Frequency Alternating Current (rHFAC) to the patient; and subsequent to delivery of rHFAC, delivering defibrillation energy to the patient. The defibrillation energy may be automatically delivered less than 40 milli-seconds after end of delivery of the rHFAC. The rHFAC may be delivered over a period of at least 0.5 seconds.

[0118] The voltage of the rHFAC can be ramped up over the period that the rHFAC is applied. The peak voltage of the rHFAC can be less than 140 volts. An MRI defibrillator may be configured to perform any of the methods described herein. An MRI conditional defibrillator may be configured to perform any of the methods described herein.Selected Terminology

[0119] The elements described in this document include actions, features, components, items, attributes, and other terms. Whenever it is described in this document that a given element is present in “some embodiments,” “various embodiments,” “certain embodiments,” “certain example embodiments, “some example embodiments,” “an exemplary embodiment,” “an example,” “an instance,” “an example instance,” or whenever any other similar language is used, it should be understood that the given element is present in at least one embodiment, though is not necessarily present in all embodiments. Consistent with the foregoing, whenever it is described in this document that an action “may,” “can,” or“could” be performed, that a feature, element, or component “may,” “can,” or “could” be included in or is applicable to a given context, that a given item “may,” “can,” or “could” possess a given attribute, or whenever any similar phrase involving the term “may,” “can,” or “could” is used, it should be understood that the given action, feature, element, component, attribute, etc. is present in at least one embodiment, though is not necessarily present in all embodiments.

[0120] Terms and phrases used in this document, and variations thereof, unless otherwise expressly stated, should be construed as open-ended rather than limiting. As examples of the foregoing: “and / or” includes any and all combinations of one or more of the associated listed items (e.g., a and / or b means a, b, or a and b); the singular forms “a”, “an”, and “the” should be read as meaning “at least one,” “one or more,” or the like; the term “example”, which may be used interchangeably with the term embodiment, is used to provide examples of the subject matter under discussion, not an exhaustive or limiting list thereof; the terms “comprise” and “include” (and other conjugations and other variations thereof) specify the presence of the associated listed elements but do not preclude the presence or addition of one or more other elements; and if an element is described as “optional,” such description should not be understood to indicate that other elements, not so described, are required.

[0121] The claims are not intended to invoke means-plus-function construction / interpretation unless they expressly use the phrase “means for” or “step for.” Claim elements intended to be construed / interpreted as means-plus- function language, if any, will expressly manifest that intention by reciting the phrase “means for” or “step for”; the foregoing applies to claim elements in all types of claims (method claims, apparatus claims, or claims of other types) and, for the avoidance of doubt, also applies to claim elements that are nested within method claims. Consistent with the preceding sentence, no claim element (in any claim of any type) should be construed / interpreted using means plus functionconstruction / interpretation unless the claim element is expressly recited using the phrase “means for” or “step for.”

[0122] Whenever it is stated herein that a hardware element (e.g., a processor, a network interface, a display interface, a user input adapter, a memory device, or other hardware element), or combination of hardware elements, is “configured to” perform some action, it should be understood that such language specifies a physical state of configuration of the hardware element(s) and not mere intended use or capability of the hardware element(s). The physical state of configuration of the hardware elements(s) fundamentally ties the action(s) recited following the “configured to” phrase to the physical characteristics of the hardware element(s) recited before the “configured to” phrase. In some embodiments, the physical state of configuration of the hardware elements may be realized as an application specific integrated circuit (ASIC) that includes one or more electronic circuits arranged to perform the action, or a field programmable gate array (FPGA) that includes programmable electronic logic circuits that are arranged in series or parallel to perform the action in accordance with one or more instructions (e.g., via a configuration file for the FPGA). In some embodiments, the physical state of configuration of the hardware element may be specified through storing (e.g., in a memory device) program code (e.g., instructions in the form of firmware, software, etc.) that, when executed by a hardware processor, causes the hardware elements (e.g., by configuration of registers, memory, etc.) to perform the actions in accordance with the program code.

[0123] A hardware element (or elements) can be therefore be understood to be configured to perform an action even when the specified hardware element(s) is / are not currently performing the action or is not operational (e.g., is not on, powered, being used, or the like). Consistent with the preceding, the phrase “configured to” in claims should not be construed / interpreted, in any claim type (method claims, apparatus claims, or claims of other types), as being a meansplus function; this includes claim elements (such as hardware elements) that are nested in method claims.Additional Applications of Described Subject Matter

[0124] Although process steps, algorithms or the like may be described or claimed in a particular sequential order, such processes may be configured to work in different orders. In other words, any sequence or order of steps that may be explicitly described or claimed in this document does not necessarily indicate a requirement that the steps be performed in that order; rather, the steps of processes described herein may be performed in any order possible. Further, some steps may be performed simultaneously (or in parallel) despite being described or implied as occurring non-simultaneously (e.g., because one step is described after the other step). Moreover, the illustration of a process by its depiction in a drawing does not imply that the illustrated process is exclusive of other variations and modifications thereto, does not imply that the illustrated process or any of its steps are necessary, and does not imply that the illustrated process is preferred.

[0125] Although various embodiments have been shown and described in detail, the claims are not limited to any particular embodiment or example. None of the above description should be read as implying that any particular element, step, range, or function is essential. All structural and functional equivalents to the elements of the above-described embodiments that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the invention. No embodiment, feature, element, component, or step in this document is intended to be dedicated to the public.

Claims

CLAIMS1 . An MRI conditional defibrillator comprising: isolated power supply circuitry configured to be couple to a non-isolated mains power supply, the isolated power supply circuitry comprising a first H-bridge circuit driving a first non-magnetic transformer; and shock capacitor charging circuitry comprising: a second non-magnetic transformer having a primary winding and at least one secondary winding, a voltage multiplier having an input electrically coupled to the secondary winding of the second non-magnetic transformer and an output, a shock capacitor electrically coupled to the output of the voltage multiplier, and a second H-bridge circuit configured to discharge the shock capacitor to produce a defibrillation waveform.

2. The MRI conditional defibrillator of claim 1 , the shock capacitor charging circuit further including a resonant capacitor connected in series with the primary winding of the second non-magnetic transformer.

3. The MRI conditional defibrillator of any one of the above claims, wherein the voltage multiplier may be preferably at least 5 times, and more preferably between 10-12 times.

4. The MRI conditional defibrillator of any one of the above claims, wherein the at least one secondary winding of the second non-magnetic transformer includes first, second, and third secondary windings.

5. The non-magnetic transformer of any one of the above claims, wherein a core of the first non-magnetic transformer and / or the second non-magnetic transformer is UHMW Polyethylene.

6. The non-magnetic transformer of any one of the above claims, further comprising an rHFAC generator is configured to generate a peak voltage below 140 V that is delivered to a patient.

7. An MRI conditional defibrillator comprising: isolated power supply circuitry configured to couple to a non-isolated mains power supply, the isolated power supply circuitry including a first H-bridge circuit;a first non-magnetic transformer having a primary winding and at least one secondary winding, wherein output from the first H-bridge is coupled to the primary of the first non-magnetic transformer; and shock capacitor charging circuitry comprising: a resonant capacitor coupled to the secondary winding of the first non-magnetic transformer, rectifying circuitry configured to rectify current from the resonant capacitor, a shock capacitor electrically coupled to the rectifying circuitry, and a second H-bridge circuit configured to discharge the shock capacitor to produce a defibrillation waveform.

8. The MRI conditional defibrillator of claim 7, wherein the rectifying circuitry includes a diode.

9. The MRI conditional defibrillator of claim 7, wherein the non-magnetic transformer rectifying circuitry includes a voltage step-up of at least 100x.

10. The MRI conditional defibrillator of claim 7, wherein the first nonmagnetic transformer comprises UHMW Polyethylene.11 . The MRI conditional defibrillator of claim 7, wherein the shock capacitor charging circuitry further comprises a second non-magnetic transformer connected in series with the first non-magnetic transformer.

12. An MRI conditional defibrillator comprising: a first non-magnetic transformer; a first resonant capacitor that is connected, in series, with the first nonmagnetic transformer; and a second non-magnetic transformer, wherein the second non-magnetic transformer is connected in series to the first non-magnetic transformer through the first resonant capacitor.

13. The MRI conditional defibrillator of claim 12, further comprising: a second resonant capacitor in series with the first non-magnetic transformer.

14. The MRI conditional defibrillator of any one of claims 12-13, wherein the second non-magnetic transformer includes a first secondary and a second secondary.

15. The MRI conditional defibrillator of any one of claims 12-14, wherein the first and second non-magnetic transformers include a voltage step-up of at least 5 to 20 times.

16. An MRI conditional defibrillator comprising:A non-magnetic transformer that is used in a single transformer capacitor charging circuit.

17. The MRI conditional defibrillator of claim 16, wherein the non-magnetic transformer includes first, second, and third secondaries.

18. The MRI conditional defibrillator of claim 17, wherein the non-magnetic transformer has a voltage step-up of at least 90 times.

19. The MRI conditional defibrillator of claim 17, further comprising: a first H-Bridge that is configured to generate a square wave.

20. The MRI conditional defibrillator of claim 19, wherein the square wave that is generate is at least 400 kHz from supplied DC power.21 . The MRI conditional defibrillator of claim 20, further comprising:a first resonant capacitor, wherein the at least 400 kHz is applied to a primary of the non-magnetic transformer via the first resonant capacitor.

22. The MRI conditional defibrillator of claim 21 , further comprising: a second resonant capacitor; and a shock capacitor, wherein a secondary of the non-magnetic transformer is connected to the second resonant capacitor to apply output of the non-magnetic transformer to a diode to charge a shock capacitor.

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