ct scanner basic

TRNG I HC BCH KHOA H NI VIN IN T - VIN THNG

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BO CO H THNG THNG TIN Y T

ti:

Tm hiu s lc v my CT scanner

Ging vin hng dn: ThS.Hong Quang Huy

Sinh vin thc hin: Nhm 13 Trng Vn Gia 20090844 ng Th Hng 20091009 Phm nh Hong 20091173 Hong Nam Phong 20092004

H Ni, 3/2013

S lc v my ct lp in ton CT scanner

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MC LC

MC LC ............................................................................................................................. 2

DANH SCH HNH V ....................................................................................................... 3 LI NI U ....................................................................................................................... 4 I. Lch s, qu trnh pht trin................................................................................................ 5

I.1. Lch s hnh thnh ....................................................................................................... 5

I.2 Qu trnh pht trin ...................................................................................................... 7 I.2.1 Cc th h my CT t 1970 n nay ..................................................................... 7

I.2.2 Ci tin v cng ngh, cc phng php chp ..................................................... 8

II. u im ca chp CT .................................................................................................... 11

III. Cu to ........................................................................................................................... 12

III.1 S khi ................................................................................................................ 12

III.2 Chi tit cc khi ....................................................................................................... 13

III.2.1 Khi chp nh .................................................................................................. 13

III.2.2 Khi my tnh ................................................................................................... 14

III.2.3 Hin th, lu tr v ghi nh .............................................................................. 14

III.2.4 Khi thu nhn d liu(DAS) ............................................................................ 14 III.2.5 Gantry ............................................................................................................... 15

IV. Nguyn l ti to nh ..................................................................................................... 17 V. ng dng ......................................................................................................................... 22

LI CM N ...................................................................................................................... 25

TI LIU THAM KHO ................................................................................................... 26


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DANH SCH HNH V

Hnh 1. 1 Bn phc tho ca Sir Godfrey Hounsfield v my CT .................................. 5 Hnh 1. 2 My CT u tin .............................................................................................. 6 Hnh 1. 3 My CT ton thn u tin c pht trin ..................................................... 6 Hnh 1. 4 My CT th h I ............................................................................................... 7 Hnh 1. 5 My CT th h II ............................................................................................. 7 Hnh 1. 6 My CT th h III ............................................................................................ 7 Hnh 1. 7 My CT th h IV ............................................................................................ 8 Hnh 1. 8 K thut chp CT thng thng ...................................................................... 8 Hnh 1. 9 K thut chp CT xon c ............................................................................... 9 Hnh 1. 10 CT a detector ............................................................................................... 9 Hnh 1. 11 CT chm electron ........................................................................................ 10 Hnh 2. 1 Nguyn l chp X quang v CT .................................................................... 11 Hnh 3. 1 S khi my chp ct lp CT ................................................................... 12 Hnh 3. 2 Hnh nh my chp ct lp CT trn thc t .................................................. 12 Hnh 3. 3 Khi chp nh ................................................................................................ 13 Hnh 3. 4 Cu to bng X quang trong my chp ct lp CT ....................................... 14 Hnh 3. 5 Cng ngh thu nhn d liu ........................................................................... 15 Hnh 3. 6 Cc thit b bn trong gantry ......................................................................... 15 Hnh 4. 1 C s ti to nh CT ...................................................................................... 17 Hnh 4. 2 tng v ti to nh ca my chp ct lp CT .......................................... 18 Hnh 4. 3 Ti to nh theo thut ton s hc ART ........................................................ 19 Hnh 4. 4 Ti to nh bng phng php chiu li n gin Hnh nh km nhiu hnh sao .................................................................................................................................. 20 Hnh 4. 5 Mt dng ph bin ca hm s lc ................................................................ 21 Hnh 5. 1 ng dng trong chp thn ............................................................................. 22 Hnh 5. 2 ng dng trong chp phi ............................................................................. 23 Hnh 5. 3 ng dng chp mch mu 3D ....................................................................... 23 Hnh 5. 4 ng dng trong dng nh 3D ........................................................................ 24


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LI NI U

Cng vi s pht trin khng ngng ca cng ngh h tr khm, cha bnh, lnh vc chn on hnh nh cng lin tc c ci tin nhm p ng cc nhu cu chn on ca nn y hc hin i. Trong cc dng my phc v chn on hnh nh, my CT scanner ng mt vai tr quan trng khng th ph nhn. My CT l s cn bng gia gi thnh v cht lng hnh nh. N c th to ra cc hnh nh ct lp, 3D sc nt vt tri hn rt nhiu so vi phng php X quang thng thng, c th so snh vi k thut chp cng hng t nhng li c gi thnh r hn nhiu. Hn 40 nm pht trin, my CT ang l loi my rt ph bin trn th trng. Chnh v nhng l do , nhm em quyt nh chn ti tm hiu v my CT scanner cho ti gia k ca mnh. Trong khun kh mn hc, bi bo co ca nhm hy vng mang n cho ngi c nhng khi nim, hiu bit c bn v cu to, nguyn l hot ng ca my chp ct lp - CT scanner.

Nhm sinh vin


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I. Lch s, qu trnh pht trin I.1. Lch s hnh thnh

Ti ngy 8 thng 11 nm 1895, sau khi ri phng th nghim mt qung, sc nh qun cha ngt cu dao in cao th dn vo ng tia catod, Wilhelm Conrad Rntgen quay li phng v nhn thy mt vt sng mu xanh lc trn bn tuy phng ti om.

Vi u c nhy bn, y kinh nghim ca mt nh vt l hc, vic ny li cun ng v 49 ngy sau ng lin tc l trong phng th nghim, cm nc do b v tip t, mi ngy ng ch ngng cng vic nghin cu t pht n ung, v sinh v chp mt ngh ngi vi gi. Nh th, ng tm ra tnh cht ca th tia b mt m ng tm t tn l tia X v mang li cho ng gii Nobel v vt l u tin vo nm 1901.

Nm 1970, Nhn thy cc hn ch ca phng php chp X quang thng thng v k thut chp tomography, kt hp vi hiu bit v tia X c nghin cu trc , Sir Godfrey Hounsfield v Cormack c lp nghin cu v tm ra k thut chp ca my CT. ng dng u tin ca my CT l chp no. Nh pht minh ny, h cng nhau chia s gii thng Nobel nm 1979.

Hnh 1. 1 Bn phc tho ca Sir Godfrey Hounsfield v my CT


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Hnh 1. 2 My CT u tin

Nm 1974, DR. ROBERT LEDLEY pht trin my CT ton thn u tin trn th gii

Hnh 1. 3 My CT ton thn u tin c pht trin


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I.2 Qu trnh pht trin I.2.1 Cc th h my CT t 1970 n nay

T khi c tm ra, My CT tri qua nhiu ci tin, pht trin vi 4 th h my CT. CT th h 1: chm tia song song; ngun, detector tnh tin v quay .

Hnh 1. 4 My CT th h I

CT th h 2: chm tia r qut; mng detector tuyn tnh; ngun, detector tnh tin v quay .

CT th h 3: chm tia r qut; cung detector; ngun, detector ch quay .

Hnh 1. 5 My CT th h II

Hnh 1. 6 My CT th h III


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CT th h 4: chm tia r qut; vng detector; ngun quay .

Hnh 1. 7 My CT th h IV

I.2.2 Ci tin v cng ngh, cc phng php chp

CT thng thng( th h I, II)

Hnh 1. 8 K thut chp CT thng thng

- ng pht tia X quay quanh trc (0,5 hoc 1 ). - Chm tia X c chun trc thnh c hnh r qut phng.


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- Cc php chiu c coi l ng phng trong mt lt ct. dy lt ct ph thuc vo vic chun trc chm tia.

CT xon c( th h III, IV)

Hnh 1. 9 K thut chp CT xon c

- Ngun, detector quay lin tc; bn bnh nhn dch chuyn lin tccc php chiu c thc hin dc theo ng xon c.

- Qut 1 th tch ln trong 1 thi gian ngn. - Phc tp trong vic ti to nh. - c s dng to nh th tch 3-D ca cc cu trc trong c th.

CT a detector( th h II, III, IV)

Hnh 1. 10 CT a detector

- S dng mng a detectornhn c ng thi nhiu php chiu lin ktc qut tng.

- phn gii khng gian ng hng, cao hn so vi cc k thut CT c. CT chm electron


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Hnh 1. 11 CT chm electron

- Anode cong 180 vi nhiu ming Vonfram. - Chm tia electron c hi t qut nhanh qua cc ming Vonfram v lm pht

ra tia X. - phn gii thi gian lnto nh chuyn ng sinh l trong c th nh nhp p ca tim, s lun chuyn ca dng mu.


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II. u im ca chp CT

K thut chp ct lp CT

- Nguyn l ging chp X-quang thng thng. - Chm tia X c chun trc.

Hnh 2. 1 Nguyn l chp X quang v CT

u im - Hin tng xp chng c hn ch nh vic qut trong mt phng ngang trc. - nh c ti to li nh cc thut ton ti to nh bin i Fourier, bin i

Radon, thut ton chiu ngc, thut ton ART - Phn bit c nhiu loi m, t bo hn X-quang thng ( nhy l 1% so

vi 10%) - C th hiu chnh nh sau khi chp


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III. Cu to III.1 S khi

Hnh 3. 1 S khi my chp ct lp CT

Hnh 3. 2 Hnh nh my chp ct lp CT trn thc t

T khi ra i ti nay, tri qua nhiu s thay i, ci tin, tuy nhin my ct lp CT v c bn vn c chia lm bn thnh phn chnh l:

- Khi chp nh - Khi my tnh - Khi hin th, lu tr, ghi d liu - Khi thu nhn d liu


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III.2 Chi tit cc khi III.2.1 Khi chp nh

Hnh 3. 3 Khi chp nh

Nhim v chnh ca khi ny l: - To tia X - nh dng chm tia X - Lc chm tia X loi b tia X mm

C cu to c bn bao gm mt bng pht tia X quang v mt hay nhiu detector ty thuc vo th h my nh th h I ch c 1 detetor, th h II, III c nhiu detetor v c bit s lng detetor th h th IV ln ti 4800 detector c phn b u trn mt vng trn c nh.

Bng X quang ca My CT khng khc nhiu so vi bng X-quang ca my X quang thng thng. Hot ng in p gia hai cc anode va catode c 80-150 KV. C catt lm bng tungsten pha trn Mo. Bng c bc mt lp ch m bo an ton v c tm lc cng nh mt collimater trc ng ra ca chm tia X loi b cc tia X mm v nh dng chm tia X


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Hnh 3. 4 Cu to bng X quang trong my chp ct lp CT

III.2.2 Khi my tnh Thnh phn chnh l mt minicomputer c cu hnh tng i cao c GHz nhm

mc ch: - Ti to v x l nh - iu khin ton b cc thit b Scan - iu khin qu trnh thu nhn d liu, x l v hin th - nh hng dng d liu

III.2.3 Hin th, lu tr v ghi nh

Nhim v va khi ny l: - Hin th nh - In nh - Lu tr truy xut nhng ln sau - H tr gi d liu nh ti cc my trong mng

III.2.4 Khi thu nhn d liu(DAS) y l khi ng vai tr rt quan trng trong my CT. N l cu ni trung gian

gia cc detector v h thng my tnh trung tm. Khi ny thu nhn tn hiu cc trung thc, cng chi tit s to tin cho qu trnh x l ca h thng my tnh em li mt kt qu r rng v chnh xc h tr cho cng vic chn on.


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Hnh 3. 5 Cng ngh thu nhn d liu

III.2.5 Gantry

Hnh 3. 6 Cc thit b bn trong gantry

L b phn s nht ca my CT scanner n cha ng cc b phn quan trng ca my CT nh:

- CT X-ray tube - High voltage generator: Trong cc th h my CT c, b phn ny c tch

ring ra khi my v t trong High voltage tank sau tip in cao p n my qua dy cp. iu ny gy tr ngi cho chuyn ng quay ca bng v tng i nguy him. Khi cng ngh ch to pht trin, khi ny tr nn nh


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gn v c tch hp trong gantry quay cng vi bng X quang cc th h my th III v IV.

- Detector array: Cng nh khi High voltage generator, khi ny c nhiu thay i theo thi gian. Ban u, My CT ch c mt detector chuyn ng song song v quay cng bng X quang. Ti th h th II v III, s lng detector c tng ln v cch thc chuyn ng cng c ci tin. th h IV, s lng detetor l 4800 detetor! V chng c b tr c nh trn mt vng dng nhn trong gantry.

- Data acquistion system

- Slip ring: l mt thit b a in p cp t ngun ti bng X quang. Khi khi High voltage generator c tch hp vo gantry, vng slip ring tr nn an ton hn trc rt nhiu khi n ch phi chuyn tip in p 220V hay 380V thay v in p c kV nh trc.


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IV. Nguyn l ti to nh My chp ct lp CT ti to nh da trn hnh chiu m cc detector thu c.

Cc detector c nhim v thc cht l o mc suy hao ca tia X sau khi i qua c th bnh nhn. Ti mi gc chp, tia X i theo cc con ng khc nhau qua c th bnh nhn v b suy hao khc nhau. Cc detector cc v tr khc nhau thu nhn c s suy gim khc nhau ca tia X. Sau qua h thng thu nhn d liu s khc nhau ny c chuyn v h thng my tnh thng qua cc thut ton c th ti to li nh lt ct vi mc xm khc nhau cho tng im nh cng nh tnh ton v tr ca cc im nh mt cch chnh xc. Trc khi ti to, php chiu s c trn vi cc hm lc sau bc tin x l trc khi c xp chng tr li ma trn.

Hnh 4. 1 C s ti to nh CT

tng c bn gii quyt bi ton ti to nh ca my CT xut pht t s khc nhau v mc suy hao ca tia X khi i qua c th bng nhng con ng khc nhau m cc detector c th pht hin c. Gi s mi gc , v tr cc detector cho chng ta mt hm hay mt phng trnh biu din mc suy hao ca tia X th bng cch tng hp v gii h cc phng trnh ny ta s thu c gi tr mc xm v v tr tng ng ca cc im nh. S phng trnh m cc detector thu c hay ni mt cch khc l s gc quay khc nhau m my chp ct lp CT thc hin khi chp nh s quyt nh phn gii ca nh. iu ny gii thch v sao th h my CT u tin (c mt detector v bng X quang quay khong 0.5 n 1 mi ln chp), ta ch thu c nh 64x64 cn vi loi my th h IV( c ti 4800 detector) ta c th thu c nh vi phn gii 512x512.


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Hnh 4. 2 tng v ti to nh ca my chp ct lp CT

Cc thut ton Thut ton s hc (ART)

y l phng php ti to xa nht. Vi phng php ny, i tng nh c xem nh bao gm nhiu i tng hnh vung. Mt s hu hn nh im tng ng vi s lng gn ng d liu o c.

Nguyn l: 1. Trong mt chu k lp li, nhng d liu ca 1 nh c ti to gn ng s

c em so snh vi d liu thc theo cng phng chiu v cng s phn t nm trn phng chiu.

2. S chnh lch hiu s cua hai tp d liu s c chiu ngc li vo ma trn nh to ra nh gn ng.

3. Khi ton b cc tp d liu t cc hng chiu c s dng, mt chu k lp li c hon tt v mt chu k tnh ton lp mi c bt u s dng kt qu ca chu k lp trc.

V d: to nh mt i tng ch bao gm 9 im nh ma trn (a) vi cc suy gim tng ng l 2,9,4, 4, 9, 2 , 1, 5, 0. Sau 4 ln qut ngang, dc v cho ta thu c cc tp d liu tng ng | 15, 15, 6| |1, 9, 11, 11, 4| |7, 23, 6| |2, 13, 14, 7, 0|.

Da trn nguyn tc ny, bt u t tp d liu chiu nganh trn hnh 21, v s lng phn t theo hng chiu ny l 3 cho mi php chiu nn tng s o ca tp d liu ny s c chia 3 ri chiu li vo ma trn rng cng gm 9 phn t, kt qu c c ma trn nh (b).


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Hnh 4. 3 Ti to nh theo thut ton s hc ART

Sau tp d liu ngang l tp d liu cho phi, v vy ta chiu cho phi ma trn nh (b) v nhn c d liu gm 5 phn t | 2, 7, 12, 10, 5|. Ly hiu ca tp d liu cho phi gc vi tp d liu ny ta c mt tp d liu cho phi mi | -1, 2, -1, 1, -1|, chia tng gi tr ca tp d liu mi ny cho s phn t nm trn ng cho phi ri cng vi tng phn t nm trn ng cho ca ma trn (b) s c ma trn (c)

By gi s s dng tp d liu s o theo chiu dc, ly hiu ca hai tp d liu gc v tp d liu t ma trn (a) c tp d liu | -4.7, 9.8, -5.2|, chia tng gi tr ca tp gi liu mi ny cho 3 ri cng vi tng phn t nm trn ng chiu dc tng ng ca ma trn (a) ta c ma trn (d).

Tip n s dng tp d liu cho tri theo phng php tng t v c c kt qua ca chu k tnh lp ln 1 nh ma trn (e)


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Mt s gi tr trong ma trn (e) cha tha mn chnh xc v vy phi thc hin mt s chu k lp tip theo, xut pht t d liu ca ma trn kt qu ca chu k lp trc. kt qu sau 3 chu k lp t c ma trn (g) c th xem l tha mn. Sai s rt nh so vi tp d liu gc, phn nh trung thc hnh nh i tng. Phng php ti to nh tch phn

Phng php ny da trn c s ca vic chiu li nhng d liu thu c t cc php chiu vo ma trn ti to nh. Tuy nhin nu ch n gin t chng nhng d liu ring r vo ma trn nh th hnh nh to ra s em theo nhiu di dng cc bng m. kh bng m ny, cc d liu ca tng php chiu s c x l bi mt hm lc s theo mt phng php c bit gi l thut ton cun trc khi c xp chng tr li vo ma trn.

Hnh 4. 4 Ti to nh bng phng php chiu li n gin Hnh nh km nhiu hnh sao

Nguyn l: Hm s lc thc cht l mt phn mm c chc nng nh mt b lc, c

thit k ph hp v cc loi i tng nh xng, s no, bng

Hin nay, hu ht cc my CT u ng dng loi hm s lc c dng ng dc v c cha cc thnh phn dng v m. Cc nh ca ng biu din hm s theo v tr khng gian c chn trng vi v tr ca cc php chiu cn k. Bi vy, d liu c x l bi hm s lc s mang c thnh phn m v dng v s b tr cc thnh phn tn hiu gy nhiu. Nu hm lc c chn la thch ng th c th ti to c nh khng cn b nhiu.


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Hnh 4. 5 Mt dng ph bin ca hm s lc

Phng php convolution c thc hin nh sau: - t nh ca ng biu din hm s lc vo mt d liu th ca mt nh im

cn ti to - Tnh tch ca gi tr ca tng im ti b lc vi tng im tng ng ca tp

d liu nh - Cng cc tch tnh c ri t vo v tr tng ng trong ma trn nh ti to - Tun t dch chuyn b lc sang d liu th thuc nh im ln cn cho ti ht

tp d liu th v lp li cc bc trn

V d minh ho cho phng php ny c ch ra nh trn hnh v, trong o hm s lc ch c cc gi tr n gin l: 0, -1, 3, -1, 0 . X l d liu c gi tr 8 nh trn hnh v, ta t nh ca hm s lc (c gi tr 3) vo vi tr ny, sau tnh tch ca cc gi tr nh ca b lcvi cc gi tr tng ng ca tp d liu th ri cng cc tch li ta c: 7*(-1)+8*3+1*(-1) = 16. Bng cch tng t ta c mt tp d liu x l dng ti to nh, trong tp d liu ny c c thnh phn m nh: -1, -13, -2.


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V. ng dng c ng dng rng ri trong chn on hnh nh cng nh trong sinh tit

- Chn on cc m nh: s no, ct sng, xng CT cho hnh nh v cc m cng r nht trong cc phng php chn on nh

- Pht hin, chn on sm ung th - Cc bnh tim mch, tc nghn mch mu, hay nha khoa, nhn khoa - Tr gip sinh thit: sinh thit tuyn tin lit, sinh thit ung th v, sinh thit c

t cung

Trong cc chuyn khoa:

Hnh 5. 1 ng dng trong chp thn


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Hnh 5. 2 ng dng trong chp phi

Hnh 5. 3 ng dng chp mch mu 3D


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Hnh 5. 4 ng dng trong dng nh 3D


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LI CM N Bt u tm hiu mt thit b c qu trnh pht trin khng lu, cha ng hm

lng cng ngh ln, bn cnh l kh nng cn hn ch v ngoi ng khin nhm gp rt nhiu kh khn trong qu trnh tm hiu v my CT. Nhm em xin chn thnh cm n Thy Hong Quang Huy gip nhm hon thin ti, nh c nhng gii p c th, kp thi ca thy m nhm tng bc gii quyt c cc kh khn pht sinh trong qu trnh tm hiu ti!

Nhm sinh vin


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TI LIU THAM KHO

1. www.google.com 2. http://vi.wikipedia.org 3. Gio trnh Cng Ngh chn on hnh nh I on Nht nh

ct scanner basic

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