Patent Publication Number: US-2021166494-A1

Title: System and method for image processing

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. application Ser. No. 15/510,175, filed Sep. 15, 2014, the contents of which is incorporated herein by reference. 
    
    
     FIELD 
     The specification relates generally to medical imaging, and specifically to a computing device, system and method for image processing. 
     BACKGROUND 
     The planning and execution of surgical procedures, particularly complex procedures such as brain surgery, may require the gathering and organization of large volumes of information, including various medical images of the patient. Such images can include, for example, MRI scans. 
     Accessing such information, particularly during a surgical procedure, may require extensive preparation of different image views prior to the procedure; in other cases, significant portions of the images may simply not be available during the procedure, or may require additional operators and time-consuming programming and computational efforts to produce. 
     SUMMARY 
     According to an aspect of the specification, a computing device is provided, comprising: a memory; an input device; a display; and a processor interconnected with the memory, the input device and the display, the processor configured to: acquire a three-dimensional image of an anatomical structure of a patient and store the three-dimensional image in the memory; render on the display (i) an initial volume of the three-dimensional image corresponding to an initial portion of the anatomical structure, and (ii) a moveable control element; the initial volume having an initial outer surface defined by a position of the control element; receive, from the input device, input data updating the position of the control element on the display relative to the initial volume; responsive to receiving the input data, render on the display, in place of the initial volume, a further volume of the three-dimensional image, corresponding to a further portion of the anatomical structure and having a further outer surface defined by the updated position of the control element; the processor configured to select the further volume by identifying a portion of the three-dimensional images that intersects with the at least one plane or volume, and excluding the identified portion from the further volume. 
     According to another aspect of the specification, method is provided of processing images in a computing device having a memory, an input device, a display and a processor interconnected with the memory, the input device and the display, the method comprising: acquiring a three-dimensional image of an anatomical structure of a patient and storing the three-dimensional image in the memory; at the processor, rendering on the display (i) an initial volume of the three-dimensional image corresponding to an initial portion of the anatomical structure, and (ii) a moveable control element; the initial volume having an initial outer surface defined by a position of the control element; receiving, at the processor from the input device, input data updating the position of the control element on the display relative to the initial volume; responsive to receiving the input data, controlling the display at the processor to render, in place of the initial volume, a further volume of the three-dimensional image, corresponding to a further portion of the anatomical structure and having a further outer surface defined by the updated position of the control element. 
    
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
       Embodiments are described with reference to the following figures, in which: 
         FIG. 1  depicts an operating theatre, according to a non-limiting embodiment; 
         FIG. 2  depicts a computing device for deployment in the operating theatre of  FIG. 1 , according to a non-limiting embodiment; 
         FIG. 3  depicts a method of processing images, according to a non-limiting embodiment; 
         FIG. 4  depicts a method of rendering initial and further volumes in the method of  FIG. 3 , according to a non-limiting embodiment; 
         FIG. 5  depicts an example of the performance of block  310  of the method of  FIG. 3 , according to a non-limiting embodiment; 
         FIG. 6  depicts another example of the performance of block  310  of the method of  FIG. 3 , according to a non-limiting embodiment; 
         FIG. 7  depicts a further example of the performance of block  310  of the method of  FIG. 3 , according to a non-limiting embodiment; 
         FIGS. 8A and 8B  depict examples of performances of block  320 , according to a non-limiting embodiment; 
         FIGS. 9A and 9B  depict other examples of performances of block  320 , according to a non-limiting embodiment; and 
         FIGS. 10A and 10B  depict further examples of performances of block  320 , according to a non-limiting embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Various embodiments and aspects of the disclosure will be described with reference to details discussed below. The following description and drawings are illustrative of the disclosure and are not to be construed as limiting the disclosure. Numerous specific details are described to provide a thorough understanding of various embodiments of the present disclosure. However, in certain instances, well-known or conventional details are not described in order to provide a concise discussion of embodiments of the present disclosure. 
     As used herein, the terms, “comprises” and “comprising” are to be construed as being inclusive and open ended, and not exclusive. Specifically, when used in the specification and claims, the terms, “comprises” and “comprising” and variations thereof mean the specified features, steps or components are included. These terms are not to be interpreted to exclude the presence of other features, steps or components. 
     Unless defined otherwise, all technical and scientific terms used herein are intended to have the same meaning as commonly understood to one of ordinary skill in the art. 
       FIG. 1  depicts a surgical operating theatre  100  in which a healthcare worker  102  (e.g. a surgeon) operates on a patient  104 . Specifically, surgeon  102  is shown conducting a minimally invasive surgical procedure on the brain of patient  104 . Minimally invasive brain surgery involves the insertion and manipulation of instruments into the brain through an opening that is significantly smaller than the portions of skull removed to expose the brain in traditional brain surgery techniques. 
     The opening through which surgeon  102  inserts and manipulates instruments is provided by an access port  106 . Access port  106  typically includes a hollow cylindrical device with open ends. During insertion of access port  106  into the brain (after a suitable opening has been drilled in the skull), an introducer (not shown) is generally inserted into access port  106 . The introducer is typically a cylindrical device that slidably engages the internal surface of access port  106  and bears a conical atraumatic tip to allow for insertion of access port  106  into the sulcal folds of the brain. Following insertion of access port  106 , the introducer may be removed, and access port  106  may then enable insertion and bimanual manipulation of surgical tools into the brain. Examples of such tools include suctioning devices, scissors, scalpels, cutting devices, imaging devices (e.g. ultrasound sensors) and the like. 
     Also shown in  FIG. 1  is an equipment tower  108  supporting a computing device (not shown) such as a desktop computer, as well as one or more displays  110  connected to the computing device for displaying images provided by the computing device. The computing device, display  110 , or both, may also be supported by other structures. Indeed, the computing device may be located outside of operating theatre  100 , and where multiple displays are provided, at least one display may also be located outside of operating theatre  100 . 
     Equipment tower  108  may also support a tracking system  112 . Tracking system  112 , when included, is generally configured to track the positions of one or more reflective markers (not shown) mounted on access port  102 , any of the above-mentioned surgical tools, or any combination thereof. Such markers, also referred to as fiducial markers, may also be mounted on patient  104 , for example at various points on patient  104 &#39;s head. Tracking system  112  may therefore include a camera (e.g. a stereo camera) and a computing device (either the same device as mentioned above or a separate device) configured to locate the fiducial markers in the images captured by the camera, and determine the spatial positions of those markers within the operating theatre. The spatial positions may be provided by tracking system  112  to the computing device in equipment tower  108  for subsequent use. An example of tracking system  112  is the “Polaris” system available from Northern Digital Inc. 
     Also shown in  FIG. 1  is an automated articulated arm  114 , also referred to as a robotic arm, carrying an external scope  116  (i.e. external to patient  104 ). External scope  116  may be positioned over access port  102  by robotic arm  114 , and may capture images of the brain of patient  104  for presentation on display  110 . The movement of robotic arm  114  to place external scope  116  correctly over access port  102  may be guided by tracking system  112  and the computing device in equipment tower  108 . The images from external scope  116  presented on display  110  may be overlaid with other images, including images obtained prior to the surgical procedure. The images presented on display  110  may also display virtual models of surgical instruments present in the field of view of tracking system  112  (the positions and orientations of the models having been determined by tracking system  112  from the positions of the markers mentioned above). 
     Both before and during a surgical procedure such as the one illustrated in  FIG. 1 , images of anatomical structures within patient  104  may be obtained using various imaging modalities. For example, images of the brain of patient  104  may be obtained using Magnetic Resonance Imaging (MRI), Optical Coherence Tomography (OCT), ultrasound, Computed Tomography (CT), optical spectroscopy and the like. As will be discussed in further detail below, such images may be stored in the computing device mentioned above, and subsequently processed by the computing device for presentation and manipulation on display  110 . 
     Before a discussion of the functionality of the computing device, a brief description of the components of the computing device will be provided. Referring to  FIG. 2 , a computing device  200  is depicted, including a central processing unit (also referred to as a microprocessor or simply a processor)  202  interconnected with a non-transitory computer readable storage medium such as a memory  204 . 
     Processor  202  and memory  204  are generally comprised of one or more integrated circuits (ICs), and can have a variety of structures, as will now occur to those skilled in the art (for example, more than one CPU can be provided). Memory  204  can be any suitable combination of volatile (e.g. Random Access Memory (“RAM”)) and non-volatile (e.g. read only memory (“ROM”), Electrically Erasable Programmable Read Only Memory (“EEPROM”), flash memory, magnetic computer storage device, or optical disc) memory. In the present example, memory  204  includes both a volatile memory and a non-volatile memory. Other types of non-transitory computer readable storage medium are also contemplated, such as compact discs (CD-ROM, CD-RW) and digital video discs (DVD). 
     Computing device  200  can also include a network interface  206  interconnected with processor  200 . Network interface  206  allows computing device  200  to communicate with other computing devices via a network (e.g. a local area network (LAN), a wide area network (WAN) or any suitable combination thereof). Network interface  206  thus includes any necessary hardware for communicating over such networks, such as radios, network interface controllers (NICs) and the like. 
     Computing device  200  can also include an input/output interface  208 , including the necessary hardware for interconnecting processor  202  with various input and output devices. Interface  208  can include, among other components, a Universal Serial Bus (USB) port, an audio port for sending and receiving audio data, a Video Graphics Array (VGA), Digital Visual Interface (DVI) or other port for sending and receiving display data, and any other suitable components. In general, I/O interface  208  connects computing device  200  to “local” input and output devices, while network interface  206  connects computing device  200  to “remote” computing devices, which may themselves be connected to additional input and output devices. This arrangement may be varied, however. For example, any suitable combination of the input and output devices to be discussed below may be connected to computing device  200  via network interface  206  rather than I/O interface  208 . Indeed, in some embodiments I/O interface  208  may be omitted entirely, while in other embodiments network interface  206  may be omitted entirely. 
     In the present example, via interface  208 , computing device  200  can be connected to input devices including a keyboard and mouse  210 , a microphone  212 , as well as scope  116  and tracking system  112 , mentioned above. Also via interface  208 , computing device  200  can be connected to output devices including illumination or projection components  214  (e.g. lights, projectors and the like), as well as display  110  and robotic arm  114  mentioned above. It is contemplated that other combinations of devices may also be present, omitting one or more of the above devices, including other input (e.g. touch screens) and output (e.g. speakers, printers) devices, and the like. 
     Computing device  200  stores, in memory  204 , an image manipulation application  216  (also referred to herein as application  216 ) comprising a plurality of computer readable instructions executable by processor  202 . When processor  202  executes the instructions of application  216  (or, indeed, any other application stored in memory  204 ), processor  202  performs various functions implemented by those instructions, as will be discussed below. Processor  202 , or computing device  200  more generally, is therefore said to be “configured” or “operating” to perform those functions via the execution of application  216 . 
     Also stored in memory  204  is a patient data repository  218 . Patient data repository  218  can contain a surgical plan defining the various steps of the minimally invasive surgical procedure to be conducted on patient  104 , as well as images of patient  104  (e.g. MRI and CT scans). 
     As mentioned above, computing device  200  is configured, via the execution of application  216  by processor  202 , to perform various functions related to presenting and manipulating images of patient  104  on display  110 . Those functions will be described in further detail below. 
     Referring now to  FIG. 3 , a method  300  of processing images is depicted. Method  300  will be discussed in conjunction with its performance on computing device  200  as deployed in operating theatre  100 . It will be apparent to those skilled in the art, however, that method  300  can also be implemented on other computing devices in other systems. 
     Beginning at block  305 , computing device  200  is configured to acquire at least one three-dimensional image of an anatomical structure of patient  104  and store the three-dimensional image in memory  204  (for example, in patient data repository  218 ). In the present example, the anatomical structure is the brain of patient  104 , but a variety of other anatomical structures may also be imaged instead of, or in addition to, the brain. The mechanism of acquisition of the image is not particularly limited. For example, computing device  200  can obtain the image directly from an imaging device (not shown), such as an MRI scanner. In other examples, computing device  200  can obtain the image from another computing device which itself obtained the image from an imaging device. 
     The exact nature of the image may also vary. In the present example, the three-dimensional image is assumed to be an MRI scan. The collection of two-dimensional MRI slices, together representing a three-dimensional scan of the brain, is referred to herein as the three-dimensional image. In other examples other imaging modalities may be employed instead of, or in addition to, MRI. 
     Proceeding to block  310 , computing device  200  is configured to control display  110  (e.g. via I/O interface  208 ) to render an interface for presenting and manipulating the three-dimensional image. In general, the interface includes a rendering of an initial volume of the three-dimensional image corresponding to an initial portion of the anatomical structure (that is, the brain of patient  104 ). The interface rendered at block  310  also includes at least one moveable control element, which will be discussed in greater detail below. Broadly, the initial volume rendered on display  110  has an initial outer surface defined by a position of the control element relative to the initial volume. 
     In other words, the three-dimensional image contains data depicting a given volume of the anatomical structure. In the case of the brain, the three-dimensional image may in fact depict a volume of patient  104  that is larger than the brain itself. An MRI scan of the brain, for example, can depict the skull as well as the brain. The initial volume rendered on display  110  at block  310  need not contain the entire volume of the three-dimensional image (although it may contain the entire volume). The initial volume referred to above, therefore, is some portion (up to and including 100%) of the three-dimensional image. Which portion of the three-dimensional image is rendered at block  310  is computed by processor  204  based on the positions of the above-mentioned control elements. 
     As will be discussed in greater detail below, the control elements define geometrical planes or volumes having positions relative to the three-dimensional image (e.g. coordinates within a coordinate system associated with the three-dimensional image). At those positions, the planes or volumes defined by the control elements intersect with the volume of the three-dimensional image. Such intersections define the outer surface of the initial volume to be rendered from the complete three-dimensional image. That is, the intersections of the control elements with the three-dimensional image define the boundaries of the initial volume to be rendered (i.e. what portion of the image will be rendered and what portion will be excluded from the rendering). 
     Turning now to  FIGS. 4-7 , three examples of control elements and the manner in which they are rendered and processed by computing device  200  will be discussed.  FIG. 4  depicts a method  400 , performed by computing device  200  (via the execution of application  216 , discussed earlier), of performing blocks  310  and  320  (that is, the rendering steps) of method  300 . Method  400  will be described with reference to  FIGS. 4, 5 and 6 , which depicts examples of the interfaces generated at block  310  (and, as will be seen later herein, at block  320 ). 
     Referring to  FIG. 4 , at block  405 , having acquired the three-dimensional image, computing device  200  is configured to select one or more control elements. The definitions of the control elements are stored in memory  204 , for example as part of application  216 . The selection at block  405  can be automatic—for example, application  216  can contain instructions to select a default control element, or set of control elements—or the selection can be received as input data, for example from keyboard/mouse  210 . 
     In the present example, three types of control elements are contemplated, though it will be understood that these are only examples—other types of control elements will occur to those skilled in the art in light of the present description. As seen in  FIG. 4 , any combination of the three types of control elements may be selected. For simplicity, the control elements will be discussed individually, however. Thus, when computing device  200  determines that the plane control elements have been selected at block  410 , performance of method  400  proceeds to block  415 . 
     The plane control elements include a plurality of planes. In the present example, three orthogonal planes are contemplated, although other numbers of planes, disposed at other angles relative to each other, may also be employed. 
     The planes each have an initial default location relative to the three-dimensional image, such that each plane intersects the three-dimensional image. Thus, it will now be apparent that the planes, by intersecting the three-dimensional image, divide the image into quadrants (in particular, eight quadrants in the case of three orthogonal planes). At block  415 , computing device  200  is configured to select one of the quadrants, and clip the intersection of that selected quadrant and the three-dimensional image, before proceeding to block  310  to render the resulting initial volume on display  110 . 
     Referring now to  FIG. 5 , an example of the interface generated at block  310  following the performance of blocks  405 ,  410  and  415  is illustrated.  FIG. 5  depicts an interface  500  generated on display  110  that includes a rendering of an initial volume  504  and control elements  508 ,  512  and  516  in the form of orthogonal planes. In the present example, control elements  508 ,  512  and  516  are the sagittal, coronal, and transverse anatomical planes, respectively. In addition to initial volume  504 , two-dimensional slices of the three-dimensional image are also illustrated, each corresponding to the position of one of the three planes within the three-dimensional image. The two-dimensional views may be omitted in other embodiments. 
     As seen from  FIG. 5 , initial volume  504  includes the entire volume of the three-dimensional image (that is, the MRI scan of patient  104 &#39;s head), with the exception of the portion intersected by one of the quadrants defined by planes  508 ,  512  and  516 . The intersecting quadrant has been cut away, or clipped, and therefore is not rendered in interface  500 , which allows certain interior portions of the brain to be rendered. In other words, the position of the three planes defines the outer surface of initial volume  504 . 
     Returning to  FIG. 4 , whether or not the determination at block  410  is affirmative, at block  420  computing device  200  may also (or alternatively) determine that a cone control element has been selected at block  405 . If the determination at block  420  is affirmative, performance of method  400  proceeds to block  425 . 
     The cone control element is a volume in the shape of a cone, or in some embodiments, a truncated cone, having an initial default position relative to the three-dimensional image. At block  425 , computing device  200  is configured to clip the portion of the three-dimensional image that intersects with the conical volume, before proceeding to block  310 . 
     Turning to  FIG. 6 , an example interface  600  generated as a result of the performances of blocks  405 ,  420  and  425  is illustrated. Interface  600  includes an initial volume  604  and a control element  608 . Control element  608  corresponds to a cone  612 , which may be omitted from interface  600  (in the present example, cone  612  is shown in  FIG. 6  only for illustrative purposes, and does not appear on interface  600 ). More particularly, control element  608  comprises an axis  616  along which a model  620  of an access port may be positioned at various depths relative to the three-dimensional image (and by extension, to initial volume  604 ). In other words, input data received at processor  204  may act to slide model  620  along axis  616 . As seen in  FIG. 6 , the summit of cone  612  coincides with the point of model  620 . Thus, as model  620  is moved along axis  616  towards the brain as represented by the three-dimensional image, cone  612  will begin to intersect with the three-dimensional image. Computing device  200  is configured to clip any portions of the three-dimensional image that intersect with cone  612 . In the present example, however, the default initial position for cone  612  does not intersect with the three-dimensional image, and initial volume  604  has not had any portions clipped therefrom by computing device  200 . 
     Returning to  FIG. 4 , whether or not the determinations at blocks  410  and  420  are affirmative, at block  430  computing device  200  may also (or alternatively) determine that a mask control element has been selected at block  405 . If the determination at block  430  is affirmative, performance of method  400  proceeds to block  435 . 
     The mask control element is an irregular surface having an initial default position relative to the three-dimensional image. The initial position of the mask is determined by computing device  200  by any suitable algorithm or combination of algorithms to identify the border between skull and brain. As mentioned above, images such as MRI scans generally include data depicting the entire head of patient  104 , including skull and facial features. The mask control element is an estimate of the outer surface of the patient  104 &#39;s brain, and divides the three-dimensional image into an “outer” part representing non-brain tissues, and an “inner” part representing brain tissues. At block  435 , computing device  200  is configured to clip the portion of the three-dimensional image that intersects with the above-mentioned outer part, before proceeding to block  310 . Thus, as with the plane and cone control elements, the mask control element defines the outer surface of the initial volume. 
     Turning to  FIG. 7 , an example interface  700  generated as a result of the performances of blocks  405 ,  430  and  435  is illustrated. Interface  700  includes an initial volume  704  and a control element  708 . Control element  708  corresponds to the mask, an irregular surface not illustrated in conjunction with initial volume  704 . The mask, however, may be illustrated in a second two-dimensional view as an outline  712  delineating the boundary between the outer part (excluded from initial volume  704 ) and the inner part (included in initial volume  704 ). The nature of control element  708  is not particularly limited, and in the present example comprises an axis  716  and a depth indicator  720  indicating the depth of the mask along axis  716 . 
     As mentioned earlier, the control elements described herein may be combined. For example, while interface  500  does not show the application of a mask (thus, the patient  104 &#39;s skull and ears are visible in initial volume  504 ), interface  600  does apply the mask, in addition to cone  612 . 
     Returning now to  FIG. 3 , having presented an initial interface on display  110 , computing device  200  is configured to proceed to block  315 . At block  315 , processor  204  is configured to receive input data updating the position of the control element(s) rendered at block  310 , relative to the initial volume rendered at block  310 . In other words, the position of the control element(s) within the coordinate system of the three-dimensional image may change in response to input data. 
     Referring to  FIGS. 5, 6 and 7 , the input data received at block  315  can include the selection and dragging, or other repositioning, or the control elements shown therein. For example, processor  204  may receive input data from keyboard/mouse  210  representing a selection and moving operation performed on any one or more of planes  508 ,  512  and  516 . With respect to interface  600 , processor  204  may receive input data from keyboard/mouse  210  representing a change in depth of model  620  along axis  616 , a change in angle of axis  616 , and the like. With respect to interface  700 , processor  204  may receive input data from keyboard/mouse  210  representing a change in depth of depth indicator  720  along axis  716 . In further embodiments, input data can also be received form a touchscreen interface, a joystick input, a gesture control or a voice control interface. 
     Having received updated positions for the control elements, computing device  200  is configured, at block  320 , to control display  110  to present an updated interface. The updated interface includes a rendering of a further volume of the three-dimensional image, as well as the control elements rendered in block  310 , but in their updated positions. The generation of an updated interface is performed as described above in connection with method  400 , substituting the updated control element positions for the previous (e.g. initial) control element positions. 
     Having rendered an updated interface on display  110 , computing device  200  is configured to repeat blocks  315  and  320  until an exit command is received at block  325 . 
       FIGS. 8A and 8B  illustrate the interfaces rendered in two subsequent performances of blocks  315  and  320 .  FIG. 8A  illustrates an interface  800  in which the position of plane  516  has been updated to raise plane  516  in the superior direction (that is, towards the top of patient  104 &#39;s head as depicted by the three-dimensional image). As a result, the clipped quadrant that intersects with the three-dimensional image has changed in dimensions. In other words, the outer surface of a further volume  802  of the three-dimensional image has changed. Although the example above shows only a translation of plane  516 , it is contemplated that any of the planes may also be rotated, angled and the like. 
       FIG. 8B  illustrates another interface  804  in which plane  516  has been returned to its previous position (as shown in  FIG. 5 ), but in which a further volume  806  has been rotated on display  110 . As mentioned earlier, when the plane control elements are selected at block  405 , computing device  200  is configured to select one of the quadrants defined by the intersecting planes. In the present example, computing device  200  is configured to automatically select the quadrant of which the greatest proportion is visible on display  110 . Thus, for the same plane positions, different quadrants may be selected for clipping based on the position of the illustrated volume on the display. 
     Turning to  FIGS. 9A and 9B , two further interfaces generated at subsequent performances of blocks  315  and  320  are illustrated, using the cone control element. Interface  900  in  FIG. 9A  depicts a further volume  902  in which control element  608  has been relocated in the inferior direction (that is, model  620  has been moved down axis  616 ). As a result, a portion of the three-dimensional image intersects with cone  612 , and the intersection portion has been clipped, resulting a cone-shaped cavity in further volume  902 . Interface  904  in  FIG. 9B  depicts a further volume  906  which has been rotated in comparison to further volume  902 . In addition, the angle of control element  608  has been altered. 
     Turning to  FIGS. 10A and 10B  two further interfaces generated at subsequent performances of blocks  315  and  320  are illustrated, using the mask control element. Interface  1000  in  FIG. 10A  depicts a further volume  1002  of the three-dimensional image, in which depth marker  720  has been raised “outwards” from the brain along axis  716 , in comparison with  FIG. 7 . Thus, the mask defined by control element  708  defines an outer surface of further volume  1002  that lies outside the outer surface of the three-dimensional image for the majority of the patient  104 &#39;s skull. Thus, the skull and facial features are visible in further volume  1002 , as they do not intersect with the “outer” part mentioned earlier.  FIG. 10B , in contrast, depicts an interface  1004  in which depth marker  720  has been relocated inwardly along axis  716 , contracting the mask and thus adjusting the outer surface of a further volume  1006 . The boundary of the mask is clearly visible in  FIG. 10B  on the two-dimensional pane. 
     The adjustment of the mask depth as shown in  FIGS. 10A and 10B  may be implemented in a variety of ways. In the present example, the brain/skull boundary detection parameters are not altered. Rather, those parameters are set once, and computing device is configured to shift each point of the mask inwards or outwards by a number of pixels (or voxels, or any other unit of measurement within the three-dimensional image) proportional to the distance travelled by depth marker  720  along axis  716 . 
     Variants to the techniques described above are contemplated. For example, the three-dimensional image may be supplemented by other three-dimensional images acquired by computing device  200 . In some embodiments, patient data repository may contain one or more images of fluid flow tracts for patient  104 , one or more images or models of a tumour within the brain of patient  104 , and the like. Such images can be overlaid on the initial and further volumes discussed above. In addition, such images can be exempt from the clipping behaviour discussed above. Thus, for example,  FIG. 10B  shows an image  1008  of a tumour in conjunction with further volume  1006 . As seen in  FIG. 10B , the tumour is not subject to the masking behaviour exhibited with further volume  1006 . It will now be apparent to those skilled in the art that  FIG. 5  also shows an image  524  of a tumour. 
     As another example,  FIG. 9B  shows, in addition to further volume  906 , an image  908  of fluid tracts. Image  908  can be a portion selected from a larger image of fluid tracts (for example, the selected portion can be limited to those tracts that would be intersected by the access port if the access port were inserted to the illustrated position of model  620 ). 
     Image overlays such as fluid tracts and tumours may be enabled and disabled by way of input data received at processor  204  (e.g. from keyboard/mouse  210 ). For example, the interfaces discussed above may include one or more selectable toggle elements for enabling and disabling such overlays. Other types of overlays contemplated can display or hide different types of tissue. For example, the three-dimensional image can include identifiers of which type of tissue each voxel (or group of voxels) depicts. Such identifiers may be added to the three-dimensional image manually, or by execution of a tissue identification algorithm. An interface  100  on display  110  may then include selectable elements that disable or enable the display of various portions of the three-dimensional image. In other words, an additional selection of data from the three-dimensional image can occur at or before block  310 , depending on which tissue types are selected for display. In further variations, certain tissue types may be identified as being exempt from the “clipping” behaviour discussed above (similar to the illustration of the tumour model in  FIG. 10B , which is exempt from the clipping imposed by the mask). Thus, the volumes mentioned above can correspond to particular tissue types, and computing device  200  can render additional volumes whose outer surfaces are not defined by control element positions (as they are exempt from clipping). 
     In other variations, when an interface includes a two-dimensional view, the corresponding initial or further volume (that is, the three-dimensional view) may include an illustration of the plane from which the two-dimensional view is taken. This is shown in  FIG. 5 ; a similar mechanism can be applied to other interfaces, such as that shown in  FIGS. 7, 10A and 10B . 
     In further variations, computing device  200  may colorize control elements to enhance their visibility on display  110 . For example, the “outer” part beyond the boundary of the mask shown in  FIGS. 7, 10A and 10B  may be colorized differently than the inner part. As another example, each one of planes  508 ,  512  and  516  may be assigned a colour. The planes as illustrated on initial volume  504  and any subsequently presented further volumes, as well as in the accompanying two-dimensional views, may bear the same colours. 
     In other variations, some aspects of the control elements may be configurable. For example, the radius of cone  612  may be altered by processor  204  in response to input data. 
     Persons skilled in the art will appreciate that there are yet more alternative implementations and modifications possible for implementing the embodiments, and that the above implementations and examples are only illustrations of one or more embodiments. The scope, therefore, is only to be limited by the claims appended hereto.