Patent Application: US-201113642065-A

Abstract:
this invention relates to a scanning apparatus for imaging the breast that employs both x - ray and ultrasound technologies to enhance the diagnosis of cancer . there is provided a method for acquiring and co - registering the x - ray and ultrasound images in three - dimensional space , so that : the breast is in the same orientation and degree of compression when x - ray and ultrasound images are obtained ; both sets of images are acquired simultaneously so as to minimize the time the woman &# 39 ; s breast is held stationary ; automated breast ultrasound images of the whole breast are acquired in a single scan ; both image modalities are acquired in three dimensions ; and radiation dose exposure to the woman is minimized . the method incorporates , in a single device , a system for acquiring full - field digital mammography and automated breast ultrasound images , and an algorithm for performing digital tomosynthesis reconstruction using these images .

Description:
fig1 and 2 are pictorial illustrations of an example embodiment of the dual - modality scanning apparatus according to the present invention . the apparatus includes a support pillar 10 on which is mounted a c - arm . the c - arm includes a breast support platform 14 , an upright member 16 mounted rotatable to the pillar 10 , a further upright member 22 mounted rotatable to the upright member 16 , and an x - ray source 18 with an associated beam - shaper 19 and pre - collimator 20 , attached to the upright member 22 , which extends parallel to the platform 14 . the entire c - arm can be moved up and down in the direction of the arrows e and rotated about its attachment point on the pillar 10 about an axis of rotation , as indicated by the arrows d in fig3 , by respective drives . the breast support platform 14 defines a breast support surface 30 on which a breast 32 of a human subject can be placed . a breast compressor plate 34 with an associated clamp mechanism is positioned adjacent to the breast support surface . the breast compressor has its own linear drive and can be adjusted in the direction of the arrows c to compress the breast 32 firmly against the breast support surface 30 . the dimensions of the breast support platform 14 are chosen to be as narrow as possible , consistent with the width of the largest breast to be measured . this allows positioning of the subject &# 39 ; s breast over an outer corner of the platform , thus enabling the breast compression plate 34 to draw the subject &# 39 ; s axilla tissue into the scanner &# 39 ; s field of view . this ensures that the tissue in the subject &# 39 ; s axillary breast region is fully imaged . conventional imaging systems having a wide breast support platform cannot easily achieve this . below the breast support surface 30 ( which is defined by a material that is both transparent to x - rays and has low acoustical impedance , such as polymethylpentene , which is also known as tpx ) is a linear slot x - ray detector assembly 36 and an ultrasound transducer assembly 37 which are mounted on a pair of rails 38 for transverse movement in a plane parallel to the breast support surface and parallel to a plane defined by the transverse movement of the x - ray source 18 . this is indicated by the arrows b . thus , the linear slot x - ray detector and the ultrasound transducer together define a dual - modality linear scanning element , enabling simultaneous acquisition of x - ray and ultrasound images . the x - ray source 18 has an associated beam shaper 19 that generates a cone beam of x - rays that diverges outwardly towards the platform 14 , with a diameter sufficient to ensure coverage of a breast 32 to be imaged by the resultant fan beams . the cone beam has a central upright reference axis that is normal to the plane defined by the breast support surface 30 and the planes in which the x - ray source and the linear x - ray slot detector assembly 36 move . typically , the cone beam has a cone angle of approximately 30 degrees . the pre - collimator 20 defines a linear slot which , when placed in the path of the x - ray cone beam , generates a generally planar fan beam which is narrowest adjacent to the pre - collimator and which broadens in the direction of the platform 14 . the pre - collimator 20 can be moved in the direction of the arrows a in a plane parallel to the breast support surface 30 so that a number of fan beams f , each having a different inclination relative to the upright reference axis of the x - ray cone beam , can be generated , according to the orientation of the pre - collimator slot . this is indicated schematically in fig2 . thus , each fan beam is inclined at a different pre - determined angle relative to the reference axis of the x - ray cone beam . the pre - collimator can be arranged to be indexed between predetermined positions , but is preferably driven continuously between desired positions which are selected according to the number of fan beams required and the size of the breast to be scanned . with reference now also to fig4 , a post - collimator 78 is located between the breast support surface 30 of the platform 14 and the detector 36 . the post - collimator will typically comprise a layer of lead sandwiched between layers of aluminium . the post - collimator has slots with a width calculated to eliminate any penumbra from the impinging fan beams , typically having a width of about 4 mm for a pre - collimator slot width of 0 . 4 mm . the upright member 22 , to which is attached the x - ray source 18 , can be uncoupled from the upright member 16 , and rotated in the direction of the arrows g , thus allowing a plurality of x - ray images of the breast 32 to be captured from the different angles ( see fig3 ). these multiple two - dimensional images can be used to generate a three - dimensional image of the breast using a digital tomosynthesis algorithm . the linear scanning element used in the prototype embodiment of the apparatus was a ccd based detector of approximately 6 millimetre width , comprising 128 rows of pixels , each with a 48 micron width . this , in conjunction with a fan beam of 3 to 5 millimetres width , permits operation of the ccd detector in a time delay and integration ( tdi ) mode which provides superior sensitivity and lower noise , enabling the use of a lower x - ray dose than would otherwise be required . it is expected that a cmos detector will allow faster data clocking and consequently a higher scan speed of approximately 150 mm / second compared to the ccd detector . fig4 is a schematic block diagram showing major components of the apparatus . the pre - collimator 20 has an associated linear axis drive 52 which adjusts the position of the pre - collimator slot in order to generate an x - ray fan beam at the required angle . the breast compressor plate 34 has an associated linear axis drive 54 , and the x - ray detector 36 and ultrasound transducer 37 have an associated linear axis drive 56 that moves the detector 36 and the transducer 37 transversely in the platform 14 below the breast support surface 30 . the c - arm has two associated drives , a rotational axis drive 60 which permits rotation of the c - arm on the pillar 10 , and a vertical axis drive 62 which allows adjustment of the vertical position of the c - arm on the pillar . high precision 25 linear position encoders associated with the pre - collimator and the slot detector drives provide the alignment control position data required for the fan beam to be incident on the slot detector &# 39 ; s imaging element . the apparatus is assembled in such a way that the linear guides of the x - ray source , pre - collimator and slot detector linear axes are precisely parallel and the slot detector itself is precisely parallel to the fan beam ( that is , orthogonal to its linear axis ). the x - ray source or tube 18 is powered by a high frequency generator 64 that is controlled by an image acquisition and scanning controller 66 . the controller 66 also controls the respective linear axis drives , and the rotational and vertical c - arm drives 60 and 62 . the controller 66 is connected to a human machine interface 68 , typically a computer terminal , with an associated 3d image display unit 70 . the x - ray detector 36 has associated readout electronics 72 integrated with it , and the ultrasound transducer 37 has associated electronics 73 integrated with it , both of which feed raw data to an image reconstruction processor 74 . the operation of the apparatus will now be described in greater detail . prior to an imaging examination the c - arm is rotated about its axis of rotation on the pillar 10 to the desired angle , between 0 and 180 degrees , and driven to the correct vertical height on the pillar to match the subject &# 39 ; s breast height . the three linear axes of the respective drives on the c - arm for the pre - collimator 20 , the breast compressor plate 14 , and the detector assembly 36 are synchronized and all moved to their home positions . the subject &# 39 ; s breast 32 is then placed on the breast support surface 30 of the platform 14 and the breast compressor plate 34 is activated to provide a preliminary compressive pressure , to immobilize the breast and pull breast tissue away from the chest wall . a start signal is then issued via the human machine interface 68 to initiate a breast scan . an extra compressive force is then applied by the drive of the breast compressor plate 34 . the x - ray source 18 is energized by the high frequency generator 64 , with a preliminary exposure technique ( kv & amp ; ma ) based on the breast thickness , implied from the breast compressor linear position , to generate an x - ray cone beam which is pre - collimated by the pre - collimator 20 and filtered by the x - ray filter 76 to produce a filtered x - ray fan beam f . tight collimation ( 0 . 4 mm ) near the source minimizes the back scatter to the subject when compared with collimation techniques applied on top of the breast . with an x - ray source focal spot size of 0 . 3 mm and a source to detector distance of 650 mm , cone beam collimation using a slot with a width of 0 . 4 mm results in a primary fan beam width of approximately 4 mm incident on the detector 36 , which has an active width of 6 mm . this provides significantly greater x - ray flux and better tube loading characteristics when compared with slit scanning configurations that collimate to the width of single pixel detectors 0 . 1 mm wide . the pre - collimator 20 moves in synchronization with the x - ray detector 36 to cause the x - ray fan beam to move across the breast at a linear velocity of up to 150 mm / s . the relative positioning of the x - ray source 18 , the pre - collimator 20 , and the x - ray detector 36 to achieve correct beam alignment is performed according to the calibration data acquired from an automatic beam alignment process . the filtered x - ray fan beam is attenuated and scattered by the breast . the x - ray fan beam post - collimator 78 collimates the x - ray photon flux exiting the breast to eliminate the scattered photons and ensure that only the primary photons impinge on the x - ray slot detector 36 . the multi row linear slot x - ray detector 36 operates in time delay and integration ( tdi ) mode and the detector readout line clock is electronically synchronized with the detector linear axis velocity . the detector accumulates charge across each row of pixels in the imaging element to provide a single image line to an analogue - to - digital convertor in the readout electronics 72 . digitized line data is compiled into a two - dimensional image projection during the scan by the image reconstruction processor 74 . the linear ultrasound transducer 37 , together with its associated control electronics 73 , generates two - dimensional images for each position of the transducer . because the transducer 37 moves in synchrony with the x - ray detector 36 along the pair of guide rails 38 and 40 , it is able to capture multiple 2d images which , when fed into the image reconstruction processor 74 , generates 3d ultrasound images of the breast 32 . the processor 74 is also able to co - register the 2d x - ray image with the 3d ultrasound image , thus aiding in the diagnosis of underlying pathology . the apparatus can also be used to gather multiple 2d x - ray images of the breast . this is accomplished by rotating the x - ray tube 18 in the direction of the arrows g by means of the angular axis drive 50 , and repeating the x - ray image 10 acquisition sequence described previously . the multiple 2d images can then be sent to the image reconstruction processor 74 which then implements a digital tomosynthesis algorithm to generate 3d x - ray images of the breast . these 3d x - ray images can be co - registered with the 3d ultrasound images to improve diagnosis . the above described example embodiment of scanning apparatus according to the invention has a number of advantages compared with known apparatus . by locating an ultrasound transducer in parallel with a linear slot scanning x - ray detector , it allows for the simultaneous capture of x - ray and ultrasound images , thus improving the sensitivity of the apparatus significantly . the use of a narrow breast support platform allows positioning of a subject &# 39 ; s breast over the platform corner , enabling the compressor plate to draw the subject &# 39 ; s axillary tissue into the scanner &# 39 ; s field of view . the use of a slot detector that utilizes tdi techniques to optimise signal - to - noise ratio and reduce scatter is also advantageous , allowing clear imaging at low x - ray doses . a suitable cmos detector , in particular , is relatively inexpensive compared with photon counter detectors used in known apparatus . the use of a cmos detector is also desirable as its high speed ( relative to ccd circuitry ) allows fast data clocking and thus scan speeds , typically 150 mm / s . this enables the collection of a full data set of a large breast ( 250 mm wide ) in less than two seconds . the scan duration is minimized by edge detection of the breast under examination , limiting the scan travel to the edge extent of the breast . berg w a , blume j d , cormack j b , mendelson e b , lehrer d , böhm - 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