This invention relates to medical diagnostic ultrasonic imaging and, in particular, to ultrasonic imaging of invasive devices inserted into the body during a medical procedure.
Many invasive procedures are augmented by noninvasive imaging, particularly when an invasive device is inserted into the body to treat a target tissue. For instance, a biopsy needle is often visually assisted by ultrasound so that a target tissue or cell mass is accessed directly and positively by the needle. The clinician can visually observe the path of the needle as it is inserted into the body to sample or remove suspect pathology inside the body. Another example is an r.f. ablation needle, which is inserted into the body to engage a tumor which is to be grasped or surrounded by the tines of the needle before r.f. energy is applied. The visualization assures that the needle tines have correctly and fully engaged the tumor. A further example is an intravascular catheter, which may be guided over long distances inside the body from its access point at a femoral artery, for instance. The tip of the catheter may be observed by ultrasonic imaging to assure its accurate placement in a targeted chamber of the heart, for example.
However, it can often be difficult to clearly visualize an invasive device in an ultrasound field. Invasive devices like needles are generally inserted into the body in close proximity to the ultrasound probe. These solid instruments are specular reflectors which present a shallow angle of incidence to the ultrasound beams from the probe. Many times the position of the instrument is virtually parallel to the beam directions. Consequently the sound waves can be reflected deeper into the body rather than providing a strong return signal. As a result the device will present a broken or indistinct appearance in the ultrasound image. Attempts have been made to mitigate this problem such as forming a diffraction grating near the tip of a needle as described in U.S. Pat. No. 4,401,124 (Guess et al.), but this approach is also angle-dependent. Another approach is to Doppler demodulate the motion of the needle as described in U.S. Pat. No. 5,095,910 (Powers), but this technique is only effective while the needle is moving. Another Doppler approach is to inject a steady flow of fluid into the body and detect the locus of the injecting device from Doppler sensing of the flow rate of the fluid flow, as described in international publication no. WO 2004/082749 (Keenan et al.) Accordingly it is desirable to be able to clearly image an invasive instrument with ultrasound regardless of its position in the sound field and without the need to create motional effects.
In accordance with the principles of the present invention, an invasive medical instrument which is to be imaged by ultrasound utilizes a fluid of microbubbles for improved visualization. Microbubbles are encapsulated gaseous particles or gaseous pre-cursors suspended in fluid. The microbubbles can be very small, on the order of tens of microns, and carried in saline or other fluids. The fluid can be continuously flowing or circulated through the instrument in a closed path, or can exit the distal end of the instrument to enable the tip of the device to be clearly located in the image. The microbubbles in the fluid present diffuse reflectors of harmonic signals to the impinging ultrasound waves, enabling the device to be clearly imaged regardless of its position in the ultrasound field. The harmonic signal returns clearly segment the locus of the microbubbles around the distal tip of the instrument from the fundamental signals returned from other scatterers, and are produced without the need for motional effects.
In the drawings:
a is an enlarged view of the tip of the needle of
a is a cross-sectional view of the needle sheath of
Referring first to
In accordance with the principles of the present invention a flow 26 of a fluid containing microbubbles is supplied through the lumen of the needle. In this embodiment the fluid path is open at the distal tip of the insertion needle and the microbubble fluid can flow out of the tip of the insertion needle 21 and surround the tip of the stylet 24. The microbubble fluid may be any biocompatible fluid such as water or saline solution which contains gaseous particles. The gaseous particles may be air bubbles, encapsulated microbubbles, phase-converted nanoparticles, agitated saline, or ultrasonic contrast agent to name a few candidates. The microbubbles are high echogenic particles which provide relatively strong echo returns from impinging ultrasound waves. In comparison with a needle which is a specular reflector from which the strength of the returning echoes is highly angle-dependent, the spherical microbubbles or other particles will return a significant echo signal with little or no angle dependency. Thus the bath 26 of microbubbles which surrounds the tip of the needle 24 will illuminate the tip location and the shaft of the needle and stylet regardless of the angle of the needle. The needle, on the other hand, may cause impinging ultrasound to glance off at the angle of the needle and scatter deeper into the tissue rather than return to the ultrasound transducer, resulting in dropout and an irregular appearance of the needle and stylet in the ultrasound image. This difficulty is resolved by the microbubble fluid path which returns ultrasound from along the length of the needle with little or no angle dependency or image dropout.
a is an enlarged view of the tip of the stylet 24, which illustrates the microbubbles 26 surrounding the tip of the instrument. The echo returns from the microbubbles 26 will thus illuminate the location of the tip in the ultrasound image.
In accordance with the principles of the present invention, a bag 40 contains a microbubble fluid 26. The microbubble fluid is supplied to a fluid coupling 12 of the needle 10 by a tube 44. A pump 42 such as an infusion pump or roller pump will gently pump the microbubble fluid from the supply bag 40 to the needle. The pump pressure need be only sufficient to cause the microbubble fluid to reach the tip of the needle, and to enable passage alongside a deployed tool through the aperture cut by the tool, such as the tines of an r.f. ablation needle. Thus, the fluid pressure need only be sufficient to overcome the occluding pressure of the tissue which surrounds the tines, for example. In this example a return tube 46 is coupled to the fluid coupling 12 through which returning fluid is expelled into a container 48 for disposal. A return tube will be desirable for a closed path system when the microbubble fluid is continuous supplied to the tip of the instrument as for cooling, for example. A return tube may also be desirable for an open path system in which a supply of fresh microbubble fluid is continuously supplied to the instrument.
In other embodiments the microbubble fluid bag 26 and the pump 42 may comprise a syringe pump with the microbubble fluid contained within a syringe which is operated by the syringe pump. The microbubble fluid can be supplied by the pump system which is a part of an r.f. ablation device or by any other pumping or irrigation subsystem that is part of the invasive device. The flow of microbubble fluid may be controlled by the ultrasonic imaging system, which controls the delivery of fluid for improved imaging, either with or without operator involvement. For example, automatic, semi-automatic or manual image analysis may detect a poor image of the invasive device and call for a greater or pre-determined (e.g., a pulsatile flow) delivery of microbubble fluid.
The ultrasound system of
The transducer array 112 receives echoes from the body containing linear and nonlinear components which are within the transducer passband. These echo signals are coupled by the switch 110 to a beamformer 118 which appropriately delays echo signals from the different transducer elements, then combines them to form a sequence of coherent echo signals along the beam from shallow to deeper depths. Preferably the beamformer is a digital beamformer operating on digitized echo signals to produce a sequence of discrete coherent digital echo signals from a near field to a far field depth of field. The beamformer may be a multiline beamformer which produces two or more sequences of echo signals along multiple spatially distinct receive scanlines in response to the transmission of one or more spatially distinct transmit beams, which is particularly useful for 3D imaging. The beamformed echo signals are coupled to a harmonic signal separator 120.
The harmonic signal separator 120 can separate the linear and nonlinear components of the echoes signal in various ways. One way is by filtering. Since certain nonlinear components such as the second harmonic are at a different frequency band (2fo) than the fundamental transmit frequencies (fo), the harmonic signals which are the signature of microbubbles can be separated from the linear components by band pass or high pass filtering. There are also a number of multiple pulse techniques for separating nonlinear components which are generally referred to as pulse inversion techniques. In pulse inversion the image field is insonified by the transmission of multiple, differently modulated transmit signals in each beam direction, returning multiple echoes from the same location in the image field. The transmit signals may be modulated in amplitude (as described in U.S. Pat. No. 5,577,505 (Brock Fisher et al.)), phase or polarity (as described in U.S. Pat. No. 5,706,819 (Hwang et al.)), or a combination thereof. When the received echoes from a common location are combined, the linear signal components are canceled and the nonlinear signal components reinforce each other (or vice versa, as desired), thereby producing separated nonlinear (e.g., harmonic) echo signals for imaging.
The echo signals are detected by a B mode detector 122. An advantage of the inventive technique over the prior art techniques discussed above is that Doppler processing is not necessary. The present invention may be carried out using Doppler processing if desired in a given embodiment, however the use of B mode signals avoids the reduction in real time frame rate caused by the acquisition of long Doppler ensembles. The detected echo signals are then converted into the desired image format such as a sector or pyramidal image by a scan converter 124. The scan converted image is temporarily stored in an image buffer 126 from which it can undergo further processing. The image data is coupled to a pixel classifier where the strong harmonic signal returns from microbubbles can be segmented and, if desired, highlighted in the image as by coloring or brightness control, e.g., to emphasize the small pool of microbubbles around the tip of the needle. The image of the needle with its tip clearly indicated by the harmonic signals from surrounding microbubbles is coupled to a display buffer 142, from which it is shown on a display 116.
This application claims the priority of international application number PCT/IB2008/054843, filed Nov. 18, 2008. This application claims the benefit of U.S. provisional application Ser. No. 60/990,638, filed Nov. 28, 2007.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB08/54843 | 11/18/2008 | WO | 00 | 6/7/2010 |
Number | Date | Country | |
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60990638 | Nov 2007 | US |