Nucl ear I nst rument s and Met hods in Physi cs Resear ch B71 ( 1992) 209- 213 Nort h-Hol l and Feasi bi l i t y of in vi vo t i ssue char act er i sat i on by Compt on scat t er i ng pr of i l e measurement s A. Tar t ar i ", E. Casnat i ", J . Fel st ei ner ', C . Bar al di " and B . Si ngh Di part i ment o di Fi si ea Unr r er si t d, 1- 4410( 1 Fer r ar a, I t al y n Depar t ment of Physi cs, Tcchni on - I sr ael I nst i t ut e of Technol ogy, 32000 Hinfit, I sr ael ` Depar t ment of Physi cs, Punj abi Uni ver si t y, Pat i al a- 147002 I nel i a Recei ved 13 November 1991 and in r evi sed f or m 5 Mar ch 1992 The aut hor s i nvest i gat e a t echni que f or t he char act er i sat i on of bi ol ogi cal t i ssues, based on ener gy anal ysi s of Compt on scat t er ed phot ons. The i nci dent beamconsi st s of 59 . 54 keV phot ons and a backscat t er geomet ry is used. Compar ed to t he t echni que based on t he r at i o of phot ons coher ent l y scat t er ed due to t he Rayl ei gh ef f ect and t hose i ncoher ent l y scat t er ed due to t he Compt on ef f ect , t he pr esent t echni que pr ovi des si m i l ar r esul t s f or m i ner al cont ent eval uat i on, with an er r or l ower t han 1%. However it al l ows t he det er m i nat i on of f at cont ent ina sof t t i ssue mat ri x - even in t he cases in whi ch t he Rayl ei gh peak is not measurabl e - al t hough t he er r or can rise up to 3%r . 1 . I nt r oduct i on The r at i o R, = l r / 1, of phot ons coher ent l y scat - t er ed due to t he Rayl ei gh ef f ect ( 1, ) and t hose i ncoher - ent l y scat t er ed duc to t he Compt on ef f ect ( 1, ) has Cor r espondence to : Dr . A. Tar t ar i , Di part i ment o di Fi si ca Uni ver si t i a, Fer r ar a 1- 44100, I t al y. a r é a V á 10-1 10 s pr oved usef ul in t he "in vi vo" char act er i sat i on of t i s- sues in t erms of bone m i ner al and sof t t i ssue cont ent [ 1- 41. Thi s t echni que m i ni m i ses t he possi bi l i t y of sys- t emat i c uncer t ai nt i es in t he eval uat i on of r el evant quant i t i es such as scat t er i ng vol ume and at t enuat i on of i nci dent and scat t er ed beams . Such a t echni que has al so been appl i ed to f at cont ent eval uat i on [ 5, 61, t hough no ext ensi ve i nvest i gat i on has been per f or med to our knowl edge . The use of hi gh scat t er i ng angl es i mprove% 1O9 ~~ TT 44 52 60 54 57 844 Ener gy ( keV) Ener gy ( keV) Fi g. 1. ( a) Wei ght ed Compt on cr oss sect i on pr of i l es of s ome wet cor t i cal bone el ement al component s . The r esul t s ar e f or 59, 54 keV i nci dent phot ons and 120° scat t er i ng angl e . A, cal ci um; B, oxygen ; C, car bon; D, hydr ogen . Ar r ow, Ca K- shel l Compt on edge. ( b) Hi gh moment um t r ansf er r egi on of 120' Compt on scat t er ed phot ons with 59 . 54 keV i nci dent phot ons. A, wet cor t i cal bone; B, muscl e; C, pl exi gl as ; D, f at ; O, adi pose t i ssue; v wat er . Si ngl e ar r ow, Ca K- shel l Compt on edge ; doubl e ar r ow, P K- shel l Compt on edge . 0168- 583X/ 92/ $115 . 00 © 1992 - El sevi er Sci ence Publ i sher s B.V. Al l r i ght s r eser ved BeamI nt er act i ons with Mat eri al s &At oms