Geological Society, London, Special Publications 2003 Mees 1 6

8/13/2019 Geological Society, London, Special Publications 2003 Mees 1 6

1/7

Geological Society, London, Special Publications

doi: 10.1144/GSL.SP.2003.215.01.01p1-6.

2003, v.215;Geological Society, London, Special PublicationsF. Mees, R. Swennen, M. Van Geet and P. JacobsgeosciencesApplications of X-ray computed tomography in the

serviceEmail alerting

new articles cite this articleto receive free e-mail alerts whenhereclick

requestPermission

part of this articleto seek permission to re-use all orhereclick

Subscribe

CollectionLondon, Special Publications or the Lyell

to subscribe to Geological Society,hereclick

Notes

The Geological Society of London 2014

by guest on January 21, 2014http://sp.lyellcollection.org/Downloaded from by guest on January 21, 2014http://sp.lyellcollection.org/Downloaded from
http://www.lyellcollection.org/cgi/alertshttp://www.geolsoc.org.uk/permissionshttp://www.lyellcollection.org/site/subscriptionshttp://sp.lyellcollection.org/http://sp.lyellcollection.org/http://sp.lyellcollection.org/http://sp.lyellcollection.org/http://sp.lyellcollection.org/http://sp.lyellcollection.org/http://sp.lyellcollection.org/http://www.lyellcollection.org/site/subscriptionshttp://www.geolsoc.org.uk/permissionshttp://www.lyellcollection.org/cgi/alerts


2/7

Applications of X ray com puted tomography in the geosciencesF . M E E S l , R . S W E N N E N 2, M . V A N G E E T 2 & P . J A C O B S 1

1Department of Geology and Soil Science, Ghent University, Krijgslaan 281 8,B-9000 Ghent, Belgium (e-mail: [email protected])2 Physico-chemical Geology, K.U. Leuven, Celest(jnenlaan 200C, B-3001 Heverlee, Belgium

3 SCK-CEN, Waste & Disposal Department, Boeretang 200, B-2400 Mol, BelgiumAbstract X-ray com puted tom ography (CT) is a non-des truct ive technique with wide appl i -cations in various geological disciplines. It reveals the internal structure of objects, deter-mined by var ia t ions in dens i ty and a tomic compos i t ion . Large numbers of para l le l 2Dsections can be ob tained, which allows 3D imaging of selected features . I m po rtan t applica-tions are the s tudy o f porosity and fluid f low, applied to investigations in the f ields of petro-leum geology, rock m echanics and soil science. Expected future developm ents include thecom bined use o f CT systems with different resolutions, the wider use of related X -ray tech-niques and the integ ration of CT d ata w ith results o f compatible non-destructive techniques.

X - r a y c o m p u t e d t o m o g r a p h y ( C T ) i s a n o n -d e s t ru c t i v e t e c h n i q u e t h a t a l l o w s v i s u a li z a t i o n o ft h e i n t e r n a l s t r u c t u r e o f o b j e ct s , d e t e r m i n e dm a i n l y b y v a r i a t i o n s i n d e n si t y a n d a t o m i c c o m -p o s i t i o n . I t r e q u i r e s t h e a c q u i s i t i o n o f o n e - o rt w o - d i m e n s i o n a l r a d i o g r a p h s f o r d i f f e re n t p o si -t i o n s d u r i n g s te p -w i se r o t a t i o n a r o u n d a c e n t r a la x i s , w h e r e b y e i t h e r t h e s o u r c e a n d d e t e c t o r o rt h e s a m p l e a r e m o v e d . T h i s i s f o l l o w e d b y t h er e c o n s t r u c t i o n o f t w o - d i m e n s i o n a l c r o s s -s e c t io n sp e r p e n d i c u l a r t o t h e a x is o f r o t a t i o n .C T i m a g e s r e c o r d d i f f e r e n c e s i n t h e d e g r e eo f a t t e n u a t i o n o f t h e X - r a y s, w h i c h i s m a t e r i a l -a n d e n e r g y - d e p e n d e n t . T h e i n t e r a c t i o n s t h a t a r er e s p o n si b l e f o r t h i s a t t e n u a t i o n a r e m a i n l y C o m p -t o n s c a t t e r i n g a n d p h o t o e l e c t r i c a b s o r p t i o n . T h ec o n t r i b u t i o n o f t h e p h o t o e l e c t r i c ef fe c t d e p e n d so n t h e e f fe c ti v e a t o m i c n u m b e r a n d i s e s p e c ia l lyi m p o r t a n t a t l o w e n e rg i es . A t h i g h e n e r g ie s , th eC o m p t o n e ff ec t p r e d o m i n a t e s a n d a t t e n u a t i o n i sm a i n l y d e t e r m i n e d b y d e n s i t y .X - r a y C T w a s d e v e l o p e d a s a m e d i c a l im a g -i n g t e c h n i q u e i n t h e e a r l y 1 9 7 0 s ( H o u n s f i e l d1972 , 1973 ) . Th e po s s ib i l i ty o f it s u s e in geo logya n d e n g i n e e r i n g w a s s o o n r e c o g n i s e d , r e s u l ti n gi n l ar g e n u m b e r s o f p u b l i c a t io n s f r o m t h e e a r ly1 98 0s o n w a r d s . E a r l y a p p l i c a t i o n s in c l u d e s t u -d ie s in the f i e ld s o f s o i l s c i ence (P e t rov ic et al.1 9 8 2 ; H a i n s w o r t h & A y l m o r e 1 9 8 3 ) , m e t e o r i t i c s( A r n o l d et al. 1 9 82 ), p e t r o l e u m g e o l o g y ( V i n e g a r1 9 8 6 ; V i n e g a r & W e l l i n g t o n 1 9 8 6 ) , p a l a e o n t o l -o g y ( H a u b i t z et al. 1 98 8) , g e o t e c h n i c s ( R a y n a u det al. 1 98 9) a n d s e d i m e n t o l o g y ( K e n t e r 1 98 9) .I n t h i s i n t r o d u c t o r y p a p e r , w e p r e s e n t s o m eg e n er a l i n f o r m a t i o n a b o u t t h e t e c h n iq u e a n d a

b r i e f o v e r v i e w o f i t s a p p l i c a t i o n s i n g e o l o g y ,w i t h r e f e r e n c e s t o s o m e r e c e n t s t u d i e s . M o r ed e t a i l e d i n f o r m a t i o n c a n b e f o u n d i n r e c e n tr e v ie w a rt i cl e s b y D u l i u ( 1 9 99 ) a n d K e t c h a m &C a r l s o n ( 2 0 0 1 ) .A c q u i s i t i o n o f t r a n s m i s s i o n d a t aT h e b a s i c c o m p o n e n t s o f X - r a y C T s c a n n e r s a rea n X - r a y s o u r c e , a d e t e c t o r a n d a r o t a t i o n s y s -t e m . V a r i o u s p o s s i b l e c o n f i g u r a t i o n s e x is t , w h e r e -b y t h e s e le c t ed c o n f i g u r a t i o n i s d e t e r m i n e d b ys a m p l e s i z e a n d t h e d e s i r e d r e s o l u t i o n , b e s i d e sa v a i l a b i l i t y a n d a c c e ss r e s t r i c t i o n s . I d e a l l y , t h eX - r a y b e a m s h o u l d b e p a r a l l e l r a t h e r t h a n f a n -o r c o n e - s h a p e d ( w i t h a f i n i t e s i z e o f t h e o r i g i n ) ,i n w h i c h c a s e t h e r e s o l u t i o n i s o n l y d e t e r m i n e db y d e t e c t o r q u a l i t y . H i g h r e s o l u t i o n ( 1 0 ~ tm ) c a na l s o b e a t t a i n e d w i t h m i c r o f o c u s X - r a y t u b e s .A n o t h e r a s p e c t o f a c q u i s i t i o n is t h e e n e r g y s p e c -t r u m o f t h e X - r a y s o u r c e. U n l e s s t h e X - r a y s a r ep r o d u c e d b y r a d i o a c t i v e d e c a y, t h e y a r e a l w a y sp o l y c h r o m a t i c w i th a w i d e r a n g e i n e n e r g y . T h i sc o m p l i c a t e s q u a n t i t a t i v e a n a l y s i s a n d c r e a t e sa r t e f a c t s i n t h e C T i m a g e s , d u e t o t h e s t r o n g e ra t t e n u a t i o n o f X - r a y s w i t h l o w e r e n e rg i e s. M o n o -c h r o m a t i s a t i o n b y d i f f r a c t i o n e l i m i n a t e s t h e s ep r o b l e m s , b u t i n v o l v e s a g r e a t d e c r e a s e i n i n t e n -s i t y a n d i s t h e r e f o r e o n l y f e a s i b l e f o r s y s t e m s w i t hh i g h i n i t i a l i n t e n s i t ie s , s u c h a s l i n e a r e l e c t r o na c c e l e r a to r s a n d s y n c h r o t r o n i n s ta l l a t io n s .M o s t X - r a y C T s t u d ie s o f g e o l o g ic a l m a t e -r i a l s a r e c a r r i e d o u t u s i n g m e d i c a l s c a n n e r s o fd i f fe r e n t g e n e r a t io n s , w h i c h d i ff e r m o s t l y i n c o n -f i g u r a t i o n o f th e s o u r c e a n d d e t e c t o rs . T h e h i g h e s t

From MEE S F . SWENNEN R., VAN GEET M. & JACOBS P. (eds) 2003. Applications of X-ray Computed Tomog-raphy in the Geosciences.Geolog ical Society, Lond on, Special Publications, 215, 1-6. 0305-8719/03/$15. 9 TheGeological Socie ty of London .

by guest on January 21, 2014http://sp.lyellcollection.org/Downloaded from
http://sp.lyellcollection.org/http://sp.lyellcollection.org/http://sp.lyellcollection.org/


3/7

2 F . M E E S E T A Lre so lu t i on t ha t can be ob t a ined wi th m ed ica lscanne rs i s ra the r l ow , i n t he o rde r o f 600 lam 600 pm 1 m m .S canners t ha t have be en deve loped spec if i ca l lyfo r m a te r i a l re sea rc h a re now a l so ava i lab l e , bo thw i t h f a n - b e a m a n d c o n e - b e a m c o n f i g u r a t i o n s .T h e l a t t e r al lo w t h e a c q u i s it io n o f d a t a f o r m a n ycross -sec t i ons a t t he sam e t im e , bu t t he i r u seinvo lves m ore com pl i ca t ed recons t ruc t i on p roce -d u r e s . T h e a d v a n t a g e s o f C T s y s te m s f o r m a t e r i a lre sea rch i nc lude t he poss ib i l i t y o f u s ing h ighe rX-ray i n t ens i t i e s and the poss ib i l i t y o f a t t a in ingh i g h e r r e s o l u t i o n s b y u s i n g m i c r o f o c u s X - r a yt u b e s a n d b y r o t a t i n g t h e s p e c i m e n r a t h e r t h a nthe sou rce and d e t ec to r . C T im ages o f t he h ighes tq u a l i ty a r e o b t a i n e d w i th s y n c h r o t r o n r a d i a t io n ,w h i c h h a s t h e a d v a n t a g e o f n e a r - p a r a l l e l i s m o ft h e X - r a y b e a m a n d t h e p o s s i bi li ty o f m o n o -c h r o m a t i s a t i o n . A d r a w b a c k o f h ig h - r e s o lu t i o nsys t em s i s t ha t h igh re so lu t i ons can on ly beo b t a i n e d f o r s m a l l s a m p le s , e .g . < 2 m m d i a m e t e rfo r a 5 ~tm re so lu t i on i n m ic ro focus CT scans.Reconstruct ion of CT imagesT h e m a t h e m a t i c a l p r i n ci p le s o f b a c k p r o j e c t io np r o c e d u r e s r e q u i r e d f o r r e c o n s t r u c t i o n h a v e b e e nknown fo r a l ong t im e . In X-ray CT, a p re -r e c o n s t r u c ti o n t r a n s f o r m a t i o n o f t h e r a d i o g r a p h si s r e q u i re d t o e n h a n c e c o n t r a s t a n d s h a r p n e s s o fthe CT im ages . Th i s is done by ap p ly ing a d ig i t alf i l t e r t o t he ob t a ined s igna l s . Var ious t ypes o ff i lt e rs can be u sed fo r t h i s ope ra t i on . To be ab l eto pe r fo rm a recons t ruc t i on fo r a spec i f i c c ross -sec t i on , da t a fo r t he en t i re ob j ec t m us t be ava i l -able for th is level , in radiographs for a l l d i fferentang les . The ob j ec t shou ld be com ple t e ly i n t hef ie ld o f v iew fo r each o f t hese ang le po s i t ions ,i . e . su r rounded by a i r i n each rad iog raph , wh ichl im i t s t he m ax im um sam ple s i ze .Im age qua l i t y op t im iza t i on requ i re s a reduc -t i on o f a r te fac t s , wh ich a re i nh e ren t t o t he t ech -n i q u e o f X - r a y C T . S e v er a l c o m m o n t y pe s o fa r t e fac t s can a l ready be reduced to som e ex t en tby op t im i s ing acqu i s i t i on cond i t i ons , bu t a fu r -t he r reduc t ion du r ing recons t ruc t i on i s o f t enneeded. This i s the case for: ( i ) misa l ignmenta r t e fac t s , re l a t ed t o an im per fec t a l i gnm en t o fsou rce , de t ec to r and ax i s o f ro t a t ion ; ( ii ) ri ng a r t e -fac ts , re la ted to detec tor defects ; ( i i i ) s tar ar te-fac t s , re la t ed t o t he p re sence o f dense ob j ec ts ; and( iv ) l ine a r t e fac t s , re l a t ed t o t he p re sence o f anom -a lous ly b r igh t p ixe l s i n t he rad iog raph s . T he m o s ti m p o r t a n t a r t e f a c t s i n C T i m a g e s a r e r e l a t e d t o'bea m ha r den ing ' , wh ich re fe rs t o t he p re fe ren t i a la t t e n u a t i o n o f lo w - e n e r g y X - r a y s w h e n a p o l y -c h r o m a t i c X - r a y b e a m p a s s e s t h r o u g h a n o b j ec t .Th i s e f fec t can be reduce d to som e ex t en t by u s ing

a hardware f i l te r , which involves a loss in in ten-s it y o f th e X - r a y b e a m a n d a l o w e r in g o f co n -t r a s t i n t h e r a d i o g r a p h s . F o r b e a m h a r d e n i n ga r t e fac t reduc t ion du r ing recons t ruc t i on , l i nea r -i s a t i o n p r o c e d u r e s a r e h i g h l y r e c o m m e n d e d f o rm o n o m i n e r a l ic s y st em s ( H a m m e r s b e r g M a n -ga rd 1998) . F o r po lym ine ra l i c sy s t em s , a dua le n e r g y a p p r o a c h a l lo w s a d r a m a t i c im p r o v e m e n ti n i m a g e q u a l i t y ( D e M a n e t a l 2001).The deve lopm en t o f s im u la to rs i s a u se fu la p p r o a c h f o r a r t e f a c t r e d u c t i o n , a s t h e y a l l o wop t im i sa t i on o f t he cho i ce o f acqu i si t i on pa ra -m e te rs i n func t ion o f t he ob j ec t to be s tud i ed .A m a j o r p r o b l e m w i t h t h i s a p p r o a c h i s t h ef a c t t h a t t h e X - r a y s p e c t r u m i s o f t e n u n k n o w na n d v e r y d i f f i c u l t t o m e a s u r e ( H a m m e r s b e r ge t a l 1998).

pplications in the geosciencesS u i t a b l e m a t e r i a l sX - r a y C T c a n b e u se d f o r q u a l i ta t iv e a n d q u a n t i -t a t i ve ana lys i s o f i n t e rna l fea tu res o f geo log i ca lm a te r i a l s , i f t hose fea tu res a re m a rke d by su ff i-c i en t ly g rea t d i f fe rences i n a tom ic com pos i t i onand /o r dens i t y .A s t rong con t ra s t m a in ly ex i s t s be tween so l i dp h a s e s a n d t h e a t m o s p h e r e . A n i m p o r t a n t a p p li -ca t i on o f X-r ay CT i s, the re fo re , t he s tudy o fpo ros i t y , i nc lud ing po ros i t y rep resen t ed by po reswi th d im ens ions be low the re so lu t ion o f t he CTim ages . Exam ples o f app l i ca t i ons i n t h i s f i e ldinc lude s tud i e s o f so il m ac ro -po ro s i t y (e .g . P e r re te t a l 1999) and re se rvo i r rock cha rac t e r i za t i on(e .g . Va n G ee t e t a l 2000). The cont rast wi th thea tm osph ere i s a l so u sed a s a m eans o f v i sua li z ingthe ex t e rna l m orpho logy o f ob j ec t s , e . g . fo r su r -face roughness ana lys i s (e .g . F oh re r e t a l 1999)o r f o r d o c u m e n t i n g t h e m o r p h o l o g y o f fo s si ls(e.g. Rogers 1999).The con t ra s t be tween l i qu id phases and thea tm osphere f i nds w ide app l i ca t i ons i n t he s tudyof hydr aul ic pro pert ies , bo th in so il science (e .g .M oo ney 2002) and pe t ro l eum geo logy (e .g . P e t e rse t a l 1996) . Recen t t echno log i ca l im provem en t sa l l ow the d i sc r im ina t ion be tween em pty and(water-)f i l led pores (Roels e t a l in press) . In ear-l i e r s t ud i e s , heavy e l em en t s had t o be added a st race rs (e .g . Mor i e t a l 1999), which has a lso beend o n e t o m o n i t o r g a s t r a n s p o r t ( e . g . K a r a c a nOkandan 2001) .V i sua l i za t i on o f the d i s t r i bu t ion o f d i f fe ren tso li d phases gene ra l ly requ i re s p ronoun ced va r i a -t i ons i n a tom ic com pos i t i on . The few pub l isheds tud i e s m a in ly conce rn m a te r i a l s w i th i ron -bea r -ing min era ls (e .g . Tivey 1998; Spiess e t a l 2001)o r m ine ra l s w i th excep t iona l ly l ow a t t enua t ion



4/7

A P P L I C A T I O N S O F X - R A Y C T I N G E O S C I E N C E S 3va lues (e .g . Tay lo r e t a l . 2000) . S ynch ro t ron CTw i t h m o n o c h r o m a t i c X - r a y s i s r e q u i r e d t o d i ff e r-en t i a t e be tween l e ss con t ra s t i ng m a te r i a l s .F o r m a n y a p p l i c a t i o n s , a c o r r e l a t i o n w i t hresu l t s ob t a ined by m ore t rad i t i ona l t echn iques ,such a s op t i ca l m ic roscopy and scann ing e l ec -t ron m ic roscopy , i s requ i red (e .g . Van Gee t e t a l .2001).N o n - d e s t r u c t i v e a n a l y sOn e o f t he s t reng ths o f X-r ay C T i s i ts en t i re lynon-des t ruc t i ve na tu re , a t l ea s t a t t he sca l e o f t hesam ple . Th i s a spec t rende rs t he t echn ique h igh lysu i t ab le fo r m on i to r ing o f ac ti ve p rocesses , suchas wa te r and so lu t e m ovem en t (e .g . Kas t ee l e t a l .2000; Perre t e t a l . 2000) and de fo rm a t ion (e .g .Besuelle e t a l . 2000; Wong 2001). These experi -m en t s can be ca r r i ed ou t a t e l eva t ed p ressu resa n d t e m p e r a t u r e s , w h i c h i s a m a j o r a d v a n t a g eove r m ore conven t iona l t echn iques , e .g . i n s t u -d i e s o f f rac tu re cha rac t e r i s t i c s a t re se rvo i r con -d i t ions . The non -des t ruc t i veness o f the t echn iquea l so a l l ows ana lys i s o f va luab l e o r un ique speci -mens, such as fossi l s (e .g . Rowe e t a l . 2001) andm eteo r i t e s (e .g . Gnos e t a L 2002).3 D r e n d e r in gC T a n a l ys i s c a n p r o d u c e l a r ge n u m b e r s o f co n -t i guous pa ra l l e l c ro ss -sec t i ons , wh ich a l l ows 3Dvi sua l i sa t i on o f se l ec t ed fea tu res and quan t i f i ca -t i o n o f 3 D v o l u m e s . E x a m p l e s o f a p p l i c a t i o n stha t exp lo i t t h is a spec t o f X-ra y CT inc ludes tud i e s o f so il m a c ro por os i t y (e .g . Capowiez e t a l .1998; P ierre t e t a l . 2002) and rock t ex tu res (e .g .De n i son Car l son 1997).

T h i s v o l u m eThe open ing pape r i n t he p re sen t co l l ec t i on , by

a r l so n e t a L , g ives an ex t ens ive i l l u s t ra t i on o fthe poss ib l e app l i ca t i ons o f X-r ay C T in i gneousa n d m e t a m o r p h i c p e t r o l o g y , m e t e o r i t i c s a n dp a l a e o n t o l o g y . T h e p a p e r , w h i c h i s b a s e d o ns tud i e s ca r r i ed ou t a t t he H igh - re so lu t i on X-rayC T F a c i li ty o f th e U n i v e r s it y o f T e x a s a t A u s t i n ,d e m o n s t r a t e s h o w C T a n a l y s e s c a n c o n t r ib u t e t owide r i nves t i ga t i ons by p rov id ing i n fo rm a t iont h a t c a n n o t b e o b t a i n e d b y o t h e r m e t h o d s . I n asecond rev i ew, Ak in Kovseek d i scuss app l i ca -t i ons o f CT in pe t ro l eum geo logy , cove r ingm e a s u r e m e n t s o f p o r o s i t y a n d m u l t i p h a s e f lu i df low cha rac t e r i s ti c s . Exp e r im e n ta l des ign andim age p rocess ing m e thods a re a l so cove red .CT ana lyses o f po re cha rac t e r i s t ic s a re t he sub -j ec t o f t he nex t fou r con t r i bu t ions . Jones e t a L

p r e s e n t t h e r e s ul ts o f s y n c h r o t r o n C T s t u di e s o fva r ious po rous m a te r i a l s , ca r r i ed ou t a t t h ree d i f -fe ren t re sea rch fac i l i t i e s (Brookhaven , Argonnea n d G r e n o b l e ) . T h e y a d d r e s s t h e p o t e n t i a l o fh igh re so lu t i on (2 -10 ~ tm ) sync h ro t ro n C T a na l -y s i s fo r po ros i t y cha rac t e r i za t i on i n unconso l i -d a t e d s e d i m e n t s a n d s a n d s t o n e s a m p l e s , u s i n gW o o d ' s m e t a l ( a l ow - m e l t in g B i - P b - S n - C d a l l oy )f o r c o n t r a s t e n h a n c e m e n t i n o n e e x a m p l e . T h es tudy a l so i l lu s t ra t e s t he u se o f X- ray f l uo res -c e n c e t o m o g r a p h y i n e n v i r o n m e n t a l g e o c h e m -i s t ry s tud i e s. Van G ee t e t a l . presen t t he re su l t s o fp o r o s i t y m e a s u r e m e n t s w i t h m i c r o f o c u s C T ,w h i c h a r e c o m p a r e d w i t h r e s u l t s o b t a i n e d b ym o r e t r a d i t i o n a l m e t h o d s . T h e a u t h o r s d e s c r i b ep rocedu res fo r a r t e fac t reduc t ion , wh ich i s neces -sa ry t o a l l ow q uan t i t a t i ve ana lys i s o f g rey va lues .The y d i scuss t he u se o f a l i nea r i za t ion t echn iquef o r m o n o m i n e r a l i c r o c k s , s u c h a s l im e s t o ne . F o rh e t e r o g e n e o u s m a t e r i a l s , a d u a l e n e r g y a p p r o a c hi s p ropo sed . Vanders t een e t a l . exam ine d i f fe ren tm e t h o d s f o r t h e q u a n t if i c a t io n o f f r a c t u r e a p e r -t u r e s b y m i c r o f o c u s C T , u s i n g p h a n t o m o b j ec t sand op t i ca l m ic roscopy fo r ca l i b ra t i on and ve r i fi -ca t i on . Th e i r re su l t s a re o f im p or t anc e i n i nves ti -g a t i o n s r e q u i r in g q u a n t i t a t i v e c h a r a c t e r i z a t i o n o fp l ana r vo ids , e .g . i n so i l re sea rch and re se rvo i rs tudies . Sel lars e t a l . desc r ibe s tud i es o f f rac tu restha t deve loped by app ly ing t r i ax i a l s t re ss t o cub i cq u a r t z i te b l o c k s w i t h t a b u l a r g a p s . T h e f r a c t u r ep a t t e r n s r e v e a l e d b y 3 D r e n d e r i n g o f C T d a t a h e l pt o v e r i f y t h e p r e d i c t i o n s m a d e b y n u m e r i c a lm ode l s t ha t a re cu r ren t ly u sed t o a ssess f rac tu red e v e l o p m e n t a r o u n d d e e p m i n i n g e x c a v a t i o n s .T h e a u t h o r s a l s o c o m m e n t o n l i m i t a t i o n s i m -posed by t he p re sence o f a r t e fac t s , wh ich h inde rt h e p r o d u c t i o n o f 3 D i m a g e s o f f r a c tu r e s .Voge l Brown p resen t a geos t a t i s ti ca l a ssess-m e n t o f v a r i a t i o n s in g a m m a r a y a t t e n u a t i o n i nscans w i th d i f fe ren t re so lu t i ons . The i r s t udyassesses he t e rogene i t i e s i n bu lk dens i t y t ha toccu r i n a do lom i t e fo rm a t ion a t a nuc l ea r was t ed i sposa l s i t e . The au tho rs p rov ide an eva lua t i ono f t he e f fec t o f re so lu t i on and sca l e on sem iva r -i o g r a m p a r a m e t e r s .The nex t fou r pape rs focus on f l u id f l ow inrocks . G~ raud e t a l . e x a m i n e t h e h y d r a u l i c p r o p -e r t i e s o f a rock wi th ve ry l ow po ros i t y by us ingcap i l l a ry sa tu ra t i on expe r im en t s . Us ing a f l u idwi th h igh a t t enua t ion va lues , t hey a re ab l e t od o c u m e n t d i f f e r e n c e s i n m i c r o p o r o s i t y b e t w e e nd i f fe ren t cons t i t uen t s o f a g ran i t e , wh ich a f fec tf l ow pa t t e rn s w i th in t he t e s t sam ples . H i rono e t a Lu s e X - r a y C T f o r d i r e c t i m a g i n g o f f l u i d f l o wa l o n g f a u l t s i n h e t e r o g e n e o u s d e f o r m e d r o c k s .T h e s e l a b o r a t o r y e x p e r i m e n t s , u s i n g K I a s at race r , he lp t o c l a r i fy t he re l a t i onsh ip be tween thet ex tu re and hydrau l i c p rope r t i e s o f fau l t zones .



5/7

4 F. MEES E T A LRousset-Tournier e t a L present a study of watermigration during drying experiments in sand-stones. Their findings show that drying behaviouris influenced by the method of saturation. Rniz deArgandofia e t a l describe the patterns of wateruptake during the total immersion of a porouslimestone, showing that CT helps to relate watermovement to petrographical characteristics of therock. Both of the last two studies address issuesthat are impor tant in the field of cultural heritageconservation.In a first of three studies of soil behaviour,A nders o n t a L describe the determination ofporosity and hydraulic conductivity in soils byX-ray CT measurements during solute break-through experiments. Differences between mea-sured values and simulated breakthrough curvesderived by a finite element method are explainedby the existence of small-scale heterogeneities,which can be assessed by X-ray CT. Rogasik e t a Luse X-ray CT to study variations in structure,macroporosity and calculated bulk density forsoils with different textures and under differentmanagement systems. A quantitative study ofcompaction around earthworm burrows is alsoincluded. Delerue e t a L present a novel quantita-tive method for 3D image analysis of soil macro-porosity using CT images to obtain calculatedhydraulic conductivity and permeability values.The method is based on the segmentation of thepore space into elementary objects and quanti-fication of their characteristics, followed by thecreation of a network model t hat allows conduc-tivity calculations.Two papers describe the results of compres-sion tests using specially designed triaxial cells,both providing detailed information on theexperimental set-up. Karacan e t a L describe atriaxial cell that permits permeability measure-ments during deformation. Using X-ray CT tomonitor deformation experiments with this cell,the authors evaluate changes in porosity, perme-ability and fluid flow under conditions of brittleand ductile failure. Thomson Wong describe asystem for performing triaxial tests under un-drained conditions, which they use as a means forstudying the deforma tion behaviour o f unconso-lidated sands. They discuss the observed voidratio redistributions and indicate directions forfuture research. O'Neill e t a L present a qualita-tive assessment of a test that simulates the evolu-tion of backfill material of an opencast mine.They use CT to unravel the nature of particulateinteractions undergoing creep settlement.The last group of papers illustrates the appli-cations of X-ray CT in a number of geologicaldisciplines. Flisch Becker investigate sedimen-tary and deforma tion structures in lake deposits

by CT scanning of sediment cores. They illus-trate the potentia l of CT for core analysis and thestudy of unconsolidated sediments. The contri-bution by Schreurs t a l illustrates an applicationof X-ray CT in structural geology that involvesthe CT-monitoring of deformation experimentswith sand-box models. These authors documentchanges in structure in three dimensions throughtime, which allows analysis of complex geologicalstructures in contractional and extensional set-tings. A palaeontological study is presented bySto ck V e i s , who perform micro-focus CT anal-yses of Jurassic echinoid fragments. Some of thefeatures tha t they describe are interpreted as dia-genetic modifications.

F u t u r e d e v e l o p m e n t sOne expected trend is the combined use ofvarious CT instruments, whereby a material isscanned at different resolutions. For example, arock core can be scanned at full size with a med-ical scanner at moderate resolution, followed bymicrofocus and synchrotron CT analysis of sub-samples of different sizes. Optical microscopy andscanning electron microscopy will continue to beimpor tant sources of additional information.A more widespread use can be expected forcertain special procedures that have been devel-oped for medical applications. One techniquetha t has already been used in a number of geolog-ical studies is dual energy scanning (e.g. Kalendare t a l 1987), which allows quantif ication of den-sity and effective atomic number. It involves theprocessing of scans that were recorded for ener-gies at which the relative cont ribu tions of Comp-ton scattering and photoelectric absorption aredifferent. A promising technique is 'region ofinterest' scanning, providing high resolution CTimages of a region in the interior of a sample.It requires high resolution acquisition for theregion of interest, combined with a second scan ofthe same plane for the full width o f the object, atlow resolution; the second scan is used to provideinformation about the part of the object that isoutside the field of view during acquisition for thehigh resolut ion scan (e.g. Gentle Spyrou 1990).The potential of a number of powerful tech-niques that are related to X-ray CT is still largelyunexplored fo r geological materials. They mainlyrequire a monochromatic or very intense X-raybeam, which means that they are main ly availableat synchrotron installations. Examples are fluor-escence X-ray tomography, recording elementdistributions down to trace level concentrations(e.g. Simionovici e t a l 2001); phase contrastX-ray tomography, which allows visualisationof discontinuities by phase shifts of a coherent



6/7

APPLICATIONS OF X-RAY CT IN GEOSCIENCES 5X-ray beam, in materials with low attenuationcoefficients (e.g. Cloetens et al. 1997, 1999), anddiffraction X-ray tomography, which allowsmappi ng o f variations in mineralogical composi-tion (e.g. Hall et al. 1998).An integration of X-ray CT results with dataobtained by other non-destructive techniques canbe expected to become more common. Neutrontomography is a compatible technique, becauseneutrons interact with the nuclei of atoms, where-as X-ray CT is based on an interaction withelectrons (e.g. Winkle r et al. 2002). This results inlarge differences in element sensitivity wherebyneutron tomography, in contrast to X-ray CT,is highly sensitive to elements such as hydrogenand carbon. A m ore widely used compatible tech-nique is Nuclear Magnetic Resonance (NMR)analysis, which allows imaging of fluid flow inporous media and also provides informationabout pore size distributions (e.g. WatsonChang 1997; Amin et al. 1998; Bar aka- Lokma neet al. 2001). Its use for geological materials islimited by the rather low resolution and by theproblems that can be caused by the presence ofiron compounds.Since medical CT scanners became widelyavailable, CT results for geological materialshave been successfully integ rated with ot her ana-lytical data in vari ous g eological disciplines. It isexpected that in the near future, CT will beused more and more as a routine research tool.In future studies, CT data will be obtained formuch greater numbers of samples, allowing astatistical evalu ation of a large bod y of CT results.

e f e r en c e sAMIN, M.H.G., HALL, L.D., CHORLEY, R.J.RICHARDS, K.S. 1998. Infiltration into soils, withparticular reference to its visualization and mea-surement by magnetic resonance imaging (MRI).

Progress in Physical Geography 22, 135-165.ARNOLD, J.R., TESTA, J.P.J., FRIEDMAN, P.J.KAMBIC, G.X. 1982. Computed tomographic anal-ysis of meteorite inclusions. Science 219, 383-384.BARAKA-LOKMANE, S., TEUTSCH, G. MAIN, G.2001. Influence of open and sealed fractures onfluid flow and water saturat ion in sandstone coresusing Magnetic Resonance Imaging. GeophysicalJournal International 147, 263-271.BESUELLE, P., DESRUES, J. RAYNAUD, S. 2000.Experimental characterisation of the localisationphenomenon inside a Vosges sandstone in a tri-axial cell. International Journal of Rock Mechanicsand Mining Sciences 37, 1223-1237.CAPOWlEZ,Y., PIERRET, A., DANIEL, 0., MONESTIEZ,P.KRETZSCHMAR, A. 1998. 3D skeleton recon-structions of natural earthworm burrow systemsusing CAT scan images of soil cores. Biology andFertility of Soils 27, 51-59.

CLOETENS, P., PATEYRON-SALOMI~, M., BUFFII~RE,J.Y., PEIX, G., BARUCHEL, J., PEYRIN, F.SCHLENKER, M. 1997. Observation of microstruc-ture and damage in materials by phase sensitiveradiography and tomography. Journal of AppliedPhysics 81, 5878-5886.CLOETENS, P., LUDWIG, W., BARUCHEL, J., VANDYCK, D., VAN LANDUYT, J., GUIGAY, J.P.SCHLENKER M. 1999. Holotomography: quanti-tative phase tomography with micrometer resolu-tion using hard synchrotron radiation X-rays.Applied Physics Letters 75, 2912-2914.DE MAN, B., NUYTS, J., DUPONT, P., MARCHAL, G.SUETENS, P. 2001. An iterative maximum-like-lihood polychromatic algorithm for CT. Institute ofElectrical and Electronics Engineers Transactionson Medical Imaging 20, 999-1008.DENISON, C. CARLSON, W.D. 1997. Three-dimen-sional quantitative textural analysis of metamor-phic rocks using high-resolution computed X-raytomography. 2. Application to natural samples.Journal of Metamorphic Geology 15, 45-57.DULIU, O.G. 1999. Computer axial tomography ingeosciences: An overview. Earth-Science Reviews48, 265-281.FOHRER, N., BERKENHAGEN, J., HECKER, J.M.RUDOLPH, A. 1999. Changing soil and surfaceconditions during rainfall. Single rainstorm/sub-sequent rainstorms. Catena 37, 355-375.GENTLE, D.J. SPYROU, N.M. 1990. Region of inter-est tomography in industrial applications. NuclearInstruments and Methods in Physics Research Sec-tion A, 299, 534-537.GNOS, E., HOFMANN, B., FRANCHI, I.A., AL-KATHIRI,A., HAUSER, M. MOSER, L. 2002. Sayh alUhaymir 094: A new martian meteorite from theOman desert. Meteoritics and Planetary Science37, 835-854.HAINSWORTH, J.M. AYLMORE, L.A.G. 1983.The use of computer-assisted tomography todetermine spatial distribution of soil watercontent. Australian Journal of Soil Research 21,435-443.HALL, C., BARNES, P., COCKCROFT, J.K., COLSTON,S.L., HAUSERMANN, D., JACQUES, S.D.M., JUPE,A.C. KUNZ, M. 1998. Synchrotron energy-dispersive X-ray diffraction tomography. NuclearInstruments and Methods in Physics ResearchSection B 140, 253-257.HAMMERSBERG, P. d~ MANGARD, M. 1998. Correctionof beam hardening artefacts in computerized tom-ography. Journal of X-ray Science and Technol-ogy 8, 75-93.HAMMERSBERG, P., STENSTRt)M, M., HEDTJ.ARN, H.MANGARD, M. 1998. Measurements o f absoluteenergy spectra for an industrial micro focal X-raysource under working conditions using a Comp-ton scattering spectrometer. Journal of X-rayScience and Technology 8, 5-18.HAUBITZ, B., PROKOP, M., Dt)HRING, W., OSTROM,J.H. WELLNHOFER, P. 1988. Computed tomog-raphy of Archeopterix. Paleobiology 14, 206-213.HOUNSFIELD, G.N. 1972. A method o f and appar-atus for examination of a body by radiation such



7/7

6 F . M E E S E T A L .a s X - o r g a m m a - r a d i a t i o n . B r i t i s h P a t e n t N o1.283 .915 , London.HOUNSFIELD, G .N . 1973. Com pute r i zed t ransve rse ax ia ls c a n n i n g ( t o m o g r a p h y ) . P a r t 1 : D e s c r i p t i o n o fsys t em. British Journ al of Radiology, 46, 1016-22.

KALENDAR, W ., BAUTZ, W ., FELSENBERG, D ., S0SS, C.KLOTZ, E . 1987 . Ma te r i a l s e l ek t ive Bi ldge -bu ngu n d D i c h t e r n e s s u n g m i t d e r Z w e i - S p e k t r e n -M e t h o d e . I . G r u n d l a g e n u n d M e t h o d i k . DigitaleBilddiagnose, 7, 66-72 .KARACAN, C.O . OKANDAN, E . 2001 . Ad sorp t iona n d g a s t r a n s p o r t i n c o a l m i c r o s t r u c t u r e : i nv e s ti -g a t i o n a n d e v a l u a t i o n b y q u a n t i t a t i v e X - r a y C Ti m a g i n g . Fuel, 80, 509-520.KASTEEL, R. , VOGEL, H .J . ROTH , K . 2000. F ro mloca l hydrau l i c p rope r t i e s to e f fec t ive t ranspor t i nsoil. European Jou rnal o f Soil Science, 51, 81-91.K E N T ER , J . A . M . 1 9 8 9 . A p p l i c a t i o n s o f c o m p u t e r i z e dt o m o g r a p h y i n s e d i m e n t o l o g y . Marine Geotech-nology, 8, 201-211.KETCHAM, R. A. CARLSONW.D. 2001 . Acqui s i t i on ,o p t i m i z a t i o n a n d i n t e r p r e t a t i o n o f X - r a y c o m p u t -e d t o m o g r a p h i c i m a g e r y : a p p l i c at i o n s t o t h e g e o -sciences . Com puters a nd Geosciences, 27, 381-400.MOONEY, S . J. 2002. T hree -d imen s iona l v i sua l i za t iona n d q u a n t i f i c a ti o n o f s o il m a c r o p o r o s i t y a n d w a t e rf l o w p a t t e r n s u s i n g c o m p u t e d t o m o g r a p h y . Soi lUse and Managem ent , 18, 142-151.MOR I, Y. , IWAMA, K., M ARUYAMA, T. MITSUNO, T.1999 . D i sc r imina t ing the in f luence of so i l t ex turea n d m a n a g e m e n t - i n d u c e d c h a n g es i n m a c r o p o r ef low us ing sof t X- rays . Soil Science, 164, 467-482 .PERRET, J . , PRASHER, S.O. , KANTZAS, A. LANG-FORD, C. 1999 . Thre e -d im ens ion a l quant i f i ca t iono f m a c r o p o r e n e t w o r k s i n u n d i s t u r b e d s oi l c o r e s .Soil Science Society o f America Journal, 63, 1530-1543.PERRET, J . , PRASHER, S.O. , KANTZAS, A. LANG-F O RD , C . 2 0 0 0. A t w o - d o m a i n a p p r o a c h u s i n gC A T s c a n n i n g t o m o d e l s o l u t e t r a n s p o r t i n s o i l .Journa l of Environm ental Quality , 29, 995-1010 .PETERS, E.J . , GHARBI, R. AFZAL, N. 1996 . A loo k atd i s p e r s i o n i n p o r o u s m e d i a t h r o u g h c o m p u t e dt o m o g r a p h y i m a g i n g . Journal o f Pe tro leum Sc ienceand E ngineering, 15, 23 31.

PETROVIC, A.M., SIEBERT J .E. RIEK E, P .E. 1982.Soi l bu lk dens i ty ana lys i s in th ree d imens ions byc o m p u t e d t o m o g r a p h i c s c a n n i n g . Soil ScienceSociety of America Journal, 46, 445-450 .PIERRET, A., CAPOWIEZ,Y ., BELZUNCES,L. MORAN,C . J . 2 00 2 . 3 D r e c o n s t r u c t i o n a n d q u a n t i f ic a t i o n o fm a c r o p o r e s u s i n g X - r a y c o m p u t e d t o m o g r a p h ya n d i m a g e a n a ly s i s. Geoderma, 106, 247-271 .RAYNAUD, S., FABRE, D., MAZEROLLE,F. , GERAUD, Y.LATII~RE, H .J . 1989 . Ana lys i s o f the in t e rna ls t r u c t u r e o f r o ck s a n d c h a r a c t e r i s a t i o n o f m e c h a n -i c a l d e f o r m a t i o n b y a n o n - d e s t r u c t i v e m e t h o d :X - r a y t o m o d e n s i t o m e t r y . Tectonophysics, 159,1 4 9 1 5 9 .ROLLS, S., VANDERSTEEN, K . CARMELIET, J. inp r e ss . M e a s u r i n g a n d s i m u l a t in g m o i s t u r e u p t a k ei n a f r a c t u r e d p o r o u s m e d i u m . Advances in WaterResources.

ROGERS, S .W. 1999. A l losau rus , c ro codi l e s , and b i rds :e v o l u t i o n a r y c l u e s f r o m s p i r a l c o m p u t e d t o m o g -r a p h y o f a n e n d o c a s t . Anatomical Record, 257,1 6 2 1 7 3 .ROWE, T. , KETCHAM, R.A ., DENISON,C., COLBERT, M .,Xu , X . CURRIE, P . J . 2001 . Foren s ic pa laeo n-t o l o g y : T h e A r c h a e o r a p t o r f o r g e r y . Nature, 410,539-540 .SIMIONOVICI, A. , CHUKA LINA, M ., GUNZLE R, F . ,SCHROER, C ., SNIGIREV, A ., SN1GIREVA, I., TUM -MLER, J . WEITKAMP, T. 2001. X -ra y m icro tom eb y f l u o r e sc e n c e to m o g r a p h y . Nuclear Instrumentsand Metho ds in Phys ics Research Sec t ion A , 467,8 8 9 - 8 9 2 .SPIESS, R., PERU ZZO, L., PRIOR, D .J. WH EELER, J.2 0 01 . D e v e l o p m e n t o f g a r n e t p o r p h y r o b l a s t s b ym u l t i p l e n u c l e a t i o n , c o a l e s c e n c e a n d b o u n d a r ym i s o r i e n t a t i o n - d r i v e n r o t a t i o n s . Journal o f Me ta-morphic Geology, 19, 269-290 .TAYLOR, L.A . , KELLER, R.A ., SNYDER, G.A ., WANGW .Y. , CARLSON, W .D. , HAUR1, E .H . , MCCAND-LESS, T. , KIM, K .R . , SOBOLEV, N.V . BEZ-BORODOV, S .M. 2000 . D ia m on ds and the i r mine ra linc lus ions , and wh a t they t e l l us : A de ta i l ed ' pu l l -a p a r t ' o f a d i a m o n d i f e r o u s e c l o g it e . InternationalGeology Review, 42, 959-983 .T IV EY , M . K . 1 9 9 8 . D o c u m e n t i n g t e x t u r e s a n d m i n e r a la b u n d a n c e s i n m i n i c o r e s f r o m t h e T A G a c t i v eh y d r o t h e r m a l m o u n d u s i n g X - r a y c o m p u t e d t o m -o g r a p h y . In: HER ZIG, P .M . , HUMPHRIS , S .E . ,MILLER, D. J . ZIERENBERG, R.A . (eds) Proceed-ings of the Ocean Drilling Pogram, ScientificResults , 158, 201-210.VAN GE ET, M ., SWENNEN, R. WEVERS, M . 2000.Q u a n t i t a ti v e a n a l y si s o f r e s e r v o i r r o c k s b y m i c r o -f o c u s X - r a y c o m p u t e r i s e d t o m o g r a p h y . Sedimen-tary Geology, 1 3 2 , 2 5 - 3 6 .VAN GE ET , M ., SWENNEN, R. 8~ DAV ID, P . 2001.Q u a n t i t a t i v e c o a l c h a r a c t e r i s a t i o n b y m e a n s o fm i c r o f o c u s X - r a y c o m p u t e r t o m o g r a p h y , c o l o u ri m a g e a n a l y s i s a n d b a c k s c a t te r s c a n n i n g e l e c t ro nm i c r o s c o p y . International Journal of Coal Geol-ogy, 46, 11-25.VINEGAR H . J . 1 9 8 6 . X - r a y C T a n d N M R i m a g in go f r o c k s . Journal o] Petroleum Technology, 38,257-259 .VINEGAR, H.J . WELLINGTON, S.L. 198 6. To m o-g r a p h i c i m a g i n g o f t h r e e - p h a s e f l o w e x p e r i m e n ts .Review o f Scienti f ic Instruments, 58, 96-107.WATSON, A .T . CHANG, C.T .P . 1997 . Ch arac te r i z ingp o r o u s m e d i a w i t h N M R m e t h o d s . Progress inNuclear Magnetic Resonance Spectroscopy, 31,343-386 .WINKLER, B. , KNOR R, K. , KAHLE, A. , VONTOBEL, P . ,LEHMANN, E., HENNION , B. BAYON, G. 2002.N e u t r o n i m a g i n g a n d n e u t r o n t o m o g r a p h y a sn o n - d e s t r u c t i v e t o o l s t o s t u d y b u l k - r o c k s a m p l es .European Journal o f Mineralogy , 14, 349-354.WONG, R.C .K. 2001. S t reng th of two s t ru c tured so i lsin t r i ax ia l compres s ion . International Journal forNumerical and Analytical Methods in Geomecha-nics, 25, 131-153.


Documents

Geological Society, London, Special Publications 2003 Mees 1 6