Patent Application
20200107751
Aspects of the present invention relate to a compact radar system for detecting displacement of an internal organ of a patient positioned in a medical scanner, and more particularly, to a compact radar system for detecting displacement of an internal organ of a patient in a medical scanner that includes at least one transmitting antenna and at least one receiving antenna wherein the receiving antenna is located a predetermined distance from a patient reference location to enable detection of asymmetric displacement of the internal organ.
Medical imaging techniques such as positron emission tomography (PET), computed tomography (CT), single-photon emission computed tomography (SPECT) and others are used to obtain images of the interior of a patient's body. During a diagnostic scan utilizing such imaging techniques, the patient's respiratory motion can cause undesirable image artifacts, or the incorrect alignment of two modalities due to internal organ movement that occurs during patient respiration.
In order to overcome these disadvantages, conventional imaging systems utilize respiration-correlated gating techniques to obtain a respiration waveform. The waveform is then used to correlate respiration with time so as to provide motion correction of image data. Such systems typically include devices and sensors that are positioned on the patient by a trained operator. For example, a strain gauge or an optical tracker may be attached to a patient to measure chest elevation during respiration. However, the operation and accuracy of such systems is dependent on system setup and operator training. For example, pressure sensors used in some types of systems require adjustment by a trained operator prior to use. Further, the pressure sensors may loosen during a scan and require repositioning by the operator in order to maintain accuracy. In other types of systems that utilize optical detection of skin location, a line of sight path between a target and sensor is required that may be obscured by blankets, bent knees etc. of the patient. Moreover, the systems require substantial setup time and are not user friendly.
Alternatively, a Doppler radar system may be used to detect internal organ movement. Such systems operate within the ultra high frequency (UHF) bandwidth of the electromagnetic spectrum and include a patch antenna that emits electromagnetic (EM) radiation that irradiates a relatively large volume of the patient's body. This creates undesirable reflections of EM radiation from various organs within the body that are not of interest for detecting respiration. In addition, EM radiation may reflect off surfaces located outside of the patient's body, such as a CT gantry surface of an imaging system, wall or other surface. The reflections from organs that are not of interest and from surfaces outside the body result in undesirable noise in the reflected radar signal and a relatively low signal to noise ratio (SNR).
A compact radar system is disclosed for detecting displacement of an internal organ of a patient in a medical scanner. The system includes at least one transmitting antenna and at least one receiving antenna located in a bed arrangement that supports the patient. In particular, the receiving antenna is located a predetermined distance from a patient reference location to enable detection of electromagnetic energy reflected from a region of the internal organ undergoing asymmetric displacement. The system further includes a radar energizing system that energizes the transmitting and receiving antennas wherein the transmitting antenna irradiates a volume of the patient's body that includes the internal organ. In addition, the receiving antenna detects the reflected electromagnetic energy from the region of the internal organ undergoing asymmetric displacement to enable determination of inhalation and exhalation by the patient.
Those skilled in the art may apply the respective features of the present invention jointly or severally in any combination or sub-combination.
The exemplary embodiments of the invention are further described in the following detailed description in conjunction with the accompanying drawings, in which:
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale.
Although various embodiments that incorporate the teachings of the present disclosure have been shown and described in detail herein, those skilled in the art can readily devise many other varied embodiments that still incorporate these teachings. The scope of the disclosure is not limited in its application to the exemplary embodiment details of construction and the arrangement of components set forth in the description or illustrated in the drawings. The disclosure encompasses other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings.
The entire disclosure of U.S. patent application Ser. No. 15/972,445, filed May 7, 2018, entitled UHF PHASED ARRAY RADAR FOR INTERNAL ORGAN DETECTION IN A MEDICAL SCANNER by Ahmadreza Ghahremani and James J. Hamill, and that of US Patent Publication No. 2015/0005673 A1 are hereby incorporated by reference in their entirety.
Medical imaging techniques such as positron emission tomography (PET), computed tomography (CT), single-photon emission computed tomography (SPECT) and others are used to obtain images of the interior of a patient's body. During a diagnostic scan utilizing such imaging techniques, the patient's respiratory motion can cause undesirable image artifacts, or the incorrect alignment of two modalities due to internal organ movement that occurs during patient respiration. In order to overcome these disadvantages, it is important to correlate patient inhalation and exhalation with time in a respiration signal so as to provide motion correction of image data.
Referring to
Referring to
The transmitting antenna 18 is located such that the diaphragm 34 is irradiated by EM radiation emitted from the transmitting antenna 18. In an embodiment, the transmitting antenna 18 may be located approximately near a midsection 25 of the patient 28. Due to its proximity to the diaphragm 34, the patient's heart 38 is also irradiated. The diaphragm 34 and heart 38 are structurally more dense and have a higher dielectric constant than nearby organs. Thus, the reflection of EM radiation from the diaphragm 34 and heart 38 is stronger than that from the other organs having a relatively low dielectric constant such as the lung. This facilitates detection of diaphragm and heart movement.
Movement or displacement of the diaphragm 34 is indicative of patient respiration. In addition an object undergoing symmetric movement results in reflected EM radiation that generates a periodic radar signal. It is difficult to determine whether a selected portion of the periodic signal corresponds to either inhalation or exhalation by the patient 28. In accordance with an aspect of the invention, the receiving antenna 20 is located on the bed 22 relative to the diaphragm 34 to enable detection of EM radiation reflected from a portion of the diaphragm 34 undergoing asymmetric movement. Inhalation and exhalation by the patient can then be readily determined from the reflected EM radiation detected by the receiving antenna. In an embodiment, asymmetric movement occurs in an upper region of the diaphragm 34 (i.e. a tip 40 of diaphragm 34) wherein the diaphragm 34 expands and contracts asymmetrically in three dimensional space. Thus, the detection of EM radiation reflected from the diaphragm tip 40 enables determination of patient inhalation and exhalation. It is understood that other areas of the diaphragm 34 that undergo asymmetric movement may be used.
A study was conducted to determine a location on the bed 22 for the receiving antenna 20 (i.e. low gain receiving antenna 20) suitable for detecting asymmetric movement of the diaphragm 34. In the study, a distance D between an ear canal 42 (i.e. a patient reference location) in the patient's ear 44 and the diaphragm tip 40 was measured in topogram images obtained for a plurality of adult patients. As a result of the study, it was determined that the average distance between the ear canal 42 and the diaphragm tip 40 (for adult patients) is approximately 31.7 cm. In accordance with an aspect of the invention, a location for the receiving antenna 20 on the bed 22 suitable for detecting asymmetric movement of the diaphragm 34 is approximately 31.7 cm from the ear canal 42. It is understood that other statistical measures may be used to locate the receiving antenna 20. In addition, physical features of the patient other than, or in addition to, the ear canal 42 may be used as a patient reference location.
In order to optimize placement of the receiving antenna 20 relative to the diaphragm tip 40, an additional approach may be used wherein a cardiac signal is also detected while measuring a respiration signal of the patient. It is known that the heart 38 and diaphragm tip 40 are located relatively close to each other in the human body. Thus, placement of the receiving antenna 20 may be adjusted based on the detected cardiac signal.
A test was conducted to detect radar signals reflected from internal organs in a patient's body. As part of a test setup, low gain antennas 18, 20 of the invention were configured for use in a Doppler radar system as previously described. The receiving antenna 20 was located on the patient bed approximately 31.7 cm from the patient's ear canal 42 and thus positioned to detect asymmetric movement of the diaphragm 34. Further, the transmitting antenna 18 is configured as a linear polarized antenna and the receiving antenna 20 is configured as a circular polarized antenna, although it is understood that both antennas 18, 20 may be configured as circular polarized antennas in order to improve the SNR. A first chart 44 of a reflected radar signal 46 detected during the test is shown in an upper portion of
Referring to
I(t)=Vi+A cos(φ(t)+φ0) Eqn. (1)
Q(t)=Vq+A sin(φ(t)+φ0) Eqn. (2)
wherein I(t) is a reference signal, Q(t) is the signal shifted by 90 degrees, Vi, Vq, and φ0 denote constant offsets that are caused by parasitic effects such as antenna crosstalk or nonlinear behavior of the first 64 and second 66 I/Q mixers, A denotes the amplitude of the signal and φ(t) is the phase shift between transmitted and received signals. The phase shift φ(t) is proportional to the distance d(t) from the transmitting antenna to a reflection point on the object 68 and back to the receiving antenna 20. A receiving unit have first 70 and second 72 channels is used in the system 58 to be still able to measure motion if one channel is in a so-called null point. This occurs if the mean distance between the object 68 and the antennas 18, 20 results in a phase shift near to an even multiple of π/2, where small changes of d(t) yield to I(t)=Vi=constant. To overcome this circumstance, the second mixer 66 of the second channel 72 receives an input signal from the oscillator 60 that includes a phase shift of π/2, so that its output is a sine function, as set forth in Eqn. (2). Thus, if one channel is in a null point, the other channel will be in an optimum point.
The invention may be used in conjunction with any type of medical scanning or imaging systems such as positron emission tomography (PET), single-photon emission computed tomography (SPECT), computed tomography (CT), PET/CT systems or radiotherapy systems. For purposes of illustration, the invention will be described in conjunction with a CT system 74 as shown in
The table base 84 includes a control unit 90 connected to a computer 92 to exchange data. The control unit 90 can actuate the system 58 (
While particular embodiments of the present disclosure have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the disclosure. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this disclosure.
