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TS N g u y in HCru Quoc Nguyen

GS TS Ton Thj Kim Thanh

Sieu am

Nhan khoa co ban

TS NGUYiN hQU QUOC NGUYEN GS.TS TON THj KIM THANH

L O l N O I D A U

Hien nay, sieu am da trd thanh pho bien trong linh vUc chan doan cac benh ly toan than dac biet la trong nhan khoa TCf cac bac si nhan khoa cho den cac ky thuat vien cung nhu ngUdi dan deu hieu dUdc tinh Uu viet cua sieu am qua cac phUOng tien thong tin dai chung va tU van cua cac bac si nhan khoa cung nhu truyen mieng tCf ngUOi nay sang ngUdi khac V6i ky thuat tUdng doi ddn gian khong gay nguy hiem cho

cd the, thdi gian kham benh nhanh va khong co nhiJng yeu cau phiic tap, sieu am da ho trd cho lam sang nhCing ket qua tUdng doi chmh xac, gop phan ti'ch cUc trong dieu tri, theo doi dien tien cua benh va tien lUdng benh Sieu am da noi len dUdc sU vUdt troi so vdi cac ky thuat khac trUdc day.

Chung toi viet cuon sach nay vdi muc di'ch la muon cung cap mot so khai niem va kien thtic cd ban cua sieu am mat va hoc mat den cac bac si nhan khoa m6i vao nghe va cac ky thuat vien de lam tU lieu tham khao sd dang ve cac tinh nang

ly hoc, cac ky thuat kham, cac thao tac, kien thiic ve ly thuyet

va cac van de lien quan

Chung toi rat han hoan don nhan nhutng ldi gop y, chi giao cua toan the ban doc Cuon sach se kho tranh khoi nhiJng sai sot Toi xin chan thanh cam dn tat ca nhutng ldi g6p y cua ban doc

Moi chi tiet xin gui ve

TS NGUYiN HUfU QUOC NGUYEN

60 Triing Nuf Vifc#ng Da Nang

LjCH SUT SIEU AM MAT

Sieu am da trd nen can thiet trong chan doan nhan khoa bdi vi no co kha nang phat hien, phac hoa va biet dUdc tinh chat ciing, mem cua cac ton thUdng trong nhan cau va hoc m&t lien quan den viec van due cac moi trUdng trong suot Sieu am can co sii bo sung cua cac phUdng phap khac khi can co can thiep ngoai khoa trong cac ca nhU: Bong vong mac, xuat huyet dich kfnh

Chan doan sieu am doi vdi cac mo mem thi tUdng tU nhu kham X quang Cac s6ng am tan so” cao dUdc truyen xuyen qua cac to chiic mem va phan hoi b&ng cac do hoi am khac nhau tuy theo hudng di cua chum am Am sii dung cac nang liidng phan hoi tvf cac mat ph&ng to chiic de phac hoa nen cau true cua to chiic cung nhu sii khac nhau ve am hoc gifla hai to chiic

Su ghi nhan bieu do cua cac song hoi am nay co the tao ra mot mat c i t nhan cau theo khong gian hai chieu (Sieu am B) vdi cac chi tiet lien quan den mat cat to chiic hoc Cung co the ghi nhan theo dang ke do hinh trong khong gian mot chieu (sieu

am A) tUdng tii nhu bieu do dien tim; Sii chuyen dang co the cho thay tinh dac hieu cua sU hoi am cua to chiic cung nhu cac sii do dac chinh xac theo cac hudng cua to chiic

Co ba loai hien thi sieu am dUdc dung trong sieu am mat: Sieu am A (sieu am bien do theo thdi gian) Sieu am B (sieu am dieu chinh cUdng do difdc quet b&ng cac cham sang Sieu am dong M Sieu am A la ky thuat ddn gian nhat va hien thi chieu cao cua am doi tUdng ling vdi vi tri cua no doc theo dUdng di cua chum sieu am Trong sieu am B va sieu am dong M thi bien do cua cac am doi dUdc chuyen hda thanh diem sang nhii

la cac cham tren man hinh cua may hien song Trong sieu am

B, sU dinh hudng khong gian cua bo cam bien dUdc bieu thi tren be mat cua may hien song, bieu thi cho mot mat cat cua nhan cau hay hoc mat trong khong gian hai chieu Ky thuat nay thUdng dUdc dung nhat va la phUdng phap hien thi sinh

cham dUdc chuyen hoa thanh diem sang nhUng vdi bo cam bien dUdc giuf on dinh va sU hien thi di chuyen len xuong va di ngang qua may hien song trong mot thdi diem Bang cach nay,

sU chuyen dong cua to chiic ch&ng han nhu mach mau hoac ap lUc hit vao se dUdc bieu hien tren man hinh hien song.

Sieu am nhan khoa dUdc mo ta dau tien bdi M undt va Hughes nam 1956 Ve sau co nhieu nha nghien ciiu, trong do

co Oksala, Bronson va Ossoinig da phat trien ky thuat nay len nhieu miic do khac nhau

Sieu am B dUdc Baum va Greenwood ap dung l&n d&u tien trong nhan khoa vao nam 1958 va ve sau Purnell va Sokollu, Coleman da dat dUdc cac ky thuat sieu am B phiic tap hdn nCta

va da doi chieu mot loat cac benh ly lam sang tUdng quan vdi

do chuan xac cao khi chan doan benh ly ve mat va hoc mat bang sieu am A va sieu am B

Ky thuat sieu am dong M dUdc Coleman va W eininger gidi thieu vao nam 1967 trong viec xac dinh nhiing thay doi ve mach mau trong cac trUdng hdp khoi u cung nhu nhiing thay doi ve lam sang va tac dung cua thuoc len cac cau true mach mau cua hac mac va hoc mat Sieu am dong M cung dUdc ap dung trdng viec xac dinh cac tinh chat tii tinh trong cac di vat noi nhan

Cac phUdng phap danh gia sieu am cua mat va hoc m lt co the chi bang mot ky thuat sieu am A, hoac sieu am B, hoac phoi hdp ca sieu am A va B Bdi vi cung nhu moi ky thuat tham kham lam sang phiic tap khac, kham sieu am cung doi hoi cac thao tac chinh xac de dam bao cho nhiing ket qua dang tin cay Kham sieu am mat dUdc thUc hien tot nhat bdi bac si

nhan khoa bdi vi ho co day du cac kien thiic ve benh ly mat va hoc mSt de giai thich dUdc cac kieu bien dang va cac di dang tren bieu do sieu am.

Nhin chung sieu am B cung cap mot liidng thong tin ldn nhat vi no ve ra mot biic tranh toan canh dinh khu cua nhan cau va hoc mat, ve ra nhiing cau true bat thUdng Sieu am A cung cap do chinh xac nhat trong moi tUdng quan giiia bien do cua am doi vdi cac to chiic khac nhau cho phep suy luan ra thanh phan cua to chiic

Vao nhiing nam 70 cac nha nghien ciiu ve sieu am d Hoa

Ky, Chau au, va Nhat Ban da co nhiing hieu biet kha sau sac

ve cac dau hieu sieu am trong lam sang nhan khoa ve cac benh

ly khac nhau d mat va hoc m a t

SIEU AM CHUAN HOA la mot phUdng phap chan doan sieu am

da dUdc pho bien suot 30 nam qua vdi nhieu nghien ciiu lam sang va thiic nghiem.

La sii ket hdp cua sieu am A, sieu am B va nhiing ky thuat Doppler thUdng dUdc ap dung biing cach tiep xiic triic tiep dau

do sieu am vao be mat cua mat dua tren nguyen ly ban dau cua nhiing ky thuat va dung cu sieu am A chuan hoa hoac tiep xuc len da mi mat doi vdi Sieu am B Nhiing ket qua ddn nhat

va bien do rong cua cac lat cat sieu am chuan hoa ve cac benh

ly quanh hoc m&t, hoc m&t va noi nhan se dUdc ban luan vdi mot so" nhiing minh hoa dien hinh dUdc sii dung de nhan manh

y nghla lam sang cua phUdng phap nay

Tham kham sieu am phai gom co mot tham do theo phUdng thiic B va mot tham do theo phUdng thiic A NhUng trong quyen sach nay chung toi noi chu yeu den nhiing hinh anh cua phUdng thiic sieu am A va B chuan hoa Bdi vi no de hieu hdn doi vdi ngUdi mdi lam va cho ngay lap tiic mot anh hai chieu trong khong gian theo phUdng thiic B va anh mot

chieu theo phUdng thiic A Nhiing cai ma ta thay dUdc d phUdng thiic B thi ta cung phai thay dUdc d phUdng thiic A va ngUdc lai

Thiic the nen nhd rang nhiing cai ma chung ta can nghien ciiu la mot khoang khong gian ba chieu

Tfnh chat ddn gian, nhanh chong, co the lap di lap lai cua viec tham kham sieu am, da lam cho phUdng phap nay ngay cang quan trong hdn trong viec chan doan cac benh nhU:

- Due thuy tinh the

- Benh dich kinh — vong mac

- Khoi u cua nhan cau

- Khoi u cua hoc mat, benh hoc cua thi than kinh va benh Basedow

- Chan thUdng m&t va nhiing di vat Nhiing hieu biet nhieu hdn ve trieu chiing hoc va nhiing cai tien may moc, phat trien ky thuat tham kham lam tang kha nang chan doan cua sieu am

Viec chan doan sieu am trong nhan khoa phu thuoc vao chat lvfcfng cua may moc sif dung va tinh chinh xac cua viec kham benh, no dua chu yeu tren hai nguyen ly khong thd’ tach rdi:

- Sii thau hieu nhiing hien tUdng vat ly giai thfch sii lan truyen cua sieu am trong nhiing moi trUdng sinh vat

- Su hieu biet tUdng tan ve giai phau hoc va benh hoc nhan khoa.

Tu! hai nguyen ly tren doi hoi sii chinh xac cua nhiing ky thuat tham do va sii phan tich co he thong nhiing dau hieu va trieu chiing tren lam sang Cung can nhan manh den nhiing dac diem khi tham kham m it va lam mot ban phac hoa ve giai phau mat va hoc m a t

Vi vay trong moi phan, chung ta se nhac lai nhiing net chinh ve lam sang de hieu dUdc nhiing trieu chiing sieu am dUdc bieu hien.

Chung ta cung doi chieu nhiing bieu hien sieu am v6i nhiing ket qua giai phau benh ly

Cuoi cung can ltfu y tam quan trong cua sieu am dong la: khoang khong gian nghien ciiu la mot khoang sinh dong, linh hoat, no co tam quan trong trong viec nghien ciiu nhiing tinh chat cd dong va sii phan bo' cac mach mau

NhU the, vdi ky thuat tham kham co he thong va mot sii phan tich trieu chiing hoc hoan hao, doi chieu vdi cac dau hieu lam sang, sieu am cho phep phan biet diidc hdn 80 kieu hay nhom ton thUdng m&t va hdn 70 ton thUdng hay nhom ton thUdng cua hoc m&t

Cung nhu cac phiidng tien chan doan hinh anh khac nhU:

chup X quang thong thUdng, chup X quang cit 16p (CT

Scanner), MRI sieu am co nhiing gia tri rieng trong tham kham benh ly nhan cau va hoc m&t Moi phUdng phap co nhiing chi dinh rieng hoac bo sung lan nhau

Kinh nghiem va ky nang ca nhan dong mot vai tro trong chan doan va sieu am A va sieu am B Sii chuan hoa cho phep moi ngUdi kham sieu am deu dat nhiing bieu do sieu am giong nhau khi tham kham cung mot loai to chiic, co the lap lai dUdc, dat nhiing ket qua so sanh dUdc va sii dung nhiing kinh nghiem chon loc cua phiidng phap chan doan nay Sii chuan hoa cho phep cac ky thuat vien lam nhieu cong viec lien quan den kham xet sieu am ngay ca chan doan Ngoai ra chung ta thao luan ve vai tro sieu am A so vdi sieu am B va nhiing dong gop cua 2 phUOng phap hien thi nay

CAC LfNG DUNG LAM SANG VA KET QUA

Sieu am trong lam sang, diia tren sii ket hdp cua sieu am

A, sieu am B va sieu am Doppler, co the diidc ap dung trong moi tinh huong; trong phong kham, trong phong mo hoac canh giiidng benh nhan Cong dung cua sieu am chuan hoa khong bj han che bdi tuoi benh nhan hay do siic khoe chung cua benh nhan Tuy nhien d tre em tif 6 thang den 3 nam tuoi can phai gay me de cho sii tham kham toan dien va ky cang, day du Nhiing triidng hdp gay dau hoac nhiing vet thiidng kin hoac hd cua nhan cau sau chan thiidng xuyen thung hoac phau thuat nhan cau, thUdng khong diidc kham bang sieu am A va sieu am

B bdi vi dau do 16n va can mot liidng dich nhay nhieu va cung nhu stic ep cua dau do de co sii xuyen am day du hieu qua

Sieu am chuan hoa phat hien diidc:

1) Nhiing bat thufdng d phan triidc nhan cau

2) Nhiing ton thUdng d phan sau (ton thiidng dich kinh dam dac anh hUdng quang hoc co kich thiidc 16n hdn 0,05mm

va nhiing ton thUdng day mat ma gho len it nhat 0,75mm tii cung mac)

3) Nhiing ton thiidng hoc m&t 16n hdn 1mm (hoc m it triidc), 2mm (hoc mat sau), 3mm (dinh hoc m&t)

4) Nhiing ton thifdng to chiic quanh hoc mat n&m gan vdi xiidng hoc mat va xiidng mat hoac lo ra do khuyet xiidng Trong khi khong phai tat ca cac benh ly cua nhan cau deu diidc phat hien bang sieu am (chang han, tac tinh mach trung tam vong mac thi khong phat hien diidc), thi hau nhii tat ca nhiing ton thiidng hoc mat gay ra cac dau hieu va trieu chiing deu diidc phat hien bang sieu am

Vdi sieu am chuan hoa, nhiing ton thiidng quanh hoc mat, hoc mat, noi nhan co the diidc dinh vi va do dac mot cach chi'nh xac 80 tinh trang trong nhan cau va 60 tinh trang quanh hoc

mat va hoc mat co the phan biet diidc Do nhay va do chinh xac cua sii phan biet nay thay doi tuy theo loai ton thiidng.

Sau day la nhiing tinh trang d mat co the phan biet bang sieu am:

Sii bien dang nhan cau

Can thi true

Vien thi true

Mat to

M lt nho

Loi ciic sau nhan cau

Tien teo nhan cau

Teo nhan cau

Nhufng ton thiiofng phan trtfdc nhan cau

Day hoac mong giac mac

Nong hoac xep tien phong

Tien phong sau bat thiidng

Mang sau giac mac

Day mong mat

Due thuy tinh the chm

Due thuy tinh the diidi bao

Due thuy tinh the vo

Due thuy tinh the nhan

Due thuy tinh the dang mang

Due thuy tinh the phong

Thuy tinh the hinh cau

Voi hoa the thuy tinh

Lech thuy tinh the

Khong co thuy tinh the

Thuy tinh the nhan tao

Nhu’ng tinh trang dich kinh

Van due dich kinh

Ong anh dich kinh dang sao

Thuy hoa dich kinh

Bong dich kinh sau

Bong dich kinh toan bo

Xuat huyet dich kinh rai rac, tiidi

Xuat huyet dich kinh kern mang gia

Xuat huyet to chiic hoa dich kinh cu (dang dai, mang)Xuat huyet dich kinh lan toa, cu (dong nhat)

Xuat huyet dudi dich kinh

Nhiing boc chiia mau dich (trong benh ly vong mac dai diidng) Viem mu noi nhan

Nhe (te bao rai rac trong dich kinh)

Abces (lan toa hoac khu tru)

Viem mu toan nhan

Mang the mi

Nhufng ton thvfdng u h ie to ac tinh the mi va h^c mac

Day hac mac lan toa

- Deu (nhUdc nhan ap, cUdng tu xung huyet)

- Khong deu (tien teo nhan, viem hac mac)

Bong hac mac

- Xuat tiet

- Xuat huyet

- Xuat huyet tong

Bong the mi

U hSc to" ac tinh the mi hac mac

Carcinoma di can (ung thu tuyen di can)

U mau hac mac

U xiidng hac mac

Thoai hoa hoang diem dang dla

Gia u day hiat

Nevi hac mac (ung thu te bao hac to)

Voi hoa h&c mac, vong mac (sii tao xiidng)

Nhiing tinh trang khac

Di vat nhan cau

Bong khi (hdi)

Phu gai thi than kinh

Lom gai glaucom

Drusen dla thi

Nhufng ton thifcfng vong mac va dong tu’ trang

Benh ly vong mac vdi sii day len cua 16p vong mac (phu)

Co keo tren vong mac (do nhiing dai day len khu tru cua vong mac)

Benh ly vong mac khong co sii day len cua ldp vong mac (sii phan chieu vong mac giam trong dai diidng)

Bong vong mac

- Dang pheu toan bo

- Tam giac (dau hieu cua benh ly vong mac tang sinh)

- Cling

- Tach ldp vong mac (bong mang gidi han trong)

- U nguyen bao vong mac

- Xd san sau thuy tinh the

- Tang san dich kinh nguyen phat

- Benh COATS

Loan san vong mac

Nhufng benh cua cd ngoai nhan

Cd day len

* Ca hai ben ro ret

- Benh ly hoc mat do noi tiet

- U bach mach, benh u hat man ti'nh

- Day v ia d benh nhan ung thtf

* Mot ben ro ret

- Ciidng tu (Do DTM keo dai)

- Viem cd cap tinh

- Viem cd man tinh

Nhufng ton thiidng thiic the hoc m&t va quanh hoc mat

Nhiing ton thiidng hoc mat

U mau hoc mat (chan thiidng hoac tii nhien)

U mau dudi mang xUdng

Gay hd xiidng hoc mat

Gay vun xiidng hoc m&t

Khi thung (tran khf)

Di vat (ngoai trif d dinh hoc m&t)

Nhiing bat thiidng than kinh thi giac

Phu thi than kinh

Glioma

Day len cua th<3 sdi than kinh

Dich dudi nhen tang

U mang nao

Teo thi than kinh

S hung u va gia u quanh hoc mat

Benh ve xoang 'khong khuyet xiidng1

Benh ti'nh quanh hoc ma:

U hoc mat va gia u hoc mat

Gia loi mat

Gia lom mat

Phu hoc mat lan toa

Viem te bao hoc m it

A bees hoc mat

Abces dtfdi m ane xiidng

Tham nhiem cnir.g

C’Jdng tu sung huyet

U dam roi than kinh

U mau xoang hang 'dang tru’dng thanh)

U man xoang hang (dang tre em)

U bach mach

U hon hdp cua tuyen le

Ung thut tuyen di can den phan mem hoc m&t

Do dong tinh mach (Dan hoc m it do do dong tinh mach

keo dai)

Phinh dong mach hoc mat / Di dang dong tinh mach

Trifdng tinh mach

Nang bi (dermoide)

Nang thvfdng bi

U bao schwan A

U bao schwan B

U bach mach / gia u / u lien ket

U sdi than kinh

Gia u xd

Khong co nhan cau bam sinh (co ho&c khong co nang)

G ift THIEU VE MAY SIEU AM

Co nhieu loai may sieu am diidc thiet ke de sii dung cho cac muc dich khac nhau Tong quat, co the chia lam 3 loai sau:

- May sieu am mau da chiic nang hien dai

- May sieu am da chiic nang, giai quyet diidc moi yeu cau chuyen khoa

- May sieu am xach tay chiic nang ddn gian, chuyen dungVdi sii phat trien cua ky thuat, mot so" may xach tay gan day cung co kha day du cac chiic nang can thiet

Ngiidi sii dung can biet ro yeu cau cua minh de chon lila thiet bi thich hdp

Sau day la mot so diem cd ban can biet de sii dung mot may

sieu am thong thiidng

1 CAU TAO MAY SIEU AM

M ot may sieu am thiidng gom 3 phan:

- Phan nhap dut lieu: Dau do

- Phan xii ly dut lieu: Than may va ban phim

- Phan xuat duf lieu: Man hinh

1.1 Dau do

Dau do dtfdc tao bdi mot nhom cac chan tik co nhiem vu lan lifdt phat va thu song sieu am

Tinh nang cua dau do dtfdc xac dinh qua cac yeu to sau:

1.1.1 Hinh dang: co 3 loai dau do thtfdng dung:

+ Tuyen tinh (Linear)

+ Tia (Sector)

+ Cung (Convex)

Stf khac biet la do viec s&p xep cac chan tv£ tren dau do, dan den viec tai tao anh khac nhau Ta co the nhan biet loai dau do dtia vao hinh dang ben ngoai hay hinh anh mat c&t sieu am.Doi vdi moi loai dau do, can co danh gia khac nhau ve kha nang cua no

- Dau do linear:

• Be ngang cua trtfdng khao sat

• Chieu sau cua trtfdng ma sat

- Dau do sector va convex

• Be ngang cua trifdng phan nong

• Goc quet

Cac chi tiet nay cho biet kha nang tai tao hinh va khao sat

cd quan cua dau do

1.1.2 Tan s o : Tan so diidc dung trong kham nhan khoa thiidng

tu: 5.5-20 Mhz

1.1.3 Do ly giai va do xuyen thau

Do ly giai la yeu to' quan trong nhat quyet dinh tinh chat cua mot dau do Do ly giai thiidng diidc hieu la do ly giai theo true Tren thiic te, do ly giai cua dau do bao gom 3 yeu to":

• Ly giai theo true: Phu thuoc vao t in so" d iu do

• Ly giai theo chieu ngang: Phu thuoc vao so" chan tut va kha nang hoi tu song sieu am cua may

• Ly giai theo chieu day (be mat cua lat c&t): Phu thuoc vao chat liidng cua 16p hoi tu

Do ly giai cua dau do cung phu thuoc vao dang cua dau do

va kha nang xU ly hinh anh cua may

Vi vay, khong phai moi dau do cung tan so" deu co do ly giai nhii nhau

Mot cach ddn gian, co the van dung nguyen tac ly giai

xuyen thau de chon tan so thich hdp: T in so cang cao thi do ly

giai cang cao va do xuyen thau cang kern

Do do, khi can khao sat cac to chiic d nong, ta nen chon tan so' cao Khi can khao sat cac to chiic d sau, ta chon tan so' thap hdn Gan day, cac d iu do da diidc thiet ke' da tan so' nen rat thuan ldi cho ngiidi sii dung.

1.2 Than may

Cac bo phan chinh thiidng gap d may sieu am

1.2.1 Gain: Cong suat phat song sieu am

C in tuan thu nguyen tac la: dung song sieu am vdi cong suat thap nhat co the diidc

Co 2 p h in de dieu chinh gain: Gain tong cong va gain tiing phan

Gain tiing phan diidc thiet ke de bu lai nang liidng hao hut tren diidng di cua song sieu am O cac may ddn gian, no diidc chia lam 2 phan gain g in va gain xa O cac may phiic tap hdn,

co phan tinh chinh cho tiing miic do sau 2cm

Nguyen tac chinh: la tao diidc hinh anh dong dang

Thiidng dung gain tong cong d miic thap nhat va gain tiing phan d miic cao nhat co the diidc

1.2.2 Cac bien phap xurly anh

Co nhieu cach xU ly anh khac nhau nh&m quan sat ton thtfdng ro hdn

Mot cach tong quat, co 2 loai xtf ly anh: trvfcfc va sau khi co" dinh anh

Can chu y la do min ty le nghich vdi do ttfdng phan

Nhiing bien phap lam tang do tiidng phan se lam thay ro hdn bd cua ton thiidng nhiing lai lam giam kha nang phat hien ton thiidng va ngiidc lai.

Yeu to ky thuat quan trong nhat la viec xac dinh vung khao sat Neu vung khao sat nho, hinh co do tiidng phan cao nhiing khong min va ngiidc lai

1.2.3: Cac bo phan nhap d O’lieu:

Ban phim giup:

• Do dai true nhan cau

• Do cong suat thuy tinh the nhan tao

1.2.5 Cac yeu to xurly anh khac

1.2.5.1 Vung ti§u diSm (Focus) co thS thay doi tClnong den sau

Chu y chon dung vung khao sat can thiet, thvfdng co lien quan den do sau.

Do sau diidc chon liia trong da so" triidng hdp Neu can khao sat ton thiidng d ngoai vung tieu diem, can chu y dinh lai.

Tuy nhien, viec xac dinh qua nhieu vung tieu diem cung luc co the lam cham qua trinh xii ly anh

1.2.5.2 Phong dai (Zoom)

1.2.6 Thang xam (Grayscale) Thiidng tCf 16 - 64 nac

So nac tren thang xam cang cao thi kha nang phat hien ton thiidng cang cao

1.2.7 Phan hwong d in djnh vi dj vat nhan cau

2 MOT SO VAN BE LIEN QUAN

2.1 The nao la mot may sieu am tieu chuan cho kham m lt?

Toi liu la co mot dau do tu: 5-8MHz cho hoc mat va mot dau

do tu: 9-12MHz cho nhan cau

Dau do linear phai co chieu ngang # 4.5cm, chieu dai 10cm

Co kha nang ghi nhan moc nhan cau, hoc mat, dfl lieu cua

benh nhan, chu thich

Co kha nang ltfu trQ

2.2 Van de djnh hi/dng tren hinh sieu am

Tren cac dau do he thong B luon co mot dau hieu goi la marker Do la dau hieu de cho ngiidi lam sieu am biet diidc tii the cat, vi tri cat va dien cat cua to chiic ttfdng ling vdi hinh anh sieu am nhin thay tren man hinh nhif the nao Cue tren mang hinh tiidng ting vdi hiidng co dau marker tren dau do

2.3 Cac sai lam thirdng gap khi sur dung may sieu am

Can nhd la sieu am khong bao gid sai, chi co ngiidi doc sieu

am sai ma thoi

Nhiing sai lam khi chan doan bang may sieu am co the nam trong 2 nhom

- Nhom loi ky thuat phu thuoc vao kha nang sii dung may

1 Dung may sai muc dich

2 Chon sai dau do

3 Chinh sai gain (gan/xa)

4 Chon cac thong so" khong dung

5 Do khong chuan

- Nhom loi nhan dinh phu thuoc vao kinh nghiem

Hiidng d in benh nhan van dong nhan cau theo dung y dinh cua ngiidi lam sieu am

2.4 Cac dieu can biet trong bao quan may

Than may: Chu y dien the sU dung, tranh di chuyen dan xocDau do: Khong lam rdi, khong ngam vao nhiing dung dich khong phu hdp

Trong cac phiidng phap chan doan hinh anh, sieu am la

de sii dung nhat va mang lai ket qua tot ve cac benh ly nhan cau va hoc m&t Tuy nhien de co the phat huy het kha nang cua thiet bi, ta can n im ro cac nguyen ly vat ly, dinh vi tren man hinh

NHAC LAI CO SOT VAT LY TAO HINH SIEU AM

Ban chat cua song am trong moi triidng chat: cac moi triidng chat dan hoi (khi, long hay ran) co the coi nhii nhiing moi triidng lien tuc gom nhiing phan tti lien ket chat che vdi nhau Binh thiidng, moi phan til co mot vi tri can bang ben trong moi triidng Neu tac dong mot liic len mot phan tti A bat

ky thi phan tti nay se rdi khoi vi tri can bang, va thiic hien dao dong Hien tiidng nay tiep tuc xay ra doi vdi cac phan tti khac tao ra nhiing dao dong cd lan truyen trong moi triidng dan hoi goi la song cd hoc

Ve ban chat song am la song cd hoc nen phai tuan theo moi quy luat doi vdi song cd, va cd the tao ra song am bang cach tac dong mot liic cd hoc vao moi triidng truyen am

1 PHAN LOAI SONG AM

1.1 Theo phi/dng dao dong

Diia vao cach truyen song, ngiidi ta chia song cd ra lam hai loai: song doc va song ngang

- Song ngang la song ma phiidng dao dong cua cac phan tu moi triidng vuong goc vdi tia song Tinh chat nay chi cd d vat din

- Song doc la song ma phiidng dao dong cua cac phan tti moi triidng trung vdi tia song Song doc truyen diidc trong cac vat ran cung nhii moi triidng long va khi

Song sieu am ting dung trong sieu am chan doan thuoc loai song doc

1.2 Theo tan so

Song am dUdc chia theo dai tan so" thanh 3 vung chinh:

+ Song am tan so ciic thap hay con goi la vung ha am.

f < 16Hz

Vf du: Song dia chan

+ Song am tan so nghe thay

f = 16Hz - 20kHz + Song sieu am

“sieu am” Tan so" cua sieu am sii dung trong chan doan y hoc thay doi tii 2 den 20MHz (Megahertz) (2 den 20 trieu chu ky /giay) Ve thiic hanh, sieu am diidc san xuat bang cach dung mot dong dien xoay chieu chay tren mot mieng (manh) thach anh (hay mot chat lieu gom) ap dien Diidi tac dung cua dong dien tinh the gian ra va co lai, tuy theo tinh doi ciic cua dong dien di vao dan den sii hinh thanh cac song am

Trong nhan khoa, tan so" sieu am diidc sii dung trong

khoang tii 1 den 25 trieu chu ky /giay (25MHz) Nang liidng

am co the hoi tu lai, bi phan xa, bi khuc xa tiidng tii nhii anh sang Dinh luat Snell trong phan xa anh sang cung co y nghia tiidng tii nhii trong phan xa sieu am Tuy nhien, pho nang liidng sieu am thi hoan toan khac vdi pho dien tii Am n im trong pho nang liidng cd hoc va di chuyen bang cach nen ep luan phien de lam loang cac phan ta Bdi vi am diidc truyen

bang cach nen ep cac phan tu va lam loang cac phan tu nen

khong khi khong truyen am dude tot dich thi can thiet de

Sieu am diidc truye: vao mat tti mot bo chuyen doi (Transducer - bo cam bien) Bo cam bien gom mot vat lieu cong hudng ma co cac dac tinh ap dien Dac tinh nay dtfOc Curie phat hien vao nam 1880 lien quan den tinh chat cua mot so thuy tmh gom sti khi tiep xuc vdi nguon dien lam bien dang

be mat va tao ra cac song am Tac dong qua lai cua bang tinh the ap dien khi song am dap vao bang tinh the thi tao ra mot

su tfch dien ma co the do diidc Ket qua la khi nang liidng dien diidc nap vao trong bo chuyen doi, thi cac song cd hoc dUdc hudng vao trong m it va nang liidng phan hoi (hoi am) dUdc nhan lai bdi bo cam bien va diidc hien thi tren may hien song

Am diidc phan hoi lai bo cam bien tti cac mat phan cach to chtic ma co cac dac tmh trd khang am khac nhau Trd khang

am ctia cac to chtic tUdng ting vdi mat do cua no Ranh gidi gitia hai to chtic co do trd am khac nhau la mot mat phan gidi phan hoi am, gan giong nhii tam giidng soi mat la mot mat phan gidi phan xa anh sang Am diidc phan hoi tti mot be mat phan gidi tiidng tu nhii vav, vdi goc phan hoi bang goc tdi Am dUdc phan hoi ve bo cam bien ty le vdi ki'ch thiidc va hiidng khong gian cua mat phan gidi diidc chieu tia am va stf khac nhau ve cac dac tinh am hoc gitia cac moi triidng khac nhau.Ung dung trong chan doan lam sang, ngudi ta dung cac tan so' cao hdn, chang han nhii 20MHz, thi co biidc song n gin

hdn va vi the do phan giai se tot hdn cac tan so thap chang

han 10M Hz Vdi tan so 20MHz thi do phan giai theo ly thuyet la khoang 0.01mm be day ctia to chtic Khi budc song cang dai thi cac tin hieu co tan so' cang thap va do phan giai cang yeu nhu'ng kha nang xuyen sau vao to chtic cang xa triidc khi tin hieu bi hap thu Cac bo cam bien co do phan giai

cao, tan so cao (15-20MHz) thiidng diidc dung cho c h in doan

nhan cau va phan triidc nhan cau, con cac bo cam bien co co tan so thap (5-10MHz) thiidng diidc dung cho chan doan ca nhan cau va hoc mat.

Tat ca cac he thong hien thi sieu am deu bieu thi thdi gian ma song di chuyen giuia cac to chiic, nhiing khong bieu thj khoang cach thiic te" giiia cac to chiic Bdi vi song am di chuyen xuyen qua cac to chiic vdi mot toe do phu thuoc vao van toe am dac hieu cua to chiic, nen van toe to chiic co the diidc dung de do thdi gian can thiet de song am di xuyen qua

to chiic nhii la mot cach de do do day cua to chiic Cac tri so" h&ng dinh cua van toe am trong cac to chiic cua mat diidc ghi nhan d bang diidi day

Giac mac 1610

Thuy dich va dich kinh 1532

Thuy tinh the ngirdi Idn 1641

Thuy tinh the tre em 1659

Thuy tinh the bi due 1629

1.3 Do sinh hoc nhan cau

Chieu dai true nhan cau co the diidc xac dinh tot nhat bang cach do cac khoang cach thdi gian giiia cac song am doi lai doc theo chieu dai true quang hoc cua nhan cau Nhii da noi

d tren, sii do dac chinh xac nhat la vdi tan so" cao chang han nhii 20 - 25MHz Mot so" ky thuat diidc nghi ra de lam sao cho

chum sieu am di that th&ng doc theo true quang hoc hay true thi giac Muon do dac sinh hoc that chinh xac thi c&n phai tao

ra mot be rong cua chum am cang hep de cho cac bd cua cac mat phan gi6i cong khong tao ra nhiing sai so Khi do tuyet doi khong diidc de len nhan cau Ngoai ra can co mot moi triidng dich ket noi giiia bo cam bien va nhan cau de cho hau het cac

am doi cua phan triidc giac mac co the tach khoi phtic help bo cam bien ban dau

Cach ddn gian nhat de tao ra sii cach biet la dung mot cai bao hinh tru mong, rong bao boc phan dau cua bo cam bien (dau do) va lam day niidc hoac niidc muoi Bdi vi ban than cai mang co the de ep len giac mac nen mot phiidng phap chinh xac hdn do la sii dung giac mac de bao boc dau cam bien Khi dau do tiia rat nhe len vung ria thi nhan cau khong bi bien dang hoac bien dang khong dang ke cho nen am doi cua giac mac triidc la diem dau tien de do dac so vdi nhiing cau true khac trong nhan cau

Cung cach do mot nang liidng cd hoc tac dung tren mot tam thach anh co the bien thanh tin hieu dien Nhii the may do co the viia la may phat viia la may thu Viec phat am la ciic ki ngan, thdi gian con lai la may do phan tich nhiing am phan hoi

Tan so sieu am phat ra luon khong doi doi vdi mot may do

cho san, bieu hien so"chu ky tinh bSng giay (Hz)

Mat va nhiing cau true cua hoc mat la rat nong, nen tan so" cua nhiing may do thay doi tii 5 den 20 MHz Tot nhat cho sii tham nhap cua nhiing cau true nay va sii phan tich cua nhiing

chi tiet la mot tan so tti 8 den 10 MHz.

Toi liu la mot may do tii 5-8MHz de nghien ctiu hoc mat va mot may do tti 9 - 12 MHz de nghien ctiu nhan cau

Chieu dai toan bo cua mot chu ky la do dai ctia song Toe

do lan truyen hay van toe thay doi tuy theo nhiing moi triidng

tham do khac nhau Doi vdi cung mot moi triidng, van toe (V)

do dai cua song (X) va tan so" (f) gan lien v6i nhau bdi dang thiic V = X f.

Ciidng do cua chum sieu am la sii do nang liidng cua no Ddn vi thiic hanh de do nang liidng cua chum sieu am la C (dB) dexiben

Sii truyen sieu am trong mot moi triidng phu thuoc vao dien trd khang cua am trong moi triidng do Dien trd khang (Z)

la tich so" cua khoi am liidng (0.137) vdi van toe cua nhiing sieu

am (V ) trong moi triidng Z = 0.137 x V :

th in g goc vdi mat phan gidi, ti le cua chum tia phan chieu (r)

la tuy thuoc vao sii chenh lech cua van to'c cua am trong moi triidng:

r = Z2 - Zj/Za + Zj

Neu sii khac biet cua dien trd khang yeu thi chum sieu am

se phan chieu yeu, ngiidc lai chum am se phan xa hoan toan hay gan nhii hoan toan neu sii khac biet dien trd khang la ldn

Vi du: khong the nghien ciiu mot cau true cua khong khi hay cua xiidng

Goc tdi thay doi ti le cua phan xa bdi mat phan gidi Khi chum sieu am tiep tuyen vdi mot mat phan gidi, thi cau true khong the khao sat dtfde.

2 S I/ PHAN HOI VA SLT KHUC XA

Am dtfdc truyen di theo nhtfng tia goi la tia am Tia am cung

co the bi phan xa, khuc xa, tan xa va hap thu nhtf tia sang

+ Phan xa va khuc xa: Khi song am truyen trong moi trtfdng dong nhat va dang htfdng no se truyen theo phtfdng

thang; khi gap mat phan cach du 16n (ki'ch thtfdc 0 » X ) gitia hai

moi trtfdng co trd khang am khac nhau, ttic la co van toe truyen

am khac nhau, tia am se tuan theo dinh luat phan xa va khuc

xa Mot phan nang ltfdng cua song am se phan xa ngtfdc trd lai

va phan con lai se truyen tiep vao moi trtfdng thti hai

Do ldn cua nang ltfdng phan xa phu thuoc vao stf khac biet cua trd khang am Az gitfa hai moi trtfdng He so" phan xa K dtfdc ti'nh theo cong thtic:

9 ,: goc tdi; 6; goc phan xa; 0 goc khuc xa

Pr - bien do ap ltfc cua song phan hoi;

Pi - bien do ap ltfc cua song tdi;

Zj, Z2: trd khang am cua hai moi trtfdng

O day se xay ra hai trtfdng hdp:

- Trtfdng hdp 1: Tia tdi vuong goc vdi mat phan cach: 0=0r=O

He so phan hoi cua mat phan cach se dtfdc ti'nh theo cong thiic:

Cos#, = Cos0r- 1 nen:

Z - Z

K =

Z 2 + Z,

- Trtfdng hop 2: Tia tdi tao mot goc 0, * 0 Theo dinh luat

phan xa goc phan xa bang goc tdi = 6r Song truyen tiep luc nay khong con cung htfdng vdi song tdi va tao mot goc 6, =£ 0( , hien ttfdng nay goi la hien ttfdng khuc xa, goc khuc xa 6t phu

thuoc vao van toe truyen am trong hai moi trtfdng va dtfdc xac dinh bdi cong thtic:

Sin 0t - (c2lci) x sin^

+ Vdi c2>cj, khi s in # (=c!/c2, ta co 9crUic - arcsin (c,/^ ) thi sin 6t- 1 va 6t- 90° Hien ttfdng nay goi la hien ttfdng phan xa

toan phan Nhtf vay vdi tat ca cac goc > 9crUic song am se

khong khuc xa dtfdc sang moi trtfdng thti hai ben kia mat phan cach va toan bo nang ltfdng dtfdc phan xa trd lai moi trtfdng thtf nhat

+ Ngoai ra du vdi c2>c! hay c2<c!, neu goc tdi 6t «9 0 ° (tia

tdi di gan nhtf tiep tuyen vdi mat phan cach) thi song am chi trtfdt tren be mat phan cach ma khong truyen tiep vao moi trtfdng thtf hai

Ttf hai cong thtic neu tren ta thay he so phan hoi ctia mat

phan cach gitia hai moi trtfdng phu thuoc vao AZ = (Zr Z2) gitia hai moi trtfdng:

+ AZ cang ldn thi nang ltfdng phan xa cang ldn va chi con mot phan rat nho nang ltfdng song sieu am di dtfdc xuong moi

trtfdng ben dtfdi mat phan cach Neu AZ la v i a dti de nhan

biet mat phan cach thi mot phan 16n nang ltfdng ctia song sieu

am se truyen dtfdc tfuong dtfdi mat phan cach va tiep tuc cho them thong tin ve cau true ben dtfdi.

3 S I/T A N XA

Trong tao hinh bang sieu am co hien ttfdng tan xa cua sieu

am khi gap cac cau true nho (co ki'ch thtfdc 0 « A ) hoac vdi be

mat khong dong deu Khi do tia sieu am se bi tan xa di khap cac htfdng, va chi co mot phan rat nho chac chan tdi dtfdc dau

do Du viec ghi nhan cac tia tan xa la rat kho khan, nhtfng chung co tfu diem la khong phu thuoc vao goc tdi cua tia sieu

am, va rat can thiet trong viec danh gia cac cau true nho, vi du cac ldp vong mac, hac mac

Chum sieu am tat dan bdi phan chieu, phan xa, giai phong nang ltfdng cua no

Dtfdng cong giam dan la so" mu ham so" cua dien trd khang cua moi trtfdng va nhat la tan so cua may do; tan so cang cao thi do giam cang ldn

3.1 Sir khuyech dai - Gain

Tin hieu dtfdc thu nhan tai dau do trtfdc khi the hien thanh hinh anh deu phai dtfdc xvt ly, mot trong nhtfng btfdc xtf ly quan trong la khuech dai tin hieu do bien do cua chung qua nho He so khuech dai, thtfdng dtfdc tinh bang dB, la mot

ty so gitfa bien do sau khi khuech dai va bien do trtfdc khi khuech dai:

Gain = RX = 20 Log (U2/U1) = [dB]

U2: Bien do tin hieu sau khi khuech dai

U l: Bien do tin hieu trtfdc khi khuech dai

Vi du mtfc Gain = 40 dB co nghla la:

20 Log (U2/U1) = 40 -> Log (U2/U1) = 2 -> U2/U1 =100Tin hieu da dtfdc khuech dai len 100 lan

3.2 Khuech dai bu trirtheo do sau

Trong khuech dai tin hieu co mot yeu to ^uan trong la hien ttfdng lam suy giam nang ltfdng song am cua moi trtfdng, dan den lam cho tin hieu trd ve dau do tti do sau cang xa thi co bien do cang be, vi vay can phai co stf bu lai cho mat mat nang ltfdng noi tren Sau khi song am dtfdc truyen di, nhtfng tin hieu hoi am tti nhtfng mat phan hoi d xa thi dtfdc khuech dai nhieu hdn so vdi tin hieu hoi am tti nhtfng mat phan hoi d gan.Stf dieu chinh dung ctfdng dovcua chum sieu am tdi phai dtfdc thi'ch tfng vdi nhtfng cau true de nghien ctiu Mot khuyech dai qua cao lam tang tat ca nhting cau true am va kho xac dinh cau true ctia am ben trong Ngtfdc lai mot khuyech dai qua thap se lam giam tat ca cac am bao gom nhting am co bien do cao nen kho phat hien nhting gidi han ben ngoai Stf tham kham phai luon bat dau b&ng khuyech dai ”To chtfc” ; dieu nay thay doi vdi moi mot may, moi kieu to chtfc dung de tham kham Can co stf phan tich ve ltfdng sieu am khuyech dai thap hoac cao de biet chac chan ctfdng do ctia cac am phan chieu d mtic mot mat ph&ng phan gidi hay de khao sat ve ltfdng cau true am ben trong ctia mot ton thtfdng

4 KY THUAT CUA PHUONG PHAP TAO HINH BANG SIEU AM

4.1 Nguyen ly tao hinh

Dau do khi dtfdc ki'ch thi'ch bdi xung dien co chieu dai va ctfdng do co the dieu chinh dtfdc thi khi phat ra xung am lan truyen theo htfdng ctia dau do vao moi trtfdng d mot van toe xac dinh bdi dac ti'nh ctia moi trtfdng, song am se gap cac mat

phan gidi tren dtfdng truyen va tao ra cac song phan xa va tan

xa quay trd ve dau do va diidc thu nhan tai day

Khoang thdi gian cho song am di den va quay ve til mat phan hoi se xac dinh do sau cua mat phan hoi bdi cong thtic:

d = c x t/2Trong do:

d: Khoang cach tti dau do den mat phan gidi

c: Van toe song am trong moi trtfdng

t/2: Thdi gian cho song am di ttf dau do den mat phan hoi

Do ldn cua bien do song phan hoi phu thuoc vao bien do song phat di, goc tdi ctia song am va trd khang am cua mat phan hoi

Dau do se bien doi song hoi am thanh tin hieu dien thong qua hieu ting ap dien, tin hieu dien nay mang thong tin ve do ldn bien do, thdi gian tiep nhan, cac thong tin nay sau do dtfdc xti ly va the hien thanh hinh anh tren man hinh

4.2 Chan doan sieu am trong nhan khoa

Cd ba dang hien thi chinh dtfdc dung trong sieu am chan doan nhan khoa: Sieu am A, sieu am B, va sieu am M Sieu am

A la phtfdng tien tot nhat de danh gia stf khac nhau ve trd khang am gitfa cac to chtfc Sieu am B la tao ra mot stf hien thi

dinh khu trong khong gian hai chieu ctia cac mat phan cach to

chtic; sieu am M la phtfdng tien de khao sat stf chuyen dong cua to chtic trong mot thdi diem Noi chung, sieu am B cho nhting ket qua tot nhat ve hinh dang ton thtfdng khac nhau

cua cac to chtfc, trong khi sieu am A cho nhting ket qua tot ve

noi dung ben trong cua cac to chtfc

Sieu am A va sieu am B deu cd the thtfc hien dtfdc bang ca hai phtfdng phap tiep xuc hoac ngam ntfde B&ng phtfdng phap tiep xuc, dau do cd the dtfdc dat trtfc tiep len tren mi mat hoac

nhan cau Dau do A co the dat vao tat ca moi htfdng cua nhan cau va hoc mat mot cach he thong va co the de ep nhan cau de khao sat Thiet bi nay co the dtfdc dat trong phong mo de danh gia trtfdc mo va khu tru di vat.Sieu am B cung co the khao sat nhan cau va hoc mat nhtf sieu am A mot cach he thong nhtfng doi khi khong thuan ldi neu dat dau do tren bd mi vi do phan giai se bi giam do bd mi lam cho am doi d phan trtfdc va phan sau nhan c&u bi mat.

4.2.1 Sieu am theo phutyng thut A (A - mode: Amplitude Mode)

Tin hieu hoi am dtfdc the hien bang xung hinh gai tren dao dong ky qua he thong true tung va true hoanh, chieu cao cua xung the hien do ldn cua bien do tin hieu hoi am, vi tri cua xung the hien khoang cach tti dau do den mat phan hoi Loai hinh the hien nay thtfdng dtfdc dung trong do dat vi cd do chinh xac cao

Phtfdng thtic A (bien do) tren man hinh vo tuyen cd 1 hoanh do va 1 tung do Hoanh do bieu thi true cua thdi gian

Do dac bieu thi bang micro giay (ms) Toe do trung binh cua cac sieu am trong nhting to chtic mem, dtfdc thay the bang mot thang do b&ng milimet True tung la true ctia nhting bien do Chinh la stf the hien mot chieu cua tin hieu dtfdi hinh thtfc ctia nhting stf lech, nhting dinh nhon cao nhieu hay it tuy thuoc vao tinh chat cua nhting am phan chieu

'7^rnvwT^ ,,TM TwrnrT rr

4.2.2 Sieu am theo phuong thuc B (B - mode: Brightness Mode)

Tin hieu hoi am dtfdc the hien bdi nhtfng cham sang, do sang cua cac cham nay the hien bien do tin hieu hoi am, vi tri cac cham sang xac dinh khoang cach ttf dau do den mat phan hoi.Phtfdng thtic B (do sang choi) la mot hinh anh the hien 2 chieu nhting tin hieu dtfdi dang nhting cham Bang (tat ca hoac khong co gi) cham chi la cu the hoa neu am phan chieu vtia du bien do Thang xam bieu thi khai niem ve bien do b&ng cach phan cap d moi mot cham mau xam it hay nhieu tham mau tuy theo bien do ctia am Ghi vang am cat ldp (echotomographie) la the hien b&ng phtfdng thtic B cua toan bo nhting phan chieu ctia mot chum sieu am di chuyen trong mot mat phang ngang Neu nhip dieu ctia nhting dtfdng quet la du nhanh, vong mac

se cho nhting hinh anh khac nhau, nhtf the ngtfdi ta dat dtfdc mot ghi vang sieu am”b&ng thdi gian thtfc te'\ Nhting am khac nhau cho phep nhting kham nghiem la nhting hinh bau due chtia nhieu tinh the vdi nhting may do quay trdn va dao dong Trong nhan khoa nhting may do dao dong hay quay tron la nhting may do thtfdng dung nhat

4.2.3 Sieu am dong theo phutfng thut M (TM - mode: Time Motion Mode)

Dung de the hien stf chuyen dong cung phtfdng vdi tia sieu

am cua cac vat the theo thdi gian b&ng cach the hien hinh anh

B - mode vdi cac toe do quet khac nhau Ket qua la neu nguon hoi am dting yen thi se tao ra dtfdng thang ngang qua man hinh, con neu mat phan hoi chuyen dong thi se ra dtfdng cong phan anh stf chuyen dong cua mat phan hoi

Tren man hinh hien thi cua M - mode, bien do chuyen dong cua mat phan hoi dtfdc bieu thi tren true tung, thdi gian tren true hoanh, nhd vay cd the tm h toan dtfdc van toe chuyen dong cua mat phan hoi, khi toe do qu6t da dtfdc xac dinh

Phiidng thiic M (dong) nghien ciiu dong thai cua nhiing tin hieu bien thien theo thdi gian, thuan ldi trong viec nghien ciiu cau true mach mau dang dap va nhiing di vat co tii ti'nh.

Diia vao phiidng thiic B ngiidi ta co the lam lai mot phiidng thiic A theo mot vec td kiem soat

4.3 Cac hinh thtic the hien