Freehand ultrasound imaging systems and methods providing position quality feedback

1. An ultrasound system comprising:

an ultrasound transducer operable to receive ultrasound echo signals returning from a portion of the body;

at least one first position marker connectable to the ultrasound transducer;

at least one second position marker connectable to the instrument;

a controller communicatively coupled to the ultrasound transducer and the first and second position markers; and

a display communicatively coupled to the controller;

wherein, when the at least one first position marker is connected to the ultrasound transducer and the at least one second position marker is connected to the instrument, the controller is configured to:

monitor a spatial location and orientation of the ultrasound transducer based on a first position signal from the at least one first position marker, wherein the first position signal is a first magnetic field;

monitor a spatial location and orientation of the instrument based on a second position signal from the at least one second position marker, wherein the second position signal is a second magnetic field;

monitor a quality of the first magnetic field by monitoring a first quality measure of the first magnetic field, wherein the first quality measure of the first magnetic field is a first characteristic of the first magnetic field, by monitoring a received power of the first magnetic field;

monitor a quality of the second magnetic field by monitoring a second quality measure of the second magnetic field, wherein the second quality measure of the second magnetic field is a second characteristic of the second magnetic field, by monitoring a received power of the second magnetic field;

generate a two dimensional ultrasound image based on the ultrasound echo signals;

determine a spatial location of the portion of the body depicted in the ultrasound image based on the spatial location and orientation of the ultrasound transducer; and

display on the display a plurality of display elements including:

the ultrasound image; and

a marker corresponding to a projection of at least a portion of the longitudinal axis of the instrument onto the plane of the ultrasound image based on the spatial location and orientation of the instrument and the spatial location of the portion of the body depicted in the ultrasound image; and

when at least one of:

the first characteristic of the first magnetic field is below a first predetermined quality threshold, wherein the first characteristic is a first mean received power level of the first position signal, and

the second characteristic of the second magnetic field is below a second predetermined quality threshold, wherein the second characteristic is a second mean received power level of the second position signal,

generate an alert on the display by changing an appearance characteristic of at least one of the plurality of display elements.

2. The ultrasound system of claim 1 wherein the controller is configured to inhibit display of the ultrasound image when the first quality measure of the first position signal is below the first quality threshold.

3. The ultrasound system of claim 1 wherein the controller is configured to change an appearance characteristic of the ultrasound image when the first quality measure of the first position signal is below the first quality threshold.

4. The ultrasound system of claim 1 wherein the controller is configured to inhibit display of the marker when the second quality measure of the second position signal is below the second quality threshold.

5. The ultrasound system of claim 2 wherein the controller is configured to inhibit display of the marker when the second quality measure of the second position signal is below the second quality threshold.

6. The ultrasound system of claim 3 wherein the controller is configured to inhibit display of the marker when the second quality measure of the second position signal is below the second quality threshold.

7. The ultrasound system of claim 1 wherein the controller is configured to change an appearance characteristic of the marker when the second quality measure of the second position signal is below the second quality threshold.

8. The ultrasound system of claim 2 wherein the controller is configured to change an appearance characteristic of the marker when the second quality measure of the second position signal is below the second quality threshold.

9. The ultrasound system of claim 3 wherein the controller is configured to change an appearance characteristic of the marker when the second quality measure of the second position signal is below the second quality threshold.

10. A method in an ultrasound system comprising:

receiving ultrasound echo signals returning from a portion of the body;

monitoring a spatial location and orientation of an ultrasound transducer at which the ultrasound echo signals are received based on a first position signal from at least one first position marker connected to the ultrasound transducer, wherein the first position signal is a first electromagnetic signal;

monitoring a spatial location and orientation of the instrument based on a second position signal from at least one second position marker connected to the instrument, wherein the second position signal is a second electromagnetic signal;

monitoring a first electrical quality of the first electromagnetic signal by monitoring a first received electrical power of the first electromagnetic signal;

monitoring a second electrical quality of the second electromagnetic signal by monitoring a second received electrical power of the second position signal;

generating a two dimensional ultrasound image based on the ultrasound echo signals;

determining a spatial location of the portion of the body depicted in the ultrasound image based on the spatial location and orientation of the ultrasound transducer;

displaying a plurality of display elements including:

the ultrasound image; and

a marker corresponding to a projection of at least a portion of the longitudinal axis of the instrument onto the plane of the ultrasound image based on the spatial location and orientation of the instrument and the spatial location of the portion of the body depicted in the ultrasound image; and

when at least one of:

the first received electrical power is below a first electrical power threshold, and

the second received electrical power is below a second electrical power threshold,

generating an alert on the display by doing one or more of:

inhibiting display of at least one of the plurality of display elements; and

changing an appearance characteristic of at least one of the plurality of display elements.

11. The ultrasound system of claim 7 wherein the appearance characteristic is from a group consisting of a color, an intensity, a shape, or linestyle.

12. The ultrasound system of claim 1 wherein the controller displays at least one of a numerical indication of the first characteristic or a numerical indication of the second characteristic.

13. The ultrasound system of claim 1 wherein the controller generates an audible indication at least one of first characteristic or the second characteristic.

14. The ultrasound system of claim 1 wherein the alert includes an audible tone.

15. The ultrasound system of claim 1 wherein in response to the second characteristic of the second magnetic field being above a third quality threshold, which indicates at least one of high magnetic field distortion or malfunctioning of position marker, the controller generate the alert on the display.

16. The ultrasound system of claim 14 wherein the controller is configured to inhibit display of the marker when the second quality measure of the second position signal is above the third quality threshold.

17. The ultrasound system of claim 14 wherein the controller is configured to change an appearance characteristic of the marker when the second quality measure of the second position signal is above the third quality threshold.

18. The ultrasound system of claim 7 wherein in response to the second characteristic of the second magnetic field being above a third quality threshold, which indicates at least one of high magnetic field distortion or malfunctioning of position marker, the controller generate the alert on the display.

19. The ultrasound system of claim 1 wherein the second quality threshold is indicative of a predetermined separation between the marker and a base unit of a magnetic position sensing systems.

20. The ultrasound system of claim 1 wherein the second quality threshold is indicative of a presence of metal near the marker.