ENDOENTERIC BALLOON COIL

Abstract

A catheter for use in magnetic resonance imaging includes a catheter shaft having a proximal end and a distal end. A flexible lumen is supported on the distal end of the shaft, and the flexible lumen is configured to be expanded and contracted using a fluid introduced via the proximal end of the catheter shaft. A magnetic resonance coil formed on the flexible lumen such that the magnetic resonance coil may expand and contract with the flexible lumen. The magnetic resonance coil is coupled to an external match and tune circuit via magnetic resonance imaging device. The balloon coil includes nested bazooka or sleeve baluns along the length of the cable to minimize common mode currents on the outer surface of the cable to prevent high current hot spots that cause heating of the cable.

Claims

1. A catheter comprising: a catheter shaft including a proximal end and a distal end; a flexible lumen supported on the distal end of the shaft, the flexible lumen configured to be expanded and contracted using a fluid introduced via the proximal end of the catheter shaft; and a magnetic resonance coil formed on an exterior surface of the flexible lumen.

2. The catheter of claim 1, wherein the magnetic resonance coil deforms to expand and contract with the flexible lumen.

3. The catheter of claim 1, wherein the magnetic resonance coil is at least partially formed from a conductive ink.

4. The catheter of claim 3, wherein the magnetic resonance coil is formed from a metal coupled to the conductive ink.

5. The catheter of claim 1, wherein the proximal end is disposed externally to a patient.

6. The catheter of claim 5, wherein the proximal end is coupled to a match and tune circuit of a magnetic resonance imaging device.

7. The catheter of claim 1, wherein the magnetic resonance coil is coupled to a magnetic resonance imaging device via a cable including at least one balun.

8. A magnetic resonance imaging system comprising: a magnetic resonance imaging device; a catheter including a magnetic resonance coil that is coupled to the magnetic resonance imaging device, the catheter including a catheter shaft including a proximal end and a distal end; a flexible lumen supported on the distal end of the shaft, the flexible lumen configured to be expanded and contracted using a fluid introduced via the proximal end of the catheter shaft; and the magnetic resonance coil formed on an exterior surface of the flexible lumen; wherein the magnetic resonance imaging device includes a match and tune circuit that is disposed remotely from the magnetic resonance coil.

9. The magnetic resonance imaging system of claim 8, wherein the match and tune circuit is disposed externally to a patient when the magnetic resonance imaging system is being operated.

10. The magnetic resonance imaging system of claim 8, wherein the magnetic resonance coil is coupled to the match and tune circuit via a cable that includes at least one balun.

11. The magnetic resonance imaging system of claim 8, wherein the magnetic resonance coil deforms to expand and contact with the flexible lumen.

12. The magnetic resonance imaging system of claim 8, wherein the magnetic resonance coil is at least partially formed from a conductive ink.

13. The magnetic resonance imaging system of claim 12, wherein the magnetic resonance coil is formed from a metal coupled to the conductive ink.

14. A method for magnetic resonance imaging of anatomical locations within a patient, the method comprising: inserting a catheter into the patient, the catheter including a flexible lumen supported on a distal end of the catheter that is configured to be expanded and contracted using a fluid introduced via a proximal end of the catheter, a magnetic resonance coil formed on an exterior surface of the flexible lumen, the flexible lumen being contracted during insertion; locating the catheter to a desired anatomical location within the patient; expanding the flexible lumen; and performing magnetic resonance imaging using a magnetic resonance imaging system.

15. The method of claim 14, further including matching and tuning the magnetic resonance coil based on the anatomical location of the catheter via a match and tune circuit that is disposed externally to the patient.

16. The method of claim 15, wherein the match and tune circuit is coupled to the magnetic resonance coil via a cable including at least one balun.

17. The method of claim 14, wherein expanding the flexible lumen includes expanding the magnetic resonance coil formed on the flexible lumen.

18. The method of claim 14, wherein inserting the catheter includes placing the catheter into a gastrointestinal tract of a patient.

19. The method of claim 14, wherein the magnetic resonance coil is at least partially formed from a conductive ink.

20. The method of claim 19, wherein the magnetic resonance coil is formed from a metal coupled to the conductive ink.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1A is a side view of a balloon catheter with RF coil for MRI known in the prior art.

[0022] FIG. 1B is a front view of a balloon catheter with RF coil for MRI known in the prior art.

[0023] FIG. 2 is a perspective view of an exemplary RF balloon coil in an inflated state.

[0024] FIG. 3 is a perspective view of the RF balloon coil in a deflated state.

[0025] FIG. 4 is a schematic diagram of the RF balloon coil coupled to an MRI device.

[0026] FIG. 5 is a photograph of a set of RF coils used for testing.

[0027] FIG. 6 is a graph of relative signal to noise ratio vs. distance including plots for the coils shown in FIG. 5.

[0028] Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

DETAILED DESCRIPTION

[0029] FIGS. 2 and 3 illustrate a catheter-based radio frequency (RF) balloon coil or balloon coil 40 according to an embodiment of the present invention. The balloon coil 40 is configured to be inserted into a patient (e.g., into the gastrointestinal (GI) tract) and is used to acquire high resolution MRI images (i.e., high signal to noise ratio (SNR)) by achieving high sensitivity and rapid image acquisition speed. The balloon coil 40 may be used in MRI imaging of various locations within the human body, but is particularly useful for imaging the pancreas and upper GI tract (i.e., esophagus, stomach, duodenum, etc.). As a result of the high resolution MRI images obtained when using the balloon coil 40, health professionals may identify very small lesions that may otherwise not be identified in standard MRI processes. The increased resolution also allows health professionals to more accurately characterize lesions identified in MRI images. In addition, due to the high resolution imaging, the balloon coil 40 has been contemplated as useful in Focused Ultrasound (FUS) treatments. Specifically, FUS treatments could be monitored for a number of factors, such as temperature.

[0030] With continued reference to FIGS. 2 and 3, the balloon coil 40 includes a balloon 44 supported on a distal end 48 of a catheter shaft 52. The balloon 44 is defined by a flexible lumen 56 delimiting an inflatable interior volume and an exterior surface. The exterior surface supports a thin, flexible metal 60 (i.e., copper, silver, etc.) that is generally deformable with the flexible lumen 56. In the illustrated embodiment, the metal 60 forms a single, generally continuous strip extending radially around the lumen 56. However, other suitable patterns and formations (e.g., arrays) may be used. In some embodiments, a second balloon may be placed over the balloon 44 as a protective sheath to provide, among other things, water proofing and abrasion protection for the balloon coil 40.

[0031] The catheter shaft 52 includes a body extending from a proximal end (not shown) to the distal end 48 of the shaft 52. The proximal end includes a fluid inlet fluidly coupled to a fluid outlet, located on the distal end 48 of the shaft 52 within the interior volume of the lumen 56, by a conduit extending through an interior of the body. The conduit allows a user to introduce or remove a fluid (i.e., air, saline solution, etc.) through the inlet in order to inflate (FIG. 2) and deflate (FIG. 3) the balloon 44. Inflation is generally accomplished after the distal end has been inserted into a patient.

[0032] As noted above, RF coils for use with MRI devices include a match and tune circuit that is coupled at or near a feed point of a loop of the coil in order to match the received MRI signal to a cable (e.g., a coax cable) that carries the MRI signal to a preamp of the MRI device for amplification. The balloon coil 40, however, is configured to be inserted into a patient. Therefore, a match and tune circuit that results in an increase in size or complexity of the balloon coil 40 may be disadvantageous in certain embodiments.

[0033] In the embodiment illustrated in FIG. 4, the balloon coil 40 is configured to be coupled to a preamp 64 of an MRI device 68 via a half wavelength cable 72 such a match and tune circuit 76 may be positioned remotely from the balloon coil 40 (e.g., external to the patient and/or proximate to the preamp) thereby reducing the overall size and complexity of the balloon coil 40. This configuration enables tuning and matching of the balloon coil 40 to any anatomy the balloon coil 40 may be used for because it enables external tuning and matching after the balloon coil 40 has been positioned within a patient. In addition, the cable 72 is in electrical isolation along the entire length of the cable 72 such that risk of electrical shock and arcing (i.e., RF burns) are mitigated.

[0034] In the embodiment described above, the length of the half wavelength cable 72 may pose difficulties for operations. For example, during the transmit portion of an MRI pulse sequence, RF power deposition may be negatively affected by an outer shield of the cable 72 becoming an antenna that picks up transmit power from a transmit coil of the MRI device resulting in hot spots along the cable 72. Hot spots along the cable could potentially reach temperatures that would damage tissue of a patient that is adjacent to the cable 72.

[0035] To counteract this potential downfall, the balloon coil 40 includes nested bazooka or sleeve baluns 80 along the length of the cable to minimize common mode currents on the outer surface of the cable 72 to prevent high current hot spots that cause heating of the cable 72.

[0036] Two methods of constructing the balloon coil 40 have been specifically contemplated, although other construction methods are possible. The first involves constructing a metal loop on the balloon substrate using an electroless plating bath followed by an electroplating process to deposit metal 60 onto the exterior surface of the lumen 56. In this process, the entire exterior surface is plated with metal, and then unwanted metal is removed using an etching process. In one example, the etching process includes using ferric chloride to remove metal 60 from the balloon 44. However, other metal removal processes have been contemplated as useful. Then, the metal 60 is tuned to an MRI acceptable frequency of approximately 123 MHz using tuning wires attached to the loop so the coil is functional for MRI.

[0037] As seen in FIGS. 2-3, this construction method yields a balloon coil 40 that provides high coil conductivity while also providing a high degree of balloon coil 40 flexibility. FIG. 2 illustrates the balloon coil 40 in an inflated state, in which the metal 60 is generally continuous with the lumen 56 of the balloon 44. FIG. 3 illustrates the balloon coil 40 in a deflated state, in which the metal 60 has deformed with the lumen 56 as the balloon 44 was deflated such that the overall profile of the balloon coil 40 is greatly reduced. This allows a medical professional to easily introduce the balloon coil 40 into a patient while also providing a high degree of maneuverability for placing and orienting the balloon coil 40.

[0038] In a second method of constructing the balloon coil, a conductive ink (e.g., silver containing ink, etc.) is applied to the exterior surface of the lumen 56 in a pattern corresponding to the desired metal geometry. The ink is then cured to form a conductive surface lumen 56.

[0039] In one embodiment, the balloon 44 is subsequently electroplated such that metal 60 (e.g., copper, etc.) is deposited on the patterned conductive ink thereby increasing conductivity. The metal 60 is deposited such that it forms a thick enough layer to be operational as an MRI coil, yet flexible enough to be collapsible with the balloon lumen 56. Next, each of the coils will be tuned to acceptable MRI frequencies.

[0040] One advantage of the conductive ink lies in the fact that a specific pattern may be applied to the lumen and metal may be electroplated only to that surface. This negates the tedious etching process described above. In addition, this process also aids in optimizing balloon coil characteristics, such as metal thickness, balloon coil flexibility, and balloon coil SNR capabilities.

[0041] Testing has revealed the ability of silver conductive ink, and electroplated conductive ink, to be an effective radio frequency MRI coil. In an exemplary study, illustrated in FIGS. 5 and 6, six coils were evaluated with all imaging done on a Siemens Tim Trio 3T MRI Scanner. All coils were constructed on fiberglass formers as 52/62 mm inner/outer diameter coils with a single gap. The comparison standard (Coil-A, see Tablel below for characteristics) was solid copper. Coils B and C were thick and thin silver ink traces (Creative Materials Inc., 120-07), respectively, without plating. Coils D-F were thin silver ink traces that were copper plated for 5, 10 and 15 minutes, respectively. All loops were coated with varnish to keep the thin copper layers from oxidizing. 18-gauge tinned-copper wire leads and a tune/match circuit were positioned at the gap (FIG. 5). Leads were connected to Coil-A with solder and with silver ink for all other loops. Silver ink traces were cured at 130 C. for 5 minutes. Electrode copper plating was performed for coils D-F after an acid wash at 0.5 volts. The DC resistance was measured for each loop before circuitry was added. Each loop was tuned and matched at 123 MHz with an insertion loss better than 35 dB. Active and preamp detuning were better than 35 dB and 20 dB, respectively. SNR measurements were made using standard GRE sequences (TR/TE/flip/FOV=500 ms/4 ms/90/280 mm, 128128 matrix). SNR plots were constructed by averaging 5 image pixels through the axis of the coil, over 5 different scans for each coil.

TABLE-US-00001 TABLE 1 ink plating copper thickness time thickness ohms coil (m) (min) (m) (DC) rSNR description A 0 0 35 0.3 209.3 standard copper coil.sup.2 B ~15.sup.1.sup. 0 0 1 159.5 thick silver ink.sup.3 C ~6 0 0 1.7 139.7 thin silver ink.sup.4 D ~11 5 ~3 0.7 181.8 thin ink, 5 min plate.sup.5 E ~7 10 ~6 0.7 177.1 thin ink, 10 min plate F ~6 15 ~9 0.7 195.7 thin ink, 15 min plate .sup.1Approximate silver ink and copper thickness was measured by averaging measurements at 3 different positions on the loop using a hand held micrometer. .sup.2Copper etched on 1 oz. copper clad Kapton substrate (Dupont FR9150). .sup.3Thick silver ink trace constructed using masking tape mask and squeegeeing the ink with a plastic ruler. .sup.4Thin silver ink trace constructed using a masking tape mask and painting the trace with a small paintbrush. .sup.5Plating voltage was set at 0.5 volts.

[0042] Results from this study show that the silver ink used can be electroplated with copper and, although the plating only occurs on one side of the silver trace, the electrical conductivity of the loop does increase. Silver ink thickness, plated copper thickness and DC resistance measurements are presented in Table 1. In addition, Table 1 shows example relative SNR measurements from ROIs near the coil. FIG. 6 shows the relative SNR results for the 6-coil comparison. As expected, these plots show the significant difference in SNR between the solid copper loop and the ink loops. They also demonstrate how conductivity is increased with copper plating. Results for Coil-E were not expected since its copper thickness would indicate a resulting SNR between those of Coil-D and Coil-F. Although every effort was made to keep the coil tune and match properties consistent, the loops were very sensitive and there may have been some unresolved problem with the silver ink wire attachments for Coil-E during the SNR measurements.

[0043] This work demonstrates that copper plating of silver ink coils is possible and it indicates that significant improvements in coil trace conductivity can be achieved. Consequently, the SNR performance of silver ink coils that have been plated with copper improves over silver ink coils without plating.

[0044] Although the invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of one or more independent aspects of the invention as described.