Abstract:
Imaging devices for identification of target regions are generally described. Medical ultrasound is a popular medical imaging modality primarily used for diagnostic imaging of soft tissue but also for interventional procedures such as guidance of a needle or catheter placement. Examples include diagnostic imaging of organs, such cardiac or liver strictures. Common interventional procedures that rely on ultrasound guidance are central line placement and guidance of nerve blocks, both of which are high volume procedures in certain hospital settings such as the intensive care unit (ICU).

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application Ser. No. 61/770,448, filed Feb. 28, 2013, and entitled “Localization of Imaging Target Regions and Associated Systems and Devices,” which is incorporated herein by reference in its entirety for all purposes. 
     
    
     GOVERNMENT SPONSORSHIP 
       [0002]    This invention was made with government support under award number R43EB015232 awarded by the National Institute of Biomedical Imaging And Bioengineering of the National Institutes of Health and award number 1214788 awarded by the National Science Foundation. The government has certain rights in this invention. 
     
    
     TECHNICAL FIELD 
       [0003]    Imaging devices for identification of target regions are generally described. 
       BACKGROUND 
       [0004]    Medical ultrasound is a popular medical imaging modality primarily used for diagnostic imaging of soft tissue but also for interventional procedures such as guidance of a needle or catheter placement. Examples include diagnostic imaging of organs, such cardiac or liver structures. Common interventional procedures that rely on ultrasound guidance are central line placement and guidance of nerve blocks, both of which are high volume procedures in certain hospital settings such as the intensive care unit (ICU). Current ultrasound systems are mostly cart-based and optimized for superior contrast and resolution in soft tissue. However, these systems are generally expensive, and in a hospital setting with multiple physicians per ultrasound system, they can be difficult to access. 
       SUMMARY 
       [0005]    Handheld ultrasound imaging devices are generally described. Certain embodiments have improved portability relative to prior imaging systems. In addition, attachable accessories that facilitate interventional procedures (including interventional ultrasound procedures) involving directing a probe (e.g., needle or catheter) to a probe target (e.g., blood vessel or nerve bundle) are also described. Certain embodiments can be used in handheld imaging devices, which address many of the limitations of prior art systems by, for example, providing standard imaging capabilities in a low cost portable device. The subject matter of the present invention involves, in some cases, interrelated products, alternative solutions to a particular problem, and/or a plurality of different uses of one or more systems and/or articles. 
         [0006]    In one aspect, a handheld ultrasound-imaging device is provided. In certain embodiments, the handheld ultrasound imaging device comprises a housing comprising a first end comprising an ultrasound imaging unit, a second end comprising a display, and a hand grip region between the ultrasound imaging unit and the display. 
         [0007]    In certain embodiments, the handheld ultrasound imaging device comprises a housing comprising an ultrasound imaging unit, and a marking unit detachably coupled to the housing and comprising a probe indicator configured to indicate proper placement of a probe at or near a target that is to be imaged, and positioned such that, during use, aline extending between the target and the ultrasound imaging unit intersects the marking unit. 
         [0008]    The handheld ultrasound-imaging device comprises, according to some embodiments, a housing comprising an ultrasound imaging unit, a handgrip region, and a rotatable display, wherein the rotatable display is configured to be rotated, relative to at least another portion of the housing, about at least one rotational axis by at least about 30 degrees. 
         [0009]    Any of the above handheld ultrasound imaging devices may comprise, according to some embodiments, an actuator on the handgrip region configured such that when the actuator is activated, data from the ultrasound-imaging unit is recorded and/or manipulated. The actuator may be, according to certain embodiments, configured to perform one or more of a number of other functions including, but not limited to, video save, device power on/off, image settings adjustment (e.g., imaging mode, gain, frequency, contrast, depth), and/or menu navigation. 
         [0010]    Any of the above handheld ultrasound imaging device may comprise, according to certain embodiments, a marking unit comprising a vacuum-generating unit configured to adhere the marking unit to a surface associated with the target. 
         [0011]    In one aspect, imaging devices are provided. In one set of embodiments, the imaging device comprises a housing comprising an imaging unit and a handle; and a rotatable display connected to the housing, wherein the rotatable display is configured to be rotated about at least one rotational axis by at least about 30 degrees. The imaging device can be configured, in some embodiments, to have one or more of the following properties. In some embodiments, the imaging device is configured to produce an image along a scanning plane. In certain embodiments, the housing is elongated and comprises a longitudinal axis. In some embodiments, the smallest angle between the scanning plane of the imaging unit and the longitudinal axis of the housing is less than about 45°. 
         [0012]    In certain embodiments, the scanning plane of the imaging unit is substantially parallel to the longitudinal axis of the housing. According to certain embodiments, the rotatable display is configured to be rotated such that the display can be oriented in a first position substantially parallel to a scanning plane of the imaging unit and in a second position substantially perpendicular to the scanning plane of the imaging unit. In some embodiments, the handle is located directly above the imaging unit during operation of the imaging device. The imaging device can be a handheld imaging device, according to certain embodiments. In some embodiments, the imaging device occupies a volume of equal to or less than about 500 cm 3 . The imaging unit can comprise, according to certain embodiments, an ultrasound transducer. 
         [0013]    In certain embodiments, the imaging device comprises a handheld self-contained ultrasound imaging device comprising a display directly attached to the top of a housing, an ultrasound transducer positioned at the bottom of the housing, and a handle incorporated with the housing and positioned between the display and the ultrasound transducer, wherein the display is rotatable about at least one rotational axis by at least about 30°. 
         [0014]    In another aspect, a cover for an imaging device is provided. The cover comprises, in certain embodiments, a cover body configured to be attached to an imaging device and a marking unit attached to the cover body and configured to indicate proper placement of a probe along a target that is to be imaged. The cover can have any one or more of the following properties, according to various embodiments. In some embodiments, the cover is configured such that when it is attached to the imaging device, an image can be produced without the use of transmission medium. For example, in certain embodiments, the cover is configured such that when it is attached to an ultrasound-imaging device, an image can be produced without the use of ultrasound gel or other ultrasound transmission medium. In some embodiments, the marking unit is configured to identify a target surface location corresponding to a center of an imaging scan plane. In some embodiments, the marking unit comprises an identifying mark indicating the target surface location corresponding to a center of an imaging scan plane. In certain embodiments, the identifying mark comprises a hole. In some embodiments, the marking unit comprises an adhesive material configured to adhere the marking unit to a surface of a target. In some embodiments, the marking unit comprises a moveable tab configured to indicate a site corresponding to a center of a scan plane. In certain embodiments, the moveable tab is configured to make a visible indentation at a site corresponding to the center of the scan plane. The probe can be, in certain embodiments, a needle and/or a catheter. For example, according to certain embodiments, the marking unit attached to the cover body is configured to indicate proper placement of a needle or a catheter. The cover can be, in certain embodiments, configured to be attached to an ultrasound imaging device. 
         [0015]    Other advantages and novel features of the present invention will become apparent from the following detailed description of various non-limiting embodiments of the invention when considered in conjunction with the accompanying figures. In cases where the present specification and a document incorporated by reference include conflicting and/or inconsistent disclosure, the present specification shall control. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Non-limiting embodiments of the present invention will be described by way of example with reference to the accompanying figures, which are schematic and are not intended to be drawn to scale. In the figures, each identical or nearly identical component illustrated is typically represented by a single numeral. For purposes of clarity, not every component is labeled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention. In the figures: 
           [0017]      FIG. 1  is a schematic illustration of an exemplary imaging device, according to certain embodiments; 
           [0018]      FIGS. 2A-2C  are, according to one set of embodiments, a series of schematic illustrations outlining the rotation of a display of an exemplary imaging device; 
           [0019]      FIG. 3A  is a schematic illustration of an imaging device comprising an exemplary detachable marking unit, according to some embodiments; 
           [0020]      FIG. 3B  is a schematic cross-sectional illustration of a marking unit, according to certain embodiments; 
           [0021]      FIGS. 4A-4D  are a series of schematic illustrations showing the use of an exemplary detachable marking unit, according to certain embodiments; 
           [0022]      FIGS. 5A-5E  are, according to certain embodiments, a series of schematic illustrations showing the use of an exemplary detachable marking unit; 
           [0023]      FIG. 6  is a series of schematic illustrations showing the connectivity between an exemplary detachable marking device and an imaging device, according to one set of embodiments; 
           [0024]      FIG. 7  is a schematic illustration of an exemplary detachable marking unit comprising a needle sleeve, according to certain embodiments; and 
           [0025]      FIG. 8  is an exemplary imaging unit display, according to one set of embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    Imagining devices for identification of target regions are generally described. Certain embodiments relate to handheld ultrasound imaging devices. Various embodiments are related to configurations that may provide, in some cases but not necessarily all cases, one or more advantages during operation of the imaging device. 
         [0027]    Certain embodiments are related to handheld ultrasound imaging devices in which the imaging unit, the display, and the handgrip region are positioned relative to each other such that operation of the imaging device is made easier, under certain circumstances. In one set of embodiments, the handheld ultrasound imaging device comprises a housing, which can include an ultrasound imaging unit at one end, a display at another end, and a handgrip region between the ultrasound imaging unit and the display. As described in more detail below, arranging the imaging unit, the hand grip region, and the display in this manner can allow one to direct the movement of the handheld device relatively easily (e.g., by resting the side of the hand on a surface of the object that is being imaged) while maintaining the ability to see the display screen. 
         [0028]    Certain embodiments are related to the use of rotatable displays in handheld ultrasound imaging devices. Generally, ultrasound-imaging devices in the past have included fixed displays or displays that are spatially separated from the housing in which the imaging unit is contained. Imaging devices with fixed displays can be difficult to operate, as they do not allow one to adjust the angle of the display relative to the eye of the user without rotating or otherwise moving the housing to which the display is connected. While imaging devices with displays that are spatially separated from the device housing allow one to adjust the position of the display relative to the imaging unit, they are generally difficult to transport and/or store when they are not in use. By integrating the display with the housing while maintaining the ability to rotate the display relative to the housing one can realize the benefit of portability and ease of storage while also allowing for relatively easy repositioning of the display relative to the users eye. 
         [0029]    Some embodiments are directed to inventive configurations of marking units—configured to direct the placement of a probe such as a needle or catheter—in the handheld ultrasound imaging devices. For example, according to certain embodiments, a handheld ultrasound imaging device can comprise a marking unit detachably coupled to the housing of the device and positioned such that the target that is being imaged, the ultrasound-imaging unit, and the marking unit are aligned during use. Maintaining alignment of these components can allow one, according to certain embodiments, to properly align the marking unit relative to the target relatively easily during use. As described in more detail below, this alignment, according to some embodiments, may allow one to position the marking unit while the imaging unit is still in place, which can, according to certain embodiments, improve the accuracy of the placement of a probe such as a needle, a catheter, or other device. 
         [0030]      FIG. 1  is an exemplary schematic illustration of a handheld ultrasound-imaging device  100 , according to certain embodiments. In certain embodiments, the handheld ultrasound imaging device comprises a housing. For example, in  FIG. 1 , imaging device  100  comprises housing  102 . According to certain embodiments, the housing comprises a first end associated with an ultrasound-imaging unit. Referring to  FIG. 1 , for example, imaging unit  104  is associated with end  105  of housing  102 . As shown in  FIG. 1 , ultrasound-imaging unit  104  is enclosed within housing  102 . Other arrangements are also possible. 
         [0031]    In some embodiments, imaging unit  104  can comprise, for example, an ultrasound transducer  108 . The ultrasound-imaging unit  104  can be configured, in certain embodiments, to produce an image along at least one scanning plane  110 . The imaging unit can be configured to produce an image using standard ultrasound image processing techniques known to those of ordinary skill in the art of ultrasound imaging, and described in more detail below. 
         [0032]    The imaging device  100  comprises, in certain embodiments, display  112  (e.g., an LCD display, an OLED display, or any other suitable type of display). The display can be located at a second end of the housing. For example, in  FIG. 1 , display  112  is located at end  107  of housing  102 . According to certain embodiments, ultrasound transducer  108  can be configured to produce data along at least one scanning plane  110  that can be subsequently output on display  112 . 
         [0033]    In certain embodiments, an ultrasound transducer surface (e.g., configured to be applied on or near a target site) can be located at one end of the housing and the display can be attached to the housing at the opposite end. For example, in  FIG. 1 , ultrasound transducer surface  109  is located at end  105  of housing  102 , and display  112  is located at second end  107  of housing  102 . In certain embodiments, the display can be directly attached to the top of the housing. For example, in  FIG. 1 , display  112  is directly attached to the top of housing  102 . 
         [0034]    According to certain embodiments, the display of the imaging unit can be a rotatable display. For example, referring to  FIG. 1 , display  112  can be connected to housing  120  via pivot  114 , which can allow rotatable display  112  to rotate about at least one rotational axis  116 . Any suitable pivot may be used. For example, as shown in  FIG. 1 , cylindrical pivot  114  can be used to rotate display  112  about a single rotational axis  116 .  FIGS. 2A-2C  are exemplary schematic illustrations showing the rotation of display  112  about single rotational axis  116  (going into and out of the page in  FIGS. 2A-2C ). In  FIGS. 2A-2C , display  112  is rotated about device handgrip region  120 . In certain embodiments, pivot  114  comprises a ball-and-socket arrangement or other type of arrangement, which can allow for rotation of display  112  about multiple rotational axes. In some such embodiments, display  112  can be rotated about more than one axis so that twisting or rotation in other dimensions is allowed. In other such embodiments, the display  112  can be attached to the housing via magnets, hook and loop fastener (e.g., Velcro), or other attachment means. 
         [0035]    In some embodiments, the rotatable display is configured to be rotated, relative to at least another portion of the housing (e.g., the handgrip region, the imaging unit, and/or another portion of the housing), about at least one rotational axis by at least about 30 degrees, at least about 60 degrees, at least about 90 degrees, at least about 120 degrees, at least about 150 degrees, or at least about 175 degrees. For example, in  FIGS. 2A-2C , display  112  is illustrated as being rotated about both handgrip region  120  and ultrasound transducer  108  by 180 degrees. 
         [0036]    In certain embodiments, the rotatable display is configured to be rotated such that the display can be oriented in a first position substantially parallel to a scanning plane of the imaging unit and in a second position substantially perpendicular to the scanning plane of the imaging unit. For example, in  FIGS. 2A and 2C , imaging device  100  is shown in which display  112  is substantially parallel to scanning plane  110  of imaging device  100 . In addition, in  FIG. 2B , display  112  is substantially perpendicular to scanning plane  110  of imaging device  100 . Display  112  can be said to be in a 0-degree configuration in  FIG. 2A , a 90-degree configuration in  FIG. 2B , and a 180-degree configuration in  FIG. 2C . In the exemplary embodiment of  FIGS. 2A-2C , display  112  can be configured to a position at any angle relative to scan plane  110  of imaging device  100  within the range between the 0-degree configuration ( FIG. 2A ) and the 180-degree configuration ( FIG. 2C ). 
         [0037]    While a rotatable display has been described in association with the above embodiments, it should be understood that the invention is not so limited, and in other embodiments, non-rotatable displays could be used. 
         [0038]    In certain embodiments, the housing is elongated and comprises a longitudinal axis. For example, referring back to  FIG. 1 , housing  102  is elongated and comprises longitudinal axis  106 . 
         [0039]    In some embodiments, the imaging device is configured such that the smallest angle between the scanning plane  110  of the ultrasound imaging unit  104  and the longitudinal axis  106  of the device housing  102  is relatively small (e.g., less than about 45°, less than about 30°, less than about 15°, less than about 5°). In certain embodiments, the smallest angle between the scanning plane  110  of the ultrasound imaging unit  104  and the longitudinal axis  106  of the device housing  102  is less than about 1°, in which case, the scanning plane  110  of the ultrasound imaging unit  104  is said to be substantially parallel to the longitudinal axis  106  of the device housing  102 . 
         [0040]    In some embodiments, the imaging device can be relatively small. For example, in certain embodiments, the imaging device may occupy a volume of equal to or less than about 500 cm 3  or less than about 100 cm 3  (as determined by sealing any openings on the external surfaces of the imaging device and measuring the volume of liquid displaced by the sealed imaging device). In some embodiments, the imaging device is configured such that the entire device may be arranged to fit into a pocket. For example, the ultrasound imaging device can be configured such that the entire device fits into a side pants pocket, according to certain embodiments. 
         [0041]    In some such embodiments, the imaging device is portable such that it may be, for example, carried or otherwise manipulated by hand (e.g., by a single hand). In some embodiments, the imaging device is completely self-contained with portable dimensions such that it can be manipulated with one hand. 
         [0042]    In certain embodiments, the housing comprises a hand grip region (e.g., a handle), which can be configured to be grasped by the user during operation of the imaging device. In some embodiments, the hand grip region can be between the ultrasound imaging unit and the display. For example, referring to  FIG. 1 , hand grip region  120  of imaging device  100  is positioned between imaging unit  104  and display  112 . In certain embodiments, the hand grip region may be between the imaging interface of the ultrasound transducer and the display. The imaging interface of an ultrasound transducer is known to those of ordinary skill in the art to refer to the interface of the transducer from which the ultrasonic signal emanates. For example, referring to  FIG. 1 , ultrasound transducer  108  comprises imaging interface  109 . 
         [0043]    The hand grip region (e.g., handle) may be positioned, in certain embodiments, such that it is directly above the imaging unit during operation of the imaging device. For example, referring to  FIG. 1 , hand grip region  120  is positioned such that it is directly above imaging unit  104  (as well as transducer  108  and imaging interface  109  of transducer  108 ) during operation of imaging device  100 . 
         [0044]    In some embodiments, the imaging device can be battery operated. For example, in certain embodiments, the imaging device is powered using a cell-phone class battery, such as a 2000 mAh Li-ion battery. 
         [0045]    In certain embodiments the display can be integrated with the device housing (e.g., such that display and the device housing form a monolithic unit). For example, referring to  FIG. 1 , device housing  102  is integrated with imaging unit  104  (and transducer  108 ) to form an integrated, monolithic unit. In addition, in  FIG. 1 , display  112  and device housing  102  are integrated to form a monolithic unit. In other embodiments the display can be detachable from the housing unit. In some such embodiments, the ultrasound imaging unit (e.g.,  104  in  FIG. 1 ) can communicate with the display via wireless connection. 
         [0046]    Certain of the imaging devices described herein can provide one or more of a variety of advantages, relative to prior devices. For example, according to certain embodiments, by attaching the display to the base of the housing (e.g., in direct contact with the base of the housing), the display can be located relatively close to the target site that is being imaged (e.g., a subject such as a human subject). This can make, according to certain embodiments, operation of the inventive imaging device easier than systems that include, for example, a transducer probe with a cable and the display that is not in the same vicinity as the user&#39;s hand and probe. In certain embodiments, the closest distance between the image display and the target site (e.g., skin surface  412  in  FIGS. 4A-4D ) is less than about 1 meter, less than about 500 cm, less than about 100 cm, less than about 50 cm, or less than about 25 cm. 
         [0047]    Certain of the embodiments described herein do not include a separate transducer-to-display cable, which would otherwise complicate operation and handling of the imaging device. In addition, as noted above, the imaging device can be configured to be portable and adopt a form factor that can be more easily transported in a user&#39;s pocket. While other handheld ultrasound devices have been proposed with an attached screen (i.e., no transducer-to-display cable), such systems possess a form factor where the hand is placed along a handle region that is extended from the transducer face. That is to say, in such systems, the longitudinal axis of the handle forms a smallest angle with the imaging plane of the imaging unit that is close to 90 degrees. In contrast, certain of the embodiments described herein place the hand immediately above the transducer face, which possesses the benefit of allowing for finer control of the scan plane. That is to say, certain of the embodiments described herein include a smallest angle between the longitudinal axis of the hand grip region and the imaging plane of the imaging unit that is relatively small (e.g., a smallest angle of less than about 45°, less than about 30°, less than about 15°, or less than about 5°) and/or are configured such that the longitudinal axis of the hand grip region is substantially parallel to the imaging plane of the imaging unit. Those of ordinary skill in the art are familiar with the longitudinal axis of a hand grip region, which refers to the elongated axis around which the hand grasps when grasping the handgrip region. In certain embodiments, the longitudinal axis of the handgrip region corresponds to the longitudinal axis of the housing in which the handgrip region is formed. 
         [0048]    According to certain embodiments, there may be a clinical benefit to using an ultrasound imaging device in which the display screen is housed within the same device housing as the imaging unit and/or is rotatable about the longitudinal axis of the device. In some embodiments, the rotating display can allow the user to adjust the display angle to account for different angles between the user&#39;s eye level and the central longitudinal axis of the device. Thus, the user may hold the imaging device above, below, to the left of, or to the right of their eye level and still have a good viewing angle to the display. The ability to adjust the eye level can be important for scanning different anatomies with the same device while still being able to view the display screen. As one example, performing a cardiac scan and a lumbar spine scan while maintaining the user&#39;s body in a substantially fixed position (e.g., standing or sitting) will generally necessitate positioning the imaging device such that the angle between the device and the user&#39;s eye level varies. Without a rotatable screen, the user would need to substantially move their body orientation in order to view the screen with sufficient clarity for both types of scans. With the rotatable screen, however, there is greater flexibility in uses of the ultrasound device, while maintaining a smaller form factor compared with ultrasound devices that have a separate transducer and display screen connected by a cable. 
         [0049]    Moreover, positioning the hand grip region as illustrated in  FIG. 1  (and other figures) can produce greater control over the position of the scan plane and/or can facilitate clinical acceptance. Precise control over the scan plane relative to the anatomy of interest is often important in ensuring that the anatomy is accurately captured by the scan plane and can be assessed via review of the display screen. In certain embodiments in which the hand grip region is configured such that the longitudinal axis of the hand grip region is substantially parallel to the imaging plane, the user&#39;s hand can be used to control the imaging device by placing the hand on the hand grip region while also resting the hand on the target skin surface. During testing of this configuration, it was discovered that arranging the imaging unit components in this manner leads to greater stability. Without wishing to be bound by any particular theory, it is believed that this increase in stability is observed because the hand, target skin surface, and device are all connected and can all move together. Frequently, a subject (e.g., a patient) may move during an ultrasound scan (e.g., due to discomfort, restlessness, or for another reason). Certain embodiments, including that illustrated in  FIG. 1  and other figures can allow for a stable image to be captured regardless of patient motion. 
         [0050]    In certain embodiments, the imaging device comprises an actuator on the hand grip region configured such that when the actuator is activated, data from the ultrasound imaging unit is recorded and/or manipulated. For example, in  FIG. 1 , imaging device  100  comprises actuator  130 , which is in the form of a button. According to certain embodiments, when actuator  130  is depressed, data from the ultrasound imaging unit is recorded, for example, to memory within the ultrasound imaging device or to an external memory unit outside the imaging device (e.g., after being transported via a wireless or wired connection between the imaging unit and the external memory unit). The data from the ultrasound imaging unit that is recorded can correspond to, for example, imaging data (e.g., data related to a B-mode image, a C-mode image, an M-mode image, a tissue harmonic image, a three-dimensional image, a Color Doppler image, a Power Doppler image, a Pulse-wave Doppler image, a continuous wave Doppler image, an ultrasound contrast agent enhanced image, a B-flow image, or any other type of image). In this way, the actuator can be configured to take a “snapshot” of the data being collected by the ultrasound imaging device at that point in time during its use. In some embodiments, the actuator can be configured to perform one or more of a number of other functions including: video save, device power on/off, image settings adjustment (e.g., imaging mode, gain, frequency, contrast, depth), and/or menu navigation. In some embodiments, the imaging device  100  comprises a plurality of actuators, such as the actuator  130  in  FIG. 1 , which can perform different functions, such as the aforementioned functions. 
         [0051]    While the actuator illustrated in  FIG. 1  is a button, any suitable actuator type can be used. Examples include, but are not limited to, touch sensors (e.g., resistive, capacitive, optical), switches, proximity sensors, and/or optical sensors. 
         [0052]    It can be advantageous, according to certain but not necessarily all embodiments, to locate the actuator on the hand grip region of the imaging device. Locating the actuator on the hand grip region can allow a user to activate the data saving function, or other aforementioned functions, relatively easily, for example, by simply activating the actuator using a digit of the hand (e.g., a finger and/or thumb) holding the imaging device. In some embodiments, the hand may activate the actuator for purposes of activating a desired function, such as a saving function, simultaneously while performing an image scan without requiring the user to reorient the hand on the hand grip region of the ultrasound device. That is to say, according to certain embodiments, the user does not need to reorient their hand to save an image during an ultrasound scan. 
         [0053]    According to certain embodiments, the imaging device comprises a marking unit detachably coupled to the housing. For example, in  FIG. 3A , imaging unit  300  comprises marking unit  302 , which can be detachably coupled to housing  102 . Similar arrangements are illustrated in the embodiments shown in  FIGS. 4A-4D ,  5 A- 5 E,  6 , and  7 , described in more detail below. 
         [0054]    The marking unit and the housing can be detachably coupled in any suitable fashion. In some embodiments, the marking unit can be indirectly coupled to the housing. For example, as described in more detail below, according to certain embodiments, a cover body is attached to the housing. In some such embodiments, the marking unit is detachably coupled to the cover body. Exemplary embodiments of such an arrangement are illustrated in FIGS.  3 A and  4 A- 4 D. In certain embodiments, the marking unit is present alone, without the cover body. In some such embodiments, the marking unit is directly coupled to the housing. For example, in  FIGS. 5A-5E  and  6 , marking unit  302  is directly coupled to the housing of the imaging unit. The marking unit can be “self-attaching” to the imaging device (or the cover body, when present), in certain embodiments. That is to say, in some embodiments, substantially no separate attaching material (such as a rubber band) is required to attach the marking unit to the imaging device (or to the cover body, when present). Examples of mechanisms that can be used to attach the marking unit to the imaging device (and/or the cover body, when employed) in this way include, but are not limited to, magnetic fittings (e.g., a pair of magnets between the housing and the marking unit), mechanical attaching mechanisms (such as a fitted plastic inserts, spring-loaded retaining clips, frictional fittings, elastic bands, hook and loop fasteners, screw threads), and the like. Of course, other attachment mechanisms, such as adhesive-based attachment mechanisms, could also be used. 
         [0055]    The marking unit can be configured to indicate proper placement of a probe (e.g., a needle and/or a catheter) along a target that is to be imaged, in some embodiments. In certain embodiments, the marking unit is configured to identify a target surface location (e.g., an insertion location) corresponding to a center of an imaging scan plane. The marking unit can comprise, in certain embodiments, a probe indicator configured to indicate proper placement of a probe at or near a target that is to be imaged. For example, in some embodiments, the marking unit comprises an identifying mark indicating the target surface location. The identifying mark can comprise, for example, a hole, an indentation, or other identifying mark. 
         [0056]    In some such embodiments, the detachable marking unit can be mechanically removed from the imaging device during use. In some such embodiments, the detachable marking unit  302  can be left at or near the target site (e.g., on the skin) to identify the center of the transducer along the skin after the transducer itself has been removed. 
         [0057]      FIGS. 4A-4D  are exemplary schematic illustrations outlining such use of the detachable marking unit. In  FIG. 4A , the detachable marking unit is used to identify the location of needle insertion (i.e. the target insertion location  410 ) in a spinal anesthesia procedure, although use of the detachable marking unit to locate other types of target anatomy (e.g., blood vessels, nerves, joints, or organ tissues) is also possible. In  FIG. 4A , marking unit  302  is placed over an imaging device hand grip region  120 . Marking unit  302  can be configured to indicate proper placement of a needle (shown as  402  in  FIG. 4D ) along a target skin surface  412 , which is to be the imaging surface, in some embodiments. 
         [0058]    As shown in  FIG. 4B , ultrasound imaging device  100  can be scanned across target skin surface  412  with a user&#39;s hand  404  until the user identifies the target anatomy in the ultrasound image displayed on device display  112 . 
         [0059]    According to certain embodiments, marking unit  302  can be configured to identify a location along skin surface  412  that corresponds to the center of the scanning plane produced by ultrasound transducer  108  of the imaging device. 
         [0060]    Next, as illustrated in  FIG. 4C , marking unit  302  can be detached by user&#39;s hand  404  from both the device hand grip region  120  (and optional cover body  304 , described in more detail below). In certain embodiments, the marking unit is configured to be attached to a target surface. For example, in some embodiments, the marking unit comprises an adhesive material configured to adhere the marking unit to a surface of a target (e.g., the skin of a subject). In  FIG. 4C , for example, marking unit  302  can comprise an adhesive material configured to adhere marking unit  302  to skin surface  412 . Other attachment mechanisms could also be employed. For example, in some embodiments, the marking unit comprises a vacuum-generating unit configured to adhere the marking unit to a surface associated with the target. The marking unit  302  can comprise, for example, suction cups or other vacuum means to support adhesion of the marking unit to the target surface. 
         [0061]    As noted above, in certain embodiments, the marking unit comprises, a probe indicator configured to indicate proper placement of a probe at or near a target that is to be imaged. For example, in some embodiments, the marking unit comprises an identifying mark indicating the target surface location. The identifying mark can comprise, for example, a hole, an indentation, or other identifying mark. In  FIG. 4D , marking unit  302  comprises identifying marks  408 , which are configured to indicate the proper placement of needle  402  along skin surface  412 . In certain embodiments, the marking unit  302  comprises a hole  408  in the middle where the center of the transducer  108  was located when the unit  302  was detached from the imaging device housing, such that when left on skin  412 , marking unit  302  identifies the place along skin surface  412  corresponding to the center of ultrasound scan plane  110 . 
         [0062]    According to certain embodiments, with the marking unit  302  adhered to the skin surface  412 , the user can insert a probe  402  at the target insertion location  410  using the hole guide  408  along the marking unit  302 . 
         [0063]    The detachable marking unit, in some embodiments, can comprise a wing component. For example, referring to  FIG. 4D , detachable marking unit  302  comprises wing  420 . The wing component can be advantageous, according to certain although not necessarily all embodiments, because it can improve one&#39;s ability to adhere the marking unit to a target skin surface by increasing surface area of the marking unit along the target skin surface. 
         [0064]    While identifying marks are illustrated in  FIG. 4D  as guiding the placement of the probe, other embodiments are also possible. For example, in some embodiments, the marking unit comprises a moveable tab configured to indicate a site corresponding to a center of a scan plane. The moveable tab can be configured, in certain embodiments, to make a visible indentation at a site corresponding to the center of the scan plane (which can correspond, for example, to the center of a cavity, hole, or other indicator formed in the marking unit).  FIGS. 5A-5E  is a set of schematic illustrations outlining the use of a moveable tab to indicate a target region. In  FIG. 5A , tab  502  can be folded into a center cavity  408  within the marking unit  302  to make an indentation along target skin surface  412  at target insertion location  410  corresponding to the center of cavity  408 . In  FIG. 5A  ultrasound transducer  108  is illustrated with an exemplary embodiment of the marking unit  302  comprising a cavity  408  and moveable tabs  502 . Marking unit  302  can be attached to the hand grip region  120  of the ultrasound device  100  to cover transducer region  302 .  FIG. 5B  illustrates ultrasound device  100  with marking unit  302  attached and pressed against the target skin surface  412  where ultrasound imaging can be conducted. As shown in  FIG. 5C , a user&#39;s hand  404  can press against marking unit tab regions  420  in order to remove marking unit  302  from ultrasound device  100  while maintaining marking unit  302  along the target skin surface  412  at the target insertion location  410 . As illustrated in  FIG. 5D , marking unit  302  can be removed from imaging device  100 . As shown in  FIG. 5E , the user&#39;s hand  404  can activate moveable tabs  502 , which can make an indentation along target skin surface  412  at the target insertion location  410 . According to certain embodiments, a probe may then be inserted at the point at which the indentation has been made. 
         [0065]      FIG. 6  is a schematic illustration showing an exemplary mechanical attachment scheme that can be used to connect a marking unit  302  with an imaging device  100 . The marking unit  302  in  FIG. 6  is configured to “self-attach” to the device housing  102 . Self-attachment can be achieved by previously described means including, in one embodiment, a form fitting between the device housing  102  and marking unit  302  such that frictional forces are sufficient to ensure attachment. The wings  420  of the marking unit  302  in  FIG. 6  can be advantageous, according to certain although not necessarily all embodiments, because it can improve one&#39;s ability to adhere the marking unit to a target skin surface. Additionally, wing regions can provide areas whereby a user can press against to detach the marking unit  302  from the device housing  102 . 
         [0066]    In some embodiments, the marking unit  302  comprises a sleeve  702  comprising an elongated lumen passing through it. The sleeve can be used as a probe indicator, as described above. For example, the elongated lumen of the sleeve can be used to guide or otherwise house an elongated device such as a probe  402 .  FIG. 7  is a schematic illustration of one set of embodiments in which a cover  312  comprises a sleeve  702 , which is being used to house a probe, such as a needle  402 . The sleeve  702  can be configured to control the angle  708  of the elongated probe  402  that is threaded through the lumen (e.g., a needle  402  to be inserted at the target region  350 ). The imaging device display  112  can convey the angle  708  information with indicators such as, for example, dashed lines  802  superimposed on the ultrasound image. The user can then manually scan the imaging device  100  across the target skin surface  412  until the dashed line(s)  802  pass through the target of interest (e.g., blood vessel, nerve structure, epidural space) and then project the probe  402  through the sleeve  702 . An example image display  112  in which overlaying indicator lines  802  are used to indicate the projected path of a probe  402  relative to the image if inserted through the sleeve  702  is illustrated in  FIG. 8 . 
         [0067]    As noted above, certain aspects are related to configurations of a handheld ultrasound imaging device in which the target that is being imaged, the ultrasound imaging unit, and the marking unit are aligned during use. Alignment of these components during use can make location of target regions relatively easy for the user. According to certain embodiments, the marking unit is positioned such that, during use, a line extending between the target and the ultrasound imaging unit intersects the marking unit. 
         [0068]    For example, referring to  FIG. 3A , target region  350 , marking unit  302 , and imaging unit  104  are aligned such that line  352  (which extends infinitely, as indicated by the arrow at the ends of the line) intersects marking unit  302 . It should be understood that a line is said to “intersect” a marking unit when the line passes through any region that lies within the outer geometric boundary of the marking unit, which includes both regions of the solid material that makes up the marking unit as well as voids (e.g., holes and the like) within such regions. As an illustrative example,  FIG. 3B  is a schematic cross-sectional schematic illustration of marking unit  302  shown in  FIG. 3A . Marking unit  302  includes cavity  354  formed within a surrounding solid material  356 , and defines outer geometric boundary  358 . Although cavity  354  is not formed of any material per se, a line extending through cavity  354  would still be said to “intersect” marking unit  302 . 
         [0069]    Referring to  FIGS. 4A-4C , marking unit  302 , imaging unit  104 , and target region  350  are also aligned such that line  352  intersects marking unit  302 . In  FIG. 5D , marking unit  302 , imaging unit  104 , and target region  350  are aligned such that line  352  intersects marking unit  302 . In  FIG. 7 , imaging unit  104 , and target region  350  are aligned such that line  352  intersects marking unit  302 . 
         [0070]    According to certain embodiments, the longitudinal axis of the housing intersects the marking unit (and, in some such embodiments, the longitudinal axis of the housing extends between the target and the ultrasound imaging unit). In some embodiments, the longitudinal axis of the hand grip region intersects the marking unit (and, in some such embodiments, the longitudinal axis of the hand grip region extends between the target and the ultrasound imaging unit). 
         [0071]    According to certain embodiments, during use, the marking unit is positioned between the ultrasound imaging unit and the target that is to be imaged. For example, in  FIG. 3A , marking unit  302  is positioned such that imaging unit  104  is above marking unit  302 , and target region  350  is below marking unit  302 . In other embodiments, the imaging unit could be located between the marking unit and the target region, for example, by sliding the marking unit up the hand grip region  120  of the housing. 
         [0072]    In certain embodiments, a cover for an ultrasound imaging device is described. The cover comprises, in certain embodiments, a cover body configured to be attached to an imaging device, and a marking unit attached to the cover body and configured to indicate proper placement of a probe (e.g., a needle and/or a catheter) along a target that is to be imaged. Such imaging can allow a target anatomy to be reached with the probe, according to certain embodiments. 
         [0073]      FIG. 3A  is an exemplary schematic illustration of a cover  312  including a cover body  304  and detachable marking unit  302  connected to an imaging device  100 . In  FIG. 3A , the cover body covers the hand grip region  120  (e.g., including the imaging unit  104  and ultrasound transducer  108 ). The cover  312  can be used, in certain embodiments, as a sterile shield to the target skin surface  412  (e.g., the skin of a subject). According to certain embodiments, cover  312  can comprise an elastomeric band  306  and tab  308 , for example, to facilitate the placement of cover  312  over hand grip region  120 . 
         [0074]    The cover body can be “self-attaching” to the imaging device, in certain embodiments. That is to say, in some embodiments, substantially no separate attaching material (such as a rubber band) is required to attach the cover body to the imaging device. Examples of mechanisms that can be used to attach the cover body to the imaging device in this way include, but are not limited to, a pair of magnets between the cover body and the hand grip region, mechanical attaching mechanisms (such as a fitted plastic inserts, spring-loaded retaining clips, elastic bands), and the like. 
         [0075]    In certain embodiments, cover body  304  and/or marking unit  302  may be disposable. In some embodiments, cover body  304  and/or marking unit  302  may be sterile. 
         [0076]    In certain embodiments in which a cover body is employed, the cover body and the marking unit can be removably attached to each other. For example, the cover body and the marking unit can be attached to each other, in certain embodiments, such that separation of the cover body and the marking unit does not damage either of the cover body and the marking unit. In some embodiments, the cover body and the marking unit can be attached to each other such that separation of the cover body and the marking unit can be achieved by hand, and does not require an additional tool (e.g., a screwdriver or other such tool). Examples of mechanisms that can be used to attach the marking unit to the imaging device (and/or the cover body, when employed) in this way include, but are not limited to, magnetic fittings (e.g., a pair of magnets between the housing and the marking unit), mechanical attaching mechanisms (such as a fitted plastic inserts, spring-loaded retaining clips, frictional fittings, elastic bands, hook and loop fasteners, screw threads), and the like. 
         [0077]    In some embodiments, the marking unit is configured such that when it is attached to the imaging device, an image can be produced without the use of transmission medium. According to certain embodiments, when marking unit is attached to the imaging device, an image can be produced without substantial acoustic attenuation derived from the marking unit and without the use of transmission medium. For example, in some embodiments, less than 6 dB round-trip acoustic attenuation is observed at 1 MHz center frequency, without the use of transmission medium, when the marking unit is positioned as described elsewhere herein (e.g., when the marking unit is aligned with the ultrasound imaging unit and the target, as described elsewhere herein). In some embodiments, the cover can be configured such that when it is attached to an ultrasound imaging device, received ultrasound data can be recorded for display of an image to the device display without the use of ultrasound gel or other ultrasound transmission medium being placed in between the transducer and the cover and/or marking unit. In contrast, other ultrasound imaging systems generally require the use of ultrasound gel to produce an image with acceptable image quality. The requirement for ultrasound transmission medium between the transducer and cover and/or marking unit can be eliminated, according to certain embodiments, by attaching the cover and/or marking unit to the transducer such that substantially no air is present between the two objects. For example, in some embodiments, an elastomeric band or other attaching mechanism can be configured such that the when the cover is attached to the ultrasound imaging device, it is pressed with high tension against the transducer surface. The tension can be made to be sufficiently high such that there substantially no air can be present between the two objects. In this way, the ultrasound beam can transmit between the two materials (i.e. transducer and cover) without requiring transmission medium. Exemplary materials from which the marking unit can be made include, for example, polyurethane, polyethylene, and silicone. 
         [0078]    In some embodiments in which a cover body is employed (in addition to the marking unit), the cover is configured such that when it is attached to the imaging device, an image can be produced without substantial acoustic attenuation derived from the cover and without the use of transmission medium. For example, the cover can be configured, in certain embodiments, such that when it is attached to an ultrasound imaging device, received ultrasound data can be recorded for display of an image to the device display without the use of ultrasound gel or other ultrasound transmission medium being placed in between the transducer and the cover. The cover can be configured for us without transmission medium, for example, by using a cover material that is thin (e.g., less than about 5 mm thick) and/or by employing a self-attaching mechanism that holds the cover material against the transducer face with sufficient strength during operation of the imaging device. In this way, substantially no air is trapped between the cover and transducer face, and the cover itself is too thin to cause appreciable attenuation or reflections that can lead to unacceptable image quality (e.g., less than 6 dB round-trip acoustic attenuation at 1 MHz center frequency). Example cover materials can include, for example, polyurethane, polyethylene, and silicone. 
         [0079]    As noted above, the ultrasound imaging devices described herein can produce ultrasound images using a variety of known techniques. In certain embodiments the ultrasound transducer (e.g., ultrasound transducer  108 ) can include a mechanically scanned single element transducer. In some embodiments, the ultrasound transducer can be a linear array, a two-dimensional array, or an annual array. In certain embodiments the ultrasound imaging unit (e.g., ultrasound imaging unit  104 ) can be configured to produce, for example, a B-mode image, a C-mode image, an M-mode image, a tissue harmonic image, a three-dimensional image, a Color Doppler image, a Power Doppler image, a Pulse-wave Doppler image, a continuous wave Doppler image, an ultrasound contrast agent enhanced image, a B-flow image, or any other mode or combination of modes whereby an image is formed from information received by the ultrasound transducer. Those of ordinary skill in the art of ultrasound understand that an ultrasound imaging unit generally comprises a combination of one or more of an ultrasound transducer, and circuitry and processing units for conditioning, processing, and transferring image data to the display unit. The ultrasound imaging unit can be contained within the device housing. For example, in some embodiments, the ultrasound-imaging unit can comprise an ultrasound transducer, an ultrasonic signal conditioning circuit, and a processor circuit, which can be communicatively connected via a bus. The ultrasonic signal conditioning circuit can include a number of conventional processing circuitries such as beam-forming circuitry or other processing circuitry. For example, the ultrasonic signal conditioning circuit can be configured to amplify, phase-shift, time-gate, filter, or otherwise condition received ultrasonic information (e.g., echo information), such as provided to the processor circuit. In a further example, the receive path from each transducer element can include one or more of a low noise amplifier, a main-stage amplifier, a band-pass or a low-pass filter, or an analog-to-digital converter. In one example, one or more signal conditioning steps can be performed digitally, such as by using the processor circuit. The term processor is used to generically refer to digital circuitry that can be used to manipulate ultrasound information obtained from the ultrasound transducer. Such circuitry can include one or more of a field-programmable gate array (FPGA) or other programmable logic devices (PLDs), microprocessor, a system-on-chip including one or more execution cores or other circuitry, a microcontroller, or one or more or other circuits. Those of ordinary skill in the art of ultrasound and image processing will understand that the signal conditioning and processing steps and their order of operation to be performed by the signal conditional circuit and processor circuit will vary depending on the desired image to be rendered to the display (e.g., B-mode image, C-mode image, M-mode image, tissue harmonic image, three-dimensional image, Color Doppler image, Power Doppler image, Pulse-wave Doppler image, continuous wave Doppler image, ultrasound contrast agent enhanced image, or B-flow image). 
         [0080]    U.S. Provisional Patent Application Ser. No. 61/770,448, filed Feb. 28, 2013, and entitled “Localization of Imaging Target Regions and Associated Systems and Devices,” is incorporated herein by reference in its entirety for all purposes. 
         [0081]    While several embodiments of the present invention have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the functions and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the present invention. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings of the present invention is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, the invention may be practiced otherwise than as specifically described and claimed. The present invention is directed to each individual feature, system, article, material, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, and/or methods, if such features, systems, articles, materials, and/or methods are not mutually inconsistent, is included within the scope of the present invention. 
         [0082]    The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.” 
         [0083]    The phrase “and/or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to “A and/or B,” when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc. 
         [0084]    As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and/or” as defined above. For example, when separating items in a list, “or” or “and/or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of” or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law. 
         [0085]    As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and/or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc. 
         [0086]    In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.