FLASH: Clinical three-dimensional magnetic resonance imaging

Transcription

1 RdioGrphics index terms: Imging technology NEWIEXPERIMEIITAL TECHNIQUE Mgnetic resonnc#{149} imging TECHNICAL Cumultive index terms: Mgnetic resonnce (MR) technology FLAH: Clinicl three-dimensionl mgnetic resonnce imging Vl M. Runge, M.D. Michel L. Wood, Ph.D. Den M. Kufmn, M.. Kevin L. Nelson, M.D. Mrk R. Trill, M.D. Absfrct: Using -D FLAH, high resolution, very thin section TI weighted Imges ofthe CN, spine, nd extremities cn be obtined. From these single dt sets, reformtted imges whose resolution is equl to tht of the originl dt set cn be constructed in ny desired plne. This pproch my led to the replcement ofconventlonl TI weighted spin echo Imging by D FLAH techniques. THI EXHIBIT WA DIPLAYED AT THE 7RD CIENTIFIC AEMBLY AND ANNUAL MEETING OF THE RA- DIOLOGICAL OCIETY OF NORTH AMERICA, NOVEMBER 29-DECEM- BER 4, 1987, CHICAGO, ILLINOI. IT WA RECOMMENDED BY THE NEU- ROLOGIC IMAGING AND MAGNET- IC REONANCE IMAGING PANEL AND WA ACCEPTED FOR PUBLI- CATION AFTER PEER REVIEW AND REVIION ON APRIL 5, From the Division of Mgnetic Resonnce Imging, Deprtment of Rdiology, Tufts University-New Englnd Medicl Center Hospitls, Boston, Msschusetts. Address reprint request to V.M. Runge, M.D., New Englnd Medicl Center Hospitls, 75 Wshington treet, Box 864, Boston, MA IntroductIon The focus of this presenttion is the ppliction of fst -D imging to the exmintion of the brin. References will lso be mde to the use of this technique in the exmintion of the spine nd extremities. Regrdless of the region of interest, thin, high resolution, contiguous slices cn be cquired through lrge volume of tissue by employing either FLAH or FIP in -D mode. In 1981, -D imging ws introduced s technique for obtining multiple contiguous slices (1). Multislice 2-D techniques rpidly displced -D becuse of the reltively long imging time of the ltter. A short explntion of the technicl differences between these two techniques is wrrnted. In 2-D spin echo imging, slice selection is chieved with the combintion of frequency selective RF pulse nd mgnetic field grdient (G in the trnsxii plne) perpendiculr to the desired plne of selection. In -D imging, nonselective excittion pulse typiclly replces tht used for slice selection in 2-D. This leds to simultneous dt cquisition from the entire imging volume. Resolution long the z xis is chieved by the implementtion of n dditionl phse encoding grdient, G2. Thus with -D, in contrst to 2-D, imging time is dependent upon the number of slices used (or equivlently, the number of phse encoding steps used with the second grdient). Volume 8, Number 5 #{149}eptember, 1988 #{149}RcdloGrcphics 947 I

2 FLAH-C/inic/ -D MR/ Runge et ci. C 4 Ū V Imging time for -D technique = (nns) TR C where: n = number of cquisitions, s = number of slices or prtitions, nd N = mtrix size on phse encoding steps, TR = repetition time For exmple, with TR = 2. seconds, one cquisition, 2#{24} phse encoding steps, nd 16 prtitions, the scn time for -D imge set would be (1 X 256 X 16) - 2 sec or pproximtely 2.5 hours. With multislice technique, the sme scn would require only 8.5 minutes. The dvent of fst imging (such s FLAH nd FIP), with TRs O msec hs mde -D scns prcticl. For exmple, with fst imging, 128 one millimeter thick slices cn now be cquired in fewer thn ten minutes. At this time, 2-D spin echo techniques cnnot provide such thin section, high signl-to-noise rtio imges. Technique Vrious formuls hve been proposed for describing imge contrst with fst (fst ccquisition with shllow tip ngle) imging techniques (2-5). Although the following represents simplified pproch, FLAH (Fst Low Angle Hot) cn be viewed s sequence with TI contrst nd FIP (Fst Imging with tedy tte Free Precession) s sequence with mixture of TI nd T2 contrst (Figure 1). In relity, TI, T2, T2, TE, TR, tip ngle, nd slice profile ll contribute in complex mnner to tissue contrst with these techniques. To illustrte furthen the complexity of this issue, it is possible to employ FLAH with very low tip ngles (IOO) nd long TRs (1 msec) to chieve some T2 contrst. Our work, however, hs focused on the ppliction of FLAH to chieve TI contrst. Figure 1 Tronsxil FLAH (A) nd FIP (B) imges of ptient with ventniculomegly. FLAH cn be used to chieve Ti contrst. Thus in A, the intensity of the signl from white mtter is greter thn tht from gry mtter, nd the signl from CF is of very low intensity. FIP is commonly employed to chieve contrst between fluid nd soft tissue. This is illustrted in B by the very high signl intensity of CF. (Reprinted with permission from Wood, et l., Mgnetic Resonnce Imging 1987; 5: ) 948 RcdioGrcphlcs #{149}eptember, 1988 #{149}Volume 8, Number

3 Rung. et ci. FLAH-C/inic/ -D MR/ With FLAH, one cn indeed chieve TI contrst superior to tht of spin echo techniques (6). Attempts to optimize T2 contrst hve been mde primrily with FIP, but up to this time, the T2 contrst chieved with spin echo imging hs been superior to tht demonstrted with FIP. This hs led to some concern bout the implementtion of T2 weighted fst scns. For exmple, dehydrted disks my be visulized on T2 weighted spin echo scns, yet missed on FIP exmintions. Using the sme line of resoning, cord lesion might be missed if one employed FIP in plce of T2 weighted spin echo technique. It should be noted, however, tht fst imging techniques hve not yet been optimized for the disply of T2 contrst. With -D imging, dt for the entire region of interest is obtined throughout the imging time. Unfortuntely, this mens tht motion occurring t ny time during imging ffects the entire dt set. The strength of this technique, however, is the potentil for reformtting imges in ny rbitrry plne. From theoreticl point of view, imges reformtted in plnes orthogonl to the originl plne selected will hve resolution equivlent to tht of the primry imges (if very thin-section originl imges re cquired). Plnes cut obliquely or long rbitrry curved surfces would hve resolution only slightly less thn tht of the originl dt set. Thus, the power of -D fst imging emerges: It hs the potentil for high resolution imging in ll three plnes, in ddition to imging in rbitrry, tilted plnes or curved surfces, ll from single 5-1 minute dt set (7). The mjority of our -D FLAH ptient scns, including those illustrted in Figures 7-12 were mde with TR = 4 msec, TE = 8 msec, tip ngle = 5, rectngulr pixels nd one cquisition. At this time, more thn 1 ptient exmintions hve been performed with -D FLAH. In ech instnce, the results were compred with those obtined using stndrd TI weighted spin echo technique (TR/TE = 6/ 17). Ninety percent of these exmintions hve been of the centrl nervous system in ptients with neoplstic or demyelinting disese. All studies were performed with iemens1 1. T MgnetomTM. ptil resolution in MR imging depends on slice thickness, mtrix size (the number of redout nd phse encoding steps), nd field of view (FOV). For the mjority of -D FLAH studies included in this report, the slice thickness ws mm; the mtrix size, 256 x 128, nd the FOV, cm. ptil resolution, s trditionlly evluted in phntom studies, is independent of whether spin echo or grdient echo technique is selected C Contrst Optimiztion (FLAH) TR, TE, nd tip ngle my be vried to mximize TI contrst with -D FLAH (Figure 2). Results from work with 2-D FLAH suggest the combintion of TRs in the rnge of -O msec with tip ngles of 4O_5, when contrst between gry mtter nd white mtter is used s the stndrd of reference. Indeed, TI contrst cn be chieved tht is superior to tht obtmed with short TR nd TE spin echo techniques. In Figure, 1 mm spin echo trnsxil section (TRITE = 6/17) of ptient with low grde strocytom is presented together with I mm -D FLAH section (TRITE = 6/17, 4 tip ngle) of the sme ptient. Despite the differences in slice thickness, contrst-to-noise rtio mesurements reveled improved TI contrst (between the lesion nd surrounding norml brin) on the -D FLAH imge. The optimum tip ngle nd TR my, of course, be dependent upon the tissues being compred. For exmple, the contrst optimiztion process my be quite different in the cervicl spine, where the signl intensities of disk, CF, nd cord must ll be differentited. 1iemens Medicl ystems. Iselin. NJ Volume 8, Number #{149}eptember, 1988 #{149}RcdioGrcphics 949

4 FLAH-C/inic/ -D MR/ Rungeetci. I) - II- C N E. C Figure 2 The vrition in contrst-to-noise rtio s function of the tip ngle nd TR selected for FLAH imging is illustrted using white nd gry mtter for reference. For TR in the rnge of 5 msec, tip ngle of pproximtely 5 provides the gretest contrst between white nd gry mtter. CNR BETWEEN WHITE MATTER AND CRAY MATTER ck z Li C,,) U) z 1O FLIP ANGLE (degrees) Figure A spin echo exmintion (A) is compred with -D FLAH exmintion (B) in ptient with low grde strocytom. Despite the 1 mm slice thickness of the -D FLAH imge, good Ti contrst hs been chieved between the lesion nd the surrounding white mtter s well s between norml gry nd white mtter. When -D FLAH (4/i 2/ 5) ws compred with 2-D spin echo (6/i 7), the contrst-tonoise rtio between gry mtter nd white mtter ws 1 17 ± 58% greter with the -D FLAH technique (n = 4). 95 RcdioGrcphlcs #{149}eptember, 1988 #{149}Volume 8, Number 5

5 Rung. et ci. FL4H-C/inic/ - MRI Becuse of its sensitivity to mgnetic susceptibility effects, -D FLAH cn be superior to 2-D spin echo techniques for the detection of hemosiderin (Figure 4). The ptient whose scns re shown in Figure 4 hd multiple intrprenchyml hemorrhgic lesions of unknown etiology. On -D FLAH (A), frontl nd pontine lesions re noted. On 2-D spin echo imges (B), only the frontl lobe lesion is detected. The pontine lesion ws lso missed on conventionl T2 weighted spin echo imges. ince ir lso cretes mgnetic susceptibility inhomogeneity, these results cn be extrpolted to the cse of intrprenchyml ir. The expected dvntge of -D FLAH hs been confirmed in niml studies. In work described elsewhere (6), -D FLAH ws compred to 2-D spin echo technique, using equivlent slice thicknesses nd scn times, in rt model of pneumocephlus. Lesion detection in -D FLAH imges ws improved 15% compred with the 2-D spin echo imges, nd the contrst-to-noise rtio between ir nd surrounding norml brin ws improved by 9 ± 8% (p <.25) in the -D FLAH imges. V B N #{149}TI I- ( I Figure 4 A comprison of -D FLAH (A) with 2-D spin echo (B) for the detection of iron contining lesions (rrows). Becuse of its greter sensitivity to mgnetic susceptibility differences, -D FLAH is supenor. Techniques: (A) -D FLAH (6/i 8, 4#{176} tip ngle, 2 mm slice thickness); (B) 2-D spin echo (6/i 7, 1 mm slice thickness). 4A 4B Volume 8, Number 5 #{149}eptember, 1988 #{149}RcdioGrcphics 951

6 FL,AH-C/inic/ -D MR/ Rung. et ci. = U).4 U. C N E. C A short discussion of the origin of mgnetic susceptibility effects in fst imging is wrrnted here. Inhomogeneities in the mgnetic field cn cuse misregistrtion of sptil informtion, since the liner mpping of frequency to position is destroyed. Metllic objects re the most frequent source of this form of distortion, with ferromgnetic mterils producing the gretest distortion. The 18#{176} pulse in spin echo imging compenstes for this effect. In fst imging, however, the grdient reversl used to refocus signl does not correct for these mgnetic susceptibility inhomogeneities. It is this filure of -D FLAH to correct for mgnetic susceptibility inhomogeneities tht is dvntgeous for the demonstrtion of ir or iron deposited in the brin, s noted bove. Becuse of its TI sensitivity, -D FLAH cn be used for the demonstrtion of Gd DTPA. In Figure 5, suprsellr meningiom is illustrted in imges generted before nd fter the dministrtion of Gd DTPA. A nd B re mm spin echo imges (TR/TE = 6/17); C nd D re 2. mm -D FLAH imges (TR/TE = 4/1 with n RF tip ngle of 5#{176}). The scn durtion ws pproximtely minutes for ech sequence. Although sttisticl comprisons hve not yet been mde in lrge number of ptients, the visuliztion of contrst enhncement with -D FLAH ppers to be t lest equivlent to tht obtined with short TR nd TE spin echo techniques. It hs lso been noted tht the enhncement of norml vsculture following Gd DTPA dministrtion is much more obvious with -D FLAH thn with spin echo techniques. Figure 5 A suprsellr meningiom recorded with spin echo technique before (A) nd fter (B) the dministrtion of Gd-DTPA is compred with -D FLAH imges of the sme lesion mode before (C) nd fter (D) Gd- DTPA enhncement. Enhncement of intrcrnil neoplstic disese with Gd-DTPA is well visulized on Ti weighted -D FLAH sections. 952 RcdioGrcphics #{149}eptember, 1988 #{149}Volume 8, Number

7 Rung. #{149}t ci. FLAH-C/inic/ -D MR/ V B N I- 14 5C 5D Reformtted One of the mjor dvntges with -D grdient echo techniques is the bility to obtm thin, high resolution sections tht cn be reformtted in the orthogonl plnes without significnt loss of sptil resolution. Reformtted MR imges re superior to those obtined with x-ry CT for two resons. First, the slice thickness of the originl sections cn be much thinner (.5-I. mm). econd, dt for the entire -D volume is obtined througout the durtion of the MR scn; wheres, with x-ry CT, motion between slices cn result in misregistrtion of imges. Figure 6 is I mm sgittl imge from n originl -D FLAH cquisition together with Imges thin section reformtted imges in trnsxil nd coronl plnes. A meningiom is seen rising from the sphenoid wing nd extending long the tentorium posteriorly. Gd DTPA hd been dministered intrvenously to provide enhncement. Tilted (A) nd curved (B) plnes cn lso be esily derived from the originl dt set (Figure 7). As illustrted, curved plnes my be prticulrly useful in the evlution of the spinl cord. The softwre lgorithm employed corrects for ny potentil distortion with respect to vrible mgnifiction long the curved plne. Volume 8, Number #{149}eptember, 1988 #{149}RcdloGrcphics 95

8 FL4H-C/inic/ -D MR/ Rung. #{149}t ci. i E V E Figure 6 A 1 mm sgittl -D FLAH section (A) is shown together with i mm trnsxil (B) nd coronl (C) imges obtined by reformtting the originl sgittl dt set in this ptient with meningiom. All three orthogonl plnes cn be generted routinely from single cquisition. 954 RcdloGrcphics #{149}eptember, 1988 #{149}Volume 8, Number

9 Rung. et ci. FLAH-C/inic/ -D MR/. Figure 7 Tilted trnsxil (A) nd curved coronl (B) imges of the Gd- DTPA enhnced meningiom shown in Figure 6 hve been obtmed by dditionl reformtting of the originl dt set. Reformtted imges cn be generted in ny orbitrry plne from single -D FLAH cquisition. lb Volume 8, Number #{149}eptember, 1988 #{149}RcdloGrcphics 955

10 FLAH-C/inic/ -D MR/ Rung. #{149}t ci. E V E This typicl ppliction of -D FLAH in the exmintion of the hed results in 128 one mm sgittl sections. Reformtting these in coronl nd trnsxil plnes could potentilly triple the number of imges vilble for interprettion by the rdiologist. This number of imges would be overwhelming in routine prctice. Thus, we hve developed progrms to integrte number of djcent thin sections, whether these be the originl sections or reformtted slices. This technique llows for depiction of 15 thick imges in ech of three plnes (sgittl, trnsxil nd coronl), covering the entire hed. In individul cses, in which the rdiologist desires thinner sections, specific I mm cuts cn be derived from the originl dt set. This pproch is illustrted in Figure 8. The thicker sections hve been creted by dding together four djcent thin sections. The rdiologist reding the cse would be presented with 4 mm cuts through the brin in ll three xes. If thinner sections were desired for dditionl informtion, these could redily be supplied. 8A Figure 8 Thin nd thick reformtted trnsxil nd coronl imges re compred in this ptient with pontine metstsis. ections A nd B re 1 mm thick; C nd D re 4 mm thick. To lessen the number of imges the rdiologist must review, thick sections cn be creted by dding together number of djcent thin sections. The resulting thick sections hve higher signl-to-noise rtios thn the component thin sections. There is slight loss of resolution in the thick section owing solely to the thickness of the slice. 956 RcdioGrcphics #{149}eptember, 1988 #{149}Volume 8, Number

11 Rung. #{149}t ci. FLAH-C/inic/ - MR/ B. B Rottions nd urfce Mps With -D fst imging techniques, nerly cubic voxel is obtined with pproximte dimensions of I x I x I mm. As resuit, -D FLAH nd FIP dt lend themselves to -D mnipultion nd disply. Three dimensionl projections of region of interest cn be displyed nd rotted in spce, surfce mps cn be constructed, nd tissue volumes cn be clculted. In Figure 9, we hve chosen to disply the externl contour of ptient s hed. Two projections, which differ by 45, re iilustrted. These imges were obtined by processing -D FLAH dt set. Instructing the computer to disply tissue 12 mm beneth the surfce of the hed (from ll directions), yields the imges in Figure 1. Figure 9 Two surfce projections (A&B) of -D FLAH ptient exmintion Volume 8, Number #{149}eptember, 1988 #{149}RdioGrcphics 957

12 FLAH-C/inic/ -D MR/ Rung. t cl. U U) V C C Figure 1 -D projections (A&B) obtined from set of -D FLAH imges. In this cse, tissue pproximtely i 2 mm beneth the surfce of the hed is displyed. Using these sme techniques, we hve creted the projections illustrted in Figure I I. In this instnce, we hve displyed tissue which is locted pproximtely 4 mm beneth the surfce. Both lcunr infrct (open rrow) nd Gd DTPA enhnced coustic neurom (closed rrow) cn be identified. Other types of surfce mps could yield further informtion from -D dt sets. Distinct interfces, such s those between the surfce of the brin nd djcent CF, between cerebrl edem nd norml brin, or between the border of high contrst intrprenchyml lesion nd the surrounding brin, cn be used s the bsis for such reconstructions. One immedite ppliction of this technology is the disply of brin lesions in -D, relegting to the pst the problem of loclizing such lesions ntomiclly. With the bility to distinguish interfces such s those between edem nd norml brin or between lesion nd surrounding edem, better estimte of the tissue volume involved by specific pthologic process could potentilly be mde. An immedite ppliction of this technology is the estimtion of ventriculr volumes. The shrp interfce between CF nd surrounding white mtter fcilittes the process by which the ventriculr spce is isolted from surrounding brin. In similr fshion, tumor volume could be clculted from Gd DTPA enhnced -D imges. 958 RdioGrcphlcs #{149}eptember, 1988 #{149}Volume 8, Number 5

13 Rung. et ci. FLAH-C/mic! -D MR/. (4) C V Figure 1 1 This -D FLAH exmintion with Gd-DTPA enhncement shows both locunr infrct (open rrow) nd n coustic neurom (solid rrow). The imges presented re -D projections generted from single dt set. They represent difference of pproximtely 2 in viewing ngle. pine For spine imging, thin sections re often required in plnes ngled with respect to the stndrd trnsxil, sgittl nd coronl views. This is prticulrly true for the ssessment of disk disese in the lumbr spine nd forminl disese in the cervicl spine, nd for the evlution of ptients with exggerted kyphotic or scoliotic deformities. The downfll of trditionl spin echo techniques is their inbility to produce high signl-to-noise rtio, thin sections without lrge interslice gps. Three-D imging offers the potentil for high signl-to-noise rtio, thin (1-2 mm), truly contiguous sections. As in the hed, there is the potentil for reformtting in rbitrry plnes. This would serve s simple solution to the problem of obtining tilted plnes. A coronl -D FLAH exmintion of the lumbr spine with 2 mm slice thickness is illustrted in Figure 12. Deserving comment, is the fct tht motion rtifcts re significnt problem for -D imging of the spine. This is ccentuted by the use of two phse-encoding grdients in -D imging, s contrsted with single phse-encoding grdient in 2-D spin echo techniques. The lterntives vilble for the reduction of motion rtifcts include motion compensting grdients, preferentil orienttion of the phse-encoding grdients, nd sturtion pulses. Volume 8, Number #{149}eptember, 1988 #{149}RcdioGrcphlcs 959

14 FLAH-C/mic! -D MR/ Rung. #{149}t ci. C. U) Figure 12 Two mm coronl sections from -D FLAH exmintion of the lumbr spine of norml volunteer The nerve roots re well visulized exiting through the neurl formin beneth the pedicles. Three-D FLAH cn be combined with intrvenous Gd DTPA dministrtion for improved delinetion of disk disese. Trnsxil nd sgittl TI weighted spin echo scns mde before nd fter the dministrtion of Gd-DTPA re illustrted in Figure 1. cr (rrow) enhnces immeditely fter the dministrtion of the contrst gent, differentiting it from disk mteril. The use of Gd-DTPA with -D FLAH should, thus, provide for the differentition of postopertive scr from disk mteril with thin sections (1-2 mm) nd offers the potentil for reformtted imges in ny desired plne. 96 RcdioGrcphlcs #{149}eptember, 1988 #{149}Volume 8, Number

15 Rung..t ci. FLAH-C/inic/ - MR/ U) V 1A Figure 1 Trnsxil 2-D spin echo scns of the lumbr spine before (A) nd fter (B) the dministrtion of. i mmol/kg Gd DTPA. After contrst enhncement (B), scr is noted to be wrpped round nerve root on the right. The use of Gd DTPA in this cse mkes cler tht the soft tissue moss (rrow) consists entirely of scr tissue. A rehernition or extruded frgment is ruled out. This dignosis could not hve been mde from the unenhnced scn lone. Volume 8, Number 5 #{149}eptember, 1988 #{149}RcdioGrcphlcs 961

16 FLAH-C/inic/ - MR/ Rung..t ci. Extremities Limited experience with FLAH in joint disese suggests tht it provides improved sensitivity to vsculr necrosis when compred with spin echo technique. Figure 14 illustrtes ptient with posttrumtic vsculr necrosis of the lunte. A mm spin echo coronl section is compred with 1. mm -D FLAH cquisition. Loss of norml mrrow signl in the cpitte nd scphoid in ddition to the lunte is consistent with vsculr necrosis nd is better pprecited on the FLAH imge thn on the spin echo section. The heled frcture lines in the distl rdius re lso more pprent with the thin section -D FLAH technique. The use of -D FLAH hs lso proved dvntgeous for the study of neoplstic bone lesions (Figure 15). tructurl detil within such lesions tht is not pprecited with spin echo technique is reveled in -D FLAH sections. In the exmple shown, there is lesion in the proximl tibi tht involves the epiphysis. The histologic dignosis ws primry lymphom. A coronl 1 mm spin echo section is compred with I mm -D FLAH section. Reformtted xil nd sgittl sections obtined from the originl coronl -D FLAH cquisition re lso presented. Figure 14 A mm spin echo exmintion of ptient with vsculr necrosis nd multiple old frctures is compred with i. mm -D FLAH exmintion. Disese in the cpitte nd scphoid s well s in the Iunte is better demonstrted in the -D FLAH imge, nd the heled frcture lines in the distl rdius re lso more pprent on the -D FLAH section. Techniques: (A) spin echo (8/25); (B) -D FLAH (5/18 with 4#{176} tip ngle). 962 RdioGrphics #{149}eptember, 1988 #{149}Volume 8, Number 5

17 Rung..t ci. FLAH-C/inic/ -D MR/ TI -. B Figure 15 A coronl spin echo imge of the knee of ptient who hd primry lymphom is compred with coronl -D FLAH imge nd reformtted trnsxil nd sgittl -D FLAH sections. This figure gin illustrtes the bility of -D FLAH to provide high resolution imges in ny plne from single cquisition. Techniques: (A) spin echo ( i mm section; 6/i 7; scn time 5.i mm); (B) -D FLAH ( i mm section; 6/i 8 with 4#{176} tip ngle; scn time 8.2 mm). h5c Volume 8, Number 5 #{149}eptember, 1988 #{149}RdloGrphics 96

18 FL4H-C/inic/ -D MR/ Rung. #{149}t ci. E IN Three-D imging my lso emerge s the technique of choice for the evlution of meniscl injuries (Figure 16). Once gin, the vlue of very thin sections nd contiguous slices my led to replcement of spin echo imging by -D fst techniques. Further support for this solution is provided by the superior visuliztion of crtilge with fst imging techniques. Figure 16 giftl Ti weighted -D FLAH sections of the knee of norml volunteer lice thickness: 1.5 mm. Conclusion Three-D FLAH cn be employed to provide high resolution, high contrst, thin section, TI weighted imges of the brin nd extremities. Grdient echo imging, employed with - D FLAH, offers modest dvntge in signlto-noise nd contrst-to-noise rtios per unit of cquisition time over spin echo imging for TI weighted scns (8). Imge degrdtion due to motion, whether physiologicl or involuntry, remins significnt problem with -D FLAH imging. High resoiution, thin section MR imging lso lends itself to successful imge reformtting. A primry dvntge of -D FLAH my be the bility to obtin reformtted imges of high sptil resolution in ny plne, regrdless of the orienttion of the originl cquisition. Thus, one -D cquisition cn provide ntomicl informtion tht is superior to tht recorded with spin echo cquisitions performed in three plnes: trnsxil, coronl nd sgittl. Three-D FLAH permits the visuliztion of contrst enhncement following Gd DTPA dministrtion. Thus, the use of prmgnetic gents is not restricted by the implementtion of this new imging technique. Preliminry experience indictes tht lesion enhncement with -D FLAH is t lest equivlent to tht obtmed with spin echo technique nd the enhncement of rteril nd venous structures is superior. Mgnetic susceptibility effects mke -D FLAH superior to spin echo for detection of pneumocephlus nd bnorml iron deposition. This sensitivity limits, however, the use of -D grdient echo techniques for the study of soft tissues ner bone or ir. Two such res re the pituitry glnd nd the internl uditory cnl. In both regions, thin I mm section imging could ply vitl role. One pproch to minimizing the sensitivity of -D FLAH to mgnetic susceptibility effects might be the development of very short TE (5 msec) sequences. 964 RcdioGrcphlcs #{149}eptember, 1988 #{149}Volume 8, Number

19 Rung. #{149}t ci. FLAH-C/inic/ - MR/ Three-D fst imging lso offers the potentil for ngiogrphy (Figure 17). By combintion of rephsing nd dephsing sequences, flow in the rteries nd veins cn be depicted. Becuse of differentil flow ptterns, it should be possible to depict rteril flow seprtely from venous flow nd vice vers. In summry, -D FLAH is dvocted for high resolution imging of the brin nd extremities. This new technique offers dvntges in lesion locliztion, visuliztion of very smll bnormlities, nd ptient throughput. C Figure 17 This ngiogrm-like imge of the knee ws obtined with -D FIP sequence tht combined both rephsing nd dephsing grdients. References I. Krmer DM, chneider J, Rudin AM. Luterbur PC. True three-dimensionl nucler mgnetic resonnce zeugmtogrphic imges of humn brin. Neurordiology 1981; 21(5): Frhm J. Hse A. Mtthei D. Rpid three-dimensionl MR imging using the FLAH technique. J Comput Assist Tomogr 1986; 1O(2): Frhm J. Hse A. Mtthei D. Rpid NMR imging of dynmic processes using the FLAH technique. Mgn Reson Med 1986; (2): Mills TC, Ortendhl DA. Hylton NM. et l. Prtil flip ngle MR imging. Rdiology 1987: 162: Oppelt A. Grumnn P. Brfub H. et l. FIP- new fst MRI sequence. Electromedic 1986; 54(1): Runge VM, Wood ML, Kufmn DM. et l. MR study of intrcrnil disese with three-dimensionl FLAH (bstr). Rdiology 1987; 165(P): Wood ML, Runge VM. Appliction of imge enhncement techniques to mgnetic resonnce imging. RdioGrphics 1988; 8(4): Henrick RE. Kneelnd JB, trk DD. Mximizing signl-tonoise nd contrst-to-noise rtios in FLAH imging. Mgn Reson Imging 1987; 5: We re especilly pprecitive of the ssistnce provided by Mrth Pcetti, Jnis Breslin. Jonne Incerpi. Eileen Mrr, heli Quinn, Rosenn Cormeo, Norlene lsh. Nncy Wysocki. B. J. zirger, nd Dr. Robert Pul. Jr. We wish to thnk iemens Medicl ystems Inc. nd prticulrly Dr. Gerhrd Lub who provided the -D ngiogrphy technique. s well s KONTRON Electronics for their technicl ssistnce nd support. Volume 8, Number 5 #{149}eptember, 1988 #{149}RcdioGrcphics 965