· nodul?s ar? hypoint?ns? du? to T2* short?ning

·       
Ultrasound is not abl? to d?t??t liv?r iron ov?rload.
Although it is not us?d to dir??tly ass?ss iron ov?rload, ultrasound ?an b? us?d
to ass?ss th? s?qu?la? of liv?r injury r?lat?d to iron ov?rload su?h as ?irrhosis,
HCC, and portal hyp?rt?nsion. (Sirlin and R??d?r .,2010).

·       
Th? ov?rall att?nuation of liv?r in CT is in?r?as?d in
iron-ov?rload stat?s. Iron ov?rload of th? liv?r par?n?hyma ?an b? susp??t?d on
CT wh?n liv?r d?nsity m?asur?s 75 HU, provid?d that no IV ?ontrast has b??n giv?n.
Although CT may b? abl? to d?t??t iron ov?rload qualitativ?ly, in?r?as?d att?nuation
in th? liv?r is not sp??ifi? to iron ov?rload. S?v?ral ?onfounding fa?tors, in?luding
st?atosis, gly?og?n d?position, Wilson’s dis?as?, as w?ll as ??rtain drugs (?g,
amioradon? or gold) may alt?r h?pati? att?nuation. (Fis?h?r ?t al
.,2011).

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·       
B??aus? of th? limitations of th?s? t??hniqu?s, and du?
to th? wid?spr?ad availability of MRI s?ann?rs, signifi?ant ?fforts hav? b??n
mad? to ass?ss liv?r iron ?ont?nt using MR-bas?d m?thods. (H?rnando ?t al
.,2014).

 

·       
Pati?nts with ?irrhosis, a disord?r in whi?h iron d?position
is usually h?t?rog?n?ous and bio?h?mi?al h?pati? iron ?on??ntration ?an vary gr?atly
from on? nodul? to anoth?r, MRI ?an ?xamin? transv?rs? s??tions of th? ?ntir?
liv?r, and r?gion of int?r?st signal int?nsity m?asur?m?nts av?rag? larg?r
volum?s of tissu? ?ompar?d with liv?r biopsy sampl?s, This finding ?ould sugg?st
that in pati?nts with ?irrhosis, ov?rall ass?ssm?nt of h?pati? iron ?on??ntration
would b? ?v?n mor? a??urat? than biopsy wh?n don? with MRI. (Gandon ?t
al.,2004).

 

·       
Th?
distribution of iron ov?rload is usually diffus? and homog?n?ous but it may b?
h?t?rog?n?ous with a lobar/s?gm?ntal, h?t?ro?g?nous, or pat?hy patt?rn in pati?nts
with ?irrhosis, th? a??umulation also may b? fo?al r?fl??ting s?l??tiv? a??umulation
of iron in sid?roti? nodul?s (Fig.16). (Claud? and S?ott.,2012).

Fig.16: T2*-w?ight?d gradi?nt ??ho imag?s aft?r
administration of a gadolinium bas?d ?ontrast ag?nt in two pati?nts with ?irrhosis
s??ondary to h?patitis C viral inf??tion. Sid?roti? nodul?s ar? hypoint?ns? du?
to T2* short?ning ?ff??ts of iron. In th? pati?nt on th? l?ft, s?att?r?d sid?roti?
nodul?s ar? ?vid?nt in pat?hy distribution, whil? in th? pati?nt on th? right
th?y ar? diffus?ly distribut?d. Hyp?rint?ns? r?ti?ulations in th? liv?r in both
pati?nts r?pr?s?nt gadolinium-?nhan??d fibroti? bands. (Claud? and S?ott.,2012).

 

·       
Th?r? ?an b? ?o?xisting h?pati? iron ov?rload and fat a??umulation,
?o?xist?n?? of st?atosis in pati?nts with primary iron ov?rload was shown to a???l?rat?
liv?r injury. In su?h ?ir?umstan??s, in and out of phas? imag?s ?an ?aus?
diagnosti? ?onfusion and both d?t??tion and quantifi?ation of iron and fat b??om?
diffi?ult, ?sp??ially in ?onv?n­tional MRI. How?v?r, quantifi?ation of both fat
and iron is possibl? with r???nt m?thods that ?al?ulat? T2* and proton d?nsi­ty
fat fra?tion simultan?ously. This approa?h?s ?an h?lp to ?larify ?o?xist?n?? of
sid?rosis and st?atosis and ?onfusing patt?rns of fat and iron a??umulation. (Ilkay ?t al.,2016).

·       
Sin?? th? fatty liv?r signal is in?r?as?d only on T1-w?ight?d
imag?s, On GR? T2-w?ight?d imag?s st?atosis do?s not gr?atly modify magn?ti? r?sonan??
liv?r signal, sin?? s?l??t?d ??ho tim?s ar? in-phas?. In ?as? of pr?s?n?? of
fat and wat?r in th? sam? pix?l a r?lativ? loss of signal int?nsity o??urs with
oppos?d-phas? GR? imag?s. Good ?orr?lation was r?port?d b?tw??n MRI and bio?h?mi?al
ass?ssm?nt of iron ov?rload. On th? whol?, pr?s?n?? of liv?r st?atosis and fibrosis
did not aff??t th? a??ura?y of our t??hniqu?. (Gandon ?t al.,2004).

 

·       
Gradi?nt-r??all?d-??ho (GR?) t??hniqu?s mor? s?nsitiv?
to fi?ld inhomog?n?iti?s indu??d by paramagn?ti? substan??s than spin-??ho s?qu?n??s
hav? b??n sugg?st?d to quantify liv?r iron ?x??ss. This s?nsitivity mak?s MRI
th? most a??urat? routin? imaging pro??dur? to ass?ss h?pati? iron ?ont?nt. B??aus?
of th? paramagn?ti? prop?rti?s of iron, magn?ti? r?sonan?? signal diminish?s in
liv?r as iron ?on??ntration in?r?as?s (Fig.17,18).  (Gandon ?t al.,2004).

 

 

 

 

Fig.17: In this t??hniqu?, s?v?ral spin-??ho
imag?s ar? a?quir?d with in?r?asing ??ho tim?s. Imag?s ar? subs?qu?ntly pro??ss?d
to ?stimat? th? T2 r?laxation rat? at ?a?h vox?l. ?xampl?s show T2 maps from a
normal volunt??r without iron ov?rload (top), and from a pati?nt with iron ov?rload
(bottom). (H?rnando ?t al .,2014).

 

 

·       
MRI ?an ?xploit th? paramagn?ti? prop?rti?s of tissu?
iron to provid? dir??t, non-invasiv? iron ass?ssm?nts and ?lini?ally this has b??n
a?hi?v?d by ass?ssing th? T2 and T2* r?laxation param?t?rs. Magn?ti? r?sonan??
do?s not imag? th? iron dir??tly but inst?ad imag?s wat?r protons as th?y
diffus? n?ar iron d?posits in th? tissu? of int?r?st. Th? iron a?ts as small
magn?ts, d?stroying th? homog?n?ity of th? magn?ti? fi?ld in iron-lad?n tissu?s.
Th? moving wat?r protons ?xp?ri?n?? signifi?antly diff?r?nt magn?ti? profil?s
and b??am? d?syn?hroniz?d from on? anoth?r. This ?aus?s th? imag? to dark?n at
a rat? proportional to th? iron ?on??ntration. (Fahmy ?t al .,2015).

·       
Th?
basis of using MRI for iron d?t??tion is that iron a???l?rat?s T2 r?laxation
and T2* signal d??ay, th?r?by ?ausing signal loss on T2w spin ??ho and T2*w
gradi?nt ??ho MR imag?s. Th? T1-short?ning ?ff??t may b? diffi?ult to obs?rv?
on ?lini?al MR imag?s b??aus? th? T? is v?ry short. In ?lini?al pra?ti?? th?r?for?,
T1 w?ight?d imaging is not us?d to d?t??t iron. Th? T2 and T2* short?ning ?aus?d
by iron ?an b? d?t??t?d by ?onv?ntional MRI using T2w or T2*w imag?s. Th? d?gr??
of signal loss d?p?nds on th? amount of iron and th? ??ho tim?, in g?n?ral th?
gr?at?r th? ??ho tim?, th? gr?at?r th? signal loss (Fig.18). (?laud?
and S?ott.,2012).

 

Fig.18: T2- or T2*-w?ight?d imag?s ?nabl?
qualitativ? ass?ssm?nt of liv?r iron. Imag?s show r?pr?s?ntativ? T2- and T2*-w?ight?d
imag?s in pati?nts with diff?r?nt l?v?ls of iron ov?rload. (H?rnando ?t al .,2014).

 

 

·       
Th? r?sults of ?xamination of unaff??t?d subj??ts show that
th? h?pati? par?n?hyma d?monstrat?s high?r signal int?nsity than that of th?
paraspinal mus?ulatur? with all s?qu?n??s. Slight to mod?rat? iron ov?rload is
b?tt?r id?ntifi?d and ?valuat?d on th? GR? imag?s obtain?d with long?r ??ho tim?s,
whi?h d?monstrat? a d??r?as? in th? signal int?nsity of th? liv?r par?n?hyma in
a d?gr?? proportionat? to th? s?v?rity of h?pati? iron ov?rload (Fig.19). (Mar?ony ?t al.,2009).

a     
                                              b                                     

  

 

 

 

 

 

?

 

Fig.19: GR? T2*-w?ight?d MR imaging p?rform?d
in a d?di?at?d study to inv?stigat? iron ov?rload. (a) On an axial imag? of a h?althy subj??t,
th? liv?r is hyp?rint?ns? ?ompar?d with paraspinal mus?ulatur?. (b) Axial imag? of a subj??t with slight
iron ov?rload d?monstrat?s a mild d??r?as? in th? signal int?nsity of th? liv?r
and spl??n (dark?r than th? paraspinal mus?ulatur?). (?) Axial imag? of a pati?nt with s?v?r?
iron ov?rload d?monstrat?s a???ntuat?d d??r?as? in th? liv?r signal int?nsity.
(Mar?ony ?t al.,2009).

·       
Th? pro??dur? w? propos? has s?v?ral advantag?s ov?r
liv?r biopsy, r?pr?s?nting a dir??t, non-invasiv? and saf? t??hniqu? that ?an b?
p?rform?d qui?kly. Unlik? liv?r biopsy, it do?s not r?quir? pr?op?rativ? bio?h?mi?al
and ??hographi? ass?ssm?nt nor admission, thus it is mu?h l?ss ?ostly and ?asily
a???pt?d by pati?nts. (Gandon ?t al.,2004).