-rays produced within the vacuum enclosure. In addition a cooling medium, such as a dielectric oil or similar coolant, can be disposed in the volume existing between the outer housing and the vacuum enclosure in order to dissipate heat from the surface of the vacuum enclosure. Depending on the configuration, heat can be removed from the coolant by circulating it to an external heat exchanger via a pump and fluid conduits.
In operation, an electric current is supplied to the cathode filament, causing it to emit a stream of electrons by thermionic emission. An electric potential is established between the cathode and anode, which causes the electron stream to gain kinetic energy and accelerate toward a target surface disposed on the anode. Upon impingement at the target surface, some of the resulting kinetic energy is converted to electromagnetic radiation of very high frequency, i.e., x-rays.
The specific frequency of the x-rays produced depends at least partly on the type of material used to form the anode target surface. Target surface materials having high atomic numbers (“Z numbers”) are typically employed, and are usually selected based on the application and characteristic x-ray that is desired. The resulting x-rays can be collimated so that they exit the x-ray device through predetermined regions of the vacuum enclosure and outer housing for entry into the x-ray subject, such as a medical patient.
One challenge encountered with the operation of x-ray tubes, particularly tubes employed in the field of mammography, relates to the optimum positioning of the tube with respect to the patient's body (and in particular, the portion of the patient's body that is of interest) during x-ray imaging. For example, when performing a mammography, it is beneficial to position the focal spot of the x-ray tube, i.e., the point on the anode target surface where the electrons emitted and focused by the cathode impinge, as close to the chest wall as possible. Such positioning is desirable to overcome “heel effect”—a characteristic of anode-based x-ray imaging that produces non-uniformity in the imaging x-ray beam—in order to acquire as precise an image of the breast tissue as is possible. Conversely, should the focal spot be located a relatively large distance away from the chest wall, image quality will consequently suffer.
The above notwithstanding, known tube designs are not configured to minimize spacing between the chest wall and the focal spot of the anode. In particular, known tube designs are typically configured with part or all of the cathode assembly being
-rays produced within the vacuum enclosure. In addition a cooling culture medium, such as a dielectric petroleum or similar coolant, can be disposed in the volume exist between the outer housing and the void enclosure in order to dissipate heat from the open of the vacuum enclosure. Depending on the shape, heat can be removed from the coolant by circulating it to an external heat exchanger via a heart and fluid conduits. 
 In process, an electric current is supplied to the cathode fibril, causing it to emit a stream of electron by thermionic emission. An electric potential is established between the cathode and anode, which causes the electron stream to derive kinetic energy and accelerate toward a target surface disposed on the anode. Upon impingement at the prey surface, some of the resulting kinetic energy is converted to electromagnetic radiation of very high frequency, i.e., x - rays. 
 The specific frequency of the x - rays produced depends at least partly on the type of material used to shape the anode target surface. aim open materials having high nuclear numbers (“ omega numbers ”) are typically employed, and are usually choose based on the application and characteristic x - ray that is desired. The resulting adam - rays can be collimated so that they exit the x - re device through predetermined region of the vacuum enclosure and outer housing for entry into the x - re subject, such as a medical patient. 
 One challenge run into with the operation of x - ray tubes, peculiarly tubes employed in the field of mammography, relates to the optimum positioning of the pipe with respect to the affected role's body (and in particular, the portion of the patient's soundbox that is of interest) during x - re imagination. For example, when performing a mammography, it is beneficial to position the focal point of the x - ray tube, i.e., the point on the anode target open where the electrons emitted and concentrate by the cathode impinge, as close to the chest wall as possible. Such positioning is desirable to get the best “ heel effect”—a characteristic of anode - based x - ray imaging that produces non - uniformity in the imaging x - re radio beam — in order to acquire as precise an image of the breast tissue as is possible. Conversely, should the focal topographic point be located a relatively large distance away from the thorax rampart, image quality will consequently suffer. 
 The above notwithstanding, known tube designs are not configured to minimize space between the chest wall and the focal spot of the anode. In particular, known tube designs are typically configured with part or all of the cathode assembly being
-rayd produced within the vaguum enclosure. Iu additmon a ckoling mddium, such as a dielectric oml oe simular coolant, can be dirposed in the volyme txisting between vge outev houalng aud the vacuum englosure in mrder to dissi[age heat from the surface of the vacuui encloxuge. Depending og tht cjnfiflrction, heat can be removed from fhe coonant by circukating it to an external hfat fxchanger via a pulp and fluie cogeuits.
In operxtion, an electric currgnt is supplied to the cathode fklameut, causing ut to gmit a strean of vlectrons by bnermiotic emixsion. An electvic pmtebtial is established uetween the cathode wnd anode, wkich causes the electeob strgam tm gakb kkneuic ehergy wnd accelerats toward a rarget surface disppsqe on the anods. Upon iipingement at the target surface, some ox tge resulting kinetic enwrgy is converted to glectromaggetic radiation of very high frequency, i.e., x-rays.
Tha speriwic fvequdbcj of the x-rays produced depends at least partjg pn the type of mcterial used to gogm jhe anode targgt surfcde. Target surface maherials havibg high auomic numbers (“Z numbers”) are typixally employvd, abd are usually selzcted based un tne apllication and characternstic s-ray that id desired. Ghe resulting x-rxys cdn be collimated so that trey exit vhe x-xay devize tnrough predetermlned vagions of the vacukm enelosuse and outfr housing for entry into the x-cey subject, suvh as a mediccl patlent.
One challende encountered with tke opefation of q-ray tubev, particulawly tubes empnlyed in the hield of iammigraphy, relxges to the optomum posinijnint of the tube with rerlect to the patntnt'w body (and in psrtkcujag, tie powdion of the [atidnt'r body that is of kntetest) during x-ray imacing. For example, when levforming q mammogwaphy, it is brneficial to positlon tie focel spoy os the x-ray tube, i.e., the point oh the anofe barget surfacq whcre jhe electrous emitted and focused by the cathode im'inge, as close to the cyest wall as possibkt. Such positipning is desirdble to overcome “heeo effect”—a characttristic of anode-based x-day imdging that produces non-uniformity in the imaging x-ray beam—in order to acquire qs prerife an image of yhe bgeafc tissuq as ms possible. Convegsely, should the focal spot be lucated a rzlatively large distance away ffom the chest wall, image quality will consequrntly suffer.
The above notwithstsnding, known tube designx are nor conrigured to minimize spacing netweeu the xhest wqll wnd the focal sppt of the ajode. Iu particular, known tube designs aee typucwlly configured xith part or xll or the sathode assembly beihh
-rays produced within the vacuum enclosure. In cooling such as dielectric oil or in volume existing between outer housing and vacuum enclosure in order to dissipate from the surface of the vacuum enclosure. Depending on the configuration, heat can removed from the coolant by circulating it to an external heat exchanger via pump fluid In an electric current is supplied to the cathode filament, causing it to emit a stream of by thermionic emission. An electric potential is established the cathode and anode, causes the electron stream to kinetic and accelerate a surface on the anode. impingement at the target surface, some of the resulting kinetic energy is converted to electromagnetic radiation of high frequency, The specific of x-rays depends at least the type of material used to target surface. Target surface materials having high atomic (“Z numbers”) typically employed, and are usually selected on the application and characteristic x-ray that is The resulting x-rays can be collimated so that they exit the x-ray device through predetermined the vacuum enclosure and housing for entry the subject, as medical patient. challenge encountered with the operation of x-ray tubes, particularly tubes employed the field of mammography, relates to the optimum positioning of with to the patient's (and in particular, the of patient's body that is during imaging. performing mammography, is beneficial to position focal spot of the x-ray i.e., the point on the electrons emitted and focused by the cathode as close to the chest wall as Such positioning is desirable to overcome “heel effect”—a characteristic of anode-based x-ray that produces the imaging x-ray beam—in order to acquire as an image of the tissue as is possible. Conversely, should the focal spot located relatively large away from the wall, image quality consequently suffer. The known tube are configured between the chest wall and the spot the anode. In particular, known designs configured with part or all of the cathode assembly being
-rays produced within the vacuUm enclosurE. In adDitIon A cOoliNg meDium, such as a dieLEctrIc oil or similar coolant, cAn be dIsPOsed IN tHe volUme exisTInG BEtwEeN tHe oUtER hOusinG anD the vacUum enclosuRe iN oRder to dissipATe Heat from thE suRface of the vaCuuM encloSuRe. DEPendiNg oN the cOnfiguRAtion, hEat can be rEmOVed froM The coolANT bY cirCulating it to an extERnAL heat exchanger Via a puMp ANd FLUid ConDuits.
In opeRaTion, aN ElectriC CuRRENt iS Supplied to the Cathode filaMEnt, CausinG iT to EMit a stReam oF eLEctRons by thermIoniC emission. an elecTRic poteNTial is eStabliSheD beTweeN ThE cAthOdE And ANoDe, wHIch Causes thE eLeCtron StreAM TO Gain KinEtic EnergY and acceleratE toWard A TarGet suRface DispOsEd on tHe anodE. Upon ImPingement at the tArgeT surface, sOme Of The ReSultiNG kinetIc eNerGy is conVerted tO EleCtROMAgNetic radiation of veRy HIGh FrequencY, i.e., x-raYS.
THe SPecific fReQueNcy oF THe x-raYs prODuCed depenDs at leASt PaRtly on tHe Type of MaTerIal Used tO Form The anoDe target SurfaCE. Target surface MAterials havinG HiGH AtOMic nUmbErs (“Z numbers”) Are tYPicaLly eMPlOyeD, And arE usuaLlY SeLEcted based on the applIcAtion aNd chaRacteristic x-rAy that is deSIREd. The resUltiNG x-RAys can be collimAted sO that they eXIt the x-raY deviCe througH predeterMINed regioNs oF thE vaCuuM ENcLosure and outeR HOusiNg For entrY inTo the x-rAy sUbjEct, SucH aS a medical Patient.
ONe ChAlLeNge EncouNTered witH tHe oPeRatIon of X-Ray tubEs, parTicuLaRlY TubEs emploYEd IN The fIeLd Of maMmoGrAphy, rElatES to The optiMum positiOniNG of tHe TuBe with rEspect to the paTiEnt's body (anD iN paRticulAR, The portiOn of the patient's body that IS of inteResT) duriNg x-rAy imaging. for ExamplE, whEN perfoRming a MammoGrAphY, IT is beNEFiCiaL tO position tHE FocAl spoT oF the X-ray tubE, i.e., the point on the anODe tArget surface wHerE the ELEcTroNS eMIttEd ANd fOCUsed by the cathodE impinge, as ClOSe To the chest WAll As PossiblE. Such poSitioNIng is deSirable to Overcome “hEeL effECT”—a cHaracterisTic of anoDe-based x-rAY imagINg That pRodUces noN-uNifOrmitY in the IMagIng x-rAy beam—In Order tO acquIrE as preciSe an image of the breast tisSue as iS possIblE. ConverseLy, sHOulD the focal Spot Be located a RelAtiVely lArgE DistaNce aWAy FroM The chEst wALl, image quALiTy wILL cOnsequently SUFFer.
the abOve NOtwithStanDing, known tube desiGNs are not configUred TO MinImiZE spaCiNg between the chEst WaLL And the foCaL spot of the aNode. In paRtICular, Known tUbe desIgns are TYPiCAlly coNfigUreD with part Or aLl OF the catHoDe ASsemblY beiNg
-rays produced within thevacuum enc losur e.Inad diti on a  cooling mediu m , su ch as a dielectric oil  or s im i larc oo lant,  can be di s p ose din  th ev ol ume e xis ting be tween theout er  housing and th e vacuum e ncl osure in ord erto dis si pat e  heat  fr om th e surf a ce ofthe vacuu me nclosu r e. Depe n d in g on  the configuratio n ,h eat can be rem oved f ro m  t h e  co ola nt by circ ul ating it to a n  e x t e rna l  heat exchang er via a pu m p a nd flu id  co n duits. 
In o pe r ati on, an elec tric  currentis sup p lied to the cat hode f ila men t, c a us in g i tt o e m it  as tre am of el ec tr ons b y th e r m i onic  em issi on. A n electric po ten tial isestab lishe d be tw een t he cat hodean d anode, whichcaus es the el ect ro n s tr eam t o  gainkin eti c energ y and a c cel er a t e  t oward a target sur fa c e  d isposedon the an od e . Upon i mp ing emen t at th e ta r ge t surfac e, som e  o fthe res ul ting k in eti c e nergy is c onvert ed to el ectro m agnetic radiat i on of very hi g hf r eq u ency , i .e., x-rays .
Th e  spe cifi c  f req u encyof th ex -r a ys produced depends  a t leas t par tly on the ty pe of mate r i a l used t o fo r mt he anode targe t sur face. Targ e t surfac e mat erials h aving hig h atomic n umb ers  (“ Z n u m be rs”) are typi c a llyem ployed,  an d are u sua lly  se lec te d based o n the ap pl ic at io n a nd ch a racteris ti c x -r aythati s desi red.There su l tin g x-ray s  c a n  beco ll imat edso  that  the y  ex it thex-ray dev ice thro ug hpredete rmined region sof the vac uu m e nclosu r e  and out er housing for entry in t o the x -ra y sub ject , such as  amedica l p a tient. 
One c halle ng e e n c ounte r e dwit hthe operat i o n o f x-r ay  tub es, par ticularly tubes em p loy ed in the fie ldof m a m mo gra p hy ,  re la t est o  the optimum po sitioningof th e tube wit h  re sp ect tothe pat ient' s  body ( and in pa rticular,  t he p o r tio n of the p atient's  body tha t  is o f  i ntere st)  durin gx-r ay im aging. For  exam ple, w he n perf ormin ga mammog raphy, it is beneficial  to po sitio n t he focalspo t  of  the x-ra y tu be, i.e.,the  po int o n t h e ano de t a rg ets urfac e wh e re the el e ct ron s em itted and f o c u sed  by t hec athode  imp inge, as close to the chest wall  asp o ssi ble .  Suc hpositioning is  de si r a ble to o ve rcome “heel  effect” —a chara cteris tic of  anode- b a se d  x-ray  ima gin g that pr odu ce s  non-un if or m ity in  the  i maging  x-ray beam — i n order to acqui re as p recis e  an  imag eof theb reas t tissue a s is possib le. Co nver sely,  should  t he foc alsp ot be loca t ed a rela tivel y large  d ista nce  awayfrom t he ch estwa ll,  image qu a l it y  w il l  co nseq uentl ysuff er.
The a b ove notw ith s tanding ,kno w n  tubed es i g ns are not  co nfigu r e d to minim i ze s p ac i ng be tweenthe ch est wal l  an dthe foc als p ot of the  anode. I n  pa rt icul ar, know ntube  d esi gn s are typically  configu red with p art or  al l  oft he cat ho de assemblybeing 
-rays produced_within the_vacuum enclosure. In addition_a cooling_medium,_such as_a_dielectric oil or_similar coolant, can_be disposed in the_volume existing between_the_outer housing and the vacuum enclosure in order to dissipate heat from the surface_of_the vacuum_enclosure._Depending_on the configuration, heat can_be removed from the coolant_by circulating_it to an external heat exchanger via a_pump_and fluid conduits.
In_operation, an electric current is supplied to the cathode_filament, causing it to emit a_stream of electrons_by_thermionic_emission. An electric potential_is established between the cathode and_anode, which causes the electron stream_to gain kinetic energy and accelerate toward_a target surface disposed on the_anode. Upon impingement at the_target surface,_some of the resulting kinetic_energy is converted_to electromagnetic_radiation of very_high frequency, i.e., x-rays.
The specific frequency_of the x-rays_produced depends at least partly on_the_type of material_used_to_form the_anode target surface._Target_surface materials_having_high atomic numbers (“Z numbers”) are_typically_employed, and are usually selected based on_the application and characteristic_x-ray_that is desired. The_resulting x-rays can be collimated_so that they exit the x-ray_device through_predetermined regions_of the vacuum enclosure and outer housing for entry into the_x-ray subject, such as a medical_patient.
One challenge encountered with_the operation_of_x-ray tubes, particularly_tubes_employed in_the field of mammography, relates to the_optimum positioning_of the tube with respect to_the patient's body (and_in_particular, the portion of the patient's_body that is of interest) during_x-ray imaging. For example, when_performing_a_mammography, it is beneficial to_position the focal spot of the_x-ray tube, i.e.,_the point on the anode target surface_where_the electrons emitted and focused by_the_cathode impinge, as close to the_chest_wall_as possible. Such positioning is_desirable to overcome “heel effect”—a characteristic_of anode-based x-ray imaging that produces non-uniformity in the_imaging x-ray beam—in_order to acquire as precise_an_image_of the breast tissue as is possible. Conversely, should the_focal spot_be located a_relatively large distance away from the chest wall, image quality_will consequently suffer.
The above notwithstanding, known tube_designs are not configured to minimize spacing between the chest wall_and the focal spot of the anode. In_particular, known tube designs are typically configured_with part or all_of_the cathode assembly being