Ultrasound Notes, Part I The Basics

Transcription

1 Noll 4 US Nos : g Ulrsoud Nos r I Th Bss Ulrsoud mgg s dr o-rosruv orm o mgg whr mg ormo s obd by lolg ulrso wv o smll volum 3D s. Two dmso o lolo r rormd by dro ousg s os. O dmso s rormd by ulsg s RADAR. Th ulrso wv s rodud by lrl o o olr rsdur whh s usully rsmd o h body hrough md mhg gl. Ulrso wvs r dd by h sm rsdur d ovrd o lrl sgl or rossg d dsly. A sml sysm s show hr rom Movsk: - A ulsr s h rsdur wh shor uls whh rogs hrough h body rlg o o mhl homogs. Th m rlosh bw h rsmd uls d rvd sgl s gv by ho whr s h dh rom h rsdur d s h vloy o soud h body ~ 5 ms or.5 mmµs - Rld sgl m r ssod wh mhl homogs dh. - Th lrl o h uls ho s drmd by h ross-so o h bm. Ths ross-so s dh dd. - O l o mg b obd by rordg h rld sgl s uo o m h sh o h rsos s drmd by h uls rors rsdur rors d

2 Noll 4 US Nos : g dro. I w lo hs mlud s uo o m w g A-mod or mlud s: - D d 3D mgs b grd by movg h rsdur o dr osos d y hus movg h bm. Imgs b grd by mkg h mlud o h rsos grysl lvl or brghss d wh ll s ls hv b qurd rsd h orm o mg. Ths s kow s B-mod or brghss s. A sml D sysm s show hr:

3 Noll 4 US Nos : g 3 - B-mod mgg lso b do by lro moo o h bm s wll b dsussd lr lurs. - Flly sgl l b md ovr dr m rms d lso rsd s grysl mg. Ths s kow s M-mod or moo. Sour o US sgls #: Sur Rlos I ulrsoud w mk mgs h rlvy h body Ry. O mjor sour o R s sur rlos whh r grd h sur o mrls. W d h hrrs ousl md s Z ρ whr ρ s h dsy o h mrl kgm 3 d s h rogo vloy o ous wvs ms. Aohr rlosh holds ous Ohm s lw: Zv whr s h rssur Nm kgm s d v s h rl vloy ms. No h dso bw h mroso bhvor o h osu rls v d h mroso bhvor o h wvro. For h ollowg lyss w ll ssum h h d gl d rld gls r boh ro. Lk mrror h mrror s ld h rlo wll o om bk o you hus US w ylly oly s sur rlos rom sours h r rlll o h wvro hs s quvl o θ θ r θ.

4 Noll 4 US Nos : g 4 Thr r vry o boudry odos h d o b ssd. Frs h rl vloy mus b h sm o hr sd o h boudry ohrws rls wll ross h boudry: v v r v Z r Z Z Sod h rssurs o hr sd o h boudry mus b qul h boudry wll sh o mk h rssurs mh rll w r workg luds W ow solv or h rlvy: R + r r Z Z Z + Z whr Z s vrg ous md h ssu. Z Z Z Comms: As w s R [-] R< ds h h hs o h rld sgl s rvrsd d R> ds h h hs o h rld sgl s rsrvd. Tylly rlos h hum body ohr h ssubo or ssur rs r vry smll o h ordr o 5% or lss log R < -5 db. Iss US r rlv msur o bsd o y bsolu or hr ssu rory. Thus rlv drs Z r wh s mor drmg rld ss. Th sy o h ous wv s I Z rgymu r. I r I R d I I R [ A o vry rsg sd: how dos hs srg I Z rlosh om bou. Ergy dsy s: E mv V ρ v. Bu w s h moo susodl so E should b ½

5 Noll 4 US Nos : g 5 o hs? No h ohr hl h rgy s sord s ol rgy. Isy s h rogo o rgy hrough sur: rgym r or I E ρv whr s h rogo vloy o h wv d ssod rgy. Usg v Z d Z ρ w g I Z. Wh bou us? Us o rssur: Nm Jm 3 kgm s ; us o md kgm s J sm 4. I hror hs us o Jm s. ] Sour o US sgls #: Volum srg O mroso lvl < λ homogs ssu sr soud wvs. W d rmr η volumr bksr o bksr ross so r u volum. Bksr s: - wk db lss h sur rlos - soro srs ll dros - lwys rs hs s rs rory o ssu - hs wll b dsussd urhr blow h so o Skl Nos Wv Equos Assumos: - homogous mdum - o-dssv mdum - logudl wvs omrsso or rssur wvs luds wll o suor rsvrs or shr wvs surs h dr s smlr o h dr bw soud rogg hrough oud d rls rogg log h sur - h orml drl quo or ous wvs rogg hrough lud mdum s: whr + y +

6 Noll 4 US Nos : g 6 Soluos: - moohrom l wv - grl soluo or l wvs whr s h dsrbuo o sohroms. W d uls uo whh s h vrs FT o by lookg h m dom sgl : d F { } d by subsuo w g - -. Thus w hv uls uo h rogs vloy m h uls s oso. d - shrl wv r r r whr r + y + hs dsrbs h bhvor o y o srr. Th mlud lls o wh r. Dsrso rvous soluos ssumd o-dssv mdum bu so ssus o h body do dss u h soud wvs d do so mr h s rquy dd whh mks s dsrsv mdum. - w wll us quos h r smlr o hos drvd bov bu w ll dd uo rm -l whr s lr uo o us: m - d l s h h lgh m. - Tyl uo or MH so ssus o h body - dbm. m - wry luds <. dbm Lookg our roggrlg uls h ol roudr h lgh rvr s l uo - lso h uo s rquy dd or ml. m - MH - Th rvd rld wv s ow:

7 Noll 4 US Nos : g 7 d R How dos hs rl o } { F? [I our oo w us o rrs h rssur uo h rvr or rlor dh d o rrs h rsmd wvorm.] - Assumg R d orro or h m dly -. { } { } * * d F F d whr d s h dd dsrso uo dh dd blurrg How do w dl wh hs? - mk log: δ whh rsuls : m roblm oor dh rsoluo ll dhs - Us Guss rquy srum. Suos β d W h + W W W W β β β β h wdh o hs uls hs o b dgrdd d s sll ~W bu h r rquy hs shd dow slghly by W β. As rl mr ulss usd US o hv Guss vlo m d hus wll hv Guss shd srum suh s h usd hr.

8 Noll 4 US Nos : g 8 - S hs ommoly usd uls sh s o drmlly d by dsrso or mos o hs lss homwork roblm w wll gl dsrsv s. Nobly w wll ssum β d Bdss Sgls Th bov uls wh h Guss srum s ml o bdss uls h b rrsd s vlo modulg rrr rquy : whr d A Ths s oml rrso kow s h ly sgl. I grl w wll work quos rrsg h ly sgl wh h udrsdg h w drv h rl rssur sgl by kg h rl r o : { } os ~ R. For h grl s o dsrsv mdum w lso d h vlo h rvr s: { } * ' * d F d A d A + + For h o-dsrsv romo d g ssumg R : Flly w dsrb h m-dom sgl h rvr or rlor dh ludg h roudr rogo dly s: Ag h ul rvd sgl s h rl r:

9 Noll 4 US Nos : g 9 os ~ Th Sgl Now w look wh h rvd volg s h rsdur or dsrbuo o rlors R. Th volg m wll b rld o suroso o h sgls rom ll rlors h rur o h rsdur h o m h rly rs o h uls wll hv rvld rhr dss d h lr rs o h uls wll hv rvld shorr dss. d R K v Comms: Whl h rssur uo s rl.g. ~ du o rulr mhods h rvr lros w rrs h sgl s h bsolu vlu o h sum o ly sgls. Mor o hs uur lurs. W hv gld dsrso o h uls. Skl Nos Skl os rsuls rom volumr sr h s sr rom ssu homogs h r smllrmor losly sd h h rsoluo lm o h sysm. I h mrl rsd blow w wll drv h dsrbuo o skl os. Igorg h lrl dmsos y d uo w m h rsso or h rvd sgl US: d R v

10 Noll 4 US Nos : g I w look som o m orrsodg o rulr dh loo h w g: v R + d Rll h rvously w dsrbd uls hvg wdh T or h dom hvg wdh. W wll ow subsu wh rt: k v + r v R d R' d whr R s h rlvy ovr h rsoluo lm. W wll mk som ssumos o dsr hs: - R b rrsd by my N dsr rlors ssu s - Th mlud o h rlor s A ssu s - Th loo o h rlor s rdom R ' Aδ whr s rdom vrbl. - Th hs o h h rlor s rdom φ k d w wll ssum h s uormly dsrbud bw d. S s ls - wvlghs h hs gos ovr svrl yls hus ll hss should b rrsd wh qul robbly. - Th grl b rrsd by h sum o hs rlors Thus: φ A A osφ + v sφ W ow m h dsrbuo o v. Frs l s m h jo sss o U N os φ dvn Frs s rlvly sy o s h E [ ] d E [ ] [ ] U N V N sφ. Also E U N E osφ osφm E os φ + osφ osφm N + m m N whr N s h umbr o rlors h sum. Smlrly:

11 Noll 4 US Nos : g d: [ V ] N E N E [ U ] os s os s + NVN E φ φm E φ φ osφ sφm m d r uorrld. Flly by h rl lm horm w kow h h dsrbuos o U N d V N wll roh h orml dsrbuo. Thus o U N d V N r dd uorrld joly orml R.V. s r dd r boh ormlly dsrbud wh ro m d vr N. m Now V v A U + N N whh b show o b Rylgh dsrbud wh rmr A N hs h ollowg sss Rylghσ ~ σ : σ [ ] E v A N A N d σ v. Som omms: - Ths s o lld skl os bsd o s r. - I oms rom osruvdsruv rr suroso o wvros. - Th sgl sy [ ] v E d os vro σ v hv smlr orms h s hy boh r roorol o A N. - Thus s h sgl rss so dos h os. - For uorm ssu wh mroso mhl homogs usg volumr sr h sgl-o-os ro SNR or h ssu s d. I :

12 Noll 4 US Nos : g [ ] E v SNR σ v.9 whh s vry oor sgl o os ro. - Avrgg whou movg h rsdur oso or hgg mgg rqus o b usd o mrov h skl SNR hs s bus h hs rlosh bw ll o h rlors dos o hg. - Avrgg wh h rsdur ohr oso or usg dr rsmr rquy wll ld o dr skl os bus h hs rlosh s drmd by Ths dr os rs ould b vrgd o mrov h SNR. - Vwg o log sl s o usul s mks h os look ddv h os s mullv h us o v.. D Imgg W ow dsrb sml modl or D mgg sysm whh h rsdurrvr s movd o dr osos: Hr h rsdur volg s: v K R B d d whr s h loo h rsdur d s h -oord dh h rlg obj bg mgd. B s h bm r or h rsdur osod h org d b dsrbd s:

13 Noll 4 US Nos : g 3 B h T h R whr h T s h rquy dd rsm ld r dro r d h R s h rquy dd rv ld r. A hs o s ov o ssum h h uls duro s shor h s: << T whr T s h uls duro. Th by h sg rory o dl uos. W ow mk g omsd rv sgl by rsg h g s uo o m: d d B R K v v - Imuls rsos uo or o srd uo w drm h muls rsos uo dh by sg R δ - : sg : B v I h ; whh h bm r wr os s uo o dh would b s vr. - For rl osv bm r d vlo w smly g: B I B d d B v δ

14 Noll 4 US Nos : g 4 d hus h bm dro r drly orols h sl rsoluo d y d h uls vlo dro orols h rsoluo. - O objv US mgg s o mk B δ mk h bm vry rrow o gv good rsoluo d δ mk h uls vry shor o gv good rsoluo. I w do so h w g mg o h rlvy: v R R Issus rld o Dh Rsoluo As dsrbd bov dh rsoluo s lrgly drmd by h vlo uo. Rll h uls uo s: ~ R os Th wvlgh o rvlg wv s gv by: { } λ Thus or h yl rg o US rqus o o MH w hv wvlghs h rg rom.5 o.5 mm rsvly. Commoly s hos so h hs duro o -3 rods.g. T 3. T Th dh muls rsos uo s romly h wdh o whh s T.g..5.5 λ. - I US w ow hv SNR rsoluo rd-o: hghr smllr λ smllr bu hghr hghr β smllr sgl or d ssus - Rll h uo s bou dbmmh so or 5 m d org m roudr h uo wll b MH bu db MH.