MRI Appearance of Pathologic Entities. MRI Appearance of Normal Anatomy. Segment VII

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1 Focl Liver Lesions 11 Segment VII Fig. 1.8 Segmentl ntomy of the liver. If heptoiliry contrst medium is used to differentite heptocellulr tumors (focl nodulr hyperplsi, welldifferentited heptocellulr crcinom), dditionl delyed imges should e otined no erlier thn 2 h fter contrst injection. MRI Appernce of Norml Antomy The norml liver is of uniform signl intensity, which is higher thn tht of the spleen on T1w imges nd lower on T2w imges. Hepticvessels pper drk on T1w imges due to flow-relted signl loss (see Fig. 1.2). They re lso drk on T2w imges unless grdient moment nulling (flow compenstion) is used, in which cse intrheptic vessels re right. The rnches of the portl vein nd intrhepticveins serve to identify the liver segments (Fig. 1.8). Differentition of the liver from other structures in the upper domen is usully strightforwrd. MRI Appernce of Pthologic Entities Most enign nd mlignnt liver tumors re hypointense on T1w imges nd hyperintense on T2w imges. Cysts, hemngioms, nd metstses from neuroendocrine tumors re visulized with high contrst, s re intrtumorl necrosis nd scesses. The vst mjority of other liver metstses nd cholngiocrcinom (CCA) re less conspicuous on oth T1w nd T2w imges. Liver tumors thtreisointenseornerlyisointensetonormlliver prenchym re focl nodulr hyperplsi (FNH) s well s n occsionl denom or heptocellulr crcinom (HCC) (Tle 1.4). T1w sequences contriute little to lesion chrcteriztion, except for cysts, which re clerly identified s shrply demrcted lesions of very low signl intensity on T1w imges. In ll other cses, chrcteriztion of focl liver lesions is primrily sed on T2w sequences, which enle good evlution of tumor mrgins nd internl structures. Use of different T2 weightings, including imges generted from lte echoes, llows fur-

2 12 1TheLiver Fig. 1.9, Multiple liver cysts in ptient with utosoml dominnt polycystic kidney disese (1.5 T). Single-shot T2w TSE imge. T1w GRE imge. Both imges were cquired during reth-hold. The liver cysts re depicted s homogeneous lesions of very high SI on the T2w imge nd very low SI on the T1w imge. Also seen re multiple cysts in oth kidneys. Tle 1.4 Signl intensities of different liver lesions reltive to liver tissue on unenhnced imges. Note: opposed-phse signl intensities (T1w OP) for ptients without heptic stetosis T1w IP T1w OP T2w Benign tumors Cysts Hemngiom FNH 0 ( ) 0 ( ) 0 ( ) Adenom 0 Mlignnt tumors Metstses Melnotic melnom Neuroendocrine tumors Other primries HCC 0 CCA Tle 1.5 List of typiclly hypervsculr liver tumors Benign liver tumors FNH Adenom Mlignnt liver tumors HCC Metstses Renlcellcrcinom Brest cncer (my lso e hypovsculr) Neuroendocrine tumors (e. g., crcinoid, insulinom) Melnom Srcom ther chrcteriztion nd improves ccurcy in differentiting cysts nd hemngioms from solid liver tumors. Intrlesionl hemorrhge nd ftty components s well s melnotic liver metstses from mlignnt melnom exhiit typicl signl ehvior with hyperintensity on oth T1w nd T2w imges. Additionl informtion for chrcterizing focl liver lesions is provided y dynmic contrst-enhnced MRI, which enles the importnt differentition of hypervsculr nd hypovsculr lesions nd revels some typicl enhncement ptterns such s the progressive centripetl enhncement chrcteristic of liver hemngiom (Tle 1.5). Below we descrie the MR ppernce of the most importnt enign nd mlignnt focl liver lesions on unenhnced imges nd dynmic contrst-enhnced imging with nonspecific Gd-sed contrst medi. A seprte section illustrtes the use of tissue-specific MR contrst medi for selected tumor entities. Benign Focl Liver Lesions Cyst Becuse they contin wter, cysts hve long T1 nd T2 relxtion times, resulting in very low signl intensity on T1w imges nd uniform high signl intensity on T2w imges. A liver cyst is usully shrply demrcted from the surrounding tissue ut my pper lurred due to prtil volume effects if the plne of section is tngentil to it (Fig. 1.9). In cses where cysts nd hemngioms cnnot e differentited ecuse of similr T2 signl intensities, T1w sequence or dynmic imging will help distinguish the two (Fig. 1.10). MRI clerly differentites the cyst fluid from the solid wll nd sept in echinoccocl cysts, while the chrcteristic curviliner clcifictions (eggshell clcifictions) re fr etter reveled with CT.

3 Focl Liver Lesions 13 c d Fig e Liver hemngiom nd cyst in segment II (1.5 T). Axil T2w TSE imge. e Axil T1w GRE imges otined efore () nd 15 s (c), 2 min (d), nd 10 min (e) fter IV injection of Gdsed contrst medium. Before contrst medium dministrtion, oth lesions hve very high T2 SI () nd low T1 SI(). On dynmic contrst-enhnced imges, the hemngiom is chrcterized y initil nodulr peripherl enhncement (c) with progressive fill-in (d), resulting in complete hyperintensity of the lesion 10 min fter contrst dministrtion (e). The cyst hs unchnged low SI on ll postcontrst imges. e Hemngiom Hemngioms re the most common enign heptic tumors. They re incidentlly detected in c. 5 % of ptients undergoing dominl imging for other resons. Hemngioms re mesenchyml tumors chrcterized y densely pcked, dilted vessels with n endothelil lining. Regressive chnges such s scrs nd centrl hyliniztion my e present in lrge hemngioms. Although they hve no mlignnt potentil, hemngioms my pose dignostic chllenge ecuse they must e differentited from liver metstses. This is especilly importnt in ptients with multiple hemngioms (up to 35 % of cses). Hemngioms re well-circumscried msses of uniform signl intensity on T1w nd T2w imges nd my occsionlly e loulr. They re modertely hypointense on T1w imges nd clerly distinct from cysts, which hve very low T1 signl intensity, while distinguishing them from other solid liver tumors is more difficult. On T2w imges, on the other hnd, hemngioms re of high signl intensity nd therefore t times resemle cysts

4 87 4 The Spleen M. Lnido nd F. Dmmnn Introduction The spleen is lymphtic orgn tht cn e regrded s lrge lymph node integrted into the lood circultory system. At the sme time, with its specil vsculr rchitecture, the spleen lso ffects the nonlymphtic cells in the lood. As functionlly complex orgn, the spleen thus hs centrl, though not vitl, role in dult life, which is why mny disese processes involve the spleen, while primry splenic disese is firly uncommon. 1,2 with the lignment light of the scnner centered t the level of the xiphoid process. Imging Plnes The xil plne is the ckone of dedicted exmintion of the spleen (Fig. 4.1). Additionl coronl imging is helpful if the ptient s reth-hold cpcity nd the MR equipment llow cquisition of good-qulity imges during reth-hold (Fig. 4.2). The spleen is imged with slice thickness of 6 8 mmndninterslicegpof2mm. Indictions There re no estlished indictions for MRI of the spleen ecuse ultrsound nd CT llow excellent dignostic evlution of this orgn. Reltive indictions for MRI exist in the stging of lymphoprolifertive disese (Hodgkin nd non-hodgkin lymphom) nd chrcteriztion of focl splenic lesions. MRI is lso suitle imging modlity for plnning infrdiphrgmtic rdiotherpy in ptients with lymphoprolifertive disese s coronl sequences give n excellent overview of the vsculr ntomy in the splenic hilum. Another reltive indiction is the follow-up of posttrumtic splenic hemtom in peditric ptients with inconclusive sonogrphic findings fter nonsurgicl tretment. Imging Technique Before the exmintion, the ptient is given generl explntion of the procedure (e. g., durtion of rethholds) including informtion out plcement of n intrvenous line for contrst injection either Gd-sed extrcellulr contrst medium or SPIO prticles (superprmgnetic iron oxide) nd the need for dministering n ntispsmodic drug (e. g., utylscopolmine or glucgon). Orl contrst is not required for MRI exmintions of the spleen. Coil selection depends on the equipment ville (e. g., torso or ody phsed-rry coil). Scnning is performed with the splenic hilum in the isocenter of the mgnet. To this end, the ptient is positioned supine Pulse Sequences The sic protocol consists of unenhnced T1w nd T2w sequences. T1w imges re cquired with n SE or TSE sequence ut preferly with 2D GRE sequence during reth-hold. All of these sequences re cquired with the shortest possile TE to optimize imge contrst. Unenhnced T2w imging is performed with reth-hold single-shot TSE sequence (e. g., HASTE). Becuse these 2D sequences hve short cquisition times, sic imging in the xil plne cn e supplemented y coronl sequence, or even sgittl imges if needed, with only minimum of dditionl time. A free-rething TSE sequence with ft suppression (e. g., inversion recovery technique, spectrl ft sturtion) my improve imge qulity ut tkes longer to cquire. The imge qulity of free-rething T2w sequences cn e improved y using respirtory gting (respirtory ellows, nvigtor echo technique), which will mrkedly reduce motion rtifcts. (Tles 4.1 nd 4.2). Contrst Medi Intrvenous olus injection of extrcellulr Gd-sed contrst medium (e. g., Mgnevist, Dotrem) with dynmic cquisition of seril contrst-enhnced T1w imges is recommended to detect nd chrcterize focl lesions in the spleen. The dynmic imges re cquired with GRE sequence during reth-holds efore nd 15 s, 45 s, 90 s, nd c. 3 min fter injection of the contrst medium t dose of 0.1 mmol Gd per kg ody weight. Immedite

5 88 4TheSpleen c d e f Fig. 4.1 f Norml MR ppernce of the spleen t 0.2 T (, )nd 1.5 T (c f)., At 0.2 T,the spleen hs lower SI thn the liver on T1w imge (SE 450/15) (),while it is hyperintense on T2w imge (FSE 3000/102; turo fctor,13) (). A solid tumor of low SI is seen in the upper pole of the right kidney. c, d At1.5T,thespleenisgin hypointense to the liver on T1w imge (GRE 126/5;75 ) (c) nd hyperintense on T2w imge (FSE 2000/128; turo fctor,23) (d). e On T2w HASTE imge,the SI difference etween spleen nd liver is less pronounced (HASTE /90). f On ft-suppressed T2w imge,the spleen hs mrkedly higher SI thn the liver (FSE 2000/128; turo fctor,23).

6 Imging Technique 89 Fig. 4.2 Coronl T2w imge cquired with HASTE sequence t 1.0 T (HASTE /43). Using this technique,the norml spleen is nerly isointense to liver. Bowel is seen in the splenic hilum. Tle 4.1 Recommended pulse sequences nd imging prmeters for MRI of the spleen Weighting Sequence type TR (ms) TE (ms) Flip ( ) ETL FS No. of slices Scn time No. of cquisitions Brethhold T1 T1 T2 Unenhnced nd dynmic Gd-enhnced Alterntive (unenhnced) GRE (e. g.,flash) No/(yes) s Yes SE No 19 (16 20) min No Single-shot TSE No < 20 1 < 20 s Yes (e. g.,haste) T2 Alterntive TSE (or FSE) T2 Alterntive FSE (or TSE); my e performed with respirtory gting (elt or nvigtor echo) T2 Alterntive IR (e. g.,tirm, STIR) No + yes 6(3 8) min Yes c No 19 (16 20) c Yes 19 (16 20) PD TSE doule-echo > , No 19 (16 20) T1 Dynmic Gd-enhnced 3D GRE (e. g.,vibe) T2* GRE (e. g.,flash) min No min No min No Yes s Yes 141 (77 196) No 6 (3 8) 1 16 (16 23) s Use of torso or ody phsed-rry coil is recommended; mtrix, ; FOV, mm; rectngulr FOV,75 %; slice thickness, 5 8 mm; distnce fctor, ; plnes xil,coronl (optionlly),sgittl (rrely). Note: All recommendtions for imging t T. The suggested prmeters re only exmples nd hve to e djusted for use on different rnds of scnners. Prllel imging techniques cn e used to shorten scn time ut my come with penlty in SNR. Yes postcontrst T1w GRE imges llow sensitive detection of focl splenic lesions 3,4 (Fig. 4.3). Additionl lte postcontrst imges should e cquired fter c min using ft-suppressed SE or TSE sequence or ft-suppressed GRE sequence. Alterntively, the dynmic T1w series cn e cquired with 3D GRE sequence (e. g., VIBE), which hs higher sptil resolution nd produces n ngiogrphic effect while slightly reducing soft tissue contrst. InstedofnextrcellulrGd-sedcontrstmedium, n SPIO preprtion cn e infused or injected. Exmples

7 90 4TheSpleen Fig. 4.3 c Splenic lesion in 28-yer-old mn on chemotherpy for Hodgkin disese. Unenhnced nd dynmic postcontrst imges otined immeditely nd 5 min fter injection of Gd-sed contrst medium (0.1 mmol/kg Gd). Unenhnced T1w imge does not llow relile differentition of the splenic lesion. Erly postcontrst imge clerly revels the lesion within the inhomogeneously enhncing norml spleen. c Lesion conspicuity is reduced gin on 5-min postcontrst imge (1.0 T; GRE 64/5;70 ). c Tle 4.2 Recommended sequence protocol for MRI of the spleen Sequence Plne Breth-hold Indiction ) T1w GRE Axil Yes Bsic protocol ) T2w HASTE Axil Yes Bsic protocol c) T2w TSE -/+ ft suppression,my e performed with respirtory gting Optionl T1w GRE with dynmic Gd-enhnced series with delyed imges Axil No Bsic protocol; improves imge qulity compred with () Axil Yes (Suspected) focl lesion Optionl T1w SE or TSE Axil No If () not possile Optionl TIRM Axil No If (c) not possile d) Post-Gd T1w GRE Axil Yes Bsic protocol Optionl Optionl Post-Gd T1w GRE + ft sturtion Post-SPIO T2w HASTE,TSE Axil Yes For exmple in ptients with extrsplenic disese extension or suspected pthology of surrounding structures Axil No Improved chrcteriztion of focl nd diffuse chnges Note: Axil imges cn e replced or supplemented y other plnes (primrily coronl) depending on the ntomic sitution. of commercilly ville SPIO preprtions re Endorem nd Resovist (Europe) nd Feridex (e. g., USA), which re pproved for liver imging nd cn therefore e used in ptients whose spleen is imged s prt of n MRI exmintion of the liver (see Chpter 1, Contrst Medi, p. 8 ff.). In this cse, the precontrst protocol is supplemented y proton density (PD) sequence. 5,6 Identicl T2w, PD, nd T1w sequences re otined efore nd fter SPIO dministrtion. The pre- nd postcontrst PD imges re idelly cquired with doule-echo TSE sequence, producing T2w imge with the second echo.

8 MRI Appernce of Pthologic Entities 321 Fig , Renl rtery stenosis ner the origin of the left renl rtery. Contrst-enhnced MRA overestimtes the degree of stenosis () compred with rteril DSA (). signl voids due to susceptiility effects, precluding evlution of the stent lumen (see Aortic Aneurysm, p. 313 f). Renl Trnsplnts Another ppliction of contrst-enhnced 3D MRA is in evlutingthe lood supply (rteries nd veins including nstomoses) nd perfusion of renl trnsplnts (Figs , 15.24, 15.25, 15.26). Scrutiny of the source imges of the 3D dtsets is necessry to detect loclized perfusion defects in trnsplnt kidney nd prenchyml or vsculr dmge secondry to trum. 73 Portl Venous System Detiled nd ccurte informtion on the portl venous system is crucil for comprehensively evlutingthe vsculr sttus nd plnningtherpy in ptients with portl hypertension. This comprises vsculr ntomy, detection of normlities such s stenosis nd thromosis, nd identifiction of relevnt portosystemic collterl pthwys. Postinterventionl or postopertive follow-up MRA serves to otin informtion on vsculr morphology, nstomoses, nd shunt ptency. Fig Erly rnching of the right renl rtery close to its origin from the dominl ort. Also seen is lower polr rtery rising from the left common ilic rtery. Portl Veins nd Portosystemic Collterls MRI of the portl vein ws performed s erly s 1985 in ptients with portl hypertension usingse sequences. 74 In this study, the investigtors rted little or no signl in the portl veins s norml nd mrked intrportl signl intensity s thromosis. In lter study, norml signl intensity ws defined s einghigher thn tht of surroundingliver tissue on T2w imges nd isointense to liver on T1w imges. 75 Zirinsky et l. reported MRI to hve higher sensitivity nd specificity thn CT or sonogrphy for confirmingor excludingportl vein thromosis. 76 Conventionl SE sequences were lso found to enle demonstrtion of cvernous trnsformtion. 77 Fig Contrst-enhnced MRA reveling three right renl rteries nd two left renl rteries.

9 Mgnetic Resonnce Angiogrphy of the Adomen Fig c Contrst-enhnced MRA of left renl rtery neurysm. Illustrtion of different postprocessing techniques: MIP (), xil MPR (), nd surfce-rendered disply (c). c Fig Clmp stenosis of the left externl ilic rtery proximl to the rteril nstomosis of trnsplnted kidney (rrows). Fig Norml ppernce of trnsplnt kidney on contrstenhnced MRA. Anstomosis t the level of the left ilic ifurction.

10 MRI Appernce of Pthologic Entities 323 Fig Hemodynmiclly relevnt rteriovenous fistul (rrow) fter iopsy. The fistul leds to premture enhncement of the pelvic veins on the left side. v Fig High-grde trnsplnt renl rtery stenosis. Contrstenhnced MRA imge fils to depict the residul lumen (rrow). Fig Contrst-enhnced MRA in ptient with liver cirrhosis. Imge shows dilttion of the left gstric vein (rrows) s n indirect sign of portl hypertension. Erly optimism out portl venous MRI ws dmpened when it ecme pprent tht intrluminl dephsingphenomen in tortuous vessels cn cuse signl inhomogeneity nd led to misinterprettion. A reduction of the flow-relted rtifcts degrding SE imges ws chieved y usingimproved GRE sequences. 78 On GRE imges, flowing lood is hyperintense (right), while thromus is hypointense. SupplementingGRE sequences with olus trckingtechniques or PC MRA, one cn otin semiquntittive dt on portl venous lood flow. 79,80 These MRA techniques depict the portl veins directly nd hence provide more informtion on the vsculr system compred with invsive, indirect splenoportogrphy. 81,82 Contrst-enhnced 3D MRA hs evolved into the method of choice for imging the portl veins. It is superior to nonenhnced MRA ecuse it ffords higher contrst-to-noise rtio (CNR), etter sptil resolution, nd lrger FOV. More recent studies suggest tht contrst-enhnced 3D MRA regulrly enles good evlution of the portl venous system with high sptil resolution, relily demonstrtingportl vein thromosis, its extent, nd collterl vessels. 83,84 Moreover, iphsic imging protocol fter single contrst injection llows evlution of the rteril nd portl venous lood supply to the liver. The use of new time-resolved or MP-RAGE (mgnetiztion-prepred rpid cquisition grdient echo) techniques hs een reported to further improve vsculr conspicuity y incresingintrvsculr signl compred with routinely used 3D FLASH. This dvntge would e especilly eneficil for evlution of intrheptic portl rnches nd heptic veins. 85 The left gstric vein is the most commonly encountered portosystemic collterl. 86 Dilttion of this vein to >5 6 mm is considered n indirect sign of portl hypertension (Fig ). The sme holds true for the short gstric veins, which drin the gstric fundus. 87 Esophgel nd presophgel vrices receive lood from the left gstric vein nd drin into the zygos nd hemizygos veins. The splenoportl venous xis nd left renl vein re connected vi the left nd short gstric veins or other

11 MRI Appernce of Norml Lymph Nodes 335 Fig. 16.2, Norml pelvic lymph nodes long the pelvic sidewll on oth sides (oturtor chin). Axil T1w () nd T2w () TSE imges (1.5 T). Elongted lymph nodes (rrows) with low SI reltive to surrounding ft on T1w imge () nd ner isointensity on T2w imge (). Fig Digrm of retroperitonel lymph nodes. Fig. 16.4, Enlrged nd metsttic pr-ortic lymph node elow the renl pedicle in ptient with renl cell crcinom. Axil T1w GRE () nd T2w single-shot TSE () imges (1.5 T). In this cse, the short-xis dimeter of the lymph node of c. 1.5 cm (rrow) suggests metsttic involvement,while its SI is similr to tht of the norml lymph nodes in Figs nd 16.2.