Balloon catheter

1. A catheter comprising:

a flexible heat transfer element provided on an outer surface of the catheter;

a first conduit arranged to supply an inflation fluid for inflating the flexible heat transfer element so as to form an inflated outer balloon; and

an inner balloon, coaxially arranged with the inflated outer balloon;

a second conduit arranged to supply an inflation fluid for inflating the inner balloon;

a plurality of cooling elements arranged to cool said inflation fluid for inflating the outer balloon;

wherein each cooling element comprises a first tube provided inside a second tube, wherein the first tube is substantially parallel to the second tube;

wherein the second tube is configured to receive a flow of a coolant for cooling the cooling element from the first tube;

wherein each cooling element comprises an elongate cooling chamber configured to receive coolant from the first tube and provide said coolant to the second tube; wherein each of the cooling elements is arranged on an outer surface of the inner balloon; and

wherein, when the inner balloon and the outer balloon are inflated, the cooling elements are spaced from an inner surface of the outer balloon.

2. The catheter according to claim 1 , wherein the cooling elements are arranged within the catheter so that the inner surface of the outer balloon is cooled substantially uniformly.

3. The catheter according to claim 1 , wherein said cooling elements are elongate and arranged parallel to one another.

4. The catheter according to claim 3 , wherein each cooling element has substantially the same lateral spacing from an axis of the outer balloon parallel to the cooling elements.

5. The catheter according to claim 1 , wherein, as viewed in the plane normal to the longitudinal axis of the cooling elements and relative to the center of the outer balloon, each of a plurality of the cooling elements is separated from an adjacent cooling element by a substantially equal angle.

6. The catheter according to claim 1 , wherein said cooling elements are configured such that, when the flexible heat transfer element is inflated, a spacing between the cooling elements is larger than when the outer balloon is not inflated.

7. The catheter according to claim 1 , wherein said plurality of cooling elements comprises at least three cooling elements.

8. The catheter according to claim 1 , wherein said catheter is a perfusion catheter further comprising a central perfusion lumen configured to convey a bodily fluid along the center of the catheter, wherein said cooling elements are arranged around said perfusion lumen.

9. The catheter according to claim 1 wherein, in use in a vessel, the inflated flexible heat transfer element occludes fluid flow between the walls of the vessel and the inflated flexible heat transfer element.

10. The catheter according to claim 1 , wherein said plurality of cooling elements are provided inside the flexible heat transfer element.

11. The catheter according to claim 1 , wherein, in use, the first tube and the second tube are operated such that the pressure of the second tube is lower than the first tube.

12. The catheter according to claim 1 , wherein for each cooling element, the elongate cooling chamber is arranged co-linearly with an end of the second tube.

13. The catheter according to claim 1 , wherein each cooling element further comprises a restriction tube configured to convey the coolant from the first tube to the cooling chamber, wherein said restriction tube has narrower internal diameter than the first tube.

14. The catheter according to claim 13 , wherein the restriction tube and cooling chamber are configured such that when the coolant conveyed along the first tube is a liquid, at least some of the coolant undergoes a phase change in the restriction tube and/or in the cooling chamber and returns through the second tube as a gas.

15. The catheter according to claim 1 , wherein the first conduit is further configured to provide a return flow of the inflation fluid of the flexible heat transfer element.

16. The catheter according to claim 1 , further comprising a guide wire lumen, wherein each of the cooling elements is not attached to an end of the guide wire lumen and wherein each cooling element is configured such that, when in use, the flow of the coolant causes the cooling element to vibrate.

17. The catheter according to claim 1 , wherein each cooling element is configured such that, when the outer balloon is inflated, each cooling element is configured to at least partially have a helical shape.

18. A catheter comprising:

a plurality of heat transfer elements, wherein each heat transfer element is flexible and is configured to be inflated with an inflation fluid so as to form a respective cooling element balloon;

wherein each cooling element balloon comprises a cooling element arranged to cool said inflation fluid;

wherein each cooling element comprises a first tube provided inside a second tube, wherein the first tube is substantially parallel to the second tube; and the second tube is configured to receive a flow of a coolant for cooling the cooling element from the first tube,

wherein the cooling element balloons are elongate and extend along a common axis; and

wherein the cooling element balloons are laterally displaced from each another in a direction perpendicular to the common axis.