GUIDANCE SYSTEM

Abstract

A guidance system for guiding a clinician in delivering a needle to a target location within a hollow organ in a patient's body. The guidance system includes: a computing device; a target sensor configured to provide target sensor data describing the position of the target sensor, wherein the target sensor is configured to be positioned at or proximate to the target location within the hollow organ; a needle sensor configured to be carried by the needle or a device on which the needle is mounted, and to provide needle sensor data describing the position and orientation of the needle; at least one information delivery device configured to deliver information to the clinician. The computing device is configured to, using the target sensor data and needle sensor data, compute targeting information describing at least the orientation of the needle relative to the target location, and to use the at least one information delivery device to deliver guidance information to the clinician for assisting the clinician in delivering the needle to the target location, based on the targeting information

Claims

1. A guidance system for guiding a clinician in delivering a needle to a target location within a hollow organ in a patient's body, wherein the guidance system includes: a computing device; a target sensor configured to provide target sensor data describing the position of the target sensor, wherein the target sensor is configured to be positioned at or proximate to the target location within the hollow organ; a needle sensor configured to be carried by the needle or a device on which the needle is mounted, and to provide needle sensor data describing the position and orientation of the needle; at least one information delivery device configured to deliver information to the clinician; wherein the computing device is configured to, using the target sensor data and needle sensor data, compute targeting information describing at least the orientation of the needle relative to the target location, and to use the at least one information delivery device to deliver guidance information to the clinician for assisting the clinician in delivering the needle to the target location, based on the targeting information.

2. A guidance system according to claim 1, wherein the targeting information includes an orientation parameter indicating the extent to which a longitudinal axis of the needle deviates from being aligned with the target location.

3. A guidance system according to claim 2, wherein the orientation parameter represents a shortest distance between a line projected along the longitudinal axis of the needle and the target location.

4. A guidance system according to claim 1, wherein: the target sensor is configured to provide target sensor data describing the position and orientation of the target sensor; the target sensor is configured to be aligned in a predetermined orientation with respect to the hollow organ when positioned at or proximate to the target location within the hollow organ such that a longitudinal axis of the hollow organ can be determined/inferred from the target sensor data; the targeting information includes information which describes the extent to which the longitudinal axis of the needle deviates from being perpendicular to the longitudinal axis of the hollow organ and/or the direction in which the longitudinal axis of the needle deviates from being perpendicular to the longitudinal axis of the hollow organ.

5. A guidance system according to claim 1, wherein the targeting information describes the distance of the needle tip relative to the target location.

6. A guidance system according to claim 1, wherein the targeting information describes the position of the needle sensor and the target sensor on the frontal (coronal) plane of the patient.

7. A guidance system according to claim 1, wherein the guidance system includes a target sensor delivery device, configured to carry the target sensor and position the target sensor at or proximate to the target location within the hollow organ.

8. A guidance system according to claim 7, wherein the target sensor delivery device is an endoscope including a camera.

9. A guidance system according to claim 1, wherein the needle sensor is configured to be carried by the needle by being inserted into a channel in the needle.

10. A guidance system according to claim 1, wherein the at least one information delivery device comprises a display configured to deliver guidance information visually to the clinician.

11. A guidance system according to claim 10, wherein the computing device is configured to use the at least one information delivery device to deliver to the clinician guidance information by causing the display to display a colour determined based on a colour code and the targeting information.

12. A guidance system according to claim 1, wherein the at least one information delivery device comprises a loudspeaker configured to deliver guidance information audibly to the clinician.

13. A guidance system according to claim 12, wherein the computing device is configured to use the at least one information delivery device to deliver to the clinician guidance information by causing the loudspeaker to generate beeps that get progressively closer together as the targeting information changes towards indicating that the needle is correctly oriented.

14. A guidance system according to claim 12, wherein the computing device is configured to use the at least one information delivery device to deliver to the clinician guidance information by causing the loudspeaker to generate sound having a pitch and/or amplitude that changes as the targeting information changes towards indicating that the needle is correctly oriented.

15. A guidance system according to claim 1, wherein the at least one information delivery device comprises a haptic device configured to deliver guidance information haptically to the clinician.

16. A guidance system according to claim 15, wherein the haptic device is included in a device on which the needle is mounted.

17. A guidance system according to claim 15, wherein the computing device is configured to use the at least one information delivery device to deliver to the clinician guidance information by causing the haptic device to generate vibrations that get progressively weaker, as the targeting information changes towards indicating that the needle is correctly oriented.

18. A machine readable medium comprising instructions configured to cause a guidance system according to claim 1 to perform a method that includes: the computing device using target sensor data provided by the target sensor and needle sensor data provided by the needle sensor to compute targeting information describing at least the orientation of the needle relative to the target sensor; the computing device using the at least one information delivery device to deliver to the clinician guidance information for assisting the clinician in delivering the needle to the target location, based on the targeting information.

19. A method, performed by a clinician, of delivering a needle to a target location within a hollow organ in a patient's body using a guidance system according to claim 1, wherein the needle sensor is carried by the needle or by a device on which the needle is mounted, wherein the method includes: positioning the target sensor at or proximate to the target location within the hollow organ in the patient's body; the computing device using target sensor data provided by the target sensor and needle sensor data provided by the needle sensor to compute targeting information describing at least the orientation of the needle relative to the target sensor; the computing device using the at least one information delivery device to deliver to the clinician guidance information for assisting the clinician in delivering the needle to the target location, based on the targeting information.

Description

SUMMARY OF THE FIGURES

[0089] Embodiments and experiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which:

[0090] FIG. 1a shows an example guidance system for guiding a clinician in delivering a needle to a target location within a hollow organ in a patient's body.

[0091] FIG. 1b shows planes used to reference orientations with respect to a human body.

[0092] FIGS. 2a-c show an endoscope from FIG. 1a in more detail.

[0093] FIGS. 3a-c show a needle from FIG. 1a in more detail.

[0094] FIGS. 4a-c show three example delivery devices.

[0095] FIG. 5 shows an example method that the computing device might employ to compute targeting information.

[0096] FIG. 6 shows an example of guidance information that could be displayed by the display of FIG. 4a.

[0097] FIG. 7 illustrates possible misalignment between the longitudinal axis of a needle and the longitudinal axis of a trachea.

DETAILED DESCRIPTION OF THE INVENTION

[0098] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0099] FIG. 1a shows an example guidance system 100 for guiding a clinician in delivering a needle to a target location within a hollow organ in a patient's body. In this example, the hollow organ is a patient's trachea, and the guidance system is for guiding a clinician in delivering a needle to a target location within the trachea during a tracheostomy.

[0100] The guidance system 100 of FIG. 1 includes a computing device 110, a target sensor 120, a needle sensor 130 (not shown in FIG. 1), and one or more information delivery devices 140a-c.

[0101] The target sensor 120 is configured to provide target sensor data describing the position of the target sensor, preferably describing the position and orientation of the target sensor. The target sensor 120 is configured to be positioned at or proximate to the target location within the trachea.

[0102] FIG. 1a also shows an endoscope 122 (which may be referred to as a bronchoscope), a needle 150 which is mounted on a device 152 held by a clinician 160, an electromagnetic transmitter 170, as well as a patient 180 who has been intubated with a tracheal tube 182. The endoscope 122, needle 150, the device 152 on which the needle 150 is mounted, the clinician 160, the patient 180 and the tracheal tube 182 are not part of the guidance system 100.

[0103] The device 152 on which the needle 150 is mounted may be a syringe, preferably with some water in (since this allows the clinician to see air bubbles from air aspirated from the trachea after a successful puncture of the trachea). However, a device 152 on which the needle 150 is mounted is not required, since in some examples the needle 150 may be held directly by a clinician, without the need for the device 152.

[0104] In the example of FIG. 1, the target sensor 120 is positioned at the target location within the trachea of the patient, which in this case is a location within the trachea determined by the clinician (using visual feedback from the camera 126 in the endoscope) to be the safest entry point for the needle. Typically, this would be somewhere towards the top of the trachea (10 o'clock to 2 o'clock), probably somewhere around the 12 o'clock position, where the clock face is perpendicular to the longitudinal axis of the trachea, and 12 o'clock is aligned with an insertion point at the front of the patient's neck.

[0105] In this example, the wire on which the target sensor 120 is mounted is rigid enough to permit the target sensor 120 to be moved by the clinician to the target location by moving the endoscope 122. In other examples, the wire (and hence the position of the target sensor) might be manipulable independently of the endoscope.

[0106] It is also to be noted that the working channel 124 and the target sensor 120 are appropriately sized such that a predetermined orientation of the target sensor with respect to the endoscope is achieved, by suitably aligning the endoscope 122 with respect to the trachea, and in particular by aligning the longitudinal axis of the endoscope 122 with the longitudinal axis of the trachea, a predetermined orientation of the target sensor 120 with respect to the trachea can be achieved, which is useful if target sensor information describing the orientation of target sensor is used to determine/infer the orientation of the trachea (e.g. as in the discussion of FIG. 6, below). Alternatively, the target sensor may be advanced out of the working channel 124 to achieve a predetermined orientation of the target sensor 120 with respect to the trachea (see discussion below).

[0107] The one or more information delivery devices 140a-c may comprise a display 140a, a loudspeaker 140b and/or a haptic device 140c. Although the one or more information delivery devices 140a-c are illustrated in FIG. 1 as being separate from the device 152 on which the needle is mounted, this need not be the case. For example, the device 152 on which the needle 150 is mounted may include one or more of the information delivery devices 140a, 140b, 140c.

[0108] FIGS. 2a-c show the endoscope 122 in more detail, and shows that the endoscope includes a working channel 124, a camera 126, and two lights 128.

[0109] FIGS. 2a-c show the endoscope 122 as it is used to carry the target sensor 120 prior to positioning the target sensor 120 at the target location within the trachea. Thus, in FIGS. 2a-c (unlike FIG. 1), the target sensor 120 is shown as being located in the working channel 124 of the endoscope, to facilitate smooth passage of the endoscope 122 through the patient's body.

[0110] To deliver the target sensor 120 to the target location within the trachea, the endoscope 122 may be inserted via the patient's mouth (and tracheal tube) to an entry point for the trachea, such that the camera 126 can be used to visualise the interior of the trachea, preferably in real time. Next, the target sensor 120 is advanced out from the working channel of the endoscope 122 to the target location (see FIG. 1), preferably in a predetermined orientation with respect to the trachea, noting that the position of the target sensor can be verified by a clinician visually at the patient's bedside, using the camera 126.

[0111] FIGS. 3a-c show the needle 150 in more detail. As shown by FIGS. 3a-c, the needle 150 is a hollow needle which includes a channel 154 formed therein. In this example, the needle 150 is a percutaneous dilatation tracheostomy (PDT) needle.

[0112] FIGS. 3a-c show the needle 150 as it is used when the clinician 160 is delivering the needle 150 to the target location within the patient's trachea, i.e. when the needle 150 is being pushed into the neck of the patient. Thus, in FIGS. 3a-c, the needle sensor 130 is shown in the channel 154 of the needle 150, proximate to the tip of the needle 150, such that the position of the needle sensor 130 corresponds (approximately) to the position of the tip of the needle 150. FIG. 1 shows the longitudinal axis of the needle sensor z.sub.N (which also serves as the longitudinal axis of the needle 150).

[0113] As shown in FIGS. 3a-c, the needle sensor 130 is sized so as to be accommodated by the channel 154 in the needle 150, but to be large enough so as to adequately fill the channel 154 so that the position and orientation of the needle sensor is adequately fixed with respect to the needle 150. In particular, so that the longitudinal axis z.sub.N of the needle sensor is adequately fixed with respect to the needle 150.

[0114] The needle sensor 130 can be withdrawn from the channel 154 in the needle 150, after the needle 150 has been delivered to the target location (e.g. so as to allow performance of subsequent steps according to the Seldinger technique).

[0115] In this example, the electromagnetic transmitter 170 is used to produce a time-varying electromagnetic field 172 (e.g. a low intensity time varying electromagnetic field), which is used by each of the target sensor 120 and the needle sensor 130 to identify its position in the (global) reference frame of the electromagnetic transmitter 170 (x.sub.G, y.sub.G, z.sub.G) and, at least in the case of the needle sensor 130 (preferably also the target sensor 120), its orientation. In particular, using the electromagnetic field 172, the target sensor 120 provides target sensor data describing the position (e.g. cartesian coordinates x, y, z) of the target sensor 120, and preferably also the orientation (e.g. azimuth ?), elevation ?) of the target sensor 120. This target sensor data is communicated to the computing device 110 via a wire (not shown in FIG. 1). The needle sensor 130 provides needle sensor data describing the position (e.g. cartesian coordinates x, y, z) and orientation (e.g. azimuth ?), elevation ?,) of the needle sensor 130. This needle sensor data is communicated to the computing device 110 via a wire (again, not shown in FIG. 1).

[0116] By way of example, 6DOF 3D Guidance? Sensors by Northern Digital, Inc. may be used as the target sensor 120 and needle sensor 130, along with a compatible electromagnetic transmitter 170, also by Northern Digital, Inc.

[0117] The computing device 110 may include a general purpose computer, which may be connected to an apparatus configured to interpret the sensor data from the target and needle sensors. In other examples, the computing device may include a bespoke computing device, e.g. which may be incorporated into the device 152 on which the needle 150 is mounted.

[0118] In use, with the target sensor 120 positioned at the target location within the trachea of the patient 180 (as shown in FIG. 1), the computing device 110 uses the target sensor data and the needle sensor data to compute targeting information describing at least the orientation of the needle 150 relative to the target location, and uses the at least one information delivery device 140 to deliver to the clinician guidance information for assisting the clinician in delivering the needle 150 to the target location, based on the targeting information.

[0119] FIGS. 4a-c show three example information delivery devices 140a-c which may be used, individually or in combination, to deliver to the clinician guidance information for assisting the clinician in delivering the needle to the target location, based on the orientation parameter R described in FIG. 4.

[0120] Information delivery device 140a is a display configured to deliver guidance information visually to a clinician, e.g. in manners described in more detail.

[0121] Information delivery device 140b is a loudspeaker configured to deliver guidance information audibly to the clinician.

[0122] Information delivery device 140c is a haptic device configured to deliver guidance information haptically to the clinician.

[0123] FIG. 5 shows an example method that the computing device 110 might employ to compute targeting information describing at least the orientation of the needle 150 relative to the target location in real time.

[0124] In FIG. 5, the respective coordinate frames of the electromagnetic transmitter 170 (x.sub.G, y.sub.G, z.sub.G), the target sensor 120 (x.sub.B, y.sub.B, z.sub.B) and the needle sensor 130 (x.sub.N, y.sub.N, z.sub.N) are all shown.

[0125] In this example, the targeting information includes an orientation parameter R, which represents a shortest distance between a line projected along a longitudinal axis (z.sub.N) of the needle 150 and the target location (which in this case is the location of the target sensor 120, since the target sensor 120 is positioned at the target location).

[0126] Here we note that the orientation parameter R can be calculated without using data describing the orientation of the target sensor 120 (even if the target sensor data provided by the target sensor 120 includes data describing the orientation of the target sensor 120). That is, using basic vector algebra, it is possible for the orientation parameter R to be calculated using data which describes the position of the needle sensor (three degrees of freedom, e.g. x.sub.N, y.sub.N, z.sub.N), data which describes the orientation of the needle sensor (two degrees of freedom, e.g. azimuth ?, elevation ?), and data which describes the position of the target sensor (three degrees of freedom, e.g. x.sub.B, y.sub.B, z.sub.B), but without using data which describes the orientation of the target sensor.

[0127] In some examples, the display 140a may be configured to visually deliver guidance information to a clinician by visually representing the orientation parameter R, e.g. by displaying the orientation parameter R as a numerical value (see e.g. FIG. 6). A clinician inserting a needle into the patient's neck can therefore verify they are on target to deliver the tip of the needle to the target location, by ensuring that the numerical value R is at or close to 0. As would be appreciated by a skilled person, this is only an example, and alternative ways of delivering guidance information to the clinician via the display 140a, without necessarily using an orientation parameter, are possible (see e.g. FIG. 6, discussed below).

[0128] In some examples, the loudspeaker 140b may be configured to audibly deliver guidance information to a clinician by audibly representing the orientation parameter R, e.g. by generating beeps that get progressively closer together, as the orientation parameter R changes towards a value indicating that the needle is correctly oriented (R=0). In this example, when the orientation is at the value indicating that the needle is correctly oriented (R=0), the loudspeaker may generate a continuous beep. A clinician inserting a needle into the patient's neck can therefore verify they are on target to deliver the tip of the needle to the target location, by ensuring that the beep is continuous. As would be appreciated by a skilled person, this is only an example, and alternative ways of deliver guidance information to the clinician via the loudspeaker 140b, without necessarily using an orientation parameter, are possible.

[0129] In some examples, the haptic device 140c may be attached to the needle 150 or to the device 152 carrying the needle 150, and may be configured to haptically deliver guidance information to a clinician by haptically representing the orientation parameter R, e.g. by generating vibrations that get progressively weaker, as the orientation parameter changes towards a value indicating that the needle is correctly oriented (R=0). A clinician inserting a needle into the patient's neck can therefore verify they are on target to deliver the tip of the needle to the target location, by ensuring the absence of vibrations. As would be appreciated by a skilled person, this is only an example, and alternative ways of deliver guidance information to the clinician via the haptic device 140c, without necessarily using an orientation parameter, are possible.

[0130] Prior to inserting the needle into the patient's neck, a pre-procedural ultrasound may be used to help the provide a clinician with an understanding of where the trachea is located, as well as any blood vessels between the surface of the skin and the trachea (that the clinician might want to avoid).

[0131] At the time of inserting the needle into the patient's neck, the entry point of the needle may be determined according to a standard medical technique, e.g. the so-called landmark technique in which the entry point of the needle would be around halfway between the patient's Adam's apple and sternal notch. The entry point of the needle is ultimately a medical decision, and the exact point may vary from person to person. So the guidance system would primarily be used to guide the needle after it has been inserted into a patient's neck.

[0132] However, the guidance system can be used to help determine the entry point for the needle, e.g. by hovering the needle at 90? to the patient's neck at the top of their neck (in line with Adam's apple, on the windpipe axis), with the clinician using guidance information delivered by the guidance system to help with identifying a possible insertion location (e.g. by hovering the needle until the orientation parameter R is at or close to 0, or by ensuring that the icons 220 and 230 described below with reference to FIG. 6 are approximately on top of each other).

[0133] After insertion of the needle, but prior to the needle reaching the trachea, the clinician can use the guidance information to make adjustments to the trajectory of the needle whilst it is being inserted (noting that the tissues of neck move relative to each other, such that a clinician can change the angle of the needle and move the needle laterally) to ensure the needle is accurately delivered to the target location.

[0134] Once the needle has been successfully delivered to the target location, the clinician can visually verify that this has been achieved successfully via the camera on the endoscope. Note that although the target sensor is in this example located at the target location, the needle need not damage the target sensor, since the target sensor can be withdrawn from the endoscope 122 once the needle has penetrated the trachea.

[0135] FIG. 6 shows an example of guidance information that could be displayed by the display 140a to visually deliver the guidance information to the clinician, based on targeting information that describes both the orientation of the needle relative to the target location and the distance of the needle tip relative to the target location.

[0136] In the example of FIG. 6, the computing device 110 calculates the position (e.g. cartesian coordinates x, y, z) and orientation (e.g. azimuth ?), elevation ?) of the needle sensor 130 and the position (e.g. cartesian coordinates x, y, z) and orientation of the target sensor 120. This information is used to determine, via vector mathematics, the guidance information shown in FIG. 6.

[0137] In this example, the guidance information of FIG. 6 includes (under the heading Position in frontal plane) a visual representation of the position of the target sensor 120 (indicated by the icon labelled with reference numeral 220) and the position of the needle sensor 130 (indicated by the icon labelled with reference numeral 230) on the frontal plane (see FIG. 1b for an understanding of how the frontal plane in relation to the human body). A clinician can, prior to inserting the needle into the patient's neck, ensure that the icons 220 and 230 are approximately on top of each other, to ensure that the insertion point of the needle is directly above the target location on the frontal plane.

[0138] A convenient way for the computing device to compute targeting information that describes the position of the needle sensor and the target sensor on the frontal (coronal) plane of the patient is for the electromagnetic transmitter 170 to be set up with the x.sub.G-y.sub.G plane of the electromagnetic transmitter 170 aligned with the frontal plane of the patient. In this way, the position of the target sensor 120 and the position of the needle sensor 130 can be obtained simply by taking the positions of these sensors in the x.sub.G-y.sub.G coordinate frame. Setting up the electromagnetic transmitter 170 with the x.sub.G-y.sub.G plane of the electromagnetic transmitter 170 aligned with the frontal plane of the patient may be achieved by mounting the electromagnetic transmitter 170 in/on an adjustable mechanical device which is positioned by the side of the patient's head and which allows the orientation of the electromagnetic transmitter 170 to be adjusted.

[0139] In this example, the guidance information of FIG. 6 includes (under the heading Depth) a visual representation of the distance of the needle tip relative to the target location, which here is shown pictorially and numerically. A clinician can use this information to understand how close the needle tip is to the (bronchoscope) target location. This distance can easily be calculated by the computing device 110 using position information from the target sensor data and needle sensor data. This distance may be a distance in a direction normal to the frontal (coronal) plane of the patient.

[0140] In this example, the guidance information of FIG. 6 includes (under the heading Alignment) a visual representation of the orientation parameter R, which here is represented in numerical form (in distance units) and is referred to here as Error.

[0141] If the parameter R is kept at 0 as the needle is inserted then, as described previously, a clinician can be confident that the needle will be accurately delivered to the target location. However, this does not mean that the needle will enter the trachea perpendicular the longitudinal axis of the trachea (which is preferred to minimise the risk of tearing). This can be understood by referring to FIG. 7, which shows the anatomy of the neck of a patient 180 neck in the x.sub.G-z.sub.G plane, noting that this is a diagrammatical illustration in which the angles are exaggerated for better understanding of the reader.

[0142] In FIG. 7, it can be seen that the skin 182 of the neck of the patient 180 might not be aligned to the frontal plane of the patient (noting that the frontal plane of the patient is also the x.sub.G-y.sub.G plane, since the x.sub.G-y.sub.G plane has deliberately been aligned with the frontal plane of the patientsee above), and also shows that the longitudinal axis of the trachea 121 is not aligned the skin 182 of the neck (due to anatomy of the patient 180). As illustrated in FIG. 7, the longitudinal axis of the needle z.sub.N is aligned so as to be perpendicular to the skin 182 of the neck and is directly pointing at the target sensor (R=0), but due to the alignment of the trachea in the patient, the needle will not enter the trachea perpendicular to the longitudinal axis of the trachea 121, but will instead enter the trachea at a slight angle ?.sub.mis from perpendicular.

[0143] A similar misalignment ?.sub.mis may also occur in the x.sub.G-y.sub.G plane.

[0144] To account for the potential angular misalignments ?.sub.mis, ?.sub.mis, the guidance information of FIG. 6 also includes (under the heading Alignment) information which describes the direction in which (and the extent to which) the longitudinal axis of the needle deviates from being perpendicular to the longitudinal axis of the hollow organ in the form of parameters ?.sub.mis (azimuth misalignment) and ?.sub.mis (elevation misalignment) which are displayed in both numerical and visual form. A clinician can thus ensure that the needle enters the trachea perpendicular the longitudinal axis of the trachea by manipulating the orientation of the needle to bring the parameters ?.sub.mis, ?.sub.mis close to zero.

[0145] Here it is noted that in order for the parameters ?.sub.mis, ?.sub.mis to be computed, the target sensor 120 should be configured to provide (to the computing device) target sensor data which describes the position and orientation of the target sensor 120, and the target sensor 120 should be configured to be aligned in a predetermined orientation with respect to the trachea when positioned at or proximate to the target location within the trachea, such that a longitudinal axis of the trachea 121 can be determined/inferred from the target sensor data. Aligning the target sensor in a predetermined orientation with respect to the trachea is most easily achieved by orienting the target sensor 120 so that its longitudinal axis is aligned with the longitudinal axis of the trachea, as shown in FIG. 7.

[0146] In use, a clinician viewing the guidance information of FIG. 6 may first hover the needle 150 over the patient's neck and use the Position in frontal plane information to find a location for the needle in which the icons 220 and 230 are approximately on top of each other, to identify an insertion point for the needle that is directly above the target location on the frontal plane. The clinician can then use the Alignment information to ensure that the needle 150 is oriented so as to reach the target location (R=0) and so as to enter the trachea perpendicular to the longitudinal axis of the trachea 121 (?.sub.mis=0, ?.sub.mis=0). As the needle 150 is being pushed into the patient's neck, the Depth information can be used to verify how far away the needle is from the target location whilst the Alignment information is used to ensure that the alignment of the needle remains within clinically acceptable parameters, i.e. such that the needle 150 penetrates the trachea at the target location and at an acceptable angle with respect to the longitudinal axis of the trachea 121.

[0147] The guidance information can include colour coding, e.g. according to a traffic light system. For example, green may indicate correct needle position/orientation, red may indicate incorrect needle position/orientation, and amber may indicate that adjustment of needle position/orientation is recommended. For example, the system may be configured to display red when any of one or more orientation parameter (e.g. R, ?.sub.mis, ?.sub.mis) values is above a respective upper threshold value, green when all of the one or more orientation parameter (e.g. R, ?.sub.mis, ?.sub.mis) values are below respective lower threshold values, and amber otherwise. Other colour codes would be possible. For example, different colours and/or numbers of colours and/or threshold arrangements could be used.

[0148] The guidance systems described above are intended to enable a clinician to quickly and accurately puncture a needle in a preferred anatomical target location in the trachea for subsequent PDT. This contrasts the current PDT method, based on palpation, estimation, dead reckoning and a degree of trial and error. Given the potentially life-threatening consequences of failure to accurately cannulate the trachea, a precisely guided solution is believed by the present inventors to be highly desirable.

[0149] Simulated PDT experiments were conducted using an obese neck model and the guidance system described herein. The anatomical model was orally intubated with a size 8.0 mm trans-laryngeal tracheal tube, terminating just below the model's vocal cords. A bronchoscope was inserted via the tracheal tube and secured so that the target insertion point could be clearly visualised. The target sensor was advanced through the working channel of the bronchoscope to emerge into the bronchoscope's field of view. The model simulated an impalpable trachea in an obese neck using simulated soft tissue to a depth of 25 mm. Needle insertion was performed using a standard PDT kit with the needle sensor passing internally via the hollow needle and fixed so the sensor was at the needle tip.

[0150] Twenty participants each undertook a total of eight insertion attempts: two attempts with no guidance system feedback (palpation only), and two attempts with each of three guidance system feedback (information delivery) modalities: visual feedback only; haptic and visual feedback; and audio and visual feedback. For each attempt, the trachea was randomly readjusted in position and angle to reduce effects of potential repetition bias. For each attempt, Distance to Target (i.e. the distance from the PDT needle sensor to the tracheal (bronchoscope) target sensor at the completion of the attempt) was measured. Results are summarised in Table I.

TABLE-US-00001 TABLE I Summary of Distance to Target results for three different guidance system feedback modalities and palpation only. Standard Feedback deviation Interquartile modality Count Mean (SD) Median range (IQR) Distance to Palpation 40 13.5 10.8 11.3 12.3 Target at Visual 40 3.18 2.23 2.87 2.09 completion Haptic-Visual 40 3.50 2.87 3.02 2.54 (mm) Audio-Visual 40 3.77 2.96 3.07 2.12

[0151] Multiple pairwise comparison showed that Distance to Target was significantly smaller with all guidance system feedback modalities (p<0.001), compared to no feedback (palpation only) being used. That is, the results demonstrated that each feedback modality significantly improved accuracy, as compared to no guidance system feedback. The improvements in accuracy were considered to be clinically meaningful (a 10 mm mean difference when targeting a 10 mm diameter trachea). Questionnaire feedback further indicated that study participants found each feedback modality to be informative and intuitive to use.

[0152] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0153] For example, the hollow organ could be a hollow organ other than a trachea, e.g. a kidney, the bladder, the stomach, the bowel. For example, a similar guidance system may be employed in percutaneous endoscopic gastrostomy (PEG), in which a flexible feeding tube is placed through the abdominal wall and into the stomach (a first step of which involves pushing a needle into a target location in the stomach).

[0154] For example, the target sensor 120 could be integrated into the endoscope 122, rather than being inserted into the working channel of the endoscope.

[0155] For example, the target sensor 120 might not be positioned at the target location, but could be positioned proximal to the target location and in a predetermined spatial relationship with respect to the target location (albeit the vector mathematics would need to be updated accordingly).

[0156] For example, the needle sensor 130 might not be positioned proximal to the tip of the needle, but might instead be carried by the device 152 on which the needle is mounted such that the position and orientation of the needle sensor 130 is adequately fixed with respect to the needle 150 (again, the vector mathematics would need to be updated to account for this).

[0157] For example, additional sensors (additional to the needle sensor and target sensor described above) may be employed to obtain further information.

[0158] For example, guidance information may be delivered to a clinician in different ways, or in different combinations, from those described above.

[0159] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0160] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0161] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0162] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word comprise and include, and variations such as comprises, comprising, and including will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0163] It must be noted that, as used in the specification and the appended claims, the singular forms a, an, and the include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, another embodiment includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent about, it will be understood that the particular value forms another embodiment. The term about in relation to a numerical value is optional and means for example +/?10%.