Ebook Siêu âm nhãn khoa cơ bản: Phần 1

TS. N g u yin HCru Quoc Nguyen
GS. TS. Ton Thj Kim Thanh

Sieu am
Nhan khoa co ban


TS. NGUYiN

h QU

QUOC NGUYEN

GS.TS. TON THj KIM THANH

SIEU AM
NHAN KHOA CO BAN

D£l HQC THAI M*uYti\i

t b u n g t Am h q c l $ l

NHA XUAT BAN Y HOC
HA NOI - 2005


L O lN O ID 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

3


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 it 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
5


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
dong nhat. Ky thuat sieu am dong M cung sU dung nhiing
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
6


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

7


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 .
8


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.

9


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
10


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
11


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

12


- 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)
13


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
- Thanh dich
- Xuat tiet
- Ling dong diidi vong mac.
- Xuat huyet
- Co tinh the cholesterol
- Co keo
- 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
14


- 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
- Gia u
- Ung thu tuyen di can
- U mang nao
- U than kinh ngoai bien
- U mau
- Teo
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
15


Dich dudi nhen tang
U mang nao
Teo thi than kinh
Shung u va gia u quanh hoc mat
Benh ve xoang 'khong khuyet xiidng1
Benh ti'nh quanh hoc ma:
U nhay
Thoat vi mang nao
Thoat vi nao
Loan san xd
Dan tui le
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 mane 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
16


U hon hdp cua tuyen le
Ung thut tuyen di can den phan mem hoc m&t
Do dong tinh mach (Dan hoc mit 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)

17


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 dung
Vdi 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
Mot 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

18


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.
19


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 so : 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.
21


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.

23


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:
- Chu thi'ch
- Chi thi mat cat
- Ho sd benh nhan
1.2.4. C4c c h u t nang tinh todn
- Tong quat
•

Khoang cach

•

Dien tfch

•

The tfch

•

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.

24


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

^

!
;i

*

1.2.5.3. Lan hinh (Scroll)

t

1.2.5.4. D oi chieu

25


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
1.3. Thiet bi xuat
- Man hinh
- May in nhiet
- Phim Polaroid
- Thu video
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.

26