27
`
`PSF improvements in single shot GRASE imaging
`
`T. Schaffter, P. Bériierti, D. Leilifritr.
`I‘ia(‘ltli£‘rPit‘l] (iheinie, Universitiit Bremen‘ l)-28355»! firemen. (iPrl]1?\l))';
`t l‘hihps ftesearcli. Department Technical Systeins, Roiitgeiistralie 24-'26. D—22Zt35 Hanihurg, (flei'iiiaiiy.
`
`Iiiti'<i(li1r:ti()1i:
`ln (‘f’M(il liased imaging sclieines like RARE or CHASE the
`[It|l]]i spread function (PSF) in the pliase—eii<'odiiig direction is
`'ls'lI‘rI]]l[1Ptl hy the transverse relaxation time T3. For species
`with short T3 21
`lirond PSF will occur. degrading image res—
`tiliitiriu Using snizill refocusing pulses ('9, < 180° high order
`uiitm of traiis\'erszi|
`iiiagiietizatioii are generated, which con
`triliiitv later to the detectable iiiagnctization
`For species
`with T1 >> T3 the llzihn echo aiiiplit.ud<~s in the CPi\‘l(i sequeiice
`’l<’t"|}' more slowly. hut
`instziliilities t“ripple") in the early erlioes
`:‘i'iI|
`l.e ff(>lI.\' et al
`[3] suggested an algoritlini to avoid these
`\.iri:iti<iiis in sigiizil amplitude using Varialile refocusing pulses.
`In this work [it] relax:ition was iieglected and the echo ampli~
`tiidws \\'-*r<‘ stahilized to a constant value. Taking relaxation in
`ihi
`liiglier order states into coiisideratioii after some time no
`Iitit‘_’llf‘il'(J1ti()H is left
`to stabilize to a constant value. i.e. a dis
`Itil’Itt'il1 of the PSF will O<'(’lH‘.
`ln this alistract
`the relaxation
`piucesses are taken into account. using an exponential signal
`ilcctiy with T which is greater tlian T-_i. This approach offers a
`sinnotli PSF and makes it possihle to image an ohject with fast
`lg relaxing species.
`"the nietliod was iuiplemented in a single
`~hot (IR v\‘il-I experiment
`Methods:
`.s'll0\\'l1 that after i-th pulse ?(i+ 1) longi—
`lii [l],[I§] it has l)P(‘ll
`pi and transvcrsal t/Q71,
`qt‘),
`qI‘- magv
`iiidinal p‘_l_I ,
`pi},
`Using the spinor formalism the echo
`:i+=ti'/atioii states exist
`it|il]ilttH(lt“ |q},l after the I-th refocusing pulse can he calculated
`tmiii the previous states using a hard pulse approxiinatioiiiu the
`lilrirli erpizitioiis. If the signal distribution of the (i— l )th state is
`l(lltt\\'li. the refociisiiig pulse for the f~tl] echo can he calciilzited,
`;»ir>l«ling the desired echo aniplitiide. The echo aiiiplitudes are
`\‘[[{i)illZl_‘(l to an exponential decay qf, = S’. : S0 -exp(—i-TE/T)
`witli
`the stahilizatioii zunplitude So. The flip angle (-)0 for the
`first echo is given ti} Gr) : 2-arcsin \/5'" -e:\'p(TE/T3). lfenough
`i
`signal is left
`in the high order states (1/‘ , 41"" ). the refoctising
`l‘tll.’~t‘.s (3),
`(‘an l)t‘Cdl(‘llldit‘(l31121l}'ii(‘all)'Z
`
`
`then all available transversal iiiagnetization has to he refocused
`((3 — 180°).
`fig.
`2 shows the resulting spin echo zunplitudes
`in the (i‘Pl\lC sequence. Theoretical (lines) and experiiiiental
`(points) Values are in good agreement except for the deviation
`in Sial\lll7,E\IlOHHl1][3litl1(lt? Sn 2 0.3 ¢ 0.34 : 48. The T : l0Oiiis
`curve (+) shows that the lifetiiiie ofrapidly relaxing transversal
`iiiagiietizatioii could be prolonged at
`least h_v a factor of 3 and
`with no ripple at
`the beginning of the echo train . This l’(‘tlllt't’S
`the distortioii in the PSF and narrows it in the image doiiiain.
`The Fllll|')ll[lt(l0 of the PSF is given by the integral of the echo
`decay in k—space. That ineans with regard to SNR.
`the areas
`under the curves in Fig. 2 indicate that the signal in an iriiage
`is only reduced l>_v ii factor of 0.675 using the stahiliqation with
`'1' : 10()ins. This factor increases if niore echoesiare used.
`lniages ohtaiiied with the stabilization niethod show a new
`contrast
`lieliavioiir.
`In these images fast relaxing tissue, e.g.
`liver or iniiscle.
`is clearly visible and distiiiguisliahle from siir—
`rouiidiiig tissiie. However, this heiiefit
`is associated with asriiall
`reduction of SIVR.
`
`Concli ‘ion:
`This work deinonstrates the feasibility of imaging rapidly re»
`laxing tissue using single shot GRASE imaging by improving the
`PSF. This can he advaiitageous in diaguozing different liver disv
`eases Stabilizing the Hahn echo amplitudes to an exponential
`decay offers new contrast lieliaviour. The reduced signal ampli—
`tudtrs caiisv only a small redurrtion in SNR.
`l“urthe.riiioi'e,
`the
`method seeins to he favorable to avoid SAR limitatioiis in high
`field applicatioiis. Future work will stuil_\' feasiliility of inea.'sur—
`ing siiigle sliot CHASE images with a larger matrix size (lt3U"'l.
`due to the prolonged lifetime Tofthe trziiisversal iiiagiietizatioii
`Refe1'eimes:
`IURR.
`.397.
`.l Magn. R(‘S0ll.. 78.
`.
`[1]
`llennig,
`.l
`f~’l “i°"‘~‘"”- D- 5- l- Clmmr Ph.V-‘iv 34- 3”-'>7i W51»
`Le Roux. Patrick. lliiiks. R. 9., Magn. Reson i’\Ied., 30, 183. 1119.3.
`[4] F(*rt1('ri,.l.T...9tark. D D.‘ .-\
`.l. R-4 155i 943,
`lf-J90.
`180
`
`innt -
`‘
`(—)il'l)
`«_;
`
`‘
`pffl
`‘(lift _ S,
`
`i
`
`‘
`\
`[fl
`/
`V Kq(l]—l \ H1 )
`
`_
`
`A
`:
`qt” ~ Si“
`q(zy~1 __ S,
`
`J
`
`(
`
`)
`
`i:'.ti
`1 W
`'
`
`V
`t.
`_
`_
`\[al)ili7/Ptl tn T : ‘ztlflms
`staliilized to T .. lUUnis
`>0 : 0.3- illii
`
`<>
`‘lr
`
`(2) g
`
` Hymns’ S4 Discussion:
`
`is determined
`75)). Otherwise O,
`: .8" -<‘.\'p(T];/(2
`wuli
`iiiiinerically li_v miiiiniiziiig the quadratic deviation from the de
`sired signal decay.
`
`(-), zinin (tifl, —— .5" )3)
`_‘
`‘
`_
`_
`'
`lhe stahilizing algoritliin was applied to a ( PMG sequence
`with 1.3 eclioes and an inter»echo time of 10 ms. The signal
`il»~r:i_x ofzi doped water tuhe (T1 : 38tJiii.s. '15 : Iifiins) was mea-
`siired on in modified O.-3T Wll()l(’4l)0(l'\'
`[‘t’St‘r'll‘(‘l1 iinager (Philips
`\lf*tl|t‘r’1l Systeiiis) The tlieoretiral predictions for two exporieii
`tin! t'ii~r;,_ys
`{Ls}, : ti 3 . ‘\[n_ T : ltttt ms or T : ‘20Un1s) were
`\:i|i<l:ite-l. To «|eiiit>nstrate the effect on image coiitmst
`the al-
`L”’iTilllllt \\'}l.\"t'l[ti\llt‘(l to 71 (JRASE sequence Single shot (JRASE
`uii;i_:,cs H28‘) with 20 spin echoes ((9 : 180°) and 5 gradient
`ecliiws pet
`llahn r’t‘llti were rihtained from the ah-.l0nniial region
`rl
`is healt|i_t volunteer
`lihc in|er~z-cho time was set
`to 13 ms.
`lhe iinagrs were coiiipareil \\'llll those olilained using stahiliza—
`lltilt
`to an e.\'ponenti:il decay Si; : 0.33
`ll”: T : ‘2UUiiis «if fast
`FI‘lit.\Plilt1IitlSS\lt‘,5\§Q1lH1ll]gtllZit Ti : -itlllllis and '[7_, : lthiis
`
`1 slimxs the xzilues of the i’ef<i<’ii.siiiL; pulse train for
`lilg
`\ti’tl’tlllZ£1tlOHSiOt\\'0tlliT€l't’l1lf‘X[IOl1t‘l1il«lltlt‘(‘Zt)5(.‘l[iC 1.3.
`/fl :
`ltttiiiis or T : ‘zllttinsi. For 7‘ I ltltliiis tinl} list
`1 was used
`liir T * ‘jtlfhiis the first
`ll]
`I't‘fU(‘ll\lI1LL [tl|l\>$ \Vt‘l‘t> t';ilt‘|Ili’it*".l
`tiiiiiii lit
`1.
`for the ilt‘\t
`liq
`'2 was iisril
`liliat
`lIlt‘(1ll\
`that
`wiwiigli signal
`t\ hft
`fwi ~litli|il/lit};
`thi
`lii~t
`ttll‘H\.
`l/ill
`aft.-i
`
`9,
`
`‘J0 K
`
`ti
`
`U
`
`Figure l
`
`2
`
`4
`
`8
`6
`E,C1mm”nhH.,
`refociisiug pulse angles used for stahilizatioii
`
`10
`
`1.2
`
`M
`
`tlivurethal
`,_
`qabillzw‘ W T ___ mm":
`dabmzmhn T : 100'» +
`G, : mm D
`
`‘
`
`_
`
`”
`
`3
`
`4
`
`R
`"
`Nil" ”"”‘l"‘f’
`liguiw '2 wclzim ziniplitiivlvs iiftvr -<t;itv.ili/.;iti'
`
`1'7‘
`
`H
`
`l‘
`
`ii
`
`General Electric Co. 1026 - Page 1
`
`General Electric Co. 1026 - Page 1
`
`PSF improvements in single shot GRASE imaging
`
`T. Schaffter, P. Bériierti, D. Leilifritr.
`I‘ia(‘ltli£‘rPit‘l] (iheinie, Universitiit Bremen‘ l)-28355»! firemen. (iPrl]1?\l))';
`t l‘hihps ftesearcli. Department Technical Systeins, Roiitgeiistralie 24-'26. D—22Zt35 Hanihurg, (flei'iiiaiiy.
`
`Iiiti'<i(li1r:ti()1i:
`ln (‘f’M(il liased imaging sclieines like RARE or CHASE the
`[It|l]]i spread function (PSF) in the pliase—eii<'odiiig direction is
`'ls'lI‘rI]]l[1Ptl hy the transverse relaxation time T3. For species
`with short T3 21
`lirond PSF will occur. degrading image res—
`tiliitiriu Using snizill refocusing pulses ('9, < 180° high order
`uiitm of traiis\'erszi|
`iiiagiietizatioii are generated, which con
`triliiitv later to the detectable iiiagnctization
`For species
`with T1 >> T3 the llzihn echo aiiiplit.ud<~s in the CPi\‘l(i sequeiice
`’l<’t"|}' more slowly. hut
`instziliilities t“ripple") in the early erlioes
`:‘i'iI|
`l.e ff(>lI.\' et al
`[3] suggested an algoritlini to avoid these
`\.iri:iti<iiis in sigiizil amplitude using Varialile refocusing pulses.
`In this work [it] relax:ition was iieglected and the echo ampli~
`tiidws \\'-*r<‘ stahilized to a constant value. Taking relaxation in
`ihi
`liiglier order states into coiisideratioii after some time no
`Iitit‘_’llf‘il'(J1ti()H is left
`to stabilize to a constant value. i.e. a dis
`Itil’Itt'il1 of the PSF will O<'(’lH‘.
`ln this alistract
`the relaxation
`piucesses are taken into account. using an exponential signal
`ilcctiy with T which is greater tlian T-_i. This approach offers a
`sinnotli PSF and makes it possihle to image an ohject with fast
`lg relaxing species.
`"the nietliod was iuiplemented in a single
`~hot (IR v\‘il-I experiment
`Methods:
`.s'll0\\'l1 that after i-th pulse ?(i+ 1) longi—
`lii [l],[I§] it has l)P(‘ll
`pi and transvcrsal t/Q71,
`qt‘),
`qI‘- magv
`iiidinal p‘_l_I ,
`pi},
`Using the spinor formalism the echo
`:i+=ti'/atioii states exist
`it|il]ilttH(lt“ |q},l after the I-th refocusing pulse can he calculated
`tmiii the previous states using a hard pulse approxiinatioiiiu the
`lilrirli erpizitioiis. If the signal distribution of the (i— l )th state is
`l(lltt\\'li. the refociisiiig pulse for the f~tl] echo can he calciilzited,
`;»ir>l«ling the desired echo aniplitiide. The echo aiiiplitudes are
`\‘[[{i)illZl_‘(l to an exponential decay qf, = S’. : S0 -exp(—i-TE/T)
`witli
`the stahilizatioii zunplitude So. The flip angle (-)0 for the
`first echo is given ti} Gr) : 2-arcsin \/5'" -e:\'p(TE/T3). lfenough
`i
`signal is left
`in the high order states (1/‘ , 41"" ). the refoctising
`l‘tll.’~t‘.s (3),
`(‘an l)t‘Cdl(‘llldit‘(l31121l}'ii(‘all)'Z
`
`
`then all available transversal iiiagnetization has to he refocused
`((3 — 180°).
`fig.
`2 shows the resulting spin echo zunplitudes
`in the (i‘Pl\lC sequence. Theoretical (lines) and experiiiiental
`(points) Values are in good agreement except for the deviation
`in Sial\lll7,E\IlOHHl1][3litl1(lt? Sn 2 0.3 ¢ 0.34 : 48. The T : l0Oiiis
`curve (+) shows that the lifetiiiie ofrapidly relaxing transversal
`iiiagiietizatioii could be prolonged at
`least h_v a factor of 3 and
`with no ripple at
`the beginning of the echo train . This l’(‘tlllt't’S
`the distortioii in the PSF and narrows it in the image doiiiain.
`The Fllll|')ll[lt(l0 of the PSF is given by the integral of the echo
`decay in k—space. That ineans with regard to SNR.
`the areas
`under the curves in Fig. 2 indicate that the signal in an iriiage
`is only reduced l>_v ii factor of 0.675 using the stahiliqation with
`'1' : 10()ins. This factor increases if niore echoesiare used.
`lniages ohtaiiied with the stabilization niethod show a new
`contrast
`lieliavioiir.
`In these images fast relaxing tissue, e.g.
`liver or iniiscle.
`is clearly visible and distiiiguisliahle from siir—
`rouiidiiig tissiie. However, this heiiefit
`is associated with asriiall
`reduction of SIVR.
`
`Concli ‘ion:
`This work deinonstrates the feasibility of imaging rapidly re»
`laxing tissue using single shot GRASE imaging by improving the
`PSF. This can he advaiitageous in diaguozing different liver disv
`eases Stabilizing the Hahn echo amplitudes to an exponential
`decay offers new contrast lieliaviour. The reduced signal ampli—
`tudtrs caiisv only a small redurrtion in SNR.
`l“urthe.riiioi'e,
`the
`method seeins to he favorable to avoid SAR limitatioiis in high
`field applicatioiis. Future work will stuil_\' feasiliility of inea.'sur—
`ing siiigle sliot CHASE images with a larger matrix size (lt3U"'l.
`due to the prolonged lifetime Tofthe trziiisversal iiiagiietizatioii
`Refe1'eimes:
`IURR.
`.397.
`.l Magn. R(‘S0ll.. 78.
`.
`[1]
`llennig,
`.l
`f~’l “i°"‘~‘"”- D- 5- l- Clmmr Ph.V-‘iv 34- 3”-'>7i W51»
`Le Roux. Patrick. lliiiks. R. 9., Magn. Reson i’\Ied., 30, 183. 1119.3.
`[4] F(*rt1('ri,.l.T...9tark. D D.‘ .-\
`.l. R-4 155i 943,
`lf-J90.
`180
`
`innt -
`‘
`(—)il'l)
`«_;
`
`‘
`pffl
`‘(lift _ S,
`
`i
`
`‘
`\
`[fl
`/
`V Kq(l]—l \ H1 )
`
`_
`
`A
`:
`qt” ~ Si“
`q(zy~1 __ S,
`
`J
`
`(
`
`)
`
`i:'.ti
`1 W
`'
`
`V
`t.
`_
`_
`\[al)ili7/Ptl tn T : ‘ztlflms
`staliilized to T .. lUUnis
`>0 : 0.3- illii
`
`<>
`‘lr
`
`(2) g
`
` Hymns’ S4 Discussion:
`
`is determined
`75)). Otherwise O,
`: .8" -<‘.\'p(T];/(2
`wuli
`iiiiinerically li_v miiiiniiziiig the quadratic deviation from the de
`sired signal decay.
`
`(-), zinin (tifl, —— .5" )3)
`_‘
`‘
`_
`_
`'
`lhe stahilizing algoritliin was applied to a ( PMG sequence
`with 1.3 eclioes and an inter»echo time of 10 ms. The signal
`il»~r:i_x ofzi doped water tuhe (T1 : 38tJiii.s. '15 : Iifiins) was mea-
`siired on in modified O.-3T Wll()l(’4l)0(l'\'
`[‘t’St‘r'll‘(‘l1 iinager (Philips
`\lf*tl|t‘r’1l Systeiiis) The tlieoretiral predictions for two exporieii
`tin! t'ii~r;,_ys
`{Ls}, : ti 3 . ‘\[n_ T : ltttt ms or T : ‘20Un1s) were
`\:i|i<l:ite-l. To «|eiiit>nstrate the effect on image coiitmst
`the al-
`L”’iTilllllt \\'}l.\"t'l[ti\llt‘(l to 71 (JRASE sequence Single shot (JRASE
`uii;i_:,cs H28‘) with 20 spin echoes ((9 : 180°) and 5 gradient
`ecliiws pet
`llahn r’t‘llti were rihtained from the ah-.l0nniial region
`rl
`is healt|i_t volunteer
`lihc in|er~z-cho time was set
`to 13 ms.
`lhe iinagrs were coiiipareil \\'llll those olilained using stahiliza—
`lltilt
`to an e.\'ponenti:il decay Si; : 0.33
`ll”: T : ‘2UUiiis «if fast
`FI‘lit.\Plilt1IitlSS\lt‘,5\§Q1lH1ll]gtllZit Ti : -itlllllis and '[7_, : lthiis
`
`1 slimxs the xzilues of the i’ef<i<’ii.siiiL; pulse train for
`lilg
`\ti’tl’tlllZ£1tlOHSiOt\\'0tlliT€l't’l1lf‘X[IOl1t‘l1il«lltlt‘(‘Zt)5(.‘l[iC 1.3.
`/fl :
`ltttiiiis or T : ‘zllttinsi. For 7‘ I ltltliiis tinl} list
`1 was used
`liir T * ‘jtlfhiis the first
`ll]
`I't‘fU(‘ll\lI1LL [tl|l\>$ \Vt‘l‘t> t';ilt‘|Ili’it*".l
`tiiiiiii lit
`1.
`for the ilt‘\t
`liq
`'2 was iisril
`liliat
`lIlt‘(1ll\
`that
`wiwiigli signal
`t\ hft
`fwi ~litli|il/lit};
`thi
`lii~t
`ttll‘H\.
`l/ill
`aft.-i
`
`9,
`
`‘J0 K
`
`ti
`
`U
`
`Figure l
`
`2
`
`4
`
`8
`6
`E,C1mm”nhH.,
`refociisiug pulse angles used for stahilizatioii
`
`10
`
`1.2
`
`M
`
`tlivurethal
`,_
`qabillzw‘ W T ___ mm":
`dabmzmhn T : 100'» +
`G, : mm D
`
`‘
`
`_
`
`”
`
`3
`
`4
`
`R
`"
`Nil" ”"”‘l"‘f’
`liguiw '2 wclzim ziniplitiivlvs iiftvr -<t;itv.ili/.;iti'
`
`1'7‘
`
`H
`
`l‘
`
`ii
`
`General Electric Co. 1026 - Page 1
`
`General Electric Co. 1026 - Page 1
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