This is the national phase under 35 U.S.C. § 371 of International Application No. PCT/US2013/030166 filed on Mar. 11, 2013, the entire disclosure of which is incorporated by reference herein.
Provided are devices and methods for limiting the rotational force imparted on an imaging probe spinning inside a patient to reduce the likelihood of an unsafe condition should the imaging probe suddenly bind but still provides sufficient rotational force when there are no unsafe conditions.
Imaging of body lumens (e.g., vasculature) can require relatively high torque and relatively high rotational speeds to spin an imaging probe, such as an optical coherence tomography (OCT) probe, intravascular ultrasound probe (IVUS), or fractional flow reserve probe (FFR), inside the body lumen. Generally, an imaging probe is inserted in a body lumen of a patient and a motor located outside the patient spins a torque wire which is connected to the imaging probe. Imaging systems have unique torque wire requirements as the optical fiber rotates with the torque wire, adding mass and stiffness. However, high torque and high speed rotation can pose a significant risk of patient harm should the imaging probe unexpectedly bind because the motor will continue spinning the torque wire and the binding will spin the catheter sheath which encloses the torque wire inside the body lumen, potentially causing patient harm.
The invention relates, in part, to a frictional torque limiter assembly for an imaging core spinning in a patient's body. The torque limiter assembly torsionally isolates the imaging core from a motor that spins the imaging core. The motor is connected to an optical connector which, in turn, is directly or indirectly connected to a drive tube. A spacer tube is secured in the lumen of the drive tube by interference fit. The interference fit is made possible by an axial slit in the drive tube that extends from one end partially along the length of the drive tube. The spacer tube is connected to a torque wire which, in turn, is attached to the imaging probe. An optic fiber or wire is disposed in the torque wire and connects the optical connector to the imaging probe. During imaging, the optical connector, the drive tube, the spacer tube, the torque wire, and the imaging probe spin in unison. The interference fit between the spacer tube and the drive tube is configured such that, if the torque wire or the imaging probe binds, the spacer tube slips within the drive tube. The spacer tube therefore acts as a clutch that allows torque wire to stop or spin at a slower rate than drive tube until the motor is stopped, thereby preventing an unsafe condition.
The invention provides, in part, a torque limiter for an intravascular imaging probe. The torque limiter includes a drive tube. The drive tube has a wall that defines a drive tube lumen having an inside diameter. The drive tube wall defines or forms a slit extending from a first end of the drive tube lumen along a portion of the drive tube wall. The torque limiter also includes a spacer tube received in the first end of the drive tube lumen. The spacer tube has a spacer tube wall that defines an outside diameter. At least a portion of the spacer tube wall is in interference fit with the inside diameter of the drive tube wall. In addition, the torque limiter includes a torque wire attached to the spacer tube. Accordingly, the spacer tube spins within the drive tube if torque on the torque wire exceeds a predetermined threshold, thereby preventing an unsafe patient condition.
In some embodiments, the spacer tube wall forms a circumferential collar and the circumferential collar is interference fit with the inside diameter of the drive tube wall. The circumferential collar can be located at an end of the spacer tube, or the circumferential collar can be located between the ends of the spacer tube, such as at or near the center of the spacer tube. The circumferential collar also can have a chamfered edge to facilitate insertion into the drive tube during assembly.
In some embodiments, substantially the entire spacer tube wall is interference fit with the inside diameter of the drive tube wall. In some embodiments, the slit extends axially along the drive tube wall. In some embodiments, the device includes an optical coherence tomography probe coupled to an optical fiber disposed in the torque wire. In some embodiments, the device includes an intravascular ultrasound probe. In some embodiments, the interference fit has a torsional strength of about 0.1 ounce-inches to about 0.4 ounce-inches. In some embodiments, the slit is wider at its closed end than at its open end. In some embodiments, the drive tube wall has a thickness and the thickness is reduced along at least a portion of the slit. In some embodiments, the drive tube wall forms a slot parallel to the slit, the slot having closed ends.
The invention relates, in part, to a torque limiter for an intravascular imaging probe. The torque limiter includes a clutch that includes a first rotatable tube defining a first bore, the first tube comprising a first tube wall defining a slit extending from a first end of the first rotatable tube, the first rotatable tube having a length T1; and a second rotatable tube defining a second bore, the second tube comprising a second tube wall, the first rotatable tube having a length T2, the second rotatable tube disposed within the first rotatable tube such the first bore is substantially concentric with the second bore, the second bore aligned to receive a torque wire below the slit, the second rotatable tube clutched by the first tube wall on either side of the slit such that the second rotatable tube is configured to slip or rotate if a torque on the torque wire exceeds a predetermined threshold. The torque limiter can further include the torque wire.
In one embodiment, T1 is greater than T2. In one embodiment, the slit is wider at its closed end than at its open end. In one embodiment, the second rotatable tube is interference fit within the first rotatable tube. In one embodiment, the interference fit has a torsional strength of about 0.1 ounce-inches to about 0.4 ounce-inches. In one embodiment, the second tube wall includes a circumferential collar interference fit with an inside diameter of the first bore.
The figures are not necessarily to scale, emphasis instead generally being placed upon illustrative principles. The figures are to be considered illustrative in all aspects and are not intended to limit the invention, the scope of which is defined only by the claims.
An intralumenal imaging system generally comprises an imaging core that is mechanically coupled to a motor 102 that spins one or more components of the imaging core.
With continued reference to
In some embodiments, spacer tube 108 forms a protrusion 204 and the protrusion is configured to cause an interference fit with the drive tube wall. Protrusion 204 can be any suitable shape that provides sufficient friction between the spacer tube 108 and the drive tube 106. In some embodiments, protrusion 204 is a circumferential collar that has a width 205. In some embodiments, the spacer tube 108 has a substantially uniform diameter (see
Torque wire 112 is securely attached to spacer tube 108, such as by glue or welding 208 so that rotational force applied to the spacer tube is transferred to the torque wire. The torque wire is attached at least to the distal end of the spacer tube, and can be partially or completely inserted through the lumen 111 of the spacer tube.
The spacer tube 108 and the drive tube 110 mate by interference fit. They are not attached (e.g., welded or glued). This interference fit transmits torque from the patient interface unit (PIU) motor 102, through connector 104, into drive tube 106, through the interference fit to spacer tube 108 and finally to torque wire 112 and imaging probe 114. Should torque wire 112 experience unsafe binding to the non-rotating sheath or catheter 120 which covers it, spacer tube 108 will slide within drive tube 106 at the interference fit. The torque transmitted will decrease as sliding friction is lower than static friction and additional torque and rotations of the sheath cannot be generated. As spacer tube 108 spins inside the drive tube 106, the optical fiber or wire 118 winds up. After a few winds the optic fiber or wire 118 breaks, and loss of signal can automatically trigger the motor 102 to stop, ending the unsafe condition. In some embodiments, fiber or wire breakage is detected using software. The frictional torque limiter therefore provides an immediate response to unsafe torque levels until the motor can be stopped.
Referring to
Referring to
The spacer tube also is substantially cylindrical in shape. In preferred embodiments, spacer tube 108 has an outside diameter of 0.035 inches and an inside diameter of 0.023 inches, and is manufactured by Swiss machining. Thus, the outside diameter of the spacer tube is slightly larger than the inside diameter of the drive tube. The spacer tube is made of 300 series stainless steel, in one embodiment. In another embodiment, the spacer tube is made of aluminum.
The interference between the spacer tube and the drive tube has a tight tolerance. Preferred dimensions and tolerances are provided in Table 1.
Using the sum of tolerances, a conservative method, the interference fit between the drive tube and space tube can vary by ±0.0007 inches. This tight tolerance is sufficient to provide a repeatable torque at which the joint consistently slips. The following analysis can be used to calculate the torque value:
The coefficient of static friction controls the limiting torque value. The static friction (μ) for steel on steel is:
μ=0.8
The frictional force (F) is:
F=μN
Where
N=the normal force between the drive tube and the spacer tube
The limiting torque (T) is:
T=rF
Where
r=the radius of the protrusion on the spacer (half the diameter).
When the spacer tube is inserted into the drive tube, the slit in the drive tube opens up from the interference fit. Once the spacer tube is inserted and the slit expanded, the drive tube no longer is round as a result the interference fit. Thus, the interference force is not uniform around the spacer.
The length of the slit is chosen such that over the tolerance of the optical core, the spacer will be located in an area where the breakaway torque will be invariant of position. The tolerances of the spacer welding to the torque wire and the optical length determine the location of the spacer in the slit. Referring to
Frictional torques can be calculated over the expected range of interferences. Table 2 shows frictional torques calculated based on the expected range of interferences. Based on the formulas above, the following is the frictional torque variation over the tolerance range of the drive tube and the spacer tube:
Thus, the upper limit is about 4.0 times the lower limit. This range would be decreased if the nominal interference was increased. The spinning of the spacer tube in the drive tube is not destructive. Thus, each drive tube and spacer tube can be tested after manufacture for quality control, if desired.
To increase the nominal interference for the same torque, a number of options can be pursued such as, for example, coating the outside diameter of the spacer tube from a material that has a lower coefficient of friction such as Teflon or reducing the wall thickness of the drive tube from about 0.003 inches to about 0.002 inches.
Referring to
The spacer tube protrusion also can be located in the in central portion of the spacer tube. Multiple protrusions also can be used and would help anchor the spacer tube in the drive tube with the disadvantage that a longer slit length would be needed to keep the spacer tube in the region of invariant torque. Alternatively, a longer single protrusion would behave similarly to multiple protrusions. The torque wire can go through all or a portion of the spacer tube, or the torque wire can be butted against the spacer tube. The spacer tube and torque wire can be attached anywhere along the length or ends of the spacer tube.
During use, a portion of the imaging core is inserted to a target location within a body lumen. The imaging core then is rapidly pulled back relative to the catheter or sheath, which remains relatively stationary. Faster pullback speeds allow for shorter flush times, which reduce flush agent use and the amount of time the vessel is without blood. As pullback speeds increase, however, the tensile forces on the image core also increase. The present invention is suitable for use with high pullback speeds.
In tight bends, such as in a blood vessel, the friction between the imaging core sheath and the torque wire can approach 0.1 pounds. Assuming a 125 μm optic fiber is used, the optic fiber can easily withstand the 0.1 pounds load without breaking, however it will stretch by the following amount:
Where:
Thus, a 0.1 pound force stretches the whole optic fiber by 0.032 inches. This stretch is taken up by the torque limiter assembly. Thus it can elongate by as much as 0.032 inches (0.8 mm). The spacer tube can move by this amount relative to the drive tube, but with the preferred embodiment the spacer tube protrusion remains in the location of invariant torque (400 in
In addition, 0.032 inches of stretch is not seen in practice because the torque wire is very stretchy compared to the fiber. Consequently, the torque wire takes up most of the stretch, not the torque limiter assembly.
A variety of spacer tube configurations can be used in accordance with the invention. For example,
When the drive tube is made of Nitinol, the strain on the drive tube when the spacer tube is inserted is about 0.5%. Nitinol can take strains of up to about 5% before undesirable permanent deformation occurs. Thus, Nitinol has a significant margin above the maximum strain of the mating parts. On the other hand, stainless steel will show a permanent deformation at 1% strain, which means it is practical but not with much margin, especially if the break away region is subjected to bending during operation. While Nitinol is preferred, the drive tube can be made of any suitable shape metal.
The friction force created by a single slit is provided by the compression of the circular shape of the drive tube. This is repeatable, as the wall thickness and inside diameter are well controlled. If additional cuts are added to the drive tube, then the end of the cuts become important in maintaining the interference fit. In addition, the lower strength of the tube would make the design more sensitive to bending. A single slit in the drive tube avoids these drawbacks and also is easier to manufacture, and therefore is preferred.
In some embodiments, a wider slit is used.
Currently at a nominal torque value of 0.24 oz-in (from Table 2) the tensile strength of the design is the torque value divided by the radius of the spacer (0.0175 inches), which gives 0.85 lbs. As discussed previously, the fiber takes up the majority of the tensile load of the image core but additional strength can be gained from this torque limiter. 0.85 lbs is sufficient for this application. Having a repeatable tensile strength of this joint is desirable because, under some conditions, the image core could get caught during image core withdrawal and having a maximum tensile force of this joint helps the safety of the design.
An alternative would be to make the spacer tube out of Teflon or another material that would have a low bonding strength to glue and fill the joint between the drive tube (e.g., Nitinol) and the spacer tube with glue at an elevated temperature. Nitinol has a higher coefficient of expansion than Teflon and thus when the assembly cools the glue would have an interference fit to the Teflon. This could provide a repeatable break away friction.
The aspects, embodiments, features, and examples of the invention are to be considered illustrative in all respects and are not intended to limit the invention, the scope of which is defined only by the claims. Other embodiments, modifications, and usages will be apparent to those skilled in the art without departing from the spirit and scope of the claimed invention.
Throughout the application, where compositions are described as having, including, or comprising specific components, or where processes are described as having, including or comprising specific process steps, it is contemplated that compositions of the present teachings also consist essentially of, or consist of the recited components, and that the processes of the present teachings also consist essentially of or consist of, the recited process steps.
It should be understood that the order of steps or order for performing certain actions is immaterial so long as the present teachings remain operable. Moreover, two or more steps or actions may be conducted simultaneously.
Where a range or list of values is provided, each intervening value between the upper and lower limits of that range or list of values is individually contemplated and is encompassed within the invention as if each value were specifically enumerated herein. In addition, smaller ranges between and including the upper and lower limits of a given range are contemplated and encompassed within the invention. The listing of exemplary values or ranges is not a disclaimer of other values or ranges between and including the upper and lower limits of a given range.
Filing Document | Filing Date | Country | Kind |
---|---|---|---|
PCT/US2013/030166 | 3/11/2013 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2014/163601 | 10/9/2014 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
2050630 | Reid | Aug 1936 | A |
2773369 | Klemm | Dec 1956 | A |
3306291 | Burke | Feb 1967 | A |
4266815 | Cross | May 1981 | A |
4434904 | D'Amico et al. | Mar 1984 | A |
4669999 | Miller | Jun 1987 | A |
4971267 | Fulton et al. | Nov 1990 | A |
5185004 | Lashinski | Feb 1993 | A |
5228441 | Lundquist | Jul 1993 | A |
5321501 | Swanson et al. | Jun 1994 | A |
5368480 | Balfour et al. | Nov 1994 | A |
5459570 | Swanson et al. | Oct 1995 | A |
5465147 | Swanson | Nov 1995 | A |
5509093 | Miller et al. | Apr 1996 | A |
5596996 | Johanson et al. | Jan 1997 | A |
5619368 | Swanson | Apr 1997 | A |
5748598 | Swanson et al. | May 1998 | A |
5784352 | Swanson et al. | Jul 1998 | A |
5820614 | Erskine et al. | Oct 1998 | A |
5913437 | Ma | Jun 1999 | A |
5956355 | Swanson et al. | Sep 1999 | A |
6111645 | Tearney et al. | Aug 2000 | A |
6134003 | Tearney et al. | Oct 2000 | A |
6160826 | Swanson et al. | Dec 2000 | A |
6191862 | Swanson et al. | Feb 2001 | B1 |
6282011 | Tearney et al. | Aug 2001 | B1 |
6421164 | Tearney et al. | Jul 2002 | B2 |
6445939 | Swanson et al. | Sep 2002 | B1 |
6485413 | Boppart et al. | Nov 2002 | B1 |
6501551 | Tearney et al. | Dec 2002 | B1 |
6552796 | Magnin et al. | Apr 2003 | B2 |
6564087 | Pitris | May 2003 | B1 |
6570659 | Schmitt | May 2003 | B2 |
6582368 | Holdaway et al. | Jun 2003 | B2 |
6706004 | Tearney et al. | Mar 2004 | B2 |
6879851 | McNamara et al. | Apr 2005 | B2 |
6891984 | Petersen et al. | May 2005 | B2 |
7066819 | Ueda et al. | Jun 2006 | B2 |
7121947 | Ueda et al. | Oct 2006 | B2 |
7208333 | Flanders et al. | Apr 2007 | B2 |
7231243 | Tearney et al. | Jun 2007 | B2 |
7241286 | Atlas | Jul 2007 | B2 |
7311625 | Nosaka et al. | Dec 2007 | B2 |
7407440 | White | Aug 2008 | B2 |
7414779 | Huber et al. | Aug 2008 | B2 |
7415049 | Flanders et al. | Aug 2008 | B2 |
7625366 | Atlas | Dec 2009 | B2 |
7813609 | Petersen et al. | Oct 2010 | B2 |
7848791 | Schmitt et al. | Dec 2010 | B2 |
7916387 | Schmitt | Mar 2011 | B2 |
7935060 | Schmitt et al. | May 2011 | B2 |
20020151799 | Pantages et al. | Oct 2002 | A1 |
20020161351 | Samson et al. | Oct 2002 | A1 |
20040186368 | Ramzipoor et al. | Sep 2004 | A1 |
20050201662 | Petersen et al. | Sep 2005 | A1 |
20060095065 | Tanimura et al. | May 2006 | A1 |
20070232892 | Hirota | Oct 2007 | A1 |
20070232893 | Tanioka | Oct 2007 | A1 |
20070250036 | Volk | Oct 2007 | A1 |
20070260227 | Phan | Nov 2007 | A1 |
20080097293 | Chin | Apr 2008 | A1 |
20090174931 | Huber et al. | Jul 2009 | A1 |
20090292199 | Bielewicz | Nov 2009 | A1 |
20090306520 | Schmitt et al. | Dec 2009 | A1 |
20100076320 | Petersen et al. | Mar 2010 | A1 |
20100094127 | Xu | Apr 2010 | A1 |
20100253949 | Adler et al. | Oct 2010 | A1 |
20110007315 | Petersen et al. | Jan 2011 | A1 |
20110071404 | Schmitt et al. | Mar 2011 | A1 |
20110071405 | Judell et al. | Mar 2011 | A1 |
20110101207 | Schmitt | May 2011 | A1 |
20110151980 | Petroff | Jun 2011 | A1 |
20110251519 | Romoscanu | Oct 2011 | A1 |
20140142553 | Poncon | May 2014 | A1 |
Number | Date | Country |
---|---|---|
0387980 | Sep 1990 | EP |
0445918 | Sep 1991 | EP |
07-184888 | Jul 1995 | JP |
10-66696 | Mar 1998 | JP |
2007139457 | Dec 2007 | WO |
2008121234 | Oct 2008 | WO |
Entry |
---|
International Search Report and Written Opinion for International Patent Application No. PCT/US2010/061613, dated Feb. 22, 2011, 9 pages. |
Mondofacto, Charrie Scale, [online] Mar. 5, 2000 [retrieved Feb. 1, 2012]. Retrieved from the Internet URL: http://www.mondofacto.com/facts/dictionary?Charriere+scale. |
PCT Written Opinion for PCT International Patent Application No. PCT/US2013/030166, dated Jun. 12, 2014 (5 pages). |
PCT International Search Report for PCT International Patent Application No. PCT/US2013/030166, dated Jun. 12, 2014 (3 pages). |
Number | Date | Country | |
---|---|---|---|
20160000406 A1 | Jan 2016 | US |